IMAGE FORMING APPARATUS

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-166100 filed in Japan on Jul. 23, 2010, the entire contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an image forming apparatus such as a printer, a copier, and a multifunction peripheral.

As a conventional image forming apparatus, an apparatus is known that sorts sheets discharged by a discharge roller for discharging sheets such as recording papers to the outside, by causing shift of the discharge roller in the axial direction of the discharge roller (see JP H3-42460A, for example).

In such an image forming apparatus, when sheet types such as surface smoothnesses or basis weights are different (in particular, when sheets other than designated standard sheets are used), the stack properties of sheets discharged to a sheet discharge tray become poor, and, thus, the sheets are scattered in the sheet discharge tray, resulting in the problem that the sheets cannot be reliably separated and sorted.

In order to solve this problem, the sorting width of sheets discharged to the sheet discharge tray can be increased by increasing the shift width of the discharge roller, but, at that time, the width of the image forming apparatus in the axial direction of the discharge roller increases.

Regarding this aspect, JP 2000-153946A discloses a configuration in which, in order to obliquely discharge paper, a pair of discharge rollers for sandwiching and discharging paper are arranged such that they can be brought into contact with or separated from each other on one end side, and the conveying force applied to the paper at the time of paper discharge is applied to only one side.

Furthermore, JP 2009-069464A discloses a configuration in which, in order to obliquely discharge recording paper, a first and a second discharge roller are arranged in a line along an axis that extends in a direction perpendicular to the recording paper convey direction on the upstream side from the discharge tray, the discharge rollers are driven by mutually independent drive sources, and, thus, the revolving velocity of the first discharge roller is set higher than that of the second discharge roller.

According to these conventional configurations, the sorting width of discharged sheets can be increased without increasing the width of the image forming apparatus in the axial direction of the discharge roller. However, the mechanical structure of an existing discharge roller portion has to be changed, which accordingly increases the complexity and the cost of the mechanical structure in the image forming apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image forming apparatus that can increase the sorting width of discharged sheets, without increasing the width of the image forming apparatus in the axial direction of a discharge roller, and without changing the mechanical structure of an existing discharge roller portion, and, thus, can reliably separate and sort the sheets.

In order to solve the above-described problem, according to the present invention, the sorting width of discharged sheets is made larger than the shift amount of a discharge roller for discharging sheets to the outside, by adjusting a paper discharge timing for a sheet that is being discharged from the discharge roller with respect to shift of the discharge roller in the axial direction of the discharge roller.

That is to say, in order to solve the above-described problem, the present invention is directed to an image forming apparatus that sorts sheets discharged by a discharge roller for discharging sheets to the outside, by causing shift of the discharge roller along an axial direction of the discharge roller, including: a rotation driving portion configured to drive rotation of the discharge roller; a shift driving portion configured to drive shift of the discharge roller, thereby causing the shift; and a control portion configured to control driving of rotation of the rotation driving portion and driving of shift of the shift driving portion; wherein the control portion controls a discharge timing for a sheet that is being discharged such that a discharge direction upstream edge (trailing edge) of the sheet moves past the discharge roller during the shift of the discharge roller.

According to the present invention, only the control configuration of the control portion is changed, and, thus, the width of the image forming apparatus in the axial direction of the discharge roller is not increased, and the mechanical structure of an existing discharge roller portion is not changed. The control portion controls a discharge timing for a sheet that is being discharged such that the discharge direction upstream edge of the sheet moves past the discharge roller during the shift of the discharge roller, and, thus, the sheet whose upstream edge has moved past the discharge roller is discharged in a direction based not only on a discharge direction vector of the force of inertia in the discharge direction but also on an axial direction vector of the force of inertia in the axial direction. That is to say, the sheet whose upstream edge has moved past the discharge roller is discharged in a direction of a resultant vector obtained by adding the discharge direction vector and the axial direction vector, and, thus, the sheet whose upstream edge has moved past the discharge roller can be discharged to obliquely outer sides with respect to the discharge direction. Therefore, it is possible to increase the sorting width of discharged sheets, and, thus, it is possible to reliably separate and sort the sheets.

In an example mode of the present invention, the discharge timing at which the discharge direction upstream edge of the sheet that is being discharged moves past the discharge roller during the shift is a timing at which a movement velocity of the shift of the discharge roller is a maximum velocity.

With this specific mode, when the force of inertia in the axial direction is maximum, the discharge direction upstream edge of the sheet moves past the discharge roller during the shift. Thus, it is possible to accordingly increase the sorting width of discharged sheets.

In an example mode of the present invention, the discharge timing at which the discharge direction upstream edge of the sheet that is being discharged moves past the discharge roller during the shift is substantially equivalent to a timing at which the discharge roller reaches a movement end in the axial direction.

With this specific mode, the discharge direction upstream edge of the sheet that is being discharged moves past the discharge roller when the discharge roller reaches the vicinity of a movement end in the shift direction. Thus, it is possible to increase the movement distance in which the discharge roller conveying the sheet is shifted to the extent possible, and, thus, it is possible to accordingly increase the sorting width of discharged sheets.

Here, in order to improve the image forming speed, it is preferable to improve the sheet conveying velocity, but if the sheet conveying velocity is too large, a sheet pops out from the discharge roller in the discharge direction with too strong force, and, thus, a deterioration in the stack properties of the sheets occurs. From this point of view, the control portion preferably reduces a revolving velocity of the discharge roller before the discharge direction upstream edge of the sheet that is being discharged moves past the discharge roller.

With this specific mode, it is possible to convey the sheets at a high speed before the discharge direction upstream edge of the sheet that is being discharged moves past the discharge roller, and, thus, it is possible to suppress a deterioration in the stack properties of the sheets while accordingly increasing the image forming speed.

In an example mode of the present invention, the control portion more preferably reduces the revolving velocity of the discharge roller when starting the shift of the discharge roller.

With this specific mode, it is possible to prolong the period of time during which the sheets are conveyed at a high speed to the extent possible, and, thus, it is possible to suppress a deterioration in the stack properties of the sheets while accordingly increasing the image forming speed.

In an example mode of the present invention, the control portion rotates the discharge roller at a first revolving velocity, at a second revolving velocity that is higher than the first revolving velocity after a discharge direction downstream edge (leading edge) of the sheet has moved past the discharge roller, at a third revolving velocity that is higher than the first revolving velocity and lower than the second revolving velocity before the discharge direction upstream edge of the sheet moves past the discharge roller, and again at the first revolving velocity after the discharge direction upstream edge of the sheet has moved past the discharge roller.

