Sheet conveying device

Abstract

To prevent quality degradation of a product.SOLUTION: A sheet conveying apparatus includes: first roller pairs (32a, 32b, 32c) that is switchable between a nipping conveyance state and a non-nipping state; a second roller pair (31) that is arranged on a downstream side of the first roller pairs in a sheet conveyance direction, and conveys a sheet; and a control part that switches the first roller pairs to the nipping conveyance state, conveys the sheet from the first roller pairs to the second roller pair by controlling rotation speeds of the first roller pairs and the second roller pair to a first rotation speed, switches the first roller pairs to the non-nipping state, and reduces a conveyance speed of the sheet by reducing the rotation speed of the second roller pair to a second rotation speed lower than the first rotation speed. The control part executes a mode of reducing the rotation speed of the first roller pairs from the first rotation speed to the second rotation speed or less, when reducing the rotation speed of the second roller pair from the first rotation speed to the second rotation speed.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet, and an image forming apparatus. [Background technology]

[0002] Generally, in a sheet conveying device (paper conveying device) for conveying a sheet (paper) provided in an image forming device or the like, a plurality of roller pairs for clamping and conveying a sheet are arranged side by side from upstream to downstream in the conveying direction. In such a sheet conveying device, in order to prevent the rollers from being stained or scratched by ink adhering to the rollers, a device has been proposed in which the upstream roller pair is separated when the sheet is conveyed by the downstream roller pair in the conveying direction (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-8110 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned sheet conveying device, in order to improve productivity, it is desirable that the sheet conveying speed by the roller pair is high. However, for example, in a transfer section that transfers an image onto a sheet, in order to transfer the image with high quality or to adjust the transfer position on the sheet, it is required to reduce the sheet conveying speed. For this reason, the sheet is conveyed at a high speed, and the sheet conveying speed is reduced by the roller pair, for example, just before the transfer section.

[0005] When the sheet conveying speed is reduced in this way, it is desirable to separate the roller pair located upstream in the conveying direction from the roller pair whose rotation speed is reduced, while maintaining the rotation speed of the roller pair located upstream, in order not to delay the conveying of the following sheet. However, in recent years, printing corresponding to various types of sheets is required, and for example, there are cases where sheets are conveyed, such as very thick paper such as cardboard or cardboard, which are quite thick. In such a case, even if the roller pair located upstream is separated, the roller pair may come into contact with the rear end of the sheet at a rotation speed faster than the conveying speed of the sheet, which may cause the edge of the rear end of the sheet to turn up, which is called edge curling, and may result in a deterioration in the quality of the finished product.

[0006] Therefore, the present invention aims to provide a sheet conveying device and an image forming apparatus that can prevent a deterioration in the quality of the finished product by slowing down the sheet conveying speed using a second pair of rollers downstream and releasing the clamping of the sheet by a first pair of rollers upstream. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a sheet conveying device including a first roller pair that is switchable between a clamping conveying state in which a sheet is clamped and conveyed and a non-clamping state in which the clamping of the sheet is released, a first drive unit that drives the first roller pair, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying direction and conveys the sheet, and a second drive unit that drives the second roller pair, and a sheet conveying device that switches the first roller pair to the clamping conveying state and controls the first drive unit and the second drive unit to control the rotational speeds of the first roller pair and the second roller pair to a first rotational speed to convey the sheet forward from the first roller pair. The sheet conveying device is equipped with a control unit that conveys a sheet to the second roller pair, switches the first roller pair to the non-clamping state, and controls the second drive unit to reduce the rotational speed of the second roller pair to a second rotational speed slower than the first rotational speed, thereby reducing the conveying speed of the sheet, wherein when reducing the rotational speed of the second roller pair from the first rotational speed to the second rotational speed, the control unit controls the first drive unit to execute a mode in which the rotational speed of the first roller pair is reduced from the first rotational speed to less than or equal to the second rotational speed. Effect of the Invention

[0008] According to the present invention, the conveying speed of the sheet is reduced by the second roller pair located downstream, and the clamping of the sheet by the first roller pair located upstream is released, thereby preventing a decrease in the quality of the finished product. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an image forming apparatus according to an embodiment of the present invention. [Diagram 2] 2 is a block diagram showing a configuration of a control system of the image forming apparatus according to the present embodiment. FIG. [Diagram 3] FIG. 2 is a perspective view showing a registration unit according to the present embodiment. [Figure 4] FIG. 2 is a top view showing the registration unit according to the embodiment. [Diagram 5] FIG. 2 is a cross-sectional view showing a registration unit according to the present embodiment. [Figure 6] 1A is a top view showing a state in which a sheet is conveyed by a pair of conveying rollers, and FIG. [Figure 7] 1A is a top view showing a state in which a sheet is abutted against a side abutment plate by a pair of oblique feed rollers, and FIG. 1B is a cross-sectional view showing a state in which a sheet is abutted against a side abutment plate by a pair of oblique feed rollers. [Figure 8] 1A is a top view showing a state in which a sheet is conveyed to a shift roller by a pair of oblique feed rollers, and FIG. 1B is a cross-sectional view showing a state in which a sheet is conveyed to a shift roller by a pair of oblique feed rollers. [Figure 9] 1A is a top view showing a state in which a sheet is shifted in the width direction by a shift roller, and FIG. 1B is a cross-sectional view showing a state in which a sheet is shifted in the width direction by the shift roller. [Figure 10] 5 is a flowchart showing sheet transport control according to the present embodiment. [Figure 11] 1A is a cross-sectional view showing a state in which the leading edge of the sheet is detected by the first sheet detection sensor in the first mode according to the present embodiment; (b) is a cross-sectional view showing a state immediately before the leading edge of the sheet reaches the secondary transfer section in the first mode according to the present embodiment; and (c) is a cross-sectional view showing a state in which the trailing edge of the sheet passes through the oblique feed roller section in the first mode according to the present embodiment. [Figure 12] 5 is a time chart showing the passing position of a sheet and the rotation speed of each roller in a first mode in the present embodiment. [Figure 13] 10 is a cross-sectional view showing a state in which the trailing edge of the sheet passes through the oblique feed roller portion in a second mode according to the embodiment. FIG. [Figure 14] 10 is a time chart showing the position through which a sheet passes and the rotation speed of each roller in a second mode in the present embodiment. [Figure 15]1A is a cross-sectional view showing the rear end of plain paper passing through a pair of skew rollers with the rotation speed maintained, and FIG. 1B is a cross-sectional view showing the rear end of extra-thick paper passing through a pair of skew rollers with the rotation speed maintained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the present embodiment will be described with reference to the drawings. First, a schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing an image forming apparatus according to the present embodiment.

[0011] [General configuration of image forming device] The printer 1, which serves as an image forming apparatus, is an electrophotographic full-color laser beam printer. As shown in Fig. 1, the printer 1 includes a housing 1a that houses a unit for feeding sheets and forming images, and a housing 1b that houses a unit for fixing and cooling.

[0012] The housing 1a has feeding units 10a and 10b, pulling units 20a and 20b, a registration unit 30 as a sheet conveying device, an image forming unit 40 as an image forming section, and a first double-sided conveying unit 60. The housing 1b has a fixing unit 100, a cooling unit 110, a branching conveying unit 120, a reversing conveying unit 130, a second double-sided conveying unit 140, and a discharge decurling unit 150.

[0013] The image forming unit 40 includes four process cartridges 40Y, 40M, 40C, and 40K that form toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), and exposure devices 43Y, 43M, 44C, and 44K. The four process cartridges 40Y, 40M, 40C, and 40K have the same configuration except that they form images of different colors. Therefore, only the configuration and image forming process of the process cartridge 40Y will be described, and descriptions of the process cartridges 40M, 40, and 40K will be omitted.

