Image forming system

Abstract

This invention provides an image forming system that can reduce the positional variation of the developer image transferred from the intermediate transfer belt to the recording material, even in an image forming apparatus for monochrome imaging. [Solution] An image forming system comprising a first image forming apparatus 1m for forming a monochrome image and a second image forming apparatus for forming a color image, wherein the first intermediate transfer belt (intermediate transfer belt 41) of the first image forming apparatus 1m and the second intermediate transfer belt of the second image forming apparatus have a common configuration, the first image forming apparatus 1m is equipped with an optical sensor unit 44m for measuring the circumference of the intermediate transfer belt 41, and has a control unit 3c that controls the secondary transfer timing by the secondary transfer roller 45 based on the circumference obtained from the information obtained from the optical sensor unit 44m.

Description

Technical Field

[0001] The present invention relates to an image forming system for forming an image on a recording material.

Background Art

[0002] In image forming apparatuses such as printers, copiers, and multifunction devices, a full-color image forming apparatus is known in which a plurality of photoreceptors are arranged in parallel on an intermediate transfer belt, a developer image is primarily transferred from the photoreceptor to the intermediate transfer belt, and the developer image is secondarily transferred from the intermediate transfer belt to a recording material. In such an image forming apparatus using an intermediate transfer belt, a technique including an optical sensor for performing corrections such as alignment of a plurality of color developer images on the intermediate transfer belt and density adjustment is also known (see, for example, Patent Documents 1 and 2).

[0003] In recent years, a configuration has been proposed that can be used as a device that removes various components for forming a color image from a full-color image forming apparatus and performs only monochrome image formation (see, for example, Patent Document 3). By adopting such a configuration, components and systems other than the image forming unit can be shared between the full-color machine and the monochrome machine, and the device cost and development investment can be reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when image formation is performed using an intermediate transfer belt, the distance from the primary transfer position to the secondary transfer position may differ between multiple image forming machines due to manufacturing variations in the image forming machines. If the distance from the primary transfer position to the secondary transfer position varies, the position of the developer image transferred from the intermediate transfer belt to the recording material will vary on the recording material.

[0006] The object of the present invention is to provide an image forming system that can reduce the variation in the position of the developer image transferred from the intermediate transfer belt to the recording material, even in an image forming apparatus for monochrome. [Means for solving the problem]

[0007] The image forming system of the present invention is An image forming system comprising a first image forming apparatus for forming monochrome images and a second image forming apparatus for forming color images, The first image forming apparatus is The first photosensitive drum, A first developing means for developing the electrostatic latent image formed on the first photosensitive drum, A first intermediate transfer belt onto which the black developer image formed on the first photosensitive drum is transferred, A first recording material transfer means for secondarily transferring the developer image transferred to the first intermediate transfer belt to a recording material, Equipped with, The second image forming apparatus is The second photosensitive drum, Multiple color photosensitive drums, A second developing means for developing the electrostatic latent image formed on the second photosensitive drum, Multiple color developing means for developing the electrostatic latent images formed on the multiple color photosensitive drums, A second intermediate transfer belt onto which the black developer image formed on the second photosensitive drum and the developer images formed on the plurality of color photosensitive drums are transferred, A second recording material transfer means for secondarily transferring the developer image transferred to the second intermediate transfer belt to a recording material, Equipped with, The first intermediate transfer belt and the second intermediate transfer belt have a common configuration, The first image forming apparatus includes measuring means for measuring the perimeter of the first intermediate transfer belt, and has a control unit that controls the secondary transfer timing by the first recording material transfer means based on the perimeter obtained from the information obtained by the measuring means.

Advantages of the Invention

[0008] As described above, according to the present invention, even in a monochrome image forming apparatus, the secondary transfer position of the developer image from the intermediate transfer belt to the recording material can be stabilized.

Brief Description of the Drawings

[0009] [Figure 1] A diagram for explaining the overall configuration of the first image forming apparatus of Example 1 [Figure 2] A perspective view of the monochrome transfer unit and the optical sensor unit of Example 1 [Figure 3] A schematic diagram of the positioning of the optical sensor unit of Example 1 [Figure 4] A perspective view of the monochrome optical sensor unit of Example 1 [Figure 5] A schematic diagram of the optical sensor of Example 1 [Figure 6] A schematic diagram of the output of the optical sensor of Example 1 [Figure 7] A diagram for explaining the overall configuration of the second image forming apparatus of Example 1 [Figure 8] A perspective view of the full-color optical sensor unit of Example 1 [Figure 9] A perspective view of the monochrome transfer unit and the optical sensor unit of Example 2 [Figure 10] A schematic diagram of the output of the optical sensor of Example 2

Modes for Carrying Out the Invention

[0010] Hereinafter, with reference to the drawings, embodiments for implementing the present invention will be illustratively and detailedly described based on examples. However, dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those, unless otherwise specifically described.

[0011] The image forming system according to this embodiment is applicable to copiers, printers, facsimiles, and multifunction machines having a plurality of these functions. However, in the following embodiments, the case of applying it to a printer will be described as an example. And the image forming system according to this embodiment has a first image forming apparatus that forms a monochrome image and a second image forming apparatus that forms a color image. And the first image forming apparatus and the second image forming apparatus have common configurations (components and members) for purposes such as cost reduction. The first image forming apparatus and the second image forming apparatus do not necessarily need to be connected. Therefore, the first image forming apparatus and the second image forming apparatus may be used at physically separated locations, and the image forming system can also be referred to as a group of image forming apparatuses. Also, in the image forming system, cases where users of the first image forming apparatus and the second image forming apparatus are different are included. In the following description, for the second image forming apparatus, an apparatus capable of forming a full-color image will be described as an example.

