Sheet conveyance device and image forming device

Abstract

To improve correction accuracy of the positional deviation of a sheet.SOLUTION: A sheet conveyance device includes: a drive roller; steering means for changing a tilt angle of a rotation axis of the drive roller; a driven roller constituted so as to rotate around a rotation axis following the change in the tilt angle of the drive roller; a contact separation mechanism for switching the drive roller and the driven roller between a contact state and a separated state; first detection means for detecting the vibration of the driven roller; second detection means for detecting the positional deviation of a sheet; and control means for executing a correction operation for correcting the positional deviation of the sheet. The control means executes predetermined processing for starting a correction operation after the drive roller and the driven roller are switched into the contact state from the separated state and after the vibration of the driven roller in the rotation direction converges within a predetermined range, based on the detection result of the first detection means.SELECTED DRAWING: Figure 13

Description

[Technical Field]

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

[0002] Patent Document 1 describes a sheet conveying device that roughly adjusts the amount of skew of the paper in a first skew correction unit, and then finely adjusts the amount of skew of the paper in a second skew correction unit. Patent Document 2 describes a conveying device that controls positional deviations in the width direction and rotation direction of a sheet sandwiched between a pair of clamping rollers by sliding a holding member that holds the pair of clamping rollers in the width direction and rotating the holding member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-252918 [Patent Document 2] Japanese Patent Application Publication No. 2018-199572 Summary of the Invention [Problem to be solved by the invention]

[0004] As a mechanism for correcting sheet misalignment (including skew, which is misalignment in the rotational direction), a configuration has been considered that has a drive roller whose rotation axis can be changed and a driven roller that can rotate following the drive roller, and the drive roller and the driven roller come into contact with and separate from each other. However, there is a possibility that the accuracy of correcting misalignment will decrease due to vibration of the driven roller in the rotational direction when the drive roller and the driven roller come into contact with each other.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet conveying device and an image forming apparatus that are capable of improving the accuracy of correcting misalignment of a sheet. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet conveying device including a drive roller that rotates by receiving a driving force, a steering device that changes the inclination angle of the rotation axis of the drive roller with respect to a sheet width direction that is perpendicular to a sheet conveying direction, a driven roller that sandwiches and conveys a sheet together with the drive roller, the driven roller being configured to rotate around a rotation axis that intersects both the sheet conveying direction and the sheet width direction in accordance with changes in the inclination angle of the drive roller, and a contact / separation mechanism that switches the drive roller and the driven roller between a contact state in which the drive roller and the driven roller are in contact with each other and a separation state in which the drive roller and the driven roller are separated from each other. a first detection means for detecting vibration of the driven roller in the rotation direction around the rotation axis; a second detection means for detecting positional deviation of the sheet; and a control means for executing a correction operation to correct the positional deviation of the sheet based on the detection result of the second detection means, wherein the control means executes a predetermined process for starting the correction operation after the drive roller and the driven roller are switched from the separated state to the abutting state and after the vibration of the driven roller in the rotation direction has converged to within a predetermined range based on the detection result of the first detection means. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a sheet conveying device and an image forming apparatus that can improve the accuracy of correcting the positional deviation of a sheet. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an inkjet recording apparatus according to a first embodiment. [Figure 2] FIG. 2 is a top view of the register unit according to the first embodiment. [Figure 3] FIG. 2 is a perspective view of a register unit according to the first embodiment. [Figure 4] 2A to 2E are explanatory views of a register unit according to the first embodiment. [Figure 5] FIG. 2 is a cross-sectional view of the register unit according to the first embodiment. [Figure 6] 1A is a diagram showing a contact and separation mechanism for a caster roller according to a first embodiment, and FIG. 1B is a top view of the caster roller. [Figure 7] FIG. 2 is a block diagram showing a control system according to the first embodiment. [Figure 8] 5A to 5E are explanatory diagrams of skew correction according to the first embodiment. [Figure 9] 3A to 3E are explanatory diagrams of lateral deviation correction according to the first embodiment. [Figure 10] 3A and 3B are explanatory diagrams of lateral deviation correction according to the first embodiment. [Figure 11] 5A to 5D are conceptual diagrams of control for simultaneously correcting skew and lateral deviation according to the first embodiment. [Figure 12] 5A and 5B are explanatory diagrams of control for simultaneously correcting skew and lateral deviation according to the first embodiment. [Figure 13] 4 is a flowchart showing a control example according to the first embodiment. [Figure 14] 5A and 5B are diagrams showing an example of transition of the turning angle of the caster roller according to the first embodiment. [Figure 15] 10 is a flowchart showing a control example according to the second embodiment. [Figure 16] FIG. 10 is an explanatory diagram of an optical sensor according to a third embodiment. [Figure 17] 10A and 10B are diagrams showing an example of transition of the turning angle of the caster roller according to the fourth embodiment. [Figure 18] 10 is a flowchart showing a control example according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] In this disclosure, the term "image forming apparatus" refers to a general device that forms an image on a sheet of recording material (recording medium), and includes at least a single-function printer, a copying machine, a multifunction machine, and a large commercial printing machine. Furthermore, the term "image forming apparatus" is not limited to the inkjet recording apparatus described in the following embodiments, but may also be an electrophotographic image forming apparatus equipped with an electrophotographic image forming engine as an image forming means, or may be one that uses another method (for example, offset printing).

[0011] First Embodiment 1 is a schematic diagram showing an example of the general configuration of an inkjet recording apparatus 1 as an image forming apparatus according to a first embodiment. This inkjet recording apparatus 1 is a sheet-fed inkjet recording apparatus that produces a recorded matter by forming an ink image on a sheet S using two liquids: a reaction liquid and ink. The sheet S, which is the recording material (recording medium), can be a variety of sheet materials of different sizes and materials, including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic film, cloth, etc.

[0012] 1, the inkjet recording apparatus 1 of this embodiment includes a feeding module 1000, a printing module 2000, a drying module 3000, a fixing module 4000, and a cooling module 5000. The inkjet recording apparatus 1 of this embodiment also includes a reversing module 6000 and a stacking module 7000. A cut sheet S supplied from the feeding module 1000 is transported along a transport path, processed in each module, and stacked in the stacking module 7000.

[0013] The feeding module 1000 includes three storage cabinets 1100a, 1100b, and 1100c, each of which stores sheets S. The storage cabinets 1100a to 1100c can each be pulled out toward the front of the apparatus relative to the housing of the feeding module 1000. The feeding module 1000 feeds the sheets S stored in each of the storage cabinets 1100a to 1100c one by one using a separation belt and a transport roller, and transports the sheets to the print module 2000. The number of storage cabinets 1100a to 1100c is not limited to three, and may be one, two, four, or more.

[0014] The print module 2000 has a registration unit (hereinafter referred to as the registration unit 100), a print belt unit 200, and a recording section 300. Hereinafter, registration may be abbreviated to "registration." The sheet S conveyed from the feeding module 1000 is conveyed to the print belt unit 200 after the registration unit 100 corrects the positional deviation of the sheet S.

[0015] The register unit 100 (and the drive source, power supply, control unit, etc. required for the operation of the register unit 100) is an example of a sheet conveying device that conveys the sheet S. The print module 2000 or the inkjet recording device 1 is an example of an image forming device (image forming system) that includes the register unit 100 (sheet conveying device) and a recording unit 300 as an image forming means.

[0016] In this embodiment, the "positional deviation" of the sheet S includes both the positional deviation of the sheet S in the sheet width direction (hereinafter referred to as "lateral deviation") and the positional deviation of the sheet S in the rotational direction when viewed in the thickness direction of the sheet S (hereinafter referred to as "skew"). Correcting the skew of the sheet S is called skew correction. Correcting the lateral deviation of the sheet S and aligning it to a desired position in the sheet width direction is called lateral registration. As will be described later, the registration unit 100 of this embodiment performs a correction operation multiple times to simultaneously correct both the skew and lateral deviation of the sheet S. Note that the registration unit 100 may correct only either the lateral deviation or the skew, or may perform the correction operation only once.

[0017] The print belt unit 200 includes a breathable print belt 225 stretched over multiple rollers, and a pump unit that generates negative pressure in the space inside the print belt 225. The recording unit 300 is a sheet processing unit (image forming unit) that performs a recording process (printing) on ​​the conveyed sheet S from above using a recording head to form an image on the sheet S. The print belt unit 200 conveys the sheet S while adsorbing it onto the print belt 225, thereby ensuring clearance between the recording head and the sheet S. Multiple recording heads are arranged along the conveyance direction. In this embodiment, in addition to the four colors of Y (yellow), M (magenta), C (cyan), and Bk (black), the unit has a total of five line-type recording heads corresponding to the reaction liquids.

[0018] The number of colors and recording heads is not limited to five. The inkjet method can be a method using a heating element, a piezoelectric element, an electrostatic element, or a MEMS (microelectromechanical system) element. Each color of ink is supplied to the recording head from an ink tank via an ink tube. The sheet S on which an image is formed in the recording unit 300 is transported by the print belt unit 200, and an in-line scanner located downstream of the recording unit in the transport direction detects misalignment and color density of the image formed on the sheet S, allowing the printed image to be corrected.

[0019] The drying module 3000 includes a decoupling section 3200, a drying belt unit 3300, and a hot air blowing section 3400. The drying module 3000 reduces the liquid content of the ink applied to the sheet S by the recording section 300, improving the fixation of the ink to the sheet S. The sheet S, on which an image has been formed by the recording section 300 of the print module 2000, is transported to the decoupling section 3200 located within the drying module 3000. The decoupling section 3200 transports the sheet S using air pressure from above and belt friction. By loosely holding the sheet S on the belt, the sheet S on the belt is prevented from shifting on the print belt unit 200 where the ink image is formed. The sheet S transported from the decoupling section 3200 is adsorbed and transported by the drying belt unit 3300, and simultaneously, hot air is blown from the hot air blowing section 3400 located above the belt to dry the ink-applied surface of the sheet S. In addition to the method of applying hot air, the drying method may be a combination of a method of irradiating the surface of the sheet S with electromagnetic waves (ultraviolet rays, infrared rays, etc.) or a conductive heat transfer method using contact with a heating element.

