Sheet conveying device and image forming apparatus

Abstract

To reduce such a possibility that wrinkles are generated.SOLUTION: A sheet conveying device includes: a first roller pair (122); a second roller pair (120) arranged on the downstream of the first roller pair; registration means (130) that is arranged on the downstream of the second roller pair and sandwiches and conveys the sheet after skew of the sheet has been corrected; a separation mechanism (140) for contacting and separating the second roller pair; and control means. When sheet conveyance speed by the registration means is represented by V1 and sheet conveyance speed by the first roller pair is represented by V2, after skew of the sheet has been corrected in a state in which the second roller pair is separated by the separation mechanism, the control means executes conveyance operation of allowing the first roller pair and the registration means to convey to the sheet at the sheet conveyance speed V1 and V2 satisfying V1<V2.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Some sheet conveying devices used in image forming devices such as printers, copiers, and multifunction machines correct the skew of a sheet by abutting the leading edge of the sheet against a nip portion of a pair of registration rollers or an abutting member in the vicinity of the nip portion to deflect the sheet. The sheet whose skew has been corrected is conveyed by the pair of registration rollers. In this case, the sheet conveying speed of the conveying roller pair upstream of the pair of registration rollers is often set to be slightly faster than the sheet conveying speed of the pair of registration rollers so that the speed at which the sheet is sent out from the pair of registration rollers does not fluctuate.

[0003] In addition, in recent years, in order to accommodate the diversification of sheets used as recording media, sheet conveying devices are required to convey sheets of various sizes. Since a sheet needs to be sandwiched between at least one pair of rollers in order to be conveyed, the distance between the pair of rollers in the conveying direction tends to be narrowed in order to accommodate sheets that are short in the conveying direction.

[0004] Here, the narrower the gap between the roller pairs, the greater the out-of-plane deformation of the sheet when correcting the skew of the sheet, and the sheet is more likely to wrinkle when the portion where the out-of-plane deformation occurs is pinched in the nip portion of the registration roller pair. In the image forming device described in Patent Document 1, the leading edge of the sheet sent out from the conveying roller pair is abutted against a gate member (abutting member) to correct the skew, and then the sheet is pinched between the registration roller pair, and the conveying roller pair is separated. By separating the conveying roller pair, the positional deviation of the sheet on the upstream side of the registration roller pair is eliminated, and the sheet approaches a straight state. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-106572 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the sheet conveying speed of the upstream conveying roller pair is set faster than the sheet conveying speed of the registration roller pair when conveying the sheet after the skew correction, the out-of-plane deformation of the sheet increases as the sheet conveyance proceeds. Even if the upstream conveying roller pair is separated as in Patent Document 1, the out-of-plane deformation of the sheet increases as the sheet conveyance proceeds due to the difference in conveyance speed between the conveying roller pair further upstream of the upstream conveying roller pair and the registration roller pair. As a result, wrinkles may occur in the sheet.

[0007] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to provide a sheet conveying device and an image forming apparatus that are capable of reducing the possibility of wrinkles occurring. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a sheet conveying apparatus including a first roller pair that sandwiches and conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying direction and sandwiches and conveys the sheet, a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction and corrects skew of the sheet by abutting a leading edge of the sheet against the sheet, and then sandwiches and conveys the sheet, a separation mechanism that brings the second roller pair into contact with and separates the sheet, and a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism, wherein a sheet conveying speed by the registration unit is V1 and a sheet conveying speed by the first roller pair is V2, and the control unit controls the sheet conveying speed by the second roller pair to be V1 after the skew of the sheet is corrected with the second roller pair separated by the separation mechanism. >The sheet is conveyed to the first roller pair and the registration means at sheet conveying speeds V1 and V2 that satisfy V2. of Delivery Start to make 1. Transport operation and a second conveying operation for causing the first roller pair and the registration means to start conveying the sheet at a sheet conveying speed V1, V2 that satisfies V1≦V2 after skew correction of the sheet, with the second roller pair separated by the separating mechanism, wherein the control means executes the first conveying operation when conveying a sheet having a first length in the sheet conveying direction, and executes the second conveying operation when conveying a sheet having a second length shorter than the first length. The sheet conveying device is characterized in that it executes the above. Another aspect of the present invention is a sheet conveying apparatus including a first roller pair that pinches and conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying direction and pinches and conveys the sheet, a registration means that is disposed downstream of the second roller pair in the sheet conveying direction and corrects skew of the sheet by abutting the leading edge of the sheet against the registration means and then pinches and conveys the sheet, a separation mechanism that brings the second roller pair into contact with and separates the sheet, a control means that controls the first roller, the second roller pair, the registration means, and the separation mechanism, a cassette that can be pulled out with respect to an apparatus body and that stores sheets, and a tray that protrudes outside the apparatus body and on which sheets are placed, wherein the sheet conveying speed by the registration means is V1, the sheet conveying speed by the first roller pair is V2, a sheet conveying device in which the control means is capable of executing a first conveying operation in which, with a speed of V2, the control means causes the first roller pair and the registration means to start conveying the sheet at a sheet conveying speed V1, V2 that satisfies V1>V2 after skew correction of the sheet, while the second roller pair is separated by the separation mechanism; and a second conveying operation in which, with the second roller pair separated by the separation mechanism, the first roller pair and the registration means to start conveying the sheet at a sheet conveying speed V1, V2 that satisfies V1≦V2 after skew correction of the sheet, and the control means executes the first conveying operation when conveying a sheet fed from the tray, and executes the second conveying operation when conveying a sheet fed from the cassette. Another aspect of the present invention is a sheet conveying device that includes a first roller pair that sandwiches and conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying direction and sandwiches and conveys the sheet, a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction and corrects skew of the sheet by abutting a leading edge of the sheet against the sheet, and then sandwiches and conveys the sheet, a separation mechanism that brings the second roller pair into contact with and separates the sheet, and a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism, and in which a sheet conveying speed by the registration unit is V1 and a sheet conveying speed by the first roller pair is V2, the control unit controls the first roller pair and the registration unit to start conveying the sheet at sheet conveying speeds V1 and V2 that satisfy V1>V2 after the skew of the sheet is corrected in a state where the second roller pair is separated by the separation mechanism, and a second conveying operation in which, with the two roller pairs separated, the first roller pair and the registration means start conveying the sheet at a sheet conveying speed V1, V2 that satisfies V1≦V2 after skew correction of the sheet; and a third conveying operation in which, with the second roller pair abutted by the spacing mechanism, the second roller pair and the registration means convey the sheet after skew correction of the sheet, wherein the control means, when conveying a sheet having a first basis weight and a third length in the sheet conveying direction, separates the second roller pair by the spacing mechanism to perform the first conveying operation or the second conveying operation, and, when conveying a sheet having a second basis weight greater than the first basis weight and when conveying a sheet having a fourth length in the sheet conveying direction shorter than the third length, causes the second roller pair to abut by the spacing mechanism to perform the third conveying operation. Another aspect of the present invention is a sheet conveying apparatus including a first roller pair that pinches and conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying direction and pinches and conveys the sheet, a registration means that is disposed downstream of the second roller pair in the sheet conveying direction and pinches and conveys the sheet after correcting skew of the sheet by abutting a leading edge of the sheet against the registration means, a separation mechanism that abuts and separates the second roller pair, and a control means that controls the first roller, the second roller pair, the registration means, and the separation mechanism, The control means is capable of executing a conveying operation in which the first roller pair and the registration means convey the sheet while the second roller pair is separated by the spacing mechanism at a conveying speed V2, and the control means, in the conveying operation, starts conveying the sheet by the first roller pair and the registration means at sheet conveying speeds V1, V2 that satisfy V1>V2 after the skew of the sheet has been corrected, and when the value of V1 is changed before the rear end of the sheet in the sheet conveying direction passes through the first roller pair, the control means changes the value of V2 in conjunction with V1 so that V1 does not fall below V2. Effect of the Invention

