Sheet transport device

Abstract

To provide a configuration that comprises a single-sided conveyance path 201 and a double-sided conveyance path 202, the configuration capable of appropriately correcting the skew of a sheet while preventing an increase in size of a device.SOLUTION: In a single-sided conveyance path 201, a leading end of a sheet abuts against a registration unit 102, and thereby the registration unit corrects the skew of the sheet. In the single-sided conveyance path 201, a pre-registration roller pair 108 are arranged on the upstream side of the registration unit 102 in a sheet conveyance direction to convey the sheet. A double-sided conveyance path 202 conveys the sheet inverted by an inversion unit 164 and merges with the single-sided conveyance path 201 at a merging part 203. A pre-registration roller pair 109 convey the sheet on the double-sided conveyance path 202. The pre-registration roller pair 108 can be separated by a separation mechanism, and at least one roller constituting the pre-registration roller pair 109 is made slide movable by a slide mechanism in a width direction intersecting with the sheet conveyance direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a sheet conveying device for conveying a sheet.

Background Art

[0002] As a sheet conveying device, there is one having a configuration for performing skew correction to align the posture and position of the sheet. As a configuration for performing skew correction of the sheet, it is common to abut the leading end of the sheet against the nip portion of a pair of stopped registration rollers and correct the leading end of the sheet in the width direction of the sheet orthogonal to the sheet conveying direction.

[0003] However, in the conveyance after the correction of the leading end of the sheet, in the width direction of the sheet, there is a risk of buckling (especially prominent in thin paper and wrinkles occur) or skew of the sheet due to the difference (twist) in the amount of loop formed upstream of the pair of registration rollers. Therefore, a technique has been disclosed (Patent Document 1) for avoiding wrinkles and skew by separating the nip of the pair of conveying rollers upstream of the pair of registration rollers and not restraining the sheet by the pair of conveying rollers at the rear end of the sheet.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, some configurations include a single-sided transport path (first transport path) for performing image formation on one side of the sheet, as well as a double-sided transport path (second transport path) for inverting and transporting the sheet to perform image formation on the back side. Furthermore, the transport roller pair (rotating body pair) located upstream of the registration roller pair (skew correction unit) in the single-sided transport path and the transport roller pair located upstream of the registration roller pair in the double-sided transport path may be composed of different roller pairs. In this case, although the sheet's skew is corrected once when forming an image on one side, there is a risk that the sheet may become skewed due to resistance from the transport guide when it is inverted and transported to the double-sided transport path after the image has been formed on one side.

[0006] The present invention Registration roller vs Upstream of it are a first transport path and a second transport path, each with different Conveyor roller pair The objective is to provide a configuration that can appropriately correct the skewness of the sheet in a configuration that includes such a feature. [Means for solving the problem]

[0007] One aspect of the present invention includes a storage compartment for storing sheets, a feeding unit for feeding sheets stored in the storage compartment, a pair of first conveying rollers for gripping and conveying sheets fed by the feeding unit, and a component for gripping and conveying sheets by forming a nip section. Conveyed by the first pair of conveying rollers The tip of the sheet The nip portion Hitting the end to form a loop on the sheetA pair of registration rollers that correct the skewness of the sheet; a first transport path provided between the first transport roller pair and the registration roller pair in the sheet transport direction, through which the sheet transported by the first transport roller pair passes; a pair of reversing rollers provided downstream of the registration roller pair in the sheet transport direction, which grips and reverses the sheet; a second transport path provided between the reversing roller pair and a merging section where the sheet reversed by the reversing roller pair merges in the first transport path downstream of the first transport roller pair and upstream of the registration roller pair, through which the sheet passes; and a second transport roller pair provided between the reversing roller pair and the merging section in the second transport path, which grips and transports the sheet reversed by the reversing roller pair with the registration roller pair. The leading edge of the sheet, inverted by the pair of reversing rollers, is brought against the nip portion of the pair of registration rollers to form a loop in the sheet. A second pair of transport rollers, and a separation mechanism that can move the nip portion of the first pair of transport rollers between a contact state that grips the sheet and a separated state that releases the grip of the sheet, A driven roller, which is one of the second transport roller pairs, is given driving force to transport a sheet, while a driven roller, which is the other of the second transport roller pairs, is driven by the rotation of the driven roller. The sheet conveying device is characterized by comprising a sliding mechanism that is movable in the width direction of the sheet, perpendicular to the sheet conveying direction. [Effects of the Invention]

