JP7225350B2 - Sheet conveying device and image forming device - Google Patents

Description

The present invention relates to a sheet conveying device that conveys a sheet and an image forming apparatus that forms an image on a sheet.

2. Description of the Related Art Some sheet conveying apparatuses for conveying sheets in an image forming apparatus perform skew correction of a sheet by a side registration method. In such a sheet conveying apparatus, the sheet is shifted to a reference member arranged on the side of the sheet conveying path by the oblique feed roller, and the side edge of the sheet is brought into contact with the reference member, thereby correcting the inclination of the sheet. . For example, Japanese Patent Application Laid-Open No. 2002-200001 describes a sheet alignment device that performs skew correction by bringing a side edge of a sheet into contact with a reference guide using a plurality of rollers arranged along a sheet conveying path.

JP-A-11-189355

By the way, in the side registration method, when the sheet is shifted to the reference member along the direction in which the angle with respect to the reference member is small, the sheet is conveyed a relatively long distance before coming into contact with the reference member. In this case, the device becomes complicated or large-sized due to the structure for coping with the movement of the sheet in the width direction, such as the structure for opening the nip of the pair of conveying rollers upstream of the oblique feed rollers during the width alignment. On the other hand, if the direction of movement of the sheet during width alignment is configured to form a large angle with respect to the reference member, there is a concern that the side edges of the sheet will strongly abut against the reference member, causing the sheet to buckle.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a sheet conveying apparatus and an image forming apparatus capable of correcting the skew of a sheet in a short conveying distance while avoiding buckling of the sheet.

A sheet conveying device according to an aspect of the present invention includes a contact member that extends along a sheet conveying direction and has a contact surface capable of coming into contact with an end portion of a sheet in a width direction perpendicular to the sheet conveying direction; is inclined in a first direction with respect to the sheet conveying direction, is rotatable about an axis perpendicular to the first direction, and approaches the contact surface in the width direction. a first skew-feeding roller pair having a first skew-feeding roller that skew-feeds a sheet and a first driven roller that follows the rotation of the first skew-feeding roller; a second oblique feed roller provided so as to incline in the second direction, rotatable about an axis orthogonal to the second direction, and obliquely feeds the sheet so as to approach the contact surface in the width direction; and a second driven roller driven by the rotation of the second skew-feed roller; a conveying roller provided for conveying a sheet in the sheet conveying direction; a first switching means for switching between a pressurized state in which pressure is applied and a released state in which the pressure applied to the first skew feed roller is released; a second switching means for switching between a pressurized state in which pressure is applied to the second skew feed roller so as to be able to pinch the sheet, and a release state in which the pressure on the second skew feed roller is released; control means for controlling the first switching means and the second switching means, wherein in the width direction, the second oblique feed roller is aligned with the transport center line of the sheet transport path along which the sheet is transported by the transport roller. On the other hand, the first oblique feed roller is arranged on the same side as the contact member, is arranged on the side opposite to the contact member with respect to the conveying center line, and is arranged in the first direction with respect to the sheet conveying direction. is larger than the angle of the second direction with respect to the sheet conveying direction, and the control means controls the first driven roller to pressurize and the second driven roller to release. After starting oblique feeding of the sheet by one pair of oblique feeding rollers, the second switching means switches the second driven roller to a pressurized state to start oblique feeding of the sheet by the second pair of oblique feeding rollers; It is characterized by

According to the present invention, sheet skew correction can be performed in a short conveying distance while avoiding buckling of the sheet.

1 is a schematic diagram of an image forming apparatus according to the present disclosure; FIG. FIG. 4 is a plan view showing an outline of a registration unit according to the first embodiment; Schematic diagrams showing cross-sectional configurations of a pre-registration conveying unit in a pressurized state (a) and a released state (b). FIG. 4 is a perspective view showing a driving configuration of a pre-registration conveying section; FIG. 3A is a plan view showing an outline of the skew correcting portion, and FIG. 3B is a schematic diagram showing a cross-sectional configuration of the reference member; 3A and 3B are a perspective view and a side view, respectively, showing a pressure mechanism for the oblique feed roller. FIG. FIG. 4 is a side view showing the pressurizing mechanism in a pressurized state (a) and a released state (b); FIG. 2 is a block diagram showing the control configuration of a registration unit; 5 is a flow chart showing a control method of a registration unit according to the first embodiment; 4 is a table showing the setting of pressure applied to each oblique feed roller in the first embodiment; Schematic diagrams showing the first stage (a) and the second stage (b) of the butting alignment operation. 4A and 4B are schematic diagrams showing sheet loop formation (a) and elimination thereof (b) by an abutment alignment operation; 4A and 4B are schematic diagrams showing a sheet position adjustment operation by a registration roller pair; FIG. 4A and 4B are schematic diagrams for explaining the magnitude relationship of the conveying speed of the oblique feed roller and the behavior of the sheet in Example 1 (a) and Reference Examples (b and c). 4A and 4B are schematic diagrams for explaining the arrangement of oblique feed rollers and the behavior of a sheet in Example 1(c) and Reference Examples (a, b); 10 is a flow chart showing a control method of a registration unit according to the second embodiment; 10 is a flow chart showing a control method of a registration unit according to the third embodiment; FIG. 11 is a table showing setting of pressure applied to each oblique feed roller in the third embodiment; FIG. 14 is a flow chart showing a control method of a registration unit according to the fourth embodiment; FIG. 11 is a table showing the setting of pressure applied to each oblique feed roller in the fourth embodiment; FIG. FIG. 11 is a plan view showing an outline of a registration unit according to Example 5; 11 is a flow chart showing a control method of a registration unit according to the fifth embodiment; FIG. 11 is a table showing the setting of pressure applied to each oblique feed roller in the fifth embodiment; FIG. Schematic diagrams (a) and (b) for explaining the angle of the oblique feed roller in the side registration method.

An image forming apparatus according to the present disclosure will be described below with reference to the drawings. 2. Description of the Related Art Image forming apparatuses include printers, copiers, facsimiles, and multifunction machines, and form images on sheets used as recording media based on image information input from an external PC or image information read from a document.

(Overview of Image Forming Apparatus)
The sheet conveying device according to the present disclosure constitutes a part of an image forming apparatus 1, which is an electrophotographic full-color laser printer shown in FIG. The image forming apparatus 1 is a POD machine capable of printing for purposes other than general office use, and uses recording media such as paper such as paper and envelopes, glossy paper, plastic films such as overhead projector sheets (OHT), and cloth. Various sheets can be used. An apparatus main body 1A of the image forming apparatus 1 accommodates a feed cassette 51 that stores sheets S and an image forming engine 10 that forms an image on the sheets S fed from the feed cassette 51 . The image forming engine 10, which is an example of image forming means, includes four image forming units PY, PM, PC, and PK that form yellow, magenta, cyan, and black toner images, and an intermediate transfer belt 506 that is an intermediate transfer member. and a tandem-type intermediate transfer system. The image forming units PY to PK are electrophotographic units each having photosensitive drums 1Y, 1M, 1C, and 1K, which are photosensitive members.

Since the image forming units PY to PK are configured in the same manner except that the color of the toner used for development is different, the image forming unit configuration and toner image forming process (image forming operation) will be described using the image forming unit PY for yellow as an example. will be explained. The image forming unit PY has an exposure device 511, a developing device 510, and a drum cleaner 509 in addition to the photosensitive drum 1Y. The photosensitive drum 1Y is a drum-shaped photosensitive member having a photosensitive layer on its outer periphery, and rotates in a direction (arrow R1) along the rotation direction (arrow R2) of the intermediate transfer belt 506. FIG. The surface of the photosensitive drum 1Y is charged by being supplied with charges from a charging means such as a charging roller. The exposure device 511 emits laser light modulated according to image information, and scans the photosensitive drum 1Y with an optical system including a reflection device 512, thereby drawing an electrostatic latent image on the surface of the photosensitive drum 1Y. The developing device 510 accommodates developer containing toner, and develops the electrostatic latent image into a toner image by supplying the toner to the photosensitive drum 1Y. The toner image formed on the photosensitive drum 1Y is primarily transferred onto the intermediate transfer belt 506 in a primary transfer portion, which is a nip portion between the primary transfer roller 507 and the intermediate transfer belt 506, which are primary transfer devices. Residual toner remaining on the photosensitive drum 1Y after transfer is removed by the drum cleaner 509 .

The intermediate transfer belt 506 is wound around a drive roller 504, a driven roller 505, a secondary transfer inner roller 503, and a primary transfer roller 507, and is rotationally driven by the drive roller 504 in the clockwise direction (arrow R2) in the figure. The image forming operation described above is carried out in parallel in each of the image forming units PY to PK, and a full-color toner image is formed on the intermediate transfer belt 506 by multiple-transferring four-color toner images so as to overlap each other. . This toner image is borne on the intermediate transfer belt 506 and conveyed to the secondary transfer portion. The secondary transfer portion is configured as a nip portion between a secondary transfer roller 56 as a transfer means and a secondary transfer inner roller 503, and a bias voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 56. As a result, the toner image is secondarily transferred to the sheet S. Residual toner remaining on the intermediate transfer belt 506 after transfer is removed by a belt cleaner.

The sheet S to which the toner image has been transferred is transferred to the fixing unit 58 by the pre-fixing conveying section 57 . The fixing unit 58 has a pair of fixing rollers for nipping and conveying the sheet S and a heat source such as a halogen heater, and applies pressure and heat to the toner image carried on the sheet S. FIG. As a result, the toner particles are fused and fixed, and a fixed image fixed on the sheet S is obtained.

Next, the configuration and operation of a sheet conveying system that feeds the sheets S accommodated in the feed cassette 51 and discharges the sheets S on which an image is formed to the outside of the apparatus will be described. The sheet conveying system roughly includes a sheet feeding section 54 , a registration section 50 , a branch conveying section 59 , a reversing conveying section 501 and a duplex conveying section 502 .

The feeding cassette 51 is detachably attached to the apparatus main body 1A, and the sheets S stacked on the elevating plate 52 are fed one by one by the feeding unit 53 . The feeding unit 53, which is a sheet feeding means, includes a belt system (see FIG. 1) in which the sheet S is conveyed by being attracted to a belt member by a suction fan, and a friction separation system using rollers or pads. The sheet S sent out from the feeding unit 53 is conveyed along the feeding path 54a by the pair of conveying rollers 54b and transferred to the registration section 50 .