[0012] (Example 1) Referring to FIGS. 1 to 8, the image forming system according to this embodiment will be described. Hereinafter, after describing the first image forming apparatus 1m that forms a monochrome image, the second image forming apparatus 1c that forms a color image will be described. After describing the first image forming apparatus 1m that forms a monochrome image, the second image forming apparatus 1c that forms a color image will be described.

[0013] <Overall Configuration of the First Image Forming Apparatus> <Figure 1 is a schematic diagram of the first image forming apparatus 1m according to this embodiment. The apparatus body 1A is equipped with a scanner 2m, a control unit 3m, a sheet feeding unit 30, a transfer unit 40m, a tray unit 50m, and a fixing device 80. The sheet feeding unit 30 has a loading tray 31 for loading sheets S and a feeding roller 32. The loading tray 31 is configured to be pullable toward the door 20, thereby replenishing the sheets S. The monochrome tray unit 50m has a tray 51 and a cartridge PK. The tray 51 has a handle 52 and is configured to be pullable toward the door 20. The cartridge PK is detachably supported on the tray 51 and can be replaced by pulling out the tray unit 50m from the apparatus body 1A. The process cartridge PK contains black (K) toner (developer) and is equipped with a photosensitive drum 61K as a first photosensitive drum, a charging roller 62K, and a developing unit. The developing unit has a developing roller 71K as a first developing means for developing the electrostatic latent image formed on the photosensitive drum 61K. The rotation axis of the photosensitive drum 61K, the rotation axis of the developing roller 71K, and the rotation axis of the charging roller 62K are all parallel.

[0014] Above the secondary transfer section within the main body 1A of the device, a fixing device 80 is positioned as the first fixing means. The fixing device 80 is a thermal fixing device that fixes the toner image (developer image) onto the sheet S by heating and pressurizing. This fixing device 80 includes, for example, a fixing roller and a pressure roller 81 that grip and transport the sheet S, and a heat source (for example, a halogen lamp or ceramic heater) that heats the toner image on the sheet S via the fixing roller.

[0015] <Intermediate Transfer Belt> The black toner image formed on the photosensitive drum 61K is transferred to the intermediate transfer belt 41, which serves as the first intermediate transfer belt. This intermediate transfer belt 41 is a rotatable endless belt stretched over a drive roller 46, a tension roller, and a tension roller 47 that rotate around mutually parallel axes, and rotates counterclockwise in the figure due to the rotation of the drive roller 46. On the inner circumference side of the intermediate transfer belt 41, a primary transfer roller 42K, which serves as a primary transfer means, is positioned opposite the photosensitive drum 61K via the intermediate transfer belt 41 with a predetermined offset amount. The portion where the toner image is transferred from the photosensitive drum 61K to the intermediate transfer belt 41 by the primary transfer roller 42K is hereinafter referred to as the primary transfer portion. On the outer circumference side of the intermediate transfer belt 41, a secondary transfer roller 45, which serves as the first recording material transfer means, is provided at a position opposite the drive roller 46 via the intermediate transfer belt 41. The portion where the toner image is transferred from the intermediate transfer belt 41 to the sheet S by the secondary transfer roller 45 is hereinafter referred to as the secondary transfer portion.

[0016] The tension roller 47 contacts the inner surface of the intermediate transfer belt 41 downstream of the primary transfer section and upstream of the secondary transfer section in the rotational direction of the intermediate transfer belt 41, thereby tensioning the intermediate transfer belt 41. The intermediate transfer belt 41 and the nip portion of the secondary transfer roller 45 form the secondary transfer section as described above. The intermediate transfer belt 41, primary transfer roller 42K, and secondary transfer roller 45 constitute an intermediate transfer unit for transferring the toner image formed on the photosensitive drum 61K to the sheet S.

[0017] <Image Formation Process> The image forming operation by the first image forming apparatus 1m will now be described. The control unit 3m starts the image forming operation on the sheet S based on the image signal received from the external host device 400. The external host device 400 is, for example, a personal computer, an image reader, and a facsimile machine. When the image forming operation starts, the sheet S is fed from the loading tray 31 of the apparatus body 1A by the feed roller 32, which is a feeding means. This sheet S is in a stopped state. The tip of the sheet is corrected when it comes into contact with the pair of registration rollers 4. The pair of registration rollers 4 feed the sheet S to the secondary transfer unit in a timing synchronized with the progress of the toner image creation process by the image forming unit.

[0018] Meanwhile, in the image forming section, the photosensitive drum 61K rotates, and the charging roller 62K uniformly charges the surface of the photosensitive drum 61K. Based on the image information to be recorded on the sheet S, the scanner 2m irradiates the photosensitive drum 61K with laser light to write an electrostatic latent image. This electrostatic latent image is visualized as a black toner image when the developing unit develops it using black toner. The toner image formed on the photosensitive drum 61K is transferred to the intermediate transfer belt 41 by the primary transfer roller 42K, and is transported toward the secondary transfer section by the rotation of the intermediate transfer belt 41. Then, when a voltage is applied to the secondary transfer roller 45, the toner image is transferred (secondary transfer) to the sheet S fed from the registration roller pair 4.

[0019] The sheet S, having passed through the secondary transfer section, is sent to the fuser unit 80. As it passes through the nip sections of the fuser roller and pressure roller 81, the toner image is heated and pressurized, causing the toner to soften and then solidify, thereby fixing the toner image to the sheet S. The sheet S, having passed through the fuser unit 80, is guided to the paper output path 1d and discharged from the main unit 1A by a pair of discharge rollers, and is sequentially loaded onto the discharge tray 1f located on the top of the main unit 1A. The door 20 is provided with a double-sided transport path 20a through which the sheet S that has passed through the fuser unit 80 passes, and is used when forming images on both sides of the sheet S.

