JP2006058586A - Image forming apparatus and driving method for the apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing the occurrence of a toner band during an image forming operation, and extending the durability of developing components. <P>SOLUTION: The image forming apparatus includes: a laser scanner 3 for forming a latent image on a photoreceptor 1; a developing unit 4 having a developing roll 7 driven in order to supply toner to the surface of the photoreceptor 1 on which the latent image is formed by the laser scanner 3; and a developing roll drive control section 88 for driving the developing roll 7 and altering the rotating speed of the developing roll 7 during the drive of the developing roll 7. The developing roll drive control section 88 drives the developing roll 7 at a first rotating speed during the period of time that the area in which the latent image is formed by the laser scanner 3 passes through the facing part of the photoreceptor 1 and developing roll 7. The developing roll drive control section 88 drives the developing roll 7 at a second rotating speed lower than the first rotating speed, until the area where the latent image is formed passes through the facing part and then the subsequent area where a latent image is formed reaches the facing part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus and a driving method thereof.

  In an image forming apparatus such as a copying machine or a printer that forms an image by electrophotography, an image is formed on a sheet (a material to be transferred) in accordance with an image forming process including charging, exposure, development, transfer, and fixing. Further, a developing roll is incorporated in a developing device used in this type of image forming apparatus. The developing roll is driven to supply toner to the surface of the photoconductor when developing an electrostatic latent image (hereinafter referred to as “latent image”) formed on the surface of the photoconductor. Alternatively, they are arranged to face each other in a contact state.

  When developing the latent image actually formed on the photoconductor with toner, it is necessary to rotate the developing roll in order to continuously supply the toner to the surface of the photoconductor. For this reason, in the conventional image forming apparatus, the developing roll in the developing device is continuously driven at a constant rotational speed from the start to the end of a series of image forming operations (for example, a copying operation). Yes. However, when the developing roll is driven by such a method, there has been a problem that the development roll and the roll drive system are rapidly abraded and the durability of the developing component is shortened.

  As a countermeasure, a developing roll is driven every time one latent image is developed, and driving of the developing roll is stopped between the development of the previous latent image and the development of the next latent image. It is possible to adopt it. However, in this method, when developing a plurality of latent images in sequence, the driving and stopping of the developing roll are repeated many times. In such a series of operations, when the driving of the developing roll is started and stopped, A phenomenon that toner is unnecessarily transferred from the developing roll to the photosensitive member and adheres in a belt shape (hereinafter referred to as “toner band”) occurs, which leads to an increase in toner consumption and an increase in dirt inside the machine. there were.

  Therefore, Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for switching the bias voltage applied to the developing roll between a DC component bias voltage and a bias voltage obtained by superimposing an AC component on the DC component.

JP 2002-328497 A

  However, in the technique described in Patent Document 1, when the bias voltage of the developing roll is changed, the response time (rise time) until the value of the bias voltage actually applied to the developing roll reaches the changed voltage value. It was difficult to sufficiently suppress the generation of toner bands.

  An image forming apparatus according to the present invention includes a latent image forming unit that forms a latent image on a photoconductor, and a developing roll that is driven to supply toner to the surface of the photoconductor on which the latent image is formed by the latent image forming unit. And a developing unit that drives the developing roll and that controls the rotation speed of the developing roll while the developing roll is being driven.

  In the image forming apparatus according to the present invention, when a plurality of latent images are continuously formed by the latent image forming unit by providing a control unit that varies the rotation speed of the developing roll during the driving of the developing roll, By continuously driving the developing roll without stopping, generation of a toner band is suppressed, and by changing the roll rotation speed during driving of the developing roll, wear of the developing roll and the roll driving system can be suppressed.

  According to the present invention, the generation of toner bands can be sufficiently suppressed to effectively prevent an increase in toner consumption and an increase in dirt inside the machine. In addition, it is possible to extend the durability of the developing component by suppressing the progress of wear of the developing roll and the roll drive system.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

  1A and 1B show a configuration example of an image forming apparatus to which the present invention is applied. FIG. 1A is a schematic side view thereof, and FIG. 1B is a partial plan view of FIG. In the figure, the photoreceptor 1 is formed in a drum shape as a whole. The photoreceptor 1 is driven to rotate in the counterclockwise direction in the figure. Around the photoconductor 1, there are a charger 2, an exposure laser scanner 3 as a latent image forming unit, a developing device 4, a transfer roll 5, and a cleaner 6 according to the rotation direction of the photoconductor 1. Arranged in order.

