JP2016108145A - Sheet conveying apparatus and control method of sheet conveying apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress conveyance failure of sheets without using drive means with high torque even when a conveying speed increases.SOLUTION: A sheet conveying apparatus comprises a plurality of roller pairs for conveying a transfer material, and a control part 200 for controlling the rotation of the plurality of roller pairs. The control part holds the transfer material with adjacent roller pairs in a conveyable state. When a conveying speed of the adjacent roller pairs is accelerated, if a time until a conveying speed of a downstream side roller pair 28 of the adjacent roller pairs, which is located on the downstream side in a conveying direction of the transfer material, reaches a predetermined conveying speed is longer than a time until a conveying speed of an upstream side roller pair 29, which is located on the upstream side of the downstream side roller pair 28, reaches the predetermined speed, the control part controls the rotation of the upstream side roller pari 29 so that the conveying speed of the upstream side roller pair 29 is decelerated at least one time before the conveying speed of the downstream side roller pair 28 reaches the predetermined speed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sheet conveying apparatus that conveys a transfer material such as a sheet. Further, the present invention relates to a method for controlling the sheet conveying apparatus.

  In a paper conveyance device such as an image forming apparatus, a plurality of roller pairs are arranged in a paper conveyance path, and each roller pair has a transfer material such as paper (hereinafter referred to as paper) between the rollers. The paper is conveyed by nipping and rotating in a predetermined direction. Each roller pair is driven and controlled by various driving means according to the required performance.

  For example, a registration roller that performs skew correction of a sheet is driven by a stepping motor. On the other hand, an unstable load is applied to the paper feed roller used in the part that feeds the paper while feeding the paper one by one. For this reason, a paper feed roller or the like that is subjected to a winding load is driven by being connected to a DC brushless motor via an electromagnetic clutch, for example, instead of a stepping motor.

  By the way, the time until the roller pair driven by the stepping motor reaches the predetermined speed is longer than the time until the roller pair driven by connecting the electromagnetic clutch reaches the predetermined speed. For this reason, the rise of the roller pair driven by the stepping motor is slower than the rise of the roller pair driven by being connected to the DC brushless motor via the electromagnetic clutch.

  Therefore, when a plurality of roller pairs driven by different driving means are in a state where the sheet is straddled, when the plurality of roller pairs are started from a stopped state, the rise of the downstream roller pair is the rise of the upstream roller pair. If it is slower, the paper will bend. When the deflection of the paper increases, wrinkles, folds, and the like may occur, and paper conveyance failure may occur.

  In Patent Document 1, an image forming apparatus includes a registration roller driven by a stepping motor, and a pre-registration roller that is arranged upstream of the registration roller in the sheet conveyance direction and is driven by connecting a clutch to a DC motor. The following measures are taken in the apparatus. First, when the registration roller is stopped in advance, a bend (initial loop) is created in the paper that straddles the registration roller and the pre-registration roller. Thereafter, the activation timing of the registration rollers is delayed compared to the activation timing of the pre-registration rollers. At this time, the timing at which the clutch is connected is set to be higher than the timing at which the stepping motor is started so that the loop that increases due to the rising speed difference between the registration roller and the pre-registration roller is within the range where the initial loop does not grow from the range where the initial loop does not grow By delaying, the occurrence of excessive loops is prevented.

JP 2002-179291 A

  However, since the space in the sheet conveyance path in the apparatus is finite, there is a limit to the amount of initial loop that can be formed in advance. The maximum deflection amount (hereinafter referred to as loop amount) of a sheet formed in a normal image forming apparatus is when the downstream roller pair is stopped and the sheet is fed about 10 mm in the transport direction by the upstream roller pair. The loop amount is as much as possible. Therefore, a loop larger than this cannot be formed in advance as an initial loop.

  On the other hand, when the speed of the apparatus is increased, the time required for each roller pair to reach a predetermined rotational speed also increases. For this reason, in the method of reducing the paper loop amount by delaying the upstream roller pair activation timing compared to the downstream roller pair activation timing, the necessary loop amount increases in advance. In the space in the paper conveyance path, a loop having the required size cannot be formed. Therefore, when the speed of the apparatus is increased, there is a problem that a conveyance failure cannot be avoided by a method in which a difference is made in the starting timing between the registration roller and the pre-registration roller.

  On the other hand, for such a problem, for example, a method of transporting a sheet by driving only a roller pair on the downstream side can be considered. However, in such a case, as compared with the case where the downstream roller pair and the upstream roller pair are driven simultaneously, a high torque driving means is required as the driving means for the downstream roller pair, and the device is As the size increases, the apparatus becomes expensive.

  Accordingly, an object of the present invention is to suppress paper conveyance failure without using high-torque driving means even when the conveyance speed is increased.

