Sheet conveying 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 transport device that transports a sheet. [Background technology]

[0002] Some sheet conveying devices are provided with a configuration for performing skew correction to adjust the posture and position of a sheet. In general, the configuration for performing skew correction of a sheet is abutting the leading edge of the sheet against a nip portion of a pair of stopped registration rollers to correct the leading edge of the sheet in the sheet width direction perpendicular to the sheet conveying direction.

[0003] However, in the conveyance after the leading edge of the sheet is corrected, there is a risk that the sheet may buckle (particularly in thin paper, which may cause wrinkles) or become skewed due to the difference in the amount of loop (twist) formed on the upstream side of the registration roller pair in the width direction of the sheet. Therefore, a technology has been disclosed that prevents wrinkles and skew by separating the nip of the conveyance roller pair upstream of the registration roller pair and not restraining the sheet by the conveyance roller pair at the trailing edge of the sheet (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-83523 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in addition to a single-sided conveying path (first conveying path) for performing image formation on one side of a sheet, there is also a configuration that includes a double-sided conveying path (second conveying path) for inverting and conveying a sheet and forming an image on the back side of the sheet. In addition, the conveying roller pair (rotating body pair) provided upstream of the registration roller pair (skew correction unit) in the single-sided conveying path and the conveying roller pair provided upstream of the registration roller pair in the double-sided conveying path may be configured with different roller pairs. In this case, when an image is formed on one side of the sheet, the sheet is once corrected for skew, but when the image is formed on one side of the sheet, it is turned over and conveyed to the double-sided conveying path, and there is a risk that the sheet will skew due to resistance from the conveying guide, etc.

[0006] The present invention has an object to provide a configuration in which a first transport path and a second transport path are provided upstream of a skew correction unit, and in which different pairs of rotors are provided on each of the first transport path and the second transport path, the skew of a sheet can be appropriately corrected. [Means for solving the problem]

[0007] The sheet transporting device of the present invention is characterized in that it comprises a first transport path along which a sheet is transported, a skew correction section which corrects skew of the sheet by causing the leading edge of the sheet to hit the first transport path, a first pair of rotating bodies which is arranged on the first transport path upstream of the skew correction section in the sheet transport direction and which clamps and transports the sheet, an inversion section which inverts the sheet transported from the first transport path, a second transport path along which the sheet inverted by the inversion section is transported and which merges with the first transport path at a junction between the skew correction section and the first pair of rotating bodies, a second pair of rotating bodies which clamps and transports the sheet on the second transport path, a separation mechanism capable of separating the first pair of rotating bodies, and a slide mechanism capable of sliding at least one of the rotating bodies constituting the second pair of rotating bodies in a width direction intersecting the sheet transport direction. Effect of the Invention

[0008] According to the present invention, in a configuration in which the first transport path and the second transport path are provided upstream of the skew correction unit and different pairs of rotors are provided on each path, skew of a sheet can be appropriately corrected. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a sheet conveying section according to the first embodiment. [Diagram 3] FIG. 13A is a perspective view showing a state where there is a gap between a sheet stored in the storage compartment and a side regulating plate; FIG. 13B is a perspective view showing a state where there is no gap between a sheet stored in the storage compartment and a side regulating plate. [Figure 4] 1A is a perspective view of a single-sided conveying path showing a state in which a twist occurs in a sheet during skew correction of the sheet, and FIG. 1B is a perspective view of the single-sided conveying path showing a state in which a twist is restored after skew correction of the sheet. [Diagram 5] FIG. 4 is a cross-sectional view of a separation mechanism of the single-sided conveying path according to the first embodiment. [Figure 6] FIG. 2 is a control block diagram relating to sheet conveyance according to the first embodiment. [Figure 7] 5 is a flowchart of control regarding sheet conveyance according to the first embodiment. [Figure 8] FIG. 2 is a perspective view of a slide mechanism of a double-sided conveying path according to the first embodiment. [Figure 9] 10 is a flowchart of control regarding sheet conveyance according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <First embodiment> The embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0011] [Image forming equipment] The image forming apparatus 100 of this embodiment is an electrophotographic color printer, and employs an intermediate transfer tandem system in which a plurality of (four in this embodiment) image forming units 120 are arranged side by side on an intermediate transfer belt 130. Such an image forming apparatus 100 has the advantage of being highly adaptable to a wide variety of sheets S available in recent years and having excellent print productivity. Examples of the sheets S include sheet materials such as paper, plastic film, and cloth.

