JP4928285B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus in which a plurality of image forming units are arranged in tandem.

  2. Description of the Related Art Conventionally, as an image forming apparatus for forming a color image, an image forming unit that forms magenta, shear, yellow, and black toner images in a tandem arrangement is known. In this type of image forming apparatus, each color toner image formed by each image forming unit is superimposed and transferred onto a transfer belt, and the color toner images superimposed and transferred onto the transfer belt are collectively transferred onto a sheet. .

  In such an image forming apparatus, when the linear velocity of the transfer belt is unstable, the toner images are not accurately superimposed on the transfer belt from each image forming unit, and the colors that are collectively transferred onto the sheet are transferred. A color shift occurs in the toner image.

Therefore, Patent Document 1 proposes setting the peripheral speed of the photosensitive drum of each image forming unit to be slower than the linear speed of the transfer belt. According to this, the photosensitive drum in close contact with the transfer belt is apparently transferred. Since the belt is driven and the torque of each photosensitive drum is applied to the transfer belt, fluctuations in the speed of the transfer belt and each photosensitive drum can be suppressed.
JP-A-11-65222 (second and third pages, FIGS. 1 and 3)

  By the way, in the image forming apparatus, color misregistration correction and belt correction using a toner patch are performed at the time of startup or the like. Here, the color misregistration correction is performed by detecting a toner patch of each color formed in each image forming unit and transferred onto the transfer belt by a sensor, measuring a deviation of a time interval when the toner patch of each color is detected, and controlling the control unit. Is performed by adjusting the irradiation timing of light to each photosensitive drum so as to eliminate this deviation.

  The belt speed correction includes the time when the image forming unit irradiates light on the transfer belt to form an electrostatic latent image of the toner patch, and the time when the sensor detects each toner patch formed on the transfer belt. This is performed by the control unit based on the time interval deviation and the driving rotation speed of the transfer belt.

  Therefore, if there is slack in the transfer belt, the slack state changes during use, and the color misregistration correction and belt speed correction are distorted, resulting in color misregistration in the color image. For this reason, it is necessary to always maintain the rotating transfer belt without slack between the image forming units.

  However, in the image forming apparatus proposed in Patent Document 1, when the transfer belt is loose between the photosensitive drums at the time of activation, the photosensitive drum and the transfer belt are in close contact with each other while the transfer belt is operating. However, this tends to remain loose, and there is a problem that it takes time until the transfer belt is free of slack.

  In particular, when the photosensitive drum is an OPC photosensitive drum, if the transfer belt is driven before the OPC photosensitive drum, a minute scratch is generated at the contact portion of the OPC photosensitive member with the transfer belt, and the scratch is damaged after the rotation. A difference in surface friction coefficient is generated in the cleaning blade portion, which causes rotational fluctuations in the OPC photosensitive drum and causes image defects such as lateral stripes.

  The present invention has been made in view of the above problems, and its object is to prevent the occurrence of image defects such as color misregistration caused by the slack of the transfer belt and horizontal stripes caused by scratches on the OPC photosensitive drum. An object of the present invention is to provide an image forming apparatus capable of stably obtaining an image.

  In order to achieve the above object, the invention according to claim 1 is characterized in that an endless transfer belt is stretched and supported on a driving roller and a driven roller, and a plurality of image forming drums each provided with an OPC photosensitive drum in contact with the transfer belt. In an image forming apparatus having units arranged in tandem, the peripheral speed of the OPC photosensitive drum is set to be larger than the linear speed of the transfer belt, and rotation starts sequentially from the OPC photosensitive drum on the downstream side in the moving direction of the transfer belt. Finally, the transfer belt is driven.

  According to a second aspect of the present invention, in the first aspect of the present invention, the drive roller is disposed in the vicinity of the OPC photosensitive drum that is the most downstream in the traveling direction of the transfer belt.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, after the transfer roller is disposed at a position facing the OPC photosensitive member with the transfer belt interposed therebetween, and all the OPC photosensitive drums start to rotate. A bias voltage is continuously applied to the transfer roller.

