JP6827729B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An image forming apparatus such as an electrophotographic system transfers a toner image by rotating a photoconductor drum and an intermediate transfer body at substantially the same peripheral speed (surface speed). If a large error occurs between these peripheral velocities, density unevenness (so-called banding) of the toner image may occur. According to Patent Document 1, torque characteristics are extracted by changing the rotation speed of the photoconductor drum while rotating the intermediate transfer body at a constant peripheral speed, and the rotation speed of the photoconductor drum is determined according to the torque characteristics. A method has been proposed.

Japanese Unexamined Patent Publication No. 2012-32515

By the way, while performing the above method for setting the difference between the peripheral speed of the intermediate transfer body and the peripheral speed of the photoconductor drum to a predetermined value, the image forming apparatus cannot form a toner image on the sheet. That is, there is downtime, which is the time when the user cannot form an image. On the other hand, the image forming apparatus executes various adjustment processes such as a process of adjusting an image forming position with respect to a sheet (color shift correction). Therefore, if the peripheral speed adjustment process is executed together with the adjustment process at the timing when the image forming apparatus executes some adjustment process, the downtime will be reduced. Since the execution interval of color shift correction and the like is relatively long, it may not be possible to maintain the peripheral speed appropriately if the peripheral speed adjustment process is executed only at this execution timing. Therefore, an object of the present invention is to adjust the peripheral speed of the photoconductor with respect to the peripheral speed of the intermediate transfer material at a more appropriate timing.

The present invention is, for example,
Photoreceptor and
An exposure means that exposes the photoconductor to form an electrostatic latent image,
A developing means having a developer carrier that supports and rotates a developer and develops the electrostatic latent image on the photoconductor using the developer supported on the developer carrier.
An intermediate transfer body to which an image visualized by development by the developing means is transferred, and
A transfer means for transferring the image from the intermediate transfer body to the sheet,
A photoconductor motor that rotates the photoconductor and
An intermediate transfer motor that rotates the intermediate transfer,
Motor control that controls the photoconductor motor so that the rotation speed of the photoconductor becomes the photoconductor target speed, and controls the intermediate transfer body motor so that the rotation speed of the intermediate transfer body becomes the intermediate transfer body target speed. Means and
In the first state in which the photoconductor, the intermediate transfer body, and the developer carrier are rotating, the first information regarding the load of the photoconductor motor is acquired, the rotation of the developer carrier is stopped, and the developer carrier is rotated. In the second state in which the photoconductor and the intermediate transfer body are rotating, the second information regarding the load of the photoconductor motor is acquired, and whether or not the target speed of the photoconductor is changed is determined by the first information and the first information. It has a control means for controlling based on two pieces of information.
When the predetermined condition regarding the number of sheets on which the image is formed is satisfied while the image is formed on a plurality of sheets while the photoconductor, the intermediate transfer body, and the developer carrier are rotated. The control means provides an image forming apparatus characterized in that the rotation of the developer carrier is stopped to acquire the second information.

According to the present invention, it is possible to adjust the peripheral speed of the photoconductor with respect to the peripheral speed of the intermediate transfer material at a more appropriate timing.

The figure which shows the image forming apparatus The figure which shows the image formation part The figure which shows the surface potential of a photoconductor drum The figure which shows the relationship between the patch image and the deviation of the image formation position. The figure which shows the driving part of a photoconductor drum The figure which shows the driving part of the intermediate transfer body Diagram showing rotational torque with respect to the number of images Diagram showing the control system Flow chart showing the measurement process of rotational torque The figure which shows the relationship between the speed setting value and the PWM duty Flowchart showing color shift correction and rotation speed adjustment Diagram showing rotational torque with respect to the number of images

<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 a multicolor image. The image forming units 5y, 5c, 5m, and 5bk form toner images using toners having different colors. Here, toners 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 toner.

The photoconductor drum 10 is an image carrier that supports an electrostatic latent image or a toner image (developer image), and is rotationally driven by a motor. The primary charger 21 is a charging means that uniformly charges the surface of the photoconductor drum 10. The exposure device 22 is an exposure means (latent image forming means) for forming an electrostatic latent image by exposing the surface of the photoconductor drum 10 with light modulated according to image information. The exposure device 22 may be a scanning optical device or the like having a rotating multifaceted mirror or the like for scanning light in the main scanning direction. The developing device 1 is a developing means for developing an electrostatic latent image using toner to form a toner image. The developing apparatus 1 uses, for example, a two-component developer containing a non-magnetic toner and a carrier having low magnetization and high resistance. A one-component type developer may be used. The primary transfer roller 23 primary transfers the toner image carried on the photoconductor drum 10 to the intermediate transfer body 24. When the intermediate transfer body 24 comes into contact with the photoconductor drum 10, the toner image on the photoconductor is transferred onto the intermediate transfer body. The secondary transfer roller 29 secondary transfers the toner image carried on the intermediate transfer body 24 to the sheet P. The fixing device 27 fixes the toner image on the sheet P. The drum cleaner 26 removes the toner remaining on the photoconductor drum 10. The belt cleaner 28 removes the toner remaining on the intermediate transfer body 24. The toner replenishment tank 20 replenishes the developing device 1 with toner. The image sensor 14 is a sensor that reads a toner image formed on the intermediate transfer body 24. The reading result of the toner image is used to correct the writing timing (exposure timing) of the electrostatic latent image. The image sensor 14 is a sensor having a light emitting element and a light receiving element.