[0012] The sheets S are stored in a storage case 101 serving as a storage unit. The storage case 101 is provided with a lift-up unit that lifts up the sheets, and the sheets S in the storage case 101 are stacked on the lift-up unit. The sheets S stored in the storage case 101 are fed to a single-sided conveying path 201 serving as a first conveying path by a feeding unit 106 formed of a pair of rollers.

[0013] A registration unit 102 as a skew correction unit and a pre-registration roller pair 108 as a first rotating body pair are arranged on the single-sided conveying path 201. The pre-registration roller pair 108 sandwiches and conveys a sheet on the upstream side of the registration unit 102 in the sheet conveying direction. The sheet S sent to the single-sided conveying path 201 by the feeding section 106 passes through the pre-registration roller pair 108, is subjected to skew correction in the registration unit 102, passes through the conveying unit, and is conveyed to the secondary transfer section 103.

[0014] The secondary transfer unit 103 is a transfer nip portion for transferring a toner image to the sheet S, which is formed by opposing secondary transfer inner roller 104, intermediate transfer belt 130, and secondary transfer outer roller 105. In the secondary transfer unit 103, a predetermined pressure force and an electrostatic additional bias are applied to cause an unfixed image to be adsorbed onto the surface of the sheet S from the intermediate transfer belt 130. Note that a single-sided conveying path 201 for conveying the sheet S is composed of a sheet conveying unit (for example, a roller pair or an adsorption belt) arranged at an appropriate interval to hold and transfer the sheet S, and a sheet guide 107 for guiding the sheet S while controlling its behavior.

[0015] The registration unit 102 is a pair of registration rollers, and has a function of correcting skew by abutting the sheet S conveyed by the pre-registration roller pair 108 and creating a loop so as to conform to the leading edge of the sheet S. The registration unit 102 also has a function of conveying the sheet S to the secondary transfer section 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. After correcting skew, the registration unit 102 sends the sheet S to the secondary transfer section 103 at a desired timing.

[0016] The process of forming an image sent to the secondary transfer unit 103 at the same timing as the above-described process of conveying the sheet S to the secondary transfer unit 103 will be described. The image forming unit 120 mainly includes 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 photosensitive body, and is rotated in the direction of arrow A in FIG. 1. The surface of the photosensitive drum 121 is uniformly charged in advance by the charging device 122. Then, the exposure device 123 is driven based on a signal of image information sent from a connected PC (personal computer) or image reading device, 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 is developed with toner by the developing device 124, and becomes visible as a toner image on the photosensitive drum 121. Thereafter, a predetermined pressure force and an electrostatic load bias are applied by the primary transfer device 125, and the toner image is transferred onto the intermediate transfer belt 130 serving as an image carrier.

[0018] After that, the small amount of residual toner remaining on the photosensitive drum 121 is collected by the drum cleaner 126, and prepared for the next image formation. The image forming unit 120 described above has four sets of yellow (Y), magenta (M), cyan (C) and black (Bk) in the case of Fig. 1. Of course, the number of colors is not limited to four, and the order of the colors is not limited to this.

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

[0020] Through the above-described conveying process of the sheet S and the image forming process, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 103, and then the sheet S is conveyed to the fixing device 150. The fixing device 150 melts and fixes the toner image on the sheet S by applying a predetermined pressure force from an opposing roller or belt, etc., and a heating effect generally from a heat source such as a heater.

