JPH1124355A - Multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multicolor image forming device capable of performing accurate alignment of position between plural color images affected by such as the dispersion in outside dimension of a tensioner, in the case of adopting a driving force transmission mechanism of an intermediate transfer belt composed of a pulley, the timing belt and the tensioner. SOLUTION: This device is constituted so that, peripheral length ratio of a photoreceptor 414 and an intermediate transfer belt 415 lies in the integral ratio, while both are rotary driven by the same timing belt 454 with teeth on both side, and the timing pulley 451 fixed to the shaft of the photoreceptor, the timing pulley 452 fixed to the shaft of roller for extending the intermediate transfer belt 415, and the timing pulley 453 as the driving pulley is respectively engaged with the both side teeth belt, and moreover, teeth numbers of the fixed position tensioner pulley 456 being engaged with the inside periphery or the outside periphery of the intermediate transfer belt 415 in a state of being held in press contact therewith are set so as to become the integral ratio with respect to the teeth numbers of nother pulleys and the timing belt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine, and more particularly, to a color toner having a photosensitive member and an intermediate transfer member and formed on the photosensitive member. The present invention relates to an improvement in an image forming apparatus of a type in which images are sequentially transferred to an intermediate transfer member to form a superimposed transfer image, and the superimposed transfer image is collectively transferred onto transfer paper.
More specifically, when an intermediate transfer belt is used as the intermediate transfer member, misalignment of the multi-color toners caused by fluctuation in the tension of the timing belt used for the driving mechanism is eliminated. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art A conventional multicolor image forming apparatus includes a drum-shaped photosensitive member which is driven to rotate, and a photosensitive member which is disposed opposite to the outer peripheral surface of the photosensitive member and is in contact with the outer peripheral surface of the photosensitive member. A belt-shaped intermediate transfer body rotated at the same peripheral speed as the body, a mark provided on a part of the intermediate transfer body, and a mark detection sensor provided in a pass area of the mark; It is known that a primary transfer unit is arranged at a primary transfer unit where a photoconductor and an intermediate transfer body are in contact, and a charging unit is arranged at a charging position upstream of a photoconductor in a rotation direction of the photosensitive member from a position where the primary transfer unit is arranged. I have. At the time of image formation by the multicolor image forming apparatus, an image forming process is started after a certain timing from the time when the sensor detects the mark during rotation of the photosensitive member and the intermediate transfer member, and passes through the charging position. A toner image of an arbitrary color is formed on the charged area of the charged photoconductor by optical writing and development. Subsequently, the step of transferring the toner image of an arbitrary color to the intermediate transfer body by the primary transfer unit in the primary transfer unit is repeated for each of the different colors to form a color superimposed toner image on the intermediate transfer body. Then, a step of collectively transferring this superimposed toner image onto transfer paper to obtain a color image is performed. In such a multicolor image forming apparatus, the circumference ratio of the photosensitive member, the intermediate transfer member, and the rotation means of the intermediate transfer member is made an integer,
Further, by setting the reduction ratios of the gears and the timing belts of the respective driving means to be integers, the speed fluctuations of the respective colors are made equal to enable accurate alignment. For example, Japanese Patent Application Laid-Open No. 61-83557 discloses a "multicolor image forming apparatus" in which the peripheral length of the transfer means is set to an integral multiple of that of the photoreceptor so that one point on the photoreceptor and a plurality of points of the peripheral length of the transfer means are provided. In response to the above, there is disclosed a technique for preventing a developed image of a plurality of colors from shifting on a transfer unit. Also, Japanese Patent Application Laid-Open No. 1-30
In the "color image forming apparatus" disclosed in Japanese Patent No. 7774, good image quality can be obtained by setting all reduction ratios of teeth engaged by a reduction gear connecting the photosensitive member driving means and the photosensitive member to an integer ratio. Such a technique is disclosed.