[0009] According to the present invention, the possibility of wrinkles occurring can be reduced. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present disclosure. [Diagram 2] FIG. 4 is a diagram illustrating a state in which the pre-registration roller pair according to the first embodiment is in contact with each other. [Diagram 3] FIG. 4 is a diagram illustrating a state in which the pre-registration roller pair according to the first embodiment is separated from the other. [Figure 4] 11 is a diagram illustrating a state in which the pre-registration roller pair according to the first embodiment is separated from the other roller pair and the sheet conveying speed of the pull-out roller pair is slower than the sheet conveying speed of the registration roller pair. FIG. [Diagram 5] FIG. 4 is a diagram illustrating a driving configuration of a pair of pre-registration rollers according to the first embodiment. [Figure 6] FIG. 4 is a diagram illustrating a driving configuration of a pair of pre-registration rollers according to the first embodiment. [Figure 7] FIG. 4 is a schematic diagram of a drive configuration when rotating a pair of pre-registration rollers according to the first embodiment. [Figure 8] FIG. 4 is a schematic diagram of a drive configuration when the spacing mechanism according to the first embodiment is operated. [Figure 9] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus according to the first embodiment. [Figure 10] 4 is a flowchart showing a control method of the image forming apparatus according to the first embodiment. [Figure 11] FIG. 11 is a diagram illustrating a driving configuration of a pair of pre-registration rollers according to a second embodiment. [Figure 12] FIG. 11 is a block diagram showing a control configuration of an image forming apparatus according to a second embodiment. [Figure 13] 10 is a flowchart showing a control method of an image forming apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, exemplary embodiments according to the present disclosure will be described with reference to the drawings.

[0012] "Image forming apparatus" includes printers, copiers, facsimiles, and multifunction machines, and forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from an original. Sheets used as recording media include paper such as paper and envelopes, plastic films for overhead projectors, and cloth. EXAMPLES

[0013] As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment includes an apparatus main body 100A that houses an image forming section 150, and an image reading device 300 that is disposed above the apparatus main body 100A and reads image information from a document. The image forming section 150, which is an example of an image forming means, is configured as an intermediate transfer tandem system including four image forming units PY, PM, PC, and PK and an intermediate transfer belt 155. The image forming section 150 transfers a toner image formed by the image forming units PY to PK onto a sheet S via the intermediate transfer belt 155. The configurations of the image forming units PY to PK are basically the same except for the color of the toner used for development. Therefore, the configuration of the image forming units and the toner image forming operation will be described using the yellow image forming unit PY as an example.

[0014] When the image forming unit PY forms a toner image, the photosensitive drum 151, which is a photosensitive member, is rotated and the charging device uniformly charges the surface of the photosensitive drum 151. The exposure device 152 provided at the bottom of the apparatus main body 100A irradiates the photosensitive drum 151 with laser light based on image information to expose the drum surface, and forms an electrostatic latent image on the photosensitive drum 151. The electrostatic latent image is then visualized (developed) by toner supplied from the developing device 153, and a toner image is formed on the surface of the photosensitive drum 151.

[0015] Similarly, in the image forming units PM, PC, and PK, toner images of corresponding colors are formed on the photosensitive drums. The toner images formed by each of the image forming units PY to PK are primarily transferred from the photosensitive drum 151 to an intermediate transfer belt 155, which is an intermediate transfer body, by a primary transfer roller 154. Adherents such as toner remaining on the photosensitive drum 151 are removed by cleaning devices provided in each of the image forming units PY to PK.

[0016] The intermediate transfer belt 155 is wound around a secondary transfer inner roller 156, a tension roller 157, and a tension roller 158, and is driven to rotate in a counterclockwise direction in the figure. The toner image carried on the intermediate transfer belt 155 is transported toward a secondary transfer portion formed between the intermediate transfer belt 155 and a secondary transfer roller 159 facing the secondary transfer inner roller 156.

[0017] In parallel with the above process, a feeding operation is performed to feed the sheet S from the cassette feeding section 11 or the multi-feeding section 12 (also called a multipurpose feeding section or manual feeding section) toward the secondary transfer section. The cassette feeding section 11 includes a first cassette 110 and a second cassette 111 as a sheet storage section, and a feeding unit 113 and a feeding unit 114 as a feeding means provided in the first cassette 110 and the second cassette 111, respectively. The multi-feeding section 12 has a multi-tray 112 (multipurpose tray) that protrudes to the outside of the device main body 100A as a sheet support section that supports the sheet, and a feeding unit 115 as a feeding means. The multi-tray 112 can be set (placed) with a required sheet each time a user causes the image forming apparatus to perform an image forming operation. Meanwhile, the first cassette 110 and the second cassette 111 can store a large amount of frequently used sheets (e.g., A4 plain paper).

[0018] The feeding units of the cassette feeding section 11 and the multi-feeding section 12 may include a pickup roller that feeds out sheets from a cassette, and a pair of separation rollers that receive the sheets from the pickup roller and separate and transport them one by one. The separation mechanism of the pair of separation rollers may be configured such that a retard roller, to which a driving force in a direction against the rotation of the feed roller is input via a torque limiter, is in contact with a feed roller that transports the sheets in the same direction as the pickup roller. The above is not limited to the above, and other feeding mechanisms such as a separation pad type or an air feeding type may be used instead.

[0019] The sheet S stored in the first cassette 110 is conveyed by the feeding unit 113 to the registration roller pair (hereinafter referred to as the registration roller pair) 130 via the pre-registration roller pair (hereinafter referred to as the registration roller pair) 120. The sheet S stored in the second cassette 111 is conveyed by the feeding unit 114, and then conveyed to the pre-registration roller pair 120 and the registration roller pair 130 via the pull-out roller pair 121. The sheet set in the multi-tray 112 is conveyed by the feeding unit 115, and then conveyed to the pre-registration roller pair 120 and the registration roller pair 130 via the pull-out roller pair 122. Note that, for the sheet fed from the first cassette 110, no roller pair other than the pre-registration roller pair 120 is disposed on the conveying path from the feeding unit 113 to the registration roller pair 130. The pull-out roller pairs 121 and 122 are the first roller pair in this embodiment, and the pre-registration roller pair 120 is the second roller pair in this embodiment. The pair of registration rollers 130 is the registration means of this embodiment.