<Developer>
FIG. 2 shows the developing apparatus 1. The developing device 1 has a stirring member 6 such as a screw that conveys the toner supplied from the toner supply tank 20 and the carrier while stirring. The stirring member 6 is driven by the motor M1. The toner is charged by stirring the toner and the carrier. The developing sleeve 8 is a developer carrier that supports toner. The developing sleeve 8 is arranged so as to face the photoconductor drum 10. The developing sleeve 8 is driven by the motor M2. A predetermined development bias is applied to the development sleeve 8 by the development power supply 2. A predetermined transfer bias is also applied to the primary transfer roller 23 by the transfer power supply 3.

FIG. 3 shows the surface potential of the photoconductor drum 10 and the like. When the primary charger 21 uniformly charges the surface of the photoconductor drum 10, the surface potential of the photoconductor drum 10 becomes a negative charging potential Vd. The surface potential of the region exposed by the exposure apparatus 22 on the surface of the photoconductor drum 10 is the exposure potential VL. For example, the charging potential Vd is −700V and the exposure potential VL is −200V. The developer containing the negatively charged toner in the developing apparatus 1 is conveyed to the vicinity of the photoconductor drum 10 by the developing sleeve 8. The development bias Vdc applied to the development sleeve 8 is set to a potential between the charging potential Vd and the exposure potential VL. The development bias Vdc is, for example, −550 V. A negative development bias Vdc acts on the negatively charged toner supported on the development sleeve 8. The toner flies toward the photoconductor drum 10 and adheres to the surface of the photoconductor drum 10. The amount of toner adhered depends on the contrast potential difference Vcont. The contrast potential difference Vcont is the difference between the development bias Vdc and the exposure potential VL. Therefore, the image density is adjusted by adjusting the contrast potential difference Vcont. A positive primary transfer bias Vtr1 is applied to the primary transfer roller 23. Therefore, the negative electrode toner carried on the photoconductor drum 10 flies from the photoconductor drum 10 toward the primary transfer roller 23 at the primary transfer unit and is transferred to the intermediate transfer body 24. The primary transfer bias Vtr1 is, for example, + 1500V.

<Adjustment of image formation position>
A multicolor image is formed by superimposing toner images of each color on the image forming apparatus 100. Therefore, if the position of the toner image of each color shifts from the ideal position, so-called color shift occurs.

FIG. 4 shows an example of a test image used for color shift correction. When the color shift correction is started, the image forming apparatus 100 forms a test image on the intermediate transfer body 24, and the formation position of the test image is measured by the image sensor 14. The color shift correction is executed when a predetermined execution condition is satisfied. The execution conditions include, for example, being instructed by the operator, activating the image forming apparatus 100, or having reached a predetermined number of image forming sheets. By executing the color shift correction, the color shift caused by the manufacturing variation of the image forming apparatus 100, the rise in the internal temperature, and the like is corrected and reduced.

As shown in FIG. 4, the test image includes patch images 48y, 40m, 48c, and 40bk having different colors, respectively. The locus of the reading position of the image sensor 14 is a two-dot chain line shown in FIG. That is, the time when the reading position of the image sensor 14 passes through the patch images 48y, 48m, 48c, and 48bk is measured. For example, Lys indicates the transit time for the yellow patch image 48y to pass the reading position of the image sensor 14. Lms indicates the transit time for the magenta patch image 48m to pass the reading position of the image sensor 14. Lcs indicates the transit time for the cyan patch image 48c to pass the reading position of the image sensor 14. Lbks indicates the transit time for the magenta patch image 48bk to pass the reading position of the image sensor 14. Note that Lys, Lms, Lcs, and Lbks represent image formation positions in the main scanning direction of the patch image (direction orthogonal to the rotation direction of the intermediate transfer body 24). The magnitudes of Lys, Lms, Lcs, and Lbks indicate the relative positional relationship of each patch in the main scanning direction. That is, if Lys, Lms, Lcs, and Lbks have the same value, the color shift in the main scanning direction of each color is eliminated.

