Image forming apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an image forming apparatus adopting the electrophotographic process, the electrostatic recording process or the like, and particularly to an image forming apparatus using a transfer material transporting member and a transfer medium as an intermediate transfer member, and having the function of automatically correcting image misregister during image-on-image formation.

2. Description of Related Art

There has heretofore been proposed an image forming apparatus in which there are disposed a plurality of image forming means each for applying a laser beam modulated in conformity with recording information to a photosensitive drum which is an image bearing member or light emitted by a light emitting element such as an LED (light emitting diode), developing an electrostatic latent image formed on the photosensitive drum by the electrophotographic process and transferring a toner image of each color to transfer paper or an intermediate transfer belt, and the toner images of respective colors are multi-transferred on the transfer paper while the transfer paper is sequentially transported to the respective image forming means by a transfer material transporting belt or the toner images of respective colors are multi-transferred on the intermediate transfer belt, thereafter a color image can be formed by a method of collectively transferring the polychromatic toner images primary-transferred to the intermediate transfer belt to the transfer paper.

In the image forming apparatus of this type, there is a case where the positions (registrations) of the respective color images formed on the respective photosensitive drums are not registered with one another on the transfer material to which they are finally multi-transferred, for such reasons as the mechanical mounting errors among the photosensitive drums, the optical path length errors of the respective laser beams, the changes in the optical path and the warp of the LED by the environmental temperature.

Therefore, as shown in

FIG. 2

of the accompanying drawings, an image misregister detection pattern

3

formed from each photo-sensitive drum onto the transfer material transporting belt or the intermediate transfer belt

31

which is a transfer medium is read by light sensors

2

a

,

2

b

, and the deviation of registration on the photosensitive drum corresponding to each color is detected, and electrical correction is effected on an image signal to be recorded and a turn-back mirror provided in the optical path of the laser beam is driven to thereby effect the correction of any change in the optical path length or any change in the optical path.

Various patterns have been proposed as the image misregister detection pattern

3

, and for example, in Japanese Patent Application Laid-Open No. 2000-98810, there is proposed a pattern comprising a first segment disposed with a predetermined angle with respect to a process direction which is the direction of movement of a transfer belt and a second segment disposed axisymmetrically with the first segment with respect to an imaginary line orthogonal to the process direction.

FIG. 2

shows the manner in which the light sensors

2

a

,

2

b

detect the image misregister detection pattern

3

on the intermediate transfer belt

31

which is a belt member, and the image misregister detection pattern

3

is read by the light sensors

2

a

,

2

b

of an LED

4

a

which is a light emitting element and a phototransistor

4

b

which is a light receiving element. These light sensors

2

a

,

2

b

are disposed in two sets (

2

a

and

2

b

) at a predetermined distance therebetween in a direction orthogonal to the process direction, and the image misregister detection pattern

3

is formed so as to pass on the light sensors

2

a

,

2

b.

As the material of the intermediate transfer belt

31

, use is made of a material of which the reflectance for the light (e.g. infrared light) applied from the LED

4

a

which is a light emitting element in the light sensors

2

a

,

2

b

is great as compared with the reflectance of the image misregister detection pattern

3

, and by this difference in reflectance, the pattern detection of the image misregister detection pattern

3

is made possible.

FIG. 3

of the accompanying drawings shows a light receiving circuit

17

for reflecting the light applied from the LED

4

a

to the image misregister detection pattern

3

or the intermediate transfer belt

31

, and converting the output signal when the reflected light thereof is received by the phototransistor

4

b

which is a light receiving element into an electrical signal.

In

FIGS. 2 and 3

, when a region of the intermediate transfer belt

31

is detected by the light sensors

2

a

,

2

b

, the quantity of reflected light is great and therefore a great deal of photocurrent passes through the phototransistor

4

b

and it is current/voltage-converted by a resistor

5

, and is amplified by resistors

6

,

7

,

8

and an operational amplifier

9

.