[0020] When the leading edge (downstream edge in the sheet conveying direction) of the fed sheet S abuts against the registration roller pair 130 in the stopped state, the sheet S bends (forms a loop), and the leading edge of the sheet S follows the nip portion of the registration roller pair 130 to correct the skew. Thereafter, the registration roller pair 130 starts conveying the sheet S at a timing synchronized with the image formation process by the image forming unit 150, and conveys the sheet S to the secondary transfer unit. Note that the registration means is not limited to a means for abutting the leading edge of the sheet against the nip portion of the registration roller pair 130, and may be a means for abutting the leading edge of the sheet S against an abutting member (shutter member) provided in the vicinity of the nip portion of the registration roller pair 130 to correct the skew.

[0021] In the secondary transfer portion, the toner image carried on the intermediate transfer belt 155 is secondarily transferred to the sheet S by a secondary transfer roller 159. Adherents such as toner remaining on the intermediate transfer belt 155 are removed by a belt cleaning device. The sheet S to which the toner image has been transferred is delivered to a fixing device 160. The fixing device 160 has a pair of fixing rollers that sandwich and transport the sheet S, and a heating means such as a halogen lamp or ceramic heater that heats the sheet S, and applies heat and pressure to the toner image while transporting the sheet S. As a result, the toner is melted and fixed to the sheet S.

[0022] The sheet S on which an image has been formed by passing through the secondary transfer unit and the fixing device 160 is delivered to a discharge path 172 of the sheet discharge unit 170 and discharged by a discharge roller pair 171 to a discharge tray 180 provided between the apparatus main body 100A and the image reading device 300. When performing double-sided printing, the sheet S on which an image has been formed on the first side is switchback-conveyed by the discharge roller pair 171, which is a reversing roller pair, and delivered to a double-sided conveying unit 190, and is conveyed by a conveying roller pair 193 via a double-sided path 192. Then, the sheet S reaches the registration roller pair 130 again, an image is formed on the back side by the image forming unit 150, and the sheet S is discharged by the discharge roller pair 171 to the discharge tray 180.

[0023] (Sheet conveying mechanism upstream of the registration roller pair) Next, the registration roller pair 130 and the sheet conveying mechanism on the upstream side thereof in the image forming apparatus 100 according to the first embodiment will be described with reference to FIGS. 2 to 10. FIGS. 2 and 3 are schematic diagrams of the sheet conveying mechanism, respectively showing a state where the pre-registration roller pair 120 is in contact with each other and a state where the pre-registration roller pair 120 is separated from each other. In the drawings, the broken lines indicate the sheet S fed from the multi-feeding unit 12. FIG. 4 shows a state where the pre-registration roller pair 120 is separated from each other and the sheet conveying speed V2 of the pull-out roller pair is slower than the sheet conveying speed V1 of the registration roller pair. FIGS. 5 and 6 are diagrams showing a drive configuration of the pre-registration roller pair 120, including a separation mechanism 140 that causes the pre-registration roller pair 120 to come into contact with each other and separate from each other. FIG. 5 shows a state where the pre-registration roller pair 120 is in contact with each other, and FIG. 6 shows a state where the pre-registration roller pair 120 is separated from each other.

[0024] First, the components included in the sheet conveying mechanism will be described with reference to Fig. 2 and Fig. 3. The pull-out roller pair 121, 122 is composed of pull-out driving rollers 121a, 122a driven by a motor and pull-out driven rollers 121b, 122b which rotate following the pull-out rollers. The pre-registration roller pair 120 is composed of a pre-registration driving roller 120a driven by a motor and a pre-registration driven roller 120b which rotates following the pull-out rollers, and is configured so that the roller pair can be brought into contact with and separated from each other by a separation mechanism 140 which will be described later. The registration roller pair 130 is composed of a registration driving roller 130a driven by a motor and a registration driven roller 130b which rotates following the pull-out rollers.

[0025] In the image forming apparatus 100, a sheet sensor 132 is disposed as a detection unit capable of detecting the sheet S at a detection position between the pre-registration roller pair 120 and the registration roller pair 130. The sheet sensor 132 may be, for example, a reflective photoelectric sensor that irradiates light onto the sheet transport path and detects reflected light from the sheet S, or a transmissive photoelectric sensor that detects the rotation of a flag that protrudes into the sheet transport path.

[0026] The image forming apparatus 100 according to the present embodiment is of a vertical conveying type (see FIG. 1) in which an image is formed on a sheet S conveyed approximately upward inside the apparatus main body 100A. The sheet S fed from the multi-feeding unit 12 arranged on the side of the apparatus main body 100A is conveyed toward the secondary transfer unit through a curved sheet conveying path. That is, as shown in FIG. 2, the sheet conveying path has a shape curved from an approximately horizontal direction to an approximately vertical direction between the pull-out roller pair 122 and the registration roller pair 130 when viewed from the width direction perpendicular to the sheet conveying direction. The sheet conveying path between the pre-registration roller pair 120 and the registration roller pair 130 has a portion that protrudes toward the outside of the curved shape (leftward in the figure), and a space is formed to allow the sheet to bend (loop formation) when it hits the registration roller pair 130.

[0027] However, with the diversification of sheets used as recording media, a sheet conveying device used in an image forming apparatus is required to be able to stably convey sheets of various sizes. Specifically, the distance between the conveying roller pairs in the sheet conveying direction is set narrow so that a small sheet (e.g., a postcard) is reliably transferred from the conveying roller pair on the upstream side to the conveying roller pair on the downstream side. In the present embodiment, the distance between the pre-registration roller pair 120 and the registration roller pair 130 in the sheet conveying direction is set shorter than the shortest length in the sheet conveying direction of the sheets on which the image forming apparatus 100 can perform image formation.

[0028] (Separation mechanism for pair of pre-registration rollers) In this embodiment, a configuration is adopted that allows the pre-registration roller pair 120 to be separated (to open the nip portion) as necessary. The configuration of a separating mechanism 140 for the pre-registration roller pair 120 will be described below.

[0029] 5 and 6, the separation mechanism 140 includes a separation gear 146, a separation transmission shaft 148, a cam 149, a lever 127, a position determination spring 128, a separation shaft 141, a separation arm 142, and a separation sensor 129. The separation mechanism 140 is driven by a pre-registration drive motor 145, which is a drive source shared with the pre-registration roller pair 120, and acts on a rotation shaft 120d of the pre-registration driven roller 120b to switch the pre-registration roller pair 120 between a contact state and a separated state.

[0030] The separation gear 146 and the cam 149 are supported by a separation transmission shaft 148, and rotate integrally with the separation gear 146 as the separation gear 146 is driven to rotate by the pre-registration drive motor 145. The cam 149, which is a cam member, presses a lever 127 provided on the separation shaft 141, thereby rotating the separation shaft 141. A position determination spring 128 connected to the separation shaft 141 biases the separation shaft 141 so as to press the lever 127 against the cam 149. The separation arm 142, which is a swinging member attached to the separation shaft 141, swings in accordance with the movement of the lever 127, and moves the rotation shaft 122d of the pre-registration driven roller 122b in a direction approaching and moving away from the pre-registration drive roller 120a. The separation sensor 129 is a transmissive photoelectric sensor capable of detecting the flag portion 141a provided on the separation shaft 141, and detects the rotation angle of the separation shaft 141 corresponding to the contact state (FIG. 5) and separation state (FIG. 6) of the pre-registration roller pair 120. Note that the separation sensor 129 is an example of a position detection means capable of detecting the contact / separation of the pre-registration roller pair 120, and may be replaced with a configuration that detects the position of the rotation shaft 120d of the pre-registration driven roller 120b, for example.