Lym indicates the time difference from the position where the passage time Lys of the patch image 48y is half to the position where the passage time Lym of the patch image 48m is half. That is, Lym indicates the positional relationship between the yellow patch image 48y and the magenta patch image 48m in the sub-scanning direction. In this way, the relative position of each patch in the sub-scanning direction is calculated from Lym. For the cyan patch image 48c and the black patch image 48bk, the time difference Lyc and Lybk based on the patch image 48y are also required. The relative positions of the cyan patch image 48c and the black patch image 48bk in the sub-scanning direction are calculated from the time difference Lyc and Lybk, respectively.

From the passing times of the patch images 48y, 48m, 48c, and 48bk, 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. For example, for the sub-scanning direction, the writing timing of the remaining colors is determined with yellow as a reference. The color shift is corrected by reflecting the determined correction amount in the writing timing of the exposure apparatus 22 in charge of each color. The writing timing may be referred to as an exposure start timing or an image formation timing.

<Speed control of photoconductor drum and intermediate transfer member>
The toner image is transferred while the photoconductor drum 10 and the intermediate transfer body 24 are in contact with each other. Therefore, if the difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 is not a predetermined value, expansion and contraction or banding of the toner image may occur. Therefore, the difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 is adjusted to such an extent that expansion and contraction and banding of the toner image do not become apparent.

FIG. 5 shows a driving unit that drives the photoconductor 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 photoconductor drum 10 is fixed on the shaft of the drum drive gear 35, and the photoconductor drum 10 rotates when the motor M3 drives the drum drive gear 35. An encoder 34 is also 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 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 32 and 33 are averaged and used. This is to reduce the influence of the eccentricity of the encoder 34. The image forming apparatus 100 feedback-controls the duty of the drive signal (PWM signal) supplied to the motor M3 so that the rotation speed detected by the speed sensors 32 and 33 becomes the target speed. PWM is an abbreviation for pulse width modulation.

FIG. 6 shows a driving unit that drives the intermediate transfer body 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 body 24 is also rotated by the drive roller 40. An encoder 39 is further provided on the shaft of the drive gear 41. The encoder 39 is a 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 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 and used. This is to reduce the influence of the eccentricity of the encoder 39. The image forming apparatus 100 feedback-controls the duty of the drive signal (PWM signal) supplied to the motor M4 so that the rotation speed detected by the speed sensors 37 and 38 becomes the target speed. In particular, the image forming apparatus 100 sets the duty of the PWM signal supplied to at least one of the motors M3 and M4 so that the difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 becomes a predetermined value. Control.

In this way, the target speeds of the motors M3 and M4 are determined so that the difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 becomes a predetermined value. Further, feedback control is executed so that the rotation speeds of the motors M3 and M4 match the target speeds. However, as the internal temperature of the image forming apparatus 100 (internal temperature) rises, the target speeds of the motors M3 and M4 need to be adjusted appropriately. The reason for this will be explained.

When the image forming apparatus 100 continuously forms an image on a large number of sheets P, the temperature inside the machine rises. As the temperature inside the machine rises, the coefficient of friction μb on the surface of the intermediate transfer body 24 also rises. In the initial setting, the rotation speed of the photoconductor drum 10 is slightly faster than the rotation speed of the intermediate transfer body 24. Therefore, as the temperature inside the machine rises, the rotational torque required to drive the photoconductor drum 10 also increases.

FIG. 7A shows a rotational torque (PWM duty) with respect to the number of images formed (the number of images). The rotational torque may be referred to as load torque. The broken line shows the rotational torque when the internal temperature is 30 ° C. The solid line shows the rotational torque when the internal temperature is 40 ° C. As shown in FIG. 7A, the rotational torque of the photoconductor drum 10 does not increase so much even if the image formation is continued in a state where the internal temperature is low. On the other hand, if image formation is continued in a state where the temperature inside the machine is high, the rotational torque of the photoconductor drum 10 increases due to the frictional force caused by the difference in peripheral speed of the primary transfer unit.

FIG. 7B shows the PWM duty with respect to the number of images. In particular, the broken line indicates the PWM duty when the image formation mode (eg, cardboard mode) that causes the temperature inside the machine to rise when the temperature inside the machine is low is switched to in the middle. The solid line shows the rotational torque when the internal temperature is 40 ° C. In this example, in the case where the in-flight temperature is 30 ° C., when the number of images reaches 10,000, the plain paper mode is switched to the thick paper mode. Since a higher fixing temperature is required in the thick paper mode as compared with the plain paper mode, the in-flight temperature tends to rise. Even if the environmental temperature is low as described above, the rotational torque of the photoconductor drum 10 may increase depending on the image formation mode.

When a load such that the PWM duty exceeds 60% is applied to the motor M3 that drives the photoconductor drum 10, color shift and banding are likely to become apparent. Therefore, the rotation speed of the motor M3 that drives the photoconductor drum 10 must be appropriately controlled so that color shift and banding do not become apparent.

