JP2006039268A - Image forming apparatus - Google Patents

Abstract

In an image forming apparatus, a positional shift in which the amount of positional shift is not constant but gradually shifts is prevented.
A rotating photosensitive member 1 on which a single color image of different colors to be overlaid is written by a writing unit 5; a developing unit 6 that develops an image on the rotating photosensitive member into a corresponding color toner image; In an image forming apparatus having a rotary transfer member 10 to which a toner image is transferred from the rotary photosensitive member 1, a rotational load on the rotary photosensitive member 1 and the rotary transfer member 10 during an image forming process in a predetermined color When there is a difference from the color image forming process, the image writing magnification of the monochromatic image written on the rotating photosensitive member 1 by the writing unit 5 in the image forming process is changed according to the difference in rotational load.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus that multiplexly forms a plurality of color images as a single color image, and more particularly to a technique for reducing color misregistration caused by misregistration between a plurality of superimposed images.

  In recent years, in image forming apparatuses such as copying machines, printers, and facsimiles that output multicolor images, as the number of images that can be output increases, from the viewpoint of image forming timing accuracy, Since the load fluctuation of the secondary transfer unit cannot be ignored, a design that fully considers the situation is required.

  FIG. 1 is a schematic cross-sectional view showing an example of the overall configuration of a color image forming apparatus. In this exemplary apparatus, the photosensitive member 1 serving as a flexible belt-like image carrier is a rotating photosensitive member that carries an electrostatic latent image formed by laser writing and a developed toner image. The photosensitive belt 1 is laid between the rotating rollers 2, 31, 32, and the belt surface becomes an image forming surface. By the rotational driving of the rotating roller 2, which is a driving roller, the photosensitive belt 1 is rotated in the direction indicated by the arrow A (clockwise). ) Is rotated (sub-scanned).

  As means for forming an electrostatic latent image and a toner image on the photosensitive belt 1, a charging charger 4 for uniformly charging the surface of the photosensitive belt 1, a laser writing unit 5, a color developing device 6a, 6b, 6c, 6d. The color developing devices 6a, 6b, 6c, and 6d are composed of developing units for magenta, cyan, yellow, and black, which are color constituent colors. The developing unit used here includes means for developing with a one-component developer (toner).

  In addition, this exemplary apparatus is based on a system in which an image on the photosensitive belt 1 is formed on a transfer sheet via an intermediate transfer member, and has an intermediate transfer belt 10 as a rotary transfer member. The intermediate transfer belt 10 is installed between the rotation rollers 11 and 12, and is rotated in the arrow B direction (counterclockwise direction) in the drawing by the rotation drive of the rotation roller (medium transfer drive roller) 11. The photosensitive belt 1 and the intermediate transfer belt 10 are in contact with each other at a portion where the rotation roller 32 of the photosensitive belt 1 is provided. On the intermediate transfer belt 10 side of the contact portion, a conductive bias roller 13 is in contact with the back surface of the intermediate transfer belt 10 under predetermined conditions.

  A mark 102 for alignment of the intermediate transfer belt 10 is provided on the back surface 102 ′ of the intermediate transfer belt 10, and a detection means (medium transfer belt mark sensor) 101 for detecting this mark is provided. Based on this mark detection, the image writing signal is controlled.

  The illustrated apparatus includes, as components related to the processing of transfer paper, a paper feed unit composed of a paper feed table (paper feed cassette) 17, a paper feed roller 18, transport roller pairs 19a and 19b, and resist roller pairs 20a and 20b, and an intermediate The image forming apparatus includes a transfer roller 14 for transferring an image from the transfer belt 10, a fixing device 80, paper discharge roller pairs 81 a and 81 b, and a paper discharge stack unit 82.

  Here, the image forming operation of the color image forming apparatus of the embodiment shown in FIG. 1 will be briefly described. In FIG. 1, a photosensitive belt 1 as a flexible belt-like image carrier is uniformly charged by a charging charger 4 and then light emission is controlled by a laser writing unit 5 based on image information. As a result of this scanning exposure, an electrostatic latent image is formed on the surface.