[0008] According to the present invention, Registration roller vs Upstream of it are a first transport path and a second transport path, each with different Conveyor roller pair In a configuration that includes this feature, the skew of the sheet can be appropriately corrected. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the sheet transport unit according to the first embodiment. [Figure 3] (a) A perspective view showing a gap between the seat stored in the storage compartment and the side restraint plate, (b) A perspective view showing a state where there is no gap between the seat stored in the storage compartment and the side restraint plate. [Figure 4](a) Perspective view of a single-sided transport path showing the state in which the sheet has twisted when the sheet's skew correction is performed, (b) Perspective view of a single-sided transport path showing the state in which the twist has returned to its original state after the sheet's skew correction is performed. [Figure 5] A cross-sectional view of the separation mechanism for a single-sided transport path according to the first embodiment. [Figure 6] A control block diagram relating to sheet transport according to the first embodiment. [Figure 7] A flowchart of the control for sheet transport according to the first embodiment. [Figure 8] A perspective view of the sliding mechanism of a double-sided transport path according to the first embodiment. [Figure 9] A flowchart of the control for sheet transport according to the second embodiment. [Modes for carrying out the invention]

[0010] <First Embodiment> Embodiments will be described using Figures 1 to 8. First, the schematic configuration of the image forming apparatus of this embodiment will be described using Figure 1.

[0011] [Image forming apparatus] The image forming apparatus 100 of this embodiment is a color printer using an electrophotographic method, employing an intermediate transfer tandem system in which multiple (four in this embodiment) image forming units 120 are arranged side by side on an intermediate transfer belt 130. This type of image forming apparatus 100 has the advantage of being highly adaptable to the wide variety of sheets S available today and having excellent print productivity. Examples of sheets S include paper, plastic film, and cloth.

[0012] The sheet S is stored in a storage compartment 101. The storage compartment 101 is provided with a lift-up section for lifting up the sheet, and the sheet S inside the storage compartment 101 is loaded onto the lift-up section. The sheet S stored in the storage compartment 101 is fed to a single-sided transport path 201, which serves as the first transport path, by a feeding section 106 consisting of a pair of rollers.

[0013] On the single-sided conveyance path 201, a registration unit 102 as a skew correction unit and a first rotating body pair (Pair with the first conveyor roller) A registration pre-roller pair (registration pre-roller pair) 108 as is arranged. The registration pre-roller pair 108 sandwiches and conveys the sheet on the upstream side in the sheet conveyance direction of the registration unit 102. The sheet S sent out to the single-sided conveyance path 201 by the feeding unit 106 passes through the registration pre-roller pair 108, is skew-corrected in the registration unit 102, then passes through the conveyance unit, and is sent to the secondary transfer unit 103.

[0014] The secondary transfer unit 103 is a transfer nip portion of the toner image to the sheet S formed by the opposed secondary transfer inner roller 104, the intermediate transfer belt 130, and the secondary transfer outer roller 105. In the secondary transfer unit 103, an unfixed image is adsorbed from the intermediate transfer belt 130 to the surface of the sheet S by applying a predetermined pressing force and an electrostatic addition bias. The single-sided conveyance path 201 for conveying the sheet S is composed of a sheet conveyance unit (for example, a roller pair, an adsorption belt, etc.) arranged at an appropriate interval for delivering while holding the sheet S, and a sheet guide 107 for guiding while suppressing the behavior of the sheet S.

[0015] The registration unit 102 is a registration roller pair, and has a function of correcting the skew by following the leading end of the sheet S by creating a loop by abutting the sheet S conveyed by the registration pre-roller pair 108. Further, the registration unit 102 also has a function of conveying the sheet S to the secondary transfer unit 103 at a predetermined timing in accordance with the timing of image formation on the sheet S, that is, in accordance with the toner image carried on the intermediate transfer belt 130. Such a registration unit 102 sends out the sheet S to the secondary transfer unit 103 at a desired timing after correcting the skew.

[0016] Next, we will describe the image formation process that arrives at the secondary transfer unit 103 at a similar timing to the sheet S transport process described above. The image forming unit 120 mainly consists of a photosensitive drum 121 as an image carrier, a charging device 122, an exposure device 123, a developing device 124, a primary transfer device 125, and a drum cleaner 126. The photosensitive drum 121 is a cylindrical photoreceptor that is rotated in the direction of arrow A in Figure 1. The surface of the photosensitive drum 121 is uniformly charged in advance by the charging device 122. Then, based on the image information signal sent from a connected PC (personal computer) or image reading device, the exposure device 123 is driven, and exposure light is irradiated onto the surface of the rotating photosensitive drum 121, forming an electrostatic latent image on the surface of the photosensitive drum 121.

[0017] The electrostatic latent image formed on the photosensitive drum 121 becomes apparent as a toner image on the photosensitive drum 121 after toner development by the developing device 124. Subsequently, a predetermined pressure and electrostatic load bias are applied by the primary transfer device 125, and the toner image is transferred onto the intermediate transfer belt 130, which acts as an image carrier.

