JP6742842B2 - Image forming device - Google Patents

Description

The present invention relates to speed control for controlling the difference in peripheral speed between a photoconductor and an intermediate transfer member.

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

The image forming apparatus is required to control the peripheral speed (surface speed) of the surface of the photosensitive member and the peripheral speed (surface speed) of the surface of the intermediate transfer member to be constant. This is because the laser light for forming the 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 also changes, so that the length of the image changes or the density of the image on the photoconductor becomes uneven. Further, in an image forming apparatus that transfers the images of the respective colors formed by the plurality of image forming units in an overlapping manner onto the intermediate transfer member in order to form a full-color image, the relative position of the images of the respective colors is changed. Misalignment occurs and the color changes. Therefore, in order to control the surface speed of the photoconductor and the surface speed of the intermediate transfer member, the image forming apparatus executes, for example, feedback control based on the output of the encoder.

Here, the target speeds of the surface speed of the photosensitive member and the surface speed of the intermediate transfer member will be described. It is preferable to control the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member to be different from each other. This is because it is possible to suppress the occurrence of transfer failure in the image transferred from the photoconductor to the intermediate transfer body when forming an image such as characters or thin lines. If the peripheral speed of the photoconductor is faster than the peripheral speed of the intermediate transfer body, the force with which the photosensitive body presses the intermediate transfer body is increased, and the pressure in the nip portion between the photosensitive body and the intermediate transfer body is increased to suppress transfer defects. Is known to do. Therefore, the target value of the peripheral speed of the photosensitive member and the target value of the peripheral speed of the intermediate transfer member are set so that the peripheral speed of the photosensitive member becomes faster than the peripheral speed of the intermediate transfer member.

By the way, in an image forming apparatus in which the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer body are controlled to be different from each other, the friction coefficient of the photosensitive body or the intermediate transfer body is changed according to the internal temperature of the image forming apparatus or the number of printed sheets. May change. While the image is being formed, the developer is supplied to the nip portion for transferring the image on the photoconductor to the intermediate transfer body, so even if the friction coefficient of the photoconductor or the intermediate transfer body changes, The surface speed of the body and the intermediate transfer body is controlled to the target speed. However, at the timing when the state in which the developer is not present in the nip portion is changed to the state in which the developer is present in the nip portion, the load of the motor for driving the photoconductor and the intermediate transfer member is suddenly changed. There is a possibility that the rotation speed of the motor may become uncontrollable. This timing occurs, for example, immediately after starting the rotational driving of the photoconductor or the intermediate transfer member to form an image. When the rotation speed of the motor cannot be controlled, the above-mentioned image defect occurs.

Therefore, in order to reduce the difference between the motor load when the developer is supplied to the nip portion and the motor load when the developer is not supplied to the nip portion, the peripheral speed of the photoconductor and the intermediate transfer are reduced. An image forming apparatus that adjusts the difference from the peripheral speed of the body is known (Patent Document 1). This image forming apparatus supplies a developer to the nip portion to switch the motor speed command value to obtain a motor drive signal, and supplies the developer to the nip portion to switch the motor speed command value to switch the motor speed command value. Get the drive signal of. Then, in the image forming apparatus described in Patent Document 1, the difference between 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 is the smallest. The motor speed command value is determined based on the motor drive signal.

JP, 2016-1268, A

The image forming apparatus described in Patent Document 1 controls the rotation speed of the motor stepwise in order to acquire the load of the motor for each of the plurality of peripheral speed differences. Therefore, the image forming apparatus described in Patent Document 1 has a long downtime for the adjusting operation.

For example, whether to change the rotation speed of the motor based on the drive signal of the motor in a state where the motor is controlled so that the difference in the peripheral speed becomes a predetermined value without changing the difference in the peripheral speed stepwise. A configuration for controlling the is considered. According to this configuration, since the difference in peripheral speed is not changed, it is possible to suppress downtime spent for the adjusting operation.

However, as a result of experiments conducted by the inventors with the above-described configuration, when the difference in peripheral speed between the photoconductor and the intermediate transfer member is reduced, the load on the motor may increase. It is considered that this is because the characteristics of the difference in peripheral speed between the photoconductor and the intermediate transfer member and the load are reversed. In other words, if the peripheral speed of the photoconductor is faster than the peripheral speed of the intermediate transfer member, the load on the motor when the developer is not present in the nip portion is greater than the load on the motor when the developer is present in the nip portion. Should be big. However, it has been found that, for some reason, the load on the motor when the developer is present in the nip portion is larger than the load on the motor when the developer is not present in the nip portion. When the characteristics of the peripheral speed difference and the load were reversed, increasing the peripheral speed difference suppressed the motor load. Further, it was found by experiments that the phenomenon in which the characteristics of the difference in peripheral speed and the load are reversed suddenly occurs even during image formation.

Therefore, an object of the present invention is to reduce the load on the motor while suppressing downtime even when the characteristics of the difference in peripheral speed and the load are reversed.

