JP2009300471A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality by transferring a toner image on a photoreceptor drum at an appropriate position of an endless belt based on thickness information of the endless belt. <P>SOLUTION: When a mark detection signal is output from a mark sensor, a transfer timing calculation part calculates moving speed of an intermediate transfer belt. The transfer timing calculation part calculates time taken until an area having little thickness variation of the intermediate transfer belt is laid on a driving roller from the moving speed and the thickness information stored in a belt thickness information storage part. An exposure timing calculation part calculates exposure start timing by using the calculated time, and an exposure control part outputs a signal for designating start of exposure to the exposure device in accordance with the calculated exposure timing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus represented by a copying machine, a facsimile machine, a printer, and the like.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a photosensitive drum is widely used as an image carrier. A general image forming process using the photosensitive drum is as follows. The surface of the photosensitive drum is uniformly charged with a predetermined potential by a charging device, and by irradiating the LED light or the like from the exposure device there, the potential is partially attenuated to form an electrostatic latent image of an original image. The By developing the electrostatic latent image with a developing device, the toner image is developed.

  For example, a tandem type color image forming apparatus that forms a color image includes an image forming unit corresponding to each color of yellow, cyan, magenta, and black. The toner images formed on the photosensitive drums of the respective image forming units are sequentially transferred onto an intermediate transfer belt as an endless belt, and a color image is formed on the intermediate transfer belt. Thereafter, the color image is transferred to a sheet material such as paper by a secondary transfer mechanism.

When forming a color image by multiple transfer of toner images of each color, suppressing the occurrence of color misregistration of the transferred toner is cited as one of the important technical issues for improving image quality, and various improvements have been made. Has been made. Patent Documents 1 and 3 describe a method in which an encoder is installed on a driven roller that rotates following the endless belt, and driving of the endless belt is controlled using the belt speed obtained from the rotation of the driven roller and the thickness information of the endless belt. Is described. Patent Document 2 describes a method in which marks indicating reference positions are formed at equal intervals on the endless belt surface after molding an endless belt, and a toner image is detected by the sensor or the like to adjust the transfer position of the toner image.
JP 2000-310897 A Patent No. 3893300 JP 2006-184601 A

  However, when the belt speed is calculated by installing an encoder on the driven roller as described in Patent Documents 1 and 3, the speed of the endless belt is not directly measured, the individual characteristics of the driven roller, etc. From the viewpoint of being affected, it was difficult to obtain an accurate belt speed. Further, the length of the endless belt in the circumferential direction (moving direction) has a large individual difference after molding, and it is difficult to form all marks as described in Patent Document 2 at equal intervals.

  The present invention has been made in order to solve the above-described problem. Image formation for improving image quality by transferring a toner image on a photosensitive drum at an appropriate position of an endless belt based on thickness information of the endless belt. The object is to provide an apparatus.

  The invention according to claim 1 of the present invention has an image carrier, an image forming means for forming a toner image on the image carrier, and a toner image of the image carrier in contact with the image carrier. An endless belt to which the endless belt is suspended, a driving roller for driving the endless belt in a suspended state, storage means for storing thickness information in the moving direction of the endless belt, and the stored thickness Based on the information, a control is performed to form a toner image on the image carrier at a position where a toner image is transferred from the image carrier at a timing when a region having a small thickness variation on the endless belt is placed on the drive roller. And a control unit that controls the image forming unit.

  It is generally known that the surface speed of an endless belt changes when a region where the thickness variation of the endless belt is large is placed on a driving roller. Therefore, the control means controls the toner image to be transferred to the endless belt at the timing when the region where the thickness variation of the endless belt is small is put on the driving roller, using the endless belt thickness information stored in the storage means in advance. Thus, the toner image can be transferred at a timing when the surface speed of the endless belt is stable. Accordingly, it is possible to prevent deterioration in image quality due to toner image transfer position deviation, toner image distortion, and the like.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein a detection unit that detects a predetermined reference position on the endless belt and a detection result by the detection unit are used. Based on the calculated endless belt moving speed and the thickness information stored in the storage unit, the endless belt has a small thickness variation. Transfer timing calculating means for calculating a timing at which the region is placed on the drive roller, and the control means controls the image forming to form a toner image on the image carrier based on the calculated transfer timing. It is characterized by being performed on the means.

