JP2013025302A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep an image forming pitch in a sub-scan direction of an image carrier uniform, even after shifting from normal image formation to image reduction formation is performed and to maintain an excellent image by preventing moire, etc. when changing magnification.SOLUTION: An image forming apparatus includes: an operation and display part 48 to which the setting of a single-sided printing mode or a double-sided printing mode is inputted; and a controller 90 selecting a normal writing mode, according to the single-sided printing mode set in the operation and display part 48 or the normal writing mode and a small variable power mode, according to the double-sided printing mode set in the operation and display part 48, to control the rotations of an intermediate transfer belt 6, a photoreceptor drum 1Y, and a polygon mirror 9Y. When executing the small variable power mode, the rotational speeds of the photoreceptor drum 1Y and the polygon mirror 9Y are changed according to a variable power ratio, in such a state that the rotational speed of the intermediate transfer belt 6 in the normal writing mode is maintained as it is and the photoreceptor drum 1Y after the speed of the photoreceptor drum 1Y is changed is scanned with a plurality of laser beams, to write an image.

Description

  This invention is capable of setting a single-sided printing mode and a double-sided printing mode, and is capable of writing an image in a micro-magnification mode when executing the double-sided printing mode. The present invention relates to an image forming apparatus and an image forming method suitable for application to the above.

  In recent years, color printers that form color images based on image information, color copiers that have a scanning function that reads an image of an original and outputs an image signal for color image reproduction, and multifunction devices are used. More and more cases. For example, digital color copying machines that read color originals to acquire red (R), green (G), and blue (B) image data and form color images based on the image data are widely used. .

  In this type of color copying machine, an electrophotographic image forming unit is provided. In the image forming unit, RGB image data is color-converted into YMCK-based image data, and the color-converted yellow (Y) color, A color toner image is formed based on image data for magenta (M), cyan (C), and black (BK). The image forming unit includes image forming units that share Y, M, C, and BK image forming output functions, and image data is applied to a photosensitive drum that is uniformly charged by the charging unit for each image forming color. Based on the above, an electrostatic latent image is formed by an optical writing unit using a polygon mirror or the like.

  The electrostatic latent image is developed by a developing device for each image forming color. The color toner image formed on the photosensitive drum after being charged, exposed and developed in this manner is superimposed on the intermediate transfer member, and the superimposed color toner image is transferred onto the paper by the transfer unit. The sheet is transported from the sheet feeding tray to the transfer section by the sheet feeding section. The toner image transferred onto a predetermined sheet is fixed by the fixing unit. As a result, a color image based on the image data can be formed on a predetermined sheet.

  There is also used an image forming apparatus that can set a single-sided printing mode and a double-sided printing mode, and that can write an image in a minute scaling mode when the double-sided printing mode is executed. Image writing in the micro scaling mode is a technique for minutely changing the image magnification on the front and back of the paper during image formation. This technology is adopted regardless of color machines and monochrome machines, and can ensure image position accuracy even if the paper after fixing shrinks.

In general, according to a color tandem and high-quality monochrome machine using an intermediate transfer member, basically the following three methods can be considered for changing the magnification in the sub-scanning direction.
(1) The speed of the intermediate transfer member is changed without changing the exposure density (the speed of the polygon motor). (2) The exposure density is changed without changing the speed of the intermediate transfer member.
(3) The magnification of the image data is changed by image processing without changing the speed of the image forming system.

  Note that the magnification does not change when both the exposure density and the speed of the intermediate transfer member are changed. Of these methods, the method (1) is difficult to ensure productivity because the exposure of the next page image cannot be started until the transfer of the previous page image (toner image) to the paper is completed. Further, although the method (3) does not cause a decrease in productivity, it is inevitable that the image quality deteriorates in principle. Therefore, according to the conventional image forming apparatus, the method (2) is adopted in order to minimize the deterioration of the image quality and the decrease of the productivity.

  According to the micro-magnification mode employing the method (2), the intermediate transfer member, the photosensitive drum, and the polygon mirror are rotated at a predetermined rotational speed, and a predetermined laser beam is scanned onto the photosensitive drum. When the writing operation is in the normal writing mode, the intermediate transfer member and the photosensitive drum in the normal writing mode are used when an image is formed on one side of the paper and the paper is reversed to form an image on the other side. In this state, the rotation speed of the polygon mirror is changed according to the image reduction ratio, and the image is written by scanning the laser beam on the photosensitive drum.

  On the other hand, recently, for the purpose of high resolution and high productivity, a multi-beam has been adopted in the optical writing unit to realize uniform exposure resolution and image magnification. Multi-beam exposure scanning has a technical feature in that images are simultaneously written on a plurality of lines by scanning one surface of a polygon mirror.

  An optical system lens is formed so that the image forming pitch in the sub-scanning direction of the multi-beam LDi (i = 1 to n: n is the number of beams) corresponding to scanning on one surface of the polygon mirror is imaged on the photosensitive drum. By adjusting the focal point, etc., the state is within a predetermined error range with respect to the reference pitch. For example, the image formation pitch is about 21.21 μm at a resolution of 1200 dpi.

  In this state, when exposure scanning is performed by operating the polygon mirror and the photosensitive drum at a reference speed, the multi-beams LD1 to LD8 are simultaneously exposed by scanning one surface of the polygon mirror. Each image forming pitch in one scan is a predetermined value adjusted. That is, the image formation pitch between the multi-beam LDn on the first surface of the polygon mirror and the multi-beam LD1 on the second surface is similarly within a predetermined error range with respect to the reference pitch. .

  As described above, during normal (non-magnification: standard magnification), the multi-beam LDn by scanning the first surface of the polygon mirror and the multi-beam by scanning the second surface of the photosensitive drum rotating at the reference speed. The image forming pitch of LD1 is also set to have a similar value. This setting determines the resolution and magnification of the apparatus, and is a standard apparatus setting state (standard conditions).

  FIG. 7A to FIG. 7F are explanatory diagrams illustrating examples of image writing at the time of normal (non-magnification) and reduction (micro-magnification) according to a conventional example. In this example, the multi-beam LDi (i = 1 to n) is composed of n = 8 laser beam lights, and the image forming pitch of the eight laser beam lights is uniformly adjusted.

  A white circle of 8 columns × 10 rows shown in FIG. 7A is an 8-beam scanning image when an image is formed on one side of the paper in the double-sided printing mode. In this example, by one deflection scanning of the multi-beams LD1 to LD8 by one surface of the polygon mirror, white circles of 8 columns in the sub-scanning direction of the photosensitive drum and 10 rows in the main scanning direction are formed. In this 8-beam scanned image, eight multi-beams LD1 to LD8 are simultaneously scanned (1 Index) on the photosensitive drum through the first surface of the polygon mirror, and the electrostatic latent image formed on the photosensitive drum is The developed image is transferred and formed on the intermediate transfer member.

  8B × 10 rows of black triangular marks shown in FIG. 7B indicate that eight multi-beams LD1 to LD8 are simultaneously scanned (1Index) on the photosensitive drum through the second surface of the polygon mirror, and the photosensitive drum The electrostatic latent image formed in the above is developed, and the developed image is transferred to the intermediate transfer member. In FIG. 7C, 8 columns × 10 rows of X marks indicate that eight multi-beams LD1 to LD8 are simultaneously scanned (1Index) on the photosensitive drum through the third surface of the polygon mirror, The formed electrostatic latent image is developed, and the developed image is transferred to the intermediate transfer member.

  The white circles of 8 columns × 10 rows shown in FIG. 7D are 8-beam scanning reduced images when an image is formed on the back side of the recording paper on which one side of the image is formed in the double-sided printing mode. When the micro-magnification mode is set for the white circled 8-beam scanning reduced image, the rotation speed of the intermediate transfer member and the rotation speed of the photosensitive drum are maintained as they are, and only the rotation speed of the polygon mirror is changed. It is changed according to the setting. The 8-beam scanning reduced image is obtained by scanning the photosensitive drum with eight multi-beams LD1 to LD8 all at once (1Index) through the first surface of the polygon mirror, and forming an electrostatic latent image formed on the photosensitive drum. Is developed, and the developed image is transferred to an intermediate transfer member to be formed.

  The black triangles of 8 columns × 10 rows shown in FIG. 7E indicate that the eight multi-beams LD1 to LD8 are simultaneously scanned onto the photosensitive drum through the second surface of the polygon mirror (1Index) in the minute magnification mode. The electrostatic latent image formed on the photosensitive drum is developed, and the reduced image after development is transferred to the intermediate transfer member. In FIG. 7F, 8 columns × 10 rows of X marks indicate that the eight multi-beams LD1 to LD8 are simultaneously scanned on the photosensitive drum through the third surface of the polygon mirror 9Y (1Index) in the minute magnification mode. The electrostatic latent image formed on the photosensitive drum is developed, and the reduced image after development is transferred to the intermediate transfer member.

  Note that, regarding the above-described minute zoom mode, according to the image forming apparatus disclosed in Patent Document 1, when shifting from image formation on one side of the recording paper to image formation on the other side, the pixel clock signal And the frequency of the polygon clock signal are changed. When the image forming apparatus is configured in this way, the image sizes of the front and back sides can be matched.

  Further, according to the image forming apparatus disclosed in Patent Document 2, when the change rate of the image formation adjustment magnification is compared with a threshold value, and the change rate of the image formation adjustment magnification is smaller than the threshold value, The polygon drive clock is adjusted so that the PLL lock is not released. When the image forming apparatus is configured in this manner, the PLL lock of the PLL circuit and the synchronization of the polygon motor do not go out of synchronization, so that the stabilization time of the polygon motor can be shortened, and the recording paper is transferred from the intermediate transfer body of the image being formed. Even before the transfer to is completed, the exposure of the next page can be started for each color. For this reason, productivity is not reduced.