On the other hand, when the image misregister detection pattern

3

is detected by the light sensors

2

a

,

2

b

, the quantity of reflected light is small and therefore, a photocurrent small as compared with that in the region of the intermediate transfer belt

31

passes through the phototransistor

4

b

, and it is likewise current/voltage-converted by the resistor

5

, and is amplified by the resistors

6

,

7

,

8

and the operational amplifier

9

.

FIG. 4

of the accompanying drawings shows a state in which the light receiving circuit

17

has detected the reflected light in the order of a region of the intermediate transfer belt

31

→the image misregister detection pattern

3

→a region of the intermediate transfer belt

31

. In

FIG. 4

, a threshold level Vt is set intermediately of a transfer belt detection level Va at which the intermediate transfer belt

31

has been detected by the light sensors

2

a

,

2

b

and a pattern detection level Vb at which the image misregister detection pattern

3

has been detected.

This threshold level Vt is set by a variable resistor

18

shown in

FIG. 3

, and by a voltage value outputted from the operational amplifier

9

after the photocurrent passing through the phototransistor

4

b

has been current/voltage-converted and the voltage value of the threshold level Vt set by the variable resistor

18

being compared with each other by a comparator

19

, a pattern detection output

28

shown in

FIG. 4

can be created.

Design is made such that the pattern detection output

28

sequentially sent is read, and the deviation of registration is detected from the width, interval or the like of the image misregister detection pattern

3

and electrical correction is effected on an image signal to be recorded and further, the turn-back mirror provided in the optical path of the laser beam is driven to thereby effect the correction of any change in the optical path length or any change in the optical path.

However, when in the aforedescribed example of the conventional art, an unexpected stain, scar or the like occurs on the intermediate transfer belt

31

, reflectance is reduced on such portions and the reflected light may not be received in some cases by the phototransistor

4

b

in the light sensors

2

a

,

2

b.

In that case, the stain or scar on the intermediate transfer belt

31

is recognized as the detection pattern

3

, and the accurate width or interval of the image misregister detection pattern

3

cannot be read, and this has led to the problem that the deviation of registration cannot be corrected accurately.

SUMMARY OF THE INVENTION

The present invention solves the above-noted problem and the object thereof is to provides, in a construction for detecting an image misregister detection pattern, and on the basis of the result thereof, effecting the registration correction of image forming means, an image forming apparatus which is free from wrong detection due to the stain, scar or the like of a transfer medium and which precisely reads only the image misregister detection pattern to thereby effect highly accurate correction and realize a high quality of image.

A preferred form of the present invention for achieving the above object is an image forming apparatus comprising:

at least two image forming means;

transferring means for successively superimposing and transferring images formed by the image forming means onto a transfer medium;

pattern forming means for forming an image misregister detection pattern for detecting the positional deviation between the images formed by the image forming means;

pattern detection means for detecting the image misregister detection pattern formed on the transfer medium by the pattern forming means;

pattern position detecting means for detecting the position of the image misregister detection pattern from a detection signal obtained from the pattern detecting means; and

positional deviation correcting means for correcting the positional deviation of at least one of the image forming means on the basis of the result of the detection of the pattern position detecting means;

wherein the pattern positional detecting means detects the time at a point of time whereat the detection signal of the pattern detecting means has been continuously outputted for a predetermined time, and the time at a point of time whereat thereafter the outputting of the detection signal has been stopped, to thereby detect the position of the image misregister detection pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a cross-sectional illustration showing the construction of an image forming apparatus according to the present invention.

FIG. 2

is a typical illustration showing the manner in which an image misregister detection pattern on a belt member is read by a light sensor.

FIG. 3

shows the construction of a light receiving circuit for receiving the output of the light sensor.

FIG. 4

shows the output of the light sensor and the pattern detection output of the light receiving circuit when the image misregister detection pattern has been read.

FIG. 5

shows an example of the image misregister detection pattern formed on the belt member.

FIG. 6

is a timing chart when the data of the image misregister detection pattern are stored.

FIG. 7

is a timing chart when the data of the image misregister detection pattern are stored.

FIG. 8

is a flowchart illustrating the registration correcting operation.

FIG. 9

is a block diagram showing the construction of a control system.

