JP2006276427A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of compensating distortion of an image according to skew generated on a belt even when the skew is generated on the belt by disturbance of temperature, humidity, paper size, paper kind, image size and image concentration, etc. and capable of forming a high definition color image without image distortion without requiring complicated control. <P>SOLUTION: In the image forming apparatus which forms the image with an image formation means using an endless belt member to be stretched and conveyed by a plurality of rolls, it is constituted so as to rotatably support the endless belt member by providing a skew detection means for detecting that the endless belt member is conveyed while being skewed to the conveyance direction of the endless belt member and an image compensation means for compensating the distortion of the image by the image formation means based on an amount of skew of the endless belt member detected by the skew detection means when the skew of the endless belt member is detected by the skew detection means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of forming a color image such as a color printer, a color facsimile, or a color copying machine adopting an electrophotographic method, and more particularly to an endless belt member stretched and conveyed by a plurality of rolls. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that forms an image by using the image forming apparatus, which can detect and correct an image distortion caused by a position variation of an endless belt member.

JP 2001-146335 A Japanese Patent Laid-Open No. 11-295948 JP 2000-233843 A JP-A-8-184774 JP 2003-274142 A

  Conventionally, as an image forming apparatus capable of forming a color image, such as a color printer, a color facsimile, or a color copying machine, yellow (Y), magenta (M), cyan (C), black (K), etc. Images of each color such as yellow (Y), magenta (M), cyan (C), and black (K) are formed by a plurality of image forming units corresponding to the respective colors, and these yellow (Y), magenta (M), Whether images of each color such as cyan (C) and black (K) are primary transferred in a state of being superimposed on each other on the intermediate transfer belt, and then secondary transferred collectively onto the recording paper from the intermediate transfer belt. Alternatively, there is a configuration in which a color image is formed by transferring images on a recording sheet conveyed by a sheet conveying belt while being superimposed on each other.

  In such an image forming apparatus, since an endless belt member such as an intermediate transfer belt or a paper transport belt is used, unevenness in thickness occurs due to a manufacturing error of the endless belt member or the endless belt member Manufacturing error of the stretching roll for stretching the belt-shaped belt member, error in the mounting position, and the like occur. In the image forming apparatus, as shown in FIG. 19, due to the manufacturing error of these endless belt members, the manufacturing error of the stretching roll, the error of the mounting position, etc. However, so-called “belt meandering” occurs in which the position changes in a direction perpendicular to the conveying direction.

  As described above, when the “belt meandering” occurs in the endless belt member such as the intermediate transfer belt or the paper transport belt, the position of the image transferred onto the intermediate transfer belt or the recording paper transported by the paper transport belt is shifted. This causes color misregistration and image distortion.

  Therefore, in a conventional image forming apparatus, as a technique for preventing “belt meandering” that occurs in an endless belt member such as an intermediate transfer belt or a sheet conveying belt, for example, a technique disclosed in Japanese Patent Laid-Open No. 2001-146335 is disclosed. Is configured to adopt.

  An image forming apparatus according to Japanese Patent Application Laid-Open No. 2001-146335 includes a plurality of image carriers that carry toner images, and a transfer material conveyance belt that is arranged to face the plurality of image carriers and carries and conveys a transfer material. A transfer means for transferring the toner image of the image carrier onto the transfer material carried on the transfer material conveyance belt, and the transfer material conveyance belt is stretched to prevent the transfer material conveyance belt from being displaced. A belt deviation regulating member provided coaxially with the rotation shaft, and a circumferential length of the belt deviation regulating member between the transfer positions on the transfer material conveying belt facing the plurality of adjacent image carriers. It is constituted by a substantially integer number or a substantially integer multiple of the separation distance.

  In the case of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2001-146335, although a simple configuration in which a belt deviation regulating member is provided coaxially with a rotation shaft that stretches the transfer material conveyance belt, the belt deviation regulating member is acceptable. The belt meandering accuracy is affected by the reliability problem of the belt deviation regulating member itself, such as deformation of the belt, and the manufacturing accuracy of the belt provided with the belt deviation regulating member. There has been a problem that color registration shift (color shift) or the like due to positional shift occurs.

  Therefore, as a technique for solving such problems and improving the accuracy of preventing meandering generated in the belt and suppressing the occurrence of color registration shift (color shift) or the like, for example, Japanese Patent Laid-Open No. Hei 11- As disclosed in Japanese Patent No. 295948, there has already been proposed a steering system in which a roll for stretching a belt is tilted. In this steering system, stress applied to the belt is small, and highly accurate meandering control is possible.

  The belt driving device according to the above-mentioned Japanese Patent Application Laid-Open No. 11-295948 has an endless belt and a predetermined number of rolls that support the endless belt, and any one of the predetermined number of rolls is used as a driving roll. In a belt driving device that causes the endless belt to travel by rotation of a driving roll, driving means for driving to correct a position variation in the width direction of the endless belt, and detection means for detecting an edge position in the width direction of the endless belt; The storage means for storing the edge shape data of the endless belt is compared with the edge shape data stored in the storage means for the edge position detection data by the detection means, and the drive means is determined based on the comparison result. And a control means for controlling the drive.

  However, the conventional technique has the following problems. That is, in the case of the belt driving device according to the above-mentioned Japanese Patent Application Laid-Open No. 11-295948, so-called “belt meandering” in which an endless belt such as an intermediate transfer belt moves in a direction perpendicular to the conveying direction is prevented. However, as shown in FIG. 20, there is a problem that the so-called “belt skew” in which the endless belt is conveyed while being inclined with respect to the conveying direction cannot be prevented. When "belt skew" occurs in an endless belt such as the intermediate transfer belt, as shown in FIGS. 21 and 22, the edges are essentially parallel to the edge of the recording sheet and in the vertical and horizontal directions. The image to be formed at a right angle along the edge of the recording sheet is formed in a state inclined with respect to the edge of the recording paper, and the edge in the vertical direction and the horizontal direction is formed in a distorted state without being at a right angle. Will be.

  As described above, the distortion of the image formed on the recording paper is almost as small as about 1 mm or less at both ends along the longitudinal direction of the A3 size paper. When images are formed on both sides, when the paper is folded in half, or when the paper is folded in half, the images on both sides of the recording paper do not overlap with each other accurately, There is a problem of reducing the image quality.

  In addition, as disclosed in Japanese Patent Application Laid-Open No. 2000-233843, the present applicant has already proposed a technique that can correct “belt meandering” and can also correct “belt skew”. is doing.

