JP2018010155A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress downtime caused for determining a target speed of an image carrier. SOLUTION: An image forming unit 5 having a developing sleeve 8 and forming an image on a photosensitive drum 10, an intermediate transfer belt 24 on which the image is transferred, a motor M3 of the photosensitive drum 10, and rotation of the photosensitive drum 10 The motor driver 1300 that controls the motor M3 so that the speed becomes the target speed, the PWM signal value (PWMduty1) of the motor M3 in the state where the developing sleeve 8 is rotating while the photosensitive drum 10 is rotating, and the photosensitive drum 10 It has a target speed determination unit 1002 that determines the target speed of the photosensitive drum 10 based on the PWM signal value (PWMduty2) of the motor M3 in a state where the developing sleeve 8 is rotating while the development sleeve 8 is not rotating, and has a target speed determination unit 1002. The 1002 is characterized in that PWMduty1 is acquired after image formation, and PWMduty2 is acquired after the rotation of the developing sleeve 8 is stopped. [Selection diagram] Fig. 9

Description

  The present invention relates to speed control of the image carrier in an image forming apparatus that forms an image on the image carrier.

  An electrophotographic image forming apparatus forms an electrostatic latent image on an image carrier and develops the electrostatic latent image using a developer to form an image. The image developed on the image carrier is once transferred to an intermediate transfer member, and then the image on the intermediate transfer member is transferred to a sheet.

  The image forming apparatus is required to control the speed at which the surface of the image carrier moves (surface speed) and the speed at which the surface of the intermediate transfer member moves (surface speed) at a constant speed. This is because the laser beam for forming the electrostatic latent image on the image carrier scans the image carrier at a predetermined timing. For example, if the surface speed of the image carrier changes, the scanning line pitch changes, so that the length of the image changes, or density unevenness occurs in the image on the image carrier. Therefore, the image forming apparatus executes feedback control based on the output of the encoder, for example, in order to control the surface speed of the image carrier and the surface speed of the intermediate transfer body.

  By the way, even if the surface speed of the image carrier and the surface speed of the intermediate transfer member can be controlled at a constant speed, the image is transferred depending on the load state of the nip portion for transferring the image on the image carrier to the intermediate transfer member. There is a possibility that the surface speed of the carrier and the surface speed of the intermediate transfer body may become uncontrollable. In other words, when changing from the state where the developer is present in the nip portion to the state where the developer is not present in the nip portion, the load on the motor changes suddenly, and the rotational speed of the motor becomes uncontrollable. There was a possibility of becoming. In the state where the rotation speed of the motor is not controlled, the above-described image defect occurs.

  Therefore, the image for adjusting the target speed of the image carrier so that the load of the motor when the developer is supplied to the nip portion and the load of the motor when the developer is not supplied to the nip portion are reduced. A forming apparatus is known (Patent Document 1). This image forming apparatus obtains a motor drive signal while supplying a developer to the nip portion and switching a motor speed command value, and switches a motor speed command value without supplying a developer to the nip portion. The driving signal is acquired. Since this image forming apparatus performs feedback control so that the rotation speed of the motor becomes a speed corresponding to the speed command value, the drive signal of the motor changes according to the load of the motor. That is, the image forming apparatus predicts the motor load from the motor drive signal.

Japanese Patent Laying-Open No. 2006-1268

  However, since the image forming apparatus described in Patent Document 1 switches the rotational speed of the motor, there is a problem that a long downtime occurs in order to determine the target speed of the image carrier.

  Therefore, an object of the present invention is to suppress downtime that occurs in order to determine the target speed of the image carrier.

  In order to solve the above problems, an image forming apparatus according to the present invention uses an image carrier, a developer carrier that rotates while carrying a developer, and the developer carried on the developer carrier. An image forming means for forming an image on the image carrier, an intermediate transfer member to which the image on the image carrier is transferred at a nip portion between the image carrier, and the image carrier. A motor, control means for controlling the motor so that the rotational speed of the image carrier becomes a target speed, and the developer carrier while the motor rotates the image carrier. A first signal value that changes according to the torque of the motor is acquired, and a second value that changes according to the torque of the motor in a state where the developer carrier does not rotate while the motor rotates the image carrier. Get signal value, previous Determining means for determining the target speed of the image carrier based on the first signal value and the second signal value, and after the image forming means has finished forming the image, the determining means Acquires the first signal value, and after the image forming means has finished forming all images based on the image data, the rotation of the developer carrier is stopped and the rotation of the developer carrier is stopped. Thereafter, the determination means acquires the second signal value.

  In order to solve the above problems, another image forming apparatus according to the present invention includes a first image carrier, a first developer carrier that rotates while carrying a developer, and the first developer carrier. A first image forming means for forming a first image on the first image carrier, a second image carrier, and a second developer that carries the developer and rotates using the developer carried on the body; A second image forming unit that forms a second image on the second image carrier using the developer carried on the second developer carrier; and the first image carrier; An intermediate transfer member to which the first image on the first image carrier is transferred at a nip portion of the second image carrier, and the second image on the second image carrier is transferred at a nip portion with the second image carrier. A first motor that rotationally drives the first image carrier, a second motor that rotationally drives the second image carrier, The first motor is controlled so that the rotational speed of the first image carrier becomes the first target speed, and the second motor is controlled so that the rotational speed of the second image carrier becomes the second target speed. And a first signal value that changes in accordance with the torque of the first motor in a state where the first developer carrier rotates while the first motor rotates the first image carrier. And acquiring a second signal value that changes according to the torque of the first motor in a state where the first developer carrier is not rotating while the first motor rotates the first image carrier. First determination means for determining the first target speed of the first image carrier based on the first signal value and the second signal value, and the second motor rotating the second image carrier. While the second developer carrier is rotating. A third signal value that changes in accordance with the motor torque is acquired, and the second motor rotates the second image carrier while the second developer carrier does not rotate. Second determination means for acquiring a fourth signal value that changes according to torque, and determining the second target speed of the second image carrier based on the third signal value and the fourth signal value; And after the first image forming means finishes forming the first image, the first determining means obtains the first signal value, and the second image forming means forms the second image. After finishing, the second determination means acquires the third signal value, and after the first image forming means finishes forming all the first images based on the image data, the first developer carrier After the rotation of the first developer carrier is stopped, the first developer carrier is stopped. The determining means acquires the second signal value, and after the second image forming means finishes forming all the second images based on the image data, the rotation of the second developer carrier is stopped, The second determination unit acquires the fourth signal value after the rotation of the second developer carrier is stopped.

