Image forming apparatus with control to divert sheet to usable path

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus that functions to form images on both sides of a sheet.

2. Description of the Related Art

Hitherto, in some image forming apparatuses such as copying machines and page printers, after reversing a sheet having an image formed on one (front) side, the sheet is transported again to an image forming section to form an image on the other (rear) side of the sheet. Such an image forming apparatus includes a duplex (double-sided) feed mechanism for reversing a sheet having an image formed on one side, and then transporting the sheet again to the image forming section.

There is also known an image forming apparatus provided with a mechanism for reversing each sheet from a face-up to a face-down state before ejection so that sheets having images formed thereon are ejected in proper page order.

Then, a demand for increasing the efficiency in operation of those duplex feed mechanism and reversing mechanisms has arisen.

For example, a duplex feed mechanism disclosed in Japanese Patent Laid-Open No. 58-182655 includes a duplex copying aid means that comprises a sheet ejection section, a switching gate, a switchback section, a return section, and a reversing section. When copying an image on the rear side of a sheet on the front side of which an image has been copied, the duplex copying aid means increases a copy return speed so that the sheet having finished copying of an image on the front side more quickly reaches a predetermined return position from which copying of an image on the rear side can start. As a result, efficiency of duplex copying can be increased.

In the conventional image forming apparatus including the duplex feed mechanism to increase the speed in transporting a sheet, on one side of which an image has been printed, to a reversing unit as disclosed in Japanese Patent Laid-Open No. 58-182655, a great improvement in processing speed cannot be expected even though a slight increase in speed of the duplex image formation is expected.

Also, in an apparatus provided with a plurality of sheet reversing routes as disclosed in Japanese Patent Laid-Open No. 6-35265, the overall size of the apparatus is enlarged, the cost is increased, and the apparatus is not satisfactorily convenient for users.

Meanwhile, speedups in operation of image forming apparatuses have increased the output volume in recent years. Correspondingly, a problem has occurred with an increase of the time during which the image forming apparatus cannot be temporarily used, i.e., the so-called “downtime”, and how to reduce the downtime has become a very important issue to be overcome. The downtime is increased because of a part failure, a sheet jam, and other troubles.

SUMMARY OF THE INVENTION

In view of the state of the art set forth above, it is an object of the present invention to provide an image forming apparatus capable of forming images on both sides of a sheet at high speed, and with reduced downtime.

To achieve the above object, the present invention provides an image forming apparatus comprising an image forming section; a plurality of reversing units each for reversing a sheet having an image formed thereon by the image forming section; and a control unit for controlling the plurality of reversing units so that when one of the plurality of reversing units is unusable, a sheet feed operation continues using reversing units which are usable.

Also, the present invention provides an image forming apparatus comprising a reversing feed path for reversing a sheet; a re-feed path for re-feeding the sheet having been reversed in the reversing feed path to the image forming section; a reversing inlet feed path for transporting, to the reversing feed path, a sheet having an image formed on one side by the image forming section; a plurality of reversing outlet feed paths branched from the reversing feed path at plural points and for transporting, to the re-feed path, the sheets having been transported to the reversing feed path; and a control unit for controlling the plurality of reversing outlet feed paths so that when one of the plurality of reversing outlet feed paths is unusable, a sheet feed operation continues by using reversing outlet feed paths which are usable.

Further, the present invention provides an image forming apparatus comprising a reversing feed path for reversing a sheet; a re-feed path for re-feeding the sheet having been reversed in the reversing feed path to an image forming section; a plurality of reversing inlet feed paths joining with the reversing feed path at plural points and transporting, to the reversing feed path, sheets each having an image formed on one side by the image forming section; a plurality of reversing outlet feed paths branched from the reversing feed path at plural points and for transporting, to the re-feed path, the sheets having been transported to the reversing feed path; and a control unit for controlling the plurality of reversing inlet feed paths so that when one of the plurality of reversing inlet feed paths is unusable, a sheet feed operation continues by using reversing inlet feed paths which are usable.

Still further, the present invention provides an image forming apparatus comprising a main feed unit for feeding a sheet having an image formed thereon by an image forming section; a first sheet switchback transport unit and a second sheet switchback transport unit arranged side by side, for transporting the sheet fed from the main feed unit to a downstream side when rotated forward, and then for transporting the sheet backward to an upstream side when rotated backward; a sheet switchback transport path selecting unit for selectively advancing the sheet fed from the main feed unit to the first sheet switchback transport unit and the second sheet switchback transport unit; a failure detecting unit for detecting a failure in operation of at least one of the first sheet switchback transport unit and the second sheet switchback transport unit; and a control unit for controlling the first sheet switchback transport means and the second sheet switchback transport means so that when information indicating a failure in operation of one of the first sheet switchback transport unit and the second sheet switchback transport unit is recognized based on information from the failure detecting unit, operation of the non-failed sheet switchback transport unit continues.

Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic overall view of a copying machine as one example of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2

illustrates a construction of a duplex feed mechanism in the copying machine.

FIGS. 3A

to

3

C are a first set of illustrations for explaining a sheet flow when a sheet is re-fed to an image forming section using the duplex feed mechanism.

FIGS. 4A

to

4

C are a second set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section using the duplex feed mechanism.

FIGS. 5A and 5B

are a third set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section using the duplex feed mechanism.

FIGS. 6A and 6B

are a fourth set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section using the duplex feed mechanism.

FIGS. 7A and 7B

are a first set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 8A and 8B

are a second set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 9A and 9B

are a third set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 10A and 10B

are a fourth set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 11A and 11B

are a fifth set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 12A and 12B

are a sixth set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIGS. 13A and 13B

are a seventh set of illustrations for explaining a sheet flow when a sheet is re-fed to the image forming section in passing control using the duplex feed mechanism.

FIG. 14

illustrates a unit having one reverse inlet path and a plurality of reversing paths and reversing outlet paths.

FIG. 15

illustrates a unit having one reversing inlet path and a plurality of reversing paths and reversing outlet paths.

FIG. 16

is a schematic overall view of an image forming apparatus provided with a plurality of sheet ejection trays according to a second embodiment of the present invention.

FIG. 17

is a flowchart for control executed in the second embodiment.

FIG. 18

is an illustration showing the order of output sheets in the first embodiment.

FIG. 19

is an illustration showing the order of output sheets in the second embodiment.

FIGS. 20A and 20B

are illustrations showing the operation of the ejecting trays serving as properly combining means.

FIG. 21

illustrates a construction of a duplex feed mechanism provided with intermediate trays according to a third embodiment of the present invention.

FIG. 22

is a flowchart for control executed in the third embodiment.

FIG. 23

is an illustration showing the order of sheets stored in the intermediate tray in the third embodiment.

FIG. 24

is a schematic front sectional view of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 25

is a detailed view of a main sheet feed section shown in FIG.

24

.

FIG. 26

is a flowchart for sheet feed control in the face-up sheet ejection mode in the image forming apparatus of FIG.

24

.

FIG. 27

is a flowchart, continued from

FIG. 26

, showing the duplex copying mode in the image forming apparatus of FIG.

24

.

FIGS. 28A

to

28

C are flowcharts, continued from

FIG. 26

, showing the face-down sheet ejection mode in the image forming apparatus of FIG.

24

.

FIG. 29

is a flowchart, continued from

FIG. 26

, showing failure determination on a sheet reversing path in the image forming apparatus of FIG.

24

.

FIGS. 30A

to

30

G are schematic views showing a series of process flow for sheet feed control in the face-down sheet ejection mode in the image forming apparatus of

FIG. 24

when the apparatus is free from failures and troubles.

FIGS. 31A

to

31

G are schematic views showing a series of process flow for sheet feed control in the face-down sheet ejection mode in the image forming apparatus of

FIG. 24

when a failure or a trouble has occurred in a second reversing inlet path.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the drawings.

First Embodiment

FIG. 1

is a schematic overall view of a copying machine as one example of an image forming apparatus according to a first embodiment of the present invention. Note that the image forming apparatus embodying the present invention is not limited to a copying machine, but it may be embodied as a facsimile machine, a printer, a composite machine, etc. Further, a sheet as used herein is not only a piece of plain paper, but may also be a thin resin sheet, a postcard, a piece of cardboard, an envelop, a plastic thin sheet, etc. which are used instead of plain paper.

Referring to

FIG. 1

, a copying machine

100

comprises a printer unit

101

including an image forming section

105

, and an image reader

102

. Also, the copying machine

100

includes an automatic document feeder

103

provided above the image reader

102

. The automatic document feeder

103

automatically feeds documents (not shown) set thereon one by one onto a platen glass

102

a

at the top of the image reader

102

. The document is scanned by the image reader

102

, and digital information from a CCD camera

102

b

is stored as latent image data in a memory (not shown).

Further, in the copying machine

100

, a latent image is formed on a photoconductive drum

106

of the image forming section

105

using a scanner

104

in accordance with the stored latent image data. The latent image is then developed with a toner, whereby a toner image is formed on the photoconductive drum

106

.

Sheet supply cassettes

113

A,

113

B,

113

C and

113

D are disposed below the image forming section

105

of the printer unit

101

to serve as sheet containers each containing a number of sheets. Sheets contained in the sheet supply cassettes

113

A,

113

B,

113

C and

113

D are supplied one by one respectively by sheet supply units

111

E,

111

F,

111

G and

111

H, and are transported to an in-register introducing section

116

at predetermined timing through a feed path

115

a

or

115

b

serving as a part of sheet feed paths.

A register roller pair

117

is provided in the in-register introducing section

116

. Skewing of each sheet is corrected by the register roller pair

117

, and thereafter the sheet is transported to a transfer/separation charger

118

at a predetermined timing. The transfer/separation charger

118

transfers the toner image onto the sheet from the photoconductive drum

106

.

Further, a sheet feed section

107

transports the sheet, onto which the toner image has been transferred, to a fusing section

108

. The toner image on the sheet having been transported through the sheet feed section

107

is fused by a fusing roller pair

119

of the fusing section

108

. After the toner image has been fused, the sheet is selectively advanced to a sheet ejection tray

109

, a first reversing inlet path

111

A or a second reversing inlet path

111

B by sheet ejection flappers

110

A,

110

B provided in a (first) sheet ejection path

108

A.

The sheet ejection flappers

110

A,

110

B are controlled by a controller

80

(described later) such that they are switched over for transporting a sheet to the sheet ejection tray

109

in the one-sided copying mode in which an image is formed on only one side of a sheet, and to the duplex feed mechanism

101

A in the duplex copying mode in which images are formed on both sides of a sheet or in the multi-copying mode in which images are formed on one side of a sheet plural times.

FIG. 2

illustrates construction of the duplex feed mechanism

101

A for reversing a sheet having an image formed on one side and transporting the reversed sheet again to the image forming section

105

in the duplex copying mode, for example. As shown in

FIG. 2

, the duplex feed mechanism

101

A comprises the first reversing inlet path

111

A which is branched from the sheet ejection path

108

A and includes a roller pair R

61

and a roller unit R

62

, the second reversing inlet path

111

B which is branched from the sheet ejection path

108

A and includes roller pairs R

6

, R

7

, and a duplex feed path

121

, i.e., a re-feed path, including re-feed roller pairs R

8

, R

9

for feeding a reversed sheet again to the image forming section

105

.

The duplex feed mechanism

101

A also comprises a reversing path

112

in which the first reversing inlet path

111

A and the second reversing inlet path

111

B merge with each other, and which reverses sheets having been transported from the first reversing inlet path

111

A and the second reversing inlet path

111

B, the reversing path

112

comprising a first reversing path

112

A provided with a roller pair R

2

and a second reversing inlet path

112

B provided with roller pairs R

1

, R

1

A. Further, the duplex feed mechanism

101

A comprises a first reversing outlet path

120

A which is branched from the reversing path

112

and includes roller pairs R

4

, R

5

for transporting a sheet to the duplex feed path

121

, and a second reversing outlet path

120

B which is branched from the reversing path

112

and includes a roller pair R

3

for transporting a sheet to the duplex feed path

121

. A set of the first reversing path

112

A and the first reversing outlet path

120

A and a set of the second reversing path

112

B and the second reversing outlet path

120

B constitute each reversing means in the present invention. In addition, the duplex feed mechanism

101

A comprises a first flapper

114

A and a second flapper

114

B for selectively introducing a sheet from the second reversing path

112

B to the second reversing outlet path

120

B, and a third flapper

114

C and a fourth flapper

114

D for selectively introducing a sheet from the first reversing path

112

A to the first reversing outlet path

120

A or a (second) sheet reversing ejection path

108

B.