[0020] <Monochrome intermediate transfer unit and measurement means (optical sensor unit)> Figure 2 is a perspective view of the intermediate transfer unit 40m and optical sensor unit 44m for monochrome. The optical sensor unit 44m, as a measuring means, is supported by a stay member 44c that constitutes the frame 100. Figure 3 is a detailed view showing the relationship between the longitudinal end of the optical sensor unit and the tension roller. The sensor stay 44e is provided with a groove-shaped positioning opening (receiving part) 44f configured to fit the rotation shaft 47c of the tension roller 47. The positioning opening 44f has a concentric (coaxial) shape with respect to the rotation shaft 47c. By fitting the rotation shaft 47c into this positioning opening 44f, the optical sensor unit 44m can be attached to the intermediate transfer unit 40m. This allows for accurate positioning of the tension roller 47 and the optical sensor unit 44m, and enables accurate maintenance of the positional relationship (distance) between the surface of the intermediate transfer belt 41 and the optical sensor 44a. In this manner, the optical sensor 44a, which has a light-emitting element and a light-receiving element, is supported by a support member (sensor stay 44e) supported by the rotation axis 47c of the tension roller 47 that is in contact with the inner circumferential surface of the intermediate transfer belt 41.

[0021] <Monochrome Optical Sensor Unit> The outline of the optical sensor unit according to this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a perspective view of the monochrome optical sensor unit according to this embodiment. The optical sensor unit 44m is supported by a stay member 44c that constitutes the frame 100, and positioning openings 44f are provided at both longitudinal ends of the sensor stay 44e. In addition, a cable 44d for sending the output signal of the optical sensor 44a to the control unit 3m is connected to the optical sensor 44a.

[0022] Figure 5 is a schematic diagram of the optical sensor unit in this embodiment. The optical sensor 44a has a light-emitting element 44n composed of an LED or the like, a diffuse reflection light-receiving element 44k composed of a photodiode or the like that receives scattered reflected light 44s, and a specular reflection light-receiving element 44h that receives specular reflected light 44r. In this embodiment, the light-emitting element 44n, the diffuse reflection light-receiving element 44k, and the specular reflection light-receiving element 44h are all composed of chip-type elements directly mounted on a substrate.

[0023] The illuminated surface of the light-emitting element 44n is the surface of the intermediate transfer belt 41. The optical axis 44t of the light-emitting element 44n, the optical axis of the specularly reflected light 44r, and the optical axis of the scattered reflected light 44s are each illuminated from the surface mounted on the substrate with a predetermined light intensity distribution. Hereinafter, the axis connecting the center (light-emitting point) of the light-emitting element 44n and the detection position DP on the illuminated surface (surface of the intermediate transfer belt 41) is defined as the central optical axis of the illuminated light. Furthermore, the axis connecting the center (light-receiving point) of the photodetector element 44k and the detection position DP is defined as the central optical axis of the scattered reflected light, and the axis connecting the center (light-receiving point) of the photodetector element 44h and the detection position DP is defined as the central optical axis of the specularly reflected light.

[0024] The control unit 3m can control the density adjustment of the black toner image formed on the intermediate transfer belt 41. In other words, the optical sensor 44a is configured to detect the density of the black toner image formed on the intermediate transfer belt 41.

[0025] In the case of the optical sensor 44a, in the second image forming apparatus capable of forming full-color images as described later, a diffuse reflection light-receiving element 44k may be provided to enable alignment and density adjustment of the toner images of each color. However, in the case of the first image forming apparatus that forms monochrome images, the diffuse reflection light-receiving element 44k is not used, so it is possible to reduce costs by not providing the diffuse reflection light-receiving element 44k. In other words, the optical sensor 44a provided in the first image forming apparatus can have a specular reflection light-receiving element 44h and not a diffuse reflection light-receiving element 44k.

[0026] <Circumference measurement using optical sensors> Figure 6 is a schematic diagram showing an example of the output of a monochrome optical sensor according to this embodiment. The vertical axis represents the voltage value output from the specular reflection photodetector 44h, and the horizontal axis represents the sampling time. The reflectivity of light on the surface of the intermediate transfer belt 41 has a unique profile along the direction of movement (rotation) of the intermediate transfer belt 41. Therefore, the control unit 3m calculates and obtains the circumference of the intermediate transfer belt 41 from the information obtained from the optical sensor unit 44m as a measuring means (light reception information obtained by the specular reflection photodetector 44h), and controls the secondary transfer timing by the secondary transfer roller 45 based on this circumference. More specifically, as shown in Figure 6, the intermediate transfer belt 41 is rotated at a constant speed, and the profile pf during belt rotation is obtained by sampling multiple rotations. That is, the control unit 3m extracts the estimated times t1, t2, t3... for which the intermediate transfer belt 41 has completed one rotation, and performs calculation processing to determine the time required for the intermediate transfer belt 41 to complete one rotation. This allows the circumference of one belt rotation to be measured from the rotational speed of the intermediate transfer belt 41 during sampling.

[0027] From the circumference measured in this way, the circumferential distance on the intermediate transfer belt 41 from the primary transfer roller 42K to the secondary transfer roller 45 can be predicted with high accuracy. Based on this distance, the timing of the secondary transfer by the secondary transfer roller 45 can be controlled. Therefore, variations in the position of the toner image transferred from the intermediate transfer belt 41 to the sheet S can be reduced.

[0028] As described above, in this embodiment, the circumference of the intermediate transfer belt 41 is measured by the light received information obtained from the reflected light of the intermediate transfer belt 41 against the substrate. The control unit 3m can also determine whether or not the intermediate transfer belt 41 is attached to the main body 1A of the device based on the light received information obtained by the specular reflection light receiving element 44h. That is, if the light received information obtained by the specular reflection light receiving element 44h is abnormal, it can be determined that the intermediate transfer belt 41 is not attached to the main body 1A of the device. In this way, if the control unit 3m determines that the intermediate transfer belt 41 is not attached to the main body 1A of the device, it can notify the outside by sound, light, etc., thereby preventing the intermediate transfer belt 41 from being forgotten to be attached.

