JP2010204255A - Belt conveying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image distortion and color shift due to displacement of a main-scanning direction by precisely and simultaneously detecting a meandering amount and a skewing amount of an endless belt and by correcting conveyance condition of a belt or correcting an image forming position on a image carrier by a steering roller. <P>SOLUTION: The image forming apparatus has: a plurality of position detection means to detect positions of belt, disposed at different positions in a conveyance direction of the endless belt; a calculation means to calculate a movement amount in belt width direction and a rotation amount around the center point, of the center point in an image forming region, from position information of the endless belt simultaneously obtained by the plurality of position detection means; a first correction means to correct an image shift accompanying the movement in the belt width direction of the endless belt based on the movement amount calculated in the calculation means; and a second correction means to correct the image shift accompanying the rotation around the center point of the endless belt based on the rotation amount calculated in the calculation means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a belt conveyance device having a function of correcting color misregistration caused by meandering and skewing of an endless belt stretched around a plurality of support members, and an image forming apparatus such as a copying machine, a printer, and a facsimile machine. It is.

  Conventionally, image forming apparatuses capable of forming color images, such as electrophotographic and line head ink jet color printers and color copying machines, include yellow (Y), magenta (M), cyan (C), and black (K). ), Etc., and images are formed by a plurality of image forming sections, and these images are superimposed on the intermediate transfer belt, and after the primary transfer, the secondary transfer is performed from the intermediate transfer belt onto the recording paper. There is a configuration in which a color image is formed by transferring or superimposing images on a recording sheet on a paper conveyance belt.

  In such an image forming apparatus, an endless belt member (hereinafter simply referred to as a “belt”) such as an intermediate transfer belt or a paper transport belt is generally used. The belt thickness is nonuniform in the circumferential direction and the width direction. In addition, manufacturing errors and mounting position errors also occur in cylindrical rollers that stretch the belt. Due to such an error, when the belt is driven, a so-called “belt meander” is generated in which the belt central portion moves while being displaced in the belt width direction (direction perpendicular to the endless movement direction on the belt surface). When the meandering of the belt occurs, the images of the respective colors cannot be accurately superimposed on the belt, and color misregistration of the image occurs.

In order to suppress such problems, a belt driving device as disclosed in Patent Document 1 is known. This belt drive device employs a roller that stretches the belt and that can be tilted in a direction that suppresses meandering of the belt. An edge sensor that detects the position of the edge in the width direction of the belt is disposed on the fixed end side opposite to the movable end portion that performs the tilting operation of the steering roller.
In this belt drive device, the position of the end in the width direction of the belt extending along the endless movement direction of the belt is detected by the edge sensor, so that the position in the belt width direction can be detected continuously. Therefore, it is possible to determine a change in position in the belt width direction as meandering of the belt, and to feed back the change in position to the control of the tilting operation of the steering roller continuously or at fine intervals. Therefore, according to this belt drive device, the meandering of the belt can be corrected with high accuracy.

  However, since not only the meandering of the belt but also the skew of the belt is a cause of image color misregistration, there is a problem that the belt driving device of Patent Document 1 cannot obtain sufficient color overlay accuracy. Here, the skew of the belt indicates that the belt is conveyed in a direction inclined with respect to an ideal straight line in the conveyance direction. Therefore, when the skew of the belt occurs, the belt is obliquely incident on the image forming portions of the respective colors arranged in the belt conveyance direction, so that an image to be formed at a right angle with respect to the belt width direction. It will be formed diagonally. Further, when the belt is skewed, the belt travel path is inclined with respect to the image forming units arranged in the ideal conveyance direction of the belt, and therefore should be formed at a predetermined position in the belt width direction. An image is formed with a shift from a predetermined position in each color.

  In order to suppress such problems, Patent Document 2 discloses a belt drive device that corrects belt meandering and belt skewing. This belt drive device detects the meandering of the belt by the detecting means for detecting the belt position in the belt width direction, and at the same time, installs two detecting means in the belt traveling direction, from the difference value of the signals obtained from the two detecting means. Belt skew is detected. As the correction mechanism, two steering rollers for correcting the meandering of the belt and a steering roller for correcting the skewing of the belt are installed, and the two steering rollers are controlled alternately to meander and skew the belt. The line is corrected.

  However, in order to correct the meandering of the belt and the skew of the belt in this way, even if a plurality of detection means are provided in the belt conveying direction to detect the generation amount of both, the meandering amount and the skewing amount of the belt can be reduced. At the same time, it is difficult to detect accurately. The reason for this difficulty is that the meandering of the belt and the skewing of the belt often occur simultaneously, and a value in which the meandering amount of the belt and the skewing amount are superimposed is detected by the respective detection means. Therefore, in the belt drive device of Patent Document 2, first, only the belt meandering correction steering roller is controlled to suppress the belt meandering amount to an allowable level or less, and then the belt skew amount (skew amount) is detected. Is adopted.

  In such a method in which one of the meandering amount and the skewing amount is suppressed within an allowable range of detection error and the other is detected, a time lag occurs in correction of color misregistration. For this reason, the user's image output standby time is significantly increased, or an image is output without performing color misregistration correction. In particular, in the meandering and skew correction of the belt in the steering system, correction is performed while the belt is transported several times. However, since the belt circumference of the image forming apparatus is about 1000 mm, the time required for suppressing the belt meandering and skew is extremely long. Will become bigger. Further, when detecting meandering or skewing of the belt, detection data for one or more rounds of the belt may be required to correct a detection error due to the belt edge shape, resulting in an increase in detection time.

  As described above, both the meandering and skewing of the belt, which causes image distortion and color misregistration, have been conventionally considered as a phenomenon of movement in the width direction of the belt. Although the method of detecting and correcting the other is adopted, it has been difficult to detect and correct both at the same time. Therefore, in order to correct the belt meandering and skewing, the down time (non-operation period) of the image output apparatus is large.

  Therefore, the present invention accurately detects the amount of movement of the endless belt in the main scanning direction (meandering amount) and at the same time accurately detects the inclination conveyance amount (skewing amount) of the endless belt to correct the belt conveyance state or By correcting the image forming position on the image carrier, image distortion and color misregistration due to misalignment in the main scanning direction can be prevented, the output image can be greatly improved in image quality, and the time required for correction is greatly reduced. An object of the present invention is to realize an image forming apparatus.

  According to the present invention, according to the present invention, the image forming apparatus includes an endless belt stretched by a plurality of rollers and a belt conveyance device having a driving unit that is connected to any one of the rollers and drives the endless belt. A plurality of image forming units arranged in the conveying direction on the conveying surface of the endless belt, arranged at different positions in the conveying direction of the endless belt, and detecting a position of the endless belt in the belt width direction orthogonal to the belt conveying direction Position detection means and the position information of the endless belt obtained at the same time by the plurality of position detection means, in the belt width direction of the center point of the image forming area including the plurality of image forming portions on the conveying surface of the endless belt. Based on the movement amount and the rotation amount around the center point of the endless belt, and the movement amount calculated by the calculation unit, the endless belt is moved along the belt width direction. Solved by having a first correction unit that corrects image shift and a second correction unit that corrects image shift due to rotation around the center point of the endless belt based on the rotation amount calculated by the calculation unit. Is done.