[0014] The process cartridge 40Y has a photosensitive drum 41, a charging roller (not shown), a developing device 42, and a cleaner 45. The photosensitive drum 41 is formed by coating an organic photoconductive layer on the outer periphery of an aluminum cylinder, and is rotated by a drive motor (not shown). The image forming unit 40 is provided with an intermediate transfer belt 50 as an image carrier that is rotated in the direction of an arrow T by a drive roller 52, and the intermediate transfer belt 50 is wound around a tension roller 51, the drive roller 52, and a secondary transfer inner roller 53. Primary transfer rollers 55Y, 55M, 55C, and 55K are provided on the inner side of the intermediate transfer belt 50, and a secondary transfer outer roller 54 as a transfer roller is provided on the outer side of the intermediate transfer belt 50 in opposition to the secondary transfer inner roller 53.

[0015] The feeding unit 10a has a lift plate 11a which moves up and down while stacking sheets S, a pickup roller 12a which feeds the sheets S stacked on the lift plate 11a, and a separation roller pair 13a which separates the fed sheets one by one. Similarly, the feeding unit 10b has a lift plate 11b which moves up and down while stacking sheets S, a pickup roller 12b which feeds the sheets S stacked on the lift plate 11b, and a separation roller pair 13b which separates the fed sheets one by one.

[0016] The registration unit 30, which will be described in more detail later, has a shift roller pair 31 that corrects the positional misalignment of the sheet S, multiple oblique feed roller pairs 32 that correct the skew of the sheet S, and multiple conveying roller pairs 33, 34 that convey the sheet S to the oblique feed roller pair.

[0017] On the other hand, the fixing unit 100 disposed in the housing 1b has a pair of heatable fixing rollers 101. The cooling unit 110 also has an upper cooling belt 111a rotated in the direction of the arrow T by an upper cooling drive roller 112a. Similarly, the cooling unit 110 has a lower cooling belt 111b rotated in the direction of the arrow T by a lower cooling drive roller 112b. Also, the cooling unit 110 has a heat sink 113 for cooling the sheet.

[0018] [Image formation operation] Next, a description will be given of an image forming operation of the printer 1 configured as above. For example, when an image signal is input to the exposure device 43 from a computer 300 (see FIG. 2), such as an external personal computer, the exposure device 43 irradiates a laser beam corresponding to the image signal onto the photosensitive drum 41 of the process cartridge 40Y.

[0019] At this time, the surface of the photosensitive drum 41 is uniformly charged to a predetermined polarity and potential in advance by a charging roller (not shown), and an electrostatic latent image is formed on the surface by irradiating the surface with laser light from an exposure device 43 via a mirror 44. The electrostatic latent image formed on the photosensitive drum 41 is developed by a developing device 42, and a yellow (Y) toner image is formed on the photosensitive drum 41.

[0020] Similarly, the laser light is irradiated from the exposure devices 43M, 40C, and 40K to the photosensitive drums of the process cartridges 40M, 40C, and 40K, and magenta (M), cyan (C), and black (K) toner images are formed on the photosensitive drums. The toner images of each color formed on each photosensitive drum are transferred to the intermediate transfer belt 50 by the primary transfer rollers 55Y, 55M, 55C, and 55K. The full-color toner image is then conveyed to the secondary transfer nip T2 formed by the secondary transfer inner roller 53 and the secondary transfer outer roller 54 by the intermediate transfer belt 50 rotated by the drive roller 52. The toner remaining on the photosensitive drum 41 is collected by the cleaner 45. The image forming process of each color is performed at a timing to overlap the upstream toner image that has been primarily transferred onto the intermediate transfer belt 50.

[0021] In parallel with this image forming process, a sheet S is fed from one of the feeding units 10a, 10b, and conveyed to the registration unit 30 by one of the drawing units 20a, 20b. The registration unit 30 includes a shift roller pair 31, a plurality of skew roller pairs 32, a plurality of conveying roller pairs 33, and the like, which will be described in detail later. The registration unit 30 corrects the positional deviation and skew of the sheet S, and conveys the sheet S to the secondary transfer nip T2 in accordance with the timing when the full-color toner image formed on the intermediate transfer belt 50 reaches the secondary transfer nip T2. The full-color toner image on the intermediate transfer belt 50 is transferred to the first sheet surface (front surface) of the sheet S by the secondary transfer bias applied to the secondary transfer outer roller 54. The residual toner remaining on the intermediate transfer belt 50 is collected by the belt cleaner 56.

[0022] The sheet S onto which the toner image has been transferred is conveyed to the fixing unit 100 by the pre-fixing conveying section 70. The sheet S is then guided to the nip of a pair of fixing rollers 101, where a predetermined amount of heat and pressure is applied to melt and fix the toner (fix). The sheet S that has passed through the fixing unit 100 is nipped by an upper cooling belt 111a and a lower cooling belt 111b, which are endless belts, in the cooling unit 110, and the sheet S is conveyed by the rotation of an upper cooling drive roller 112a and a lower cooling drive roller 112b. The sheet S is then brought into contact with a heat sink 113 via the upper cooling belt 111a, and the sheet S is cooled by transferring heat to the heat sink 113.

[0023] Next, the branching conveying unit 120 selects a path to convey the sheet S to either the discharge decurling unit 150 or the inverting conveying unit 130. After the sheet S is conveyed to the inverting conveying unit 130, the sheet S can be inverted so that the first sheet surface on which the image is formed at the secondary transfer nip T2 faces downward, and the sheet S can be conveyed to the decurling unit 170.

[0024] When an image is formed on only one side of the sheet S, the sheet S is conveyed from the branching conveying unit 120 to the discharge decurling unit 150, where the curl of the sheet is corrected by a small-diameter hard roller and a large-diameter soft roller. Subsequently, the sheet S that has passed through the discharge decurling unit 150 is either discharged outside the machine or delivered to an optional discharge device (not shown).

[0025] When images are formed on both sides of the sheet S, the sheet S is transported to the inversion transport unit 130 by the branching transport unit 120 and is switched back in the inversion transport unit 130. The switched back sheet S is transported from the inversion transport unit 130 to the second double-sided transport unit 140 and the first double-sided transport unit 60, and is guided to the registration unit 30. Thereafter, an image is formed on the second sheet surface (back surface) of the sheet S in the secondary transfer nip T2, and the sheet S is discharged outside the apparatus via the branching transport unit 120 and the discharge decurling unit 150, or is delivered to a discharge option device (not shown).

[0026] [Control system configuration] Next, the configuration of the control system in the printer 1 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the configuration of the control system of the image forming apparatus according to this embodiment.

[0027] The printer 1 is equipped with a control unit 200, to which a computer 300 and various sensors, etc. are connected so as to be able to input signals, and which is also connected so as to be able to control the image forming unit 40 and various motors, etc.

[0028] In detail, the control unit 200 has a CPU 201 and hardware components such as RAM, ROM, etc. (not shown). In the control unit 200, these hardware components are configured to achieve the functions of a memory unit 202, an operation control unit 203, an image formation control unit 204, a sheet conveyance control unit 205, a sensor control unit 206, and a shift control unit 207 by programs or the like.

[0029] The memory unit 202 is configured to be able to temporarily store various signals and data. The operation control unit 203 is connected to an operation unit such as an operation panel (not shown) provided in the printer 1, and controls input of signals from the operation unit and display of images. The image formation control unit 204 is connected to the image formation unit 40 and controls it. The image formation control unit 204 transmits an image signal included in a print job or the like transmitted from the computer 300, for example, to the image formation unit 40, and forms a toner image on the intermediate transfer belt 50 as described above while controlling each process cartridge.