[0021] The sheet S having the fixed image thus obtained is selectively discharged to discharge trays 162, 163 by discharge sections 160, 161 by the switching member 11. Alternatively, when double-sided image formation is required, a route is selected by the switching member 21 to be conveyed from the reversing section 164 to a discharge conveying path 165 or a double-sided conveying path 202 as a second conveying path.

[0022] The reversing unit 164 includes a pair of conveying rollers 164a, and after the sheet S conveyed from the single-sided conveying path 201 by the switching member 21 is handed over to the pair of conveying rollers 164a, the pair of conveying rollers 164a is stopped during the conveying of the sheet S. The pair of conveying rollers 164a is then rotated in the reverse direction to convey the sheet S to the double-sided conveying path 202. The sheet S conveyed to the double-sided conveying path 202 is conveyed again to the secondary transfer unit 103 in a reversed state, and a toner image is secondarily transferred to the back side in the same manner as described above, and the toner image is fixed by the fixing device 150. The sheet S is then selectively discharged to the discharge trays 162 and 163.

[0023] [Sheet transport section] Next, the sheet conveying section 200 as a sheet conveying device including the above-mentioned single-sided conveying path 201 and double-sided conveying path 202 will be described with reference to FIG. 2. As described above, the single-sided conveying path 201 has the registration unit 102 as a skew correction section and the pre-registration roller pair 108 as a first rotating body pair. The pre-registration roller pair 108 conveys a sheet toward the registration unit 102 on the single-sided conveying path 201. The registration unit 102 is a registration roller pair consisting of a pair of rollers (rotating bodies) 102a, and corrects skew of the sheet S by hitting the registration roller pair 108 when the sheet S conveyed by the pre-registration roller pair 108 stops rotating. The registration unit 102 starts conveying the sheet at a predetermined timing after the sheet hits the registration roller pair. That is, the sheet conveying starts in accordance with the timing when the toner image on the intermediate transfer belt 130 reaches the secondary transfer section 103.

[0024] On the other hand, the double-sided conveying path 202 has a pre-registration roller pair 109 as a second rotating body pair. The pre-registration roller pair 109 is composed of a pair of rollers (rotating bodies) consisting of a drive roller 191 and a driven roller 192, and conveys the sheet by pinching it between them. Similarly to the single-sided conveying path 201, the double-sided conveying path 202 is composed of a sheet conveying section (for example, a roller pair or an adsorption belt) arranged at an appropriate interval to hold and transfer the sheet S, and a sheet guide 202b that guides the sheet S while controlling its behavior.

[0025] The sheet S inverted by the inverting unit 164 is transported along the duplex conveying path 202, and merges with the single-sided conveying path 201 at a junction 203 located between the registration unit 102 and the pre-registration roller pair 108. For this reason, the duplex conveying path 202 has a curved portion 202a that curves toward the junction 203 on the downstream side of the pre-registration roller pair 109 in the sheet conveying direction. The curved portion 202a is a portion of the sheet guide 202b curved so that the sheet S transported approximately downward along the duplex conveying path 202 can be smoothly delivered to the single-sided conveying path 201 that transports the sheet approximately upward in FIG. 2. In other words, the curved portion 202a is shaped to make a U-turn for the sheet.

[0026] [About sheet movement on single-sided transport path] Here, the operation of the sheet in the single-sided conveying path 201 will be described with reference to Figs. 3(a) to 4(b). First, the relationship between the sheet stack 180 stored in the storage 101 and the side regulating plates 181, 182 will be described with reference to Figs. 3(a) and 3(b). The side regulating plates 181, 182 are arranged on both sides in the width direction of the sheet stack 180 stacked in the storage 101, and regulate the positions of both ends in the width direction of the sheet stack 180. Note that the width direction is the sheet width direction that intersects with (orthogonal in this embodiment) the sheet conveying direction in which the sheets S are conveyed.

