JP2011075858A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus that stably obtains a high quality color image free from color shift. <P>SOLUTION: The color image forming apparatus includes: a drive roller 8 which is rotated and driven by a rotating power transmitted from a motor via a gear train; an endless intermediate transfer belt 7 which is rotated and driven by the drive roller 8; a plurality of photoreceptor drums (image carriers) 2a to 2d which are arranged tandem along the running direction of the intermediate transfer belt 7; and an ID sensor 25 which detects a color toner images superposed and transferred to the surface of the intermediate transfer belt 7 from the photoreceptor drums 2a to 2d. In the color image forming apparatus, the gear ratio of a plurality of gears composing the gear train is set to an integral multiple. The arrangement spacing between the ID sensor 25 and the photoreceptor drum 2d is set to an integral multiple of each of the arrangement spacings D between the photoreceptor drums 2a to 2d, while setting each of the arrangement spacings L between the photoreceptor drums 2a to 2d to an integral multiple of the circumference length of the drive roller 8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus such as a color copying machine or a color printer that forms a color image by electrophotography.

  In recent years, there has been a strong demand for colorization of image forming apparatuses such as copiers and printers that form images on paper by electrophotography, and color image forming apparatuses have been developed in response to this demand and are already in practical use. Since this color image forming apparatus is required to have a monochrome output speed, a tandem type color image forming apparatus has attracted attention.

  A tandem type color image forming apparatus includes a driving roller that is rotationally driven by rotational power transmitted from a motor through a gear train, an endless intermediate transfer belt that is rotationally driven by the driving roller, and an intermediate transfer belt A plurality of image carriers arranged in tandem along the running direction, and a plurality of primary transfer rollers that contact the image carrier via the intermediate transfer belt, and each color formed on each image carrier A color image is formed by superimposing and transferring a toner image onto an intermediate transfer belt.

  By the way, in such a color image forming apparatus, in order to prevent color misregistration of the color image, it is necessary to align the positions of the toner images of the respective colors superimposed and transferred on the intermediate transfer belt. For this reason, the position of the patch image formed on the intermediate transfer belt using the toner of each color is detected by an ID sensor, and the exposure timing for each image carrier is changed based on the detection result to change the toner image of each color. Alignment is performed. Specifically, the speed of the intermediate transfer belt is obtained by measuring the time from when the toner image is transferred from the image carrier onto the intermediate transfer belt until it reaches the ID sensor, and between this speed and the image carrier. The writing timing of each color is adjusted based on the interval.

  In Patent Document 1, the toner density sensor (ID sensor) is moved to the detection position in cooperation with the separation claw moving mechanism when the toner pattern image is read, and otherwise the toner density sensor is moved away from the detection position. There has been proposed a configuration in which the toner density sensor is prevented from being soiled by being moved to the storage position, and the toner density sensor is cleaned by a cleaning member.

Japanese Patent Laid-Open No. 1-128080

  By the way, in the color image forming apparatus, the running speed of the intermediate transfer belt depends on the peripheral speed of the driving roller, and the time from when the toner image is transferred from the image carrier onto the intermediate transfer belt until reaching the ID sensor. Strictly speaking, the time varies depending on the peripheral speed of the driving roller. Accordingly, when the peripheral speed of the driving roller varies due to rotation unevenness or shake of the driving roller, the writing timing of each color cannot be adjusted with high accuracy, and a color shift occurs in the color image.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a color image forming apparatus capable of stably obtaining a high-quality color image without color misregistration.

  To achieve the above object, the present invention provides a driving roller that is rotationally driven by rotational power transmitted from a motor via a gear train, an endless intermediate transfer belt that is rotationally driven by the driving roller, and the intermediate transfer belt. A plurality of image carriers arranged in tandem along the belt traveling direction, a plurality of primary transfer rollers contacting the image carrier via the intermediate transfer belt, and from each image carrier on the intermediate transfer belt In the color image forming apparatus provided with the ID sensor for detecting the color toner image superimposed and transferred to the image sensor, the interval between the image carriers is set to one round length of the drive roller, and the image sensor of the ID sensor and The arrangement interval is set to an integral multiple of the arrangement interval of each image carrier.

  According to a second aspect of the present invention, in the first aspect of the present invention, the gear ratio of a plurality of gears constituting the gear train from a motor that rotationally drives the drive roller is an integral multiple.

