JP6859040B2 - Image forming device - Google Patents

Description

The present invention relates to speed control of the photoconductor in an image forming apparatus for forming an image on the photoconductor.

The electrophotographic image forming apparatus forms an electrostatic latent image on the photoconductor, and develops the electrostatic latent image with a developing agent to form an image. The image developed on the photoconductor is once transferred to the intermediate transfer body, and then the image on the intermediate transfer body is transferred to the sheet.

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

By the way, even if the surface speed of the photoconductor and the surface speed of the intermediate transfer body can be controlled to a constant speed, the photoconductor may be subjected to a load state of a nip portion for transferring an image on the photoconductor to the intermediate transfer body. The surface velocity and the surface velocity of the intermediate transfer material could become uncontrollable. That is, when the state in which the developer is present in the nip is changed to the state in which the developer is not present in the nip, the load of the motor changes suddenly and the rotation speed of the motor becomes uncontrollable. There was a possibility that it would become. When the rotation speed of the motor is not controlled, the above-mentioned image defect occurs.

Therefore, an image that adjusts the target rotation speed of the photoconductor so that the load of the motor when the developer is supplied to the nip and the load of the motor when the developer is not supplied to the nip are small. A forming device is known (Patent Document 1). This image forming apparatus acquires the drive signal of the motor while supplying the developer to the nip part and switching the speed command value of the motor, and switches the speed command value of the motor without supplying the developer to the nip part. Get the drive signal of. Since this image forming apparatus executes 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, this image forming apparatus predicts the load of the motor from the drive signal of the motor.

Japanese Unexamined Patent Publication No. 2016-1268

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

For example, when the image forming apparatus continuously forms a plurality of images, the target rotation speed of the photoconductor cannot be updated to an appropriate value, so that image defects may occur.

An object of the present invention is to appropriately update the target rotation speed of the sensitive light body.

In order to solve the above problems, the image forming apparatus of the present invention includes a photoconductor, a first motor for rotating the photoconductor, a latent image forming means for forming an electrostatic latent image on the photoconductor, and a developing agent. An image forming means for forming an image by having a developing agent carrier that carries and rotates the photofinishing body and developing the electrostatic latent image on the photoconductor with the developing agent supported on the developing agent carrier. The intermediate transfer body formed by the image forming means to which the image is transferred, the second motor for rotating the rotating member for driving the intermediate transfer body, and the rotation speed of the photoconductor are the target rotation speeds. The drive control means for controlling the first motor so as to control the second motor so that the rotational speed of the rotating member becomes a predetermined rotational speed, and information on the torque of the first motor are acquired. an acquisition unit, the photoconductor is acquired first information about the torque of the first motor before Symbol acquisition means Te first state smell the rotating member and the developer carrying member is rotated, the developing phase carrying body stops rotating, and the photosensitive member and the rotating member so that acquired the second information about the torque of the first motor before Symbol acquisition means Te second state odor which is rotating, the target rotational speed It has a control means for controlling whether or not to change based on the first information and the second information, and the control means has the developer carrier after the developer carrier starts to rotate. In the first state, after the first time elapses until the developer supplied to the surface of the photoconductor reaches the nip portion between the photoconductor and the intermediate transfer body due to the rotation of the photoconductor. The acquisition means acquires the first information, and the control means supplies the photoconductor-bearing body to the surface of the photoconductor when the rotation of the developer-supporting body is stopped after the developer-supporting body has stopped rotating. In the second state, after a second time elapses until the developer being processed passes through the nip portion between the photoconductor and the intermediate transfer body due to the rotation of the photoconductor, the acquiring means is used. It is characterized in that the second information is acquired.

According to the present invention, the target rotational speed of the sensitive light body can be appropriately updated.

Schematic cross-sectional view of the image forming apparatus Schematic diagram of the main part of the image forming part Schematic diagram of pattern image Schematic diagram of the main part of the drive unit of the photosensitive drum Schematic diagram of the main part of the drive unit of the intermediate transfer belt Explanatory drawing of frictional force characteristics Control block diagram of image forming apparatus Flow chart showing image formation operation Flow chart showing the adjustment process of the target rotation speed of the motor Timing chart diagram regarding the stop timing of the developing sleeve The figure which illustrated the measurement result of the number of image formations and the PWM signal value of a motor Torque characteristic diagram showing the transition of motor torque fluctuation Schematic diagram for explaining development bias The figure which exemplifies the experimental data which measured the PWM signal of a motor and the peripheral speed difference.

(Image forming device)
FIG. 1 shows a main part of the image forming apparatus 100. The image forming apparatus 100 has four image forming portions 5y, 5c, 5m, and 5bk for forming an image. The image forming portions 5y, 5c, 5m, and 5bk form an image using developing agents having different colors. Here, color developers of colors such as yellow (Y), magenta (M), cyan (C) and black (Bk) are used. The letters y, c, m, and bk added to the end of the reference code indicate the color of the developer.

The photosensitive drum 10 is an image carrier that supports an electrostatic latent image or an image (developer image). A photosensitive layer that functions as a photoconductor is formed on the surface of the photosensitive drum 10. The charger 21 uniformly charges the surface of the photosensitive drum 10. The exposure device 22 exposes the charged photosensitive drum 10 to form an electrostatic latent image. The exposure device 22 functions as a latent image forming means for forming an electrostatic latent image on the photosensitive drum 10. The direction in which the laser beam of the exposure apparatus 22 scans the surface of the photosensitive drum 10 is referred to as the main scanning direction. The exposure apparatus 22 has an optical member such as a rotary multifaceted mirror, a mirror, or a lens that is rotationally driven to scan the laser beam. The developing device 1 develops an electrostatic latent image using a developing agent to form an image. The developer is, for example, a two-component developer containing a non-magnetic developer and a magnetic carrier. A transfer bias Vtr1 is applied to the primary transfer roller 23 in order to transfer the image supported on the photosensitive drum 10 to the intermediate transfer belt 24. The intermediate transfer belt 24 functions as an intermediate transfer body on which the image on the photosensitive drum 10 is transferred. A transfer bias Vtr2 is applied to the secondary transfer roller 29 in order to transfer the image supported on the intermediate transfer belt 24 to 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 comes into contact with 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 for removing the developer on the photosensitive drum 10. The belt cleaner 28 has a blade that abuts on 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 the developer to the developing apparatus 1. The sensor 14 is an optical sensor having a light emitting element and a light receiving element, and measures the reflected light from the measurement image formed on the intermediate transfer belt 24 by the image forming portions 5y, 5m, 5c, and 5bk.