[0027] When a user sets sheets in the storage 101, as shown in Fig. 3(a), the sheets may be set with a gap between the set sheet stack 180 and the side regulating plates 181, 182. When a gap is generated between the sheet stack 180 and the side regulating plates 181, 182 in this way, the leading end side or the trailing end side of the sheet S moves in the width direction by the gap, and the sheet S is conveyed skewed with respect to the conveying direction. In this case, as shown in Fig. 3(b), the amount of skew of the conveyed sheet (the inclination of the sheet with respect to the conveying direction) becomes larger than when there is almost no gap between the sheet stack 180 and the side regulating plates 181, 182.

[0028] The sheet S in the storage 101 is transported to the single-sided transport path 201 and is subjected to skew correction by the registration unit 102. For this reason, when a gap occurs between the sheet stack 180 and the side regulating plates 181, 182 as shown in Fig. 3(a), the registration unit 102 needs to correct a larger skew of the transported sheet S than in the case of Fig. 3(b). When a large skew correction is performed, as shown in Fig. 4(a), the leading edge of the sheet S hits the registration unit 102, causing a large twist in the loop shape of the sheet S.

[0029] That is, when the registration unit 102 corrects the skew of the sheet S, a loop of the sheet S is formed between the registration unit 102 and the pair of pre-registration rollers 108. Then, the leading edge of the sheet S is abutted against the registration unit 102 by a reaction force that tries to return the loop shape of the sheet S, so that the leading edge of the sheet S is aligned with the nip line of the pair of rollers 102a of the registration unit 102, and the skew of the leading edge of the sheet S is corrected. At that time, as shown in FIG. 4(a), a twist due to a different loop amount occurs in the width direction of the sheet S due to the correction of the skew of the sheet S.

[0030] When the rollers 102a of the registration unit 102 rotate and transport the sheet S in this twisted loop shape, there is a risk of the sheet S buckling or skew returning as shown in FIG. 4(b). Buckling of the sheet S causes wrinkles, particularly noticeable in thin paper. Skew returning is a movement that attempts to return the leading edge of the sheet S 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 pre-registration roller pair 108 on the upstream side of the registration unit 102 in the sheet transport direction.

[0031] [Separation mechanism] Next, the separation mechanism 170 of the pre-registration roller pair 108 will be described with reference to FIG. 5. First, the pre-registration roller pair 108 is composed of a pair of rollers (rotating bodies) consisting of a drive roller 173 and a driven roller 174. The driven roller 174 rotates around a rotation shaft 172 in response to the drive roller 173. The drive roller 173 and the driven roller 174 sandwich and convey a sheet. The separation mechanism 170 has a separation cam 171 and a link member 175. The separation cam 171 is driven to rotate by a motor M2 (FIG. 6 described later). The link member 175 is connected to a rotation shaft 172 of the driven roller 174 and engages with the separation cam 171. When the separation cam 171 is rotated by the motor M2, the link member 175 moves, and the rotation shaft 172 connected to the link member 175 also moves. As a result, the driven roller 174, which is one of the pair of rollers, is separated from the drive roller 173, which is the other roller.

[0032] In this embodiment, when the registration unit 102 corrects the skew of the sheet S conveyed in the single-sided conveying path 201, the pre-registration roller pair 108 is separated, so that the occurrence of the buckling or skew return of the sheet S as described above can be reduced. That is, when the leading edge of the sheet S is abutted against the registration unit 102 to form a loop, the trailing edge side of the sheet S is not clamped by the pre-registration roller pair 108, so that the loop shape is unlikely to be significantly twisted. Therefore, even if the registration unit 102 starts conveying the sheet in this state, the sheet is unlikely to buckle. In particular, as shown in FIG. 3A, even if the sheet S is conveyed in the single-sided conveying path 201 in a state where there is a gap between the sheet stack 180 in the storage 101 and the side regulating plates 181 and 182, the sheet is unlikely to buckle.