[0018] Subsequently, any remaining toner on the photosensitive drum 121 is collected by the drum cleaner 126 and prepared again for the next image formation. In the case of Figure 1, the image forming unit 120 described above consists of four sets: yellow (Y), magenta (M), cyan (C), and black (Bk). Of course, the number of colors is not limited to four, nor is the order of the colors limited to this.

[0019] Next, the intermediate transfer belt 130 will be described. The intermediate transfer belt 130 is an endless belt that is stretched by rollers such as the drive roller 131, tension roller 132, and secondary transfer inner roller 104, and is driven to transport in the direction of arrow B in the figure. The image formation processes for each color, which are processed in parallel by the image forming units 120 of Y, M, C, and Bk described above, are performed at the timing when they are superimposed on the toner image of the upstream color that has been primary transferred onto the intermediate transfer belt 130. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 130 and transported to the secondary transfer unit 103.

[0020] As described above, the sheet S transport process and image formation process are used to transfer a full-color toner image onto the sheet S in the secondary transfer unit 103, after which the sheet S is transported to the fuser unit 150. The fuser unit 150 melts and fixes the toner image onto the sheet S by applying a predetermined pressure using opposing rollers or belts, and generally by applying a heating effect using a heat source such as a heater.

[0021] The sheet S having the fixed image obtained in this way is selectively discharged to the discharge trays 162 and 163 by the discharge units 160 and 161 via the switching member 11. Alternatively, if double-sided image formation is required, the switching member 21 selects a transport path from the reversal unit 164 to the discharge transport path 165 or the double-sided transport path 202 as a second transport path.

[0022] The reversal unit 164 is equipped with a pair of transport rollers 164a. After the sheet S transported from the single-sided transport path 201 by the switching member 21 is handed over to the pair of transport rollers 164a, the reversal unit stops the pair of transport rollers 164a midway through the transport of the sheet S. Furthermore, by reversing the rotation of the pair of transport rollers 164a, the sheet S is transported to the double-sided transport path 202. The sheet S transported to the double-sided transport path 202 is then transported again to the secondary transfer unit 103 with its front and back sides reversed. After the toner image is secondary transferred to the back side as described above, the toner image is fixed by the fixing device 150. Finally, it is selectively discharged to the discharge trays 162 and 163.

[0023] [Sheet transport section] Next, the sheet transport unit 200, which is a sheet transport device equipped with the single-sided transport path 201 and the double-sided transport path 202 described above, will be explained with reference to Figure 2. As described above, the single-sided transport path 201 has a register unit 102 as a skew correction unit and a register front roller pair 108 as a first rotating body pair. The register front roller pair 108 transports the sheet toward the register unit 102 in the single-sided transport path 201. The register unit 102 is a register roller pair composed of a pair of rollers (rotating bodies) 102a, and corrects the skew of the sheet S when the sheet S transported by the register front roller pair 108 hits it while the rotation is stopped. The register unit 102 also starts transporting the sheet at a predetermined timing after the sheet hits it. That is, it starts transporting the sheet in accordance with the timing when the toner image on the intermediate transfer belt 130 reaches the secondary transfer unit 103.

[0024] On the other hand, the double-sided transport path 202 is opposite the second rotating body (Pair with the second conveyor roller) It has a pair of front-register rollers (front-registration rollers) 109 as a register. The front-register rollers 109 are a pair of rollers (rotating bodies) which are drive rollers. (Second drive roller) 191 and driven roller (Second driven roller) It consists of 192, which grips and transports the sheet. The double-sided transport path 202, like the single-sided transport path 201, consists of sheet transport sections (e.g., pairs of rollers or suction belts) arranged at appropriate intervals to hold and transfer the sheet S, and a sheet guide 202b that guides the sheet S while suppressing its movement.

[0025] In this double-sided transport path 202, the sheet S, which has been inverted at the inversion section 164, is transported and merges with the single-sided transport path 201 at the merging section 203 located between the register unit 102 and the pair of front register rollers 108. For this purpose, the double-sided transport path 202 has a curved section 202a that curves toward the merging section 203 on the downstream side of the front register roller pair 109 in the sheet transport direction. In Figure 2, the curved section 202a is the part of the sheet guide 202b that is curved so that the sheet S, which is transported approximately downward in the double-sided transport path 202, can be smoothly transferred to the single-sided transport path 201, which transports the sheet approximately upward. In other words, the curved section 202a has a shape that causes the sheet to make a U-turn.

