JP2023128148A - Image formation device - Google Patents

Abstract

To provide an image formation device which can improve accuracy of correction of conveyance deviation of a sheet in a conveyance direction.SOLUTION: An image formation device 10 decelerates sheet conveyance speeds V1 and V2 to first setting speed VL from reference speed V0, when sheet correction time by a sheet correction mechanism 60 is equal to or first setting time T1 or more.SELECTED DRAWING: Figure 8

Description

The present invention relates to an image forming apparatus that forms an image on a sheet conveyed to an image transfer position.

2. Description of the Related Art Image forming apparatuses such as printers, copiers, facsimile machines, and multifunction peripherals equipped with these functions transfer images onto sheets that are conveyed to image transfer positions. This image forming apparatus is provided with a sheet conveyance device that conveys the sheet to the image transfer position. A conventional sheet conveying device includes a pair of registration rollers for performing a registration operation (also called registration) on a sheet. Here, the registration operation is an operation in which a conveyance force is applied to the sheet in the conveyance direction while the leading edge of the sheet is abutted against the nip portion of a pair of stopped registration rollers. By performing this registration operation, the skew of the sheet being conveyed is corrected.

Conventionally, devices for correcting skewed feeding of sheets include a rotating mechanism that rotatably supports the sheet while pinching it while being conveyed, and when it is detected that skewed feeding has occurred, the device corrects the skewed feeding. A skew correction mechanism that rotates a rotation mechanism in a correction direction is known (see Patent Document 1).

Japanese Patent Application Publication No. 2006-27859

However, when skew correction is performed by a conventional skew correction mechanism while the sheet conveyance speed remains constant, the rotating mechanism moves to a position to receive the sheet for skew correction. If the sheet reaches the rotating mechanism before being conveyed, there is a risk that the skew correction of the sheet will not be performed accurately.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can improve the accuracy of correcting sheet conveyance misalignment in the conveyance direction.

The image forming apparatus according to one aspect of the present invention includes a detection unit that detects a conveyance deviation of the sheet conveyed in the conveyance direction in a cross direction intersecting the conveyance direction; a correction unit that is provided on the downstream side of the sheet and that conveys the sheet in the conveyance direction and corrects the conveyance position when the detection unit detects the conveyance deviation; a sheet conveyance control section that controls conveyance of the sheet. The sheet conveyance control unit sets the conveyance speed of the sheet by the conveyance unit to a predetermined reference speed when the correction time calculated based on the conveyance deviation of the sheet is less than a predetermined first setting time. and when the correction time is equal to or longer than the first set time, the conveyance speed is decelerated from the reference speed.

According to the present invention, it is possible to improve the accuracy of correcting sheet conveyance deviation in the conveyance direction.

FIG. 1 is a perspective view showing the configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the internal configuration of the image forming apparatus. FIG. 3 is a schematic diagram showing the configuration around the sheet conveyance path of the image forming apparatus. FIG. 4 is a block diagram showing the configuration of the image forming apparatus. FIG. 5 is a schematic diagram showing the configuration of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 6 is a schematic diagram showing the configuration of a sheet conveying unit included in the image forming apparatus. FIG. 7 is a diagram showing the configuration of a sheet correction mechanism included in the image forming apparatus. FIG. 8 is a flowchart illustrating an example of the procedure of sheet correction processing executed by a control unit included in the image forming apparatus. FIG. 9 is a flowchart illustrating an example of a procedure of sheet correction processing executed by a control unit included in the image forming apparatus. FIG. 10 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 11 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 12 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 13 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 14 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 15 is a diagram for explaining the operations of a sheet conveyance unit and a sheet correction mechanism included in the image forming apparatus. FIG. 16 is a flowchart illustrating another example of the sheet correction process executed by the control unit included in the image forming apparatus. FIG. 17 is a flowchart illustrating an example of a procedure of a transfer timing determination process executed by a control unit included in an image forming apparatus.

Embodiments of the present invention will be described below with reference to the drawings as appropriate. The embodiments described below are merely examples embodying the present invention, and do not limit the technical scope of the present invention.

FIG. 1 is a perspective view showing the configuration of an image forming apparatus 10 according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the internal configuration of the image forming apparatus 10. As shown in FIG. In FIG. 2, illustration of the image reading section 12 is omitted. In the following description, the vertical direction D1 is defined based on the state in which the image forming apparatus 10 is installed so that it can be used (the state in FIG. 1), and the front-back direction is defined with the near side (front side) of the image forming apparatus 10 as the front. D2 is defined, and a left-right direction D3 is defined when the image forming apparatus 10 is viewed from the front side (front side).

[Image forming apparatus 10]
As shown in FIG. 1, the image forming apparatus 10 is a multifunction device that can print images on sheets such as printing paper, and has various functions such as a print function, a copy function, a facsimile function, and a scan function. The image forming apparatus 10 is not limited to the above-mentioned multifunction machine, but may be any apparatus as long as it has a print function of printing an image on a conveyed sheet, and may be, for example, a printer, a copying machine, a facsimile machine, or the like.

The image forming apparatus 10 includes an image reading section 12 and an image forming section 14. The image reading unit 12 performs a process of reading an image of a document, and is provided at the top of the image forming apparatus 10. The image forming section 14 performs a process of forming a color image based on an electrophotographic method, and is provided at the lower part of the image forming apparatus 10. Furthermore, a sheet discharge section 15 is provided on the right side of the image forming section 14.

A discharge space 22 is provided above the image forming section 14 . The sheet discharge section 15 vertically connects the image forming section 14 and the image reading section 12 while forming a discharge space 22 between the image forming section 14 and the image reading section 12 .

The sheet discharge section 15 discharges the sheet after image formation to the discharge space 22 . A sheet discharge port 15A (see FIG. 2) is formed on the left side of the sheet discharge portion 15 on the discharge space 22 side. The sheet member is discharged from the sheet discharge port 15A.

The image forming section 14 includes a housing 11 (an example of the main body of the apparatus of the present invention). Inside the casing 11, various parts constituting the image forming section 14 are arranged. The housing 11 includes an exterior frame that covers the entire image forming section 14 and an internal frame that supports each part of the image forming section 14 .

FIG. 2 is a schematic diagram showing the internal configuration of the image forming apparatus 10. As shown in FIG. In FIG. 2, illustration of the image reading section 12 is omitted.

The image forming unit 14 forms a color image on a sheet such as printing paper based on a so-called tandem method. As shown in FIG. 2, the image forming section 14 includes a plurality of image forming units 4, an intermediate transfer unit 5, a belt cleaning device 6, an optical scanning device 13, a secondary transfer roller 20 (an example of a transfer section of the present invention), Fixing device 16, sheet tray 18, sheet storage section 27, feeding unit 28, operation display section 17 (see FIG. 1), sheet conveyance path 26 (hereinafter abbreviated as conveyance path 26), sheet conveyance unit 23 (main The present invention includes a sheet correction mechanism 60 (an example of a correction section of the invention), a container mounting section 35, a toner container 3, a control section 90 (see FIG. 4), and the like.

As shown in FIG. 2, the sheet storage section 27 is provided at the bottom of the image forming apparatus 10. The sheet storage section 27 stores sheets on which images are formed by the image forming unit 4, and is formed, for example, in the shape of a tray with an open top. The sheet storage section 27 is supported by the housing 11.