[0003]

However, in each of the prior arts described above, when a timing pulley and a timing belt are used as means for transmitting the driving force from the motor to the intermediate transfer belt, the timing belt is disposed between the plurality of pulleys. Is endlessly wound, a predetermined tension is applied by a tensioner (timing pulley), and then the loop is fixed by fastening the tensioner with a screw or the like. Therefore, if there is a variation (eccentricity or the like) in the external dimensions of the tensioner, the tension of the timing belt fluctuates (the belt expands and contracts), and the reproducibility of the speed fluctuation (tension fluctuation) for each color deteriorates, and the multi-color image Hinders accurate alignment of That is, a shift occurs in the transfer position of each color, and the image quality deteriorates. In other words, when the belt expands and contracts during driving of the belt as a result of variations in the outer dimensions of the tensioner pulley, each time the belt makes one rotation (reciprocating operation for a predetermined distance in the case of the switchback type), a different configuration is used. Occurs, and the transfer positions do not match. Even with the same type of image forming apparatus originally manufactured based on the same specifications, the tension pattern applied to the timing pulley is different due to the variation in accuracy of the components such as the tensioner pulley. If the external dimensions of the image forming apparatus are eccentric, when the intermediate transfer belt of one image forming apparatus performs one rotation or reciprocating operation in a switchback manner, the tension pattern is different for each operation. Causes a shift in the transfer position between the colors. The present invention has been made in view of the above, and an object of the present invention is to transfer a toner image on a photoreceptor onto an intermediate transfer belt by superimposing one color at a time, and then collectively superimpose images on the intermediate transfer belt on a transfer paper. When a driving force transmission mechanism including a pulley, a timing belt, and a tensioner is used as a means for driving the intermediate transfer belt in a multicolor image forming apparatus of a type that transfers images to It is an object of the present invention to provide a multi-color image forming apparatus which solves the problem of misregistration between a plurality of color images and enables accurate alignment.

[0004]

In order to solve the above-mentioned problems,
The invention according to claim 1 includes a photosensitive member comprising a rotating member, and an intermediate transfer belt rotated at the same target peripheral speed as the photosensitive member in contact with the outer peripheral surface of the photosensitive member. A primary transfer unit is disposed at a primary transfer unit formed by the intermediate transfer belt in a state of contact with the charging unit, and a charging unit is disposed at a charging position on a rotation direction upstream side of the photosensitive member from a position where the primary transfer unit is disposed. A toner image of an arbitrary color is formed by light writing and development on the charged area of the photoconductor charged when passing through the position, and then the toner image of the arbitrary color is transferred onto the intermediate transfer belt by a primary transfer unit. Is repeated for each different color to form a superimposed color image on the intermediate transfer belt, and collectively transfer the superimposed toner image onto transfer paper to obtain a color image. Body and The intermediary transfer belt has a circumference ratio of an integer ratio, and both are driven by the same two-toothed timing belt so that they are rotated by a timing pulley fixed to the shaft of the photoconductor and a roller that stretches the intermediate transfer belt. A timing pulley fixed to a shaft is meshed with each of the two-toothed timing belts, a timing pulley as a drive pulley is meshed with the inner surface of the intermediate transfer belt, and meshed with the inner surface or the outer surface of the intermediate transfer belt in a press-contact state. A tensioner pulley is fixedly arranged, and the number of teeth of the tensioner pulley is set to be an integer ratio with the number of teeth of the other timing pulley and the timing belt. In the invention of claim 2, the tensioner pulley in which the position is fixed can be disposed on either the inner side or the outer side of the loop of the two-tooth timing belt, and the number of teeth of the tensioner pulley is The number of teeth of the timing pulley and the timing belt are in an integer ratio. According to a third aspect of the present invention, in the driving mechanism of the intermediate transfer belt, wherein at least one idler timing pulley is mounted to arrange the loop shape of the timing belt in an arbitrary layout arrangement, the idler timing pulley has the number of teeth. The number of teeth of the other timing pulleys and the timing belt is set to be an integer ratio.

