JP2011149985A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, suitably preventing deterioration of image quality due to an instantaneous speed change in driving speed of an intermediate transfer body or an image carrier, which is caused by impulsive vibration occurring when a skewed recording paper enters a transfer part. <P>SOLUTION: The apparatus includes: a computing means for computing the time elapsed until the corner part at the leading edge of recording paper reaches an image transfer part based on the paper bending amount of recording paper obtained by a paper bending detecting means; and a control means for controlling one or both of the gain amount of a driving motor and a gain switching time of the driving motor for one or both of a belt driving motor and an image carrier driving motor prior to the leading edge reach time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording sheet by, for example, electrophotography.

  Conventionally, in an electrophotographic copying machine, printer, facsimile, etc., a toner image on an image carrier (hereinafter also simply referred to as a photoreceptor) is transferred to a recording medium (hereinafter also referred to as recording paper or simply as paper). As a method for doing this, a method is known in which a toner image formed on a photoreceptor is directly transferred to a recording sheet.

  On the other hand, an image forming method using an intermediate transfer member is known. This method includes another transfer step in the step of transferring a toner image from a photosensitive member to a recording paper, and the photosensitive member is transferred to the intermediate transfer member. After the primary transfer, the primary transfer image of the intermediate transfer member is secondarily transferred to the recording paper to obtain a final image.

  In the so-called full-color image forming apparatus, the intermediate transfer method reproduces a color-separated document image using subtractive color mixing with toners such as yellow (Y), magenta (M), cyan (C), and black (K). In many cases, it is adopted as a method of superimposing and transferring toner images of respective colors.

  In such an image forming apparatus, a momentary impact is applied to the photoconductor or the intermediate transfer body when the recording paper enters or leaves the transfer unit that transfers the photoconductor or the intermediate transfer body to the recording paper. Further, there is a known problem that the load torque of the transfer member changes and the rotation speed of the photosensitive member or transfer member changes.

  This problem may cause transfer deviation of the transfer portion and exposure unevenness during exposure, thereby degrading image quality.

  As techniques for solving the above-mentioned problems, the following patent documents and the like are disclosed.

JP 2001-265127 A JP 2004-61882 A

  In Patent Document 1, an adverse effect of the impact on the transfer portion of the recording paper is suppressed by providing a mechanism for suppressing the impact mechanically in the vicinity of the transfer portion. However, since a dedicated mechanical mechanism is required, there is a problem that the cost of the apparatus increases.

  Further, in Patent Document 2, the intermediate transfer belt and the secondary transfer belt are driven by a separate motor at a constant relative speed, and the synchronization control is temporarily stopped at the timing when the recording paper enters the secondary transfer unit. The relative speed between the intermediate transfer belt and the secondary transfer belt is not increased. In this case, the operation mode of synchronous driving with another motor is premised, and there is a problem that lacks versatility.

  Further, in Patent Documents 1 and 2, no special consideration is given to the recording paper moving obliquely with respect to the transport direction and entering the transfer portion, and leaving the transfer portion.

  The present invention has been made in order to solve the above-described problems. When the recording paper is skewed with respect to the transport direction and enters the transfer unit, and the recording paper is skewed with respect to the transport direction. Therefore, it is possible to appropriately prevent the image quality from deteriorating due to instantaneous speed fluctuations in the driving speed of the intermediate transfer belt or the photoconductor due to the shocking vibration generated when the transfer part is detached. An object is to realize an image forming apparatus.

1. An image transfer unit that transfers an image formed on the image carrier, a conveyance unit that conveys the recording paper to the image transfer unit, a conveyance direction of the recording paper, and a vertical direction along the conveyance surface. A paper bending detection means for detecting the amount of paper bending with respect to the recording paper transport direction by detecting the leading edge in the recording paper transport direction, a belt drive motor for driving the intermediate transfer belt, and a belt for driving the belt drive motor A drive unit; an image carrier drive motor that drives an image carrier provided for each of the image carriers for yellow, magenta, cyan, and black; and an image carrier drive unit that drives the image carrier drive motor. An image forming apparatus having
Based on the amount of paper bending at the leading edge of the recording paper detected by the paper bending detection means and the width of the recording paper to be conveyed, the corner of the leading edge of the recording paper from the time when the paper bending detection means detects the leading edge of the recording paper. Computation means for calculating the tip arrival time until the part reaches the image transfer part,
Before the tip end time elapses, either or both of the belt driving unit and the image carrier driving unit are controlled to change the gain amount of the motor, and after the predetermined determination time has elapsed, the motor An image forming apparatus comprising control means for performing control to return the gain amount of the image.