  According to the first aspect of the present invention, since the rotation is started sequentially from the OPC photosensitive drum on the downstream side in the traveling direction of the transfer belt and finally the transfer belt is driven, the transfer belt between the OPC photosensitive drums immediately after activation. All the slack in the image is eliminated, and the color misregistration can be corrected with high accuracy, and a high-quality color image without color misregistration can be obtained. Finally, the transfer belt is driven and the peripheral speed of the OPC photosensitive drum is set to be larger than the linear speed of the transfer belt, so that scratches on the surface of the OPC photosensitive drum are prevented, and the OPC photosensitive drum rotates. Occurrence of image defects such as horizontal stripes is prevented, and a high-quality color image can be stably obtained. In addition, since the rotation is started sequentially from the OPC photosensitive drum on the downstream side in the moving direction of the transfer belt, it is not necessary to supply a starting current to all the motors that drive each OPC photosensitive drum at once, and the capacity of the power source is kept low. Cost can be reduced.

  According to the second aspect of the present invention, since the driving roller is disposed in the vicinity of the OPC photosensitive drum on the most downstream side in the moving direction of the transfer belt, the transfer belt between the driving roller and the OPC photosensitive drum on the most downstream side in the moving direction of the transfer belt is arranged. The slack can be removed immediately after the transfer belt is activated.

  According to the third aspect of the present invention, since the bias voltage is continuously applied to the transfer roller after all the OPC photosensitive drums have started to rotate, there is a state in which the transfer belt and the OPC photosensitive drum are attracted by the bias voltage. Maintained. As a result, the state in which the transfer belt is not loose between the OPC photosensitive drums and the color misregistration correction is performed is maintained, and a high-quality color image can be stably obtained.

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

  FIG. 1 is a longitudinal sectional view showing a schematic configuration of a color printer as an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a partially enlarged view in the vicinity of an image forming unit of the color printer, and FIG. 3 is a schematic configuration diagram of a sensor. It is.

  The color printer 10 according to the present embodiment includes a control unit 12, a paper feeding unit 40, an image forming unit 50, and a fixing unit 70 inside the main body. Here, the control unit 12 controls a sheet conveying operation, an image forming operation, and the like.

  The paper feed unit 40 includes a paper feed cassette 41, a paper feed roller 42, a transport roller pair 43 and a registration roller pair 44. Here, the paper feed cassette 41 is detachably provided at the lower part of the main body, and a plurality of sheets P are stacked and accommodated therein. Then, the paper P is sent one by one to the paper transport path 46 by the paper feed roller 42, and transported along the paper transport path 46 by the transport roller pair 43, the registration roller pair 44, and the like.

  The image forming unit 50 is arranged corresponding to each of the image forming units 60a, 60b, 60c, 60d for magenta, cyan, yellow, and black arranged in tandem and the image forming units 60a to 60d. Further, a primary transfer roller 51, an endless intermediate transfer belt 52, a sensor 54, and a belt cleaner 57 are provided.

  The image forming units 60a to 60d all have the same configuration, and as shown in FIG. 2, an OPC photosensitive drum 61 that rotates in the direction indicated by the arrow (counterclockwise) in accordance with the rotation of the intermediate transfer belt 52. The charger 62, the LED print head 63, the developing device 64, the drum cleaner 65, and the static eliminator 66 are arranged around the OPC photosensitive drum 61. The primary transfer roller 51 is rotatably disposed at a position facing the OPC photosensitive drum 61 with the intermediate transfer belt 52 interposed therebetween.

  Here, the intermediate transfer belt 52 is stretched and supported by a driving roller 55 and driven rollers 56a, 56b, and 56c, and the OPC photosensitive drums of the image forming units 60a to 60d are provided on the lower outer surface of the intermediate transfer belt 52. 61 is in contact. The driving roller 55 drives the intermediate transfer belt 52, and the intermediate transfer belt 52 rotates in the arrow direction (clockwise direction) in FIG.