According to the first aspect of the present invention, when a fixed loop type timing belt driving method is employed, the ratio of the number of teeth of the concave and convex portions between each timing pulley and the timing belt is set to an integer ratio. Of the timing pulleys,
Since the number of teeth of the idler pulley functioning as a tensioner is also set to be an integer ratio, at least one of the timing pulleys has a variation in external dimensions such as eccentricity, and as a result, the timing belt tension is reduced. Even if there is a variation, the reproducibility of the driving locus for each color is guaranteed. In the image forming apparatus according to the second aspect, the tension pulley can be arranged on either side of the inside and outside of the loop by using the timing belt of both teeth, and the number of teeth of the tension pulley is set to an integer ratio with the number of other teeth. As in the case of the first aspect, it is possible to realize image formation without transfer position shift. In the image forming apparatus according to the third aspect, when at least one idler pulley (including not only the tensioner timing pulley but also other timing pulleys) is added to arbitrarily lay out the loop shape of the timing belt, the idler pulley may be used. Since the number of teeth is an integer ratio to the number of teeth of other pulleys or belts,
As in the case of 2, image formation without displacement can be realized.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings. [Configuration and Operation of Multicolor Image Forming Apparatus] First, as an example of a multicolor image forming apparatus suitable for carrying out the present invention, the configuration and operation of a color image forming apparatus will be described with reference to the overall configuration diagram of FIG. A color image reading device (hereinafter, referred to as a color scanner) 200 converts an image of a document 180 on a contact glass 202 into an illumination lamp 205, a mirror group 204A,
An image is formed on the color sensor 207 via the lenses 204B, 204C, etc. and the lens 206, and the color image information of the document is converted into, for example, blue (hereinafter, referred to as B), green (hereinafter, referred to as G), red (hereinafter, referred to as R). Is read for each color separation light, and converted into an electric image signal. In this example, the color sensor 207 includes B, G, and R color separation means and a photoelectric conversion element such as a CCD (solid-state imaging device), and performs simultaneous reading of three colors. Based on the intensity levels of the B, G, and R color separation image signals obtained by the color scanner 200, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter, referred to as B)
It is called K. ), Cyan (hereinafter, referred to as C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y) color image data is obtained. Using this color image data, a color image recording device (hereinafter, referred to as
It is called a color printer. ) 400, BK,
The operation method of the color scanner 200 for obtaining the C, M, and Y image data is such that the operation method of the color scanner 400 receives a scanner start signal that is timed with the operation of the color printer 400.
Illumination lamp 205 and mirror group 204A, 204B, 20
The illumination / mirror optical system composed of 4C or the like scans the original in the direction of the left arrow, and obtains one color image data for each scan. Each time, the images are superimposed sequentially while being visualized by the color printer 400 to form a full-color image of four colors.

Next, an outline of the color printer 400 will be described. Writing optical unit 401 as exposure means
Converts the color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to the original image, and applies electrostatic charge to the photosensitive drum 414, which is a latent image carrier corresponding to the photosensitive member according to the present invention. Form a latent image. The optical writing optical unit 401 includes a laser light emitting unit 441, a light emission drive control unit (not shown) for driving the laser light emitting unit 441, a polygon mirror 443, a rotation motor 444 for driving the polygon mirror 443, an fθ lens 442, a reflection mirror 446, and the like. I have. The photoconductor drum 414 rotates in a counterclockwise direction as indicated by an arrow. Around the photoconductor cleaning unit 421, a neutralization lamp 414M, a charger 419 as a charging unit, and a latent image on the photoconductor drum. A potential sensor 414D for detecting a potential, a selected developing device of the revolver developing device 420, a development density pattern detector 414P, an intermediate transfer belt 415 as an intermediate transfer member according to the present invention, and the like are arranged. The revolver developing device 420 includes a BK developing device 420K, a C developing device 420C, an M developing device 420M,
It comprises a Y developing unit 420Y and a revolver rotation drive unit (not shown) for rotating each developing unit in a counterclockwise direction as shown by an arrow. In order to develop the electrostatic latent image, each of these developing units rotates developing sleeves 420 KS and 42, which are rotated by bringing the ears of the developer into contact with the surface of the photosensitive drum 414.
OCS, 420MS, and 420YS, and a developing paddle that rotates to pump and agitate the developer. Now, in the standby state, the revolver developing device 420
Is set at a position where development is performed by the BK developing device 420, and when the copying operation is started, the color scanner 20
At 0, the reading of the BK image data starts at a predetermined timing, and based on this image data, the optical writing / latent image formation by laser light starts (hereinafter, an electrostatic latent image based on the BK image data is referred to as a BK latent image C). , M, and Y. The rotation of the developing sleeve 420KS before the leading end of the latent image reaches the developing position of the BK developing device 420K so that development can be performed from the leading end of the BK latent image. Start and BK latent image
Develop with toner. Thereafter, the developing operation of the BK latent image area is continued. When the rear end of the latent image passes the BK latent image position, the developing operation of the next color developing unit is immediately performed from the developing position of the BK developing unit 420K. The revolver developing device 420 is driven and rotated to the position. This rotation operation
The process is completed at least before the leading end of the latent image based on the next image data arrives. When the image formation cycle begins,
The photoconductor drum 414 rotates counterclockwise as indicated by the arrow, and the intermediate transfer belt 415 rotates clockwise by a drive motor (not shown). With the rotation of the intermediate transfer belt 415, BK toner image formation, C toner image formation, M toner image formation, and Y toner image formation are sequentially performed, and finally the intermediate transfer belt BK, C, M, and Y are sequentially arranged. 4
The toner image is formed so as to be superimposed on the toner image 15.