[0033] [Separation control during skew correction] On the other hand, some types of sheets are less likely to wrinkle or buckle. For example, thin paper is more likely to wrinkle, but thick paper or other sheets with a large basis weight are less likely to wrinkle. In this embodiment, therefore, a first mode in which the pre-registration roller pair 108 is kept separated and a second mode in which the pre-registration roller pair 108 is not separated can be selectively executed depending on the type of sheet during skew correction. First, the control configuration of the image forming apparatus 100 of this embodiment will be described with reference to FIG. 6.

[0034] 6, the control unit 300 has a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, and a RAM (Random Access Memory) 303. The CPU 301 controls each unit while reading a program corresponding to a control procedure stored in the ROM 302. In addition, working data and input data are stored in the RAM 303, and the CPU 301 performs control by referring to the data stored in the RAM 303 based on the above-mentioned programs and the like.

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

[0036] Next, an example of the control of the separating mechanism 170 according to the type of sheet performed by the control unit 300 will be described with reference to FIG. 7. First, when the user sets a sheet in the storage 101, information on the type of sheet in the storage 101 is input from the operation unit 306 or a PC connected to the device. The control unit 300 ascertains the type of sheet in the storage 101 from the input information (S1). Next, the control unit 300 judges whether the type of sheet to be transported from the storage 101 corresponds to a sheet that is likely to wrinkle, such as thin paper (S2). For example, if the basis weight of the sheet is equal to or less than a predetermined value, it is judged to be a sheet that is likely to wrinkle.

[0037] If the sheet is one that is prone to wrinkles (Y at S2), the control unit 300 drives the motor M2 to separate the pre-registration roller pair 108 using the separation mechanism 170 (S3). Then, the feeding unit 106 starts conveying the sheet from the storage 101 to the single-sided conveying path 201 (S5). That is, in this embodiment, the pre-registration roller pair 108 is separated by the separation mechanism 170 before the feeding unit 106 feeds the sheet.

[0038] The fed sheet is then abutted against the registration unit 102 to form a loop (S6). At this time, the sheet passes through the separated pre-registration roller pair 108. Since the pre-registration roller pair 108 is separated even when the sheet forms a loop, twisting of the loop is reduced. Next, at a predetermined timing, the motor M1 is driven to start rotating the roller 102a of the registration unit 102 (S7), and the sheet is transported by the registration unit 102 (S8).

[0039] On the other hand, if the sheet is not prone to wrinkles in S2 (N in S2), the pre-registration roller pair 108 is kept attached (S4), and the feeding unit 106 starts conveying the sheet (S5). The rest of the process is the same as S6 to S8 described above, except that the pre-registration roller pair 108 is not separated. In this way, the control unit 300 can selectively execute the first mode and the second mode according to the type of sheet. The first mode is a mode in which the pre-registration roller pair 108 is kept separated when the skew of the sheet is corrected by the registration unit 102. The second mode is a mode in which the pre-registration roller pair 108 is not separated even when the skew of the sheet is corrected by the registration unit 102.

[0040] [Skewing correction for sheets transported along the duplex transport path] As described above, when correcting skew of the sheet S transported on the single-sided transport path 201, the occurrence of wrinkles or the like in the sheet S can be reduced by separating the pre-registration roller pair 108 according to the sheet type. On the other hand, in the case of the sheet S transported on the double-sided transport path 202, the sheet S transported by the pre-registration roller pair 109 passes through the curved portion 202a and hits the registration unit 102, and the skew is corrected.

