JP2019026452A - Sheet feeding device - Google Patents

Abstract

To reduce occurrence of wrinkles while securing stability of sheet feeding operation.SOLUTION: A sheet feeding device (130) comprises: first feeding means (121); second feeding means (131) arranged at a downstream of the first feeding means (121); and switching means (140) that can switch a state of the first feeding means (121). When feeding a sheet with a first basis weight, a first mode, in which feeding of the sheet by the second feeding means (131) is started with a first feeding member (121a) and a second feeding member (121b) of the first feeding means (121) contacted with each other, is executed. When feeding a sheet with a second basis weight smaller than the first basis weight, a second mode, in which feeding of the sheet by the second feeding means (131) is started with the first feeding member (121a) separated from the second feeding member (121b) is started, is executed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet.

  Some sheet conveying apparatuses used in image forming apparatuses and the like correct sheet skew by abutting the leading edge of a sheet against a nip portion of a roller pair or a shutter member. For example, in Patent Document 1, the leading edge of a sheet fed from a conveyance roller pair is brought into contact with a nip portion of a registration roller pair in a stopped state, and the sheet is bent between the conveyance roller pair and the registration roller pair. Thus, a configuration for performing skew correction is described.

  On the other hand, in order to cope with diversification of sheets used as recording media, the sheet conveying device is required to convey sheets of various sizes. In order to stably convey the sheet, it is necessary to always hold the sheet by at least one conveying roller pair and other conveying means, and therefore the distance between the upstream and downstream conveying means tends to be narrowed.

JP-A-6-345294

  However, in the configuration of Patent Document 1, as the distance between the conveying roller pair and the registration roller pair is set narrower, the skew-corrected sheet tends to be largely deformed in the vicinity of the registration roller pair. If the registration roller pair starts conveying the sheet in a state where the sheet is deformed out of plane, the deformed portion may be sandwiched between the nip portions of the roller pair, and wrinkles may occur. On the other hand, when examining a configuration that reduces the out-of-plane deformation of the sheet to reduce wrinkles, the stability of the sheet conveying operation may decrease.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet conveying apparatus that can reduce the occurrence of wrinkles while ensuring the stability of the sheet conveying operation.

  A sheet conveying apparatus according to an aspect of the present invention includes a rotatable first conveying member and a second conveying member, respectively, and the sheet is sandwiched between the first conveying member and the second conveying member in the sheet conveying direction. A first conveying means capable of conveying, and disposed downstream of the first conveying means in the sheet conveying direction, capable of correcting sheet skew by contacting a downstream end of the sheet in the sheet conveying direction; and The second conveying means that can be nipped and conveyed in the sheet conveying direction; the first conveying means; a first state where the first conveying member and the second conveying member are in contact; the first conveying member; Switching means that can switch to a second state in which the second conveying member is separated, and after the downstream end of the sheet in the sheet conveying direction abuts on the second conveying means, the first conveying means is in the first state. It is in In this state, the first mode for starting the conveyance of the sheet by the second conveyance unit, and the downstream end of the sheet in the sheet conveyance direction abuts the second conveyance unit, and then the first conveyance unit is in the second state. And a control unit capable of executing a second mode for starting the conveyance of the sheet by the second conveying unit in a state in which the control unit is configured to convey the sheet having the first basis weight. When the first mode is executed and a sheet having a second basis weight smaller than the first basis weight is conveyed, a switching operation for controlling the switching means to execute the second mode can be executed. It is characterized by that.

  According to the sheet conveying apparatus of the present invention, it is possible to reduce the generation of wrinkles while ensuring the stability of the sheet conveying operation.

1 is a schematic diagram of an image forming apparatus according to the present disclosure. FIG. 3 is a schematic diagram of the skew feeding correction device according to the first embodiment, and illustrates a state in which a pair of pre-registration rollers is in contact with each other. FIG. 3 is a schematic diagram of the skew feeding correction device according to the first embodiment and illustrates a state in which a pair of pre-registration rollers is separated. FIG. 3 is a perspective view illustrating a driving mechanism for the pre-registration roller pair according to the first embodiment, and illustrates a state in which the pre-registration roller pair is in contact with the driving mechanism. FIG. 3 is a perspective view illustrating a driving mechanism for the pre-registration roller pair according to the first embodiment, and illustrates a state in which the pre-registration roller pair is separated. FIG. 3 is a schematic diagram of a drive mechanism when a pre-registration roller pair is driven to rotate in the first embodiment. FIG. 3 is a schematic diagram of a driving mechanism when operating a separation mechanism for a pre-registration roller pair in the first embodiment. FIG. 3 is a block diagram illustrating a control configuration of the skew feeding correction apparatus according to the first embodiment. 3 is a flowchart illustrating a control method of the skew correction device according to the first embodiment. FIG. 10 is a perspective view illustrating a driving mechanism for a pre-registration roller pair according to a second embodiment, and illustrates a state in which the pre-registration roller pair is separated. FIG. 6 is a block diagram illustrating a control configuration of a skew correction device according to a second embodiment. 9 is a flowchart illustrating a control method of the skew feeding correction apparatus according to the second embodiment.