  Regarding the optical writing unit using the above-described polygon mirror or the like, according to the scanning optical system disclosed in Patent Document 3, one lens is added to change the magnification of the entire scanning optical system, and this lens is moved. I tried to do it. When the scanning optical system is configured in this way, the distance between the light beams on the scanning target surface can be adjusted despite the minimum number of lenses added.

  Regarding the multi-beam, the image forming apparatus disclosed in Patent Document 4 includes an optical element driving unit and a plurality of beam generating units. When changing the pitch of a plurality of scan lines on the photosensitive member, an optical element is provided. The element driving means moves or rotates at least one of the plurality of optical elements arranged on the optical axis. If the image forming apparatus is configured in this way, the pitch of a plurality of scan lines by a multi-beam can be easily and accurately adjusted with a simple configuration. In addition, the adjusted pitch can always be accurately maintained.

JP 2003-262991 A JP 2006-201566 A JP 2004-109347 A JP 09-090332 A

  By the way, a high-resolution and high-speed optical writing unit is configured using the image reduction technology as seen in Patent Literatures 1 and 2 and the multi-beam technology as seen in Patent Literatures 3 and 4, and the paper shrinks. When trying to manufacture an image forming apparatus that changes the minute magnification of the combined images, there are the following problems.

  When the image forming apparatus shown in Patent Documents 1 to 4 is combined with the reduction / magnification mode of the method (2) and the polygon mirror (polygon motor) is shifted to change the exposure density, FIG. 7D and FIG. As shown in 7E, an 8-beam scanning reduced image is formed in which the white circle mark by the multi-beam LD8 and the black triangle mark by the multi-beam LD1 (between 1 index) are bound. Similarly, as shown in FIGS. 7E and 7F, a beam scanning reduced image is formed in which the black triangle mark by the multi-beam LD8 and the x mark by the multi-beam LD1 (1 index) are bound. The bound portion of the reduced beam scanning image causes image deterioration such as moire (image defect).

  The image forming pitch of the multi-beams LD1 to LD8 in one scan shown in FIGS. 7A to 7C is the same as that in normal (non-magnification: standard condition), and is a polygon mirror with respect to a photosensitive drum rotating at a reference speed. Only the image forming pitch of the multi-beam LDn on the first surface and the multi-beam LD1 on the second surface changes. The amount of change in the image formation pitch at that time is a value obtained by multiplying the normal image formation pitch by n times the number of beams. The normal image formation pitch is about 21.21 μm.

  For example, in the case of a resolution of 1200 [dpi] and multi-beam LDi (i = 1 to 8), if the polygon motor rotation speed is changed by 1%, 21.21 μm × 8 = 16% 1% (1.69 μm) ) Between the white circle mark by the multibeam LD8 and the black triangle mark by the multibeam LD1 (between 1 index), between the black triangle mark by the multibeam LD8 and the x mark by the multibeam LD1 (between 1 index), etc. Will change.

  As a result, the image formation pitch (exposure pitch) changes every 8 lines depending on the scanning cycle of the multi-beams LD1 to LD8. Moire or the like occurs due to interference with the screen when the amount of change in the image formation pitch between 1 index exceeds a predetermined value. There is a problem that image degradation such as moire occurs due to interference between the periodic pitch fluctuation and the screen.

  It is known that when one pixel is set to 20 μm, screen interference occurs when the amount of change in the image formation pitch between 1 index changes to about 5 to 6 μm, which is about ¼, and screen interference causes image degradation. The impact is great. It is also known that screen interference corresponds to about 30% of moire generation factors.

  Accordingly, the present invention solves the above-described problems, and after devising the speed control method in the image carrier, the intermediate transfer member, and the optical scanning, even after shifting from normal image formation to image reduction formation, Provided is an image forming apparatus and an image forming method that can maintain a uniform image formation pitch in the sub-scanning direction of an image carrier and can maintain a good image by preventing moire during a magnification change. The purpose is to do.

  In order to solve the above-described problem, an image forming apparatus according to claim 1 writes an image by simultaneously scanning a plurality of laser beam lights onto an image carrier through a polygon mirror rotator, and writing the image on the image carrier. An image forming apparatus that forms an electrostatic latent image, thereafter develops the electrostatic latent image, and transfers the developed image from an image carrier to an intermediate transfer member, and forms the image on a predetermined sheet material When the operation is set to the print mode and the image forming condition is a condition for forming an image on the sheet material in the print mode including the type of the sheet material, an operation unit for inputting the setting of the image forming condition, and a predetermined rotation speed Rotate the intermediate transfer member, the image carrier, and the polygon mirror rotator, scan the image carrier with a plurality of laser beam lights adjusted to a predetermined image formation pitch, and write an image as a normal writing mode. Normal of the intermediate transfer member The rotation speed of the image carrier and the rotation speed of the polygon mirror rotator are changed according to the image reduction ratio while maintaining the rotation speed in the recording mode as it is, and a plurality of the image carriers after the shift are transferred to the image carrier. When the operation of writing an image by scanning a laser beam is set to the reduced writing mode, the normal writing mode is selected corresponding to the image forming condition set by the operation unit, or the image forming condition is supported. And a control unit that controls the rotation of the intermediate transfer member, the image carrier, and the polygon mirror rotator by selecting the normal writing mode and the reduced writing mode.

  According to the image forming apparatus of the first aspect, a plurality of laser beam lights are simultaneously scanned on the image carrier through the polygon mirror rotator to write an image, and an electrostatic latent image is formed on the image carrier. Then, when the electrostatic latent image is developed and the developed image is transferred from the image carrier to the intermediate transfer member, the operation unit forms an image on the sheet material in the printing mode including the type of the sheet material. Enter the settings for the image forming conditions to be performed. The control unit selects the normal writing mode corresponding to the image forming conditions set by the operation unit, or selects the normal writing mode and the reduced writing mode corresponding to the image forming conditions to select the intermediate transfer member and the image carrier. The rotation of the body and the polygon mirror rotating body is controlled.

  By controlling the rotation of the intermediate transfer member, the image carrier, and the polygon mirror rotator, the rotation speed of the polygon mirror rotor and the rotation speed of the image carrier are maintained while maintaining the rotation speed of the intermediate transfer member in the normal writing mode. Can be changed at the same ratio, and the image forming pitch in the sub-scanning direction of the image carrier can be kept uniform even after shifting from normal image formation to image reduction formation.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the plurality of laser beam lights are simultaneously scanned on the image carrier through the polygon mirror rotating body to write an image, and the image carrier is electrostatically charged. An image forming unit is formed for forming a latent image, thereafter developing the electrostatic latent image, and transferring the developed image from the image carrier to the intermediate transfer member. The image forming unit is provided for each image forming color. A tandem color machine is constructed.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the rotational speed of the polygon mirror rotating body and the rotational speed of the image carrier are changed at the same ratio corresponding to an image reduction ratio. To do.

  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect, wherein when the rotational speed of the image carrier and the rotational speed of the polygon mirror rotational speed are changed according to the image reduction ratio, the image transfer apparatus is transferred to the intermediate transfer body. The adjustment of the rotational speed is started sequentially from the upstream side to the downstream side of the image forming color, and the change rate of the rotational speed corresponding to the image reduction rate is determined by the intermediate transfer member between the center points of the image carrier. It is characterized in that the time for traveling through the separation distance is set to be uniform.

  The image forming method according to claim 5, wherein a plurality of laser beam lights are simultaneously scanned on the image carrier through the polygon mirror rotator to write an image, thereby forming an electrostatic latent image on the image carrier, and thereafter , Developing the electrostatic latent image, and transferring the developed image from the image carrier to the intermediate transfer member to form an image, wherein the operation of forming an image on a predetermined sheet material is a printing mode, When the conditions for forming an image on the sheet material in the printing mode including the type of the sheet material are the image forming conditions, the setting of the image forming conditions is input, and the intermediate transfer body and the image carrier at a predetermined rotation speed. And an operation for writing an image by rotating the polygon mirror rotating body and scanning the image carrier with a plurality of laser beam lights adjusted to a predetermined image forming pitch, and a normal writing mode for the intermediate transfer body. The rotational speed of the hour In the maintained state, the rotational speed of the image carrier and the rotational speed of the polygon mirror rotator are decelerated in accordance with the image reduction ratio, and the image carrier after the deceleration is scanned with a plurality of laser beam lights to form an image. When the writing operation is the reduced writing mode, the normal writing mode is selected corresponding to the set image forming condition, or the normal writing mode and the reduced writing mode are set corresponding to the set image forming condition. Is selected and control is branched.

  According to the image forming apparatus according to claim 1 and the image forming method according to claim 5, in accordance with image forming conditions for forming an image on the sheet material in the printing mode including the type of the sheet material. A control unit that selects the normal writing mode or controls the rotation of the intermediate transfer member, the image carrier, and the polygon mirror rotating member by selecting the normal writing mode and the reduced writing mode corresponding to the image forming condition. It is.

  With this configuration, the rotation speed of the polygon mirror rotating body and the rotation speed of the image carrier can be changed at the same ratio in the reduction writing mode while maintaining the rotation speed of the intermediate transfer body in the normal writing mode. In addition, even after shifting from normal image formation to image reduction formation, the image forming pitch of the image carrier in the sub-scanning direction can be kept uniform. In addition, the rotational speed of the polygon mirror and the rotational speed of the image carrier change with respect to the state in which the rotational speed of the intermediate transfer body is maintained as it is. Thus, an image can be reduced and formed by changing the slip. Thereby, it is possible to prevent moire and the like when changing the magnification and maintain a good image.