[0031] 2, the pre-registration roller pair 120 is pressurized by a pressure spring 143, which is an elastic member provided between a rotation shaft 120d of the pre-registration driven roller 120b and a metal plate 144 fixed to the frame of the image forming apparatus 100. The pressure spring 143 is an example of a pressure means that presses one roller of the pre-registration roller pair 120 toward the other roller, and determines the contact pressure (nip pressure) of the pre-registration roller pair 120 in the contact state.

[0032] As shown in Fig. 7 and Fig. 8, the output gear of the pre-registration driving motor 145 meshes with both the pre-registration driving gear 147 attached to the drive shaft 120c of the pre-registration driving roller 120a and the separation gear 146. Hereinafter, the clockwise direction of the rotation of the pre-registration driving motor 145 as viewed from the direction of the output shaft is referred to as the CW direction, and the opposite counterclockwise direction is referred to as the CCW direction. The pre-registration driving gear 147 is provided with a one-way clutch mechanism that transmits the driving force of the pre-registration driving motor 145 to the drive shaft 120c only when the output gear rotates in the CW direction. In addition, the separation gear 146 is provided with a one-way clutch mechanism that transmits the driving force of the pre-registration driving motor 145 to the separation transmission shaft 148 only when the output gear rotates in the CCW direction.

[0033] When the pre-registration drive motor 145 rotates in the CW direction (first direction), the driving force is transmitted to the drive shaft 120c via the pre-registration drive gear 147, and the pre-registration roller pair 120 is rotated. At this time, the driving force is not transmitted to the separation transmission shaft 148, and the separation mechanism 140 does not operate. On the other hand, when the pre-registration drive motor 145 rotates in the CCW direction (second direction), the driving force is transmitted to the separation transmission shaft 148 via the separation gear 146, and the separation mechanism 140 switches the pre-registration roller pair 120 between the contact state and the separation state. That is, the lever 127 is pressed by the rotation of the cam 149, and the separation arm 142 swings via the separation shaft 141, so that the pre-registration driven roller 122b comes into contact with (FIG. 5) and separates from (FIG. 6) the pre-registration drive roller 120a. At this time, no driving force is transmitted to the drive shaft 120c, and the pre-registration roller pair 120 is not rotated. In this manner, the drive configuration of the pre-registration roller pair 120 according to this embodiment can switch between the rotational drive of the pre-registration roller pair 120 and the drive of the separation mechanism 140 by switching the rotation direction of the pre-registration drive motor 145, which is a single motor.

[0034] Next, the conveying operation that the sheet conveying mechanism can perform will be described with reference to Fig. 2 to Fig. 4. The sheet conveying mechanism of this embodiment conveys a sheet by performing one of a plurality of conveying operations (modes) described below based on the attributes of the sheet (e.g., information such as size and basis weight) and the sheet feed source. Note that, although the following mainly describes the conveying operation for the sheet S fed from the multi-feed unit 12, basically the same conveying operation can also be performed for the sheet S fed from the cassette feed unit 11 unless otherwise specified.

[0035] (Conveying operation of bringing the pair of pre-registration rollers into contact) 2 shows a conveying operation (a third conveying operation in this embodiment) in which the sheet S is conveyed while being in contact with the pre-registration roller pair 120. In this conveying operation, the sheet S conveyed by the pull-out roller pair 122 is sandwiched by the pre-registration roller pair 120 and further conveyed. Then, the leading edge of the sheet S abuts against the nip portion of the stopped registration roller pair 130, and a loop is formed between the pre-registration roller pair 120 and the registration roller pair 130, thereby correcting the skew of the leading edge of the sheet S.

[0036] In this conveying operation, the sheet S is conveyed with the pre-registration roller pair 120 in contact with the sheet S even after the skew correction of the sheet S. Therefore, when the conveyance of the registration roller pair 130 starts after the skew correction of the sheet S, the pre-registration roller pair 120 conveys the sheet S together with the registration roller pair 130. At this time, in order to avoid the sheet from pulling against each other, the sheet conveying speed V2 of the pre-registration roller pair 120 (the peripheral speed of the drive roller when the speed fluctuation due to the conveying resistance of the sheet and the like is ignored) is set to be equal to or slightly faster than the sheet conveying speed V1 of the registration roller pair 130.

[0037] This conveying operation has the advantage that even if the sheet is a cardboard or other sheet with a relatively large conveying resistance, the leading edge of the sheet is reliably pushed into the nip portion of the pair of registration rollers 130 to correct the skew, and the sheet can be stably conveyed with the assistance of the pair of pre-registration rollers 120. In addition, since it is possible to prevent fluctuations in the speed at which the sheet is sent out from the pair of registration rollers 130 due to the pulling of the sheet, it is possible to improve the quality of the image transferred to the sheet in the secondary transfer section.

[0038] (Transportation operation for separating the pair of pre-registration rollers) 3 shows a conveying operation (a second conveying operation in this embodiment) in which the sheet S is conveyed with the pre-registration roller pair 120 separated from each other. In this conveying operation, the leading edge of the sheet S conveyed by the pull-out roller pair 122 passes through the pre-registration roller pair 120 in the open state, and the leading edge of the sheet S abuts against the nip portion of the stopped registration roller pair 130. The pull-out roller pair 122 further conveys the sheet S, forming a loop between the pull-out roller pair 122 and the registration roller pair 130 to correct the skew of the sheet S.

[0039] In this conveying operation, the sheet S is conveyed with the pre-registration roller pair 120 separated even after the skew correction of the sheet S. Therefore, when the conveyance of the registration roller pair 130 starts after the skew correction of the sheet S, the pull-out roller pair 122 conveys the sheet S together with the registration roller pair 130. At this time, the sheet conveying speed V2 of the pull-out roller pair 122 is set to be equal to or slightly faster than the sheet conveying speed V1 of the registration roller pair 130.

[0040] According to this conveying operation, the distance between the rollers where the loop is formed can be made longer compared to the state of FIG. 2 where the pre-registration roller pair 120 is in contact. That is, in the state of FIG. 2, the loop is formed in a short conveying path from the pre-registration roller pair 120 to the registration roller pair 130, but in this conveying operation, the loop is formed in the conveying path from the pull-out roller pair 122 to the registration roller pair 130 as shown in FIG. 3. Therefore, the out-of-plane deformation of the sheet S caused by the skew correction is mitigated, and the possibility of wrinkles occurring in the sheet S is reduced. In addition, since it is possible to avoid fluctuations in the speed at which the sheet is sent out from the registration roller pair 130 due to the pulling of the sheet, the image quality of the image transferred to the sheet in the secondary transfer section can be improved.