  The first correction means is a steering roller, and includes first adjustment means for adjusting the posture of the roller. The first adjustment means tilts one end of the roller with respect to the other end. The endless belt is moved, the movement of the endless belt in the width direction is controlled to correct the image shift, and the second correction unit is another steering roller, and the second adjustment unit that adjusts the posture of the roller is provided. The second adjusting means preferably corrects the image shift by moving the endless belt by tilting one end of the roller with respect to the other end and adjusting the rotation around the center point of the endless belt.

  Further, the first correction unit and the second correction unit are preferably one latent image formation position correction unit that corrects the image formation position in the belt width direction in a plurality of image forming units on the endless belt.

  The first correction means is a steering roller, and includes first adjustment means for adjusting the posture of the roller. The first adjustment means tilts one end of the roller with respect to the other end. The endless belt is moved and the movement of the endless belt in the width direction is controlled to correct image misalignment. The second correction unit corrects the image forming position in the belt width direction in a plurality of image forming portions on the endless belt. It is preferable to have a latent image forming position correcting means.

  In addition, any one of the rollers includes a first adjustment unit that adjusts the posture of the roller, and the first adjustment unit moves the endless belt by tilting one end of the roller with respect to the other end. And adjusting the position in the width direction of the endless belt, and the first correction unit and the second correction unit correct one image forming position in the belt width direction in the plurality of image forming units on the endless belt. The formation position correcting means is preferable.

In addition, it is preferable that the position detecting means is installed at two positions that are separated from the center of the image forming area by an equal interval.
Further, the calculation means calculates the time transition of the movement amount in the belt width direction and the rotation amount around the center point of the endless belt from the position information of the endless belt continuously obtained at constant time intervals over one or more rounds of the endless belt. The first correction means corrects the image shift caused by the movement in the width direction of the endless belt based on the result of the time shift calculation of the movement amount in the belt width direction by the calculation means, and the second correction means The correcting means preferably corrects the image shift caused by the rotation of the endless belt based on the time transition calculation result of the rotation amount around the center point of the endless belt by the calculating means.

The image forming method in the image forming unit is preferably an electrophotographic method.
Further, it is preferable that the image forming method in the image forming unit is a line head type ink jet system.

Further, the belt conveying device according to the present invention is arranged at an endless belt stretched by a plurality of rollers, a driving means connected to any one of the rollers to drive the endless belt, and a position where the conveying direction of the endless belt is different. A plurality of position detecting means for detecting the position of the endless belt in the belt width direction orthogonal to the belt conveying direction, and calculated by the calculating means from the position information of the endless belt obtained at the same time by the plurality of position detecting means. A first correction unit that corrects an image shift caused by the movement based on the amount of movement in the belt width direction of the center point of the image forming region including the plurality of image forming units on the transport surface of the endless belt, It is preferable to have a second correction unit that corrects an image shift caused by the rotation based on the rotation amount around the center point of the endless belt calculated by the calculation unit.
The first correction means is a steering roller, and includes first adjustment means for adjusting the posture of the roller. The first adjustment means tilts one end of the roller with respect to the other end. The endless belt is moved, the movement of the endless belt in the width direction is controlled to correct the image shift, and the second correction unit is another steering roller, and the second adjustment unit that adjusts the posture of the roller is provided. The second adjusting means preferably corrects the image shift by moving the endless belt by tilting one end of the roller with respect to the other end and adjusting the rotation around the center point of the endless belt.
In addition, it is preferable that the position detecting means is installed at two positions that are separated from the center of the image forming area by an equal interval.

  According to the image forming apparatus of the present invention, the center point of the primary transfer surface (image forming region) on the belt is the belt center point, the movement of the center point in the width direction is meandering, and the rotational movement around the center point is performed. Can be detected as two linear movements and rotational movements as separate linear movements and rotational movements at the same time and without being affected by each. Therefore, the correction operation by the correction means can be performed quickly and accurately, and the downtime of the apparatus can be greatly shortened.

  Further, by adopting a steering system as the first and second correction means, it is possible to correct both meandering and skewing of the belt on the belt primary transfer surface, and an image caused by color misregistration or skewing between images. It is possible to prevent distortion and deviation of the entire image due to belt meandering.

Further, one latent image forming position correcting means such as optical writing (electrophotographic method) or ink discharge nozzle (inkjet) is adopted as the first and second correcting means, and the meandering of the belt on the belt primary transfer surface. The color misregistration can be corrected by correcting the image forming position in the belt width direction based on the color misregistration amount calculated from the skew amount.
Due to the electrical operation such as the adjustment of the writing timing in the electrophotographic method and the selection of the discharge nozzle in the ink jet method, the responsiveness of the correction operation is high, and the downtime can be greatly shortened. There is no time lag until the correction operation is completed, and the cost can be reduced by not requiring a correction mechanism in the belt conveyance device.

  In addition, by adopting a steering system for meandering movement in the belt width direction, color misregistration can be prevented, and the belt can be held in an appropriate roller shaft range to prevent the belt from falling off. Durability is improved. Further, since the meandering of the belt only needs to correct the meandering speed instead of the meandering position, the belt can be corrected with high response and in a short time compared with the correction of the skew. On the other hand, by correcting the skew of the belt on the image forming side using the latent image forming position correcting means, the responsiveness is improved and the downtime can be shortened.

  Further, by adopting a steering system for meandering which is the movement in the belt width direction, it is possible to prevent the belt from falling off the roller, and the durability of the belt is improved. Further, while controlling the meandering speed of the belt with the steering roller, the meandering speed information (steering meandering speed control error) and the skew information of the belt are used on the image forming side using the latent image forming position correcting means. Since the meandering and skewing are corrected, the correction accuracy is further improved, responsiveness is improved, and downtime can be shortened.

Further, by arranging the sensors at two positions that are separated from the center of the image forming area by equal intervals, the calculation can be simplified because the movement and rotation based on the center point are calculated.
The belt edge shape is a periodic variation that repeats every belt revolution, and the sensor installation error is a steady deviation, whereas the variation relating to meandering and skewing is a straight line or a gentle curve (low-order function). Therefore, by sampling the data of one belt or more and approximating the sample data with a straight line or a gentle curve, there is no belt edge (edge) shape error included in the detection data or sensor installation error, The meandering amount and the skew amount can be calculated separately from the steady deviation.

  Further, by adopting an electrophotographic method or a line head type ink jet method as an image forming method in the image forming unit, a highly accurate full color image without color misregistration can be obtained.

  In addition, according to the belt conveyance device according to the present invention, it is possible to correct both the meandering and skewing of the belt on the belt primary transfer surface, the image misalignment between the images, the image distortion due to the skewing, and the image due to the belt meandering. The overall bias can be prevented.