  2. The determination time is at least a time from the time when the corner portion of the leading edge of the recording paper reaches the image transfer portion to the time until all the leading edge reaches the image transfer portion. The image forming apparatus according to 1 above.

3. The control means includes
When the amount of paper bending of the recording paper detected by the paper bending detection means is compared with a predetermined first threshold, and when it is determined that the amount of paper bending of the recording paper is smaller than the first threshold, the belt drive motor and Perform control to make the determination time of either or both of the image carrier drive motor shorter than a reference time,
When the paper bending amount of the recording paper detected by the paper bending detection means is compared with a predetermined second threshold value that is larger than the first threshold value, and when it is determined that the paper bending amount is larger than the second threshold value, 3. The image forming apparatus according to 1 or 2, wherein control is performed to make the determination time of one or both of the belt driving motor and the image carrier driving motor longer than the reference time.

  4). 4. The control device according to any one of 1 to 3, wherein the control unit controls a gain amount of either or both of the belt driving motor and the image carrier driving motor according to a basis weight of the recording paper. The image forming apparatus described in 1.

  5. The control means controls the determination time of either or both of the belt driving motor and the image carrier driving motor according to the paper width of the recording paper. The image forming apparatus according to one item.

  6). In the monochrome mode, the intermediate transfer belt and the black image carrier are in pressure contact, and the yellow image carrier, the magenta image carrier, and the cyan image carrier are separated from the intermediate transfer belt. When performing image formation, the control unit performs control to change either or both of the gain amount of the belt driving motor and the gain amount of the black image carrier driving motor. The image forming apparatus according to claim 5.

7). Based on the amount of bending of the trailing edge of the recording paper detected by the paper bending detection means and the width of the recording paper to be conveyed, the trailing edge of the recording paper is detected from the time when the trailing edge of the recording paper conveyed by the conveying means is detected. Computation means for calculating the trailing edge arrival time until the corner of the edge reaches the image transfer portion,
Control is performed to change the gain amount of the motor for either or both of the belt driving unit and the image carrier driving unit before the trailing edge arrival time elapses. 7. The image forming apparatus according to claim 1, further comprising a control unit that performs control for returning the gain amount.

  In the image forming apparatus of the present invention, the control means, based on the detection result of the paper bending detection means of the recording paper, at the timing when the corner of the leading edge of the recording paper enters the image transfer portion, Since the gain amount of at least one motor of the body drive unit is controlled, the drive speed of the intermediate transfer belt or the image carrier due to the impact vibration generated when the recording paper enters the image transfer unit Instantaneous fluctuation can be suppressed more strongly than usual, and deterioration of image quality can be appropriately suppressed.

1 is a central sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a mounting position of a paper bending detection sensor of the image forming apparatus according to the embodiment of the present invention. 1 is a circuit block diagram showing an electrical configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a schematic diagram illustrating a paper bending detection sensor and a paper bending state of a recording paper of the image forming apparatus according to the embodiment of the present invention. FIG. FIG. 6 is a calculation diagram of the amount of paper bending of the recording paper by the paper bending detection sensor of the image forming apparatus according to the embodiment of the present invention. 3 is a timing chart of speed control of the image forming apparatus according to the embodiment of the present invention. 3 is a flowchart 1 of speed control of the image forming apparatus according to the embodiment of the present invention. 3 is a flowchart 2 of speed control of the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is applicable to both an image forming apparatus such as a printer that does not include an image reading unit such as a scanner, and an image forming apparatus such as a copying machine that includes an image reading unit such as a scanner. It is possible.

In this embodiment, an electrophotographic copying machine will be described as an example of an image forming apparatus.
(Mechanical configuration of image forming apparatus)
FIG. 1 is an overall configuration diagram of an image forming apparatus according to the present invention.

  The image forming apparatus includes an image forming apparatus GH and an image reading apparatus YS.

