JP4322077B2 - Belt moving device and image forming apparatus - Google Patents

Description

  The present invention relates to a belt moving device that moves the transfer belt in an image forming apparatus that primarily transfers an image formed on a photosensitive member to a transfer belt and then secondarily transfers the image from the transfer belt to a transfer member. By correcting the detection position error between the sensors when switching the detection signal of the marker provided on the transfer belt between the two detection sensors, the position fluctuation of the control system at the time of switching is suppressed, thereby achieving high accuracy The present invention relates to a belt moving device capable of position control.

2. Description of the Related Art Today, electrophotographic apparatuses are increasing in color, such as color copiers and color printers, according to market demands.
A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photoconductor, and a toner is attached by these developing devices to form a composite toner image on the photoconductor, and the toner image is transferred. A so-called one-drum type that records a color image on a sheet, and a plurality of photoconductors provided side by side are each provided with a developing device, and a single-color toner image is formed on each photoconductor. There is a so-called tandem type that sequentially transfers and records a composite color image on a sheet.
Comparing the 1-drum type and the tandem type, the former has only one photoconductor, so that there is an advantage that it can be relatively downsized and cost can be reduced. (4 times) Since image formation is repeated to form a full-color image, it is difficult to speed up image formation. The latter, on the contrary, has the disadvantage of increasing the size and cost, but it is easy to speed up image formation. There is an advantage that is.
Recently, tandem type has been attracting attention because the demand for full-color monochrome speed is desired.
As prior art, Japanese Patent Laid-Open No. 2002-123056 (synchronization detection means for detecting a light beam from an exposure optical system and outputting a synchronization detection signal, belt position detection means for detecting the position of an intermediate transfer belt, And a control means for controlling the position of the intermediate transfer belt based on the signal from the belt position detection means and the synchronization detection signal from the synchronization detection means), Japanese Patent Application Laid-Open No. 11-249526 It is an integral multiple of the circumference of each photoconductor, and the circumference of the driving roller of the transport belt is made the same as the circumference of the photoconductor, and a registration mark (position shift detection mark) provided on the transport belt is set in units of one pixel. By detecting the absolute position on the conveyor belt with a photo sensor, the registration mark (position deviation detection mark) for correcting the displacement of the conveyor belt is accurately and inexpensively detected. ), And the like.
JP 2002-123056 A JP-A-11-249526

However, in the above conventional image forming apparatus, the transfer belt is moved during the transfer to perform the transfer. However, the transfer belt movement control cannot be performed with high accuracy due to various factors. There was a point.
An object of the present invention is to suppress a position fluctuation of a control system at the time of switching by correcting a detection position error between the sensors when a signal of a marker provided on a transfer belt is detected by switching between two detection sensors. Thus, it is to provide a belt moving device capable of highly accurate position control.
Another object of the present invention is to suppress the position fluctuation of the control system at the time of switching by correcting the detection position error between the sensors when switching between the position sensor for translational motion and the position sensor for rotational motion. Accordingly, a belt moving device capable of highly accurate position control is provided.

To achieve the above object, an invention according to claim 1, a belt moving device which moves the transfer belt, a marker provided on the surface of the transfer belt, a first detection sensor for reading the marker And a second detection sensor for reading the marker, a sensor switching means for switching between the first detection sensor and the second detection sensor, and when the home position signal of the belt marker is ON and OFF, A surface position control means for reading a belt position signal by switching between the first detection sensor and the second detection sensor and comparing the belt surface target position with the belt position signal, and obtained by the surface position control means; comparison with to follow the transfer belt to the target position according to the result, the first detection sensor and the second detection sensor in the sensor switch means The marker position error Δx is measured by pre-driving the transfer belt by the belt moving device in advance, and in the main driving of the transfer belt by the belt moving device, the first detection sensor and the second detection sensor Δx is corrected at the time of switching.
The invention of claim 2, wherein, there is provided a belt moving device which moves the transfer belt, a marker provided on the surface of the transfer belt, a first detection sensor for reading the marker, the driving of the transfer belt And a third detection sensor for reading the rotation of the shaft or the motor shaft , and the position signal of the third detection sensor is converted into a surface position from the rotation angle of the drive shaft or motor shaft of the transfer belt. A sensor switching means for switching between the first detection sensor and the third detection sensor, and the first detection sensor and the third detection signal when the home position signal of the belt marker is turned on and off. read the belt position signal is switched to a detection sensor, and a surface position control means for comparing the belt surface target position belt position signal, to the surface position control means Ri said transfer belt according to the comparison results obtained with to follow the target position, the transfer of the marker position error Δx of the first detection sensor and the third sensor in said sensor switching means, the advance said belt moving device Measurement is performed by pre-driving the belt, and Δx is corrected at the time of switching between the first detection sensor and the third detection sensor in the main driving of the transfer belt by the belt moving device.

According to a third aspect of the present invention, in the belt moving device according to the first aspect, when both the first detection sensor and the second detection sensor are in the home position signal OFF, the increment value of the marker is compared. When the value is different from the prescribed value, the belt is caused to follow the target position by switching to a normal detection sensor.
According to a fourth aspect of the present invention, in the belt moving device according to the first aspect, when both the first detection sensor and the second detection sensor are OFF in the home position signal, the increment value of the marker is compared. When the value is different from the specified value, it is judged as abnormal.
The invention of claim 5, wherein, in the belt moving apparatus according to claim 1 or 3 or 4, wherein the position of the first sensor and the second sensor is arranged at a position facing the transfer belt It is arranged near the image carrier.
The invention of claim 6, wherein the belt moving device according to any one of claims 1 to 5, using an intermediate transfer belt or a paper conveying belt as the transfer belt, used in tandem-type image forming apparatus It is characterized by being able to.
The invention of claim 7, wherein the belt moving device according to any one of claims 1 to 4, using an intermediate transfer belt or a paper conveying belt as the transfer belt, the one-drum type image forming apparatus It is used.
The invention according to claim 8 is characterized by comprising the belt moving device according to any one of claims 1 to 7.