  According to the present invention, it is possible to suppress downtime that occurs in order to determine the target speed of the image carrier.

Schematic sectional view of the image forming apparatus Schematic diagram of main parts of image forming unit Schematic diagram of pattern image Schematic diagram of main parts of photosensitive drum drive Schematic diagram of the main part of the drive section of the intermediate transfer belt Explanatory diagram of friction force characteristics Control block diagram of image forming apparatus Flowchart diagram showing image forming operation Flowchart diagram showing target speed adjustment processing The figure which illustrated the measurement result of the image formation number of sheets and the PWM signal value of the motor Illustration of sampling timing of PWM signal value

(Image forming device)
FIG. 1 shows a main part of the image forming apparatus 100. The image forming apparatus 100 includes four image forming units 5y, 5c, 5m, and 5bk for forming a multicolor image. The image forming units 5y, 5c, 5m, and 5bk form images using developers of different colors. Here, developers of colors such as yellow (Y), magenta (M), cyan (C) and black (Bk) are used. The letters y, c, m and bk given at the end of the reference numerals indicate the color of the developer.

  The photosensitive drum 10 is an image carrier that carries an electrostatic latent image or an image (developer image). The charger 21 is a charging unit that uniformly charges the surface of the photosensitive drum 10. The exposure device 22 is an exposure unit that exposes the charged photosensitive drum 10 to form an electrostatic latent image. The laser beam of the exposure device 22 scans the surface of the photosensitive drum 10. A method in which the laser beam scans the photosensitive drum 10 is referred to as a main scanning direction. The exposure device 22 includes an optical member such as a rotary polygon mirror, a mirror, and a lens that are rotationally driven to scan the laser beam. The developing device 1 is a developing unit that develops an electrostatic latent image using a developer and forms an image. The developer is, for example, a two-component developer including a nonmagnetic developer and a magnetic carrier. The primary transfer roller 23 transfers the image carried on the photosensitive drum 10 to the intermediate transfer belt 24. The intermediate transfer belt 24 functions as an intermediate transfer body to which an image on the photosensitive drum 10 is transferred. The secondary transfer roller 29 transfers the image carried on the intermediate transfer belt 24 onto the sheet P.

  The fixing device 27 heats the image on the sheet P and fixes the image on the sheet P. The drum cleaner 26 has a blade that contacts the photosensitive drum 10, and removes the developer remaining without being transferred from the photosensitive drum 10 to the intermediate transfer belt 24. The blade of the drum cleaner 26 functions as a removing member that removes the developer on the photosensitive drum 10. The belt cleaner 28 has a blade that comes into contact with the intermediate transfer belt 24 and removes the developer remaining without being transferred from the intermediate transfer belt 24 to the sheet P. The developer supply tank 20 supplies developer to the developing device 1. The sensor 14 has a light emitting element and a light receiving element, and is an optical sensor that measures reflected light from a measurement image formed on the intermediate transfer belt 24.

(Developer)
FIG. 2 is a schematic diagram of a main part of the image forming unit 5. The developing device 1 includes an agitating member 6 such as a screw that conveys the developer and the carrier supplied from the developer supply tank 20 while agitating. The stirring member 6 is driven by the motor M1. When the developer and the carrier are agitated, the developer is triboelectrically charged. The developing sleeve 8 is a developer carrying member that carries the developer. The developing sleeve 8 is disposed so as to face the photosensitive drum 10. The developing sleeve 8 is driven by a motor M2. When developing the electrostatic latent image, the power supply unit 2 applies a superimposed voltage (developing bias) obtained by superimposing an alternating voltage on a direct voltage to the developing sleeve 8. The power supply unit 2 functions as a voltage application unit that applies a superimposed voltage so as to generate a potential difference between the photosensitive drum 10 and the developing sleeve 8. The power supply unit 3 applies a predetermined DC voltage (transfer bias) to the primary transfer roller 23 when transferring the image on the photosensitive drum 10 to the intermediate transfer belt 24. The power supply unit 3 applies a DC voltage to the primary transfer roller 23 so that a potential difference is generated between the photosensitive drum 10 and the intermediate transfer belt 24.

(Adjusting the image forming position)
The images formed by the image forming units 5y, 5c, 5m, and 5bk are transferred so as to overlap the intermediate transfer belt 24. As a result, a full-color image is carried on the intermediate transfer belt 24. Therefore, if the image forming positions (image forming timings) of the image forming units 5y, 5c, 5m, and 5bk are different, the color of the full color image cannot be compensated. For example, the image forming positions of the image forming units 5y, 5c, 5m, and 5bk may change depending on the temperature change of the image forming apparatus 100 and the number of images formed. The relative displacement of the images formed in the image forming units 5y, 5c, 5m, and 5bk is called color misregistration.

  In order to correct the color misregistration, the image forming apparatus 100 forms a measurement image (pattern image) of each color on the intermediate transfer belt 24 and detects the color registration amount by the sensor 14. Then, the image forming apparatus 100 corrects the writing start timing (exposure timing) or the like when the image forming units 5y, 5c, 5m, and 5bk form an electrostatic latent image based on the detected color registration amount. The above-described processing is called color misregistration adjustment (color registration processing).

  FIG. 3 is a schematic diagram of a pattern image formed on the intermediate transfer belt 24 in color misregistration adjustment. When the color misregistration adjustment is started, the image forming apparatus 100 forms a pattern image on the intermediate transfer belt 24 and measures the pattern image by the sensor 14. The color misregistration adjustment is executed when the execution condition is satisfied. The execution conditions include, for example, a case where execution of color misregistration adjustment is instructed by an operator, a case where the main power supply of the image forming apparatus 100 is turned on, and a case where the number of formed images reaches a predetermined number.