The first reversing inlet path

111

A and the second reversing inlet path

111

B are each in the form of a U-shaped path, and connect the sheet ejection path

108

A and the reversing path

112

which is arranged substantially parallel to the sheet ejection path

108

A. Also, the first reversing outlet path

120

A and the second reversing outlet path

120

B are each in the form of a U-shaped path, and connect the reversing path

112

and the duplex feed path

121

which is arranged substantially parallel to the reversing path

112

.

A fourth sensor S

4

is disposed in the first reversing inlet path

11

A, and a seventh sensor S

7

is disposed in the second reversing inlet path

111

B. An eighth sensor S

8

is disposed in the duplex feed path

121

, a sixth sensor S

6

is disposed in the first reversing outlet path

120

A, and a fifth sensor S

5

is disposed in the second reversing outlet path

120

B. A third sensor S

3

is disposed in the first reversing path

112

A, and a second sensor S

2

is disposed in the second reversing path

112

B. In this embodiment, those sensors are each a reflecting photosensor.

The roller unit R

62

is of a three-roller structure capable of providing a transport force for advancing a sheet from the first reversing inlet path

111

A to the first reversing path

112

A and a transport force for advancing a sheet from the first reversing path

112

A to the first reversing outlet path

120

A at the same time. More specifically, the roller unit R

62

comprises a driver roller

62

a

and driven rollers

62

b

,

62

c

which are in contact with the driver roller

62

a

and rotate in the directions of respective arrows when the driver roller

62

a

is rotated in the direction of an arrow. With that structure, the transport force for advancing a sheet from the first reversing inlet path

111

A to the first reversing path

112

A and the transport force for advancing a sheet from the first reversing path

112

A to the first reversing outlet path

120

A can be developed at the same time.

Under control of a controller

80

(shown in FIG.

1

), the roller pairs R

1

-R

9

, R

61

and R

62

are driven to rotate forward and backward, and the first and second sheet ejection flappers

110

A,

110

B and the first to fourth flappers

114

A-

114

D are driven to swing. Additionally, S

1

denotes a first sensor for detecting that a sheet has passed the fusing roller

119

.

A description is now made of the control operation of re-feeding a sheet having an image formed on one side to the image forming section

105

in an ordinary state by the controller

80

through the duplex feed mechanism

101

A having the above-described construction.

Duplex Feed of Short-Sized Sheet

The duplex feed operation of reversing, e.g., a short-sized sheet having an image formed on one side and feeding it to the image forming section

105

, will be first described.

In the case of the duplex sheet feed, when sheets are transported at predetermined intervals between them as shown in FIG.

2

and the first sensor S

1

detects that the leading end of a first sheet

1

, i.e., a lead sheet, having an image formed on one side has passed the fusing roller

119

, the controller

80

switches over the first sheet ejection flapper

110

A and the second sheet ejection flapper

110

B, causing subsequent sheets, including the first sheet

1

, to be selectively transported to the first reversing inlet path

111

A and the second reversing inlet path

111

B. In this embodiment, the first sheet ejection flapper

110

A and the second sheet ejection flapper

110

B are controlled such that the (2n+1)-th (n is an integer equal to or more than 0) sheet is transported to the second reversing inlet path

111

B and the (2n+2)-th sheet is transported to the first reversing inlet path

111

A.

With that control, as shown in

FIG. 3A

, the first sheet

1

is transported to the second reversing inlet path

111

B. Then, when the seventh sensor S

7

detects the leading end of the first sheet

1

, the controller

80

confirms whether a preceding sheet is present in the second reversing path

112

B on the downstream side. Since no preceding sheet is present in this case, the first sheet

1

is continuously advanced toward the second reversing path

112

B. After the first sheet

1

is transported to the second reversing path

112

B, when the first sensor S

1

detects that a second sheet

2

, i.e., a succeeding sheet, has passed the fusing roller

119

, the controller

80

switches over the first sheet ejection flapper

110

A and the second sheet ejection flapper

110

B, causing the second sheet

2

to be transported to the first reversing inlet path

111

A. Subsequently, a third sheet

3

and a fourth sheet

4

are also transported in a similar way.

Then, as shown in

FIG. 3B

, when the first sheet

1

is transported to the second reversing path

112

B and the second sensor S

2

disposed in the second reversing path

112

B detects the passage of the first sheet

1

, the driving of the roller pairs R

1

, R

1

A in the forward (advance) direction is stopped to cease the transport of the first sheet

1

. In this embodiment, a stepping motor is used as a roller driving source. In order to prevent of the stepping motor from being out of synchronism, a sheet is stopped for a predetermined time until specific vibrations of the motor are stabilized. Subsequently, after the lapse of the predetermined time, the roller pairs R

1

, R

1

A are driven to rotate in the backward direction to transport the first sheet

1

. When the second sensor S

2

detects again the first sheet

1

thereafter, the first flapper

114

A and the second flapper

114

B are controlled such that the first sheet

1

is transported to the second reversing outlet path

120

B.

On the other hand, when the fourth sensor S

4

detects the leading end of the second sheet

2

transported to the first reversing inlet path

111

A, the controller

80

confirms whether a preceding sheet is present in the first reversing path

112

A on the downstream side. Since no preceding sheet is present in this case, the second sheet

2

is continuously transported to the first reversing path

112

A.

As a result, as shown in

FIG. 3C

, the first sheet

1

is transported to the second reversing outlet path

120

B and the second sheet

2

is transported to the first reversing path

112

A. Thereafter, when the fifth sensor S

5

detects the first sheet

1

, the roller pair R

3

is stopped to temporarily cease transport of the first sheet

1

. Then, the driving of the roller pair R

3

is controlled so as to resume the transport of the first sheet

1

in step with the timing of re-feeding the first sheet

1

from the duplex feed path

121

after a seventh sheet (not shown), i.e., a sheet subsequent to a sixth sheet

6

, which is supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D (see FIG.

1

). Also, when the third sensor S

3

detects the passage of the second sheet

2

, the roller pair R

2

is stopped and thereafter the roller pair R

2

is driven to rotate backward, causing the second sheet

2

to be transported in the backward direction. Then, when the third sensor S

3

detects again the passage of the second sheet

2

, the third flapper

114

C and the fourth flapper

114

D are controlled such that the second sheet

2

is transported to the first reversing outlet path

120

A.

In parallel to the above operation of transporting the first sheet

1

and the second sheet

2

, the first sheet ejection flapper

110

A and the second sheet ejection flapper

110

B are controlled, causing the third sheet

3

, i.e., the (2n+1)-th sheet, to be transported to the second reversing inlet path

111

B. Then, when the seventh sensor S

7

detects the leading end of the third sheet

3

transported to the second reversing inlet path

111

B, the controller

80

confirms whether a preceding sheet is present in the second reversing path

112

B. Since no preceding sheet is present in this case, the third sheet

3

is continuously transported to the second reversing path

112

B. Subsequent sheets are also controlled in a similar way.

Next, as shown in

FIG. 4A

, the first sheet

1

having resumed its transport is transported to the duplex feed path

121

. As mentioned above, the first sheet

1

is transported at the timing of re-feeding it from the duplex feed path

121

subsequent to a seventh sheet

7

. In this embodiment, the number of sheets, which can be held on standby in the first reversing inlet path

111

A, the second reversing inlet path

111

B, the first reversing path

112

A, the second reversing path

112

B, the first reversing outlet path

120

A, the second reversing outlet path

120

B, and the duplex feed path

121

, is five. Thus, as shown in

FIG. 4C

described later, at the time when the sixth sheet

6

is transported to the first reversing inlet path

111

A, the first sheet

1

is transported through the feed path

115

a.

When the first sheet

1

is transported through the feed path

115

a

in such a manner, an interval between the first sheet

1

and the sixth sheet

6

is too large. In this embodiment, therefore, the seventh sheet

7

is transported after the sixth sheet

6

and the first sheet

1

is transported after the seventh sheet

7

. As a result, the sheets can be fed at a predetermined sheet interval without accelerating the motor. Subsequent sheets are fed likewise such that, for example, the second sheet

2

follows the eighth sheet, the third sheet

3

follows a ninth sheet, and so on.

When the sixth sensor S

6

detects the second sheet

2

in the first reversing outlet path

120

A, the driving of the roller pairs R

4

, R

5

is temporarily stopped. Then, the driving of the roller pairs R

4

, R

5

is controlled so as to resume the transport of the second sheet

2

in step with the timing of re-feeding the second sheet

2

after an eighth sheet (not shown) that is supplied after the first sheet

1

re-fed from the duplex feed path

121

. Subsequent sheets are also controlled in a similar way.

Then, as shown in

FIG. 4B

, the first sheet

1

is transported to the feed path

115

a

after the seventh sheet

7

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. Note that, in

FIG. 4B

, the seventh sheet

7

is supplied from one of the sheet supply cassettes

113

A,

113

C and

113

D. At this time, the eighth sheet is not yet supplied, and therefore the second sheet

2

is held stopped. The third sheet

3

is transported from the second reversing path

112

B to the second reversing outlet path

120

B with control of the first flapper

114

A and the second flapper

114

B. On this occasion, when the fifth sensor S

5

detects the leading end of the third sheet

3

, the driving of the roller pair R

3

is temporarily stopped to hold the third sheet

3

on standby because the second sheet

2

, i.e., the preceding sheet, is still held on standby in the first reversing outlet path

120

A.

Also, the fourth sheet

4

is transported from the first reversing inlet path

111

A and reaches the first reversing path

112

A. On this occasion, when the third sensor S

3

detects the tailing end of the fourth sheet

4

, the third flapper

114

C and the fourth flapper

114

D are controlled so as to transport the fourth sheet

4

to the first reversing outlet path

120

A. However, because the second sheet

2

, i.e., the preceding sheet, is still held on standby in the first reversing outlet path

120

A at this time, the driving of the roller pair R

2

is temporarily stopped to hold the fourth sheet

4

on standby in the first reversing path

112

A. Subsequent sheets are also controlled in a similar way.

Next, as shown in

FIG. 4C

, at the time when the first sheet

1

has already passed the register roller pair

117

in the in-register introducing section

116

and the eighth sheet

8

, which should follow the first sheet

1

, is transported to the feed path

115

a

, the second sheet

2

is already transported from the first reversing outlet path

120

A to the duplex feed path

121

in step with the timing of re-feeding it to the feed path

115

a

after the eighth sheet

8

as mentioned above. Correspondingly, the fourth sheet

4

is transported to the first reversing outlet path

120

A and its leading end is detected by the sixth sensor S

6

. However, because the third sheet

3

, i.e., the preceding sheet, is still held on standby in the second reversing outlet path

120

B at this time, the driving of the roller pairs R

4

, R

5

is stopped to temporarily cease the transport of the fourth sheet

4

. Likewise, the fifth sheet

5

is held on standby in the second reversing path

112

B because the second reversing outlet path

120

B on the downstream side is occupied. Subsequent sheets are also controlled in a similar way.

Subsequently, as shown in

FIG. 5A

, when the leading end of the first sheet

1

reaches the first sensor S

1

after passing the fusing roller

119

and is detected by the first sensor S

1

, the first sheet ejection flapper

110

A and the second sheet ejection flapper

110

B are controlled, causing the first sheet

1

to be transported to the first sheet ejection path

108

A. At this time, the second sheet

2

is transported to the feed path

115

a

after the eighth sheet

8

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. The third sheet

3

is still held stopped, and the fourth sheet

4

is held on standby because the third sheet

3

is in the standby state in the second reversing outlet path

120

B. Further, the fifth and sixth sheets

5

,

6

are also held on standby because the respective preceding sheets remain in the downstream side.

