JP2013257462A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent positional deviation of an image in a width direction of paper caused by inclination of an intermediate transfer belt without the need for a user to perform operation to specify the amount to move an exposure position.SOLUTION: An image forming apparatus transfers a toner image formed on a photoreceptor 41K to a transfer material S via an intermediate transfer belt 50, and includes: an inclination detection unit that detects an inclination amount and an inclination direction of the intermediate transfer belt 50; and a position adjustment unit that adjusts a relative position between the transfer material S and the toner image transferred to the transfer material S on the basis of a detection result of the inclination detection unit.

Description

  The present invention relates to an image forming apparatus that transfers a toner image formed on a photoreceptor onto a transfer material via an intermediate transfer belt, and more particularly to an apparatus that prevents image misalignment due to the inclination of the intermediate transfer belt.

  The charged photoconductor is exposed based on image data to form an electrostatic latent image, and a toner image is formed by attaching toner to the photoconductor, and the toner image is transferred to the photoconductor by a primary transfer roller. 2. Description of the Related Art Image forming apparatuses that transfer from an intermediate transfer belt to an intermediate transfer belt and then transfer from an intermediate transfer belt to a transfer material such as a sheet (hereinafter also simply referred to as a sheet) by a secondary transfer roller are widely used.

  Conventionally, in such an image forming apparatus, as a technique for preventing image positional deviation in the paper width direction (direction orthogonal to the paper conveyance direction in the image forming apparatus), the following [1] to [3] are known. Something like that was proposed.

  [1] When the paper reaches the registration roller pair positioned on the upstream side of the secondary transfer roller on the paper conveyance path, the position of the side edge of the paper is detected by a sensor, and the registration roller pair is detected according to the detection result. Is swung in the width direction of the paper.

  [2] At the time of double-sided image formation or multiple image formation on the paper, the position of the image in the width direction of the paper after the image is formed on the first surface of the paper is detected by a sensor, and 2 of the paper is detected according to the detection result. The position of the image formed on the face in the width direction of the paper is corrected (see Patent Document 1).

  [3] By detecting the position of the edge of the intermediate transfer belt with a sensor and controlling the tilting amount of the steering roller in accordance with the detection result, meandering control for gradually decreasing the meandering amplitude of the intermediate transfer belt is performed (Patent Document) 2).

JP 2003-316208 A JP 2011-175012 A

  However, in the conventional technique [1], it is possible to prevent the positional deviation of the image in the width direction of the sheet due to the deviation of the sheet generated on the sheet conveyance path, but the secondary transfer from the primary transfer roller. It is not possible to prevent the positional deviation of the image in the width direction of the sheet due to the inclination of the intermediate transfer belt that occurs up to the transfer roller.

  Also in the prior art [2], when the inclination of the intermediate transfer belt changes between when the first side image is formed and when the second side image is formed, the first side image and the second side image It is not possible to prevent misalignment.

  Further, since the conventional technique [3] also meanders the intermediate transfer belt with a certain amplitude, there is always an inclination of the intermediate transfer belt itself, and the image in the width direction of the sheet due to the inclination is present. It is not possible to prevent misalignment.

  Here, the positional deviation of the image in the width direction of the sheet due to the inclination of the intermediate transfer belt will be described with reference to FIGS. FIG. 8 shows a configuration example of the intermediate transfer belt and its peripheral part in the image forming apparatus. In order from the top, four photoconductors 200Y, 200M, 200C, and 200K on which yellow, magenta, cyan, and black toner images are formed are arranged in the vertical direction (up and down in the drawing) in the image forming apparatus. . Four primary transfer rollers 211Y, 211M that form primary transfer nips with the photoconductors 200Y, 200M, 200C, and 200K, respectively, with the intermediate transfer belt 210 sandwiched between the photoconductors 200Y, 200M, 200C, and 200K. , 211C, 211K are arranged. The intermediate transfer belt 210 is sandwiched between the intermediate transfer belt 210 on the downstream side in the rotation direction of the intermediate transfer belt 210 as viewed from the primary transfer nip (hereinafter referred to as the primary transfer nip K) by the photosensitive member 200K and the primary transfer roller 211K. A pair of secondary transfer rollers 212 and 213 forming a secondary transfer nip for transferring the toner image on 210 to a sheet is disposed.