  As shown in FIG. 3, the pattern image includes color patterns 48y, 48m, 48c, and 48bk having different colors. The color patterns 48y, 48m, 48c, and 48bk are V-shaped measurement images, for example. The intermediate transfer belt 24 moves along the transport direction. A two-dot chain line in FIG. 3 indicates the locus of the measurement position of the sensor 14.

  The image forming apparatus 100 acquires the time when each of the color patterns 48y, 48m, 48c, and 48bk passes the measurement position of the sensor 14 based on the output value of the sensor 14. For example, the image forming apparatus 100 measures the passage time Lys when the yellow color pattern 48y has passed the measurement position of the sensor 14 based on the measurement result of the sensor 14. In the passage time Lys, the other edge of the color pattern 48y reaches the measurement position of the sensor 14 in the conveyance direction from the timing when one edge of the color pattern 48y passes the measurement position of the sensor 14 in the conveyance direction of the intermediate transfer belt 24. Corresponds to the time until. Similarly, the image forming apparatus acquires the passage time Lms of the magenta color pattern 48m, the passage time Lcs of the cyan color pattern 48c, and the passage time Lbks of the black color pattern 48bk based on the measurement result of the sensor 14.

  The passage times Lys, Lms, Lcs, and Lbks represent image forming positions in the main scanning direction of the color pattern (a direction orthogonal to the conveyance direction of the intermediate transfer belt 24). That is, the relationship between the passage times Lys, Lms, Lcs, and Lbks indicates the relative positional relationship of the patches in the main scanning direction. Therefore, if the image writing timing of each color image is corrected in the main scanning direction so that the passage times Lys, Lms, Lcs, and Lbks have the same value, the color misregistration amount in the main scanning direction is corrected.

  Next, a method for correcting the writing start timing of each color image in the sub-scanning direction will be described. The passage time Lym corresponds to the time from when the center position of the color pattern 48y passes the measurement position of the sensor 14 until the center position of the color pattern 48m reaches the measurement position of the sensor 14. That is, the passage time Lym corresponds to the relative positional relationship between the yellow color pattern 48y and the magenta color pattern 48m in the sub-scanning direction. The image forming apparatus 100 corrects the writing timing of the magenta image in the sub-scanning direction so that the passage time Lym becomes a predetermined target passage time.

  The passage time Lyc corresponds to the time from when the center position of the color pattern 48y passes the measurement position of the sensor 14 until the center position of the color pattern 48c reaches the measurement position of the sensor 14. The passage time Lybk corresponds to the time from when the center position of the color pattern 48y passes the measurement position of the sensor 14 until the center position of the color pattern 48bk reaches the measurement position of the sensor 14. The image forming apparatus 100 corrects the writing timing of the cyan image in the sub-scanning direction so that the passage time Lyc becomes the target passage time, and the black image in the sub-scanning direction so that the passage time Lybk becomes the target passage time. Correct the export timing.

  As described above, the correction amount of the writing timing in the main scanning direction and the correction amount of the writing timing in the sub-scanning direction are determined from the passage times of the color patterns 48y, 48m, 48c, and 48bk. By reflecting the determined correction amount on the writing start timing of the exposure device 22 in charge of each color, the color shift is corrected.

(Speed control of photosensitive drum and intermediate transfer belt)
The photosensitive drum 10 and the intermediate transfer belt 24 are rotationally driven while being in contact with each other. For this reason, if the peripheral speed of the photosensitive drum 10 does not match the peripheral speed of the intermediate transfer belt 24, image expansion and contraction and banding may occur. Therefore, the difference between the peripheral speed of the photosensitive drum 10 and the peripheral speed of the intermediate transfer belt 24 is adjusted to such an extent that image expansion and contraction and banding do not become apparent. In the image forming apparatus described below, the target speed of the photosensitive drum 10 and the intermediate transfer belt 24 are set so that the peripheral speed of the photosensitive drum 10 is higher than the peripheral speed of the intermediate transfer belt 24 in order to increase the transfer efficiency. The target speed is set to a different value.

  FIG. 4 shows a drive unit for driving the photosensitive drum 10. The motor M3 drives the motor gear 31. The motor gear 31 meshes with the drum driving gear 35 and transmits the driving force transmitted from the motor M3 to the drum driving gear 35. The photosensitive drum 10 is fixed on the shaft of the drum driving gear 35, and the photosensitive drum 10 rotates when the motor M3 drives the drum driving gear 35. An encoder 34 is also provided on the shaft of the drum drive gear 35. The encoder 34 is a rotating plate provided with a large number of slits. Two speed sensors 32 and 33 are provided so as to detect the slit. Each of the speed sensors 32 and 33 has a light receiving element and a light emitting element, and counts the number of times light emitted from the light emitting element is received by the light receiving element through the slit. The number of counts per unit time corresponds to the rotational speed of the photosensitive drum 10. The outputs of the two speed sensors 32, 33 are averaged. This is to reduce the influence of the eccentricity of the encoder 34.

  The image forming apparatus 100 includes a motor driver 1300 (FIG. 7). The motor driver 1300 has a current value (PWM) that flows through the motor M3 so that the rotation speed detected by the speed sensors 32 and 33 becomes a target speed. Signal). PWM is an abbreviation for pulse width modulation. The PWM signal value supplied to the motor M3 corresponds to the electric power supplied to the motor M3 per predetermined time. Further, in a state where the rotational speed of the photosensitive drum 10 is controlled to the target speed, the PWM signal value input to the motor M3 changes according to the load on the photosensitive drum 10. That is, the PWM signal value input to the motor M3 is information regarding the torque of the motor M3. The above-described configuration is provided in each of the image forming units 5y, 5c, 5m, and 5bk.