FIG. 10

shows the constructions of a pattern width and position storing portion.

FIG. 11

shows another form of the image forming apparatus to which the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As an example of an image forming apparatus according to the present invention, an embodiment in which the present invention is applied to a tandem type color image outputting apparatus having a plurality of image forming means arranged in a row will hereinafter be described specifically with reference to the drawings.

Referring to

FIG. 1

, the image forming apparatus

1

is of the electrophotographic type and is constructed as a so-called tandem type color image outputting apparatus having a plurality of image forming means arranged in a row.

The color image forming apparatus

1

shown in

FIG. 1

comprises an image reading portion

1

a

and an image outputting portion

1

b

, and the image reading portion

1

a

optically reads the image of an original placed on a platen glass plate

1

c

or transported by an auto original feeder (not shown) and converts it into an electrical signal and sends it to the image outputting portion

1

b.

The image outputting portion

1

b

is broadly divided into an image forming portion

10

, in which four stations a, b, c and d as image forming means are juxtaposed and are the same in construction, a feed unit

20

for feeding transfer materials P contained in feed cassettes

21

a

,

21

b

and a manual feed tray

27

, an intermediate transfer unit

30

for secondary-transferring to the transfer material P toner images primary-transferred to an intermediate transfer belt

31

which is a transfer medium and comprises an intermediate transfer member at the stations a, b, c and d, a fixing unit

40

for fixing the toner images secondary-transferred to the transfer material P, a cleaning unit

50

for removing any residual toners on the intermediate transfer belt

31

, and a control unit

60

for comprehensively controlling these units.

In the image forming portion

10

, photosensitive drums

11

a

,

11

b

,

11

c

and

11

d

as image bearing members are supported at the centers thereof and are rotatively driven in the directions indicated by the arrows in FIG.

1

. Primary chargers

12

a

,

12

b

,

12

c

,

12

d

, optical systems

13

a

,

13

b

,

13

c

,

13

d

, turn-back mirrors

16

a

,

16

b

,

16

c

,

16

d

and developing devices

14

a

,

14

b

,

14

c

,

14

d

are disposed around the photosensitive drums

11

a

to

11

d

and in opposed relationship with the outer peripheral surfaces of the photosensitive drums

11

a

to

11

d.

First, charges of a uniform charging amount are given to the surfaces of the photosensitive drums

11

a

to

11

d

by the primary chargers

12

a

to

12

d

, whereafter by the optical systems

13

a

to

13

d

, the photosensitive drums

11

a

to

11

d

are exposed to a light such as a laser beam modulated in conformity with a recording image signal to thereby form electrostatic latent images thereon.

Further, developers of four colors, i.e., yellow, cyan, magenta and black (hereinafter referred to the toners) are supplied to the electrostatic latent images by the developing devices

14

a

to

14

d

containing these toners therein to thereby visualize the electrostatic latent images.

Downstream of primary transfer areas Ta, Tb, Tc and Td for transferring the visualized visible images to the intermediate transfer belt

31

which is an intermediate transfer member, any residual toners left on the photosensitive drums

11

a

to

11

d

without being transferred to the transfer material P are scraped off by the cleaning devices

15

a

,

15

b

,

15

c

and

15

d

to thereby effect the cleaning of the surfaces of the photosensitive drums

11

a

to

11

d

. By the image forming process shown above, the image formation by the toners of the respective colors is sequentially effected.

The feed unit

20

is comprised of the feed cassettes

21

a

,

21

b

and the manual feed tray

27

for containing the transfer materials P therein, pickup rollers

22

a

,

22

b

,

26

for feeding the transfer materials P one by one from the feed cassettes

21

a

,

21

b

or the manual feed tray

27

, a pair of feed rollers

23

and a feed guide

24

for transporting the transfer materials P fed by the pickup rollers

22

a

,

22

b

,

26

to a pair of registration rollers

25

, and the pair of registration rollers

25

for feeding the transfer material P to a secondary transfer area Te in timed relationship with the image formation by the image forming portion

10

.