1 shows a configuration of an image forming apparatus to which the present invention is applied. An example of a position detection sensor is shown. Another embodiment of a position detection sensor is shown. Another embodiment of a position detection sensor is shown. FIG. 5 is a diagram illustrating a mechanism of color misregistration when only belt meandering occurs on the primary transfer surface. FIG. 6 is a diagram illustrating a color misregistration generation mechanism when only belt skew occurs on the primary transfer surface. It is a schematic diagram which shows the state which is detecting the position of the width direction of a belt center line using the 1st position detection sensor and the 2nd position detection sensor. FIG. 4 is a diagram illustrating the principle of meandering correction of an intermediate transfer belt. It is a figure which shows the latent image formation position correction means based on this invention. It is a figure which shows the inkjet recording head which concerns on this invention.

  FIG. 1 shows the configuration of a belt conveying apparatus and an image forming apparatus according to the present invention. The image forming apparatus forms a full-color image on an intermediate transfer belt using four photosensitive drums provided with developing units arranged side by side. It is a schematic block diagram which shows the principal part. In this image forming apparatus, at the time of image formation, four image carriers (hereinafter referred to as photosensitive drums) 101, 102, 103, 104 are rotationally driven in the directions of arrows (counterclockwise), and the surfaces thereof are charged by the chargers 111, 112. , 113, 114 are uniformly charged, and then exposure is performed in accordance with input image information by exposure devices 121, 122, 123, 124 to form an electrostatic latent image. Then, the yellow developing device 131 attaches toner to the electrostatic latent image on the photosensitive drum 101 to develop it as a yellow toner image, and the magenta developing device 132 attaches toner to the electrostatic latent image on the photosensitive drum 102. Then, the toner is developed as a magenta toner image, and the cyan developing device 133 attaches the toner to the electrostatic latent image on the photosensitive drum 103 to develop it as a cyan toner image. The black developing device 134 develops the electrostatic latent image on the photosensitive drum 104. The toner is attached to the image and developed as a black toner image.

  The yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are 1 on an intermediate transfer body (intermediate transfer belt) 200 that rotates in contact with the photosensitive drums 101, 102, 103, and 104. Next transferred. The intermediate transfer belt 200 is driven to rotate in the direction of the arrow in FIG. 1 (clockwise) while being stretched around cylindrical support rollers 14, 15, 16, 17, and 18 that are five support members. In this way, after the four-color toner images are superimposed on the intermediate transfer belt 200 by primary transfer, the full-color image is transferred to the recording material P conveyed from a paper feed cassette (not shown), thereby being secondary-transferred. can get. The recording material P is transported to a secondary transfer position formed by contacting a pair of rollers 18 and 19 facing each other with the secondary transfer transport belt 210 and the intermediate transfer belt 200 interposed therebetween. Further, the recording material P is conveyed to the secondary transfer position by the registration roller 22 at a predetermined timing. At this secondary transfer position, a predetermined bias voltage is applied to the back surface of the recording material P by the secondary transfer roller 19, and the secondary transfer electric field generated by the bias application and the contact pressure at the secondary transfer position are applied. The four color toner images on the intermediate transfer belt 200 are secondarily transferred onto the recording material P all at once. Thereafter, the recording material P onto which the toner image has been secondarily transferred is subjected to fixing processing by the fixing roller pair 24 and 25 and then discharged out of the apparatus.

Next, the main configuration and color misregistration correction operation of the present invention will be outlined. Among the supporting rollers of the intermediate transfer belt 200, the roller 14 is a driving roller to which a rotational driving force is transmitted by a driving motor (not shown), and conveys the intermediate transfer belt 200 in the arrow direction. A first position detection sensor 201 that detects the position of the intermediate transfer belt 200 in the width direction is installed in the vicinity of the drive roller 14. Here, the width direction of the intermediate transfer belt 200 refers to a direction parallel to the axis of the cylindrical roller. In addition, a second position detection sensor 204 is provided in the vicinity of the roller 15 at an opposite position across the image forming units of the respective colors, and the sensor 204 is intermediate to the first position detection sensor 201. It is on the upstream side in the moving direction of the transfer belt 200.
According to the present invention, after the two position detection sensors 201 and 204 are arranged in this way, the belt edge is detected by the two position detection sensors at the same time, and the output value is sampled. The skew amount of the belt can be calculated from the difference data. Further, the meandering amount of the belt is calculated from the data of the output values of both sensors in consideration of the installation distance of both sensors.
Then, based on the detected meandering amount of the belt, the steering roller 16 corrects the meandering of the belt, and on the basis of the detected meandering amount of the belt, the latent image forming position correction corrects the image forming position on the photosensitive drum of each color. The occurrence of color misregistration is suppressed by the means. Because the amount of meandering and skewing of the belt is accurately detected from the data sampled at the same time, it is possible to correct both meandering and skewing at the same time, greatly reducing the downtime of the image forming apparatus. Can do. The meandering and skewing correcting means of the belt is configured to correct both meandering and skewing with two steering rollers, or to form an image so as to suppress color misregistration caused by both meandering and skewing. A configuration including latent image forming position correcting means for correcting the position can be employed.

A method for simultaneously detecting the meandering and skewing of the belt from the position detection sensor and its output value will be described below.
FIG. 2 is a schematic explanatory view showing a first embodiment of a position detection sensor 201 which is a main component of the belt edge detection mechanism. In the present exemplary embodiment, a position detection sensor 201 that detects the position in the width direction of the edge of the intermediate transfer belt 200 in the vicinity of the drive roller 14 is provided. Note that only the position detection sensor 201 that detects the position in the width direction of the edge of the intermediate transfer belt 200 in the vicinity of the drive roller 14 is shown, but the second position detection sensor 204 is also arranged as shown in FIG. Are configured similarly. Therefore, only the position detection sensor 201 will be described here.
As shown in FIG. 2, the position detection sensor 201 according to the present embodiment employs an area laser sensor. Between the light emitting element 202 and the light receiving element 203 of the position detection sensor 201, the light from the light emitting element 202 is used. The edge in the width direction of the intermediate transfer belt 200 is positioned so as to partially block the laser beam. As a result, when the meandering of the belt occurs and the position in the width direction edge of the intermediate transfer belt 200 is displaced, the amount of light to be blocked changes according to the amount of displacement, and thus the amount of light received by the light receiving element 203 is also increased. Change. A detection signal corresponding to the change in the amount of received light is output from the position detection sensor 201. For this reason, by using the two position detection sensors 201 and 204, the position in the belt width direction in the vicinity of the driving roller 14 and the position in the belt width direction in the vicinity of the roller 15 on the upstream side of the belt conveyance with the image forming unit interposed therebetween are continuously detected. can do.

Next, a second embodiment of the position detection sensor will be described with reference to FIG.
The conveyance direction of the intermediate transfer belt 200 is the direction of the arrow X, and in this embodiment, a position detection sensor 201 that detects the edge position of the belt is installed so as to contact the edge of the belt. The position detection sensor 201 includes an L-shaped contact 30 and a displacement sensor 31. The contact 30 includes a plate-like member 30a and a member 30b, and is supported so as to be rotatable in the directions of arrows Z and Z ′ about the support shaft 32. A spring 33 is attached to one member 30a, and the other member 30b is always in contact with the edge of the intermediate transfer belt 10 by its pulling force. On the other hand, one displacement sensor 31 is disposed in the length direction adjacent to the member 30a of the contact 30. Although the detailed description is omitted here, the displacement sensor 31 includes, for example, a light emitting unit and a light receiving unit, and the light emitted from the light emitting unit is reflected by the object to be measured, and the position and reference of the reflected light received by the light receiving unit. The distance to the object to be measured can be detected from the displacement of the position.
Therefore, when the belt meanders and the edge of the belt is displaced in the direction of the arrow Y, the member 30b of the contact 30 that is in contact with the edge of the belt by the pulling force of the spring 33 is also linked to the Z 'direction in the figure. Therefore, the member 30a connected to the member 30b of the contact 30 is also displaced in the Z direction in the figure. Then, the distance between the displacement sensor 31 and the member 30a of the contact 30 fluctuates, an electric signal corresponding to the distance change is generated, and the amount of meandering of the belt is detected.