  Hereinafter, an image forming apparatus according to the present disclosure will be described with reference to the drawings. The image forming apparatus includes a printer, a copying machine, a facsimile machine, and a multifunction machine, 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 a document. Sheets used as recording media include paper such as paper and envelopes, plastic films for overhead projectors, and cloth.

  As shown in FIG. 1, the image forming apparatus 100 includes an apparatus main body 100A that houses an image forming unit 150, and an image reading apparatus 300 that is disposed above the apparatus main body 100A and reads image information from a document. The image forming unit 150, which is an example of an image forming unit, includes an intermediate transfer tandem type configuration including four image forming units PY, PM, PC, PK and an intermediate transfer belt 155. The image forming unit 150 transfers the toner images formed by the image forming units PY to PK to the sheet S via the intermediate transfer belt 155. The configuration of each of the image forming units PY to PK is basically the same except that the color of the toner used for development is different. Therefore, the configuration of the image forming unit and the toner image forming operation are exemplified by using the yellow image forming unit PY as an example. Will be described.

  When the image forming unit PY is requested to form a toner image, the photosensitive drum 151 as a photosensitive member is rotationally driven, and the charging device uniformly charges the surface of the photosensitive drum 151. The exposure device 152 provided in the lower part 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. Then, the electrostatic latent image is visualized (developed) by the toner supplied from the developing device 153, whereby a toner image is formed on the surface of the photosensitive drum 151.

  Similarly, in the image forming units PM, PC, and PK, a corresponding color toner image is formed on the photosensitive drum. The toner images formed by the image forming units PY to PK are primarily transferred by the primary transfer roller 154 from the photosensitive drum 151 to the intermediate transfer belt 155 that is an intermediate transfer member. Deposits such as toner remaining on the photosensitive drum 151 are removed by a cleaning device provided in each of the image forming units PY to PK.

  The intermediate transfer belt 155 is wound around the secondary transfer inner roller 156, the tension roller 157, and the stretching roller 158, and is driven to rotate counterclockwise in the drawing. The toner image carried on the intermediate transfer belt 155 is secondarily transferred to the sheet S at a secondary transfer portion formed between the secondary transfer roller 159 and the intermediate transfer belt 155 facing the secondary transfer inner roller 156. The Deposits 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 is transferred is transferred to the fixing device 160. The fixing device 160 includes a pair of fixing rollers that sandwich and convey the sheet S and a heat source that heats the sheet S, and applies heat and pressure to the toner image while conveying the sheet S. As a result, the toner is melted and fixed and fixed on the sheet S.

  In parallel with such an image forming process, a feeding operation for feeding the sheet S from the cassette feeding unit 110 or the manual feed unit 115 toward the sheet S is executed. The cassette feeding unit 110 includes a feeding cassette 111 as a sheet supporting unit, and a feeding unit 112 that feeds the sheet S from the feeding cassette 111. The manual feeding unit 115 includes a manual tray 116 which is another example of the sheet supporting unit, and a feeding unit 117 which feeds the sheet S set on the manual tray 116. The feeding units 112 and 117 include feeding rollers 112a and 117a that feed the sheet S, and separation rollers 112b and 117b that separate the sheet S conveyed by the feeding rollers 112a and 117b from other sheets. The feeding units 112 and 117 are an example of a sheet feeding unit that feeds the sheet S, and may be replaced with another feeding mechanism such as a separation pad method or an air feeding method.

  The sheet S fed by the feeding units 112 and 117 is conveyed to the skew feeding correction device 130 via the drawing roller pair 113 and 119. As will be described in detail later, the skew correction device 130 corrects the skew of the sheet S and sends the sheet S to the secondary transfer unit at a timing that matches the progress of the image forming process by the image forming unit 150.

  The sheet S on which an image has been formed by passing through the secondary transfer unit and the fixing device 160 is transferred to a discharge path 172 of the sheet discharge unit 170, and the discharge roller pair 171 causes the apparatus main body 100A and the image reading apparatus 300 to move. The paper is discharged to a discharge tray 180 provided therebetween. When duplex printing is performed, the sheet S is switchback conveyed by the discharge roller pair 171 that is a pair of reversing rollers and is transferred to the duplex conveyance unit 190, and is conveyed via the duplex path 192 by the conveyance roller pair 193. Then, the sheet S that has reached the skew feeding correction device 130 is formed on the back surface by the image forming unit 150 and then discharged to the discharge tray 180 by the discharge roller pair 171.

  Next, the configuration and operation of the skew feeding correction device 130 according to the first embodiment will be described. 2 and 3 are schematic views of the skew feeding correction device 130. FIG. 2 corresponds to the contact state of the pre-registration roller pair 121, and FIG.

  As shown in FIGS. 2 and 3, the skew correction device 130 is provided with a registration roller pair (hereinafter referred to as a registration roller pair) 131, a pre-registration roller pair 121 disposed upstream thereof, and further disposed upstream thereof. A sheet conveying apparatus including a drawing roller pair 119. Hereinafter, the direction in which the sheet moves sequentially through the pulling roller pair 119, the pre-registration roller pair 121, and the registration roller pair 131 is referred to as a sheet conveyance direction.