The construction of the intermediate transfer unit

30

will now be described in detail. The intermediate transfer belt

31

which is a belt member is formed, for example, of PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride) or the like, and is looped around a drive roller

32

for transmitting a rotative driving force to the intermediate transfer belt

31

, a tension roller

33

for giving moderate tension to the intermediate transfer belt

31

by the biasing of a spring or the like (not shown) and a driven roller

34

opposed to the secondary transfer area Te with the intermediate transfer belt

31

interposed therebetween.

The intermediate transfer belt

31

has a primary transfer flat surface A formed between the drive roller

32

and the tension roller

33

.

The drive roller

32

comprises a metal roller having its surface coated with rubber (e.g. urethane rubber or chloroprene rubber) having a thickness of several millimeters to thereby prevent the slip thereof relative to the intermediate transfer belt

31

. Also, the drive roller

32

is rotatively driven by a pulse motor (not shown).

Primary transfer chargers

35

a

,

35

b

,

35

c

, and

35

d

are disposed on the backside of the intermediate transfer belt

31

at the primary transfer areas Ta, Tb, Tc, and Td in which the photosensitive drums

11

a

to

11

d

are opposed to the intermediate transfer belt

31

.

A secondary transfer roller

36

is disposed in opposed relationship with the driven roller

34

with the intermediate transfer belt

31

interposed therebetween, and the secondary transfer area Te is formed by the nip portion thereof with respect to the intermediate transfer belt

31

.

The secondary transfer roller

36

is urged against the intermediate transfer belt

31

, which is a belt member and is an intermediate transfer member under a moderate pressure. Also, the cleaning unit

50

for cleaning the image forming surface of the intermediate transfer belt

31

is provided on the intermediate transfer belt

31

and downstream of the secondary transfer area Te in the direction of rotation of the intermediate transfer belt

31

.

The cleaning unit

50

is provided with a cleaning blade

51

abutting against the surface of the intermediate transfer belt

31

, and a waste toner box

52

for containing therein the residual toners scraped off by the cleaning blade

51

.

The fixing roller

40

is comprised of a fixing roller

41

a

provided with a heat source such as a halogen heater therein, a pressure roller

41

b

urged against the fixing roller

41

a

(in some cases, the pressure roller

41

b

is also provided with a heat source therein), a transport guide

43

for guiding the transfer material P to the nip portion between the above-described pair of rollers

41

a

and

41

b

, fixing adiabatic covers

46

,

47

for confining the heat of the fixing unit

40

therein, a pair of inner delivery rollers

44

and a pair of outer delivery rollers

45

for further directing the transfer material P delivered from the above-described pair of rollers

41

a

and

41

b

to the outside of the image forming apparatus

1

, and a delivery tray

48

for stacking thereon the transfer materials P delivered to the outside of the apparatus.

The control unit

60

, as shown in detail in

FIG. 9

, is comprised of a CPU (central processing unit)

61

for controlling the operation of a mechanism in each of the above-described units, a RAM (random access memory)

62

, a ROM (read only memory)

63

, a motor driver portion

64

, etc., and further a light receiving circuit

17

, a pattern width shaping portion

29

and a pattern width and position storing portion (register)

37

which will be described later in detail.

The image forming operation of the image forming apparatus

1

will now be described in detail. When an image forming operation starting signal is generated from the CPU

61

shown in

FIG. 9

, the feeding operation is started from the feeding means selected in conformity with the selected paper size or the like of the transfer material P.

Describing a case where the transfer material has been fed, for example, from the upper feeding means shown in

FIG. 1

, the transfer materials P are first fed one by one from the feed cassette

21

a

by the pickup roller

22

a

. The transfer material P is then guided between the feed guides

24

by the pair of feed rollers

23

and is transported to the pair of registration rollers

25

.

At that time, the pair of registration rollers

25

are at a stop and the leading edge of the transfer material P hits against the nip portion between the pair of registration rollers

25

. Thereafter, the pair of registration rollers

25

start to be rotated in timed relationship with the start of the image formation by the image forming portion

10

.