  The distance between the displacement sensor 31 and the member 30a is set to a predetermined length, for example, 6.5 mm. The detection range of the displacement sensor 31 is 6.5 mm ± 1 mm, that is, a range of 2 mm from 5.5 mm to 7.5 mm, and the detection accuracy is ± 10 μm.

  The position detection sensor 201 including the light emitting element 202 and the light receiving element 203 in the first embodiment directly detects the position in the width direction of the edge of the intermediate transfer belt with an optical sensor. Although the detection error may occur due to dust adhering to the sensor surface, the second embodiment indirectly detects the position in the width direction of the intermediate transfer belt edge using the contact 30. Therefore, the member 30a of the position detection sensor 201, the displacement sensor 31 and the like can be packaged in the sensor casing. Thereby, dust such as toner is prevented from adhering to the sensor surface, and detection errors are suppressed.

  Next, a third embodiment of the position detection sensor will be described with reference to FIG. 4 which is an explanatory diagram viewed from the back surface (inner peripheral surface) side of the intermediate transfer belt 200. Here, position detection sensors 201 and 204 for detecting the width direction position of the edge of the intermediate transfer belt 200 in the vicinity of the drive rollers 14 and 15 are shown. In the third embodiment, a reflective tape 300 extending in parallel to the belt endless moving direction is provided at the center in the width direction on the back surface of the intermediate transfer belt 200. The reflective tape 300 is parallel to the belt endless moving direction. As long as it extends, it does not have to be the central portion in the width direction. The position detection sensors 201 and 204 are so-called optical reflective sensors, and are arranged across the edges from the vicinity of the center of the reflective tape in order to detect the edge position of the reflective tape 300. Therefore, when the belt meandering occurs and the position in the width direction of the edge position of the reflective tape 300 is displaced, the amount of reflected light received by the position detection sensors 201 and 204 also changes, and the amount of edge displacement is detected.

  In the first and second embodiments, the position detection sensor 201 needs to be disposed outside the region surrounded by the intermediate transfer belt 10. On the other hand, in the third embodiment, the position detection sensors 201 and 204 can be installed in a region surrounded by the intermediate transfer belt 10 having a relatively large space. This reduces the size of the device and reduces the manufacturing cost.

Next, the meandering of the belt, the skew of the belt, and the color shift that occurs in the present invention will be described in detail.
FIG. 5 shows a color misregistration generation mechanism when only the meandering of the belt occurs on the primary transfer surface of the present invention. The intermediate transfer belt 200 is conveyed from the support roller 15 toward the drive roller 14 in the direction of the arrow in the drawing, and each color image passes through the primary transfer portion of each image forming portion in the order of yellow, magenta, cyan, and black. Superimposed. Position detection sensors 201 and 204 detect positions in the belt width direction in the vicinity of the rollers 14 and 15, respectively. The transfer positions of the respective colors on the primary transfer surface are indicated by vertical lines crossing the intermediate transfer belt 200, and the transfer positions of 54y (yellow), 54m (magenta), 54c (cyan), and 54k (black), respectively. Indicates. The transferred color images on the intermediate transfer belt 200 are 55y (yellow), 55m (magenta), 55c (cyan), and 55k (black), respectively. Note that the yellow, magenta, and cyan images also show movement transitions in order to show the positional relationship with images of different colors that are superimposed and transferred on the downstream side in the belt conveyance direction.

  Here, a description will be given of color misregistration when belt meandering occurs and the edge position of the intermediate transfer belt 200 changes from the position of the line 52 at the time of yellow color transfer to the position of the line 51 at the time of black color transfer. . Here, in order to distinguish clearly from the skew of the belt described later, the meandering of the belt is defined as the vertical movement of the belt center point in the belt width direction (vertical direction in the figure), and the movement amount of the belt center is defined as The amount of meandering. The belt center point refers to the center in the width direction and the circumferential direction of the belt on the primary transfer surface including the image forming portion of each color on the intermediate transfer belt. The belt center during yellow color transfer and black color transfer. The points are indicated by points 56 and 57, respectively. If the belt meanders upward at a constant meandering speed from the time of yellow color transfer to the time of black color transfer, the yellow image 55y transferred first moves upward in the figure according to the movement of the belt meandering. . On the other hand, since the image of the other color is transferred to a predetermined center position, a positional deviation occurs between the image of the other color and the yellow color image. The color misregistration amount 53 indicates the color misregistration amount between the yellow color image and the black color image, and is equal to the belt meandering amount generated between the yellow color transfer and the black color transfer, that is, the distance between the points 56 and 57. On the other hand, if the edge position of the intermediate transfer belt 200 does not move from the position of the line 51 at the time of black color transfer or the line 52 at the time of yellow color transfer and remains at the position of the line 51 or 52, color misregistration occurs. Absent. As described above, the color misregistration is caused by the meandering of the belt. However, the color misregistration does not occur if the belt edge position is shifted up and down from a desired position on the support roller as long as the belt width is maintained. This is caused by the belt meandering speed in the direction. When the belt meandering speed is high, the color misregistration amount 53 is large, and when the belt meandering speed is low, the color misregistration amount 53 is also small.

  FIG. 6 shows the color misregistration generation mechanism when only the skew of the belt occurs on the primary transfer surface of the present invention. Similarly to FIG. 5, the respective color images on the intermediate transfer belt 200 to which the respective colors have been transferred are 65y (yellow), 65m (magenta), 65c (cyan), and 65k (black), respectively. Note that the yellow, magenta, and cyan images also show movement transitions in order to show the positional relationship with images of different colors that are superimposed and transferred on the downstream side.

  Here, it is assumed that only the belt skew occurs, and the edge position of the intermediate transfer belt 200 changes from the state line 62 without the belt skew to the line 61 in the belt skew state. Here, since the belt meandering does not occur, the position of the belt center point is not displaced from the point 66. That is, the skew of the belt is defined as a rotational movement with respect to the belt center point. Therefore, even if the belt is continuously conveyed, the belt does not move in the vertical direction in the figure, and is stabilized in the skewed state of the line 61. The phenomenon that the belt in the skew state is stabilized without the meandering of the belt is caused by the shaft inclination due to the mounting error of each roller in the belt conveyance device stretched by three or more support rollers as in the present invention. If the belt is skewed, color misregistration occurs. As shown in FIG. 6, assuming that the belt is skewed from the support roller 15 to the driving roller 14 in a downward-sloping manner, the yellow image 65y transferred first is lower in the figure as the belt is conveyed in the skew direction. Move to. On the other hand, since the image of the other color is transferred to a predetermined center position in the figure, a color shift occurs with the yellow color image. The color misregistration amount 68 indicates the color misregistration amount between the yellow color image and the black color image. The color misregistration amount 68 includes the skew angle θ indicating the skew state of the belt and the distance between the transfer positions of the yellow color and the black color. L is represented by L × tan θ.