  The drawing roller pair 119 includes a drawing driving roller 119a and a drawing driven roller 119b driven by a drawing motor, and conveys the sheet S received from the feeding unit 117 (see FIG. 1) of the manual feeding unit 115 in the sheet conveying direction. To do. The pre-registration roller pair 121 includes a pre-registration drive roller 121a and a pre-registration driven roller 121b, and is configured so that the nip portion of the roller pair can be separated by a separation mechanism 140 as described later. The registration roller pair 131 includes a registration driving roller 131a and a registration driven roller 131b. The registration roller pair 131 sandwiches the sheet S and conveys the sheet S toward the secondary transfer unit.

  In the skew feeding correction device 130, a registration detection sensor 132 is disposed as a detection unit that can detect the sheet S at a detection position between the pre-registration roller pair 121 and the registration roller pair 131. The registration detection sensor 132 is, for example, a reflective photoelectric sensor that can detect light reflected from the sheet S by irradiating the sheet conveyance path, or a transmission type that can detect rotation of a flag protruding in the sheet conveyance path. A photoelectric sensor can be used.

  The pre-registration roller pair 121 corresponds to a first conveying unit that can convey a sheet by sandwiching the sheet between a rotatable first conveying member and a second conveying member. The registration roller pair 131 corresponds to a second conveying unit that can correct the skew of the sheet by contacting the front end of the sheet, that is, the downstream end in the sheet conveying direction, and can convey the sheet while sandwiching the sheet. In the following description, the drawing roller pair 119 is described as an example of the upstream conveying unit disposed upstream of the first conveying unit, but the drawing roller pair 113 that conveys the sheet from the cassette feeding unit 110 is also upstream. It is another example of a side conveyance means.

  The image forming apparatus 100 according to the present embodiment has a vertical conveyance type (see FIG. 1) configuration that forms an image on a sheet S conveyed upward in the apparatus main body 100A. The sheet S fed from the manual feeding unit 115 disposed on the side surface of the apparatus main body 100A is conveyed toward the secondary transfer unit via the curved sheet conveyance path. That is, as shown in FIG. 2, the conveyance guide 126 constituting the sheet conveyance path is viewed from a substantially horizontal direction between the drawing roller pair 119 and the registration roller pair 131 when viewed from the width direction orthogonal to the sheet conveyance direction. It has a shape curved in a substantially vertical direction.

  In particular, the conveyance guide 126 includes a first guide portion 126 a that protrudes toward the outside of the curved shape (leftward in the drawing) between the pre-registration roller pair 121 and the registration roller pair 131. Between the first guide portion 126a and the second guide portion 126b opposed to the first guide portion 126a, a loop space that allows a loop-like bending (hereinafter referred to as a loop) L1 of the sheet S is formed. In general, when the loop L1 formed on the sheet S is set large, even if the sheet S is skewed to some extent, the skew can be removed. For this reason, the width of the loop space is set so as to sufficiently remove the skew that may occur in the sheet fed to the skew feeding correction device 130 from the manual feed unit 115 or other parts.

  By the way, with the diversification of sheets used as recording media, sheet conveying apparatuses used in image forming apparatuses are required to be able to stably convey sheets of various sizes. Specifically, the interval between the conveying roller pairs in the sheet conveying direction is set to be narrow so that a small sheet (for example, a postcard) is reliably delivered from the upstream conveying roller pair to the downstream conveying roller pair. Is done. Also in this embodiment, the interval between the pre-registration roller pair 121 and the registration roller pair 131 in the sheet conveyance direction is configured to be shorter than the minimum sheet supported by the image forming apparatus 100.

  However, in such a configuration in which the interval between the pre-registration roller pair 121 and the registration roller pair 131 is narrow, there is a concern that the sheet S is wrinkled when the registration roller pair 131 starts conveying the sheet S. That is, in a state before the registration roller pair 131 starts to rotate, the front end of the sheet S is abutted against the nip portion of the registration roller pair 131, and the sheet S is in the loop space between the pre-registration roller pair 121 and the registration roller pair 131. A relatively large loop L1 is formed. In this state, out-of-plane deformation of the sheet S may occur in the vicinity of the registration roller pair 131, and when the registration roller pair 131 starts to rotate, a portion where the out-of-plane deformation occurs is sandwiched between the registration roller pair 131. In some cases, the sheet S was wrinkled. Such wrinkling of the sheet has a great concern that a sheet having low rigidity (weak stiffness) that is likely to cause out-of-plane deformation is conveyed.

  In this embodiment, therefore, the pre-registration roller pair 121 is separated as necessary to reduce wrinkles when the registration roller pair 131 starts conveying the sheet S. Hereinafter, the configuration of the separation mechanism 140 of the pre-registration roller pair 121 will be described with reference to FIGS. 4 and 5 are perspective views showing the separation mechanism 140 of the pre-registration roller pair 121. FIG. 4 corresponds to the contact state of the pre-registration roller pair 121, and FIG. 5 corresponds to the separation state of the pre-registration roller pair 121. . 6 and 7 are schematic diagrams for explaining the operation of the separation mechanism 140.