  Even if the endless belt is controlled so as to move at a predetermined speed, the surface speed of the endless belt changes if a region where the endless belt has a large thickness variation is placed on the drive roller. According to this configuration, the detection unit detects the reference position on the endless belt, and the speed calculation unit calculates the actual moving speed of the endless belt using the detection result. It is possible to accurately calculate the timing at which the roller is placed on the drive roller and the transfer timing.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the image quality of the toner image formed by the image forming unit is standard and higher than the standard mode. A setting unit configured to set at least one of the modes, wherein the control unit sets the thickness of the endless belt when the setting unit sets the high image quality mode. The image forming unit is controlled to form a toner image on the image carrier so that the toner image is transferred from the image carrier at a timing when a region with little fluctuation is placed on the drive roller. It is characterized by.

  According to this configuration, only when the high image quality mode is set, by controlling so that the toner image is transferred to the endless belt at the timing when the portion where the thickness variation in the endless belt is small is placed on the driving roller, Image quality can be improved compared to the standard mode.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming unit includes the plurality of image carriers, and the endless belt includes Is characterized in that the toner images of the plurality of image carriers are transferred in a multiple manner.

  When the image forming means has a plurality of image carriers, each color toner image carried by each image carrier is transferred onto the endless belt to form a color image. The occurrence of image distortion greatly affects the image quality. Therefore, the image quality of the color image can be improved by adopting the configuration described in claim 4.

  According to the present invention, the toner image is transferred to the endless belt at a timing when the control unit uses the thickness information of the endless belt stored in advance in the storage unit so that the region where the thickness variation of the endless belt is small is placed on the driving roller. By controlling in this way, the toner image can be transferred at a timing when the surface speed of the endless belt is stable. Accordingly, it is possible to prevent deterioration in image quality due to toner image transfer position deviation, toner image distortion, and the like.

  Hereinafter, an image forming apparatus according to the present invention will be described with reference to FIGS. An example of an image forming apparatus according to the present invention is a tandem color image forming apparatus. FIG. 1 is a schematic vertical sectional view showing a schematic structure of a printer 100 as a tandem type color image forming apparatus.

  The printer 100 includes a paper feed unit 1, a vertical conveyance path 2, a registration roller pair 3, a belt conveyance unit 4, an image forming unit 50, a secondary transfer unit 6, a fixing unit 7, a discharge conveyance path 8, a discharge tray 9, and a mark sensor. 10 is comprised. The image forming unit 50 includes image forming units 5B, 5M, 5C and 5Y (hereinafter collectively referred to as “black (B) magenta (M)”, “cyan (C)”, and “yellow (Y)” in the apparatus main body. Image forming unit 5 ”) is provided side by side.

  The printer 100 performs the following image forming process. The sheet P is conveyed from the sheet feeding cassette 1 a of the sheet feeding unit 1 to the vertical conveyance path 2 by the pickup roller 1 b and is conveyed to the secondary transfer unit 6 through the registration roller pair 3.

  In the image forming unit 50, the intermediate transfer belt 11 is sent in the direction of the arrow by the drive roller 41. On the intermediate transfer belt 11, the toner images of the respective colors of yellow, cyan, magenta, and black formed on the respective photosensitive drums 51 in the image forming units 5Y, 5C, 5M, and 5B are sequentially transferred in a multiple manner to form a color image. Is formed. The color image formed here is secondarily transferred by the secondary transfer unit 6 onto the paper P conveyed from the intermediate transfer belt 11 from the paper feed cassette 1a. A color image is formed on the paper P.