(Developer)
FIG. 2 is a schematic view of a main part of the image forming unit 5. The developing apparatus 1 has a stirring member 6 such as a screw that conveys the developing agent supplied from the developing agent supply tank 20 and the carrier while stirring. The stirring member 6 is driven by the motor M1. By stirring the developer and the carrier, the developer is triboelectrically charged. The developing sleeve 8 is a developing agent carrier that supports a developing agent. The developing sleeve 8 is arranged so as to face the photosensitive drum 10. The developing sleeve 8 is driven by the motor M2. When developing an electrostatic latent image, the power supply unit 2 applies a superimposed voltage (development bias) in which an AC voltage is superimposed on a DC voltage to the developing sleeve 8. The power supply unit 2 functions as a voltage applying means for applying a superposed voltage so as to generate a potential difference between the photosensitive drum 10 and the developing sleeve 8. When the image on the photosensitive drum 10 is transferred to the intermediate transfer belt 24, the power supply unit 3 applies a predetermined DC voltage (transfer bias) to the primary transfer roller 23. 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.

(Adjustment of image formation position)
The images formed by the image forming portions 5y, 5c, 5m, and 5bk are transferred so as to overlap the intermediate transfer belt 24. As a result, a full-color image is supported on the intermediate transfer belt 24. Therefore, if the image forming positions (image forming timing) of the image forming portions 5y, 5c, 5m, and 5bk are different, the tint of the full-color image cannot be compensated. For example, when the temperature of the image forming apparatus 100 or the number of image forming sheets changes, the image forming positions of the image forming portions 5y, 5c, 5m, and 5bk may change. The relative positional deviation of the images formed in the image forming portions 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 the sensor 14 detects the color registration amount. Then, the image forming apparatus 100 corrects the writing timing (exposure timing) when the image forming portions 5y, 5c, 5m, and 5bk form the electrostatic latent image based on the detected color registration amount. The above-mentioned process is called color shift correction (color registration process).

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

As shown in FIG. 3, the pattern image includes color patterns 48y, 48m, 48c, and 48bk having different colors, respectively. The color patterns 48y, 48m, 48c, and 48bk are, for example, V-shaped measurement images. The intermediate transfer belt 24 moves along the transport direction. The two-dot chain line in FIG. 3 shows 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 has passed the measurement position of the sensor 14 based on the output value of the sensor 14. The image forming apparatus 100 measures, for example, the passing time Lys in which the yellow color pattern 48y passes the measurement position of the sensor 14 based on the measurement result of the sensor 14. The transit time Lys is such that the other edge of the color pattern 48y reaches the measurement position of the sensor 14 in the transfer direction from the timing when one edge of the color pattern 48y passes the measurement position of the sensor 14 in the transfer direction of the intermediate transfer belt 24. Corresponds to the time until. Similarly, the image forming apparatus acquires the passing time Lms of the magenta color pattern 48m, the passing time Lcs of the cyan color pattern 48c, and the passing time Lbks of the black color pattern 48bk based on the measurement results of the sensor 14.

The transit times Lys, Lms, Lcs, and Lbks represent the image formation positions in the main scanning direction of the color pattern (direction orthogonal to the transport direction of the intermediate transfer belt 24). That is, the relationship between the transit times Lys, Lms, Lcs, and Lbks indicates the relative positional relationship of each patch in the main scanning direction. Therefore, if the writing timing of the image of each color is corrected in the main scanning direction so that the passing times Lys, Lms, Lcs, and Lbks are the same value, the amount of color shift in the main scanning direction is corrected.

Subsequently, a method of correcting the writing timing of the image of each color in the sub-scanning direction will be described. The transit time Lym corresponds to the time from when the center position of the color pattern 48y passes the measurement position of the sensor 14 to when the center position of the color pattern 48m reaches the measurement position of the sensor 14. That is, the passing 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 passing time Lym becomes a predetermined target passing time.

The transit time Lyc corresponds to the time from when the center position of the color pattern 48y passes the measurement position of the sensor 14 to when the center position of the color pattern 48c reaches the measurement position of the sensor 14. The transit time Lybk corresponds to the time from when the center position of the color pattern 48y passes through the measurement position of the sensor 14 to when 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 passing time Lyc becomes the target passing time, and the black image in the sub-scanning direction so that the passing time Lybk becomes the target passing 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 passing times of the color patterns 48y, 48m, 48c, and 48bk. The color shift is corrected by reflecting the determined correction amount in the writing timing of the exposure device 22 in charge of each color.

(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. Therefore, if the peripheral speed of the photosensitive drum 10 and the peripheral speed of the intermediate transfer belt 24 do not match, expansion and contraction of the image 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 expansion and contraction of the image and banding do not become apparent. The image forming apparatus 100 sets a target value of the surface speed (peripheral speed) of the photosensitive drum 10 so that the peripheral speed of the photosensitive drum 10 becomes faster than the peripheral speed of the intermediate transfer belt 24 for the purpose of increasing the transfer efficiency. The target value of the surface speed (peripheral speed) of the intermediate transfer belt 24 is different. The target value of the surface velocity of the photosensitive drum 10 is set to, for example, 0.15 [%] faster than the target value of the surface velocity of the intermediate transfer belt 24.

FIG. 4 shows a driving unit that drives the photosensitive drum 10. In the following description, the driving unit of the photosensitive drum 10 on which the yellow image is formed by the yellow image forming unit 5y will be described. The photosensitive drums 10 of the image forming portions 5m, 5c, and 5bk each have the same configuration. Therefore, the image forming apparatus 100 includes a motor M3, a motor gear 31, speed sensors 32 and 33, an encoder 34, and a drum drive gear 35 for each photosensitive drum 10.

The motor M3 drives the motor gear 31. The motor gear 31 meshes with the drum drive gear 35, and transmits the driving force transmitted from the motor M3 to the drum drive gear 35. A photosensitive drum 10 is fixed on the shaft of the drum drive gear 35, and the photosensitive drum 10 rotates when the motor M3 drives the drum drive gear 35. An encoder 34 fixed to the shaft of the drum drive gear 35 is provided on the shaft of the drum drive gear 35. The encoder 34 is a rotary plate provided with a large number of slits. Two speed sensors 32 and 33 are provided to detect this slit. The speed sensors 32 and 33 each have a light receiving element and a light emitting element, and count the number of times that the light emitted by the light emitting element passes through the slit and is received by the light receiving element. The number of times per unit time corresponds to the rotation 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) for each photosensitive drum 10. Each motor driver 1300 feedback-controls the current value (PWM signal) flowing through the motor M3 based on the rotation speed (rotation information) of the drum drive gear 35 detected by the speed sensors 32 and 33. PWM is an abbreviation for pulse width modulation. The PWM signal value supplied to the motor M3 corresponds to the current flowing through the motor M3 per predetermined time. Further, in a state where the rotation speed of the photosensitive drum 10 is controlled to the target rotation speed (first target rotation speed), the PWM signal value input to the motor M3 changes according to the load of the photosensitive drum 10. That is, the PWM signal value input to the motor M3 is information regarding the torque of the motor M3.