In order to solve the above problems, an image forming apparatus of the present invention includes a motor that rotates a photoconductor, the photoconductor, and a developer carrier that carries and rotates a developer. An image forming unit that forms an image on the photoconductor by using the developer carried on the image forming member, an intermediate transfer member that carries and conveys the image formed by the image forming unit, and the image on the photoconductor. In the nip portion for transferring the image on the intermediate transfer body, a transfer means for transferring the image on the photosensitive body to the intermediate transfer body, and a difference between the peripheral speed of the photosensitive body and the peripheral speed of the intermediate transfer body. So as to be the target value, drive control means for controlling the torque of the motor, acquisition means for acquiring a signal according to the torque of the motor, and the drive so that the difference between the peripheral speeds becomes the target value. A control unit that controls the target value based on the signal acquired by the acquisition unit by causing the acquisition unit to acquire the signal while the control unit controls the torque of the motor. When the peripheral speed difference is changed from a first target value to a second target value, the drive control means controls the motor torque so that the peripheral speed difference becomes the first target value. The first signal obtained by the obtaining means during the first period for controlling the motor and the second period during which the drive control means controls the torque of the motor so that the peripheral speed difference becomes the second target value. Comparing the second signal acquired by the acquisition means, and determining the third target value based on the comparison result and the other second signal acquired by the acquisition means in the second period. And

According to the present invention, even when the characteristics of the difference in peripheral speed and the load are reversed, the load on the motor can be reduced while suppressing downtime.

Schematic cross-sectional view of the image forming apparatus Sectional view of the main part of the image forming unit Schematic diagram of the pattern image formed on the intermediate transfer belt Perspective view of essential parts of photosensitive drum drive mechanism Perspective view of essential parts of drive mechanism of intermediate transfer belt Control block diagram of image forming apparatus Flowchart diagram showing image forming operation Flowchart diagram showing the adjustment process Flowchart diagram showing the determination process 1 Flowchart diagram showing the determination process 2 Transition diagram of motor drive signal when reverse rotation occurs Transition diagram of motor drive signal when another reverse rotation phenomenon occurs

FIG. 1 shows a main part of the image forming apparatus 100. The image forming apparatus 100 has 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 having different colors. The image forming unit 5y forms a yellow image, the image forming unit 5m forms a magenta image, the image forming unit 5c forms a cyan image, and the image forming unit 5bk forms a black image.

The configurations of the image forming units 5y, 5c, 5m, and 5bk are the same except for the color of the developer, and therefore the configuration of the image forming unit 5y will be described here. The photosensitive drum 10 is an image carrier that carries an electrostatic latent image or an image. A photosensitive layer that functions as a photoconductor is formed on the surface of the photosensitive drum 10. The charger 21 charges the surface of the photosensitive drum 10. The exposure device 22 exposes the charged photosensitive drum 10 to form an electrostatic latent image on the photosensitive drum 10. The exposure device 22 functions as a latent image forming unit that forms an electrostatic latent image on the photosensitive drum 10. The direction in which the laser light of the exposure device 22 scans the photosensitive drum 10 is called the main scanning direction. The exposure device 22 has optical members such as a rotating polygon mirror, a mirror, and a lens that are driven to rotate for scanning a laser beam. The developing device 1 develops an electrostatic latent image using a developer 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 carried on the photosensitive drum 10 to the intermediate transfer belt 24. As a result, the image on the photosensitive drum 10 is transferred to the intermediate transfer belt 24 at the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24. The intermediate transfer belt 24 functions as an intermediate transfer member onto 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 carried on the intermediate transfer belt 24 onto the sheet P. As a result, the image on the intermediate transfer belt 24 is transferred to the sheet P passing through the nip portion between the intermediate transfer belt 24 and the secondary transfer roller 29.

The fixing device 27 heats the image on the sheet P to fix 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 on the intermediate transfer belt 24 without being transferred from the photosensitive drum 10. 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 container 20 contains a developer to be supplied to the developing device 1. When the developer in the developing device 1 is reduced, a replenishing mechanism (not shown) replenishes the developing device 1 with a required amount of developer from the developer container 20. The sensor 14 is an optical sensor that has a light emitting element and a light receiving element, and measures reflected light from a measurement image formed on the intermediate transfer belt 24 by the image forming units 5y, 5m, 5c, and 5bk.

FIG. 2 is a schematic view of a main part of the image forming unit 5. The developing device 1 has a stirring member 6 such as a screw that conveys the developer supplied from the developer container 20 and the carrier while stirring. The stirring member 6 is driven by the motor M1. As the developer and the carrier are stirred, the developer is triboelectrically charged. The developing sleeve 8 is a developer carrier that carries a developer. 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 the electrostatic latent image, the power supply unit 2 applies a superimposed voltage (developing bias) obtained by superimposing an AC voltage on a DC voltage to the developing sleeve 8. The power supply unit 2 functions as a voltage applying unit that applies a superimposed 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.

(Color misregistration correction)
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 tint of the full-color image cannot be compensated. Therefore, the image forming apparatus 100 executes the color misregistration correction for correcting the relative misalignment of the formation positions of the images of the other colors with respect to the formation positions of the images of the reference colors.

The image forming apparatus 100 may change the image forming position even when the temperature of the image forming apparatus 100 changes or when a large number of images are formed. Therefore, in the image forming apparatus 100, when the internal temperature of the image forming apparatus 100 detected by a temperature sensor (not shown) changes by a predetermined temperature or more, or when the cumulative number of images formed on the sheet P (the number of formed images) is predetermined. Perform color misregistration correction after exceeding the number of sheets. Furthermore, for example, when the operator issues an instruction to perform color misregistration correction, when the main power supply of the image forming apparatus 100 is turned on, and when the number of image formations reaches a predetermined number, the color misregistration correction is performed. To be done.

When the color misregistration correction is executed, the image forming apparatus 100 forms a measurement image (pattern image) of each color on the intermediate transfer belt 24, and the sensor 14 measures the measurement image (pattern image). Then, the image forming apparatus 100 detects the amount of color misregistration based on the measurement result of the sensor 14. Then, the image forming apparatus 100 corrects the writing start timing (exposure timing) when the image forming units 5y, 5c, 5m, and 5bk form an electrostatic latent image based on the detected color shift amount.