[0020] The fixing module 4000 has a fixing belt unit 4100 equipped with an upper belt unit and a lower belt unit. The fixing module 4000 can fix the ink to the sheet S by passing the sheet S conveyed from the drying module 3000 between the heated upper belt unit and lower belt unit.

[0021] The cooling module 5000 has multiple cooling units 5100, which cool the high-temperature sheet S transported from the fixing module 4000. The cooling units 5100 use a fan to draw in outside air into the cooling box, increasing the pressure inside the cooling box, and then blow air from nozzles formed in the transport guide onto the sheet S, thereby cooling the sheet S. The cooling units 5100 are arranged on both sides of the transport path, allowing the sheet S to be cooled from both sides. A transport path switching unit is also arranged within the cooling module 5000. The transport path switching unit switches the transport path of the sheet S between a path for transporting the sheet S to the inversion module 6000 and a duplex transport path used during duplex printing. During duplex printing, the sheet S with an image formed on its first side is transported to the transport path below the cooling module 5000 and then transported through each of the duplex transport paths of the fixing module 4000, the drying module 3000, the print module 2000, and the feeding module 1000. Then, the sheet S is conveyed again to the register unit 100, print belt unit 200 and recording section 300 of the print module 2000, where an image is formed on the second side opposite to the first side.

[0022] The double-sided conveying section of the fixing module 4000 is provided with a first reversing section 4200 that reverses the front and back of the sheet S. The reversing module 6000 also has a second reversing section that can reverse the front and back of the sheet S being conveyed, and can freely change the front and back orientation of the sheet S being discharged.

[0023] The stacking module 7000 has a top tray 7200 and a stacking portion 7500, and stacks the sheets S conveyed from the reversing module 6000 while aligning them.

[0024] (Register unit) An overview of the register unit 100 will now be described. Fig. 2 is a top view showing the register unit 100. Fig. 3 is a perspective view showing the register unit 100. Figs. 4(a) to 4(e) are explanatory diagrams relating to the operation of the register rollers 109 and 110. Fig. 5 is a cross-sectional view of the register unit 100 in a plane perpendicular to the sheet width direction. Figs. 6(a) and 6(b) are schematic diagrams showing the configuration of caster rollers 120 and 121 (driven rollers).

[0025] In the following description and drawings, the conveying direction of the sheet S in the register unit 100 is called the sheet conveying direction, and is represented by an arrow X in the drawings. The sheet width direction perpendicular to the sheet conveying direction is represented by an arrow Z in the drawings. With respect to the sheet width direction (Z), the left side (the tip side of the arrow Z, the +Z side) when viewed toward the sheet conveying direction (X) is expressed as "left," and the right side (the opposite side of the arrow Z, the -Z side) is expressed as "right." Furthermore, the direction perpendicular to both the sheet conveying direction (X) and the sheet width direction (Z) is represented by an arrow Y in the drawings.

[0026] In the registration unit 100, a pair of registration rollers (109, 110) may be used to skew the sheet S in order to correct the sheet position in the sheet width direction. The "sheet conveying direction (X)" is a fixed direction regardless of whether the sheet S is skewed or not. Specifically, the sheet conveying direction (X) in this embodiment is parallel to the conveying direction of the sheet S by conveying members that convey the sheet S without skew on the upstream and downstream sides of the pair of registration rollers (109, 110). An example of a conveying member on the upstream side of the pair of registration rollers (109, 110) is the below-described pair of conveying rollers (118, 119), and an example of a conveying member on the downstream side is the below-described print belt 225.

[0027] 2, 3, and 5, the register unit 100 includes pairs of conveying rollers 118 and 119, register rollers 109 and 110, caster rollers 120 and 121, conveying drive motors 105 and 106, and steering motors 107 and 108. The register unit 100 also includes image sensors 101 and 102, pre-register sensors 131 and 132, first register sensors 103 and 104, second register sensors 122 and 123, and turning angle sensors 133 and 134.

[0028] The registration rollers 109 and 110 are both examples of drive rollers that rotate under a driving force. The caster rollers 120 and 121 are both examples of driven rollers that sandwich and transport a sheet together with the drive roller. If the registration roller 109 and caster roller 120 on one side in the sheet width direction (Z) are referred to as the first drive roller and first driven roller, the registration roller 110 and caster roller 121 on the other side can be referred to as the second drive roller and second driven roller.

[0029] The registration rollers 109 and 110, the caster rollers 120 and 121, the transport drive motors 105 and 106, and the steering motors 107 and 108 are arranged one on each of the left and right sides. Similarly, the image sensors 101 and 102, the pre-registration sensors 131 and 132, the first registration sensors 103 and 104, the second registration sensors 122 and 123, and the turning angle sensors 133 and 134 are arranged one on each of the left and right sides.

[0030] In the sheet conveying direction (X), a conveying roller pair 119 is disposed downstream of the conveying roller pair 118, a registration roller pair (109, 110, 120, 121) is disposed downstream of the conveying roller pair 119, and a print belt unit 200 is disposed downstream of the registration roller pair. Each of the conveying roller pairs 118 and 119 is formed by an upper roller, which is a rubber roller, and a lower roller that abuts against the upper roller. The upper roller is driven to rotate by a motor. The lower roller is biased toward the upper roller by a spring and rotates following the upper roller.

[0031] The registration rollers 109, 110 and the caster rollers 120, 121 form a pair of rollers (a registration roller pair) that sandwich and transport the sheet S. In this embodiment, the left registration roller 109 and the left caster roller 120 form a left registration roller pair, and the right registration roller 110 and the right caster roller 121 form a right registration roller pair.

[0032] The registration rollers 109 and 110 are rubber rollers (elastic rollers) having outer peripheries made of, for example, polyurethane. The left registration roller 109 is rotated by a left conveyance drive motor 105, and the right registration roller 110 is rotated by a right conveyance drive motor 106.

[0033] Furthermore, the steering angle of the left registration roller 109 is changed by the left steering motor 107. The steering angle of the right registration roller 110 is changed by the right steering motor 108. By changing the steering angles of the registration rollers 109 and 110, a component in the sheet width direction (Z) is generated in the conveying force that the registration rollers 109 and 110 apply to the sheet S, so that the sheet S can be conveyed (obliquely fed) obliquely with respect to the sheet conveying direction (X).

[0034] The steering angle of the registration rollers 109, 110 is the inclination angle of the rotation axis of the roller with respect to the sheet width direction (Z) when viewed in the Y direction, which is perpendicular to both the sheet conveyance direction (X) and the sheet width direction (Z). The steering angle can also be referred to as the angle between the sheet conveyance direction (X) and the direction of movement of the roller surface at the contact point with the sheet S, or the inclination angle of the vector of the force (conveyance force) applied to the sheet S by the registration rollers 109, 110 with respect to the sheet conveyance direction (X). In the following description, the "pivot" of the roller refers to the movement in which the steering angle of the roller changes as the rotation axis of the roller rotates around an axis that intersects both the sheet width direction (Z) and the sheet conveyance direction (X). The above "intersecting axis" is, for example, an axis parallel to the Y direction, but it does not necessarily have to be parallel to the Y direction.

[0035] The left caster roller 120 is a driven roller that rotates following the left registration roller 109. The right caster roller 121 is a driven roller that rotates following the right registration roller 110. The caster roller 120 can rotate following the rotation of the registration roller 109. The caster roller 121 can rotate following the rotation of the registration roller 110. In other words, the caster rollers 120, 121 (driven rollers) are configured to rotate around a rotation axis that intersects with both the sheet conveyance direction and the sheet width direction, following changes in the inclination angle of the registration rollers 109, 110 (drive rollers). In this embodiment, the rotation axis is parallel to the Y direction.

[0036] For each of the caster rollers 120, 121, the inclination angle of the roller's rotation axis relative to the sheet width direction (Z) is defined as the "swivel angle." The left swivel angle sensor 133 detects the swivel angle of the left caster roller 120, and the right swivel angle sensor 134 detects the swivel angle of the right caster roller 121. Both the swivel angle sensors 133, 134 function as first detection means for detecting vibration of the caster rollers 120, 121 (driven rollers) in the swivel direction around the swivel axis.

[0037] (Skew detection unit) A set of two or more sensors arranged at different positions in the sheet width direction (Z) can function as a skew detection unit for detecting the amount of skew of the sheet S. The "amount of skew" corresponds to the angle of inclination of the leading edge of the sheet S (the downstream end in the sheet conveying direction) relative to the sheet width direction (Z).

[0038] The pair of left and right pre-registration sensors 131 and 132, the pair of left and right first registration sensors 103 and 104, and the pair of left and right second registration sensors 122 and 123 are all examples of detection means for detecting misalignment of the sheet S. In this embodiment, the pair of left and right pre-registration sensors 131 and 132, the pair of left and right first registration sensors 103 and 104, and the pair of left and right second registration sensors 122 and 123 are skew detection units that detect skew, which is misalignment in the rotational direction of the sheet S. When the pair of second registration sensors 122 and 123 is defined as the second detection means, the pair of first registration sensors 103 and 104 can be called the third detection means, and the upstream pre-registration sensors 131 and 132 can be called the fourth detection means.