[0041] Here, the sheet S reaching the double-sided conveying path 202 undergoes skew correction on the single-sided conveying path 201, passes through the secondary transfer unit 103 and the fixing device 150, is inverted by an inverting unit 164 located at the upper portion of the interior, and is conveyed into the double-sided conveying path 202. The sheet S then passes through the double-sided conveying path 202, merges with the single-sided conveying path 201 at a junction 203, and is subjected to skew correction by the registration unit 102. Since the sheet S passing through the double-sided conveying path 202 in this manner reaches the registration unit 102 via a long path, even if the sheet S has been subjected to skew correction on the single-sided conveying path 201, it will be conveyed skewed again.

[0042] On the other hand, the sheet S that has reached the double-sided conveying path 202 has had its skew corrected by the registration unit 102 in the single-sided conveying path 201, and therefore the amount of skew is not large. For example, in a state in which a gap exists between the sheet stack 180 and the side regulating plates 181 and 182 shown in FIG. 3A and a large skew occurs, the possibility that the sheet S will be conveyed to the double-sided conveying path 202 is low. In addition, in this embodiment, the double-sided conveying path 202 has a curved portion 202a on the downstream side of the pre-registration roller pair 109 in the sheet conveying direction. Therefore, when the sheet S abuts against the registration unit 102 to perform skew correction, the sheet S is curved along the curved portion 202a.

[0043] Therefore, similarly to when the pre-registration roller pair 108 is separated in the single-sided conveying path 201, when the pre-registration roller pair 109 is separated in performing skew correction, it is difficult to ensure a sufficient abutting force of the sheet S against the registration unit 102. As a result, there is a possibility that skew correction cannot be performed reliably. For this reason, when the sheet S is abutted against the registration unit 102 from the double-sided conveying path 202, it is preferable to sandwich the sheet S between the pre-registration roller pair 109 in order to ensure the abutting force. For the above reasons, in the case of this embodiment, the pre-registration roller pair 109 of the double-sided conveying path 202 does not employ a separation mechanism, but employs a slide mechanism 190 as shown in FIG. 8 to perform skew correction of the sheet S conveyed from the double-sided conveying path 202.

[0044] [Slide mechanism] The slide mechanism 190 will be described with reference to FIG. 2 and FIG. 8. As shown in FIG. 2, the pre-registration roller pair 109 is composed of a drive roller 191 and a driven roller 192. As shown in FIG. 8, the slide mechanism 190 can slide the driven roller 192, which is at least one of the rotating bodies constituting the pre-registration roller pair 109, in the width direction intersecting the conveying direction of the sheet. As shown in FIG. 2, the driven roller 192 is a roller disposed on the outside as seen from the center of curvature of the curved portion 202a. Therefore, the sheet S that hits the registration unit 102 via the curved portion 202a while being sandwiched and conveyed by the pre-registration roller pair 109 strongly contacts the outside of the curvature, that is, the driven roller 192 side. Therefore, when the skew of the sheet S is corrected, a larger force acts from the sheet S on the driven roller 192 side than on the drive roller 191. Therefore, 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 disposed around the rotation shaft 192a so as to be movable in the direction of the rotation axis. In the present embodiment, two driven rollers 192 are provided on the rotation shaft 192a with a gap between them. The width direction of the sheet is approximately parallel to the direction of the rotation axis of the driven roller 192. Two drive rollers 191 are also provided on the rotation shaft so as to form a nip portion that sandwiches the sheet with the driven roller 192.

[0046] The slide mechanism 190 has a coil spring 193 as an elastic member and a regulating portion 194. A pair of the coil springs 193 are arranged on both sides of the rotation axis direction of each driven roller 192. A pair of the regulating portions 194 are arranged so as to sandwich the pair of coil springs 193 between the driven rollers 192, and are immovable in the rotation axis direction with respect to the rotation shaft 192a. In this embodiment, the regulating portion 194 also serves as a bearing for the rotation shaft 192a. In other words, the driven rollers 192 are respectively arranged between the pair of regulating portions 194. The coil springs 193 are respectively arranged between the regulating portion 194 on one side and one end of the driven roller 192, and between the regulating portion 194 on the other side and the end of the driven roller 192 on the other side. The rotation shaft 192a passes through the inside of each coil spring 193.