  As described above, both the meandering and the skewing of the belt are conventionally considered to be the movement of the belt edge in the width direction. It was found that the phenomenon of meandering and skewing can be clearly distinguished and detected by defining the belt skew as a rotational movement around the belt center point. In addition, by defining the belt center point as the center point of the primary transfer surface on the belt including each color image forming unit, it is possible to accurately grasp the amount of color misregistration caused by each phenomenon of meandering and skewing. The color misregistration can be suppressed by the correcting means.

<About the principle of simultaneous detection of meandering and skewing using a simple model (no time series)>
Next, a method for simultaneously detecting the meandering and skewing of the belt using two position detection sensors will be described in detail.
FIG. 7 is a schematic diagram showing a state in which the position in the width direction of the belt center line is detected using the first position detection sensor 201 and the second position detection sensor 204 of the present invention. The embodiment of FIGS. 2 to 4 detects the meandering and skewing of the belt edge or the belt center by increasing or decreasing the amount of received light. Here, the distance between the sensors 201 and 204 and the belt edge or the belt center is shown. The principle of calculating the meandering amount and the skew amount of the belt by detecting these distances using the fact that is proportional to the amount of received light will be described.

  The first and second position detection sensors 201 and 204 are belt widths at a point at a position 72 at a distance Ls1 and a point at a position 73 at a distance Ls2 with reference to the central portion 71 of the primary transfer surface on the intermediate transfer belt 200. The direction position is detected. The detection target is the same at both the belt edge and the belt center. The belt center line 74 represents an ideal belt center line without meandering and skewing of the belt. A belt center line 75 indicates a belt center line in a state where only the skew of the belt (skew angle θ) is generated, and changes A and B are detected by the position detection sensor due to the belt skew. On the other hand, the belt center line 76 is a belt center line in a state in which the belt skew (skew angle θ) and the belt meandering (meandering amount C) of the belt having moved from the point 77 to the point 78 are generated. Show.

When detecting the belt center line 76, the output value E ₂ of the output value E ₁ and the second position detecting sensor 204 of the first position detection sensor 201 is as follows.
E ₁ = −A + C (1)
E ₂ = B + C (2)
However, the sensor output value was positive for the movement in the width direction upward in FIG. 7 with the ideal belt center line 74 as a reference.
Detection of skew angle θ of the belt is the difference of the position detection sensor output _value, is calculated from _{E 2 -E 1 = B + C} + A-C = B + A. Therefore, the meandering amount C included in each sensor output value is canceled, and the skew angle θ is calculated by the following equation (3).

However, the sensor installation position was positive in the right direction (belt conveyance direction) in FIG.
On the other hand, detection of the meandering amount of the belt is calculated from E ₁ + E ₂ = −A + B + C + C = C + C, which is an addition of the position detection sensor output values.
Here, when the installation positions Ls1 and Ls2 of the position detection sensor are equal, the skew amounts A and B are also equal, and the skew amount included in each sensor output value is canceled by addition.

However, when the sensor installation position is different, it is necessary to consider the sensor installation position. Since the skew is a rotational movement around the center of the belt, the farther the sensor installation position is (the larger Ls1 and Ls2), the larger the skew amounts A and B included in the sensor output value. Further, A × Ls2 = B × Ls1 holds from the relationship of A: B = Ls1: Ls2 that is the ratio of these.
Here, considering the sensor installation position, A = Ls1 · tan θ, B = Ls2 · tan θ, and tan = (E ₂ −) so that the skew amounts A and B are canceled out, so that E ₁ + E ₂ = −A + B + 2C. Substituting E ₁ ) / (Ls1 + Ls2) for C. Eventually, the following expression (4) is obtained.

  In this way, by taking into account the detection position of each position detection sensor with reference to the central portion 71 of the primary transfer surface, an accurate belt meandering amount can be obtained by offsetting the skew amount from the output value of each position detection sensor. Can be calculated. In this embodiment, the reference of the sensor positions Ls1 and Ls2 is set to the central portion 71 of the primary transfer surface for the purpose of grasping and correcting the amount of color misregistration generated. A central portion between the two rollers 14 and 15 may be used.

From the viewpoint of the present invention, it can be seen that the prior art has the following problems. For example, erroneous detection occurs when meandering is determined based on the output value of one of the position detection sensors. For example, the detection value of the sensor 204 in FIG. 7 is that if the belt center line 75 is detected in a state where there is no belt meandering and only skewing occurs, the value B is output, and this is erroneously detected as the meandering amount. End up. Further, erroneous detection may occur if the mean of two sensor values is meandering without considering the distance from the center of the primary transfer surface. For example, in FIG. 7, when the relationship between the installation distances of both position detection sensors is Ls1 / 2 = Ls2, the value of the sensor 201 that detects the belt center line 76 in a state where the meandering and skewing of the belt has occurred is −A + C, On the other hand, the value of the sensor 204 is B / 2 + C. The average of the two sensor output values is (−A + B / 2 + 2C) / 2. That is, the intention of detecting only the belt meandering amount C is included in the amount of change A and B due to the belt skew without being canceled.
Incidentally, when the sensor output value and the sensor installation distance relationship Ls1 / 2 = Ls2 are substituted into the equation (4), the following equation (5) is established, the skew amount is canceled, and only the meandering amount C is calculated. .

<When there are time series and edge shape>
By the way, since the output value of the position detection sensor actually includes various error components, in the following, the error components actually included, and the meandering component and the skew component of the belt are accurately removed by removing them. A method of extracting the will be described.
The output values of the position detection sensor for the belt edge and the belt center mark mainly include the following components.
1. 1. Detection error due to belt edge shape (central reflection tape mounting position fluctuation) 2. Detection error due to sensor mounting error or sensor zero point error 3. Position change due to belt meandering Position change due to belt skew

  Regarding the above 1, the edge shape of the intermediate transfer belt 200 is not actually an ideal linear shape over one circumference in the belt circumferential direction, and the edge has a slight distortion as shown in FIG. Is a curved shape including This occurs due to a mold error, a cutting error, or deformation of the belt at the time of manufacturing the belt. Further, in the third embodiment of FIG. 4, it occurs due to a change in the mounting position of the reflective tape 300 over one round in the belt circumferential direction. Furthermore, regarding the above 2, when detecting using a plurality of sensors, a variation in mounting accuracy and output characteristics of each sensor becomes a detection error.

In order to remove the error components 1 and 2 described above, and since the generation of the belt meandering speed causes a color shift, not the position due to the meandering of the belt at a certain time t but the transition of the belt meandering position. Since it is necessary to determine the meandering speed of the belt, sensor output value data sampled continuously for a predetermined time is used for detection of meandering and skewing of the belt. Output value data E ₁ (t) and E ₂ (t) of the first and second position detection sensors at a certain time t are expressed by the following equations.