  Image information used in one step (one image forming step) of scanning exposure while rotating the photoreceptor belt 1 to form an electrostatic latent image is obtained by converting a desired full-color image into magenta, cyan, yellow, and black color information. This is monochromatic image information obtained by decomposition, and the light emission of the semiconductor laser is controlled based on this information. The generated laser beam is scanned and optical path adjusted by an optical device including a polygon mirror, and output as writing beam light L. The electrostatic latent image writing magnification in the laser writing unit is determined depending on the moving speed (linear speed) of the photosensitive belt 1 and the deflection speed (rotational speed) of the polygon mirror.

  The writing timing of each color is controlled by a signal obtained by detecting the mark provided on the intermediate transfer belt by the detecting means 101, and the electrostatic latent images formed based on single-color image information are color developing devices 6a, 6b, 6c. , 6d, the corresponding magenta (M), cyan (C), yellow (Y), and black (Bk) toners are respectively developed in a single color, and the respective color images are sequentially formed on the photosensitive belt 1.

  Each monochrome image of M, C, Y, Bk formed on the photosensitive belt 1 rotating in the direction of arrow A in FIG. 1 is biased on the intermediate transfer belt 10 rotating in the direction of arrow B in FIG. The images are sequentially superimposed and transferred by the action of a predetermined transfer bias applied to the roller 13.

  The images of M, C, Y, and Bk superimposed on the intermediate transfer belt 10 pass from the paper feed table (paper feed cassette) 17 through the paper feed roller 18, the transport roller pair 19a, 19b, and the registration roller pair 20a, 20b. The transfer roller 14 collectively transfers the transfer paper 17a conveyed to the transfer unit. After the transfer is completed, the image on the transfer paper 17a is fixed by the fixing device 80 to complete a full-color image, and the print image is discharged to the paper discharge stack unit 82 through the paper discharge roller pair 81a and 81b.

  Note that the toner on the photosensitive belt 1 is cleaned as the final step of image formation on the photosensitive belt 1 in FIG. For this purpose, a cleaning blade 15 that is always in contact with the surface of the photoreceptor belt 1 is provided. Similarly, a cleaning device 16 is provided on the intermediate transfer belt 10 so as to be able to contact and separate. The cleaning brush 16a of the cleaning device 16 is held at a position separated from the surface of the intermediate transfer belt 10 during the image forming operation, and after the formed image is transferred onto the transfer paper 17a, it is brought into contact with the surface of the intermediate transfer belt 10. The The photosensitive belt 1, the charger 4, the intermediate transfer belt 10, the cleaning blade 15, and the cleaning device 16 can be integrated into a process cartridge that can be attached to and detached from the main body.

  Next, the control system of the color image forming apparatus shown in FIG. 1 will be described. FIG. 2 is a schematic block diagram showing an example of the control system of this color image forming apparatus. As shown in FIG. 2, the control system includes a main control unit 201 and a plurality of peripheral control units. The main control unit 201 includes a CPU 202 as a constituent element, a ROM 203 that stores a control program and various data, a RAM 204 that temporarily stores various data as a work area, parameters for determining operating conditions of the apparatus, and information necessary for managing the apparatus NVRAM 209 which is a non-volatile memory for storing. The main control unit 201 supervises the overall operations related to image formation outlined above.

  The main control unit 201 also connects a laser optical system control unit 206, a development bias control unit 207, a toner adhesion amount sensor 100, a photoconductor / transfer belt drive control unit 208, and the like via an I / O interface 205. The laser optical system control unit 206 controls the laser writing unit 5, and the development bias control unit 207 controls the development bias applied to each of the color development devices 6 a, 6 b, 6 c, 6 d, and photoreceptor / transfer belt drive control. The unit 208 controls the rotation of the photosensitive belt 1 and the intermediate transfer belt 10. These control operations are all performed according to commands from the CPU 202.