[0026] [Regarding the movement of sheets in a single-sided transport path] Here, the movement of the sheets in the single-sided transport path 201 will be explained using Figures 3(a) to 4(b). First, the relationship between the sheet bundle 180 stored in the storage compartment 101 and the side restricting plates 181 and 182 will be explained using Figures 3(a) and (b). The side restricting plates 181 and 182 are positioned on both sides in the width direction of the sheet bundle 180 loaded in the storage compartment 101, and restrict the position of both ends of the sheet bundle 180 in the width direction. The width direction refers to the width direction of the sheet that intersects (orthogonal in this embodiment) with the sheet transport direction in which the sheets S are transported.

[0027] When a user sets a sheet inside the storage compartment 101, as shown in Figure 3(a), there is a possibility that the sheet may be set with a gap between the set sheet bundle 180 and the side restrictor plates 181 and 182. When a gap is created between the sheet bundle 180 and the side restrictor plates 181 and 182 in this way, the leading edge or the trailing edge of the sheet S moves in the width direction by the amount of this gap, causing the sheet S to be transported at an angle to the transport direction. In this case, as shown in Figure 3(b), the amount of skew of the transported sheet (the inclination of the sheet with respect to the transport direction) is greater than when there is almost no gap between the sheet bundle 180 and the side restrictor plates 181 and 182.

[0028] The sheets S in the storage compartment 101 are transported along the single-sided transport path 201 and their skew is corrected by the register unit 102. Therefore, if a gap occurs between the sheet bundle 180 and the side regulating plates 181 and 182, as shown in Figure 3(a), the register unit 102 needs to correct a larger skew for the transported sheets S compared to the case in Figure 3(b). When a large skew is corrected, as shown in Figure 4(a), the leading edge of the sheet S comes into contact with the register unit 102, causing a large twist in the loop shape of the sheet S.

[0029] In other words, when the register unit 102 corrects the skew of the sheet S, a loop is formed in the sheet S between the register unit 102 and the pair of front register rollers 108. Then, the reaction force that tries to return the loop shape of the sheet S causes the tip of the sheet S to abut against the register unit 102, so that the tip of the sheet S is aligned with the nip line of the pair of rollers 102a of the register unit 102, and the skew of the tip of the sheet S is corrected. At that time, as shown in Figure 4(a), the correction of the skew of the sheet S causes twisting due to different loop amounts in the width direction of the sheet S.

[0030] When the sheet S is twisted into a loop shape as described above, and the rollers 102a of the register unit 102 rotate to transport it, there is a risk of buckling or skewed return of the sheet S, as shown in Figure 4(b). Buckling of the sheet S causes wrinkles that are particularly noticeable in thin paper. Skewed return is the movement of the leading edge of the sheet S returning to the angle of the trailing edge of the sheet S. For this reason, in this embodiment, a separation mechanism 170 is provided that can separate the pair of front register rollers 108 on the upstream side in the sheet transport direction of the register unit 102.

[0031] [Separation mechanism] Next, the separation mechanism 170 for the front roller pair 108 will be explained using Figure 5. First, the front roller pair 108 is a pair of rollers (rotating bodies) which are drive rollers. (First drive roller) 173 and driven roller (First driven roller)The system consists of 174. The driven roller 174 rotates in a driven motion relative to the drive roller 173 around the rotation axis 172. The sheet is then gripped and conveyed between the drive roller 173 and the driven roller 174. The separation mechanism 170 has a separation cam 171 and a link member 175. The separation cam 171 is rotationally driven by a motor M2 (Figure 6, described later). The link member 175 is connected to the rotation axis 172 of the driven roller 174 and engages with the separation cam 171. When the separation cam 171 rotates due to the motor M2, the link member 175 moves, and the rotation axis 172 connected to the link member 175 also moves. As a result, the driven roller 174, which is one of the rollers in the roller pair, separates from the drive roller 173, which is the other roller.

[0032] In this embodiment, when the sheet S being transported along the single-sided transport path 201 is corrected for skew by the register unit 102, the pair of front register rollers 108 are kept apart, thereby reducing the occurrence of buckling and skew correction of the sheet S as described above. That is, when the leading edge of the sheet S abuts against the register unit 102 to form a loop, the rear end of the sheet S is not gripped by the pair of front register rollers 108, so large twisting of the loop shape is less likely to occur. Therefore, even if the register unit 102 starts transporting the sheet in this state, buckling of the sheet is less likely to occur. In particular, as shown in Figure 3(a), even when the sheet S is transported along the single-sided transport path 201 with a gap between the sheet bundle 180 in the storage compartment 101 and the side regulating plates 181 and 182, buckling of the sheet is less likely to occur.

[0033] [Separation control during skew correction] On the other hand, some types of sheets are less prone to wrinkling and buckling. For example, thin paper is prone to wrinkling, but thick paper with a high basis weight is less prone to wrinkling. Therefore, in this embodiment, during skew correction, it is possible to selectively execute a first mode in which the pair of front rollers 108 are separated, and a second mode in which the pair of front rollers 108 are not separated, depending on the type of sheet. First, the control configuration of the image forming apparatus 100 of this embodiment will be explained with reference to Figure 6.