  According to the image forming apparatus of the second aspect, the image forming unit is provided for each image forming color, and the image forming pitch of the image carrier for each image forming color can be maintained uniformly. In addition, the rotation speed of the polygon mirror and the rotation speed of the image carrier change with respect to the state where the rotation speed of the intermediate transfer body is maintained as it is, so that the image carrier and the intermediate transfer for each image forming color are changed. A minute slip is generated between the body and the slide, so that the color image can be reduced and formed.

  According to the image forming apparatus of claim 3, by changing the rotation speed of the polygon mirror and the rotation speed of the image carrier at the same ratio corresponding to the image reduction ratio, image formation of the image carrier is performed. The pitch can be kept uniform.

  According to the image forming apparatus of the fourth aspect, the adjustment of the rotational speed is started sequentially from the upstream side to the downstream side of the image forming color transferred to the intermediate transfer body, and the rotational speed change corresponding to the image reduction ratio is started. The rate is set so that the time for the intermediate transfer member to travel the separation distance between the center points of the image carrier is uniform, so that the image forming pitch of the image carrier can be kept uniform. In addition, the rotation speed of the image carrier and the rotation speed of the image carrier can be changed smoothly.

1 is a conceptual diagram illustrating a configuration example of a color copying machine 100 as an embodiment according to the present invention. 2 is a block diagram illustrating a configuration example of an image writing system of the color copying machine 100. FIG. (A)-(J) are the operation | movement time charts which show the motor control example of the image writing system as a 1st Example. (A)-(F) is explanatory drawing which shows the example of image writing at the time of normal (non-magnification) and reduction (micro magnification). (A)-(J) are the operation | movement time charts which show the motor control example of the image writing type | system | group as 2nd Example. 3 is a flowchart showing an example of control of the color copying machine 100 as an embodiment. (A)-(F) is explanatory drawing which shows the example of the image writing at the time of the normal (non-magnification) and reduction (micro magnification) concerning a prior art example.

  Hereinafter, an image forming apparatus and an image forming method according to embodiments of the present invention will be described with reference to the drawings. The description in this section does not limit the technical scope described in the claims, the meaning of terms, and the like.

  A color copying machine 100 shown in FIG. 1 constitutes an example of a tandem type electrophotographic image forming apparatus, and includes an image forming unit for each image forming color, and a plurality of laser beam lights (hereinafter referred to as a multi-beam LD). The image carrier is scanned simultaneously through the polygon mirrors of each image forming system, the image is written on the image carrier, an electrostatic latent image is formed for each image carrier, and then the electrostatic latent image is developed. In this apparatus, the developed image is transferred from the image carrier to the intermediate transfer member.

  The color copying machine 100 has an apparatus main body 101. The apparatus main body 101 includes an intermediate transfer belt 6, a fixing device 17, an operation & display unit 48, an image forming unit 60, a control device 90, and an image reading device 102.

  The image reading apparatus 102 is arranged on the upper part of the apparatus main body 101. A document placed on a document table is scanned and exposed by an optical system of a scanning dew apparatus, and an image is read by a line image sensor. The image information signal photoelectrically converted by the image reading device 102 is subjected to analog processing, analog / digital (hereinafter referred to as A / D) conversion processing, sudo correction, image compression processing, and the like in an image processing unit (not shown). Later, it is input to the optical writing unit of the image forming unit 60.

  The image forming unit 60 forms a toner image having a predetermined density on the intermediate transfer belt 6 that has a belt surface and is moved at a predetermined speed. The image forming unit 60 includes an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image forming unit that forms a cyan (C) image. A unit 10C and an image forming unit 10K that forms a black (K) image are configured. In this example, common function names, for example, Y, M, C, and K indicating colors to be formed are added to the back of the reference numeral 10.

  The image forming unit 10Y includes a photosensitive drum 1Y (image carrier), and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a cleaning unit 8Y are disposed around the photosensitive drum 1Y. The image forming unit 10M includes a photosensitive drum 1M, and a charging unit 2M, an optical writing unit 3M, a developing device 4M, and a cleaning unit 8M are disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charging unit 2C, an optical writing unit 3C, a developing device 4C, and a cleaning unit 8C are disposed around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, and a charging unit 2K, an optical writing unit 3K, a developing device 4K, and a cleaning unit 8K are disposed around the photosensitive drum 1K.

  Respective photosensitive drums 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, charging units 2Y, 2M, 2C, and 2K, optical writing units 3Y, 3M, 3C, and 3K, and developing devices 4Y and 4M , 4C, 4K and the cleaning units 8Y, 8M, 8C, 8K have the same contents. In the following description, Y, M, C, and K are not used unless particularly distinguished.

  In the image forming unit 10, the charging unit 2 charges the photosensitive drum 1. For the optical writing unit 3, for example, a polygon mirror type multi-beam exposure scanning apparatus is used. The optical writing unit 3 operates to scan multi-beams on the photosensitive drum 1 based on the image data for each image forming color and write information on a plurality of lines at a time. An electrostatic latent image is formed on the photosensitive drum 1 by a multi-beam scanned by a polygon mirror. The developing device 4 develops the electrostatic latent image. As a result, a toner image which is a visible image is formed on the photosensitive drum 1.

  In the image forming unit 60, yellow (Y) color, magenta (M) color, cyan (C) color, and the like are respectively added to the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units 10Y, 10M, 10C, and 10K. A black (K) color image is formed. The toner images of the respective colors formed on the respective photosensitive drums 1 are subjected to intermediate transfer by operating the primary transfer rollers 7Y, 7M, C, K corresponding to the photosensitive drums 1 for Y, M, C, and K colors. Transferred to the belt 6 (primary transfer).

  The intermediate transfer belt 6 constitutes an example of an intermediate transfer member, and has an endless belt. The toner images on the photosensitive drums 1Y, 1M, 1C, and 1K are transferred to the intermediate transfer belt 6. The intermediate transfer belt 6 is wound around a plurality of rollers and supported so as to be able to run. The color image formed on the intermediate transfer belt 6 is conveyed toward the secondary transfer portion 7A as the intermediate transfer belt 6 rotates clockwise. The secondary transfer unit 7 </ b> A is disposed below the image forming unit 60 and at the lowest position of the intermediate transfer belt 6.

  A paper transport unit 20 is provided below the image forming unit 60, and transports the paper P to the image forming unit 60. The paper transport unit 20 includes paper feed trays 291, 292, and 293, and stores paper P.

  The paper P is fed by the first paper feed unit 21 and conveyed to the secondary transfer unit 7A through the conveyance rollers 22A, 22B, 22C and the registration roller 23. The toner image on the intermediate transfer belt 6 is collectively transferred from the intermediate transfer belt 6 to the paper P by the secondary transfer portion 7A (secondary transfer).

  A fixing device 17 is provided on the downstream side of the secondary transfer portion 7A, and the paper P on which the color image is transferred is fixed. The recording sheet P ′ after the fixing process is discharged out of the apparatus through a fixing conveyance roller 24 and a discharge roller 25.

  The color copying machine 100 includes a paper reversing unit 26, and guides the recording sheet P ′ having been fixed from the fixing conveyance roller 24 to the paper reversing unit 26 in accordance with the setting of the single-sided printing mode or the double-sided printing mode. The front and back sides are reversed, and an image is formed on the reverse side (both sides of the paper P) of the discharge or recording paper P ′. Here, the single-sided printing mode refers to an operation of forming an image on one side of a predetermined paper P (sheet material). The duplex printing mode refers to an operation for forming images on both sides of the paper P.

  Below the left side of each of the photosensitive drums 1, cleaning units 8Y, 8M, 8C, and 8K are provided corresponding to the photosensitive drums 1 for Y, M, C, and K colors. It operates to remove (clean) the toner agent remaining in 1. A cleaning unit 8A is provided on the upper left side of the intermediate transfer belt 6 and operates to clean the toner agent remaining on the intermediate transfer belt 6 after the secondary transfer. Thus, the color copying machine 100 is configured.

  An image writing system of the color copying machine 100 shown in FIG. 2 includes photosensitive drums 1Y, 1M, 1C, and 1K, optical writing units 3Y, 3M, 3C, and 3K, an intermediate transfer belt 6, an operation & display unit 48, and a control device 90. It is comprised. The control device 90 has a semiconductor integrated circuit device (Application Specific Integrated Circuit: hereinafter referred to as ASIC 53) for generating timing.

  The optical writing unit 3Y includes a multi-beam generation source 5Y, a polygon mirror 9Y, and a polygon motor 11Y. The multi-beam generation source 5Y is arranged at a predetermined position in the optical writing unit 3Y, and generates a multi-beam LD having a predetermined intensity based on the image data Dy for Y color image formation. The multi-beam generation source 5Y is connected to the data buffer 52. The image data Dy is output from the data buffer 52 to the multi-beam generation source 5Y. A semiconductor laser light source is used as the multi-beam generation source 5Y.

  A polygon mirror 9Y is disposed on the optical axis of the multi-beam generation source 5Y. The polygon mirror 9Y has, for example, six mirror surfaces. The polygon mirror 9Y is connected to the polygon motor 11Y and rotated to reflect the multi-beam LD irradiated from the multi-beam generation source 5Y and scan it on the photosensitive drum 1Y. The polygon motor 11Y rotates the polygon mirror 9Y at a predetermined rotation speed. A polyphase induction motor is used for the polygon motor 11Y.

  Below the optical writing unit 3Y, optical writing units 3M, 3C, 3K are provided corresponding to the photosensitive drums 1 for M, C, K colors, and image data Dm, M, C, K color image data Dm, A multi-beam LD having a predetermined intensity is generated based on Dc and Dk, and the multi-beam LD is operated so as to be deflected and scanned.