[0030] The sheet conveying control section 205 is connected to the shift roller driving motor 31M as the second driving section, the skew roller driving motor 32M as the first driving section, the conveying roller driving motor 33M, the separation driving motor 32SM, and the like, and controls them. The shift roller driving motor 31M is a motor that drives the driving roller in the shift roller pair 31 of the registration unit 30, which will be described later in detail, and freely controls the rotation speed (i.e., the conveying speed of the sheet) including the driving and stopping of the shift roller pair 31. Similarly, the skew roller driving motor 32M is a motor that drives each driving roller in the multiple skew roller pairs 32, which will be described later in detail, and freely controls the rotation speed (i.e., the conveying speed of the sheet) including the driving and stopping of the skew roller pair 32. Similarly, the conveying roller driving motor 33M is a motor that drives each driving roller in the multiple conveying roller pairs 33, which will be described later in detail, and freely controls the rotation speed (i.e., the conveying speed of the sheet) including the driving and stopping of the conveying roller pair 33. That is, in the printer 1 according to the present embodiment, the shift roller pair 31, the plurality of oblique feed roller pairs 32, and the plurality of transport roller pairs 33 are configured so that their rotation speeds can be freely controlled independently by separate motors.

[0031] The separation drive motor 32SM drives to switch between a nip conveying state in which the drive rollers and driven rollers of the multiple skew roller pairs 32 are pressed against each other to nip and convey the sheet, and a non-nip conveying state in which the drive rollers and driven rollers are separated from each other to release the nip of the sheet. In short, the sheet conveying control unit 205 drives and controls these motors to convey the sheet to the secondary transfer nip T2 in time with the toner image on the intermediate transfer belt 50 while correcting the skew of the sheet, as will be described later in detail. The drive control of each of these motors will be described later in detail.

[0032] The sensor control unit 206 is connected to sensors such as a first leading edge detection sensor 311 and a second leading edge detection sensor 312 (see FIG. 3), which will be described in detail later, and receives signals from these sensors. The sensor control unit 206 detects the position of the sheet by receiving a signal indicating that the first leading edge detection sensor 311 and the second leading edge detection sensor 312 have detected the leading edge of the sheet in the registration unit 30.

[0033] The shift control unit 207 is connected to the side abutment plate shift motor 301SM and the shift motor 31SM, and drives and controls these motors. The side abutment plate shift motor 301SM drives and controls the side abutment plate 301, which will be described in detail later, in the width direction perpendicular to the sheet conveying direction. The shift motor 31SM drives and controls the shift roller pair 31 in the width direction.

[0034] [Registration Unit Details] Next, a specific configuration of the registration unit 30 will be described in detail. Fig. 3 is a perspective view showing the registration unit according to this embodiment. Fig. 4 is a top view showing the registration unit according to this embodiment. Fig. 5 is a cross-sectional view showing the registration unit according to this embodiment.

[0035] 3, 4, and 5, a plurality of conveying roller pairs 33, a plurality of skew roller pairs 32, a shift roller pair 31, and a secondary transfer roller pair 500 are arranged in this order from the upstream in the sheet conveying direction in which the sheet is conveyed. The secondary transfer roller pair 500 is composed of a pair of rollers consisting of a secondary transfer inner roller 53 and a secondary transfer outer roller 54.

[0036] The shift roller pair 31 as the second roller pair is composed of a pair of rollers including a shift drive roller 31d and a shift driven roller 31f. The shift drive roller 31d is driven by the shift roller drive motor 31M and the rotation speed is controlled. The shift roller pair 31 is driven by the shift motor 31SM in the direction of the arrow A, which is the width direction, to move and correct the position of the sheet in the width direction.

[0037] In this embodiment, the plurality of oblique feed roller pairs 32 include three oblique feed roller pairs 32a, 32b, and 32c. In the following description, when it is not necessary to distinguish between these three oblique feed roller pairs 32a, 32b, and 32c, they are simply referred to as oblique feed roller pairs 32. The oblique feed roller pair 32a as the first roller pair is composed of a pair of rollers consisting of a oblique feed drive roller 32ad and a oblique feed driven roller 32af. Similarly, the oblique feed roller pair 32b as the second roller pair is composed of a pair of rollers consisting of a oblique feed drive roller 32bd and a oblique feed driven roller 32bf. Similarly, the oblique feed roller pair 32c is composed of a pair of rollers consisting of a oblique feed drive roller 32cd and a oblique feed driven roller 32cf. The oblique feed drive rollers 32ad, 32bd, and 32cd are driven by the oblique feed roller drive motor 32M, and the rotation speed is controlled. In addition, the oblique feed roller pair 32 can be driven by the separation drive motor 32SM so that the oblique feed driven rollers 32af, 32bf, and 32cf are separated from the oblique feed drive rollers 32ad, 32bd, and 32cd in the direction of the arrow E. That is, the oblique feed roller pair 32 is switched between the clamping conveying state and the non-clamping state by the separation drive motor 32SM. In this embodiment, the oblique feed roller pair 32a located most downstream in the sheet conveying direction is described as the first roller pair, and the oblique feed roller pair 32b located further upstream is described as the third roller pair. However, this is not limited to this, and the first roller pair and the third roller pair may be any oblique feed roller pair as long as they are in the upstream and downstream relationship in the sheet conveying direction.

[0038] Further, on one side of the width direction of the positions where the plurality of oblique feed roller pairs 32 are arranged, a side abutment plate 301 as an abutting section is arranged so as to be movable in the width direction, that is, the arrow B. That is, the side abutment plate 301 is driven in the arrow B direction by a side abutment plate shift motor 301SM to control the position in the width direction, and the position is changed and set at the start of a print job according to the length in the width direction of the sheet S (size in the width direction).

[0039] In the present embodiment, the plurality of conveying roller pairs 33 include four conveying roller pairs 33a, 33b, 33c, and 33d. In the following description, when it is not necessary to distinguish between the four conveying roller pairs 33a, 33b, 33c, and 33d, they are simply referred to as conveying roller pairs 33. The conveying roller pair 33a is composed of a pair of rollers consisting of a conveying drive roller 33ad and a conveying driven roller 33af. Similarly, the conveying roller pair 33b is composed of a pair of rollers consisting of a conveying drive roller 33bd and a conveying driven roller 33bf. Similarly, the conveying roller pair 33c is composed of a pair of rollers consisting of a conveying drive roller 33cd and a conveying driven roller 33cf. Similarly, the conveying roller pair 33d is composed of a pair of rollers consisting of a conveying drive roller 33dd and a conveying driven roller 33df. The conveying drive rollers 33ad, 33bd, 33cd, and 33dd are driven by the conveying roller drive motor 33M and the rotation speed is controlled. Further, the conveying roller pair 33 can be driven by the separation drive motor 32SM so that the conveying driven rollers 33af, 33bf, 33cf, and 33df are separated from the conveying drive rollers 33ad, 33bd, 33cd, and 33dd in the direction of the arrow D. That is, the conveying roller pair 33 can be switched between a clamping conveying state and a non-clamping state by the separation drive motor 32SM in the same manner.

[0040] A first leading edge detection sensor 311 serving as a sheet detection sensor is disposed near the downstream side in the sheet conveying direction of the shift roller pair 31. A second leading edge detection sensor 312 is disposed near the upstream side in the sheet conveying direction of the conveying roller pair 33a. That is, the conveying timing of the sheet S is detected by the first leading edge detection sensor 311 or the second leading edge detection sensor 312. If the conveying timing of the sheet S is slower than a predetermined timing, it is determined to be abnormal and the print job is stopped.