[0041] (Transport operation to separate the pre-registration roller pair and reduce loops) 4 shows a conveying operation (first conveying operation in this embodiment) in which the pre-registration roller pair 120 is separated, and the sheet conveying speed of the pull-out roller pair 122 after skew correction is set to a value slower than the sheet conveying speed of the registration roller pair 130 to convey the sheet S. This conveying operation is similar to the case of FIG. 3 in that skew correction of the sheet S and conveying after skew correction are performed with the pre-registration roller pair 120 separated. Therefore, out-of-plane deformation of the sheet S accompanying the skew correction is mitigated, and the possibility of wrinkles occurring in the sheet S is reduced.

[0042] Furthermore, in this conveying operation, the sheet conveying speed of the pull-out roller pair 122 after the skew correction is set to a value smaller than the sheet conveying speed of the registration roller pair 130. That is, the sheet conveying speed of the registration roller pair 130 is set to V1, and the sheet conveying speed of the pull-out roller pair 122 is set to V2, and the sheet S is conveyed by the registration roller pair 130 and the pull-out roller pair 122 at the sheet conveying speeds V1 and V2 that satisfy V1>V2 after the skew correction. As a result, as the conveyance of the sheet S progresses until the rear end of the sheet S passes through the pull-out roller pair 122, the loop between the registration roller pair 130 and the pull-out roller pair 122 is gradually reduced (eliminated). Then, the posture of the rear end side of the sheet follows the posture of the leading end side of the sheet held by the registration roller pair 130, and the skew is easily eliminated, and the out-of-plane deformation of the sheet S is reduced. As a result, the out-of-plane deformation of the sheet S is further alleviated, and the possibility of wrinkles occurring in the sheet S is further reduced.

[0043] In this manner, in this embodiment, the possibility of wrinkles occurring in the sheet can be reduced by separating the pre-registration roller pair 120 and transporting the sheet to the registration roller pair 130 and the pull-out roller pair 122 at a sheet transport speed that satisfies V1>V2 after skew correction.

[0044] In addition, in this embodiment, a plurality of conveying operations are switchable, which differ in whether or not the pre-registration roller pair 120 is separated, and in the relationship between the conveying speed of the registration roller pair 130 after skew correction and the conveying speed of the upstream roller pair (120, 122). The conveying operation (second conveying operation) shown in Fig. 3 has a higher effect of suppressing wrinkles than the conveying operation (first conveying operation) shown in Fig. 2, and the conveying operation (first conveying operation) shown in Fig. 4 has an even higher effect of suppressing wrinkles than the conveying operation shown in Fig. 3. Therefore, by switching between a plurality of conveying operations according to the execution conditions (sheet passing conditions) of the image forming operation such as the attributes of the sheet and the sheet feed source, it is possible to reduce the possibility of wrinkles occurring while maintaining the conveying performance and skew correction ability.

[0045] (flowchart) An example of a method for controlling the sheet conveying operation by the image forming apparatus 100 will be described below with reference to Figs. 9 and 10. As shown in Fig. 9, the image forming apparatus 100 is equipped with a control unit 201, which is an example of a control unit. The control unit 201 includes a memory 204 for storing programs and data, and a central processing unit (CPU) 203 as an execution unit for executing the programs. The control unit 201 receives input signals from an operation unit 202 that includes a liquid crystal panel and various buttons and functions as a user interface, in addition to a separation sensor 129 and a sheet sensor 132. The control unit 201 controls the operation of the sheet conveying mechanism by controlling the driving of a register drive motor 133, a pre-register drive motor 145, and a pull-out motor 123, which are actuators.

[0046] The CPU 203 executes a program read from the memory 204 to realize the functions of the steps in the flowchart shown in Fig. 10. First, print information including information on the sheet S to be used as a recording medium input by the user via the operation unit 202 of the image forming apparatus 100 is acquired (F101). Examples of the information input here include the size and basis weight of the sheet S. When it is detected that the user has instructed to execute a print job via the operation unit 202 (F102), a determination is made as to whether or not to separate the pre-registration roller pair 120 (F103 to F105).

[0047] Specifically, it is determined whether the feed source of the sheet used in executing the print job (the sheet to be subjected to the image forming operation) is the first cassette 110 or not (F103). If the feed source is the first cassette 110 (F103: No), it is determined that the pre-registration roller pair 120 needs to be brought into contact to perform the conveying operation, and the contact operation of the pre-registration roller pair 120 (F106, F107a) is performed. This is to avoid poor sheet conveyance caused by separating the pre-registration roller pair 120, since there are no roller pairs other than the pre-registration roller pair 120 arranged on the conveying path from the feeding unit 113 of the first cassette 110 to the registration roller pair 130.

[0048] If the feeding source is other than the first cassette 110 (F103: Yes), it is further determined whether the length of the sheet S in the sheet conveying direction (hereinafter simply referred to as the sheet length) is equal to or greater than a preset threshold value X1 [mm] (F104). If the sheet S is shorter than X1 [mm] (F104: No), it is determined that the pre-registration roller pair 120 needs to be brought into contact for conveying, and the contact operation of the pre-registration roller pair 120 (F106, F107a) is performed. This is because, when the sheet S is short, in a state in which the pre-registration roller pair 120 is separated, the sheet may not be conveyed to a position where the leading edge of the sheet reaches the registration roller pair 130. Therefore, as the threshold value X1, a value obtained by adding a small margin to the distance from the pull-out roller pair 122 to the registration roller pair 130 measured along the conveying path can be used.

[0049] If the sheet length is equal to or greater than X1 [mm] (F103: Yes), it is determined whether the basis weight of the sheet S is less than a preset threshold value M [gsm] (F105). If the basis weight of the sheet S is less than M [gsm] (F105: No), it is determined to separate the pre-registration roller pair 120, and the separation operation of the pre-registration roller pair 120 (F107b, F108) is performed. This is because a sheet S with a small basis weight is considered to have low rigidity and a relatively high risk of wrinkles. On the other hand, if the basis weight of the sheet S is equal to or greater than M [gsm] (F105: Yes), it is determined to contact the pre-registration roller pair 120, and the contact operation of the pre-registration roller pair 120 (F106, F107b) is performed.

[0050] In the contact operation of the pre-registration roller pair 120 (F106, F107a), the pre-registration drive motor 145 is rotated in the CCW direction (FIG. 8) until the output signal of the separation sensor 129 indicates the contact state of the pre-registration roller pair 120 (OFF signal in this embodiment). Then, the separation mechanism 140 described above is activated and the pre-registration roller pair 120 enters the contact state. If the output signal of the separation sensor 129 indicates the contact state of the pre-registration roller pair 120 from the beginning, the pre-registration drive motor 145 is not rotated in the CCW direction and the process proceeds to the subsequent step.