  The toner adhesion amount sensor 100 detects the adhesion amount of the toner formed on the photosensitive belt 1 under predetermined conditions, and the CPU 202 that receives the detection data obtains an adjustment value of a developing bias described later from the toner adhesion amount. Then, it is set in the developing bias controller 207 to control the toner density.

  FIG. 3 shows a timing chart of image formation. A BK latent image is written at the writing position on the photosensitive belt 1, and a BK toner image is formed on the photosensitive belt 1 by the BK developing unit 6 d, and the intermediate transfer belt 10 is formed at the primary transfer position P. Primary transfer. This series of operations is repeated for each of the colors M, C, and Y, and after the fourth color Y is transferred, the color image is secondarily transferred to the transfer paper at the nip N, and the transfer residual toner is cleaned by the velcro 15. The flow up to is illustrated.

  In the first image formation in FIG. 3, while the BK toner image is primarily transferred, the cleaning unit 16 (hereinafter also abbreviated as “velk”) is in contact with the intermediate transfer belt 10, and M , C, and Y, the bell clip 16 is separated.

  When the bell clip 16 is in contact with the intermediate transfer belt 10, the linear speed of the intermediate transfer belt 10 is slower than when the belt 16 is separated. This is because the belt extends due to the contact load of the belt 16 or the elastic layer of the intermediate transfer roller 11 that drives the intermediate transfer belt 10 is crushed, and the diameter of the intermediate transfer roller becomes small. This occurs due to a slight slip between the roller 11 and the intermediate transfer belt 10 and insufficient torque of the drive system that drives the intermediate transfer belt 10.

  Compared to the M, C, and Y intermediate transfer belt linear speeds that do not have a Berkley contact load during the primary transfer, the BK intermediate transfer belt linear speeds that have the Berkley contact load during the primary transfer are slower. As a result, the BK is misaligned with respect to M, C, and Y on the intermediate transfer belt.

  For example, when the four colors are overlaid as in the image forming apparatus described above, the cleaning unit comes into contact with the intermediate transfer belt while the first color is transferred from the photoconductor to the intermediate transfer belt, and the cleaning units are separated from the second color and thereafter. If such a configuration is included, the linear velocity of the intermediate transfer belt for the first color becomes slower than the linear velocity for the second and subsequent colors due to the contact load of the cleaning unit. As a result, if the linear velocity for the second and subsequent colors is considered to be constant, the first color image appears as a phenomenon (gradual deviation) from the leading end to the trailing end with respect to the second and subsequent color images. This is a very unfavorable position shift state.

  In other words, when the load change is performed at the timing between non-image formation, even if a positional deviation occurs, the movement direction is only shifted in parallel with the other colors, so that the compensated color matches the other colors. It is only necessary to shift the writing timing, and the color overlay accuracy can be maintained with high accuracy relatively easily (see, for example, Patent Document 1).

  However, as described above, when the color gradually shifts by one color, the trailing edge is shifted even if the leading edge of the paper is aligned, and the leading edge is shifted even if the trailing edge is aligned. Is possible. In particular, in an image such as a halftone image, since the amount of color misregistration is different in one image, the positional misalignment is conspicuous and the color appears to change, resulting in a more serious problem.

  In order to make it easy to explain the misalignment, the intermediate transfer belt during the primary transfer of the M, C, and Y toner images is set to V1, where the linear speed of the intermediate transfer belt during the primary transfer of the BK toner image is V1. If the linear velocity of V2 is V2, V1 <V2. When the speeds V1 and V2 are assumed to be constant, a toner image (tentatively a caterpillar image) on the intermediate transfer belt primarily transferred from the photosensitive belt 1 is shown in an explanatory diagram of FIG. Assuming that the length interval in the belt movement direction of each linear image constituting the caterpillar image is L, the linear image by BK is the linear image by BK, whereas the linear image by M, C, Y is written at an interval of 4L. When written at an interval of 3L, the positional deviation of the image of the other color on the basis of the BK linear image appears as a gradual deviation in which the deviation amount increases toward the rear end of the image. In FIG. 4, since the four colors are matched at the front end (upper end in the figure), the amount of deviation increases as it goes to the rear end. The amount will increase.