FIG. 3 is a schematic diagram of a pattern image formed on the intermediate transfer belt 24 in color misregistration correction and a digital signal binarized by a comparator. As shown in FIG. 3, the pattern images 48y, 48m, 48c, 48bk, 49y, 49m, 49c, and 49bk are formed at different positions in the conveyance direction of the intermediate transfer belt 24. The pattern image includes a pattern inclined by 45 degrees with respect to the conveyance direction of the intermediate transfer belt 24 and a pattern inclined by −45 degrees with respect to the conveyance direction. Further, the magenta pattern images 48m and 49m, which are the reference images, are formed so as to sandwich the yellow, cyan, and black pattern images 48y, 48c, 48bk, 49y, 49c, and 49bk.

The color misregistration correction unit 1003 (FIG. 6) acquires the timing at which the digital signal output from the sensor 14 switches from a high level to a low level and the timing at which the digital signal switches from a low level to a high level. The color misregistration correction unit 1003 (FIG.) determines the timing at which the sensor 14 detects the pattern image based on the timing at which the digital signal switches from the high level to the low level and the timing at which the digital signal switches from the low level to the high level. .. The color misregistration correction unit 1003 (FIG.) determines the timing T at which the pattern detection sensor 7 detects the detection pattern 990, for example, based on Expression (1).
T=(Ta+Tb)+Ta... (1)
Ta is the timing when the digital signal 302 is switched from the high level to the low level, and Tb is the timing when the digital signal 302 is switched from the low level to the high level.

That is, the timing T is an intermediate timing between the timing Ta at which the digital signal switches from the high level to the low level and the timing Tb at which the digital signal switches from the low level to the high level.

Then, the color misregistration correction unit 1003 (FIG. 6) determines the intervals Y1, Y2, C1, C2, K1, and K2 at the timing when each pattern image is detected. The color misregistration correction unit 1003 (FIG. 6) determines, based on the timing at which the pattern image is detected, whether the image of a color other than magenta (yellow, cyan, black) is formed with respect to the position where the image of magenta is formed. The difference (color shift amount) is calculated.

For example, the deviation amount ΔHy of the yellow image with respect to the magenta image in the direction orthogonal to the conveyance direction of the intermediate transfer belt 24 is calculated based on the equation (2).
Deviation amount ΔHy={(Y4-Y3)/2-(Y2-Y1)/2}/2...Equation (2)
For example, the deviation amount ΔVy of the yellow image with respect to the magenta image in the conveyance direction of the intermediate transfer belt 24 is calculated based on the equation (3).
Deviation amount ΔVy={(Y4-Y3)/2+(Y2-Y1)/2}/2...Equation (3)
The color misregistration correction unit 1003 (FIG. 6) controls the writing start timing of the yellow image based on the color misregistration amounts ΔHy and ΔVy. The color misregistration correction unit 1003 (FIG. 6) uses the image writing position in the direction orthogonal to the transport direction of the intermediate transfer belt 24 as a reference position in the direction in which the laser light emitted from the exposure device 22 is scanned. Occasionally, the pixel is shifted by a distance corresponding to the amount of deviation ΔH. The scanning speed of the laser light emitted from the exposure device 22 corresponds to the rotation speed of the polygon mirror of the exposure device 22 and is therefore predetermined. That is, the color misregistration correction unit 1003 (FIG. 6) corrects the writing timing in the main scanning direction based on the time until the laser light reaches the position shifted by the pixel corresponding to the deviation amount ΔHy from the reference position. To do.

Further, the color misregistration correction unit 1003 (FIG. 6) sets the color misregistration amount ΔVy when the image writing start position in the transport direction of the intermediate transfer belt 24 is based on the reference position in the moving direction of the surface of the photosensitive drum 10. Shift by the corresponding distance. The rotation speed of the photosensitive drum 10 is predetermined. For example, the color misregistration correction unit 1003 (FIG. 6) causes the laser light of the exposure device 22 to reach a position where the photosensitive drum 10 has moved by a distance corresponding to the color misregistration amount ΔVy with reference to a predetermined image forming timing. Calculate time. The color misregistration correction unit 1003 (FIG. 6) corrects the writing timing in the sub-scanning direction by adding the calculated time to the predetermined image forming timing.

Note that the color misregistration correction unit 1003 (FIG. 6) may similarly correct the writing start position of the cyan image and the writing start position of the black image.

(Speed control of photosensitive drum and intermediate transfer belt)
The photosensitive drum 10 and the intermediate transfer belt 24 are rotationally driven while contacting 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, image expansion and contraction or 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. 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 is higher than the peripheral speed of the intermediate transfer belt 24 in order to increase 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 speed of the photosensitive drum 10 is set to, for example, 0.15 [%] faster than the target value of the surface speed of the intermediate transfer belt 24.

FIG. 4 is a perspective view of a drive mechanism that drives the photosensitive drum 10. In the following description, a drive mechanism of the photosensitive drum 10 on which a yellow image is formed by the yellow image forming section 5y will be described. The drive mechanism for driving the photosensitive drum 10 of each of the image forming units 5m, 5c, and 5bk has the same configuration. Therefore, the image forming apparatus 100 includes the motor M3, the motor gear 31, the speed sensors 32 and 33, the encoder 34, and the 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 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 is rotated by the motor M3 driving the drum driving 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 so as to detect this 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 the light emitted from 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 MD3 (FIG. 6) for each photosensitive drum 10. Each motor driver MD3 feedback-controls the drive signal (PWM signal) of 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 value of the PWM signal supplied to the motor M3 corresponds to the current supplied to the motor M3 per predetermined time. Further, in the state where the rotation 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 of the photosensitive drum 10. That is, the PWM signal value input to the motor M3 changes according to 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 drive force transmitted from the motor M4 to the drive gear 42. The drive gear 42 further meshes with the drive gear 41. The 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 rotates, and the drive roller 40 also rotates the intermediate transfer belt 24. 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 many slits. Two speed sensors 37 and 38 are provided so as to detect this slit. Each of the speed sensors 37 and 38 has a light receiving element and a light emitting element, and counts the number of times 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 drive signal (PWM signal) of 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 surface 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. Furthermore, in the state where the rotation speed of the drive roller 40 is controlled to the target 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 a signal that changes according to the torque of the motor M4.