[0029] <Second image forming device> The second image forming apparatus 1c will be described with reference to Figure 7. Figure 7 is a diagram illustrating the overall configuration of the second image forming apparatus for full color, which is largely the same as the first image forming apparatus for monochrome according to this embodiment. The second image forming apparatus shares the same configuration as the first image forming apparatus in terms of sheet transport and fixing, but differs in the configuration related to image formation. Specifically, as the number of cartridges increases from one to four, the configurations of the scanner 2c, tray unit 50c, transfer unit 40c, and control unit 3c are different.

[0030] The full-color transfer unit 40c is largely the same as the monochrome transfer unit 40m, including the intermediate transfer belt 41, transfer frame 48, and primary transfer roller 42K.

[0031] The tray unit 50c has a tray 51 and four cartridges P that are detachable from the tray 51. This tray unit 50c is configured to be movable in and out of the second image forming apparatus 1c. This makes it easy to attach and detach the cartridges P. There are four types of cartridges P: cartridge PK which contains black (K) toner, cartridge PC which contains cyan (C) toner, cartridge PN which contains magenta (M) toner, and cartridge PY which contains yellow (Y) toner. These cartridges P are configured to be individually detachable from the tray 51. The tray unit 50c also has a photosensitive drum 61K, 61C, 61M, 61Y, a charging roller 62K, 62C, 62M, 62Y, and a developing roller 71K, 71C, 71M, 71Y, corresponding to each color. These are provided for each individual cartridge P.

[0032] Thus, the second image forming apparatus 1c comprises a photosensitive drum 61K as a second photosensitive drum and a plurality of color photosensitive drums 61C, 61M, and 61Y. The second image forming apparatus 1c also comprises a developing roller 71K as a second developing means for developing the electrostatic latent image formed on the photosensitive drum 61K, and a plurality of color developing means for developing rollers 71C, 71M, and 71Y. The developing rollers 71C, 71M, and 71Y are configured to develop the electrostatic latent images formed on each of the plurality of color photosensitive drums. A black toner image is formed on the photosensitive drum 61K, and the black toner image formed on the photosensitive drum 61K is transferred from the photosensitive drum 61K to the belt 41.

[0033] Furthermore, the first photosensitive drum in the first image forming apparatus 1m and the second photosensitive drum in the second image forming apparatus 1c share the same configuration (parts and materials). Therefore, the second photosensitive drum is also referred to as "photosensitive drum 61K," as described above, just like the first photosensitive drum. Similarly, the first developing means in the first image forming apparatus 1m and the second developing means in the second image forming apparatus 1c share the same configuration (parts and materials). Therefore, the second developing means is also referred to as "developing roller 71K," as described above, just like the first developing means. Thus, the first and second photosensitive drums, and the first and second developing means, share the same configuration, and their outer diameters are substantially identical, preferably their materials are also substantially identical. However, variations in manufacturing may cause errors in the outer diameter. For the outer diameters of the first photosensitive drum and the second photosensitive drum to be considered substantially the same, it is preferable that the variation in their respective outer diameters is ±1 mm, that is, that the difference between the outer diameters of the first photosensitive drum and the second photosensitive drum is within 2 mm. For the outer diameters of the first developing roller and the second developing roller to be considered substantially the same, it is preferable that the variation in their respective outer diameters is ±1 mm, that is, that the difference between the outer diameters of the first developing roller and the second developing roller is within 2 mm.

[0034] The transfer unit 40c includes an intermediate transfer belt 41 as a second intermediate transfer belt, primary transfer rollers 42K, 42C, 42M, 42Y, a drive roller 46 for driving the intermediate transfer belt 41, and a tension roller (driven roller) 47. The first intermediate transfer belt in the first image forming apparatus and the second intermediate transfer belt in the second image forming apparatus 1c have the same configuration (parts and materials). Therefore, the second intermediate transfer belt is also referred to as the intermediate transfer belt 41, as described above. Thus, the first intermediate transfer belt and the second intermediate transfer belt have the same configuration, and at least their circumferences are substantially the same, and preferably their materials are also substantially the same. However, errors in circumference may occur due to manufacturing variations. The range in which the circumferences of the first intermediate transfer belt and the second intermediate transfer belt can be said to be substantially the same is preferably a range of variation of ±5 mm in their respective circumferences, that is, a difference of 10 mm or less between the circumferences of the first intermediate transfer belt and the circumference of the second intermediate transfer belt.

[0035] The image forming operation of the second image forming apparatus 1c is basically the same as that of the first image forming apparatus 1m, but differs in that the toner images of each color are superimposed on the intermediate transfer belt 41 and then transferred to the sheet S in the secondary transfer section. That is, in the case of the second image forming apparatus 1c, the primary transfer rollers 42K, 42C, 42M, and 42Y sequentially transfer the toner images of each color from the photosensitive drums 61, each provided according to the color, to the intermediate transfer belt 41, so that the toner images of each color are superimposed. Then, with the toner images of each color superimposed, they are transferred to the sheet S by the secondary transfer roller 45, which acts as the second recording material transfer means. The subsequent operation is the same as in the case of the first image forming apparatus 1m. Note that the first recording material transfer means in the first image forming apparatus 1m and the second recording material transfer means in the second image forming apparatus 1c have the same configuration (parts and materials). Therefore, the second recording material transfer means is also referred to as the "secondary transfer roller (recording material transfer roller) 45," as described above, just like the first recording material transfer means. Thus, the first recording material transfer means and the second recording material transfer means have a common configuration, and at least their outer diameters are substantially the same, and preferably their materials are also substantially the same. However, errors in the outer diameter may occur due to manufacturing variations. The range in which the outer diameters of the first recording material transfer roller and the second recording material transfer roller can be said to be substantially the same is preferably a variation range of ±1 mm in their respective outer diameters, that is, a difference of 2 mm or less between the outer diameters of the first recording material transfer roller and the second recording material transfer roller.