If the rotation speed of the motor M3 that drives the photoconductor drum 10 is adjusted at the timing of color shift correction as described above, the downtime will be reduced. However, since the execution interval of the color shift correction is relatively long, it is possible that the rotation speed cannot be adjusted in time. For example, color shifts and banding will become apparent when the rotational torque rises sharply. In this embodiment, the rotation speed of the motor M3 that drives the photoconductor drum 10 is adjusted as necessary without waiting for the timing of color shift correction.

<Control system>
FIG. 8 shows a control system that controls each part of the image forming apparatus 100. The CPU 800 realizes various functions by executing a control program stored in the storage device 850. Note that some or all of these functions may be realized by hardware such as ASIC and FPGA. ASIC is an abbreviation for a special purpose integrated circuit. FPGA is an abbreviation for field programmable gate array. The storage device 850 has a memory such as a RAM or a ROM. The number of images 851, difference data 852, and the like are stored in the storage device 850. The number of images 851 is the number of images formed by the image forming apparatus 100. The difference data 852 is the difference data of the rotational torque of the motor M3.

The drive circuit 830 drives the motors M1 to M4 and the like in response to an instruction from the CPU 800 and a set value (target speed). Further, the drive circuit 830 feedback-controls the motors M3 and M4 so as to rotate at the target speed according to the speed information obtained by the speed sensors 32, 33, 37 and 38.

The load measuring unit 801 is a unit that detects or measures a load parameter that correlates with the rotational torque of the motor M3 by acquiring the duty of the PWM signal supplied to the motor M3. The rotational torque may be referred to as load torque. Instead of the motor M3, the motor M4 that drives the intermediate transfer body 24 may be the measurement target. The difference calculation unit 802 calculates the difference between the two PWM duties measured by the load measurement unit 801. The first is the PWM duty measured by the load measuring unit 801 in the driving state in which the developing sleeve 8 is driven by the motor M2. The second is the PWM duty detected by the load measuring unit 801 in the non-driven state in which the developing sleeve 8 is not driven by the motor M2. Toner is supplied to the photoconductor drum 10 in the driven state, but toner is not supplied to the photoconductor drum 10 in the non-driven state. That is, the difference between the PWM duty when the toner is present between the photoconductor drum 10 and the intermediate transfer body 24 and the PWM duty when the toner is not present is acquired. The acquired difference is stored in the storage device 850. The first statistical unit 803 obtains the average value of the latest N differences among the plurality of differences stored in the storage device 850 as statistical values. The second statistical unit 804 obtains the average value of the differences of M stored in the storage device 850 as a statistical value. It should be noted that M> N. For example, M is 30 and N is 5. When the statistical value (example: average value) obtained by the first statistical unit 803 exceeds the first threshold value (example: 10%), the speed determination unit 805 motors according to the statistical value of the difference so that the difference becomes smaller. The set value of the rotation speed of M3 is determined. The image formation control unit 806 controls the exposure device 22, the developing device 1, the developing power supply 2, the transfer power supply 3, and the like of the image forming units 5y to 5bk.

The trigger unit 810 is a unit that manages the timing of executing the color shift correction and the timing of executing the adjustment process of the rotation speed of the motor M3. The first determination unit 811 determines whether the latest N difference statistical values stored in the storage device 850 are equal to or greater than the first threshold value in order to determine whether or not the rotation speed adjustment process is necessary. The second determination unit 812 determines whether the statistical value of M differences stored in the storage device 850 is equal to or greater than the second threshold value in order to determine whether or not the rotation speed adjustment processing is required together with the color shift correction. To do. The third determination unit 813 determines whether or not the execution condition of the color shift correction is satisfied. A maximum of M differences are stored in the storage device 850. The oldest data at the acquisition time of the M data is overwritten by the new data.

The color shift correction unit 820 corrects the image formation position (writing timing) of each color so that the image formation positions between Y, M, C, and Bk match. The second adjustment unit 822 actually forms the patch images 48y, 48m, 48c, and 48bk, reads them with the image sensor 14, and adjusts the writing timing of each color according to the reading result. The first adjusting unit 821 adjusts the writing timing of each color according to the new speed determined by the speed determining unit 805. The first adjustment unit 821 adjusts the writing timing without forming the patch images 48y, 48m, 48c, and 48bk. Therefore, the adjustment time by the first adjustment unit 821 is much shorter than the adjustment time by the second adjustment unit 822. This helps reduce downtime. However, the accuracy of the detailed color shift correction of the second adjustment unit 822 is higher than that of the simple color shift correction executed by the first adjustment unit 821.

In this embodiment, when the color shift correction is executed, the rotation speed adjustment process of the photoconductor drum 10 is executed at a considerably high frequency. Further, even if it is not the timing when the color shift correction is executed, when the rotational torque of the motor M3 starts to fluctuate greatly, the rotational speed adjustment process of the photoconductor drum 10 is executed. Therefore, it is possible to adjust the peripheral speed of the photoconductor drum 10 with respect to the peripheral speed of the intermediate transfer body 24 at a more appropriate timing.