  The image forming apparatus GH is called a tandem color image forming apparatus. The image forming unit 10 includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K and an intermediate transfer belt 6 that is a belt-like intermediate transfer member. And a sheet feeding / conveying means 20 and a fixing unit 30.

  The image forming unit 10 forms a toner image on the recording paper P conveyed from the paper feed conveying unit 20 and conveys the recording paper P on which the toner image is formed to the fixing unit 30.

  On the upper part of the image forming apparatus GH, an image reading apparatus YS comprising an automatic document feeder 60 and an original reading unit 70 is installed.

  The document d placed on the document table of the automatic document feeder 60 is conveyed by a conveying unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document reading unit 70 which is a document image scanning exposure unit. It is read into the line image sensor CCD.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in the reading processing unit 101, and then exposure means (image writing means) 3Y, 3M, Input to 3C and 3K.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 5Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 5M. An image forming unit 10C for forming a cyan (C) color image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 5C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 5K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  Reference numerals 4Y, 4M, 4C, and 4K denote developing devices that contain a two-component developer composed of a small particle size toner of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) and synthesized by the primary transfer units 7Y, 7M, 7C, and 7K on the rotating intermediate transfer belt 6. A color image is formed.

  The recording paper P stored in the paper feeding cassette 21 of the paper feeding / conveying means 20 is fed by the paper feeding means 22 so that the paper feeding rollers 23, 24, 25 and 26, the leading edge of the paper and the leading edge of the image are aligned. Once the recording paper is stopped and passed through the registration rollers 27 and the like, the recording paper is conveyed to the secondary transfer means (secondary transfer roller 9), and the color image is transferred onto the recording paper P (secondary transfer).

  The intermediate transfer belt 6 wound around a plurality of rollers and rotatably supported functions as an image transfer unit.

  Between the registration roller 27 and the secondary transfer means (secondary transfer roller 9), a paper bending detection sensor PS2 for detecting the leading edge of the recording paper being conveyed is disposed.

  Further, a paper bending detection sensor PS1 paired with the paper bending detection sensor PS2 is arranged in a direction perpendicular to the recording paper conveyance direction and along the recording paper conveyance surface.

  The vertical direction is substantially vertical and does not allow strictly slight differences.

  As shown in FIG. 2, the paper bending detection sensor PS2 is disposed near the left end of the leading edge of the recording paper, and the paper bending detection sensor PS1 is disposed near the right edge of the leading edge of the recording paper. It functions as a paper bending detection means for detecting the bending of the recording paper from the detection time difference between the paper bending detection sensor PS2 arranged at the right and the paper bending detection sensor arranged near the right end.

  In this description, the paper bending detection sensors PS1 and PS2 that detect two positions are used, but three or more positions may be detected, or a single line sensor may be used.

  The recording paper P to which the color image has been transferred is sandwiched by the fixing unit 30 and the color toner image (or toner image) on the recording paper P is fixed by applying heat and pressure to the recording paper P. The sheet is fixed on the upper side, sandwiched between the sheet discharge rollers 28 and placed on a sheet discharge tray 29 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the secondary transfer means, the residual toner is removed by the cleaning means 8 from the intermediate transfer belt 6 from which the recording paper P is separated by curvature.

  When the recording paper P that has been subjected to the fixing process is reversely discharged, the recording paper P passes through the conveyance path on the right side of the branch plate 28A disposed between the fixing unit 30 and the paper discharge roller 28, and the lower first paper After being transported to one transport path Pa, it is transported in the reverse direction, passes through the second transport path Pb on the left side of the branch plate 28A, and is discharged out of the apparatus by the paper discharge roller 28.

  When copying on both sides of the recording paper P, after fixing the image formed on the first surface of the recording paper P, the recording paper P is fed to the first transport path Pa, and further to the fourth transport path below the branch plate 28B. After being introduced into Pd, the sheet is conveyed in the reverse direction, passed through the conveyance path on the right side of the branch plate 28B, conveyed to the third conveyance path Pc, detoured upward, and conveyed by the paper feed roller 26. The recording paper P is formed on both sides with images of the respective colors on the second surface in the image forming means 10Y, 10M, 10C, and 10K, heated and fixed by the fixing unit 30, and discharged outside the apparatus by the paper discharge roller 28.