  In order to solve the above-described problems and achieve the object of the present invention, the paper transport apparatus of the present invention has a plurality of roller pairs that transport the transfer material, and a control unit that controls the rotation of the plurality of roller pairs, The control unit is narrow in a state in which the transfer material can be transported by the adjacent roller pair, and when the transport speed of the adjacent roller pair is accelerated, the control unit is downstream of the adjacent roller pair in the transport direction of the transfer material. When the transport speed of the downstream roller pair reaches a predetermined transport speed is longer than the time until the transport speed of the upstream roller pair on the upstream side of the downstream roller pair reaches the predetermined transport speed The rotation of the upstream roller pair is controlled so that the transport speed of the upstream roller pair is decelerated at least once before the transport speed of the downstream roller pair reaches a predetermined transport speed.

  A control method for a paper transport device according to the present invention is a control method for a paper transport device having a plurality of roller pairs for transporting a transfer material and a control unit for controlling the rotation of the plurality of roller pairs. When the transfer material can be transported by the adjacent roller pair in a narrow state and the transport speed of the adjacent roller pair is accelerated, the downstream roller pair on the downstream side in the transfer material transport direction among the adjacent roller pairs. In the case where the time until the conveyance speed at the roller reaches a predetermined conveyance speed is longer than the time until the conveyance speed at the upstream roller pair on the upstream side of the downstream roller pair reaches the predetermined conveyance speed, the downstream roller The rotation of the upstream roller pair is controlled so that the conveying speed of the upstream roller pair is decelerated at least once before the conveying speed of the pair reaches a predetermined conveying speed.

  According to the present invention, even when the conveyance speed is increased, it is possible to suppress the conveyance failure of the paper without using a high torque driving unit.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram illustrating a configuration of a control system of an image forming apparatus according to a first embodiment of the present invention. FIG. 5 is a schematic configuration diagram when a loop is formed on a sheet in a registration roller pair and a loop roller pair. FIG. 4A is a diagram (part 1) illustrating a time until the sheet conveyance speed of the registration roller pair and the loop roller pair reaches a predetermined speed. FIG. 4B is a diagram (part 2) illustrating a time until the sheet conveyance speed of the registration roller pair and the loop roller pair reaches a predetermined speed. FIG. 4C is a diagram (part 3) illustrating a time until the sheet conveyance speed at the registration roller pair and the loop roller pair reaches a predetermined speed. It is a flowchart which shows the control method of the conveyance part which concerns on one Embodiment of this invention. It is the figure which showed the speed change until the conveyance speed of the registration roller pair and loop roller pair controlled with the control method which concerns on one Embodiment of this invention reaches a target value.

  Hereinafter, an example of a sheet conveying apparatus and a method for controlling the sheet conveying apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the following description, an image forming apparatus is used as an example of a sheet conveying apparatus. In addition, this invention is not limited to the following examples.

[1. Configuration of entire image forming apparatus]
First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 according to the present embodiment forms an image on a sheet by electrophotography, and superimposes toners of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). A color image forming apparatus of a tandem format to be combined.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a document transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50, and a transport unit 23. And a secondary transfer unit 60 and a fixing unit 80.

  The document transport unit 10 includes a document feeder 11 on which a document G is set, a plurality of rollers 12, a transport drum 13, a transport guide 14, a document discharge roller 15, and a document discharge tray 16. . The documents G set on the document feeder 11 are conveyed one by one to the reading position of the image reading unit 30 by the plurality of rollers 12 and the conveying drum 13. The conveyance guide 14 and the document discharge roller 15 discharge the document G conveyed by the plurality of rollers 12 and the conveyance drum 13 to the document discharge tray 16.

  The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 31 and generates an image signal. Specifically, the image of the original G is irradiated by the lamp L. The reflected light from the document G is guided in the order of the first mirror unit 32, the second mirror unit 33, and the lens unit 34 and forms an image on the light receiving surface of the image sensor 35. The image sensor 35 photoelectrically converts incident light and outputs it as a predetermined image signal. Image data is created by A / D converting the output image signal.

  Further, the image reading unit 30 includes an image processing unit 36. The image processing unit 36 performs processing such as shading correction, dither processing, and compression on the image data created by the A / D conversion, and stores it in the RAM 203 (see FIG. 2) of the control unit 200 (see FIG. 2). The image data is not limited to data output from the image reading unit 30 and may be data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus.

  The paper storage unit 20 is disposed in the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size of the paper S. The sheet S is fed by the sheet feeding unit 21 and sent to the transport unit 23. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP sheet is sent to the transfer position.

  The conveyance unit 23 is provided on the upstream side of the secondary transfer unit 60, and includes a registration roller pair 28 (corresponding to the downstream roller pair of the present invention) and a loop roller pair 29 (corresponding to the upstream roller pair of the present invention). A plurality of conveying rollers are provided. The registration roller pair 28 is provided in the vicinity of the secondary transfer unit 60 and is driven and controlled by a stepping motor 70 (see FIG. 2). The loop roller pair 29 is provided on the upstream side of the registration roller pair 28 in the sheet conveyance direction, and is provided at a position adjacent to the registration roller pair 28. The loop roller pair 29 is driven and controlled by a DC brushless motor (not shown). At this time, transmission / interruption of the driving force from the DC brushless motor to the loop roller pair 29 is switched by turning on / off (connecting / releasing) a loop clutch 71 (see FIG. 2) constituted by, for example, an electromagnetic clutch.