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 driving 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. The drive roller 40 is a rotating member that rotates to drive the intermediate transfer belt 24. An encoder 39 is further provided on the shaft of the drive gear 41. The encoder 39 is a rotary 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 that the light emitted by the light emitting element passes through the slit and is received by the light receiving element. 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 (PWM signal) flowing through the motor M4 based on the rotation speed (rotation information) of the drive gear 41 detected by the speed sensors 37 and 38. 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 flowing through the motor M4 per predetermined time. Further, in a state where the rotation speed of the drive roller 40 is controlled to the target rotation speed (second target rotation speed), the PWM signal value input to the motor M4 changes according to the load of the drive roller 40. That is, the PWM signal value input to the motor M4 is information regarding the torque of the motor M4.

Next, the harmful effects caused by the increase in the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 will be described in detail. The difference in peripheral speed between the intermediate transfer belt 24 and the photosensitive drum 10 is set so 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. The first state is a state in which the photosensitive drum 10 is rotated, the intermediate transfer belt 24 is driven, and the developing sleeve 8 is rotated. In this first state, the developer is interposed on the transfer surface (nip portion) between the photosensitive drum 10 and the intermediate transfer belt 24. The second state is a state in which the photosensitive drum 10 is rotated and the intermediate transfer belt 24 is driven, but the developing sleeve 8 is stopped rotating. In this second state, the developer does not intervene on the transfer surface (nip portion) between the photosensitive drum 10 and the intermediate transfer belt 24.

Here, when the developing sleeve 8 rotates, the developing agent is supplied to the photosensitive drum 10. That is, the developer in the developing apparatus 1 is consumed. Therefore, the image forming apparatus 100 rotates the developing sleeve 8 for the minimum time necessary for image forming. That is, the image forming apparatus 100 starts the rotation of the developing sleeve 8 at the timing immediately before the image forming, and immediately stops the rotation of the developing sleeve 8 after the image forming is completed.

When the image forming apparatus 100 forms an image based on the image data, the image forming apparatus 100 changes from a state in which the developer does not intervene in the nip portion to a state in which the developer intervenes in the nip portion. Then, when the formation of the image based on the image data is completed, the image forming apparatus 100 changes from a state in which the developer is interposed in the nip portion to a state in which the developer is not interposed in the nip portion. That is, when the difference in frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 is large between the first state and the second state, the image forming apparatus 100 has the photosensitive drum 10 and the intermediate transfer belt during the period when the state of the nip portion is switched. A large load fluctuation occurs for 24. Since the state of the nip portion is switched when image formation is started, the image forming apparatus 100 causes load fluctuation every time the first state and the second state are switched. When the load fluctuation amount exceeds the permissible range, the rotation speed of the motor M3 that rotates the photosensitive drum 10 and the motor M4 that rotates the drive roller 40 may become unstable. If image formation is executed in a state where the rotation speed of the motor M3 or the rotation speed of the motor M4 is unstable, the density of the image may fluctuate or color shift may occur in the image.

Therefore, the image forming apparatus 100 executes control to reduce the peripheral speed difference between the photosensitive drum 10 and 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 peripheral speed difference before the frictional force increases enough to cause load fluctuations that cause image defects.

Here, it will be described in detail that the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 increases as the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 increases. Generally, the frictional force between objects is divided into static frictional force and dynamic frictional force. The dynamic friction force is a constant value without changing depending on the relative velocity of the object. Therefore, the dynamic friction force becomes constant even if the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 changes. However, it is known that the dynamic friction force becomes constant when the speed difference between the objects is large to some extent. Since the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 in the image forming apparatus 100 is usually about 1%, as described above, the dynamic friction force is the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24. It does not follow the physical law of being constant. Therefore, in such a system in which the speed difference is small, it is known that the frictional force increases as the speed difference increases, as shown in FIG.

(Target speed adjustment process)
The image forming apparatus 100 of the photosensitive drum 10 is based on the PWM signal value of the motor M3 in the state where the developer is interposed in the nip portion and the PWM signal value of the motor M3 in the state where the developer is not interposed in the nip portion. Controls whether or not to change the target rotation speed. The image forming apparatus 100 can set the target rotation speed of each of the photosensitive drums 10 of the image forming portions 5y, 5m, 5c, and 5bk. The adjustment process for adjusting the target rotation speed of each of the photosensitive drums 10 of the image forming portions 5y, 5m, 5c, and 5bk will be described below.

The 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 part of the image forming apparatus 100. The ROM 1100 stores a control program executed by the CPU 1000 to execute various processes of the flowchart described later. The RAM 1200 is a system work memory for operating the CPU 1000. The temperature sensor 1005 measures the internal temperature of the image forming apparatus 100.

Further, since the image forming units 5y, 5c, 5m, and 5bk (image forming units 5 in FIG. 7), the sensor 14, the motors M1, M2, and M4, and the speed sensors 37, and 38 have already been described, they have already been described. The description here will be omitted.

The motor M3y is a motor that rotates a photosensitive drum 10 (hereinafter, referred to as a photosensitive drum 10y) on which a yellow image is formed by an image forming unit 5y. The motor M3m is a motor that rotates a photosensitive drum 10 (hereinafter, referred to as a photosensitive drum 10m) on which a magenta image is formed by an image forming unit 5m. Further, the image forming apparatus rotates a motor (not shown) for rotating the photosensitive drum 10 on which the cyan image is formed by the image forming unit 5c, and the photosensitive drum 10 on which the black image is formed by the image forming unit 5bk. It is equipped with a motor (not shown).

The speed sensors 32y and 33y are optical sensors provided in the drive gear of the photosensitive drum 10y. The speed sensors 32y and 33y output the detection result corresponding to the rotation information of the photosensitive drum 10y. Further, the speed sensors 32m and 33m are optical sensors provided in the drive gear of the photosensitive drum 10m. The speed sensors 32m and 33m output the detection result corresponding to the rotation information of the photosensitive drum 10m. The image forming apparatus 100 further includes a speed sensor that outputs rotation information of the photosensitive drum 10 on which a cyan image is formed by the image forming unit 5c, and rotation information of the photosensitive drum 10 on which a black image is formed by the image forming unit 5bk. It has a speed sensor that outputs the detection result corresponding to.

The pattern generator 70 outputs measurement image data when color shift correction 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 shift amount determining unit 1004.