  The image forming apparatus according to Japanese Patent Application Laid-Open No. 2000-233843 includes a belt driving unit that travels an endless belt, and a position of the endless belt in a belt width direction orthogonal to the belt traveling direction at different positions in the belt traveling direction. A plurality of detection means for detecting the angle, a calculation means for calculating the amount of inclination of the endless belt in the belt running direction based on the detection results of the plurality of detection means, and a belt driving direction based on the calculation result of the calculation means. And a correction means for correcting the inclination of the endless belt.

  However, in the case of the image forming apparatus disclosed in the above Japanese Patent Laid-Open No. 2000-233843 proposed by the present applicant, two sensors for detecting "belt meandering" and "belt skewing" Since the configuration is such that the image distortion is corrected by using two steering rolls that stretch the belt, there is a problem that the mechanism becomes complicated and the cost is greatly increased. .

  Further, in the case of the image forming apparatus disclosed in the above Japanese Patent Laid-Open No. 2000-233843, since it has two control systems for controlling “belt meandering” and “belt skewing” It is very difficult to stably control the driving state of the belt, and there is a new problem that the driving state of the belt may become unstable depending on conditions.

  Furthermore, as a technique for correcting the distortion of the image, for example, as disclosed in Japanese Patent Laid-Open No. 8-184774 that corrects with a mirror of ROS and Japanese Patent Application Laid-Open No. 2003-274142 that corrects with image data, There has also been proposed a technique for detecting and correcting distortion of an image printed on paper with an image reading apparatus.

  However, in the case of the technique disclosed in the above Japanese Patent Laid-Open No. 8-184774, Japanese Patent Laid-Open No. 2003-274142, etc., the test pattern is created before the image formation or once the image formation is interrupted. There has been a problem that it is impossible to cope with the case where the distortion of the image changes during the formation.

  More specifically, the distortion of the image changes due to disturbance applied to the belt, and examples of the disturbance applied to the belt include temperature, humidity, paper size, paper type, image size, image density, and the like. For example, when the temperature, humidity, etc. change, the belt deforms or the frame deforms, and when the paper size or paper type changes, the external force applied from the paper to the belt at the transfer section changes, causing the belt to skew. Will occur. Further, when the image size or image density changes, the external force applied from the photosensitive drum to the transfer belt changes. When the balance between the back side and the front side of the external force applied to the endless belt member such as the transfer belt is lost, the meandering characteristics of the belt change, and the belt stability is changed, that is, the belt is skewed. There is a problem that image distortion occurs.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is that complicated control is not required, and temperature, humidity, paper size, paper type, image Even when skew occurs in the belt due to disturbances such as size and image density, image distortion can be corrected according to the skew generated in the belt, and high image quality without image distortion can be achieved. An object of the present invention is to provide an image forming apparatus capable of forming a color image.

That is, the invention described in claim 1 is an image forming apparatus that forms an image by image forming means using an endless belt member that is stretched and conveyed by a plurality of rolls.
Skew detection means for detecting that the endless belt member is conveyed in a state inclined with respect to the conveying direction of the endless belt member;
When skew of the endless belt member is detected by the skew detection means, image distortion is corrected by the image forming means based on the skew amount of the endless belt member detected by the skew detection means. An image forming apparatus comprising: an image correcting unit configured to perform image correction.

  According to a second aspect of the present invention, the skew detection means is configured to control the endless belt based on control data of a steering roll that corrects the movement of the endless belt member in a direction orthogonal to the conveying direction. The image forming apparatus according to claim 1, wherein the skew state of the member is detected.

  Further, in the invention described in claim 3, the skew detection means detects the image position detection mark formed on the endless belt member by the mark detection means, thereby the endless belt member. The image forming apparatus according to claim 1, wherein the skew state is detected.

  According to a fourth aspect of the present invention, the skew detection means detects the skew of the endless belt member by detecting the positions of the edge portions along the transport direction of the endless belt member at a plurality of locations. The image forming apparatus according to claim 1, wherein a row state is detected.

  Furthermore, the invention described in claim 5 is characterized in that the image correcting unit corrects image distortion by the image forming unit based on control data of the steering roll. The image forming apparatus described.

  According to a sixth aspect of the present invention, the image correction unit corrects image distortion by correcting an exposure position or exposure timing of an image on the image carrier of the image forming unit. 6. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  Furthermore, the invention described in claim 7 is characterized in that the image correcting unit corrects image distortion by correcting image data of an image to be formed by the image forming unit. 6. The image forming apparatus according to any one of items 1 to 5.

  The image correction unit corrects image distortion by correcting the image position in the main scanning direction or the image forming timing in the sub-scanning direction by the image forming unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  Further, in the invention described in claim 9, the image correction unit corrects image distortion by correcting image data along the main scanning direction by the image forming unit along the sub-scanning direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  In the present invention, as described above, for example, the skew of the endless belt member can be detected by measuring the position of the belt in the axial direction at two points. Further, the skew of the endless belt member has a correlation with the angle of the steering roll, and can be estimated by the angle of the steering roll without two sensors. Since the steering roll angle is controlled by the steering controller, this control value can be used.

  According to the present invention, even when the belt is skewed due to disturbances such as temperature, humidity, paper size, paper type, paper type, image size, image density, etc., without requiring complicated control. It is possible to provide an image forming apparatus capable of correcting image distortion in accordance with the skew generated in the belt and forming a high-quality color image without image distortion.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 is a schematic configuration diagram showing a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention. Although this tandem type color electrophotographic copying machine is provided with an image reading device, the image forming device is not provided with an image reading device, and is based on image data output from a personal computer (not shown). Of course, a color printer, a facsimile, or the like that forms an image may be used.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem type color electrophotographic copying machine. The color electrophotographic copying machine main body 1 has an image reading device (IIT) for reading an image of a document 2 at an upper portion on one end side thereof. : ImageInputTerminal) 4, and the image data output from the image reading device 4 or a personal computer (not shown), or the like is sent to the inside of the color electrophotographic copying machine main body 1 via a telephone line or a LAN. An image processing apparatus (IPS: Image Processing System) 12 that performs predetermined image processing on the received image data, and an image output apparatus that outputs an image based on the image data that has been subjected to predetermined image processing by the image processing apparatus 12 (IOT: ImageOutputTerminal) 100 There.

  In the image reading device 4, an image of the original 2 pressed on the platen glass 5 by the platen cover 3 or an original conveyed automatically by an ADF (not shown) is read. The image reading device 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and reflects a reflected light image from the document 2 from a full-rate mirror 7, half-rate mirrors 8 and 9, and an imaging lens 10. The image reading element 11 composed of a CCD or the like is scanned and exposed through a reduction optical system, and the color material reflected light image of the document 2 is formed at a predetermined dot density (for example, 16 dots / mm) by the image reading element 11. It is configured to read.