  Thereafter, the sheet P on which the unfixed color image is transferred is conveyed from the intermediate transfer belt 11 to the fixing unit 7. Then, at the nip portion formed by the pressure contact between the heating roller 7a and the pressure roller 7b, the heat amount necessary for fixing is supplied to the paper P, and the fixing process of the color image is performed. The heating roller 7a incorporates a heater (not shown), and this heater is controlled to generate a predetermined temperature necessary for fixing. After the fixing process is performed by the fixing unit 7, the paper P is discharged to the discharge tray 9 through the discharge conveyance path 8.

  Next, the configuration of the image forming unit 50 that is a main component of the printer 100 will be described in detail. The image forming unit 50 includes a belt conveyance unit 4, an image forming unit 5 including a developing device 56, and an intermediate transfer cleaning unit 45.

  As shown in FIG. 1, the belt conveyance unit 4 includes a driving roller 41, a driven roller 42, and an endless intermediate transfer belt 11 that is stretched over the two rollers. The intermediate transfer belt 11 is maintained at an appropriate tension by a tension roller 44. In this state, the driving roller 41 is transmitted with a driving force from a driving motor (not shown), and the surface speed of the outer periphery of the photosensitive drum 51 of each image forming unit and the feeding of the intermediate transfer belt 11 of the belt conveying unit 4 are transmitted. The speed is driven so as to be a constant speed close to a constant speed.

  The image forming unit 5 is arranged side by side below the belt conveyance unit 4. Arrangements of the respective image forming units are for yellow (Y), cyan (C), magenta (M), and black (B) in order from the upstream side in the sheet conveying direction. . Therefore, in the image forming unit 5, the same reference numerals are given to portions having the same configuration.

  The image forming unit 5 includes a photosensitive drum 51, a main charging device 52, an exposure device 53, a primary transfer roller 54, a cleaning device 55, and a developing device 56. The image forming unit 5 is combined into a housing made of resin or the like to form one unit. It is attached to the device body. The photosensitive drum 51 is charged by the main charging device 52 so that the dark potential at the development position becomes a predetermined potential. An electrostatic latent image is formed on the surface of the photosensitive drum 51 by the exposure device 53 irradiating the charged surface of the photosensitive drum 51 with light corresponding to image information.

  The developing device 56 applies toner particles supplied from a toner tank (not shown) to the surface of the developing roller 57, and the toner is transferred from the developing roller 57 to the electrostatic latent image formed on the surface of the photosensitive drum 51. The toner image is developed on the photosensitive drum 51 by supplying the particles. The toner that has not been transferred onto the photosensitive drum 51 is removed by the cleaning device 55.

  Subsequently, in order to lower the residual potential on the surface of the photoconductive drum 51 and make it uniform, the photoconductive drum 51 is decharged by the static eliminating lamp 58 and is prepared for the next series of processes. The printer 100 develops an image corresponding to black, magenta, cyan, and yellow on the photosensitive drum 51 by each image forming unit 5 on the intermediate transfer belt 11 based on the method of the image forming unit 5 described above. In this manner, one color image is formed by repeating multiple transfers without deviation and multiple transfer.

  The intermediate transfer cleaning unit 45 includes an intermediate transfer cleaning roller 45a and an intermediate transfer cleaning blade 45b. The intermediate transfer cleaning roller 45 a is in pressure contact with the intermediate transfer belt 11 and is rotated in the same direction as the rotation direction of the intermediate transfer belt 11. The intermediate transfer cleaning blade 45b contacts the intermediate transfer belt 11 on the downstream side from the position of the intermediate transfer cleaning roller 45a in the moving direction of the intermediate transfer belt 11, thereby removing residual toner on the intermediate transfer belt 11. Scratch off.