Next, the adverse 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 peripheral 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. The first state is a state in which the photosensitive drum 10 rotates, the intermediate transfer belt 24 drives, and the developing sleeve 8 rotates. In this first state, the developer intervenes 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 rotates and the intermediate transfer belt 24 is driven, but the developing sleeve 8 stops rotating. In this second state, no developer intervenes 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 developer is supplied to the photosensitive drum 10. That is, the developer in the developing device 1 is consumed. Therefore, the image forming apparatus 100 starts the rotation of the developing sleeve 8 immediately before the image formation, and stops the rotation of the developing sleeve 8 after the image formation is completed.

When forming 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 after the rotational driving of the developing sleeve 8 is started. To do. Then, in the image forming apparatus 100, after the formation of the image based on the image data is completed and the rotational drive of the developing sleeve 8 is stopped, the state in which the developer is present in the nip portion is the state in which the developer is not present in the nip portion. Change to. That is, in the image forming apparatus 100, when there is a large difference in frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 between the first state in which the developing sleeve 8 rotates and the second state in which the developing sleeve 8 stops rotating, the image is formed. Load fluctuations occur when forming is started. When the load fluctuation amount exceeds the allowable range, the rotation speeds of the motor M3 that rotates the photosensitive drum 10 and the motor M4 that rotates the drive roller 40 become unstable. If the 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 changes or the color shift occurs in the image.

Therefore, the image forming apparatus 100 controls the difference in peripheral speed 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. Accordingly, the image forming apparatus 100 can control the peripheral speed difference before the frictional force increases enough to cause the load fluctuation that causes the image defect.

Generally, the frictional force between objects is divided into static frictional force and dynamic frictional force. The dynamic friction force has a constant value without changing depending on the relative speed of the object. Therefore, the dynamic friction force is 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 difference in speed between 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%, the dynamic friction force is equal to the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 as described above. It does not follow the physical law of being constant. According to the experiment, when the peripheral speed difference between the photosensitive drum 10 and the intermediate transfer belt 24 is small, it is found that the frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 also changes when the peripheral speed difference changes.

Therefore, the image forming apparatus 100 sets the current value flowing through the motor in the first state in which the developing sleeve 8 is rotating and the current value flowing in the motor in the second state in which the developing sleeve 8 is stopped rotating. Remember. Then, the image forming apparatus 100 updates the target speed of the motor M3 that rotates the photosensitive drum 10 based on the stored current value before executing the color misregistration correction. Further, when changing the target speed next time, the image forming apparatus 100 determines the target speed based on the load fluctuation amount calculated at the previous target speed and the load fluctuation amount calculated at the current target speed. Is increased or the target speed is decreased. Further, the image forming apparatus 100 acquires the current value in the first state and the current value in the second state at different timings, and when the current value in the first state becomes larger than the current value in the second state. Increases the target speed.

(Target speed adjustment process)
Next, the adjustment process for adjusting the target speed of the photosensitive drum 10 of the image forming unit 5y will be described below. The image forming apparatus 100 adjusts the target speed of the photosensitive drum 10 of each of the image forming units 5y, 5m, 5c, and 5bk. However, in order to simplify the description, description regarding the adjustment processing of the target speed for the image forming units 5m, 5c, and 5bk is omitted.

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 that is necessary to execute various processes in the flowcharts described below. The RAM 1200 is a system work memory for the CPU 1000 to operate.

The image forming units 5y, 5c, 5m, and 5bk (image forming unit 5 in FIG. 6), the sensor 14, the motors M1, M2, M3, and M4, the speed sensors 32, 33, 37, and 38 have already been described. Therefore, the description is omitted here.

The motor driver MD1 controls the current flowing through the motor M1 that rotates the stirring member 6. The motor M1 rotates with a torque according to the supplied current. The motor driver MD2 controls the current flowing through the motor M2 that rotates the developing sleeve 8. The motor M2 rotates with a torque according to the supplied current.

The motor driver MD3 controls the current flowing through the motor M3 that rotates the photosensitive drum 10. That is, the motor driver MD3 controls the PWM signal value input to the motor M3. The motor driver MD3 executes feedback control of the motor M3 based on the rotation information output from the speed sensors 32 and 33 so that the rotation speed of the photosensitive drum 10 becomes the target speed Vdrum corresponding to the speed command value. .. The motor driver MD3 functions as a drive control unit that controls the torque of the motor M3 so that the difference between the peripheral speed of the photosensitive drum 10 and the peripheral speed of the intermediate transfer belt 24 becomes a target value. Further, the motor driver MD3 outputs the value of current flowing through the motor M3. The motor M3 rotates with a torque according to the supplied current.

The motor driver MD4 controls the current flowing through the motor M4 that rotates the drive roller 40. That is, the motor driver MD4 controls the PWM signal value input to the motor M4. The motor driver MD4 executes feedback control of the motor M4 based on the rotation information output from the speed sensors 37 and 38 so that the rotation speed of the drive roller 40 becomes the target speed Vbelt corresponding to the speed command value. .. Further, the motor driver MD4 outputs the value of current flowing through the motor M4. The motor M4 rotates with a torque according to the supplied current.