  The separation mechanism 140 can switch between a contact state in which the pre-registration driving roller 121a and the pre-registration driven roller 121b abut and a separation state in which the pre-registration driving roller 121a and the pre-registration driven roller 121b are separated. That is, the separation mechanism 140 can switch the first conveyance means between a first state where the first conveyance member and the second conveyance member abut and a second state where the first conveyance member and the second conveyance member are separated. It is an example of a switching means.

  As shown in FIGS. 4 and 5, the separation mechanism 140 is interposed between the rotation shaft 121 d of the pre-registration driven roller 121 b and the pre-registration drive motor 145 that is the drive source of the pre-registration roller pair 121. The separation mechanism 140 includes a separation gear 146, a separation transmission shaft 148, a cam 149, a lever 127, a posture determining spring 128, a separation shaft 141, a separation arm 142, and a separation sensor 129.

  The separation gear 146 and the cam 149 are supported by the separation transmission shaft 148, and the separation gear 146 can be rotated integrally by being driven to rotate by the pre-registration drive motor 145. The cam 149 which is a cam member rotates the separation shaft 141 by pressing a lever 127 provided on the separation shaft 141. The posture determining spring 128 connected to the separation shaft 141 urges 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 with the movement of the lever 127, and moves the rotation shaft 121d of the pre-registration driven roller 121b toward and away from the pre-registration drive roller 121a. It can move in the direction. The separation sensor 129 is a transmissive photoelectric sensor that can detect the flag portion 141a provided on the separation shaft 141, and corresponds to the contact state (FIG. 4) and the separation state (FIG. 5) of the pre-registration roller pair 121. The rotation angle of the separation shaft 141 can be detected. The separation sensor 129 is an example of a position detection unit that can detect the contact / separation of the pre-registration roller pair 121, and may be replaced with a configuration that detects the position of the rotating shaft 121d of the pre-registration driven roller 121b, for example.

  As shown in FIG. 3, the pre-registration roller pair 121 is provided between the rotation shaft 121 d of the pre-registration driven roller 121 b and the sheet metal 144 fixed to the frame of the image forming apparatus 100. Pressure is applied by a pressure spring 143 that is an elastic member. The pressure spring 143 is an example of a biasing unit that biases and presses the second transport member against the first transport member, and defines the contact pressure (nip pressure) in the contact state of the pre-registration roller pair 121. .

  As shown in FIGS. 6 and 7, the output gear 145a of the pre-registration drive motor 145 meshes with both the pre-registration drive gear 147 attached to the drive shaft 121c of the pre-registration drive roller 121a and the separation gear 146. Yes. Hereinafter, regarding the rotation direction of the pre-registration drive motor 145 as viewed from the output shaft direction, the clockwise direction is represented as the CW direction, and the opposite counterclockwise direction is represented as the CCW direction. The pre-registration drive gear 147 is provided with a one-way clutch mechanism that transmits the driving force of the pre-registration drive motor 145 to the drive shaft 121c only when the output gear 145a rotates in the CW direction. The separation gear 146 is provided with a one-way clutch mechanism that transmits the driving force of the pre-registration drive motor 145 to the separation transmission shaft 148 only when the output gear 145a rotates in the CCW direction.

  When the pre-registration drive motor 145 rotates in the CW direction (first direction), driving force is transmitted to the drive shaft 121c via the pre-registration drive gear 147, and the pre-registration roller pair 121 is rotationally driven. 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 contacts the pre-registration roller pair 121. And the separated state are switched. At this time, no driving force is transmitted to the drive shaft 121c, and the pre-registration roller pair 121 is not rotationally driven. As described above, the drive configuration of the pre-registration roller pair 121 according to the present embodiment switches the rotation direction of the pre-registration drive motor 145 that is a drive motor, thereby driving the rotation of the pre-registration roller pair 121 and driving of the separation mechanism 140. And can be switched.

  Next, the behavior of the sheet in the skew feeding correction device 130 when the pre-registration roller pair 121 is in contact with and separated from the pair will be described with reference to FIGS. 2 and 3.

  When the pre-registration roller pair 121 is in the contact state, as shown in FIG. 2, the sheet S conveyed by the drawing roller pair 119 is nipped and conveyed by the pre-registration roller pair 121 in the contact state. Then, after the front end of the sheet S comes into contact with the nip portion of the registration roller pair 131 in the stopped state, the pre-registration roller pair 121 rotates by a predetermined amount, so that the sheet S between the pre-registration roller pair 121 and the registration roller pair 131 is rotated. Loop L1 is formed. At this time, the skew of the front end of the sheet is corrected so that the front end of the sheet S follows the nip portion of the registration roller pair 131.