The formation of a BK image is performed as follows. The charger 419 uniformly charges the photosensitive drum 414 with a negative charge to about -700 V in the dark by corona discharge. Subsequently, the laser diode 441 performs raster exposure based on the BK signal. When the raster image is thus exposed, the photosensitive drum 414 initially charged uniformly
In the exposed portion, the charge proportional to the exposure light amount disappears, and an electrostatic latent image is formed. The toner in the revolver developing device 420 is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420KS of the present developing device is connected to the metal base layer of the photosensitive drum 414 by a power supply unit (not shown). It is biased to a potential at which a negative direct current and an alternating current are superimposed. As a result, the toner does not adhere to the portion of the photosensitive drum 414 where the charge remains, and the BK toner is attracted to the portion having no charge, that is, the exposed portion, and a BK visible image similar to the latent image is formed. Is done. The intermediate transfer belt 415 is
5D, the transfer opposing roller 415T, the cleaning opposing roller 415C, and the driven roller group are stretched, and are driven and controlled by a drive motor (not shown). The BK toner image formed on the photoconductor drum 414 is applied to the surface of the intermediate transfer belt 415 which is driven at a constant speed in contact with the photoconductor, and a belt transfer corona discharger (hereinafter, referred to as a belt transfer unit) 416. Is transcribed. Hereinafter, the transfer of the toner image from the photosensitive drum 414 to the intermediate transfer belt 415 will be described.
This is called belt transfer.

A small amount of untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe. The intermediate transfer belt 41
5 includes BK, C, and BK sequentially formed on the photosensitive drum 414.
The M and Y toner images are sequentially aligned on the same surface to form a four-color superimposed belt transfer image, and then collectively transferred to transfer paper by a corona discharge transfer device. By the way, on the photosensitive drum 414 side, the process proceeds to the C image forming process after the BK image forming process. At a predetermined timing, reading of the C image data by the color scanner 200 is started, and the laser beam writing by the image data is performed. A latent image is formed. The C developing device 420C rotates the revolver developing device with respect to the developing position after the trailing end of the previous BK latent image has passed and before the leading end of the C latent image has arrived, and converts the C latent image into the C latent image. Develop with toner. Thereafter, the development of the C latent image area is continued, but when the rear end of the latent image has passed, the revolver developing device 420 is driven in the same manner as in the case of the BK developing device, and the C
The developing device 420C is sent out, and the next M developing device 420M is positioned at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit. In the process of forming each of the M and Y images, the operations of reading, forming a latent image, and developing each image data are performed by the above-described BK image and C image processing.
The description is omitted because it conforms to the image process.