The registration unit 50 includes a pre-registration conveying unit 20, a skew correction unit 30, and a pair of registration rollers (hereinafter referred to as registration rollers) 7, corrects the skew of the sheet S, and transfers the sheet S to the secondary transfer unit. transport towards. At this time, the registration rollers 7 send the sheet S to the secondary transfer portion based on the detection signal of the registration sensor 8 at a timing that matches the progress of the image forming operations of the image forming portions PY to PK. The sheet S on which the toner image has been transferred in the secondary transfer portion and the image has been fixed by the fixing unit 58 is conveyed to the branch conveying portion 59 having a switching member capable of switching the conveying path of the sheet S. When the image formation on the sheet S is completed, the sheet S is discharged to the discharge tray 500 arranged outside the apparatus main body 1A by the discharge roller pair. When forming an image on the back surface of the sheet S, the sheet S is transferred to the double-sided conveying unit 502 via the reversing conveying unit 501 . The reversing conveying unit 501 has a pair of reversing rollers that can rotate forward and backward, switches back the sheet S, and delivers it to the double-sided conveying unit 502 . The double-sided conveying section 502 conveys the sheet S toward the pre-registration conveying section 20 via the re-conveying path 54c that merges with the feeding path 54a. After an image is formed on the back surface of the sheet S, the sheet S is discharged to the discharge tray 500 .

Note that the above configuration is an example of an image forming apparatus, and for example, an image forming apparatus having an inkjet image forming unit instead of an electrophotographic image forming unit may be used. Further, some image forming apparatuses are provided with accessory devices such as an optional feeder and a sheet processing device in addition to the device main body provided with the image forming means. It may be used for conveying sheets in

(side registration)
Here, skew correction of the sheet S by the skew correction unit 30 will be described. The skew correction unit 30 according to the present disclosure is a side registration type sheet alignment device. That is, the skew correcting unit 30 causes the side edge of the sheet, that is, the edge in the width direction orthogonal to the sheet conveying direction, to contact a reference member having a contact surface extending along the sheet conveying direction, thereby correcting the sheet. To correct skew feeding of a sheet so that a side edge follows a contact surface. However, the sheet conveying direction is the conveying direction of the sheet before the sheet S is shifted toward the reference member by the skew correcting section 30 . The transport direction of S is indicated.

A skew correction unit 30A as a reference example shown in FIG. Each oblique feed roller 32A is arranged in a posture inclined at an angle α with respect to a reference surface 301 of a reference member 300 extending along the sheet conveying direction (leftward direction in the drawing). The skew feeding roller 32A applies a diagonal conveying force in the lower left direction in the drawing to the sheet S sent downstream in the sheet conveying direction from the conveying roller pair 21 of the pre-registration conveying unit 20, thereby moving the side edge of the sheet S. is brought into contact with the reference surface 301 .

Each conveying roller pair 21 of the pre-registration conveying unit 20 can switch between a pressurized state in which the sheet S can be nipped in the nip portion and a separated state in which the nip portion is opened. The separated state is maintained during the period in which the movement is being performed. This is to prevent the conveying roller pair 21 from interfering with the widthwise alignment of the sheet S and to avoid damage to the sheet S due to friction and stress on the sheet S.

of the oblique feed roller 32A is relatively small, the sheet S moves along a small angle of inclination with respect to the sheet conveying direction, and is gradually moved toward the reference member 300. As shown in FIG. That is, the movement distance Lα of the sheet in the sheet conveying direction from when the skew feeding roller 32A starts to shift the sheet S to when the side edge of the sheet S comes into contact with the reference surface 301 of the reference member 300 becomes a large value. . However, since it is necessary to be able to release the transport roller pair 21 that may contact the sheet S at least at the position (see the dashed line) at which the widthwise alignment is started, the mechanical configuration for moving the transport roller pair 21 and its control configuration are required. Accordingly, the device becomes large or complicated.

In particular, in the case of a long sheet, that is, a sheet having a large ratio of long sides to short sides compared to widely used standards such as A size and B size, the number of conveying roller pairs 21 that need to be openable increases. become more. For example, when dealing with a long sheet S having a length from the sheet feeding section 54 to the skew correcting section 30 in FIG. . In addition to the structure for moving the conveying roller pair, it is necessary to take measures such as avoiding bending of the sheet conveying path as much as possible in order to suppress sheet conveying resistance in a section where the sheet is obliquely conveyed. lead to larger and more complicated systems.

Therefore, as shown in FIG. 24(b), it is conceivable to set the angle β of the oblique feed roller 32B large (β>α). As the angle β of the oblique feed roller 32B increases, the position (see the dashed line) at which the width adjustment starts can be set downstream in the sheet conveying direction, so that the configuration for separating the upstream conveying roller pair 21 can be omitted. Become. For example, in the example of FIG. 24A, it is necessary to separate the four conveying roller pairs 21 (Nα=4), while in the example of FIG. =2) can be opened. However, since the angle β of the oblique feed roller 32B is large, the side edge of the sheet S is strongly abutted against the reference member 300, and there is a concern that the sheet S may be buckled.

Therefore, the sheet conveying device according to the present disclosure overcomes such inconvenience by providing a plurality of oblique feeding means having different inclination angles with respect to the sheet conveying direction. The configuration and operation of the sheet conveying device will be described below along with specific examples.

First, the configuration of the registration unit 50, which is the sheet conveying apparatus according to the first embodiment, will be described. As shown in FIG. 2, the registration unit 50 includes a pre-registration conveying unit 20 that conveys the sheet in the sheet conveying direction Dx, a skew correction unit 30 arranged downstream of the pre-registration conveying unit 20, and a skew correction unit 30. and a registration roller 7 arranged downstream of the .

The pre-registration conveying unit 20 has at least one (four in this embodiment) conveying roller pair 21, and each conveying roller pair 21 sends out the sheet S in the sheet conveying direction Dx. The pre-registration conveying unit 20 moves the sheet S by a center reference method, that is, so that the center of the sheet S is aligned with the central position (hereinafter referred to as the conveying center) L0 of the sheet conveying path with respect to the width direction Dy orthogonal to the sheet conveying direction Dx. A sheet S is conveyed. In this embodiment, the position of the transport center L0 is the center position in the width direction Dy of the area where the pair of transport rollers 21 can pinch the sheet S, that is, the contact area between the rollers.

A pre-registration sensor S<b>1 as a detecting means for detecting the sheet S is arranged near the most downstream conveying roller pair 21 and near the conveying center L<b>0 . For the pre-registration sensor S1, for example, a reflective photoelectric sensor having a light-emitting portion and a light-receiving portion can be used. The passage timing of the sheet S is detected by the detection.

The skew correction section 30 includes a reference member 300 , a rear skew feeding unit 31 and a front skew feeding unit 32 . However, the front side and the back side represent the positional relationship in the depth direction when the image forming apparatus 1 is viewed from the front (viewpoint in FIG. 1). The reference member 300 has a reference surface 301 extending in the sheet conveying direction Dx, and is arranged on one side of the sheet conveying path in the width direction Dy. The reference surface 301 extends along the sheet conveying direction and corresponds to a contact surface capable of contacting the side edge of the sheet.

The rear oblique feeding unit 31 is arranged on one side of the transport center L0 in the width direction Dy, that is, on the opposite side of the reference member 300, and the front oblique feeding unit 32 is arranged on the other side of the transport center L0, that is, on the same side as the reference member 300. It is The front oblique-feeding unit 32 and the back oblique-feeding unit 31 each have at least one oblique-feeding roller 311, 321, 322, 323. In this embodiment, the back-side oblique-feeding unit 31 has one oblique-feeding roller and the front oblique-feeding unit 31 has at least one oblique-feeding roller. 32 are arranged.

The oblique feed rollers 311, 321 to 323 on the back side and the front side all rotate about axes inclined with respect to the width direction Dy. That is, the tangential direction of the back side skew-feeding roller 311 corresponding to the first roller (first skew-feeding roller) at the contact portion with respect to the sheet S is inclined at an angle of θ1 with respect to the sheet conveying direction Dx. are arranged as Further, the tangential direction of the front-side skew-feeding rollers 321 to 323, each corresponding to a second roller (second skew-feeding roller), at the contact portion with respect to the sheet S is inclined at an angle of θ2 with respect to the sheet conveying direction Dx. are arranged parallel to each other so as to be oriented. Therefore, each of the oblique feed rollers 311, 321 to 323 rotates in contact with the sheet S, and thus tilts toward the reference surface 301 of the reference member 300 in the width direction Dy as it goes downstream in the sheet conveying direction Dx. A conveying force is applied to the sheet S in the direction shown in FIG.

The back-side oblique feeding unit 31 corresponds to a first oblique feeding unit that applies a conveying force in a first direction oblique to the sheet conveying direction to the sheet to bring the sheet closer to the contact surface. The front oblique feeding unit 32 is arranged at a position closer to the contact surface than the first oblique feeding means in the width direction, and applies a conveying force in a second direction inclined with respect to the sheet conveying direction to the sheet to abut the sheet. It corresponds to the second oblique feeding means that is brought into contact with the surface. Each of the pair of conveying rollers 21 and the registration rollers 7 of the pre-registration conveying section 20 is an example of sheet conveying means capable of conveying a sheet in the sheet conveying direction. Among them, the conveying roller pair 21 corresponds to the first conveying means for transferring the sheet to the first oblique feeding means and the second oblique feeding means. It corresponds to a second conveying unit that receives and conveys the sheet.

Here, the inclination angle .theta.1 of the oblique feed roller 311 on the back side is set larger than the inclination angle .theta.2 of the oblique feed rollers 321 to 323 on the front side (.theta.1>.theta.2). That is, the inclination angle (first angle) of the force applied to the sheet by the first oblique feeding means with respect to the sheet conveying direction is the same as the inclination angle (second angle) of the force applied to the sheet with respect to the sheet conveying direction by the second oblique feeding means (second angle). angle). The sheet conveying operation of the registration unit 50 and the behavior of the sheet in the configuration having such a configuration will be described later in detail.

In the skew correction unit 30, a skew feed sensor S2 and a pre-registration sensor S3 are arranged as detection means capable of detecting the sheet S, respectively. The skew sensor S<b>2 is arranged near a position where the sheet S skew-fed by the skew-feeding units 31 and 32 is expected to come into contact with the reference member 300 in the sheet conveying direction Dx. The pre-registration sensor S3 is arranged downstream from the oblique feed sensor S2 and upstream from the registration roller 7 with respect to the sheet conveying direction Dx. As the oblique feed sensor S2 and the pre-registration sensor S3, similar to the pre-registration sensor S1, known sensors such as a reflective photoelectric sensor can be used.