[0034] As shown in Figure 6, the control unit 300 includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, and a RAM (Random Access Memory) 303. The CPU 301 controls each part while reading programs corresponding to control procedures stored in the ROM 302. The RAM 303 stores working data and input data, and the CPU 301 controls the system by referring to the data stored in the RAM 303 based on the aforementioned programs.

[0035] Furthermore, the control unit 300 controls the motor M1 that drives the roller 102a of the register unit 102 via the driver 304, and the motor M21 that drives the separation mechanism 170 via the driver 305. In addition, the control unit 300 is connected to the operation unit 306 of the image forming apparatus 100. The operation unit (input unit) 306 is, for example, an operation panel located on the front side of the image forming apparatus 100, and in addition to operating the image forming apparatus 100, various data can be input. The CPU 301 controls each part based on the signals input from the operation unit 306.

[0036] Next, an example of the control of the separation mechanism 170 according to the type of sheet performed by the control unit 300 will be explained using Figure 7. First, when a user sets a sheet in the storage compartment 101, information regarding the type of sheet in the storage compartment 101 is input from the operation unit 306 or a PC connected to the device. The control unit 300 determines the type of sheet in the storage compartment 101 from the input information (S1). Next, the control unit 300 determines whether the type of sheet to be transported from the storage compartment 101 is a sheet that is prone to wrinkling, such as thin paper (S2). For example, if the basis weight of the sheet is below a predetermined level, it is determined to be a sheet that is prone to wrinkling.

[0037] If the sheet is prone to wrinkling (Y in S2), the control unit 300 drives the motor M2 to separate the front roller pair 108 using the separation mechanism 170 (S3). Then, the feeding unit 106 starts transporting the sheet from the storage compartment 101 to the single-sided transport path 201 (S5). In other words, in this embodiment, the front roller pair 108 is separated by the separation mechanism 170 before the sheet is fed by the feeding unit 106.

[0038] Then, the fed sheet is brought against the register unit 102 to form a loop (S6). At this time, the sheet passes the separated pair of front register rollers 108. Also, since the pair of front register rollers 108 are separated even when the sheet is forming a loop, twisting of the loop is reduced. Next, at a predetermined timing, the motor M1 is driven to start the rotation of the roller 102a of the register unit 102 (S7), and the register unit 102 conveys the sheet (S8).

[0039] On the other hand, in S2, if the sheet is not one that is prone to wrinkling (N in S2), the sheet is transported by the feeding unit 106 while the front roller pair 108 remains in contact (S4) (S5). The following steps are the same as those described in S6 to S8, except that the front roller pair 108 is not separated. In this way, the control unit 300 can selectively execute the first mode and the second mode depending on the type of sheet. The first mode is a mode in which the front roller pair 108 is separated when the sheet's skew is corrected by the register unit 102. The second mode is a mode in which the front roller pair 108 is not separated even when the sheet's skew is corrected by the register unit 102.

[0040] [Regarding correction of skew of sheets being transported along a double-sided transport path] As described above, when correcting the skew of a sheet S being transported along the single-sided transport path 201, the pair of front register rollers 108 can be separated according to the type of sheet to reduce the occurrence of wrinkles and other damage to the sheet S. On the other hand, in the case of a sheet S being transported along the double-sided transport path 202, the sheet S transported by the front register roller pair 109 passes through the curved section 202a and hits the register unit 102, thereby correcting the skew.

[0041] Here, the sheet S that reaches the double-sided transport path 202 has its skew correction performed in the single-sided transport path 201, then passes through the secondary transfer section 103 and the fixing device 150, is reversed in the reversal section 164 located at the top of the machine, and is transported into the double-sided transport path 202. The sheet S then travels through the double-sided transport path 202 and merges with the single-sided transport path 201 at the merging section 203, where it is skew corrected by the registration unit 102. In this way, the sheet S that passes through the double-sided transport path 202 travels a long path to reach the registration unit 102, so even if its skew correction is performed in the single-sided transport path 201, it will be transported skewed again.

[0042] On the other hand, the amount of skew of the sheet S that reaches the double-sided transport path 202 is not large because it has been corrected for skew by the register unit 102 in the single-sided transport path 201. For example, if there is a gap between the sheet bundle 180 and the side regulating plates 181 and 182 as shown in Figure 3(a), and a large amount of skew occurs, it is unlikely that the sheet S will be transported to the double-sided transport path 202. Also, in this embodiment, the double-sided transport path 202 has a curved portion 202a on the downstream side in the sheet transport direction of the register front roller pair 109. Therefore, when the sheet S is brought against the register unit 102 in order to correct for skew, the sheet S is in a curved state along the curved portion 202a.