With this specific mode, it is possible to perform efficient discharge timing control in which improvement in the image forming speed and suppression of a deterioration in the stack properties of sheets are well balanced.

In an example mode of the present invention, the control portion starts the shift of the discharge roller after the discharge direction upstream edge of the sheet that is being discharged has moved past a closest roller disposed closest to the discharge roller on an upstream side therefrom in a discharge direction of the sheet.

With this specific mode, the shift of the discharge roller is started after the discharge direction upstream edge of the sheet has moved past the closest roller, and, thus, the discharge roller can be shifted in a state where the sheet has been released from the closest roller. Therefore, it is possible to cancel the load by the closest roller on the sheet in the axial direction applied when the discharge roller is shifted, and, thus, it is possible to reduce damage to the sheet.

In an example mode of the present invention, a timing of starting the shift of the discharge roller can be adjusted.

With this specific mode, it is possible to change the timing of starting the shift of the discharge roller according to the driving properties of the rotation driving portion and the shift driving portion (e.g., the revolving velocity of the discharge roller driven by the rotation driving portion, or the shift width or the movement velocity of the discharge roller driven by the shift driving portion).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention when viewed from the front.

FIG. 2 is a schematic cross-sectional view showing a discharge roller in the image forming apparatus shown in FIG. 1 and portions close thereto.

FIG. 3 is a schematic side view of a sorting configuration in the image forming apparatus shown in FIG. 1 when viewed in a paper discharge direction.

FIG. 4 is a system block diagram of a control system of the image forming apparatus shown in FIG. 1.

FIGS. 5A to 5D are views for illustrating conventional timing control in the sorting configuration shown in FIG. 3, wherein FIG. 5A is a schematic plan view showing a state in which paper is discharged at a shift end on one side in the shift direction, FIG. 5B is a schematic plan view showing a state in which the paper is discharged at a shift end on the other side in the shift direction, FIG. 5C is a schematic cross-sectional view showing a state in which the paper is discharged at a point in time where a discharge roller shift unit reaches the shift end on the one side in the shift direction or the shift end on the other side, when viewed in the shift direction, and FIG. 5D is a schematic plan view showing the sorting width of paper discharged to a discharge tray and the positional relationship with respect to the discharge roller shift unit.

FIG. 6 is a timing chart showing a discharge timing according to conventional timing control in the sorting configuration shown in FIG. 3.

FIGS. 7A to 7C are views for illustrating timing control of this embodiment in the sorting configuration shown in FIG. 3, wherein FIG. 7A is a schematic plan view showing a state in which paper is discharged near the shift end on the one side in the shift direction, FIG. 7B is a schematic plan view showing a state in which the paper is discharged near the shift end on the other side in the shift direction X, and FIG. 7C is a schematic cross-sectional view showing a state in which the paper is discharged at a point in time where the discharge roller shift unit reaches the shift end on the one side in the shift direction X or the shift end on the other side, when viewed in the shift direction.

FIGS. 8A to 8D are views for illustrating timing control of this embodiment in the sorting configuration shown in FIG. 3, wherein FIGS. 8A and 8B are respectively a schematic plan view and a schematic side view showing a state in which the paper pops out from a nip portion of the discharge roller, FIG. 8C is a schematic side view showing a state in which the paper is placed on the discharge tray, and FIG. 8D is a schematic plan view showing the sorting width of the paper discharged to the discharge tray.

FIG. 9 is a timing chart showing a discharge timing according to timing control of this embodiment in the sorting configuration shown in FIG. 3.

FIG. 10 is a timing chart obtained by adding a chart of the shift velocity of the discharge roller to FIG. 9.

FIG. 11 is a timing chart showing a timing substantially equivalent to a timing at which the discharge roller shift unit reaches the shift end on the one side in the shift direction or the shift end on the other side in the configuration shown in FIG. 10.

FIG. 12 is a timing chart obtained by adding, to FIG. 11, timing control that increases the revolving velocity of the discharge roller after the leading edge of the paper has moved past the discharge roller and reduces the revolving velocity of the discharge roller before the trailing edge of the paper moves past the discharge roller.

FIG. 13 is a timing chart showing a timing at which shift of the discharge roller is started after the trailing edge of the paper has moved past the closest roller disposed closest to the discharge roller on the upstream side therefrom in the discharge direction in the configuration shown in FIG. 12.

FIG. 14 is a graph showing the measurement results of an example checking the relationship between the sorting width of the paper and the discharge timing of the paper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are only examples in which the present invention is embodied, and are not intended to limit the technical scope of the present invention.

(Description of the Overall Configuration of the Image Forming Apparatus)

FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention when viewed from the front.

The image forming apparatus 100 shown in FIG. 1 is a color image forming apparatus that forms multicolor and monochrome images on a sheet P such as recording paper (hereinafter, referred to as “paper”) in response to image data transmitted from the outside. The image forming apparatus 100 includes an original reading device 108 and an apparatus body 110, and the apparatus body 110 includes an image forming portion 102 and a sheet conveying system 103.

The image forming portion 102 includes a light exposure unit 1, a plurality of development units 2, a plurality of photosensitive drums 3, a plurality of cleaning portions 4, a plurality of chargers 5, an intermediate transfer belt unit 6, a plurality of toner cartridge units 21, and a fixing unit 7.

Furthermore, the sheet conveying system 103 includes a paper feed tray 81, a manual paper feed tray 82, and a discharge tray 91.

An original placement plate 92 made of transparent glass on which an original (sheet) is placed is provided above the apparatus body 110, and an optical unit 90 for reading an original is provided below the original placement plate 92. The original reading device 108 is provided above the original placement plate 92. The original reading device 108 conveys automatically an original onto the original placement plate 92. The original reading device 108 is attached pivotally to the apparatus body 110 with the front side openable, and an original can be placed manually after exposing the surface of the original placement place 92.

The original reading device 108 can read an original automatically conveyed or an original placed on the original placement plate 92. The entire image of the original read by the original reading device 108 is transmitted as image data to the apparatus body 110 of the image forming apparatus 100, and an image formed based on the image data is recorded on paper P in the apparatus body 110.

The image data that can be processed in the image forming apparatus 100 is that corresponding to color images using multiple colors (black (K), cyan (C), magenta (M), yellow (Y) in this embodiment). Therefore, for each unit group of the development units 2, the photosensitive drums 3, the cleaning portions 4, the chargers 5, and the toner cartridge units 21, a plurality of units (four in this embodiment, respectively corresponding to black, cyan, magenta and yellow) are provided, such that images of multiple kinds (four kinds in this embodiment) corresponding to four colors can be formed, and accordingly a plurality of image stations (four image stations in this embodiment) are configured.