On this occasion, the seventh sheet

7

is transported to the second reversing inlet path

111

B. Upon the leading end of the seventh sheet

7

being detected by the seventh sensor S

7

, the driving of the roller pairs R

6

, R

7

is stopped to temporarily cease the transport of the seventh sheet

7

when the preceding sheet is present in the second reversing path

112

B or when the roller pair R

1

is rotated in a direction opposed to the transport direction of the seventh sheet

7

. Subsequent sheets are also controlled in a similar way.

Thereafter, as shown in

FIG. 5B

, the first sheet

1

is transported to the sheet ejection path

108

A and then ejected out of the copying machine. The second sheet

2

is transported similarly to the first sheet

1

as the preceding sheet, and the third sheet

3

is already transported from the second reversing outlet path

120

B to the duplex feed path

121

in step with the timing of re-feeding it to the feed path

115

a

after a ninth sheet

9

.

Correspondingly, the fifth sheet

5

is transported to the second reversing outlet path

120

B. Upon the leading end of the fifth sheet

5

being detected by the fifth sensor S

5

, because the fourth sheet

4

, i.e., the preceding sheet, is still held on standby in the first reversing outlet path

120

A, the driving of the roller pair R

3

is stopped to temporarily cease the transport of the fifth sheet

5

. Subsequent sheets are also controlled in a similar way.

Then, as shown in

FIG. 6A

, the second sheet

2

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the second sheet

2

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the second sheet

2

to be transported to the first sheet ejection path

108

A. Also, the third sheet

3

is transported to the feed path

115

a

after the ninth sheet

9

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D.

Further, when the fourth sensor S

4

detects the eighth sheet

8

, the driving of the roller pair R

6

is stopped to temporarily cease the transport of the eighth sheet

8

because it is known that the sixth sheet

6

is still present in the first reversing path

112

A on the downstream side. Subsequent sheets are also controlled in a similar way.

Thereafter, as shown in

FIG. 6B

, the second sheet

2

is transported to the sheet ejection path

108

A and then ejected onto the sheet ejection tray

109

outside the copying machine. The third sheet

3

is transported similarly to the second sheet

2

as the preceding sheet, and the fourth sheet

4

is transported to the duplex feed path

121

in step with the timing of re-feeding it to the feed path

115

a

after a tenth sheet

10

. Note that

FIG. 6B

shows a state in which the fourth sheet

4

has already been transported from the first reversing outlet path

120

A to the duplex feed path

121

. Correspondingly, the sixth sheet

6

is transported to the first reversing outlet path

120

A. Upon the leading end of the sixth sheet

6

being detected by the sixth sensor S

6

, because the fifth sheet

5

, i.e., the preceding sheet, is still held on standby in the second reversing outlet path

120

B, the driving of the roller pair R

5

is stopped to temporarily cease the transport of the sixth sheet

6

. Subsequent sheets are also controlled in a similar way. The duplex feed sequence of the sheets after this point of time is executed by repeating the process shown in

FIGS. 2

to

6

.

Thus, by providing a pair of the first reversing inlet path

111

A and the second reversing inlet path

111

B and a pair of the first reversing outlet path

120

A and the second reversing outlet path

120

B with respect to the reversing path

112

(comprising the first reversing path

112

A and the second reversing path

112

B), a maximum of six points where sheets are held on standby can be ensured in feed of short-sized sheets.

By ensuring the maximum six standby points, sheets that have been successively transported to the first reversing inlet path

111

A and the second reversing inlet path

111

B can be successively held on standby in the first reversing inlet path

111

A, the second reversing inlet path

111

B, the first reversing outlet path

120

A, the second reversing outlet path

120

B, and the duplex feed path

121

.

Then, by successively holding the sheets on standby in such a manner, the sheets can be successively re-fed from the sheet held on standby in the duplex feed path

121

in the same order as the one, in which they were transported to the in-register introducing section

116

, at a predetermined timing, i.e., at a timing such that the interval between the sheets successively transported to the first reversing inlet path

111

A and the second reversing inlet path

111

B is equal to the interval between the sheets transported to the in-register introducing section

116

. As a result, the sheets can be fed at a constant interval and images can be formed on both sides of each of the sheets at high speed.

Further, by feeding the reversed first sheet

1

after the seventh sheet

7

, the reversed second sheet

2

after the eighth sheet

8

, and so on, for example, as described above, maximum

13

sheets can be fed in a circulated manner without speeding up the motor until the seventh sheet

7

is reversed and transported to the in-register introducing section

116

(or the feed path

115

a

).

Consequently, it is possible to reduce the body size of the copying machine capable of forming images on both sides of a sheet at high speed, and to perform control with a sufficient allowance in driving of the motor because of a lack of need for high speed motor. Also, since the reversing process is distributed, the frequency of use of the motor for driving associated parts is reduced and the part life can be prolonged. Moreover, since all sheets from the first one to the last one can be fed at a predetermined interval in a circulated manner with respect to the in-register introducing section

116

, it is possible to realize 100% of duplex feed performance.

The above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths. However, the present invention is not limited to such an arrangement, but may also be applied to a copying machine including every three or more sets of reversing inlet paths, reversing paths and reversing outlet paths.

Control in Event of Trouble in One Reversing Outlet Path

While the image forming operation in the normal state operates as described above, a description will now be made of the case in which one of the reversing outlet paths is unusable because of a jam, a failure or any other reason.

Here, with reference to

FIGS. 7A and 7B

, the process is described in connection with the duplex copying operation of 10 output sheets, in which the control is performed in sequence as shown in

FIGS. 3A

,

3

B and

3

C and

FIGS. 4A and 4B

, but when the fourth sheet

4

is transported to the first reversing outlet path

120

A as shown in

FIG. 4C

, it does not reach the sixth sensor S

6

within a predetermined time because of the so-called delay jam. Since the first reversing outlet path

120

A in which the delay jam has occurred becomes unusable, the control of the other sheets is performed while the fourth sheet

4

is left as it is in the first reversing outlet path

120

A. More specifically, as shown in

FIG. 7A

, when the first sheet

1

reaches the first sensor S

1

after passing the fusing roller

119

and the first sensor S

1

detects the leading end of the first sheet

1

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the first sheet

1

to be transported to the first sheet ejection path

108

A. On the other hand, the second sheet

2

is transported to the feed path

115

a

after the eighth sheet

8

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. The third sheet

3

is still held stopped, and the fourth sheet

4

remains in the same state because the first reversing outlet path

120

A is unusable because of the jam. Further, the fifth and sixth sheets

5

,

6

are held on standby because the respective preceding sheets remain in the downstream side.

On this occasion, the seventh sheet

7

is transported to the second reversing inlet path

111

B. Upon the leading end of the seventh sheet

7

being detected by the seventh sensor S

7

, the driving of the roller pairs R

6

, R

7

is stopped to temporarily cease the transport of the seventh sheet

7

when the preceding sheet is present in the second reversing path

112

B or when the roller pair R

1

is rotated in a direction opposed to the transport direction of the seventh sheet

7

. Subsequent sheets are also controlled in a similar way.

Thereafter, as shown in

FIG. 7B

, the first sheet

1

is transported to the sheet ejection path

108

A and then ejected onto the sheet ejection tray

109

outside the copying machine. The second sheet

2

is transported similarly to the first sheet

1

as the preceding sheet, and the third sheet

3

is already transported from the second reversing outlet path

120

B to the duplex feed path

121

in match with the timing of re-feeding it to the feed path

115

a

after the ninth sheet

9

. Correspondingly, the fifth sheet

5

is transported to the second reversing outlet path

120

B. Upon the leading end of the fifth sheet

5

being detected by the fifth sensor S

5

, because the third sheet

3

is held on standby in the duplex feed path

121

, the driving of the roller pair R

3

is stopped to temporarily cease the transport of the fifth sheet

5

. Subsequent sheets are also controlled in a similar way.

Then, as shown in

FIG. 8A

, the second sheet

2

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the second sheet

2

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the second sheet

2

to be transported to the first sheet ejection path

108

A. Also, the third sheet

3

is transported to the feed path

115

a

after the ninth sheet

9

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. Further, the sixth sheet

6

is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the sixth sheet

6

, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped. Additionally, when the fourth sensor S

4

detects the eighth sheet

8

, the roller pairs R

6

, R

2

are driven to transport the eighth sheet

8

to the first reversing path

112

A because it is known that the sixth sheet

6

is not present in the first reversing path

112

A on the downstream side. The seventh sheet

7

is held on standby as it is because the sixth sheet

6

is present in the second reversing path

112

B. Subsequent sheets are also controlled in a similar way.

Thereafter, as shown in

FIG. 8B

, the second sheet

2

is transported to the sheet ejection path

108

A and then ejected out of the copying machine. The third sheet

3

is transported in similarly to the second sheet

2

as the preceding sheet, and the fifth sheet

5

is transported to the duplex feed path

121

in match with the timing of re-feeding it to the feed path

115

a

after the tenth sheet

10

. Note that

FIG. 8B

shows a state in which the fifth sheet

5

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

.

Correspondingly, the sixth sheet

6

is transported to the second reversing outlet path

120

B and its leading end is detected by the fifth sensor S

5

. However, because the fifth sheet

5

, i.e., the preceding sheet, is still held on standby in the duplex feed path

121

, the driving of the roller pair R

3

is stopped to temporarily cease the transport of the sixth sheet

6

. The seventh sheet

7

and the eighth sheet

8

remain in the standby state as they are.

Then, as shown in

FIG. 9A

, the third sheet

3

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the third sheet

3

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the third sheet

3

to be transported to the first sheet ejection path

108

A. Also, the fifth sheet

5

is transported to the feed path

115

a

after the tenth sheet

10

that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. Further, the seventh sheet

7

is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the seventh sheet

7

, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped, and at the same time the roller pair R

6

is driven to transport the ninth sheet

9

to the second reversing inlet path

111

B. Additionally, the sixth sheet

6

and the eighth sheet

8

are still held on standby.

Thereafter, as shown in

FIG. 9B

, the third sheet

3

is transported to the sheet ejection path

108

A and then ejected onto the sheet ejection tray

109

outside the copying machine. The fifth sheet

5

is transported similarly to the third sheet

3

as the preceding sheet. Then, since the tenth sheet

10

, i.e., the last output sheet, has been fed into the copying machine, a fourth A sheet

4

A, on which the image that should have been formed on the fourth sheet

4

is to be formed, is supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D and then transported to the feed path

115

a

instead of the fourth sheet

4

that is still left in the first reversing outlet path

120

A because of the jam. At the same time, the sixth sheet

6

is transported to the duplex feed path

121

. Note that

FIG. 9B

shows a state in which the sixth sheet

6

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

. Further, the seventh sheet

7

is transported to the second reversing outlet path

120

B. Upon the leading end of the seventh sheet

7

being detected by the fifth sensor S

5

, because the sixth sheet

6

, i.e., the preceding sheet, is still held on standby in the duplex feed path

121

, the driving of the roller pair R

3

is stopped to temporarily cease the transport of the seventh sheet

7

. The eighth sheet

8

and the ninth sheet

9

remain in the standby state.

Then, as shown in

FIG. 10A

, the fifth sheet

5

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the fifth sheet

5

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the fifth sheet

5

to be transported to the first sheet ejection path

108

A. Also, the sixth sheet

6

is transported to the feed path

115

a

after the fourth A sheet

4

A that has been supplied from one of the sheet supply cassettes

113

A,

113

B,

113

C and

113

D. Further, the eighth sheet

8

is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the eighth sheet

8

, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped. Simultaneously, the roller pair R

61

is driven to transport the tenth sheet

10

to the first reversing inlet path

111

A. Further, the seventh sheet

7

is still held on standby.