The rotation timing of the pair of registration rollers

25

is set so that the toner images primary-transferred onto the intermediate transfer belt

31

by the image forming portion

10

and the transfer material P may just be registered with each other in the secondary transfer area Te.

On the other hand, in the image forming portion

10

, when an image forming operation starting signal is generated, the toner image formed on the photosensitive drum

11

d

lying most upstream in the direction of rotation of the intermediate transfer belt

31

by the aforedescribed image forming process is primary-transferred to the intermediate transfer belt

31

in the primary transfer area Td by a primary transfer charger

35

d

to which a high voltage is applied.

The primary-transferred toner image is transported to the next transfer area Tc. There is being effected there image formation with a delay of the time for which the toner image is transported between the adjacent ones of the image forming portions

10

, and the next toner image is registered with and transferred onto the previous toner image. Thereafter a similar process is repeated and after all, the toner images of the four colors are successively primary-transferred on the intermediate transfer belt

31

.

Thereafter, the transfer material P comes into the secondary transfer area Te and comes into contact with the intermediate transfer belt

31

, whereupon a high voltage is applied to the secondary transfer roller

36

in timed relationship with the passage of the transfer material P.

Then, the toner images of the four colors formed on the intermediate transfer belt

31

by the aforedescribed image forming process are transferred to the surface of the transfer material P. Thereafter, the transfer material P is accurately guided to the nip portion between the fixing roller

41

a

and the pressure roller

41

b

by the transport guide

43

.

The toner images are fixed on the surface of the transfer material P by the heat of the pair of rollers

41

a

and

41

b

and the pressure of the nip. Thereafter, the transfer material P is transported to the outside of the apparatus by the pair of inner and outer delivery rollers

44

and

45

and is stacked on the delivery tray

48

.

The registration correcting operation will now be described with reference to the block diagram of the control unit shown in FIG.

9

. The control unit

60

of

FIG. 9

comprises the CPU

61

for controlling the image output portion

1

b

, the ROM

63

and RAM

62

for storing a control program and data therein, the motor driven portion

64

for driving various motors, the light receiving circuit

17

for receiving the output from the light sensors

2

a

,

2

b

shown in

FIG. 2

, and converting it into a waveform which can be processed by the pattern width shaping portion

29

, the pattern width shaping portion

29

for receiving the output from the light receiving circuit

17

and shaping the pattern width of the image misregister detection pattern

3

, and the pattern width and position storing portion (the registers D to S of

FIG. 10

)

37

for storing the pattern width and position of the image misregister detection pattern

3

therein.

The registration correcting operation is started by the instructions from the CPU

61

, and when the image misregister detection pattern

3

is detected, it is converted into an electrical signal by the light sensors

2

a

,

2

b

shown in FIG.

2

and the light receiving circuit

17

shown in

FIG. 3

, and is inputted to the pattern width shaping portion

29

.

In the pattern width shaping portion

29

, as shown in

FIG. 6

, only when the output continues for a predetermined time T set by the CPU

61

or longer, it is discriminated as the image misregister detection pattern

3

, and the control of storing the pattern width and the pattern position in the pattern width and position storing portion (register)

37

is effected. This pattern width shaping portion

29

and the control of the pattern width and position storing portion

37

will be described later in detail.

The position of the pattern is detected on the basis of the data stored in the pattern width and position storing portion

37

, and the deviation of registration on the photosensitive drums

11

a

to

11

d

corresponding to the respective colors is calculated by the use of a table or the like stored in the CPU

61

and the ROM

63

, and electrical correction is effected on an image signal to be recorded or the motor for controlling the turn-back mirrors

16

a

to

16

d

is drive-controlled by the motor driver portion

64

to thereby control the turn-back mirrors

16

a

to

16

d

provided in the optical path of the laser beam, and effect the correction of any change in the optical path length or any change in the optical path.

These correcting operations are suitably performed to the plurality of image forming means as required.

In the present embodiment, the photosensitive drums

11

a

to

11

d

which are a plurality of image forming means for forming images serve also as pattern forming means for forming the image misregister detection pattern

3

for correcting the misregister of the images formed by the photosensitive drums

11

a

to

11

d

, and pattern detecting means for detecting the image misregister detection pattern

3

uses light sensors

2

a

,

2

b

similar to the aforedescribed conventional ones.