  The charger 2 uniformly charges the surface of the photoreceptor 1 with a uniform potential, and is configured using, for example, a corona discharger. The laser scanner 3 forms a latent image on the surface of the photoconductor 1 by exposing the surface of the photoconductor 1 charged by the charger 2 by irradiating a laser beam. More specifically, the laser scanner 3 turns on and off (flashes) the laser beam applied to the photosensitive member 1 in accordance with an image signal (video signal), and scans the laser beam along the axial direction of the photosensitive member 1. As a result, a latent image is formed on the surface of the photoreceptor 1.

  The developing device 4 develops (visualizes) the latent image into a toner image by supplying toner to the surface of the photoreceptor 1 on which the latent image is formed by the laser scanner 3. The developing device 4 incorporates a developing roll 7 and a roll driving system 8 that rotationally drives the developing roll 7. The developing roller 7 is disposed in a state of facing the photoconductor 1 in the state of being in proximity to or in contact with the photoconductor 1. The toner is supplied from the developing roll 7 to the photoconductor 1 at a portion where the developing roll 7 and the photoconductor 1 face each other. That is, a thin layer of toner having a uniform thickness is formed on the outer peripheral surface of the developing roll 7, and the surface (latent image forming surface) of the photoreceptor 1 is in contact with or close to the toner layer. , 7), the toner is transferred from the developing roll 7 to the photosensitive member 1, and the latent image is developed into a toner image.

  The roll drive system 8 includes a drive motor 81 and a gear train in which a plurality of (five in the illustrated example) gears 82 to 86 are combined. The drive motor 81 is a drive source for rotationally driving the developing roll 7, and is configured by using, for example, a pulse motor. The gear 82 is coaxially fixed to the output shaft (rotary shaft) of the drive motor 81. The gear 83 integrally includes two gear portions 83A and 83B having different outer diameters. The gear 82 meshes with the large-diameter gear portion 83A, and the gear 84 meshes with the small-diameter gear portion 83B. The gear 85 is fixed to the same shaft as the gear 84. The gear 86 is fixed to the same shaft as the drive roll 7. The gear 85 and the gear 86 are meshed with each other.

  In this roll drive system 8, when the drive motor 81 is driven, the driving force is transmitted by the gears 82 to 86, whereby the developing roll 7 rotates. At this time, the developing roll 7 is rotationally driven according to the rotational direction and rotational speed of the drive motor 81. The driving of the developing roll 7 is controlled by the developing roll drive control unit 88. The development roll drive control unit 88 outputs a motor drive signal to the drive motor 81 in order to drive the development roll 7. For example, if the driving motor 81 is configured by a pulse motor as described above, the developing roll drive control unit 88 supplies a motor driving pulse to the driving motor 81 when the developing roll 7 is driven. The developing roll drive control unit 88 has a function of changing the rotation speed of the developing roll 7 by changing the frequency of the motor driving pulse supplied to the drive motor 81 while the developing roll 7 is being driven. .

  The transfer roll 5 is for transferring the toner image formed on the surface of the photoreceptor 1 by the developing device 4 to a sheet (not shown). More specifically, the transfer roll 5 imparts a charge having a polarity opposite to that of the toner from the back side of the paper, thereby attracting the toner on the photoreceptor 1 to the paper side, thereby transferring the toner image onto the surface of the paper. To do. The transfer roll 5 is pressed against the photoreceptor 1 via an endless conveyance belt 9. The conveyance belt 9 conveys the sheet so as to pass through the nip portion between the photosensitive member 1 and the transfer roll 5 by running while holding a sheet (not shown) by suction and holding on the belt surface. The conveyor belt 9 is stretched by a pair of rolls 10 and 11. The pair of rolls 10 and 11 drives the conveyor belt 9 with one being a drive roll and the other being a driven roll. The cleaner 6 removes unnecessary toner remaining on the surface of the photoreceptor 1 without being transferred by the transfer roll 5.

  Next, a basic operation (image forming operation) of the image forming apparatus having the above configuration will be described. First, the photosensitive member 1 starts rotating almost simultaneously with the start of the image forming operation, and the surface of the rotating photosensitive member 1 is charged by the charger 2. Next, the laser scanner 3 irradiates the surface of the photoconductor 1 with a laser beam, and the laser beam is scanned in the axial direction of the photoconductor 1 (in the main scanning direction, thereby forming a latent image on the surface of the photoconductor 1. Next, toner is supplied to the surface of the photoconductor 1 by the developing roll 7 of the developing device 4, whereby the latent image on the photoconductor 1 is developed into a toner image.