  Incidentally, a measure for reducing the drive load fluctuation itself of the endless belt mechanism has been generally adopted. For example, Patent Document 2 discloses a technique for reducing the drive load fluctuation of an endless belt such as an image forming apparatus. ing.

JP-A-11-212328 JP 2001-355893 A

  As described above, in the image forming apparatus, it is difficult to adjust the positional shift with respect to a phenomenon in which the amount of positional shift is not constant but gradually shifts, and the respective colors cannot be matched exactly. Accordingly, the present invention has been made in view of the circumstances as described above, and an object thereof is to prevent the above-described misalignment in the image forming apparatus as described above.

  The image forming apparatus of the present invention includes a rotating photosensitive member on which a single color image of different colors to be overwritten is written by a writing unit, a developing unit that develops the image on the rotating photosensitive member into a toner image of a corresponding color, An image forming apparatus having a toner image transferred from the rotating photosensitive member, and a rotational load of the rotating photosensitive member and the rotating transfer member during an image forming process in a predetermined color is different from that in another color. When there is a difference from the time of the image forming process, the image writing magnification of the monochromatic image written on the rotating photosensitive member by the writing unit in the image forming process is changed according to the difference of the rotation load. As a result, by setting the magnification of the toner image on the intermediate transfer belt to be the same when there is a load on the intermediate transfer belt and when there is no load, it is possible to reduce misalignment.

  In an image forming apparatus that uses an intermediate transfer belt as a rotary transfer body and includes an intermediate transfer cleaning unit provided on the intermediate transfer belt and a transfer unit that transfers a toner image of the intermediate transfer belt to a transfer medium, a rotational load applied to the intermediate transfer belt The image writing magnification in the writing unit is changed in accordance with the size of.

  With this configuration, the load condition on the intermediate transfer belt is such that the load on the first sheet is only the load on the cleaning unit and the load on the second and subsequent sheets is on both the cleaning unit and the secondary transfer unit. Even if they are different from each other, the writing magnification is controlled independently, so that it is possible to reduce the positional deviation that gradually shifts similarly in the first and second sheets.

  Further, during the image forming process by increasing the rotational load of the intermediate transfer belt that functions the cleaning unit, the image writing magnification in the writing unit may be increased in the sub-scanning direction, and gradually shifts. Misalignment can be reduced.

  Further, the image forming apparatus further includes a linear velocity measuring unit that measures a linear velocity of the intermediate transfer belt that changes in accordance with a rotational load, and feeds back a measured value output from the linear velocity measuring unit to image writing magnification in the writing unit. It is also possible to further have a writing adjustment means for optimizing the above. In this way, by providing a feedback means for measuring the linear velocity when there is a load on the intermediate transfer belt at a certain timing (process control mode) and not, and adjusting the writing magnification so that both magnifications are the same. Further, it is possible to reduce the positional deviation that gradually shifts with respect to the change with time. Further, if this correction is performed for each image formation, it is possible to adjust the positional deviation with higher accuracy.

  In each of the above-described configurations, the image writing magnification can be changed in the sub-scanning direction by controlling the deflection speed of the polygon mirror constituting the writing unit.

  According to the present invention, it is possible to prevent a positional shift in which images of different colors that are overlaid in an image forming apparatus are gradually shifted. Further, the positional deviation can be reduced equally in the first output image and the second and subsequent images. Further, it is possible to reduce the positional deviation and adjust the positional deviation more accurately regardless of the change with time.

[First Embodiment]
Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. The overall configuration of the color image forming apparatus according to the first embodiment of the present invention will be described with reference to the schematic sectional view of FIG. The image forming apparatus according to the present embodiment is similar in configuration to that shown in FIG. 1, and only the control contents of the processor executed by the CPU are different.

  Since the details of the configuration of the image forming apparatus in FIG. 1 have already been described, description thereof will be omitted to avoid duplication. However, only a main part deeply related to the present invention will be described briefly. A charging charger 4, a laser writing unit 5, and color developing devices 6 a, 6 b, 6 c, and 6 d are arranged along the photosensitive belt 1 laid between the rotating rollers 2, 31, and 32. A cleaning blade 15 that is always in contact with the surface of the photosensitive belt 1 is provided.