  On the other hand, when the pre-registration roller pair 121 is in the separated state, as illustrated in FIG. 3, the sheet S conveyed by the drawing roller pair 119 passes through the separated state pre-registration roller pair 121 to the registration roller pair 131. To reach. Then, after the front end of the sheet S comes into contact with the nip portion of the registration roller pair 131 in a stopped state, the drawing roller pair 119 rotates by a predetermined amount, whereby the sheet S loops between the drawing roller pair 119 and the registration roller pair 131. L2 is formed. That is, in this state, the interval between the pair of rollers sandwiching the sheet S is increased as compared with the case where the pre-registration roller pair 121 is in a contact state. In addition to the loop space between the first guide portion 126a and the second guide portion 126b, the sheet conveyance path between the drawing roller pair 119 and the pre-registration roller pair 121 is also used as a space that allows the sheet loop L2. The For this reason, the out-of-plane deformation of the sheet S is alleviated as compared with the case where the pre-registration roller pair 121 is in contact.

  Here, the shape of the conveyance guide 126 constituting the sheet conveyance path is set so as to support the lower surface of the sheet S on the upstream side of the pre-registration roller pair 121 and to suppress the downward sag. Specifically, the tangent line T1 passing through the nip portion of the pre-registration roller pair 121 as viewed from the width direction intersects the lower guide surface 126u of the conveyance guide 126 from above on the upstream side of the pre-registration roller pair 121. Are arranged as follows. Further, the maximum value of the width of the sheet conveyance path (interval in the sheet thickness direction) on the upstream side of the pre-registration roller pair 121 is the maximum width of the sheet conveyance path between the pre-registration roller pair 121 and the registration roller pair 131, that is, a loop. It is set smaller than the width of the space.

  If the configuration is such that the sheet S droops significantly between the pre-registration roller pair 121 and the drawing roller pair 119 in the separated state, a part of the force that the drawing roller pair 119 sends out the sheet is absorbed as the deflection of the drooping portion. End up. In this case, the force for pressing the front end of the sheet S against the nip portion of the registration roller pair 131 may be insufficient, and the skew correction function may be deteriorated. On the other hand, in the present embodiment, the sheet S is abutted while the lower surface of the sheet S is supported by the lower guide surface 126u, so that the skew correction function can be ensured to a practically sufficient level. it can.

  Hereinafter, a method for controlling the sheet conveyance operation by the skew feeding correction device 130 will be described with reference to FIGS.

  As shown in FIG. 8, the image forming apparatus 100 includes a control unit 201 that is an example of a control unit. The control unit 201 includes a memory 204 that temporarily or permanently stores programs and data, and a central processing unit (CPU) 203 as an arithmetic device that can execute the programs. In addition to the separation sensor 129 and the registration detection sensor 132, the control unit 201 receives an input signal from an operation unit 202 that includes a liquid crystal panel and various buttons and functions as a user interface. The control unit 201 controls the operation of the skew feeding correction device 130 by drivingly controlling the registration driving motor 133, the pre-registration driving motor 145, and the pulling motor 120, which are actuators.

  The CPU 203 implements the functions of the respective steps in the flowchart shown in FIG. 9 by executing a program read from the memory 204. First, information on the sheet S 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 execution of a print job via the operation unit 202 after inputting information (F102), control (F103 to F114) corresponding to the size and basis weight of the sheet S is started.

  First, it is determined whether or not the size of the sheet S in the sheet conveyance direction (hereinafter simply referred to as the sheet length) is larger than a threshold length X [mm] (F103). When the sheet S is shorter than X [mm], it is determined that the pre-registration roller pair 121 needs to be brought into contact. If the length of the sheet S is equal to or greater than X [mm], whether or not the pre-registration roller pair 121 needs to be separated is determined based on the basis weight of the sheet S (F104). That is, when the sheet having the first basis weight is conveyed, the pair of pre-registration rollers 121 is brought into a contact state, and when the sheet having the second basis weight smaller than the first basis weight is conveyed, before the registration. The roller pair 121 is set in a separated state. Specifically, when the basis weight of the sheet S is smaller than the threshold value M [gsm], it is determined that the pre-registration roller pair 121 needs to be separated, and the basis weight of the sheet S is greater than or equal to M [gsm]. In some cases, it is determined to contact the pre-registration roller pair 121.

  When the pre-registration roller pair 121 is brought into contact, the pre-registration drive motor 145 is driven in the CCW direction as necessary so that the separation sensor 129 is turned off (F105, F106). On the other hand, when the pre-registration roller pair 121 is separated, the pre-registration drive motor 145 is driven in the CCW direction as necessary so that the separation sensor 129 is turned on (F107, F108). As a result, the cam 149 of the separation mechanism 140 rotates and the separation arm 142 swings via the lever 127 and the separation shaft 141, whereby the pre-registration driven roller 121b moves relative to the pre-registration drive roller 121a. Then, when the pre-registration drive motor 145 stops based on the detection signal of the separation sensor 129, the pre-registration roller pair 121 is set to either the contact state or the separation state.

  After the pre-registration driven roller 121b is positioned, the sheet S feeding operation is started (F109), the pre-registration drive motor 145 is rotated in the CW direction, and the pre-registration roller pair 121 is rotationally driven (F110). The pre-registration drive motor 145 may be driven in the CW direction only when the pre-registration roller pair 121 is in the contact state. The resistance may be reduced.