The color shift amount determining unit 1004 calculates the transit times Lys, Lms, Lcs, and Lbks, and the transit times Lym, Lyc, and Lybk based on the measurement result of the pattern image by the sensor 14. Then, the color shift amount determining unit 1004 determines the color shift amount in the main scanning direction from the passing times Lys, Lms, Lcs, and Lbks, and determines the color shift amount in the sub-scanning direction from the passing times Lym, Lyc, and Lybk. .. The color registration amount including the color shift amount in the main scanning direction and the color shift amount in the sub-scanning direction is output to the color shift amount correction unit 1003. The color shift amount correction unit 1003 corrects the writing timing of the image of each color based on the color registration amount. Since the method by which the color shift amount correction unit 1003 adjusts the writing timing based on the color registration amount is a known technique, the description thereof is omitted here.

The motor driver 1300 belt controls the PWM signal value input to the motor M4 so that the rotation speed of the drive roller 40 detected by the speed sensors 37 and 38 becomes the target rotation speed. As a result, the current flowing through the motor M4 is controlled so that the rotation speed of the drive roller 40 for driving the intermediate transfer belt 24 becomes the target rotation speed. The motor driver 1300 belt functions as a drive control means for controlling the drive of the motor M4.

When the target rotation speed of the photosensitive drum 10y is set, the motor driver 1300y inputs a PWM signal value to the motor M3y so that the rotation speed of the photosensitive drum 10y detected by the speed sensors 32y and 33y becomes the target rotation speed. Control. As a result, the current flowing through the motor M3y is controlled so that the rotation speed of the photosensitive drum 10y becomes the target rotation speed. The PWM signal value for controlling the motor M3y output from the motor driver 1300y is stored in the RAM 1200. This is because the target speed determination unit 1002y, which will be described later, determines the target rotation speed of the photosensitive drum 10y based on the PWM signal value of the motor M3y stored in the RAM 1200. The motor driver 1300y functions as a drive control means for controlling the drive of the motor M3y.

When the target rotation speed of the photosensitive drum 10m is set, the motor driver 1300m inputs a PWM signal value to the motor M3m so that the rotation speed of the photosensitive drum 10m detected by the speed sensors 32m and 33m becomes the target rotation speed. Control. As a result, the current flowing through the motor M3m is controlled so that the rotation speed of the photosensitive drum 10m becomes the target rotation speed. The PWM signal value for controlling the motor M3m output from the motor driver 1300m is stored in the RAM 1200. This is because the target speed determination unit 1002m, which will be described later, determines the target rotation speed of the photosensitive drum 10m based on the PWM signal value of the motor M3m stored in the RAM 1200. The motor driver 1300m functions as a drive control means for controlling the drive of the motor M3m.

The image forming apparatus 100 further determines a motor driver (not shown) that controls the drive of a motor (not shown) that rotates the photosensitive drum 10 on which a cyan image is formed by the image forming unit 5c, and a target rotation speed of the motor. It is provided with a target speed determination unit for determining. Similarly, the image forming apparatus 100 includes a motor driver (not shown) that controls driving of a motor (not shown) that rotates the photosensitive drum 10 on which a black image is formed by the image forming unit 5bk, and a target rotation of the motor. It is provided with a target speed determination unit that determines the speed.

The target speed determination unit 1002y may be realized by, for example, an ASIC (application specific integrated circuit). The target speed determination unit 1002y targets a speed at which the surface speed of the photosensitive drum 10 is faster 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 is a value that causes image defects. Determined as speed. On the other hand, when the frictional force is increased enough to cause an image defect in the target speed adjustment process, the target speed determination unit 1002y changes the target speed of the photosensitive drum 10y. That is, the target rotation speed of the photosensitive drum 10y is set so as to reduce the difference between the target value of the surface speed of the photosensitive drum 10y and the target value of the surface speed of the intermediate transfer belt 24. The target speed determination unit 1002y reads the PWM signal value in the first state and the PWM signal value in the second state stored in the RAM 1200, and the PWM signal value in the first state and the PWM signal value in the second state. Based on the above, the target value of the photosensitive drum 10 is determined. The target speed determination unit 1002 may be configured such that, for example, a part of the functions of the CPU 1000 determines the target speed based on the PWM signal.

The image forming operation in which the image forming apparatus 100 forms an image based on the image data will be described with reference to the flowchart of FIG. When the image data is input from a PC (not shown), the CPU 1000 reads the program stored in the ROM 1100 and executes the process of the flowchart of FIG. In the following description, the subscripts y, m, c, and bk are omitted, and the photosensitive drum 10, the developing sleeve 8, the target speed determining unit 1002, the motor driver 1300, the motor M3, the speed sensor 32, and the like. It is described as 33.

First, the CPU 1000 rotates the photosensitive drum 10, the intermediate transfer belt 24, and the developing sleeve 8 (S800). The motor driver 1300 controls a PWM signal input to the motor M3. The motor M3 rotates the photosensitive drum 10 based on the PWM signal value input from the motor driver 1300. The motor driver 1300 belt controls the PWM signal input to the motor M4. The motor M4 rotates the drive roller 40 of the intermediate transfer belt 24 based on the PWM signal input from the motor driver 1300 belt. In step S800, the motors M1 and M2 rotate the developing sleeve 8 and the stirring member 6 of the developing device 1.

The motor driver 1300 updates the PWM signal value every 1 [msec], for example. The PWM signal value output from the motor driver 1300 is not only supplied to the motor M3 but also stored in the RAM 1200. The PWM signal values output from the motor driver 1300 for controlling the motor M3 for driving the photosensitive drums 10 of the image forming units 5y, 5m, 5c, and 5bk are stored in the RAM 1200, respectively.

In step S800, when the developing sleeve 8 rotates, a small amount of the developing agent is supplied from the developing sleeve 8 to the photosensitive drum 10 regardless of the developing bias supplied from the power supply unit 2. This small amount of the developer is supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24 as the photosensitive drum 10 rotates. Therefore, in step S800, the state of the photosensitive drum 10 and the intermediate transfer belt 24 changes from a state in which the developer is not interposed in the nip portion to a state in which the developer is interposed in the nip portion.

The CPU 1000 controls the image forming unit 5 (5y, 5m, 5c, and 5bk) to sequentially superimpose the images of each color component to form an image on the intermediate transfer belt 24 (S801). The CPU 1000 stores the PWM signal value (PWMdutyA) output from the motor driver 1300 in the RAM 1200 after the first time has elapsed since the image data was transferred (S802). When the developing sleeve 8 starts to rotate, the developing agent is supplied from the developing sleeve 8 to the photosensitive drum 10, and the developing agent supplied to the photosensitive drum 10 is conveyed to the nip portion. In order to acquire the PMW signal (PWMdutyA) in which the developing agent is interposed in the nip portion, the CPU 1000 determines the PWM signal value (PWMdutyA) after the first time has elapsed from the time when the developing sleeve 8 starts to rotate. Is stored in the RAM 1200. The first time is a time determined by the distance from the developing position where the photosensitive drum 10 and the developing sleeve 8 face each other to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24, and the rotation speed of the photosensitive drum 10. Yes, it is stored in the ROM 1100 in advance.