[0043] Therefore, if the pair of front rollers 109 is separated when performing skew correction, similar to when the pair of front rollers 108 is separated in the single-sided transport path 201, it becomes difficult to secure sufficient abutting force for the sheet S against the register unit 102. As a result, there is a possibility that skew correction cannot be reliably performed. For this reason, when the sheet S is brought into contact with the register unit 102 from the double-sided transport path 202, it is preferable to hold the sheet S between the front rollers 109 in order to secure the abutting force. Based on the above, in this embodiment, instead of employing a separation mechanism for the pair of front rollers 109 in the double-sided transport path 202, a sliding mechanism 190 as shown in Figure 8 is employed to perform skew correction for the sheet S transported from the double-sided transport path 202.

[0044] [Slide mechanism] The sliding mechanism 190 will be described using Figure 8 with reference to Figure 2. As shown in Figure 2, the front register roller pair 109 is composed of a drive roller 191 and a driven roller 192. As shown in Figure 8, the sliding mechanism 190 allows the driven roller 192, which is at least one of the rotating bodies constituting the front register roller pair 109, to slide in the width direction intersecting the sheet conveying direction. As shown in Figure 2, the driven roller 192 is a roller positioned on the outside when viewed from the center of the curve of the curved portion 202a. Therefore, the sheet S, which is being gripped and conveyed by the front register roller pair 109 and is abutting the register unit 102 via the curved portion 202a, makes strong contact with the outside of the curve, i.e., the driven roller 192 side. Therefore, when the sheet S is corrected for skew, a greater force acts from the sheet S towards the driven roller 192 side than towards the drive roller 191. For this reason, in this embodiment, the driven roller 192 is made slidable in the width direction, but the drive roller 191 may also be made slidable in the width direction.

[0045] The driven roller 192 is arranged to be movable in the direction of the rotation axis around the rotation axis 192a. In this embodiment, the driven roller (First roller, second roller)Two rollers 192 are provided on the rotating shaft 192a, spaced apart from each other. The width direction of the sheet is approximately parallel to the rotation axis direction of the driven roller 192. Two drive rollers 191 are also provided on the rotating shaft so as to form a nip portion that clamps the sheet with the driven roller 192.

[0046] The slide mechanism 190 includes coil springs 193 as elastic members and restricting parts 194. A pair of coil springs 193 are arranged on each side in the direction of the rotation axis of each driven roller 192. A pair of restricting parts 194 are arranged to sandwich each pair of coil springs 193 between themselves and the driven rollers 192, and are immovable in the direction of the rotation axis relative to the rotation axis 192a. In this embodiment, the restricting parts 194 also serve as bearings for the rotation axis 192a. In other words, each driven roller 192 is positioned between a pair of restricting parts 194. A coil spring 193 is positioned between one restricting part 194 and one end of the driven roller 192, and between the other restricting part 194 and the other end of the driven roller 192. The rotation axis 192a passes through the inside of each coil spring 193.

[0047] In this sliding mechanism 190, when the driven roller 192 moves in the sliding direction due to the force generated in the direction that eliminates the loop twist of the sheet S during diagonal correction, the coil spring 193 on the side in the direction of movement is compressed. Subsequently, as the roller 102a of the register unit 102 rotates and the sheet S is conveyed, the compressed coil spring 193 tries to return to its original length due to the spring force as the sheet S passes the driven roller 192. As a result, the driven roller 192 that has slid returns to its designated position and prepares to convey the next sheet that will be conveyed. With the above configuration, it is possible to eliminate the loop twist of the sheet S during diagonal correction in the double-sided conveying path 202 with a simple and compact configuration that allows the driven roller 192 of the front register roller pair 109 to slide, and is smaller than the separation mechanism 170.

[0048] On the other hand, since the aforementioned slide mechanism 190 is configured with coil springs 193 at both ends of the driven roller 192, when the sheet S, which has experienced significant skewing, is corrected for skewing, the twisting of the loop increases, and the amount of movement of the driven roller 192 in the sliding direction increases. As a result, when the amount of movement increases, the spring force of the coil springs 193 increases, which may prevent smooth movement in the sliding direction.

[0049] However, as described above, the amount of skew of the sheets S transported on the double-sided transport path 202 is smaller than, for example, the amount of skew of the sheets supplied in the storage compartment 101 with a gap between the sheet bundle 180 and the side regulating plates 181 and 182. For this reason, the slide mechanism 190, which is simple and smaller than the separation mechanism 170 as described above, can prevent wrinkles and reverting of the skew of the sheets S transported on the double-sided transport path 202 during skew correction.