The comparison unit 1001 acquires the PWM signal value output from the motor driver MD3, and sets the determination condition for determining the target speed Vdrum of the photosensitive drum 10 based on the comparison result of the plurality of PMW signal values. The determining unit 1002 acquires the PWM signal value output from the motor driver MD3, and determines the target speed Vdrum from the plurality of PWM signal values based on the determination condition set by the comparing unit 1001. The determining unit 1002 sets a speed command value corresponding to the determined target speed Vdrum in the motor driver MD3. Note that the determining unit 1002 may be realized by, for example, an ASIC (application specific integrated circuit). Alternatively, the determining unit 1002 may be realized by a part of the function of the CPU 1000, for example.

The color misregistration correction unit 1003 calculates the color misregistration amounts ΔH and ΔV for each color based on the measurement result of the pattern image by the sensor 14. Then, the color shift correction unit 1003 corrects the writing position in the main scanning direction based on the color shift amount ΔH based on the color shift amount ΔH, and corrects the writing position in the sub-scanning direction based on the color shift amount ΔV.

An image forming operation in which the image forming apparatus 100 forms an image based on image data will be described based on the flowchart of FIG. 7. When the main power supply of the image forming apparatus 100 is turned on, the CPU 1000 reads out the program stored in the ROM 1100 and executes the process of the flowchart of FIG. 7. The value n of the counter for counting the number of pieces of data for obtaining the PWM signal is set to 0 in response to the main power supply of the image forming apparatus 100 being turned on.

First, the CPU 1000 waits until image data is transferred from an external device (not shown) such as a PC or a scanner (S100). When the image data is transferred, the CPU 1000 causes the image forming unit 5 to form an image based on the image data on the sheet P (S101). Next, the CPU 1000 determines whether all the images included in the image data have been formed (S102). When all the images are formed in step S102, the CPU 1000 causes the image forming unit 5 to finish the image formation. Then, while the developing sleeve 8 is rotating, the CPU 1000 acquires the PWM signal value PWM1(n) output from the motor driver MD3 to the motor M3 (S103). The PWM signal value is stored in the RAM 1200. Next, the CPU 1000 stops the developing sleeve 8 (S104). In step S104, the CPU 1000 causes the motor driver MD2 to stop supplying power to the motor M2 so that the motor M2 stops rotating.

After a predetermined time elapses after the developing sleeve 8 stops rotating, the CPU 1000 acquires the PWM signal value PWM2(n) output from the motor driver MD3 to the motor M3 (S105). In step S105, the predetermined time corresponds to the time from when the developing sleeve 8 is stopped until the developer is no longer supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24. The predetermined time is determined based on the target value of the rotation speed of the photosensitive drum 10, the diameter of the photosensitive drum 10, and the distance from the developing position where the photosensitive drum 10 and the developing sleeve 8 face each other to the nip portion. The PWM signal value is stored in the RAM 1200. Then, the CPU 1000 increments the value n of the counter by 1.

Subsequently, the determination unit 1002 executes the target speed adjustment process for the photosensitive drum 10 (S106). The adjustment process of step S106 will be described later with reference to the flowchart of FIG. Then, the CPU 1000 stops the rotation of the photosensitive drum 10, stops driving the intermediate transfer belt 24, and determines whether or not the number of data of the PWM signal value has reached 5 (S107). In step S107, it is determined whether the value n of the counter is 5. If the number of data has reached 5 in step S107, the determination process 1 is executed (S108). The determination process 1 of step S108 will be described later with reference to the flowchart of FIG. After the determination process 1 is executed in step S108, the CPU 1000 determines whether the main power supply of the image forming apparatus 100 is turned off (S109). Then, when the main power supply is turned off, the CPU 1000 ends the image forming operation of the image forming apparatus. If the main power supply is not turned off in step S109, the CPU 1000 moves to step S100.

On the other hand, when the number of data is less than 5 or the number of data is more than 5 in step S107, the CPU 1000 determines whether the main power supply of the image forming apparatus 100 is turned off (S109). In steps S100 to 109 described above, the PWM signal value of the motor M3 cannot be acquired and the rotation speed of the motor M3 cannot be changed until the formation of all images based on the image data is completed. Therefore, even when the image forming apparatus 100 continuously forms a plurality of images, the CPU 1000 temporarily stops the image forming operation, acquires the PWM signal value, and changes the rotation speed of the motor M3. Hereinafter, a process in which the CPU 1000 temporarily stops the image forming operation, acquires the PWM signal value, and changes the rotation speed of the motor M3 will be described.

If all the images based on the image data are not formed in step S102, the CPU 1000 determines whether the number of images continuously formed on the sheet P reaches 200 pages without stopping the developing sleeve. Yes (S110). If the number of images continuously formed on the sheet P reaches 200 pages in step S110, the CPU 1000 temporarily stops the image forming operation (S111). Then, while the developing sleeve 8 is rotating, the CPU 1000 acquires the PWM signal value PWM1(n) output from the motor driver MD3 to the motor M3 (S112). The PWM signal value is stored in the RAM 1200. Next, the CPU 1000 stops the developing sleeve 8 (S113). In step S113, the CPU 1000 causes the motor driver MD2 to stop supplying power to the motor M2 so that the motor M2 stops rotating.

After a predetermined time has elapsed since the developing sleeve 8 stopped rotating, the CPU 1000 acquires the PWM signal value PWM2(n) output from the motor driver MD3 to the motor M3 (S114). In step S114, the predetermined time corresponds to the time from when the developing sleeve 8 is stopped until the developer is no longer supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer belt 24. The PWM signal value is stored in the RAM 1200. Then, the CPU 1000 increments the value n of the counter by 1.