  Further, as shown in FIG. 3, the sensor 54 includes an LED light emitting portion 54a and a light receiving portion 54b made of a phototransistor, and detects the signal intensity of the toner patch formed on the intermediate transfer belt 52. Therefore, it is used for correction of color misregistration, color tone, and the like. That is, in the sensor 54, light is emitted from the LED light emitting unit 54a toward the intermediate transfer belt 52, the intensity of the reflected light is detected by the light receiving unit 54b, and the detected signal is transmitted to the control unit 12. Then, it is used for correction of color misregistration and color tone.

  Further, the belt cleaning device 57 removes a toner patch formed on the intermediate transfer belt 52 as an untransferred toner remaining on the intermediate transfer belt 52 without being transferred from the intermediate transfer belt 52 to the paper P or as an image density correction pattern. It is removed by a cleaning blade (not shown).

  The fixing unit 70 includes a fixing roller 71 and a pressure roller 72 that are pressed against each other and rotate. The toner image transferred onto the paper P is heated and pressed to apply the toner image onto the paper P. It is to fix.

  Next, an image forming operation of the color printer 10 having the above configuration will be described.

  When a user instructs image formation from an external computer (not shown) connected to the color printer 10 directly or via a network, the control unit 12 receives the instruction and operates each unit.

  That is, the intermediate transfer belt 52 is rotationally driven in the direction of the arrow (clockwise) in FIG. 1 by the drive roller 55, and leftward in FIG. 1 with respect to the OPC photosensitive drums 61 of the image forming units 60a to 60d in contact therewith. Move to. When each OPC photosensitive drum 61 rotates in the direction of the arrow (counterclockwise) in FIG. 1, the surface of the OPC photosensitive drum 61 is uniformly charged by the charger 62.

  Next, when the OPC photosensitive drums 61 of the image forming units 60a to 60d are irradiated with light emitted from the LED print head 63 based on the electrical signal of the original image sent from the external computer, the respective OPC photosensitive drums. An electrostatic latent image corresponding to the document image is formed on 61. The electrostatic latent images formed on the respective OPC photosensitive drums 61 are developed by the developing devices 64 using the magenta, cyan, and black toners, and are visualized as magenta, cyan, yellow, and black toner images. It becomes.

  When the rotation of each OPC photosensitive drum 61 advances and the leading edge of the toner image carried thereon reaches the position facing each primary transfer roller 51 with the intermediate transfer belt 52 interposed therebetween, each primary transfer roller 51 is charged with toner. A bias voltage having a polarity opposite to the polarity is applied, and the toner image on each OPC photosensitive drum 61 is transferred to the intermediate transfer belt 52. Incidentally, the transfer residual toner which is not transferred from each OPC photosensitive drum 61 to the intermediate transfer belt 52 and remains on the OPC photosensitive drum 61 is removed by the drum cleaner 65, and the electric charge remaining on the surface of each OPC photosensitive drum 61 is The OPC photosensitive drum 61 is removed by the static eliminator 66 and is prepared for the next image forming operation.

  On the other hand, the paper P in the paper feed cassette 41 of the paper feed unit 40 is taken out one by one from the paper feed roller 42 and sent to the paper transport path 46, and transported to the registration roller pair 44 by the transport roller pair 43. Is in a temporary standby state.

  Thus, as described above, magenta, cyan, yellow, and black toner images are sequentially superimposed and transferred onto the intermediate transfer belt 52 from the OPC photosensitive drums 61 of the image forming units 60a to 60d. A full-color toner image is formed, and the sheet P is moved between the intermediate transfer belt 52 and the secondary transfer roller 53 by the registration roller pair 44 at the timing when the leading end of the full-color toner image reaches a position facing the secondary transfer roller 53. To the secondary transfer section. At this time, a bias voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 53, and the full-color toner image on the intermediate transfer belt 52 is collectively transferred onto the paper P. The transfer residual toner that is not transferred from the intermediate transfer belt 52 onto the paper P and remains on the intermediate transfer belt 52 is removed by the belt cleaner 57, and the intermediate transfer belt 52 is prepared for the next image forming operation.