In the first state in which the photosensitive drum 10 is rotating, the intermediate transfer belt 24 is driven, and the developing sleeve 8 is rotating while the above-mentioned image forming process is being executed, for example, 8 [msec]. The PWM signal value (PWMdutyA) is stored in the RAM 1200 each time. The PWM signal value (PWMdutyA) in the first state corresponds to the first signal value (first information) that changes according to the torque of the motor M3.

Further, there is an upper limit to the number of PWM signal values stored in the RAM 1200. Therefore, after the PWM signal value stored in the RAM 1200 reaches the upper limit number, the oldest PWM signal value stored in the RAM 1200 is erased and a new PWM signal value is stored. The RAM 1200 may be configured to store, for example, 72 pieces of data for each motor.

Subsequently, the CPU 1000 determines whether or not the formation of all the images included in the image data is completed (S803). When the formation of all the images is completed in step S803, the CPU 1000 stops the image formation by the image forming unit 5 (S804). In step S804, the CPU 1000 stops the charging process of the photosensitive drum 10 by the charger 21 and stops the irradiation of the laser beam by the exposure device 22. Then, the CPU 1000 stops the process of storing the PWM signal value (PWMdutyA) in the RAM 1200.

Subsequently, the CPU 1000 stops the rotation of the developing sleeve 8 (S805). In step S805, the CPU 1000 causes the motor driver 1300 to stop the rotation of the motor M2. At this time, the drive roller 40 of the photosensitive drum 10 and the intermediate transfer belt 24 continues to rotate.

After a second time has elapsed from the time when the rotation of the developing sleeve 8 is stopped in step S805, the CPU 1000 stores the PWM signal value (PWMdutyB) output from the motor driver 1300 in the RAM 1200 (S806). When the developing sleeve 8 stops rotating, the supply of the developing agent from the developing sleeve 8 to the photosensitive drum 10 is stopped. However, there is a time lag between when the rotation of the developing sleeve 8 is stopped and when the developing agent on the photosensitive drum 10 finishes passing through the nip portion. In order to acquire the PMW signal (PWMdutyB) in a state where the developer does not intervene in the nip portion, the CPU 1000 determines the PWM signal value (PWMdutyB) after a second time has elapsed from the time when the rotation of the developing sleeve 8 is stopped. Is stored in the RAM 1200. The second time is a time determined by the distance from the developing position where the photosensitive drum 10 and the developing sleeve 8 face each other to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24, and the rotation speed of the photosensitive drum 10. Yes, it is stored in the ROM 1100 in advance.

In the second state in which the photosensitive drum 10 is rotated, the intermediate transfer belt 24 is driven, and the developing sleeve 8 is stopped rotating, the PWM signal value (PWMdutyB) is set to RAM 1200 every 8 [msec], for example. Is remembered in. The PWM signal value (PWMdutyB) in the second state corresponds to the second signal value (second information) that changes according to the torque of the motor M3. When the PMW signal (PWMdutyB) in a state where the developer is not interposed in the nip portion is stored in the RAM 1200 for 36 pieces, for example, the CPU 1000 stops the storage of the PWM signal (PWMdutyB).

Subsequently, the target speed determination unit 1002 executes a target speed adjustment process for each of the photosensitive drums 10 of the image forming unit 5 (5y, 5m, 5c, and 5bk) (S807). Then, the CPU 1000 stops the rotation of the photosensitive drum 10 and stops the driving of the inter-transfer belt 24 to end the image forming operation. The target speed adjustment process in step S807 will be described later using the flowchart of FIG.

Further, when all the images are not formed in step S803, the CPU 1000 determines whether or not the number of continuously printed images reaches 200 without stopping the developing sleeve 8 (S809). In step S809, if the number of images printed continuously without stopping the developing sleeve 8 is less than 200, the CPU 1000 proceeds to step S802.

On the other hand, in step S809, when the number of continuously printed images reaches 200 without stopping the developing sleeve 8, the CPU 1000 stops the rotation of the developing sleeve 8 (S810). The image forming apparatus 100 temporarily stops the developing sleeve 8 in order to eliminate the immovable layer of the developing agent generated inside the developing apparatus 1. If the developer aggregates in the immovable layer inside the developing apparatus 1, image defects may occur. For example, if the aggregated developer comes into contact with the developing sleeve 8 and the thickness of the developer layer supported on the developing sleeve 8 changes, a streak image may be formed on the photosensitive drum 10. Therefore, the image forming apparatus 100 stops the developing sleeve 8 for, for example, about 2 [sec] in order to eliminate the immovable layer inside the developing apparatus 1, and then rotates the developing sleeve 8 again.

In step S810, the CPU 1000 causes the motor driver 1300 to stop the rotation of the motor M2. At this time, the drive roller 40 of the photosensitive drum 10 and the intermediate transfer belt 24 continues to rotate. After a second time has elapsed from the time when the rotation of the developing sleeve 8 is stopped in step S810, the CPU 1000 stores the PWM signal value (PWMdutyB) output from the motor driver 1300 in the RAM 1200 (S811).

In the second state in which the photosensitive drum 10 is rotated, the intermediate transfer belt 24 is driven, and the developing sleeve 8 is stopped rotating, the PWM signal value (PWMdutyB) is set to RAM 1200 every 8 [msec], for example. Is remembered in. The PWM signal value (PWMdutyB) in the second state corresponds to the second signal value (second information) that changes according to the torque of the motor M3. When the PMW signal (PWMdutyB) in a state where the developer is not interposed in the nip portion is stored in the RAM 1200 for 36 pieces, for example, the CPU 1000 stops the storage of the PWM signal (PWMdutyB).

Subsequently, the target speed determination unit 1002 executes a target speed adjustment process for each of the photosensitive drums 10 of the image forming unit 5 (5y, 5m, 5c, and 5bk) (S812). Then, the CPU 1000 stops the rotation of the photosensitive drum 10 and stops the driving of the inter-transfer belt 24 to end the image forming operation. The target speed adjustment process in step S812 is the same as the target speed adjustment process in step S807.

Then, after the development sleeve 8 is stopped for 2 seconds (S813), the CPU 1000 resumes the rotation of the development sleeve 8 (S814), restarts the formation of the image based on the image data, and the CPU 1000 proceeds to the process in step S802. ..

According to the present invention, even when the image forming apparatus 100 continuously forms a plurality of images, the rotation of the developing sleeve 8 is temporarily stopped, and the developing agent is not interposed in the nip portion. The PMW signal value (PWMdutyB) related to the torque of the motor M3 is acquired. Therefore, even when the image forming apparatus 100 continuously forms a plurality of images, the target rotation speed of the photosensitive drum 10 can be corrected, so that the image defect caused by the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 Can be suppressed.