  In the optical writing units 3M, 3C, and 3K, the multi-beam generation sources 5M, 5C, and 5K, and the polygon mirrors 9M, 9C, and 9K corresponding to the multi-beam generation source 5Y, the polygon mirror 9Y, and the polygon motor 11Y of the optical writing unit 3Y. For polygon motors 11M, 11C, and 11K, refer to Y replaced with M, C, and K.

  The polygon motor 11Y is connected to the rotation shaft of the polygon mirror 9Y. The polygon motor 11Y is connected to the ASIC 53, and rotates the polygon mirror 9Y at a predetermined rotational speed based on the speed command signal Vpy. The speed command signal Vpy is output from the ASIC 53 to the polygon motor 11Y.

  Polygon motors 11M, 12C, and 12K are connected to the rotation shafts of the other polygon mirrors 9M, 9C, and 9K corresponding to each. Each of the polygon motors 11M, 11C, and 11K is connected to the ASIC 53. The polygon motor 11M rotates the polygon mirror 9M at a predetermined rotation speed based on the speed command signal Vpm. The speed command signal Vpm is output from the ASIC 53 to the polygon motor 11M.

  The polygon motor 11C rotates the polygon mirror 9C at a predetermined rotation speed based on the speed command signal Vpc. The speed command signal Vpc is output from the ASIC 53 to the polygon motor 11C. The polygon motor 11K rotates the photosensitive drum 1K at a predetermined rotation speed based on the speed command signal Vk. The speed command signal Vk is output from the ASIC 53 to the polygon motor 11K. The rotational speed of the polygon mirror 9Y and the like is in units of tens of thousands [rpm].

  A drum motor 12Y is connected to the above-described photosensitive drum 1Y. The drum motor 12Y is connected to the rotating shaft of the photosensitive drum 1Y, for example. The drum motor 12Y is connected to the ASIC 53, and rotates the photosensitive drum 1Y at a predetermined rotation speed based on the speed command signal Vy. The speed command signal Vy is output from the ASIC 53 to the drum motor 12Y. Drum motors 12M, 12C, and 12K are connected to the rotation shafts of the other photosensitive drums 1M, 1C, and 1K, respectively.

  The drum motor 12M is connected to the ASIC 53, and rotates the photosensitive drum 1M at a predetermined rotation speed based on the speed command signal Vm. The speed command signal Vm is output from the ASIC 53 to the drum motor 12M. The drum motor 12C is connected to the ASIC 53, and rotates the photosensitive drum 1C at a predetermined rotation speed based on the speed command signal Vc. The speed command signal Vc is output from the ASIC 53 to the drum motor 12C. The drum motor 12K is connected to the ASIC 53, and rotates the photosensitive drum 1K at a predetermined rotation speed based on the speed command signal Vk. The speed command signal Vk is output from the ASIC 53 to the drum motor 12K. The rotational speed of the photosensitive drum 1Y and the like is in units of several thousand [rpm].

  A belt motor 13 is connected to a roller rotation shaft (not shown) of the intermediate transfer belt 6. The belt motor 13 is connected to the ASIC 53 and rotates the intermediate transfer belt 6 at a predetermined transport speed based on the speed command signal Vb. The speed command signal Vb is output from the ASIC 53 to the belt motor 13.

  Beam detection sensors 16Y, 16M, 16C, and 16K are arranged at positions that are separated from the beam exposure positions of the photosensitive drums 1Y, 1M, 1C, and 1K by a predetermined distance. The beam detection sensor 16Y detects the multi-beam LD and outputs a beam detection signal (index signal) to the control device 90. The other beam detection sensors 16M, 16C, and 16K also detect the multi-beam LD and output beam detection signals to the control device 90, respectively.

  A control device 90 is connected to the beam detection sensors 16Y, 16M, 16C, and 16K. The controller 90 rotates the polygon mirror 9Y and the like at a constant speed based on the beam detection signal (speed control). The control device 90 detects the phase difference between the rising edge of the Y-color beam detection signal (Y-Index) detected by the beam detection sensor 16Y and the rising edge of the divided clock signal and outputs this phase difference. Based on this, the phase of the clock signal is controlled.

  In addition to the ASIC 53, the control device 90 includes a clock generation unit 51, a data buffer 52, and a central processing unit (hereinafter referred to as CPU 55). The clock generator 51 is connected to each of the data buffer 52, the ASIC 53, and the CPU 55, and supplies a clock signal having a predetermined frequency (hereinafter referred to as a CLK signal) to these.

  The data buffer 52 temporarily holds image data Dy, Dm, Dc, Dk for each image forming color based on the CLK signal, and for each image forming color based on the image forming reference signal (hereinafter referred to as VTOP signal). Control is performed to read image data Dy, Dm, Dc, and Dk. A general purpose memory such as a RAM is used for the data buffer 52.

  The CPU 55 connected to the clock generation unit 51 has a function of switching an image reduction rate (hereinafter referred to as a scaling factor) of a print image. At the time of magnification switching, the CPU 55 changes the rotational speeds of the polygon mirrors 9Y, 9M, 9C, and 9K and the rotational speeds of the photosensitive drums 1Y, 1M, 1C, and 1K at the same ratio corresponding to the variable magnification, and the intermediate The ASIC 53 is controlled so as not to change the conveyance speed of the transfer belt 6.

Here, changing the rotation speed of the polygon mirror 9Y at the time of magnification switching and the rotation speed of the photosensitive drum 1Y at the same ratio corresponding to the variable magnification means the following contents. The rotation speed of the polygon mirror 9Y in the normal writing mode is set to VP1 [rpm], the scaling factor at the time of switching the magnification is set to several [%], the ratio is set to (1- scaling factor [%] / 100), When the rotational speed VP2 [rpm] of the polygon mirror 9Y is set, VP2 is expressed by the following equation (1), that is,
VP2 [rpm] = VP1 × (1−magnification [%] / 100) (1)
Ask from.

Similarly, when the rotation speed of the photosensitive drum 1Y in the normal writing mode is VD1 [rpm] and the rotation speed of the photosensitive drum 1Y after the magnification switching is VD2 [rpm], the same ratio (1-variable magnification). [%] / 100), VD2 can be expressed by equation (2):
VD2 [rpm] = VD1 × (1−variable magnification [%] / 100) (2)
Ask from.

  The rotation speed VP2 obtained here is set in the polygon motor 11Y via the speed command signal Vpy. Further, it means that the rotational speed VD2 is set in the drum motor 12Y via the speed command signal Vy.

  The operation & display unit 48 is connected to the CPU 55 described above. The operation & display unit 48 is operated to input the setting of image forming conditions. The image forming condition refers to a condition for forming an image on a sheet material in a predetermined printing mode including the type (paper type) of paper P and the weight (basis weight). The printing mode includes a single-sided printing mode and a double-sided printing mode. The image forming conditions include information for selecting the paper feed trays 291, 292 and 293. The paper types include plain paper, thick paper, thin paper, and coated paper. The mode setting information input by the operation & display unit 48 is output to the CPU 55 from the operation & display unit 48 as input operation data D14. The operation & display unit 48 includes a touch panel monitor (not shown), a keyboard with input keys, and the like.

  The CPU 55 selects the normal writing mode corresponding to the image forming conditions set by the operation & display unit 48, for example, the single-sided printing mode, or the normal writing mode and the reduced writing mode (hereinafter referred to as the double-sided printing mode). Is selected together with the program data D55 in the ASIC 53 so as to control the rotation of the intermediate transfer belt 6, the photosensitive drums 1Y, 1M, 1C, and 1K and the polygon mirrors 9Y, 9M, 9C, and 9K. Data Dw is output.

  The image forming conditions are not limited to the print mode, but may be selection information for the paper feed trays 291, 292, and 293. The normal writing mode can be selected according to the paper type, or the normal writing mode and the reduced writing mode can be selected according to the paper type. The setting data Dw is, for example, information for setting the normal writing mode in the ASIC 53 corresponding to the single-sided printing mode and setting the normal writing mode and the minute scaling mode in the ASIC 53 corresponding to the double-sided printing mode. Here, the normal writing mode means that the intermediate transfer belt 6, the photosensitive drums 1Y, 1M, 1C, and 1K and the polygon mirrors 9Y, 9M, 9C, and 9K are rotated at a predetermined rotational speed and adjusted to a predetermined image formation pitch. The multi-beam LD is scanned on the photosensitive drums 1Y, 1M, 1C, and 1K to write an image.

  The micro-magnification mode is a state in which the rotation speed of the intermediate transfer belt 6 in the normal writing mode is maintained as it is, and the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K and the polygon mirrors 9Y, 9M, 9C, and 9K. This is an operation of changing the rotation speed in accordance with the variable magnification, and writing an image by scanning the multi-beam LD on the photoconductor drums 1Y, 1M, 1C, and 1K after the speed change.

  The ASIC 53 controls the polygon motors 11Y, 11M, 11C, and 11K, the drum motors 12Y, 12M, 12C, and 12K, and the belt motor 13, respectively. In this example, the image forming pitch of the photosensitive drums 1Y, 1M, 1C, and 1K is changed by changing the rotational speed of the polygon mirror 9Y and the rotational speeds of the photosensitive drums 1Y, 1M, 1C, and 1K at the same magnification. It becomes possible to hold it uniformly.

  The ASIC 53 generates speed command signals Vy, Vm, Vc, Vk, Vpy, Vpm, Vpc, Vpk, Vb, a VTOP signal, and the like based on the CLK signal, signal creation program data D55, and setting data Dw. Program data D55, setting data Dw, and the like are output from the CPU 55 to the ASIC 53. The contents of the program data D55 are programmed, for example, the duty ratio for dividing or multiplying the CLK signal to create a signal with a predetermined pulse width, the timing for latching the signal with the predetermined pulse width, and the output timing Is.