Thereafter, as shown in

FIG. 10B

, the fifth sheet

5

is transported to the sheet ejection path

108

A and then ejected out of the copying machine. The fourth A sheet

4

A is transported similarly to the fifth sheet

5

as the preceding sheet, and the seventh sheet

7

is transported to the duplex feed path

121

. Note that

FIG. 10B

shows a state in which the seventh sheet

7

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

. Further, the eighth sheet

8

is transported to the second reversing outlet path

120

B. Upon the leading end of the eighth sheet

8

being detected by the fifth sensor S

5

, because the seventh sheet

7

, i.e., the preceding sheet, is still held on standby in the duplex feed path

121

, the driving of the roller pair R

3

is stopped to temporarily cease the transport of the eighth sheet

8

. The ninth sheet

9

and the tenth sheet

10

remain in the standby state as they are.

Then, as shown in

FIG. 11A

, the sixth sheet

6

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the sixth sheet

6

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the sixth sheet

6

to be transported to the first sheet ejection path

108

A. Also, the seventh sheet

7

is transported to the feed path

115

a

, and the eighth sheet

8

is transported to the duplex feed path

121

. Note that

FIG. 11A

shows a state in which the eighth sheet

8

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

. Further, the ninth sheet

9

is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the ninth sheet

9

, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped. Simultaneously, the roller pair R

6

is driven to transport the fourth A sheet

4

A to the second reversing inlet path

111

B. The tenth sheet

10

is still held on standby.

Thereafter, as shown in

FIG. 11B

, the sixth sheet

6

is transported to the sheet ejection path

108

A and then ejected out of the copying machine. The seventh sheet

7

is transported similarly to the sixth sheet

6

as the preceding sheet, and the eighth sheet

8

is transported to the feed path

115

a

. Further, the ninth sheet

9

is transported to the second reversing outlet path

120

B. The tenth sheet

10

and the fourth A sheet

4

A remain in the standby state as they are.

Then, as shown in

FIG. 12A

, the seventh sheet

7

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the seventh sheet

7

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the seventh sheet

7

to be transported to the first sheet ejection path

108

A. Also, the eighth sheet

8

is transported in a manner similar to the seventh sheet

7

as the preceding sheet, and the ninth sheet

9

is transported to the duplex feed path

121

. Note that

FIG. 12A

shows a state in which the ninth sheet

9

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

. Further, the tenth sheet

10

is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the tenth sheet

10

, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped. The fourth A sheet

4

A is still held on standby. Thereafter, as shown in

FIG. 12B

, the seventh sheet

7

is transported to the sheet ejection path

108

A and then ejected onto the sheet ejection tray

109

outside the copying machine. The eighth sheet

8

is transported similarly to the seventh sheet

7

as the preceding sheet, and the ninth sheet

9

is transported to the feed path

115

a

. Further, the tenth sheet

10

is transported to the second reversing outlet path

120

B. The fourth A sheet

4

A remains in the standby state as it is.

Next, as shown in

FIG. 13A

, the eighth sheet

8

is transported to the sheet ejection path

108

A and then ejected out of the copying machine. The ninth sheet

9

is transported similarly to the eighth sheet

8

as the preceding sheet. Further, the tenth sheet

10

is transported to the duplex feed path

121

. Note that

FIG. 13A

shows a state in which the tenth sheet

10

has already been transported from the second reversing outlet path

120

B to the duplex feed path

121

. The fourth A sheet

4

A is transported to the second reversing path

112

B with the driving of the roller pairs R

2

, R

1

and R

1

A, and when the second sensor S

2

detects the tailing end of the fourth A sheet

4

A, the driving of the roller pairs R

2

, R

1

and R

1

A is stopped.

Thereafter, as shown in

FIG. 13B

, the ninth sheet

9

passes the fusing roller

119

. When the first sensor S

1

detects the leading end of the ninth sheet

9

, the first and second sheet ejection flappers

110

A,

110

B are controlled, causing the ninth sheet

9

to be transported to the first sheet ejection path

108

A. Also, the tenth sheet

10

is transported to the feed path

115

a

, and the fourth A sheet

4

A is transported to the second reversing outlet path

120

B. Then, the sheet feed is controlled such that the ninth sheet

9

, the tenth sheet

10

and the fourth A sheet

4

A are output in sequence, whereby the output operation is completed. Furthermore, the image forming operation is completed by inserting the fourth A sheet

4

A in a proper position. After the completion of the output operation, an indication prompting the user to remove the fourth sheet

4

jammed in the first reversing outlet path

120

A is displayed on, e.g., a display unit. The copying machine is restored to the standby state after confirming that the jammed sheet has been removed.

As described above, even when one of a plurality of reversing outlet paths is unusable because of a jam or other failure, the output operation can be continued until the completion of required output operation without stopping the machine, and hence a copying machine free from the downtime can be provided.

While the fourth A sheet

4

A is transported to the second reversing inlet path

111

B in the above embodiment, it may be transported to the first reversing inlet path

111

A without problems. Also, in the above embodiment, the sheets are fed while leaving a vacant distance between the sixth and seventh sheets

6

,

7

and between the eighth and ninth sheets

8

,

9

. However, the succeeding sheet may be sped up during the feed to shorten the interval between the two sheets without problems.

While the above first embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is also applicable to the case in which the second reversing outlet path

120

B is unusable. Also, while the above first embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is also applicable to the case in which the first reversing inlet path

111

A is unusable. Further, while the above first embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is also applicable to the case in which the second reversing inlet path

111

B is unusable.

While the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including every three or more sets of reversing inlet paths, reversing paths and reversing outlet paths. Also, while the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including one reversing inlet path, plural reversing paths and plural reversing outlet paths as shown in FIG.

14

. Further, while the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including one reversing outlet path, plural reversing inlet paths and plural reversing paths as shown in FIG.

15

. Additionally, while a stepping motor is employed as the driving source for the sheet feed in the above description, a clutch may be used instead.

Second Embodiment

A second embodiment will be described below. In the second embodiment, a description is made of a method for putting output sheets in proper page order in the first embodiment. When the passing control is performed in the first embodiment, the output operation is continued with a sheet left in the unusable feed path, and hence the sequence of output sheets is disordered. The second embodiment is therefore intended for a method for putting output sheets in proper page order when the passing control is performed. The method for putting output sheets in proper page order is realized by employing and controlling two sheet ejection trays, i.e., a first sheet ejection tray

109

A and a second sheet ejection tray

109

B, as shown in FIG.

16

.

Referring to

FIG. 16

, the first sheet ejection tray

109

A and the second sheet ejection tray

109

B are each vertically movable by a motor (not shown) and are able to selectively stack thereon sheets transported through a (first) sheet ejection path

108

A or a (second) sheet reversing ejection path

108

B. Also, as shown in

FIGS. 20A and 20B

, the second sheet ejection tray

109

B is of a structure allowing the tray to open and close with two leafs from the center by a motor (not shown). By stacking sheets on the second sheet ejection tray

109

B as shown in FIG.

20

A and then opening, from the state of

FIG. 20A

, the tray

109

B with the two leafs rotated downward from the center as shown in

FIG. 20B

, the sheets stacked on the tray

109

B are dropped so as to stack on the first sheet ejection tray

109

A.

In the second embodiment, as with the first embodiment, a description is made of sheet ejection tray control in the case in which one of the reversing outlet paths is unusable because of a jam, a failure or any other reason. Here, the process is described in connection with the duplex copying operation of 10 output sheets, in which the control is performed in sequence as shown in

FIGS. 3A

,

3

B and

3

C and

FIGS. 4A and 4B

, but when the fourth sheet

4

is transported to the first reversing outlet path

120

A as shown in

FIG. 4C

, it does not reach the sixth sensor S

6

within a predetermined time because of the so-called delay jam, and the first reversing outlet path

120

A becomes unusable. However, since the sheet feed operation is the same as that in the first embodiment, a description of the sheet feed operation is omitted here and the sheet ejection tray control will be described below with reference to a flowchart of FIG.

17

.

First, it is determined in step S

1701

whether the first reversing outlet path

120

A is usable. If usable, it is determined in step S

1702

whether the second reversing outlet path

120

B is usable. If it is determined in step S

1702

that the second reversing outlet path

120

B is usable, the ordinary sheet feed operation is performed and output sheets are output to the first sheet ejection tray

109

A in output order (step S

1704

). Then, it is determined in step S

1705

whether the last sheet in the relevant job has been output. In this case, it is determined whether the tenth output sheet has been output. If the last sheet has been output, the output operation is completed (step S

1706

).

Next, if it is determined in step S

1701

that the first reversing outlet path

120

A is unusable, the passing control is performed (step S

1707

). The sheet feed operation in the passing control has been described in the first embodiment and hence the description is not repeated here. Also, if it is determined in step S

1701

that the first reversing outlet path

120

A is usable, it is determined in step S

1702

whether the second reversing outlet path

120

B is usable. If it is determined that the second reversing outlet path

120

B is unusable, the passing control is performed (step S

1707

). Then, it is determined in step S

1708

whether a sheet output to the sheet ejection tray is one prior to the jammed sheet (fourth sheet

4

in this case). If the sheet output to the sheet ejection tray is one (one of the first sheet

1

, the second sheet

2

and the third sheet

3

in this case) prior to the jammed sheet (fourth sheet

4

in this case), the output sheet is output to the first sheet ejection tray

109

A (step S

1709

). On the other hand, if the sheet output to the sheet ejection tray is one (one of the fifth to tenth sheets

5

to

10

in this case) subsequent to the jammed sheet (fourth sheet

4

in this case), the output sheet is output to the second sheet ejection tray

109

B (step S

1710

).

Then, it is determined in step S

1711

whether the sheet output to the sheet ejection tray is a substituted one (fourth A sheet

4

A in this case) for the jammed sheet (fourth sheet

4

in this case). If the output sheet is the substituted one, it is output to the first sheet ejection tray

109

A (step S

1712

). Thereafter, as shown in

FIG. 20B

, the second sheet ejection tray

109

B is opened, whereby the sheets stacked on the second sheet ejection tray

109

B are combined with the sheets stacked on the first sheet ejection tray

109

A so that all the sheets are put in proper page order (step S

1713

). The output operation is thus completed (step S

1706

).

Subsequently, though not shown in the flowchart of

FIG. 17

, the machine body operates such that, after the completion of the output operation, an indication prompting the user to remove the fourth sheet

4

jammed in the first reversing outlet path

120

A is displayed on, e.g., a display unit, and the copying machine is restored to the standby state after confirming that the jammed sheet has been removed.

FIG. 18

shows the order of output sheets in the first embodiment, and

FIG. 19

shows the order of output sheets in the second embodiment. As easily understood from those drawings, the output sheets are put in proper page order in the second embodiment in spite of the passing control. As described above, even when one of a plurality of reversing outlet paths is unusable because of a jam, a failure or any other trouble, the output operation can be achieved while the output sheets are put in proper page order, by continuing the output operation without stopping the machine and by controlling a plurality of sheet ejection trays. Hence, a copying machine free from the downtime can be provided.

In the above-described second embodiment, the second sheet ejection tray

109

B is of the structure capable of opening and closing it with two leaves for combining the output sheets stacked on the first sheet ejection tray

109

A and the output sheets stacked on the second sheet ejection tray

109

B with each other so that all the output sheets are put in proper page order. Alternatively, an indication may be displayed after the job on a display unit of a control panel, for example, to prompt the user to manually combine the sheets stacked on the first sheet ejection tray

109

A and the sheets stacked on the second sheet ejection tray

109

B with each other so that all the sheets are put in proper page order.

While the above second embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is of course applicable to the case in which the second reversing outlet path

120

B is unusable. Also, while the above second embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is of course applicable to the case in which the first reversing inlet path

111

A is unusable. Further, while the above second embodiment has been described in connection with the case in which the first reversing outlet path

120

A is unusable, the present invention is of course applicable to the case in which the second reversing inlet path

111

B is unusable.

While the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including every three or more sets of reversing inlet paths, reversing paths and reversing outlet paths. Also, while the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including one reversing inlet path, plural reversing paths and plural reversing outlet paths as shown in FIG.

14

. Further, while the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including one reversing outlet path, plural reversing inlet paths and plural reversing paths as shown in FIG.

15

. Additionally, while a stepping motor is employed as the driving source for the sheet feed in the above description, a clutch may be used instead.