  The color material reflected light image of the document 2 read by the image reading device 4 is subjected to image processing as, for example, document reflectance data of three colors of red (R), green (G), and blue (B) (8 bits each). The image processing apparatus 12 sends predetermined reflectance data such as shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. to the reflectance data of the document 2. Image processing is performed.

  The image data that has been subjected to the predetermined image processing by the image processing apparatus 12 as described above is a four-color document of yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits). Converted to color material gradation data (raster data), as will be described below, yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13Y, 13M, 13C, 13K laser writing devices (ROS) 14Y, 14M, 14C, and 14K are sent to these laser writing devices 14Y, 14M, 14C, and 14K according to the original color material gradation data of a predetermined color. Image exposure with the laser beam LB is performed.

  By the way, inside the tandem type color electrophotographic copying machine main body 1, as described above, four image forming units 13Y of yellow (Y), magenta (M), cyan (C), and black (K), 13M, 13C, and 13K are arranged in parallel at regular intervals in the horizontal direction.

  These four image forming units 13Y, 13M, 13C, and 13K are all configured in the same manner, and roughly divided, a photosensitive drum 15 as an image carrier that is rotationally driven at a predetermined speed along the arrow A direction. And a scorotron 16 for primary charging as a charging means for uniformly charging the surface of the photosensitive drum 15 and a laser beam corresponding to the image information of each color on the surface of the photosensitive drum 15 for scanning exposure. The image forming apparatus (image forming means) includes a laser writing device 14 that forms an electrostatic latent image, a developing device 17 that develops an electrostatic latent image formed on the photosensitive drum 15, a cleaning device 18, and the like. Yes.

  As shown in FIG. 2, the laser writing device 14 modulates the semiconductor laser 19 according to the image data, and emits a laser beam LB from the semiconductor laser 19 according to the image data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 via the reflection mirrors 20 and 21, and again carries an image via the reflection mirrors 20 and 21 and the plurality of reflection mirrors 23 and 24. Scanning exposure is performed on the photosensitive drum 15 as a body.

  From the image processing device 12, the laser writing devices 14Y, 14M, 14C of the image forming units 13Y, 13M, 13C, and 13K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are provided. Image data (raster data) of each color is sequentially output to 14K, and laser beams LB emitted according to the image data from these laser writing devices 14Y, 14M, 14C, and 14K are supplied to the respective photosensitive drums 15Y, 15M, The surfaces of 15C and 15K are scanned and exposed to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 15Y, 15M, 15C, and 15K are respectively yellow (Y), magenta (M), and cyan (C) by the corresponding developing devices 17Y, 17M, 17C, and 17K. , And developed as a toner image of each color of black (K).

  Yellow (Y), magenta (M), cyan (C), and black (K) sequentially formed on the photosensitive drums 15Y, 15M, 15C, and 15K of the image forming units 13Y, 13M, 13C, and 13K. The unfixed toner images of the respective colors are superimposed on the surface of the intermediate transfer belt 25 at a primary transfer position where the photosensitive drums 15Y, 15M, 15C, and 15K are in contact with the intermediate transfer belt 25 as an intermediate transfer member. Sequentially transferred. Semiconductive bias rolls 26Y, 26M, 26C, and 26K are disposed on the back surface side of the intermediate transfer belt 25 at the primary transfer position, and the intermediate transfer belt is provided by these bias rolls 26Y, 26M, 26C, and 26K. 25 abuts on the surfaces of the photosensitive drums 15Y, 15M, 15C, and 15K. The primary transfer bias rolls 26Y, 26M, 26C, and 26K are applied with a voltage having a polarity opposite to the charging polarity of the toner, and the respective colors formed on the photosensitive drums 15Y, 15M, 15C, and 15K are undetermined. The contact toner images are sequentially electrostatically attracted onto the intermediate transfer belt 25 to form a full-color image.

  The intermediate transfer belt 25 is stretched between a driving roll 27, a driven roll 28, a steering roll 29, an opposing roll (backup roll) 30 for secondary transfer, and a driven roll 32 with a constant tension. The drive roller 27 is rotationally driven by a dedicated drive motor with excellent constant speed (not shown) and is driven to circulate at a predetermined speed in the arrow B direction.

  When a single color image is formed, only the desired color image forming units 13Y, 13M, 13C, and 13K are operated, and a desired single color unfixed toner image is formed on the intermediate transfer belt 25.

  In this way, the unfixed toner images of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) that have been primary-transferred multiple times on the intermediate transfer belt 25 are intermediate transfer belt 25. Is rotated to the secondary transfer position facing the conveyance path of the recording paper 33 (sheet), and an unfixed toner image is transferred from the intermediate transfer belt 25 to the recording paper 33 at the secondary transfer position. Transcribed. The recording paper 33 is fed from the print paper tray 34 by the feed roller 35, transported to the registration roller 38 by a paper transport path 37 having a plurality of transport rollers 36, and temporarily stopped. Next, the recording paper 33 is conveyed by the registration roller 38 at a predetermined timing, and is sandwiched between the secondary transfer bias roll 39 and the intermediate transfer belt 25. Further, on the back side of the intermediate transfer belt 25 at the secondary transfer position, a backup roll 30 that is opposed to the bias roll 39 and a metal roll 41 that contacts the backup roll 30 are disposed. At the secondary transfer position, by applying a voltage (normal transfer bias) having the same polarity as the toner charging polarity to the metal roll 41, the bias roll 39 forms a transfer electric field as a counter electrode, and an intermediate transfer belt. The unfixed toner image carried on 25 is electrostatically transferred to the recording paper 33 at the secondary transfer position. The secondary transfer bias roll 39 is cleaned by a brush roll 42.

  The recording sheet 33 on which the unfixed toner image is transferred is discharged from the intermediate transfer belt 25 while being discharged by a flat plate discharging device 43, and then is used as a double transfer material transporting unit via the chute 44. Are fed to the fixing device 47 by the paper transport belts 45 and 46, and the fixing process of the unfixed toner image is performed. The paper transport belts 45 and 46 are composed of an endless rubber belt 45c stretched between a driving roller 45a and a driven roller 45b, and five rubber belts are stretched in parallel by one paper transport belt. ing.

  The fixing device 47 includes a pair of fixing rolls (fixing members) including a heating roll 48 having a heater (not shown) therein and a pressure roll 49 disposed in pressure contact with the heating roll 48. is doing. When the recording paper 33 on which the unfixed toner image is formed passes through the fixing area between the heating roll 48 and the pressure roll 49, the fixing device 47 generates a toner image on the recording paper 33 by heat and pressure. It has become established.