  Thereafter, the front end of the sheet S abuts against the registration roller pair 131, thereby forming a loop of the sheet S and correcting the skew of the sheet S (F111 to F113). Specifically, even after the front end of the sheet S is detected by the registration detection sensor 132, the driving of the pre-registration roller pair 121 or the drawing roller pair 119 is continued for a predetermined time, so that a loop of the sheet S is formed.

  At this time, when the pre-registration roller pair 121 is in the separated state, the sheet S is transported excessively compared to the case where the pre-registration roller pair 121 is in the contact state (F113), so that a relatively large loop Is formed. In other words, in the contact state (first state) of the pre-registration roller pair 121, the sheet S is transported by the first transport amount by the pre-registration roller pair 121 after the sheet S contacts the registration roller pair 131. A loop of the sheet S is formed. On the other hand, in the separated state (second state) of the pre-registration roller pair 121, the sheet S is conveyed by a second conveyance amount larger than the first conveyance amount by the drawing roller pair 119 after the sheet S comes into contact with the registration roller pair 131. As a result, a loop of the sheet S is formed. As a result, even in the second state in which the interval between the roller pairs sandwiching the sheet S increases, a loop between the pre-registration roller pair 121 and the registration roller pair 131 effective for skew feeding correction can be secured, and the first state Skew correction can be realized with the same degree of accuracy.

  Thereafter, the registration roller pair 131 and the upstream roller pair (119, 121) start to rotate at the same time, whereby the sheet S in a state where the skew feeding is corrected is sent to the secondary transfer unit (F114). At this time, when the pre-registration roller pair 121 is in the contact state, the sheet S is nipped and conveyed by the pre-registration roller pair 121, so that the conveyance of the sheet S by the registration roller pair 131 is assisted. Then, after the image is transferred to the sheet S in the secondary transfer portion, the sheet S is discharged to the discharge tray (F115), and the print job is completed (F116).

  As described above, in this embodiment, the registration roller pair 131 starts conveying the sheet by the switching operation (F104 to F108) for switching the pre-registration roller pair 121 between the separated state and the contact state based on the sheet information. The distance between the rollers that sandwich the sheet is changed. In other words, a first mode in which the first conveying unit is set to the first state and sheet conveyance of the second conveying unit is started, and a second mode in which the first conveying unit is set to the second state and sheet conveyance of the second conveying unit is started. Is selected according to the basis weight of the sheet.

  As a result, for a thin sheet that easily undergoes out-of-plane deformation, the conveyance of the sheet by the second conveyance unit is started in a state in which the nipping of the sheet by the first conveyance unit is released, so the sheet in the vicinity of the second conveyance unit The generation of wrinkles can be suppressed by reducing the out-of-plane deformation. On the other hand, for thick sheets that have high rigidity and tend to increase conveyance resistance, the first conveyance unit sandwiches and conveys the sheet together with the second conveyance unit, so that stability of sheet conveyance can be ensured.

  Further, such a switching operation is performed for a first length sheet having a relatively large size in the sheet conveying direction, and the pre-registration roller pair 121 is applied to a second length sheet having a relatively small size. The contact state is set (F103, F105, F106). Thereby, even a small sheet can be stably conveyed. Note that if the pre-registration roller pair 121 is set in the separated state at the start of driving of the registration roller pair 131, skew correction when the sheet is small (F103: No) and when the basis weight of the sheet is small (F104: No). The operation of device 130 (second mode) need not be the same.

(Modification)
In this embodiment, the skew of the sheet S is corrected by abutting the front end of the sheet S against the nip portion of the registration roller pair 131. However, the front end of the sheet S is abutted against a shutter member disposed near the registration roller pair. It is good also as a structure which hits. In that case, the sheet S can be conveyed by the pair of registration rollers by retracting the shutter member and the sheet S is sandwiched between the pair of registration rollers. However, at least before the conveyance of the sheet S is started, the pair of pre-registration rollers is separated. By doing so, the generation of wrinkles can be suppressed.

  Next, a skew feeding correction apparatus that is a sheet conveying apparatus according to the second embodiment will be described with reference to FIGS. FIG. 10 is a perspective view showing a drive configuration of the pre-registration roller pair 121 according to the present embodiment. FIG. 11 is a block diagram illustrating a control configuration of the skew feeding correction apparatus according to the present embodiment. FIG. 12 is a flowchart showing a control method of the skew feeding correction apparatus in this embodiment. In the following, elements common to the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIGS. 10 and 11, in this embodiment, apart from the pre-registration drive motor 145 for rotationally driving the pre-registration roller pair 121, a separation operation motor 301 for operating the separation mechanism 140 is provided. ing. The pre-registration drive motor 145 as the first drive means rotates the drive shaft 121c of the pre-registration drive roller 121a via the pre-registration drive gear 147. The separation operation motor 301 as the second drive means operates the separation mechanism 140 by rotating the cam-equipped gear 302 that rotates integrally with the cam 149 of the separation mechanism 140, and the pre-registration driven roller 121 b via the separation arm 142. The rotating shaft 121d is moved. The control unit 201 can independently control the drive states of the pre-registration drive motor 145 and the separation operation motor 301.