  The mark sensor 10 is a reflective sensor. The mark sensor 10 detects a reference mark indicating the reference position formed on the intermediate transfer belt 11 in a non-contact manner, and outputs a mark detection signal to a control unit described later. FIG. 2 is a view showing the reference mark 12 and the mark sensor 10 formed on the intermediate transfer belt 11. The reference mark 12 is formed at a predetermined position on the intermediate transfer belt 11 and can be detected by the mark sensor 10. The reference mark 12 is preferably formed when the intermediate transfer belt 11 is formed. Alternatively, it may be formed in advance with toner before the reference mark is detected by the mark sensor 10.

  In addition, the reference mark 12 has a predetermined length along the circumferential direction of the intermediate transfer belt 11 so that a control unit described later calculates the moving speed of the intermediate transfer belt 11 using the mark detection signal of the mark sensor 10. . The mark sensor 10 detects the start edge of the reference mark 12 in the circumferential direction and outputs a mark detection signal. When the end of the reference mark 12 passes over the mark sensor 10, the output of the mark detection signal is terminated. Therefore, the moving speed of the intermediate transfer belt 11 can be obtained by using the time during which the mark detection signal is output and the length of the reference mark 12 in the circumferential direction.

  Note that the mark sensor 10 is not limited to an optical sensor such as a reflective sensor, and may be a sensor that can detect a reference mark from an image acquired by continuously imaging the intermediate transfer belt 11, for example. Further, the arrangement positions of the mark sensor 10 and the reference mark 12 are not limited to the positions shown in FIGS. 1 and 2 and can be changed as appropriate.

  FIG. 3 is a functional block diagram showing an electrical configuration of the printer 100. The printer 100 includes a control unit 31, an image memory 32, a storage unit 33, a paper feeding unit 1, an image processing unit 35, an image forming unit 50, a mark sensor 10, an input operation unit 36, and a network I / F unit 37. Has been. In addition, the same code | symbol is attached | subjected to the same component as demonstrated in FIG. 1, and detailed description is abbreviate | omitted.

  The image memory 32 temporarily stores image data transmitted from an unillustrated external device (such as a personal computer) via the network I / F unit 37.

  The storage unit 33 stores programs and data for realizing various functions of the printer 1. In the present embodiment, it functions as a belt thickness information storage unit 331. The belt thickness information storage unit 331 stores thickness information in the circumferential direction of the intermediate transfer belt 11 measured before being attached to the printer 100. An example of the measured thickness variation in the circumferential direction of the intermediate transfer belt 11 is shown in FIG. FIG. 4 shows the position from the reference mark 12 and the thickness at that position, where either the start or end of the reference mark 12 of the intermediate transfer belt 11 is the reference position (the position of the circumferential belt position 0 mm on the horizontal axis in FIG. 4). It is the graph which showed.

  Due to manufacturing characteristics, the intermediate transfer belt 11 is often formed in a shape having a thickness peak at one point as shown in FIG. The intermediate transfer belt 11 is driven by a driving roller 41 so as to move at a preset surface speed. It is generally known that the surface speed fluctuates when the intermediate transfer belt 11 has a thickness variation. . When the surface speed fluctuates, the quality (image quality) of the image formed on the paper P is deteriorated. Further, when the toner image is transferred to an area where the thickness variation of the intermediate transfer belt 11 is large, the toner image is distorted and the image quality is similarly deteriorated.

  Therefore, in the present invention, the actual surface speed of the intermediate transfer belt 11 is accurately measured, and the photosensitive drum of each image forming unit 5 is at a timing when the region where the thickness variation of the intermediate transfer belt 11 is small is put on the driving roller 41. A printer 100 for transferring a toner image from 51 to the intermediate transfer belt 11 is proposed. In order to realize such a printer 100, the belt thickness information storage unit 331 stores at least an area where the thickness variation in the circumferential direction is small as thickness information of the intermediate transfer belt 11.