<Measurement processing of rotational torque>
FIG. 9 is a flowchart showing a rotation torque measurement process. In S901, the CPU 800 (image drawing control unit 806) determines whether or not the image drawing is instructed. For example, when the operation unit instructs the CPU 800 to copy or the host computer instructs the printing, the CPU 800 proceeds to S902. In S902, the CPU 800 (image drawing control unit 806) starts image drawing. The image formation control unit 806 executes the pre-rotation process, and controls the image forming units 5y to 5bk including the photoconductor drum 10 and the intermediate transfer body 24 in a state in which image formation can be performed. The image formation control unit 806 drives the exposure device 22 in charge of each color according to the image data input from the image scanner or the host computer, and forms an electrostatic latent image of each color. The electrostatic latent image is converted into a toner image according to the procedure described above. The toner image is transferred to the sheet P via the photoconductor drum 10 and the intermediate transfer body 24, and is fixed to the sheet P by the fixing device 27.

In S903, the CPU 800 (load measuring unit 801) determines whether or not the rotational torque measurement condition is satisfied. The measurement condition is, for example, that the number of images (the number of images) formed after the previous measurement timing has reached a predetermined number. For example, the predetermined number of sheets is 200, but it may differ depending on the model of the image forming apparatus 100. Therefore, the predetermined number of sheets may be determined by simulation, experiment, or the like, and may be stored in the ROM of the storage device 850 at the time of factory shipment of the image forming apparatus 100. If the measurement conditions are not satisfied, the CPU 800 proceeds to S904.

In S904, the CPU 800 (image drawing control unit 806) determines whether or not the image drawing is completed. For example, in the case of a job of forming X images, it is determined whether or not all X images have been formed. If the image drawing is not completed, the CPU 800 returns to S903 in order to continue the image drawing. On the other hand, if the image drawing is completed, the CPU 800 proceeds to S905.

In S905, the CPU 800 (load measuring unit 801) measures the rotational torque while the developing sleeve 8 is being driven by the motor M2 during the post-rotation process. As described above, the load measuring unit 801 measures the rotational torque by detecting the duty of the PWM signal supplied to the motor M3 as the rotational torque. The post-rotation process is a process of rotating the photoconductor drum 10, the intermediate transfer body 24, and the like for a certain period of time even after the image formation is completed. In the post-rotation process, the exposure device 22, the developing sleeve 8, the developing power source 2, the transfer power source 3, the primary charging device 21, the photoconductor drum 10, and the intermediate transfer body 24 are stopped in this order. That is, the measurement process is executed between the time when the exposure apparatus 22 is stopped and the time when the developing power source 2 is stopped. Since the developing sleeve 8 is driven, the toner in the developing device 1 is supported on the developing sleeve 8. Therefore, even if the photoconductor drum 10 is not exposed, a small amount of toner adheres to the photoconductor drum 10. The toner that adheres to the unexposed region of the surface of the photoconductor drum 10 in this way is sometimes called a fog toner. The developing power supply 2 may be stopped or may be operating. When the development power supply 2 supplies the development bias, the amount of fog toner increases as compared with the state where the development bias is not supplied. Since the amount of toner required to measure the rotational torque is very small, it is not essential to supply the development bias. Similarly, the supply of the charging bias and the transfer bias may be stopped in order to save power.

In S906, the CPU 800 (load measuring unit 801) stops the developing sleeve 8. That is, the motor M2 is stopped. In S907, the CPU 800 (load measuring unit 801) measures the rotational torque in a state where the developing sleeve 8 is not driven (non-driving state). As described above, the load measuring unit 801 measures the rotational torque by detecting the duty of the PWM signal supplied to the motor M3 as the rotational torque. The difference calculation unit 802 may calculate the difference between the PWM duty measured in the driven state and the PWM duty measured in the non-driven state, and store the difference data 852 in the storage device 850. Further, the load measuring unit 801 may store the measured two types of PWM duties as they are in the storage device 850. The difference calculation unit 802 may read out the type of PWM duty from the storage device 850 and use the difference as an operator. When the CPU 800 executes the PWM duty measurement, the number of images when the PWM duty is measured may be separately stored in the storage device 850 and used in S903. That is, the CPU 800 may determine whether or not the difference between the current number of images and the number of images stored in the storage device 850 is a predetermined number or more.

If the measurement conditions are not satisfied in S903, the CPU 800 proceeds to S910. In S910, the CPU 800 (image drawing control unit 806) interrupts image drawing. In S911, the CPU 800 (load measuring unit 801) measures the rotational torque (PWM duty) while the developing sleeve 8 is being driven by the motor M2. In S912, the CPU 800 (load measuring unit 801) stops the developing sleeve 8. In S913, the CPU 800 (load measuring unit 801) measures the rotational torque (PWM duty) in the non-driving state. At this stage, the difference calculation unit 802 may calculate the difference between the PWM duty measured in the driven state and the PWM duty measured in the non-driven state, and store the difference data 852 in the storage device 850. As described above, the two types of PWM duties may be stored in the storage device 850 as they are. In S914, the CPU 800 (image drawing control unit 806) restarts image drawing.