E ₁ (t) = P (t) + W (t) + SK ₁ (t) + e ₁ (6)
E ₂ (t) = P (t−t ₀ ) + W (t) + SK ₂ (t) + e ₂ (7)

Here, P (t) represents a profile error profile of the belt edge and is a periodic component having a period of one belt revolution. Further, when the same belt edge is detected with both the detection sides of the first and second position detection sensors at the front side, the second position detection sensor has t ₀ corresponding to the belt conveyance time of the distance between the sensors. It has a time difference and becomes P (t−t ₀ ).
Further, W (t) indicates a belt meandering change transition, and the same change is detected in the first and second sensors.
Sk (t) indicates a change transition due to the skew of the belt, and different changes are detected in the first and second sensors. Respective fluctuations are represented by Sk ₁ (t) and Sk ₂ (t).
e is a sensor mounting error and a zero point error, which can be a steady deviation inherent to the sensor.

Next, using the sensor output value data shown in the equations (6) and (7), the belt skew angle and the belt meandering amount are calculated according to the equations (3) and (4). Here, for convenience of description, it is assumed that the installation distances of the sensors are Ls1 = 1 and Ls2 = 1, respectively, and are installed at equal distances from the central portion 71. In this case, the skew angle of the belt can be calculated by calculating E ₂ −E _1, and the meandering amount of the belt can be calculated by calculating E ₁ + E ₂ . Each calculation result is as follows.

E ₂ (t) −E ₁ (t) = P (t−t ₀ ) −P (t) + SK ₂ (t) −SK ₁ (t) + e ₂ −e ₁ (8)
E ₁ (t) + E ₂ (t) = P (t) + P (t−t ₀ ) + W (t) + W (t) + e ₁ + e ₂ (9)

  Here, the belt edge shape P (t) is a periodic variation of the belt rotation cycle, while the belt skew variation Sk (t) and the belt meandering variation W (t) are straight lines or gentle curves (2 or It is a fluctuation that can be approximated by a third-order low-order function), and e is a stationary deviation component as described above. Accordingly, from the characteristics of each component, the calculation data of the formulas (8) and (9) are calculated from the sensor output value data continuously sampled over one belt or more, and the periodic fluctuation component and the steady deviation component included in the data are calculated. Remove. Alternatively, the belt skew change Sk (t) and the belt meandering fluctuation W (t) can be obtained by approximating the operation data with a cubic function or the like. Next, the correction unit is controlled so as to suppress the occurrence of color misregistration from the value of the current time t of the obtained belt skew fluctuation Sk (t). Further, the belt meandering speed at the current time t is calculated from the differential result of the obtained belt meandering fluctuation W (t), and the correction means is controlled so as to suppress the occurrence of color misregistration. Thus, the detection accuracy is further improved by calculating each fluctuation amount at the current time from the time transition. It is also possible to predict a near-future change several seconds ahead and execute correction in advance.

  As described above, the belt edge shape P (t) is not stored and corrected in advance, but is removed as a periodic variation. Therefore, the two position detection sensors each need to detect the belt edge at the same end. However, it may be installed either on the front side or on the back side of the belt. Further, in order to detect the meandering and skewing of the belt on the primary transfer surface, it is desirable to install two position detection sensors on both sides of the primary transfer surface or in the vicinity thereof. It may be installed anywhere as long as the distance from the center of the surface is known.

<About the steering correction mechanism>
It is necessary to correct these based on the meandering and skewing amounts of the belt detected in this way. Hereinafter, the steering mechanism and the latent image forming position correcting means, which are these correction methods, will be described in detail.
As shown in FIGS. 1 and 8, the belt conveyance device includes a steering roller 16 and a meandering correction mechanism 80 that corrects meandering of the intermediate transfer belt 200 connected thereto. The meandering correction mechanism 80 has a swing arm 81, one end of which is connected to the front side end of the steering roller 16 (the front side of the drawing in the roller axis direction). Further, a pressure spring 89 is installed on the swing arm 21, and presses the steering roller 16 against the belt. Therefore, the pressure applied by the pressure spring 89 applies tension to the intermediate transfer belt 200. A bearing 82 is fixed to the other end of the swing arm 81, and the swing arm 81 can rotate about the swing arm rotation shaft 83. Further, an eccentric cam 84 provided at a position where the rotation axis deviates from the center of the circle is provided below the bearing 82, and a rotation axis of a steering motor (not shown) is connected to the rotation axis. Further, the eccentric cam 84 is provided with a shielding plate 86, and the eccentric cam home position detecting means 87 detects the position of the shielding plate 86, so that the home position of the eccentric cam 84 can be grasped. Yes. The eccentric cam 84 is always kept in contact with the bearing 82 by the tension of the swing arm spring 88 connected to the swing arm 81.

  When the eccentric cam 84 rotates in the direction of arrow D, the bearing 82 moves in the direction of arrow E, so that the swing arm 81 rotates around the swing arm rotation shaft 83. On the other hand, since the rear end of the steering roller 16 (the back side in the drawing in the roller axis direction) is fixed, only the front end of the steering roller 16 is in the direction of arrow F by the rotation of the swing arm rotation shaft 83. Move to. In this case, the tension on the rear side is larger than the front side in the belt width direction of the intermediate transfer belt 200. As a result, the intermediate transfer belt 200 moves to the rear side at a meandering speed corresponding to the inclination angle of the steering roller 16.

  Conversely, when the eccentric cam 84 rotates in the direction of the arrow D ', the bearing 82 moves in the direction of the arrow E', and only the front side end of the steering roller 16 moves in the direction of the arrow F '. In this case, the tension on the front side is larger than the rear side in the belt width direction of the intermediate transfer belt 200. As a result, the intermediate transfer belt 200 moves to the front side at a meandering speed corresponding to the inclination angle of the steering roller 16.

By utilizing this principle, for example, when a meandering speed is generated on the front side of the intermediate transfer belt 200, the steering roller 16 may be tilted in the direction of arrow F so that the intermediate transfer belt 200 moves to the rear side. . On the other hand, when a meandering speed occurs on the rear side of the intermediate transfer belt 200, the steering roller 16 may be tilted in the direction of the arrow F ′ so that the intermediate transfer belt 200 moves to the front side.
As described above, the meandering control of the intermediate transfer belt 200 is performed such that the meandering speed and the tilt angle of the steering roller 16 are appropriately controlled so that the meandering speed of the intermediate transfer belt 200 is always within an allowable range. Can do. In addition, if the current meandering position of the belt (belt width direction position) is far from the target center position (generally the center point in the roller axis direction), the belt gradually approaches the target position at an allowable meandering speed. Control to reach.
Further, when controlling not only the meandering of the belt but also the skew, the belt skew may be controlled by installing a similar steering mechanism on the support roller 17 in addition to the steering roller 16. At this time, the mechanism is installed so that the tilting direction of the support roller 17 is perpendicular to the tilting direction of the steering roller 16.