[0036] In the full-color transfer unit 40c, a high voltage is supplied from a high-voltage power supply board, a printed circuit board (not shown), to the primary transfer rollers 42K, 42C, 42M, and 42Y in order to transfer the toner image from the photosensitive drum 61 to the intermediate transfer belt 41. The same voltage is applied to each of the primary transfer rollers for full color, and the toner image is transferred from each of the photosensitive drums 61 to the intermediate transfer belt 41.

[0037] Here, the rotation axis of the photosensitive drum 61K, the rotation axis of the primary transfer roller 42K, the rotation axis of the drive roller 46, and the rotation axis of the tension roller 47 are defined as the axes of rotation axis 61Kc, rotation axis 42Kc, rotation axis 46c, and rotation axis 47c, respectively.

[0038] Viewed in the direction of the rotation axis 61Kc, the positional relationship between at least one of the primary transfer roller 42K, the drive roller 46, and the tension roller 47 and the photosensitive drum 61K is substantially the same in the first image forming apparatus 1m and the second image forming apparatus 1c.

[0039] In other words, in the first image forming apparatus 1m, the rotation axis 42Kc is located at a predetermined coordinate position with respect to the rotation axis 61Kc in both the horizontal and vertical directions when viewed in the direction of the rotation axis 61Kc. On the other hand, in the second image forming apparatus 1c, a portion of the primary transfer roller 42K is located at the same predetermined coordinate position with respect to the rotation axis 61Kc in both the horizontal and vertical directions when viewed in the direction of the rotation axis 61Kc. More preferably, in the second image forming apparatus 1c, the rotation axis 42Kc is located at the same predetermined coordinate position with respect to the rotation axis 61Kc in both the horizontal and vertical directions when viewed in the direction of the rotation axis 61Kc.

[0040] Similarly, in the first image forming apparatus 1m, when viewed in the direction of the rotation axis 61Kc, the horizontal and vertical directions Regarding direction, the rotation axis 46c is located at a predetermined coordinate position with respect to the rotation axis 61Kc. On the other hand, in the second image forming apparatus 1c, with regard to the direction of the rotation axis 61Kc, a portion of the drive roller 46 is located at the predetermined coordinate position with respect to the rotation axis 61Kc in both the horizontal and vertical directions. More preferably, in the second image forming apparatus 1c, with regard to the direction of the rotation axis 61Kc, the rotation axis 46c is located at the predetermined coordinate position with respect to the rotation axis 61Kc in both the horizontal and vertical directions.

[0041] Similarly, in the first image forming apparatus 1m, the axis of the rotation axis 47c is located at a predetermined coordinate position with respect to the rotation axis 61Kc, both horizontally and vertically, when viewed in the direction of the rotation axis 61Kc. On the other hand, in the second image forming apparatus 1c, a portion of the tension roller 47 is located at the same predetermined coordinate position with respect to the rotation axis 61Kc, both horizontally and vertically, when viewed in the direction of the rotation axis 61Kc. More preferably, in the second image forming apparatus 1c, the axis of the rotation axis 47c is located at the same predetermined coordinate position with respect to the rotation axis 61Kc, both horizontally and vertically, when viewed in the direction of the rotation axis 61Kc.

[0042] In the second image forming apparatus 1c, cartridge PK is positioned closer to the secondary transfer roller 45 in the direction of movement of the intermediate transfer belt 41 (belt circumference direction) compared to cartridges PY, PM, and PC. That is, in the belt circumference direction, the distance from cartridge PK to the secondary transfer roller 45 is shorter than the distance from each of the cartridges PY, PM, and PC to the secondary transfer roller 45. Therefore, the distance from the photosensitive drum 61K to the secondary transfer roller 45 is shorter than the distance from each of the photosensitive drums 61Y, 61M, and 61C to the secondary transfer roller 45. This reduces the variation in the position of the toner image formed on the intermediate transfer belt 41 by cartridge PK on the sheet S. The position of cartridge PK (position of photosensitive drum 61K) relative to the secondary transfer roller 45 in the first image forming apparatus 1m is substantially the same as the position of cartridge PK (position of photosensitive drum 61K) relative to the secondary transfer roller 45 in the second image forming apparatus 1c. Therefore, even in the first image forming apparatus 1m, the variation in the position of the toner image formed on the intermediate transfer belt 41 by the cartridge PK on the sheet S can be reduced.

[0043] In the second image forming apparatus 1c, cartridge PK is positioned further from the fuser 80 compared to cartridges PY, PM, and PC. That is, the distance from cartridge PK to the fuser 80 is longer than the distance from each of the cartridges PY, PM, and PC to the fuser 80. Therefore, the distance from the photosensitive drum 61K to the fuser 80 is longer than the distance from each of the photosensitive drums 61Y, 61M, and 61C to the fuser 80. As a result, cartridge PK is less susceptible to the thermal influence of the fuser 80, which acts as a heat source. The position of cartridge PK relative to the fuser 80 (position of photosensitive drum 61K) in the first image forming apparatus 1m is substantially the same as the position of cartridge PK relative to the fuser 80 (position of photosensitive drum 61K) in the second image forming apparatus 1c. Therefore, even in the first image forming apparatus 1m, cartridge PK is less susceptible to the thermal influence of the fuser 80, which acts as a heat source.