The chargers 5 are charging means for uniformly charging the surface of photosensitive drums 3 to a predetermined potential, and for the chargers 5, chargers of roller type or brush type, which are contact type, can be used, as well as chargers as shown in FIG. 1.

The light exposure unit 1 is configured in a form of a laser scanning unit (LSU) provided with a laser irradiating portion and reflection mirrors. The light exposure unit 1 is provided with a polygon mirror scanned by a laser beam, and optical elements such as lenses or mirrors for guiding the laser light reflected by the polygon mirror to the photosensitive drums 3. For the light exposure unit 1, other concepts can be used, such as a concept employing a writing head in which optical elements such as EL (electroluminescence) elements or LEDs (light-emitting diodes) are aligned in an array.

The light exposure unit 1 irradiates the photosensitive drums 3 that are charged in accordance with input image data with light so that an electrostatic latent image in accordance with the image data is formed on the surfaces of the photosensitive drums 3.

The toner cartridge units 21 are units containing toner, and are configured such that the toner is supplied to the development baths of the development units 2. In the apparatus body 110 of the image forming apparatus 100, the toner supplied from the toner cartridge units 21 to the development baths of the development units 2 is controlled such that the toner concentration of a developer in the development baths is constant.

The development units 2 make the electrostatic latent images formed on the respective photosensitive drums 3 visible with four color toners (Y, M, C, and K). The cleaning portions 4 remove and recover toner that is left on the surfaces of the photosensitive drums 3 that have undergone development and image transfer.

The intermediate transfer belt unit 6 arranged above the photosensitive drums 3 includes an intermediate transfer belt 61 functioning as an intermediate transfer member, an intermediate transfer belt driving roller 62, an intermediate transfer belt idle roller 63, a plurality of intermediate transfer rollers 64, and an intermediate transfer belt cleaning unit 65.

For the intermediate transfer rollers 64, four rollers are provided corresponding respectively to colors Y, M, C, and K. The intermediate transfer belt driving roller 62 supports the intermediate transfer belt 61 in cooperation with the intermediate transfer belt idle roller 63 and the intermediate transfer rollers 64 such that the intermediate transfer belt 61 is in tension. When the intermediate transfer belt driving roller 62 is driven to rotate, then the intermediate transfer belt 61 is revolved in the movement direction (direction indicated by arrow M in FIG. 1), which causes the intermediate transfer belt idle roller 63 and the intermediate transfer rollers 64 to be idly rotated.

The intermediate transfer rollers 64 are supplied with a transfer bias for transferring toner images formed on the photosensitive drums 3 onto the intermediate transfer belt 61.

The intermediate transfer belt 61 is provided in such a manner that it is in contact with each of the photosensitive drums 3. Toner images of the respective colors formed on the photosensitive drums 3 are sequentially transferred to the intermediate transfer belt 61 so as to be superimposed one after another, so that a color toner image (multicolor toner image) can be formed on the surface of the intermediate transfer belt 61. The intermediate transfer belt 61 is formed by an endless belt made of a film having a thickness of about 100 μm to 150 μm.

Toner images are transferred from the photosensitive drums 3 to the intermediate transfer belt 61 by means of the intermediate transfer rollers 64 that are in contact with the back face of the intermediate transfer belt 61. The intermediate transfer rollers 64 are supplied with a high voltage transfer bias (high voltage having an opposite polarity (+) to the polarity (−) of the charged toner) for transferring toner images. Each intermediate transfer roller 64 is made by forming its core with a metal (e.g., stainless steel) shaft having a diameter of 8 mm to 10 mm and covering the surface of the core with a conductive elastic material (e.g., resin materials such as EPDM (ethylene propylene diene rubber) or foamed urethane). The intermediate transfer rollers 64 function as transfer electrodes that apply a high voltage uniformly to the intermediate transfer belt 61 with the conductive elastic material. Although roller-like transfer electrodes are used as the transfer electrodes in this embodiment, other transfer electrodes, for example, brush-like transfer electrodes can be used.

As described above, toner images that are made visible in accordance with the color phases on the respective photosensitive drums 3 are layered on the intermediate transfer belt 61. The toner images layered on the intermediate transfer belt 61 are transferred onto the paper P by a transfer roller 10 constituting a second transfer mechanism portion disposed in a contact position in which the paper P is in contact with the intermediate transfer belt 61, by means of the rotational movement of the intermediate transfer belt 61. However, as the configuration of the second transfer mechanism portion, not only transfer rollers, but also other transfer configurations such as those employing corona chargers or transfer belts can be used.

At this time, the transfer roller 10 is supplied with a voltage for transferring toner onto the paper P in a state where a transfer nip is formed between the transfer roller 10 and the intermediate transfer belt 61. This voltage is a high voltage having an opposite polarity (+) of the polarity (−) of the charged toner. The transfer nip is formed between the transfer roller 10 and the intermediate transfer belt 61 by the transfer roller 10 and the intermediate transfer belt driving roller 62 pressing against each other. In order to obtain the transfer nip steadily, either one of the transfer roller 10 and the intermediate transfer belt driving roller 62 is a hard roller made of a hard material such as metal and the other is an elastic roller made of a soft material such as elastic rubber or foamed resin.

When transferring a toner image from the intermediate transfer belt 61 onto the paper P with the transfer roller 10, toner may remain on the intermediate transfer belt 61 without being transferred onto the paper P.

The toner that has remained on the intermediate transfer belt 61 may cause mixture of colors in subsequent processes. Therefore, the toner that has remained on the intermediate transfer belt 61 is removed and recovered by the intermediate transfer belt cleaning unit 65. More specifically, the intermediate transfer belt cleaning unit 65 is provided with a cleaning member (e.g., a cleaning blade) that is in contact with the intermediate transfer belt 61. The idle roller 63 supports the intermediate transfer belt 61 from the inside (back face side), and the cleaning member is in contact with the intermediate transfer belt 61 so as to press against it toward the idle roller 63 from the outside.

The paper feed tray 81 is a tray accommodating in advance sheets of the paper P on which an image is to be formed (printed), and is provided below the light exposure unit 1 in the apparatus body 110. On the manual paper feed tray 82, sheets of the paper P on which an image is to be formed (printed) are placed. The discharge tray 91 is provided above the image forming portion 102 in the apparatus body 110, and sheets of the paper P on which an image has been formed (printed) are accumulated face-down on the discharge tray 91. The discharge tray 91 is configured such that the upstream side in a discharge direction (direction indicated by arrow Y1 in FIG. 1) of a placement face 91a on which the paper P is to be placed is lower than the downstream side.