<Regarding latent image forming position correcting means>
On the other hand, as image forming position correcting means for correcting the image forming position in the main scanning direction on the intermediate transfer belt in accordance with the meandering amount of the belt and the skew angle change, light for forming a latent image on the image carrier is used. An optical axis angle changing means is provided in the optical path of the writing means to change the latent image forming position on the image carrier. However, when the optical axis angle changing means is provided in the optical path of the optical writing means, it is necessary to add highly accurate and reliable optical means, and there is a problem that the cost increases.

FIG. 9 is a block diagram showing the configuration of the latent image forming position correcting means in the image forming apparatus of the present invention. In the figure, the image signal transferred from the printer driver unit 901 is input to an image signal generation unit 903 constituting the image writing control unit 902. Further, engine control information from the engine control unit 904 is also input to the image writing control unit 902. The image signal generation unit 903 performs image processing on the input image signal by processing according to engine control information. At this time, since the image signal generation unit 903 actually develops the image on the recording paper, it is processed by a pixel clock signal (wclk) that defines the minimum pixel used for image formation. This pixel clock signal is generated by a pixel clock generation unit 905 based on information from the engine control unit 904 such as resolution and photosensitive drum linear speed, and a clock signal (wclk) having a predetermined frequency is generated. Input to the circuit unit 906. The actual image signal subjected to image processing by the image signal generation unit 903 is input to the writing position control unit 907. In addition, the write position control unit 907 includes a synchronization detection signal (DETP) from the synchronization detection unit 909 of the laser writing device 908, a belt displacement signal (Δa) created based on the skew information of the intermediate transfer belt, and an output from the engine control unit 904. Engine control information is input. The synchronization detection signal (DETP) is a signal for keeping the writing start position in the main scanning direction constant when the laser beam is exposed on the photosensitive drum. This signal is an output signal from the synchronization detection plate arranged outside the scanning region on the photosensitive drum 104 of the laser beam reflected and deflected by the polygon mirror 911 in the laser writing device 908. A light receiving element such as a photodiode is cast as a synchronization detection sensor, and the synchronization detection sensor photoelectrically converts an incident laser beam and outputs a synchronization detection signal (DETP). The belt displacement signal (Δa) is a signal indicating displacement in the intermediate transfer belt main scanning direction, and is generated in accordance with the obtained belt meandering or belt skew information in the main scanning direction of the intermediate transfer belt in the image transfer surface. Is a signal calculated from belt meandering and skew information. For example, if there is information on the belt meandering speed Wa, the displacement amount assumed at the transfer position of each color is calculated by Wa * Tw. Tw is the time required to convey the belt from the reference color to each transfer position of other colors. If there is information on the belt skew angle θa, the amount of displacement assumed at the transfer position of each color is calculated by tan θa * Lw. Lw is the distance from the center of the primary transfer surface to the transfer position of each color. The writing position control unit 907 combines the real image signal from the image signal generation unit 903 with a synchronization detection signal (DETP) at a predetermined timing, and generates a signal for driving the semiconductor laser as the light source. At this time, the start timing of writing the actual image signal from the synchronization detection signal is controlled according to the belt displacement signal (Δa). A skew correction clock signal (dclk) obtained by multiplying the pixel clock signal (wclk) generated by the pixel clock generation unit 905 is input to the writing position control unit 907. The skew correction clock signal (dclk) is a signal having a frequency higher than that of the pixel clock signal obtained by multiplying the pixel clock signal (wclk) that defines the minimum pixel capable of forming an image. The skew correction clock signal (dclk) is a clock signal having a frequency corresponding to the detection resolution of the transfer slit position sensor, and one clock of the skew correction clock signal (dclk) corresponds to one resolution of the belt skew information. is doing. A belt displacement signal (Δa) calculated from the belt skew information is detected, and a synchronization detection signal (DETP) and a belt displacement signal (Δa) are input to the writing position control unit 907. Assuming that A (= N × wclk) from the synchronization detection signal when the belt displacement signal (Δa) is 0 to the start position of the actual image signal in the main scanning direction, if Δa> 0 is detected, synchronization detection is performed. The delay time from the signal to the actual image writing timing is changed to A + Δa × dclk, and the actual image writing start position is delayed with respect to the case where there is no belt skew. On the other hand, when Δa <0, the delay time is set to A−Δa × dclk, and the actual image writing start timing is relatively accelerated. The laser driving signal synthesized by the writing position control unit 907 is input to the laser driving unit. The semiconductor laser mounted on the laser drive unit is repeatedly driven to turn on / off by turning on / off the laser drive signal. The laser beam emitted by driving the semiconductor laser is incident on the laser writing device 908, passes through and reflects a plurality of lenses, mirrors, and the like and travels in the optical path. The light is rotated and deflected by a polygon mirror 911 disposed in the middle of the optical path, and a laser beam is exposed on the photosensitive drum 104 in the main scanning direction. The process from this exposure until an output image is obtained is as described above.
In the above configuration, by controlling the latent image forming position on the image carrier based on the belt skew information, it is possible to prevent image distortion and color misregistration due to misregistration in the main scanning direction, and to achieve a high cost control system. In addition, the image quality of the output image can be greatly improved without providing high-precision optical means.

<Inkjet system>
In addition, when the image forming unit adopts a line head type ink jet system instead of the exposure device, the photosensitive drum and the developing unit as described above, and uses a paper conveyance belt instead of the intermediate transfer belt, the ink is used. A similar function can be achieved by selecting the nozzle to be ejected and adjusting the image forming position in the main scanning direction.

In recent years, development of an ink jet recording apparatus using an FWA (Full Width Array) type ink jet recording head (FWA head) having discharge nozzles arranged in the axial direction in order to perform high-speed recording has been progressing more and more. In such an ink jet recording apparatus, it is effective to form a two-dimensional array of ejection nozzles in order to obtain high resolution. The recording head array has a long shape in which an effective recording area is not less than the width of the sheet (the length in the direction orthogonal to the transport direction), and includes yellow (Y), magenta (M), cyan (C), and Four ink jet recording head units (hereinafter simply referred to as head units) corresponding to each of the four colors of black (K) are arranged along the transport direction so that a full color image can be recorded. The method of ejecting ink droplets in each head unit is not particularly limited, and a known method such as a so-called thermal method or piezoelectric method can be applied.
FIG. 10 shows an ink jet recording head 1000 constituting each head unit. The ink jet recording head 1000 is an FWA type head in which an array of a large number of ejection nozzles 1001 for ejecting ink droplets is two-dimensionally formed. . In the present embodiment, the discharge nozzles 1001 are arranged along the longitudinal direction of the inkjet recording head 1000.

  As described above, as correction means for suppressing color shift from detected belt meandering and belt skew information, steering roller means for correcting the meandering and skew state of the belt by tilting the steering roller, and each image A latent image forming position correcting unit that adjusts the image forming position of the forming unit in the main scanning direction can be used.