  The sheet S fed from the sheet feeding unit 21 and sent to the conveyance unit 23 is conveyed to the secondary transfer unit 60 which is a transfer position by conveyance rollers including the loop roller pair 29 and the registration roller pair 28. In the previous stage of conveyance to the secondary transfer unit 60, the conveyance unit 23 rotates the loop roller pair 29 in a state where the sheet is abutted against the nip portion of the registration roller pair 28, and the registration roller pair 28, the loop roller pair 29, and the like. Skew correction is performed by forming a loop on the sheet between. Thereafter, the registration roller pair 28 and the loop roller pair 29 are rotationally driven at a timing at which the sheet and the toner image formed on the intermediate transfer belt 50 meet at the secondary transfer unit, whereby the sheet is moved to the secondary transfer unit 60 side. Transport. This embodiment is characterized by a method for controlling the registration roller pair 28 and the loop roller pair 29. A method for controlling the registration roller pair 28 and the loop roller pair 29 in this embodiment will be described in detail later.

  An image forming unit 40 and an intermediate transfer belt 50 are disposed between the image reading unit 30 and the paper storage unit 20. The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk). .

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, the first image forming unit 40Y will be described as a representative here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 arranged around the photoconductor 41, an exposure unit 43, a developing unit 44, and a cleaning unit 45. The photoreceptor 41 is rotated counterclockwise by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The exposure unit 43 forms an electrostatic latent image on the photoconductor 41 by performing an exposure operation on the surface of the photoconductor 41 based on image data read from the document G.

  The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41. As a result, a yellow toner image is formed on the surface of the photoreceptor 41. The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.

  The toner adhered on the photoreceptor 41 is transferred to the intermediate transfer belt 50. The cleaning unit 45 removes the toner remaining on the surface of the photoreceptor 41 after being transferred to the intermediate transfer belt 50.

  The intermediate transfer belt 50 is formed in an endless shape, and is rotated clockwise by a drive motor (not shown) in a direction opposite to the rotation direction of the photoconductor 41. A primary transfer portion 51 is provided at a position on the intermediate transfer belt 50 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 51 applies a polarity opposite to that of the toner to the intermediate transfer belt 50 to transfer the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50.

  As the intermediate transfer belt 50 rotates, the toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 50. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 50 to form a color image.

  A secondary transfer unit 60 is disposed in the vicinity of the intermediate transfer belt 50 and on the downstream side of the transport unit 23. The secondary transfer unit 60 includes a transfer roller pair including a transfer upper roller 52 with an intermediate transfer belt 50 stretched thereon and a transfer lower roller 61 pressed against the transfer upper roller 52 with the intermediate transfer belt 50 interposed therebetween. ing.

  In the secondary transfer unit 60, the sheet S that is nipped and conveyed by the registration roller pair 28 in the conveyance unit 23 is pressed by the lower transfer roller 61 toward the intermediate transfer belt 50. The secondary transfer unit 60 transfers the color toner image formed on the intermediate transfer belt 50 onto the sheet S sent from the transport unit 23. A cleaning unit 53 is provided in the vicinity of the intermediate transfer belt 50 and on the downstream side of the secondary transfer unit 60. The cleaning unit 53 removes the toner remaining on the surface of the intermediate transfer belt 50 after the transfer to the paper S.

  The fixing unit 80 is provided on the downstream side (discharge side) of the secondary transfer unit 60 where the paper S is conveyed, and includes a pair of fixing rollers including a pair of upper fixing rollers 81 and a lower fixing roller 82. In the fixing unit 80, the sheet S having an unfixed toner image is nipped by the upper fixing roller 81 and the lower fixing roller 82 and heated by pressure, thereby fixing the toner image on the sheet S.

  A switching gate 24 is disposed downstream of the fixing unit 80. The switching gate 24 switches the transport path of the paper S that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper S straight when performing face-up paper discharge in single-sided image formation. As a result, the paper S is discharged by the pair of paper discharge rollers 25. In addition, the switching gate 24 guides the paper S downward when performing face-down paper discharge for discharging the image forming surface downward in single-sided image formation and double-sided image formation.

  When face-down paper discharge is performed, the paper S is guided downward by the switching gate 24, and then the front and back sides are reversed by the paper reverse conveyance unit 26 and conveyed upward. As a result, the paper S is discharged by the pair of paper discharge rollers 25. When double-sided image formation is performed, the sheet S is guided downward by the switching gate 24, the front and back sides are reversed by the sheet reversing conveyance unit 26, and the sheet is sent again to the transfer position by the refeed path 27.