<Relationship between the presence or absence of toner and rotational torque>
FIG. 10A shows the relationship between the speed setting value of the photoconductor drum 10 and the PWM duty when the durability of the intermediate transfer body 24 is low. FIG. 10B shows the relationship between the speed setting value of the photoconductor drum 10 and the PWM duty in a state where the intermediate transfer body 24 has a high durability. The solid line shows the PWM duty in the presence of toner (driving state). The broken line indicates the PWM duty when there is no toner (non-driving state). As can be seen by comparing FIG. 10A and FIG. 10B, the PWM duty does not change significantly in the presence of toner regardless of the progress of durability. On the other hand, the PWM duty in the absence of toner largely depends on the progress of durability. As shown in FIG. 10B, when the speed setting value is less than 0.05%, the PWM duty is relatively small, so that the photoconductor drum 10 is driven by the intermediate transfer body 24. On the other hand, if the speed setting value exceeds 0.05%, the PWM duty is relatively large, so that the intermediate transfer body 24 is driven by the photoconductor drum 10. Further, when the speed setting value is 0.05%, the PWM duty in the presence of toner and the PWM duty in the absence of toner match. That is, if the speed setting value is set to 0.05%, the speed difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 becomes zero. The speed determination unit 805 determines the target speed of the motor M3 so that the difference between the PWM duty in the presence of toner and the PWM duty in the absence of toner becomes small (preferably 0). As a result, an increase in the rotational torque of the photoconductor drum 10 is suppressed, and banding is reduced.

<Color shift correction and speed adjustment processing>
FIG. 11 is a flowchart showing color shift correction and measurement adjustment processing. It is not essential to perform the color shift correction and the measurement adjustment process together, but both are described here together.

In S1101, the CPU 800 (third determination unit 813) determines whether or not the execution condition of the color shift correction is satisfied. If the execution condition of the color shift correction is satisfied, the CPU 800 proceeds to S1102. The execution condition of the color shift correction is, for example, every time the operator instructs the execution or the number of images reaches a predetermined number (example: 1000). The execution condition may be called the operating condition of the second adjusting unit 822.

In S1102, the CPU 800 (second determination unit 812) determines whether or not the second adjustment condition, which is a condition for executing the rotation speed adjustment process of the photoconductor drum 10, is satisfied. The second adjustment condition is, for example, that the average value of the M difference data stored in the storage device 850 is equal to or greater than the second threshold value. The second threshold value is set to a relatively low value (example: 2%). This is so that when the color shift correction is performed, the rotation speed adjustment is also performed quite frequently. If the second adjustment condition is not satisfied, the CPU 800 proceeds to S1105 in order to execute only the color shift correction. The CPU 800 proceeds to S1105 even when the number of difference data stored in the storage device 850 has not reached M.

In S1105, the CPU 800 (second adjustment unit 822) forms a patch image on the intermediate transfer body 24 to correct the writing timing of each color. As described above, the second adjusting unit 822 controls the image forming units 5y to 5bk through the image forming control unit 806 to form the patch image on the intermediate transfer body 24. Further, the second adjustment unit 822 causes the image sensor 14 to read the patch image, and obtains the amount of misalignment in the main scanning direction and the amount of misalignment in the sub-scanning direction for each color. The second adjustment unit 822 determines the writing timing of each color so that the amount of misalignment of each color becomes zero, and sets the image image control unit 806. The image formation control unit 806 drives the exposure device 22 for each color according to the writing timing determined for each color.

On the other hand, if the second adjustment condition is satisfied, the CPU 800 proceeds to S1103. In S1103, the CPU 800 (speed determination unit 805) determines the rotation speed (speed setting value of the motor M3) of the photoconductor drum 10 according to the difference data of the rotation torque. For example, the speed determination unit 805 determines the speed setting value based on the following equation.

Sd2 = Sd1-g × Δ ・ ・ ・ (1)
Here, Sd2 is a newly determined speed setting value. Sd1 is a speed setting value that has been used so far. g is the gain and is determined at the time of shipment from the factory. Δ is the difference data of the rotational torque. Here, the average value of M difference data is substituted for Δ.

In S1104, the CPU 800 (load measuring unit 801) erases the M difference data stored in the storage device 850. Since the M difference data stored in the storage device 850 are data acquired based on the speed setting value before the change, they are no longer necessary when the speed setting value is changed. Therefore, the M difference data stored in the storage device 850 are erased. After that, in S1105, the CPU 800 executes color shift correction using the speed setting value determined in S1103. As a result, color shift is reduced in addition to banding.