According to the first aspect of the invention, by correcting the detection position error between the sensors when the marker signal is detected by switching between the two detection sensors, the position fluctuation of the control system at the time of switching is suppressed, thereby the belt. High-precision position control is possible.
According to the second aspect of the present invention, the position fluctuation of the control system at the time of switching is suppressed by correcting the detection position error between the sensors when switching between the position sensor for translational motion and the position sensor for rotational motion. Thereby, highly accurate position control can be performed.
According to the invention of claim 3, even if dust or the like adheres to a part of the marker and a detection error occurs in one of the detection sensors, a normal marker is detected by detecting the normal marker with the other detection sensor. Is possible.
According to the invention of claim 4 , since it can be detected whether the detection sensor is abnormal, another detection sensor is abnormal, or the marker is abnormal, it is possible to replace which component.
According to the fifth aspect of the present invention, since the detection sensor is disposed in the vicinity of the transfer position, the position of the belt can be controlled at the transfer position, so that an image can be formed while suppressing color misregistration.
According to the inventions of claim 6 and claim 7 , when used in an intermediate transfer belt device or a paper transport device of an image forming apparatus, an image with suppressed color misregistration because of a belt moving device capable of positioning and tracking control with high accuracy. Can be formed.
According to the invention of claim 8, the belt moving device having the features of claims 1 to 7 enables image formation with high image quality.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, before describing the gist of the present invention, an overall schematic configuration of an image forming apparatus such as a color copying machine or a color printer to which the present invention is applied will be described.
2. Description of the Related Art Today, electrophotographic apparatuses are increasing in color, such as color copiers and color printers, according to market demands.
A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photoconductor, and a toner is attached by these developing devices to form a composite toner image on the photoconductor, and the toner image is transferred. A so-called one-drum type that records a color image on a sheet, and a plurality of photoconductors provided side by side are each provided with a developing device, and a single-color toner image is formed on each photoconductor. There is a so-called tandem type that sequentially transfers and records a composite color image on a sheet.
Comparing the 1-drum type and the tandem type, the former has only one photoconductor, so that there is an advantage that it can be relatively downsized and cost can be reduced. (4 times) Since image formation is repeated to form a full-color image, it is difficult to speed up image formation. The latter, on the contrary, has the disadvantage of increasing the size and cost, but it is easy to speed up image formation. There is an advantage that is.

First, the one-drum type image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of an image forming apparatus such as a one-drum type color copying machine or a color printer to which the present invention is applied.
In addition to the image forming apparatus shown in FIG. 1, the color copying machine is composed of a color image reading unit (not shown) (hereinafter referred to as “color scanner”), a paper feeding unit, and a control unit for driving and controlling them. The color scanner reads color image information of a document for each color separation light of, for example, red, green, and blue (hereinafter referred to as “R”, “G”, and “B”) and converts them into electrical image signals. To do. Then, based on the intensity levels of the R, G, and B color separation image signals obtained by this color scanner, color conversion processing is performed by an image processing unit (not shown), and black, cyan, magenta, yellow (hereinafter, respectively) Image data “Bk”, “C”, “M”, and “Y”) is obtained.

1 includes a photosensitive drum 200 as an image carrier, a charging charger 201 as a charging unit, a photosensitive member cleaning device 210 including a cleaning blade and a fur brush, a writing optical unit (not shown) as an exposure unit, and development. A revolver developing unit 400, an intermediate transfer unit 500, a secondary transfer unit 600, and a fixing unit 700 (not shown) using a fixing roller pair 701 (not shown) are used.
The photosensitive drum 200 rotates in a counterclockwise direction as indicated by an arrow in the drawing, and around the charging charger 201, the photosensitive member cleaning device 210, the selected developing machine of the revolver developing unit 400, and the intermediate transfer unit 500. An intermediate transfer belt 501 as an intermediate transfer member is disposed. Further, the writing optical unit converts the color image data from the color scanner into an optical signal, and applies the laser beam L corresponding to the image of the document to the surface of the photosensitive drum 200 uniformly charged by the charging charger 201. Irradiation and optical writing are performed to form an electrostatic latent image on the surface of the photosensitive drum 200. This writing optical unit can be constituted by, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.
The revolver developing unit 400 includes a Bk developing machine 401 that uses Bk toner, a C developing machine 402 that uses C toner, an M developing machine 403 that uses M toner, a Y developing machine 404 that uses Y toner, and a half of the entire unit. The developing revolver driving unit is rotated clockwise.
Each of the developing machines 401 to 404 installed in the revolver developing unit 400 develops as a developer carrying member that rotates by bringing the ears of the developer into contact with the surface of the photosensitive drum 200 in order to develop the electrostatic latent image. The sleeve includes a developer paddle that rotates to draw up and stir the developer, and a developing sleeve driving unit that rotates the developing sleeve clockwise as indicated by an arrow.

In this embodiment, the toner in each of the developing machines 401 to 404 is negatively charged by stirring with the ferrite carrier, and each developing sleeve is negatively charged with a negative DC voltage by a developing bias power source as a developing bias applying means (not shown). A developing bias voltage in which an alternating voltage VAc (alternating current component) is superimposed on Vdc (direct current component) is applied, and each developing sleeve is biased to a predetermined voltage with respect to the metal base layer of the photosensitive drum 200. In the standby state of the color copying machine main body, the revolver developing unit 400 is stopped at the home position where the Bk developing machine 401 is located at the developing position, and when the copy start key is pressed, the document starts reading image data, Based on the color image data, light writing by the laser beam L, that is, formation of an electrostatic latent image starts (hereinafter, the electrostatic latent image by Bk image data is referred to as “Bk electrostatic latent image”. The same).
In order to enable development from the leading edge of the Bk electrostatic latent image, before the leading edge of the electrostatic latent image reaches the Bk development position, rotation of the Bk developing sleeve is started to convert the Bk electrostatic latent image into Bk toner. Develop with. Thereafter, the developing operation of the Bk electrostatic latent image is continued. When the rear end portion of the Bk electrostatic latent image passes the Bk developing position, the revolver is promptly moved until the next color developing device comes to the developing position. The developing unit 400 rotates. This is completed at least before the leading edge of the electrostatic latent image based on the next image data reaches the developing position.
The intermediate transfer unit 500 includes an intermediate transfer belt 501 that is an intermediate transfer member stretched around a plurality of rollers to be described later. Around the intermediate transfer belt 501 are a secondary transfer belt 601 that is a transfer material carrier of the secondary transfer unit 600, a secondary transfer bias roller 605 that is a secondary transfer charge applying unit, and an intermediate transfer member cleaning unit. A belt cleaning blade 504, a lubricant application brush 505 that is a lubricant application means, and the like are arranged to face each other.
The intermediate transfer belt 501 is stretched around a primary transfer bias roller 507, a belt driving roller 508, a belt tension roller 509, a secondary transfer counter roller 510, a cleaning counter roller 511, and a ground roller 512 serving as a primary transfer charge applying unit. It is built. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded.