  With reference to FIGS. 3A to 3J, an example of motor control of an image writing system as the first embodiment will be described. In this example, it is assumed that the duplex printing mode is executed by the convection circulation method. Here, the convection circulation method means that when the double-sided printing mode is executed, the number of sheets (N sheets) is not formed on the back surface of the recording sheet P ′ on which the image is formed on the front surface (one surface) of the paper P without forming an image following the front surface. The recording paper P ′ on which the image is continuously formed on the surface (one side) of the paper P stays in the paper conveyance path in the apparatus main body 101, the paper reversing unit 26, etc. (convection circulation), and the paper When the recording paper P ′ staying (convection circulation) in the conveyance path, the paper reversing section 26, etc. reaches a specified number (hereinafter referred to as the convection circulation number Nr), it continuously follows the back surface of the recording paper P ′. An operation for forming an image.

  The pulse waveform shown in FIG. 3A is an image forming reference signal (hereinafter referred to as VTOP signal). T1, T2, etc. in the figure are periods connecting the high level pulses of the VTOP signal, and indicate the image forming period of one side of one sheet P. The image forming period T1 when the writing mode is switched is set to be longer than the image forming period T2 on one side of one sheet P.

  A speed command signal Vpy shown in FIG. 3B is a signal for driving the polygon motor 11Y. In the figure, side 1 image of satin is a period in which a Y color image is formed on the surface of the nth sheet P in the normal writing mode, and the polygon mirror 9Y is driven at a rotation speed based on the speed command signal Vpy. It is a period to do. A portion surrounded by the parallelogram is a period during which the polygon mirror 9Y is subjected to speed change / phase control when the magnification is switched, that is, when the normal writing mode is shifted to the minute magnification changing mode.

  The side2 image formation is a period in which a Y color image is formed on the back surface of the first sheet P after the normal writing mode is switched to the minute magnification mode, and a speed command signal Vpy obtained by calculating the magnification ratio. This is a period during which the polygon mirror 9Y is driven at a rotational speed based on the above. The side2 image formation following the above-described side2 image formation is also a period in which a Y color image is formed on the back surface of the second sheet P, and the polygon mirror 9Y is rotated at the rotation speed based on the speed command signal Vpy corrected with the variable magnification. This is a period for driving.

  A speed command signal Vpm shown in FIG. 3C is a signal for driving the polygon motor 11M. In the drawing, side 1 image formation in the shaded area is a period in which an M color image is formed on the surface of the nth sheet P in the normal writing mode, and the polygon mirror 9M is rotated at the rotation speed based on the speed command signal Vpm. This is the drive period. The portion surrounded by the parallelogram is a period during which the polygon mirror 9M is subjected to speed change / phase control when the normal writing mode is shifted to the minute magnification changing mode.

  The side2 image formation is a period in which an M color image is formed on the back surface of the first sheet P after the normal writing mode is switched to the minute magnification mode, and a speed command signal Vpm obtained by calculating the magnification ratio. This is a period during which the polygon mirror 9M is driven at a rotational speed based on the above. The side2 image formation following the above-described side2 image formation is also a period during which an M color image is formed on the back surface of the second sheet P, and the polygon mirror 9M is rotated at the rotation speed based on the speed command signal Vpm corrected with the variable magnification. This is a period for driving.

  A speed command signal Vpc shown in FIG. 3D is a signal for driving the polygon motor 11C. In the figure, side 1 image formation on the cross hatch area is a period during which a C color image is formed on the surface of the nth sheet P in the normal writing mode, and the polygon mirror 9C is rotated at a rotation speed based on the speed command signal Vpc. This is a period for driving. A portion surrounded by the parallelogram is a period during which the polygon mirror 9C is subjected to speed change / phase control when the normal writing mode is shifted to the minute magnification changing mode.

  The side2 image formation is a period in which a C color image is formed on the back surface of the first sheet P after switching from the normal writing mode to the micro-magnification mode, and a speed command signal Vpc obtained by calculating the magnification ratio. This is a period during which the polygon mirror 9C is driven at a rotational speed based on the above. The side2 image formation following the above-described side2 image formation is also a period during which a C color image is formed on the back surface of the second sheet P, and the polygon mirror 9C is rotated at the rotation speed based on the speed command signal Vpc corrected with the variable magnification. This is a period for driving.

  A speed command signal Vpk shown in FIG. 3E is a signal for driving the polygon motor 11K. In the figure, black side1 image formation is a period during which the BK color image is formed on the surface of the nth sheet P in the normal writing mode, and the polygon mirror 9K is rotated at the rotation speed based on the speed command signal Vpk. This is the drive period. The portion surrounded by the parallelogram is a period during which the polygon mirror 9K is subjected to speed change / phase control when shifting from the normal writing mode to the minute magnification changing mode.

  The side2 image formation is a period in which a BK color image is formed on the back surface of the first sheet P after switching from the normal writing mode to the micro-magnification mode, and a speed command signal Vpk obtained by calculating the magnification ratio. This is a period during which the polygon mirror 9K is driven at a rotational speed based on the above. The side2 image formation following the above-described side2 image formation is also a period in which a BK color image is formed on the back surface of the second sheet P, and the polygon mirror 9K is rotated at the rotation speed based on the speed command signal Vpk corrected with the variable magnification. This is a period for driving.

  A speed command signal Vy shown in FIG. 3F is a signal for driving the drum motor 12Y. In the drawing, the satin side1 image formation is a period in which a Y-color image is formed on the surface of the nth sheet P in the normal writing mode, and the photosensitive drum 1Y is rotated at a rotation speed based on the speed command signal Vy. This is the drive period.

  The side2 image formation is a period during which a Y color image is formed on the back surface of the first sheet P after switching from the normal writing mode to the micro-magnification mode, and a speed command signal Vy obtained by calculating the magnification ratio. Is a period in which the photosensitive drum 1Y is driven at a rotational speed based on the above. Side 2 image formation following side 2 image formation is also a period in which a Y color image is formed on the back surface of the second sheet of paper P, and the photosensitive drum is rotated at a rotational speed based on the speed command signal Vy corrected with the variable magnification. This is a period for driving 1Y.

  A speed command signal Vm shown in FIG. 3G is a signal for driving the drum motor 12M. In the drawing, side 1 image formation in the shaded area is a period in which an M color image is formed on the surface of the nth sheet P in the normal writing mode, and the photosensitive drum 1M is rotated at a rotation speed based on the speed command signal Vm. This is a period for driving.

  The side2 image formation is a period in which an M color image is formed on the back surface of the first sheet P after the normal writing mode is switched to the minute magnification change mode, and a speed command signal Vm obtained by calculating the magnification ratio. This is a period in which the photosensitive drum 1M is driven at a rotation speed based on the above. Side 2 image formation following the above-described side 2 image formation is also a period during which an M color image is formed on the back surface of the second sheet P, and the photosensitive drum is rotated at a rotation speed based on the speed command signal Vm corrected with the variable magnification. This is a period for driving 1M.

  A speed command signal Vc shown in FIG. 3H is a signal for driving the drum motor 12C. In the figure, side 1 image formation on the cross-hatched area is a period in which a C color image is formed on the surface of the nth sheet P in the normal writing mode, and the photosensitive drum is rotated at the rotation speed based on the speed command signal Vc. This is a period for driving 1C.

  The side2 image formation is a period in which a C color image is formed on the back surface of the first sheet P after switching from the normal writing mode to the micro-magnification mode, and a speed command signal Vc obtained by calculating the magnification. This is a period during which the photosensitive drum 1C is driven at a rotational speed based on the above. Side 2 image formation following the above-described side 2 image formation is also a period during which a C color image is formed on the back surface of the second sheet P, and the photosensitive drum is rotated at the rotation speed based on the speed command signal Vc corrected by the variable magnification. This is a period for driving 1C.

  A speed command signal Vk shown in FIG. 3I is a signal for driving the drum motor 12K. In the figure, black side 1 image formation is a period in which a BK color image is formed on the surface of the nth sheet P in the normal writing mode, and the photosensitive drum 1K is rotated at a rotational speed based on the speed command signal Vk. This is a period for driving.

  The side2 image formation is a period in which a BK color image is formed on the back surface of the first sheet P after switching from the normal writing mode to the micro-magnification mode, and a speed command signal Vk obtained by calculating the magnification. Is a period in which the photosensitive drum 1K is driven at a rotational speed based on the above. Side2 image formation following side2 image formation is also a period in which a BK color image is formed on the back surface of the second sheet P, and the photosensitive drum is rotated at a rotational speed based on the speed command signal Vk corrected with the variable magnification. This is a period for driving 1K.

  A solid line shown in FIG. 3J indicates a load fluctuation state applied to the intermediate transfer belt 6 from the photosensitive drums 1Y, 1M, 1C, 1K and the like. The step-like curve in the figure shows the load fluctuation state applied to the intermediate transfer belt 6 due to the speed fluctuation of the drum motors 12Y, 12M, 12C, and 12K when the magnification is switched. Periods a, b, c, and d in the stepped curve in the figure shift from the direction in which the load on the intermediate transfer belt 6 becomes lighter to lighter each time the speeds of the drum motors 12Y, 12M, 12C, and 12K are switched. It shows the state. Although the conveyance speed of the intermediate transfer belt 6 is constant, the slip due to the speed difference between the intermediate transfer belt 6 and the photosensitive drums 1Y, 1M, 1C, and 1K is in a fluctuating state.