The feeding unit 28 takes out a plurality of sheets stacked in the sheet storage section 27 one by one and feeds the sheets toward the conveyance path 26. The feeding unit 28 includes a pickup roller 29 and a feeding roller pair 30. The pickup roller 29 and the feeding roller pair 30 are provided above the right side of the sheet storage section 27.

FIG. 3 is a schematic diagram showing the configuration around the conveyance path 26. As shown in FIG. The feeding roller pair 30 receives rotational driving force from a transport motor 56 (see FIG. 4) such as a stepping motor to transport the sheet downstream in the transport direction D11. As shown in FIG. 3, the feeding roller pair 30 includes a driving roller 30A that rotates when rotational driving force is transmitted from the transport motor 56, and a driven roller 30B that rotates in contact with the driving roller 30A. have A drive transmission mechanism (not shown) that transmits the rotation of the drive roller 30A to the pickup roller 29 is provided between the pickup roller 29 and the drive roller 30A. The pickup roller 29 and the drive roller 30A are connected via the drive transmission mechanism. When the drive roller 30A is rotated by the transport motor 56, the pickup roller 29 is also rotated in the same direction and at the same circumferential speed as the drive roller 30A by the drive transmission mechanism.

When an instruction signal to start a sheet feeding operation is input to the image forming apparatus 10, the pickup roller 29 and the feeding roller pair 30 are rotated by the rotational driving force of the conveying motor 56, and the sheet is fed from the sheet storage section 27. The sheet is fed to the conveyance path 26. Specifically, the pickup roller 29 picks up the sheet in the sheet storage section 27 and sends the sheet downstream in the feeding direction, and when the leading end of the sheet reaches the nip between the pair of feeding rollers 30, The sheet is conveyed to the conveyance path 26 by a pair of feed rollers 30 .

The conveying path 26 is a guide path that guides the sheet fed by the pair of feeding rollers 30 to the sheet discharge port 15A. As shown in FIG. 2, the conveyance path 26 is curved upward from the feed roller pair 30 and then extends upward, passing through the secondary transfer roller 20 and reaching the sheet discharge port 15A.

As shown in FIG. 3, a sheet conveyance unit 23 and a sheet correction mechanism 60 are provided in the conveyance path 26.

The sheet conveyance unit 23 conveys the sheet downstream in the conveyance direction D11 toward the image transfer position P1 (see FIG. 3) by receiving rotational driving force from the conveyance motor 56 (see FIG. 4). The sheet sent out to the conveyance path 26 by the feeding unit 28 is further conveyed to the downstream side in the conveyance direction D11 through the conveyance path 26 by the sheet conveyance unit 23. The configuration of the sheet conveyance unit 23 will be described later.

The sheet correction mechanism 60 is disposed on the conveyance path 26 on the downstream side of the sheet conveyance unit 23 in the conveyance direction D11. The sheet correction mechanism 60 corrects the orientation and position of the sheet that is conveyed along the conveyance path 26 in a direction that is deviated from the conveyance direction D11, and conveys the sheet to the downstream side in the conveyance direction D11. The configuration of the sheet correction mechanism 60 will be described later.

As shown in FIG. 2, each image forming unit 4 is provided below the intermediate transfer unit 5. As shown in FIG. Each image forming unit 4 performs image forming processing (an example of image processing) to form a toner image on the surface of the transfer belt 5A based on image data input from the outside. The plurality of image forming units 4 are arranged in parallel along the running direction of the transfer belt 5A (direction indicated by arrow D10). From the left side to the right side of the transfer belt 5A, an image forming unit 4Y for yellow, an image forming unit 4C for cyan, an image forming unit 4M for magenta, and an image forming unit 4K for black are arranged in a line in that order. It is located.

Each of the image forming units 4 includes a photosensitive drum 41 (an example of an image carrier), a charging device 42, a developing device 44, a primary transfer roller 45, a drum cleaning device 46, and the like. The image forming unit 4Y forms a toner image on the surface of the photoreceptor drum 41 using yellow toner. The image forming unit 4C forms toner images on the surface of the photoreceptor drum 41 using cyan toner, the image forming unit 4M using magenta toner, and the image forming unit 4K using black toner. Developing of the toner image on the photosensitive drum 41 is performed by a developing device 44 .

The drum cleaning device 46 is disposed on the downstream side of the primary transfer roller 45 in the rotational direction of the photosensitive drum 41 . The drum cleaning device 46 is a device that removes toner remaining on the surface of the photoreceptor drum 41 (residual toner). The drum cleaning device 46 includes a cleaning member that comes into contact with the surface of the photoreceptor drum 41 to remove residual toner, and the cleaning member removes the residual toner from the photoreceptor drum 41.

The intermediate transfer unit 5 includes a transfer belt 5A (an example of an image carrier), a drive roller 5B, and a driven roller 5C. The transfer belt 5A is a belt member to which the toner images of each color formed on the photoreceptor drums 41 of each of the image forming units 4 are transferred. The transfer belt 5A is provided above the photosensitive drum 41. The transfer belt 5A is an endless annular belt. The transfer belt 5A is rotatably supported by a drive roller 5B and a driven roller 5C that are provided apart from each other in the left-right direction D3. The transfer belt 5A is supported so as to span over a drive roller 5B and a driven roller 5C. When the surface of the transfer belt 5A passes between the photoreceptor drums 41 and the primary transfer roller 45, toner images are sequentially transferred from each photoreceptor drum 41 in an overlapping manner.

The optical scanning device 13 irradiates the photoreceptor drum 41 of each image forming unit 4 with laser light based on inputted image data of each color. As a result, an electrostatic latent image is formed on each photoreceptor drum 41.

The secondary transfer roller 20 is provided at a position facing the drive roller 5B with a conveyance path 26 extending vertically in between. The secondary transfer roller 20 conveys the sheet in the conveyance direction D11 together with the drive roller 5B. The sheet that has reached the image transfer position P1 (see FIG. 3) is held and conveyed in the conveyance direction D11. A charging device 21 that applies a transfer potential to the sheet conveyed by the secondary transfer roller 20 is provided near the secondary transfer roller 20 . By applying the transfer potential by the charging device 21, a charge opposite to that of the toner image is generated on the sheet. Thereby, when the sheet passes through the image transfer position P1 where the drive roller 5B and the secondary transfer roller 20 face each other, the toner image on the transfer belt 5A is transferred to the sheet at the image transfer position P1. The sheet onto which the toner image has been transferred is conveyed to a fixing device 16.

The fixing device 16 heats and fixes the toner image transferred to the sheet member, and includes a heating roller 16A and a pressure roller 16B. The sheet member conveyed to the fixing device 16 is conveyed while being sandwiched between a heating roller 16A and a pressure roller 16B. During this conveyance, heat is transferred from the heating roller 16A to the toner image transferred to the sheet member, thereby heating the toner image. This fixes the toner image on the sheet member. Thereafter, the sheet member is discharged onto the sheet tray 18 by the sheet discharge section 15.