  Next, in accordance with the timing at which the toner image on the photosensitive member 1 is sent to the transfer position by the transfer roll 5, the paper held on the conveyance belt 9 is sent to the transfer position by driving the conveyance belt 9. The toner image on 1 is transferred to a sheet. The sheet onto which the toner image has been transferred in this manner is sent to a fixing device (not shown), where the toner image is fixed. Unnecessary toner remaining on the surface of the photoreceptor 1 without being transferred to the paper is removed by the cleaner 6. Unnecessary charges remaining on the surface of the photoreceptor 1 are removed by a static eliminator (not shown). This completes the image forming operation per sheet. When image formation is continuously performed on a plurality of sheets, the same operation as described above is repeated for the number of sheets.

  Next, a processing procedure when the developing roll drive control unit 88 controls the driving of the developing roll 7 during the image forming operation will be described with reference to the flowchart of FIG. In the case where images are continuously formed on a plurality of sheets, a plurality of latent images are sequentially formed on the photosensitive member 1 corresponding to this, but in this case, latent images formed in advance are formed. It is assumed that a predetermined interval is ensured between the image and the latent image formed next.

  First, when an image forming operation is started by the image forming apparatus, the developing roll drive control unit 88 checks whether or not the latent image forming operation (exposure operation by a laser beam) is started by the laser scanner 3 (step S1). Next, it is confirmed whether or not the elapsed time from the start of the latent image forming operation has reached a first time set in advance (step S2). A motor driving pulse is supplied to drive the developing roll 7 at the first rotation speed (step S3).

  Here, as shown in FIG. 3, when the outer peripheral surface of the photosensitive member 1 is developed in a plane, the charging position P1 by the charger 2, the exposure position P2 by the laser scanner 3, the development position P3 by the developing device 4, and the transfer roll 5 The transfer position P4 by the cleaner and the cleaning position P5 by the cleaner 6 are sequentially arranged in the rotation direction (arrow direction) of the photosensitive member 1. On the other hand, in the first time, the first scanning line of the latent image formed on the surface of the photosensitive member 1 at the exposure position P2 of the laser scanner 3 is a portion where the photosensitive member 1 and the developing roll 4 are opposed to each other. Before reaching the developing position P3, the rotational speed of the drive motor 81 is set so as to satisfy the condition for reaching the first rotational speed.

  Specifically, for example, after the laser scanner 3 starts forming a latent image on the surface of the photosensitive member 1, the first scanning line of the latent image is developed with the photosensitive member 1 according to the rotation of the photosensitive member 1. The time required to reach the portion facing the roll 4 is T1, and after the motor drive pulse corresponding to the first rotational speed is supplied to the drive motor 81, the rotational speed of the drive motor 81 is actually the first speed. Assuming that the rising time until the rotational speed is reached is T2, the first time is set to a value that is the same as or smaller than the value of “T1-T2” (a value that is shorter in time). The required time T1 is obtained by dividing the separation distance between the exposure position P2 and the development position P3 in the rotation direction of the photosensitive member 1 by the peripheral speed of the photosensitive member 1, and the rising time of the drive motor 81 is It is obtained based on the rising characteristics of the motor. The first rotation speed is a roll rotation speed suitable for supplying toner with the developing roll 7 to the surface of the photoreceptor 1 on which a latent image is formed by the laser scanner 3 (a roll rotation speed suitable for development processing). ).

  Thereafter, the developing roll drive control unit 88 confirms whether or not the latent image forming operation has been completed by the laser scanner 3 (step S4), and confirms the end of the latent image forming operation. Whether there is a latent image to be checked is checked (step S5). If there is no latent image to be formed next, the driving of the developing roll 7 is stopped at that time (step S6). If there is a latent image to be formed next, it is confirmed whether or not the elapsed time from the completion of the latent image forming operation by the laser scanner 3 has reached a second time set in advance (step S7) When the second time is reached, the developing roll 7 is driven at the second rotational speed by changing the frequency of the motor driving pulse supplied to the driving motor 81 to a lower frequency than before (S7). Step S8) and then returning to step S1 and repeating the same process. However, in that case, the rotation speed of the developing roll 7 is changed from the second rotation speed to the first rotation speed in step S3.

  Here, in the second time, the development is such that the last scanning line of the latent image formed on the surface of the photoconductor 1 at the exposure position P2 of the laser scanner 3 is a portion where the photoconductor 1 and the developing roll 4 are opposed to each other. After reaching the position P3, the rotational speed of the drive motor 81 is set so as to satisfy the condition for changing from the first rotational speed to the second rotational speed. Specifically, for example, the last scanning line of the latent image formed on the surface of the photoconductor 1 by the laser scanner 3 reaches the facing portion between the photoconductor 1 and the developing roll 4 as the photoconductor 1 rotates. Assuming that the time required for this is T3 (= T1), the second time is set to the same value as time T3 or slightly longer than time T3. Further, the second rotation speed is set to a speed slower than the first rotation speed, preferably about 1/2 of the first rotation speed.