[0041] [Overview of transport operation by the registration unit] Next, the conveying operation of the sheet S in the registration unit 30 (operation of correcting the positional deviation and skew of the sheet) will be described with reference to Figs. 6(a), 6(b), 7(a), 7(b), 8(a), 8(b), 9(a), and 9(b). Fig. 6(a) is a top view showing a state in which the sheet is conveyed by the conveying roller pair. Fig. 6(b) is a cross-sectional view showing a state in which the sheet is conveyed by the conveying roller pair. Fig. 7(a) is a top view showing a state in which the sheet is abutted against a side abutment plate by the oblique conveying roller pair. Fig. 7(b) is a cross-sectional view showing a state in which the sheet is abutted against a side abutment plate by the oblique conveying roller pair. Fig. 8(a) is a top view showing a state in which the sheet is conveyed to the shift roller by the oblique conveying roller pair. Fig. 8(b) is a cross-sectional view showing a state in which the sheet is conveyed to the shift roller by the oblique conveying roller pair. Fig. 9(a) is a top view showing a state in which the sheet is shifted in the width direction by the shift roller. FIG. 9B is a cross-sectional view showing a state in which the sheet is shifted in the width direction by the shift roller.

[0042] As shown in Fig. 6(a) and Fig. 6(b), for example, assume that the sheet S is conveyed in the direction of the arrow C by the conveying roller pairs 33a, 33b, 33c, and 33d in the registration unit 30 in a skewed state. Then, as shown in Fig. 7(a) and Fig. 7(b), when the sheet S reaches the skew roller pairs 32a, 32b, and 32c, a conveying force is applied to the sheet S in the width direction in addition to the sheet conveying direction, and the sheet S is conveyed while moving toward the side abutment plate 301. When the side edge of the sheet S abuts against the side abutment plate 301, the skew roller pairs 32a, 32b, and 32c slip, causing the sheet S to rotate and follow the side abutment plate 301, thereby correcting the skew.

[0043] 7B, when the skew is corrected by the skew roller pairs 32a, 32b, and 32c, the upstream conveying roller pairs 33a, 33b, 33c, and 33d in the sheet conveying direction are separated in the direction of the arrow D to be in a non-clamping state. That is, if the conveying roller pairs 33a, 33b, 33c, and 33d are not in a separated state, the sheet S is clamped and cannot move in the width direction, and cannot follow the side abutment plate 301. Therefore, by separating the conveying roller pairs 33a, 33b, 33c, and 33d, the sheet S can be conveyed so as to follow the side abutment plate 301.

[0044] Thereafter, as shown in FIG. 8(a) and FIG. 8(b), the first leading edge detection sensor 311 detects that the leading edge of the sheet S has reached the shift roller pair 31. Then, as shown in FIG. 9(a), the shift roller pair 31 is shifted in the direction of the arrow A so that the position of the sheet S in the width direction matches the position of the image transferred by the secondary transfer roller pair 500 in the width direction. This corrects the positional deviation of the sheet S in the width direction. In addition, the control unit 200 compares the timing at which the leading edge of the sheet S is detected by the first leading edge detection sensor 311 with the timing at which the toner image reaches the secondary transfer roller pair 500. Then, the control unit 200 controls the timing at which the rotational speed of the shift roller pair 31 is decelerated so that the timing of the toner image and the sheet S match. In this way, the transfer position of the toner image transferred to the sheet S is adjusted by the timing at which the rotational speed of the oblique feed roller pair 32 is decelerated.

[0045] As shown in FIG. 8(b), when the sheet S is shifted in the width direction by the shift roller pair 31, the oblique feed roller pairs 32a, 32b, and 32c are separated in the direction of the arrow E to be in a non-clamping state, so as to prevent twisting of the sheet S.

[0046] 9(a) and 9(b), when the sheet S is transported to the secondary transfer roller pair 500, the shift roller pair 31 also separates in the direction of the arrow F. While the sheet S is transported by the secondary transfer roller pair 500, all roller pairs upstream of the secondary transfer roller pair 500 in the sheet transport direction are separated and in a non-clamped state. As a result, while the sheet S is transported by the secondary transfer roller pair 500, it is not affected by the roller pairs upstream in the sheet transport direction via the sheet S, so that the sheet S can be transported with high accuracy without causing speed fluctuations.

[0047] [Details of Sheet Conveyance Control According to the Present Embodiment] Next, the details of the sheet conveying control according to the present embodiment will be described with reference to FIG. 10, FIG. 11(a), FIG. 11(b), FIG. 11(c), FIG. 12, FIG. 13, FIG. 14, FIG. 15(a), and FIG. 1(b). FIG. 10 is a flowchart showing the sheet conveying control according to the present embodiment. FIG. 11(a) is a cross-sectional view showing a state in which the leading edge of the sheet is detected by the first sheet detection sensor in the first mode according to the present embodiment. FIG. 11(b) is a cross-sectional view showing a state immediately before the leading edge of the sheet reaches the secondary transfer portion in the first mode according to the present embodiment. FIG. 11(c) is a cross-sectional view showing a state in which the trailing edge of the sheet passes through the oblique feed roller portion in the first mode according to the present embodiment. FIG. 12 is a time chart showing the passing position of the sheet and the rotation speed of each roller in the first mode according to the present embodiment. FIG. 13 is a cross-sectional view showing a state in which the trailing edge of the sheet passes through the oblique feed roller portion in the second mode according to the present embodiment. FIG. 14 is a time chart showing the passing position of the sheet and the rotation speed of each roller in the second mode according to the present embodiment. Fig. 15(a) is a cross-sectional view showing the trailing edge of plain paper passing through a pair of skew rollers with the rotation speed maintained, and Fig. 15(b) is a cross-sectional view showing the trailing edge of extra-thick paper passing through a pair of skew rollers with the rotation speed maintained.

[0048] First, a case where plain paper, other than super thick paper, is conveyed by the registration unit 30 will be described with reference to Figures 10 to 12. As shown in Figure 10, the control unit 200 of the printer 1 receives a print execution instruction from a user via, for example, the computer 300 (see Figure 2), and starts a print job (S1). Note that the user also instructs, for example, the number of copies to be printed via the computer 300, and specifies the type of sheet S to be used for printing.

[0049] In this embodiment, depending on whether the sheet is extra-thick paper or other paper, either a first mode or a second mode, which will be described in detail later, is selectively executed. That is, extra-thick paper is paper such as cardboard or cardboard having a first sheet thickness. Also, non-extra-thick paper is paper having a second thickness that is thinner than the first thickness, such as thin paper, regular paper, or regular cardboard. First, upon receiving the start of a print job, the control unit 200 determines whether the type of sheet S is extra-thick paper or other than extra-thick paper (S2). Here, since the sheet S is regular paper and other than extra-thick paper (NO in S2), the second mode, which is a mode in which steps S12 to S18 are executed, is executed.

[0050] (Second mode) First, since the type of the sheet S is determined to be plain paper as described above, the control unit 200 proceeds to step S12 as the second mode, sets the interval for conveying a plurality of sheets (so-called paper interval) to an interval for plain paper, and starts conveying the sheet S. Then, as shown in FIG. 11(a) and FIG. 12, the control unit 200 sets the sheet conveying speed of the conveying roller pairs 33a, 33b, 33c, and 33d to a conveying speed Vf=1000 mm / s. Also, the sheet conveying speed of the oblique feed roller pairs 32a, 32b, and 32c is set to a conveying speed Vd=1000 mm / s. And, the sheet conveying speed of the shift roller pair 31 is set to a conveying speed Vs=1000 mm / s. The conveying speed of the secondary transfer roller pair 500 is set to a conveying speed Vt=500 mm / s, which is the image forming speed.