  A registration roller pair 220 is disposed on the upstream side of the secondary transfer nip on the sheet conveyance path. Further, a fixing roller pair 230 is disposed on the downstream side of the secondary transfer nip on the sheet conveyance path.

  The toner images of the respective colors formed on the photoconductors 200Y, 200M, 200C, and 200K are transferred onto the intermediate transfer belt 210 in the order of the photoconductors 200Y, 200M, 200C, and 200K. At this time, color registration correction, which is the alignment of the toner images of the respective colors, is performed with reference to the photoconductor 200K. The positions of the toner images formed on the photoconductors 200Y, 200M, 200C, and 200K can be adjusted by adjusting the irradiation position and irradiation timing of a laser (not shown) that exposes the photoconductors. , 200C, 200K, which is the same direction as the axial direction of the first, 200C, and 200K, and is hereinafter referred to as a main scanning direction) and a direction orthogonal to the main scanning direction.

  The intermediate transfer belt 210 is stretched around a plurality of rollers including a primary transfer roller 211Y, 211M, 211C, 211K, a secondary transfer roller 212, and a driving roller 214, and a driving force is transmitted from the driving roller 214 to the intermediate transfer belt 210. Rotate clockwise. At that time, due to the deviation of the parallelism of each roller and the inclination of the belt tension, a force in a direction orthogonal to the rotational direction is applied to the intermediate transfer belt 210, and the intermediate transfer belt 210 gradually meanders.

  In order to prevent the intermediate transfer belt 210 from dropping off due to the meandering, as shown in FIG. 9, ribs 215 made of urethane are provided on the inner periphery of both ends of the intermediate transfer belt 210, and the intermediate transfer belt 210 The rib 215 is caught on the end of the roller that stretches 210. However, the intermediate transfer belt 210 continues to rotate at a position close to one side until the rib 215 at one end is caught by the end of the roller.

  Further, the intermediate transfer belt 210 is not necessarily located at the same front-rear position with respect to the upper roller and the lower roller in the vertical direction. As illustrated in FIG. Depending on the situation, the intermediate transfer belt 210 may have an inclination with respect to the rotation direction. Further, the amount and direction of this inclination change over time due to operations such as rotation of the intermediate transfer belt 210 and tension release.

  In addition, there is a configuration in which the meandering amount and meandering direction of the intermediate transfer belt 210 are detected by the belt edge position detection sensor without providing the intermediate transfer belt 210 with the rib 215 for preventing the dropping as shown in FIG. Then, based on the detection result, the tilt adjustment mechanism provided in any of the rollers that stretch the intermediate transfer belt 210 is operated, and the parallelism between the rollers is adjusted to control the meandering direction, thereby removing the drop. In some cases, it can be prevented. However, even when such an inclination adjusting mechanism is used, the intermediate transfer belt 210 still has an inclination.

  When the intermediate transfer belt 210 is inclined with respect to the rotation direction as described above, the toner images of the respective colors transferred to the intermediate transfer belt 210 using the photosensitive member 200K as a reference for color registration correction are secondary from the primary transfer nip K. Along the transfer nip, the sheet is transferred onto the sheet by shifting in the main scanning direction by an amount corresponding to the inclination. For example, as shown in FIG. 11, the peripheral length of the intermediate transfer belt 210 is 800 mm, the inclination between the rollers at the upper and lower ends in the vertical direction at the peripheral length 400 mm of the intermediate transfer belt 210 is 1 mm, and the primary transfer nip K When the peripheral length of the intermediate transfer belt 210 between the secondary transfer nip and the secondary transfer nip is 100 mm, the toner image between the primary transfer nip K and the secondary transfer nip in the main scanning direction (left-right direction in the figure). The amount of movement is 1 mm × 100 mm / 400 mm = 0.25 mm. Therefore, the toner image is transferred to the paper with a deviation of 0.25 mm in the width direction. In recent years, an image forming apparatus is required to have an accuracy that the positional deviation and variation of an image are less than 0.5 mm, so the influence of the amount of 0.25 mm is large.