The registration rollers 7 are slidable in the width direction Dy while nipping the sheet S, and move the sheet S, whose side edges are in contact with the reference surface 301 of the reference member 300, to the position of the image to be transferred in the secondary transfer portion. Together, they are moved in the width direction Dy. Note that the reference member 300 and the front oblique feeding unit 32 are also movable in the width direction Dy, and are positioned in advance according to the width of the sheet S to be conveyed. Further, the method of adjusting the position of the sheet and the image to be formed on the sheet is not limited to this. A configuration may be adopted in which the scanning direction position is adjusted.

(pre-registration transport section)
The configuration of the pre-registration transport section 20 will be described in detail with reference to FIGS. 3 and 4. FIG. 3A and 3B are schematic diagrams showing the cross-sectional configuration of the pre-registration conveying section 20, and FIG. 4 is a perspective view showing the driving configuration of the conveying roller pair 21. As shown in FIG.

As shown in FIGS. 3A and 3B, each conveying roller pair 21 of the pre-registration conveying unit 20 is composed of a driving roller 23 to which a driving force is input and a driven roller 24 that rotates following the driving roller 23. be done. At least some of the conveying roller pairs 21 can be switched between a pressurized state (FIG. 3A) in which the sheet S can be nipped in the nip portion and a separated state (FIG. 3B) in which the nip portion is opened. is. Whether or not all the conveying roller pairs 21 can be switched between the pressurized state and the separated state may be determined according to the maximum size of the sheet S supported by the image forming apparatus.

The pre-registration conveying portion 20 is provided with a cam mechanism 100 having an eccentric roller 103 as a switching means capable of switching between the pressurized state and the separated state of the conveying roller pair 21 . The eccentric roller 103 is rotationally driven via gears 105 and 106 by a pre-registration pressurizing motor Mr as a drive source to swing the arm member 101 in contact with the cam surface on the outer periphery. The arm member 101 is supported so as to be able to swing relative to the stay member 18 about a swing shaft 102, and contacts the eccentric roller 103 on one side of the swing shaft 102, and the rotation shaft of the driven roller 24 on the other side. is supported by the driven shaft 26 . By swinging the arm member 101 , the driven roller 24 appears and disappears in the sheet conveying path formed by the guide members 201 and 202 . Therefore, by controlling the rotation angle of the eccentric roller 103 via the pre-registration pressure motor Mr, which is a stepping motor, the separated state in which the driven roller 24 is separated from the drive roller 23 and the driven roller 24 is pressed against the drive roller 23 It is a configuration that can switch between a pressurized state and a pressurized state.

As shown in FIG. 4, each drive roller 23 is configured by attaching a rubber roller 23a to a drive roller shaft 25, and is connected via a belt transmission mechanism 152 to a pre-registration drive motor Mp as a drive source. Each pre-registration drive motor Mp is a stepping motor, and can change the timing of starting and stopping the drive and the drive speed of the drive roller 23 (peripheral speed of the rubber roller 23a).

(Skew Corrector)
Next, the configuration of the skew correction section 30 will be described in detail with reference to FIGS. 5 to 7. FIG. 5A is a schematic view of the skew correction unit 30 viewed from above, and FIG. 5B is a schematic view of a cross-sectional configuration of the reference member 300 viewed from the sheet conveying direction Dx. FIG. 6(a) is a perspective view showing the pressurizing structure of the oblique feeding unit, and FIG. 6(b) is a side view thereof. FIGS. 7A and 7B are schematic diagrams showing the pressurized state and released state of the oblique feed unit.

As shown in FIG. 5(a), the oblique feed rollers 311, 321 to 323 on the front and back sides are tilted according to the angles θ1 and θ2 using universal joints 31c and 32c so that the rotational axes are aligned. Fixed. The oblique feed rollers 311, 321 to 323 are connected to oblique feed drive motors Ms1, Ms2 as drive sources via a transmission mechanism including universal joints 31c, 32c, belts 31a, 32a, and pulleys 31b, 32b. The oblique feed drive motors Ms1 and Ms2 are stepping motors, and can control the drive speed and the start/stop timing of the drive.

As shown in FIG. 5B, the reference member 300 includes a reference surface 301 against which the side edge of the sheet S abuts, an upper guide surface 302 facing the upper surface of the sheet S, and a lower guide surface 303 facing the lower surface of the sheet S. It has a concave cross section consisting of The reference member 300 is preferably made of die-cast aluminum, the reference surface 301 of which is highly accurate by cutting, and the reference surface 301 of which is subjected to PTFE (polytetrafluoroethylene) electroless nickel processing. can be done. By doing so, the reference surface 301 with high flatness and high slipperiness (low frictional resistance to the sheet S) can be obtained, and the skew correction accuracy of the sheet S can be improved.

As shown in FIGS. 6 and 7, the skew correction unit 30 includes a pressure roller 320 and a driven roller 330 facing each other. A pressurizing mechanism 33 is provided that can switch between a state and a released state in which the pressurized state is released. The release state is not limited to the state in which the nip portion is opened, and includes the state in which the rollers are in contact with each other with a force weaker than that in the pressurized state. Further, the pressurized state of the oblique feed unit means that at least one oblique feed roller is in the pressurized state, and the released state of the oblique feed unit means that all the oblique feed rollers are in the released state. do.

6 and 7 is replaced with any one of the oblique feed rollers 311, 321 to 323, the oblique feed correction unit 30 of the present embodiment includes a plurality of pairs of driven rollers 330. and a pressurizing mechanism 33 are arranged. In other words, the pressurizing mechanism 33 as switching means capable of switching between the pressurized state and the released state consists of one (second switching means) corresponding to the front oblique feed rollers 321 to 323 and one corresponding to the oblique feed roller 311 on the back side. (first switching means) corresponding to . Further, when the oblique-feeding rollers of the front-side oblique-feeding unit 32 or the back-side oblique-feeding unit 31 are added, the pressure mechanism 33 is arranged for each of the added oblique-feeding rollers.

As shown in FIGS. 6A and 6B, the pressure mechanism 33 includes an arm member 332, a link member 333, a pressure gear 334, a pressure spring 335, and an oblique feed pressure motor Mk. The driven roller 330 is rotatably supported by an arm member 332 about a driven shaft 331 , and can move toward or away from the oblique feed roller 320 by swinging the arm member 332 . The driven roller 330 in this embodiment rotates along the sheet conveying direction about an axis extending in the width direction, but may be arranged on an axis parallel to the corresponding oblique feed roller. Arm member 332 is connected to pressure gear 334 via pressure spring 335 and link member 333 . The pressure gear 334 is connected to an output shaft of an oblique feed pressure motor Mk, which is a drive source.

As shown in FIG. 7(a), in the pressurized state, the pressurizing gear 334 rotates counterclockwise in the drawing, and the arm member 332 pulled by the pressurizing spring 335 swings about the pivot shaft 332a. oscillates in the counterclockwise direction. As a result, the driven roller 330 is pressed against the oblique feed roller 320 . On the other hand, as shown in FIG. 7(b), in the released state, the pressure gear 334 rotates clockwise in the drawing to press the link member 333, and the link member 333 rotates the arm member 332 clockwise. to oscillate. As a result, the driven roller 330 is separated from the skew feed roller 320, or at least the contact pressure with respect to the skew feed roller 320 becomes smaller than in the pressurized state.

The oblique feed pressure motor Mk is a stepping motor, and by controlling the rotation angle of the pressure gear 334, the extension amount of the pressure spring 335 in the pressure state can be changed. That is, the pressurizing mechanism 33 according to this embodiment can switch between the pressurized state and the released state, and change the pressurizing force in the pressurized state.

A control configuration of the registration unit 50 will be described. As shown in the block diagram of FIG. 8, the operation of the registration section 50 is controlled by a controller 600 mounted on the image forming apparatus. A controller 600, which is an example of control means, includes a central processing unit (CPU) 601, a rewritable memory (RAM) 602 and a read-only memory (ROM) 603, which are storage means, and an interface (I/O ) 604 .

The CPU 601 operates based on information input via the operation unit 412, which is a user interface, and detection signals input via the AD conversion unit 605 from the above-described pre-registration sensor S1, oblique feed sensor S2, and pre-registration sensor S3. control. The CPU 601 reads and executes a program stored in the ROM 603 or the like, and drives a group of motors (Ms, Mp, Mr, Mk) that are actuators of the registration unit 50 via drivers 606, 607, 608, 609, and 610. Control. Thereby, each step of the following control method can be executed. Note that the oblique feed pressure motors Mk are arranged in numbers (n) corresponding to the oblique feed rollers on the front side and the back side, and the CPU 601 determines whether or not the driven roller presses each oblique feed roller and the magnitude of the applied pressure. can be controlled independently.

(Registration part control method)
A method of controlling the sheet conveying operation in the registration section 50 and the behavior of the sheet during the sheet conveying operation will be described below with reference to FIGS. 10 to 13 and the flowchart of FIG. In FIGS. 11 to 13, the rollers indicated by dashed lines are in the released state, and the rollers indicated by solid lines are in the pressurized state. Further, it is assumed that each oblique feed roller is continuously driven to rotate during the execution of the following flow chart.

When an image forming job is started (S101) in a state in which information such as basis weight, size, and number of sheets on which images are to be formed is input via the operation unit 412, the front side oblique feeding unit 32 and the rear side oblique feeding unit 32 are started. The oblique feeding pressure of the feeding unit 31 is determined (S102). However, the oblique feeding pressure is the pressing force of the driven roller 330 against each oblique feeding roller, and is determined for each oblique feeding roller 311, 321 to 323 based on a table stored in advance in the ROM 603 or the like. As shown in FIG. 10, the magnitude of the oblique feeding pressure is set according to the basis weight of the sheet so that the sheet can be stably conveyed regardless of the sheet type. column). Then, based on the determined oblique feeding pressure, first, the back side oblique feeding roller 311 is started to pressurize and enter a pressurized state (S103).