  During the fixing process, the unfixed toner surface of the recording paper 33 is usually in direct contact with the outer peripheral surface of the heating roll 48, so that a part of the unfixed toner on the recording paper 33 is transferred to the heating roll 48 side. A phenomenon (toner offset phenomenon) in which the toner re-transfers to the recording paper 33 after one rotation of the heating roll 48 occurs. Therefore, in this embodiment, in order to prevent the toner offset phenomenon, a release agent coating device 50 that applies a release agent to the surface of the heating roll 48 is provided.

  On the other hand, residual toner is removed from the intermediate transfer belt 25 after the secondary transfer of the unfixed toner image is completed, as shown in FIG. 2, by a belt cleaner 55 positioned downstream of the secondary transfer portion.

  When creating a double-sided print, as shown in FIG. 2, the recording paper 33 does not pass through the fixing device 47 and the first side is fixed, and then is not discharged outside the image forming apparatus. The sheet reversing unit 57 and the double-sided sheet conveying unit 58 are switched to each other by a switching gate (not shown) disposed on the downstream side of the fixing device 47. In the paper reversing unit 57, the recording paper 33 is reversed by switchback, passes through the paper conveying unit 58, and is conveyed again to the registration roller 38. While the recording paper 33 is conveyed to the registration roller 38, an image for the second surface is formed on the intermediate transfer belt 25 in the same manner as the image forming process for the first surface. The first recording sheet 33 on which the first surface is imaged at the timing is conveyed to the secondary transfer unit, and the image is transferred to the second surface in the same manner as the first surface. Thereafter, the recording paper 33 having the toner image transferred onto the second surface is conveyed to the fixing device 47 by the paper conveying belts 45 and 46, and after fixing processing, is provided outside the image forming apparatus. The sheet is discharged onto the discharge tray 59, and the image forming process for a series of double-sided printing is completed.

As the intermediate transfer belt 25, a synthetic resin such as polyimide or polyamide containing an appropriate amount of an antistatic agent such as carbon black and formed into an endless belt shape is used, and its volume resistivity is 10 ⁶ to 10 ^14. For example, the thickness is set to about 0.1 mm.

The primary transfer bias roll 26 is made of foamed urethane rubber in which carbon black is dispersed, and has a volume resistance of 10 ⁶ to 10 ¹⁰ Ω, a roll diameter of φ28 mm, and a hardness of 35 °, for example. (Asuka C) is set.

Further, the bias roll 39 for secondary transfer is made of urethane rubber tube with carbon black dispersed on the surface, the inside is made of foamed urethane rubber with carbon black dispersed, and the roll surface is coated with fluorine, It is formed so that the resistance is 10 ³ to 10 ¹⁰ Ω and the roll diameter is φ28 mm, and the hardness is set to 30 ° (Asuka C), for example. On the other hand, the backup roll 30 is made of EPDM and NBR blend rubber tube with carbon black dispersed in the surface and EPDM rubber inside, and has a surface resistivity of 10 ⁷ to 10 ¹⁰ Ω / □ and a roll diameter. It is formed to have a diameter of 28 mm, and the hardness is set to 70 ° (Asuka C), for example.

  The rubber belts of the paper conveying belts 45 and 46 are made of rubber made of EPDM and are endless, and the thickness of the belt is set to about 1 mm.

  Further, the heating roll 48 and the pressure roll 49 are formed by coating a silicone rubber on the surface of a cylindrical core made of a metal having high thermal conductivity such as aluminum.

  In the color electrophotographic copying machine, as shown in FIG. 1, meandering of the intermediate transfer belt 25 is detected by the edge sensor 102 with reference to the home position detected by the belt home sensor 101, and these belt home sensors. The detection results of 101 and the edge sensor 102 are input to the steering control circuit 103, and the steering control circuit 103 is configured to control the intermediate transfer belt 25 so that no belt meandering occurs.

  The belt home sensor 101 detects the home position of the intermediate transfer belt 25 by detecting a mark indicating a home position formed by a reflection plate or a transmission hole (not shown) provided at an end in the width direction of the intermediate transfer belt 25. It is for detection. As shown in FIG. 1, the belt home sensor 101 is disposed, for example, downstream of the drive roll 27 and upstream of the most upstream yellow image forming unit 13Y.

  Further, as shown in FIG. 3, the edge sensor 102 includes a contactor (actuator) 104 that abuts against an end (edge) of the intermediate transfer belt 25, and the movement of the contactor 104 is detected by a displacement sensor 105. By detecting, the position (meandering) of the belt 25 in the width direction y is detected. The contact 104 is swingably supported around a fulcrum 106 and is urged clockwise by a coil spring 107. As the displacement sensor 105, a sensor that detects the tilt of the contact 104, that is, the end of the belt 25 by detecting the amount of reflected light of the light emitted from the LED, a PSD sensor, or the like may be used. good. As the displacement sensor 105, as shown in FIG. 4, a non-contact type sensor (a light amount sensor 109 comprising a CCD or the like that detects the light amount from the LED 108) that does not use a contactor is used. Also good. The edge sensor 102 is disposed further downstream of the most downstream black image forming unit 13K.

  The edge data detected by the edge sensor 102 has a shape including the shape of the belt edge. For this reason, in order to control the meandering of the belt by referring to the edge data measured in advance, it is necessary to synchronize with the belt, so that a detection signal from the belt home sensor 101 for detecting the home position of the belt is required.

  As shown in FIG. 5, one end of a steering roll 29 that stretches the intermediate transfer belt 25 is rotatably supported at the tip of the swing arm 110, and the base end of the swing arm 110 is steered. The angle θ of the steering roll 29 is controlled by swinging with an eccentric cam 112 rotated by a motor 111. The steering control circuit 103 rotationally drives a steering motor 111 made of a stepping motor or the like by a predetermined amount based on the detection results of the belt home sensor 101 and the edge sensor 102, and the eccentric cam 112 moves the swing arm 110 by a predetermined amount. It is designed to swing. The swing arm 110 is mounted so as to be swingable about a fulcrum 113.

  By the way, the intermediate transfer belt 25 has a manufacturing error of the intermediate transfer belt 25, a manufacturing error of the rolls 27, 28, 29, 30, and 32 that stretch the intermediate transfer belt 25, a mounting position error, So-called “belt meandering” that moves in a direction perpendicular to the conveying direction may occur.

  Therefore, in the color electrophotographic copying machine configured as described above, as shown in FIG. 1, the position of the end of the intermediate transfer belt 25 is detected by the edge sensor 102, and the intermediate transfer detected by the edge sensor 102 is detected. By controlling the steering roll 29 according to the end position of the belt 25, “belt meandering” is prevented, and the end position of the intermediate transfer belt 25 is controlled to be constant. .