  FIG. 5 shows a drive unit that drives the intermediate transfer belt 24. The motor M4 drives the motor gear 36. The motor gear 36 meshes with the drive gear 42 and transmits the drive force transmitted from the motor M4 to the drive gear 42. The drive gear 42 further meshes with the drive gear 41. A drive roller 40 is provided on the shaft of the drive gear 41. When the motor M4 drives the drive gears 41 and 42, the drive roller 40 is rotated, and the intermediate transfer belt 24 is also rotated by the drive roller 40. An encoder 39 is further provided on the shaft of the drive gear 41. The encoder 39 is a rotating plate provided with a large number of slits. Two speed sensors 37 and 38 are provided to detect this slit. The speed sensors 37 and 38 each have a light receiving element and a light emitting element, and count the number of times the light emitted from the light emitting element is received by the light receiving element through the slit. The number of times per unit time corresponds to the rotation speed. The outputs of the two speed sensors 37, 38 are averaged. This is to reduce the influence of the eccentricity of the encoder 39.

  The image forming apparatus 100 feedback-controls the current flowing through the motor M4 (the duty of the PWM signal) so that the rotational speed detected by the speed sensors 37 and 38 becomes the target speed. That is, the image forming apparatus 100 controls the PWM signal value supplied to the motor M4 so that the moving speed of the intermediate transfer belt 24 becomes the target speed. The PWM signal value supplied to the motor M4 corresponds to the current value flowing through the motor M4 per predetermined time. Further, in a state where the rotation speed of the driving roller 40 is controlled to the target speed, the PWM signal value input to the motor M4 changes according to the load of the driving roller 40. That is, the PWM signal value input to the motor M4 is information regarding the load on the intermediate transfer belt 24.

  Next, the adverse effects caused by the increased frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 will be described in detail. The speed difference between the intermediate transfer belt 24 and the photosensitive drum 10 is set such that the target value of the surface speed of the photosensitive drum 10 is, for example, 0.15 [%] faster than the target value of the surface speed of the intermediate transfer belt 24.

  The frictional force acting between the photosensitive drum 10 and the intermediate transfer belt 24 is roughly divided into two states. One is a state in which the developing sleeve 8 rotates as in image formation, and a small amount of developer is supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24. That is, the developer is present on the transfer surface between the photosensitive drum 10 and the intermediate transfer belt 24. The other is a state in which the rotation of the developing sleeve 8 is stopped and the developer is not supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24. That is, no developer is present on the transfer surface between the photosensitive drum 10 and the intermediate transfer belt 24. This state is, for example, a state after image development for one page is completed or before image formation is started.

  When the developing sleeve 8 rotates, the developer is supplied to the photosensitive drum 10. That is, the developer in the developing container is consumed. Therefore, the image forming apparatus rotates the developing sleeve 8 only for a minimum time necessary for image formation. That is, the image forming apparatus 100 starts the rotation of the developing sleeve 8 at a timing immediately before the image formation, and immediately stops the rotation of the developing sleeve 8 after the image formation is completed.

  When the image forming apparatus 100 forms an image based on image data, the image forming apparatus 100 changes from a state in which no developer is present in the nip portion to a state in which the developer is present in the nip portion. When the image formation based on the image data is completed, the image forming apparatus 100 changes from a state in which the developer is present in the nip portion to a state in which the developer is not present in the nip portion. At this time, if there is a large difference in frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 between the state where the developer is present in the nip and the state where the developer is not present in the nip, Large load fluctuations occur in the drum 10 and the intermediate transfer belt 24. Since the state is switched when image formation is started, load fluctuations occur in the photosensitive drum 10 and the intermediate transfer belt 24 every time image formation is started. When a load change occurs, the rotational speeds of the motor M3 that rotates the photosensitive drum 10 and the motor M4 that rotates the driving roller 40 become unstable. If image formation is executed while the rotational speed of the motor M3 or the rotational speed of the motor M4 is unstable, the density of the image fluctuates or color misregistration occurs in the image.

  Therefore, the image forming apparatus 100 executes control to reduce the difference between the surface speed of the photosensitive drum 10 and the surface speed of the intermediate transfer belt 24 according to the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24. As a result, the image forming apparatus 100 can reduce the frictional force by reducing the speed difference before the frictional force increases so as to cause the load fluctuation that causes the image defect.

  Here, the fact that the frictional force increases as the speed difference increases will be described in detail. In general, the friction force between an object and an object is classified into two, and can be divided into a static friction force and a dynamic friction force. The dynamic friction force is a constant value without changing depending on the relative speed of the object. If this is applied as it is, the dynamic frictional force is constant no matter how much the speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 occurs. However, it is generally known that the dynamic friction force is constant when the speed difference between the object and the object is large to some extent. In other words, the speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 in the image forming apparatus is normally about 1%, and thus does not follow the physical law that the dynamic friction force is constant as described above. Therefore, it is known that in such a system having a small speed difference, as shown in FIG. 6, the frictional force increases as the speed difference increases.

(Target speed adjustment process)
During the execution of the image forming operation, the image forming apparatus 100 acquires a PWM signal value in a state where the developer is present in the nip portion and a PWM signal value in a state where the developer is not present in the nip portion. Then, the image forming apparatus 100 controls whether to change the target speed of the photosensitive drum 10 based on the PWM signal values acquired in the two states. An adjustment process for adjusting the target speed of the photosensitive drum 10 will be described below. A control block diagram of the image forming apparatus 100 will be described with reference to FIG. The CPU 1000 is a control circuit that controls each unit of the image forming apparatus 100. The ROM 1100 stores a control program that is executed by the CPU 1000 and is necessary for executing various processes in the flowcharts described below. A RAM 1200 is a system work memory for the CPU 1000 to operate. A temperature sensor 1005 measures the internal temperature of the image forming apparatus 100.

  Further, since the image forming units 5y, 5c, 5m, and 5bk (the image forming unit 5 in FIG. 7), the sensor 14, the speed sensors 32 and 33, and the motor M3 have already been described, description thereof is omitted here. To do.