The belt cleaning device 6 is located at a position facing the surface of the transfer belt 5A, downstream of the image transfer position P1 by the secondary transfer roller 20 in the running direction D10, and further downstream than the image forming unit 4Y in the running direction. It is provided at a position on the upstream side of D10. In this embodiment, the belt cleaning device 6 is provided at a position facing the driven roller 5C so as to sandwich the transfer belt 5A. The belt cleaning device 6 is a device that removes toner (residual toner) remaining on the surface of the transfer belt 5A. The belt cleaning device 6 includes a cleaning member that comes into contact with the surface of the transfer belt 5A to remove residual toner, and the cleaning member removes the residual toner from the transfer belt 5A.

[Sheet conveyance unit 23]
As shown in FIG. 3, the sheet conveyance unit 23 is arranged in contact with a drive roller 23A that is rotationally driven by obtaining a driving force from a conveyance motor 56 (see FIG. 5), and an outer peripheral surface of the drive roller 23A. and a driven roller 23B. A transport roller pair is realized by the driving roller 23A and the driven roller 23B. Note that the drive roller 23A or the conveyance roller pair constituted by the drive roller 23A and the driven roller 23B is an example of a conveyance roller.

The sheet conveyance unit 23 is shown in FIG. As shown in FIG. 5, the sheet conveyance unit 23 includes two drive rollers 23A arranged at equal intervals along the front-rear direction D2 perpendicular to the conveyance direction D11. Hereinafter, the front-rear direction D2 may be referred to as the width direction D2. Each drive roller 23A is fixed to a rotating shaft 47 extending in the width direction D2, and this rotating shaft 47 is rotatably supported by the internal frame 11A of the housing 11. Driving force from a transport motor 56 (see FIG. 4) is transmitted to the rotating shaft 47. The driving force of the transport motor 56 is transmitted to the rotating shaft 47 via a transmission mechanism (not shown) such as a gear or a belt.

Further, the sheet conveyance unit 23 has two driven rollers 23B corresponding to each drive roller 23A. The drive roller 23A and the driven roller 23B constitute a transport roller pair. That is, the sheet conveyance unit 23 has two pairs of conveyance rollers arranged side by side in the width direction D2. Two rotating shafts 49 are provided on a guide member 26A (see FIG. 3) that constitutes a conveyance guide surface on the left side of the conveyance path 26. Each of the two driven rollers 23B is rotatably supported by a rotating shaft 49. Each rotating shaft 49 is provided so as to be separated in the width direction D2, and one driven roller 23B is rotatably supported on each rotating shaft 49.

As shown in FIG. 3, the driven roller 23B is urged toward the drive roller 23A by a spring 23C with a predetermined elastic force (spring force). Thereby, the driven roller 23B is pressed against the drive roller 23A. When the drive roller 23A is rotationally driven in this state, the driven roller 23B is driven.

FIG. 6 is a schematic diagram showing the configuration of the sheet conveyance unit 23, and is a diagram when the sheet conveyance unit 23 is viewed from the upstream side (see arrow VI) in the conveyance direction D11 in FIG. As shown in FIG. 6, the rotating shaft 49 of the driven roller 23B is supported by a support portion 51 provided on the guide member 26A (see FIG. 3). A shaft end portion of each rotating shaft 49 is supported by a support portion 51 .

The support portion 51 is supported by the guide member 26A (see FIG. 3) so as to be movable in the vertical direction D1. In this embodiment, the support portion 51 supports the driven roller 23B movably between a contact position (position shown in FIG. 6), which will be described later, and a release position, which will be described later. That is, the driven roller 23B is supported movably between the contact position and the release position.

The support portion 51 is urged downward by a spring 23C. In other words, the support portion 51 supports the shaft end of the rotary shaft 49 while biasing the shaft end downward in response to the spring force of the spring 23C.

With the support portion 51 disposed at the contact position shown in FIG. 6, the driven roller 23B is elastically urged toward the drive roller 23A by a predetermined spring force (elastic force) by the spring 23C. Thereby, the driving roller 23A and the driven roller 23B are brought into pressure contact with each other by the spring force. This spring force is an elastic force that can grip and convey the sheet in the conveying direction D11.

When the support portion 51 is lifted upward from the contact position and moved to the release position, the driven roller 23B is released from the pressed state with the drive roller 23A. That is, the release position is a position where the driven roller 23B is separated from the drive roller 23A and is no longer pressed against the drive roller 23A. Note that the release position will be described as a position where the driven roller 23B is separated from the driving roller 23A, but if the sheet cannot be conveyed while being held, the surface of the driven roller 23B and the surface of the driving roller 23A are It may be a position of contact. That is, the release position includes a position where the surface of the driven roller 23B and the surface of the driving roller 23A are in contact with each other to such an extent that the conveyance force by the driven roller 23B and the driving roller 23A is not transmitted to the sheet. This contact state is a state in which the pressure contact state is released.

FIG. 4 is a block diagram showing the configuration of the image forming apparatus 10. As shown in FIG. As shown in FIG. 4, a solenoid 64 is provided inside the housing 11. The solenoid 64 is connected to the control section 90 and operates when energized by the control section 90 . The plunger of the solenoid 64 is connected to the support portion 51 via a link member (not shown). When the solenoid 64 is energized, the plunger is actuated to move the support portion 51 from the contact position to the release position. When the solenoid 64 is de-energized, the plunger is returned to its original position by a tension spring provided in the solenoid 64, and the support portion 51 is returned to the contact position by the spring force of the spring 23C.

As shown in FIG. 3, the conveyance path 26 is provided with a tilt detection sensor 61 (an example of a detection unit of the present invention). The tilt detection sensor 61 detects a conveyance shift of the sheet conveyed in the conveyance direction in the width direction D2 (crossing direction) intersecting the conveyance direction D11. In this embodiment, the inclination detection sensor 61 detects the inclination of the sheet with respect to the conveyance direction D11 (an example of conveyance deviation).

Specifically, when the sheet is being conveyed at an inclination with respect to the conveyance direction D11, the inclination detection sensor 61 detects whether or not the sheet is inclined with respect to the conveyance direction D11, the inclination direction, and the amount of inclination with respect to the conveyance direction D11 ( (tilt angle), etc. (tilt information). In the conveyance path 26, the inclination detection sensor 61 is provided downstream of the sheet conveyance unit 23 in the conveyance direction D11 and upstream of the sheet correction mechanism 60 in the conveyance direction D11.

As shown in FIG. 5, the tilt detection sensor 61 is a line sensor extending in the width direction D2. The line sensor includes a plurality of image sensors arranged in a line along the width direction D2. The tilt detection sensor 61 is connected to the control section 90. The tilt detection sensor 61 outputs a detection signal including image data (density data) of the leading edge of the sheet to the control unit 90. Upon acquiring the detection signal from the tilt detection sensor 61, the control unit 90 performs various determinations based on the detection signal. Specifically, the control unit 90 performs a process of determining whether or not the sheet conveyed by the sheet conveyance unit 23 is tilted with respect to the conveyance direction D11 based on the detection signal. If so, a process such as determining the tilted posture (tilt direction) is performed. Further, the control unit 90 determines the amount of inclination (inclination angle) of the seat based on the inclination information. Since these determination methods are conventionally known, detailed explanation thereof will be omitted.