[0051] With the conveying speed of each roller pair set as described above, the sheet S is conveyed to the shift roller pair 31 while the skew is corrected as described above (see FIGS. 6 to 8). Then, when the first leading edge detection sensor 311 detects the leading edge of the sheet S, the control unit 200 starts counting the timer t (S13). At this time, in response to the detection of the leading edge of the sheet S, the control unit 200 calculates the timing to decelerate the shift roller pair 31 according to the timing at which the toner image and the sheet S match at the secondary transfer roller pair 500 as described above (S14). Furthermore, in response to the detection of the leading edge of the sheet S, the control unit 200 separates the skew roller pairs 32a, 32b, and 32c to switch to a non-clamping state (S15).

[0052] 11B and 12, the control unit 200 decelerates the conveying speed of the shift roller pair 31 from a conveying speed Vs of 1000 mm / s to a conveying speed Vs of 500 mm / s, which is the image forming speed, at the calculated timing for decelerating the shift roller pair 31 (S16). That is, if the timing at which the first leading edge detection sensor 311 detects the leading edge of the sheet S is later than normal timing, the timing for decelerating the shift roller pair 31 is delayed accordingly. Conversely, if the timing at which the first leading edge detection sensor 311 detects the leading edge of the sheet S is earlier than normal timing, the timing for decelerating the shift roller pair 31 is advanced accordingly. The timer t can be used to measure this timing.

[0053] In this way, the timing of transporting the sheet S to the secondary transfer roller pair 500 is adjusted by the shift roller pair 31, and when the sheet S is transported to the secondary transfer roller pair 500, the toner image (image) is transferred with high precision to the printing position of the sheet S (S17).

[0054] Thereafter, when the timer t reaches a third predetermined time t3 after the trailing edge of the sheet S leaves the shift roller pair 31 and before the leading edge of the succeeding sheet S reaches the shift roller pair 31, the control unit 200 restores the conveying speed of the shift roller pair 31 (S18). That is, the sheet conveying speed of the shift roller pair 31 is increased from conveying speed Vs=500 mm / s to conveying speed Vs=1000 mm / s. This completes the sheet conveying control in the second mode for one sheet S, and determines whether or not there is a succeeding sheet (successive sheet S') (S11). If there is a succeeding sheet (YES in S11), the process returns to step S2, and if the succeeding sheet is, for example, the same plain paper, the sheet conveying control in the second mode is executed again. If there is no succeeding sheet (NO in S11), the print job is ended (S19), and the sheet conveying control ends.

[0055] As described above, by transporting the sheet S to the shift roller pair 31 at a speed faster than the image formation speed in the secondary transfer roller pair 500 and then slowing it down to the image formation speed by the shift roller pair 31, it is possible to perform high-precision image formation while improving productivity.

[0056] Incidentally, when the sheet S is conveyed and skew correction is performed as described above, the pair of skew rollers 32a, 32b, and 32c convey the sheet S while abutting against the side abutment plate 301, so that the sheet S is conveyed while slipping. For this reason, while the sheet S is being conveyed by the pair of skew rollers 32a, 32b, and 32c, the conveying speed of the sheet S tends to vary greatly. In contrast, as in the present embodiment, the first leading edge detection sensor 311 detects that the leading edge of the sheet S has reached the pair of shift rollers 31, and the timing of conveying the sheet S to the pair of secondary transfer rollers 500 is calculated accordingly to control the conveying speed of the sheet S. In this way, the deceleration timing of the pair of shift rollers 31 is controlled immediately before the sheet S reaches the pair of secondary transfer rollers 500. As a result, even if the conveying timing of the sheet S by the pair of skew rollers 32a, 32b, and 32c varies, the timing of conveying the sheet S to the pair of secondary transfer rollers 500 (toner image) can be matched with high accuracy.

[0057] The conveying speed Vs of the shift roller pair 31 and the conveying speed Vt of the secondary transfer roller pair 500 are set to 1000 mm / s and 500 mm / s, respectively. However, the greater the speed difference, the greater the amount of delay of the sheet S can be recovered, so the speed difference may be further increased. This makes it possible to tolerate a greater amount of variation in the conveying timing by the oblique feed roller pair 32.

[0058] (Improvement of productivity in transporting subsequent sheets) Next, a factory of productivity when a print job is a print command for multiple sheets and image formation is performed continuously on the subsequent sheets will be described. For example, when image formation is performed continuously on multiple sheets of plain paper, the second mode is repeatedly executed (S12 to S18, YES in S11). Here, as shown in FIG. 11(b), when the subsequent sheet S' is conveyed, the conveying roller pairs 33a, 33b, 33c, and 33d are sequentially returned from the non-clamping state to the clamping conveying state at the timing when the preceding sheet S leaves the roller pairs. Then, as shown in FIG. 11(c), the subsequent sheet S' is conveyed by the conveying roller pairs 33a, 33b, 33c, and 33d at a conveying speed Vt=1000 mm / s, and thereafter, it is similarly conveyed to the oblique conveying roller pair 32 and the shift roller pair 31.

[0059] That is, as shown in Fig. 7(b), the gap between the leading sheet S and the trailing sheet S' is wide until the leading sheet S is decelerated. However, when the leading sheet S is decelerated to the image formation speed, the conveying speed of the leading sheet S becomes 500 mm / s, and the conveying speed of the trailing sheet S' becomes 1000 mm / s. Therefore, as shown in Fig. 11(c), by the time the trailing sheet S' reaches the pair of skew rollers 32a, 32b, and 32c, the gap between the leading sheet S and the trailing sheet S' becomes narrow.

[0060] As described above, while the preceding sheet S is being conveyed by the oblique conveying roller pairs 32a, 32b, and 32c, the conveying speed varies widely, and the timing of conveying the preceding sheet S to the secondary transfer roller pair 500 is controlled by the shift roller pair 31. For this reason, the sheet interval is widened so that the preceding sheet S and the subsequent sheet S' do not interfere with each other. After the preceding sheet S reaches the secondary transfer roller pair 500 and is stabilized as an image forming speed, the sheet interval is controlled so that the interval between them is narrowed due to the conveying speed difference between the preceding sheet S and the subsequent sheet S', thereby realizing high productivity. In other words, even if all the roller pairs are controlled at the same speed of, for example, 500 mm / s, it is necessary to widen the sheet interval in consideration of the conveying speed variation (deceleration) that occurs while the preceding sheet S is being conveyed by the oblique conveying roller pairs 32a, 32b, and 32c. Therefore, by controlling the conveying speed of the oblique feed roller pairs 32a, 32b, and 32c to 1000 mm / s and slowing down the sheet width just before the secondary transfer roller pair 500 using the shift roller pair 31, the sheet spacing can be narrowed, thereby achieving high productivity.

[0061] Then, the conveying speed Vs of the sheet S is decelerated to 500 mm / s by the shift roller pair 31, and the conveying speed Vd of the skew roller pairs 32a, 32b, and 32c is kept at 1000 mm / s while the sheet S is being conveyed at the image formation speed by the secondary transfer roller pair 500. As a result, immediately after the rear end of the preceding sheet S passes through the skew roller pairs 32a, 32b, and 32c, the succeeding sheet S' can be sandwiched and conveyed.