  Further, a post-processing device that folds the paper S or performs a stable process or the like on the paper S may be disposed downstream of the pair of paper discharge rollers 25.

  FIG. 2 is a block diagram including the control system of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 200. The control unit 200 includes, for example, a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202 for storing programs executed by the CPU 201, and a RAM (Random Access Memory) 203 used as a work area of the CPU 201. And having. Further, the image forming apparatus 1 includes a hard disk drive (HDD) 204 as a mass storage device and an operation display unit 205. As the ROM 202, a programmable ROM that is normally electrically erasable is used.

  The control unit 200 is connected to the image reading unit 30, the image processing unit 110, the image forming unit 40, the paper feeding unit 21, the transport unit 23, the operation display unit 205, and the HDD 204 via the system bus 107, and controls the entire apparatus. To do.

  The HDD 204 stores image data of an original image obtained by reading by the image reading unit 30 and stores output image data and the like. The operation display unit 205 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit 205 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 205 includes a plurality of keys, and serves as an input unit that receives input of various instructions, characters, numbers, and other data by user key operations.

  The image reading unit 30 optically reads a document image and converts it into an electrical signal. For example, when reading a color original, image data having luminance information of 10 bits for each of RGB per pixel is generated. Image data generated by the image reading unit 30 and image data transmitted from a PC (personal computer) 120 showing an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 110 for image processing. Is done. The image processing unit 110 performs image processing such as shading correction, image density adjustment, and image compression on the received image data as necessary. In addition, the image forming unit 40 receives the image data processed by the image processing unit 110 and forms an image on the paper S based on the image data.

  In the transport unit 23, under the control of the control unit 200, the rotation of the registration roller pair 28 is controlled by rotating the stepping motor 70, and the on / off of the loop clutch 71 is controlled to control the loop. The rotation of the roller pair 29 is controlled.

  In the present embodiment, an example in which a personal computer is used as an external device has been described. However, the present invention is not limited to this, and the external device may be a variety of other devices such as a facsimile machine.

  The image forming apparatus 1 according to the present embodiment is characterized by a method for controlling the loop roller pair 29 and the registration roller pair 28 in the transport unit 23. Hereinafter, a method for controlling the loop roller pair 29 and the registration roller pair 28 in the image forming apparatus 1 of the present embodiment will be described in detail.

[2. Conventional control method of transport unit]
In order to facilitate understanding of the control method of the image forming apparatus 1 of the present embodiment, prior to the description of the control method of the loop roller pair 29 and the registration roller pair 28 in the image forming apparatus 1 of the present embodiment, a conventional loop roller A method for controlling the pair and the registration roller pair will be described. Since the conventional image forming apparatus is different from the present embodiment only in the control method of the conveyance unit, the conventional control method will be described using the loop roller pair 29 and the registration roller pair 28 of the present embodiment.

  FIG. 3 is a schematic configuration diagram when a loop is formed on a sheet in the registration roller pair 28 and the loop roller pair 29. FIG. 4A shows the time until the sheet conveyance speed at the registration roller pair 28 and the loop roller pair 29 reaches a predetermined speed V1 when the activation timing of the registration roller pair 28 and the activation timing of the loop roller pair 29 are the same. It is a figure. FIG. 4B shows the time until the sheet conveyance speed at the registration roller pair 28 and the loop roller pair 29 reaches a predetermined speed V1 when the activation timing of the loop roller pair 29 is delayed from the activation timing of the registration roller pair 28. FIG. FIG. 4C shows the registration roller pair 28 and the loop roller pair when the activation timing of the loop roller pair 29 is delayed from the activation timing of the registration roller pair 28 when the target conveyance speed is increased as compared with FIG. 4B. 29 is a diagram illustrating the time until the paper transport speed at 29 reaches a predetermined speed V2 (> V1). In the following description, the sheet conveyance speed in each roller pair is simply referred to as “conveyance speed”.

  When correcting the skew of the paper in the registration roller pair 28, as shown in FIG. 3, the loop roller pair 29 is rotated for a predetermined time with the paper abutting against the nip portion of the registration roller pair 28 that has stopped rotating. A loop having a predetermined size is formed on the paper. In the following description, a loop formed on a sheet at the time of skew correction will be described as an initial loop. After the initial loop is formed, the registration roller pair 28 and the loop roller pair 29 are rotated at the timing when the toner image transferred to the intermediate transfer belt 50 reaches the secondary transfer unit 60, and the sheet is conveyed to the secondary transfer unit 60 side.

  Incidentally, as described above, in the registration roller pair 28 driven by the stepping motor 70 and the loop roller pair 29 driven by being connected to the DC brushless motor by the loop clutch 71, the loop roller pair 29 is more preferable than the registration roller pair. The rise time is earlier than the pair 28 until the predetermined conveying speed is reached. Therefore, as shown in FIG. 4A, when the start timings of the registration roller pair 28 and the loop roller pair 29 are the same, the time until the conveyance speed reaches the target value (indicated by V1) is the registration roller pair. 28 is longer than the loop roller pair 29. Then, the loop amount indicated by a1 in FIG. 4A is added to the initial loop due to the speed difference between the conveying speed of the registration roller pair 28 and the conveying speed of the loop roller pair 29 until the target value of the conveying speed is reached. There is a possibility that a loop exceeding the allowable amount is formed on the sheet in the conveyance path.