Here, the stop timings of the development sleeves 8 of the image forming portions 5y, 5m, 5c, and 5bk will be described with reference to the timing chart of FIG.

After the development sleeve 8 of the image forming portion 5y which is the most upstream in the conveying direction of the intermediate transfer belt 24 is stopped, the developing sleeve 8 of the image forming portion 5m located downstream of the image forming portion 5y in the conveying direction is stopped. .. Further, after the development sleeve 8 of the image forming unit 5m is stopped, the developing sleeve 8 of the image forming unit 5c located downstream of the image forming unit 5m in the transport direction is stopped. Similarly, after the development sleeve 8 of the image forming unit 5c is stopped, the developing sleeve 8 of the image forming unit 5bk located downstream of the image forming unit 5c in the transport direction is stopped. As a result, the PMW signal value (PWMdutyB) can be acquired after the developer transferred to the intermediate transfer belt 24 by the image forming unit 5y passes through the nip portion between the photosensitive drum 10 of the image forming unit 5m and the intermediate transfer belt 24.

After the sampling of the PWM signal value is completed, the developing sleeve 8 starts rotating sequentially. That is, after the developing sleeve 8 of the image forming portion 5y, which is the most upstream in the conveying direction of the intermediate transfer belt 24, starts rotating, the developing sleeve 8 of the image forming portion 5m located downstream of the image forming portion 5y in the conveying direction Start rotating. Further, after the development sleeve 8 of the image forming unit 5m resumes rotation, the developing sleeve 8 of the image forming unit 5c located downstream of the image forming unit 5m in the transport direction resumes rotation. Similarly, after the development sleeve 8 of the image forming unit 5c resumes rotation, the developing sleeve 8 of the image forming unit 5bk located downstream of the image forming unit 5c in the transport direction resumes rotation. By controlling the rotation of the developing sleeve 8 and the sampling timing of the PWM signal value as described above, the stop time of the developing sleeve 8 can be minimized.

Next, the target speed adjustment process executed in steps S807 and S812 of FIG. 8 will be described with reference to the flowchart of FIG. When executing the target speed adjustment process, the target speed determination unit 1002 executes the process of the flowchart of FIG. The target speed determination unit 1002 reads out 72 PMW signal values stored in the RAM 1200. The RAM 1200 stores 36 PMW signals (PWMdutyA) in a state where the developer is interposed in the nip portion and 36 PMW signals (PWMdutyB) in the state where the developer is not interposed in the nip portion. ..

First, the target speed determination unit 1002 determines whether or not the difference ΔPWMduty between the PMW signal value (PWMdutyA) and the PWM signal value (PWMdutyB) is larger than the first threshold value Th (S900). In step S900, the target speed determination unit 1002 calculates the average value of the 36 PWM signal values (PWMdutyA) and calculates the average value of the 36 PWM signal values (PWMdutyB). Then, the target speed determination unit 1002 calculates the difference ΔPWMduty of the average value of the PWM signal values based on the equation 1.
ΔPWMduty = PWMdutyB-PWMdutyA ... (Equation 1)
When the difference ΔPWMduty of the PWM signal value is larger than the first threshold value The, the frictional force between the state where the developer is present in the nip and the state where the developer is not present in the nip increases to the extent that an image defect is caused. It means that you are doing it.

In step S900, the target speed determination unit 1002 changes the target speed of the photosensitive drum 10 if the difference ΔPWMduty of the PWM signal values is larger than the first threshold value Th (S901). In step S901, the target speed determination unit 1002 determines the target speed of the photosensitive drum 10 based on the equation 2.
Target rotation speed Vt (n + 1) = Current target rotation speed Vt (n) -coefficient x ΔPWMduty
... (Equation 2)
Then, when the target speed determination unit 1002 changes the target speed of the photosensitive drum 10, the target speed determination unit 1002 transfers the execution instruction of the color shift correction to the CPU 1000 (S902), and ends the target speed adjustment process. The coefficient is a positive value.

When the target rotation speed of the photosensitive drum 10 is changed, the length of the image transferred from the photosensitive drum 10 to the intermediate transfer belt 24 changes in the transport direction of the intermediate transfer belt 24. For example, the writing position of the image formed on the photosensitive drum 10 in the sub-scanning direction may differ for each color. Therefore, when the target rotation speed of the photosensitive drum 10 is changed, the CPU 1000 executes color shift correction.

Further, when the difference ΔPWMduty of the PWM signal values is not larger than the first threshold value The in step S900, the target speed determination unit 1002 determines whether or not the execution condition of the color shift correction is satisfied (S903). In step S903, the execution condition is the number of sheets on which the image forming apparatus 100 has formed an image since the previous color shift correction was executed. When the cumulative value of the number of images formed reaches a predetermined number, the target speed determination unit 1002 determines that the execution condition is satisfied.

When the execution condition of the color shift correction is satisfied in step S903, the target speed determination unit 1002 determines whether or not the difference ΔPWMduty of the PWM signal values is larger than the second threshold value Thb (S904). Here, the second threshold value Thb is a value smaller than the first threshold value Tha. When changing the target rotation speed, the image forming apparatus 100 must execute the color shift correction even if the number of sheets on which the image is formed is less than a predetermined number since the previous color shift correction was executed. Therefore, when the target rotation speed is changed depending on whether or not the difference between the PWM signal values is larger than the first threshold value Th, the frequency of executing the color shift correction increases. Therefore, in the image forming apparatus 100, when the difference between the PWM signal values is smaller than the first threshold value Th and larger than the second threshold value Thb and the execution condition of the color shift correction is satisfied, the motor M3 Change the target rotation speed of and perform color shift correction. As a result, the frequency of color shift correction executed in response to the change in the target rotation speed of the motor M3 can be suppressed.

In step S904, if the difference ΔPWMduty of the PWM signal values is larger than the second threshold value Thb, the target speed determination unit 1002 shifts to the process of step S901 in order to change the target speed of the photosensitive drum 10.

On the other hand, in step S904, when the difference ΔPWMduty of the PWM signal values is not larger than the second threshold value Thb, the target speed determination unit 1002 shifts the process to step S902, transfers the color shift correction execution instruction to the CPU 1000, and targets. The speed adjustment process ends. At this time, the target rotation speed of the photosensitive drum 10 is not changed.

If the execution condition of the color shift correction is not satisfied in step S903, the target speed determination unit 1002 ends the target speed adjustment process. In this case, the target rotation speed of the motor M3 that rotates the photosensitive drum 10 is not changed.