Furthermore, the apparatus body 110 is provided with a sheet conveying path S for conveying the paper P that has been conveyed from the paper feed tray 81 or the manual paper feed tray 82, via the transfer roller 10 and the fixing unit 7 to the discharge tray 91. Arranged in the vicinity of the sheet conveying path S are pickup rollers 11a and lib, a first to a fourth conveying roller 12a to 12d, registration rollers 13, the transfer roller 10, a heat roller 71 and a pressing roller 72 of the fixing unit 7, and a discharge roller 31.

The first to the fourth conveying rollers 12a to 12d are small rollers for promoting and assisting conveying of the paper P, and are provided along the sheet conveying path S. The pickup roller 11a is provided in the vicinity of the paper feed tray 81 on the paper feeding side for picking up the paper P sheet by sheet from the paper feed tray 81 and feeds the sheets to the sheet conveying path S. Similarly, the pickup roller 11b is provided in the vicinity of the manual paper feed tray 82 on the paper feeding side for picking up the paper P sheet by sheet from the manual paper feed tray 82 and feeds the sheets to the sheet conveying path S.

The registration rollers 13 temporarily hold the paper P that is being conveyed in the sheet conveying path S. Then, the registration rollers 13 convey the paper P to the transfer roller 10 at a timing at which a leading edge of the toner image on the photosensitive drums 3 is aligned with an edge P1 on the downstream side in the discharge direction Y1 (hereinafter, referred to as a “leading edge”) of the paper P.

The fixing unit 7 fixes an unfixed toner image onto the paper P, and includes the heat roller 71 and the pressing roller 72 that function as fixing rollers. When being driven to rotate, the heat roller 71 conveys the paper P while sandwiching the paper P along with the pressing roller 72 that is idly rotated. The heat roller 71 is heated with a heater 71a provided inside it, and is maintained at a predetermined fixing temperature based on a signal from a temperature detector 71b. The heat roller 71 heated with the heater 71a performs thermo-compression bonding of a multicolor toner image transferred onto the paper P on the paper P along with the pressing roller 72, so that the multicolor toner image is melted, mixed, and pressed and thus is thermo-fixed onto the paper P. The fixing unit 7 is also provided with an external heating belt 73 for heating the heat roller 71 from the outside.

In the image forming apparatus 100 configured in the above described manner, when there is a request for simplex printing on paper P, paper P fed from the paper feed tray 81 or 82 is conveyed to the registration rollers 13 by the first conveying rollers 12a provided along the sheet conveying path S, and is conveyed by the transfer roller 10 at a timing at which the leading edge P1 of the paper P is aligned with the leading edge of the toner image on the intermediate transfer belt 61, and then the toner image is transferred onto the paper P. Thereafter, the paper P passes through the fixing unit 7, so that unfixed toner on the paper P is melted by heat and adheres to the paper P, and then the paper P is discharged onto the discharge tray 91 through the second conveying rollers 12b and the discharge roller 31.

When there is a request for duplex printing on paper P, in a state where an edge P2 on the upstream side in the discharge direction Y1 (hereinafter, referred to as a “trailing edge”) of the paper P that has passed through the fixing unit 7 is positioned between the discharge roller 31 and a branching portion Sa on the sheet conveying path S after the simplex printing as described above has completed, the discharge roller 31 is reversely rotated, so that the paper P is guided to the third and the fourth conveying rollers 12c and 12d. Then, the paper P that has been conveyed to the transfer nip through the registration rollers 13 undergoes printing on its back face, and then is discharged onto the discharge tray 91.

(Regarding the Paper Sorting Configuration)

The image forming apparatus 100 according to this embodiment is configured such that sheets of the paper P discharged by the discharge roller 31 are sorted by causing shift of the discharge roller 31 along the axial direction of the discharge roller 31.

FIG. 2 is a schematic cross-sectional view showing the discharge roller 31 in the image forming apparatus 100 shown in FIG. 1 and portions close thereto. FIG. 3 is a schematic side view of the sorting configuration in the image forming apparatus 100 shown in FIG. 1 when viewed in the discharge direction Y1 of the paper P.

As shown in FIGS. 2 and 3, the image forming apparatus 100 includes a discharge roller shift unit 30 having the discharge roller 31, a rotation driving portion 40, and a shift driving portion 50.

The discharge roller shift unit 30 is disposed reciprocally movable along the axial direction of the discharge roller 31 (direction indicated by arrow X in FIG. 3, hereinafter referred to as a “shift direction X”) with respect to the apparatus body 110. More specifically, the discharge roller shift unit 30 is supported by the apparatus body 110 via a slide member (more specifically, a slide rail) 30b (see FIG. 2) that can reciprocally move along the shift direction X. Here, the slide member 30b may have a conventionally known configuration, and a detailed description thereof has been omitted in this specification.

Furthermore, a body frame 30a of the discharge roller shift unit 30 includes a detection piece 30c that is to be detected by a position detector switch SWp described later.

The discharge roller 31 is to discharge the paper P to the discharge tray 91, and, in this example, includes discharge roller pairs 34 consisting of a discharge driving roller 32 and a discharge idle roller 33.

More specifically, the discharge driving roller 32 includes a driving roller shaft 32a and four driving roller portions 32b that are coaxially fixed to the driving roller shaft 32a. The discharge idle roller 33 includes idle roller shafts 33a and a plurality of idle roller portions 33b that are coaxially fixed to the idle roller shafts 33a in opposition to the driving roller portions 32b. Furthermore, the discharge roller 31 further includes biasing members (in this example, compression springs) 35 that bias the idle roller portions 33b toward the driving roller portions 32b.

The discharge roller pairs 34 and the biasing members 35 are arranged in the body frame 30a of the discharge roller shift unit 30, and one end portion of the discharge driving roller 32 is projected from the body frame 30a of the discharge roller shift unit 30 to the outside in the shift direction X.

The driving roller shaft 32a of the discharge driving roller 32 is a single unit in this example, and is disposed axially rotatably with respect to the body frame 30a of the discharge roller shift unit 30.