[0044] Referring to Figure 8, the full-color optical sensor unit 44 will be described. In this optical sensor unit 44, most of the components, such as the stay member 44c, sensor stay 44e, and cable 44d, are common to the monochrome optical sensor unit 44m. The full-color optical sensor 44a preferably has a diffuse reflection light receiving element 44k and a specular reflection light receiving element 44h. In other words, the monochrome optical sensor 44a may have fewer detectable light components (diffuse reflection component, specular reflection component) than the full-color optical sensor 44a. In addition to the optical sensor 44a, the full-color optical sensor unit 44 has a full-color optical sensor 44b installed at a position corresponding to the center in the width direction of the intermediate transfer belt 41. The full-color optical sensor 44b is described in Figure 5. The full-color optical sensor 44b is configured to include a light-emitting element 44n and a diffuse reflection light-receiving element 44k. Based on the information obtained from this full-color optical sensor 44b, the control unit 3c can control the alignment and density adjustment of the color toner image formed on the intermediate transfer belt 41. In other words, the full-color optical sensor 44b is configured to detect the position and density of the color toner image formed on the intermediate transfer belt 41. The other end of the cable 44d, which was not used in the monochrome sensor unit 44m, is also connected to the circuit board of the full-color optical sensor 44b, allowing it to send the detected output signal to the control unit 3c.

[0045] The control unit 3c, like the control unit 3m, can also detect the circumference of the intermediate transfer belt 41. Specifically, the control unit 3c extracts the estimated times t1, t2, t3… when the intermediate transfer belt 41 has completed one rotation, and performs calculations to determine the time required for the intermediate transfer belt 41 to complete one rotation. This allows the circumference of one rotation of the belt to be measured from the rotation speed of the intermediate transfer belt 41 at the time of sampling.

[0046] From the circumference measured in this way, the circumferential distance on the intermediate transfer belt 41 from the primary transfer roller 42K to the secondary transfer roller 45 can be predicted with high accuracy. Based on this distance, the timing of the secondary transfer by the secondary transfer roller 45 can be controlled. Therefore, variations in the position of the toner image transferred from the intermediate transfer belt 41 to the sheet S can be reduced.

[0047] As described above, in this embodiment, the circumference of the intermediate transfer belt 41 is measured by the light received information obtained from the reflected light of the intermediate transfer belt 41 against the substrate. The control unit 3c can also determine whether or not the intermediate transfer belt 41 is attached to the device body 1A based on the light received information obtained by the specular reflection light receiving element 44h. That is, if the light received information obtained by the specular reflection light receiving element 44h is abnormal, it can be determined that the intermediate transfer belt 41 is not attached to the device body 1A. In this way, if the control unit 3c determines that the intermediate transfer belt 41 is not attached to the device body 1A, it can prevent forgetting to attach the intermediate transfer belt 41 by notifying the outside with sound, light, etc.

[0048] Viewed in the direction of the rotation axis 61Kc, the positional relationship between the photosensitive drum 61K and the optical sensor unit 44m in the first image forming apparatus 1m is substantially the same as the positional relationship between the photosensitive drum 61K and the optical sensor unit 44 in the second image forming apparatus 1c.

[0049] In other words, in the first image forming apparatus 1m, a portion of the optical sensor unit 44m is positioned at a predetermined coordinate position with respect to the rotation axis 61Kc, both horizontally and vertically, when viewed in the direction of the rotation axis 61Kc. On the other hand, in the second image forming apparatus 1c, a portion of the optical sensor unit 44 is positioned at the same predetermined coordinate position with respect to the rotation axis 61Kc, both horizontally and vertically, when viewed in the direction of the rotation axis 61Kc.

[0050] In the second image forming apparatus 1c, cartridge PK is positioned closer to the optical sensor unit 44 in the direction of movement of the intermediate transfer belt 41 (belt circumference direction) compared to cartridges PY, PM, and PC. That is, in the belt circumference direction, the distance from cartridge PK to the optical sensor unit 44 is shorter than the distance from each of the cartridges PY, PM, and PC to the optical sensor unit 44. Therefore, the distance from the photosensitive drum 61K to the optical sensor unit 44 is shorter than the distance from each of the photosensitive drums 61Y, 61M, and 61C to the optical sensor unit 44. As a result, the toner image formed on the intermediate transfer belt 41 by cartridge PK can be detected earlier by the optical sensor unit 44. The position of cartridge PK (position of photosensitive drum 61K) relative to the optical sensor unit 44m in the first image forming apparatus 1m is substantially the same as the position of cartridge PK (position of photosensitive drum 61K) relative to the optical sensor unit 44 in the second image forming apparatus 1c. Therefore, even in the first image forming apparatus 1m, the toner image formed on the intermediate transfer belt 41 by the cartridge PK can be quickly detected by the optical sensor unit 44.

[0051] Furthermore, the image forming system according to this embodiment satisfies the following dimensional relationship. That is, in the first image forming apparatus 1m, L1 is the distance in the direction of movement of the intermediate transfer belt 41 from the primary transfer section from the first photosensitive drum (photosensitive drum 61K) to the first intermediate transfer belt (intermediate transfer belt 41) to the secondary transfer section by the first recording material transfer means (secondary transfer roller 45). Then, in the second image forming apparatus 1c, L2 is the distance in the direction of movement of the intermediate transfer belt 41 from the primary transfer section from the adjacent color photosensitive drum (photosensitive drum 61C), which is closest to the second photosensitive drum (photosensitive drum 61K) among the multiple color photosensitive drums, to the second intermediate transfer belt (intermediate transfer belt 41) to the secondary transfer section by the second recording material transfer means (secondary transfer roller 45). Thus, L1 is configured to be shorter than L2. By adopting such a configuration, even in the first image forming apparatus 1m which has an intermediate transfer belt 41 and uses a single photosensitive drum, the variation in the position of the toner image on the sheet S can be reduced.