  For example, in the case of FIG. 4, the thickness variation is small in the region where the position from the reference mark 12 (the position of the circumferential belt position 0 mm in FIG. 4) is 20 mm to 56 mm. Similarly, even when the position from the reference mark 12 is 80 mm to 120 mm, the thickness variation is small. Accordingly, the belt thickness information storage unit 331 stores an area where the position from the reference mark 12 is 20 mm to 56 mm as a transfer use area A and an area where the position from the reference mark 12 is 80 mm to 120 mm as a transfer use area B. The thickness information stored in the belt thickness information storage unit 331 calculates the time until the transfer use area A or B of the intermediate transfer belt 11 covers the drive roller 41 by a transfer timing calculation unit 311 of the control unit 31 described later. Used when doing.

  Returning to FIG. The image processing unit 35 performs image processing such as image correction and enlargement / reduction on the image data input via the network I / F unit 37. The input operation unit 36 includes a power key, a start button, a setting key for setting various functions, and a display panel for displaying various messages, and outputs an operation signal to the control unit 31 when an operation is performed by the user. The network I / F unit 37 includes a communication module such as a LAN board, and transmits / receives various data to / from an external device via a network (not shown) connected to the network I / F unit 37.

  The control unit 31 is configured by a CPU (Central Processing Unit) or the like, and executes processing based on a predetermined program according to an input instruction signal or the like, and outputs an instruction signal to each functional unit, data transfer, or the like. And controlling the printer 100 in an integrated manner. The control unit 31 functions as a transfer timing calculation unit 311, an exposure timing calculation unit 312, and an exposure control unit 313.

  The transfer timing calculation unit 311 calculates the moving speed of the intermediate transfer belt 12 based on the mark detection signal output from the mark sensor 10, and the transfer use area A or B of the intermediate transfer belt 11 is placed on the drive roller 41. Calculate the time until. Based on the time calculated by the transfer timing calculation unit 311, the exposure timing calculation unit 312 intermediates the toner image on the photosensitive drum 51 at a timing when the transfer use area A or B of the intermediate transfer belt 11 is placed on the driving roller 41. The exposure start timing by the exposure device 53 is calculated so as to be transferred to the transfer belt 11. The exposure control unit 313 outputs a signal that instructs the exposure apparatus 53 to start exposure according to the exposure start timing calculated by the exposure timing calculation unit 312.

  FIG. 5 is a flowchart for explaining the flow of printing processing in the printer 100. When a mark detection signal is output from the mark sensor 10 (step S11; YES), the transfer timing calculation unit 311 starts time measurement (step S12). When the output of the mark detection signal is completed (step S13; YES), the transfer timing calculation unit 311 calculates the moving speed of the intermediate transfer belt 11 using the measurement time and the circumferential length of the reference mark 12 (step S14). . The transfer timing calculation unit 311 places the transfer use region A or B on the driving roller 41 from the moving speed of the intermediate transfer belt 11 and the positions of the transfer use regions A and B stored in the belt thickness information storage unit 331. Is calculated (step S15).

  Next, the exposure timing calculation unit 312 calculates the exposure start timing using the time calculated in step S15 (step S16). In accordance with the exposure start timing, the exposure control unit 313 outputs a signal for instructing the exposure apparatus 53 to start exposure (step S17).

  The exposure device 53 exposes the surface of the photosensitive drum 51 according to the instruction signal. Thereby, a toner image is formed on the surface of the photosensitive drum 51 (step S18). Then, yellow, cyan, magenta, and black toner images formed on the respective photosensitive drums 51 are sequentially transferred onto the intermediate transfer belt 11 in a multiple transfer manner to form a color image. This color image is secondarily transferred from the intermediate transfer belt 11 to the paper P by the secondary transfer unit 6.

  As described above, the thickness information indicating the transfer use area with a small thickness variation of the intermediate transfer belt 11 stored in the storage unit 33 in advance and the detection signal of the reference mark 12 output from the mark sensor 10 are used. The toner image is transferred to the intermediate transfer belt 11 at a timing when the transfer use area A or B is placed on the drive roller 41 by controlling the exposure start timing and the like, so that the toner image has a stable surface speed at the intermediate transfer belt 11. Can be transferred. Accordingly, it is possible to prevent deterioration in image quality due to toner image transfer position deviation, toner image distortion, and the like.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, the printer 100 has been described as a color printer that forms a color image by multiply transferring four color toner images, but the present invention can also be applied to a monochrome printer.