  At this time, even if the intermediate transfer belt 25 is controlled so that the end position of the intermediate transfer belt 25 is constant, the end position itself of the intermediate transfer belt 25 is periodically shifted from a predetermined position. There is a possibility that "belt meander" may remain.

  Therefore, in the color electrophotographic copying machine, the edge sensor 102 periodically changes the end position of the intermediate transfer belt 25 as shown by the broken line in FIG. As shown by the solid line in FIG. 6, the data obtained by averaging the periodic fluctuations of the end position of the intermediate transfer belt 25 is stored in a storage means (not shown) provided in the steering control circuit 103 or the like. Let me let you. Then, based on the fluctuation information of the end position of the intermediate transfer belt 25 stored in the storage means, the actual fluctuation of the end position of the intermediate transfer belt 25 is detected to prevent “belt meandering”. It is configured. In FIG. 6, steps S1 to S8 indicate control procedures, respectively.

  The control amount of the steering motor 111 and the meandering speed generated in the intermediate transfer belt have a linearly changing relationship as shown in FIG. 7, but the control amount of the steering motor 111 and the intermediate transfer belt 25 The linear relationship with the meandering speed varies depending on conditions such as machine differences and temperature, as indicated by A and B in FIG. Therefore, when the color electrophotographic copying machine is shipped, the relationship between the control amount of the steering motor 111 and the meandering speed of the belt is calibrated, and A and B are obtained as points where the meandering speed of the belt becomes zero. Thus, adjustment is made so that a constant meandering speed of the belt is always obtained.

  Further, when the steering motor 111 is driven as described above to displace the steering roll 29, as shown in FIG. 8, a “belt skew” (belt skew) occurs in the intermediate transfer belt 28. As shown in FIG. 9, there is also a linearly varying relationship between the control amount of the steering roll 29 and the skew angle (belt skew) of the intermediate transfer belt 25. However, this linear relationship also varies depending on conditions such as machine differences and temperature, and calibration is required at the time of shipment.

  In this embodiment, in an image forming apparatus that forms an image by image forming means using an endless belt member stretched and conveyed by a plurality of rolls, the endless belt member conveys the endless belt member. A skew detecting means for detecting that the sheet is conveyed while being inclined with respect to the direction; and when the skew detecting means detects the skew of the endless belt member, the skew detecting means detects the skew. The image forming unit includes an image correcting unit that corrects image distortion by the image forming unit based on the skew amount of the endless belt member.

  In this embodiment, the skew detection means is configured to skew the endless belt member based on control data of a steering roll that corrects the movement of the endless belt member in a direction orthogonal to the conveying direction. It is configured to detect a state.

  That is, in the color electrophotographic copying machine according to this embodiment, as shown in FIG. 1, a skew is detected for detecting that the intermediate transfer belt 25 is conveyed in an inclined state with respect to the conveyance direction of the intermediate transfer belt 25. As the row detection means, a steering control circuit 103 that outputs control data for controlling the steering roll 29 is used.

  The steering control circuit 103 rotationally drives the steering motor 111 in consideration of the end position information of the intermediate transfer belt 25 stored in the storage unit based on the detection results of the belt home sensor 101 and the edge sensor 102. A control amount is determined and the control data is output to the steering motor 111.

  Further, the steering control circuit 103 is configured to output control data similar to the control data of the steering motor 111 to the image output circuit 120 as image correction means. In FIG. 1, reference numeral 121 denotes a CPU that controls the overall operation of the color electrophotographic copying machine.

  The image output circuit 120 outputs the image data 122 to each of the image forming units 13Y, 13M, 13C, and 13K, and based on the control data of the steering motor 111, the image forming units 13Y, 13M, 13C, and 13K. Control data for controlling the tilt angle of the mirror 24 (see FIG. 2) at the final stage is output to the ROSs 14Y, 14M, 14C, and 14K. In the ROSs 14Y, 14M, 14C, and 14K of the image forming units 13Y, 13M, 13C, and 13K, as shown in FIG. 10, the tilt angle of the mirror 24 at the final stage is the same as the mechanism that tilts the steering roll 29. It is comprised so that it may control by the mechanism of. The ROSs 14Y, 14M, 14C, and 14K control the tilt angle of the mirror 24 at the final stage, thereby changing the angle of the laser beam LB that scans and exposes the photosensitive drum 15 in the main scanning direction. It is possible to incline with respect to the direction.

  In the above configuration, the image forming apparatus according to this embodiment does not require complicated control as described below, and includes disturbances such as temperature, humidity, paper size, paper type, image size, and image density. Therefore, even when skew occurs in the belt, image distortion can be corrected according to the skew occurring in the belt, and a high-quality color image without image distortion can be formed. It has become.

  That is, in the color electrophotographic copying machine according to this embodiment, as shown in FIG. 2, each color image is formed by the image forming units 13Y, 13M, 13C, and 13K for each color of yellow, magenta, cyan, and black. The yellow, magenta, cyan, and black toner images formed by the respective color image forming units 13Y, 13M, 13C, and 13K are primarily transferred onto the intermediate transfer belt 25 in a state of being sequentially superimposed on each other. The yellow, magenta, cyan, and black toner images transferred onto the intermediate transfer belt 25 are collectively transferred onto the recording paper 33 and fixed by the fixing device 47, whereby a color image is obtained. It comes to form.

  At this time, in the color electrophotographic copying machine, as shown in FIG. 1, the position of the end of the intermediate transfer belt 25 is detected by the edge sensor 102, and the steering motor 111 is detected according to the position of the end of the belt 25. Is rotated to adjust the inclination of the steering roll 29 to control the meandering of the belt.

  Incidentally, the intermediate transfer belt 25 also has variations in the positions of the end portions of the belt due to manufacturing errors when the intermediate transfer belt 25 is manufactured. The variation in the end position of the intermediate transfer belt 25 is detected in advance by the edge sensor 102 and stored in the storage unit.

  Therefore, the steering control circuit 103 rotates the steering motor 111 according to the end position of the belt 25 based on the belt end position data stored in the storage means, and the steering roll 29 tilts. To adjust the meandering of the belt.

  At this time, in this embodiment, if the meandering control of the belt is performed by adjusting the inclination of the steering roll 29, the intermediate transfer belt 25 is skewed, so that the control amount (motor) for tilting the steering roll 29 is increased. The amount of skew of the belt is calculated based on the amount of control), and the image output position is controlled by the image output circuit 120 in accordance with the amount of skew of the belt.

  The correction of the image writing position is performed by controlling the tilt angle of the mirror 24 at the final stage of the lasers ROS 14Y, 14M, 14C, and 14K. As a result, the toner images of the respective colors transferred onto the intermediate transfer belt 25 are parallel to the transport direction of the intermediate transfer belt 25 with respect to the intermediate transfer belt 25 transported at an inclination as shown in FIG. Further, since the images are transferred so as to be orthogonal to each other, it is possible to prevent distortion from occurring in the image.