[0039] The skew detection unit can also be said to be a posture detection unit that detects the posture of the sheet S. The posture of the sheet S is the angle of inclination of the leading edge of the sheet S with respect to the sheet width direction (Z).

[0040] A controller 50 (FIG. 7), which will be described later, calculates the amount of skew of the sheet S at the position of the pre-registration sensors 131 and 132 (first position) based on the time difference between the timings at which the left and right pre-registration sensors 131 and 132 detect the leading edge of the sheet. Similarly, the controller 50 calculates the amount of skew of the sheet S at the position of the first registration sensors 103 and 104 (second position) based on the time difference between the detection of the leading edge of the sheet by the left and right first registration sensors 103 and 104. The controller 50 calculates the amount of skew of the sheet S at the position of the second registration sensors 122 and 123 (third position) based on the time difference between the detection of the leading edge of the sheet by the left and right second registration sensors 122 and 123. Note that instead of a set of two or more sensors, for example, an image sensor (a line sensor or an area sensor) may be used as the light blocking detection unit.

[0041] (Lateral deviation detection unit) The pair of image sensors 101 and 102 is an example of a detection means (second detection means) for detecting positional misalignment of the sheet S. In this embodiment, the pair of image sensors 101 and 102 is a lateral misalignment detection unit that detects lateral misalignment, which is positional misalignment of the sheet S in the sheet width direction (Z).

[0042] The image sensors 101 and 102 are disposed near the pair of registration rollers (109, 110, 120, 121). The image sensors 101 and 102 are line sensors having an imaging area extending in the sheet width direction (Z). The left image sensor 101 detects the position of the left edge of the sheet S, and the right image sensor 102 detects the position of the right edge of the sheet S. The image sensors 101 and 102 are disposed so as to be able to detect the side edges of the maximum and minimum size sheets on which the inkjet recording apparatus 1 can form an image. The controller 50 can calculate the amount of lateral deviation based on the detection results of the side edge positions by the left and right image sensors 101 and 102.

[0043] It should be noted that a single image sensor that covers an area (maximum paper passing area) through which the largest size sheet S passes in the sheet width direction (Z) may be used instead of the two image sensors 101 and 102. Also, only one of the left and right image sensors 101 and 102 may be used to detect the amount of lateral deviation and correct the lateral deviation based on the detection result of the side edge position on one side.

[0044] . (controller) FIG. 7 is a block diagram showing a configuration related to control of the registration unit 100. The operation of the registration unit 100 is controlled by a controller 50 serving as a control means. The controller 50 is connected to a ROM 51 and a RAM 52 serving as storage units. The controller 50 controls the operation of the registration unit 100 by reading a program stored in the ROM 51 based on an instruction from, for example, an external computer 201, and executing the program while using the RAM 52 as a work memory. The controller 50 may be a control unit that oversees the operation of the entire print module 2000. Note that some or all of the functions of the controller 50 described below may be executed by another control unit provided in the inkjet recording apparatus 1.

[0045] The controller 50 receives detection signals from the image sensors 101 and 102, the pre-registration sensors 131 and 132, the first registration sensors 103 and 104, the second registration sensors 122 and 123, and the turning angle sensors 133 and 134. The controller 50 also issues instructions to the feed motor 54, the steering motors 107 and 108, the conveyance drive motors 105 and 106, and the separation motor 138 to control the start / stop, rotation amount, angular velocity, etc. of each motor. The feed motor 54 is a drive source for the separation belt, etc. in the feed module 1000.

[0046] The controller 50 is also communicably connected to an operation unit 202, which is a user interface of the inkjet recording apparatus 1. The operation unit 202 includes a display unit such as a liquid crystal panel that displays information to the user by means of images, and an input unit such as buttons and a touch panel function of the liquid crystal panel that accepts input from the user.

[0047] As will be described below, the controller 50 executes a correction operation to correct the positional deviation of the sheet S based on the detection results of the skew detection unit and the lateral deviation detection unit. The controller 50 corrects the lateral deviation of the sheet S by controlling the rotation amount of the steering motors 107 and 108 mainly based on the detection results of the image sensors 101 and 102. The controller 50 also corrects the skew of the sheet S by controlling the angular velocities of the left and right conveyance drive motors 105 and 106 mainly based on the detection results of the pre-registration sensors 131 and 132, the first registration sensors 103 and 104, and the second registration sensors 122 and 123.

[0048] The controller 50 also uses a separation motor 138 to bring the left and right caster rollers 120, 121 into contact with and separate from the registration rollers 109, 110. The controller 50 also detects the turning angles of the left and right caster rollers 120, 121 and vibrations in the turning direction (vibrations of the turning angle) based on the detection results of the left and right turning angle sensors 133, 134.

[0049] (skew correction) The following describes skew correction of the sheet S in the registration unit 100. As shown in FIGS. 4(a) and (b), in this embodiment, conveyance drive motors 105 and 106 are provided for the left and right registration rollers 109 and 110, respectively. Therefore, it is possible to independently control the conveyance speeds LV and RV (mm / sec) of the left and right registration rollers 109 and 110 (FIGS. 4(c) and (d)). The conveyance speeds LV and RV of the registration rollers 109 and 110 refer to the peripheral speeds at the nip portions with the caster rollers 120 and 121.

[0050] When the sheet S is skewed, the controller 50 corrects the skew of the sheet S by generating a speed difference between the left and right registration rollers 109 and 110. The controller 50 of this embodiment calculates the amount of skew of the sheet S based on the detection result of the skew detection unit described above, and determines a skew correction profile based on the calculated amount of skew.

[0051] 8(a), the controller 50 calculates the skew amount ΔX of the sheet S based on the time difference between the passage timing of the leading edge of the sheet detected by the left and right sensors (e.g., first registration sensors 103 and 104) in the skew detection unit and the conveying speed of the sheet S. In the illustrated example, the skew amount ΔX is defined as the distance (mm) by which the leading edge position of the sheet at the position (Z direction position) of the left registration roller 109 lags behind or leads the leading edge position of the sheet at the position (Z direction position) of the right registration roller 110.

[0052] Here, the component of the conveying speed LV of the left registration roller 109 in the sheet conveying direction (X) is the X-direction speed LVx (mm / sec) of the registration roller 109, and the component of the conveying speed LV in the sheet width direction (Z) is the Z-direction speed LVz (mm / sec) of the registration roller 109. Similarly, the component of the conveying speed RV of the right registration roller 110 in the sheet conveying direction (X) is the X-direction speed RVx (mm / sec) of the registration roller 110, and the component of the conveying speed RV in the sheet width direction (Z) is the Z-direction speed RVz (mm / sec) of the registration roller 110.

[0053] The skew correction profile in this embodiment is time-series data of the X-direction velocities LVx and RVx of the left and right registration rollers 109 and 110. As shown in Fig. 8(b), the skew of the sheet S can be corrected by independently driving the registration rollers 109 and 110 so that a difference occurs in the X-direction velocities LVx and RVx between the left and right registration rollers 109 and 110. In the illustrated example, the difference between LVx and RVx causes the sheet S to be conveyed while turning clockwise in the drawing, thereby reducing the skew amount ΔX.

[0054] Examples of skew correction profiles are shown in Figures 8(c) to 8(e). Figure 8(c) shows an example profile when the skew amount ΔX calculated based on the detection results of the skew detection unit is 15 mm (the left side is delayed by 15 mm). Figure 8(d) shows an example profile when the skew amount ΔX is 10 mm, and Figure 8(e) shows an example profile when the skew amount ΔX is 5 mm.

[0055] The skew correction profile is preferably created so that the time integral of the difference between the X-direction velocities LVx and RVx of the registration rollers 109 and 110 is approximately equal to the skew amount ΔX. For example, a reference profile is prepared in advance assuming that the skew amount ΔX is a preset reference amount ΔX0. The reference profile is time-series data of the differences ΔLVx and ΔRVx between the X-direction velocities LVx and RVx relative to the process speed (the peripheral speed of the print belt 225). The reference profile is set so that the time integral of the difference between the left and right X-direction velocities LVx and RVx (LVx - RVx) is equal to the reference amount ΔX0 (i.e., so as to exactly cancel the skew of the reference amount ΔX0). Then, a skew correction profile corresponding to the skew amount ΔX can be created by multiplying the ΔLVx and ΔRVx of the reference profile by a coefficient equal to the ratio of the skew amount ΔX calculated based on the detection results of the skew detection unit to the reference amount ΔX0 and adding the result to the reference speed.

[0056] The above is an example of calculating the skew correction profile, and other calculation methods may be used as long as the time integral of the difference between the X-direction velocities LVx and RVx of the registration rollers 109 and 110 is approximately equal to the absolute value of the skew amount ΔX. Also, Figures 8(c) to 8(e) show examples of skew correction profiles in which the graphs of LVx and RVx form smooth curves (i.e., the acceleration does not change discontinuously). However, a skew correction profile in which the graphs of LVx and RVx form broken lines (triangular or trapezoidal) may also be used.

[0057] (lateral deviation correction) 9(a) to 9(e), the correction of lateral deviation of the sheet S in the registration unit 100 will be described. As described above, the steering angles of the left and right registration rollers 109 and 110 are changed by the corresponding steering motors 107 and 108, respectively.

[0058] Specifically, as shown in FIGS. 2 and 3, the left registration roller 109 can rotate around a steering shaft 115 extending in the Y direction, and the right registration roller 110 can rotate around a steering shaft 116 extending in the Y direction. A fan-shaped input gear 111 is attached to each of the steering shafts 115 and 116, and output gears 112 of the steering motors 107 and 108 are meshed with the input gear 111. Therefore, the rotation of the steering motors 107 and 108 rotates the left and right registration rollers 109 and 110, changing the steering angle (see FIGS. 4(b) and 4(e)). The conveyance drive motors 105 and 106 also rotate around the steering shafts 115 and 116 together with the corresponding registration rollers 109 and 110.