[0051] In the separation operation of the pre-registration roller pair 120 (F108, F107b), the pre-registration drive motor 145 is rotated in the CCW direction (FIG. 8) until the output signal of the separation sensor 129 indicates the separation state of the pre-registration roller pair 120 (an OFF signal in this embodiment). Then, the separation mechanism 140 described above is activated and the pre-registration roller pair 120 is placed in the separation state. If the output signal of the separation sensor 129 indicates the separation state of the pre-registration roller pair 120 from the beginning, the pre-registration drive motor 145 is not rotated in the CCW direction and the process proceeds to the subsequent step.

[0052] In this manner, in this embodiment, when a sheet having a first basis weight (basis weight less than M) and a third length (length equal to or greater than X1) in the sheet conveying direction is conveyed, the separation mechanism 140 separates the pre-registration roller pair 120. In this case, as described later, the first conveying operation (F115) or the second conveying operation (F116) is executed with the pre-registration roller pair 120 separated even after the skew correction. On the other hand, when a sheet having a second basis weight (basis weight equal to or greater than M) larger than the first basis weight is conveyed, the separation mechanism 140 brings the pre-registration roller pair 120 into contact with the sheet. Also, when a sheet having a fourth length (length less than X1) in the sheet conveying direction shorter than the third length is conveyed, the separation mechanism 140 brings the pre-registration roller pair 120 into contact with the sheet. In these cases, as described later, after the skew correction, the sheet is conveyed with the pre-registration roller pair 120 in contact with the sheet as the third conveying operation.

[0053] When the contact or separation of the pre-registration roller pair 120 is determined by the above processes of F103 to F108, a feeding operation is started to feed the sheet S from the cassette or tray of the feeding source (F109). When the feeding source is the multi-tray 112, the feeding unit 115 feeds one sheet S on the multi-tray 112 and conveys the sheet S toward the registration roller pair 130 via the pull-out roller pair 122. At this time, when the pre-registration roller pair 120 is in contact, the pre-registration drive motor 145 is rotated in the CW direction to convey the sheet S to the pre-registration roller pair 120 as well. When the pre-registration roller pair 120 is in a separated state, the pre-registration drive motor 145 may be rotated in the CW direction or may be stopped. In a configuration in which the peripheral surface of the pre-registration drive roller 120a protrudes into the conveying path in the separated state (FIG. 2), it is preferable to rotate the pre-registration drive motor 145 in the CW direction and drive the pre-registration drive roller 120a at the same speed as the pull-out roller pair 122.

[0054] Thereafter, as described above, the leading edge of the sheet S abuts against the stopped registration roller pair 130, forming a loop of the sheet S, and the skew of the sheet S is corrected by the registration roller pair 130 (F110). At this time, when the pre-registration roller pair 120 is in a contact state, a loop is formed between the pre-registration roller pair 120 and the registration roller pair 130, and when the pre-registration roller pair 120 is in a separated state, a loop is formed between the pull-out roller pair 122 and the registration roller pair 130. The size of the loop (the amount of sheet transport by the upstream roller pair after the leading edge of the sheet reaches the registration roller pair 130) is managed based on the elapsed time from the time when the sheet sensor 131 detects the leading edge of the sheet and the sheet transport speed of the upstream roller pair.

[0055] When a loop of a predetermined size is formed, the rotation of the pull-out roller pair 122 and the pre-registration roller pair 120 is temporarily stopped. After that, at a timing synchronized with the image forming process by the image forming unit 150, the registration roller pair 130 starts rotating at a sheet conveying speed V1 (F111). In synchronization with the start of rotation of the registration roller pair 130, the upstream pre-registration roller pair 120 and the pull-out roller pair 122 also start rotating at a sheet conveying speed V2, and at this time, the sheet conveying speed V2 is determined by the processing of F112 to F114.

[0056] Specifically, when the pre-registration roller pair 120 is in a separated state (F112: Yes), the feeding source is the multi-tray 112 (F113: Yes), and the sheet length is equal to or greater than a preset threshold value X2 [mm] (F114: Yes), the sheet conveying speed V2 is set to a value slower than the sheet conveying speed V1 of the registration roller pair 130 (F115). Otherwise, the sheet conveying speed V2 of the pre-registration roller pair 120 and the pull-out roller pair 122 is set to a value equal to or greater than the sheet conveying speed of the registration roller pair 130 (V1 or greater) (F116). In other words, when a sheet having a first length (length equal to or greater than X2) in the sheet conveying direction is conveyed, the first conveying operation (F115) is performed. Also, when a sheet having a second length (length less than X2) in the sheet conveying direction is conveyed, the second conveying operation (F116) is performed.

[0057] The reason why V1>V2 is set when the feeding source is the multi-tray 112 is that the out-of-plane deformation during skew correction may be larger than that of a sheet fed from a cassette due to the sheet being tilted when the user sets the sheet on the multi-tray 112. The reason why V1>V2 is set when the sheet length is equal to or larger than the threshold value X2 is that the longer the sheet is, the larger the out-of-plane deformation of the sheet is likely to be before the trailing end of the sheet passes through the pull-out roller pair 122 when V1≦V2 is set during conveyance after skew correction.

[0058] The sheet length threshold value X2 for setting the sheet conveying speeds V1 and V2 does not have to be the same as the sheet length threshold value X1 for whether to separate the pre-registration roller pair 120. The threshold value X2 is set from the viewpoint of the risk of wrinkles occurring due to the difference in sheet conveying speed between the registration roller pair 130 and the upstream roller pair, and is, for example, X2>X1.

[0059] When the sheet S is sent out from the pair of registration rollers 130, an image is transferred to the sheet S in the secondary transfer section, and then the sheet S is fixed by the fixing device 160 and discharged to the outside of the image forming apparatus 100 (F117). This ends the processing of the print job for one sheet (F118). Note that when image formation is performed successively on multiple sheets, the processing of F109 to F117 is executed repeatedly.

[0060] (Modification) In the sheet conveying operation described in this embodiment, the registration roller pair 130 conveys the sheet at a constant sheet conveying speed V1 after the skew correction, but the sheet conveying speed V1 of the registration roller pair 130 after the skew correction may be changed. For example, the sheet conveying speed V1 may be controlled to adjust the timing at which the leading edge of the sheet reaches the secondary transfer section in synchronization with the image forming process. In that case, the relationship V1>V2 or V1≦V2 is established at least at the timing at which the pre-registration roller pair 120 and the pull-out roller pair 122 start rotating in F115 and F116. In addition, when the sheet conveying speed V1 of the registration roller pair 130 is changed after the rotation starts, it is preferable to also change the sheet conveying speed V2 of the pre-registration roller pair 120 and the pull-out roller pair 122 so that the relationship V1>V2 or V1≦V2 is maintained.

[0061] In addition, in this embodiment, it has been described that when a loop of a predetermined size is formed on the sheet during skew correction, the pre-registration roller pair 120 and the pulling roller pair 122 temporarily stop. However, the conveyance of these roller pairs can also be continued. That is, at the timing when a loop of a predetermined size is formed on the sheet, the rotation of the pre-registration roller pair 120 and the pulling roller pair 122 may be continued, and the rotation of the registration roller pair 130 may be started. In that case, the sheet conveyance speed V1 of the registration roller pair 130 may be changed in order to adjust the timing at which the sheet leading end reaches the secondary transfer section.