  In general, the bias of the image can be adjusted by a function of moving the exposure position by an amount specified by the operation panel. However, as described above, since the inclination state of the intermediate transfer belt 210 changes every moment, the primary transfer is performed. The amount of image shift between the nip K and the secondary transfer nip also varies with time, and the image shift gradually increases. If the transition of the image misalignment is to be resolved by the function of moving the exposure position on the operation panel, the user needs to perform an operation to specify the amount by which the exposure position is moved each time a sheet of paper is printed. Cannot be improved.

  In view of the above-described points, the present invention prevents a positional deviation of an image in the width direction of a transfer material such as a sheet due to an inclination of an intermediate transfer belt without a user performing an operation of specifying an amount for moving an exposure position. For the purpose.

  In order to solve the above problems and achieve the object of the present invention, an image forming apparatus of the present invention is an image forming apparatus for transferring a toner image formed on a photosensitive member to a transfer material via an intermediate transfer belt. An inclination detection unit that detects the amount and direction of inclination of the belt, and a position adjustment unit that adjusts the relative position between the transfer material and the toner image transferred to the transfer material based on the detection result of the inclination detection unit.

  According to the image forming apparatus having the above configuration, the inclination detection unit detects the amount and direction of inclination of the intermediate transfer belt, and based on the detection result, the position adjustment unit transfers the toner image transferred to the transfer material and the transfer material. Adjust the relative position. Accordingly, it is possible to prevent the positional deviation of the image in the width direction of the transfer material such as a sheet due to the inclination of the intermediate transfer belt without performing the operation of designating the amount by which the user moves the exposure position.

FIG. 2 is a diagram illustrating a configuration of an image forming unit, an intermediate transfer belt, a secondary transfer roller, a fixing unit, and the like of the image forming apparatus according to the first exemplary embodiment of the present invention. 1 is a diagram illustrating a configuration of an intermediate transfer belt and its peripheral portion of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating an arrangement relationship between a sensor and an intermediate transfer belt according to the 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. It is a figure which illustrates the processing result of CPU in the 1st Embodiment of this invention. It is a flowchart which shows the process of CPU at the time of the single-sided continuous printing in the 1st Embodiment of this invention. It is a figure which shows the structure of the registration roller pair which concerns on the 2nd Embodiment of this invention, and its peripheral part. 2 is a diagram illustrating a configuration example of an intermediate transfer belt and its peripheral portion in an image forming apparatus. FIG. FIG. 9 is a diagram illustrating a configuration of the intermediate transfer belt in FIG. 8. FIG. 9 is a diagram illustrating the inclination of the intermediate transfer belt in FIG. 8. FIG. 9 is a diagram illustrating a positional deviation of a toner image transferred from the intermediate transfer belt of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 shows configurations of an image forming unit, an intermediate transfer belt, a secondary transfer roller, a fixing unit, and the like of an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and tandem format in which toners of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) are superimposed. The color image forming apparatus. The image forming apparatus 1 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, a secondary transfer roller 70, and a fixing unit 80.

  The document transport unit 10 includes a document feeding table 11 on which a document is set and a plurality of rollers 12. The original G set on the original feeding table 11 of the original conveying unit 10 is conveyed one by one to the reading position of the image reading unit 30 by a plurality of rollers 12. 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 13 and generates an image signal.