  However, since the image transferred onto the intermediate transfer belt 25 remains inclined with respect to the recording paper 33 as indicated by a broken line in FIG. 10, the paper is inclined and conveyed by adjusting the paper conveyance path. As a result, as shown by a solid line in FIG. 10, the image can be correctly transferred to the recording paper 33. A well-known technique can be used as the technique for conveying the sheet at an angle.

  As described above, according to the above-described embodiment, the control data of the steering control circuit 103 can be used as it is as the correction data of the image without any complicated control, and the temperature, humidity, paper size, paper type, Even when skew occurs in the intermediate transfer belt 25 due to disturbances such as image size and image density, the skew of the intermediate transfer belt 25 is immediately detected by the edge sensor 102 and is generated in the belt. Image distortion can be corrected according to skew, and a high-quality color image without image distortion can be formed.

  In addition to tilting the laser ROS mirror, the image can be corrected by changing the light emission timing in the axial direction in the case of an LED exposure apparatus.

Embodiment 2
FIG. 11 shows a second embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the first embodiment, the ROS mirror is controlled. However, the second embodiment is configured such that the same effect can be obtained by tilting image data instead of tilting the exposure position.

  That is, in the second embodiment, as shown in FIG. 11A, when skew occurs in the intermediate transfer belt 25, the mirror of the laser ROS is not tilted, but as shown in FIG. When the image data 122 is expanded on the memory of the image output circuit 120, the image data 122 is expanded in a state where the image data 122 is inclined by a predetermined angle, and the image data 122 inclined by the predetermined angle is displayed in each image forming unit. It is configured to output to 13Y, 13M, 13C, and 13K ROSs 14Y, 14M, 14C, and 14K.

  Further, the position correction of the image data may be performed by correcting the image data 122 itself, but can also be performed by the image processing circuit 120. Alternatively, in the conventional laser ROS, the same correction can be performed by changing the time of image writing timing from the SOS signal (scan reference signal) in the sub-scanning direction. In the LED exposure apparatus, the light emission start position in the main scanning direction may be changed in the sub scanning direction.

  As shown in FIG. 11B, if the position of the image data is corrected in consideration of the inclination of the image with respect to the paper 33, it is not necessary to feed the paper 33 diagonally.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 3
FIG. 12 shows a second embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the third embodiment, the skew detecting means is The skew detection state of the endless belt member is detected by detecting a mark for image position detection formed on the endless belt member by a mark detection means.

  That is, in the third embodiment, as shown in FIG. 13, an image position detection pattern 50 called a chevron pattern is formed at a predetermined timing in a non-image area located between the image areas of the intermediate transfer belt 25. Then, this image position detection pattern 50 is detected by a pattern detector (image output state detection means) 60, and the positional deviation amount of the image formed by each of the image forming units 13Y, 13M, 13C, 13K is obtained and corrected. Thereafter, a desired color image is formed. As shown in FIG. 13, the pattern detectors 60A, 60B, 60C are arranged at the detection position provided on the downstream side of the most downstream cyan image forming unit 13K, as shown in FIG. Arranged along the scanning direction on the OUT side (front side in the figure), the CENTER part (center part), and the IN side (back side in the figure) of the color copying machine main body 1, respectively. Accordingly, a plurality (four or more) may be provided at equal intervals along the width direction of the intermediate transfer belt 25, and are appropriately arranged according to the type of image position deviation to be detected.

  As the test pattern 50, various shapes can be used. For example, as shown in FIG. 14, the test pattern 50 is a straight line inclined at an equal angle along the sub-scanning direction from the center to the left and right sides as shown in FIG. In this case, a mountain-shaped mark 51 made of the above image is formed so as to correspond to the positions of the image position detectors 60A, 60B, and 60C. A plurality of the image position detection patterns 50 are formed at predetermined intervals along the sub-scanning direction (movement direction of the intermediate transfer belt 25).

  More specifically, as shown in FIG. 14, the test pattern 50 includes a first chevron mark 51CC made of a first reference color (cyan in the illustrated example), and a second measured color ( In the illustrated example, the second chevron mark 51YY consisting of yellow) and the third chevron mark 51CY mark consisting of the first color and the second color are used as a unit for all the colors to be measured. A pattern combining the above is used. The combination of the patterns 50 shown in FIG. 14 is one block for the reference color and the measured color. When this pattern is actually used, processing such as forming and sampling repeatedly for several blocks and averaging the sampling values is performed. In order to improve detection accuracy, the black chevron mark 51 has a yellow background with a high reflectance, and a black toner is applied to the black chevron mark 51 so that a predetermined chevron mark 51 is opened. It is desirable to form a black chevron mark 51. The image data for outputting the image position detection pattern 50 is stored in advance in, for example, the ROM of the control unit 5 of the image forming apparatus.

  FIG. 15 is a block diagram showing a pattern detector 60 for detecting the test pattern 50.

  In FIG. 15, 61 is a housing of the pattern detector 60, and 62 and 63 are light emitting elements composed of two LEDs or the like that respectively illuminate the image position detection pattern 50 formed on the intermediate transfer belt 8. Reference numerals 64 and 65 denote a pair of light receiving elements called “bi-cell” in which two light receiving elements are each set. As the light receiving element pair 64 and 65 called “bi-cell”, for example, as disclosed in JP-A-6-118735, the light receiving elements 64a and 64b and 65a and 65b made of two photodiodes are combined. The detectors arranged symmetrically are used. The inclination angle of the light receiving element pairs 64 and 65 is set equal to the inclination angle (for example, 45 degrees) of the mountain pattern 51. As the two light-emitting elements 62 and 63, for example, LEDs that emit light having a specific wavelength (infrared region) or light having a predetermined wavelength distribution are used. It arrange | positions so that two detection positions on the intermediate transfer belt 8 may be illuminated in a state inclined by a predetermined angle. The two pairs of light receiving element pairs 64 and 65 are elongated parallelograms arranged adjacent to each other with their center portions in contact with each other and both end portions inclined downward by a predetermined angle with respect to the horizontal direction. The light receiving elements 64a, 64b and 65a, 65b are provided, and the light receiving elements 64a, 64b and 65a, 65b have different detection timings and detection angles of reflected light as shown in FIG. 6B. Is set to

  When the pattern detector 60 detects the test pattern 50 formed on the intermediate transfer belt 8, the linear mark 51 of the test pattern 50 causes a mountain shape corresponding to the amount of reflected light from one light receiving element 64 b. And the other light receiving element 64a outputs a mountain-shaped waveform with some delay. Then, by amplifying the waveforms output from these two light receiving elements 64b and 64a, or by taking the difference and then amplifying it, as shown in FIG. From this, an output waveform that rises in a large mountain shape can be obtained. Therefore, by taking the difference between the waveforms output from the two light receiving elements 64a and 64b, the position of the linear mark 51 of the test pattern 50 can be obtained with high resolution without using a high-precision sensor such as a CCD. It becomes possible to detect with high accuracy.