After that, when the image forming operation by the image forming units PY to PK is started (S104), the delay time for starting feeding is counted (S105) based on the start timing of the image forming operation. The sheet is fed from (S106). Then, when the sheet transferred to the pre-registration transport section 20 is detected by the pre-registration sensor S1 (S107), the stop delay time is counted (S108), and then the pre-registration drive motor Mp is stopped (S109). If the pre-registration sensor S1 does not detect the sheet even after a predetermined time has elapsed from the start of feeding, a screen indicating sheet jam is displayed on the operation unit (S126), and the execution of the job ends.

After that, the restart delay time is counted according to the progress of the image forming operation (S110), and the driving of the pre-registration driving motor Mp is restarted (S111). Since the driving restart timing of the pre-registration drive motor Mp is adjusted in accordance with the image forming operation, variations in the time until the sheet reaches the pre-registration sensor S1 are absorbed. After that, the delay time for releasing the pressure applied to the conveying roller pair 21 of the pre-registration conveying section 20 is counted (S112), the driven roller 24 is separated from the drive roller 23, and the conveying roller pair 21 is separated (S113). As a result, the abutment alignment operation for abutting the sheet against the reference member 300 and correcting the skew is started. The abutting and aligning operation in this embodiment is a period (S113 to S122) from when the pressure applied to the conveying roller pair 21 is released until both of the oblique feeding units 31 and 32 are released.

When the pressure applied by the conveying roller pair 21 is released, the sheet is moved in the sheet conveying direction so as to approach the reference member 300 by the conveying force received from the rear side oblique feeding unit 31, as shown in FIG. 11(a). Start moving diagonally. In other words, the sheet S is conveyed along the tangential direction of the rear-side oblique feed roller 311 that is relatively greatly inclined with respect to the sheet conveying direction Dx, and is quickly moved toward the reference surface 301 of the reference member 300 .

After that, at the timing when the side edge of the sheet and the reference surface 301 of the reference member 300 come close to each other to some extent, the front side skew feed rollers 321 to 323 start pressing based on the determined skew feed pressure (S114). That is, after the oblique feeding operation of the sheet by the rear side oblique feeding unit 31 is started, the front side oblique feeding unit 32 starts the oblique feeding operation by starting pressurization of the front side oblique feeding unit 32 by the pressing mechanism 33 . be done. Then, as shown in FIG. 11B, the sheet S nipped by the oblique feed rollers 321 to 323 further approaches the reference member 300, and the side edge contacts the reference surface 301. As shown in FIG. That is, the sheet S is conveyed along the tangential direction of the front-side oblique feed rollers 321 to 323 that are relatively slightly inclined with respect to the sheet conveying direction Dx, and the reference plane 301 is reached while the moving speed in the width direction Dy is reduced. abut. As a result, the force applied to the sheet S when the side edge of the sheet S collides with the reference surface 301 is reduced, and buckling of the sheet S is prevented.

Note that the actual movement direction of the sheet does not necessarily coincide with the tangential direction of the oblique feed roller because the oblique feed roller slips due to the inertia of the sheet, the sheet conveying resistance, and the like. However, by setting the angle of inclination of the direction of the conveying force applied to the sheet by the back side oblique feeding unit 31 with respect to the sheet conveying direction to be larger than that of the front side oblique feeding unit 32, the sheet S can be prevented from buckling. There is no change in that the width alignment can be performed quickly.

Further, instead of transferring the sheet between the oblique feeding units by switching whether or not the oblique feeding roller applies pressure, the sheet may be transferred depending on the positional relationship between the oblique feeding units. For example, even if the back side oblique feeding unit is arranged upstream of the front side oblique feeding unit in the sheet conveying direction, the back side oblique feeding unit quickly brings the sheet closer to the reference member while the front side oblique feeding unit collides with the reference member. can be mitigated. However, by arranging the oblique feeding rollers of the front side oblique feeding unit 32 and the rear side oblique feeding unit 31 so that the oblique feeding rollers of the front side oblique feeding unit 32 and the rear side oblique feeding unit 31 are arranged so as to overlap at least partially when viewed from the width direction, as in the present embodiment, the oblique feeding can be achieved. The correction section can be configured compactly.

Returning to the flow chart of FIG. 9, the description continues. After the front skew feed rollers 321 to 323 start pressing, when the skew feed sensor S2 detects the front end of the sheet, that is, the downstream end in the sheet transport direction (S115), the pressing force of the skew feed rollers 321 to 323 is changed. is counted (S116). The length of this delay time is set so that the pressing force is changed after the side edge of the sheet comes into contact with the reference surface 301 of the reference member 300 . In this embodiment, after the delay time has passed, the process (S117) of reducing the pressing force of the front skew feed rollers 321 to 323 is executed. Further, the pressing force of each oblique feed roller after decompression is determined by referring to a table stored in the ROM or the like (see the column of pressing force during acceleration in FIG. 10). Then, processing (S118) is performed to increase the conveying speed of the front side oblique feeding unit 32 and the rear side oblique feeding unit 31. FIG.

After the acceleration is completed and before the front end of the sheet is detected by the pre-registration sensor S3, the back side skew feed roller 311 is released from the pressure (S119). As described above, the oblique feed roller 311 on the back side has a larger inclination angle with respect to the sheet conveying direction Dx than the oblique feed rollers 321 to 323 on the front side, and the force to approach the reference member 300 in the width direction Dy is relatively large. (V1y>V2y). Therefore, as shown in FIG. 12A, during the period in which the rear-side oblique-feeding unit 31 and the front-side oblique-feeding unit 32 are in a pressurized state, the sheet bends (loops) in the inter-unit area in the width direction Dy. may be formed. If the front end of the sheet enters the nip portion of the registration roller 7 while the loop is formed, the loop is crushed and wrinkles are generated, or the posture of the sheet is disturbed as the loop is eliminated, causing the sheet to skew. there is a possibility. In this embodiment, as shown in FIG. 12(a), the rear side oblique feeding unit 31 is switched to the released state before the sheet enters the registration roller 7, thereby avoiding such a problem.

When the pre-registration sensor S3 detects the front end of the sheet (S120), the delay time for releasing the front skew feed rollers 321 to 323 is counted (S121), and the pressure of the skew feed rollers 321 to 323 is released. It will be in a released state (S122). This delay time is set so that the front skew feed rollers 321 to 323 are released after the front end of the sheet enters the nip portion of the registration roller 7 . In other words, the front oblique feeding unit 32 is released from pressure after the front edge of the sheet passes through the detection position (second detection position) of the pre-registration sensor S3, which is the second detection means. On the other hand, the back side oblique feeding unit 31 presses the front end of the sheet after passing the detection position (first detection position) of the oblique feeding sensor S2, which is the first detection means, and before passing the second detection position. is configured to be released. If the pre-registration sensor S3 does not detect the sheet within a predetermined time, a screen indicating sheet jam is displayed on the operation unit (S126), and the execution of the job ends.

When the sheet is transferred to the registration rollers 7, as shown in FIG. 13, the registration rollers 7 move in the width direction while conveying the sheet. As a result, the center position of the sheet in the width direction Dy is aligned with the center position of the image formed by the image forming units PY to PK (S123). When the sheet is sent to the secondary transfer section, the value of K is decremented by a counter that manages the remaining number of sheets K for image formation (S124). If the number of remaining sheets K is not 0, that is, if there are sheets left for image formation (S125: NO), the above operations (S103 to S124) are repeated. At this time, in the pre-registration conveying section 20, the pair of conveying rollers 21 through which the trailing edge of the preceding sheet has passed is pressed in order, so that the sheets are continuously conveyed and supplied to the secondary transfer section. If the remaining number of sheets K is 0 (S125: YES), it is determined that the image forming operation is completed, and the execution of the job ends.

As described above, in this embodiment, the back-side oblique-feeding unit 31 having the oblique-feeding roller 311 having a relatively large inclination angle with respect to the sheet conveying direction Dx and the oblique-feeding rollers 321 to 323 having relatively small inclination angles are provided. The front oblique feeding unit 32 is also used. In other words, the first oblique feeding means applies a force in a first direction to bring the sheet closer to the contact surface of the reference member, and the force in a second direction having a smaller angle with respect to the sheet conveying direction than in the first direction is applied. A second oblique feeding means is provided. Since the sheet is brought to the contact surface by a short distance by the first oblique feeding means, it is possible to prevent the sheet conveying device from becoming large and complicated. Further, since the sheet is decelerated by the second oblique feeding means, buckling of the sheet can be prevented.

If the inclination angle θ1 of the rear side skew-feeding roller is increased, the sheet can be shifted to the width in a shorter conveying distance, but the difference from the inclination angle θ2 of the front-side skewing roller becomes larger. , the sheet is likely to be looped between the oblique feed rollers on the front side and the back side. Further, as the inclination angle θ1 increases, the difference from the sheet conveying direction by the pre-registration conveying portion increases, and the sheet may be rubbed and damaged during delivery. For this reason, the inclination angle θ1 is preferably in the range of 20 degrees or more and 40 degrees or less, and more preferably in the range of 25 degrees or more and 35 degrees or less. Further, it is preferable that the inclination angle θ2 of the front-side skew-feeding roller is small enough to sufficiently decelerate the sheet shifted by the rear-side skew-feeding roller in the width direction. For this reason, it is preferable to set the inclination angle θ2 to be less than half of θ1, for example, θ1=30° and θ2=10°.

(Conveyance speed setting)
Here, the setting of the sheet conveying speed in the skew correcting section 30 will be described in detail. Referring to FIG. 14, for each skew feed roller 311, 321 to 323, the peripheral speed at the contact portion with the sheet S is differentiated from the actual conveying speed of the sheet, and the skew feed speeds V1 and V2 of the skew feed rollers will be described below. and Further, let V1x and V2x be the components of the skew feeding velocities V1 and V2 in the sheet conveying direction Dx, and let V1y and V2y be the components in the width direction Dy. Incidentally, in this embodiment, the magnitude and direction of the skew feeding speed V2 are set to be the same for each of the skew feeding rollers 321 to 323 of the front side skew feeding unit 32 .

In this embodiment, the skew feeding speeds V1 and V2 of the front and rear skew feeding rollers 311 and 321 to 323 are set so that the components in the sheet conveying direction Dx are equal (V1x≈V2x, FIG. 14(a) )reference). If the speed in the sheet conveying direction Dx is not balanced between the oblique feeding units on the front side and the back side (V1x>V2x or V1x<V2x, see FIGS. 14B and 14C), the sheet S is rotated. A force arises to try. That is, a force acts on the sheet S such that the side edge of the sheet S closer to the oblique feeding unit having a higher speed in the sheet conveying direction Dx advances downstream in the sheet conveying direction Dx compared to the other side edge. Therefore, in this embodiment, while at least both the front and back skew rollers are in the pressurized state (S114 to S119), the skew feeding speeds V1 and V2 are adjusted so that the components in the sheet conveying direction Dx substantially match each other. is set. As a result, it is possible to prevent the sheet S from turning due to the speed difference of the skew feed roller in the sheet conveying direction Dx, and to correct the skew of the sheet S with high accuracy.