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. After the BK image of the first color is transferred to the belt, while the images of the second, third, and fourth colors are being transferred to the belt, the entrance seal, the rubber blade, and the like are separated from the intermediate transfer belt surface by the blade contact / separation mechanism. . A paper transfer corona discharger (hereinafter, referred to as a paper transfer device) 417 transfers AC + DC or DC components to the transfer paper and the intermediate transfer by a corona discharge method in order to transfer the superimposed toner image on the intermediate transfer belt 415 to the transfer paper. This is applied to the belt. Transfer papers of various sizes are stored in a transfer paper cassette 482 in the paper supply bank. The registration roller pair 41 is supplied by a paper supply roller 483 from a storage cassette storing paper of a designated size.
Paper is fed and conveyed in the 8R direction. Note that reference numeral 412B2
Indicates a paper feed tray for manually feeding OHP paper or thick paper. At the time when the image formation is started, the transfer paper is fed from any of the paper feed trays, and is waiting at the nip of the pair of registration rollers 418R. When the leading end of the toner image on the intermediate transfer belt 415 approaches the paper transfer unit 417, the registration roller pair 418R is driven so that the leading end of the transfer paper coincides with the leading end of this image, and the registration of the paper and the image is performed. Matching is performed.

In this way, the transfer paper is superimposed on the color superimposed image on the intermediate transfer belt and passes over the paper transfer unit 417 connected to the positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation and neutralization device by a neutralization brush (not shown) arranged on the left side of the paper transfer device 417, the transfer paper is neutralized, and the intermediate transfer belt 41 is removed.
5 and moves to the paper transport belt 422. The transfer paper on which the four-color superimposed toner image has been collectively transferred from the intermediate transfer belt surface is conveyed to a fixing device 423 by a paper conveyance belt 422, and the fixing roller 423A is controlled to a predetermined temperature.
The toner image is fused and fixed at the nip portion of the pressure roller 423B, sent out of the main body by the discharge roll pair 424, and stacked face up on a copy tray (not shown) to obtain a full color copy. The photosensitive drum 4 after the belt transfer
The surface of the cleaning member 14 is cleaned by a photoconductor cleaning unit 421 including a brush roller, a rubber blade, and the like, and is uniformly discharged by a discharge lamp 414M. Also,
Intermediate transfer belt 415 after transfer of toner image to transfer paper
Is pressed again by the blade contact / separation mechanism of the cleaning unit 415U to clean the surface.

In the case of the repeat copy, the operation of the color scanner and the image formation on the photosensitive member follow the first-color image process of the first sheet and proceed to the first-color image process of the second sheet at a predetermined timing. In the intermediate transfer belt 415, the BK toner image for the second sheet is placed in a region where the surface of the intermediate transfer belt 415 is cleaned by the belt cleaning device, following the batch transfer process of the first four-color superimposed image onto the transfer paper. The belt is transferred. After that, the operation is the same as that of the first sheet. The above is the description of the copy mode for obtaining the four-color full-color copy. However, in the case of 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. Become. Further, in the case of the single-color copy mode, until the predetermined number of sheets is completed, only the developing device of the revolver developing device 420 of the predetermined color is located at the developing position of the predetermined color, the developing operation is performed, and the belt cleaning device 415U The copying operation is continuously performed while the blade is pressed against the belt. In such an image forming apparatus, a mark for position detection is provided on the outer peripheral surface or the inner peripheral surface of the belt 415. However, on the outer peripheral surface side, it is necessary to devise a way to avoid the passage area of the belt cleaning device 415U, which may cause difficulty in arrangement. In this case, it is provided on the inner peripheral surface side. Although not shown in FIG. 1, the optical sensor is provided at a position between a driving roller 415D that supports the belt 415 and a support roller 415F.