Note that the tilt detection sensor 61 may be a pair of reflective optical sensors provided at positions equally spaced from the center of the conveyance path 26 in the width direction D2. The reflective optical sensor includes a light emitting element and a light receiving element, receives reflected light emitted from the light emitting element, and outputs a detection signal according to the amount of the received light. The control unit 90 determines whether the sheet conveyed by the sheet conveyance unit 23 is inclined with respect to the conveyance direction D11 based on the deviation in change in the detection signals sent from each of the pair of reflective optical sensors. If the seat is tilted, the seat is tilted, the tilt posture (tilt direction) is determined, and the tilt amount (tilt angle) of the seat is determined based on the tilt information.

In the conveyance path 26, a leading edge detection sensor 62 and an edge detection sensor 63 are provided downstream of the sheet correction mechanism 60 in the conveyance direction D11.

The leading edge detection sensor 62 is provided near the center P0 (see FIG. 5) in the width direction D2 in the conveyance path 26. The leading edge detection sensor 62 detects the leading edge of the sheet that has passed through the sheet correction mechanism 60. The tip detection sensor 62 is, for example, a reflective optical sensor. The tip detection sensor 62 is connected to a control section 90, and its detection signal is sent to the control section 90. The control unit 90 detects the leading edge of the sheet conveyed through the conveying path 26 based on changes in the detection signal sent from the leading edge detection sensor 62. Note that since such a detection method is conventionally known, detailed explanation thereof will be omitted.

The edge detection sensor 63 is arranged downstream of the tip detection sensor 62 in the transport direction D11. The edge detection sensor 63 detects the positions of both ends in the width direction D2 of the sheet that has passed through the sheet correction mechanism 60. The edge detection sensors 63 are a pair of line sensors provided at positions equally spaced from the center of the conveyance path 26 to the outside in the width direction D2. Each line sensor is composed of a plurality of image sensors arranged in a line along the width direction D2. In this embodiment, the edge detection sensor 63 is arranged so that the edge of the sheet in the width direction D2 passes through each line sensor.

The edge detection sensor 63 is connected to the control section 90. The edge detection sensor 63 outputs a detection signal (density signal) including image data (density data) of both ends of the sheet to the control unit 90. Upon acquiring the detection signal from the edge detection sensor 63, the control unit 90 determines the position of the sheet in the width direction D2 based on the detection signal. Specifically, the control unit 90 determines whether the sheet is located at the center in the width direction D2, whether the sheet is displaced in any direction in the width direction D2, and whether the sheet is displaced in the width direction D2. If so, it is determined how much the amount of deviation (lateral deviation amount) is. Note that, since such a determination method is conventionally known, detailed explanation thereof will be omitted.

[Sheet correction mechanism 60]
As shown in FIG. 3, the sheet correction mechanism 60 is provided on the conveyance path 26. The sheet correction mechanism 60 is provided in the conveyance path 26 on the downstream side of the sheet conveyance unit 23 in the conveyance direction D11. Specifically, the sheet correction mechanism 60 is provided between the tilt detection sensor 61 and the leading edge detection sensor 62 in the conveyance path 26 .

FIG. 7 is a schematic diagram showing the configuration of the sheet correction mechanism 60, and is a diagram when the sheet correction mechanism 60 is viewed from the upstream side (see arrow VII) in the conveyance direction D11 in FIG. As shown in FIG. 7, the sheet correction mechanism 60 includes a rotation unit 65 and a slide unit 66.

The rotation unit 65 corrects the skew of the skewed sheet conveyed by the sheet conveyance unit 23, and conveys the corrected sheet in the conveyance direction D11. Specifically, before the sheet enters the sheet correction mechanism 60, the rotation unit 65 moves the roller unit 80 from a predetermined initial position by a rotation amount (correction amount) corresponding to the amount of inclination of the sheet. The roller unit 80 is rotated to the sheet receiving position where it receives the sheet. After the sheet enters the roller unit 80 at the sheet receiving position, the rotating unit 65 returns the roller unit 80 from the sheet receiving position to the initial position while holding the sheet. As a result, the skew of the sheet is corrected.

Here, the initial position is a position where the sheet can be conveyed straight to the downstream side in the conveyance direction D11 by the roller unit 80, which will be described later, and as shown in FIG. This is the position in which it is placed straight along the In addition, when a first correction preparation operation to be described later is performed, the sheet receiving position is set such that when a first correction preparation operation to be described later is performed, the sheet is rotated in the direction of the inclination of the sheet by an amount of rotation such that the sheet traveling obliquely in the first inclination posture to be described later is straightened with respect to the conveying direction D11. This is the position rotated in the corresponding direction (upstream side in the transport direction D11), for example, the position shown in FIG. 11.

When the sheet conveyed by the sheet conveyance unit 23 is displaced in the width direction D2, the slide unit 66 corrects the displacement to return it to a predetermined center position. Specifically, the slide unit 66 moves the sheet in a direction (opposite to the direction of deviation) in which the lateral deviation is corrected by the amount of lateral deviation in the width direction D2 of the sheet. As a result, the deviation (lateral deviation) of the sheet in the width direction D2 is corrected.

As shown in FIGS. 5 and 7, the slide unit 66 has a base frame 67 that is long in the width direction D2. The base frame 67 is movably supported by the internal frame 11B of the housing 11 so as to be movable in the width direction D2. Specifically, the base frame 67 includes a horizontal flat base portion 67A and a support portion 67B (see FIG. 5) that is integrally formed at the upper end of the base portion 67A. The support part 67B has a shaft part 68 that projects outward from both ends of the base part 67A in the width direction D2, and the shaft part 68 is inserted into a shaft hole formed in the internal frame 11B and is supported. There is.

As shown in FIG. 5, a rack 71 is formed on the rear end surface of the support portion 67B. A pinion gear 72 is meshed with this rack 71. The slide unit 66 includes a second correction motor 73 such as a stepping motor. The pinion gear 72 is attached to the output shaft of the second correction motor 73. Therefore, the control unit 90 can slide the base frame 67 of the slide unit 66 in either direction (frontward or rearward) in the width direction D2 by driving and controlling the second correction motor 73.

As shown in FIG. 5, a protruding piece 69 that protrudes forward is formed at the front end of the base frame 67. As shown in FIG. Further, an optical sensor 70 capable of detecting the protruding piece 69 is provided on the front internal frame 11B. The position of the protruding piece 69 is detected by the optical sensor 70. Based on the position where the protruding piece 69 is detected by the optical sensor 70 (hereinafter referred to as the slide reference position), the control unit 90 moves the base frame 67 in the width direction D2.

Further, a support portion 74 (see FIG. 7) for pivotally supporting a rotation shaft 76 (an example of a rotation fulcrum of the present invention), which will be described later, is provided near the front end of the base portion 67A.

As shown in FIGS. 5 and 7, the rotating unit 65 includes a rotating frame 75 supported by the base portion 67A of the base frame 67, a roller unit 80 rotatably supported by the rotating frame 75, and a rotating unit 80 rotatably supported by the rotating frame 75. It has a first correction motor 85 that applies a driving force in the rotational direction to the moving frame 75. The rotation frame 75 is a plate-shaped member formed in a long shape in the width direction D2, and a rotation shaft 76 extending in the up-down direction D1 is provided at the right end thereof. The rotation shaft 76 is rotatably supported by a support portion 74 (see FIG. 7) provided on the base frame 67.