  In this example, when the magnification is switched, the polygon motors 11Y, 11M, 11C, and 11K are shifted when the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K and the rotation speed of the polygon mirror 9Y are changed at the same variable magnification. At the same time, the speeds of the drum motors 12Y, 12M, 12C, and 12K are switched. At this time, the rotational speed is sequentially adjusted from the upstream side to the downstream side of the image forming color to be transferred to the intermediate transfer belt 6, but the speed of the intermediate transfer belt 6 is maintained at the speed before the magnification change, and the intermediate transfer belt. The speed of 6 is not changed as much as possible.

  This is because if the speed of the intermediate transfer belt 6 is changed at the same ratio as the polygon motors 11Y, 11M, 11C, and 11K and the drum motors 12Y, 12M, 12C, and 12K, the image reduction magnification does not change. The image reduction magnification is realized by utilizing a phenomenon that minute slip occurs due to a speed difference between the photosensitive drums 1Y, 1M, 1C, and 1K and the intermediate transfer belt 6.

  Thus, when changing the magnification, the rotation speed of the polygon mirrors 9Y, 9M, 9C, and 9K and the rotation speed of the photosensitive drums 1Y, 1M, 1C, and 1K are changed to a variable magnification without changing the speed of the intermediate transfer belt 6. Correspondingly, by changing at the same ratio, the image forming pitches of the photosensitive drums 1Y, 1M, 1C, and 1K can be kept uniform.

  With reference to FIGS. 4A to 4C, an example of image writing at the time of normal writing and at the time of minute zooming will be described. In this example, it is assumed that the multi-beam LDi (i = 1 to n) is composed of n = 8 laser beam lights, and the image forming pitch of the eight laser beam lights is adjusted uniformly.

  A white circle of 8 columns × 10 rows shown in FIG. 4A is an 8-beam scan for forming an image on one side of the paper P (not shown) in the single-sided printing mode or the double-sided printing mode. It is an image. In this example, 8 columns in the sub-scanning direction and 10 rows in the main scanning direction are formed by one deflection scan by the first mirror surface of the polygon mirror 9Y.

  An 8-beam scanned image with open circles is formed as follows. In the single-sided printing mode or the single-sided image formation in the double-sided printing mode, when the normal writing mode is set, the intermediate transfer belt 6, the polygon mirror 9Y, and the photosensitive drums 1Y, 1M, 1C, and 1K each have predetermined Driven at rotational speed. In this driving state, the eight multi-beams LD1 to LD8 are simultaneously scanned (1Index) on the photosensitive drum 1Y via the first mirror surface of the polygon mirror 9Y, and the electrostatic latent image formed on the photosensitive drum 1Y. Is developed, and the developed image is transferred to the intermediate transfer belt 6 to be formed.

  4B × 10 rows of black triangle marks shown in FIG. 4B indicate that in the normal writing mode, the eight multi-beams LD1 to LD8 simultaneously scan the photosensitive drum 1Y through the second mirror surface of the polygon mirror 9Y (1Index The electrostatic latent image formed on the photosensitive drum 1Y is developed, and the developed image is transferred to the intermediate transfer belt 6.

  In FIG. 4C, 8 columns × 10 rows of X marks indicate that in the normal writing mode, eight multi-beams LD1 to LD8 are simultaneously scanned onto the photosensitive drum 1Y via the third mirror surface of the polygon mirror 9Y (1Index). Then, the electrostatic latent image formed on the photosensitive drum 1Y is developed, and the developed image is transferred to the intermediate transfer belt 6.

  The 8 columns × 10 rows of white circles shown in FIG. 4D are 8-beam scanning reduced images when an image is formed on the back side of the recording paper P ′ having an image formed on one side in the double-sided printing mode. is there. An 8-beam scanning reduced image with open circles is formed as follows. In the double-sided printing mode, when the micro scaling mode is set, the rotational speed of the intermediate transfer belt 6 is maintained as it is, and the rotational speed of the polygon mirror 9Y and the rotational speed of the photosensitive drums 1Y, 1M, 1C, 1K are maintained. It changes at the same ratio according to the setting of the scaling factor.

  Eight multi-beams LD1 to LD8 are simultaneously scanned (1Index) on the photosensitive drum 1Y via the first mirror surface of the polygon mirror 9Y after the magnification is set, and the electrostatic formed on the photosensitive drum 1Y. The latent image is developed, and a reduced image after development is transferred to the intermediate transfer belt 6 to be formed.

  The black triangles of 8 columns × 10 rows shown in FIG. 4E indicate that the eight multi-beams LD1 to LD8 are simultaneously scanned on the photosensitive drum 1Y via the second mirror surface of the polygon mirror 9Y in the minute scaling mode ( The electrostatic latent image formed on the photosensitive drum 1Y is developed, and the reduced image after development is transferred to the intermediate transfer belt 6.

  In FIG. 4F, 8 columns × 10 rows of X marks indicate that eight multi-beams LD1 to LD8 are simultaneously scanned on the photosensitive drum 1Y through the third mirror surface of the polygon mirror 9Y in the micro-magnification mode (1Index The electrostatic latent image formed on the photosensitive drum 1Y is developed, and the reduced image after development is transferred to the intermediate transfer belt 6.

  A comparison between the 8-beam scanning image in the normal writing mode shown in FIGS. 4A to 4C and the 8-beam scanning reduced image in the reduction magnification mode shown in FIGS. 4D to 4F is shown in FIGS. 4A and 4B. The image forming pitch corresponding to the image forming pitch between 1 index of the 8-beam scanned image (between the white circle and the black triangular mark) is between 1 index of the 8-beam scanned reduced image shown in FIGS. 4D and 4F ( (Between a white circle mark by LD8 and a black triangle mark by LD1). This image formation pitch is substantially equal to the image formation pitch such as white circle marks by LD1 to LD8 and black triangle marks by LD1 to LD8 constituting the 8-beam scanning reduced image according to the present invention after reduction scaling. As a result, even after execution of the minute magnification change mode, the image forming pitch between 1 index (between white circle marks by LD8 and black triangle marks by LD1) can be maintained uniformly.

  4F and 4G show the image formation pitch corresponding to the image formation pitch between 1 index of the 8-beam scanning image shown in FIGS. 4B and 4C (between the black triangle mark by LD8 and the x mark by LD1). It is formed between 1 index of 8-beam scanning reduced image (between black triangle mark by LD8 and x mark by LD1). This image formation pitch is substantially equal to the image formation pitch of white circle marks by LD1 to LD8 and black triangle marks by LD1 to LD8 constituting the 8-beam scanning reduced image according to the present invention. As a result, even after execution of the minute zoom mode, the image forming pitch between 1 index (between black triangle marks by LD8 and x marks by LD1) can be maintained uniformly.

  Further, an 8-beam scanning reduced image in the reduced magnification mode shown in FIGS. 7D to 7F according to the conventional example, and an 8-beam scanned reduced image in the reduced magnification mode shown in FIGS. 4D to 4F according to the present invention. 7D and 7E, 1 index (between the white circle mark by LD8 and the black triangle mark by LD1) is bound, whereas the 8 beam scanning reduced image shown in FIG. According to the 8-beam scanning reduced image, as shown in FIGS. 4D and 4F, a predetermined image formation pitch is formed between 1 index (between the white circle mark by LD8 and the black triangle mark by LD1). This image formation pitch is substantially equal to the image formation pitch of white circle marks by LD1 to LD8 and black triangle marks by LD1 to LD8 constituting the 8-beam scanning reduced image according to the present invention.

  Similarly, the 1-index portion (between the black triangle mark by LD8 and the X mark by LD1) of the reduced beam scanning image shown in FIGS. 7E and 7F is bound, while 8 according to the present invention. A predetermined image forming pitch is formed between 1 index of the beam scanning reduced image (between the black triangle mark by LD8 and the X mark by LD1). This image formation pitch is substantially equal to the image formation pitch of black triangle marks by LD1 to LD8 and x marks by LD1 to LD8 constituting the 8-beam scanning reduced image according to the present invention.

  As described above, according to the color copying machine 100 according to the first embodiment, the normal transfer mode and the minute magnification change mode are set corresponding to the double-sided printing mode, and the intermediate transfer belt 6 and the photosensitive drums 1Y, 1M, and 1C are set. , 1K and the polygon mirror 9Y, the rotational speed of the polygon mirror 9Y and the photosensitive drums 1Y, 1M, 1C, 1K are maintained while maintaining the rotational speed of the intermediate transfer belt 6 in the normal writing mode. The polygon motors 11Y, 11M, 11C, and 11K and the drum motors 12Y, 12M, 12C, and 12K are controlled by setting the same magnification as the rotation speed.

  By this motor control, the image forming pitch in the sub-scanning direction of the photoconductive drums 1Y, 1M, 1C, and 1K can be maintained uniformly even after the normal writing mode is shifted to the minute scaling mode. In addition, the rotational speed of the polygon mirror 9Y and the rotational speed of the photosensitive drum 1Y change with respect to the state in which the rotational speed of the intermediate transfer belt 6 is maintained as it is, so that the photosensitive drum 1Y and the intermediate transfer belt 6 are changed. A minute slip occurs between the two, and the change of the slip makes it possible to reduce and form an image. Thereby, it is possible to prevent moire and the like when changing the magnification and maintain a good image.

  With reference to FIGS. 5A to 5J, an example of motor control of an image writing system as the second embodiment will be described. In this example, when the rotational speeds of the photosensitive drums 1Y, 1M, 1C, and 1K and the rotational speeds of the polygon mirrors 9Y, 9M, 9C, and 9K are changed corresponding to the variable magnification, the same as in the first embodiment. Then, the adjustment of the rotational speed is started sequentially from the upstream side to the downstream side, such as Y color to BK color transferred to the intermediate transfer belt 6. At this time, the speed change rate of the drum motors 12Y, 12M, 12C, and 12K corresponding to the variable magnification is determined by the intermediate transfer belt 6 between the center points of the photosensitive drums 1Y, 1M, 1C, and 1K (inter-drum pitch). It is set so that the time to travel through the separation distance is uniform.