[0062] (Problem when transporting extra thick paper) Next, a problem that occurs when the conveying speed of the sheet S is decelerated to 500 mm / s by the shift roller pair 31 and the conveying speed of the skew roller pairs 32a, 32b, and 32c is kept at 1000 mm / s will be described with reference to Figures 15(a) and 15(b). Note that, although the skew roller pair 32a is representatively shown in Figures 15(a) and 15(b), the same applies to the skew roller pairs 32b and 32c.

[0063] For example, if the sheet S is an extremely thick paper such as cardboard or cardboard, when the trailing end of the sheet S passes through the pair of oblique feed rollers 32, one of the pair of oblique feed rollers 32 is likely to come into contact with the surface of the sheet S even if the pair of oblique feed rollers 32 is separated. At this time, if there is a large speed difference between the conveying speed Vd of the pair of oblique feed rollers 32 and the sheet S, the trailing end of the sheet S may become dirty or the trailing end surface may be damaged due to curling of the edge.

[0064] 15(a), when the sheet S is, for example, other than super-thick paper such as thin paper, normal paper, or normal cardboard having a second thickness d2, there is a sufficient distance between the sheet S and the pair of oblique feed rollers 32a when the pair of oblique feed rollers 32a is separated so as not to clamp the sheet S. Therefore, even if there is a large speed difference between the conveying speed of the sheet S and the conveying speed Vd of the pair of oblique feed rollers 32a, the rear end of the sheet S will not be soiled or the rear end surface will not be scratched.

[0065] 15(b), when the sheet S is an extra-thick paper such as cardboard or cardboard having a first thickness d1 that is thicker than the second thickness d2, even if the pair of skew rollers 32a is spaced apart so as not to clamp the sheet S, the distance between the sheet S is small. Therefore, the rear end of the sheet S may be soiled or scratched, and especially when there is a large speed difference between the conveying speed Vd of the pair of skew rollers 32a and the conveying speed S, the edge may curl up as shown in part F in the figure.

[0066] In particular, the oblique feed roller pairs 32 are arranged so that the rotation direction of each roller pair is oblique to the conveying direction in order to abut the sheet S against the side abutment plate 301. If the rotation direction of the roller pairs is arranged straight with respect to the conveying direction, the rear end of the sheet S will rub against the surface of the roller, but if they are arranged obliquely, the rear end of the sheet S will rub against the edge of the end of the roller. This increases the possibility that the rear end of the sheet S will become dirty or the rear end surface will be scratched. Below, a first mode of sheet conveying control that solves such a problem will be described.

[0067] There are various definitions for extra-thick paperboard and cardboard, with the JIS standard being 225 g / m 2 Although the above definition may be regarded as paperboard, in this embodiment, for example, a basis weight of 400 g / m 2 Paper exceeding this thickness is defined as extra thick paper.

[0068] (First mode) As described above, when the control unit 200 receives an instruction to execute printing from a user via, for example, the computer 300 (see FIG. 2), it starts a print job as shown in FIG. 10 (S1). Then, upon receiving the start of the print job, the control unit 200 determines whether the type of the sheet S is super thick paper or other than super thick paper (S2). Here, it is assumed that the sheet S is super thick paper (YES in S2), and the first mode is executed, which is a mode in which steps S3 to S10 are executed.

[0069] Since the control unit 200 has determined that the type of the sheet S is super thick paper, the control unit 200 proceeds to step S3 as the first mode, sets the interval (so-called paper interval) for conveying multiple sheets to an interval for super thick paper, and starts conveying the sheet S. Then, as shown in FIG. 11(a) and FIG. 14, the control unit 200 sets the sheet conveying speed of the conveying roller pairs 33a, 33b, 33c, and 33d to a conveying speed Vf=1000 mm / s. Also, the sheet conveying speed of the oblique feed roller pairs 32a, 32b, and 32c to a conveying speed Vd=1000 mm / s. And, the sheet conveying speed of the shift roller pair 31 is set to a conveying speed Vs=1000 mm / s. The conveying speed of the secondary transfer roller pair 500 is set to a conveying speed Vt=500 mm / s, which is the image forming speed.

[0070] With the conveying speed of each roller pair set in this way, the sheet S is conveyed to the shift roller pair 31 while the skew is corrected as described above (see FIGS. 6 to 8). Then, similar to the second mode, when the first leading edge detection sensor 311 detects the leading edge of the sheet S, the control unit 200 starts counting the timer t (S4). At this time, in response to the detection of the leading edge of the sheet S, the control unit 200 calculates the timing to decelerate the shift roller pair 31 according to the timing at which the toner image and the sheet S match at the secondary transfer roller pair 500 as described above (S5). Furthermore, in response to the detection of the leading edge of the sheet S, the control unit 200 separates the skew roller pairs 32a, 32b, and 32c to switch to a non-clamping state (S6).

[0071] 13 and 14, the control unit 200 decelerates the conveying speed of the shift roller pair 31 from conveying speed Vs=1000 mm / s to conveying speed Vs=500 mm / s which is the image forming speed at the calculated timing for decelerating the shift roller pair 31. Furthermore, at the same time (synchronized with the deceleration of the shift roller pair 31), the conveying speed of the oblique feed roller pairs 32a, 32b, 32c is decelerated from conveying speed Vd=1000 mm / s to conveying speed Vd=500 mm / s which is the image forming speed (S7).

[0072] As a result, the timing at which the shift roller pair 31 transports the sheet S to the secondary transfer roller pair 500 is adjusted, and when the sheet S is transported to the secondary transfer roller pair 500, the toner image (image) is transferred with high precision to the printing position of the sheet S (S8).

[0073] At this time, the sheet S is conveyed to the secondary transfer roller pair 500 and conveyed at a conveying speed of 500 mm / s, which is the image forming speed, but the conveying speed of the oblique conveying roller pairs 32a, 32b, and 32c is also decelerated to a conveying speed Vd=500 mm / s. As a result, even if each roller comes into contact with the surface of the sheet when the rear end of the sheet S passes through each of the oblique conveying roller pairs 32a, 32b, and 32c, there is not much difference in relative speed in the sheet conveying direction. This prevents the rear end of the sheet S from being soiled or damaged by the oblique conveying roller pairs 32a, 32b, and 32c.

[0074] When the timer t reaches the first predetermined time t1 after the trailing edge of the sheet S passes through the pair of oblique feed rollers 32a (a predetermined time after the first leading edge detection sensor detects the leading edge of the sheet), the control unit 200 restores the conveying speed of the pair of oblique feed rollers 32a, 32b, and 32c (S9). That is, the sheet conveying speed of the pair of oblique feed rollers 32a, 32b, and 32c is increased from conveying speed Vd=500 mm / s to conveying speed Vd=1000 mm / s. This restores the state in which the succeeding sheet S' can be accepted even if it reaches the pair of oblique feed rollers 32a, 32b, and 32c.

[0075] Further thereafter, when the timer t reaches a second predetermined time t2 after the trailing edge of the sheet S has passed through the shift roller pair 31 and before the leading edge of the succeeding sheet S reaches the shift roller pair 31, the control unit 200 restores the conveying speed of the shift roller pair 31 (S10). That is, the sheet conveying speed of the shift roller pair 31 is increased from the conveying speed Vs = 500 mm / s to the conveying speed Vs = 1000 mm / s.

[0076] With the above, the sheet transport control in the first mode for one sheet S is completed, and it is determined whether or not there is a subsequent sheet (subsequent sheet S') (S11). If there is a subsequent sheet (YES in S11), the process returns to step S2, and if the subsequent sheet is, for example, the same extra-thick paper, the sheet transport control in the first mode is executed again. If there is no subsequent sheet (NO in S11), the print job is ended (S19), and this sheet transport control ends.