Subsequently, the determination unit 1002 executes the target speed adjustment processing for the photosensitive drum 10 (S115). The adjustment process of step S115 is the same as the adjustment process of step S106, and will be described later with reference to the flowchart of FIG. Then, the CPU 1000 stops the rotation of the photosensitive drum 10, stops driving the intermediate transfer belt 24, and determines whether the number of data of the PWM signal value has reached 5 (S116). In step S116, it is determined whether the counter value n is 5. If the number of data has reached 5 in step S116, determination processing 1 is executed (S117). The determination process 1 of step S117 is the same as the determination process 1 of step S108, and will be described later with reference to the flowchart of FIG. After the determination process 1 is executed in step S117, the CPU 1000 causes the image forming unit 5 to restart the image forming operation (S118), and causes the image forming unit 5 to form the remaining image based on the image data on the sheet P. The CPU 1000 shifts the processing to step S101.

Next, the target speed adjustment processing executed in steps S106 and S115 of FIG. 7 will be described with reference to the flowchart of FIG. When executing the target speed adjustment processing, the CPU 1000 executes the processing of the flowchart of FIG. The RAM 1200 stores PWM signal values PWM1(n) and PWM2(n).

The CPU 1000 determines whether or not the execution condition of the color misregistration correction is satisfied (S200). In step S200, the execution condition is, for example, the number of sheets on which the image forming apparatus 100 has formed an image since the previous color misregistration correction was executed. When the cumulative value of the number of formed images reaches the predetermined number, the determining unit 1002 determines that the execution condition is satisfied. When the execution condition of the color misregistration correction is satisfied in step S200, the CPU 1000 determines whether the average value of the differences between the PWM signal values is larger than the first threshold Th1 (S201).

In step S201, the CPU 1000 reads out the plurality of PWM signals PWM1(n) and PWM2(n) stored in the RAM 1200. For example, the CPU 1000 reads 30 sets of data retroactively from the PWM signals PWM1(n) and PWM2(n) most recently stored in the RAM 1200. Then, the CPU 1000 calculates the difference ΔPWM of the PWM signal values for 30 sets of data to calculate the average value of the difference ΔPWM.

If the average value of the differences between the PWM signal values is smaller than the first threshold Th1 in step S201, the CPU 1000 executes color misregistration correction (S204). In step S201, if the average value of the differences between the PWM signal values is equal to or less than the first threshold Th1, the amount of change in the load of the motor M3 has not increased enough to cause an image defect. Therefore, the target speed of the motor M3 is not changed, and the color misregistration correction is executed in step S204.

If the average value of the differences in the PWM signal values is larger than the first threshold Th1 in step S201, the CPU 1000 causes the comparison unit 1001 to execute the determination process 2 (S202). The adjustment process of step S202 will be described later with reference to the flowchart of FIG. Then, the CPU 1000 causes the determining unit 1002 to calculate the target speed, and changes the target speed of the photosensitive drum 10 based on the calculation result of the determining unit 1002 (S203). In step S203, the determination unit 1002 calculates the target speed of the motor M3 based on the equation (4) if the value of the flag F indicating the comparison result by the comparison unit 1001 is 0. The value of the flag F is set to 0 immediately after the image forming apparatus 100 is installed.
Vdrum′=Vdrum−g×ΔPWM Equation (4)
In the equation (4), Vdrum' is the target speed after the change, Vdrum is the target speed before the change, g is a coefficient, and ΔPWM is the difference between the PWM signal values stored in the RAM 1200 (=PWM2(n)-PWM1(n)). ) Is the average value. The coefficient g is a positive value. That is, in step S203, when the value of the flag F is 0, the rotation speed of the photosensitive drum 10 is changed so that the difference in peripheral speed between the photosensitive drum 10 and the intermediate transfer belt 24 decreases.

On the other hand, in step S203, the determination unit 1002 calculates the target speed of the motor M3 based on the equation (5) if the value of the flag F indicating the comparison result by the comparison unit 1001 is 1.
Vdrum′=Vdrum+g×ΔPWM Equation (5)
In the equation (5), Vdrum′ is the target speed after the change, Vdrum is the target speed before the change, g is a coefficient, ΔPWM is the difference between the PWM signal values stored in the RAM 1200 (=PWM2(n)−PWM1(n)). ) Is the average value. The coefficient g is a positive value. That is, in step S203, when the value of the flag F is 1, the rotation speed of the photosensitive drum 10 is changed so that the difference in peripheral speed between the photosensitive drum 10 and the intermediate transfer belt 24 increases.

That is, in step S203, the determination unit 1002 determines the target value of the rotation speed of the photosensitive drum 10 based on the comparison result of the comparison unit 1001 and the PWM signal value difference ΔPWM. The speed command value corresponding to the target value determined by the determination unit 1002 is set in the motor driver MD3. After the motor driver MD3 changes the target speed of the photosensitive drum 10, the CPU 1000 proceeds to step S204 to execute the color misregistration correction. Then, after the color misregistration correction is executed, the CPU 1000 sets the value n of the counter to 0 (S205), and ends the adjustment processing.

If the execution condition of the color misregistration correction is satisfied in step S200, the CPU 1000 determines whether the average value of the differences between the PWM signal values is larger than the second threshold Th2 (S206). Here, the second threshold Th2 is larger than the first threshold Th1. That is, in step S206, when the load on the photosensitive drum 10 and the intermediate transfer belt 24 is larger than the threshold value, the CPU 1000 changes the target speed of the photosensitive drum 10 even if the execution condition of the color misregistration correction is not satisfied. Perform color misregistration correction. In step S206, if the average value of the differences between the PWM signal values is less than or equal to the first threshold Th2, the CPU 1000 ends the adjustment process.