Third Embodiment

A third embodiment will be described below. In the third embodiment, a description is made of a method for putting output sheets in proper page order in a different way from the second embodiment. As described above, when the passing control is performed in the first embodiment, the output operation is continued with a sheet left in the unusable feed path, and hence the sequence of output sheets is disordered. In the second embodiment, therefore, output sheets are put in proper page order by controlling a plurality of sheet ejection trays. In the third embodiment, the method for putting output sheets in proper page order is realized by employing and controlling two intermediate stack trays, i.e., a first intermediate tray

203

A and a second intermediate tray

203

B, as shown in FIG.

21

. Since

FIG. 21

is the same as

FIG. 2

except for a construction regarding the intermediate trays, the following description is made of only a portion regarding control of the intermediate trays.

Referring to

FIG. 21

, numeral

203

A denotes a first intermediate tray and

203

B denotes a second intermediate tray. When a sheet transported from the first reversing path

112

A is placed in the first intermediate tray

203

A, this operation is performed by controlling a first intermediate tray flapper

200

A and driving a first-intermediate-tray inlet roller pair R

201

A. Also, when transporting a sheet from the first intermediate tray

203

A to the duplex feed path

121

, this operation is performed by driving a first-intermediate-tray outlet roller pair R

202

A. Likewise, when a sheet transported from the second reversing path

112

B is placed in the second intermediate tray

203

B, this operation is performed by controlling a second intermediate tray flapper

200

B and driving a second-intermediate-tray inlet roller pair R

201

B. Also, when transporting a sheet from the second intermediate tray

203

B to the duplex feed path

121

, this operation is performed by driving a second-intermediate-tray outlet roller pair R

202

B.

In the third embodiment, as with the first and second embodiments, a description is made of sheet ejection tray control in the case in which one of the reversing outlet paths is unusable because of a jam, a failure or any other reason. Here, the process is described in connection with the duplex copying operation of 10 output sheets, in which the control is performed in sequence as shown in

FIGS. 3A

,

3

B and

3

C and

FIGS. 4A and 4B

, but when the fourth sheet

4

is transported to the first reversing outlet path

120

A as shown in

FIG. 4C

, it does not reach the sixth sensor S

6

within a predetermined time because of the so-called delay jam, and the first reversing outlet path

120

A becomes unusable. However, since the sheet feed operation is the same as that in the first and second embodiments, a description of the sheet feed operation is omitted here and the sheet ejection tray control will be described below with reference to a flowchart of FIG.

22

.

First, it is determined in step S

2101

whether the first reversing outlet path

120

A is usable. If usable, it is determined in step S

2102

whether the second reversing outlet path

120

B is usable. If it is determined in step S

2102

that the second reversing outlet path

120

B is usable, the ordinary sheet feed operation is performed and output sheets are output to the sheet ejection tray in output order (step S

2104

). Then, it is determined in step S

2105

whether the last sheet in the relevant job has been output. In this case, it is determined whether the tenth output sheet has been output. If the last sheet has been output, the output operation is completed (step S

2106

).

Next, if it is determined in step S

2101

that the first reversing outlet path

120

A is unusable, the passing control is performed (step S

2107

). The sheet feed operation in the passing control has been described in the first embodiment and hence the description is not repeated here. Thereafter, it is determined in step S

2108

whether a sheet transported to the second reversing path

112

B is one (one of the fifth to tenth sheets

5

to

10

in this case) subsequent to the jammed sheet (fourth sheet

4

in this case). If it is determined in step S

2108

that the sheet transported to the second reversing path

112

B is one (one of the fifth to tenth sheets

5

to

10

in this case) subsequent to the jammed sheet (fourth sheet

4

in this case), all of the sheets (fifth to tenth sheets

5

to

10

in this case) subsequent to the jammed sheet are placed in the second intermediate tray

203

B (step S

2109

). Then, it is determined in step S

2110

whether the last sheet in the relevant job (tenth sheet

10

in this case) has been placed in the second intermediate tray

203

B. If it is determined in step S

2110

that the last sheet (tenth sheet

10

in this case) in the relevant job has been placed in the second intermediate tray

203

B, it is determined in step S

2111

whether a sheet (fourth A sheet

4

A in this case) substituted for the jammed sheet has been transported to the feed path

115

a.

The substituted sheet (fourth A sheet

4

A in this case) for the jammed sheet is transported from the second reversing path

112

B to the second reversing outlet path

120

B without being placed in the intermediate tray, and then transported to the feed path

115

a

through the duplex feed path

121

. If it is determined in step S

2111

that the substituted sheet (fourth A sheet

4

A in this case) for the jammed sheet has been transported to the feed path

115

a

, the sheets placed in the second intermediate tray

203

B are transported from it to the duplex feed path

121

in the same order as the one in which they were placed (step S

2112

). Thereafter, the sheets are output to the sheet ejection tray in accordance with the ordinary feed sequence (step S

2104

). Then, it is determined in step S

2105

whether the last sheet (tenth sheet

10

in this case) in the relevant job has been output. If it is determined that the last sheet (tenth sheet

10

in this case) in the relevant job has been output, the output operation is completed (step S

2106

).

Further, if it is determined in step S

2101

that the first reversing outlet path

120

A is usable, it is then determined in step S

2102

whether the second reversing outlet path

120

B is usable. If it is determined that the second reversing outlet path

120

B is unusable, the passing control is performed (step S

2113

). Thereafter, it is determined in step S

2114

whether a sheet transported to the first reversing path

112

A is one subsequent to the jammed sheet. If it is determined in step S

2114

that the sheet transported to the first reversing path

112

A is one subsequent to the jammed sheet, all of the sheets subsequent to the jammed sheet are placed in the first intermediate tray

203

A (step S

2115

). Then, it is determined in step S

2116

whether the last sheet in the relevant job (tenth sheet

10

in this case) has been placed in the first intermediate tray

203

A. If it is determined in step S

2116

that the last sheet in the relevant job has been placed in the first intermediate tray

203

A, it is determined in step S

2117

whether a sheet substituted for the jammed sheet has been transported to the feed path

115

a.

The sheet substituted for the jammed sheet is transported from the first reversing path

112

A to the first reversing outlet path

120

A without being placed in the intermediate tray, and then transported to the feed path

115

a

through the duplex feed path

121

. If it is determined in step S

2117

that the sheet substituted for the jammed sheet has been transported to the feed path

115

a

, the sheets placed in the first intermediate tray

203

A are transported from it to the duplex feed path

121

in the same order as the one in which they were placed (step S

2118

). Thereafter, the sheets are output to the sheet ejection tray in accordance with the ordinary feed sequence (step S

2104

). Then, it is determined in step S

2105

whether the last sheet in the relevant job has been output. If it is determined that the last sheet in the relevant job has been output, the output operation is completed (step S

2106

).

Subsequently, though not shown in the flowchart of

FIG. 22

, the machine body operates such that, after the completion of the output operation, an indication prompting the user to remove the fourth sheet

4

jammed in the second reversing outlet path

120

B is displayed on, e.g., a display unit, and the copying machine is restored to the standby state after confirming that the jammed sheet has been removed.

FIG. 23

shows the order of sheets placed in the intermediate tray and the feed of the substituted sheet for the jammed sheet in the third embodiment. As seen from

FIG. 23

, six sheets from the fifth sheet

5

to the tenth sheet

10

are placed in the intermediate tray in order. Then, after the fourth A sheet

4

A substituted for the jammed sheet has been transported to the feed path

115

a

through the second reversing path

112

B, the second reversing outlet path

120

B and the duplex feed path

121

, the sheets placed in the second intermediate tray

203

B are transported to the feed path

115

a

in sequence from the fifth sheet

5

subsequent to the fourth A sheet

4

A, and are ejected onto the sheet ejection tray in sequence.

Thus, it is easily understood that all of the output sheets are put in proper page order in the third embodiment in spite of the passing control. As described above, even when one of a plurality of reversing outlet paths is unusable because of a jam, a failure or any other trouble, the output operation can be achieved while the output sheets are put in proper page order, by continuing the output operation without stopping the machine and by controlling a plurality of intermediate trays. Hence, a copying machine free from the downtime can be provided.

While the above third embodiment has been described in connection with the case in which the first or second reversing outlet path

120

A,

120

B is unusable, the present invention is applicable to the case in which one of the first and second reversing inlet paths

111

A,

111

B is unusable. While the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including every three or more sets of reversing inlet paths, reversing paths and reversing outlet paths. Also, while the above description has been made in connection with the copying machine including each pair of reversing inlet paths, reversing paths and reversing outlet paths, the present invention is not limited to such an arrangement, but can be applied to a copying machine including one reversing inlet path, plural reversing paths and plural reversing outlet paths as shown in FIG.

14

. Additionally, while a stepping motor is employed as the driving source for the sheet feed in the above description, a clutch may be used instead.

Fourth Embodiment

A fourth embodiment of the present invention will be described below with reference to

FIGS. 24 and 25

.

In a copying machine

2

, shown in

FIG. 24

, as one example of an image forming apparatus, a machine body

3

includes a plurality of sheet supply decks

15

and a sheet supply cassettes

16

. Sheet S of different sizes are stacked in the sheet supply decks

15

and the sheet supply cassettes

16

, and are selectively supplied to an image forming unit

11

. The body

3

of the copying machine serves also as a body for a sheet feed mechanism

1

shown in FIG.

25

.

The sheets S stacked in the sheet supply decks

15

and the sheet supply cassettes

16

are each fed out to a sheet feed path

27

by a let-out roller

17

in sequence from a top sheet, and then guided to the image forming unit

11

(described later) along the sheet feed path

27

.

The sheets S let out by the let-out roller

17

are separated one by one by a separation roller pair

18

comprising a feed roller and a retard roller, and then fed to a register roller pair

19

through the sheet feed path

27

. When the leading end of the fed sheet S abuts against a nip of the register roller pair

19

, the sheet forms a predetermined loop so that its skewed state is corrected.

The sheet S, of which its skewed state has been corrected, is transported to a gap between a photoconductive drum

4

and a transfer charger

12

in the image forming unit

11

by the register roller pair

19

that starts rotation at the timing such that the sheet is aligned with the position of a toner image on the rotating photoconductive drum

4

. In that gap, the toner image on the photoconductive drum

4

is transferred onto the sheet S by the transfer charger

12

.

In the copying machine

2

, an image of a document set on a platen glass

5

is read by a CCD

10

through an optical system comprising an illumination lamp

6

, reflecting mirrors

7

,

8

, a zoom lens

9

, and so on. A laser beam is irradiated to the photoconductive drum

4

using a laser scanner after desired image processing. An electrostatic latent image is thereby formed on the photoconductive drum

4

, and the latent image is visualized into a toner image with a black toner supplied from a developing device

14

. The sheet S, onto which the toner image has been transferred in the image forming unit

11

, is transported to a fusing unit

20

by a feed belt

13

, and the toner image is fused on the sheet S by the fusing unit

20

.

A construction of the sheet feed mechanism

1

in this fourth embodiment will now be described with reference to FIG.

25

.

Downstream of the fusing unit

20

, an inner sheet straight feed path

49

, a sheet straight feed path

50

, and an ejection path

51

are disposed in a linearly continuous arrangement. An inner sheet ejection roller pair

25

is disposed in the inner sheet straight feed path

49

, sheet ejection roller pairs

30

,

31

are disposed in the sheet straight feed path

50

, and a sheet ejection roller pair

32

and an outer sheet ejection roller pair

26

are disposed in the ejection path

51

. The ejection path

51

is open to the outside of the copying machine

2

and guides the transported sheet S to be ejected onto a sheet ejection tray

37

. The inner sheet straight feed path

49

, the sheet straight feed path

50

, the ejection path

51

, the inner sheet ejection roller pair

25

, the sheet ejection roller pairs

30

,

31

, the sheet ejection roller pair

32

, and the outer sheet ejection roller pair

26

constitute main feed means in the present invention.