[0059] The steering motor 107 is an example of a steering means (first steering means) that changes the inclination (steering angle) of the rotation axis of the registration roller 109 with respect to the sheet width direction (Z). The steering motor 108 is an example of a steering means (second steering means) that changes the inclination (steering angle) of the rotation axis of the registration roller 110 with respect to the sheet width direction (Z). The steering motors 107, 108, the input gear 111, the output gear 112, and the steering shafts 115, 116 constitute a steering mechanism that changes the steering angles of the registration rollers 109, 110.

[0060] The controller 50 calculates the lateral deviation amount ΔZ of the sheet S based on the position of the sheet S in the sheet width direction (Z) detected by the left and right image sensors 101 and 102 (FIG. 9A). The lateral deviation amount is the deviation amount of the actual position of the sheet S from a target position in the sheet width direction (Z). In this embodiment, the sheet S is registered horizontally based on the center. That is, the target position in this embodiment is the center position of the conveyance path of the sheet S in the registration unit 100 (hereinafter referred to as the conveyance center Zc). The lateral deviation amount is the deviation amount of the position of the sheet S in the sheet width direction (Z) based on the conveyance center Zc. Specifically, in this embodiment, the distance in the sheet width direction (Z) from the conveyance center Zc to the center of the left and right side edges of the sheet S detected by the image sensors 101 and 102 (hereinafter referred to as the sheet center Zs) is defined as the lateral deviation amount ΔZ of the sheet S.

[0061] The controller creates a lateral deviation correction profile based on the calculated lateral deviation amount ΔZ. In this embodiment, the lateral deviation correction profile is time-series data of the Z-direction velocities LVz and RVz (FIG. 9B) of the left and right registration rollers 109 and 110.

[0062] 9(c) to 9(e) show examples of lateral deviation correction profiles. Fig. 9(c) shows an example profile when the lateral deviation ΔZ calculated based on the detection results of image sensors 101 and 102 is 15 mm (shifted 15 mm to the left). Fig. 9(d) shows an example profile when the lateral deviation ΔZ is 10 mm, and Fig. 9(e) shows an example profile when the lateral deviation ΔZ is 5 mm.

[0063] First, for simplicity, let us consider the case where only lateral deviation correction is performed without skew correction. In this case, the conveying speeds LV and RV of the left and right registration rollers 109 and 110 are the same, and the steering angles of the left and right registration rollers 109 and 110 are always equal (FIGS. 4(a) and 4(c)).

[0064] The lateral deviation correction profile is preferably created so that the time integral of the Z-direction velocities LVz and RVz of the registration rollers 109 and 110 is approximately equal to the lateral deviation amount ΔZ. For example, a reference profile is prepared in advance when the lateral deviation amount ΔZ is a reference amount ΔZ0. The reference profile is time-series data of the Z-direction velocity Vz. The reference profile is set so that the time integral of the Z-direction velocity Vz is equal to the reference amount ΔZ0 (i.e., so as to exactly cancel the lateral deviation of the reference amount ΔZ0). Then, a lateral deviation correction profile corresponding to the lateral deviation amount ΔZ can be created by multiplying the Vz of the reference profile by a coefficient that is the ratio of the lateral deviation amount ΔZ calculated based on the detection results of the image sensors 101 and 102 to the reference amount ΔZ0, and setting this value as the Z-direction velocity LVz and RVz.

[0065] The above is an example of calculating the lateral deviation correction profile, and other calculation methods may be used as long as they result in the time integral value of the Z-direction velocities LVz and RVz of the registration rollers 109 and 110 being approximately equal to the lateral deviation amount ΔZ. Also, Figures 9(c) to 9(e) show examples of lateral deviation correction profiles in which the graphs of LVz and RVz form smooth curves (i.e., the acceleration does not change discontinuously). However, a lateral deviation correction profile in which the graphs of LVz and RVz form broken lines (triangular or trapezoidal) may also be used.

[0066] When lateral misalignment correction and skew correction are not performed simultaneously, it is desirable that the X-direction speeds LVx and RVx of the registration rollers 109 and 110 are equal to the conveying speed of the print belt unit 200 located downstream of the registration unit 100. The conveying speed of the print belt unit 200 is the circumferential speed of the print belt 225, which is the processing speed (process speed) of the recording process by the recording unit 300.

[0067] As described above, when lateral misalignment correction and skew correction are not performed simultaneously, the Z-direction speeds LVz and RVz of the registration rollers 109 and 110 are determined according to the lateral misalignment amount ΔZ, and the X-direction speeds LVx and RVx of the registration rollers 109 and 110 are set to the same conveying speed as the print belt unit 200. As shown in FIG. 9C, the X-direction speed LVx and the Z-direction speed LVz can be converted into the steering angle Lθ and conveying speed LV of the left registration roller 109 using trigonometric functions. In addition, the X-direction speed RVx and the Z-direction speed RVz can be converted into the steering angle Rθ and conveying speed RV of the right registration roller 110 using trigonometric functions.

[0068] When the Z-direction velocities LVz, RVz and the X-direction velocities LVx, RVx per unit time (FIG. 10(a)) are converted into steering angles Lθ, Rθ and conveying speeds LV, RV, time-series data of the steering angles Lθ, Rθ and conveying speeds LV, RV (FIG. 10(b)) are obtained. The upper part of FIG. 10(b) shows time-series data of the conveying speeds LV, RV of the registration rollers 109, 110, i.e., the operation profile of the conveying drive motors 105, 106. The lower part of FIG. 10(b) shows time-series data of the steering angles Lθ, Rθ of the registration rollers 109, 110, i.e., the operation profile of the steering motors 107, 108. When a lateral deviation amount ΔZ is given, the lateral deviation of the sheet S can be corrected by operating the conveying drive motors 105, 106 and the steering motors 107, 108 according to these operation profiles.

[0069] (simultaneous correction of skew and lateral deviation) In the above explanation, skew correction and lateral deviation correction have been described separately, but the registration unit 100 can simultaneously perform skew correction and lateral deviation correction using the registration rollers 109 and 110. In other words, the controller 50 can simultaneously perform control (active registration) to correct skew of the sheet S mainly by controlling the speed difference between the registration rollers 109 and 110, and control (steering operation) to correct lateral deviation of the sheet S mainly by controlling the tilt angle of the registration rollers 109 and 110. Note that correcting skew and lateral deviation "simultaneously" means that the period during which the sheet S is turned for skew correction and the period during which the sheet S is moved in the sheet width direction for lateral deviation correction at least partially overlap.

[0070] 11(a) to 11(d) are conceptual diagrams of control for simultaneously performing skew correction and lateral deviation correction. As explained in the section on lateral deviation correction, if a lateral deviation amount ΔZ is given, the Z-direction speeds LVz and RVz of the registration rollers 109 and 110 per unit time are determined as a lateral deviation correction profile (FIG. 11(a)). Also, as explained in the section on skew correction, if a skew amount ΔX is given, the X-direction speeds LVx and RVx of the registration rollers 109 and 110 per unit time are determined as a skew correction profile (FIG. 11(b)).

[0071] The Z-direction velocities LVz and RVz in FIG. 11(a) can be said to represent the Z-direction component of the vector of the conveying force that the registration rollers 109 and 110 should impart to the sheet S (vector determined by the steering angles Lθ and Rθ and the conveying speeds LV and RV). Similarly, the X-direction velocities LVx and RVx in FIG. 11(b) can be said to represent the X-direction component of the vector of the conveying force that the registration rollers 109 and 110 should impart to the sheet S. Combining the Z-direction velocities LVz and RVz with the X-direction velocities LVx and RVx per unit time yields the conveying force vectors (LVx, LVz) and (RVx, RVz) that the left and right registration rollers 109 and 110 should impart to the sheet S at each point in time. Converting these Cartesian coordinate system vectors (LVx, LVz) and (RVx, RVz) into polar coordinate system vectors (LV, Lθ) and (RV, Rθ) yields time-series data of the steering angles Lθ and Rθ and the conveying speeds LV and RV (FIG. 11(d)).

[0072] Figure 12(a) is a time-series profile of the Z-direction velocities LVz and RVz and the X-direction velocities LVx and RVx in Figure 11(c). Figure 12(b) is a conversion of Figure 12(a) into steering angles Lθ and Rθ and conveying speeds LV and RV. The upper part of Figure 12(b) is time-series data of the conveying speeds LV and RV of the registration rollers 109 and 110, i.e., the operation profile of the conveying drive motors 105 and 106. The lower part of Figure 12(b) is time-series data of the steering angles Lθ and Rθ of the registration rollers 109 and 110, i.e., the operation profile of the steering motors 107 and 108.

[0073] By performing the above-described processing, the controller 50 creates operation profiles for the conveyance drive motors 105, 106 and the steering motors 107, 108 based on the lateral deviation amount ΔZ and the skew amount ΔX. Then, the controller 50 controls the operations of the conveyance drive motors 105, 106 and the steering motors 107, 108 in accordance with the created operation profiles, thereby making it possible to simultaneously correct the skew and lateral deviation of the sheet S.

[0074] (caster roller contact / separation configuration) The configuration relating to contact and separation of the caster rollers 120, 121 will be described. Fig. 6(a) is a diagram showing the left caster roller 120 and contact / separation mechanism 140 as viewed in the seat width direction (Z). Fig. 6(b) is a diagram showing the caster roller 120 and contact / separation mechanism 140 as viewed from the Y direction.