[Characteristic Example of the Present Invention] Next, an embodiment of the present invention will be specifically described with reference to FIGS. FIG. 2 is a perspective view of an example of a driving mechanism including a driving force transmitting mechanism to the transfer belt of the present invention, and FIG. 3 is a schematic configuration diagram thereof.
In FIG. 2, a timing pulley (driven pulley) 45 is attached to a shaft 414 ′ protruding from an end surface of the photosensitive drum 414.
The shaft center of the timing pulley 452 is fixedly connected to the shaft 415D 'of the drive roller 415D of the intermediate transfer belt 415, which is arranged opposite to the photosensitive drum 414. Further, another timing pulley (driving pulley) 453 is disposed near the timing pulley (driven pulley) 452, and the shaft 4 of the timing pulley 453 is provided.
53 'is fixedly connected to the output shaft of the drive motor 457. These timing pulleys 451, 452, 453
Has an uneven portion that meshes with the uneven portion of the timing belt 454, the timing pulley 451 of the photoconductor meshes with the uneven portion on the outer surface of the loop (belt 454), and the other timing pulleys 452 and 453 are inside the loop. It is drivingly connected so as to be meshed with. Further, an idler pulley 456 (tensioner pulley) as a timing pulley is rotatably supported at one end of a bracket 456b which is pulled in the direction of the arrow by the spring 456a. It is fixed to a not-shown fixing member (fixing part on the device side). That is, the idler pulley 456 as a tensioner pulley has a position fixing structure that can change the position. Screw 4 is used to fix the bracket 456b
By adjusting the idler pulley 45,
6 can adjust the tension applied to the timing belt 454, and the loop is fixed. Note that the timing belt 454 is a double-tooth type having unevenness of the same pitch on both surfaces.

A characteristic feature of the present invention is that the number of teeth of the concave and convex portions between the timing pulleys and the timing belt is set to an integer ratio. In particular, among the timing pulleys, the teeth of the idler pulley 456 functioning as a tensioner are provided. The point is that the numbers are also set to be an integer ratio. Another feature is that teeth (irregularities) are formed at the same pitch on both sides of the timing belt 454 so that the idler pulley 456 can be arbitrarily arranged inside and outside the loop of the belt. For example, the number of teeth between each pulley and belt is set as follows. Timing pulleys 451: 452: 453: 456: timing belt 454 = 4: 2: 2: 1: 8 If the ratios are set to be an integer ratio as described above, the timing pulleys 451, 452, 453, and 456 may be temporarily set. Even if at least one of them has a variation in external dimensions such as eccentricity, as a result, the reproducibility of the drive locus for each color is guaranteed even if the tension of the timing belt 454 fluctuates. In particular, when the loop is fixed by positioning the tensioner pulley with screws as in the past, the reproducibility of the tension fluctuation in the transfer process for each color due to variations in the outer diameter of the tensioner pulley due to eccentricity etc. However, in the present embodiment, the number of teeth of the uneven portion (teeth) on the outer peripheral surface of the tensioner pulley is set so as to have an integer ratio with the number of teeth of other pulleys and belts. Therefore, such a problem can be solved at once. That is, the situation where the tension generation pattern fluctuates every time the timing belt operates due to the eccentricity of the tensioner pulley can be effectively solved by setting the number of teeth of the tensioner pulley to an integer ratio. As a driving method of the timing belt 454, there is a method of making one rotation for each color, a method of reciprocating the belt in a switchback type, and the like, and the present invention is effective for an apparatus using any of the driving methods. .

In the present invention, the photosensitive drum 414
And the peripheral lengths of the drive roller 415D and the intermediate transfer belt 415 are set such that the integer ratio is, for example, photosensitive drum 414: drive roller 415D: intermediate transfer belt 454 = 2: 1: 4. Therefore, the photosensitive drum 41
The intermediate transfer belt 4 and the intermediate transfer belt 415 can rotate at a constant speed at a portion facing each other. As described above, according to this embodiment, when the ratio of the number of teeth of each pulley is set to an integer ratio, and when used with the timing belt driving mechanism of the fixed loop, the number of teeth of the tensioner pulley 456 is changed to the number of teeth of the other pulleys and belts. Since the ratio is set to the number of teeth and the integer ratio, reproducibility of the variation of the tension is ensured, and an image forming apparatus having no positional deviation in superimposing a plurality of color images becomes possible. In particular, since a timing belt with two teeth having the same pitch on both the inner and outer surfaces is used, the tensioner pulley 456 can be arranged at any position inside and outside the loop, and the number of teeth of the tensioner pulley is also different. Since the number of pulleys and the number of teeth of the belt are set to an integer ratio, an image forming apparatus having no displacement between a plurality of colors can be realized.