A first reversing inlet path

52

is branched from the downstream side of the sheet straight feed path

50

, and a flapper

40

is disposed at a branch point so that the sheet S can be selectively transported to one of the ejection path

51

and the first reversing inlet path

52

. Also, a second reversing inlet path

53

is branched from the downstream side of the inner sheet straight feed path

49

, and a flapper

43

is disposed at a branch point so that the sheet S can be selectively transported to one of the sheet straight feed path

50

and the second reversing inlet path

53

.

The first reversing inlet path

52

is connected to a first reversing path

54

, the second reversing inlet path

53

is connected to a second reversing path

55

, and the first reversing path

54

and the second reversing path

55

are linearly connected to each other. The sheet S transported from the first reversing inlet path

52

to the first reversing path

54

and the sheet S transported from the second reversing inlet path

53

to the second reversing path

55

are each reversed from a face-up to a face-down state. A continuous feed path constituted by the inner sheet straight feed path

49

, the sheet straight feed path

50

and the ejection path

51

is arranged substantially parallel to a continuous feed path constituted by the first reversing path

54

and the second reversing path

55

. The first reversing inlet path

52

and the first reversing path

54

may serve as first sheet backward feed means in the present invention, and the second reversing inlet path

53

and the second reversing path

55

may serve as second sheet backward feed means in the present invention.

At a junction point of the first reversing path

54

and the first reversing inlet path

52

, a sheet reversing ejection path

56

as reversed sheet feed means and a duplex feed path

57

as sheet duplex feed means in the present invention join with each other. The sheet S is transported from the first reversing path

54

to a junction point of the sheet reversing ejection path

56

and the duplex feed path

57

through a three-roller unit

36

. A flapper

42

is disposed at the junction point of the sheet reversing ejection path

56

and the duplex feed path

57

so that the sheet S is selectively transported to one of the sheet reversing ejection path

56

and the duplex feed path

57

.

The sheet reversing ejection path

56

joins with the ejection path

51

at a point upstream of the outer sheet ejection roller pair

26

for returning the sheet S, which is transported from the first reversing inlet path

52

or the second reversing inlet path

53

, to the ejection path

51

, whereby the sheet S is ejected after being reversed from a face-up to face-down state. A curl removing roller unit

58

comprising three rollers is disposed in the sheet reversing ejection path

56

for giving the sheet S a curl in an opposed direction to that given to it through the first reversing inlet path

52

or the second reversing inlet path

53

, whereby the sheet S can be ejected in a flat condition.

The duplex feed path

57

joins with the sheet feed path

27

(shown in

FIG. 24

) and serves to re-feed the sheet S having an image formed on the front side to the image forming unit

11

so that an image is formed on the rear side for the so-called duplex copying. A plurality of return roller pairs

59

for re-feeding the sheet are disposed along the duplex feed path

57

.

Sheet detecting sensors for detecting the sheet S are disposed midway the above-mentioned feed paths. More specifically, a first inner sheet ejection sensor

21

is disposed upstream of the inner sheet ejection roller pair

25

, and a second inner sheet ejection sensor

22

is disposed upstream of the sheet ejection roller pair

31

. A first reversal sensor

23

is disposed upstream of the three-roller unit

36

, and a second reversal sensor

24

is disposed downstream of the re-feed roller pair

35

.

The above-mentioned rollers and flappers are controlled by a CPU (which may serve as control means)

60

, shown in

FIG. 24

, in accordance with sheet detection information obtained from the above-mentioned sensors. The operation of the copying machine thus constructed will be described below.

Face-up Sheet Ejection Mode in Single-Sided Copying

In the case of face-up sheet ejection mode in single-sided copying, the flappers

43

and

40

disposed at the respective branch points are switched over so as to transport the sheet S in a direction A. Then, as shown in

FIG. 25

, the sheet S, which has been subjected to the fusing of the toner image, is transported on the inner sheet straight feed path

49

, the sheet straight feed path

50

and the ejection path

51

by the inner sheet ejection roller pair

25

and the sheet ejection roller pairs

30

,

31

,

32

until reaching the outer sheet ejection roller pair

26

. Following this, the sheet S is ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image formed surface (front side) of the sheet faces up (face-up sheet ejection).

Duplex Copying Mode

In the case of duplex (double-sided) copying mode, the CPU

60

switches over the flapper

43

so as to transport the sheet S in the direction A, whereupon the sheet S having an image formed on the front side and transported from the inner sheet ejection roller pair

25

is introduced to the sheet straight feed path

50

and passes the sheet ejection roller pairs

30

,

31

. Further, the CPU

60

switches over the flapper

40

so as to transport the sheet S in a direction B, whereupon the sheet S is transported to the first reversing inlet path

52

and then advanced in the direction B by the re-feed roller pairs

33

,

34

and

35

.

At the time when the tailing end of the sheet S having entered the first reversing path

54

has passed the three-roller unit

36

, the flapper

42

is switched over so as to transport the sheet S in a direction D, and the re-feed roller pairs

33

,

34

and

35

are rotated backward, whereby the sheet S is transported to the duplex feed path (sheet re-feed path)

57

in a state in which the image formed surface of the sheet faces up. Then, the sheet S is re-fed by the return roller pairs

59

in the duplex feed path

57

to the image forming unit

11

in which an image formed on the rear wide of the sheet.

Thereafter, the toner image on the sheet S is fused by the fusing unit

20

, and the sheet S is ejected onto the sheet ejection tray

37

through the inner sheet straight feed path

49

, the sheet straight feed path

50

and the ejection path

51

.

In the duplex copying mode, the sheet may be reversed using only the first reversing inlet path

52

and then transported to the duplex feed path

57

. As an alternative, the sheet may be reversed using the first reversing inlet path

52

and the second reversing inlet path

53

alternately and then transported to the duplex feed path

57

. In the latter case, the sheet S is introduced to the second reversing inlet path

53

by the flapper

43

, and at the time when the tailing end of the sheet S has passed the flapper

44

, the flapper

44

is switched over so as to transport the sheet S in a direction F. Then, the re-feed roller pairs

33

,

34

and

35

are rotated backward to transport the sheet S toward the three-roller unit

36

. Thereafter, the sheet S is re-fed to the image forming unit

11

through the duplex feed path

57

.

By transporting the sheet to the duplex feed path

57

while reversing it using the first reversing inlet path

52

and the second reversing inlet path

53

alternately, productivity can be improved. In other words, because speed-up control, which has been performed in reversing the sheet in the past, is no longer required and a speed-up rate is suppressed to a small value, an increase of the motor cost can be held down. Additionally, the productivity can be further improved by employing the so-called alternate sheet supply scheme in which the sheet having an image formed on the front side is re-fed to the image forming unit

11

in an alternate relation to a sheet having no image formed thereon and supplied from the sheet supply deck

15

or the sheet supply cassette

16

.

Face-down Sheet Ejection Mode in Single-Sided Copying

In the case of face-down sheet ejection mode in single-sided copying, the sheets S each having an image formed on the front side and successively transported from the inner sheet ejection roller pair

25

are advanced as follows. The CPU

60

switches over the flapper

43

so as to transport a preceding sheet in the direction A, whereupon the preceding sheet is introduced to the sheet straight feed path

50

. Further, the CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the preceding sheet is transported to the first reversing inlet path

52

. Then, the CPU

60

switches over the flapper

43

so as to transport a succeeding sheet in a direction E, whereupon the succeeding sheet is transported to the second reversing inlet path

53

.

Thereafter, the flapper

42

is switched over so as to transport the sheet in a direction C, and at the time when the tailing end of the preceding sheet has passed the three-roller unit

36

, the re-feed roller pairs

33

,

34

are rotated backward, whereby the preceding sheet is transported to the outer sheet ejection roller pair

26

. Also, at the time when the tailing end of the succeeding sheet has passed the flapper

44

, the flapper

44

is switched over so as to transport the sheet in the direction F. Then, the re-feed roller pairs

33

,

34

and

35

are rotated backward, whereby the succeeding sheet is transported to the outer sheet ejection roller pair

26

after the preceding sheet. Accordingly, the preceding sheet and the succeeding sheet are successively ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image-formed (front) side of each sheet faces down.

Thus, sheets are alternately transported to the first reversing inlet path

52

and the second reversing inlet path

53

one by one so that the sheets having imaged formed thereon are successively ejected while the image formed surface of each sheet faces down. As a result, the productivity of the copying machine

2

can be improved without reducing the sheet interval.

The control operation executed by the CPU

60

in the face-up sheet ejection mode in single-sided copying, the duplex copying mode, and the face-down sheet ejection mode in single-sided copying will be described below with reference to flowcharts of

FIGS. 26

to

29

.

Face-up Sheet Ejection Mode in Single-Sided Copying

The operation in the face-up sheet ejection mode in single-sided copying is described with reference to FIG.

26

. Sheet feed control is common to the face-up sheet ejection mode, the duplex copying mode, and the face-down sheet ejection mode. First, whether there is a failure in the sheet reversing path is determined (step

10

; hereinafter “step” is abbreviated to “ST”). The process of determining a failure in the sheet reversing path is described later with reference to FIG.

29

.

The leading end of the sheet S, which has been subjected to the fusing of the toner image by the fusing unit

20

, is detected by the first inner sheet ejection sensor

21

(ST

100

). Then, a signal for carrying out the single-sided copying on a sheet, whose size is known in advance, is input to the copying machine (ST

101

). Note that the control flow proceeds to (I:

FIG. 27

) if the duplex copying (ejection) is determined in ST

101

, and proceeds to (II:

FIG. 28A

) if the face-down ejection is determined in ST

101

.

The CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A, whereupon the sheet is guided to the sheet straight feed path

50

(ST

102

). Then, the leading end of the sheet is detected by the second inner sheet ejection sensor

22

(ST

103

). The CPU

60

switches over the flapper

40

so as to transport the sheet in the direction A, whereupon the sheet is guided to the outer sheet ejection roller pair

26

(ST

104

). Subsequently, the sheet is ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image formed surface of the sheet faces up (ST

105

).

Duplex Copying Mode

The operation in the duplex copying mode will be described below with reference to FIG.

27

. When a signal for carrying out the duplex copying on a sheet, whose size is known in advance, is input to the copying machine, the CPU

60

executes a step of determining a failure in the sheet reversing path (ST

10

, see FIG.

26

). Note that the timing of executing the failure determination is not limited to a period during the image forming operation.

Following the determination in ST

10

, it is first confirmed whether there is neither failure nor trouble in the first reversing inlet path

52

(ST

201

). If it is confirmed that there is neither failure nor trouble in the first reversing inlet path

52

, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A, whereupon the sheet is guided to the sheet straight feed path

50

(ST

202

). On the other hand, if it is confirmed that there is a failure or trouble in the first reversing inlet path

52

, it is confirmed whether there is neither failure nor trouble in the second reversing inlet path

53

(ST

211

).

After the sheet has been guided to the sheet straight feed path

50

in ST

202

, the leading end of the sheet is detected by the second inner sheet ejection sensor

22

(ST

203

). The CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the sheet is guided to the first reversing inlet path

52

(ST

204

).

After the lapse of a predetermined time, the CPU

60

starts forward rotation of a stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

205

). The three-roller unit

36

is already rotated at this time, and the sheet is guided to the first reversing path

54

(ST

206

). Substantially at the same time as when the first reversal sensor

23

detects the tailing end of the sheet (ST

207

), the CPU

60

starts backward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

208

). Further, at the same time, the CPU

60

switches over the flapper

42

so as to transport the sheet in the direction D, whereupon the sheet is transported to the duplex feed path

57

(ST

231

).

The three-roller unit

36

includes a not-shown elastic member (e.g., a PET sheet) that serves as a valve for always guiding the direction of the sheet, which has been transported to the first reversing path

54

, toward the junction point of the sheet reversing ejection path

56

and the duplex feed path

57

while preventing the sheet from being returned to the first reversing inlet path

52

.

Further, in ST

211

of confirming whether there is neither failure nor trouble in the second reversing inlet path

53

, if it is confirmed that there is neither failure nor trouble in the second reversing inlet path

53

, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction E, whereupon the sheet is guided to the second reversing inlet path

53

(ST

212

). On the other hand, if it is confirmed that there is a failure or trouble in the second reversing inlet path

53

, it is concluded that a failure or trouble occurs in both the first reversing inlet path

52

and the second reversing inlet path

53

, whereupon the image forming process is suspended based on the determination that the duplex copying and the face-down ejection are disabled (ST

221

).