[0075] 6(a) and 6(b), the caster roller 120 has a rotation shaft 120c, a roller body 120a that rotates around the rotation shaft 120c, a base 120b that supports the rotation shaft 120c, and a caster shaft 120d. The base 120b and the caster shaft 120d are support members that support the caster roller 120 (driven roller), and have a shaft (caster shaft 120d) that extends along the rotation axis of the caster roller 120.

[0076] The caster roller 120 is held by a roller holder 135 (holding member). A caster shaft 120d of the caster roller 120 is inserted into a hole 135a of the roller holder 135 and is configured to be rotatable (swivelable) relative to the roller holder 135. In other words, the caster roller 120 can rotate around a pivot line relative to the roller holder 135, with the center line of the caster shaft 120d serving as the pivot line.

[0077] The caster roller 120 is biased by the auxiliary spring 139 toward a position where the rotation angle is 0°. In other words, the auxiliary spring 139 functions as a biasing member that biases the support member (base portion 120b) so as to bring the inclination angle of the rotation axis of the caster roller 120 (driven roller) relative to the sheet width direction (Z) closer to zero. When the rotation angle is 0°, the movement direction of the circumferential surface of the caster roller 120 at the nip portion with the registration roller 109 is parallel to the sheet conveying direction (X) (facing the straight direction of the sheet S). The auxiliary spring 139 is attached to a spring hook portion 120e provided on the base portion 120b of the caster roller 120 and a spring hook portion 135f provided on the roller holder 135.

[0078] The auxiliary spring 139 makes it easier for the turning angle of the caster roller 120 to return to 0°, reducing the vibration of the caster roller 120 in the turning direction and speeding up the convergence of the vibration. However, the spring force of this auxiliary spring 139 is set small enough so as not to affect the skew correction and lateral deviation correction of the registration unit 100.

[0079] Swing angle sensors 133 and 134 are attached to the sensor attachment portion 135e of the roller holder 135. The swing angle sensors 133 and 134 detect the rotation angle of the caster shaft 120d as the swing angle of the caster rollers 120 and 121. The swing angle sensors 133 and 134 are an example of vibration detection means for detecting vibration of the caster rollers 120 and 121 in the swing direction. The swing angle sensors 133 and 134 are, for example, rotary encoders that detect the rotation phase of a disk that rotates integrally with the caster shaft 120d.

[0080] The contact / separation mechanism 140 includes a roller holder 135, a separation motor 138, a separation cam 137, a cam follower 136, and a pressure spring 141. The contact / separation mechanism 140 switches the registration roller 109 (drive roller) and the caster roller 120 (driven roller) between a contact state in which the registration roller 109 and the caster roller 120 are in contact with each other, and a separation state in which the registration roller 109 and the caster roller 120 are separated from each other.

[0081] The roller holder 135 can swing around a swing shaft 135c as a fulcrum. The pressure spring 141 applies pressure to a pressure portion 135g of the roller holder 135, thereby biasing the roller holder 135 in a direction in which the caster rollers 120 approach the registration rollers 109.

[0082] The cam follower 136 is rotatably supported by a shaft portion 135d provided on the roller holder 135. The cam follower 136 is disposed on one end side of the swing shaft 135c, and the caster shaft 120d of the caster roller 120 and the pressure spring 141 are disposed on the other end side of the swing shaft 135c.

[0083] The separation cam 137 rotates by receiving a driving force from a separation motor 138. When the separation cam 137 presses the cam follower 136, the roller holder 135 swings clockwise in FIG. 6A against the biasing force of the pressure spring 141, and the caster roller 120 moves away from the registration roller 109. In other words, the registration roller 109 and the caster roller 120 move into a separated state in which they are spaced apart from each other. When the pressure of the separation cam 137 on the cam follower 136 is released, the roller holder 135 swings counterclockwise in FIG. 6A due to the biasing force of the pressure spring 141, and the caster roller 120 comes into contact with the registration roller 109. In other words, the registration roller 109 and the caster roller 120 move into a contact state (nip state) in which they are in contact with each other.

[0084] The right caster roller 121, like the left caster roller 120, is supported by a roller holder 135. Therefore, when the roller holder 135 swings in accordance with the rotation angle of the cam follower 136, both the left and right caster rollers 120, 121 come into contact with or separate from the registration rollers 109, 110. In other words, the separation motor 138 in this embodiment is a common drive source (actuator) for switching the left and right registration roller pairs between a contact state and a separation state. However, a drive source (actuator) for bringing the right registration roller 110 and the caster roller 121 into contact with and separating from each other may be added in addition to the separation motor 138.

[0085] Note that instead of a configuration in which the caster rollers 120, 121 are moved to bring them into contact with and separate from the registration rollers 109, 110, the registration rollers 109, 110 may be moved to bring them into contact with and separate from the caster rollers 120, 121. Furthermore, the mechanism for bringing the registration roller pair into contact with and separate from each other is not limited to one that uses a motor and a cam, and the roller holder 135 may be moved by a solenoid, for example.

[0086] After the registration unit 100 has performed skew correction and lateral deviation correction, the sheet S is further conveyed by the print belt unit 200. Here, after the sheet S is attracted to the print belt 225, the caster rollers 120 and 121 are separated from the registration rollers 109 and 110. As a result, the sheet S is conveyed without receiving conveyance resistance from the registration rollers 109 and 110, and a highly accurate image can be formed on the sheet S by the recording unit 300.

[0087] (Control example) Control including skew correction and lateral deviation correction by the registration unit 100 will be described with reference to Figs. 13 and 14. Fig. 13 is a flowchart illustrating the procedure for executing a print job by the inkjet recording apparatus 1, focusing particularly on the operation of the registration unit 100. The upper part of Fig. 14 shows an example of the detection results of the rotation angles of the caster rollers 120, 121 by the rotation angle sensors 133, 134. The lower part of Fig. 14 shows the determination results of vibration in the rotation direction of the caster rollers 120, 121.

[0088] Here, the procedure of a print job (single-sided print job) for forming an image on only one side (first side) of a sheet S will be described. The image forming operation is a series of operations in which the inkjet recording apparatus 1 as an image forming apparatus forms an image on a sheet S while transporting the sheet S. The print job is a series of tasks including an image forming operation on at least one sheet S. Each step of the flowchart is executed by the controller 50.

[0089] In S1, when the controller 50 receives an instruction (print job) to perform an image forming operation, it starts a single-sided print job. The controller 50 receives the print job when the user operates the operation unit 202 (for example, by pressing the print execution button) or from an external computer 201 to which the controller 50 is connected directly or via a network. The print job received by the controller 50 includes setting information (job information) such as the number of copies to be printed and the size of the sheets S to be used for printing, which are specified by the user. The controller 50 analyzes the received print job and performs the image forming operation in accordance with the job information.

[0090] During the execution of a print job in which images are successively formed on a plurality of sheets S, the following processes S2 to S17 are executed in parallel with a time lag for each sheet S. In the following explanation, a series of processes (S2 to S17) for one sheet S (the current sheet) during the print job will be explained. A sheet S fed after the current sheet during the print job is called a subsequent sheet. In particular, the sheet S fed after the current sheet during the print job may be called the next sheet.

[0091] In S2, the controller 50 rotates the separation motor 138 to bring the caster rollers 120 and 121, which have been separated from the registration rollers 109 and 110, into contact with the registration rollers 109 and 110, thereby preparing for a correction operation using the registration rollers 109 and 110. The controller 50 also rotates the feed motor 54 to feed a sheet S of a size specified in the job information from the feed module 1000. The controller 50 can detect the arrival of the sheet S at the registration unit 100 based on, for example, the detection results of the pre-registration sensors 131 and 132 or the detection result of a sheet sensor disposed in the feed module 1000. The controller 50 starts rotational driving of the registration rollers 109 and 110 and the conveyance roller pairs 118 and 119 located upstream thereof, and causes the conveyance roller pairs 118 and 119 to convey the sheet S toward the registration roller pair.

[0092] In S3, the sheet S reaches the registration rollers 109 and 110. The controller 50 can detect that the sheet S has reached the registration rollers 109 and 110 based on the detection of the leading edge of the sheet by the first registration sensors 103 and 104, for example.

[0093] In S4, the controller 50 acquires the skew amount ΔX of the sheet S based on the detection results of the first registration sensors 103 and 104. Specifically, the controller 50 calculates the skew amount ΔX of the sheet S based on the time difference between the timings at which the left and right first registration sensors 103 and 104 detect the leading edge of the sheet S and the sheet conveying speed of the conveying roller pairs 118 and 119.

[0094] If the skew amount ΔX of the current sheet S is equal to or greater than a predetermined value, a first correction operation (S7) to be described later may be performed on the subsequent sheet S based on the detection results of the pre-registration sensors 131, 132. In this way, if the skew detection unit whose detection results are used for skew correction is changed to one that is more upstream among the multiple skew detection units, the conveying section (the section on the conveying path or the corresponding section on the time axis) in which the correction operation can be performed becomes longer, making it easier to deal with a larger skew amount.

[0095] In S5, the controller 50 acquires the lateral deviation amount ΔZ of the sheet S based on the detection results of the image sensors 101 and 102. In this embodiment, the lateral deviation amount ΔZ of the sheet S is the deviation amount of the sheet center relative to the conveyance center, as described above. The controller 50 detects (edge ​​detection) how much of the reading range of the image sensors 101 and 102 the sheet S covers, finds the sheet center based on the detection results, and calculates the lateral deviation amount ΔZ of the sheet S.