  A control method of the skew feeding correction apparatus in this embodiment will be described with reference to the flowchart of FIG. First, information on the sheet S used as a recording medium input by the user is acquired via the operation unit 202 of the image forming apparatus 100 (F201). When it is detected that the user has instructed execution of a print job via the operation unit 202 after inputting information (F202), the separation operation motor 301 is driven as necessary so that the separation sensor 129 is turned off ( F203, F204). As a result, the pre-registration roller pair 121 is set in a contact state before the feeding of the sheet S is started.

  Thereafter, the sheet S feeding operation is started (F205), and the pre-registration roller pair 121 is rotationally driven by the pre-registration drive motor 145 (F206). Thereafter, when the front end of the sheet S abuts against the registration roller pair 131, a loop of the sheet S is formed, and the skew of the sheet S is corrected (F207). Specifically, even after the front end of the sheet S is detected by the registration detection sensor 132, the driving of the pair of pre-registration rollers 121 is continued for a certain time, so that a loop of the sheet S is formed.

  Then, before the rotational driving of the registration roller pair 131 is started, control (F209 to F213) for changing the state of the pre-registration roller pair 121 according to the sheet information is executed. That is, when the second mode is executed in the present embodiment, the sheet is conveyed by the second conveying unit after the front end of the sheet is brought into contact with the second conveying unit while the first conveying unit is in the first state. Before starting, the first transport means is switched to the second state. The determination conditions are the same as those in the first embodiment. When the length of the sheet S is equal to or greater than the threshold (X [mm]), or the basis length of the sheet S is less than the threshold (M [gsm] ]) If it is above, it is determined that the pre-registration roller pair 121 is brought into a contact state (first mode). On the other hand, when the length of the sheet S is equal to or greater than the threshold and the basis weight of the sheet S is less than the threshold, it is determined that the pre-registration roller pair 121 is in the separated state. When the pre-registration roller pair 121 is brought into contact, the separation operation motor 301 is driven as necessary so that the separation sensor 129 is turned off (F211). On the other hand, when separating the pre-registration roller pair 121, the separation operation motor 301 is driven as necessary so that the separation sensor 129 is turned on (F213).

  When the pre-registration roller pair 121 is switched from the contact state to the separated state, the distance between the rollers sandwiching the sheet S increases, so that out-of-plane deformation is reduced particularly in a thin sheet. In other words, in the first embodiment, the pre-registration roller pair 121 is in the separated state before the sheet S is abutted against the registration roller pair 131. However, even if the pre-registration roller pair 121 is switched to the separated state after the abutment as in the present embodiment. The out-of-plane deformation of the sheet S that can cause wrinkles can be suppressed. Further, since the sheet guide S is prevented from drooping by the conveyance guide 126 (see FIG. 3), it is possible to prevent the front end of the sheet S from deviating from the nip portion of the registration roller pair 131 and approaching the inclination before skewing.

  Thereafter, the registration roller pair 131 and the upstream pre-registration roller pair 121 and the drawing roller pair 119 are simultaneously started to rotate, so that the sheet S in a state where the skew feeding is corrected is sent to the secondary transfer unit (F214). . At this time, when the pre-registration roller pair 121 is in the contact state, the sheet S is nipped and conveyed by the pre-registration roller pair 121, so that the conveyance of the sheet S by the registration roller pair 131 is assisted. Then, after the image is transferred to the sheet S in the secondary transfer portion, the sheet S is discharged to the discharge tray (F215), and the print job is completed (F216).

  As described above, also in this embodiment, when the registration roller pair 131 starts conveying the sheet by the switching operation (F209 to F213) for switching the pre-registration roller pair 121 between the separated state and the contact state based on the sheet information. The distance between the rollers holding the sheet is changed. In other words, a first mode in which the first conveying unit is set to the first state and sheet conveyance of the second conveying unit is started, and a second mode in which the first conveying unit is set to the second state and sheet conveyance of the second conveying unit is started. Is selected according to the basis weight of the sheet (F209). Accordingly, it is possible to suppress the generation of wrinkles for a thin sheet that is likely to cause out-of-plane deformation, and to ensure the stability of sheet conveyance for a thick sheet having high rigidity.

  In this embodiment, a pre-registration drive motor 145 (first drive means) that rotationally drives the pre-registration roller pair 121 and a separation operation motor 301 (second drive means) that operates the separation mechanism 140 are provided separately. It has been. For this reason, the separation mechanism 140 can be operated simultaneously while rotationally driving the pre-registration roller pair 121. For example, the pre-registration roller pair 121 is switched from the contact state to the separation state while the sheet loop is being formed. be able to. That is, in the flowchart of FIG. 12, the separation operation motor 301 may be rotated (F211 and F213) before the rotation of the pre-registration drive motor 145 started in step F206 is stopped. In addition, a so-called non-stop registration operation in which driving of the registration roller pair 131 is started at a timing when a predetermined amount of loop is formed without stopping the rotation of the pre-registration drive motor 145 can be performed.