  According to a third aspect of the present invention, in the first aspect of the invention, the ID sensor is disposed so as to face the intermediate transfer belt and the upstream end portion or the vicinity of the downstream end portion of the winding portion of the drive roller. It is characterized by that.

  According to the first aspect of the present invention, since the gear ratio of the plurality of gears constituting the gear train for transmitting the rotational power of the motor to the driving roller is an integral multiple, all the gears and motors are integers by one rotation of the driving roller. It rotates only once, and the period of speed unevenness of the driving roller is every one rotation. Further, since the arrangement interval of each image carrier is set to one circumference of the drive roller, and the arrangement interval of the ID sensor with respect to the image carrier is an integral multiple of the arrangement interval of each image carrier, an intermediate caused by the drive roller. The transfer belt speed unevenness is canceled, and the writing start timing of each color is adjusted with high accuracy based on the speed of the intermediate transfer belt and the interval between the image carriers, so that a high-quality color image without color misregistration can be stably obtained. Can do.

  According to the second aspect of the present invention, since the gear ratio of the plurality of gears constituting the gear train from the motor that rotationally drives the drive roller is an integral multiple, the uneven speed of the intermediate transfer belt due to the gear train is also canceled. As a result, the accuracy of adjusting the write timing is further improved.

  According to the invention of claim 3, the intermediate transfer belt and the ID sensor are arranged by opposing the ID sensor in the vicinity of the upstream end portion or the vicinity of the downstream end portion of the intermediate transfer belt and the drive roller winding portion. Is accurately maintained, and the accuracy of adjusting the writing timing is always ensured.

1 is a side sectional view of a color image forming apparatus (color laser printer) according to the present invention. FIG. 2 is a diagram illustrating a positional relationship between a photosensitive drum and an ID sensor in a color image forming apparatus (color laser printer) according to the present invention. It is a figure which shows the arrangement | positioning relationship between the photosensitive drum and ID sensor in the color image forming apparatus which concerns on Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image forming unit is provided at the center of the main body 100. 1M, a cyan image forming unit 1C, a yellow image forming unit 1Y, and a black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, which are image carriers, and a charger 3a is disposed around each of the photosensitive drums 2a to 2d. 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are driven to rotate at a predetermined process speed in a direction indicated by an arrow (clockwise) by a driving motor (not shown). The chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between the driving roller 8 and the driven roller 9 so as to be able to run on the upper surface side of the respective photosensitive drums 2a to 2d. The transfer unit is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7. A belt cleaning device 11 is provided in the vicinity of the driven roller 9.

  By the way, above the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, toner containers 12a, 12b, 12c, and 12d for supplying toner to the developing devices 4a to 4d are arranged in a line. It is installed.

  In addition, a laser scanner unit (LSU) 13 is disposed below the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, and a paper feed cassette 14 is detachably attached to the bottom of the main body 100 below the image forming units. is set up. A plurality of sheets of paper (not shown) are stacked and accommodated in the paper feed cassette 14, and a pickup roller 15 for picking up paper from the paper feed cassette 14 and a picked up paper are placed near the paper feed cassette 14. A feed roller 16 and a retard roller 17 that are separated and fed one by one to the transport path S are provided.

  Further, the conveyance path S extending in the vertical direction on the side of the apparatus main body 100 includes a conveyance roller pair 18 that conveys the sheet, and the secondary transfer counter roller 8 and the second transfer opposing roller 8 at a predetermined timing after the sheet is temporarily held. A registration roller pair 19 is provided to be supplied to a secondary transfer portion which is a contact portion with the next transfer roller 10. Next to the conveyance path L, another conveyance path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of reversing roller pairs 20 are appropriately used for the conveyance path L ′. Are provided at regular intervals.

  By the way, the conveyance path L arranged in the vertical direction on one side in the apparatus main body 100 extends to the paper discharge tray 21 provided on the upper surface of the apparatus main body 100, and the fixing device 22 and the discharge path are in the middle. Paper roller pairs 23 and 24 are provided.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  When an image formation start signal is issued, the respective photosensitive drums 2a to 2d are rotationally driven in the image forming units 1M, 1C, 1Y, and 1K in a direction indicated by arrows (clockwise) at a predetermined process speed, and these photosensitive drums 2a. ˜2d are uniformly charged by the chargers 3a to 3d. The laser scanner unit 13 emits a laser beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d with the laser beam, and each color is applied to each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to the color image signal is formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is moved in the direction of the arrow in the figure by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 that is rotationally driven.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, in accordance with the timing at which the front end of the full-color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the drive roller 8 and the secondary transfer roller 10, The sheet fed to the conveyance path L by the feed roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 19. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 22, and the sheet on which the full-color toner image has been fixed by being heated and pressurized and thermally fixed on the surface of the sheet. Then, the paper is discharged onto the paper discharge tray 21 by the paper discharge roller pair 23 and 24, and a series of image forming operations is completed. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 11, and the intermediate transfer belt 7 is prepared for the next image formation.