[0047] In such a sliding mechanism 190, when the driven roller 192 moves in the sliding direction due to a force generated in a direction to eliminate the loop twist of the sheet S during skew correction, the coil spring 193 on the moving direction side is compressed. After that, the roller 102a of the registration unit 102 rotates to transport the sheet S, and when the sheet S passes the driven roller 192, the compressed coil spring 193 tries to return to its original length due to the spring force. Therefore, the slid driven roller 192 returns to its nominal position and prepares for the transport of the next sheet to be transported. With the above-mentioned configuration, it is possible to eliminate the loop twist of the sheet S on the double-sided transport path 202 during skew correction with a simple configuration that allows the driven roller 192 of the pre-registration roller pair 109 to slide and is smaller than the separation mechanism 170.

[0048] On the other hand, since the above-mentioned slide mechanism 190 is configured to include the coil spring 193 at both ends of the driven roller 192, when a skew correction is performed on a sheet S with a large skew, the twist of the loop becomes large, and the amount of movement in the sliding direction of the driven roller 192 becomes large. Therefore, when the amount of movement becomes large, the spring force of the coil spring 193 becomes large, and therefore, there is a possibility that smooth movement in the sliding direction cannot be performed.

[0049] However, as described above, the amount of skew of the sheet S transported to the duplex transport path 202 is smaller than that of the sheet fed in a state where there is a gap between the sheet stack 180 and the side regulating plates 181 and 182 in the storage 101. Therefore, the slide mechanism 190, which is simple as described above and has a smaller configuration than the separation mechanism 170, can prevent wrinkles and skew return during skew correction of the sheet S transported on the duplex transport path 202.

[0050] In the case of the present embodiment configured as described above, the single-sided conveying path 201 and the double-sided conveying path 202 can appropriately correct the skew of the sheet while suppressing the size of the device. That is, in the single-sided conveying path 201 where the sheet S may be conveyed with a large amount of skew, the separation mechanism 170 that separates the pair of pre-registration rollers 108 is provided to suppress the occurrence of wrinkles on the sheet during skew correction. On the other hand, in the double-sided conveying path 202 where the sheet S is conveyed with a small amount of skew, the slide mechanism 190 that slides the driven roller 192 of the pair of pre-registration rollers 109 is provided to suppress the occurrence of wrinkles on the sheet during skew correction. The slide mechanism 190 has a simpler and smaller configuration than the separation mechanism 170, so that the device can be prevented from becoming large and complicated while suppressing the occurrence of wrinkles on the sheet during skew in the configuration having two conveying paths.

[0051] <Second embodiment> The second embodiment will be described with reference to Fig. 9. In the above-described first embodiment, the timing for separating the pre-registration roller pair 108 by the separating mechanism 170 was before the sheet was fed. In contrast, in this embodiment, the separation timing is after the sheet hits the registration unit 102. Since other configurations and functions are similar to those of the above-described first embodiment, the same reference numerals are used for similar configurations, and illustrations and descriptions are omitted. The following description will focus on the points that are different from the first embodiment.

[0052] In the case of the above-described first embodiment, since the pre-registration roller pair 108 is separated when the sheet S is abutted against the registration unit 102, there is a possibility that a stably abutting force of the sheet S cannot be obtained. For this reason, in the present embodiment, the sheet S is abutted against the registration unit 102 in a state where it is sandwiched between the pre-registration roller pair 108, and after the abutment, the pre-registration roller pair 108 is separated.

[0053] An example of the control of the separation mechanism 170 of this embodiment will be described with reference to FIG. 9. First, as in the first embodiment, when the user sets a sheet in the storage 101, information on the type of the sheet in the storage 101 is input from the operation unit 306 or a PC connected to the device. The control unit 300 ascertains the type of the sheet in the storage 101 from the input information (S11). Next, the control unit 300 starts conveying the sheet from the storage 101 to the single-sided conveying path 201 by the feeding unit 106 (S12). Then, the fed sheet is abutted against the registration unit 102 to form a loop (S13).