In the description of the image forming apparatus GH, the formation of a color image has been described. However, a case of forming a monochrome image is also included in the present invention.
(Electrical configuration of image forming apparatus)
FIG. 3 is a circuit block diagram showing an electrical configuration of the image forming apparatus. The automatic document feeder (ADF) 60 includes an ADF control unit 68 that controls a drive unit (not shown). The document reading unit (scanner unit) 70 includes a line image sensor 76 and a scanner control unit 79. The scanner control unit 79 performs lighting control of the light source, movement control of the exposure scanning unit, and the like.

  The operation display unit 50 includes a display unit 51 composed of a liquid crystal display (LCD), an operation unit 52 composed of touch switches and other switches laid on the screen, and an operation control unit 53 that controls these operations. Have.

  The printer unit 40 includes a laser unit (LU) 42 and a printer control unit 41. The printer control unit 41 performs ON / OFF control of a laser diode included in the laser unit 42 and rotation control of a polygon mirror. The printer control unit 41 has a function of performing overall control of operations of the charging device, the transfer device, the voltage application to the separation device, the developing device, the cleaning device, the fixing device, the paper feeding / conveying unit 80 and the like.

  The paper feeding / conveying section 80 includes a paper feeding motor 82M for taking out the recording paper from the paper feeding cassette, a paper feeding driving section 82 for controlling the paper feeding motor M to stably rotate at a predetermined rotational speed, and a recording paper from the transfer section. A sheet feeding / conveying motor 83M for conveying to the fixing unit, a sheet feeding / conveying driving unit 83 for controlling rotation, an intermediate transfer belt driving motor 84M for rotating an intermediate transfer belt for carrying an image first transferred from the image forming means, and rotation control. An intermediate transfer belt driving unit 84, an image carrier driving motor (hereinafter referred to as a photosensitive drum driving motor) 85M for rotating a photosensitive drum as an image carrier, and an image carrier driving unit (hereinafter referred to as a photosensitive drum driving unit). 85 and the like.

  The ADF control unit 68, the scanner control unit 79, the operation control unit 53, and the printer control unit 41 are composed of circuits each including a CPU, a ROM, and a RAM, and execute various controls according to programs stored in the ROM. It is supposed to be.

  The overall control unit 100 has a function of performing overall control of the operation of the image forming apparatus GH. The overall control unit 100 includes a read processing unit 101, a DRAM control IC 102, a compression / decompression IC 103, an image memory 104, a write processing unit 105, an image control CPU 110, a program memory 106, a system memory 107, and a nonvolatile memory. The memory 108 and the I / O port 109 are provided.

  The reading processing unit 101 has a function of performing enlargement processing, mirror image processing, binarization processing by error diffusion, and the like on image data output from the document reading unit (scanner unit) 70. The compression / expansion IC 103 performs a function of compressing the binarized image data and expanding the compressed image data. The image memory 104 functions as a page memory capable of storing non-compressed image data in units of pages and as a compression memory 104a for storing compressed image data.

  The writing processing unit 105 has a function of sending the image data read out from the image memory 104 and expanded to the laser unit 42 including the exposure units 3Y, 3M, 3C, and 3K at a timing according to the operation of the printer unit 40. The DRAM control IC 102 controls read / write timing and refresh timing for the image memory 104 composed of dynamic RAM, compresses image data and stores it in the image memory 104, reads compressed data from the image memory 104, and decompresses it. The timing control at the time of doing is performed.

  The image control CPU 110 is a CPU that controls the overall operation of the image forming apparatus GH, and has a function of managing the flow of image data and a function of managing job reservation registration and execution. The program memory 106 is a memory storing a program executed by the image control CPU 110, and the system memory 107 is a work memory for temporarily storing various data during the execution of the program. The image control CPU 110 controls the entire image forming apparatus GH while performing serial communication with the printer control unit 41 according to a program stored in the program memory 106 while referring to data on the system memory 107.

  The nonvolatile memory 108 is a memory that stores user data and system data that should be stored even after the power is turned off. The I / O port 109 is connected to various sensors such as a paper size detecting means for detecting the size of the recording paper set in each paper feed tray, LED elements, and the like.