  Then, the sheet P on which the full color toner image is transferred is conveyed to the fixing unit 70 and is heated and pressed in the process of passing between the fixing roller 71 and the pressure roller 72 of the fixing unit 70 to be full color toner. After receiving the fixing of the image, the paper is discharged out of the apparatus by a pair of paper discharge rollers 81 and stacked on a paper discharge tray 75 provided at the upper part of the main body.

  The above is a series of operations for full-color image formation. In this embodiment, when the color printer 10 is started up or resumed after the operation is stopped, the image forming unit 60d on the downstream side in the rotation direction of the intermediate transfer belt 52 performs image processing. The OPC photosensitive drums 61 are sequentially rotated at predetermined time intervals in the order of the forming units 60c, 60b, 60a, and finally the intermediate transfer belt 52 is driven. However, the most upstream OPC photosensitive drum 61 and the intermediate transfer belt 52 may be driven to rotate simultaneously.

  By the way, the speed of the surface of the intermediate transfer belt 52 is constant at Vb when there is no contact with the intermediate transfer belt 52 other than the driven rollers 56a to 56c, and the peripheral speed of each photosensitive drum 61 is the same. However, in the present embodiment, the peripheral speed Vd of the OPC photosensitive drum 61 is set to be larger than the surface speed Vb of the intermediate transfer belt 52 (Vd>). Vb).

  Thus, the intermediate transfer belt 52 often has slack between the image forming units 60a to 60d when the color printer 10 is started up or when the operation is resumed after the operation is stopped. The OPC photosensitive drums 61 are sequentially rotated at predetermined time intervals in the order from the image forming unit 60d downstream of the intermediate transfer belt 52 in the rotation direction to the image forming units 60c, 60b, 60a, and finally the intermediate transfer belt 52. As a result, the slack of the intermediate transfer belt 52 between the OPC photosensitive drums 61 is eliminated immediately after activation, and as a result, highly accurate color misregistration can be corrected, and a high-quality color image without color misregistration can be obtained. can get.

  In this embodiment, the intermediate transfer belt 52 is finally driven, and the peripheral speed Vd of the OPC photosensitive drum 61 is set to be larger than the linear speed Vb of the intermediate transfer belt 52 (Vd> Vb). 61 prevents scratches on the surface, prevents image defects such as lateral streaks due to rotational fluctuations of the OPC photosensitive drum 61, and stably provides a high-quality color image.

  Further, since the rotation is started sequentially from the OPC photosensitive drum 61 on the downstream side in the traveling direction of the intermediate transfer belt 52, it is not necessary to supply a starting current to all the motors that drive each OPC photosensitive drum 61 at once, and the capacity of the power source The cost can be reduced by keeping the value low.

  In this embodiment, since the driving roller 55 is disposed in the vicinity of the OPC photosensitive drum 61 on the most downstream side in the traveling direction of the intermediate transfer belt, the OPC photosensitive drum 61 on the most downstream side in the traveling direction of the driving roller 55 and the intermediate transfer belt 52 is disposed. The slack of the intermediate transfer belt 52 can be removed immediately after the intermediate transfer belt 52 is started.

  By the way, when the color printer 10 is started up or after a certain number of images are formed, color misregistration correction and belt speed correction using a toner patch are performed. The color misregistration correction is formed in the image forming units 60a to 60d. The toner patch of each color transferred onto the intermediate transfer belt 52 is detected by the sensor 54, the deviation of the time interval at which the toner patch of each color is detected is measured, and the control unit 12 eliminates this deviation. This is done by adjusting the light irradiation timing.