  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, and is transported by the transport unit 23 to the secondary transfer roller 70 that is a transfer position to which an image is transferred from the intermediate transfer belt 50. 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.

  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, only the first image forming unit 40Y will be described 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 performs exposure scanning on the surface of the photoconductor 41 based on the image data read from the document G, and forms an electrostatic latent image on the photoconductor 41.

  The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41 that is an image carrier. 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 adhering to the photoreceptor 41 is transferred to an intermediate transfer belt 50 showing an example of an image carrier. The cleaning unit 45 removes 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 having a primary transfer roller 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 transfers the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50 by applying a polarity opposite to that of the toner 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 roller 70 is disposed in the vicinity of the intermediate transfer belt 50 and downstream of the conveyance unit 23. The secondary transfer roller 70 presses the sheet S sent by the transport unit 23 toward the intermediate transfer belt 50 side. The secondary transfer roller 70 transfers the color image formed on the intermediate transfer belt 50 onto the paper S sent by the transport unit 23 by the applied voltage. The cleaning unit 52 removes toner remaining on the surface of the intermediate transfer belt 50 after being transferred to the paper S. A fixing unit 80 is provided on the downstream side of the secondary transfer roller 70 in the transport direction of the paper S. The fixing unit 80 pressurizes and heat-fixes the toner image transferred to the paper 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. The switching gate 24 guides the paper S downward when face-down paper discharge and double-sided image formation in single-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 sent again to the transfer position by the refeed path 27.

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

  FIG. 2 shows a more detailed configuration of the intermediate transfer belt 50 shown in FIG. 1 and its peripheral portion. In order from the top, the photoconductors 41 of the four image forming units 40Y, 40M, 40C, and 40K shown in FIG. 1 (in FIG. 2, are distinguished as the photoconductors 41Y, 41M, 41C, and 41K) are in the vertical direction ( (Up and down direction in the figure). Four primary transfer rollers 53Y, which form primary transfer nips together with the photoconductors 41Y, 41M, 41C, 41K on the side facing the photoconductors 41Y, 41M, 41C, 41K across the intermediate transfer belt 50, respectively. 53M, 53C, and 53K (primary transfer rollers included in each primary transfer unit 51 shown in FIG. 1) are arranged. The intermediate transfer belt 50 is sandwiched between the intermediate transfer belt 50 on the downstream side in the rotation direction of the intermediate transfer belt 50 as viewed from the primary transfer nip (hereinafter referred to as the primary transfer nip K) by the photoconductor 41K and the primary transfer roller 53K. A pair of secondary transfer rollers 70 and 54 (secondary transfer roller 70 shown in FIG. 1) forming a secondary transfer nip for transferring the toner image on the belt 50 to a sheet are disposed.

  A pair of registration rollers 28 is arranged on the upstream side of the secondary transfer nip on the sheet conveyance path by the conveyance unit 23 shown in FIG. The conveyance unit 23 conveys the sheet to the registration roller pair 28 by a conveyance roller (not shown), and then sends the sheet toward the secondary transfer nip by the registration roller pair 28 at a timing at which the toner image can be transferred to the sheet. A fixing roller pair 81 included in the fixing unit 80 illustrated in FIG. 1 is disposed on the downstream side of the secondary transfer nip on the sheet conveyance path by the conveyance unit 23.

  The toner images of the respective colors formed on the photoconductors 41Y, 41M, 41C, and 41K are transferred onto the intermediate transfer belt 50 in the order of the photoconductors 41Y, 41M, 41C, and 41K. At this time, color registration correction, which is the alignment of the toner images of the respective colors, is performed with reference to the photoreceptor 41K. The positions of the toner images formed on the photoconductors 41Y, 41M, 41C, and 41K are adjusted by adjusting the laser irradiation position and irradiation timing by the exposure unit 43 shown in FIG. 41C and 41K, which is the same as the axial direction of 41C and 41K, hereinafter referred to as the main scanning direction) and can be arbitrarily adjusted in the direction orthogonal to the main scanning direction.