The primary transfer bias roller 507 is applied with a transfer bias controlled to a predetermined current or voltage according to the number of superimposed toner images by a primary transfer power source 801 controlled at a constant current or voltage. ing. The intermediate transfer belt 501 is driven in the direction of the arrow by a belt driving roller 508 that is driven to rotate in the direction of the arrow by a drive motor (not shown).
The intermediate transfer belt 501 is a semiconductor or an insulator and has a single layer or a multilayer structure.
In a transfer portion (hereinafter referred to as “primary transfer portion”) that transfers the toner image on the photosensitive drum 200 to the intermediate transfer belt 501, the intermediate transfer belt 501 is moved to the photosensitive drum 200 by the primary transfer bias roller 507 and the earth roller 512. A nip portion having a predetermined width is formed between the photosensitive drum 200 and the intermediate transfer belt 501 by being stretched so as to be pressed to the side.
The lubricant application brush 505 polishes zinc stearate 506 as a lubricant formed in a plate shape and applies the polished fine particles to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be adjacent to the intermediate transfer belt 501 and is controlled to contact the intermediate transfer belt 501 at a predetermined timing.
The secondary transfer unit 600 includes a secondary transfer belt 601 stretched between three support rollers 602, 603, and 604, and the stretched portion between the support rollers 602 and 603 of the intermediate transfer belt 501 is a secondary transfer. It can be pressed against the opposing roller 510. One of the three support rollers 602, 603, and 604 is a drive roller that is rotationally driven by a drive unit (not shown), and the secondary transfer belt 601 is driven in the direction indicated by the arrow in the drawing.

The secondary transfer bias roller 605 is a secondary transfer unit, and is disposed so as to sandwich the intermediate transfer belt 501 and the secondary transfer belt 601 between the secondary transfer counter roller 510 and is subjected to constant current control. A transfer bias having a predetermined current is applied by the next transfer power source 802. Further, the support roller 602 and the secondary transfer bias roller 605 are arranged so that the secondary transfer belt 601 and the secondary transfer bias roller 605 can take a position where they are pressed against and separate from the secondary transfer counter roller 510. There is provided a separation mechanism (not shown) for driving in the direction of the arrow. The secondary transfer belt 601 and the support roller 602 at the separated positions are indicated by a two-dot chain line in FIG.
Reference numeral 650 denotes a registration roller pair, which is a transfer sheet that is a transfer material at a predetermined timing between the intermediate transfer belt 501 and the secondary transfer belt 601 sandwiched between the secondary transfer bias roller 605 and the secondary transfer counter roller 510. P is sent.
A portion of the secondary transfer belt 601 that is stretched around a support roller 603 on the fixing roller pair 701 (not shown) side is a transfer sheet neutralization charger 606 that is a transfer material neutralization unit, and a transfer material carrier neutralization unit. The belt neutralizing charger 607 faces the belt. Further, a cleaning blade 608 serving as a transfer material carrier cleaning means is in contact with a portion of the secondary transfer belt 601 that is stretched around a lower support roller 604 in the drawing.
The transfer paper neutralization charger 606 neutralizes the charge held on the transfer paper so that the transfer paper can be satisfactorily separated from the secondary transfer belt 601 with the strength of the transfer paper itself. The belt neutralization charger 607 neutralizes the charge remaining on the secondary transfer belt 601. Further, the cleaning blade 608 is for removing the adhering matter adhering to the surface of the secondary transfer belt 601 for cleaning.
In the color copying machine configured as described above, when the image forming cycle is started, the photosensitive drum 200 is rotated in a counterclockwise direction indicated by an arrow by a driving motor (not shown), and the intermediate transfer belt 501 is driven by a belt driving roller 508. It is rotated clockwise as indicated by the arrow. As the intermediate transfer belt 501 rotates, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed by the transfer bias by the voltage applied to the primary transfer bias roller 507. Finally, a toner image is formed on the intermediate transfer belt 501 in the order of Bk, C, M, and Y.