  In order to prevent this, conventionally, as shown in FIG. 4B, measures have been taken to delay the start timing of the loop roller pair 29 relative to the start timing of the registration roller pair 28. As shown in FIG. 4B, by delaying the start timing of the loop roller pair 29 for a predetermined time from the start timing of the registration roller pair 28, the initial amount previously formed at the time of skew correction by the loop amount indicated by a2 in FIG. 4B. Decrease from the loop. Thereafter, when the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28, a loop amount indicated by a3 in FIG. 4B is added to the sheet between the registration roller pair 28 and the loop roller pair 29. .

  As shown in FIG. 4B, by delaying the start timing of the loop roller pair 29 from the start timing of the registration roller pair 28, the loop shown by a2 in FIG. 4B can be reduced from the pre-formed initial loop. . For this reason, even when the loop amount indicated by a3 in FIG. 4B is added, the registration roller pair 28 and the loop roller pair 29 are required to reach the predetermined speeds in both the registration roller pair 28 and the loop roller pair 29. It is possible to prevent an excessive loop from being formed on the sheet between the two.

  By the way, when the target conveyance speed increases due to the higher speed of the apparatus, the rotation speeds of the registration roller pair 28 and the loop roller pair 29 reach the target speed, and the conveyance speeds in the registration roller pair 28 and the loop roller pair 29 become the target speed. The time required to reach the conveyance speed is also increased. For this reason, since the period during which the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28 becomes longer, the amount of loop formed on the sheet increases due to the difference in speed.

  As shown in FIG. 4C, when the target value (indicated by V2) of the conveyance speed in the registration roller pair 28 and the loop roller pair 29 is larger than that in FIG. 4B, the start timing of the loop roller pair 29 is set to the registration roller pair. By increasing the time delayed from the start timing of 28 as compared with FIG. 4B, the amount of loop decreased from the initial loop (the amount of loop indicated by a4 in FIG. 4C) can be increased.

  However, as described above, the space of the sheet conveyance path is limited, and there is a limit to the amount of initial loop that can be formed in advance. Therefore, when the loop amount indicated by a4 in FIG. 4C is larger than the initial loop amount, the initial loop disappears before the transport speed in the loop roller pair 29 catches up with the transport speed in the registration roller pair 28. As a result, the sheet is pulled between the registration roller pair 28 and the loop roller pair 29, so that noise may be generated or a load may be applied to the stepping motor 70 that drives the registration roller pair 28, resulting in step-out. .

  Accordingly, there is a limit to the activation timing of the loop roller pair 29 that can be delayed from the activation timing of the registration roller pair 28. On the other hand, when the difference in the activation time between the activation timing of the registration roller pair 28 and the activation timing of the loop roller pair 29 is small with respect to the target conveyance speed, the loop amount indicated by a5 in FIG. There is a problem that excessive loops are formed on the paper.

  Therefore, hereinafter, as a control method in the transport unit 23 of the present embodiment, a control method of the transport unit 23 in which an initial loop is not lost even when the transport speed is increased and an excessive loop is not formed will be described.

[3. Control Method for Conveying Unit in the Embodiment]
FIG. 5 is a flowchart illustrating a method for controlling the transport unit 23 according to the present embodiment. FIG. 6 is a diagram showing a change in speed until the conveyance speed in the registration roller pair 28 and the loop roller pair 29 controlled by the control method of the present embodiment reaches a target value. In the present embodiment, a loop having a predetermined size (hereinafter referred to as an initial loop) is formed on the sheet between the registration roller pair 28 and the loop roller pair 29 to correct skew feeding, and then the registration roller pair 28 and the loop roller pair. The state in which the rotation of 29 is stopped is set as the initial state, and the time when the conveyance of the paper is started at the timing when the toner image is transferred by the secondary transfer unit 60 is set as a start. Note that after the initial loop is created, the rotation of the loop roller pair 29 is stopped by the loop clutch 71 being turned off, and the DC brushless motor that drives the loop roller pair 29 continues to rotate at a constant speed. . In this embodiment, the target value of the conveyance speed in the registration roller pair 28 and the loop roller pair 29 is V2. The loop amount of the initial loop is A0 (A0 is a positive value).

  When the conveyance of the paper is started in accordance with the timing at which the secondary transfer unit 60 transfers the toner image after the initial loop is formed, the control unit 200 first starts driving the stepping motor 70 to register the resist roller pair 28. Is started (step S1). Thereafter, after a predetermined time T1 has elapsed, the control unit 200 turns on the loop clutch 71 and starts driving the loop roller pair 29 (step S2). When the loop clutch 71 is turned on, the conveyance speed in the loop roller pair 29 is accelerated and exceeds the conveyance speed in the registration roller pair 28 after a predetermined time t has elapsed.