On the other hand, in step S206, if the average value of the differences between the PWM signal values is larger than the second threshold value Th2, it is highly possible that the variation amount of the load of the motor M3 has increased to cause an image defect. Therefore, the CPU 1000 causes the process to proceed to step S202. Since the processing after step S202 has been described, the description thereof is omitted here.

Here, the determination processing 1 of step S108 and step S117 will be described based on the flowchart of FIG. When the determination process 1 is executed, the CPU 1000 executes the process of the flowchart of FIG.

First, the CPU 1000 causes the comparison unit 1001 to determine the absolute value of the difference ΔPWM(prev) between the PWM signal values before the target speed of the motor M3 is changed and the PWM signal value after the target speed of the motor M3 is changed. The absolute value of the difference ΔPWM(now1) is compared (S300). In step S300, the comparison unit 1001 calculates the absolute value of the difference ΔPWM(prev) and the absolute value of the difference ΔPWM(now1) based on the PWM signal value stored in the RAM 1200.

The difference ΔPWM(prev) is calculated, for example, based on the PWM signal value acquired immediately before the target speed is changed. That is, the difference ΔPWM(prev) is a value calculated from the PWM signal value acquired during the period in which the photosensitive drum 10 was rotating at the previous target speed. The difference ΔPWM(now1) is calculated, for example, by using the average value of the PWM signal values of 5 data acquired after the target speed was changed last time.

When the absolute value of the difference ΔPWM(prev) is smaller than the absolute value of the difference ΔPWM(now1), it is determined that the photosensitive drum 10 and the intermediate transfer belt 24 have a characteristic that the load increases when the difference in peripheral speed is reduced. The above determination will be described with reference to FIG. When the motor M3 reduces the difference in peripheral speed at the previous timing when the target speed is changed, the difference ΔPWM(prev) in the PWM signal value acquired in the period before the change is acquired in the period immediately after the change. The difference between the PWM signal values is smaller than ΔPWM(now1). In this case, if the rotation speed of the motor M3 is changed so as to reduce the difference in peripheral speed again at the next change, the load will increase. Therefore, when the absolute value of the difference ΔPWM(prev) is smaller than the absolute value of the difference ΔPWM(now1), the target speed of the motor M3 is changed so that the difference in peripheral speed increases.

Returning to the explanation of FIG. When the absolute value of the difference ΔPWM(prev) is smaller than the absolute value of the difference ΔPWM(now1), the CPU 1000 determines whether the value of the flag F is 0 (S301), and if the value of the flag F is 0. The value of the flag F is changed to 1 (S302). Thus, when the target speed of the photosensitive drum 10 is changed, the changed target speed is calculated based on the equation (5).

On the other hand, when the value of the flag F is not 0 in step S301, the determination unit 1002 has already calculated the target speed based on the equation (5). Therefore, if the absolute value of the difference ΔPWM(prev) is smaller than the absolute value of the difference ΔPWM(now1) even though the target speed is changed based on the equation (5), the load will be reduced if the difference in peripheral speed is reduced. May have returned to the property of decreasing. Therefore, the CPU 1000 changes the value of the flag F to 0 (S303). Accordingly, when the target speed is changed next time, the determining unit 1002 calculates the changed target speed based on the equation (4).

Next, the determination process 2 of step S202 will be described based on the flowchart of FIG. When the determination process 2 is executed, the CPU 1000 executes the process of the flowchart of FIG.

First, the CPU 1000 causes the comparison unit 1001 to determine whether the difference ΔPWM(now1) and ΔPWM(now2) between the PWM signal values acquired after the target speed of the motor M3 was changed last time have the same sign (S400). .. In step S400, the comparison unit 1001 calculates the difference ΔPWM(now1) and the difference ΔPWM(now2) based on the PWM signal value stored in the RAM 1200. The difference ΔPWM(now1) is calculated, for example, by using the average value of the PWM signal values of 5 data acquired after the target speed was changed last time. The difference ΔPWM(now2) is calculated using, for example, an average value of a plurality of PWM signal values acquired at a timing later than the 5 data used to calculate the difference ΔPWM(now1).

When the PWM signal value difference ΔPWM(now1) and ΔPWM(now2) have different signs, it is determined that the photosensitive drum 10 and the intermediate transfer belt 24 have a characteristic that the load increases as the peripheral speed difference decreases. .. The above determination will be described with reference to FIG. In FIG. 12, the difference ΔPWM(now1) in the PWM signal values acquired in the period immediately after the target speed is changed is a positive value, and the difference ΔPWM(now2) in the PWM signal values acquired in other periods is It is a negative value. In this case, if the rotation speed of the motor M3 is changed so as to reduce the difference in peripheral speed at the next change, the load will increase. Therefore, when the difference PWM(now1) and the difference PWM(now2) have different signs, the determining unit 1002 changes the target speed of the motor M3 so that the difference in peripheral speed increases.

Returning to the description of FIG. When the difference PWM (now1) and the difference PWM (now2) have the same sign in step S400, the CPU 1000 ends the determination process 2. On the other hand, when the difference PWM (now1) and the difference PWM (now2) have different signs in step S400, the CPU 1000 determines whether the value of the flag F is 0 (S401), and the value of the flag F is 0. If so, the value of the flag F is changed to 1 (S402). Thus, when the target speed of the photosensitive drum 10 is changed, the changed target speed is calculated based on the equation (5).