[0050] In this embodiment, which is configured as described above, the system has a single-sided transport path 201 and a double-sided transport path 202, allowing for appropriate correction of sheet skew while suppressing an increase in the size of the device. Specifically, in the single-sided transport path 201, where sheets S may be transported with a large amount of skew, a separation mechanism 170 is provided to separate the pair of front rollers 108, thereby suppressing the occurrence of wrinkles in the sheet during skew correction. On the other hand, in the double-sided transport path 202, where sheets S that are less likely to be skewed are transported, a sliding mechanism 190 is provided to slide the driven roller 192 of the pair of front rollers 109, thereby suppressing the occurrence of wrinkles in the sheet during skew correction. The sliding mechanism 190 is simpler and more compact than the separation mechanism 170, thus reducing wrinkles in the sheet that occur when the sheet is skewed, while suppressing an increase in the size and complexity of the device, even with a configuration that has two transport paths.

[0051] <Second Embodiment> A second embodiment will be described with reference to Figure 9. In the first embodiment described above, the timing for separating the pair of front rollers 108 by the separation mechanism 170 was set to before the sheet was fed. In contrast, in this embodiment, the separation timing is set to after the sheet hits the register unit 102. The other configurations and operations are the same as in the first embodiment described above, so the same components are denoted by the same reference numerals and their illustration and description are omitted, and the following description will focus on the differences from the first embodiment.

[0052] In the first embodiment described above, when the sheet S is brought into contact with the register unit 102, the pair of front register rollers 108 are separated, which may make it difficult to obtain a stable force for the sheet S. Therefore, in this embodiment, the sheet S is held between the pair of front register rollers 108 and brought into contact with the register unit 102, and after contact, the pair of front register rollers 108 are separated.

[0053] An example of the control of the separation mechanism 170 of this embodiment will be explained with reference to Figure 9. First, as in the first embodiment, when a user sets a sheet in the storage compartment 101, information regarding the type of sheet in the storage compartment 101 is input from the operation unit 306 or a PC connected to the device. The control unit 300 determines the type of sheet in the storage compartment 101 from the input information (S11). Next, the control unit 300 starts transporting the sheet from the storage compartment 101 to the single-sided transport path 201 using the feeding unit 106 (S12). Then, the fed sheet is brought against the register unit 102 to form a loop (S13).

[0054] In this embodiment, in order to ensure a stable abutting force of the sheet S against the register unit 102, the front roller pair 108 of the register unit 102 are kept together and the sheet S is held between them until the leading edge of the sheet S abuts against the nip wires of the pair of rollers 102a of the register unit 102 and a loop is formed.

[0055] Next, at a predetermined timing, the motor M1 is driven to start the rotation of the roller 102a of the register unit 102 (S14). At this time, the control unit 300 determines whether the type of sheet being transported from the storage unit 101 is a sheet that is prone to wrinkling, such as thin paper (S15). For example, it is determined that a sheet is prone to wrinkling if its basis weight is below a predetermined level.

[0056] If the sheet is prone to wrinkling (Y in S15), the control unit 300 drives the motor M2 to separate the pair of front rollers 108 using the separation mechanism 170 (S16). Then, the sheet is transported by the register unit 102 (S18). On the other hand, if the sheet is not prone to wrinkling (N in S15), the pair of front rollers 108 are left in contact (S17), and the sheet is transported by the register unit 102 (S18).

[0057] In this embodiment, it is easier to secure the force with which the sheet S abuts against the register unit 102, thus enabling more reliable correction of the sheet S's skew.

[0058] <Other Embodiments> In the embodiments described above, the sheet transport device was described in the case of applying it to an image forming apparatus, but it can also be applied to devices other than image forming apparatuses. For example, it can be applied to image reading devices that read images on sheets while transporting them, and sheet processing devices that perform processing such as stapling on sheets, and configurations that have two transport paths. In addition, the image forming apparatus may be a copier, facsimile, multifunction device, etc., rather than a printer.

[0059] Furthermore, although the above embodiment described a configuration using a pair of registration rollers as the oblique correction unit, the oblique correction unit may also be a so-called registration shutter, which corrects obliqueness by pressing the leading edge of the sheet against the shutter. In addition, the pairs of rotating bodies, such as the first pair of rotating bodies and the second pair of rotating bodies, may be configured as a pair of belts or a belt and rollers, in addition to a pair of rollers.