[0054] In this embodiment, in order to stably apply the abutting force of the sheet S to the registration unit 102, the pair of pre-registration rollers 108 are not separated and the sheet S is clamped until the leading edge of the sheet S abuts against the nip line of a pair of rollers 102a of the registration unit 102 and a loop is formed.

[0055] Next, at a predetermined timing, the motor M1 is driven to start rotating the roller 102a of the register unit 102 (S14). At this time, the control unit 300 judges whether the type of the sheet conveyed from the storage 101 corresponds to a sheet that is likely to wrinkle, such as thin paper (S15). For example, if the basis weight of the sheet is equal to or less than a predetermined value, it is judged to be a sheet that is likely to wrinkle.

[0056] If the sheet is prone to wrinkles (Y in S15), the control unit 300 drives the motor M2 to separate the pre-registration roller pair 108 by the separation mechanism 170 (S16). Then, the registration unit 102 conveys the sheet (S18). On the other hand, if the sheet is not prone to wrinkles in S15 (N in S15), the pre-registration roller pair 108 is left in the attached state (S17), and the registration unit 102 conveys the sheet (S18).

[0057] In the case of this embodiment, since it is easy to ensure the abutting force of the sheet S against the registration unit 102, the skew correction of the sheet S can be performed more reliably.

[0058] <Other embodiments> In the above-mentioned embodiments, the sheet conveying device is applied to an image forming apparatus, but it can be applied to devices other than the image forming apparatus. For example, it can be applied to an image reading device that reads an image on a sheet while conveying the sheet, or a sheet processing device that performs processing such as stapling on the sheet, and the like, having two conveying paths. In addition, the image forming apparatus may be a copier, a facsimile, a multifunction machine, etc., other than a printer.

[0059] In the above embodiment, the skew correction unit uses a pair of registration rollers, but the skew correction unit may be a so-called registration shutter that corrects skew by abutting the leading edge of the sheet against a shutter. The first pair of rotating bodies and the second pair of rotating bodies may be a pair of belts or a combination of a belt and a roller, instead of a pair of rollers.

[0060] 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) for implementing one or more of the functions. [Explanation of symbols]

[0061] 100...image forming apparatus / 101...storage unit (storage section) / 102...registration unit (skew correction section) / 102a...roller (rotating body) / 106...feeding section / 108...pre-registration roller pair (first rotating body pair) / 109...pre-registration roller pair 109 (second rotating body pair) / 164...reversing section / 170...separating mechanism / 173...driving roller (the other roller) / 174...following roller (the one roller ) / 190···slide mechanism / 191···drive roller / 192···follower roller (one of the rotating bodies) / 192a···rotation shaft / 193···coil spring (elastic member) / 194···regulation section / 200···sheet transport section (sheet transport device) / 201···single-sided transport path (first transport path) / 202···double-sided transport path (second transport path) / 202a···curved section / 203···junction section / 300···control section

Claims

[Claim 1] a first transport path along which the sheet is transported; a skew correction unit that corrects skew of the sheet by abutting a leading edge of the sheet on the first transport path; a first rotating body pair that is disposed on the first conveying path upstream of the skew correction unit in a sheet conveying direction and that conveys the sheet by sandwiching the sheet; an inverting unit that inverts the sheet transported from the first transport path; a second conveying path along which the sheet inverted by the inverting unit is conveyed and which merges with the first conveying path at a junction between the skew correction unit and the first pair of rotating bodies; a second rotating body pair that sandwiches and transports a sheet in the second transport path; a spacing mechanism capable of spacing the first rotor pair apart; a slide mechanism that can slide at least one of the rotating bodies constituting the second rotating body pair in a width direction intersecting a sheet conveying direction, A sheet conveying device comprising:

Images