For example, Bk toner image formation is performed as follows. The charging charger 201 uniformly charges the surface of the photosensitive drum 200 to a predetermined potential with a negative charge by corona discharge. Then, raster exposure with laser light is performed based on the Bk color image signal by a writing optical unit (not shown). When this raster image is exposed, the charge proportional to the exposure light amount disappears in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, and a Bk electrostatic latent image is formed.
When the negatively charged Bk toner on the Bk developing roller of the Bk developing machine 401 comes into contact with this Bk electrostatic latent image, the toner does not adhere to the remaining portion of the photosensitive drum 200, and the charge is charged. Toner is adsorbed on the portion without exposure, that is, the exposed portion, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photosensitive drum 200 is transferred to the surface of the intermediate transfer belt 501 that is driven at a constant speed in contact with the photosensitive drum 200. Hereinafter, the transfer of the toner image from the photosensitive drum 200 to the intermediate transfer belt 501 is referred to as “belt transfer”.
Some untransferred residual toner remaining on the surface of the photosensitive drum 200 after the belt transfer is cleaned by the photosensitive member cleaning device 210 in preparation for the reuse of the photosensitive drum 200.
On the photosensitive drum 200 side, the process proceeds to the C image forming process after the Bk image forming process, and reading of the C image data by the color scanner starts at a predetermined timing. A C electrostatic latent image is formed on the surface.
Then, after the rear end portion of the previous Bk electrostatic latent image passes and before the front end portion of the C electrostatic latent image arrives, the revolver developing unit 400 is rotated, and the C developing device 402 is developed. The C electrostatic latent image is developed with C toner.
Thereafter, the development of the C electrostatic latent image area is continued. When the rear end of the C electrostatic latent image passes, the revolver developing unit is rotated in the same manner as in the case of the Bk developing machine 401, and the next The M developing machine 403 is moved to the developing position. This is also completed before the leading edge of the next M electrostatic latent image reaches the developing position.
Note that the M and Y image forming steps are the same as the Bk and C steps described above because the operations of reading color image data, forming an electrostatic latent image, and developing are the same as those described above.
On the intermediate transfer belt 501, Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 100 are sequentially aligned and transferred on the same surface. As a result, a toner image in which a maximum of four colors are superimposed is formed on the intermediate transfer belt 501.

At the time when the image forming operation is started, the transfer paper P is fed from a paper feed unit such as a transfer paper cassette or a manual feed tray (not shown) and is waiting at the nip of the registration roller pair 650. When the leading edge of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the secondary transfer counter roller 510 and the secondary transfer bias roller, the leading edge of the transfer paper P is just the leading edge of the toner image. The registration roller pair 650 is driven so as to match the above, and registration of the transfer paper P and the toner image is performed.
Then, the transfer paper P is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the four-color superimposed toner image on the intermediate transfer belt 501 is collectively transferred onto the transfer paper by a transfer bias by a voltage applied to the secondary transfer bias roller 605 by the secondary transfer power source 802.
The transfer paper P is neutralized and separated from the secondary transfer belt 601 when it passes through a portion facing the transfer paper neutralization charger 606 disposed downstream of the secondary transfer portion in the moving direction of the secondary transfer belt 601. To the fixing roller pair 701 (not shown).
The toner image is melted and fixed at the nip portion of the fixing roller pair 701 (not shown), sent out of the apparatus main body by a pair of discharge rollers (not shown), and stacked on the copy tray (not shown) so as to obtain a full color copy.

On the other hand, the surface of the photosensitive drum 200 after the belt transfer is cleaned by the photosensitive member cleaning device 210 and is uniformly discharged by a discharging lamp (not shown).
Further, the toner remaining on the surface of the intermediate transfer belt 501 after the toner image is transferred to the transfer paper P is cleaned by a belt cleaning blade 504 pressed against the intermediate transfer belt 501 by a not-shown separation / contact mechanism.
Here, at the time of repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are performed at a predetermined timing following the first color (Y) image formation process of the first sheet and the first color of the second sheet. The process proceeds to the image forming process (Bk). Further, the intermediate transfer belt 501 has a second Bk toner in the area cleaned by the belt cleaning blade 504 on the surface following the batch transfer process of the first four-color superimposed toner image to the transfer paper. The image is transferred to the belt. After that, the operation is the same as the first sheet.
The above is a copy mode for obtaining a four-color full-color copy. In the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times.
In the single color copy mode, only the predetermined color developing machine of the revolver developing unit 400 is in the developing operation state until the predetermined number of sheets is completed, and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501. The copy operation is performed at the same position.

Next, the tandem type image forming apparatus will be described.
FIG. 2 is a schematic configuration diagram of an image forming apparatus such as a tandem type color copying machine or a color printer to which the present invention is applied.
As shown in FIG. 3, the tandem type electrophotographic apparatus includes a direct transfer system in which an image on each photoconductor 1 is sequentially transferred onto a sheet s conveyed by a sheet conveying belt 3 by a transfer apparatus 2; As shown in FIG. 4, the images on the respective photoconductors 1 are once sequentially transferred to the intermediate transfer member 4 by the primary transfer device 2, and then the images on the intermediate transfer member 4 are transferred to the sheet s by the secondary transfer device 5. There are indirect transfer systems that perform batch transfer. The transfer device 5 is a transfer conveyance belt, but there are also roller shapes and methods.
Comparing the direct transfer type and the indirect transfer type, the former arranges the sheet feeding device 6 on the upstream side of the tandem image forming apparatus T on which the photoconductors 1 are arranged, and the fixing device 7 on the downstream side. There is a drawback in that the size increases in the sheet conveying direction.
On the other hand, the latter can set the secondary transfer position relatively freely. The sheet feeding device 6 and the fixing device 7 can be arranged so as to overlap with the tandem image forming apparatus T, and there is an advantage that downsizing is possible.
In the former, in order not to increase the size in the sheet conveyance direction, the fixing device 7 is disposed close to the tandem type image forming apparatus T. For this reason, the fixing device 7 cannot be disposed with a sufficient margin that allows the sheet s to bend, and an impact when the leading edge of the sheet s enters the fixing device 7 (particularly with a thick sheet) or fixing. There is a drawback that the fixing device 7 tends to affect image formation on the upstream side due to the difference in speed between the sheet conveyance speed when passing through the apparatus 7 and the sheet conveyance speed by the transfer conveyance belt.
On the other hand, in the latter case, the fixing device 7 can be disposed with a sufficient margin that the sheet s can be bent, so that the fixing device 7 can hardly affect the image formation.
In view of the above, recently, an indirect transfer type of tandem type electrophotographic apparatus has attracted attention.
In this type of color electrophotographic apparatus, as shown in FIG. 4, the transfer residual toner remaining on the photoreceptor 1 after the primary transfer is removed by the photoreceptor cleaning device 8 to clean the surface of the photoreceptor 1. In preparation for another image formation. Further, the transfer residual toner remaining on the intermediate transfer body 4 after the secondary transfer is removed by the intermediate transfer body cleaning device 9 to clean the surface of the intermediate transfer body 4 to prepare for image formation again.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 shows an embodiment of the present invention, which is a tandem indirect transfer type electrophotographic apparatus.
In the figure, reference numeral 100 is a copying apparatus main body, 200 is a paper feed table on which the copying apparatus is placed, 300 is a scanner mounted on the copying apparatus main body 100, and 400 is an automatic document feeder (ADF) mounted thereon.
The copying machine main body 100 is provided with an endless belt-shaped intermediate transfer member 10 at the center. As shown in FIG. 5, the intermediate transfer member 10 is formed by forming a base layer 11 made of a base material 11 made of a material that is not easily stretched, such as canvas, on a less stretched fluororesin or a large stretch rubber material, and an elastic layer thereon. 12 is provided. The elastic layer 12 is made of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer 12 is coated with, for example, a coating layer 13 having good smoothness by coating a fluorine resin.
As shown in FIG. 2, in the illustrated example, it is wound around three support rollers 14, 15, and 16 so that it can be rotated and conveyed clockwise in the figure.
In this illustrated example, an intermediate transfer body cleaning device 17 for removing residual toner remaining on the intermediate transfer body 10 after image transfer is provided on the left of the second support roller 15 among the three.
Further, among the three images, four images of yellow, cyan, magenta, and black are arranged on the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15 along the conveyance direction. The tandem image forming apparatus 20 is configured by arranging the forming units 18 side by side.
An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.
On the other hand, a secondary transfer device 22 is provided on the side opposite to the tandem image forming apparatus 20 with the intermediate transfer body 10 interposed therebetween. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet.
A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.
The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the image-transferred sheet to the fixing device 25. Of course, a transfer roller or a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveying function together.
In the illustrated example, under such a secondary transfer device 22 and a fixing device 25, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet in parallel with the tandem image forming device 20 described above. Is provided.