In the above description, a configuration for controlling whether or not to adjust the target rotation speed of the motor M3 is described based on the difference ΔPWMduty of the PWM signal values of the motor M3 that rotates one photosensitive drum 10. In the image forming apparatus 100 in which each of the yellow, magenta, cyan, and black image forming portions 5y, 5m, 5c, and 5bk includes the photosensitive drum 10, steps S900 and S904 are executed for each photosensitive drum 10. Then, when at least one target rotation speed of the yellow, magenta, cyan, and black photosensitive drums 10 is changed, the target speed determination unit 1002 transfers an execution instruction for color shift correction to the CPU 1000. That is, the CPU 1000 executes color shift correction when at least one target rotation speed of the yellow, magenta, cyan, and black photosensitive drums 10 is changed.

According to the description of the flowcharts of FIGS. 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.

FIG. 11A is a plot of the PWM signal values of the yellow photosensitive drum 10y obtained by the experiment. The arrow indicates the timing at which the target speed of the photosensitive drum 10y is changed. The difference between the PWM signal value when the developer intervenes in the nip portion and the PWM signal value when the developer does not intervene in the nip portion decreases each time the target speed is changed. Further, FIG. 11B is a plot of PWM signal values of the intermediate transfer belt 24. It can be seen that the frictional force between the photosensitive drum 10y and the intermediate transfer belt 24 is reduced by changing the target speed of the photosensitive drum 10y, and the load on the intermediate transfer belt 24 is reduced. As a result, load fluctuation does not occur, and it is possible to prevent the surface speed of the photosensitive drum 10y and the surface speed of the intermediate transfer belt 24 from becoming unstable immediately after the start of image formation.

(Sampling timing and load of photosensitive drum 10)
The image forming apparatus 100 acquires the PWM signal value of the motor M3 that rotates the photosensitive drum 10. There are two reasons for this.

The first is that the target speed can be changed for each of the plurality of photosensitive drums 10. If the target speed of the intermediate transfer belt 24 is changed based on the PWM signal value of the motor M4 that drives the intermediate transfer belt 24, the target rotation speed of the photosensitive drum 10 in which the frictional force is not increased may also be changed. is there.

Second, if the developer does not intervene even in the nip portion between the photosensitive drum 10 of interest and the intermediate transfer belt 24, the developer intervenes 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 also 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, the developer is not interposed in the nip portion between all the photosensitive drums 10 and the intermediate transfer belt 24. The PWM signal value must be acquired in. Therefore, the downtime for measuring the PWM signal value in the state where the developer is not interposed in the nip portion increases.

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, the main loads that serve are the frictional force of the intermediate transfer belt 24 and the frictional force of the blade of the drum cleaner 26 that comes into contact with the photosensitive drum 10.

In the target speed determination unit 1002, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 is generated in a state where the developing sleeve 8 is rotated and the developing agent is interposed in the nip portion and in a state where the developing agent is not interposed in the nip portion. Determine if the permissible range is exceeded. However, it is premised that the frictional force due to the blade of the drum cleaner 26 is constant in both states. By interposing the developer 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 increases. FIG. 12 shows the transition of the load of the photosensitive drum 10 when the amount of 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. ing. As shown in FIG. 12, when the amount of the developer between the photosensitive drum 10 and the blade decreases with the passage of time, the torque of the motor M3 that rotates the photosensitive drum 10 increases. That is, if the amount of the developer between the photosensitive drum 10 and the blade is reduced even when the developer is not interposed in the nip portion, the load on the photosensitive drum 10 increases. Here, it is unlikely that the amount of the developer between the photosensitive drum 10 and the blade will be significantly reduced in a state where the image forming unit 5 is actually forming an image. Therefore, even if the target rotation speed is determined based on the PWM signal value acquired in a state where the amount of the developer between the photosensitive drum 10 and the blade is significantly reduced in the target speed adjustment process, the target rotation speed is determined. It cannot be determined with high accuracy.

Therefore, in the image forming apparatus 100, even immediately after the rotation of the developing sleeve 8 is stopped and the developing agent adhering to the photosensitive drum 10 passes through the nip portion, the developing agent is interposed between the photosensitive drum 10 and the blade. There is a period of time. By acquiring the PWM signal value during that period, it is not necessary to consider the frictional force between the photosensitive drum 10 and the blade.

Further, as for the PWM signal value (PWMdutyB) in the state where the developer is not interposed between the photosensitive drum 10 and the intermediate transfer belt 24, the developing sleeve 8 stops rotating and the power supply unit 2 sets the AC voltage to 0 [. V] is set and acquired. That is, PWM in a state where the developing sleeve 8 stops rotating and the power supply unit 2 supplies a DC voltage to the developing sleeve 8 and no developer is interposed between the photosensitive drum 10 and the intermediate transfer belt 24. The signal value (PWMdutyB) is acquired. This means that when a highly releasable toner or the like is used as the developing agent, the developing agent is supplied from the developing sleeve 8 to the photosensitive drum 10 even if the developing sleeve 8 stops rotating depending on the value of the developing bias. This is to suppress it.

FIG. 13 is a diagram showing a waveform of development bias. The development bias shown in FIG. 13A is a DC voltage that does not include an AC voltage. The development bias shown in FIG. 13B superimposes an AC voltage on a DC voltage. This development bias is called a rectangular bias. The development bias shown in FIG. 13 (c) includes a period in which the AC voltage becomes 0 [V] in a part of the rectangular bias. A development bias in which a part of the rectangular bias includes a period in which the AC voltage becomes 0 [V] is called a blank pulse bias. Therefore, the PWM signal value (PWMdutyB) is acquired during the above-mentioned period of the black pulse bias.

Further, the amount of change in the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 depending on the presence or absence of the developer in the nip portion is predicted based on the difference in the PWM signal value of the motor M3. Therefore, the PWM signal value when the developer is present in the nip and the PWM signal value when the developer is not present in the nip must not be changed by any influence other than the presence or absence of the developer. ..

However, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 may change due to the transfer bias supplied from the power supply unit 3 to the primary transfer roller 23. This is because if the transfer bias is applied to the primary transfer roller 23 while the developer is not supplied to the nip portion, the electrostatic adsorption force between the photosensitive drum 10 and the intermediate transfer belt 24 increases. is there. While the image forming unit 5 is forming an image, the power supply unit 3 continues to apply a transfer bias between the photosensitive drum 10 and the intermediate transfer belt 24. Then, when the image forming unit 5 finishes forming the image, the power supply unit 3 sets the transfer bias to 0 [V].