  When the test pattern 50 is detected by the pattern detector 60, the pattern detector 60 outputs a waveform as shown at the right end of FIG. 14 only when the test pattern 50 is detected. Therefore, when the test pattern 50 is detected by comparing the output from the pattern detector 60 with a certain threshold value, the test pattern 50 changes from “OFF” to “ON” and the test pattern 50 passes. , A pulse signal changing from “ON” to “OFF” is obtained.

  As described above, when focusing on only “ON” in this result, as described above, the “ON” period is a period during which a pattern is detected, and the “OFF” period is a period during which no pattern is detected. is there. Therefore, if the time interval from “ON” to “ON” is measured, the distance between the above patterns is measured. From the result, the amount of deviation of each color with respect to the image of the reference color is calculated, and a plurality of deviations are calculated from the amount of deviation. It is possible to always obtain a stable / good image by obtaining the amount of misregistration and correcting it by each image forming unit.

  FIG. 16 is a block diagram showing a signal processing circuit of the image position detector 60.

  As shown in FIG. 16, the image position detector 60 includes a reflected light amount detection unit 66a corresponding to the LED 62 as one light emitting element, and a reflected light amount detection unit 66b corresponding to the LED 63 as the other light emitting element. ing. In one reflected light amount detection unit 66a, the output terminal of the photodiode 64a as the light receiving element is connected to the microcomputer 83 of the control unit 5 via the current-voltage converter 80, the amplifier (AMP) 81, and the A / D converter 82. The current having a magnitude corresponding to the amount of light received from the photodiode 64a is converted into digital data representing the output voltage of the photodiode 64a and input to the microcomputer 83. The microcomputer 83 is connected to a light emitting element (LED) 62 via an LED driver 84. The microcomputer 83 controls the drive current supplied to the LED 62 via the LED driver 84 so that the output voltage from the photodiode 64a is within a predetermined range.

  The output terminal of the other photodiode 64b is connected to one of the two input terminals of the differential input amplifier 86 via the current-voltage converter 85, and is connected to the other of the two input terminals. Is connected to the output terminal of a current-voltage converter 80 which is an output from the photodiode 64a. The differential input amplifier 86 amplifies and outputs a difference between signals input from the current-voltage converters 85 and 80 (corresponding to a difference in received light amount between the photodiodes 64a and 64b). In FIG. 14, an approximate change in the output voltage of the differential input amplifier 86 when the image position detector 60 detects the image position detection pattern 50 is shown in association with the pattern 51.

  The output terminal of the differential input amplifier 86 is connected to the microcomputer 83 via a comparator 87, a buffer 88, and a counter 89. The comparator 87 compares the level of the signal input from the differential input amplifier 86 with a preset threshold, and when the level of the signal is equal to or higher than the threshold, the output signal is at a high level (for convenience, referred to as “ON”). When the level is less than the threshold, the output signal is switched to a low level (referred to as “OFF” for convenience). An output signal from the comparator 87 is input to the counter 89 via the buffer 88.

  The counter 89 starts counting when the level of the input signal is switched from “OFF” to “ON”, and after the level of the signal is switched from “ON” to “OFF”, the counter 89 changes from “OFF” to “ When switched to “ON”, the count value up to that time is output to the microcomputer 83 and the count value is reset, and then the time until the signal level is switched from “OFF” to “ON” is counted repeatedly.

  The microcomputer 83 detects the position of the image position detection pattern 50 based on the count result input from the counter 89 at the time of image position correction described later (when the image position detector 60 detects the image position detection pattern 50). The image forming units 7Y, 7M, 7C, and 7Bk are configured to correct image forming position shifts (registration shifts).

  Since the circuit having the same configuration as that of the reflected light amount detection unit 66a is also connected to the photodiodes 65a and 65b of the other reflected light amount detection unit 66b, as shown in FIG. 16, it is the same as each part of the connected circuit. The description is abbreviate | omitted and the description is abbreviate | omitted.

  The microcomputer 83 controls the image forming units 7Y, 7M, 7C, and 7Bk so that the test pattern 50 as shown in FIG. 14 is formed on the outer peripheral surface of the intermediate transfer belt 8 when the registration error is corrected.

  When the test pattern 50 is formed on the intermediate transfer belt 8, the pattern detector 60 detects the test pattern 50. Here, since the detection positions by the photodiodes 64a and 64b on the outer peripheral surface of the intermediate transfer belt 8 are shifted in the sub-scanning direction, the current-voltage is detected from the differential input amplifier 86 when the test pattern 50 is detected. On the outer peripheral surface of the intermediate transfer belt 8 as shown in FIG. 14 as a waveform corresponding to the difference between the signals input from the converters 85 and 80 (difference in received light amount of the photodiodes 64a and 64b). Each time a single peak mark crosses the detection position by the photodiodes 64a and 64b, a signal having a waveform in which the level of the output signal changes in a pulse shape in the negative direction and the positive direction is output.

  The output signal of the differential input multiplier 86 is input to the comparator 87, and the comparator 87 compares the level of the output signal with a preset threshold value. The comparator 87 sets the level of the output signal to “ON” when the level of the input signal is equal to or higher than the threshold, and sets the level of the output signal to “OFF” when the level of the input signal is less than the threshold. . The signal output from the comparator 87 is input to the counter 89 via the buffer 88, and the time intervals when the signal level is switched from “OFF” to “ON” are sequentially counted. The count value obtained by the counter 89 is input to the microcomputer 83 as a pattern detection signal (see FIG. 16).

  The microcomputer 83 receives count values from two (total six) counters 89 per single image position detector 60 as pattern detection signals. In the signal output from the comparator 87, the period in which the level is “ON” corresponds to the period in which the detector detects the mountain pattern, and the period in which the level is “OFF” is detected. This corresponds to a period during which the vessel does not detect the chevron pattern (a period during which a gap between chevron patterns is detected). Therefore, the count value input from the counter 89 represents the formation interval of the chevron pattern 51 in the image position detection pattern 50.

  FIG. 12 is a block diagram showing a control circuit of the color electrophotographic copying machine according to this embodiment.

  In FIG. 12, reference numeral 130 denotes a registration detection circuit. The registration detection circuit 130 detects a color registration shift as follows.