Now, when making a copy using this color electrophotographic apparatus, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it.
When a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. At that time, the scanner 300 is immediately driven to travel the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.
When a start switch (not shown) is pressed, one of the support rollers 14, 15, and 16 is driven to rotate by a drive motor (not shown), and the other two support rollers are driven to rotate to convey the intermediate transfer member 10. To do. At the same time, the individual image forming means 18 rotates the photoconductor 40 to form black, yellow, magenta, and cyan monochrome images on each photoconductor 40. Then, along with the conveyance of the intermediate transfer member 10, the single color images are sequentially transferred to form a composite color image on the intermediate transfer member 10.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, and the separation roller 45. Then, the sheets are separated one by one into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped.
Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer body 10, the sheet is fed between the intermediate transfer body 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is recorded on the sheet.
The sheet after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25, and heat and pressure are applied to the fixing device 25 to fix the transferred image. The paper is discharged at 56 and stacked on the paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.
On the other hand, the intermediate transfer body 10 after the image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer body 10 after the image transfer, so that the tandem image forming apparatus 20 can prepare for another image formation.
Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.
In the tandem image forming apparatus 20 described above, the individual image forming means 18 includes, for example, a charging device 60 and a developing device 61 around a drum-shaped photoconductor 40 as shown in FIG. 3 for example. A primary transfer device 62, a photoconductor cleaning device 63, a charge removal device 64, and the like are provided.

Next, the belt moving device which is the gist of the present invention will be described.
FIG. 7 is a configuration diagram of a belt moving device for moving the intermediate transfer belt in the image forming apparatus (FIG. 1: 1 drum type) embodying the present invention. The present invention can be applied not only to the one-drum type image forming apparatus but also to a tandem type image forming apparatus as shown in FIG.
As shown in FIG. 7, the intermediate transfer belt 501 to be driven is a motor 523 that is a drive source via a transmission system 528 such as a drive shaft 508, a drive shaft timing pulley 520, a timing belt 521, and a motor shaft timing pulley 522. Connected to and driven. The intermediate transfer belt device 500 includes an encoder scale (marker) 524 outside the image area on the surface of the intermediate transfer belt 501. In addition, an optical head 525 (first detection sensor 525A and second detection sensor 525B) serving as marker detection means for reading the signal of the encoder scale (marker) 524 is sandwiched between the intermediate transfer belt 501 and the optical head 525 (first detection sensor 525A). The detection sensor 525A and the second detection sensor 525B) are mounted on opposite surfaces. Further, a drive shaft encoder 526 (third detection sensor) is attached to the drive shaft 508.
Although not shown in FIG. 7, the photoconductor 200 is connected to and driven by a motor as a drive source via a transmission system such as a drive shaft, a drive shaft timing pulley, a timing belt, and a motor shaft timing pulley. A sensor by a rotary encoder is attached to the photosensitive member drive shaft. The intermediate transfer belt 501 and the photosensitive member 200 rotate in contact with each other, and the intermediate transfer belt 501 and the second transfer bias roller 605 rotate in contact with each other via the second transfer belt 601 and paper. Further, a charging roller 511 and a cleaning blade 504 are provided adjacent to the intermediate transfer belt 501.
In the above description, the intermediate transfer belt 501 is used as a drive target. Although the transmission system 528 has been described with respect to the timing belt 521, a transmission mechanism using gears or a direct mechanism in which a motor is directly connected to a driving target may be used. In the above description, the mounting position of the encoder 526 is the drive shaft 508, but the motor shaft may be directly connected.