  Incidentally, in order to prevent color misregistration of a color image formed in such a laser beam printer, it is necessary to align the positions of the toner images of the respective colors superimposed and transferred onto the intermediate transfer belt 7. For this reason, the position of the patch image formed on the intermediate transfer belt 7 is detected using the toner of each color, and the exposure timing by the laser light from the laser scanner unit 13 to each of the photosensitive drums 21a to 2d based on the detection result. The positions of the toner images of the respective colors are aligned with each other.

  Here, the gist of the present invention will be described with reference to FIG.

  FIG. 2 is a diagram showing the arrangement relationship between the photosensitive drum and the ID sensor in the laser printer shown in FIG. 1, and as shown in the drawing, on the downstream side of the black photosensitive drum 2d (downstream in the running direction of the intermediate transfer belt 7). Are provided with an ID sensor (density sensor) 25 for detecting the position of each color patch image formed on the intermediate transfer belt 7. The ID sensor 25 includes a light emitting element that emits laser light toward a patch image formed on the intermediate transfer belt 7 and a light receiving element that receives reflected light from the patch image.

  Thus, the speed of the intermediate transfer belt 7 is obtained by measuring the time from when each color patch image is transferred from the photosensitive drums 2a to 2d onto the intermediate transfer belt 7 until it reaches the ID sensor 25. By adjusting the writing start timing of each color based on the speed and the interval between the photosensitive drums 2a to 2d, the occurrence of color misregistration in the color image is prevented.

  By the way, the traveling speed of the intermediate transfer belt 7 depends on the peripheral speed of the drive roller 8, and the patch image is transferred from the photosensitive drums 2a to 2d onto the intermediate transfer belt 7 until reaching the ID sensor 25. Strictly speaking, the time varies depending on the peripheral speed of the drive roller 8. Accordingly, when the peripheral speed of the driving roller 8 fluctuates due to uneven rotation or vibration of the driving roller 8, the timing for writing out each color cannot be adjusted with high accuracy, and color misregistration occurs in the color image. Is as described above. The driving roller 8 is rotationally driven by rotational power transmitted from a motor (not shown) through a gear train (not shown), and the intermediate transfer belt 7 is rotationally driven by the driving roller 8 at a predetermined speed.

  Therefore, in the present embodiment, the gear ratio of the plurality of gears constituting the gear train that transmits the rotational power from the motor to the driving roller 8 is set to an integral multiple, and the arrangement interval D of the photosensitive drums 2a to 2d is set to the driving roller 8. And the ID sensor 25 is an integral multiple of the arrangement interval D from the photosensitive drum 2d to each of the photosensitive drums 2a to 2d (in this embodiment, 1 time = one circumferential length of the driving roller 8).

  Further, the ID sensor 25 is disposed opposite to the vicinity of the upstream end portion in the moving direction at the winding portion of the intermediate transfer belt 7 and the driving roller 8. Therefore, the surface of the intermediate transfer belt 7 that faces the ID sensor 25 is a flat surface, and since it is supported by the driving roller 8, it does not flutter and the distance from the ID sensor 25 is kept constant. Thereby, fluctuations in the reflected light of the sensor 25 are suppressed and the light is accurately received, so that the patch image on the intermediate transfer belt 7 can be detected with high accuracy.

  Thus, according to the present embodiment, since the gear ratio of the plurality of gears constituting the gear train for transmitting the rotational power of the motor to the driving roller 8 is an integral multiple, all the gears are rotated by one rotation of the driving roller 8. The motor rotates only an integer number of times, and the speed unevenness cycle of the drive roller 8 is every rotation.