(Other embodiments)
In the first and second embodiments, the skew correction device disposed upstream of the secondary transfer unit has been described as an example of the sheet conveying device. However, the present technology may be applied to other sheet conveying devices. For example, in a sheet processing apparatus that performs processing such as punching a sheet discharged from the apparatus main body of the image forming apparatus, the sheet can be used as an apparatus that conveys the sheet while correcting skew of the sheet. The intermediate transfer tandem type image forming unit 150 (see FIG. 1) is an example of an image forming unit. For example, the present technology may be applied to a sheet conveying device in an ink jet type image forming apparatus.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100, 130 ... Sheet conveying device (skew correction device, image forming apparatus) / 113, 119 ... Pulling roller pair (upstream conveying means) / 121 ... First conveying means (pre-registration roller pair) / 121a ... First conveying Member (pre-registration drive roller) / 121b ... second transport member (pre-registration driven roller) / 131 ... second transport means (registration roller pair) / 140 ... switching means (separation mechanism) / 145 ... first drive means, drive motor (Pre-registration drive motor) / 150... Image forming means (image forming portion) / 301... Second drive means (separation operation motor) / F104 to F108, F209 to F213.

Claims (9)

A first conveying member having a first conveying member and a second conveying member that can rotate, respectively, a first conveying means capable of conveying a sheet in the sheet conveying direction by sandwiching a sheet by the first conveying member and the second conveying member;
The sheet is disposed downstream of the first conveying unit in the sheet conveying direction, and can be corrected to skew the sheet by contacting the downstream end of the sheet in the sheet conveying direction, and the sheet is nipped and conveyed in the sheet conveying direction. Possible second conveying means;
Switching means capable of switching the first conveying means between a first state in which the first conveying member and the second conveying member abut and a second state in which the first conveying member and the second conveying member are separated from each other. When,
A first mode in which the second conveying unit starts conveying the sheet while the first conveying unit is in the first state after the downstream end of the sheet in the sheet conveying direction contacts the second conveying unit; And after the downstream end of the sheet in the sheet conveying direction comes into contact with the second conveying unit, the second conveying unit starts conveying the sheet while the first conveying unit is in the second state. Control means capable of executing two modes,
The control means executes the first mode when transporting a sheet having a first basis weight, and performs the second mode when transporting a sheet having a second basis weight smaller than the first basis weight. A switching operation for controlling the switching means to execute the mode can be performed;
A sheet conveying apparatus. When the control unit conveys a sheet having a first length in the sheet conveyance direction, the control unit executes the first mode or the second mode according to the basis weight of the sheet by the switching operation, and the sheet conveyance Executing the first mode when conveying a sheet having a second length smaller than the first length in a direction;
The sheet conveying apparatus according to claim 1, wherein: An upstream side conveying unit that is arranged upstream of the first conveying unit in the sheet conveying direction and conveys the sheet toward the first conveying unit;
When executing the second mode, the control unit causes the upstream conveying unit to convey the sheet in a state where the first conveying unit is in the second state, thereby allowing the downstream end of the sheet in the sheet conveying direction. Abutting against the second conveying means,
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is characterized. The control means includes
When executing the first mode, after the downstream end of the sheet in the sheet conveyance direction comes into contact with the second conveyance unit, the first conveyance unit in the first state causes the sheet to be conveyed by the first conveyance amount. After conveying, start conveying the sheet by the second conveying means,
When the second mode is executed, after the downstream end of the sheet in the sheet conveyance direction comes into contact with the second conveyance unit, the upstream conveyance unit uses a first conveyance amount larger than the first conveyance amount. Starting the conveyance of the sheet by the second conveying means after conveying the sheet,
The sheet conveying apparatus according to claim 3, wherein: When the control unit executes the second mode, after the first conveying unit is in the first state, the downstream end of the sheet in the sheet conveying direction is brought into contact with the second conveying unit, Before starting the conveyance of the sheet by the second conveying means, the switching means switches the first conveying means to the second state;
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is characterized. A drive motor rotatable in a first direction and a second direction opposite to the first direction;
When the drive motor rotates in the first direction, the first transport unit is rotationally driven,
When the drive motor rotates in the second direction, the state of the first transport means is switched by the switching means.
The sheet conveying device according to any one of claims 1 to 5, wherein the sheet conveying device is characterized in that: First driving means for rotationally driving the first conveying means;
Second driving means for operating the switching means,
The control means can independently control the first drive means and the second drive means;
The sheet conveying device according to any one of claims 1 to 5, wherein the sheet conveying device is characterized in that: The second conveying means is a pair of rollers that can convey the sheet while sandwiching the sheet at the nip portion, and correct the skew of the sheet by contacting the downstream end of the sheet in the sheet conveying direction at the nip portion.
The sheet conveying apparatus according to any one of claims 1 to 7, wherein the sheet conveying apparatus is characterized in that: An image forming unit that forms an image on the sheet fed from the second conveying unit;
The sheet conveying apparatus according to any one of claims 1 to 8, wherein the sheet conveying apparatus is characterized.

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