After the sheet has been guided to the second reversing inlet path

53

in ST

212

, the leading end of the sheet is detected by the second reversal sensor

24

(ST

213

). Then, after the lapse of a predetermined time, the CPU

60

starts forward rotation of a stepping motor (not shown) for driving the re-feed roller pair

35

(ST

214

), causing the sheet to be guided to the second reversing path

55

(ST

215

). When the second reversal sensor

24

detects the tailing end of the sheet (ST

216

), the CPU

60

switches over the flapper

44

so as to transport the sheet in the direction F (ST

217

), and substantially at the same time the CPU

60

starts backward rotation of the stepping motors (not shown) for driving the re-feed roller pairs

33

,

34

and

35

(ST

218

). Further, at the same time, the CPU

60

switches over the flapper

42

so as to transport the sheet in the direction D, whereupon the sheet is transported to the duplex feed path

57

(ST

231

). At this time, the three-roller unit

36

has already rotated.

Face-down Sheet Ejection Mode in Single-Sided Copying

The operation in the face-down sheet ejection mode in single-sided copying will be described below with reference to FIG.

28

. When a signal for carrying out the single-sided copying on a sheet, whose size is known in advance, is input to the copying machine, the CPU

60

executes a step of determining a failure in the sheet reversing path (ST

10

, see FIG.

26

). Note that the timing of executing the failure determination is not limited to a period during the image forming operation.

Following the determination in ST

10

, it is first confirmed whether there is neither failure nor trouble in the first reversing inlet path

52

(ST

301

). If it is confirmed in ST

301

that there is neither failure nor trouble in the first reversing inlet path

52

, it is then confirmed whether there is neither failure nor trouble in the second reversing inlet path

53

(ST

302

). Also, if it is confirmed in ST

301

that there is a failure or trouble in the first reversing inlet path

52

, it is likewise confirmed whether there is neither failure nor trouble in the second reversing inlet path

53

(ST

331

).

If it is confirmed in ST

302

that there is neither failure nor trouble in the second reversing inlet path

53

, this is interpreted to mean that there is neither failure nor trouble in both the first reversing inlet path

52

and the second reversing inlet path

53

. Then, the control flow proceeds to ST

303

to continue the face-down ejection. If it is confirmed in ST

302

that there is a failure or trouble in the second reversing inlet path

53

, this is interpreted to mean that there is neither failure nor trouble only in the first reversing inlet path

52

. Then, the control flow proceeds to (III:

FIG. 28B

) to continue the face-down ejection from ST

401

. If it is confirmed in ST

331

that there is neither failure nor trouble in the second reversing inlet path

53

, this is interpreted to mean that there is neither failure nor trouble only in the second reversing inlet path

53

. Then, the control flow proceeds to (IV:

FIG. 28C

) to continue the face-down ejection from ST

501

. If it is confirmed in ST

331

that there is a failure or trouble in the second reversing inlet path

53

, this is interpreted to mean that there is a failure or trouble in both the first reversing inlet path

52

and the second reversing inlet path

53

. Then, the image forming process is suspended based on the determination that the duplex copying and the face-down ejection are disabled (ST

341

).

When the leading end of the sheet is detected by the first inner sheet ejection sensor

21

in ST

303

, the CPU

60

determines whether the relevant sheet is one at an odd-number page in the successively transported sheets (head sheet is an odd sheet) (ST

304

). If the relevant sheet is an odd one, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A at once, whereupon the sheet is guided to the sheet straight feed path

50

(ST

305

). When the leading end of the odd sheet is detected by the second inner sheet ejection sensor

22

(ST

306

), the CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the odd sheet is guided to the first reversing inlet path

52

(ST

307

). On the other hand, if it is determined in ST

304

that the relevant sheet is an even one, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction E at once, whereupon the even sheet is guided to the second reversing inlet path

53

(ST

321

).

After the lapse of a predetermined time, the CPU

60

starts forward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

308

). The three-roller unit

36

is already rotated at this time, and the odd sheet is guided to the first reversing path

54

(ST

309

). For the even sheet, the CPU

60

starts forward rotation of the stepping motor (not shown) for driving the re-feed roller pair

35

(ST

322

), whereby the even sheet is guided to the second reversing path

55

(ST

323

).

Substantially at the same time as when the first reversal sensor

23

detects the tailing end of the odd sheet (ST

310

), the CPU

60

starts backward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

311

). Further, at the same time, the CPU

60

switches over the flapper

42

so as to transport the sheet in the direction C, whereupon the odd sheet is transported to the sheet reversing ejection path

56

(ST

312

). The elastic member provided in the three-roller unit

36

guides the sheet to be directed toward one of the sheet reversing ejection path

56

and the duplex feed path

57

. For the even sheet, when the second reversal sensor

24

detects the tailing end of the even sheet (ST

324

), the CPU

60

temporarily stops the stepping motor (not shown) for driving the re-feed roller pair

35

(ST

325

).

Subsequently, it is determined whether the even sheet has hit the odd sheet (ST

326

). At the same time, the CPU

60

starts backward rotation of the stepping motors (not shown) for driving the re-feed roller pairs

34

,

35

(ST

327

), and switches over the flapper

44

so as to transport the sheet in the direction F (ST

328

). Since the flapper

42

is already switched over for the odd sheet so as to transport the sheet in the direction C, the even sheet is transported to the sheet reversing ejection path

56

through the first reversing path

54

. Thereafter, each sheet is ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image formed surface of the sheet faces up (ST

313

). Thus, the sheets successively transported in the face-down sheet ejection mode are ejected in sequence while passing the first reversing inlet path

52

and the second reversing inlet path

53

alternately in accordance with the flowchart described above.

If it is confirmed in ST

302

that there is a failure or trouble in the second reversing inlet path

53

, this is interpreted to mean that there is neither failure nor trouble only in the first reversing inlet path

52

. In ST

401

, therefore, the productivity of the image formation is reduced to slow an interval time between the image formations and to increase the sheet interval (FIG.

28

B). Subsequently, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A, whereupon the sheet is guided to the sheet straight feed path

50

(ST

402

). When the leading end of the sheet is detected by the second inner sheet ejection sensor

22

(ST

403

), the CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the sheet is guided to the first reversing inlet path

52

(ST

404

).

After the lapse of a predetermined time, the CPU

60

starts forward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

405

). The three-roller unit

36

is already rotated at this time, and the sheet is guided to the first reversing path

54

(ST

406

).

Substantially at the same time as when the first reversal sensor

23

detects the tailing end of the sheet (ST

407

), the CPU

60

starts backward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

(including the re-feed roller pair

34

depending on the sheet size) (ST

408

). Further, at the same time, the CPU

60

switches over the flapper

42

so as to transport the sheet in the direction C, whereupon the sheet is transported to the sheet reversing ejection path

56

(ST

409

). The elastic member provided in the three-roller unit

36

guides the sheet to be directed toward one of the sheet reversing ejection path

56

and the duplex feed path

57

. Thereafter, the sheet is ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image formed surface of the sheet faces down (ST

410

).

If it is confirmed in ST

331

that there is neither failure nor trouble in the second reversing inlet path

53

, this is interpreted to mean that there is neither failure nor trouble only in the second reversing inlet path

53

. In ST

501

, therefore, the productivity of the image formation is reduced to slow an interval time between the image formations and to increase the sheet interval (FIG.

28

C). Subsequently, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction E (ST

502

). After the lapse of a predetermined time, the CPU

60

starts forward rotation of the stepping motor (not shown) for driving the re-feed roller pair

35

(ST

503

), whereupon the sheet is guided to the second reversing path

55

(ST

504

).

Then, when the second reversal sensor

24

detects the tailing end of the sheet (ST

505

), the CPU

60

temporarily stops the stepping motor (not shown) for driving the re-feed roller pair

35

(ST

506

). Subsequently, the CPU

60

starts backward rotation of the stepping motors (not shown) for driving the re-feed roller pairs

33

,

34

and

35

(ST

507

), and switches over the flapper

44

so as to transport the sheet in the direction F and the flapper

42

so as to transport the sheet in the direction C. Hence, the sheet is transported in a reversed state to the sheet reversing ejection path

56

through the first reversing path

54

(ST

508

). Thereafter, the sheet is ejected onto the sheet ejection tray

37

outside the copying machine body by the outer sheet ejection roller pair

26

in a state in which the image formed surface of the sheet faces down (ST

509

).

Failure Determination on Sheet Reversing Path)

The failure determination on the sheet reversing path will be described below with reference to FIG.

29

. Note that the timing of executing the failure determination is not limited to a period during the image forming operation.

Upon the start of control for the failure determination on the sheet reversing path, it is first determined whether a motor driving the sheet reversing roller pair

28

in the first reversing inlet path

52

is out of synchronism (ST

601

). This determination can be made by memorizing the occurrence of out-of-synchronism based on the image forming operation in the past. As an alternative, the motor may be actually driven to make determination on out-of-synchronism. If it is determined in ST

601

that the motor is out of synchronism, the control flow proceeds to ST

603

to recognize that a failure or trouble occurs in the first reversing inlet path

52

. If it is determined in ST

601

that the motor is not out of synchronism, it is determined in ST

602

whether a jam frequently occurs in the first reversing inlet path

52

. If so, the control flow also proceeds to ST

603

to confirm that a failure or trouble occurs in the first reversing inlet path

52

. The determination on the frequent occurrence of a jam can be made based on the fact that the number of jams has exceeded a preset limit value. As an alternative, the determination may be made based on a rate of jam frequency within a certain period.

The failure determination on the second reversing inlet path

53

is likewise performed by confirming the out-of-synchronism of the associated motor and the frequent occurrence of a jam (ST

604

, ST

605

). Then, based on the determination result, the occurrence of a failure or trouble is recognized (ST

606

).

A series of control flow in the face-down sheet ejection mode when there is neither failure nor trouble in both the first reversing inlet path

52

and the second reversing inlet path

53

, will be described below with reference to schematic operational views of

FIGS. 30A

to

30

G.

First, as shown in

FIG. 30A

, sheets, each of which is subjected to the fusing of the toner image by the fusing unit

20

, are successively transported at a predetermined sheet interval. When the leading end of a sheet

1

at an odd page in total sheet order, i.e., a head sheet, is detected by the first inner sheet ejection sensor

21

, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A because the sheet

1

is an odd one, whereupon the sheet

1

is guided to the sheet straight feed path

50

. A sheet

2

at an even page in total sheet order is transported after the sheet

1

at the predetermined sheet interval.

Then, as shown in

FIG. 30B

, when the leading end of the sheet

1

is detected by the second inner sheet ejection sensor

22

, the CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the sheet

1

is guided to the first reversing inlet path

52

. Also, when the leading end of the even sheet

2

is detected by the first inner sheet ejection sensor

21

, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction E because the sheet

2

is an even one, whereupon the sheet

2

is guided to the second reversing inlet path

53

. A sheet

3

is transported after the sheet

2

at the predetermined sheet interval. Thus, of subsequent sheets, an odd sheet is guided to the first reversing inlet path

52

as with the sheet

1

and an even sheet is guided to the second reversing inlet path

53

as with the sheet

2

in sequence.

Then, as shown in

FIG. 30C

, after the lapse of a predetermined time, the CPU

60

starts forward rotation of the stepping motors (not shown) for driving the re-feed roller pairs

33

,

35

to be ready for guiding the sheet

1

to the first reversing path (first sheet re-feed path)

54

. At this time, the three-roller unit

36

is already rotated.

Thereafter, as shown in

FIG. 30D

, when the first reversal sensor

23

detects the tailing end of the sheet

1

, the CPU

60

temporarily stops the stepping motor for driving the re-feed roller pair

33

so that the sheet

1

is stopped in the first reversing path

54

. Likewise, when the second reversal sensor

24

detects the tailing end of the sheet

2

, the CPU

60

temporarily stops the stepping motor for driving the re-feed roller pair

35

so that the sheet

2

is stopped in the second reversing path

55

.