[0060] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of symbols]

[0061] 100...Image forming apparatus / 101...Storage unit (storage section) / 102...Register unit (skew correction section) / 102a...Roller (rotating body) / 106...Feeding section / 108...Front roller pair (first rotating body pair) / 109...Front roller pair 109 (second rotating body pair) / 164...Reversing section / 170...Separation mechanism / 173...Driven roller (other roller) / 174...Driven roller (one roller) ) / 190···Slide mechanism / 191···Drive roller / 192···Driven roller (one rotating body) / 192a···Rotating shaft / 193···Coil spring (elastic member) / 194···Regulating section / 200···Sheet conveying section (sheet conveying device) / 201···Single-sided conveying path (first conveying path) / 202···Double-sided conveying path (second conveying path) / 202a···Curved section / 203···Confluence section / 300···Control unit

Claims

1. A storage compartment for the seat, A feeding unit for feeding sheets to be stored in the aforementioned storage compartment, A pair of first conveying rollers that grip and transport the sheet fed by the aforementioned feeding unit, A pair of registration rollers that grips and transports a sheet by forming a nip portion, and corrects the skewness of the sheet by bringing the leading edge of the sheet being transported by the first pair of transport rollers into contact with the nip portion to form a loop in the sheet, A first conveying path is provided between the first conveying roller pair and the registration roller pair in the sheet conveying direction, through which the sheet conveyed by the first conveying roller pair passes, A pair of reversing rollers is provided downstream of the registration roller pair in the sheet transport direction, which grips and reverses the sheet, A second transport path is provided between the inverting roller pair and a merging section where the sheet inverted by the inverting roller pair merges in the first transport path downstream of the first transport roller pair and upstream of the registration roller pair, through which the sheet passes. A second transport roller pair provided between the reversing roller pair and the merging section in the second transport path, which transports the sheet that has been reversed by the reversing roller pair by gripping the sheet with the registration roller pair, wherein the second transport roller pair abuts the leading edge of the sheet that has been reversed by the reversing roller pair against the nip portion of the registration roller pair to form a loop in the sheet, A separation mechanism is provided that allows the nip portion of the first transport roller pair to move between a contact state that grips the sheet and a separated state that releases the grip of the sheet. The second transport roller pair comprises a sliding mechanism to which a driven roller, which is one of the second transport roller pairs and is driven by the rotation of the other of the second transport roller pairs and is driven by the rotation of the driven roller, moves in the width direction of the sheet perpendicular to the sheet transport direction, with respect to a driven roller to which a driving force is applied for transporting the sheet. A sheet conveying device characterized by the following features.

2. The distance between the first transport roller pair and the registration roller pair in the first transport path is smaller than the distance between the second transport roller pair and the registration roller pair in the second transport path. A sheet conveying device according to claim 1, characterized in that...

3. The second transport path has a curved section that curves toward the merging section downstream of the second transport roller pair in the sheet transport direction, The driven roller, which is slidable by the aforementioned sliding mechanism, is positioned outward when viewed from the center of curvature of the curved portion. A sheet conveying device according to claim 1 or 2, characterized in that...

4. A driven roller shaft that rotatably supports the driven roller, A biasing member provided on both sides of the driven roller in the axial direction of the driven roller shaft, which biases the driven roller in the axial direction, It has regulating parts provided on both sides of the driven roller in the axial direction, which restrict the biasing member in the axial direction, A sheet conveying device according to any one of claims 1 to 3, characterized in that

5. The separation mechanism separates the first transport roller pair before the sheet is fed by the feeding unit. A sheet conveying device according to any one of claims 1 to 4, characterized in that

6. The separation mechanism separates the first transport roller pair after the sheet has come into contact with the registration roller pair. A sheet conveying device according to any one of claims 1 to 4, characterized in that

7. The system includes a control unit that controls the separation mechanism, The control unit can selectively execute, depending on the type of sheet, a first mode in which the first transport roller pair is separated when the sheet's skewness is corrected by the registration roller pair, and a second mode in which the first transport roller pair is not separated even when the sheet's skewness is corrected by the registration roller pair. A sheet conveying device according to any one of claims 1 to 6, characterized in that

8. The aforementioned pair of registration rollers correct the sheet's skewness by having the leading edge of the sheet abut against them when rotation is stopped. A sheet conveying device according to any one of claims 1 to 7, characterized in that

9. The driven roller comprises a first roller and a second roller, The first roller and the second roller are provided with a gap between them in the axial direction. The first roller and the second roller are movable independently of each other in the axial direction. The sheet conveying device according to feature 4.

10. The nip portion of the second transport roller pair is movable in the width direction of the sheet without separating the nip portions. A sheet conveying device according to any one of claims 1 to 9.

11. The first transport roller pair comprises a first drive roller to which a driving force for transporting a sheet is applied, and a first driven roller that follows the rotation of the first drive roller. The aforementioned drive roller is designated as the second drive roller. The aforementioned driven roller is designated as the second driven roller. The separation mechanism includes a cam that changes the position of the first driven roller relative to the first driven roller. A sheet conveying device according to any one of claims 1 to 10.

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