  The photosensitive belt 1 is in contact with the intermediate transfer belt 10 that is an intermediate transfer member provided between the rotating rollers 11 and 12 at the primary transfer position P. A cleaning device 16 is detachably provided on the intermediate transfer belt 10.

  Hereinafter, the image forming operation of the color image forming apparatus shown in FIG. 1 will be described again. In FIG. 1, a photosensitive belt 1 as a flexible belt-like image carrier is uniformly charged by a charging charger 4 and then light emission is controlled by a laser writing unit 5 based on image information. As a result of this scanning exposure, an electrostatic latent image is formed on the surface. Image information used in one step of scanning exposure while rotating the photosensitive belt 1 to form an electrostatic latent image is monochromatic image information obtained by separating a desired full-color image into magenta, cyan, yellow, and black color information. Based on this information, the emission of the semiconductor laser is controlled. The generated laser beam is scanned and optical path adjusted by an optical device, and output as writing beam light L.

  The writing timing of each color is controlled by a signal that detects a mark provided on the intermediate transfer belt, and electrostatic latent images formed based on single-color image information are handled by the color developing devices 6a, 6b, 6c, and 6d. The magenta (M), cyan (C), yellow (Y), and black (Bk) toners are respectively developed in a single color, and the respective color images are sequentially formed on the photosensitive belt 1.

  Each monochrome image of M, C, Y, Bk formed on the photosensitive belt 1 rotating in the direction of arrow A in FIG. 1 is biased on the intermediate transfer belt 10 rotating in the direction of arrow B in FIG. The images are sequentially superimposed and transferred by the action of a predetermined transfer bias applied to the roller 13.

  The images of M, C, Y, and Bk superimposed on the intermediate transfer belt 10 pass from the paper feed table (paper feed cassette) 17 through the paper feed roller 18, the transport roller pair 19a, 19b, and the registration roller pair 20a, 20b. The transfer roller 14 collectively transfers the transfer paper 17a conveyed to the transfer unit. After the transfer is completed, the transfer paper 17a is fixed by the fixing device 80 to complete a full-color image, and the print image is discharged to the paper discharge stack section 82 through the paper discharge roller pair 81a and 81b.

  Note that the toner on the photosensitive belt 1 is cleaned as the final step of image formation on the photosensitive belt 1 in FIG. For this purpose, a cleaning blade 15 that is always in contact with the photosensitive belt 1 is provided. Similarly, the intermediate transfer belt 10 is also provided with a cleaning device 16. The cleaning brush 16a of the cleaning device 16 is held at a position separated from the surface of the intermediate transfer belt 10 during the image forming operation, and after the formed image is transferred onto the transfer paper 17a, it is brought into contact with the surface of the intermediate transfer belt 10. The Further, the photosensitive belt 1, the charging charger 4, the intermediate transfer belt 10, the cleaning blade 15, and the cleaning device 16 can be integrated so as to be detachable from the main body as a process cartridge.

  Next, the control system of the color image forming apparatus in this embodiment will be described. The control system of this color image forming apparatus may be structurally equivalent to that shown in the schematic block diagram of FIG. That is, the control system includes a main control unit 201 and a plurality of peripheral control units. Incidentally, this embodiment has a feature in the control of the polygon mirror in the laser writing unit, and part of the control contents of the laser writing unit 5 and the laser optical system control unit 206 and the main control unit 201 related to this are conventional. Is different.

  The main control unit 201 includes a CPU 202, a ROM 203 that stores control programs and various data, a RAM 204 that temporarily stores various data as a work area, a non-volatile storage that stores parameters for determining the operating conditions of the apparatus and information necessary for managing the apparatus. It has NVRAM 209 as a memory. The main control unit 201 supervises the entire operation related to image formation, and also, via an I / O interface 205, a laser optical system control unit 206, a developing bias control unit 207, a toner adhesion amount sensor 100, a photoreceptor / transferr. A belt drive control unit 208 and the like are connected.