Next, an optimum correction system that employs two correction means in consideration of the characteristics of each correction means will be described. As shown in FIG. 1, by installing one steering roller 16 and tilting it, the belt meandering speed is controlled within an allowable range while keeping the belt position in the center in the roller axial direction. can do. In this way, it is preferable to adopt a steering system for belt meandering correction. This is because the intermediate transfer belt 200 can be prevented from dropping off from the support roller, and, as will be described below, in the steering system, the meander correction is more responsive to the correction completion than the skew correction. is there.
On the other hand, it is preferable to correct the skew of the belt from the writing side by the latent image forming position correcting means and the ink discharge nozzle selection correcting means. The reason for adopting the correction method on the writing side is that the response to completion of correction is higher than that of the steering method.

Next, a description will be given of the characteristics and responsiveness of correction of color misregistration due to steering meandering and correction of color misregistration due to skew.
As described for the color misregistration generation mechanism, even if the meandering position of the belt, that is, the position in the width direction of the belt deviates from the target position, the color misregistration does not occur if the belt is stable there. However, when the belt meandering speed occurs, that is, when the belt moves in the width direction, color misregistration occurs. Therefore, responsiveness is required to suppress the meandering speed rather than the meandering position of the belt. In the steering system, the belt meandering speed is changed by the steering operation, and the belt meandering position changes when the conveyance is continued in this state. For this reason, the suppression of the belt meandering speed is higher in response than the correction control of the meandering position and the skew state of the belt. On the other hand, in order to correct the meandering position and the skew state of the belt, it takes time until the belt reaches a desired position and angle after being conveyed several times.
On the other hand, when the belt is skewed, a color shift immediately occurs in that state. Therefore, since a quick correction response is required, the writing side correction method is more suitable than the steering method.

Therefore, the belt meandering correction employs a steering system to suppress the belt meandering speed. It is desirable to correct the color misregistration due to the belt skew immediately from the writing side by the latent image forming position correcting means and the ink discharge nozzle selection correcting means.
In addition, when the time required for suppressing the meandering speed by steering (down time) becomes a problem, or when there is a demand for further reduction of downtime, the belt meandering speed restraining error in the steering system, that is, control by the steering system is performed. While performing, it is desirable to transmit the belt meandering speed information at the current time to the writing side correction means of the latent image forming position correction means and the ink discharge nozzle selection correction means and correct it together with the belt skew.

14, 15, 16, 17, 18 Support roller 80 Meander correction mechanism 81 Oscillating arm 82 Bearing 83 Oscillating arm rotation shaft 84 Eccentric cam 86 Shielding plate 87 Eccentric cam home position detecting means 88 Oscillating arm spring 89 Pressurization Spring 101, 102, 103, 104 Photosensitive drum 200 Intermediate transfer member (intermediate transfer belt)

JP 2000-34031 A Japanese Patent No. 3976924

Claims (12)

A belt conveying device having an endless belt stretched by a plurality of rollers and a driving unit that is connected to any one of the rollers and drives the endless belt, and a plurality of image forming units are conveyed in the conveying direction on the conveying surface of the endless belt In the image forming apparatus having side by side,
A plurality of position detection means that are arranged at different positions in the conveying direction of the endless belt and detect the position of the endless belt in the belt width direction orthogonal to the belt conveying direction;
From the position information of the endless belt obtained at the same time by a plurality of position detecting means, the amount of movement in the belt width direction of the center point of the image forming area including the plurality of image forming portions on the conveying surface of the endless belt, and the endless belt Calculating means for calculating the amount of rotation around the center point of
First correction means for correcting image displacement associated with movement of the endless belt in the belt width direction based on the movement amount calculated by the calculation means;
An image forming apparatus comprising: a second correction unit that corrects an image shift caused by rotation around the center point of the endless belt based on the rotation amount calculated by the calculation unit. The first correction means is a steering roller, and has first adjustment means for adjusting the posture of the roller, and the first adjustment means tilts one end of the roller with respect to the other end to thereby endless the belt. , Move the endless belt in the width direction to correct image misalignment,
The second correction means is another steering roller, and has a second adjustment means for adjusting the posture of the roller, and the second adjustment means is configured to tilt one end of the roller with respect to the other end. The image forming apparatus according to claim 1, wherein the image shift is corrected by moving the endless belt and adjusting the rotation around the center point of the endless belt.   The first correcting means and the second correcting means are one latent image forming position correcting means for correcting the image forming positions in the belt width direction in a plurality of image forming portions on the endless belt. Item 2. The image forming apparatus according to Item 1. The first correction means is a steering roller, and has first adjustment means for adjusting the posture of the roller, and the first adjustment means tilts one end of the roller with respect to the other end to thereby endless the belt. , Move the endless belt in the width direction to correct image misalignment,
The image forming apparatus according to claim 1, wherein the second correcting unit includes a latent image forming position correcting unit that corrects an image forming position in a belt width direction in a plurality of image forming units on the endless belt. Any one of the rollers is a steering roller, and includes a first adjustment unit that adjusts the posture of the roller. The first adjustment unit tilts one end of the roller with respect to the other end to thereby rotate the endless belt. Move it, adjust the position of the endless belt in the width direction,
The first correcting means and the second correcting means are one latent image forming position correcting means for correcting the image forming positions in the belt width direction in a plurality of image forming portions on the endless belt. Item 2. The image forming apparatus according to Item 1.   6. The image forming apparatus according to claim 1, wherein the position detecting unit is installed at two positions that are separated from the center of the image forming area by an equal interval. The calculating means calculates the time transition of the movement amount in the belt width direction and the rotation amount around the center point of the endless belt from the position information of the endless belt continuously obtained at constant time intervals over one or more rounds of the endless belt. Calculate the transition,
The first correction means corrects the image shift accompanying the movement in the width direction of the endless belt based on the time transition calculation result of the movement amount in the belt width direction by the calculation means,
The second correction means corrects image shift caused by the rotation of the endless belt based on a time transition calculation result of the rotation amount around the center point of the endless belt by the calculation means. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the image forming method in the image forming unit is an electrophotographic system.   The image forming apparatus according to claim 1, wherein the image forming method in the image forming unit is a line head type ink jet system. An endless belt stretched by a plurality of rollers, driving means connected to any one of the rollers and driving the endless belt, and a belt width arranged at different positions in the transport direction of the endless belt and perpendicular to the belt transport direction In a belt conveyance device having a plurality of position detection means for detecting the position of the endless belt in the direction,
The center point of the image forming area including the plurality of image forming portions on the conveying surface of the endless belt calculated from the position information of the endless belt obtained at the same time by the plurality of position detecting units in the belt width direction. Based on the amount of movement, a first correction unit that corrects image displacement associated with movement, and the amount of rotation around the center point of the endless belt calculated by the calculation unit corrects image displacement associated with rotation. A belt conveying device comprising: a second correcting unit. The first correction means is a steering roller, and has first adjustment means for adjusting the posture of the roller, and the first adjustment means tilts one end of the roller with respect to the other end to thereby endless the belt. , Move the endless belt in the width direction to correct image misalignment,
The second correction means is another steering roller, and has a second adjustment means for adjusting the posture of the roller, and the second adjustment means is configured to tilt one end of the roller with respect to the other end. The belt conveying device according to claim 10, wherein the endless belt is moved and the rotation of the endless belt around the center point is adjusted to correct the image shift.   The belt conveying device according to claim 10 or 11, wherein the position detecting means is installed at two positions separated by an equal interval from the center of the image forming area.

Images