[0052] Furthermore, the first image forming apparatus 1m is equipped with a fixing device 80 as a first fixing means for fixing the second-transferred developer image (toner image) onto a recording material (sheet S). Similarly, the second image forming apparatus 1c is equipped with a fixing device 80 as a second fixing means for fixing the second-transferred toner image onto the sheet S. Note that the first fixing means and the second fixing means have a common configuration, and the second fixing means in the second image forming apparatus 1c is also referred to as the fixing device 80. In the first image forming apparatus 1m, the straight-line distance from the first photosensitive drum (photosensitive drum 61K) to the fixing device 80 is defined as L3. In the second image forming apparatus 1c, the straight-line distance from the second photosensitive drum (photosensitive drum 61K) to the fixing device 80 is defined as L4, and the straight-line distance from the multiple color photosensitive drums (photosensitive drums 61C, 61M, 61Y) to the fixing device 80 is defined as L5. Although there are multiple color photosensitive drums, L5 can be considered as the straight-line distance between any of these photosensitive drums and the fuser 80. Then, L3 = L4 and L3 > L5 are satisfied. Note that errors due to dimensional tolerances are permissible for L3 = L4. By adopting this configuration, even in the first image forming apparatus 1m which has an intermediate transfer belt 41 and uses a single photosensitive drum, the photosensitive drum 61K is not significantly affected by the fuser 80, which is a heat source, and thus the variation in the position of the toner image on the sheet S can be reduced.

[0053] (Example 2) Figures 9 and 10 show Embodiment 2 of the present invention. Embodiment 1 showed a configuration in which the circumference of the first intermediate transfer belt is measured by light reception information obtained from reflected light from the substrate of the intermediate transfer belt. In contrast, this embodiment shows a configuration in which the intermediate transfer belt is provided with a mark for circumference measurement, and the light reception information obtained by the light receiving element includes information obtained from reflected light from the mark. The other configurations and operations are the same as in Embodiment 1, so the same reference numerals are used for the same components, and their descriptions are omitted as appropriate.

[0054] Referring to Figure 9, the monochrome transfer unit 140m according to Example 2 will be described. Figure 9 is a perspective view of the monochrome transfer unit and optical sensor unit according to Example 2. In Example 2, of the first and second image forming apparatuses that constitute the image forming system, the configuration of the second image forming apparatus is the same as in Example 1. Furthermore, in the first image forming apparatus, the configuration other than the monochrome transfer unit 140m is substantially the same as in Example 1.

[0055] <Intermediate transfer belt and optical sensor unit for monochrome> This section explains the positional relationship between the monochrome intermediate transfer belt 41 and the optical sensor unit 44m. The configuration of the optical sensor unit 44m is as described in Example 1. In this embodiment, a patch 41w is installed as a marker for circumference measurement at at least one end (one end in the width direction) outside the image forming area on the outer surface of the intermediate transfer belt 41. Since the patch 41w is provided outside the image forming area, it is not contaminated by toner images, and the risk of false detection can be prevented.

[0056] The patch surface is made of a material that reflects light from the light-emitting element of the optical sensor unit 44m, and for example, white tape can be used. Furthermore, the patch 41w may be installed in only one location on the circumferential direction of the belt, or multiple patches may be installed at equal intervals depending on the required circumference detection accuracy. In this embodiment, three or more patches are installed. In the optical sensor unit 44m, the optical sensor 44a is installed at a position corresponding to the width direction of the patch 41w.

[0057] <Circumference measurement using optical sensors> Figure 10 is a schematic diagram showing an example of the output of a monochrome optical sensor according to this embodiment. The vertical axis represents the voltage value output from the specular reflection photodetector 44h, and the horizontal axis represents the sampling time. By rotating the intermediate transfer belt 41 at a constant speed and sampling over multiple rotations, a rectangular wave as shown in the figure is detected each time a patch 41w provided on the belt surface passes the optical sensor 44a. The times t1, t2, t3... are the passage times of the patches 44w installed at equal intervals, and the control unit 3m can measure the circumference of one rotation of the belt by performing calculation processing.

[0058] In this embodiment, the markings provided on the outer surface of the intermediate transfer belt 41 are shown as patches attached to the belt surface. However, the markings are not limited to this example, and various detectable shapes and identification marks can be provided, such as patches printed on the belt surface or holes made in the belt. In this embodiment as well, the control unit 3m can also determine whether or not the intermediate transfer belt 41 is attached to the device body 1A based on the light information obtained by the specular reflection light receiving element 44h. That is, if the light information obtained by the specular reflection light receiving element 44h is abnormal, it can be determined that the intermediate transfer belt 41 is not attached to the device body 1A.

[0059] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention as described in the claims of the present invention.

[0060] This embodiment includes the following configuration.

[0061] (Composition 1) An image forming system comprising a first image forming apparatus for forming monochrome images and a second image forming apparatus for forming color images, The first image forming apparatus is The first photosensitive drum, A first developing means for developing the electrostatic latent image formed on the first photosensitive drum, A first intermediate transfer belt onto which the black developer image formed on the first photosensitive drum is transferred, A first recording material transfer means for secondarily transferring the developer image transferred to the first intermediate transfer belt to a recording material, Equipped with, The second image forming apparatus is The second photosensitive drum, Multiple color photosensitive drums, A second developing means for developing the electrostatic latent image formed on the second photosensitive drum, Multiple color developing means for developing the electrostatic latent images formed on the multiple color photosensitive drums, A second intermediate transfer belt onto which the black developer image formed on the second photosensitive drum and the developer images formed on the plurality of color photosensitive drums are transferred, A second recording material transfer means for secondarily transferring the developer image transferred to the second intermediate transfer belt to a recording material, Equipped with, The first intermediate transfer belt and the second intermediate transfer belt have a common configuration. The first image forming apparatus is equipped with measuring means for measuring the circumference of the first intermediate transfer belt, and the first image forming apparatus is equipped with a control unit that controls the secondary transfer timing by the first recording material transfer means based on the circumference obtained from the information obtained from the measuring means.

[0062] (Configuration 2) The aforementioned measuring means is The device comprises a light-emitting element that irradiates light toward the surface of the first intermediate transfer belt, and a light-receiving element that receives reflected light from the surface of the first intermediate transfer belt, The image forming system according to configuration 1, characterized in that the circumference of the first intermediate transfer belt is measured by the light-receiving information obtained by the light-receiving element.