In this example, two idle roller shafts 33a of the discharge idle roller 33 are arranged side by side along the shift direction X, and two idle roller portions 33b are fixed to each shaft. The idle roller shafts 33a are arranged such that the idle roller portions 33b oppose the corresponding driving roller portions 32b, can axially rotate with respect to the body frame 30a of the discharge roller shift unit 30, and can reciprocally move in the vertical direction (direction indicated by arrow Z in FIGS. 2 and 3). The discharge roller 31 is configured such that the paper P is conveyed while being sandwiched in a state where the paper P is pressed by the discharge idle roller 33 at a nip portion N between the discharge driving roller 32 and the discharge idle roller 33.

More specifically, the biasing members 35 are configured so as to bias the discharge idle roller 33 toward the discharge driving roller 32, and, in this example, are arranged between the idle roller shafts 33a and a side of the body frame 30a not facing the discharge driving roller 32 in the discharge roller shift unit 30. Here, the pressing force of the biasing members 35 applied to the discharge idle roller 33 toward the discharge driving roller 32 is a pressure that can convey the paper P properly.

The rotation driving portion 40 is to drive rotation of the discharge roller 31, and includes a conveyance driving motor 41 (in this example, a stepping motor) and a drive transmission mechanism 42 that transmits rotational drive from the conveyance driving motor 41 to the discharge roller 31.

The conveyance driving motor 41 is disposed in the apparatus body 110 such that a rotational shaft 41a is along the shift direction X.

In this example, the drive transmission mechanism 42 is configured from a gear train in which a plurality of gears are arranged in a line, and includes a driving gear 42a, a roller gear 42b, and an intermediate gear 42c.

The driving gear 42a is coupled to the rotational shaft 41a of the conveyance driving motor 41. The roller gear 42b is coupled to an end portion of the driving roller shaft 32a projected outward in the shift direction X from the body frame 30a of the discharge roller shift unit 30. The intermediate gear 42c is supported rotatably by a rotational shaft 110a fixed to the apparatus body 110, and is meshed with the driving gear 42a and the roller gear 42b. Here, gear teeth of the driving gear 42a, the roller gear 42b, and the intermediate gear 42c are formed in the shape of grooves and ridges extending in the shift direction X, and, thus, the roller gear 42b can slide in the shift direction X in a state where the roller gear 42b is meshed with the intermediate gear 42c. The length of the intermediate gear 42c in the shift direction X is set to a length that allows the movement width of the discharge roller shift unit 30 in the shift direction X, that is, a length that is obtained by adding the mesh length of the gears and the length corresponding to the shift amount, and is set to a length that does not cause the roller gear 42b to be detached from the intermediate gear 42c even when the discharge roller shift unit 30 reciprocally moves in the shift direction X.

The shift driving portion 50 is to drive shift of the discharge roller 31 (in this example, the discharge roller shift unit 30), thereby causing shift, and includes a shift driving motor 51 (in this example, a stepping motor) and a shift mechanism 52 that shifts the discharge roller shift unit 30.

The shift driving motor 51 is disposed in the apparatus body 110 such that a rotational shaft 51a is along a direction perpendicular to the shift direction X (in this example, vertical direction Z).

In this example, the shift mechanism 52 is configured from rack-and-pinion gears that convert rotational drive to linear drive, and includes a rack gear 52a that extends along the shift direction X and a cylindrical pinion gear 52b.

An end portion of the rack gear 52a in the shift direction X is coupled to an end portion of the discharge roller shift unit 30. The pinion gear 52b is coupled to the rotational shaft 51a of the shift driving motor 51, and is meshed with the rack gear 52a. Accordingly, the discharge roller shift unit 30 can be reciprocally moved in the shift direction X, by rotating the rotational shaft 51a of the shift driving motor 51 in one direction or the other direction.

FIG. 4 is a system block diagram of a control system of the image forming apparatus 100 shown in FIG. 1. The image forming apparatus 100 further includes a control portion 200, a first detector switch SW1 (see FIG. 2), a second detector switch SW2 (see FIG. 2), and the position detector switch SWp (FIGS. 2 and 3).

As shown in FIG. 4, the control portion 200 includes a processing unit 210 such as a CPU, and a storage portion 220 provided with a ROM (read only memory), a RAM (random access memory), and a rewritable non-volatile memory. The ROM can store a control program indicating the procedure of processing that is to be executed by the processing unit 210. The RAM can provide a work area for operations. The non-volatile memory can back up and hold data necessary for control, and hold and rewrite various types of data (e.g., control time period of timing control described later, etc.).

The control portion 200 is configured so as to perform timing control of the rotation driving portion 40 and the shift driving portion 50, as timing control in the sorting configuration of the image forming apparatus 100.

The first detector switch SW1 is to detect whether or not the paper P is passing through the discharge roller 31, and, in this example, is disposed in the vicinity of the upstream side from the discharge roller 31 in the discharge direction Y1. The first detector switch SW1 is electrically connected to the input system of the control portion 200 such that a paper non-passing signal indicating that the paper P is not passing through the discharge roller 31 (in this example, an OFF signal) or a paper passing signal indicating that the paper P is passing through the discharge roller 31 (in this example, an ON signal) can be transmitted to the control portion 200.

The second detector switch SW2 is to detect whether or not the paper P is passing through closest rollers (in this example, the second conveying rollers 12b) arranged closest to the discharge roller 31 on the upstream side therefrom in the discharge direction Y1, and, in this example, is disposed in the vicinity of the downstream side from the closest rollers 12b in the discharge direction Y1. The second detector switch SW2 is electrically connected to the input system of the control portion 200 such that a paper non-passing signal indicating that the paper P is not passing through the closest rollers 12b (in this example, an OFF signal) or a paper passing signal indicating that the paper P is passing through the closest rollers 12b (in this example, an ON signal) can be transmitted to the control portion 200.

The position detector switch SWp detects whether or not the discharge roller shift unit 30 is positioned at a reference position. More specifically, the reference position is a center position in the shift direction X (standard position at which sorting is not performed). The position detector switch SWp includes, in this example, a transmission-type optical sensor that detects the detection piece 30c disposed in the body frame 30a of the discharge roller shift unit 30 (see FIGS. 2 and 3). The position detector switch SWp is electrically connected to the input system of the control portion 200 such that a unit presence signal indicating that the discharge roller shift unit 30 is positioned at the reference position (in this example, an OFF signal) or a unit absence signal indicating that the discharge roller shift unit 30 is not positioned at the reference position (in this example, an ON signal) can be transmitted to the control portion 200.

The conveyance driving motor 41 and the shift driving motor 51 are electrically connected to the output system of the control portion 200 such that the drive signal (ON signal) or the drive stopping signal (OFF signal) from the control portion 200 can be obtained.