Next, the internal control structure of the belt moving device will be described with reference to FIG.
FIG. 8 is a block diagram of a control internal configuration of the belt moving device.
First, in the control internal configuration of the belt moving device, a microcomputer 700 that is responsible for overall control is provided. In the microcomputer 700, a microprocessor (CPU) 701, a read only memory (ROM) 702, and a random access memory (RAM) 703 are connected via a bus 706.
The sensor output of the encoder scale (marker) 524 via the optical head 525 (the first detection sensor 525A and the second detection sensor 525B) is sent to the correction information creation unit 704, the state detection interface 705, and the bus. The information is input to the microcomputer 700 via the 706. The state detection interface 705 includes a marker output count (coarse counter) and a signal interpolation clock count (fine counter) from the correction information creation unit 704, and a drive axis encoder 526 (third detection sensor). Is processed and converted into a digital numerical value, and has a function of counting the number of pulses. At this time, the state detection interface 705 has a function of associating (correlating) the moving position of the intermediate transfer belt 501 with the origin (home position) information of the correction information creating unit 704. In some cases.
Further, the motor 523 is connected to the microcomputer 700 via the bus 706, a driving interface 707, and a driver 708. The driving interface 707 converts the digital signal of the calculation result in the microcomputer 700 into an analog signal, gives it to the motor driving driver 708 as a driving device, and controls the current and voltage applied to the motor 523. As a result, the intermediate transfer belt 501 is driven so as to follow a predetermined target position. The position of the intermediate transfer belt 501 at this time is detected by the state detection interface 705 via the correction information creation unit 704 as a sensor output of the encoder scale (marker) 524 and is taken into the microcomputer 700. When the marker interval is wide, the correction information creation unit 704 may interpolate the position within the marker interval with a clock.
Needless to say, the belt moving device having the above configuration can also be applied to the tandem image forming apparatus shown in FIG.

Next, a position control method for the belt moving device of this embodiment will be described.
The position control method of the belt moving device according to the present embodiment is executed by the arithmetic processing function in the microcomputer 700. Further, a DSP (digital signal processor) having a high numerical calculation processing capability may be used instead of the microcomputer.
FIG. 9 is an explanatory diagram of a correction information generation method by the correction information generation unit 704 that generates correction information for correcting the position in the moving direction of the belt 501 based on the detection result of the optical head 525 as the marker detection unit. .
First, as shown in FIG. 10, the encoder scale (marker) 524 has a cut at one place for being attached to the belt 501. An origin (home position) signal mark is pasted so as to cover the cut. FIG. 10 is a diagram showing a part of the encoder scale (marker) 524 and the mark of the origin signal.
In FIG. 9, the marker 524 is read by the marker detection means 525. The break position signal of the marker 524 is detected when there is a mark of the origin signal.
Here, when the belt linear velocity is 200 mm / s, the marker interval is 169 μm, and the signal interpolation clock is 576 kHz,
200e-3 * 1 / 576e3 = 3.4722e-007
Thus, the interpolation clock 1 count is 0.347 μm.
Here, when there is no break position signal, the coarse counter (marker output count) counts every increment value of 169 μm. The fine counter (count of the signal interpolation clock) is reset at the rising edge of the coarse counter, and the interpolation clock 1 count is counted every increment value of 0.374 μm. Therefore, the position of the belt 501 can be obtained by adding both count values.

FIG. 11 is a block diagram when the position of the drive target (transfer belt 501) is controlled in the first embodiment. (Claim 1)
As shown in FIG. 11, the belt surface target position is compared with the measured belt position signal, the deviation between the two is calculated by the surface position control means, and a current is given to the motor 523 according to the calculation result, so that the drive target Is driven following the target position.
Here, assuming that the belt surface position xA detected by the first detection sensor 525A and the belt surface position xB detected by the second detection sensor 525B, xB is delayed from xA by the marker position error Δx.
xB = xA−Δx
become.
Then, in the sensor switching means, for example, when the home position signal comes to the part measured by the first detection sensor 525A, the sensor switching means switches to the second detection sensor 525B. At that time, since xB is delayed from xA by Δx, xB + Δx is used as a feedback position signal. When the home position signal is output from a portion measured by the first detection sensor 525A, the signal of the first detection sensor 525A is used as a feedback position signal (see flowcharts of FIGS. 16 and 17 described later). That is, the marker position error Δx of the first detection sensor and the second detection sensor in the sensor switching means is measured in advance by pre-driving the transfer belt by the belt moving device, and the transfer by the belt moving device. In the main driving of the belt, Δx is corrected when switching between the first detection sensor and the second detection sensor.
Here, the surface position control means and the sensor switching means are included in the correction information creation unit 704.

FIG. 12 is a block diagram when the position of the drive target (transfer belt 501) is controlled in the second embodiment. (Claim 2)
As shown in FIG. 12, the belt surface target position is compared with the measured belt surface position signal, the deviation between the two is calculated by the surface position control means, and a current is given to the motor 523 according to the calculation result to drive the belt surface target position. The object is driven following the target position.
Here, it is assumed that the belt surface position xA detected by the first detection sensor 525A, the belt drive shaft angle θd detected by the third detection sensor 526, the angle error Δθ, and the drive shaft radius r.
When θd detected by the third detection sensor 526 is converted into the belt surface position xB, xB = r * θd
Here, if xB is delayed from xA by the marker position error Δx,
xB = xA−Δx
become.
Then, the sensor switching means switches to the third detection sensor 526 when the home position signal comes to a portion measured by the first detection sensor 525A. At that time, since xB is delayed from xA by Δx, xB + Δx is used as a feedback position signal. When the home position signal is output from the portion measured by the first detection sensor 525A, the signal of the first detection sensor 525A is used as the feedback position signal. That is, the marker position error Δx of the first detection sensor and the third detection sensor in the sensor switching means is measured in advance by pre-driving the transfer belt by the belt moving device, and the transfer by the belt moving device. In the actual driving of the belt, Δx is corrected when switching between the first detection sensor and the third detection sensor.