  In accordance with the processing procedure as described above, the developing roll drive control unit 88 develops an area in which a latent image is formed on the photosensitive member 1 by the laser scanner 3 (hereinafter referred to as a “latent image forming region”) with the photosensitive member 1. While passing the portion facing the roll 7 (hereinafter referred to as “development effective period”), the developing roller 7 is driven at the first rotation speed, and the latent image forming region passes through the facing portion. The developing roll 7 is driven at the second rotational speed until the next latent image forming area reaches the facing portion (hereinafter referred to as “developing blanking period”).

  FIG. 4 is a timing chart showing a control state of the driving state and the rotation speed of the developing roll 7 when the latent image forming operation is continuously performed three times. As shown in the figure, when the first latent image is formed, the developing roller 7 is driven at the first rotation speed V1 when the first time has elapsed since the first latent image formation was actually started, and thereafter When the second time has elapsed since the first latent image formation is completed, the developing roll 7 is driven at the second rotational speed V2. Further, the developing roller 7 is driven at the second rotational speed V2 until the second latent image formation is started, and the developing roller is reached when the first time has elapsed since the second latent image formation is started. 7 is again driven at the first rotational speed V1. Thereafter, the developing roller 7 is driven in the same manner as the first latent image formation, and the driving of the developing roller 7 is stopped when the second time has elapsed after the third latent image formation is completed.

  By driving the developing roller 7 in this way, a toner band is generated with the start of driving of the developing roller 7 in the first latent image formation after the image forming operation is started. When forming an image, since the driving is continued by changing the roll rotation speed without stopping the developing roll 7, the generation of a toner band can be prevented. Further, in the developing blanking period, the developing roll 7 is driven at a second rotational speed that is slower than the first rotational speed (roll rotational speed suitable for development processing). The load can be reduced to suppress the progress of wear. Therefore, it is possible to extend the durability of the developing component while effectively preventing an increase in toner consumption accompanying the generation of the toner band and an increase in dirt inside the machine.

  In the above embodiment, the developing roller 7 is driven at the first rotational speed after the first time has elapsed from the start of the latent image forming operation. The developing roll 7 may be driven at the first rotation speed at the same timing as the start.

1 is a diagram illustrating a configuration example of an image forming apparatus to which the present invention is applied. 6 is a flowchart illustrating a processing procedure when controlling the driving of the developing roll. It is a figure which shows the positional relationship when the outer peripheral surface of a photoreceptor is expand | deployed planarly. 4 is a timing chart showing a control state of a driving state and a rotation speed of a developing roll when an image forming operation is continuously performed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive body, 3 ... Laser scanner, 4 ... Developing device, 7 ... Developing roll, 8 ... Roll drive system, 81 ... Drive motor, 82-86 ... Gear, 88 ... Developing roll drive control part

Claims (4)

Latent image forming means for forming a latent image on the photoreceptor;
A developing unit having a developing roll that is driven to supply toner to the surface of the photoreceptor on which the latent image is formed by the latent image forming unit;
An image forming apparatus comprising: a control unit that drives the developing roll and changes a rotation speed of the developing roll during driving of the developing roll. The control means drives the developing roll at a first rotational speed while a latent image forming area formed by the latent image forming means passes through a portion where the photosensitive member and the developing roll are opposed to each other. The developing roll is driven at a second rotational speed that is slower than the first rotational speed until the next latent image forming area reaches the opposing part after the formation area passes through the opposing part. The image forming apparatus according to claim 1. The image forming apparatus according to claim 2, wherein the second rotation speed is set to about ½ of the first rotation speed. An image comprising: a latent image forming unit that forms a latent image on a photoconductor; and a developing unit that includes a developing roll that is driven to supply toner to the surface of the photoconductor on which the latent image is formed by the latent image forming unit. A driving method of a forming apparatus,
The developing roll is driven at a first rotational speed while the latent image forming area formed by the latent image forming means passes through the facing portion between the photoconductor and the developing roll, and the latent image forming area is opposed to the opposing area. The developing roll is driven at a second rotational speed that is lower than the first rotational speed until the next latent image forming area reaches the counter part after passing through the part. Driving method of forming apparatus.

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