[0063] (Composition 3) The image forming system according to configuration 2, characterized in that the circumference of the first intermediate transfer belt is measured by the light reception information obtained from the reflected light from the substrate of the first intermediate transfer belt.

[0064] (Composition 4) The image forming system according to configuration 2, characterized in that the first intermediate transfer belt is provided with a mark for circumference measurement, and the light-receiving information obtained by the light-receiving element includes information obtained from the reflected light from the mark.

[0065] (Composition 5) The image forming system according to configuration 2, 3, or 4, characterized in that it is determined whether or not the first intermediate transfer belt is attached to the main body of the apparatus based on the light-receiving information obtained by the light-receiving element.

[0066] (Composition 6) The image forming system according to any one of configurations 2 to 5, characterized in that the light-emitting element and the light-receiving element are supported by a support member supported on the rotation axis of a roller that contacts the inner circumferential surface of the first intermediate transfer belt.

[0067] (Composition 7) An image forming system according to any one of configurations 1 to 6, characterized in that the distance in the direction of movement of the first intermediate transfer belt from the primary transfer section from the first photosensitive drum to the first intermediate transfer belt to the secondary transfer section by the first recording material transfer means is shorter than the distance in the direction of movement of the second intermediate transfer belt from the primary transfer section from the adjacent color photosensitive drum closest to the second photosensitive drum among the plurality of color photosensitive drums to the second intermediate transfer belt to the secondary transfer section by the second recording material transfer means.

[0068] (Composition 8) The first image forming apparatus fixes the second-transferred developer image onto the recording material. Equipped with means of attachment, The second image forming apparatus includes a second fixing means for fixing the secondary transferred developer image onto the recording material, The image forming system according to any one of configurations 1 to 7, characterized in that the straight-line distance from the first photosensitive drum to the first fixing means is equal to the straight-line distance from the second photosensitive drum to the second fixing means, and is longer than the straight-line distance from the plurality of color photosensitive drums to the second fixing means. [Explanation of Symbols]

[0069] 1m: First image forming apparatus 1c: Second image forming apparatus 3m, 3m: Control unit 40m, 40c: Transfer unit 41: Intermediate transfer belt 42C, 42K, 42M, 42Y: Primary transfer roller 44: Optical sensor unit 44a: Optical sensor 45: Secondary transfer roller 61K, 61C, 61M, 61Y: Photosensitive drum 71K, 71C, 71M, 71Y: Developing roller 80: Fixing device

Claims

1. An image forming system comprising a first image forming apparatus for forming monochrome images and a second image forming apparatus for forming color images, The first image forming apparatus is The first photosensitive drum, A first developing means for developing the electrostatic latent image formed on the first photosensitive drum, A first intermediate transfer belt onto which the black developer image formed on the first photosensitive drum is transferred, A first recording material transfer means for secondarily transferring the developer image transferred to the first intermediate transfer belt to a recording material, Equipped with, The second image forming apparatus is The second photosensitive drum, Multiple color photosensitive drums, A second developing means for developing the electrostatic latent image formed on the second photosensitive drum, Multiple color developing means for developing the electrostatic latent images formed on the multiple color photosensitive drums, A second intermediate transfer belt onto which the black developer image formed on the second photosensitive drum and the developer images formed on the plurality of color photosensitive drums are transferred, A second recording material transfer means for secondarily transferring the developer image transferred to the second intermediate transfer belt to a recording material, Equipped with, The first intermediate transfer belt and the second intermediate transfer belt have a common configuration. The first image forming apparatus is equipped with measuring means for measuring the circumference of the first intermediate transfer belt, and has a control unit that controls the secondary transfer timing by the first recording material transfer means based on the circumference obtained from the information obtained from the measuring means.

2. The aforementioned measuring means is The device comprises a light-emitting element that irradiates light toward the surface of the first intermediate transfer belt, and a light-receiving element that receives reflected light from the surface of the first intermediate transfer belt, The image forming system according to claim 1, characterized in that the circumference of the first intermediate transfer belt is measured by the light-receiving information obtained by the light-receiving element.

3. The image forming system according to claim 2, characterized in that the circumference of the first intermediate transfer belt is measured by the light reception information obtained from the reflected light from the substrate of the first intermediate transfer belt.

4. The image forming system according to claim 2, characterized in that the first intermediate transfer belt is provided with markings for circumference measurement, and the light-receiving information obtained by the light-receiving element includes information obtained from the reflected light from the markings.

5. The image forming system according to claim 2, characterized in that it is determined whether or not the first intermediate transfer belt is attached to the main body of the apparatus based on the light-receiving information obtained by the light-receiving element.

6. The image forming system according to claim 2, characterized in that the light-emitting element and the light-receiving element are supported by a support member supported on the rotation axis of a roller that is in contact with the inner circumferential surface of the first intermediate transfer belt.

7. The image forming system according to any one of claims 1 to 6, characterized in that the distance in the direction of movement of the first intermediate transfer belt from the primary transfer section from the first photosensitive drum to the first intermediate transfer belt to the secondary transfer section by the first recording material transfer means is shorter than the distance in the direction of movement of the second intermediate transfer belt from the primary transfer section from the adjacent color photosensitive drum closest to the second photosensitive drum among the plurality of color photosensitive drums to the second intermediate transfer belt to the secondary transfer section by the second recording material transfer means.

8. The first image forming apparatus includes a first fixing means for fixing the secondarily transferred developer image onto the recording material, The second image forming apparatus includes a second fixing means for fixing the secondary transferred developer image onto the recording material, The image forming system according to any one of claims 1 to 6, characterized in that the straight-line distance from the first photosensitive drum to the first fixing means is equal to the straight-line distance from the second photosensitive drum to the second fixing means and is longer than the straight-line distance from the plurality of color photosensitive drums to the second fixing means.

Images