  The laser optical system control unit 206 controls the laser writing unit 5, and the development bias control unit 207 controls the development bias applied to each of the color development devices 6 a, 6 b, 6 c, 6 d, and photoreceptor / transfer belt drive control. The unit 208 controls the rotation of the photosensitive belt 1 and the intermediate transfer belt 10. These control operations are all performed according to commands from the CPU 202.

  The toner adhesion amount sensor 100 detects the adhesion amount of the toner formed on the photosensitive belt 1 under predetermined conditions, and the CPU 202 that receives the detection data obtains an adjustment value of a developing bias described later from the toner adhesion amount. Then, it is set in the developing bias controller 207 to control the toner density.

  FIG. 3 shows a timing chart of image formation. A BK latent image is written at a writing position on the photosensitive member, and a BK toner image is formed on the photosensitive member by the BK developing unit, and is primarily transferred to the intermediate transfer belt at the primary transfer position. This operation is repeated with M, C, and Y, and the flow from the transfer of the fourth color Y to the transfer paper, the second transfer to the transfer paper, and the cleaning of the transfer residual toner by Velkuri is shown.

  The operation of this embodiment will be described by taking the case of first image formation in the timing chart of FIG. 3 as an example. In FIG. 3, processing proceeds from the left to the right in the figure. During the primary transfer of BK, the belt is in contact with the intermediate transfer belt, and the belt is separated in M, C, and Y.

  When the belt is in contact with the intermediate transfer belt, the linear speed of the intermediate transfer belt is slower than when the belt is separated. This is because the belt is stretched due to the contact load of Velkri or the elastic layer of the intermediate transfer drive roller that drives the intermediate transfer belt is crushed, so that the diameter of the intermediate transfer drive roller becomes small, and the intermediate transfer drive roller and the intermediate transfer roller This occurs due to a slight slip of the transfer belt, insufficient torque of the drive system for driving the intermediate transfer belt, and the like.

  As described above, with respect to a phenomenon in which the amount of positional deviation is not constant in each part and gradually shifts, it is impossible to precisely match each color by timing adjustment, and adjustment of positional deviation is difficult. In the present embodiment, it is possible to cope with the decrease in the linear velocity of the intermediate transfer belt, and compensate and reduce the gradually shifted positional deviation found in the conventional apparatus due to the linear velocity change.

If the intermediate transfer belt linear velocity during the image forming process of the image color that is primarily transferred when there is no Berkley load on the intermediate transfer belt is V _β ,
The length of the toner image transferred to the intermediate transfer belt 10 is V _β × t ₁ = L _β .

Here, 0 <t ₁ <t ₄
(T ₁ : Time from the start of primary transfer to one rotation of the intermediate transfer belt)
(T ₄ : Time required for one rotation of the intermediate belt)

When the intermediate transfer belt linear velocity during the image forming process of the image forming color BK that is primarily transferred when the intermediate transfer belt has a Berkri load is V _α , the length of the toner image transferred to the intermediate transfer belt 10 Is V _α × t ₁ = L _α .
When the linear velocity of the photosensitive member 1 and V _k, the length of the latent image written on the photosensitive member 1 becomes _{V k × t 1 = L k} .

When the toner image mounted on the latent image of the photoreceptor 1 is primarily transferred to the intermediate transfer belt 10 having a Berkley load on the intermediate transfer belt, the magnification reduced from the linear velocity difference is 1 / K.
L _k × K = L _α
| L _β -L _α | <100 μm
The polygon rotation speed of the writing unit is controlled so as to satisfy the following equation.

In other words, drop the rotational speed of the polygon in the writing unit, and the extended state the latent image on the photoreceptor by increasing the writing magnification, when contracted by the primary transfer to Chuten belt 10, equivalent to the L _beta To be. At this time, the modulation clock of the laser beam is controlled so that the magnification in the main scanning direction in the writing unit remains unchanged.
[Second Embodiment]

  Looking at the second image formation timing in FIG. 3, in addition to the Berkley contact load, a load of the secondary transfer roller is applied to the intermediate transfer belt during the secondary transfer. As described above, when the contact load on the intermediate transfer belt is different between the first image and the second and subsequent images, it is necessary to control the polygon rotation speed of the writing unit corresponding to each load condition. There is. A second embodiment suitable for such a case will be described below.