More specifically, the control portion 200 drives the conveyance driving motor 41 by transmitting to the conveyance driving motor 41a rotation instructing signal to instruct the motor to rotate in one direction (i.e., the direction in which the paper P is discharged, indicated by arrow A in FIG. 2), and, thus, can drive rotation of the discharge roller 31 in the one direction A. Here, in this example, the control portion 200 is configured so as to instruct the conveyance driving motor 41 to rotate also in the direction opposite the one direction A in the case of duplex printing, but this aspect does not directly relate to the control in the sorting configuration of the image forming apparatus 100, and, thus, a description thereof has been omitted.

Furthermore, the control portion 200 pulse-drives the shift driving motor 51 using the reference position as a reference by transmitting to the shift driving motor 51a movement instructing signal to instruct the motor to rotate to move the discharge roller shift unit 30 toward one side in the shift direction X (a leftward direction X1 in FIG. 3) and to rotate to move the discharge roller shift unit 30 toward the other side in the shift direction X (a rightward direction X2 in FIG. 3), and, thus, can drive shift of the discharge roller shift unit 30 in the direction X1 on one side and the direction X2 on the other side.

With the above-described sorting configuration, the conveyance driving motor 41 is driven in response to the rotation instructing signal from the control portion 200, and, thus, the driving force from the conveyance driving motor 41 is transmitted to the drive transmission mechanism 42. Accordingly, the discharge roller 31 is driven to rotate in the one direction A. Furthermore, the shift driving motor 51 is driven in response to the movement instructing signal from the control portion 200, and, thus, the driving force from the shift driving motor 51 is transmitted to the shift mechanism 52. Accordingly, the discharge roller shift unit 30 is shifted in the direction X1 on one side or the direction X2 on the other side.

FIGS. 5A to 5D are views for illustrating conventional timing control in the sorting configuration shown in FIG. 3. FIG. 5A is a schematic plan view showing a state in which the paper P is discharged at a shift end (movement end) on one side in the shift direction X. FIG. 5B is a schematic plan view showing a state in which the paper P is discharged at a shift end (movement end) on the other side in the shift direction X. FIG. 5C is a schematic cross-sectional view showing a state in which the paper P is discharged at a point in time where the discharge roller shift unit 30 reaches a shift end a on one side in the shift direction X or a shift end β on the other side, when viewed in the shift direction X. FIG. 5D is a schematic plan view showing a sorting width Sa of the paper P discharged to the discharge tray 91 and the positional relationship with respect to the discharge roller shift unit 30.

FIG. 6 is a timing chart showing a discharge timing according to conventional timing control in the sorting configuration shown in FIG. 3.

As shown in FIGS. 5A to 5D and 6, in conventional timing control in the sorting configuration shown in FIG. 3, at a point in time where the discharge roller shift unit 30 has reached the shift end (see α in FIG. 5A) on one side in the shift direction X or the shift end (see β in FIG. 5B) on the other side and shift has completed, the paper P is sandwiched in the discharge roller 31 (see FIG. 5C).

That is to say, when sorting sheets of the paper P onto one side (the left in the drawings) in the shift direction X or the other side (the right in the drawings), after it has been recognized that the discharge roller 31 is sandwiching the paper P with the paper passing signal input from the first detector switch SW1, the discharge roller shift unit 30 starts movement to the shift end a on one side in the shift direction X or the shift end β on the other side. Then, after shift of the discharge roller shift unit 30 to the shift end a on one side in the shift direction X or the shift end β on the other side has completed (stopped) (see γ1 in FIG. 6), the paper P is discharged (see γ2 in FIG. 6).

In this manner, in conventional timing control in the sorting configuration shown in FIG. 3, the sorting width Sa (see FIG. 5D, more specifically, 30 mm) of the paper P discharged to the discharge tray 91 is equivalent to a shift amount L (see FIG. 5D, more specifically, 30 mm) of the discharge roller shift unit 30 in the shift direction X. Here, the discharge roller shift unit 30 moves from the center position in the shift direction X (standard position at which sorting is not performed) by L/2 on each side, that is, the total shift amount is L consisting of the shift amount L/2 on one side and the shift amount L/2 on the other side.

On the other hand, in this embodiment, the control portion 200 is configured so as to perform timing control of the rotation driving portion 40 and the shift driving portion 50 such that the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift of the discharge roller 31.

FIGS. 7A to 7C and 8A to 8D are explanatory views for illustrating timing control of this embodiment in the sorting configuration shown in FIG. 3.

FIG. 7A is a schematic plan view showing a state in which the paper P is discharged near the shift end α on one side in the shift direction X. FIG. 7B is a schematic plan view showing a state in which the paper P is discharged near the shift end β on the other side in the shift direction X. FIG. 7C is a schematic cross-sectional view showing a state in which the paper P is discharged at a point in time where the discharge roller shift unit 30 has reached the shift end a on one side in the shift direction X or the shift end β on the other side, when viewed in the shift direction X.

FIGS. 8A and 8B are respectively a schematic plan view and a schematic side view showing a state in which the paper P pops out from the nip portion N of the discharge roller 31. FIG. 8C is a schematic side view showing a state in which the paper P is placed on the discharge tray 91. FIG. 8D is a schematic plan view showing a sorting width Sb of the paper P discharged to the discharge tray 91.

FIG. 9 is a timing chart showing a discharge timing according to timing control of this embodiment in the sorting configuration shown in FIG. 3.

As shown in FIGS. 7A to 9, in the timing control of this embodiment in the sorting configuration shown in FIG. 3, at a point in time where the discharge roller shift unit 30 has reached the shift end (see α in FIG. 7A) on one side in the shift direction X or the shift end (see β in FIG. 7B) on the other side and shift has completed, the trailing edge P2 of the paper P in the discharge direction Y1 has been released (detached) from the discharge roller 31 (see FIG. 7C).

That is to say, when sorting sheets of the paper P onto one side (the left in the drawings) in the shift direction X or the other side (the right in the drawings), after it has been recognized that the discharge roller 31 is sandwiching the paper P with the paper passing signal input from the first detector switch SW1, the discharge roller shift unit 30 moves to the shift end α on one side in the shift direction X or the shift end β on the other side. In this case, before shift of the discharge roller shift unit 30 to the shift end α on one side in the shift direction X or the shift end 13 on the other side has completed (stopped) (see γ1 in FIG. 9), the paper P is discharged (see γ2 in FIG. 9).