  By the way, after the registration roller pair 28 and the loop roller pair 29 are sequentially rotated and driven in step S1 and step S2, the difference in speed is the period during which the conveyance speed in the registration roller pair 28 is lower than the conveyance speed in the loop roller pair 29. As a result, the amount of loop formed on the sheet between the registration roller pair 28 and the loop roller pair 29 is reduced. If the decreasing loop amount exceeds the initial loop amount, there is no loop formed on the sheet between the registration roller pair 28 and the loop roller pair 29, and a conveyance failure may occur as described above. Therefore, in this embodiment, after the loop clutch 71 is turned on, the loop amount that decreases due to the speed difference until the conveyance speeds in the registration roller pair 28 and the loop roller pair 29 become the same is A1 (A1 is a negative value). ), The predetermined time T1 is set so as to satisfy A0 + A1> 0.

  Next, after a predetermined time T2 (> t) has elapsed after turning on the loop clutch 71 in step S2, the control unit 200 turns off the loop clutch 71 (step S3). In step S3, the timing to turn off the loop clutch 71 is after the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28. By turning off the loop clutch 71 in step S3, the acceleration of the loop roller pair 29 becomes a negative value, and the conveyance speed in the loop roller pair 29 is again reduced to be lower than the conveyance speed in the registration roller pair 28.

  By the way, after the loop clutch 71 is turned on in step S2, a period during which the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28, During this period, the amount of loops formed on the paper increases. If an excessive loop is formed in the sheet conveyance path due to the increased loop amount, a conveyance failure may occur as described above. Therefore, in this embodiment, the maximum value of the loop amount that can be formed in the paper conveyance path is Amax, and after the loop clutch 71 is turned on in step S2, the conveyance speed in the loop roller pair 29 is equal to the conveyance speed in the registration roller pair 28. Assuming that the amount of loop that increases during the exceeding period is A2 (A2 is a positive value), the predetermined time T2 is set so as to satisfy A0 + A1 + A2 <Amax.

  Then, after turning off the loop clutch 71 in step S3 and after a predetermined time T3 has elapsed, the control unit 200 turns on the loop clutch 71 again (step S4). As a result, the acceleration of the loop roller pair 29 again becomes a positive value, and the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28.

  After the loop clutch 71 is turned off in step S3, the period during which the conveyance speed of the loop roller pair 29 is lower than the conveyance speed of the registration roller pair 28 is determined by the difference in speed between the registration roller pair 28 and the loop roller pair 29. The amount of loops formed on the paper in between decreases. If the loop between the registration roller pair 28 and the loop roller pair 29 disappears due to the decreasing loop amount, a conveyance failure may occur as described above. Therefore, after turning off the loop clutch 71 in step S3, the amount of loop that decreases during the period in which the conveyance speed of the loop roller pair 29 is lower than the conveyance speed of the registration roller pair 28 is A3 (A3 is a negative value). Then, A3 needs to satisfy A0 + A1 + A2 + A3> 0.

  On the other hand, after the loop clutch 71 is turned on in step S4, the conveyance speed of the loop roller pair 29 again exceeds the conveyance speed of the registration roller pair 28, and the conveyance speeds of the registration roller pair 28 and the loop roller pair 29 become the same. During this period, the amount of loop formed on the sheet between the registration roller pair 28 and the loop roller pair 29 increases again due to the speed difference. If an excessive loop is formed in the sheet conveyance path due to the increased loop amount, a conveyance failure may occur as described above. Therefore, after the loop clutch 71 is turned on in step S4, the amount of loop that increases during the period in which the conveyance speed of the loop roller pair 29 exceeds the conveyance speed of the registration roller pair 28 is A4 (A4 is a positive value). Then, A4 needs to satisfy A0 + A1 + A2 + A3 + A4 <Amax.

  Therefore, the predetermined time T3 in step S4 is set so that A0 + A1 + A2 + A3> 0 is satisfied and A0 + A1 + A3 + A4 + <Amax is satisfied. Then, after the loop clutch 71 is turned on in step S4, the conveyance speeds of the registration roller pair 28 and the loop roller pair 29 both reach the target conveyance speed V2. Here, the control unit 200 ends the control of the rotation of the registration roller pair 28 and the loop roller pair 29. After the conveyance speeds of the registration roller pair 28 and the loop roller pair 29 reach the target value, the sheet is conveyed at the conveyance speed.

  In the present embodiment, the amount of loop formed between the registration roller pair 28 and the loop roller pair 29 can be reduced by delaying the activation timing of the loop roller pair 29 from the activation timing of the registration roller pair 28. it can. Thereby, it is possible to prevent the loop formed on the sheet between the registration roller pair 28 and the loop roller pair 29 from exceeding the maximum loop amount that can be formed in the sheet conveyance path, and to prevent conveyance failure. Can do.