The light sensors

2

a

,

2

b

have an LED

4

a

which is a light emitting element, and a phototransistor

4

b

which is a light receiving element, and are designed to output a signal when light emitted from the LED

4

a

is reflected by the intermediate transfer belt

31

which is a belt member looped in proximity to the photosensitive drums

11

a

to

11

d

which are the image forming means and rotatively driven and the quantity of reflected light received by the phototransistor

4

b

is a predetermined value or greater.

As registration correcting means for correcting the registration among the photosensitive drums

11

a

to

11

d

which are the image forming means on the basis of the result of the detection by pattern detecting means constituted by the light sensors

2

a

,

2

b

, the light receiving circuit

17

, the pattern width shaping portion

29

and the pattern width and position storing portion

37

, electrical correction is effected on the image signal to be recorded or the motor for controlling the turn-back mirrors

16

a

to

16

d

is drive-controlled by the motor driver portion

64

to thereby control the turn-back mirrors

16

a

to

16

d

provided in the optical path of the laser beam and effect the correction of any change in the optical path length or any change in the optical path.

A construction for accurately detecting the pattern width and interval of the image misregister detection pattern

3

even if a stain or a scar is on the intermediate transfer belt

31

, which construction is to be said to be the feature of the present embodiment, will now be described with reference to the timing charts of

FIGS. 6 and 7

.

As regards an electrical signal outputted from the light receiving circuit

17

for receiving the output from the light sensors

2

a

,

2

b

shown in

FIG. 2

, and converting it into a waveform which can be processed by the pattern width shaping portion

29

shown in

FIG. 9

, the signal is outputted as in the case of the image misregister detection pattern

3

because reflectance also lowers when a scar or a stain is on the intermediate transfer belt

31

.

So, a control is effected in a manner that the waveform due to the scar or the stain by the pattern is eliminated from the signal outputted from the light receiving circuit

17

by the width shaping portion

29

, which is the pattern detecting means. When there is obtained an output from the light sensors

2

a

,

2

b

as shown, for example, in

FIG. 6

, such an output as will not reach a preset threshold level Vt can be eliminated by the light receiving circuit

17

.

An output exceeding the threshold level Vt, however, cannot be eliminated by the light receiving circuit

17

. So, in the pattern width shaping portion

29

, control is effected by the use of a counter or the like so that no signal may be outputted until an inputted signal continues for the predetermined time T or longer.

By effecting this control, it becomes possible to eliminate a signal due to the scar or the stain or the like which is finer than the image misregister detection pattern

3

. However, when the outputting of the signal has stopped, the signal is stopped at that point of time. This is because if it is not effected, there is the possibility that when there are many fine scars or stains, the signal will continue to be outputted. Thereby, as a waveform of the pattern width of the image misregister detection pattern

3

and other width due to a scar or a stain or the like, it becomes possible to obtain a pattern width shaping portion output signal from the pattern width shaping portion

29

, as shown in FIG.

6

.

The data storing timing in the pattern width and position storing portion (register)

37

will now be described with reference to FIG.

7

. On the basis of the pattern width shaping portion output signal obtained by the pattern width shaping portion

29

shown in

FIG. 7

, the counter is operated and further, a latch timing signal is generated and data are stored.

When for example, the image misregister detection pattern

3

as shown in

FIG. 5

is obtained by a signal as shown in

FIG. 7

, a counter value “0” is stored in the D register of the pattern width and position storing portion

37

shown in FIG.

10

.

Subsequently, the storing of counter value data into respective registers is effected in such a manner that “100” is stored in E register, “150” is stored in F register, “110” is stored in G register, and so on. By these data, it is possible to detect the pattern width and further, the pattern interval of the image misregister detection pattern

3

, and it also becomes possible to find the absolute position (the position of the pattern) from a signal detected at first.

However, it must be considered in calculation that in the pattern width shaping portion

29

, the actual sensor output by the light sensors

2

a

,

2

b

is delayed by a time T that is a predetermined time.