[0096] In S6, the controller 50 creates operation profiles (collectively referred to as correction profiles) of the conveyance drive motors 105, 106 and the steering motors 107, 108 based on the skew amount ΔX and lateral deviation amount ΔZ acquired in S4 and S5. That is, the controller 50 creates a skew correction profile (time series data of X-direction speeds LVx, RVx) based on the skew amount ΔX calculated in S4. Also, the controller 50 creates a lateral deviation correction profile (time series data of Z-direction speeds LVz, RVz) based on the lateral deviation amount ΔZ calculated in S5. Then, the controller 50 converts the X-direction speeds LVx, RVx and the Z-direction speeds LVz, RVz into steering angles Lθ, Rθ and conveyance speeds LV, RV. As a result, the controller 50 determines the operation profiles of the steering motors 107, 108 as time series data of the steering angles Lθ, Rθ and the operation profiles of the conveyance drive motors 105, 106 as time series data of the conveyance speeds LV, RV.

[0097] In S7, the controller 50 executes a first correction operation (first correction operation) by controlling the operations of the transport drive motors 105, 106 and the steering motors 107, 108 in accordance with the operation profile created in S6. This performs a rough adjustment of the skew and lateral deviation of the sheet S. The first correction operation is performed in a transport section (called a first correction section 124; see FIGS. 2 and 3) from the first registration sensors 103, 104 to the second registration sensors 122, 123, with the leading edge of the sheet S as the reference.

[0098] In S8, the controller 50 monitors the vibration of the caster rollers 120, 121 in the turning direction using the turning angle sensors 133, 134. That is, as shown in Fig. 14, the controller 50 monitors fluctuations in the turning angle of the caster rollers 120, 121 during a predetermined period (convergence determination period) after the end of the first correction period 124. The graph in the upper part of Fig. 14 shows the transitions of values ​​ΔLθ and ΔRθ obtained by subtracting the steering angles Lθ and Rθ of the registration rollers 109, 110 from the turning angle of the caster rollers 120, 121 detected by the turning angle sensors 133, 134.

[0099] The controller 50 determines that the vibration of the caster rollers 120, 121 has converged if the deviation (ΔLθ, ΔRθ) of the turning angles of the caster rollers 120, 121 relative to the steering angles Lθ, Rθ remains within a predetermined range throughout the convergence determination period. The predetermined range is a range in which the absolute value of the deviation (ΔLθ, ΔRθ) of the turning angles is equal to or less than a preset threshold. The predetermined range is set to, for example, ±4 mrad (approximately ±0.2°). The predetermined range is not limited to this, and may be set to, for example, ±2 mrad (approximately ±0.1°) or a range wider than ±4 mrad. The lower part of FIG. 14 schematically shows a period (oscillation) in which the fluctuation amount of the turning angle (ΔLθ, ΔRθ) is greater than the threshold and a period (convergence) in which the fluctuation amount of the turning angle (ΔLθ, ΔRθ) is equal to or less than the threshold.

[0100] If it is determined in S8 that the vibration of the caster rollers 120, 121 has converged (S8Y), the controller 50 proceeds to S10. On the other hand, if it is determined in S8 that the vibration of the caster rollers 120, 121 has not converged (S8N), the controller 50 proceeds to S9.

[0101] In S9, the controller 50 changes the execution conditions of the first correcting operation so that the vibration of the caster rollers 120, 121 of the subsequent sheet converges more quickly. That is, it is assumed that after the first correcting operation is performed on the current sheet S, the vibration of the caster rollers 120, 121 does not converge by a predetermined timing before the start of the second correcting operation (S8N). In this case, the controller 50 executes a process (S9) to change the execution conditions of the first correcting operation so that the end timing of the first correcting operation for the subsequent sheet is accelerated. That is, the controller 50 executes a feedback process (S9) to change the execution conditions of the first correcting operation so that the vibration of the caster rollers 120, 121 converges more quickly. The feedback process of S9 is an example of a predetermined process for starting a correcting operation (second correcting operation) for subsequent sheets after the current sheet after the vibration of the caster rollers 120 in the turning direction converges within a predetermined range.

[0102] Specifically, the controller 50 applies feedback to the creation (S6) of an operation profile for the first correction operation for the subsequent sheet so that the drive control period of each motor (105 to 108) in the first correction section 124 for the subsequent sheet ends earlier.

[0103] The drive control period of the conveyance drive motors 105, 106 is a period during which a difference in conveyance speed occurs between the left and right registration rollers 109, 109 (a period during which the conveyance speeds LV, RV deviate from the process speed). In other words, the controller 50 (control means) shortens the period during which a difference in conveyance speed occurs between the left registration roller 109 (first drive roller) and the right registration roller 110 (second drive roller) in the first correction operation (S7) through a predetermined process.

[0104] The drive control period of the steering motors 107, 108 is the period during which the steering angles Lθ, Rθ are set to values ​​other than 0°, that is, the period during which the rotation axes of the registration rollers 109, 110 are tilted by the steering motors 107, 108. In other words, the controller 50 (control means) shortens the period during which the rotation axes of the registration rollers 109, 110 (drive rollers) are tilted by the steering motors 107, 108 (steering means) in the first correction operation (S7) through predetermined processing.

[0105] In the feedback process, for example, the reference profile of the skew correction profile or lateral deviation correction profile is compressed in the time axis direction so that the drive control period of each motor is shortened (the correction amounts of LVx, RVx, LVz, and RVz are increased accordingly).

[0106] Furthermore, in the feedback process (S9), the start of the first correction operation is advanced by, for example, changing the skew detection unit used in the first correction operation from the first registration sensors 103 and 104 to the pre-registration sensors 131 and 132. In other words, the controller 50 (control means) changes the detection means, the detection results of which are used in the first correction operation (S7), from the first registration sensors 103 and 104 (third detection means) to the pre-registration sensors 131 and 132 (fourth detection means) through a predetermined process.

[0107] The above-described feedback processes may be executed singly or in combination.

[0108] In S10, the controller 50 again acquires the skew amount ΔX of the sheet S based on the detection results of the second registration sensors 122 and 123. The skew amount ΔX acquired in S10 is the skew amount ΔX after correction by the first correction operation. Furthermore, as a result of the feedback control in S9, the skew amount ΔX after the vibration of the caster rollers 120 and 121 in the rotation direction has converged is usually acquired in S10.

[0109] In S11, the controller 50 again acquires the lateral deviation amount ΔZ of the sheet S based on the detection results of the image sensors 101 and 102.

[0110] In S12, the controller 50 creates operation profiles for the conveyance drive motors 105, 106 and the steering motors 107, 108 based on the skew amount ΔX and lateral deviation amount ΔZ acquired in S10 and S11. In this embodiment, the method for creating the operation profile for the second correction operation is the same as the method for creating the operation profile for the first correction operation (S6).

[0111] In S13, the controller 50 executes a second correction operation (second correction operation) by controlling the operations of the transport drive motors 105, 106 and the steering motors 107, 108 in accordance with the operation profile created in S12. This allows fine adjustment of the skew and lateral deviation of the sheet S. The second correction operation is performed in a transport section (called a second correction section 125; see FIGS. 2 and 3) from the second registration sensors 122, 123 to the print belt 225, with the leading edge of the sheet S as the reference.

[0112] In S14, the sheet S is transferred from the registration rollers 109 and 110 to the print belt 225. In S15, the controller 50 rotates the separation motor 138 to separate the caster rollers 120 and 121 from the registration rollers 109 and 110. That is, the controller 50 changes the registration roller pair from the contact state to the separation state after the leading edge of the sheet S reaches the print belt 225, which is the conveying member downstream of the registration roller pair. In this embodiment, the controller 50 changes the registration roller pair from the contact state to the separation state before the trailing edge of the sheet S passes through the registration roller pair.

[0113] In S16, the controller 50 starts the recording process by the recording unit 300. Note that the separation of the caster rollers 120, 121 (S15) may occur after the start of the recording process (S16). In S17, the controller 50 ejects the sheet S on which the image has been formed onto the stacking unit 7500 of the stacking module 7000, thereby completing the print job.

[0114] In the case of an image forming operation (double-sided printing) in which images are formed on both sides of the sheet S, the controller 50, after S16, causes the sheet S with the image formed on the first side to be transported to the double-sided transport path. The controller 50 then inverts the sheet S at the inverting section 4200 and transports it again toward the registration unit 100. Thereafter, the controller 50 executes the processes from S2 onwards on the inverted sheet S, thereby forming an image on the second side of the sheet S.

[0115] (Summary of this embodiment) The controller 50 of this embodiment executes a feedback process (S9) for starting the second correction operation after the vibration of the caster rollers 120, 121 has converged for at least the succeeding sheet, based on the detection results of the turning angle sensors 133, 134. In other words, the control means executes a predetermined process for starting the correction operation after the drive roller and the driven roller are switched from the separated state to the contact state and after the vibration of the driven roller in the turning direction has converged within a predetermined range, based on the detection result of the first detection means. This reduces the effect on the correction operation of the vibration of the driven roller in the turning direction that occurs when the drive roller and the driven roller are brought into contact.

[0116] That is, according to this embodiment, it is possible to provide a sheet conveying device and an image forming apparatus that can improve the accuracy of correcting the positional deviation of a sheet.

[0117] In this embodiment, the detection of the skew amount and lateral deviation amount for the second correction operation (S10, S11) is also performed after the vibration of the caster rollers 120, 121 has subsided. In other words, the control means executes the correction operation based on the detection result of the second detection means detecting the positional deviation of the sheet after the vibration of the driven roller has subsided. This reduces the possibility that errors will occur in the detection results of the skew amount and lateral deviation amount due to the position of the sheet S being unstable due to the vibration of the driven roller, resulting in a decrease in the correction accuracy of the positional deviation of the sheet.