On the other hand, when the value of the flag F is not 0 in step S401, the determination unit 1002 has already calculated the target speed based on the equation (5). Therefore, when the difference PWM (now1) and the difference PWM (now2) have different signs even if the target speed is changed based on the equation (5), the load is reduced when the difference in peripheral speed is reduced. It may have returned to its characteristics. Therefore, the CPU 1000 changes the value of the flag F to 0 (S403). As a result, the determination unit 1002 calculates the target speed based on the equation (4).

In consideration of the error of the PWM signal value, the value of the flag F is not changed in the range where the difference PWM(now2) of the PWM signal values is 0±5 [%]. In step S400, the comparison unit 1001 determines, for example, when the absolute value of the difference PWM(now2) is larger than a predetermined value, the difference ΔPWM(now1) is larger than 0, and the difference PWM(now2) is smaller than 0. The flag F may be changed. In this case, the positive value area corresponds to the first area and the negative value area corresponds to the second area. Alternatively, in step S400, the comparison unit 1001 has, for example, an absolute value of the difference PWM(now2) larger than a predetermined value, a difference ΔPWM(now1) smaller than 0, and a difference PWM(now2) larger than 0. In that case, the flag F may be changed. In this case, the positive value area corresponds to the second area and the negative value area corresponds to the first area.

As described above, according to the present invention, even when the load on the motor M3 increases when the difference in peripheral speed between the photosensitive drum 10 and the intermediate transfer belt 24 is reduced, a plurality of peripheral speeds are provided as in the conventional configuration. The target speed of the motor M3 is determined without switching stepwise. Therefore, even if the load on the motor M3 increases when the difference in peripheral speed between the photosensitive drum 10 and the intermediate transfer belt 24 is reduced, the load on the motor M3 is reduced while suppressing downtime as compared with the conventional configuration. Can be made.

M3 motor MD3 motor driver 5 image forming unit 8 developing sleeve 10 photosensitive drum 23 primary transfer roller 24 intermediate transfer belt 1000 CPU
1001 comparison unit 1002 determination unit 1200 RAM

Claims (9)

A motor that rotates the photoconductor,
An image forming unit that has the photoconductor and a developer carrier that carries and rotates a developer, and forms an image on the photoconductor using the developer carried by the developer carrier,
An intermediate transfer member carrying and carrying the image formed by the image forming unit;
Transfer means for transferring the image on the photosensitive member to the intermediate transfer member at a nip portion for transferring the image on the photosensitive member to the intermediate transfer member,
Drive control means for controlling the torque of the motor so that the difference between the peripheral speed of the photosensitive member and the peripheral speed of the intermediate transfer member becomes a target value;
Acquisition means for acquiring a signal according to the torque of the motor,
Based on the signal acquired by the acquisition unit, the acquisition unit acquires the signal during a period in which the drive control unit controls the torque of the motor so that the difference in the peripheral speed becomes the target value. And a control means for controlling the target value by
When the peripheral speed difference is changed from the first target value to the second target value, the drive control means controls the motor torque so that the peripheral speed difference becomes the first target value. During a second period during which the drive control unit controls the torque of the motor so that the difference between the first signal acquired by the acquisition unit and the peripheral speed becomes the second target value. Comparing the second signal acquired by the acquisition means, and determining the third target value based on the comparison result and the other second signal acquired by the acquisition means in the second period. A characteristic image forming apparatus. The signal obtained by the obtaining means is the current value flowing in the motor in the first state in which the developer carrier is rotating and the signal in the second state in which the developer carrier is stopped rotating. The image forming apparatus according to claim 1, further comprising: a current value flowing through the motor. The control means obtains the difference between the first current value in the first state and the first current value in the second state acquired by the acquisition means in the first period, and the acquisition in the second period. The image forming apparatus according to claim 2, wherein the difference between the second current value in the first state and the second current value in the second state acquired by the means is compared. The second target value is smaller than the first target value,
The difference between the first current value in the first state and the first current value in the second state is the second current value in the first state and the second current value in the second state. And the third target value is smaller than the second target value,
The difference between the first current value in the first state and the first current value in the second state is the second current value in the first state and the second current value in the second state. The image forming apparatus according to claim 3, wherein the third target value is larger than the second target value if the difference is smaller than the difference. The absolute value of the difference between the first current value in the first state and the first current value in the second state is the second current value in the first state and the second value in the second state. 2 is larger than the absolute value of the difference between the two current values, the third target value is smaller than the second target value,
The absolute value of the difference between the first current value in the first state and the first current value in the second state is the second current value in the first state and the second value in the second state. The image forming apparatus according to claim 4, wherein the third target value is larger than the second target value if the difference is smaller than the absolute value of the difference between the two current values. The acquisition means acquires the second signal at a first timing included in the second period,
The acquisition means acquires the other second signal at a second timing included in the second period,
The image forming apparatus according to claim 1, wherein the first timing is earlier than the second timing. The control means further compares the second signal with the other second signal, and based on the comparison result of the second signal with the other second signal and the other second signal. The image forming apparatus according to claim 1, wherein the third target value is determined. Difference between the other second current value in the first state in which the developer carrier rotates and the other second current value in the second state in which the developer carrier stops rotating Is larger than a predetermined value, a difference between the second current value in the first state and the second current value in the second state is included in the first region, and When the difference between the other second current value in the state and the other second current value in the second state is included in the second region different from the first region, the third target value is the third target value. The image forming apparatus according to claim 7, wherein the image forming apparatus is larger than two target values. The image forming apparatus according to claim 8, wherein the first area is larger than 0 and the second area is smaller than 0.

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