  The pattern generator 70 outputs measurement image data when color misregistration adjustment is executed. The image forming unit 5 forms a pattern image (FIG. 3) on the intermediate transfer belt 24 based on the measurement image data transferred from the pattern generator 70. The CPU 1000 conveys the pattern image on the intermediate transfer belt 24 and causes the sensor 14 to measure the pattern image. The sensor 14 outputs the measurement result of the pattern image to the color misregistration amount determination unit 1004.

  The color misregistration amount correction unit 1003 corrects the writing start timing of each color image based on the color registration amount. The color misregistration amount determination unit 1004 determines the passage times Lys, Lms, Lcs, and Lbks and the passage times Lym, Lyc, and Lybk based on the measurement result of the pattern image by the sensor 14. Then, the color misregistration amount determination unit 1004 determines the color misregistration amount in the main scanning direction from the passage times Lys, Lms, Lcs, and Lbks, and determines the color misregistration amount in the sub scanning direction from the passage times Lym, Lyc, and Lybk. . A color registration amount including the color misregistration amount in the main scanning direction and the color misregistration amount in the sub scanning direction is output to the color misregistration amount correction unit 1003.

  When the target speed of the photosensitive drum 10 (target rotational speed of the motor M3) is set, the motor driver 1300 sets the motor M3 so that the rotational speed of the photosensitive drum 10 detected by the speed sensors 32 and 33 becomes the target speed. Controls the input PWM signal value. As a result, the value of the current flowing through the motor M3 is controlled so that the rotational speed of the photosensitive drum 10 becomes the target speed. Further, the PWM signal value for controlling the motor M3 output from the motor driver 1300 is also input to the target speed determination unit 1002.

  The target speed determination unit 1002 is an ASIC (application specific integrated circuit), and determines the target speed of the photosensitive drum 10. The target speed determination unit 1002 sets a target speed at which the surface speed of the photosensitive drum 10 is higher than the surface speed of the intermediate transfer belt 24 unless the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 causes a defective image. Determine as speed. On the other hand, if the frictional force has a value that causes an image defect in the target speed adjustment process, the target speed determination unit 1002 changes the target speed of the photosensitive drum 10. That is, the difference between the target value of the surface speed of the photosensitive drum 10 and the target value of the surface speed of the intermediate transfer belt 24 is reduced. The target speed determination unit 1002 controls whether or not to lower the target value of the photosensitive drum 10 based on the PWM signal value input from the motor driver 1300. The target speed determining unit 1002 is not limited to the ASIC. For example, a configuration in which a part of the function of the CPU 1000 determines the target speed based on the PWM signal may be used.

  An image forming operation in which the image forming apparatus 100 forms an image based on image data will be described with reference to the flowchart of FIG. When image data is input from a PC (not shown), the CPU 1000 reads a program stored in the ROM 1100 and executes the processing of the flowchart of FIG.

  First, the CPU 1000 rotates the photosensitive drum 10, the intermediate transfer belt 24, and the developing sleeve 8 (S800). The motor driver 1300 performs feedback control based on the detection results of the speed sensors 32 and 33 so that the rotational speed of the photosensitive drum 10 becomes the target speed. Therefore, the motor driver 1300 controls the PWM signal input to the motor M3. The motor driver 1300 updates the PWM signal value every 8 [msec]. A motor driver (not shown) performs feedback control based on the detection results of the speed sensors 37 and 38 so that the surface speed of the intermediate transfer belt 24 becomes the target speed. Similarly, a motor driver (not shown) updates the PWM signal value every 8 [msec].

  Feedback control is executed so that the motor M1 that rotates the stirring member 6 also has a predetermined speed, and feedback control is executed so that the motor M2 that rotates the developing sleeve 8 also becomes the reference speed.

  In step S 800, when the developing sleeve 8 rotates, a small amount of developer adheres from the developing sleeve 8 to the photosensitive drum 10 regardless of the developing bias supplied from the power supply unit 2. The small amount of developer is supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24 as the photosensitive drum 10 rotates. When the developer is supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 decreases.

  After the photosensitive drum 10 is rotated, the intermediate transfer belt 24 is driven, and the developing sleeve 8 is rotated, the image forming unit 5 starts image formation based on the image data (S801). The charger 21 uniformly charges the surface of the photosensitive drum 10, and the exposure device 22 exposes the charged photosensitive drum 10 to form an electrostatic latent image. Then, the developing device 1 develops the electrostatic latent image using the developer carried on the developing sleeve 8, and an image is formed on the photosensitive drum 10. The image on the photosensitive drum 10 is conveyed to the nip portion, and is transferred from the photosensitive drum 10 to the intermediate transfer belt 24 at the nip portion.

  After the image for one page is transferred from the photosensitive drum 10 to the intermediate transfer belt 24, the target speed determination unit 1002 outputs the PWM signal value output from the motor driver 1300 to the motor M3 in a state where the developer is supplied to the nip portion. PWMduty1 is acquired (S802). At this time, the target speed determination unit 1002 acquires the PWM signal value of the motor M3 that drives the photosensitive drums 10 of the image forming units 5y, 5m, 5c, and 5bk. When a full-color image is formed, the PWM signal value of the motor M3 that rotates the upstream photosensitive drum 10 in the conveyance direction of the intermediate transfer belt 24 is first acquired. That is, the PMW signal value of the motor M3y that rotates the yellow photosensitive drum 10y is acquired from the motor driver 1300 that controls the motor M3y. Similarly, the PWM signal value of the motor M3m that rotates the magenta photosensitive drum 10m, the PWM signal value of the motor M3c that rotates the cyan photosensitive drum 10c, and the PWM signal value of the motor M3bk that rotates the black photosensitive drum 10m are obtained. Is done. Here, the current value (PMW signal value) flowing through the motor M3y that rotates the yellow photosensitive drum 10y corresponds to the first signal value that changes according to the torque of the motor M3y. Further, the current value (PWM signal value) flowing through the motor M3m that rotates the magenta photosensitive drum 10m corresponds to the 23rd signal value that changes according to the torque of the motor M3m.