Then, before the discharge roller shift unit 30 stops at the shift end α on one side in the shift direction X or the shift end β on the other side, the trailing edge P2 of the paper P is detached from the nip portion N of the discharge roller 31, and the paper P pops out from the nip portion N of the discharge roller 31 to an obliquely outer left side Y1a or an obliquely outer right side Y1b with respect to the discharge direction Y1 due to the force of inertia in the discharge direction Y1 and the force of inertia on one side X1 in the shift direction X or the other side X2 (see FIGS. 8A and 8B). Subsequently, due to inclination of the placement face 91a of the paper P in the discharge tray 91, sheets of the paper P return on the placement face 91a in a direction Y2 opposite the discharge direction Y1 (see FIG. 8C), and are aligned in the discharge direction Y1 by a wall face (in this example, a discharge tray end face 91b) provided upright at the rear end of the discharge tray 91 (see FIG. 8D).

In this manner, in the timing control of this embodiment in the sorting configuration shown in FIG. 3, the sorting width Sb (more specifically, 45 mm) of the paper P discharged to the discharge tray 91 can be made larger than the shift amount L of the discharge roller shift unit 30 in the shift direction X (i.e., the sorting width Sa (more specifically, 30 mm) according to conventional timing control, see FIG. 5D), without increasing the shift amount L (more specifically, 30 mm) in the shift direction X (see FIG. 8D).

In particular, in the case of the paper P having a large coefficient of surface friction, sheets of the paper P may be placed in a scattered manner on the discharge tray 91, but, even in this case, bundles of the paper P can be easily distinguished from each other because the sorting width Sb can be increased.

According to the timing control of this embodiment described above, only the control configuration of the control portion 200 is changed, and, thus, the width of the image forming apparatus 100 in the shift direction X does not have to be increased, and the mechanical structure of the existing discharge roller 31 does not have to be changed. Thus, an increase in the complexity and the cost of the mechanical structure of the image forming apparatus 100 can be suppressed.

Furthermore, the control portion 200 performs timing control of the rotation driving portion 40 and the shift driving portion 50 such that the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift of the discharge roller 31. Accordingly, the paper P whose trailing edge P2 has passed through the discharge roller 31 is discharged in a direction of a resultant vector obtained by adding the discharge direction vector and the shift direction vector. Thus, the paper P whose trailing edge P2 has passed through the discharge roller 31 can be discharged to the obliquely outer sides Y1a and Y1b with respect to the discharge direction Y1. Therefore, the sorting width Sb of the paper P discharged to the discharge tray 91 can be increased, and, thus, sheets of the paper P can be reliably separated and sorted.

In this embodiment, the control portion 200 is preferably configured such that the discharge timing at which the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift is a timing at which a shift velocity Vs (see FIG. 10) of the discharge roller 31 is a maximum velocity Vsmax.

FIG. 10 is a timing chart obtained by adding a chart of the shift velocity Vs of the discharge roller 31 to FIG. 9.

As shown in FIG. 10, the configuration is adopted in which, when the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift, the shift velocity Vs of the discharge roller 31 is the maximum velocity Vsmax (more specifically, 140 mm/s).

With this configuration, when the force of inertia on one side X1 in the shift direction X or the other side X2 is the largest, the trailing edge P2 of the paper P passes through the discharge roller 31 during the shift, and, thus, it is possible to accordingly increase the sorting width of discharged sheets.

Instead of or in addition to the configuration shown in FIG. 10, the control portion 200 is preferably configured such that the discharge timing at which the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift is substantially equivalent to a timing at which the discharge roller shift unit 30 reaches the shift end α (see FIG. 7A) on one side in the shift direction X or the shift end β (see FIG. 7B) on the other side.

FIG. 11 shows a timing substantially equivalent to a timing at which the discharge roller shift unit 30 reaches the shift end α on one side in the shift direction X or the shift end β on the other side in the configuration shown in FIG. 10.

As shown in FIG. 11, the configuration is adopted in which, when the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31 during the shift, the discharge roller shift unit 30 reaches the vicinity of the shift end α on one side in the shift direction X or the shift end β on the other side (in this example, an end position γ4 in a maximum velocity period γ3 of the shift velocity Vs of the discharge roller 31).

With this configuration, when the discharge roller shift unit 30 reaches the vicinity of the shift end α on one side in the shift direction X or the shift end β on the other side, the trailing edge P2 of the paper P that is being discharged passes through the discharge roller 31. Thus, the movement distance by which the discharge roller 31 conveying the paper P is shifted can be increased to the extent possible. Accordingly, the sorting width Sb of the discharged paper P can be increased. Here, a deceleration period γ5 from the end position γ4 in the maximum velocity period γ3 of the shift velocity Vs of the discharge roller 31 is reduced to the extent possible, and, thus, the sorting width Sb can be further increased.

Instead of or in addition to the configuration shown in FIG. 11, the control portion 200 is preferably configured such that a revolving velocity Vr of the discharge roller 31 is reduced after the leading edge P1 of the paper P that is being discharged has passed through the discharge roller 31 and before the trailing edge P2 passes through the discharge roller 31, more specifically, such that the revolving velocity of the discharge roller is reduced when shift of the discharge roller 31 is started.

FIG. 12 shows a timing chart obtained by adding, to FIG. 11, timing control that increases the revolving velocity Vr of the discharge roller 31 after the leading edge P1 of the paper P has passed through the discharge roller 31, and reduces the revolving velocity Vr of the discharge roller 31 before the trailing edge P2 of the paper P passes through the discharge roller 31.

As shown in FIG. 12, the control portion 200 is configured so as to rotate the discharge roller 31 at a first revolving velocity Vr1 (more specifically, 140 mm/s), at a second revolving velocity Vr2 (more specifically, 500 mm/s) that is higher than the first revolving velocity Vr1 after the leading edge P1 of the paper P has passed through the discharge roller 31, at a third revolving velocity Vr3 (more specifically, 186 mm/s) that is higher than the first revolving velocity Vr1 and lower than the second revolving velocity Vr2 before the trailing edge P2 of the paper P passes through the discharge roller 31 (in this example, when shift of the discharge roller 31 is started), and again at the first revolving velocity Vr1 after the trailing edge P2 of the paper P has passed through the discharge roller 31.

In the configuration shown in FIG. 12, the revolving velocity Vr of the discharge roller 31 is increased after the leading edge P1 of the paper P that is being discharged has passed through the discharge roller 31, the revolving velocity Vr of the discharge roller 31 is reduced before the trailing edge P2 passes through the discharge roller 31, and, thus, it is possible to convey the paper P at a high speed before the trailing edge P2 of the paper P passes through the discharge roller 31, and it is possible to suppress a deterioration in the stack properties of the paper P while accordingly increasing the image forming speed.