  Prior to the start of image formation, in a predetermined setting mode, according to the recording sheet setting screen of the sheet feeding tray displayed on the display unit 51 by the image control CPU 110, the user or the key operator loads the recording sheets to be loaded on each sheet feeding tray. The size, paper type, and the like are set from the operation display unit 50 in advance. These conditions are stored in the nonvolatile memory 108 by the image control CPU 110.

  In addition, the user performs basic copy settings such as a copy mode (single / double-sided), paper feed tray selection, magnification, and density from the operation display unit 50, sets a document on the image reading device YS, and presses the start button. Then, reading and printing of the original are started.

  In the above operation, in the color image forming mode, the photosensitive drum 1Y as a yellow (Y) image carrier, the photosensitive drum 1M as a magenta (M) image carrier, and a cyan (C) image. The photosensitive drum 1C as the carrier and the photosensitive drum 1B as the black (K) color image carrier are in pressure contact with the rotating intermediate transfer belt 6, and the recording paper enters the secondary transfer portion or There is an effect of suppressing instantaneous fluctuations in the driving speeds of the intermediate transfer belt 6 and the photosensitive drums 1Y, 1M, 1C, and 1K due to impact vibration generated at the time of separation.

  However, in monochrome mode image formation, the photosensitive drums 1Y, 1M, and 1C and the intermediate transfer belt 6 are separated from each other, and only the photosensitive drum 1K is in pressure contact with the intermediate transfer belt 6, so that the recording paper is Instantaneous fluctuations in the driving speed of the intermediate transfer belt 6 and the photosensitive drum 1K caused by impact vibration generated when entering or leaving the secondary transfer portion cause deterioration in image quality such as image unevenness and image fluctuation. Connected.

  Therefore, in the monochrome image forming mode, the below-described control is performed to prevent image quality deterioration.

  The control means for performing the control of the present invention will be described so that the printer control unit 41 functions. However, the control unit of both the overall control unit 100 and the printer control unit 41 shares functions, or the overall control unit 100 functions. You can do it.

  From here, instantaneous fluctuations in the driving speed of the intermediate transfer belt 6 and the photosensitive drum 1K caused by impact vibration generated when the recording paper enters and leaves the transfer region are suppressed more strongly than usual. For this purpose, the calculation means for calculating the time until the switching of the gain of the driving motor based on the amount of bending of the recording paper and the width of the recording paper by the paper bending detection means of the recording paper and the control of the gain amount of the driving motor according to the present invention Will be described.

  FIG. 4 shows a state in which the recording paper is detected to be bent when the recording paper P is conveyed.

  In order from the upstream in the conveyance direction of the recording paper P, a registration roller 27, paper bending detection sensors PS1 and PS2, and a secondary transfer roller 9 are arranged.

  A portion indicated by a dotted line indicates a state in which the recording paper P is conveyed in parallel to the conveyance direction, passes through the registration roller 27, and before the paper bending sensor. Similarly, a portion indicated by a solid line is A state in which the recording paper P is rotated with respect to the transport direction, that is, a paper bending state is shown.

  When the recording paper P is conveyed in a paper bent state, the paper bending detection sensors PS1 and PS2 do not detect the passage of the recording paper P at the same time, and either PS1 or PS2 detects the leading edge of the recording paper P first. Will be.

  In the example of FIG. 4, the paper bending detection sensor PS2 first detects the leading edge of the recording paper P, and then the paper bending detection sensor PS1 detects the leading edge of the recording paper P. The time difference between the detection time of PS2 and the detection time of PS1 becomes basic data for calculating the amount of bending of the recording paper.

  In addition, after the leading edge of the recording paper P is detected by the paper bending detection sensor PS2, the leading edge arrival time for the recording paper to reach the position where the intermediate transfer belt 6 and the secondary transfer roller 9 which are the secondary transfer regions face each other. Is defined as T1.

  FIG. 5 shows specifications for calculating a paper bending amount T, which is an amount preceded by the leading edge C of the recording paper P along the transport direction from the time difference t detected by the paper bending detection sensor PS1 and the paper bending detection sensor PS2. To express.

  The distance between the paper bending detection sensors PS1 and PS2 is W, the paper width of the conveyed recording paper is L, and the unit is both mm.