If the execution condition of the color shift correction is not satisfied in S1101, the CPU 800 proceeds to S1110. In S1110, the CPU 800 (first determination unit 811) determines whether or not the first adjustment condition, which is a condition for executing the rotation speed adjustment process, is satisfied. The first adjustment condition is a condition that is difficult to satisfy as compared with the second adjustment condition. This is to determine if an urgent speed adjustment is required due to a sudden rise in the cabin temperature. The first adjustment condition is that the average value of the latest N difference data among the M difference data stored in the storage device 850 is equal to or higher than the first threshold value. The first threshold value (example: 10%) is set to a value larger than the second threshold value (example: 2%). If the first adjustment condition is not satisfied, the CPU 800 returns to S1101. The CPU 800 returns to S1101 even when the number of difference data stored in the storage device 850 has not reached N. On the other hand, if the first adjustment condition is satisfied, the CPU 800 proceeds to S1111.

In S1111, the CPU 800 (speed determination unit 805) determines the rotation speed (speed set value of the motor M3) of the photoconductor drum 10 according to the difference data of the rotation torque. This determination process is the same as that of S1103. In S1104, the CPU 800 (load measuring unit 801) erases the M difference data stored in the storage device 850.

In S1113, the CPU 800 (first adjustment unit 821) determines the writing timing according to the newly determined rotation speed (speed setting value). The image formation position in the sub-scanning direction shifts according to the amount of change in the rotation speed. Therefore, the writing timing is corrected according to the amount of change in the rotation speed. The correction amount dt of the writing timing may be calculated from the following equation.

dt = X / (ω2 x D) -X / (ω1 x D) ... (2)
Here, X is the distance from the exposure position to the primary transfer position on the surface (peripheral surface) of the photoconductor drum 10. D is the diameter of the photoconductor drum 10. ω1 is an angular velocity corresponding to the speed setting value Sd1 before the change. ω1 is an angular velocity corresponding to the changed speed setting value Sd2.

In this way, the rotation speed of the photoconductor drum 10 is adjusted not only when the color shift correction timing but also when the difference in rotation torque suddenly increases. Therefore, even in the case where the temperature inside the machine rises sharply, the rotation speed of the photoconductor drum 10 is appropriately adjusted, so that banding is reduced.

12 (A) and 12 (B) are diagrams showing the effects of the examples. FIG. 12A corresponds to a state in which the in-flight temperature shown in FIG. 7A is high. When the temperature inside the machine is 40 ° C., the frictional force with respect to the photoconductor drum 10 gradually increases, so that the PWM duty also gradually increases. However, in this case, the second adjustment condition is satisfied in S1102, and the rotation speed is adjusted. That is, the rotation speed is adjusted and the color shift is corrected every predetermined number of sheets (example: 1000 sheets). As a result, an increase in PWM duty is suppressed, and color shift and banding are reduced.

FIG. 12B corresponds to a state in which the in-flight temperature shown in FIG. 7B is low and the image formation mode is switched in the middle. In this example, when the number of images reaches 10,000, the image formation mode is switched from the plain paper mode to the thick paper mode, and the temperature inside the machine rises sharply from 30 ° C. to 40 ° C. Under such conditions, a significant increase in PWM duty may occur before the second adjustment condition is satisfied. In this embodiment, the first adjustment condition is satisfied under such conditions, and the rotation speed adjustment and the color shift correction are executed. As a result, an increase in PWM duty is suppressed, and color shift and banding are reduced.