  The belt speed correction is formed on the intermediate transfer belt 52 and the time when the image forming units 60a to 60d irradiate light from the LED print head 63 to form an electrostatic latent image of the toner patch on the intermediate transfer belt 52. This is performed by the control unit 12 based on the deviation of the time interval from the time when the sensor 54 detected each toner patch and the driving rotation speed of the intermediate transfer belt 52.

  Thus, when the color misregistration correction and the belt speed correction are performed in a state where the intermediate transfer belt 52 is slack, if the operation state of the intermediate transfer belt 52 is changed after the correction, the full color image is displayed. Color misregistration will occur.

  However, in the present embodiment, as described above, the slack of the intermediate transfer belt 52 can be quickly removed both when the color printer 10 is started and when the operation is resumed after the operation is stopped, so that a high-quality full-color image is obtained. be able to.

  Further, in the image forming apparatus in which the image forming unit is tandemly arranged with respect to the belt and the toner image is directly transferred from the image forming unit to the sheet conveyed by the belt, the belt and the photosensitive drum are rotated in the same manner as described above. Therefore, it is possible to remove the slack of the belt immediately after the start of the apparatus, so that the color misregistration correction can be accurately performed using the toner patch formed on the belt, and a high-quality color image can be stably displayed. Obtainable.

  By the way, in the present embodiment, after all the OPC photosensitive drums 61 start to rotate and the intermediate transfer belt 52 between the image forming units 60a to 60d is not loosened, a bias voltage is applied to each primary transfer roller 51. It keeps applying.

  Then, since the electrostatic attraction force continues to act between the intermediate transfer belt 52 and each OPC photosensitive drum 61, even if the intermediate transfer belt 52 is attached to a curl due to long-term use, a state without slack is maintained. The rotational speed of the intermediate transfer belt 52 can be made constant with the torque serving as the rotational resistance of the intermediate transfer belt 52 generated by the difference between the linear speed Vb of the intermediate transfer belt 52 and the peripheral speed Vd of the OPC photosensitive drum 61 being constant. Can be made constant. Therefore, when color misregistration correction is performed, the state is maintained, so that color misregistration hardly occurs and a high-quality full color image can be stably obtained.

1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus (color printer) according to the present invention. FIG. 3 is a partially enlarged view of the vicinity of an image forming unit of an image forming apparatus (color printer) according to the present invention. 1 is a schematic configuration diagram of a sensor of an image forming apparatus (color printer) according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color printer 12 Control part 40 Paper feed part 41 Paper feed cassette 42 Paper feed roller 43 Conveyance roller pair 44 Registration roller pair 46 Paper conveyance path 50 Image formation part 51 Primary transfer roller 52 Intermediate transfer belt 54 Sensor 54a LED light emission part 54b Light reception Section 55 Drive roller 55a to 55c Driven roller 57 Belt cleaner 60a to 60d Image forming unit 61 OPC photosensitive drum 62 Charger 63 LED print head 64 Developer 65 Drum cleaner 66 Charger 70 Fixing section 71 Fixing roller 72 Pressure roller 75 Paper discharge tray 81 Paper discharge roller pair P Paper

Claims (3)

In an image forming apparatus in which an endless transfer belt is stretched and supported on a driving roller and a driven roller, and a plurality of image forming units each provided with an OPC photosensitive drum in contact with the transfer belt are arranged in tandem.
The peripheral speed of the OPC photosensitive drum is set to be larger than the linear speed of the transfer belt, the rotation starts sequentially from the OPC photosensitive drum on the downstream side in the traveling direction of the transfer belt, and finally the transfer belt is driven. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the driving roller is disposed in the vicinity of the OPC photosensitive drum located downstream in the traveling direction of the transfer belt.   2. A transfer roller is disposed at a position facing the OPC photosensitive member with the transfer belt interposed therebetween, and a bias voltage is continuously applied to the transfer roller after all the OPC photosensitive drums start rotating. Or the image forming apparatus of 2.

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