  The intermediate transfer belt 50 is stretched around a plurality of rollers including a primary transfer roller 53Y, 53M, 53C, 53K, a secondary transfer roller 54, and a driving roller 55, and a driving force is transmitted from the driving roller 54 to the intermediate transfer belt 50. Rotate clockwise.

  A housing of an intermediate transfer belt unit (not shown) in which the intermediate transfer belt 50 is stored and attached in the image forming apparatus 1 is provided at two locations in the rotational direction of the intermediate transfer belt 50 on one side of the intermediate transfer belt 50. A sensor for detecting the position of the end is arranged. FIG. 3 shows a simplified arrangement relationship between this sensor and the intermediate transfer belt 50. A sensor 56 is arranged on the circumference of the intermediate transfer belt 50 so as to detect the position of one end of the intermediate transfer belt 50 at a location 20 mm upstream from the primary transfer nip K that serves as a reference for color registration correction. Has been. In addition, another sensor 57 is disposed so as to detect the position of one end of the intermediate transfer belt 50 at a location 30 mm downstream from the secondary transfer nip. The peripheral length of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip is 100 mm, and therefore the peripheral length of the intermediate transfer belt 50 between the sensor 56 and the sensor 57 is 150 mm.

  The sensors 56 and 57 are fixed to the same surface of the casing of the intermediate transfer belt unit, and the position of the end portion is measured by measuring the distance from the fixed surface to the end portion on one side of the intermediate transfer belt 50. Is detected. The sensors 56 and 57 may directly detect the end portion of the intermediate transfer belt 50 with a reflection type or transmission type laser displacement sensor, or the actuator is brought into contact with the end portion of the intermediate transfer belt 50 and the actuator. It is also possible to detect displacement of the position or angle.

  FIG. 4 shows the configuration of the control system of the image forming apparatus 1. The image forming apparatus 1 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs executed by the CPU 101, and a RAM (Random Access Memory) used as a work area of the CPU 101. 103. Further, it has a hard disk drive (HDD) 104 as a mass storage device and an operation display unit 105. As the ROM 102, an electrically erasable programmable ROM is usually used.

  The CPU 101 is an example of a control unit, and is connected to the ROM 102, the RAM 103, the HDD 104, and the operation display unit 105 via the system bus 107, and controls the entire apparatus. The CPU 101 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, and the sensors 56 and 57 shown in FIG.

  The HDD 104 stores image data of an original image obtained by reading by the image reading unit 30, or stores output image data and the like. The operation display unit 105 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 105 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 105 includes a plurality of keys, and receives input of various instructions, data such as characters and numbers by a user's key operation, and outputs an input signal.

  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 processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  In this example, a personal computer is used as an external device. However, the present invention is not limited to this, and various other devices such as a facsimile device can be used as the external device.

  For example, when color printing is executed by the image forming apparatus 1, R, G, B image data generated by the image reading unit 30 or the like is input to a color conversion LUT (look up table) in the image processing unit 110. Then, the image processing unit 110 performs color conversion on the R, G, and B data to Y, M, C, and Bk image data. Then, correction of gradation reproduction characteristics, screen processing such as halftone dots with reference to the density correction LUT, or edge processing for emphasizing thin lines is performed on the color-converted image data.

  The image forming unit 40 receives the image data processed by the image processing unit 110 and forms an image on the paper S.