  The time difference t is the time difference from when the paper bending detection sensor PS2 detects the leading edge of the recording paper P to when the PS1 detects the leading edge of the recording paper, and is expressed in msec.

  When the paper bending sensor PS1 detects the leading edge of the recording paper P, the amount preceded by the leading edge C of the recording paper P with respect to the transport direction (hereinafter referred to as the paper bending amount T) is the following approximate value: Can be represented.

T≈ (L + W) / 2 × W × t
The conveyance speed (mm / msec) of the recording paper is determined at the time of designing according to the type of recording paper, and the amount of paper bending T of the recording paper is expressed in time (msec).

  In addition, the recording paper is transported by passing the intermediate point of the leading edge of the recording paper through the substantially intermediate point between the paper bending detection sensors PS1 and PS2.

  The leading edge arrival time T1 shown in FIG. 4 can be corrected and expressed as T1 = T1−T because the paper bending amount T of the recording paper P precedes the transfer area.

  Further, based on a time difference t from when the paper bending detection sensor PS2 detects the trailing edge of the recording paper P to when the PS1 detects the trailing edge of the recording paper P, the paper bending amount T of the recording paper and the recording paper are detected. T1 as the trailing edge arrival time can be expressed.

The calculation means for calculating T1 as the leading edge arrival time and T1 as the trailing edge arrival time is the CPU (not shown) itself of the printer control unit 41, and is stored in the ROM mounted on the printer control unit 41. It is executed according to the program.
(Operation of the embodiment)
The operation of the speed variation control for the image forming apparatus GH of this embodiment will be described below with reference to the time chart of FIG. 6, the flowchart 1 of FIG. 7, and the flowchart 2 of FIG.

  In this embodiment, the description will focus on the speed fluctuation control portion that is executed in parallel when normal control for executing image formation is being executed.

When the leading edge of the recording paper enters the transfer area, or when the trailing edge of the recording paper leaves the transfer area, the intermediate transfer belt 6 and the photosensitive drum 1K due to impact vibration also change instantaneously in driving speed. In order to generate this, a period for changing the gain of the speed control is defined as T2. ((C) and (d) of FIG. 6)
First, when there is an image formation output instruction from the operation unit 52, the flowchart 1 in FIG. 7 starts. The overall control unit is registered in the non-volatile memory 108 with reference to the paper type (basis weight and size) data of the recording paper loaded in the paper feeding cassette that is recorded in the non-volatile memory 108. The gain increase time T2 of the drive motor is transmitted to the printer control unit 41, and is set as a determination time from when the gain is increased until it is restored. The printer controller 41 holds the gain-up time T2 in a memory (not shown) and starts paper feeding (step S10 in FIG. 7).

  When the leading edge of the fed recording paper is detected by the paper bending detection sensor PS1 or PS2, the printer control unit 41 starts counting the leading edge arrival time T1 with the first timer (step S11 in FIG. 7).

When the leading edge of the recording paper is detected by the paper bending detection sensors PS1 and PS2, a paper bending amount T corresponding to the recording paper width of the paper type being fed is calculated based on the time difference t shown in FIG. (T in FIG. 6, step S12 in FIG. 7)
Here, the processing of the subroutine for the gain-up time and gain-up amount for the speed control of the drive motor starts. (Step S13 in FIG. 7)
In the flowchart 2 of FIG. 8, when the paper bending amount T is smaller than the predetermined first threshold value, the predetermined correction value α is subtracted from the gain-up time T2, which is a reference time for gain-up of the drive motor, or the predetermined first If the threshold value is larger than 2, the correction value α is added to the gain-up time T2 of the drive motor (Y in step S20 in FIG. 8), and the leading edge of the recording paper corresponds to the amount of bending T of the recording paper. More than the time until the end side passes after the entry is secured (T2 in FIG. 6, step S22 in FIG. 8). The predetermined first threshold value, the second threshold value, and the correction value α are determined at the time of design, and the first threshold value is smaller than the second threshold value.

  When Step S20 in FIG. 8 is N, the gain up time T2 held in the memory is not changed.