After the sheet

1

has been temporarily stopped in

FIG. 30D

, the CPU

60

starts backward rotation of the stepping motor for driving the re-feed roller pair

33

at once, whereupon the sheet

1

is transported to the sheet reversing ejection path

56

, as shown in FIG.

30

E. At this time, the elastic member provided in the three-roller unit

36

guides the sheet to be directed toward the junction point of the sheet reversing ejection path

56

and the duplex feed path

57

. On the other hand, after the sheet

2

has been temporarily stopped, whether the sheet

2

does hit the sheet

1

, i.e., the preceding sheet, is determined prior to starting backward transport of the sheet

2

. If it is determined that the sheet

2

does not hit the sheet

1

, the CPU

60

starts backward rotation of the stepping motors (not shown) for driving the re-feed roller pairs

34

,

35

, and at the same time switches over the flapper

44

so as to transport the sheet in the direction C, whereupon the sheet

2

is guided to the sheet reversing ejection path

56

. At this time, the flapper

42

for selectively guiding the sheet to one of the sheet reversing ejection path

56

and the duplex feed path

57

is already switched over so as to transport the sheet the sheet reversing ejection path

56

.

Then, as shown in

FIG. 30F

, the sheet

1

is transported through the sheet reversing ejection path

56

in the ejection direction, and the sheet

2

is guided to the sheet reversing ejection path

56

through the first reversing path

54

after the sheet

1

. On the other hand, before the leading end of the sheet

3

bites into the three-roller unit

36

, the timing of finishing the use of the re-feed roller pair

33

for the sheet

2

is compared with the timing of starting the use of the re-feed roller pair

33

for the sheet

3

. If it is determined that the timing of starting the use of the re-feed roller pair

33

for the sheet

3

is earlier, the sheet

3

is temporarily stopped to stand by before the three-roller unit

36

. After repeating the comparison between the timing of finishing the use of the re-feed roller pair

33

for the sheet

2

and the timing of starting the use of the re-feed roller pair

33

for the sheet

3

, if it is determined that the timing of starting the use of the re-feed roller pair

33

for the sheet

3

is later, the transport of the sheet

3

is resumed. The three-roller unit

36

is of a structure allowing the sheet

3

transported toward the first reversing path

54

and the sheet

2

transported toward the sheet reversing ejection path

56

to pass each other in the opposite directions.

Then, as shown in

FIG. 30G

, the sheets

1

and

2

are continuously transported in the ejection direction. The sheet

3

is transported to the first reversing path

54

while passing by the sheet

2

in the opposed direction, and a sheet

4

is guided to the second reversing path

55

, respectively, in a similar manner to the preceding odd and even sheets. Subsequent sheets are successively transported to the respective reversing paths and then transported backward as with the sheets

1

and

2

in sequence, whereby the face-down ejection mode is continuously performed.

The sheet straight feed path

50

, the first reversing inlet path

52

, the second reversing inlet path

53

, the first reversing path

54

, and the second reversing path

55

are each formed to have a feed path length greater than the sheet size. With such an arrangement, if it is determined that the feed of the preceding sheet is delayed or that the sheet interval is reduced because of earlier arrival of the relevant sheet, the relevant sheet can be held on standby in each feed path so as to absorb variations in feed of the preceding sheet.

A series of control flow in the face-down sheet ejection mode when there is neither failure nor trouble in the first reversing inlet path

52

, but there is a failure or trouble in the second reversing inlet path

53

, will be described below with reference to schematic operational views of

FIGS. 31A

to

31

G.

First, as shown in

FIG. 31A

, sheets, each of which is subjected to the fusing of the toner image, are successively transported at a greater sheet interval by reducing the productivity of the copying machine than the predetermined one set for the case in which there is neither failure nor trouble in both the first reversing inlet path

52

and the second reversing inlet path

53

, because it is recognized from the failure determination on the sheet reversing path that a failure or trouble occurs in the second reversing inlet path

53

. When the leading end of a sheet

1

, i.e., a head sheet, is detected by the first inner sheet ejection sensor

21

, the CPU

60

switches over the flapper

43

so as to transport the sheet in the direction A, whereupon the sheet

1

is guided to the sheet straight feed path

50

.

The reason why the sheet interval must be increased when sheets are all reversed using only one sheet reversing path, is as follows. The sheets are drawn one by one from the sheet reversing inlet path into the sheet reversing path. After stopping the drawn sheet in the sheet reversing path, it is transported backward through the sheet reversing path, and then guided to the sheet reversing ejection path

56

or the duplex feed path

57

. Before starting to draw the next sheet, therefore, the process of reversing the preceding sheet in the sheet reversing inlet path to the sheet reversing path must have been finished to be ready for drawing the next sheet. Correspondingly, the sheet interval must be increased in comparison with that required in the case of reversing sheets using two sheet reversing paths.

More particularly, when a sheet is reversed using the first reversing inlet path

52

, the sheet interval can be reduced to some extent because the three-roller unit

36

allows a preceding sheet and a succeeding sheet to pass each other in the opposite directions. However, because a preceding sheet and a succeeding sheet are not allowed to pass each other in the opposite directions when using the second reversing inlet path

53

, the succeeding cannot be drawn into the second sheet reversing path

55

before the preceding sheet has completely passed the junction point of the second reversing inlet path

53

and the second reversing path. This raises the necessity of increasing the sheet interval.

Subsequently, as shown in

FIG. 31B

, when the leading end of the sheet

1

is detected by the second inner sheet ejection sensor

22

, the CPU

60

switches over the flapper

40

so as to transport the sheet in the direction B, whereupon the sheet

1

is guided to the first reversing inlet path

52

. Because of the result of the failure determination, the succeeding sheet

2

is transported after the sheet

1

at the sheet interval corresponding to the reduced productivity.

Then, as shown in

FIG. 31C

, after the lapse of a predetermined time, the CPU

60

starts forward rotation of the stepping motor (not shown) for driving the re-feed roller pair

33

, whereupon the sheet

1

is transported to the first reversing path

54

. Because it is determined that the second reversing inlet path

53

is disabled due to a failure, the sheet

2

is also transported in the direction A as with the sheet

1

. At this time, the three-roller unit

36

is already rotated.

Thereafter, as shown in

FIG. 31D

, when the first reversal sensor

23

detects the tailing end of the sheet

1

, the CPU

60

temporarily stops the stepping motor for driving the re-feed roller pair

33

so that the sheet

1

is stopped in the first reversing path

54

. The sheet

2

is transported through the same feed rout as that for the sheet

1

.

After the sheet

1

has been temporarily stopped in

FIG. 31D

, the CPU

60

starts backward rotation of the stepping motor for driving the re-feed roller pair

33

at once and switches over the flapper

42

so as to transport the sheet in the direction toward the sheet reversing ejection path

56

, whereupon the sheet

1

is transported to the sheet reversing ejection path

56

, as shown in FIG.

31

E. At this time, the elastic member provided in the three-roller unit

36

guides the sheet to be directed toward the junction point of the sheet reversing ejection path

56

and the duplex feed path

57

. The sheet

2

is likewise transported. Furthermore, a sheet

3

is transported at the sheet interval corresponding to the reduced productivity as with the sheet

2

.

Then, as shown in

FIG. 31F

, the sheet

1

is transported through the sheet reversing ejection path

56

in the ejection direction, and the sheet

2

is guided to the first reversing path

54

after the sheet

1

. The sheet

3

is transported through the same feed rout as that for the preceding sheet.

Then, as shown in

FIG. 31G

, the sheet

1

is continuously transported in the ejection direction, the sheet

2

is transported to the first reversing path

54

, and the sheet

3

is transported through the same feed rout as that for the preceding sheet. Thus, subsequent sheets are successively transported to the first reversing path and then transported backward as with the sheets

1

and

2

, whereby the face-down ejection mode is continuously performed.

Fifth Embodiment

In a fifth embodiment of the present invention, first and second sheet jam detecting units S

1

, S

2

(shown in

FIG. 25

) for detecting a sheet jam are disposed in the first reversing inlet path

52

and the second reversing inlet path

53

, respectively, to directly detect an operation failure. The remaining arrangement is the same as that in the embodiments described above.

In the above-described basic operation of the face-down sheet ejection mode in single-sided copying and of the duplex copying mode, the sheet transported from the inner sheet ejection roller pair

25

is selectively advanced in the direction B (toward the first reversing inlet path

52

) or in the direction E (toward the second reversing inlet path

53

) under control of the CPU

60

.

When a jam of the sheet is detected by the first sheet jam detecting unit Si in the first reversing inlet path

52

, the CPU

60

controls the flapper

43

to be operated such that the sheet is transported only in the direction E. As a result, the face-down sheet ejection mode in single-sided copying and the duplex copying mode are performed using only the second reversing inlet path

53

.

When a jam of the sheet is detected by the second sheet jam detecting unit S

2

in the second reversing inlet path

53

, the CPU

60

controls the flapper

43

to be operated such that the sheet is transported only in the direction A. As a result, the face-down sheet ejection mode in single-sided copying and the duplex copying mode are performed using only the first reversing inlet path

52

.

The first reversing inlet path

52

and the second reversing inlet path

53

are each of a structure capable of drawing it from the front side of the image forming apparatus even during the operation of the apparatus unless the relevant reversing inlet path is operated. Even if a jam occurs in one reversing inlet path, the apparatus can continue the operation using the other reversing inlet path. Accordingly, the sheet jammed in the reversing inlet path can be removed without interrupting the apparatus operation.

When the reversing inlet path restored from the jam is inserted in the apparatus and the associated jam detecting unit detects the absence of a jam, the CPU

60

control sheets to be transported through both the first reversing inlet path

52

and the second reversing inlet path

53

in the same manner as that prior to the occurrence of a jam.

With a sheet feed mechanism constructed as described above, in the face-down sheet ejection mode in single-sided copying and the duplex copying mode, when the sheet jam detecting unit in one reversing inlet path detects a jam, the apparatus operation is prevented from being stopped by feeding sheets through the other reversing inlet path in which a jam does not occur. Also, by removing the jammed sheet during the apparatus operation, restoring the apparatus to a normal condition, and then operating the apparatus in the same way as that before the occurrence of jam, the jam eliminating process can be realized without stopping the apparatus at all.

The present invention is not limited to the above-described embodiment. For example, while a stepping motor is employed as the driving source for the duplex feed in the above-described embodiment, a clutch may be used instead. Also, while productivity is improved in the above-described embodiment without speed-up control in the reversing process to suppress an increase of the motor cost, it is possible to further improve productivity with the speed-up control. Thus, the sheet transport speed in the reversing and duplex sections is not limited to a constant speed, but may be freely set.

Additionally, in the above-described embodiment, when a sheet is transported backward after passing the position at which the sheet is reversed, the CPU

60

controls the sheet to be transported backward when the tailing end of the sheet is detected by the first reversal sensor

23

or the second reversal sensor

24

. However, the backward transport of the sheet may be started on an assumption that the tailing end of the sheet reaches the reversal position after a predetermined time from the timing at which the leading end of the sheet has been detected by the first inner sheet ejection sensor

21

or the second inner sheet ejection sensor

22

. This modification is effective in reducing the number of parts and hence cutting the cost.

While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Number	Date	Country	Kind
2002-103937	Apr 2002	JP
2002-137090	May 2002	JP

Number	Name	Date	Kind
4573789	Wada	Mar 1986	A
5393043	Nitta	Feb 1995	A
5532793	Kogure	Jul 1996	A
5727784	Sagawa	Mar 1998	A
6317581	Boehmer et al.	Nov 2001	B1
6330422	Sato et al.	Dec 2001	B1
6549748	Miura	Apr 2003	B2
6556794	Miura	Apr 2003	B2
6615018	Funato	Sep 2003	B2
6647243	Sato et al.	Nov 2003	B2

Number	Date	Country
58-182655	Oct 1983	JP
06-035265	Feb 1994	JP

Image forming apparatus with control to divert sheet to usable path

Information

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Date Filed

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Agents

CPC

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US

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Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (10)

Foreign Referenced Citations (2)