By the way, the direction of the force applied to the sheet by the oblique feed roller 311 on the back side is greatly inclined with respect to the sheet conveying direction Dx compared to the oblique feed rollers 321 to 323 on the front side. Therefore, when the component V1x in the sheet conveying direction of the skew feeding speed V1 by the rear skew roller 311 is set equal to that of the front skew rollers 321 to 323, the width component V1y is equal to the front skew roller 321 to 323. Larger than 323. (V1y>V2y when V1x≈V2x). This means that the back-side oblique-feeding unit 31 quickly moves the sheet S between the release of the pressure applied by the conveying roller pair 21 (S113) and the start of the pressure applied by the front-side oblique-feeding unit 32 (S114). It is also convenient for aligning with the reference member 300 (see FIG. 11(a)). On the other hand, when the front skew feed rollers 321 to 323 are pressurized, the width direction movement speed is suppressed by the front skew feed rollers 321 to 323, which have a smaller speed component in the width direction than the rear skew feed roller 311. will be This is convenient for reducing the collision between the sheet S and the reference surface 301 of the reference member 300 .

(Turn suppression after skew correction)
Next, the acceleration process (S118) of the oblique feed rollers and the decompression process (S117) of the front oblique feed unit 32 prior to the acceleration process will be described in detail. In general, the higher the sheet conveying speed, the higher the productivity of the image forming apparatus. Become. In this embodiment, the oblique feed rollers 321 to 323 of the front oblique feed unit 32 are rotationally driven at a relatively slow speed until the sheet contacts the reference member 300, and after the contact, the drive speed of the oblique feed rollers 321 to 323 is increased. are increasing.

In other words, the operation (second operation) of increasing the conveying speed of the sheet is performed after the operation (first operation) of bringing the sheet into contact with the contact surface by the second oblique feeding means. When the driving speeds of the first oblique-feeding means and the second oblique-feeding means in the first operation are the first speed and the second speed, the first oblique-feeding means and the second oblique-feeding means are driven at the first speed in the second operation. and a fourth speed greater than the second speed. As a result, it is possible to reduce the impact applied to the sheet at the time of contact, and to ensure productivity. Further, since the skew feeding speeds of the first skew feeding device and the second skew feeding device are both accelerated, the sheet is less likely to turn than when only one of them is accelerated. Note that it is preferable to set the skew feeding speeds V1 and V2 after acceleration so that the components in the sheet conveying direction are equal (V1x≈V2x).

However, when the acceleration process is performed, care must be taken so that the orientation of the sheet whose skew has been corrected is not disturbed again by abutting against the reference member. When a sheet having a mass of m is accelerated with an acceleration of a by the acceleration of the oblique feed roller, a force of F=m×a (hereinafter referred to as an acceleration force F) acts on the sheet compared to the state before the acceleration. become. At this time, a moment M (M=F×X, where X is the arm length of the moment generated by the acceleration force F) is generated to turn the seat due to the acceleration force F, and the posture of the seat is disturbed. Sometimes.

The behavior of the seat due to this phenomenon is determined by the relationship between the point of action of the acceleration force F, the direction of the acceleration force F, and the moment center. The point of action of the acceleration force F is the contact position between the oblique feed rollers 311, 321 to 323 and the sheet. The direction of the acceleration force F is the rotation direction of each oblique feed roller at the contact position with the sheet. The center of the moment is the position at which the area-integrated transfer resistance to the sheet is balanced with respect to the first surface and the second surface of the sheet, and is the apparent center of gravity of the sheet. Assuming that the sheet conveying resistance is uniform, the center of the moment coincides with the center of gravity of the sheet. In reality, the center of the moment does not necessarily coincide with the center of gravity of the sheet due to factors such as the difference in friction coefficient with respect to the sheet between the pair of conveying rollers and the conveying guide and the curvature of the sheet conveying path. Experimentally, for example, the center of the moment can be estimated by observing the turning direction of the sheet when the sheet is accelerated while changing the conditions of the angle and position of a single oblique feed roller. can.

A configuration for stabilizing the behavior of the seat during the acceleration process will be described below with the point "O" in FIG. 15 as the center of the moment. 15(a) and 15(b) are schematic diagrams showing a skew correction unit of a reference example, and the arrangement of skew feed rollers is different from that of the skew correction unit 30 of this embodiment shown in FIG. 15(c).

When moments M1 and M2 act on the sheet S due to the acceleration of the front oblique-feeding unit 32 and the back oblique-feeding unit 31, the following three situations can be assumed.
(A) Both the front and rear oblique feed rollers generate a moment in the clockwise direction (CW) in the figure (Fig. 15(a)).
(B) Both the front side/rear side oblique feed rollers generate a moment in the counterclockwise direction (CCW) in the drawing (FIG. 15(b)).
(C) The front oblique feed roller generates a moment in the clockwise direction (CW) in the drawing, and the rear oblique feed roller generates a moment in the counterclockwise direction (CCW) in the drawing (Fig. 15(c)). ).

In the case of (A), the front end of the sheet S exhibits a behavior of turning away from the reference member 300 due to the clockwise moments M1 and M2 in the figure as the sheet S is accelerated. In the case of (B), the trailing edge of the sheet S turns away from the reference member 300 due to the acceleration process due to the counterclockwise moments M1 and M2 in the figure. In both cases (A) and (B), the moment caused by the acceleration of the front and rear oblique feeding units 31 and 32 act additively, and the sheet tends to turn.

On the other hand, in the case of (C), the accelerations of the front oblique-feeding unit 32 and the back oblique-feeding unit 31 generate moments in opposite directions. In this case, the moments caused by the acceleration of the oblique feed rollers on the front side and the back side act to cancel each other, so that the sheet is less likely to turn, and the posture of the sheet during acceleration can be stabilized. In the present embodiment, the configuration shown in (C), that is, the front oblique-feeding unit 32 and the back oblique-feeding unit 32 and the back oblique-feeding unit 32 are arranged with respect to the center O of the moment from when the sheet comes into contact with the reference member 300 until it reaches the registration roller 7 . 31 are positioned on one side and the other side in the width direction. Specifically, the front oblique feeding unit 32 is arranged on one side of the transport center L0 (see FIG. 2), and the back oblique feeding unit 31 is arranged on the other side of the transport center L0. As a result, the moments generated by the oblique feeding units 31 and 32 cancel each other out, and the behavior of the sheet is stabilized.

In addition, in this embodiment, in order to further stabilize the posture of the sheet during acceleration, processing for reducing the force with which the front oblique feeding unit 32 pinches the sheet during acceleration (see S117 in FIG. 9 and FIG. 10) is performed. Is going. One reason for such processing is the difference in the number of skew rollers, and another reason is the difference in moment arm length.

As for the difference in the number of skew-feeding rollers, the front-side skew-feeding unit 32 has three skew-feeding rollers 321 to 323 , while the back-side skew-feeding unit 31 is composed of one skew-feeding roller 311 . Therefore, when all the skew feeding rollers are in contact with the sheet, the moment M2 generated by the front side skew feeding unit 32 during acceleration tends to be larger than the moment M1 generated by the rear side skew feeding unit 31. . In this case, the sheet S may turn clockwise in FIG. 15(c).

Regarding the length of the arm of the moment, the center O of the moment from contacting the reference member 300 to reaching the registration roller 7 is near the transportation center L0 and oblique to the pre-registration transportation section 20 in the case of this embodiment. It is positioned near the boundary of the row correction unit 30 (see FIG. 2). In such a case, arm lengths X21, X22, and X23 of the moment caused by the front oblique feed rollers 321 to 323 are shorter than when the moment center O is positioned further upstream in the sheet conveying direction. The moment arm length X1 of the oblique feed roller 311 is increased. Therefore, when the conveying force applied to the sheet by the oblique feeding rollers by the oblique feeding units 31 and 32 increases due to the acceleration of the oblique feeding units 31 and 32, the increment of the moment M2 by the front side oblique feeding unit 32 is the moment M1 by the back side oblique feeding unit 31. It tends to be larger than the increment.

Based on such knowledge, in the present embodiment, the pressing force of the front oblique feeding unit 32 is reduced before performing the acceleration process (S117 in FIG. 9). In other words, in the case where the second operation (S118) of accelerating the conveying speed of the sheet is performed after the first operation (S114) of bringing the sheet into contact with the contact surface, the acceleration of the second oblique feeding means in the second operation. The pressure is set lower than in the first operation. As a result, the moments M1 and M2 generated by the oblique feeding units 31 and 32 are balanced (M1≈M2) in the latter half of the abutting alignment operation, that is, after the sheet abuts against the reference member 300, and the sheet can be turned. less likely to occur.

The following (1) to (3) can be given as methods for reducing the pressure applied by the front side oblique feeding unit 32 .
(1) A method of weakening the pressure applied to each of the three oblique feed rollers (2) A method of releasing the pressure applied to one or two of the three oblique feed rollers A method of releasing the pressure on one or two of them and weakening the pressure on the remaining oblique feed rollers.

In this embodiment, one of the methods (1) to (3) is executed according to the type of sheet, as shown in the column of "applied pressure during acceleration" in FIG. As a result, regardless of the type of sheet, the nip pressure is set to prevent the sheet from turning and to be stably conveyed.

Next, a sheet conveying device according to Example 2 will be described with reference to FIG. The registration section of the sheet conveying apparatus in this embodiment differs from the first embodiment in the timing of starting pressurization of the back side oblique feeding unit in the sheet conveying operation. Since other configurations are the same as those of the first embodiment, common elements are denoted by the same reference numerals as those of the first embodiment, and descriptions thereof are omitted. A method of controlling the sheet conveying operation according to this embodiment will be described below with reference to the flowchart of FIG.

When an image forming job is started (S201) in a state in which information such as the basis weight, size, and number of sheets on which image formation is to be performed is input via the operation unit 412, the front side oblique feeding unit 32 and the rear side oblique feeding unit 32 are started. The oblique feeding pressure of the feeding unit 31 is determined (S202). Unlike the first embodiment, pressurization of the back side oblique feeding unit 31 is not started at this stage.