FIG. 13 is an explanatory diagram when the detection sensor 525 in the third embodiment is normal and abnormal. (Claim 3)
As shown in FIG. 13, when the detection sensor 525 is normal and the belt moving device is moving in a steady state, the first detection sensor 525A is always advanced or delayed by Δx from the second detection sensor 525B. Here, if dust adheres to the marker 524, when the position of the dust reaches the first detection sensor 525A, an abnormal state occurs and detection becomes impossible. Therefore, if the second detection sensor 525B is not at the home position (when the home position signal is off), the value of the second detection sensor 525B is used as a feedback signal. Here, it is natural to correct Δx. That is, when the home position signal is OFF for both the first detection sensor and the second detection sensor, the increment value of the marker is compared. If the value is different from the specified value, the belt is switched to a normal detection sensor. Is made to follow the target position.
FIG. 14 is an explanatory diagram when the detection sensor 525 according to the fourth embodiment is normal and when it is abnormal. (Claim 4)
As shown in FIG. 14, when the detection sensor is normal and the belt moving device is moving in a steady state, the first detection sensor 525A is always advanced or delayed by Δx from the third detection sensor 526. The third detection sensor 526 converts the rotation angle of the rotary encoder into a surface position and uses it as a feedback signal. Here, if dust adheres to the marker, when the position of the dust comes to the first detection sensor 525A, the state becomes abnormal and cannot be detected. Therefore, both the first detection sensor 525A and the third detection sensor 526 use the value of the third detection sensor 526 as a feedback signal when the home position signal is OFF. Here, it is natural to correct Δx. That is, here, the position signal of the third detection sensor that reads the rotation of the drive shaft of the transfer belt is converted from the rotation angle of the drive shaft of the transfer belt to the surface position, and the first detection sensor and the third detection sensor Both of the detection sensors compare the increment value of the marker when the home position signal is OFF, and when the value is different from the specified value, the detection sensor is switched to a normal detection sensor so that the belt follows the target position.

FIG. 15 is an explanatory diagram of operations in the fifth embodiment. (Claim 5)
As shown in FIG. 15, here, the difference between the target position and the first detection sensor 525A and the second detection sensor 525B, that is, the position deviation is checked when the home position signal is OFF. The target position locus is a profile that drives the belt at a linear velocity of 200 mm / s, and the rising is a smooth locus. The steady state is reached after 1 sec.
In the detection sensor 525, when dust adheres to the marker 524 and cannot be read for one slit, the fine counter continues to count as shown in FIG. 9, but when the next pulse comes, the value increases by 169 μm.
For this reason, the position deviation is 169 μm smaller. In FIG. 15, the marker 524 is in a state where it cannot read one slit after 1.2 sec. Here, if the specified value is set from −50 μm to +50 μm, it can be determined that there is an abnormality from the position deviation. If an abnormality occurs at a position interval where the positional deviation between the first detection sensor 525A and the second detection sensor 525B is determined, it can be determined that the marker 524 is abnormal. If the first detection sensor 525A or the second detection sensor 525B is always deviated from the specified value in a steady state, it is known that the detection sensor is abnormal.

16 and 17, the marker position error Δx of the first detection sensor 525A and the second detection sensor 525B is measured in advance by driving the belt moving device. In this drive, Δx is corrected when the detection sensor is switched. It is an operation | movement flowchart.
That is, in step 700 of FIG. 16, when the power of the belt moving device is turned on, pre-driving is performed (step 701), and feedback control is performed by the first detection sensor (step 703). Next, when the first detection sensor is turned off from the home position signal (Yes in Step 704), the counters A and B are reset (Step 705), and the feedback control by the first detection sensor is performed. Performed (step 706).
Next, when the belt reaches a steady speed (Yes in Step 707), marker position error measurement of the first detection sensor and the second detection sensor is performed (Step 708), and the first detection sensor is at the home position. The belt is stopped when the signal turns from on to off (step 709).
Next, the main drive is started (step 710 in FIG. 17), feedback control is performed by the first detection sensor (step 711), and the first detection sensor is turned on from the OFF of the home position signal (step 711). In step 712, feedback control is performed by the second detection sensor (step 713). When the first detection sensor is turned off from the home position signal (Yes in Step 714), the process returns to Step 711.
In the embodiment of the present invention, as shown in FIG. 18, the first detection sensor A and the second detection sensor B are arranged on the back surface of the belt facing the drum. For this reason, when the detector is arranged on the tension roller or secondary transfer roller side, belt speed fluctuations occur due to position detection errors caused by belt P-direction fluctuations and position detection errors caused by expansion and contraction in the belt movement direction. In the embodiment of the present invention, the belt speed fluctuation does not occur due to the position detection error.