  The CPU 101 serves as an inclination detection unit that detects the amount and direction of inclination of the intermediate transfer belt 50 from the detection results of the sensors 56 and 57, and a position adjustment unit that adjusts the relative position between the paper and the toner image based on the detection result. Execute the process. FIG. 5 exemplifies the result of the processing executed by the CPU 101 as the tilt detection unit and the position adjustment unit. When the detection results of the sensors 56 and 57 are, for example, 8.45 mm and 8.00 mm, respectively, the intermediate transfer belt 50 is between the primary transfer nip K and the secondary transfer nip (8.45 mm−8.00 mm). ) × 100 mm / 150 mm = 0.3 mm is inclined to the front side (left side in the figure) in the main scanning direction (left and right direction in the figure). Accordingly, in this case, the toner images of the respective colors transferred to the intermediate transfer belt 50 move forward by 0.3 mm between the primary transfer nip K and the secondary transfer nip in the main scanning direction. The CPU 101 performs a calculation to detect the inclination amount and the inclination direction of the intermediate transfer belt 50 immediately before executing printing.

  Then, the CPU 101 cancels the position shift of the toner image at the secondary transfer nip due to the detected tilt amount and tilt direction, among the photoconductors 41Y, 41M, 41C, and 41K shown in FIG. The exposure unit 43 of the image forming unit 40K shown in FIG. 1 is controlled so that the exposure position on the photoconductor 41K serving as a correction reference is offset in advance by 0.3 mm toward the back side in the main scanning direction. FIG. 5 shows the width direction of the sheet S caused by the inclination of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip by offsetting the exposure position on the photoreceptor 41K in this way. A state in which the positional deviation of the image is 0 mm is shown. A black arrow in the drawing indicates the moving direction of the intermediate transfer belt 50, and a white arrow in the drawing indicates the moving direction of the paper S.

  At the same time, the CPU 101 performs color registration correction on the photoconductors 41Y, 41M, and 41C. In color registration correction, a test image called a registration mark is transferred from each of the photoconductors 41Y, 41M, 41C, and 41K to the intermediate transfer belt 50, and the positional deviation between the registration marks is detected to eliminate the positional deviation. In addition, the exposure positions on the photoconductors 41Y, 41M, and 41C other than the photoconductor 41K serving as a reference are corrected. Since color registration correction is a known technique, a detailed description thereof is omitted.

  At the time of continuous printing in which a plurality of sheets are continuously printed, the CPU 101 acquires the detection results of the sensors 56 and 57 in parallel during the printing operation, and performs the primary operation from the detection result immediately before the timing of exposing the photoreceptor 41Y. By detecting the amount and direction of inclination of the intermediate transfer belt 50 between the transfer nip K and the secondary transfer nip, the control of the exposure position on the photoconductor 41K and the photoconductors 41Y, 41M, and 41C as described above are performed. Repeat color registration correction.

  FIG. 6 is a flowchart illustrating processing executed by the CPU 101 during single-sided continuous printing. When printing starts, the CPU 101 determines the amount of inclination of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip based on the detection results of the sensors 56 and 57 acquired immediately before the exposure timing of the photoreceptor 41Y. And the inclination direction is detected (step S1). Then, the CPU 101 calculates an offset amount of the exposure position of the photoconductor 41K that cancels the deviation of the position of the toner image at the secondary transfer nip due to the detected tilt amount and tilt direction (step S2).

  The CPU 101 includes the image forming unit 40 and the intermediate transfer belt 50 shown in FIG. 1 including the control of the exposure position on the photoconductor 41K by the calculated offset amount and the color registration correction for the photoconductors 41Y, 41M, and 41C. The primary transfer unit 51, the secondary transfer roller 70, the transport unit 23, and the like are controlled to execute charging, exposure, development, and transfer (step S3).

  Subsequently, the CPU 101 determines whether or not the paper currently being printed is the paper of the last page (step S4). If it is not the paper of the last page, the CPU 101 controls the fixing unit 80, the switching gate 24, etc. shown in FIG. 1 to execute fixing and paper discharge for the paper currently being printed (step S5). Then, the CPU 101 returns to step S1 for printing the next sheet, and repeats steps S1 and S2 in parallel during execution of fixing and paper discharge under the control in step S5 described above, and then steps S3 and S4. repeat.