  Then, the CPU 1000 determines whether or not all the images included in the image data have been formed (S803). If all the images are not formed in step S803, the image forming unit 5 continues to form images, and the CPU 1000 acquires the PWM signal value PWMduty1 again in step S802. The processes in steps S802 and S803 are repeated until the image forming unit 5 finishes forming all the images included in the image data.

  On the other hand, when all the images are formed in step S803, the image forming unit 5 stops image formation (S804). Then, the CPU 1000 stops the rotational drive of the motor M2 that rotates the developing sleeve 8 (S805). After a predetermined time has elapsed since the rotation of the developing sleeve 8 stopped in step S805, the target speed determining unit 1002 acquires the PWM signal value PWMduty2 output from the motor driver 1300 (S806). At this time, the target speed determination unit 1002 acquires the PWM signal value of the motor M3 that drives the photosensitive drums 10 of the image forming units 5y, 5m, 5c, and 5bk. The target speed determination unit 1002 first acquires the PWM signal value of the motor M3 that rotates the upstream photosensitive drum 10 in the conveyance direction of the intermediate transfer belt 24. That is, the PMW signal value of the motor M3y that rotates the yellow photosensitive drum 10y is acquired from the motor driver 1300 that controls the motor M3y. Similarly, the PWM signal value of the motor M3m that rotates the magenta photosensitive drum 10m, the PWM signal value of the motor M3c that rotates the cyan photosensitive drum 10c, and the PWM signal value of the motor M3bk that rotates the black photosensitive drum 10m are obtained. Is done. Here, the current value (PMW signal value) flowing through the motor M3y that rotates the yellow photosensitive drum 10y corresponds to the second signal value that changes according to the torque of the motor M3y. Further, the current value (PWM signal value) flowing through the motor M3m that rotates the magenta photosensitive drum 10m corresponds to a fourth signal value that changes according to the torque of the motor M3m.

  Note that the predetermined time in step S806 corresponds to the time from when the rotation of the developing sleeve 8 stops until the developer attached to the photosensitive drum 10 finishes passing through the nip portion. The predetermined time is determined by the rotational speed of the photosensitive drum 10 and the distance from the position where the developing sleeve 8 and the photosensitive drum 10 face each other to the nip portion. In this embodiment, the fixed time is stored in the ROM 1100 regardless of the target speed of the photosensitive drum 10.

  After the target speed determination unit 1002 finishes acquiring the PWM signal value PWMduty2 in step S806, the CPU 1000 stops the rotation of the photosensitive drum 10 and stops driving the intermediate transfer belt 24 (S807). The motor driver 1300 stops the supply of the PWM signal to the motor M3, and stops the supply of the PWM signal from the motor driver (not shown) to the motor M4. Then, the CPU 1000 ends the image forming operation.

  Next, target speed adjustment processing executed by the CPU 1000 will be described with reference to the flowchart of FIG. After executing the image forming operation based on the image data, the CPU 1000 reads the program stored in the ROM 1100 and executes the processing of the flowchart of FIG.

First, the CPU 1000 determines whether or not the difference ΔPWM duty between the PWM signal values acquired by the target speed determination unit 1002 is larger than the first threshold value Tha (S900). In step S900, the target speed determination unit 1002 calculates a difference ΔPWM duty between PWM signal values based on Equation 1.
ΔPWM duty = PWM duty 2−PWM duty 1 (Expression 1)
When the difference ΔPWM duty between the PWM signal values is larger than the first threshold value Tha, the frictional force between the state where the developer is present in the nip portion and the state where the developer is not present in the nip portion increases so as to cause an image defect. Means that

In step S900, the target speed determination unit 1002 changes the target speed of the photosensitive drum 10 if the PWM signal value difference ΔPWMduty is greater than the first threshold Tha (S901). In step S901, the target speed determination unit 1002 determines the target speed of the photosensitive drum 10 based on Equation 2.
Target speed Vt (n + 1) = current target speed Vt (n) −coefficient × ΔPWM duty (Expression 2)
Then, the CPU 1000 executes color misregistration adjustment (S902), and ends the target speed adjustment processing. The coefficient is a positive value.

  When the target speed of the photosensitive drum 10 is changed, the length of the image changes in the rotation direction of the photosensitive drum 10 formed on the photosensitive drum 10. For example, the writing position in the sub-scanning direction may be different for each color. Therefore, when the target speed of the photosensitive drum 10 is changed, the CPU 1000 executes color misregistration adjustment in step S902.

  If the difference ΔPWM duty in the PWM signal value is not larger than the first threshold Tha in step S900, the CPU 1000 determines whether or not the color misregistration adjustment execution condition is satisfied (S903). In step S903, for example, when the cumulative value of the number of formed images has reached a predetermined number since the previous color misregistration adjustment was executed, the CPU 1000 determines that the execution condition is satisfied. When the color misregistration adjustment execution condition is satisfied in step S903, the CPU 1000 determines whether or not the difference ΔPWMduty of the PWM signal value acquired by the target speed determination unit 1002 is larger than the second threshold Thb (S904). . Here, the second threshold value Thb is smaller than the first threshold value Tha. In step S904, if the PWM signal value difference ΔPWMduty is larger than the second threshold Thb, the CPU 1000 shifts to the processing in step S901 in order to change the target speed of the photosensitive drum 10.

  On the other hand, in step S904, if the PWM signal value difference ΔPWMduty is not larger than the second threshold value Thb, the CPU 1000 shifts the process to step S902, executes the color misregistration adjustment, and ends the target speed adjustment process.

  If the color misregistration adjustment execution condition is not satisfied in step S903, the CPU 1000 ends the target speed adjustment process without executing the color misregistration adjustment.

  The target speed adjustment process described above is executed for each motor that drives the photosensitive drum. Therefore, when at least one target speed of the photosensitive drum 10 for yellow, magenta, cyan, and black is changed, the CPU 1000 performs color misregistration adjustment.