After that, when the image forming operation by the image forming units PY to PK is started (S203), the delay time for starting feeding is counted (S204) based on the start timing of the image forming operation. The sheet is fed from (S205). Then, when the sheet transferred to the pre-registration conveying unit 20 is detected by the pre-registration sensor S1 (S206), the stop delay time is counted (S207), and then the pre-registration drive motor Mp is stopped (S208). If the pre-registration sensor S1 does not detect the sheet even after a predetermined time has passed since the start of feeding, a screen showing sheet jam is displayed on the operation unit (S226), and the execution of the job ends.

After that, the delay time for starting pressurization of the back side oblique feeding unit 31 is counted (S209) according to the progress of the image forming operation, and the oblique feeding roller 311 of the back side oblique feeding unit 31 is moved to the determined oblique direction. It is pressurized based on the pressure feeding (S210). Thereafter, the stopped pre-registration drive motor Mp is restarted (S211). Then, the delay time for releasing the pressure applied to the conveying roller pair 21 of the pre-registration conveying section 20 is counted (S212), the driven roller 24 is separated from the drive roller 23, and the conveying roller pair 21 is separated (S213).

In the first embodiment, the sheet is fed from the pre-registration conveying section 20 to the skew correcting section 30 while the back side skew feeding unit 31 is pressurized in advance. On the other hand, in the present embodiment, the start of pressurization of the back side oblique feeding unit 31 is delayed, and the period (from S210 to S212) is made as short as possible. As a result, it is possible to reduce deterioration of the rubber on the surface of the roller and damage to the sheet due to friction between the oblique feed roller 311 and the sheet. Also in this embodiment, as a result, the driving restart timing of the pre-registration drive motor Mp is adjusted in accordance with the image forming operation, so that the variation in the time until the sheet reaches the pre-registration sensor S1 is absorbed.

It should be noted that a configuration may be adopted in which pressurization of the back-side oblique feed unit 31 is started after the pre-registration drive motor Mp is restarted. Further, in order to reliably transfer the sheet from the pre-registration conveying section 20 to the skew correction section 30, it is preferable that the conveying roller pair 21 is separated after the back side skew feeding unit 31 starts pressing.

When the pressurization of the conveying roller pair 21 is released (S213), the abutment alignment operation by the skew correction section 30 is started. That is, the back-side oblique feeding unit 31 starts obliquely feeding the sheet, and the sheet is shifted toward the reference surface 301 of the reference member 300 . After that, at the timing when the side edge of the sheet and the reference surface 301 of the reference member 300 approach each other to some extent, the front side skew feed rollers 321 to 323 start to apply pressure based on the determined skew feed pressure (S214). As a result, the sheet moves closer to the reference member 300, and the side edges abut against the reference surface 301, thereby correcting the skew.

As described above, also in this embodiment, the rear side oblique feeding unit 31 as the first oblique feeding means and the front side oblique feeding unit 32 as the second oblique feeding means are used together. As a result, the collision of the sheet against the reference member 300 is alleviated to prevent buckling of the sheet, and the sheet is quickly shifted to the width, thereby contributing to the miniaturization and simplification of the apparatus.

After the front skew feed rollers 321 to 323 start applying pressure, when the skew feed sensor S2 detects the front end of the sheet (S215), the delay time for changing the pressing force of the skew feed rollers 321 to 323 is counted ( S216). Then, after the delay time has elapsed, the processing (S217) is executed to reduce the pressing force of the front oblique-feed rollers 321 to 323, and then the conveying speeds of the front-side oblique-feed unit 32 and the rear-side oblique-feed unit 31 are increased. Processing (S218) is performed.

After the acceleration is completed and before the front edge of the sheet is detected by the pre-registration sensor S3, the back side skew feed roller 311 is released from the pressure (S219). As a result, the loop of the sheet is eliminated before the sheet rushes into the registration rollers 7. - 特許庁When the pre-registration sensor S3 detects the front end of the sheet (S220), the delay time for releasing the front skew feed rollers 321 to 323 is counted (S221), and the pressure of the skew feed rollers 321 to 323 is released. It will be in a release state (S222). This delay time is set so that the front skew feed rollers 321 to 323 are released after the front end of the sheet enters the nip portion of the registration roller 7 . If the pre-registration sensor S3 does not detect the sheet within a predetermined time, a screen showing sheet jam is displayed on the operation unit (S226), and the execution of the job ends.

When the sheet is transferred to the registration rollers 7, the registration rollers 7 move in the width direction while conveying the sheet, and the center position of the sheet in the width direction is aligned with the center position of the image formed by the image forming units PY to PK. It is positioned (S223). When the sheet is sent to the secondary transfer section, the value of K is decremented by a counter that manages the remaining number of sheets K for image formation (S224). If the number of remaining sheets K is not 0, that is, if there are sheets left for image formation (S225: NO), the above operations (S203 to S224) are repeated. If the remaining number of sheets K is 0 (S225: YES), it is determined that the image forming operation is completed, and the execution of the job ends.

Next, a sheet conveying device according to Example 3 will be described with reference to FIGS. 17 and 18. FIG. The registration unit of the sheet conveying apparatus according to the present embodiment differs from that of the second embodiment in the method of preventing the turning of the sheet when accelerating the conveying speed of the sheet when conveying a sheet such as thick paper. Since other configurations are the same as those of the second embodiment, common elements are assigned the same reference numerals as those of the second embodiment, and descriptions thereof are omitted. Hereinafter, a method for controlling the sheet conveying operation in this embodiment will be described along the flow chart of FIG. 17 while referring to FIG. 18 as appropriate.

When an image forming job is started (S301) in a state in which information such as the basis weight, size, and number of sheets on which images are to be formed is input via the operation unit 412, the front side oblique feeding unit 32 and the rear side oblique feeding unit 32 are started. The oblique feeding pressure of the feeding unit 31 is determined (S302).

After that, when the image forming operation by the image forming units PY to PK is started (S303), the delay time for starting feeding is counted (S304) based on the start timing of the image forming operation. The sheet is fed from (S305). Then, when the sheet transferred to the pre-registration conveying unit 20 is detected by the pre-registration sensor S1 (S306), the stop delay time is counted (S307), and then the pre-registration drive motor Mp is stopped (S308). If the pre-registration sensor S1 does not detect the sheet even after a predetermined time has passed from the start of feeding, a screen showing sheet jam is displayed on the operation unit (S326), and the execution of the job ends.

After that, the delay time for starting pressurization of the back side oblique feeding unit 31 is counted (S309) according to the progress of the image forming operation, and the oblique feeding roller 311 of the back side oblique feeding unit 31 is moved to the determined oblique Pressure is applied based on the pressure feeding (S310). Thereafter, the stopped pre-registration drive motor Mp is restarted (S311). Then, the delay time for releasing the pressure applied to the conveying roller pair 21 of the pre-registration conveying section 20 is counted (S312), the driven roller 24 is separated from the drive roller 23, and the conveying roller pair 21 is separated (S313).

When the pressurization of the conveying roller pair 21 is released (S313), the abutment alignment operation by the skew correction section 30 is started. That is, the back-side oblique feeding unit 31 starts obliquely feeding the sheet, and the sheet is shifted toward the reference surface 301 of the reference member 300 . After that, at the timing when the side edge of the sheet and the reference surface 301 of the reference member 300 come close to each other to some extent, the front side skew feed rollers 321 to 323 start to apply pressure based on the determined skew feed pressure (S314). As a result, the sheet moves closer to the reference member 300, and the side edges abut against the reference surface 301, thereby correcting the skew.

As described above, also in this embodiment, the rear side oblique feeding unit 31 as the first oblique feeding means and the front side oblique feeding unit 32 as the second oblique feeding means are used together. As a result, the collision of the sheet against the reference member 300 is alleviated to prevent buckling of the sheet, and the sheet is quickly shifted to the width, thereby contributing to the miniaturization and simplification of the apparatus.

Here, in this embodiment, after the front side skew feeding rollers 321 to 323 start pressing, when the skew feeding sensor S2 detects the front end of the sheet (S315), the pressing force of the rear side skew feeding roller 311 is changed. A delay time is counted (S316). Then, after the delay time has passed, the processing (S317) is executed to reduce the pressing force of the back side skew feeding roller 311, and then the processing to increase the conveying speed of the front side oblique feeding unit 32 and the back side oblique feeding unit 31. (S318) is performed.

As described above, when the acceleration process for increasing the sheet conveying speed is performed, the difference in the number of oblique feed rollers on the front side and the back side and the difference in the inclination angle with respect to the sheet conveying direction (difference in the length of the moment arm) cause the sheet A moment may occur that tends to turn the In the first embodiment, by reducing the force with which the front oblique-feeding unit 32 pinches the sheet, the moment M1 generated by the front-side oblique-feeding unit 32 during acceleration is suppressed and balanced with the moment M2 by the back-side oblique-feeding unit. .

However, in the case of a sheet having a relatively large conveying resistance, such as a thick sheet, if the pressing force of the front oblique feed rollers 321 to 323 is reduced, the sheet conveying delays or the stability of the conveying operation deteriorates due to insufficient conveying force. There are concerns that Therefore, in the present embodiment, when conveying a sheet having a basis weight of 300 gsm or more, the pressure applied to the back side skew feed roller 311 is increased without reducing the pressure applied to the front side skew feed rollers 321 to 323 ( See the bottom of FIG. 18). That is, in the present embodiment, when the second operation (S318) of accelerating the conveying speed of the sheet is performed after the first operation (S314) of bringing the sheet into contact with the contact surface, the first oblique movement of the second operation (S318) is performed. The pressurizing force of the feeding means is set higher than that in the first operation.

As a result, the force with which the rear oblique-feeding unit 31 clamps the sheet increases, and the moment M1 generated by the rear-side oblique-feeding unit 31 during acceleration increases. (See FIG. 15(c)). Therefore, it is possible to prevent a shortage of the conveying force, reduce the rotation of the sheet during acceleration, and perform stable skew correction.