The operation of the image forming apparatus according to the second embodiment will be described with reference to the timing of the second image formation in the timing chart of FIG. When the intermediate transfer belt linear velocity of the image forming color that is primarily transferred when the intermediate transfer belt is not subjected to a Berkri load is V _β , the length of the toner image transferred to the intermediate transfer belt 10 is V _β × t ₁ = the L _β.

0 <t ₁ <t ₄ (t ₄ = time required for one rotation of the intermediate transfer belt)
When the intermediate transfer belt linear velocity of the primary transfer image color is V _α1 when the intermediate transfer belt has a Berkley load and a secondary transfer load, the length of the toner image transferred to the intermediate transfer belt 10 is
V _α1 × t ₂ = L _α1 .
(T ₂ : Time from the start of primary transfer until the secondary transfer load disappears)

When the intermediate transfer belt linear velocity of the image forming color that is primarily transferred when the intermediate transfer belt has only a Berkri load is V _α2 , the length of the toner image transferred to the intermediate transfer belt 10 is
V _α2 × t ₃ = L _α2 .
(T ₃ : Time from the disappearance of the secondary transfer load to the disappearance of the Berkley load)
When the linear velocity of the photoreceptor 1 is V _k , the length of the latent image written on the photoreceptor 1 is
The _{V k1 × t 2 = L k1} , V k2 × t 3 = L k2.

When the toner image mounted on the latent image on the photosensitive member 1 is primarily transferred to the intermediate transfer belt 10 having the Berkley load and the secondary transfer load on the intermediate transfer belt, the magnification reduced by the linear velocity difference is 1 /. K ₁ ,
When the toner image mounted on the latent image on the photoreceptor 1 is primarily transferred to the intermediate transfer belt 10 having a Berkley load on the intermediate transfer belt, the magnification reduced from the linear velocity difference is 1 / K ₂ ,
L _k1 × K ₁ = L _α1
L _k2 × K ₂ = L _α2
| L _β − (L _α1 + L _α2 ) | <100 μm
The polygon rotation speed of the writing unit is controlled so as to satisfy the following equation. .

[Third Embodiment]
The linear speed of the intermediate transfer belt changes due to various influences such as load fluctuations on the intermediate transfer belt. For example, (a) the brush of the cleaning unit has fallen or hastened, (b) when the blade is attached, the load decreases due to wear of the tip, (c) the change in the elongation of the intermediate transfer belt over time, (d ) When a lubricant such as Mars is applied to the intermediate transfer belt, the linear velocity of the intermediate transfer belt changes due to various factors such as a change in μ on the intermediate transfer belt due to the degree of lubricant application.

  A third embodiment for dealing with such a linear speed fluctuation / change of the intermediate transfer belt will be described. In the third embodiment, a feedback means for measuring the linear velocity when there is a load on the intermediate transfer belt at a certain timing and adjusting the writing magnification so that the magnifications of both are the same (process control mode) To have.

  The mark detection unit 101 detects the mark 102 of the intermediate transfer belt 10 and performs writing timing control. Based on the mark count (detection timing) by the mark detection unit 101, a calculation unit that does not explicitly indicate (for example, When the linear velocity of the intermediate transfer belt or the time of one rotation of the intermediate transfer belt is calculated by the CPU, and the conditional expressions shown in the first embodiment and the second embodiment are not satisfied, The polygon rotation speed of the writing unit is corrected so as to satisfy the conditional expression.