As shown in FIG. 7, a pair of support walls 77 and 78 are provided on the left surface 75A (the upper surface in the paper of FIG. 7) of the rotating frame 75, and are spaced apart from each other by a predetermined distance in the width direction D2. There is. A pair of support walls 77 and 78 vertically protrude leftward from the left surface 75A. The predetermined interval is a length that allows the sheet to be conveyed between the pair of support walls 77 and 78. The roller unit 80 is rotatably supported by the support walls 77 and 78.

The roller unit 80 is rotationally driven by the third correction motor 79. The roller unit 80 transports the sheet that has entered the sheet correction mechanism 60 to the downstream side in the transport direction D11. The roller unit 80 includes a drive roller 80A that is rotated by receiving rotational driving force from the third correction motor 79, and a driven roller 80B that is disposed in contact with the outer peripheral surface of the drive roller 80A. A transport roller pair is realized by the driving roller 80A and the driven roller 80B. Note that the drive roller 80A or the conveyance roller pair constituted by the drive roller 80A and the driven roller 80B is an example of the correction roller of the present invention.

The roller unit 80 has four drive rollers 80A arranged at equal intervals along the width direction D2. Each drive roller 80A is fixed to a rotating shaft 81 extending in the width direction D2, and this rotating shaft 81 is rotatably supported by the support walls 77 and 78. A third correction motor 79 such as a stepping motor is fixed to the support wall 78 . The rotational driving force of the third correction motor 79 is transmitted to the rotation shaft 81 through an output gear 79A fixed to the output shaft of the third correction motor 79 and an input gear 81A fixed to the end of the rotation shaft 81. Ru. Moreover, the roller unit 80 has four driven rollers 80B corresponding to each drive roller 80A. Each of the four driven rollers 80B is rotatably supported by a rotating shaft 82 provided on a guide member that constitutes the upper conveyance guide surface of the conveyance path 26. Two rotating shafts 82 are provided so as to be separated in the width direction D2, and two driven rollers 80B are rotatably supported on each rotating shaft 82.

The driven roller 80B is urged toward the drive roller 80A by a spring 80C (see FIG. 3). Thereby, the driven roller 80B is pressed against the drive roller 80A. When the drive roller 80A is rotationally driven in this state, the driven roller 80B is driven.

A first correction motor 85 such as a stepping motor is attached to the rear internal frame 11B. The first correction motor 85 is fixed to the outer surface of the internal frame 11B, and its output shaft 85A extends through the internal frame 11B to the opposite side (front side). A pinion gear 86 is fixed to the tip of the output shaft 85A of the first correction motor 85. A rack 87 extending in the up-down direction D1 (direction perpendicular to the plane of FIG. 7) is formed at the rear end of the left surface 75A of the rotation frame 75. The rack 87 meshes with the pinion gear 86. The rack 87 has parallel teeth arranged in the vertical direction D1. The control unit 90 can rotate the roller unit 80 together with the rotation frame 75 of the rotation unit 65 about the rotation shaft 76 by driving and controlling the first correction motor 85 .

In this embodiment, when the obliquely conveyed sheet is in the first tilted posture, the rotation unit 65 rotates the roller unit 80 from the initial position to the upstream side in the conveyance direction D11. A first correction preparation operation is performed. Here, the first tilted posture is a tilted state (tilted posture) in which the front end of the seat is ahead of the rear end, and is a posture shown by the broken line in FIG. be. Further, when the inclined posture of the sheet being conveyed obliquely is a second inclined posture that is opposite to the first inclined posture, the rotating unit 65 is moved from the initial position to the downstream side in the conveying direction D11. A second correction preparation operation is performed in which the roller unit 80 is rotated. Here, the second tilted position is a tilted state (tilted position) in which the rear end of the seat precedes the front end.

[Control unit 90]
The control unit 90 performs overall control of the image forming apparatus 10, controls the conveyance operation by the sheet conveyance unit 23, the correction operation by the sheet correction mechanism 60, and controls the conveyance speed by each pair of conveyance rollers. Note that the control section 90 is an example of a sheet conveyance control section of the present invention.

As shown in FIG. 4, the control unit 90 includes a CPU 91, a ROM 92, a RAM 93, a flash memory 94, a motor driver 95, and the like. The control section 90 is an example of a speed control section of the present invention. The control unit 90 is electrically connected to each motor 56, 73, 79, 85, each sensor 61, 62, 63, and solenoid 64 via a signal line or the like. Each of the motors 56, 73, 79, and 85 is connected to a motor driver 95 of the control unit 90, and is driven and controlled by receiving individual control signals from the motor driver 95.

Incidentally, if a sufficient space is not secured between the sheet conveying unit 23 and the sheet correction mechanism 60 inside the image forming apparatus 10, the following problem may occur. For example, if the rotation unit 65 performs a correction operation on a sheet that is traveling skew while the conveyance speed of the sheet is maintained at a constant speed (for example, reference speed V ₀ described later), the rotation unit 65 performs a correction operation for a sheet that is traveling skew while the conveyance speed of the sheet is maintained at a constant speed (for example, reference speed V 0 described later). In some cases, the sheet reaches the rotation unit 65 before the rotation unit 65 moves to the sheet receiving position where it receives the sheet. In this case, the sheet is pinched and conveyed by the drive roller 80A of the rotation unit 65 before the rotation unit 65 moves from the initial position by the amount of rotation corresponding to the inclination of the sheet, and the skew correction of the sheet cannot be performed accurately. There is a risk that it may not be possible. Such problems tend to occur, for example, when the inclination angle of the seat is large.

In this embodiment, as will be described later, the control unit 90 determines the conveyance speed V1 (an example of the conveyance speed of the present invention) of the sheet conveyed by the sheet conveyance unit 23 and the pair of feed rollers 30, and the conveyance speed V1 of the sheet conveyed by the sheet conveyance unit 23 and the feed roller pair 30, The conveyance speed V2 of the conveyed sheet is controlled. Specifically, when the control unit 90 determines that the sheet is skewed based on the detection signal received from the tilt detection sensor 61, the control unit 90 drives and controls the conveyance motor 56. The driving roller 23A of the sheet conveying unit 23 and the driving roller 30A of the feeding roller pair 30 are drive-controlled so that the sheet conveying speed V1 is reduced from a predetermined reference speed _V0 , and the driving roller 80A of the roller unit 80 is controlled. to drive and control. In the following description, the control unit 90 also controls the conveyance speed V2 in the same manner as the conveyance speed V1.

In this way, the conveyance speeds V1 and V2 of the sheet are decelerated from the reference speed _V0 , so that the sheet can be transferred to the roller unit 80 after the roller unit 80 has moved to the sheet receiving position for skew correction. reach. As a result, the sheet correction mechanism 60 appropriately performs the skew correction, and it is possible to improve the accuracy of the sheet skew correction.

In the present embodiment, the control unit 90 causes the correction time calculated based on the inclination information of the sheet to be set to a predetermined time when the first correction preparation operation or the second correction preparation operation is performed. It is determined whether or not the correction time is less than the first set time T1, and if the correction time is less than the first set time T1, the transport speeds V1 and V2 are maintained at the reference speed _V0 . Further, when the correction time is equal to or longer than the first set time T1, the control unit 90 reduces the conveyance speeds V1 and V2 to a first set speed V _L that is slower than the reference speed V ₀ .