Note that the flowchart shown in FIG. 17 is executed when the basis weight of the sheet is 300 gsm or more, and the same control as in the second embodiment is performed for the sheet with a basis weight of less than 300 gsm. That is, for sheets with a basis weight of less than 300 gsm, the process of reducing the pressing force of the front oblique feeding unit 32 (S217 in FIG. 16) is performed before the acceleration process. As a result, a relatively thin sheet can be easily slipped by the skew feed roller 311 on the far side, and it is possible to suppress the occurrence of excessive loops that cause wrinkles and skew in the registration rollers 7 . As described above, in this embodiment, a mode in which the pressing force of the first oblique feeding means during acceleration is set high and a mode in which the pressing force of the second oblique feeding means during acceleration is set low are set according to the basis weight of the sheet. They are used accordingly.

Returning to the flowchart of FIG. 17, the description is continued. After the acceleration is completed and before the front edge of the sheet is detected by the pre-registration sensor S3, the back side skew feed roller 311 is released from the pressure (S319). As a result, the loop of the sheet is eliminated before the sheet rushes into the registration rollers 7. - 特許庁When the pre-registration sensor S3 detects the front end of the sheet (S320), the delay time for releasing the front skew feed rollers 321 to 323 is counted (S321), and the pressure of the skew feed rollers 321 to 323 is released. It will be in a release state (S322). This delay time is set so that the front skew feed rollers 321 to 323 are released after the front end of the sheet enters the nip portion of the registration roller 7 . Note that if the pre-registration sensor S3 does not detect the sheet within a predetermined time, a screen indicating sheet jam is displayed on the operation unit (S326), and the execution of the job ends.

When the sheet is transferred to the registration rollers 7, the registration rollers 7 move in the width direction while conveying the sheet, and the center position of the sheet in the width direction is aligned with the center position of the image formed by the image forming units PY to PK. It is positioned (S323). When the sheet is sent to the secondary transfer section, the value of K is decremented by a counter that manages the remaining number of sheets K for image formation (S324). If the number of remaining sheets K is not 0, that is, if there are sheets left for image formation (S325: NO), the above operations (S303 to S324) are repeated. If the remaining number K is 0 (S325: YES), it is determined that the image forming operation has been completed, and the execution of the job ends.

Next, a sheet conveying device according to Embodiment 4 will be described with reference to FIGS. 19 and 20. FIG. The registration unit of the sheet conveying apparatus in this embodiment differs from the above-described third embodiment in the method of controlling the sheet conveying operation when conveying some sheets including very thin ultra-thin paper. Since other configurations are the same as those of the third embodiment, common elements are denoted by the same reference numerals as those of the third embodiment, and descriptions thereof are omitted. A method of controlling the sheet conveying operation according to the present embodiment will be described below along the flowchart of FIG. 19 while referring to FIG. 20 as appropriate.

When an image forming job is started (S401) in a state in which information such as basis weight, size, and number of sheets on which image formation is to be performed is input via the operation unit 412, the front oblique feeding unit 32 and the rear oblique feeding unit 32 are started. The oblique feeding pressure of the feeding unit 31 is determined (S402).

After that, when the image forming operation by the image forming units PY to PK is started (S403), the delay time for starting feeding is counted (S404) based on the start timing of the image forming operation. The sheet is fed from (S405). Then, when the sheet transferred to the pre-registration conveying unit 20 is detected by the pre-registration sensor S1 (S406), the stop delay time is counted (S407), and then the pre-registration drive motor Mp is stopped (S408). If the pre-registration sensor S1 does not detect the sheet even after a predetermined time has elapsed since the start of feeding, a screen indicating sheet jam is displayed on the operation unit (S426), and the execution of the job ends.

After that, the delay time for starting pressurization of the back side oblique feeding unit 31 is counted (S409) in accordance with the progress of the image forming operation, and the oblique feeding roller 311 of the back side oblique feeding unit 31 is moved to the determined oblique direction. Pressure is applied based on the pressure feeding (S410). After that, the stopped pre-registration drive motor Mp is restarted (S411). Then, the delay time for releasing the pressure applied to the conveying roller pair 21 of the pre-registration conveying section 20 is counted (S412), the driven roller 24 is separated from the drive roller 23, and the conveying roller pair 21 is in a separated state (S413).

When the pressurization of the conveying roller pair 21 is released (S413), the abutment alignment operation by the skew correction section 30 is started. That is, the back-side oblique feeding unit 31 starts obliquely feeding the sheet, and the sheet is shifted toward the reference surface 301 of the reference member 300 . After that, at the timing when the side edge of the sheet and the reference surface 301 of the reference member 300 come close to each other to some extent, the front side skew feeding rollers 321 to 323 start to apply pressure based on the determined skew feeding pressure (S414). As a result, the sheet moves closer to the reference member 300, and the side edges abut against the reference surface 301, thereby correcting the skew.

As described above, also in this embodiment, the rear side oblique feeding unit 31 as the first oblique feeding means and the front side oblique feeding unit 32 as the second oblique feeding means are used together. As a result, the collision of the sheet against the reference member 300 is alleviated to prevent buckling of the sheet, and the sheet is quickly shifted to the width, thereby contributing to the miniaturization and simplification of the apparatus.

Here, in this embodiment, after the front side skew feeding rollers 321 to 323 start pressing, when the skew feeding sensor S2 detects the front end of the sheet (S415), the back side skew feeding unit 31 releases the pressure. is counted (S416). Then, after the delay time has passed, the processing (S417) of releasing the pressure applied to the back side skew feeding roller 311 is executed, and then the processing of increasing the conveying speed of the front side skew feeding unit 32 and the back side skew feeding unit 31. (S418) is performed.

In the case of a sheet having a low transport resistance, such as an ultra-thin paper having a basis weight of 40 gsm or more and less than 60 gsm, the sheet is less likely to turn even if the sheet transport speed is accelerated, but the skew feed direction of the skew feed units 31 and 32 is reduced. There is a concern that sheet loops may occur due to the difference. That is, the sheet is drawn toward the reference member 300 by the rear skew feeding roller 311 having a large inclination angle with respect to the sheet conveying direction, and a sheet loop is likely to occur between the front and rear skew feeding units 31 and 32 .

In this embodiment, after the front edge of the sheet is detected by the skew feed sensor S2, the pressurization of the back side skew feed unit 31 is released (S417) before the acceleration process (S418). Therefore, the loop is eliminated before the leading edge of the sheet reaches the registration roller 7, and the occurrence of wrinkles and skew can be reduced.

On the other hand, since a sheet having a basis weight of 60 gsm or more has a relatively large conveyance resistance, it is preferable to reduce the turning of the sheet when accelerating the sheet conveyance speed. The flowchart shown in FIG. 19 is executed when the basis weight of the sheet is 40 gsm or more and less than 60 gsm, and the same control as in the third embodiment is performed for the sheet with a basis weight of less than 60 gsm. That is, for sheets with a basis weight of 60 gsm or more and less than 300 gsm, the process of reducing the pressing force of the front oblique feeding unit 32 (see FIG. 20) is performed before acceleration. Also, for sheets having a basis weight of 300 gsm or more, processing is performed to increase the pressing force of the rear oblique feeding unit 31 before acceleration (see FIG. 20).

That is, in this embodiment, the first mode and the second mode are switched according to the basis weight of the sheet, and the sheet conveying operation in the first mode is executed for the sheet having the first basis weight. A sheet conveying operation in the second mode is executed for a sheet having a second basis weight smaller than the basis weight. However, the first mode is an acceleration operation (second operation) while the rear-side oblique-feeding unit 31 is kept in a pressurized state even after the front-side oblique-feeding unit 32 starts the sheet skew-feeding operation (first operation). ) is the mode to start. In the second mode, after the oblique feeding operation (first operation) of the sheet by the front oblique feeding unit 32 is started, the rear oblique feeding unit 31 is switched to the released state and the accelerating operation (second operation) is started. mode.

Returning to the flow chart of FIG. 19, the description is continued. When the pre-registration sensor S3 detects the front end of the sheet (S419), the delay time for releasing the front skew feed rollers 321 to 323 is counted (S420), and the pressure of the skew feed rollers 321 to 323 is released. The release state is entered (S421). This delay time is set so that the front skew feed rollers 321 to 323 are released after the front end of the sheet enters the nip portion of the registration roller 7 . Note that if the pre-registration sensor S3 does not detect the sheet within a predetermined time, a screen indicating sheet jam is displayed on the operation unit (S425), and the execution of the job ends.

When the sheet is transferred to the registration rollers 7, the registration rollers 7 move in the width direction while conveying the sheet, and the center position of the sheet in the width direction is aligned with the center position of the image formed by the image forming units PY to PK. Positioned (S422). When the sheet is sent to the secondary transfer section, the value of K is decremented by a counter that manages the remaining number of sheets K for image formation (S423). If the number of remaining sheets K is not 0, that is, if there are sheets left for image formation (S424: NO), the above operations (S403 to S423) are repeated. If the remaining number of sheets K is 0 (S424: YES), it is determined that the image forming operation has been completed, and the execution of the job ends.

Next, a sheet conveying device according to Example 5 will be described with reference to FIGS. 21 to 23. FIG. The registration section of the sheet conveying apparatus of this embodiment differs from that of the first embodiment in that the back side oblique feeding unit has a plurality of oblique feeding rollers. Since other configurations are the same as those of the first embodiment, common elements are denoted by the same reference numerals as those of the first embodiment, and descriptions thereof are omitted.

As shown in FIG. 21, in the skew correcting section 30 of this embodiment, a depth-side skew feed unit 31 having three skew feed rollers 311, 312, and 313 is arranged. The skew feeding rollers 311 to 313 are arranged parallel to each other along a direction inclined so as to approach the reference member 300 in the width direction Dy as they go downstream in the sheet conveying direction Dx. As in the first embodiment, the skew feed rollers 311 to 313 on the back side are arranged so that the direction of the conveying force applied to the sheet has a larger angle with respect to the sheet conveying direction Dx than the skew feed rollers 321 to 323 on the front side ( θ1>θ2) are arranged.

Driven rollers face the oblique feed rollers 311 to 313 of the back side oblique feed unit 31, and each driven roller is pressurized and released by a pressurizing mechanism 33 similar to that shown in FIGS. and are configured to be switchable. Hereinafter, a method for controlling the sheet conveying operation in this embodiment will be described along the flowchart of FIG. 22 with appropriate reference to FIG.

When an image forming job is started (S501) in a state in which information such as the basis weight, size, and number of sheets on which images are to be formed is input via the operation unit 412, the front oblique feeding unit 32 and the rear oblique feeding unit 32 are started. The oblique feeding pressure of the feeding unit 31 is determined (S502). Then, based on the determined oblique feeding pressure, the back side oblique feeding rollers 311 to 313 first start to pressurize and enter a pressurized state (S503). As shown in the table of FIG. 23, the magnitude of the oblique feeding pressure is set according to the basis weight of the sheet so that the sheet can be stably conveyed regardless of the sheet type.