  In the present embodiment, the arrangement interval L of the photosensitive drums 2a to 2d is set to one circumference of the drive roller 8, and the arrangement interval of the ID sensor 25 to the photosensitive drum 2d is set to the arrangement interval of the photosensitive drums 2a to 2d. Therefore, the unevenness in the speed of the intermediate transfer belt 7 caused by the drive roller 8 is canceled, and the writing timing of each color is adjusted with high accuracy based on the speed of the intermediate transfer belt 7 and the arrangement interval D of the photosensitive drums 2a to 2d. The For this reason, according to the present embodiment, it is possible to stably obtain a high-quality color image without color misregistration.

FIG. 3 is a diagram showing the positional relationship between the photosensitive drum and the ID sensor in the color image forming apparatus according to Embodiment 2 of the present invention. The intermediate transfer belt 7 ′ is stretched by a plurality of driven rollers 9 ′ and a driving roller 8 ′, and is circulated so that the upper surface is a horizontal plane and curves downward. Above the intermediate transfer belt 7 ′, image forming units for the respective colors are arranged so that the photosensitive drums 2a ′ to 2d ′ are in contact with the horizontal surface of the upper surface. Since the basic configuration of the image forming unit is the same as that of the image forming units 1M, 1C, 1Y, and 1K in the previous embodiment, the description thereof is omitted. Each photosensitive drum 2a 'to 2d
The interval of 'is set to D'. In addition, a secondary transfer roller 10 'is disposed at the lowermost portion of the downwardly curved portion of the transfer belt 7' so as to face the driven roller 9 'as a counter roller.

  Here, as in the previous embodiment, the arrangement interval D ′ of the photosensitive drums 2 a ′ to 2 d ′ is set to be the same as the circumferential length of the drive roller 8 ′. Similarly, the gear ratio of a plurality of gears constituting a gear train for transmitting the rotational power of the motor to the drive roller 8 'is also an integer multiple. An ID sensor (density sensor) 25 ′ for detecting a patch image formed on the intermediate transfer belt 7 ′ has a downstream end portion in the moving direction at the winding portion of the intermediate transfer belt 7 ′ and the drive roller 8 ′. It is arranged opposite to the vicinity. Similarly to the previous embodiment, the length from the nip portion of the intermediate transfer belt 7 ′ with the photosensitive drum 2 d ′ to the position where the ID sensor 25 ′ faces is the arrangement interval D of the photosensitive drums 2 a ′ to 2 d ′. Is set to be '. As a result, the uneven speed of the intermediate transfer belt 7 ′ caused by the drive roller 8 ′ is canceled and the patch image can be detected with high accuracy.

  In the above, the embodiment in which the present invention is applied to a color laser printer has been described. However, the present invention can be similarly applied to any other color image forming apparatus such as a color copying machine. Of course.

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drums 2a 'to 2d' Photosensitive drums 3a to 3d Chargers 4a to 4d Developing devices 5a to 5d Transfer rollers 6a to 6d Drum cleaning device 7, 7 'Intermediate transfer belt 8, 8' Drive roller 9, 9 'Driven roller 10, 10' Secondary transfer roller 11 Belt cleaning device 12a-12d Toner container 13 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Pickup roller 16 Feed roller 17 Retard roller 18 Conveyance roller pair 19 Registration roller pair 20 Conveyance roller pair 21 Paper discharge tray 22 Fixing device 23, 24 Paper discharge roller pair 25, 25 'ID sensor 100 D, D 'photosensitive drum arrangement interval L, L' transport path

Claims (3)

A driving roller that is rotationally driven by rotational power transmitted from the motor through a gear train, an endless intermediate transfer belt that is rotationally driven by the driving roller, and a tandem arrangement along the traveling direction of the intermediate transfer belt A plurality of image carriers, a plurality of primary transfer rollers in contact with the image carrier via the intermediate transfer belt, and a color toner image superimposed on the intermediate transfer belt from each image carrier. In a color image forming apparatus provided with an ID sensor,
The interval between the image carriers is an integral multiple of the circumference of the drive roller, and the interval between the ID sensor and the image carrier is an integer multiple of the interval between the image carriers. A color image forming apparatus.   2. The color image forming apparatus according to claim 1, wherein a gear ratio of a plurality of gears constituting the gear train from a motor for rotationally driving the drive roller is an integral multiple. The color image forming apparatus according to claim 1, wherein the ID sensor is disposed opposite to an upstream end or a vicinity of a downstream end of the intermediate transfer belt and the winding portion of the driving roller.

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