1 is a schematic configuration diagram of an image forming apparatus such as a one-drum type color copying machine or a color printer to which the present invention is applied. 1 is a schematic configuration diagram of an image forming apparatus such as a tandem type color copying machine or a color printer to which the present invention is applied. FIG. 3 is an explanatory diagram of one transfer method in the image forming apparatus shown in FIG. 2. FIG. 3 is an explanatory diagram of one transfer method in the image forming apparatus shown in FIG. 2. FIG. 3 is a structural diagram of an intermediate transfer member in the image forming apparatus shown in FIG. 2. FIG. 3 is a configuration diagram around a photoconductor in the image forming apparatus illustrated in FIG. 2. It is a block diagram of the belt moving apparatus which implemented this invention. It is a block diagram of the control internal structure of the belt moving apparatus shown in FIG. It is explanatory drawing of the correction information creation method by the correction information creation part 704 which produces the correction information for correct | amending the position of the moving direction of the belt 501 based on the detection result of the optical head 525 as a marker detection means. It is a figure which shows one part of the encoder scale (marker) 524 and the mark of an origin signal. FIG. 6 is a block diagram when the position of a drive target (transfer belt 501) is controlled in the first embodiment. FIG. 10 is a block diagram when the position of a drive target (transfer belt 501) is controlled in the second embodiment. It is explanatory drawing when the detection sensor 525 in 3rd Embodiment is normal, and when it is abnormal. It is explanatory drawing when the detection sensor 525 in 4th Embodiment is normal, and when it is abnormal. It is operation | movement explanatory drawing in 5th Embodiment. The marker position error Δx of the first detection sensor 525A and the second detection sensor 525B is measured by driving the belt moving device in advance, and this driving is an operation flowchart for correcting Δx when the detection sensor is switched. The marker position error Δx of the first detection sensor 525A and the second detection sensor 525B is measured by driving the belt moving device in advance, and this driving is an operation flowchart for correcting Δx when the detection sensor is switched. It is explanatory drawing which shows an example of the belt moving apparatus by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Transfer device, 3 ... Sheet conveyance belt, 4 ... Intermediate transfer body, 5 ... Transfer device, 6 ... Paper feed device, 7 ... Fixing device, 8 ... Photoconductor cleaning device, 9 ... Intermediate transfer body Cleaning device, 10 ... intermediate transfer member, 11 ... base layer, 12 ... elastic layer, 13 ... coat layer, 14 ... first support roller, 15 ... second support roller, 16 ... third support roller, 17 ... Intermediate transfer member cleaning device, 18 ... image forming means, 20 ... tandem image forming device, 21 ... exposure device, 22 ... next transfer device, 23 ... roller, 24 ... next transfer belt, 25 ... fixing device, 26 ... fixing belt, DESCRIPTION OF SYMBOLS 27 ... Pressure roller, 28 ... Sheet reversing device, 30 ... Document stand, 32 ... Contact glass, 33 ... 1st traveling body, 34 ... 2nd traveling body, 35 ... Imaging lens, 36 ... Sensor, 40 ... Photoconductor 42 ... feed roller, 4 ... Paper bank, 44 ... Paper cassette, 45 ... Separation roller, 46 ... Paper feed path, 48 ... Paper feed path, 49 ... Registration roller, 50 ... Feed roller, 51 ... Tray, 52 ... Separation roller, 53 ... Feed Paper path 55... Switching claw 56. Ejection roller 57. Ejection tray 60. Charging device 61. Development device 62 62 Next transfer device 63. Photoconductor cleaning device 64. Body drum, 201 ... charger charger, 210 ... photoconductor cleaning device, 300 ... scanner, 400 ... revolver developing unit, 400 ... automatic document feeder, 401 ... Bk developing machine, 401-404 ... developing machine, 402 ... C developing machine , 403 ... M developing machine, 404 ... Y developing machine, 500 ... Intermediate transfer belt device, 501 ... Intermediate transfer belt, 504 ... Belt cleaning blade, 505 ... Moisture Agent coating brush, 506 ... zinc stearate, 507 ... next transfer bias roller, 508 ... belt drive roller, 509 ... belt tension roller, 510 ... next transfer counter roller, 511 ... charge roller, 512 ... earth roller, 520 ... drive shaft Timing pulley, 521 ... Timing belt, 522 ... Motor shaft timing pulley, 523 ... Motor, 524 ... Marker, 525 ... Marker detection means, 525 ... Optical head, 525A ... First detection sensor, 525B ... Second detection sensor, 526: Encoder, 526: Third detection sensor, 526: Drive shaft encoder, 528: Transmission system, 600: Next transfer unit, 601: Next transfer belt, 601: Second transfer belt, 602: Support roller, 603 ... Support Roller, 604 ... support roller, 605 ... second transfer bias roller , 606... Transfer paper neutralization charger, 607. Belt neutralization charger, 608. Cleaning blade, 700. Microcomputer, 701. Fixing roller pair, 704. Correction information creation unit, 705. ... Driver, 708 ... Driver for motor drive

Claims (8)

A belt moving device for moving a transfer belt,
A marker provided on the surface of the transfer belt, a first detection sensor that reads the marker, a second detection sensor that reads the marker, and a sensor that switches between the first detection sensor and the second detection sensor The belt position signal is read by switching between the first detection sensor and the second detection sensor between the switching means and the home position signal ON and OFF of the belt marker, and the belt surface target position and the belt position signal And a surface position control means for comparing
In accordance with the comparison result obtained by the surface position control means, the transfer belt follows the target position,
The marker position error Δx of the first detection sensor and the second detection sensor in the sensor switching means is measured in advance by driving the transfer belt in advance by the belt moving device, and the transfer belt by the belt moving device is measured. In this driving, the belt moving device is characterized in that Δx is corrected when switching between the first detection sensor and the second detection sensor. A belt moving device for moving a transfer belt,
A marker provided on a surface of the transfer belt, a first detection sensor for reading the marker, and a third detection sensor for reading rotation of a drive shaft or a motor shaft of the transfer belt, The position signal of the detection sensor is a belt moving device that converts the rotation angle of the drive shaft or motor shaft of the transfer belt into a surface position,
Sensor switching means for switching between the first detection sensor and the third detection sensor, and switching between the first detection sensor and the third detection sensor when the belt marker home position signal is ON and OFF. A surface position control means for reading the belt position signal and comparing the belt surface target position with the belt position signal,
In accordance with the comparison result obtained by the surface position control means, the transfer belt follows the target position,
The marker position error Δx of the first detection sensor and the third detection sensor in the sensor switching means is measured in advance by pre-driving the transfer belt by the belt moving device, and the transfer belt by the belt moving device is measured. In this driving, the belt moving device is characterized in that Δx is corrected when switching between the first detection sensor and the third detection sensor.   2. The belt moving device according to claim 1, wherein when both the first detection sensor and the second detection sensor are home position signals OFF, the increment value of the marker is compared and the value is different from the specified value. A belt moving device characterized by switching to a normal detection sensor to cause the belt to follow a target position.   2. The belt moving device according to claim 1, wherein when both the first detection sensor and the second detection sensor are home position signals OFF, the increment value of the marker is compared and the value is different from the specified value. A belt moving device characterized by determining an abnormality. The belt moving device according to claim 1 or 3 or 4, wherein the position of the first sensor and the second detection sensor, be placed in proximity of the image bearing member arranged at a position facing the transfer belt A belt moving device. The belt moving device according to any one of claims 1 to 5, using an intermediate transfer belt or a paper conveying belt as the transfer belt, a belt moving device characterized in that it is used in tandem-type image forming apparatus. Belt moving device according to any one of claims 1 to 4, the intermediate transfer belt or using a sheet conveying belt, belt moving device characterized by use in a one-drum type image forming apparatus as the transfer belt .   An image forming apparatus comprising the belt moving device according to claim 1.

Images