  Note that the image formation reference signal (VTOP signal) shown in FIG. 5A, the speed command signal Vpy (polygon motor 11Y) shown in FIG. 5B, the speed command signal Vpm (polygon motor 11M) shown in FIG. 5C, and the speed command signal shown in FIG. Vpc (polygon motor 11C), speed command signal Vpk (polygon motor 11K) shown in FIG. 5E, speed command signal Vy (drum motor 12Y) shown in FIG. 5F, speed command signal Vm (drum motor 12M) shown in FIG. Since the speed command signal Vc (drum motor 12C) shown in 5H and the speed command signal Vk (drum motor 12K) shown in FIG. 5I are the same as those described in the first embodiment, the description thereof is omitted. See FIGS. 3A-3J.

  A solid line shown in FIG. 5J indicates a load fluctuation state applied to the intermediate transfer belt 6 from the photosensitive drums 1Y, 1M, 1C, 1K and the like. A monotonically decreasing curve in the figure shows a load fluctuation state applied to the intermediate transfer belt 6 due to speed fluctuations of the drum motors 12Y, 12M, 12C, and 12K when the magnification is switched. The periods α, β, γ, and η in the monotonically decreasing curve in the figure shift from the direction in which the load on the intermediate transfer belt 6 becomes lighter to lighter each time the speed of the drum motors 12Y, 12M, 12C, and 12K is switched. It shows the state. The conveyance speed of the intermediate transfer belt 6 is constant, but the slip due to the speed difference between the intermediate transfer belt 6 and the photosensitive drums 1Y, 1M, 1C, and 1K is in a uniform state.

  In this example, when the magnification is switched, the polygon motors 11Y, 11M, 11C, and 11K are shifted when the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K and the rotation speed of the polygon mirror 9Y are changed at the same variable magnification. At the same time, the speeds of the drum motors 12Y, 12M, 12C, and 12K are switched.

  At that time, the ratio of the moving time to the moving distance when the intermediate transfer belt 6 moves between arbitrary points is represented by the change rate of the rotational speed of the drum motors 12Y, 12M, 12C, and 12K corresponding to the variable magnification. At least the time when the intermediate transfer belt 6 advances the separation distance between the center points of the photosensitive drums 1Y-1M and the time when the intermediate transfer belt 6 advances the separation distance between the center points of the photosensitive drums 1M-1C The speed ratios of the rotational speeds of the drum motors 12Y, 12M, 12C, and 12K are set so that the time for the intermediate transfer belt 6 to travel the separation distance between the center points of the photosensitive drums 1C-1K becomes uniform.

  As described above, according to the color copying machine 100 according to the second embodiment, the adjustment of the rotational speed is started sequentially from the upstream side to the downstream side as Y color → BK color transferred to the intermediate transfer belt 6. The rotation speeds of the drum motors 12Y, 12M, 1C, and 12K corresponding to the variable magnification are uniform so that the time for the intermediate transfer belt 6 to travel the separation distance between the center points of the photosensitive drums 1Y, 1M, 1C, and 1K is uniform. Is set to set the rate of change.

  With this setting, the image forming pitch of the photosensitive drums 1Y, 1M, 1C, and 1K can be maintained uniformly. Moreover, in the periods α, β, γ, and η of the monotonic decreasing curve in FIG. 5j, the time for the intermediate transfer belt 6 to travel the separation distance between the center points of the photosensitive drums 1Y, 1M, 1C, and 1K is uniform. Since the rate of change of the rotational speed of the drum motors 12Y, 12M, 1C, 12K with respect to the variable magnification is set, the rotational speed of the photosensitive drums 1Y, 1M, 1C, 1K and the rotational speeds of the photosensitive drums 1Y, 1M, 1C, 1K are set. The rotation speed can be changed smoothly.

  Thereby, compared with the first embodiment, the load fluctuation of the belt motor 13 of the intermediate transfer belt 6 due to the speed change of the photosensitive drums 1Y, 1M, 1C, 1K is smoothed, and the intermediate transfer belt 6 on the intermediate transfer belt 6 due to this load fluctuation is smoothed. Image degradation (color misregistration) can be suppressed to a minimum.

  Next, with reference to FIG. 6, a control example of the color copying machine 100 as an embodiment will be described with respect to the image forming method of the present invention. In this embodiment, it is possible to set a single-sided printing mode or a double-sided printing mode, and a convection circulation system is adopted during double-sided printing. Of course, the multi-beam LD is simultaneously scanned on the corresponding photosensitive drums 1Y, 1M, 1C, and 1K via the polygon mirrors 9Y, 9M, 9C, and 9K, and the corresponding photosensitive drums 1Y, 1M, 1C, and 1K are scanned. An image is written to form an electrostatic latent image, then the electrostatic latent image is developed, and the developed image is transferred from the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 6 to form an image. Assuming that

  In this example, an image is formed on a predetermined sheet P, the number of prints of the recording sheet P ′ after image formation is set to the set number Nx, and the recording sheet P ′ after image formation that can be circulated in the apparatus main body 101 is used. The number is the convection circulation number Nr. For example, although depending on the internal structure of the apparatus main body 101, the number of convection circulations Nr is about 3 to 5. Further, the number of recording sheets P ′ after image formation circulating in the apparatus main body 101 is defined as the number Np of image formations, and the number of recording sheets P ′ after image formation discharged from the apparatus main body 101 to the outside. Is the number of image forming outputs.

  With these as control conditions, the CPU 55 inputs the setting of image forming conditions in step ST1 shown in FIG. For example, the print mode and the number of prints are input as image forming conditions. The user operates the operation & display unit 48 illustrated in FIG. 1 to set the single-sided printing mode or the double-sided printing mode in the CPU 55. The user operates the operation & display unit 48 to set the mode setting, the number of prints, the paper quality of the paper P, the amount of paper, and the like. The number of prints is set in the CPU 55 as the set number Nx.

  In step ST2, the CPU 55 branches the control in accordance with the setting of the single-sided printing mode or the double-sided printing mode. The CPU 55 selects the normal writing mode corresponding to the single-sided printing mode set in step ST1, or selects the normal writing mode and the minute scaling mode corresponding to the set double-sided printing mode and branches the control. .

  If the single-sided printing mode is set in step ST2, the process goes to step ST3, and the CPU 55 sets the normal writing mode to the ASIC 53 and executes the single-sided printing mode. In the normal writing mode, the intermediate transfer belt 6, the photosensitive drums 1Y, 1M, 1C, and 1K and the polygon mirror 9Y are rotated at a predetermined rotational speed, and the multi-beam LD adjusted to a predetermined image forming pitch is transferred to the photosensitive drum 1Y. , 1M, 1C, 1K to scan and write an image.

  Thereafter, in step ST4, the CPU 55 determines whether or not the image forming output number No has reached the set number Nx. At this time, the CPU 55 compares the image formation output sheet number No and the set sheet number Nx. If the image formation output sheet number No has not reached the set sheet number Nx, the CPU 55 returns to step ST3 and continues the write control for the normal write mode. . When the image formation output number No reaches the set number Nx, the writing control based on the single-sided printing mode is ended.

  If the double-sided printing mode is set in step ST2, the CPU 55 proceeds to step ST5 and sets the double-sided printing mode to ASIC 53. First, an image is printed on one side of the paper based on the normal writing mode. Form. At this time, the CPU 55 shown in FIG. 2 outputs program data D55, setting data Dw, and the like to the ASIC 53. The ASIC 53 controls the polygon motors 11Y, 11M, 11C, and 11K, the drum motors 12Y, 12M, 12C, and 12K, and the belt motor 13 based on the CLK signal, signal creation program data D55, and setting data Dw. Then, speed command signals Vy, Vm, Vc, Vk, Vpy, Vpm, Vpc, Vpk, Vb, a VTOP signal and the like are generated.

  The image formation reference signal (VTOP signal) illustrated in FIG. 3A is output to the CPU 55 and the data buffer 52. The speed command signal Vpy shown in FIG. 3B is output to the polygon motor 11Y. The polygon motor 11Y drives the polygon mirror 9Y based on the speed command signal Vpy. The speed command signal Vpm shown in FIG. 3C is output to the polygon motor 11M. The polygon motor 11M drives the polygon mirror 9M based on the speed command signal Vpm.

  The speed command signal Vpc shown in FIG. 3D is output to the polygon motor 11C. The polygon motor 11C drives the polygon mirror 9C based on the speed command signal Vpc. The speed command signal Vpk shown in FIG. 3E is output to the polygon motor 11K. The polygon motor 11K drives the polygon mirror 9K based on the speed command signal Vpk.

  The speed command signal Vy shown in FIG. 3F is output to the drum motor 12Y. The drum motor 12Y drives the photosensitive drum 1Y based on the speed command signal Vy. The speed command signal Vm shown in FIG. 3G is output to the drum motor 12M. The drum motor 12M drives the photosensitive drum 1M based on the speed command signal Vm. The speed command signal Vc shown in FIG. 3H is output to the drum motor 12C. The drum motor 12C drives the photosensitive drum 1C based on the speed command signal Vc. The speed command signal Vk shown in FIG. 3I is output to the drum motor 12K. The drum motor 12K drives the photosensitive drum 1K based on the speed command signal Vk.

  In step ST6, the CPU 55 determines whether the image formation number Np has reached the convection circulation number Nr. At this time, the CPU 55 compares the image formation number Np with the convection circulation number Nr. If the image formation number Np has not reached the convection circulation number Nr, the CPU 55 proceeds to step ST7 and the CPU 55 sets the image formation number Np. It is determined whether the number Nx has been reached. If the image forming number Np has not reached the set number Nx, the process returns to step ST5 to continue the writing control for the normal writing mode.