Furthermore, the revolving velocity Vr of the discharge roller 31 is reduced when shift of the discharge roller 31 is started. Thus, it is possible to prolong the period of time during which the sheets are conveyed at a high speed to the extent possible, and it is possible to suppress a deterioration in the stack properties of the paper P while accordingly increasing the image forming speed.

Furthermore, the discharge roller 31 is rotated basically at the first revolving velocity Vr1 when the paper P is not passing through the discharge roller. Thus, it is possible to reduce the power consumption of the conveyance driving motor 41, and realize a longer life. Moreover, the discharge roller 31 is rotated at the second revolving velocity Vr2 that is higher than the first revolving velocity Vr1 after the leading edge P1 of the paper P has passed through the discharge roller 31. Thus, it is possible to convey the paper P at a speed higher than the first revolving velocity Vr1, and it is possible to accordingly increase the image forming speed. Furthermore, the discharge roller 31 is rotated at the third revolving velocity Vr3 that is higher than the first revolving velocity Vr1 and lower than the second revolving velocity Vr2 before the trailing edge P2 of the paper P passes through the discharge roller 31. Thus, it is possible to accordingly suppress a deterioration in the stack properties of the paper P. Therefore, it is possible to perform efficient discharge timing control in which improvement in the image forming speed and suppression of a deterioration in the stack properties of the paper P are well balanced.

Instead of or in addition to the configuration shown in FIG. 12, the control portion 200 is preferably configured such that shift of the discharge roller 31 is started after the trailing edge P2 of the paper P has passed through the closest rollers 12b.

FIG. 13 shows a timing at which shift of the discharge roller 31 is started after the trailing edge P2 of the paper P has passed through the closest rollers 12b disposed closest to the discharge roller 31 on the upstream side therefrom in the discharge direction Y1 in the configuration shown in FIG. 12.

As shown in FIG. 13, the configuration is adopted in which shift of the discharge roller 31 is started after the trailing edge P2 of the paper P has passed through the closest rollers 12b. More specifically, the control portion 200 starts shift of the discharge roller 31 after recognizing that the closest rollers 12b are not sandwiching the paper P with the paper non-passing signal input from the second detector switch SW2.

With this configuration, the discharge roller 31 can be shifted in a state where the paper P has been released from the closest rollers 12b. Therefore, it is possible to cancel the load by the closest rollers 12b on the paper P in the shift direction X applied when the discharge roller 31 is shifted, and, thus, it is possible to reduce damage to the paper P.

Instead of or in addition to the configuration shown in FIG. 13, the control portion 200 is preferably configured such that the timing of starting the shift of the discharge roller 31 can be adjusted.

The timing of starting the shift of the discharge roller 31 can be adjusted by adjusting a shift start time Tc (see FIG. 13) from when the leading edge P1 of the paper P passes through the discharge roller 31 to when shift of the discharge roller 31 is started. The shift start time Tc can be adjusted as appropriate via a setting screen such as a service simulation screen (not shown) using the relationship with a time Ta for the paper P to pass through the discharge roller 31 and a time Tb for the discharge roller shift unit 30 to be shifted (Ta>Tc>(Ta−Tb)). Here, the shift start time Tc is stored in a non-volatile memory, and the data is rewritten when being changed. Furthermore, the shift start time Tc may be adjusted by a user operating a setting screen of a user simulation or the like.

With this configuration, it is possible to change the timing of starting the shift of the discharge roller 31 according to the driving properties of the conveyance driving motor 41 and the shift driving motor 51 (e.g., the revolving velocity Vr of the discharge roller 31, or the shift width or the shift velocity Vs of the discharge roller 31).

Here, in this embodiment, the configuration is adopted in which switching between a discharge operation of the discharge roller 31 at the reference position and a discharge operation in the sorting width Sb is possible. However, this is not a limitation, and the configuration may be adopted in which switching to a conventional discharge operation in the shift width of the discharge roller 31 is also possible. Furthermore, in this embodiment, a sorting operation in which a discharge operation in the sorting width Sb and a discharge operation of the discharge roller 31 at the reference position are combined may be performed, and a sorting operation in which a discharge operation in the sorting width Sb and a conventional discharge operation in the shift width of the discharge roller 31 are combined may be performed. Furthermore, a sorting operation in which a discharge operation in the sorting width Sb, a discharge operation of the discharge roller 31 at the reference position, and a conventional discharge operation in the shift width of the discharge roller 31 are combined may be also performed.

EXAMPLES

A research was conducted on the relationship between the sorting width Sb of the paper P and the discharge timing of the paper P. Hereinafter, the research results will be described.

In this example, in the image forming apparatus 100, the third revolving velocity Vr3 of the discharge roller 31 was set to 186 mm/s, and the maximum velocity Vsmax of the shift velocity Vs of the discharge roller 31 was set to 140 mm/s. The discharge roller 31 was decelerated from a point 4.5 mm short of the shift ends α and β. The shift amount L of the discharge roller shift unit 30 in the shift direction X was set to 30 mm (15 mm on each side from the center position in the shift direction X), plain paper for color printing was used as the paper P, and the sorting width Sb of the paper P discharged to the discharge tray 91 was measured while changing the discharge timing of the paper P.

Table 1 and FIG. 14 show the measurement results. Here, in Table 1 and FIG. 14, a time T and a distance L for discharge timing of the paper P indicate a time and a distance for the discharge roller shift unit 30 to reach the shift ends α and β at a timing at which the trailing edge P2 of the paper P passes through (moves out of the discharge roller 31. Thus, at the value “0 ms” of the discharge timing of the paper P, the trailing edge P2 of the paper P moves out of the discharge roller 31 at a timing at which the discharge roller shift unit 30 reaches the shift end α or β. Here, the time elapsed from when the discharge roller shift unit 30 reaches the shift end α or β to when the trailing edge P2 of the paper P moves out of the discharge roller 31 is indicated in a negative value as the time T.

As shown in Table 1 and FIG. 14, according to the configuration in which the trailing edge P2 of the paper P passes through the discharge roller 31 during the shift when reaching the end position γ4 in the maximum velocity period γ3 of the shift velocity Vs of the discharge roller 31 (see FIG. 12), the sorting width Sb, which had been conventionally 30 mm, was increased to 45 mm.

The present invention can be embodied and practiced in other different forms without departing from the spirit and essential characteristics thereof. Therefore, the above-described embodiments are considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations and modifications falling within the equivalency range of the appended claims are intended to be embraced therein.

IMAGE FORMING APPARATUS

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CPC

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