For example, assuming that the waveform shown in

FIG. 7

is the output waveform when it has been set as being delayed by 10(T=10) in terms of the counter value, the width of the pattern (

1

) is 110 counts. Also, the pattern (

2

) has a pattern width of 120 counts (110 counts+10(=T) counts), and the absolute distance of the central value of the pattern (

2

) from the central value of the pattern (

1

) is 255 counts (pattern (

1

) (55 counts)+interval (150 counts)+pattern (

3

)(50 counts)).

Such a count value correcting operation can be performed to the data stored in the register

37

by the CPU

61

, which is control means, for example, during the registration correcting operation of the CPU

61

. Thus, by this count value correcting operation being performed, the position of the pattern can be detected.

By the above-described control, it becomes possible to prevent the wrong detection of the image misregister detection pattern

3

due to a scar or a stain on the intermediate transfer belt

31

, and accurately detect the pattern width and interval and position of the image misregister detection pattern

3

.

That is, in the present embodiment, when in the pattern width shaping portion

29

which is pattern detecting means, the time for which the signal from the light sensors

2

a

,

2

b

is outputted is to be read by the counter, the counting of the time is started at a point of time whereat the signal from the light sensors

2

a

,

2

b

has been continuously outputted for the predetermined time T, and the count value of that time is read at a point of time whereat the signal output from the light sensors

2

a

,

2

b

has been stopped.

Also, when the time for which the signal from the light sensors

2

a

,

2

b

is not outputted is to be read by the counter, the counting of the time is started at the point of time whereat the signal output from the light sensors

2

a

,

2

b

has been stopped, and the count value of that time is read at the point of time whereat the signal has been continuously outputted for the predetermined time T.

Reference is now had to the flowchart of

FIG. 8

to describe the registration correcting operation sequence by the registration correcting means for correcting the registration of the photosensitive drums

11

a

to

11

d

which are the image forming means on the basis of the result of the detection by the pattern width shaping portion

29

which is the above-described pattern detecting means.

The CPU

61

shown in

FIG. 9

performs the registration correcting operation, for example, when the power supply switch of the image forming apparatus

1

is closed or when a predetermined time has passed after the power supply switch is closed.

When the registration correcting operation is started, the intermediate transfer belt

31

is rotatively driven at a step S

1

shown in

FIG. 8

, and at a step S

2

, the writing of the image misregister detection pattern

3

onto the intermediate transfer belt

31

is started by the photosensitive drums

11

a

to

11

d

. The LED

4

a

is turned on (step S

3

) before the image misregister detection pattern

3

written onto the intermediate transfer belt

31

passes the light sensors

2

a

,

2

b

, and at a step S

4

, the detecting operation for the image misregister detection pattern

3

is started.

At the step S

4

, as previously described, the signal from the light sensors

2

a

,

2

b

is passed through the light receiving circuit

17

and the pattern width shaping portion

29

for shaping the pattern width of the image misregister detection pattern

3

to thereby eliminate the wrong detection signal due to a scar or a stain or the like, and the pattern widths and positions of the image misregister detection pattern

3

are sequentially stored in registers D to S shown in the pattern width and position storing portion (register)

37

.

At a step S

5

, the LED

4

a

is turned off and the rotative driving of the intermediate transfer belt

31

is stopped, and the pattern width and interval detecting operation is terminated and advance is made to a step S

6

, where electrical correction is effected on the image signal to be recorded on the basis of the data stored in the aforementioned registers D to S and the table or the like stored in the ROM

63

, and the turn-back mirrors

16

a

to

16

d

provided in the optical path of the laser beam are driven to thereby effect the correction of any change in the optical path length or any change in the optical path, thus terminating the registration correcting operation.

For example,

FIG. 5

shows a state in which the image misregister detection patterns

3

are read and output thereof are stored. The position data and width data of a image misregister detection pattern

3

a

are stored in the registers D, E, F and G on the basis of an image misregister detection pattern output obtained by the light sensors

2

a

,

2

b

reading the image misregister detection pattern

3

a.