FIG. 3 shows another embodiment of the driving force transmission mechanism of the present invention, and an idler pulley (tensioner pulley) 456 as a timing pulley for convenience of layout.
Is an example in which the shape of the loop is arbitrarily set by changing the arrangement of. That is, the timing belt 454 is stretched endlessly using the timing pulleys 451, 452, 453, and 458 as idler pulleys, and another idler pulley 456 is pressed from the outer surface of the belt 454 to be pressed by the elastic member 456a. I'm trying to energize. In this example, the gear ratio is the timing pulley 451: 452: 453: 456: 4
58: Timing belt 454 = 4: 2: 2: 1: 2:
8 is set. Therefore, even if any one of the timing pulleys has a variation in the outer shape such as eccentricity, even if the tension of the timing belt 454 fluctuates, the reproducibility of the driving locus for each color is guaranteed. Become.

Further, even if the tensioner pulley 456 and the idler pulley 458 in FIG. As long as is set to an integer ratio, the same effect can be obtained. That is, in the embodiment of FIG. 3, when adding a tensioner pulley and another idler timing pulley in order to arbitrarily lay out the loop shape of the timing belt 454, the number of teeth of each pulley is changed to the number of teeth of the other pulley and belt. And an integer ratio, it is possible to effectively prevent the occurrence of misalignment between a plurality of colors in a timing belt having any crawling structure. It is to be noted that the examples of the integer ratios described in the description of each of the above embodiments are merely examples, and it is a matter of course that the present invention is not limited to these.
Further, the example of the crawling structure of the timing belt 454 is only an example.

[0018]

According to the image forming apparatus of the first aspect, when the fixed loop type timing belt driving method is employed, the ratio of the number of teeth of the concave and convex portions between each timing pulley and the timing belt is set to an integer ratio. In particular, among the timing pulleys, the number of teeth of the idler pulley that functions as a tensioner is also set to be an integer ratio, so that at least one of the timing pulleys has a variation in external dimensions such as eccentricity, As a result, even if the tension of the timing belt fluctuates, repetitive reproducibility of the driving locus for each color is guaranteed. In particular, when the loop is fixed by positioning the tensioner pulley with screws as in the past, the reproducibility of the tension fluctuation in the transfer process for each color due to variations in the outer diameter of the tensioner pulley due to eccentricity etc. However, in the present embodiment, the number of teeth of the uneven portion (teeth) on the outer peripheral surface of the tensioner pulley is set so as to have an integer ratio with the number of teeth of other pulleys and belts. Therefore, such a problem can be solved at once. That is, due to the eccentricity of the tensioner pulley,
The situation where the tension generation pattern fluctuates every time the timing belt operates can be effectively solved by setting the number of teeth of the tensioner pulley to an integer ratio. In the image forming apparatus according to the second aspect, the tension pulley can be arranged on either side of the inside and outside of the loop by using the timing belt of both teeth, and the number of teeth of the tension pulley is set to an integer ratio with the number of other teeth. As in the case of the first aspect, it is possible to realize image formation without transfer position shift. In the image forming apparatus according to the third aspect, when at least one idler pulley (including not only the tensioner timing pulley but also other timing pulleys) is added to arbitrarily lay out the loop shape of the timing belt, the idler pulley may be used. Since the number of teeth is an integer ratio to the number of teeth of the other pulleys and belts, image formation without displacement can be realized as in the first and second aspects.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an example of a multicolor image forming apparatus to which the present invention is applied.

FIG. 2 is a perspective view of a main part of an example of an intermediate transfer belt driving mechanism of the present invention.

FIG. 3 is a schematic diagram of a main part of an example of an intermediate transfer belt driving mechanism according to another embodiment.