[0118] Furthermore, the controller 50 of this embodiment executes the first correction operation (S7) using the registration rollers 109, 110 and the caster rollers 120, 121 before the second correction operation (S13). The controller 50 starts the first correction operation (S7) after switching the registration rollers 109, 110 and the caster rollers 120, 121 from a separated state to a contact state and before the vibration of the caster rollers 120, 121 in the rotation direction converges. In other words, the fine adjustment (second correction operation), in which the influence of the vibration of the caster rollers 120, 121 is likely to become apparent, is performed after the vibration converges, while the coarse adjustment (first correction operation), in which the influence of the vibration is less likely to become apparent, is started without waiting for the vibration to converge. Therefore, compared to a configuration in which the first correction operation is started after the vibration of the caster rollers 120, 121 converges, for example, it is possible to improve productivity while maintaining the accuracy of correction of sheet position misalignment.

[0119] In this embodiment, the sheet position is roughly adjusted and finely adjusted by performing two correction operations (S7, S13) at one correction unit (registration rollers 109, 110). Therefore, the device size can be made smaller than a configuration in which the sheet position is roughly adjusted at the first correction unit and then finely adjusted at the second correction unit.

[0120] Furthermore, in this embodiment, skew correction of the sheet S can be performed without performing skew correction (stop registration) of a type in which the leading edge of the sheet is abutted against the nip portion of the pair of registration rollers or a shutter. Also, in this embodiment, skew correction of the sheet S can be performed without performing lateral deviation correction of a type in which the pair of rollers that sandwich the sheet S slide (shift) in the sheet width direction. This eliminates the need for waiting time to stop the leading edge of the sheet or to return the slide mechanism (shift mechanism) of the pair of rollers to the home position, which is advantageous in terms of improving productivity.

[0121] (Variation) In this embodiment, an example has been described in which the rotation angle sensors 133, 134 are used to monitor the vibrations in the rotation direction of each of the left and right caster rollers 120, 121. However, the present invention is not limited to this, and it is also possible to monitor the vibrations of only one of the left and right caster rollers 120, 121 and apply the control described in Fig. 13. Because the time scales required for the vibrations of the left and right caster rollers 120, 121 to converge are considered to be the same, this modification also makes it possible to improve productivity while maintaining the accuracy of correcting sheet positional misalignment.

[0122] Second Embodiment A second embodiment will be described. This embodiment differs from the first embodiment in some of the control contents of the print job. Below, elements with the same reference symbols as the first embodiment will have basically the same configurations and functions as those described in the first embodiment unless otherwise specified, and differences from the first embodiment will be mainly described.

[0123] Figure 15 is a flowchart showing the procedure for a single-sided print job in the second embodiment. Compared to the first embodiment (Figure 13), S4, S8, S9, and S10 have been replaced with S4', S8', S9', and S10', respectively. Steps other than S4', S8', S9', and S10' are the same as those in the first embodiment (Figure 13), so a description thereof will be omitted.

[0124] In S4', the controller 50 detects the edge position of the sheet S multiple times using the image sensors 101 and 102, and acquires the skew amount ΔX of the sheet S based on the detection results. One method for acquiring the skew amount ΔX using the image sensors 101 and 102 is to detect (edge ​​detect) the leading edge of the sheet S based on two-dimensional image data in which line images acquired at each image capture are arranged in the sub-scanning direction, and determine the inclination of the leading edge. The procedure for performing the first correction operation (S7) including skew correction of the sheet S based on the acquired skew amount ΔX is the same as in the first embodiment.

[0125] In S8', from the end of the first correction operation (S7), the controller 50 monitors the vibration of the caster rollers 120, 121 in the turning direction using the turning angle sensors 133, 134. In this embodiment, when the deviations (ΔLθ, ΔRθ) of the turning angles of the caster rollers 120, 121 relative to the steering angles Lθ, Rθ become equal to or smaller than preset thresholds, it is determined that the vibration of the caster rollers 120, 121 in the turning direction has converged.

[0126] If it is determined in S8' that the vibration of the caster rollers 120, 121 has converged (S8'Y), the controller 50 proceeds to S10. That is, in this embodiment, as soon as the vibration of the turning angle of the caster rollers 120, 121 becomes equal to or less than the threshold value after the first corrective operation (S7), the controller 50 proceeds to S10' and starts the second corrective operation (S13).

[0127] On the other hand, if it is determined in S8' that the vibration of the caster rollers 120, 121 has not converged (S8'N), the controller 50 proceeds to S9'. In S9', the controller 50 determines whether the time limit for starting the second correction operation has arrived. The time limit is set in advance as the latest timing at which the second correction operation should be started so that the second correction operation is completed before the sheet S is transferred to the print belt 225. The time limit is, for example, the upper limit of the time that has elapsed since the leading edge of the sheet S reached the image sensors 101, 102.

[0128] If it is determined in S9' that the time limit has been reached before it is determined in S8' that the vibration of the caster rollers 120, 121 has converged, the controller 50 forcibly proceeds to S10' to start the second correction operation (S13).

[0129] In S10', the controller 50 detects the edge position of the sheet S multiple times using the image sensors 101 and 102, and again acquires the skew amount ΔX of the sheet S based on the detection result. The procedure for performing the second correction operation (S13) including skew correction of the sheet S based on the acquired skew amount ΔX is the same as in the first embodiment.

[0130] (Summary of this embodiment) The controller 50 of this embodiment executes a determination process (S8') for starting the second correction operation for the current sheet after the vibration of the caster rollers 120, 121 has converged, based on the detection results of the turning angle sensors 133, 134. In other words, the control means determines whether the vibration of the driven roller has converged based on the detection result of the first detection means, and executes a determination process to allow the start of the correction operation (S13) when it is determined that the vibration of the driven roller has converged within a predetermined range (S8'Y). This reduces the effect on the correction operation of the vibration of the driven roller in the turning direction that occurs when the drive roller and the driven roller are brought into contact.

[0131] That is, according to this embodiment, it is possible to provide a sheet conveying device and an image forming apparatus that can improve the accuracy of correcting the positional deviation of a sheet.

[0132] Furthermore, in this embodiment, if a predetermined time (time limit) has elapsed since the end of the first correction operation, the start of the second correction operation is permitted regardless of whether it has been determined that the vibration of the caster rollers 120, 121 has converged (S9'Y). This prevents a situation in which the second correction operation is not performed and improves the stability of the operation, and even if the vibration of the caster rollers 120, 121 does not converge easily, the second correction operation is started with the vibration as small as possible. This makes it possible to achieve both the stability of the operation of the device and the improvement of the accuracy of correcting the positional deviation of the sheet.

[0133] Furthermore, according to this embodiment, if the vibration of the caster rollers 120, 121 converges quickly after the first correction operation, the second correction operation can be started early. In this case, the reference profile used in the second correction operation is stretched in the time axis direction (reducing the correction amount accordingly), thereby further improving the correction accuracy.

[0134] Third Embodiment As the third embodiment, an example will be described in which the configuration relating to vibration detection of caster rollers 120, 121 is different from that of the first embodiment. Below, unless otherwise specified, elements with the same reference symbols as those in the first embodiment have basically the same configurations and functions as those described in the first embodiment, and the following mainly describes the parts that are different from the first embodiment.

[0135] As shown in FIG. 16, the register unit 100 of this embodiment has a home position sensor 142 as a vibration detection means for detecting vibration of the caster rollers 120. The home position sensor 142 is, for example, an optical sensor (photointerrupter) having a light-emitting element and a light-receiving element and capable of detecting a slit 120f provided in the base portion 120b of the caster rollers 120. That is, the home position sensor 142 emits a detection signal indicating a state in which light from the light-emitting element reaches the light-receiving element through the slit 120f (transmitting state) and a state in which light from the light-emitting element is blocked by the base portion 120b (light-blocking state). The slit 120f is formed so that the home position sensor 142 is in the transmitting state when the rotation angle of the caster rollers 120 is within a predetermined range centered on 0°, and is in the light-blocking state when the rotation angle is outside the predetermined range. That is, the home position sensor 142 is configured so that the detection signal changes depending on whether the caster roller 120 (follower roller) is within a predetermined range in the turning direction or outside the predetermined range.

[0136] The home position sensor 142 is attached to a roller holder 135 (FIG. 6(a)) that rotatably holds the caster roller 120. A similar home position sensor is also provided for the caster roller 121. The home position sensor 142 is an example of a first detection means for detecting the caster rollers 120, 121 (vibration of the driven rollers) in the turning direction.

[0137] The home position sensor 142 may be used as the vibration detection means instead of the turning angle sensors 133 and 134 of the first and second embodiments. In the flow of the first embodiment (FIG. 13), the controller 50 can determine that the vibration of the caster rollers 120 and 121 has converged (S8Y) when the detection signal of the home position sensor 142 indicates the light-transmitting state throughout the convergence determination section. In the flow of the second embodiment (FIG. 15), the controller 50 can determine that the vibration of the caster rollers 120 and 121 has converged (S8'Y) when the detection signal of the home position sensor 142 changes from the light-blocking state to the light-transmitting state after the first correction operation (S7).

[0138] Even when the above-described home position sensor 142 is used, the same advantages as those of the first and second embodiments can be obtained.

[0139] It is also possible to use vibration detection means other than the turning angle sensors 133 and 134 and the home position sensor 142. For example, an optical sensor that detects a flag protruding from the base portion 120b of the caster roller 120 may be used.

[0140] Fourth Embodiment In the first to third embodiments, a configuration has been exemplified in which the detection result of the vibration detection means is used to execute the corrective operation (second corrective operation) after the rotation of the caster rollers 120 in the rotation direction has converged. However, if the configuration is such that the corrective operation is executed after the rotation of the caster rollers 120 in the rotation direction has converged, the vibration detection means can be omitted.