Likewise, the position data and width data of image misregister detection patterns

3

b

to

3

d

are stored in registers H to S, respectively, on the basis of image misregister detection pattern outputs obtained by the light sensors

2

a

,

2

b

reading the image misregister detection patterns

3

b

to

3

d.

Also, while in the present embodiment, description has been made of the registration correcting process in the intermediate transferring process (collectively transferring process) by the intermediate transfer belt

31

on which images are formed by the photosensitive drums

11

a

to

11

d

which are the image forming means, of course the present invention is also effectively applicable to the multi-transfer process by a transfer material transporting belt which is transfer material transporting means for transporting the transfer materials P on which images are formed by the image forming means.

FIG. 11

shows another form of the image forming apparatus to which the present invention is applicable, and this apparatus uses a transfer material transporting belt, which is a transfer material transporting member. In this apparatus, toner images formed by a plurality of image forming means

110

Y to

110

K are successively superimposed and transferred onto a transfer material borne on and transported by a transfer material transporting belt

108

, whereby a color image is formed. Describing the image forming means

110

Y in detail, an electrostatic latent image is formed on the surface of an image bearing member

113

Y uniformly charged by primary charging means

114

, by the exposure by exposing means

115

, and this latent image is developed as a toner image by developing means

116

. This toner image is transferred to a transfer material by transferring means

121

Y, and any untransferred toner is collected by a cleaner

117

.

The transfer material fed from a cassette

101

by feeding means

102

,

103

, and

104

starts to be fed by registration rollers

107

in synchronism with the image formation timing in the image forming means, and is borne on and transported by the transfer material transporting belt

108

and at the same time, toner images formed by the image forming means

110

Y to

110

K are successively superimposed and transferred onto the transfer material. After the transfer of all toner images is terminated, the transfer material is separated from the belt

108

, and the fixing of the toner images is effected by fixing means

118

.

In such an image forming apparatus, for the registration of the images among the image forming means, an image misregister detection pattern is formed on the transfer material transporting belt

108

and the detection thereof by the light sensors

2

a

,

2

b

is effected. During this detection, the method shown in the previous description is used.

While in the aforedescribed embodiment, description has been made of a case where the time until the signal of the pattern width shaping portion

29

is outputted is defined as the predetermined time T and set as a fixed value, it becomes possible for the CPU

61

of the control unit

60

to perform the detecting operation for detecting any stain or scar on the intermediate transfer belt

31

prior to performing the operation of detecting the image misregister detection pattern

3

, detect in advance the time during which the scar or stain can be removed, and determine the time T until the signal of the pattern width shaping portion

29

is outputted, to thereby enhance accuracy.

That is, before the correction of the registration of the photosensitive drums

11

a

to

11

d

which are the image forming means is effected by registration correcting means, the scar or stain detecting operation for detecting any scar or stain on the intermediate transfer belt

31

which is a belt member is performed by the light sensors

2

a

,

2

b

which are pattern detecting means, and in conformity with the width of the scar or stain detected by the pattern detecting means, the predetermined time T regarding the reading of the pattern detecting means is controlled.

For example, the detecting operation for the surface of the belt is performed while the belt is moved in a state in which the formation of the image misregister detection pattern

3

is not effected. If at this time, there is a signal detected by the length of a time T′ exceeding the time T, the scar or stain will be wrongly detected if the value of the time T remains unchanged. So, by changing the value of this time T to a value exceeding T′, it is possible to prevent the wrong detection due to the scar or stain.

Number	Name	Date	Kind
5740492	Deki et al.	Apr 1998	A
6128459	Iwata et al.	Oct 2000	A
6137517	Furst et al.	Oct 2000	A
6327453	Imaizumi et al.	Dec 2001	B1
6346958	Kanno	Feb 2002	B2
6385406	Funamizu et al.	May 2002	B1

Number	Date	Country
09185308	Jul 1997	JP
10198111	Jul 1998	JP
2000-98810	Apr 2000	JP

Image forming apparatus

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (6)

Foreign Referenced Citations (3)