  8 and 9, the target speed of the photosensitive drum 10 is changed before the frictional force increases, and the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 can be reduced. Further, when the condition for executing the color misregistration adjustment is satisfied, the target speed is changed before the frictional force is sufficiently increased. Therefore, the target speed is changed as compared with the configuration having only one threshold value. Accordingly, it is possible to suppress the frequency of color misregistration adjustment performed.

  FIG. 10A is a plot of the PWM signal values of the yellow photosensitive drum 10 obtained by experiments. The arrow indicates the timing when the target speed of the photosensitive drum 10 is changed. The difference between the PWM signal value when the developer is present in the nip portion and the PWM signal value when the developer is not present in the nip portion is reduced every time the target speed is changed. FIG. 10B is a plot of the PWM signal value of the intermediate transfer belt 24. It can be seen that when the target speed of the photosensitive drum 10 is changed, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 decreases, and the load on the intermediate transfer belt 24 decreases. As a result, load fluctuation does not occur, and the surface speed of the photosensitive drum 10 and the surface speed of the intermediate transfer belt 24 immediately after the start of image formation can be suppressed from becoming unstable.

(PWM signal value acquisition method)
In the description of FIG. 8, the PWM signal value PWMduty1 is acquired and updated every time an image is formed. However, for example, the PWM signal value may be sampled a plurality of times during the period in which the photosensitive drum 10 rotates once, and the PWM duty 1 may be determined from the average value of the plurality of PWM signal values. According to this configuration, a change in the PWM signal value can be acquired with high accuracy. This is because when the motor M3 rotates the photosensitive drum 10, the PWM signal value changes due to backlash such as a gear that transmits the driving force of the motor M3 or the eccentricity of the photosensitive drum 10.

(Sampling timing and photosensitive drum 10 load)
The image forming apparatus 100 is configured to acquire the PWM signal value of the motor M3 that rotates the photosensitive drum 10. There are two reasons for this. The first reason is that the target speed can be changed for each of the plurality of photosensitive drums 10. If the target speed of the photosensitive drum 10 is changed based on the PWM signal value of the motor M4 that drives the intermediate transfer belt 24, the photosensitive drum 10 having an increased frictional force cannot be specified. Second, if no developer is present even in the nip portion between the photosensitive drum 10 of interest and the intermediate transfer belt 24, the developer is present in the nip portion between the other photosensitive drum 10 and the intermediate transfer belt 24. This is because the PWM signal value PWMduty1 can be acquired. If the target speed of the photosensitive drum 10 is changed based on the PWM signal value of the motor M4 that drives the intermediate transfer belt 24, no developer is present in the nip portion between all the photosensitive drums 10 and the intermediate transfer belt 24. It is necessary to acquire the PWM signal value at Therefore, when the image data is continuously transferred, the developer is not present in the nip portion between all the photosensitive drums 10 and the intermediate transfer belt 24, and the opportunity to acquire the PWM signal value is reduced. Resulting in.

  By the way, there are some things to consider when acquiring the load information of the photosensitive drum 10. When driving the photosensitive drum 10, main loads are a frictional force caused by the intermediate transfer belt 24 and a frictional force caused by a blade of the drum cleaner 26 that contacts the photosensitive drum 10.

  In the image forming apparatus 100, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 is within an allowable range when the developing sleeve 8 rotates and the developer is interposed in the nip portion and when the developer is not interposed in the nip portion. It is judged whether or not it exceeds. However, it is assumed that the frictional force by the blades of the drum cleaner 26 is constant in both situations. When the developer is interposed between the photosensitive drum 10 and the blade, the frictional force between the photosensitive drum 10 and the blade is reduced. On the other hand, when the developer between the photosensitive drum 10 and the blade is depleted, the frictional force between the photosensitive drum 10 and the blade is increased. FIG. 11 shows the transition of the load on the photosensitive drum 10 when the developer between the photosensitive drum 10 and the blade decreases from the state where the developer is supplied between the photosensitive drum 10 and the blade. . As shown in FIG. 11, when the developer is reduced, the load on the photosensitive drum 10 is rapidly increased and the frictional force is converged to a constant value. That is, if the developer between the photosensitive drum 10 and the blade is depleted even when no developer is present in the nip portion, the load on the photosensitive drum 10 increases. If the PWM signal value is acquired while the load on the photosensitive drum 10 is increasing, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 cannot be predicted with high accuracy due to the frictional force between the photosensitive drum 10 and the blade.

  Therefore, in the image forming apparatus 100, immediately after the rotation of the developing sleeve 8 stops and the developer attached to the photosensitive drum 10 passes through the nip portion, the developer is interposed between the photosensitive drum 10 and the blade. During this period, the PWM signal value is acquired. As shown in FIG. 11, since the developer is interposed between the photosensitive drum 10 and the blade for a certain period of time, it is not necessary to consider the load on the blade by sampling the PWM signal value during that period.

  As for the sampling of the PWM signal value when the developing sleeve 8 is rotating, it is desirable to sample immediately before the developing sleeve 8 stops rotating. Even in the state where the developer is interposed between the photosensitive drum 10 and the blade, the rubbing between the photosensitive drum 10 and the blade always occurs, the blade is worn by the rubbing, and the load applied to the photosensitive drum 10 is also increased. Because it changes.

(Modification)
When using a developer having high releasability, the developer may fly from the developing sleeve 8 to the photosensitive drum 10 due to the developing bias even if the rotation of the developing sleeve 8 is stopped. Here, when the AC voltage of the developing bias was set to 0, the amount of developer flying from the developing sleeve 8 to the photosensitive drum 10 was substantially zero. Therefore, the power supply unit 2 applies only a DC voltage when acquiring the PWM signal value PWMduty2 in a state where no developer is present in the nip portion.