After that, when the image forming operation by the image forming units PY to PK is started (S504), the delay time for starting feeding is counted (S505) based on the start timing of the image forming operation. The sheet is fed from (S506). Then, when the sheet transferred to the pre-registration conveying unit 20 is detected by the pre-registration sensor S1 (S507), the stop delay time is counted (S508), and then the pre-registration drive motor Mp is stopped (S509). If the pre-registration sensor S1 does not detect the sheet even after a predetermined time has passed from the start of feeding, a screen indicating sheet jam is displayed on the operation unit (S525), and the execution of the job ends.

After that, the restart delay time is counted according to the progress of the image forming operation (S510), and the driving of the pre-registration driving motor Mp is restarted (S511). Since the driving restart timing of the pre-registration drive motor Mp is adjusted in accordance with the image forming operation, variations in the time until the sheet reaches the pre-registration sensor S1 are absorbed. After that, the delay time for releasing the pressure applied to the conveying roller pair 21 of the pre-registration conveying section 20 is counted (S512), the driven roller 24 is separated from the drive roller 23, and the conveying roller pair 21 is in a separated state (S513).

When the pressurization of the conveying roller pair 21 is released (S513), the abutment alignment operation by the skew correction section 30 is started. That is, the back-side oblique feeding unit 31 starts obliquely feeding the sheet, and the sheet is shifted toward the reference surface 301 of the reference member 300 . After that, at the timing when the side edge of the sheet and the reference surface 301 of the reference member 300 come close to each other to some extent, the front side skew feed rollers 321 to 323 start pressing based on the determined skew feed pressure (S514). As a result, the sheet moves closer to the reference member 300, and the side edges abut against the reference surface 301, thereby correcting the skew.

As described above, also in this embodiment, the rear side oblique feeding unit 31 as the first oblique feeding means and the front side oblique feeding unit 32 as the second oblique feeding means are used together. As a result, the collision of the sheet against the reference member 300 is alleviated to prevent buckling of the sheet, and the sheet is quickly shifted to the width, thereby contributing to the miniaturization and simplification of the apparatus.

Further, in the configuration in which the first oblique feeding means has a plurality of oblique feeding rollers as in the present embodiment, it is easier to secure the feeding force for aligning the sheet compared to the case where there is only one oblique feeding roller. , it is possible to stably bring the sheet to the reference member even if the sheet is thicker. Further, since the pressing force of each skew feed roller can be kept small, deterioration of the rubber on the surface of the roller and damage to the sheet due to friction between the sheet and the skew feed roller can be suppressed.

After the front side skew feed rollers 321 to 323 start pressing, when the skew feed sensor S2 detects the front end of the sheet (S515), the delay time for changing the drive speed of the skew feed units 31 and 32 is counted ( S516). Then, after the delay time has passed, processing (S517) for increasing the conveying speed of the front side oblique feeding unit 32 and the rear side oblique feeding unit 31 is performed.

In this embodiment, since the number of oblique feed rollers is the same in the oblique feed units 31 and 32 on the front side and the back side, processing for changing the pressing force of the oblique feed rollers during acceleration is not performed. This is because, in this configuration, the moments accompanying acceleration cancel each other out and are naturally balanced. However, if the moment balance is lost (for example, if the arm lengths of the moment arms are significantly different between the front and rear oblique feed units 31, 32), one or both of the oblique feed units 31, 32 in the acceleration operation It is possible to adjust the pressure of

After the acceleration is completed and before the front end of the sheet is detected by the pre-registration sensor S3, the rear side skew feed rollers 311 to 313 are released from the pressure (S518). . As a result, the loop of the sheet is eliminated before the sheet rushes into the registration rollers 7. - 特許庁When the pre-registration sensor S3 detects the front end of the sheet (S519), the delay time for releasing the front skew feed rollers 321 to 323 is counted (S520), and the pressure of the skew feed rollers 321 to 323 is released. It will be in a released state (S521). This delay time is set so that the front skew feed rollers 321 to 323 are released after the front end of the sheet enters the nip portion of the registration roller 7 . If the pre-registration sensor S3 does not detect the sheet within a predetermined time, a screen indicating sheet jam is displayed on the operation unit (S525), and the job execution ends.

When the sheet is transferred to the registration rollers 7, the registration rollers 7 move in the width direction while conveying the sheet, and the center position of the sheet in the width direction is aligned with the center position of the image formed by the image forming units PY to PK. Positioned (S522). When the sheet is sent to the secondary transfer section, the value of K is decremented by a counter that manages the remaining number of sheets K for image formation (S523). If the number of remaining sheets K is not 0, that is, if there are sheets left for image formation (S524: NO), the above operations (S503 to S523) are repeated. If the remaining number of sheets K is 0 (S524: YES), it is determined that the image forming operation is completed, and the execution of the job ends.

(Other embodiments)
In the above first to fifth embodiments, as an example of the sheet conveying device, the registration section arranged upstream of the transfer section where the image is transferred has been described. It can also be applied to a sheet conveying device. For example, an apparatus that is connected to the main body of the image forming apparatus and conveys the sheet while correcting the skew of the sheet inside the sheet processing apparatus, or a double-sided conveying unit 502 (see FIG. 1) that conveys the sheet while correcting the skew of the sheet. It can be used as a device. That is, the sheet conveying device is not limited to the one housed in the apparatus main body of the image forming apparatus or the one used for sheet conveying before image formation.

Also, the elements described in each embodiment can be combined with each other, and for example, the configuration of the skew correction unit 30 of the fifth embodiment may be used to perform the same control as in any one of the first to fourth embodiments.

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

Reference Signs List 1, 50 Sheet conveying device (image forming apparatus, registration section) / 7 Second conveying means (registration roller pair) / 10 Image forming means (image forming engine) / 21 First conveying means (conveying rollers) pair)/301... contact surface (reference surface)/31... first oblique-feeding means (rear-side oblique-feeding unit)/32... second oblique-feeding means (front-side oblique-feeding unit)/311, 312, 313... first Roller, first oblique feed roller (oblique feed roller)/321, 322, 323... Second roller, second oblique feed roller (oblique feed roller)/33... Switching means (pressure mechanism)/600... Control means (controller )/Dx Sheet conveying direction/Dy Width direction/θ1 Angle in first direction/θ2 Angle in second direction/S114, S214, S314, S414, S514 First operation/S118, S218, S318, S418 , S517... second operation

Claims (7)

a contact member extending along the sheet conveying direction and having a contact surface capable of coming into contact with an end portion of the sheet in a width direction orthogonal to the sheet conveying direction;
The sheet moving direction is inclined in a first direction with respect to the sheet conveying direction, the sheet is rotatable about an axis orthogonal to the first direction, and the contact surface is approached in the width direction. a first skew-feeding roller pair having a first skew-feeding roller that skew-feeds a sheet to and a first driven roller that follows rotation of the first skew-feeding roller;
It is provided so that the moving direction of the sheet is inclined in the second direction with respect to the sheet conveying direction, is rotatable about an axis perpendicular to the second direction, and approaches the contact surface in the width direction. a second skew-feeding roller pair having a second skew-feeding roller that skew-feeds a sheet and a second driven roller that follows rotation of the second skew-feeding roller;
a conveying roller provided upstream of the first skew-feeding roller and the second skew-feeding roller in the sheet conveying direction for conveying the sheet in the sheet conveying direction;
a pressurized state in which the first driven roller is pressed against the first oblique feed roller so that a sheet can be sandwiched between the first driven roller and the first oblique feed roller; a first switching means for switching to a released state in which pressurization is released;
a pressurized state in which the second driven roller is pressed against the second skew-feed roller so that a sheet can be sandwiched between the second driven roller and the second skew-feed roller; a second switching means for switching to a released state in which pressurization is released;
and a control means for controlling the first switching means and the second switching means,
In the width direction, the second skew-feed roller is arranged on the same side as the contact member with respect to the center line of the sheet transport path along which the sheet is transported by the transport roller, and the first skew-feed roller is arranged on the side opposite to the contact member with respect to the transport center line,
an angle of the first direction with respect to the sheet conveying direction is greater than an angle of the second direction with respect to the sheet conveying direction;
The control means causes the first skew-feeding roller pair to start skew-feeding the sheet in a state in which the first driven roller is in a pressurized state and the second driven roller is in a released state. switching the second driven roller to a pressurized state by a switching means to start oblique feeding of the sheet by the second oblique feeding roller pair;
A sheet conveying device characterized by: After the first driven roller is in a pressurized state and the second driven roller is in a released state, the control means starts skew feeding of the sheet by the first pair of skew feeding rollers, While maintaining the driven roller in the pressurized state, the second switching means switches the second driven roller to the pressurized state, and the sheet is skew-fed by the first skew-feed roller pair and the second skew-feed roller pair. ,
2. The sheet conveying apparatus according to claim 1, wherein: Equipped with a detection means for detecting the leading edge of the sheet,
The control means switches the first driven roller from the released state to the pressurized state by the first switching means based on detection of the leading edge of the sheet by the detection means.
3. The sheet conveying apparatus according to claim 1, wherein: The angle of the first direction with respect to the sheet conveying direction is at least twice the angle of the second direction with respect to the sheet conveying direction, and the angle of the first direction with respect to the sheet conveying direction is 20 degrees or more and 40 degrees. is the following
The sheet conveying device according to any one of claims 1 to 3, characterized in that: The first skew-feeding roller and the second skew-feeding roller are arranged so as to partially overlap each other when viewed from the width direction.
The sheet conveying device according to any one of claims 1 to 4, characterized in that: a second conveying roller arranged downstream of the first pair of skew-feeding rollers and the second pair of skew-feeding rollers in the sheet conveying direction and configured to convey the sheet;
After the first driven roller is put in a pressurized state and the first skew feeding roller starts skew feeding the sheet, the control means controls the control unit to perform the sheet feeding before the leading edge of the sheet in the sheet feeding direction reaches the second feeding roller. , switching the first driven roller from the pressurized state to the released state;
The sheet conveying device according to any one of claims 1 to 5, characterized in that: A sheet conveying device according to any one of claims 1 to 6;
image forming means for forming an image on a sheet conveyed by the sheet conveying device;
An image forming apparatus characterized by:

Images