[Explanation of symbols]

180 ... manuscript, 200 ... color image reading device (color scanner), 202 ... contact glass,
204A, 204B, 204C: mirror group, 205 ...
-Illumination lamp, 206 ... Lens, 207 ... Color sensor, 400 ... Color image recording device (color printer), 401 ... Writing optical unit, 412B2
・ ・ ・ Manual feed tray, 414 ・ ・ ・ Photoconductor drum, 41
4M: static elimination lamp, 414D: potential sensor, 41
4P: development density pattern detector, 414 ': axis, 4
15 ... Intermediate transfer belt, 415C ... Cleaning opposing roller, 415D ... Driving roller, 415D '...
Shaft, 415F ... Support roller, 415T ... Rolling opposing roller, 415U ... Belt cleaning device, 416 ...
-Belt transfer unit, 417 ... Paper transfer corona discharger (paper transfer unit), 418R ... Registration roller pair, 419 ... Charger, 420 ... Revolver developing device, 420K ... B
K developing device, 420C ... C developing device, 420M ... M developing device, 420Y ... Y developing device, 420KS / 420CS /
420MS / 420YS: developing sleeve, 421 ...
Photoconductor cleaning unit 422 、 ４ Paper transport belt 423 定 着 Fixing device 423 A Fixing roller 42
3B: pressure roller, 424: discharge roll pair, 441
Laser diode, 442 ・ ・ ・ fθ lens, 44
3 ... polygon mirror, 444 ... rotation motor, 44
6 Reflective mirror, 451 Timing pulley (driven pulley), 452 Timing pulley (driven pulley), 453 Timing pulley (drive pulley), 4
53 '... shaft, 454 ... timing belt, 456 ...
Idler pulley (tensioner pulley), 456a ...
Spring, 456b ... Bracket, 456c ...
Screw, 457: Drive motor, 482: Transfer paper cassette, 483: Feed roller

Claims (3)

[Claims] An image forming apparatus, comprising: a photosensitive member comprising a rotating member; and an intermediate transfer belt rotated at the same target peripheral speed as the photosensitive member in contact with the outer peripheral surface of the photosensitive member. A primary transfer unit is disposed at a primary transfer unit formed by the intermediate transfer belt in a state in which the charging unit is disposed at a charging position on a rotation direction upstream side of the photosensitive member from a position at which the primary transfer unit is disposed,
A toner image of an arbitrary color is formed by light writing and development on a charged area of the photoconductor charged when passing through the charging position, and then the toner image of the arbitrary color is transferred onto the intermediate transfer belt by a primary transfer unit. A multi-color image forming apparatus that forms a color superimposed image on the intermediate transfer belt, and collectively transfers the superimposed toner image onto transfer paper to obtain a color image, The circumferential length ratio of the photoconductor and the intermediate transfer belt is set to an integer ratio, and the timing pulley fixed to the shaft of the photoconductor and the timing pulley fixed to the shaft of the roller on which the intermediate transfer belt is stretched are meshed with the two-tooth timing belt, respectively. By rotating the photoreceptor and the intermediate transfer belt by the two-toothed timing belt, an inner surface of the intermediate transfer belt serves as a drive pulley. A tensioner pulley meshed with an inner surface or an outer surface of the intermediate transfer belt in a press-contact state is fixedly arranged, and the number of teeth of the tensioner pulley is reduced by adjusting the number of teeth of the other timing pulley and the timing belt. A multicolor image forming apparatus, wherein the number of teeth is set to an integer ratio. 2. The tensioner pulley in which the position is fixed may be disposed on either the inner side or the outer side of the loop of the two-toothed timing belt, and the number of teeth of the tensioner pulley is equal to the number of teeth of each of the timing pulleys. 2. The multi-color image forming apparatus according to claim 1, wherein the number of teeth of said timing belt is in an integer ratio. 3. A driving mechanism for an intermediate transfer belt on which at least one idler timing pulley is mounted in order to arrange the loop shape of the timing belt into an arbitrary layout arrangement, wherein the idler timing pulley has the other teeth. 3. The multicolor image forming apparatus according to claim 1, wherein the number of teeth of the timing pulley and the timing belt is set to be an integer ratio.