  When the paper of the last page is reached in step S4, the CPU 101 executes fixing and paper discharge for the paper currently being printed in the same manner as in step 5 (step S6), and ends the printing.

  As described above, according to the image forming apparatus according to the first embodiment, the positions of the end portions of the intermediate transfer belt 50 in the vicinity of the primary transfer nip K and in the vicinity of the secondary transfer nip are detected. From the detection results of the sensors 56 and 57, the CPU 101 detects the amount and direction of inclination of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip immediately before execution of printing. Then, the CPU 101 controls the exposure position of the photoconductor 41K as a reference for color registration correction based on the detection result, and performs color registration correction on the photoconductors 41Y, 41M, and 41C, so that paper and paper can be printed. The relative position with the transferred toner image is adjusted. Accordingly, it is possible to prevent image misalignment in the width direction of the sheet due to the inclination of the intermediate transfer belt 50 without the user performing an operation of designating the amount by which the exposure position is moved.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Note that in the second embodiment, redundant description of the same components as those in the first embodiment will be omitted. In the second embodiment, the target of offset control by the CPU 101 shown in FIG. 4 is different from that of the first embodiment. Other configurations are the same as those of the first embodiment.

  In the second embodiment, the CPU 101 sets the registration roller pair 28 shown in FIG. FIG. 7 is a diagram illustrating a configuration of the registration roller pair 28 and its peripheral portion in the transport unit 23 illustrated in FIG. 1. When the sheet S is conveyed to the registration roller pair 28 in the conveying unit 23, the position of the side edge in the width direction (left and right direction in the drawing) of the sheet S is detected by the line sensor 29. Based on the detection result, the registration roller pair 28 is swung in the width direction of the paper S by a motor (not shown), thereby correcting the position in the width direction of the paper S being conveyed by the conveyance unit 23.

  The CPU 101 performs the calculation for detecting the inclination amount and the inclination direction of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip as described with reference to FIG. The conveyance unit 23 is controlled so that the swing amount of the registration roller pair 28 is offset in accordance with the deviation of the toner image at the secondary transfer nip due to the tilt direction. For example, when the intermediate transfer belt 50 is inclined 0.3 mm forward in the main scanning direction between the primary transfer nip K and the secondary transfer nip, the CPU 101 sets the position after the swing of the registration roller pair 28 from the default. Is also offset to the front side (left side in FIG. 7) by 0.3 mm. At the same time, the CPU 101 performs color registration correction on the photoconductors 41Y, 41M, and 41C.

  According to the image forming apparatus according to the second embodiment, the sensors 56 and 57 detect the positions of the ends of the intermediate transfer belt 50 in the vicinity of the primary transfer nip K and in the vicinity of the secondary transfer nip, respectively. From the result, the CPU 101 detects the amount and direction of inclination of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip immediately before execution of printing. Then, the CPU 101 controls the swing amount of the registration roller pair 28 based on the detection result, and performs color registration correction on the photoconductors 41Y, 41M, and 41C, so that the sheet and the toner image transferred to the sheet are transferred. Adjust the relative position. Accordingly, it is possible to prevent image misalignment in the width direction of the sheet due to the inclination of the intermediate transfer belt 50 without the user performing an operation of designating the amount by which the exposure position is moved.

[Modification]
The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention described in the claims.

  For example, in each of the above-described embodiments, the example in which the image forming unit 40 is provided with four image forming units 40Y, 40M, 40C, and 40K to form a color image has been described. However, only one image forming unit is provided. You may apply to the image forming apparatus which forms a monochromatic image.

  In each of the above-described embodiments, the positions of the end portions of the intermediate transfer belt 50 at two locations in the rotation direction of the intermediate transfer belt 50 are detected by the sensors 56 and 57. The position of the end portion of the intermediate transfer belt 50 at the above three or more locations may be detected by a sensor, and the tilt amount and tilt direction of the intermediate transfer belt 50 may be detected from the detection result.