  Further, the transfer bias supplied from the power supply unit 3 to the primary transfer roller 23 is also set as follows. The same transfer bias is applied to the transfer bias when the developer is present in the nip portion and the transfer bias when the developer is not present in the nip portion. According to this configuration, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 is increased by the electrostatic force. Therefore, the target speed determination unit 1002 acquires the PWM signal value PWMduty2 in a state where the power supply unit 3 applies a transfer bias to the primary transfer roller 23.

M3 motor 5 image forming unit 8 developing sleeve 10 photosensitive drum 24 intermediate transfer belt 1000 CPU
1002 Target speed determination unit 1300 Motor driver

Claims (11)

An image carrier;
A developer carrying member that carries the developer and rotates;
Image forming means for forming an image on the image carrier using the developer carried on the developer carrier;
An intermediate transfer member to which the image on the image carrier is transferred at a nip portion with the image carrier;
A motor for rotationally driving the image carrier;
Control means for controlling the motor so that the rotational speed of the image carrier becomes a target speed;
A first signal value that changes according to the torque of the motor is acquired in a state where the developer carrier rotates while the motor rotates the image carrier, and the motor rotates the image carrier. While the developer carrier is not rotating, a second signal value that changes in accordance with the torque of the motor is acquired, and the image carrier is in accordance with the first signal value and the second signal value. Determining means for determining the target speed,
After the image forming means finishes forming the image, the determining means obtains the first signal value,
After the image forming unit finishes forming all images based on the image data, the rotation of the developer carrier is stopped,
The image forming apparatus according to claim 1, wherein after the rotation of the developer carrier is stopped, the determination unit acquires the second signal value. And further includes another motor that rotates to drive the intermediate transfer member,
The image forming apparatus according to claim 1, wherein the control unit further controls the other motor so that the moving speed of the intermediate transfer member becomes another target speed.   The determining means further acquires the second signal value after the rotation of the developer carrying member is stopped and before the driving of the intermediate transfer member is stopped by the other motor. The image forming apparatus according to claim 2. A removal member that contacts the image carrier and removes the developer on the image carrier;
4. The determination unit according to claim 1, wherein the determination unit further acquires the second signal value in a state where the developer is interposed between the image carrier and the removal member. 5. The image forming apparatus described in 1. The control means controls the electric power supplied to the motor so that the rotational speed of the motor becomes the target speed,
The first signal value corresponds to a first current value flowing through the motor in a state where the developer carrying member is rotating,
5. The image formation according to claim 1, wherein the second signal value corresponds to a second current value that flows through the motor in a state where the developer carrying member is not rotating. 6. apparatus.   The image forming apparatus according to claim 5, wherein the determination unit decreases the target speed if a difference between the first current value and the second current value is larger than a threshold value. The image forming unit further includes a voltage applying unit that applies a voltage so as to generate a potential difference between the developer carrier and the image carrier.
The voltage application means applies a superimposed voltage obtained by superimposing an alternating voltage and a direct current voltage when the image forming means forms the image,
The said voltage application means applies a direct current voltage, without applying an alternating voltage, when the said determination means acquires the said 2nd signal value, The Claim 1 thru | or 6 characterized by the above-mentioned. Image forming apparatus. The image forming unit further includes another voltage applying unit that applies a voltage so that a potential difference is generated between the image carrier and the intermediate transfer member.
The image forming apparatus according to claim 1, wherein the determination unit acquires the second signal value during a period in which the voltage is applied by the other voltage application unit. . A first image carrier;
A first developer carrier that carries and rotates the developer;
First image forming means for forming a first image on the first image carrier using the developer carried on the first developer carrier;
A second image carrier;
A second developer carrying member that carries and rotates the developer;
Second image forming means for forming a second image on the second image carrier using the developer carried on the second developer carrier;
The first image on the first image carrier is transferred at the nip with the first image carrier, and the second image on the second image carrier at the nip with the second image carrier. An intermediate transfer member to which is transferred,
A first motor for rotationally driving the first image carrier;
A second motor for rotationally driving the second image carrier;
The first motor is controlled so that the rotational speed of the first image carrier becomes a first target speed, and the second motor is controlled so that the rotational speed of the second image carrier becomes a second target speed. Control means for
In the state where the first developer carrier is rotating while the first motor rotates the first image carrier, a first signal value that changes according to the torque of the first motor is acquired, and the first motor A second signal value that changes according to the torque of the first motor in a state where the first developer carrier is not rotating while the first motor rotates the first image carrier, and the first signal is obtained. First determining means for determining the first target speed of the first image carrier based on a value and the second signal value;
Acquiring a third signal value that changes according to the torque of the second motor in a state where the second developer carrier is rotating while the second motor rotates the second image carrier; A fourth signal value that changes according to the torque of the second motor when the second motor rotates the second image carrier and the second developer carrier does not rotate; Second determining means for determining the second target speed of the second image carrier based on the value and the fourth signal value;
After the first image forming means finishes forming the first image, the first determining means obtains the first signal value,
After the second image forming means finishes forming the second image, the second determining means obtains the third signal value,
After the first image forming unit finishes forming all the first images based on the image data, the rotation of the first developer carrier is stopped,
After the rotation of the first developer carrier is stopped, the first determination means acquires the second signal value,
After the second image forming unit finishes forming all the second images based on the image data, the rotation of the second developer carrier is stopped,
The image forming apparatus according to claim 1, wherein the second determination unit acquires the fourth signal value after the rotation of the second developer carrier is stopped. Measuring means for measuring an image for measurement on the intermediate transfer member;
Adjusting means for adjusting a relative position between the first image and the second image based on a measurement result of the measuring means;
When the first target speed is changed, the adjusting unit causes the first image forming unit to form a first measurement image, causes the second image forming unit to form a second measurement image, and performs the measurement. 10. The image forming apparatus according to claim 9, wherein the image forming apparatus measures the first measurement image and the second measurement image. 10.   When the second target speed is changed, the adjusting unit causes the first image forming unit to form a first measurement image, causes the second image forming unit to form a second measurement image, and performs the measurement. 11. The image forming apparatus according to claim 10, wherein the image forming apparatus causes the first measurement image and the second measurement image to be measured.

Images