  The operation of the image forming apparatus according to this embodiment will be described with reference to the flowchart of FIG. 5 (intermediate transfer belt linear velocity correction). During the image forming operation, the mark detection unit 101 detects the mark 102 on the intermediate transfer belt 10 as the intermediate transfer belt rotates (step; S01: YES), and the detection timing of the detected mark 102 (detection output pulse of the detection output pulse). The current linear velocity of the intermediate transfer belt 10 is calculated from the time difference (rising, etc.) (S02). Subsequently, it is determined whether or not the calculated linear velocity and the set writing magnification satisfy the above-described conditional expression (S03).

  If the conditional expression is satisfied (step; S03: YES), the setting value for writing magnification control is not corrected (S04). On the other hand, if the conditional expression is not satisfied (step; 03: NO), the setting value of the writing magnification control is corrected (S05), and then the process returns to step; S03 and the determination is repeated again. At the time of image writing, the image is written by controlling the polygon rotation speed in accordance with the currently set writing magnification.

  As described above, in the present exemplary embodiment, the intermediate transfer belt mark 102, the mark detection unit 101, and the calculation unit, which serve as feedback units, are caused by variations in the linear speed of the intermediate transfer belt and its drive system or changes over time. This can be reduced even with respect to a positional shift that gradually shifts. Further, this correction may be performed for each image formation, and in this way, a more accurate adjustment is possible. A configuration in which the writing magnification is corrected a plurality of times during one image formation is also conceivable.

1 is a schematic sectional view of an overall configuration of a color image forming apparatus according to the present invention. FIG. 2 is a schematic block diagram illustrating an example of a control system of the color image forming apparatus in FIG. 1. 3 is an image forming timing chart in a color image forming apparatus. FIG. 6 is an explanatory diagram of gradual misregistration taking a toner image on an intermediate transfer belt as an example. 5 is a flowchart of intermediate transfer belt linear velocity correction.

Explanation of symbols

1 ... photosensitive belt (rotating photoconductor)
2 ... photosensitive belt drive roller 32 ... rotating roller 4 ... charger charger 5 ... laser writing units 6a, 6b, 6c, 6d ... color developing device (developing means)
10: Intermediate transfer belt (rotary transfer member)
12 ... Intermediate transfer driving roller 13 ... Bias roller 16 ... Cleaning device (Berkuri)
17 ... Paper tray (paper cassette)
17a ... transfer paper 80 ... fixing device 82 ... paper discharge stack unit 100 ... toner adhesion amount sensor 101 ... intermediate transfer belt mark sensor 102 ... intermediate transfer belt mark 201 ... main control unit 202 ... CPU
203 ... ROM
204 ... RAM
205... I / O interface 207... Development bias controller 209.

Claims (5)

A rotating photoconductor in which single-color images of different colors to be overlaid are written by a writing unit, developing means for developing the image on the rotating photoconductor into a corresponding color toner image, and a toner image from the rotating photoconductor In an image forming apparatus having a rotary transfer body to be transferred,
When the rotational load of the rotating photosensitive member and the rotating transfer member during the image forming process with a predetermined color is different from that during the image forming process with another color, the rotational photosensitive member is used in the writing unit in the image forming process. An image forming apparatus characterized by changing an image writing magnification of a monochrome image written on a body in accordance with a difference in rotational load.   An intermediate transfer belt as the rotary transfer member, an intermediate transfer cleaning unit provided for the intermediate transfer belt, and a transfer unit for transferring a toner image of the intermediate transfer belt to a transfer medium, The image forming apparatus according to claim 1, wherein the image writing magnification is changed in accordance with the magnitude of a rotational load applied to the intermediate transfer belt.   3. The image writing magnification in the writing unit is increased in the sub-scanning direction during an image forming process by increasing the rotational load of the intermediate transfer belt that functions the cleaning unit. Image forming apparatus.   It further has a linear velocity measuring means for measuring the linear velocity of the intermediate transfer belt that changes according to the rotational load, and feedback of the measured value output from the linear velocity measuring means to optimize the image writing magnification in the writing unit. The image forming apparatus according to claim 2, further comprising a writing adjustment unit configured to convert the image forming unit into the image forming unit. The image forming apparatus according to claim 1, wherein the image writing magnification is changed by controlling a deflection speed of a polygon mirror constituting the writing unit.

Images