Here, the correction time is the time required for the roller unit 80 to move from the initial position to the sheet receiving position when the correction operation is performed. This correction time can be calculated by the control unit 90 based on the inclination angle of the sheet, the rotation amount of the roller unit 80 corresponding to the inclination angle, the rotation speed of the roller unit 80 by the first correction motor 85, and the like.

Further, the reference speed V ₀ is the speed at which the sheet is conveyed during transfer by the secondary transfer roller 20.

Further, the first set time T1 determines whether or not the skew correction can be appropriately performed by the correction operation when the sheet is conveyed toward the sheet correction mechanism 60 at the reference speed _V0 . This is the threshold for In the present embodiment, the first set time T1 is such that after the tip of the sheet is detected by the inclination detection sensor 61, the roller rotates by the maximum amount of rotation (maximum correction amount), which is the upper limit that can be corrected by the first correction preparation operation. The time is set to be equivalent to the time required for the sheet to reach the sheet receiving position when the unit 80 rotates upstream in the conveyance direction D11. Here, in this embodiment, the maximum rotation time required for rotation of the maximum rotation amount by the first correction preparation operation is longer than the first set time T1 (the required time).

The first set speed V _L is, for example, a predetermined constant speed, and is an arbitrarily set element. Note that the first set speed V _L may be a speed calculated by the control unit 90 at each time of correction according to the amount of rotation during the correction operation.

Further, after the correction operation by the sheet correction mechanism 60 is completed, the control unit 90 changes the conveyance speeds V1 and V2 from the first set speed _VL to a second set speed _VH higher than the reference speed _V0 . The speed is increased for a predetermined period of time. That is, when the correction operation is completed, the control unit 90 changes the conveyance speeds V1 and V2 from the first set speed V _L to the second set speed V _H , and at a timing when the predetermined time has elapsed since the change. Then, the conveyance speeds V1 and V2 are returned from the second set speed _VH to the reference speed _V0 . This makes it possible to recover the delay caused by decelerating the seat.

The second set speed V _H is, for example, a predetermined constant speed, and is an element that is arbitrarily set according to the first set time T1. The second set speed V _H is set to a speed that can recover the delay caused by decelerating the seat. Note that the second set speed V _H may be a speed calculated each time the controller 90 performs the correction based on the second set speed V _H calculated each time the controller 90 performs the correction.

Further, the control unit 90 temporarily stops the sheet conveyance by the sheet conveyance unit 23 when the correction time is equal to or longer than the second set time T2, which is longer than the first set time T1. Specifically, when the first correction preparation operation or the second correction preparation operation is performed, the control unit 90 determines whether the correction time is equal to or longer than the second set time T2, and When the correction time is longer than the second set time T2, the conveyance motor 56 is stopped, and the conveyance by the sheet conveyance unit 23 is stopped for a predetermined period of time. Thereafter, when the roller unit 80 is rotated to the sheet receiving position, conveyance of the sheet is resumed, and the correction operation by the sheet correction mechanism 60 is continued.

Note that the second set time T2 determines whether the skew correction by the correction operation can be appropriately performed when the sheet is transported at the transport speeds V1 and V2 (first set speed V _L ) after deceleration. This is a threshold value for determining whether or not. In this embodiment, the second set time T2 is set to a time equivalent to the time required from when the tip of the sheet is detected by the inclination detection sensor 61 until the sheet after deceleration reaches the sheet receiving position. be done. Here, in this embodiment, the maximum rotation time required for rotation of the maximum rotation amount by the first correction preparation operation is longer than the second set time T2 (the required time).

Further, the control unit 90 determines whether the sheet after deceleration is delayed from the first transfer timing at which the toner image (image) on the transfer belt 5A is transferred to the sheet at the image transfer position P1 (see FIG. 3). If it is determined that the sheet is delayed in the first transfer timing, processing is performed to cause the image forming unit 4 to form the same toner image as the toner image on the transfer belt 5A again. In this case, the control unit 90 stops the application of the transfer potential by the charging device 21 at the first transfer timing, and transfers the toner image to the belt cleaning device 6 while the toner image is carried on the surface without being transferred. (See Figure 2). The belt cleaning device 6 removes the toner image from the transfer belt 5A so that the next toner image can be formed on the surface of the transfer belt 5A.

Further, when it is determined that the conveyance of the sheet is delayed to the first transfer timing, the control unit 90 stops the sheet at a predetermined stop position P2 upstream of the image transfer position P1 in the conveyance direction D11. . Then, the control unit 90 controls the sheet so that the sheet reaches the image transfer position P1 at a second transfer timing at which the toner image re-formed by the image forming unit 4 is transferred onto the sheet at the image transfer position P1. transport will be resumed. The stop position P2 is, for example, a position upstream of the image transfer position P1 in the transport direction D11 and downstream of the sheet correction mechanism 60 in the transport direction D11. The stop position P2 is a position specified by the detection position by the tilt detection sensor 61, the distance from the detection position to the image transfer position P1, the conveyance speed of the sheet, and the like.

Thereby, the toner image can be transferred to an appropriate position on the sheet without shifting the transfer position.

[Sheet correction processing]
Hereinafter, an example of the procedure of the sheet correction process executed by the control unit 90 will be described using the flowcharts of FIGS. 8 and 9 while referring to the operation explanatory diagrams of FIGS. 10 to 15. Here, FIGS. 10 to 15 are diagrams for explaining the operations of the sheet conveyance unit 23 and the sheet correction mechanism 60. The figure is a view of each drive roller 23A, 80A viewed from the axial direction. The feeding roller pair 30 is not shown in FIGS. 10 to 15.

It is assumed that in the image forming apparatus 10, before the sheet correction process is performed, the rotation unit 65 is placed at the initial position and the slide unit 66 is placed at the slide reference position.

When an instruction signal indicating the start of an image forming operation is input to the image forming apparatus 10, the image forming apparatus 10 starts image forming processing. Specifically, the motor driver 95 of the control unit 90 drives the transport motor 56, the third correction motor 79, other motors (not shown), etc., and drives the drive roller 30A of the feeding roller pair 30 and the pickup roller 38. , the drive roller 23A of the sheet conveyance unit 23, the drive roller 80A of the roller unit 80, the discharge roller pair, etc. are rotated. As a result, the sheet 100 is taken out from the sheet storage section 27 and fed to the conveyance path 26, and the sheet 100 is conveyed downstream in the conveyance direction D11 by the pair of feed rollers 30 and the sheet conveyance unit 23. At this time, the control unit 90 controls each motor so that the conveyance speeds V1 and V2 become the reference speed _V0 .

In step S<b>11 , the control unit 90 determines whether the leading edge of the sheet 100 has been detected based on the detection signal output from the tilt detection sensor 61 . That is, the control unit 90 determines whether the leading edge of the sheet 100 has passed the detection position by the tilt detection sensor 61.

In step S11, when it is determined that the leading edge of the sheet 100 is detected at the detection position by the tilt detection sensor 61 (see FIG. 10), the control unit 90 controls the conveyance path 26 based on the detection signal of the tilt detection sensor 61. It is determined whether or not the sheet 100 being conveyed has a conveyance shift. Specifically, it is determined whether the sheet 100 is skewed (S12). This determination process is performed before the leading edge of the sheet 100 enters the sheet correction mechanism 60.

In the next step S13, the control unit 90 determines the inclination posture of the seat 100 based on the output signal of the inclination detection sensor 61, and calculates the amount of inclination of the seat 100.