[0062] The criteria for determining whether or not to separate the pre-registration roller pair 120 and the sheet conveyance speeds V1 and V2 after skew correction are not limited to those described in this embodiment. For example, regarding whether or not to separate the pre-registration roller pair 120, it is also possible to make a determination using only a part of the conditions shown in F103 to F105 in FIG. 10. Further, the sheet conveyance speeds V1 and V2 after skew correction may be determined using only one of F113 or F114 in FIG. 10. Even in that case, due to the reasons described in the embodiment, an appropriate conveyance operation can be executed according to the execution conditions of the image forming operation such as the attributes of the sheet and the sheet feeding source.

[0063] Also, in this embodiment, when the sheet conveyance speeds V1 and V2 after skew correction are set such that V1 > V2, it has been described that the pre-registration roller pair 120 is always in a separated state. However, it is not limited to this. A mode may be added in which the pre-registration roller pair 120 is brought into contact and the sheet conveyance speed V2 of the pulling roller pair 122 and the pre-registration roller pair 120 after skew correction is set faster than the sheet conveyance speed V1 of the registration roller pair 130 (V1 < V2) to convey the sheet S.

Embodiment

[0064] Next, a sheet conveying mechanism of an image forming apparatus 100 according to a second embodiment will be described with reference to Figs. 11 to 13. Fig. 11 is a perspective view showing a drive configuration of a pair of pre-registration rollers 120 according to this embodiment. Fig. 12 is a block diagram showing a control configuration of the image forming apparatus 100 according to this embodiment. Fig. 13 is a flowchart showing a control method of the image forming apparatus 100 according to this embodiment. Hereinafter, elements common to those in the first embodiment are given the same reference numerals and description thereof will be omitted.

[0065] As shown in Figs. 11 and 12, in this embodiment, a separation operation motor 301 is provided as a second motor for operating the separation mechanism 140, in addition to a pre-registration drive motor 145 as a first motor for rotating the pre-registration roller pair 120. The pre-registration drive motor 145 rotates the drive shaft 120c of the pre-registration drive roller 120a via a pre-registration drive gear 147. The separation operation motor 301 operates the separation mechanism 140 by rotating a cam gear 302 that rotates integrally with a cam 149 of the separation mechanism 140, and moves the rotation shaft 120d of the pre-registration driven roller 120b via the separation arm 142. The control unit 201 can independently control the drive states of the pre-registration drive motor 145 and the separation operation motor 301. The spacing mechanism 140 of the pre-registration roller pair 120 according to the second embodiment is configured to operate the spacing mechanism 140 by driving a spacing operation motor 301, as shown in FIG.

[0066] A control method for image forming apparatus 100 in this embodiment will be described with reference to the flowchart in Fig. 13. The control in this embodiment differs from that in embodiment 1 in the timing of operating separation mechanism 140. Other parts that perform substantially the same processes as those in embodiment 1 are given the same reference numerals and will not be described.

[0067] When a print job is started (F102), feeding of a sheet is started from a cassette or tray as a feeding source (F109), and control is performed (F201, F202) to bring the pre-registration roller pair 120 into contact with each other. That is, in this embodiment, the pre-registration roller pair 120 is kept in contact with each other while the skew correction of the sheet is being performed, and after the skew correction, control is performed (F103 to F108) to separate the pre-registration roller pair 120 as necessary.

[0068] Specifically, when the sheet starts to be fed (F109), if the separation sensor 129 is not OFF, the separation operation motor 301 is rotated to bring the pre-registration roller pair 120 into contact (F201, F202). After that, when the leading edge of the sheet is abutted against the registration roller pair 130 that is in a stopped state and a loop of a predetermined size is formed in the sheet (F110), the registration roller pair 130 starts to rotate (F111).

[0069] Furthermore, to determine whether to separate the pre-registration roller pair 120 after the skew correction, the sheet feed source (F103), the sheet length (F104), and the sheet basis weight (F105) are determined. The criteria for F103 to F105 can be the same as those in the first embodiment. If it is determined that the pre-registration roller pair 120 should be separated, the separating operation motor 301 is rotated to separate the pre-registration roller pair 120 (F108, F202), otherwise, the pre-registration roller pair 120 is kept in contact with each other, and the process proceeds to the next step F112.

[0070] In addition, in order to determine the sheet conveying speed V2 of the pre-registration roller pair 120 and the pull-out roller pair 122 after the skew correction, the state of the pre-registration roller pair 120 (F112), the sheet feed source (F113), and the sheet length (F114) are determined. The determination criteria of F112 to F114 can be the same as those in the first embodiment. The pre-registration roller pair 120 and the pull-out roller pair 122 start rotating at the determined sheet conveying speed V2 (F115, F116). The subsequent processing contents are the same as those in the first embodiment.

[0071] In this embodiment, whether to separate the pre-registration roller pair 120 in the conveying operation after the skew correction and the magnitude relationship between the sheet conveying speeds V1, V2 of the registration roller pair 130 and the upstream roller pair are determined depending on conditions such as the sheet attribute and the feed source. Therefore, as in the first embodiment, an appropriate conveying operation is performed depending on the conditions, and it is possible to suppress the occurrence of wrinkles while maintaining conveying performance and skew correction ability.

[0072] In addition, since this embodiment has the separation operation motor 301 in addition to the pre-registration drive motor 145, when the pre-registration roller pair 120 is separated in the conveying operation after the skew correction, even if the pre-registration roller pair 120 is in a contact state during the skew correction, a decrease in productivity is avoided. In other words, if the rotation of the pre-registration roller pair 120 and the drive of the separation mechanism 140 are performed by a single pre-registration drive motor 145 as in the first embodiment, it is necessary to reverse the rotation direction of the motor before and after the separation of the pre-registration roller pair 120. Specifically, in F110 in FIG. 13, the pre-registration drive motor 145 is rotated in the CW direction, in F202, the pre-registration drive motor 145 is rotated in the CCW direction, and in F115 and F116, the pre-registration drive motor 145 is rotated in the CW direction. Then, due to the waiting time for stopping the rotation of the pre-registration drive motor 145 and starting the rotation in the reverse direction, the time required from the start of sheet feeding to the discharge outside the image forming apparatus becomes longer. In contrast, in this embodiment, since it is not necessary to reverse the pre-registration drive motor 145, it is possible to minimize the delay in sheet transport caused by the separation operation of the pre-registration roller pair 120.

[0073] (Modification) In the flow shown in FIG. 13, the separation operation of the pre-registration roller pair 120 (F108, F202) is performed after the registration roller pair 130 starts to rotate (F111) and before the pre-registration roller pair 120 and the pull-out roller pair 122 start to rotate (F115, F116). However, the separation operation of the pre-registration roller pair 120 may be performed at other timing. For example, after a loop of a predetermined size is formed in the sheet (F110), a determination as to whether or not the separation operation is performed and the separation operation (F103 to F108, F202) may be performed before the registration roller pair 130 starts to rotate (F111). In that case, the rotation of the pre-registration roller pair 120 and the pull-out roller pair 122 can be started simultaneously with the rotation of the registration roller pair 130 starts (F111). In addition, since this embodiment has a separating operation motor 301 in addition to the pre-registration drive motor 145, the rotational drive of the pre-registration roller pair 120 and the pull-out roller pair 122 and the separating operation of the pre-registration roller pair 120 may be performed simultaneously.