  Further, when the printer 100 has a standard mode in which the image quality of the print image is standard and a high image quality mode in which the image quality is higher than that of the standard mode, the control unit 31 is set to the exposure start timing only when the image quality mode is set. May be calculated so that the toner image is transferred to the intermediate transfer belt 11 at the timing when the transfer use area A or B is placed on the drive roller 41. By doing so, the image quality in the high image quality mode can be improved as compared with the standard mode. Further, in the standard mode, the control unit 31 does not control the transfer of the toner image to the intermediate transfer belt 11 at the timing when the transfer use area A or B is placed on the driving roller 41, so that the standard mode mode is compared with the high quality mode. Printing time can be shortened, and further, the processing load on the control unit 31 can be reduced.

  Here, the standard mode or the high image quality mode can be set by the user via the input operation unit 36, and the control unit 31 sets the standard mode or the high image quality mode in accordance with the user operation input.

FIG. 2 is a schematic vertical sectional view showing a schematic structure of a printer. FIG. 4 is a diagram illustrating a reference mark and a mark sensor formed on an intermediate transfer belt. FIG. 2 is a functional block diagram illustrating an electrical configuration of a printer. An example of the measured thickness variation in the circumferential direction of the intermediate transfer belt. 6 is a flowchart for explaining a flow of printing processing in the printer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Printer 1 Paper feed part 2 Vertical conveyance path 3 Registration roller pair 4 Belt conveyance part 41 Drive roller 11 Intermediate transfer belt (endless belt)
50 Image forming unit (image forming means)
6 Secondary transfer section 7 Fixing section 8 Discharge transport path 9 Discharge tray 10 Mark sensor (detection means)
31 Control unit (control means, setting means)
311 Transfer timing calculation unit (speed calculation means, transfer timing calculation means)
312 Exposure timing calculation unit (control means)
313 Exposure control unit (control means)
32 Image memory 33 Storage unit (storage means)
331 Belt thickness information storage unit 35 Image processing unit 36 Input operation unit 37 Network I / F unit

Claims (4)

An image forming unit having an image carrier and forming a toner image on the image carrier;
An endless belt in contact with the image carrier and onto which a toner image of the image carrier is transferred;
The endless belt is suspended, and a driving roller that drives the suspended endless belt;
Storage means for storing thickness information in the moving direction of the endless belt;
Based on the stored thickness information, a toner image is transferred onto the image carrier at a position where a toner image is transferred from the image carrier at a timing when a region with little thickness variation on the endless belt is placed on the drive roller. Control means for controlling the image forming means to form an image;
An image forming apparatus comprising: Detecting means for detecting a predetermined reference position on the endless belt;
Using the detection result by the detection means, speed calculation means for calculating the moving speed of the endless belt;
Transfer timing calculating means for calculating a timing at which an area of the endless belt having a small thickness variation is placed on the drive roller based on the calculated moving speed of the endless belt and the thickness information stored in the storage means; ,
The image according to claim 1, further comprising: controlling the image forming unit to form a toner image on the image carrier based on the calculated transfer timing. Forming equipment. A setting unit configured to set at least one of the modes, including at least a standard mode in which the image quality of the toner image formed by the image forming unit is standard and a high image quality mode in which the image quality is higher than the standard mode; Prepared,
When the setting unit is set to the high image quality mode, the control unit is configured to transfer the toner image from the image carrier at a timing when the region where the thickness variation in the endless belt is small is set on the driving roller. 3. The image forming apparatus according to claim 1, wherein the image forming unit is controlled to form a toner image on the image carrier.   The image forming means includes the plurality of image carriers, and toner images of the plurality of image carriers are transferred onto the endless belt in a multiple manner. The image forming apparatus described.

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