[0077] In addition, when setting the sheet interval for extra thick paper in step S3, it is necessary to set the interval between the preceding sheet S and the succeeding sheet S' wider than in the case of paper other than extra thick paper in order to secure time to accelerate or decelerate the conveying speed Vd of the oblique feed roller pair 32. As a result, as shown in Figures 13 and 14, after the preceding sheet S passes through the oblique feed roller pair 32a (when the first predetermined time t1 has elapsed), the conveying speed of the oblique feed roller pair 32a, 32b, 32c can be restored and the succeeding sheet S' can be received.

[0078] As described above, in the sheet transport control of the printer 1 according to the present embodiment, when ultra-thick paper is transported, the first mode is executed, and the skew roller pair 32 also decelerates in accordance with the deceleration of the shift roller pair 31. This makes it possible to prevent the rear end of the sheet S, which has been decelerated to the image forming speed by the shift roller pair 31, from being soiled or damaged by the skew roller pair 32, which has been switched to the non-clamping state, and makes it possible to prevent a decrease in the quality of the finished product.

[0079] In addition, in the sheet transport control of the printer 1 according to the present embodiment, when transporting paper other than ultra-thick paper (such as plain paper), the second mode is executed, which makes it possible to perform high-precision image formation while improving productivity. Therefore, depending on the type of sheet, it is possible to prevent a decrease in the quality of the finished product while improving productivity.

[0080] [Possibility of other embodiments] In the above-described embodiment, the first roller pair that can be switched between a clamping conveying state and a non-clamping state is the oblique feed roller pair 32, and the second roller pair that slows down the sheet conveying speed is the shift roller pair. However, the present invention is not limited to this, and any roller pair may be used as long as it includes a roller pair that slows down the sheet conveying speed downstream in the sheet conveying direction and a roller pair that is separated upstream and switched to a non-clamping state.

[0081] In the present embodiment, the first mode is executed when the sheet type is super thick paper, and the second mode is executed when the sheet type is other than super thick paper, but the present invention is not limited to this, and the first mode may be executed for all sheet types. In this case, although the productivity is lower than that of the second mode, it is possible to prevent the sheet from being soiled or damaged regardless of the sheet type.

[0082] In addition, in the present embodiment, the first mode and the second mode are selected according to the type of sheet, but the present invention is not limited to this, and the user may select the mode using, for example, the operation unit or the computer 300. In this case, it is conceivable that the first mode may be a quality-oriented mode, and the second mode may be a productivity-oriented mode, etc.

[0083] In the first mode of the present embodiment, the oblique feed roller pair 32 (first roller pair) is decelerated to the same conveying speed as the shift roller pair 31 (second roller pair). However, this is not limiting, and if the rotation speed of the first roller pair is decelerated to a speed equal to or lower than the rotation speed of the second roller pair, edge curling as shown in FIG. 15(b) can be prevented. In other words, in the first mode, when the rotation speed of the second roller pair is decelerated to the second rotation speed, the effect of preventing deterioration in the quality of the finished product can be obtained by decelerating the rotation speed of the first roller pair from the first rotation speed to the second rotation speed or lower.

[0084] In the second mode of the present embodiment, the rotation speed of the oblique feed roller pair 32 (first roller pair) is maintained as it is when the rotation speed of the shift roller pair 31 (second roller pair) is decelerated. However, in this case, if the rotation speed of the first roller pair is faster than the rotation speed of the second roller pair, it is possible to prevent the sheet conveying speed of the first roller pair from being lower than that of the second roller pair. In other words, in the second mode, when the rotation speed of the second roller pair is decelerated to the second rotation speed, the rotation speed of the first roller pair is made faster than the second rotation speed, thereby obtaining the effect of improving productivity.

[0085] In the first mode of the present embodiment, the rotation speed of the oblique feed roller pair 32 is decelerated in synchronization with the deceleration of the rotation speed of the shift roller pair 31. However, the present invention is not limited to this, and the oblique feed roller pair 32 may be decelerated at a predetermined timing using a timer t. If this timing is before the rear end of the sheet passes through the oblique feed roller pair 32, it is possible to prevent the rear end of the sheet from being curled up, and therefore the time for which this effect can be obtained may be measured by the timer.

[0086] In the first mode of the present embodiment, the decelerated rotation speed of the pair of skew rollers is restored when the first predetermined time t1 has elapsed since the first leading edge detection sensor detected the leading edge of the sheet. However, the present invention is not limited to this, and the rotation speed of the pair of skew rollers may be restored, for example, when the leading edge of the succeeding sheet S' is detected by the sensor. Similarly, the decelerated rotation speed of the pair of shift rollers may be restored, for example, when the leading edge of the succeeding sheet S' is detected by the sensor.

[0087] In the present embodiment, the printer 1 is described as being an electrophotographic full-color laser beam printer, but the present invention is not limited to this. For example, the image forming unit that forms an image on a sheet may be any configuration or method, such as an inkjet printer.

[0088] The present disclosure can also be realized by a process in which a program for implementing one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0089] [Summary of this embodiment] [Configuration 1] a first roller pair that is switchable between a nip-and-convey state in which the sheet is nipped and conveyed and a non-nip-and-convey state in which the nip-and-convey state of the sheet is released; a first drive unit that drives the first roller pair; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to convey the sheet; a second drive unit that drives the second roller pair; a control unit that switches the first roller pair to the nip and conveyance state, controls the first drive unit and the second drive unit to control rotational speeds of the first roller pair and the second roller pair to a first rotational speed to convey a sheet from the first roller pair to the second roller pair, and switches the first roller pair to the non-nip state, and controls the second drive unit to reduce the rotational speed of the second roller pair to a second rotational speed slower than the first rotational speed to reduce a conveyance speed of the sheet, the control unit, when decelerating the rotation speed of the second roller pair from the first rotation speed to the second rotation speed, executes a mode in which the rotation speed of the first roller pair is decelerated from the first rotation speed to the second rotation speed or lower by controlling the first drive unit. A sheet conveying device comprising: [Configuration 2] In the mode, the control unit reduces the rotation speed of the first roller pair from the first rotation speed to the second rotation speed that is the same as the rotation speed of the second roller pair. 2. The sheet conveying device according to configuration 1, [Configuration 3] In the mode, the control unit reduces the rotation speed of the first roller pair in synchronization with the reduction in the rotation speed of the second roller pair. 3. The sheet conveying device according to configuration 1 or 2. [Configuration 4] a sheet detection sensor disposed downstream of the second roller pair in a sheet conveying direction and detecting a leading edge of the sheet; the control unit reduces a rotation speed of the second roller pair from the first rotation speed to the second rotation speed so as to adjust a timing at which a leading end of the sheet conveyed by the second roller pair reaches an image forming unit that is disposed downstream of the second roller pair in a sheet conveying direction and that forms an image on the sheet. 4. The sheet conveying device according to any one of configurations 1 to 3. [Configuration 5] in the mode, the control unit increases the rotation speed of the first roller pair from the second rotation speed or less to the first rotation speed before the trailing end of the sheet, the conveying speed of which has been reduced, passes through the first roller pair and a subsequent sheet reaches the first roller pair; 5. The sheet conveying device according to configuration 4. [Configuration 6] the control unit increases the rotation speed of the first roller pair from the second rotation speed or less to the first rotation speed a predetermined time after the sheet detection sensor detects the leading edge of the sheet. 6. The sheet conveying device according to configuration 5. [Configuration 7] the mode is a first mode, the control unit selectively executes the first mode and a second mode in which, when the rotation speed of the second roller pair is reduced from the first rotation speed to the second rotation speed, the rotation speed of the first roller pair is made faster than the second rotation speed. 7. The sheet conveying device according to any one of configurations 1 to 6, [Configuration 8] The control unit maintains the rotation speed of the first roller pair at the first rotation speed in the two modes. 8. The sheet conveying device according to configuration 7, [Configuration 9] The control unit selects the first mode when the sheet has a first thickness, and selects the second mode when the sheet has a second thickness that is thinner than the first thickness. 9. The sheet conveying device according to configuration 7 or 8. [Configuration 10] The sheet conveying device includes a stopper disposed on one side of the sheet width direction perpendicular to the sheet conveying direction, the first roller pair, in the nip-and-convey state, nip the sheet and obliquely convey the sheet toward the abutment portion; the second roller pair moves in the width direction while holding the sheet abutted against the abutting portion; 10. The sheet conveying device according to any one of configurations 1 to 9. [Configuration 11] a third roller pair that is disposed upstream of the second roller pair in a sheet conveying direction and is switchable between a clamping conveying state in which the sheet is clamped and obliquely conveyed toward the abutting portion and a non-clamping state in which the clamping of the sheet is released; When the control unit decelerates the rotation speed of the second roller pair from the first rotation speed to the second rotation speed in the mode, the control unit also decelerates the rotation speed of the third roller pair from the first rotation speed to the second rotation speed or lower. 11. The sheet conveying device according to configuration 10. [Configuration 12] A sheet conveying device according to any one of configurations 1 to 11, an image forming unit disposed downstream of the second roller pair in a sheet conveying direction and forming an image on the sheet, 1. An image forming apparatus comprising: [Configuration 13] the image forming unit includes an image carrier that carries a toner image, and a transfer roller that transfers the toner image carried on the image carrier onto a sheet; the control unit controls the rotation speed of the transfer roller to the second rotation speed, and adjusts a transfer position of the toner image to be transferred onto the sheet by a timing at which the rotation speed of the second roller pair is reduced to the second rotation speed that is slower than the first rotation speed. 13. The image forming apparatus according to claim 12, [Explanation of symbols]