  In the first embodiment described above, the amount and direction of inclination of the intermediate transfer belt 50 between the primary transfer nip K and the secondary transfer nip are detected, and the photoconductor 41K is detected based on the detection result. The exposure positions of the photoconductors 41Y, 41M, and 41C are corrected and the color resist correction is performed for all the photoconductors 41Y, 41M, 41C, and 41K. The amount and direction of inclination of the intermediate transfer belt 50 may be detected and control may be performed to offset the exposure positions on all the photoconductors 41Y, 41M, 41C, and 41K based on the detection result.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Document conveyance part, 20 ... Paper storage part, 23 ... Conveyance part, 28 ... Registration roller pair, 30 ... Image reading part, 40 ... Image formation part, 40Y, 40M, 40C, 40K ... Image Formation unit 41, 41Y, 41M, 41C, 41K ... photosensitive member, 43 ... exposure unit, 50 ... intermediate transfer belt, 51 ... primary transfer unit, 53Y, 53M, 53C, 53K ... primary transfer roller, 56,57 ... Sensor, 70 ... Secondary transfer roller, 80 ... Fixing section, 101 ... CPU

Claims (7)

In an image forming apparatus that transfers a toner image formed on a photoreceptor to a transfer material via an intermediate transfer belt,
An inclination detector for detecting an inclination amount and an inclination direction of the intermediate transfer belt;
An image forming apparatus comprising: a position adjusting unit that adjusts a relative position between the transfer material and a toner image transferred to the transfer material based on a detection result of the tilt detection unit. A sensor for detecting the position of the end of the intermediate transfer belt at two or more locations in the rotational direction of the intermediate transfer belt;
The image forming apparatus according to claim 1, wherein the inclination detection unit detects an inclination amount and an inclination direction of the intermediate transfer belt from a detection result of the sensor. The inclination detection unit includes a primary transfer nip where a toner image is transferred from the photoreceptor to the intermediate transfer belt, and a secondary transfer nip where a toner image is transferred from the intermediate transfer belt to the transfer material. The image forming apparatus according to claim 1, wherein an inclination amount and an inclination direction of the intermediate transfer belt are detected. The image forming apparatus according to claim 1, wherein the position adjustment unit adjusts the relative position by controlling an exposure position on the photoconductor based on a detection result of the tilt detection unit. Provide a plurality of photoconductors that form toner images of different colors,
The inclination detecting unit includes a primary transfer nip in which a toner image is transferred from the photosensitive member serving as a reference for color resist correction among the plurality of photosensitive members to the intermediate transfer belt, and toner from the intermediate transfer belt to the transfer material. Detecting the amount and direction of inclination of the intermediate transfer belt with respect to the secondary transfer nip to which the image is transferred;
The position adjustment unit controls the exposure position on the reference photoconductor based on the detection result of the tilt detection unit, and performs color resist correction on a photoconductor other than the reference photoconductor, The image forming apparatus according to claim 4, wherein the relative position is adjusted. The position adjustment unit adjusts the relative position by controlling a swing amount of a registration roller that feeds the transfer material toward the secondary transfer nip based on a detection result of the inclination detection unit. The image forming apparatus according to claim 3. Provide a plurality of photoconductors that form toner images of different colors,
The inclination detecting unit includes a primary transfer nip in which a toner image is transferred from the photosensitive member serving as a reference for color resist correction among the plurality of photosensitive members to the intermediate transfer belt, and toner from the intermediate transfer belt to the transfer material. Detecting the amount and direction of inclination of the intermediate transfer belt with respect to the secondary transfer nip to which the image is transferred;
The position adjustment unit controls the swing amount of the registration roller based on the detection result of the tilt detection unit, and performs color registration correction on a photoconductor other than the reference photoconductor, thereby adjusting the relative position. The image forming apparatus according to claim 6, which is adjusted.