[0074] (Other embodiments) In the above-described embodiment, a sheet transport device that transports a sheet inside an image forming apparatus has been described, but the present technology may be applied to other sheet transport devices. For example, the present technology may be used as a device that transports a sheet while correcting the skew of the sheet in a sheet processing device that performs processing such as punching holes on a sheet discharged from the main body of an image forming apparatus. In addition, the intermediate transfer tandem type image forming unit 150 (FIG. 1) is an example of an image forming means, and the present technology may be applied to a sheet transport device in an inkjet type image forming apparatus, for example.

[0075] The present invention can also be realized by a process in which a program for implementing one or more of the 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. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions. [Explanation of symbols]

[0076] 100... image forming apparatus / 121, 122... first roller pair (pulling roller pair) / 120... second roller pair (pre-registration roller pair) / 130... registration means (registration roller pair) / 140... separation mechanism / 150... image forming means (image forming unit) / 201... control means (control device)

Claims

1. a first roller pair that holds and conveys a sheet; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to sandwich and convey the sheet; a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction, and that clamps and conveys the sheet after correcting skew of the sheet by abutting a leading edge of the sheet; a separation mechanism for causing the second roller pair to contact and separate from each other; a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism; Equipped with The sheet conveying speed by the registration means is V1, and the sheet conveying speed by the first roller pair is V2, the control means is capable of executing a first conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1>V2 after skew correction of the sheet, with the second roller pair separated by the separation mechanism; and a second conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1≦V2, with the second roller pair separated by the separation mechanism, after skew correction of the sheet, the control unit executes the first conveying operation when conveying a sheet having a first length in the sheet conveying direction, and executes the second conveying operation when conveying a sheet having a second length in the sheet conveying direction that is shorter than the first length. A sheet conveying device comprising:

2. A first roller pair for clamping and transporting a sheet; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to sandwich and convey the sheet; a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction, and that clamps and conveys the sheet after correcting skew of the sheet by abutting a leading edge of the sheet; a separation mechanism for causing the second roller pair to contact and separate from each other; a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism; a cassette that can be pulled out from the main body of the apparatus and that stores sheets; a tray that protrudes outside the device body and on which sheets are placed; Equipped with The sheet conveying speed by the registration means is V1, and the sheet conveying speed by the first roller pair is V2, the control means is capable of executing a first conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1>V2 after skew correction of the sheet, with the second roller pair separated by the separation mechanism; and a second conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1≦V2, with the second roller pair separated by the separation mechanism, after skew correction of the sheet, the control unit executes the first transport operation when transporting a sheet fed from the tray, and executes the second transport operation when transporting a sheet fed from the cassette. A sheet conveying device comprising:

3. A first roller pair that clamps and transports a sheet; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to sandwich and convey the sheet; a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction, and that clamps and conveys the sheet after correcting skew of the sheet by abutting a leading edge of the sheet; a separation mechanism for causing the second roller pair to contact and separate from each other; a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism; Equipped with The sheet conveying speed by the registration means is V1, and the sheet conveying speed by the first roller pair is V2, the control means is capable of executing a first conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1>V2 after skew correction of the sheet, with the second roller pair separated by the spacing mechanism; a second conveying operation of causing the first roller pair and the registration means to start conveying the sheet at sheet conveying speeds V1, V2 that satisfy V1≦V2, with the second roller pair separated by the spacing mechanism, after skew correction of the sheet; and a third conveying operation of causing the second roller pair and the registration means to convey the sheet after skew correction of the sheet, with the second roller pair brought into contact with the spacing mechanism; The control means when conveying a sheet having a first basis weight and a third length in the sheet conveying direction, the first conveying operation or the second conveying operation is performed by separating the second roller pair by the separating mechanism; when conveying a sheet having a second basis weight greater than the first basis weight, and when conveying a sheet having a fourth length in the sheet conveying direction shorter than the third length, the separating mechanism brings the second roller pair into contact with each other to perform the third conveying operation. A sheet conveying device comprising:

4. the control unit sets a sheet transport speed of the first roller pair and the second roller pair in the third transport operation to a sheet transport speed of the registration unit in the third transport operation or higher.

4. The sheet transport device according to claim 3.

5. A cassette for storing the sheets; a feeding unit that feeds a sheet from the cassette toward the second roller pair; Further equipped with When no roller pair other than the second roller pair is disposed on a conveying path from the feeding unit to the registration means, When a sheet is fed from the cassette, the control unit causes the second roller pair and the registration unit to convey the sheet while the second roller pair is brought into contact with the first roller pair by the separating mechanism.

5. The sheet transport device according to claim 3, wherein the sheet transport device is a sheet conveying device.

6. When the control means changes the value of V1 in the first conveying operation after conveying of the sheet by the first roller pair and the registration means has started and before the rear end of the sheet in the sheet conveying direction passes through the first roller pair, the control means changes the value of V2 in conjunction with V1 so that V1 does not fall below V2.

6. The sheet transport device according to claim 1, wherein the sheet transport device is a sheet conveying device.

7. A first roller pair for clamping and transporting a sheet; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to sandwich and convey the sheet; a registration unit that is disposed downstream of the second roller pair in the sheet conveying direction, and that clamps and conveys the sheet after correcting skew of the sheet by abutting a leading edge of the sheet; a separation mechanism for causing the second roller pair to contact and separate from each other; a control unit that controls the first roller, the second roller pair, the registration unit, and the separation mechanism; Equipped with The sheet conveying speed by the registration means is V1, and the sheet conveying speed by the first roller pair is V2, the control unit is capable of executing a conveying operation for causing the first roller pair and the registration unit to convey the sheet in a state in which the second roller pair is separated by the separating mechanism, the control means, in the conveying operation, starts conveying the sheet by the first roller pair and the registration means at sheet conveying speeds V1 and V2 that satisfy V1>V2 after the skew of the sheet is corrected, and when changing the value of V1 before the rear end of the sheet in the sheet conveying direction passes through the first roller pair, changes the value of V2 in conjunction with V1 so that V1 does not fall below V2. A sheet conveying device comprising:

8. a motor connected to the second roller pair and the spacing mechanism, The second roller pair is driven by the motor rotating in a first direction, and the separation mechanism is driven by the motor rotating in a second direction opposite to the first direction.

8. The sheet transport device according to claim 1, wherein the sheet transport device is a sheet conveying device.

9. a first motor that drives the second roller pair; A second motor that drives the spacing mechanism; Further equipped with the control unit causes the separation mechanism to keep the second roller pair in contact with each other until the registration unit performs skew correction of the sheet, and causes the separation mechanism to separate the second roller pair from each other after the skew correction of the sheet.

8. The sheet transport device according to claim 1, wherein the sheet transport device is a sheet conveying device.

10. A sheet conveying device according to any one of claims 1 to 9, an image forming means for forming an image on the sheet fed from the registration means; An image forming apparatus comprising:

Images