The printer control unit 41 determines the value of T1 of the first timer started in step S11 in FIG. 7 based on the leading edge arrival time T1 determined by the recording paper conveyance speed corresponding to the recording paper type. It is replaced with the value of T1 ′ shown below, and it is set as the gain up start time. ((C), (d) of FIG. 6, step S23 of FIG. 8)
T1 ′ = T1-T−0.5 × T2
The leading edge arrival time T1 is a value determined by the distance from the position of the paper bending detection sensor PS1 / PS2 to the secondary transfer area and the conveyance speed of the recording paper, and when the conveyance time is changed depending on the paper type or the like. Is also changed in conjunction with the initial value of T1. When T1 is changed, T2 and T1 ′ are also changed in conjunction with each other.

When the printer control unit 41 counts T1 ′ (step S24 in FIG. 8), the intermediate transfer belt drive unit 84 that controls the intermediate transfer belt drive motor 84M and the photoconductor that controls the photoconductor drum drive motor 85M. The gain of the speed control of the drum drive unit 85 is set to a value higher than the normal value of the basis weight of the recording paper loaded in the paper feeding cassette. (Step S25 in FIG. 8)
An example of the gain increase amount according to the basis weight is shown in Table 1. This gain increase amount is determined at the time of design.

The printer control unit starts counting T2 set in step S21 or S22 with the second timer (step S26 in FIG. 8), and when counting T2 (step S27 in FIG. 8), the intermediate transfer belt driving unit 84 and The gain of speed control of the photosensitive drum driving unit 85 is returned to a normal value. (Step S28 in FIG. 8 and (c) and (d) in FIG. 6)
Returning to FIG. 7, when the trailing edge of the conveyed recording paper is detected by the paper bending detection sensor PS1 or PS2, the printer control unit 41 starts counting the leading edge arrival time T1 with the first timer. (Step S14 in FIG. 7)
When the trailing edge of the recording paper is detected by the paper bending detection sensors PS1 and PS2, a paper bending amount T corresponding to the paper type being fed is calculated based on the time difference t shown in FIG. (T in FIG. 6, step S15 in FIG. 7)
Here, the processing of the subroutine for the gain-up time and gain-up amount for the speed control of the drive motor starts. (Step S16 in FIG. 7)
Similarly to the processing of the leading edge of the recording paper, the intermediate transfer belt drive motor 84M is controlled based on the paper bending amount T, the drive motor gain-up time T2, and the gain-up time T1 'in the flowchart 2 of FIG. The gain of the speed control of the intermediate transfer belt driving unit 84 and the photosensitive drum driving unit 85 that controls the photosensitive drum driving motor 85M is set to a value higher than the normal value, and after the elapse of T2 time, Return to the value of. (Steps S20 to S28 in FIG. 8)
If image formation is continuing (N in step S17 in FIG. 7), the printer control unit 41 returns to step S10 in FIG. 7, continues the above processing, and ends output of image formation (in FIG. 7). In the case of Y in step S17), the speed control process of the intermediate transfer belt drive unit 84 that controls the intermediate transfer belt drive motor 84M and the photosensitive drum drive unit 85 that controls the photosensitive drum drive motor 85M. Exit.

  In the above description, the speed control gains of both the intermediate transfer belt drive motor 84M and the photosensitive drum drive motor 85M are controlled, but the speed control gain of one of the intermediate transfer belt drive motor 84M or the photosensitive drum drive motor 85M is controlled. You may control.

  As described above, the speed control of the photosensitive drum 1K and the intermediate transfer belt 6 are performed at the timing when the recording paper bent with respect to the conveyance direction of the recording paper enters the secondary transfer region and the timing at which the recording paper leaves the secondary transfer region. Since the speed control gain is set to be higher than that in the normal speed control, the impact property that occurs when the recording paper enters and leaves the secondary transfer roller 9 that sandwiches and conveys the recording paper in the secondary transfer region. Instantaneous fluctuations in the driving speed of the intermediate transfer belt 6 and the photosensitive drum 1K due to the vibration of the image can be suppressed more strongly than usual, and the deterioration of the image quality due to the impact vibration is appropriately suppressed. It becomes possible.