  The registration detection circuit 130 forms the mountain-shaped mark 51 formation time interval (shown in FIG. 17A) in each part in the image position detection pattern 50 based on the count value input from each counter 89 shown in FIG. The time intervals a, b, c, d) are detected. The time intervals a, b, c, and d obtained from the two count values input from the single image position detector 60 are the main scanning direction (hereinafter referred to as FS (Fast Scan) direction) and the sub scanning direction ( If there is no shift in the pattern formation position (hereinafter referred to as SS (Slow Scan) direction), the values are equal to each other (a = b = c = d) as shown in FIG. 17B, but FIG. Or, when the pattern formation position is shifted in the FS direction as shown in (D), or when the pattern formation position is shifted in the SS direction as shown in FIG. At least one of the intervals a, b, c, d is different from the other values.

  For this reason, the registration detection circuit 130, according to the following arithmetic expression, uses the specific color (for example, C) as a reference and the color shift amount FSerr in the FS direction and the color in the SS direction for the other three colors (for example, Y, M, and Bk). The shift amount SSerr is calculated based on the count values input from the image position detectors 60A, 60B, and 60C.

FSerr [sec] = (ba) / 2
FSerr [mm] = FSerr [sec] (distance per unit time) [mm / sec]
SSerr [sec] = (dc) + (ba) / 2
SSerr [mm] = SSerr [sec] (distance per unit time) [mm / sec]
Here, for example, the value of SSerr [mm], which is the amount of positional deviation along the sub-scanning direction in the image position detector 60B in the center, becomes the amount of positional deviation along the SS direction as it is.

  The registration detection circuit 130 is configured to calculate the skew amount of the intermediate transfer belt 25 based on the above value.

  The regicon pattern is usually formed before the start of image formation or by interrupting the image forming operation. However, by using an inter image, the skew amount of the belt can be detected even during the image forming operation. The detection of the regicon pattern can detect the amount of skew of the belt even when detecting a single color.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 4
FIG. 18 shows a fourth embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the fourth embodiment, the skew detection means is The skew state of the endless belt member is detected by detecting the position of the edge portion along the conveying direction of the endless belt member at a plurality of locations.

  That is, in the fourth embodiment, as shown in FIG. 18, by providing a plurality of edge sensors 141 and 142, the skew of the intermediate transfer belt 25 can be detected and corrected. By installing at least two edge sensors 141 and 142 on the transfer surface including the image forming unit (photosensitive drum), it is possible to accurately detect the skew amount of the belt.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  In the above-described embodiment, the case of the intermediate transfer belt as the endless belt member has been described. However, the present invention is not limited to this, and it is needless to say that the present invention can be similarly applied to a sheet conveying belt and a photosensitive belt.

  In addition to the embodiment using the steering control value, the same applies to a method of using a belt guide member or a method of directly guiding a belt end, and can be similarly applied to all methods of mechanically guiding a belt.

  Furthermore, in the above-described embodiment, the tandem type color image forming apparatus has been described. However, it is also effective in a multi-pass (4-cycle) color image forming apparatus, and the image position can be corrected even in a single color apparatus. It is valid.

FIG. 1 is a block diagram showing a main part of a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing the edge sensor. FIG. 4 is a block diagram showing another edge sensor. FIG. 5 is an explanatory view showing the control of the steering roll. FIG. 6 is an explanatory diagram showing control of the edge position of the intermediate transfer belt. FIG. 7 is a graph showing the relationship between the steering control amount and the meandering speed of the belt. FIG. 8 is an explanatory diagram showing the amount of skew of the belt accompanying the control of the steering roll. FIG. 9 is a graph showing the relationship between the steering control amount and the belt skew. FIG. 10 is an explanatory view showing the control operation in the tandem type color electrophotographic copying machine as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 11 is an explanatory diagram showing another control operation in the tandem type color electrophotographic copying machine as the image forming apparatus according to the first embodiment of the present invention. FIG. 12 is a block diagram showing a main part of a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 2 of the present invention. FIG. 13 is a perspective view showing a register misalignment detection mark. FIG. 14 is a plan view showing a registration deviation detection mark. FIG. 15 is a block diagram showing an image position detector. FIG. 16 is a block diagram showing a registration error detection circuit. FIG. 17 is an explanatory diagram showing a registration error detection state using a registration error detection mark. FIG. 18 is a block diagram showing a main part of a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 3 of the present invention. FIG. 19 is an explanatory diagram showing meandering of the belt. FIG. 20 is an explanatory view showing the skew of the belt. FIG. 21 is an explanatory diagram showing image distortion accompanying belt skew. FIG. 22 is an explanatory diagram showing image distortion in the case where the belt is not skewed and in the case where the belt is not skewed.

Explanation of symbols

  25: intermediate transfer belt, 29: steering roll, 101: belt home sensor, 102: edge sensor, 103: steering control circuit, 120: image output circuit.

Claims (9)

In an image forming apparatus that forms an image by image forming means using an endless belt member stretched and conveyed by a plurality of rolls,
Skew detection means for detecting that the endless belt member is conveyed in a state inclined with respect to the conveying direction of the endless belt member;
When skew of the endless belt member is detected by the skew detection means, image distortion is corrected by the image forming means based on the skew amount of the endless belt member detected by the skew detection means. An image forming apparatus comprising: an image correcting unit that performs the correction. The skew detection means detects a skew state of the endless belt member based on control data of a steering roll that corrects movement of the endless belt member in a direction orthogonal to the conveyance direction. The image forming apparatus according to claim 1. The skew detection means detects the skew state of the endless belt member by detecting a mark for image position detection formed on the endless belt member by the mark detection means. The image forming apparatus according to claim 1. The skew detection means detects the skew state of the endless belt member by detecting the position of the edge portion along the conveying direction of the endless belt member at a plurality of locations. The image forming apparatus according to 1. The image forming apparatus according to claim 1, wherein the image correcting unit corrects image distortion by the image forming unit based on control data of the steering roll. 6. The image correction unit according to claim 1, wherein the image correction unit corrects image distortion by correcting an exposure position or exposure timing of an image on an image carrier of the image forming unit. The image forming apparatus described. 6. The image forming apparatus according to claim 1, wherein the image correcting unit corrects image distortion by correcting image data of an image to be formed by the image forming unit. 6. The image correction unit according to claim 1, wherein the image correction unit corrects image distortion by correcting an image position in the main scanning direction or an image forming timing in the sub-scanning direction by the image forming unit. An image forming apparatus according to claim 1. 6. The image correction unit according to claim 1, wherein the image correction unit corrects image distortion by correcting image data along the main scanning direction along the sub-scanning direction by the image forming unit. An image forming apparatus according to claim 1.

Images