In the next step S14, it is determined whether the seat 100 is in the first tilted posture or the second tilted posture based on the tilted posture, and a correction operation corresponding to either of the tilted postures is determined.

Hereinafter, as shown in FIG. 11, the sheet correction process will be described by exemplifying a case where the sheet 100 is conveyed in the first tilted posture.

In the next step S15, the control unit 90 calculates the correction time required to perform the operation determined in step S14 (first correction preparation operation) by the amount of inclination.

In step S16, the control unit 90 determines whether the correction time is greater than or equal to the first set time T1 or less than the first set time T1.

If it is determined in step S16 that the correction time is less than the first set time T1, the control unit 90 maintains the sheet conveyance speeds V1 and V2 at the reference speed _V0 (S17).

On the other hand, if it is determined in step S16 that the correction time is greater than or equal to the first set time T1, the control unit 90 changes the sheet conveyance speeds V1 and V2 to the first set time T1, which is lower than the reference speed _V0 . The speed is decelerated to the set speed V _L (S18).

Thereafter, in step S19, the control unit 90 controls the drive of the first correction motor 85 to control the roller unit 80 of the rotation unit 65 according to the amount of inclination before the sheet 100 enters the sheet correction mechanism 60. is rotated from the initial position to the sheet receiving position where skew correction is started (see FIG. 11). Specifically, the roller unit 80 is rotated from the initial position to the sheet receiving position by the amount of inclination in a direction opposite to the direction in which the sheet 100 is inclined.

For example, as shown in FIG. 11, when the sheet 100 is conveyed in the first inclined position, the rotation unit 65 moves from the initial position to the upstream side in the conveyance direction D11 (in the direction approaching the leading end of the sheet 100). The first correction preparation operation of rotating the roller unit 80 is performed. Thereafter, when the sheet 100 enters the sheet correction mechanism 60, the sheet 100 is transported downstream in the transport direction D11 at the first set speed _VL by the sheet transport unit 23 and the feeding roller pair 30 (see FIG. 12). .

Thereby, the timing at which the sheet enters the roller unit 80 can be delayed. Further, it is possible to prevent the sheet from entering the roller unit 80 before the roller unit 80 is rotated to the sheet receiving position.

Note that when the second correction preparation operation is performed, the rotation unit 65 rotates the roller unit 80 from the initial position to the downstream side (direction away from the leading end of the sheet 100) in the conveyance direction D11.

When the leading edge of the sheet 100 reaches the leading edge detection sensor 62 and the controller 90 detects the leading edge of the sheet 100 (S20), the controller 90 controls the solenoid 64 in the next step S21 to activate the driven roller. 23B to the release position (see FIG. 13).

In this embodiment, the leading edge of the sheet 100 is detected by the leading edge detection sensor 62 as a condition for moving the driven roller 23B to the release position, but the present invention is not limited to this processing example. For example, the control unit 90 may move the driven roller 23B to the release position on the condition that the roller unit 80 has rotated to the sheet receiving position, that is, the rotation of the roller unit 80 has been completed. . Note that the completion of the rotation of the roller unit 80 can be determined by, for example, providing a position sensor (not shown) such as a rotary encoder in the first correction motor 85 and determining the amount of rotation based on the output signal from the position sensor and the amount of rotation in step S13. This can be determined from the calculated amount of inclination.

Thereafter, when the driven roller 23B is moved to the release position (S21), in step S22, the control unit 90 returns the roller unit 80 of the rotating unit 65 from the sheet receiving position to the initial position (see FIG. 13). ). That is, the roller unit 80 is rotated by the amount of inclination in a direction opposite to the direction in which it was rotated in step S19. As a result, the skew of the sheet 100 is corrected.

For example, when the first correction preparation operation is performed in step S19, the control unit 90 rotates the roller unit 80 downstream in the conveyance direction D11 (in the direction away from the leading end of the sheet 100), and Return to initial position. Note that if the second correction preparation operation has been performed in step S19, the control unit 90 rotates the roller unit 80 upstream in the conveying direction D11 (in the direction approaching the leading end of the sheet 100). Return to the initial position.

Further, when the leading edge of the sheet 100 is detected by the control unit 90 in step S20, the control unit 90 decelerates the conveyance speeds V1 and V2 from the reference speed V ₀ to the first set speed V _L in step S18. If so, the conveyance speeds V1 and V2 are increased to the second set speed _VH , which is faster than the reference speed _V0 (S23). Thereafter, after a predetermined time has elapsed, the transport speeds V1 and V2 are returned to the reference speed _V0 (S24). Note that if the conveyance speeds V1 and V2 are maintained at the reference speed _V0 , the process proceeds to the next step S25 (see FIG. 9) without performing the speed increasing process of steps S23 and S24. Further, the speed increasing process in step S23 may be performed before the procedure in step S21.

When the leading edge of the sheet 100 reaches the edge detection sensor 63 as shown in FIG. 14, in the next step S25, as shown in FIG. It is determined whether or not the position is shifted in either direction (front side or rear side) in the width direction D2. Here, if a deviation (lateral deviation) in the width direction D2 has occurred, the process proceeds to step S26, and the lateral deviation direction and lateral deviation amount are determined. On the other hand, if no lateral shift has occurred, the process proceeds to step S28.

In step S26, the control unit 90 determines the direction of lateral displacement of the sheet 100, and calculates the amount of lateral displacement. Thereafter, in step S27, the control section 90 slides the slide unit 66 in the direction of deviation correction (see the arrow in FIG. 14) according to the amount of lateral deviation. Specifically, the control unit 90 drives and controls the second correction motor 73 to move the slide unit 66 from the slide reference position by the amount of lateral deviation in a direction opposite to the lateral deviation direction of the seat 100. As a result, the lateral shift of the sheet 100 is corrected (see FIG. 15). After the slide movement in step S27 is performed, the process proceeds to step S28.

In step S28, the control unit 90 determines whether the rear end of the sheet 100 has passed through the sheet correction mechanism 60. Then, when it is determined that the rear end of the sheet 100 has passed the sheet correction mechanism 60, the control unit 90 moves the driven roller 23B from the release position to the contact position (S29), and moves the slide unit 66 to the slide position. Return to the reference position (S30). When the image forming process on the sheet is completed, the control unit 90 stops driving each motor 56, 73, 79, and 85, and ends the series of processes.

As described above, in the present embodiment, when the correction time is equal to or longer than the first set time T1, the sheet conveying speeds V1 and V2 change from the reference speed _V0 to the first set speed _VL . Slowed down. In this way, the conveying speeds V1 and V2 are reduced from the reference speed _V0 , so that the sheet reaches the roller unit 80 after the roller unit 80 has rotated to the sheet receiving position for skew correction. do. As a result, the sheet correction mechanism 60 appropriately performs the skew correction, and it is possible to improve the accuracy of the sheet skew correction.

Further, in the present embodiment, if the conveyance speeds V1 and V2 are decelerated after the correction operation by the sheet correction mechanism 60 is completed, the conveyance speeds V1 and V2 are changed from the first set speed _VL . The speed is increased to the second set speed _VH for a predetermined time. This makes it possible to recover the delay caused by the deceleration of the seat.