[0090] 1... printer (image forming apparatus) / 30... registration unit (sheet conveying device) / 31... shift roller pair (second roller pair) / 31M... shift roller drive motor (second drive section) / 32a... skew roller pair (first roller pair) / 32b... skew roller pair (third roller pair) / 32M... skew roller drive motor (first drive section) / 40... image forming unit (image forming section) / 50... intermediate transfer belt (image carrier) / 54... secondary transfer outer roller (transfer roller) / 200... control section / 301... side abutment plate (abutment section) / 311... first leading edge detection sensor (sheet detection sensor) / S... sheet

Claims

1. A first roller pair including a first roller and a second roller, the first roller and the second roller abutting against each other to sandwich and transport a sheet; a separation mechanism that switches the second roller between a contact position where the first roller and the second roller are in contact with each other to convey a sheet and a separation position where the first roller and the second roller are separated from each other; a first driving unit that drives the first roller; a second roller pair disposed downstream of the first roller pair in the sheet conveying direction, and configured to sandwich and convey the sheet; a control unit that controls the separating mechanism and the first drive unit, the control unit controls the first driving unit to change the rotation speed of the first roller based on the basis weight of the sheet while the second roller is positioned at the separated position. A sheet conveying device characterized by:

2. The control unit a first process of controlling the separating mechanism to switch the second roller from the contact position to the separated position after the sheet is sandwiched and conveyed by the second roller pair; a second process of controlling the first driving unit to change the rotation speed of the first roller based on the basis weight of the sheet before the trailing edge of the sheet passes through the second roller positioned at the separation position.

2. The sheet transport device according to claim 1.

3. The control unit, in the second processing, controlling the first driving unit so that the rotation speed of the first roller changes from a first rotation speed to a second rotation speed that is equal to or lower than the first rotation speed when the basis weight of the sheet is a first basis weight; When the basis weight of the sheet is a second basis weight that is larger than the first basis weight, the first driving unit is controlled to decelerate the rotation speed of the first roller from the first rotation speed to a third rotation speed that is slower than the second rotation speed.

3. The sheet transport device according to claim 2.

4. The control unit controls the first drive unit in the second process so that the rotational speed of the first roller is decelerated to the third rotational speed in synchronization with the deceleration of the rotational speed of the second roller pair when the basis weight of the sheet is the second basis weight.

4. The sheet transport device according to claim 3.

5. In the second process, the control unit decelerates the rotational speed of the second roller pair from the first rotational speed to the third rotational speed.

4. The sheet transport device according to claim 3.

6. In the second process, the control unit adjusts the timing at which the rotational speed of the second roller pair is reduced from the first rotational speed to the third rotational speed, thereby adjusting the transfer position of the toner image to be transferred to the sheet.

6. The sheet transport device according to claim 5.

7. An image forming unit that forms an image; a transfer unit that is disposed downstream of the second roller pair in the conveying direction and that transfers the image formed by the image forming unit onto the sheet while conveying the sheet, the control unit controls a conveying speed of the sheet conveyed by the transfer unit to the third rotation speed while the transfer unit is transferring the image onto the sheet.

4. The sheet transport device according to claim 3.

8. The control unit controls the rotation speed of the second roller pair to be the first rotation speed when the first roller pair and the second roller pair are clamping a sheet.

4. The sheet transport device according to claim 3.

9. An image forming unit that forms an image; a transfer unit disposed downstream of the second roller pair in the conveying direction and configured to transfer the image formed by the image forming unit onto the sheet while conveying the sheet; a sheet detection sensor disposed between the second roller pair and the transfer unit in the conveying direction, the sheet detection sensor detecting a leading edge of the sheet; and the control unit, in the second process, when the basis weight of the sheet is the second basis weight, adjusts the timing of decelerating the rotation speed of the second roller pair from the first rotation speed to the third rotation speed based on the detection result of the sheet detection sensor and the timing of forming the image on the sheet by the transfer unit.

9. The sheet transport device according to claim 8.

10. The control unit increases the rotational speed of the first roller from the third rotational speed to the first rotational speed after the second processing when the basis weight of the sheet is the second basis weight, when the rear end of the first sheet passes through the first roller pair and before the second sheet following the first sheet reaches the first roller pair.

10. The sheet transport device according to claim 9.

11. The control unit increases the rotational speed of the first roller from the third rotational speed to the first rotational speed after a predetermined time has elapsed since the sheet detection sensor detected the leading edge of the first sheet.

11. The sheet transport device according to claim 10.

12. When the basis weight is the second basis weight, the second rotation speed is the same as the first rotation speed.

4. The sheet transport device according to claim 3.

13. The control unit controls the first drive unit so that the rotational speed of the first roller becomes the first rotational speed when the first roller is located at the abutting position.

4. The sheet transport device according to claim 3.

14. An image forming unit that forms an image; a transfer unit that is disposed downstream of the second roller pair in the conveying direction and that transfers the image formed by the image forming unit onto the sheet while conveying the sheet, the control unit controls a conveying speed of the sheet conveyed by the transfer unit to be a constant speed while changing the rotation speed of the first roller.

2. The sheet transport device according to claim 1.

15. The sheet conveying device further includes a stopper portion that can contact one end of the sheet in a width direction perpendicular to the conveying direction, the first roller pair is a pair of oblique feed rollers that obliquely feed the sheet toward the abutting portion, the second roller pair is a shift roller pair that is movable in the width direction while sandwiching the sheet that has been abutted against the abutting portion; 2. The sheet transport device according to claim 1.

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