  When the image formation number Np reaches the convection circulation number Nr in step ST6, the process proceeds to step ST8, and the CPU 55 switches the writing mode from the normal writing mode to the minute magnification / reduction mode.

  After that, in step ST9, the CPU 55 forms an image on the other side of the paper P based on the micro scaling mode. In the micro scaling mode, the rotational speed of the photosensitive drums 1Y, 1M, 1C, and 1K and the polygon mirrors 9Y, 9M, 9C, and 9K are rotated while maintaining the rotational speed of the intermediate transfer belt 6 in the normal writing mode. The speed is changed in accordance with the variable magnification, and the image is written by scanning the multi-beam LD on the photosensitive drums 1Y, 1M, 1C, and 1K after the change. As for the control contents at that time, either the write control according to the first embodiment or the second embodiment may be set and executed.

  According to the writing control according to the first embodiment, the rotation speed of the polygon mirrors 9Y, 9M, 9C, and 9K and the rotation of the photosensitive drums 1Y, 1M, 1C, and 1K are changed without changing the speed of the intermediate transfer belt 6. The speed is changed at the same ratio corresponding to the scaling factor. In this way, by changing the rotation speed of the polygon mirror 9Y and the rotation speed of the photosensitive drums 1Y, 1M, 1C, and 1K at the same magnification, the image forming pitch of the photosensitive drums 1Y, 1M, 1C, and 1K is changed. It becomes possible to hold it uniformly.

  In step ST10, the CPU 55 determines whether the image forming output number No has reached the set number Nx. If the image forming output number No has not reached the set number Nx, the process proceeds to step ST11, and the CPU 55 determines whether the image forming number Np has reached the convection circulation number Nr. If the image forming number Np has not reached the convection circulation number Nr, the process returns to step ST9 to continue the writing control for the micro scaling mode.

  If the image formation number Np reaches the convection circulation number Nr in step ST11, the CPU 55 returns to step ST5, and the CPU 55 resumes image formation based on the normal writing mode on one side of the sheet.

  Thereafter, when the image forming number Np has reached the convection circulation number Nr in step ST6 or when the set number Nx has been reached in step ST7, the process proceeds to step ST8 and the writing mode is changed from the normal writing mode to the micro scaling mode. Switch.

  In step ST9, the CPU 55 forms an image on the other surface of the paper P based on the micro scaling mode. Thereafter, in step ST10, when the image forming output number No reaches the set number Nx, the CPU 55 ends the writing control related to the duplex printing mode.

  As described above, according to the control example of the color copying machine 100 as the embodiment, the multi-beam LD is simultaneously transmitted to the corresponding photosensitive drums 1Y, 1M, 1C, and 1K via the polygon mirrors 9Y, 9M, 9C, and 9K. To write an image, form an electrostatic latent image on the photosensitive drums 1Y, 1M, 1C, and 1K, and then develop the electrostatic latent image, and develop the developed image into the photosensitive drums 1Y, 1M, and 1K. When transferring from 1C, 1K to the intermediate transfer belt 6, the normal writing mode is selected corresponding to the single-sided printing mode set by the operation & display unit 48, or the normal writing mode and the double-sided printing mode are selected. By selecting the micro scaling mode, the rotation of the intermediate transfer belt 6, the photosensitive drums 1Y, 1M, 1C, 1K and the polygon mirror 9Y is controlled.

  When executing the micro-magnification mode corresponding to the duplex printing mode, the rotational speeds of the polygon mirrors 9Y, 9M, 9C, and 9K are maintained while maintaining the rotational speed of the intermediate transfer belt 6 in the normal writing mode. The rotational speeds of the photosensitive drums 1Y, 1M, 1C, and 1K are changed at the same ratio, and even after the transition from the normal writing mode to the minute magnification mode, the photosensitive drums 1Y, 1M, 1C, and 1K The image forming pitch in the sub-scanning direction can be kept uniform.

  In addition, the rotational speed of the polygon mirror 9Y and the rotational speed of the photosensitive drum 1Y change with respect to the state in which the rotational speed of the intermediate transfer belt 6 is maintained as it is, so that the photosensitive drum 1Y and the intermediate transfer belt 6 are changed. A minute slip occurs between the two, and the change of the slip makes it possible to reduce and form an image. Thereby, it is possible to prevent moire and the like when changing the magnification and maintain a good image.

  In the above-described embodiment, the case where the print mode and the number of prints are input as the image forming condition has been described. However, the present invention is not limited to this. Even when the paper type is changed as a requirement for paper feed tray selection as an image forming condition, after the transition from the normal writing mode to the minute scaling mode, the photosensitive drums 1Y, 1M, 1C, and 1K in the sub-scanning direction. The image forming pitch can be kept uniform.

  The present invention is capable of setting a single-sided printing mode or a double-sided printing mode, and capable of writing an image in a micro-magnification mode when executing the double-sided printing mode, a color printer, a black-and-white printer, a copying machine, and a complex machine thereof. It is very suitable when applied to.

1Y, 1M, 1C, 1K Photosensitive drum (image carrier)
2Y, 2M, 2C, 2K Charging unit (image forming unit)
3Y, 3M, 3C, 3K Optical writing unit (image forming unit)
4Y, 4M, 4C, 4K Development device (image forming unit)
6 Intermediate transfer belt (intermediate transfer member)
8A, 8Y, 8M, 8C, 8K Cleaning unit 10Y, 10M, 10C, 10K Image forming unit (image forming unit)
11Y, 11M, 11C, 11K Polygon motor
12Y, 12M, 12C, 12K drum motor
DESCRIPTION OF SYMBOLS 13 Belt motor 17 Fixing device 20 Paper conveyance part 21 1st paper feeding part 22A-22C Conveyance roller 23 Registration roller 24 Fixation conveyance roller 25 Paper discharge roller 26 Paper inversion part 48 Operation & display part 51 Clock generation part 52 Data buffer 53 ASIC
55 CPU
60 Image Forming Unit 90 Control Device 100 Color Copier 101 Device Main Body 102 Exposure Scanning Device

Claims (5)

A plurality of laser beam lights are simultaneously scanned on the image carrier through a polygon mirror rotator to write an image, an electrostatic latent image is formed on the image carrier, and then the electrostatic latent image is developed. An image forming apparatus for transferring an image after development from an image carrier to an intermediate transfer body,
When the operation for forming an image on a predetermined sheet material is set as a print mode, and the condition for forming an image on the sheet material in the print mode including the type of the sheet material is set as the image formation condition, the setting of the image formation condition is input. An operation unit to
Usually, the intermediate transfer member, the image carrier and the polygon mirror rotator are rotated at a predetermined rotation speed, and a plurality of laser beam lights adjusted to a predetermined arrangement pitch are scanned on the image carrier to write an image. Write mode,
While maintaining the rotational speed of the intermediate transfer member in the normal writing mode as it is, the rotational speed of the image carrier and the rotational speed of the polygon mirror rotating body are changed according to the image reduction ratio, and the image bearing after the shifting is performed. When the operation of scanning the body with a plurality of the laser beam lights and writing an image is a reduced writing mode,
Select the normal writing mode corresponding to the image forming conditions set by the operation unit, or select the normal writing mode and the reduced writing mode corresponding to the image forming conditions, the intermediate transfer member, An image forming apparatus comprising: a control unit that controls rotation of the image carrier and the polygon mirror rotating body. The plurality of laser beam lights are simultaneously scanned on the image carrier through the polygon mirror rotator to write an image, form an electrostatic latent image on the image carrier, and then develop the electrostatic latent image. An image forming unit for transferring the developed image from the image carrier to the intermediate transfer member;
The image forming apparatus according to claim 1, wherein the image forming unit is provided for each image forming color to constitute a tandem color machine.   The image forming apparatus according to claim 2, wherein the rotation speed of the polygon mirror rotating body and the rotation speed of the image carrier are changed at the same ratio corresponding to an image reduction ratio. When the rotational speed of the image carrier and the rotational speed of the polygon mirror rotational speed are changed according to the image reduction ratio, the rotational speed is sequentially increased from the upstream side to the downstream side of the image forming color transferred to the intermediate transfer body. Start adjusting
The rate of change of the rotation speed corresponding to the image reduction rate is set so that the time for the intermediate transfer member to travel the separation distance between the center points of the image carrier is uniform. The image forming apparatus according to 3. A plurality of laser beam lights are simultaneously scanned on the image carrier through a polygon mirror rotator to write an image, an electrostatic latent image is formed on the image carrier, and then the electrostatic latent image is developed. A method of forming an image by transferring an image after development from an image carrier to an intermediate transfer member,
When the operation for forming an image on a predetermined sheet material is set as a print mode, and the condition for forming an image on the sheet material in the print mode including the type of the sheet material is set as the image formation condition, the setting of the image formation condition is input. And
Usually, the intermediate transfer member, the image carrier and the polygon mirror rotator are rotated at a predetermined rotation speed, and a plurality of laser beam lights adjusted to a predetermined arrangement pitch are scanned on the image carrier to write an image. Write mode,
While maintaining the rotational speed of the intermediate transfer member in the normal writing mode as it is, the rotational speed of the image carrier and the rotational speed of the polygon mirror rotating body are reduced according to the image reduction ratio, and the image carrier after the deceleration is carried out. When the operation of scanning the body with a plurality of the laser beam lights and writing an image is a reduced writing mode,
The normal writing mode is selected corresponding to the set image forming condition, or the control is branched by selecting the normal writing mode and the reduced writing mode corresponding to the set image forming condition. An image forming method.

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