Hereinafter, another processing example of the sheet correction processing executed by the control unit 90 will be described using the flowchart of FIG. 16.

As shown in FIG. 16, the process up to step S15 described above is performed to calculate the correction time, and then, when it is determined that the correction time is equal to or greater than the first set time T1 (Yes in S16), the correction time is calculated. ), in the next step S161, the control unit 90 determines whether the correction time is equal to or longer than the second set time T2.

If it is determined in step S161 that the correction time is less than the second set time T2, the control unit 90 executes the processes from step S18 onwards.

On the other hand, if it is determined in step S161 that the correction time is equal to or longer than the second set time T2, the control section 90 stops the sheet conveyance unit 23 from conveying the sheet in the next step S162. Thereafter, in step S163, the control section rotates the roller unit 80 from the initial position to the sheet receiving position according to the amount of inclination, similarly to step S19.

Thereafter, the control unit 90 determines whether or not the rotation of the roller unit 80 has been completed (S164), and if it is determined that the rotation of the roller unit 80 has been completed, the control unit 90 stops the sheet conveyance unit 23 from conveying the sheet. It restarts (S165). The sheet conveyance speeds V1 and V2 after restarting may be the reference speed V ₀ or the second set speed V _H . For example, when the conveyance speeds V1 and V2 after restarting are the reference speed _V0 , the control unit 90 increases the conveyance speeds V1 and V2 to the second set speed _VH in the subsequent step S23. do. Further, when the conveyance speeds V1 and V2 after restarting are the second set speed _VH , the control unit 90 does not perform the speed increasing process in the subsequent step S23, but executes the processes from step S24 onwards.

Even when such processing is performed, the sheet can be made to reach the roller unit 80 after the roller unit 80 has rotated to the sheet receiving position. As a result, the sheet correction mechanism 60 appropriately performs the skew correction, and it is possible to improve the accuracy of the sheet skew correction.

[Transfer timing determination process]
Hereinafter, an example of the procedure of the transfer timing determination process executed by the control unit 90 will be described using the flowchart of FIG. 17. The transfer timing determination process is executed when the conveyance speeds V1 and V2 are decelerated or stopped in the sheet correction process described above.

When an instruction signal indicating the start of an image forming operation is input to the image forming apparatus 10, image forming processing by the image forming apparatus 10 is started, and a toner image is formed on the transfer belt 5A.

In step S41, the control unit 90 determines whether or not the decelerated sheet lags behind the first transfer timing at which the toner image is transferred to the sheet at the image transfer position P1 (see FIG. 3). The control unit 90 determines the first position based on the position (detection position) or detection timing at which the leading edge of the sheet is detected by the leading edge detection sensor 62, the distance from the detected position to the image transfer position P1, the conveyance speed of the sheet, etc. It is possible to determine whether or not conveyance of the sheet is delayed at the transfer timing. Note that the control unit 90 that performs the determination process in step S41 is an example of the determination unit of the present invention.

If it is determined in step S41 that the conveyance of the sheet does not lag behind the first transfer timing, the control unit 90 maintains conveyance of the sheet (S42), and then ends the series of processes.

On the other hand, if it is determined in step S41 that the conveyance of the sheet is delayed from the first transfer timing, the control unit 90 stops conveyance of the sheet at the stop position P2 (S43). At this time, application of the transfer potential by the charging device 21 is temporarily stopped. Thereby, the toner image is carried to the belt cleaning device 6 (see FIG. 2) while being carried on the transfer belt 5A, and is removed by the belt cleaning device 6.

Subsequently, the control section 90 performs a process of causing the image forming unit 4 to again form the same toner image as the toner image on the transfer belt 5A (S44).

Thereafter, the control unit 90 determines whether the retransmission timing corresponding to the second transfer timing has arrived (S45), and if it is determined that the retransmission timing has arrived, the re-formed toner image The conveyance of the sheet is resumed so that the image is transferred to the sheet at the image transfer position P1 at the second timing (S46).

Thereby, even if the conveyance of the sheet is delayed after the first transfer timing, the toner image can be transferred to the sheet at an appropriate position without shifting the transfer position with respect to the sheet.

In the above-described embodiment, the feeding roller pair 30 and the sheet conveying unit 23 are exemplified as the conveying section of the present invention, but for example, the sheet conveying unit 23 may be the only conveying section of the present invention.

10: Image forming device 14: Image forming section 20: Secondary transfer roller 23: Sheet transport unit 26: Sheet transport path 30: Feeding roller pair 60: Sheet correction mechanism 61: Skew detection sensor 65: Rotation unit 76: rotation axis

Claims (6)

a conveyance unit that conveys the sheet in a conveyance direction toward an image transfer position where the image is transferred to the sheet;
a detection unit that detects a conveyance shift of the sheet conveyed in the conveyance direction in a cross direction intersecting the conveyance direction;
is provided downstream of the conveyance section in the conveyance direction, conveys the sheet conveyed in the conveyance direction in the conveyance direction, and detects the conveyance displacement when the conveyance displacement is detected by the detection section. a correction section that corrects;
a sheet conveyance control section that controls conveyance of the sheet,
The sheet conveyance control section includes:
If the correction time calculated based on the conveyance deviation of the sheet is less than a predetermined first setting time, the conveyance speed of the sheet by the conveyance section is maintained at a predetermined reference speed, and the correction time is The image forming apparatus is configured to reduce the conveying speed from the reference speed when the first set time is longer than the first set time. The sheet conveyance control section includes:
The image forming apparatus according to claim 1, wherein the conveyance speed is increased from the reference speed by a predetermined time after the correction by the correction section is completed. The sheet conveyance control section includes:
The image forming apparatus according to claim 1 , wherein the image forming apparatus temporarily stops transport by the transport unit when the correction time is longer than a second set time that is longer than the first set time. When the detection unit detects the conveyance deviation of the sheet, the correction unit receives the sheet from an initial position by a predetermined correction amount corresponding to the conveyance deviation of the sheet before the sheet enters. a correction roller that is moved to a position and returned from the sheet receiving position to the initial position while pinching and conveying the sheet when the sheet enters;
The image forming apparatus according to claim 1 , wherein the correction time is a time required for the correction roller to move from the initial position to the sheet receiving position. The correction roller is
It is rotatable around a predetermined rotation fulcrum, and before the sheet enters, it is rotated from the initial position by a rotation amount corresponding to the conveyance deviation of the sheet, and when the sheet enters, the sheet The image forming apparatus according to claim 4, wherein the image forming apparatus is configured to return to the initial position while holding and transporting the image forming apparatus. an image carrier that carries the image to the image transfer position;
an image forming section that forms the image on the image carrier;
a transfer unit that transfers the image on the image carrier to the sheet at the image transfer position;
a determination unit that determines whether or not the sheet after the conveyance speed has been decelerated is behind a first transfer timing at which the image is transferred to the sheet at the image transfer position;
The image forming unit re-forms the same image as the image on the image carrier when the determining unit determines that the sheet is delayed in the first transfer timing;
The sheet conveyance control unit is configured to stop the sheet at a position before the image transfer position, and cause the image forming unit to restart the sheet when the determination unit determines that the sheet is delayed in the first transfer timing. 6. The conveyance of the sheet is restarted so that the formed image reaches the image transfer position at a second transfer timing at which the image is transferred to the sheet at the image transfer position. Image forming device.