1Y yellow photosensitive drum 1M magenta photosensitive drum 1C cyan photosensitive drum 1K black photosensitive drum 6 intermediate transfer belt 9 secondary transfer roller 10 image forming unit 20 paper feeding / conveying means 27 registration roller 30 fixing unit 40 printer unit 41 Printer Control Unit 50 Operation Display Unit 60 Automatic Document Feeder 70 Document Reading Unit (Scanner Unit)
80 Paper Feeder 84 Intermediate Transfer Belt Drive 84M Intermediate Transfer Belt Drive Motor 85 Photosensitive Drum Drive 85M Photosensitive Drum Drive Motor 100 Overall Control Unit 101 Read Processing Unit 105 Write Processing Unit 106 Program Memory 107 System Memory 108 Nonvolatile Memory 109 I / O port 110 Image control CPU
GH image forming apparatus YS image reading apparatus PS2 paper bending detection sensor T paper bending amount T1 leading edge arrival time (rear edge arrival time)
T1 'Gain up start time T2 Gain up time

Claims (7)

An image transfer unit that transfers an image formed on the image carrier, a conveyance unit that conveys the recording paper to the image transfer unit, a conveyance direction of the recording paper, and a vertical direction along the conveyance surface. A paper bending detection means for detecting the amount of paper bending with respect to the recording paper transport direction by detecting the leading edge in the recording paper transport direction, a belt drive motor for driving the intermediate transfer belt, and a belt for driving the belt drive motor A drive unit; an image carrier drive motor that drives an image carrier provided for each of the image carriers for yellow, magenta, cyan, and black; and an image carrier drive unit that drives the image carrier drive motor. An image forming apparatus having
Based on the amount of paper bending at the leading edge of the recording paper detected by the paper bending detection means and the width of the recording paper to be conveyed, the corner of the leading edge of the recording paper from the time when the paper bending detection means detects the leading edge of the recording paper. Computation means for calculating the tip arrival time until the part reaches the image transfer part,
Before the tip end time elapses, either or both of the belt driving unit and the image carrier driving unit are controlled to change the gain amount of the motor, and after the predetermined determination time has elapsed, the motor An image forming apparatus comprising control means for performing control to return the gain amount of the image.   The determination time is at least a time from the time when the corner portion of the leading edge of the recording paper reaches the image transfer portion to the time until all the leading edge reaches the image transfer portion. The image forming apparatus according to claim 1. The control means includes
When the amount of paper bending of the recording paper detected by the paper bending detection means is compared with a predetermined first threshold, and when it is determined that the amount of paper bending of the recording paper is smaller than the first threshold, the belt drive motor and Perform control to make the determination time of either or both of the image carrier drive motor shorter than a reference time,
When the paper bending amount of the recording paper detected by the paper bending detection means is compared with a predetermined second threshold value that is larger than the first threshold value, and when it is determined that the paper bending amount is larger than the second threshold value, The image forming apparatus according to claim 1, wherein control is performed to make the determination time of one or both of the belt drive motor and the image carrier drive motor longer than the reference time.   4. The control unit according to claim 1, wherein the control unit controls a gain amount of one or both of the belt driving motor and the image carrier driving motor in accordance with a basis weight of the recording paper. The image forming apparatus described in the item.   5. The control unit according to claim 1, wherein the control unit controls the determination time of one or both of the belt driving motor and the image carrier driving motor according to a paper width of the recording paper. The image forming apparatus according to claim 1.   In the monochrome mode, the intermediate transfer belt and the black image carrier are in pressure contact, and the yellow image carrier, the magenta image carrier, and the cyan image carrier are separated from the intermediate transfer belt. 2. The image forming apparatus according to claim 1, wherein when image formation is performed, the control unit performs control to change either or both of a gain amount of the belt driving motor and a gain amount of the black image carrier driving motor. 6. The image forming apparatus according to any one of items 1 to 5. Based on the amount of bending of the trailing edge of the recording paper detected by the paper bending detection means and the width of the recording paper to be conveyed, the trailing edge of the recording paper is detected from the time when the trailing edge of the recording paper conveyed by the conveying means is detected. Computation means for calculating the trailing edge arrival time until the corner of the edge reaches the image transfer portion,
Control is performed to change the gain amount of the motor for either or both of the belt driving unit and the image carrier driving unit before the trailing edge arrival time elapses. The image forming apparatus according to claim 1, further comprising a control unit that performs control to return the gain amount.

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