  Further, in the present embodiment, the loop clutch 71 is turned on to activate the loop roller pair 29, and after the conveyance speed in the loop roller pair 29 exceeds the conveyance speed in the registration roller pair 28, the conveyance speed in the loop roller pair 29 is increased. Before reaching the target value, the loop clutch 71 is once turned off. Thus, the amount of additional loops formed on the sheet between the registration roller pair 28 and the loop roller pair 29 can be adjusted so as not to be excessive, and the additional formed loops can be reduced again. it can.

  Thus, in the present embodiment, after the rotation of the registration roller pair 28 and the loop roller pair 29 is started, before the conveyance speed in the registration roller pair 28 and the loop roller pair 29 reaches the target value, The loop amount of the paper between the loop roller pair 29 can be adjusted. As a result, there is no loss of paper loop between the registration roller pair 28 and the loop roller pair 29, and there is no excess. For this reason, it is possible to prevent paper conveyance failure due to the absence or excess of the paper loop between the registration roller pair 28 and the loop roller pair 29.

  In this embodiment, it is only necessary to change the control method in the transport unit 23 as compared with the conventional case, and a motor generally used as a drive source for rotationally driving the roller pair can be used as it is. For this reason, it is not necessary to make a change such as using a high-torque drive source on the downstream side in preparation for speeding up the apparatus. Furthermore, when implementing the control method of the transport unit 23 of the present embodiment, it is not necessary to add hardware such as a PMW circuit or a chopping circuit. As described above, in the control method of the present embodiment, it is possible to increase the transport speed without making a major change from a general paper transport apparatus (image forming apparatus). As a result, even when the transport speed is increased, the apparatus does not increase in size or increase in price.

  In addition, if the paper loop is crushed (eliminated) between two adjacent roller pairs, there is a problem that noise is generated due to the paper being pulled. Conversely, if the loop is excessively formed on the paper, There is a problem in that noise is generated by colliding with a guide plate forming a paper conveyance path. On the other hand, in this embodiment, since it is possible to prevent the loop from being crushed or excessively formed, it is also effective in suppressing noise.

  As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the configuration described in the above-described embodiment, and the configuration can be appropriately changed without departing from the gist thereof. Is.

  In this embodiment, after the loop clutch 71 is turned on in step S2, the conveyance speed of the loop roller pair 29 is once decelerated by turning the loop clutch 71 off once. In addition, the timing for turning on the loop clutch 71 in step S4 is after the conveyance speed of the loop roller pair 29 falls below the conveyance speed of the registration roller pair 28, but is not limited thereto. For example, even when the timing at which the loop clutch 71 is turned on in step S4 is before the conveyance speed in the loop roller pair 29 is lower than the conveyance speed in the registration roller pair 28, compared to the case where the loop clutch 71 is not turned off in step S3. The increase in the loop amount can be moderated. In this way, by adjusting the reacceleration timing and the number of times of deceleration of the loop roller pair 29, the amount of loops formed on the paper between the registration roller pair 28 and the loop roller pair 29 is appropriately adjusted. Can do.

  In the present embodiment, the loop clutch 71 is turned on / off in a time-controlled manner. However, a loop sensor capable of detecting the loop amount is provided, and the loop clutch 71 is controlled according to the loop amount detected by the loop sensor. The clutch 71 may be turned on / off. In this case, there is no loop formed on the sheet between the registration roller pair 28 and the loop roller pair 29 until the conveyance speeds in the registration roller pair 28 and the loop roller pair 29 reach the target values. Alternatively, the loop amount is detected by a loop sensor at any time so as not to become excessive, and the on / off of the loop clutch 71 is controlled.

  In the present embodiment, the loop roller pair 29 and the registration roller pair 28 are described as an example of the upstream roller pair and the downstream roller pair, respectively, but the present invention is not limited to this. Appropriately when paper is transported by an upstream roller pair and a downstream roller pair adjacent to each other in the transport direction, and the acceleration applied to the paper by the upstream roller pair is greater than the acceleration provided by the downstream roller pair to the paper Applicable technology.

  In this embodiment, the initial loop is formed to correct the skew of the sheet between the upstream roller pair (loop roller pair 29) and the downstream roller pair (registration roller pair 28). The present invention can also be applied to the case where the conveyance of the sheet is started from a state where the initial loop is not formed. In this case, when the control of the upstream roller pair and the downstream roller pair is started from the initial state, the upstream roller pair and the downstream roller pair are set at the same start timing, and the upstream roller pair is appropriately decelerated. Let That is, in this embodiment, in step S1 and step S2, the downstream roller pair and the upstream roller pair are activated in this order. However, when the initial loop is not formed, the downstream roller pair and the upstream roller are simultaneously formed. After starting the roller pair, the upstream roller pair is decelerated as appropriate. Accordingly, it is possible to prevent an excessive loop formed on the sheet between the upstream roller pair and the downstream roller pair, and it is possible to prevent conveyance failure.