[0141] The control in this embodiment will be described with reference to Figs. 17 and 18. The upper part of Fig. 17 shows an example of the transition of the rotation angle of the caster rollers 120, 121. The lower part of Fig. 17 is a conceptual diagram showing the presence or absence of vibration in the rotation direction of the caster rollers 120, 121. Fig. 18 is a flowchart showing the execution procedure for a single-sided print job in this embodiment.

[0142] In this embodiment, the correction operation is performed only once in the registration unit 100. That is, as shown in FIG. 18, the processing related to the first correction operation in the first embodiment (S4 to S9 in FIG. 13) is not performed, and only the correction operation is performed in S13″.

[0143] In S10", the controller 50 acquires the skew amount ΔX of the sheet S based on the detection result of the registration sensor (corresponding to the second registration sensors 122, 123 in the first embodiment). In S11 and S12, the controller 50 acquires the lateral deviation amount ΔZ of the sheet S in the same manner as in the first embodiment, and creates an operation profile for the correction operation. Then, in S13", the controller 50 executes the correction operation in accordance with the operation profile. The processes of S1 to S3 and S14 to S17 are the same as in the first embodiment, and therefore description thereof will be omitted.

[0144] 17, the timing at which the leading edge of the sheet reaches the registration sensor is after the timing at which the vibration of the caster rollers 120, 121 converges (vibration convergence point) after the caster rollers 120, 121 come into contact with the registration rollers 109, 110. In other words, the contact timing of the registration rollers 109, 110 and the arrangement of the registration sensor are determined so that there is a margin between the convergence of the vibration of the caster roller 120 and the period during which the correction operation is performed (correction interval).

[0145] According to this embodiment, the correction operation is started after the vibration of the caster rollers 120 and 121 has converged. Therefore, the same advantages as those of the first embodiment can be obtained. This embodiment is particularly effective when the skew and lateral deviation of the sheet S at the time of reaching the registration unit 100 are relatively small.

[0146] Note that the convergence of vibration of the caster rollers 120 can be accelerated by adjusting the mass of the caster rollers 120 and 121 and the biasing force of the auxiliary spring 139. Also, in this embodiment, an example has been given in which the vibration convergence of the caster rollers 120 and 121 is ensured by the arrangement of the registration sensors. However, this is not limiting, and for example, when the skew amount ΔX is obtained by the image sensors 101 and 102 as in the second embodiment, the convergence of vibration of the caster rollers 120 and 121 may be ensured by adjusting the timing of obtaining the skew amount ΔX.

[0147] (Variation)

[0148] Furthermore, if the required accuracy for skew correction and lateral deviation correction is not high, the steering function of the registration rollers 109, 110 can be omitted. In this case, skew and lateral deviation can be corrected simultaneously by controlling the speed difference between the left and right conveyance drive motors 105, 106 and the timing of delivery to the downstream conveyance member. In either case, the accuracy of correcting the sheet posture (skew and / or lateral deviation) can be improved by starting the correction operation after the vibration in the rotation direction of the caster rollers 120, 121 has sufficiently subsided.

[0149] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0150] 50...control means (controller) / 101, 102, 122, 123...second detection means (image sensor, second registration sensor) / 107, 108...steering means (steering motor) / 109, 110...driving roller (registration roller) / 120, 121...followed roller (caster roller) / 133, 134, 142...first detection means (turning angle sensor, home position sensor) / 140...contact / separation mechanism / S13...correction operation (second correction operation)

Claims

1. a drive roller that rotates by receiving a driving force; a steering means for changing an inclination angle of the rotation axis of the drive roller with respect to a sheet width direction perpendicular to a sheet conveying direction; a driven roller that sandwiches and conveys a sheet together with the drive roller, the driven roller being configured to rotate around a rotation axis that intersects both the sheet conveying direction and the sheet width direction in accordance with a change in the inclination angle of the drive roller; a contact / separation mechanism that switches the drive roller and the driven roller between a contact state in which the drive roller and the driven roller are in contact with each other and a separation state in which the drive roller and the driven roller are separated from each other; a first detection means for detecting vibration of the driven roller in a rotational direction around the rotation axis; a second detection means for detecting a positional deviation of the sheet; a control unit that executes a correction operation to correct the positional deviation of the sheet based on the detection result of the second detection unit; Equipped with the control means executes a predetermined process for starting the correction operation after the drive roller and the driven roller are switched from the separated state to the contact state and after the vibration of the driven roller in the rotation direction has converged to within a predetermined range, based on the detection result of the first detection means. A sheet conveying device characterized by:

2. the control means executes the correction operation based on a detection result of the second detection means detecting the positional deviation of the sheet after the vibration of the driven roller has subsided.

2. The sheet transport device according to claim 1.

3. the correcting operation is a second correcting operation, the control unit executes a first correcting operation for correcting a positional deviation of the sheet using the drive roller and the driven roller before the second correcting operation; the control means starts the first correction operation after the drive roller and the driven roller are switched from the separated state to the contact state and before vibration of the driven roller in the rotation direction converges.

2. The sheet transport device according to claim 1.

4. the correcting operation is a second correcting operation, the control unit executes a first correcting operation for correcting a positional deviation of the sheet using the drive roller and the driven roller before the second correcting operation; The predetermined process is a process of changing an execution condition of the first correction operation so that the end timing of the first correction operation for a subsequent sheet that is conveyed after the current sheet is advanced when vibration of the driven roller does not converge before the second correction operation for the current sheet is started during execution of a job of conveying a plurality of sheets continuously.

2. The sheet transport device according to claim 1.

5. the control means, by the predetermined processing, shortens a period during which the rotation axis of the drive roller is tilted by the steering means in the first correction operation; 5. The sheet transport device according to claim 4.

6. The drive roller is a first drive roller, the sheet conveying device further includes a second drive roller arranged alongside the first drive roller in the sheet width direction, the second drive roller having a conveying speed controlled independently of the first drive roller; the control means shortens a period during which a difference in conveying speed occurs between the first drive roller and the second drive roller in the first correction operation by the predetermined processing; 5. The sheet transport device according to claim 4.

7. a third detection means for detecting a positional deviation of the sheet; a fourth detection means disposed upstream of the third detection means in the sheet conveying direction, for detecting a positional deviation of the sheet; Further provided with the control means changes the detection means, the detection result of which is used for the first correction operation, from the third detection means to the fourth detection means by the predetermined processing.

5. The sheet transport device according to claim 4.

8. the predetermined process is a determination process of determining whether or not the vibration of the driven roller has converged based on the detection result of the first detection means, and allowing the start of the correction operation when it is determined that the vibration of the driven roller has converged within the predetermined range.

2. The sheet transport device according to claim 1.

9. the correcting operation is a second correcting operation, the control means executes a first correcting operation for correcting the positional deviation of the sheet before the second correcting operation; when a predetermined time has elapsed since the end of the first correction operation, the control means allows the start of the second correction operation regardless of whether it is determined that the vibration of the driven roller has converged within the predetermined range.

9. The sheet transport device according to claim 8.

10. the control means determines that the vibration of the driven roller has converged when a difference between the angle of the driven roller in the rotation direction and the tilt angle of the drive roller remains within the predetermined range throughout a predetermined period of time.

2. The sheet transport device according to claim 1.

11. the control means determines that the vibration of the driven roller has converged when a difference between the angle of the driven roller in the rotation direction and the tilt angle of the drive roller falls within the predetermined range.

2. The sheet transport device according to claim 1.

12. The drive roller is a first drive roller, the steering means is a first steering means, and the driven roller is a first driven roller; the sheet conveying device, a second drive roller disposed alongside the first drive roller in the sheet width direction; a second steering means for changing an inclination angle of a rotation axis of the second drive roller with respect to the sheet width direction; a second driven roller that conveys a sheet by nipping it together with the second driving roller, the second driven roller rotating in accordance with a change in the inclination angle of the second driving roller; Further comprising:

2. The sheet transport device according to claim 1.

13. the control unit corrects the positional deviation of the sheet in the sheet width direction by controlling the inclination angles of the first drive roller and the second drive roller based on the detection result of the second detection unit in the correction operation.

13. The sheet transport device according to claim 12.

14. the second drive roller has a conveying speed controlled independently of the first drive roller; the control unit corrects the skew of the sheet by controlling a difference in conveying speed between the first drive roller and the second drive roller based on the detection result of the second detection unit in the correction operation.

13. The sheet transport device according to claim 12.

15. the correcting operation is a second correcting operation, the control unit executes a first correction operation for correcting a positional deviation of the sheet using the first drive roller, the second drive roller, the first driven roller, and the second driven roller before the second correction operation.

13. The sheet transport device according to claim 12.

16. a support member that supports the driven roller and has a shaft portion that extends along the pivot axis; a roller holder that holds the shaft portion rotatably around the pivot axis; a biasing member connected to the support member and the roller holder, which biases the support member so as to cause the tilt angle of the rotation axis of the driven roller with respect to the sheet width direction to approach zero; Further comprising:

2. The sheet transport device according to claim 1.

17. the first detection means is a rotary encoder that detects the angle of the driven roller in the rotation direction; 2. The sheet transport device according to claim 1.

18. the first detection means is an optical sensor configured to change a detection signal depending on whether the driven roller is within the predetermined range in the rotation direction or outside the predetermined range.

2. The sheet transport device according to claim 1.

19. the second detection means is two or more sensors that detect the sheet at positions spaced apart from each other in the sheet width direction; 2. The sheet transport device according to claim 1.

20. the second detection means is an image sensor having an imaging area extending in the sheet width direction, 2. The sheet transport device according to claim 1.

21. a sheet conveying device according to any one of claims 1 to 20; an image forming means for forming an image on the sheet conveyed by the sheet conveying device; An image forming apparatus comprising:

Images