FIG. 14 is an experimental result showing the PMW signal value of the motor M4 that rotates the drive roller 40 when the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 is changed. FIG. 14A shows the PWM signal value of the motor M4 when the transfer bias is applied, and FIG. 14B shows the PWM signal value of the motor M4 when the transfer bias is not applied. .. As shown in FIG. 14, the difference between the PWM signal value when the transfer bias is applied and the difference between the PWM signal value when the transfer bias is not applied are different. Further, when the developer is interposed in the nip portion, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 does not change so much regardless of whether or not the transfer bias is applied. Therefore, when the image forming apparatus 100 stores the PWM signal value in the RAM 1200 in a state where the CPU 1000 does not intervene in the nip portion, the CPU 1000 is prevented from applying the transfer bias in order to suppress the influence of the transfer bias. Controls the power supply unit 3.

According to the present invention, even when the image forming apparatus 100 continuously forms a plurality of images, a timing for stopping the rotation of the developing sleeve 8 is provided while the plurality of images are formed, and the timing is provided. Acquires the PWM signal value of the motor M3. As a result, the PMW signal value of the motor M3 can be acquired without the developer intervening between the photosensitive drum 10 and the intermediate transfer belt 24, so that the image forming apparatus 100 forms a plurality of images. Even in this case, the target rotation speed of the motor M3 can be adjusted. Therefore, while the image forming apparatus 100 is continuous with a plurality of images, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 increases, and the possibility of causing image defects can be suppressed.

(Modification example)
In the description of FIG. 8, when the image forming apparatus 100 continuously forms a plurality of images, the developing sleeve 8 rotates every time the number of continuously printed images reaches 200 without stopping the developing sleeve 8. To stop. This is executed in order to eliminate the immovable layer of the developer generated inside the developing apparatus 1. However, the conditions for stopping the rotation of the developing sleeve 8 in order to eliminate the immovable layer of the developing agent generated inside the developing apparatus 1 are not limited to the above-mentioned conditions.

The stop condition may be the time during which the image forming apparatus 100 is continuously driven while the image forming apparatus 100 continuously forms a plurality of images. For example, when the time in which the image forming unit 5 is continuously driven is longer than a predetermined time, the CPU 1000 temporarily stops the rotation of the developing sleeve 8. Since the developing sleeve 8 continues to rotate while the image forming unit 5 is continuously driven, there is a high possibility that an immovable layer of the developing agent is generated inside the developing apparatus 1. Therefore, when the continuous rotation time of the developing sleeve 8 reaches a predetermined time, the image forming operation is temporarily suspended, the rotation of the developing sleeve 8 is stopped, and the immovable layer of the developer generated inside the developing device 1 is formed. Eliminate.

Further, the stop condition may be the consumption of the developer while the image forming apparatus 100 continuously forms a plurality of images. For example, the consumption of the developer is predicted based on the image data, and when the consumption of the developer of the image formed on a predetermined number of sheets is less than the predetermined amount, the CPU 1000 temporarily stops the rotation of the developing sleeve 8. .. It is known that when the consumption of the developer is small, there is a high possibility that an immovable layer of the developer is generated inside the developing apparatus 1. Therefore, when the consumption of the developing agent is less than a predetermined amount, the image forming operation is temporarily interrupted at an arbitrary timing while the plurality of images are continuously formed, and the rotation of the developing sleeve 8 is stopped. The immovable layer of the developer generated inside the developing apparatus 1 is eliminated.

According to the present invention, even when the image forming apparatus 100 continuously forms a plurality of images, a timing for stopping the rotation of the developing sleeve 8 is provided while the plurality of images are formed, and the timing is provided. Acquires the PWM signal value of the motor M3. As a result, the PMW signal value of the motor M3 can be acquired without the developer intervening between the photosensitive drum 10 and the intermediate transfer belt 24, so that the image forming apparatus 100 forms a plurality of images. Even in this case, the target rotation speed of the motor M3 can be adjusted. Therefore, while the image forming apparatus 100 is continuous with a plurality of images, the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 increases, and the possibility of causing image defects can be suppressed.

M3 motor M4 motor 1 developing device 8 developing sleeve 10 photosensitive drum 22 exposure device 24 intermediate transfer belt 1000 CPU
1002 Target speed determination unit 1300 Motor driver

Claims (5)

Photoreceptor and
The first motor that rotates the photoconductor and
A latent image forming means for forming an electrostatic latent image on the photoconductor,
An image in which a developer carrier that supports and rotates a developer is provided, and the electrostatic latent image on the photoconductor is developed using the developer supported on the developer carrier to form an image. Forming means and
An intermediate transfer body to which the image formed by the image forming means is transferred, and
A second motor that rotates a rotating member for driving the intermediate transfer body, and
A drive control means that controls the first motor so that the rotation speed of the photoconductor becomes a target rotation speed, and controls the second motor so that the rotation speed of the rotating member becomes a predetermined rotation speed.
An acquisition means for acquiring information on the torque of the first motor, and
It said photosensitive member and said rotary member and said developer carrying member to obtain the first information about the torque of the first motor before Symbol acquisition means Te first state odor which is rotating, the development phase carrier is a rotating stop, and, whether the rotating member and the photosensitive member to obtain a second information about the torque of the first motor before Symbol acquisition means Te second state smell is rotating, to change the target rotation speed It has a control means for controlling the torque based on the first information and the second information.
In the control means, after the developer carrier starts to rotate, the developer supplied from the developer carrier to the surface of the photoconductor is rotated between the photoconductor and the intermediate transfer body by the rotation of the photoconductor. After the first time until reaching the nip portion has elapsed, in the first state, the acquisition means is made to acquire the first information.
In the control means, after the developer support has stopped rotating, the developer supplied to the surface of the photoconductor when the rotation of the developer stop has stopped is caused by the rotation of the photoconductor. Image formation characterized in that, in the second state, the acquisition means acquires the second information after the second time until the photoconductor and the intermediate transfer body passes through the nip portion has elapsed. apparatus. Further, since the control means acquires the second information while continuously forming a plurality of images based on the image data, when the number of sheets on which the plurality of images are formed reaches a predetermined number. The image forming apparatus according to claim 1, wherein the rotation of the developer carrier is stopped. Said control means further for obtaining said second information during the formation of multiple consecutive images based on the image data, the time of forming successively a plurality of images wherein when longer than the predetermined time the image forming apparatus according to claim 1, characterized in that locked stop the rotation of the developer carrying member. Further, the control means acquires the second information while continuously forming a plurality of images based on the image data, so that the consumption amount of the developer is predicted based on the image data and a predetermined number of sheets are obtained. the image forming apparatus according to claim 1 in which the amount of developer consumed for developing the plurality of images is characterized by causing locked stop the rotation of the developer bearing member is less than a predetermined amount. Said control means further after the image forming unit has finished forming the plurality of images, in the second state, claims 1 to 4, characterized in that to obtain the second information to the acquisition unit The image forming apparatus according to any one of the above.

Images