  Furthermore, the control method of the present embodiment has been described by taking as an example the case where the skew correction of the paper is performed between the upstream roller pair (loop roller pair 29) and the downstream roller pair (registration roller pair 28). It is not limited to this. In addition, the present invention can be applied to a control method at the time of starting conveyance from a state in which the paper is temporarily stopped in order to perform the paper synchronization operation after the occurrence of JAM or in the paper feeding portion. In addition, the present invention is not limited to the control at the time of restarting the conveyance of the paper once stopped, but when shifting to a higher process line speed during a constant speed operation at a predetermined process line speed. Is also applicable.

  Further, in the present embodiment, an example in which a sheet cut into a predetermined size is used as the recording medium, but the configuration of the present embodiment can be applied to the case where roll paper is used.

  In this embodiment, the upstream roller pair (loop roller pair 29) is rotationally driven by being clutch-connected to the DC brushless motor, and the downstream roller pair (registration roller pair 28) is rotationally driven by the stepping motor 70. However, this is not a limitation. Applicable when the rise time until the conveyance speed of the downstream roller pair reaches a predetermined speed in two adjacent roller pairs is longer than the rise time until the conveyance speed of the upstream roller pair reaches a predetermined speed For example, even when each of the downstream roller pair and the upstream roller pair is driven by a motor having the same torque specification, the present invention can be employed when the acceleration by the motor is different. . In this embodiment, the upstream roller pair (loop roller pair 29) is decelerated by turning on / off the loop clutch 71 (electromagnetic clutch). For example, the rotational drive of the motor is stopped for a short time. The upstream roller pair may be decelerated depending on the configuration.

  In the present exemplary embodiment, the image forming apparatus 1 has been described as an example of the sheet conveying apparatus. However, the present invention can be applied to an apparatus including a conveyance unit that conveys a sheet, such as a sheet feeding apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Document conveyance part, 20 ... Paper storage part, 28 ... Registration roller pair, 29 ... Loop roller pair, 30 ... Image reading part, 40. ..Image forming section 50... Intermediate transfer belt 60. Secondary transfer section 70. Stepping motor 71. Loop clutch 80. Fixing section 110 110 Image processing Part, 200... Control part

Claims (6)

A plurality of roller pairs for conveying the transfer material;
A controller that controls rotation of the plurality of roller pairs,
The control unit is narrowed in a state in which the transfer material can be conveyed by the adjacent roller pair, and when accelerating the conveyance speed in the adjacent roller pair, in the conveyance direction of the transfer material among the adjacent roller pairs The time until the conveyance speed in the downstream roller pair on the downstream side reaches a predetermined conveyance speed is the time until the conveyance speed in the upstream roller pair on the upstream side of the downstream roller pair reaches the predetermined conveyance speed. If the time is longer than the time, the rotation of the upstream roller pair is controlled so that the conveyance speed of the upstream roller pair is decelerated at least once before the conveyance speed of the downstream roller pair reaches a predetermined conveyance speed. Yes Paper transport device. When the conveyance is started from the state where the conveyance of the transfer material is stopped, the control unit determines that the rotation timing of the rotation of the upstream roller pair of the two roller pairs is the rotation activation of the downstream roller pair. The paper conveyance device according to claim 1, wherein the paper conveyance device is controlled so as to be later than the timing. Before starting the conveyance from the state where the conveyance of the transfer material is stopped, the control unit rotates the two roller pairs so that a deflection is formed in the transfer material between the two roller pairs. The paper conveyance device according to claim 1 or 2. The sheet conveying device according to claim 3, wherein the downstream roller pair of the two roller pairs is a registration roller pair. Of the two roller pairs, the downstream roller pair is driven by a stepping motor, and the upstream roller pair is driven by being connected to a driving source driven at a constant speed via a clutch,
The control unit controls rotation of the downstream roller pair by controlling driving of the stepping motor, and controls rotation of the upstream roller pair by controlling on / off of the clutch. The paper conveying apparatus in any one of -4. A plurality of roller pairs for conveying the transfer material;
A control method for a sheet conveying device having a control unit for controlling rotation of the plurality of roller pairs,
The control unit is narrowed in a state in which the transfer material can be conveyed by the adjacent roller pair, and when accelerating the conveyance speed in the adjacent roller pair, in the conveyance direction of the transfer material among the adjacent roller pairs The time until the conveyance speed in the downstream roller pair on the downstream side reaches a predetermined conveyance speed is the time until the conveyance speed in the upstream roller pair on the upstream side of the downstream roller pair reaches the predetermined conveyance speed. If the time is longer than the time, the rotation of the upstream roller pair is controlled so that the conveyance speed of the upstream roller pair is decelerated at least once before the conveyance speed of the downstream roller pair reaches a predetermined conveyance speed. Yes Method for controlling the paper transport device.

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