<Summary>
As described with reference to FIG. 1, the photoconductor drum 10 is an example of an image carrier. As described with reference to FIG. 5, the motor M3 is an example of the first driving means for driving the photoconductor drum 10. As described with reference to FIG. 2, the developing sleeve 8 is arranged at a position facing the photoconductor drum 10, carries a developer, and supplies the developer to the electrostatic latent image formed on the photoconductor drum 10. This is an example of a developer carrier to be developed. The motor M2 is an example of a second driving means for driving the developer carrier. The intermediate transfer body 24 is an example of an intermediate transfer body that conveys a developer image (toner image) transferred from the photoconductor drum 10. As shown in FIG. 6, the motor M4 is an example of a third driving means for driving the intermediate transfer body 24. The load measuring unit 801 is an example of a detecting means for detecting a load parameter (eg, PWM duty) correlated with the rotational torque of the motor M3 or the motor M4. Further, the load measuring unit 801 is an example of an acquisition means for acquiring information on the rotational torque of the motor. In the above embodiment, the rotation torque of the motor M3 has been described as being detected, but the rotation torque of the motor M4 of the intermediate transfer body 24 may be detected. Since the photoconductor drum 10 and the intermediate transfer body 24 rotate while being in contact with each other, the increase in the frictional force of the photoconductor drum 10 is also reflected in the rotational torque of the motor M4. In this case, the first adjustment condition and the second adjustment condition are changed to the condition using the rotational torque of the motor M4. The rotation speed of the motor M3 of each color may be changed or the rotation speed of the motor M4 may be changed according to the rotation torque of the motor M4 measured by the load measuring unit 801. This is because it is sufficient if the difference between the peripheral speed of the photoconductor drum 10 and the peripheral speed of the intermediate transfer body 24 finally becomes a predetermined value. The storage device 850 is an example of a storage means for storing the difference in PWM duty detected by the load measuring unit 801. This difference is the difference between the first information and the second information. The first information is the PWM duty detected by the load measuring unit 801 in the driving state in which the developing sleeve 8 is driven by the motor M2. The second information is the PWM duty detected by the load measuring unit 801 in the non-driving state in which the developing sleeve 8 is not driven by the motor M2. Instead of storing the difference, these PWM duties required for obtaining the difference may be stored in the storage device 850. In the first determination unit 811, the statistical value (eg, moving average, etc.) of the difference (or the difference obtained from the stored first information and the second information) stored in the storage device 850 is the first threshold value (eg). : 10%) or more is an example of a determination means for determining whether or not. As described with respect to S1110 and S1111 This is an example. Further, the speed determination unit 805 is an example of a changing means for changing the target speed based on the first information and the second information stored in the storage device 850. As described above, in this embodiment, the peripheral speed of the photoconductor drum 10 with respect to the peripheral speed of the intermediate transfer body 24 can be adjusted at a more appropriate timing. That is, the adjustment timing of the rotation speed of the motor M3 that drives the photoconductor drum 10 is a timing that depends on the rotation torque of the motor M3, and may be other than the timing of color shift correction. Therefore, the rotation speed is adjusted at a more appropriate timing.

When the correction process is executed by the correction means, the speed determination unit 805 reduces the downtime by changing the target speed based on the first information and the second information stored in the storage means. Further, when the first information and the second information stored in the storage means satisfy the predetermined conditions, the speed determination unit 805 changes the target speed even if it is not the timing to execute the correction process by the correction means. As a result, the rotation speed can be adjusted at a more appropriate timing.

In other words, the speed determination unit 805 changes the set value of the rotation speed when the operating conditions of the second adjustment unit 822 are satisfied and the statistical value of the load parameter is equal to or higher than the second threshold value. Further, the speed determination unit 805 changes the set value if the statistical value of the load parameter is equal to or greater than the first threshold value larger than the second threshold value even if the operating conditions of the second adjustment unit 822 are not satisfied. As a result, the peripheral speed of the photoconductor drum 10 with respect to the peripheral speed of the intermediate transfer body 24 will be adjusted at a more appropriate timing.

As described with reference to FIG. 9, the load measuring unit 801 may acquire a difference each time the number of toner images formed by the image forming apparatus 100 reaches a predetermined number and store the difference in the storage apparatus 850. Further, the load measuring unit 801 may acquire the difference in the post-rotation process executed after the job of forming a series of toner images is completed and store it in the storage device 850. As described with respect to S903, the predetermined number is 200 sheets or the like, which is less than the execution condition of the color shift correction (example: 1000 sheets to 5000 sheets). This makes it possible to detect a sudden increase in rotational torque that occurs between the previous color shift correction and the current color shift correction. Further, since the measurement of the rotation torque and the acquisition of the difference are also executed in the post-rotation process executed after the image formation job is completed, it becomes easy to detect a sudden increase in the rotation torque. Also, since the measurements are performed during the post-rotation process, there will be less downtime associated with the measurements.

As described with respect to S1110, the first statistical unit 803 is an example of the first statistical means for obtaining the average value of the latest N differences stored in the storage device 850 as a statistical value. The first statistics unit 803 may obtain the latest N differences from the latest N first information and the latest N second information stored in the storage device 850. The first determination unit 811 determines whether the average value of the latest N differences is equal to or greater than the first threshold value. Statistical processing such as moving average is effective in reducing the effect of variation in measurement results. However, the latest measurement results are required to detect a sudden increase in rotational torque. In this embodiment, since the latest average value of N differences is adopted, it is possible to both reduce the variation in the measurement result and detect a sudden increase in the rotational torque.

As described with respect to S1112, the CPU 800 serves as an erasing means for erasing the difference stored in the storage device 850 when the set value of the rotation speed of the motor M3 is changed to the set value determined by the speed determination unit 805. Also works. The CPU 800 may also function as an erasing means for erasing the first information and the second information stored in the storage device 850. When the set value of the rotation speed of the motor M3 is changed, the difference measured before the change is deleted because it is no longer useful. As a result, it becomes possible to appropriately determine whether or not the rotation speed is adjusted according to the rotation torque based on the changed set value.

When the set value of the rotation speed of the motor M3 is changed to the set value determined by the speed determining unit 805, the first adjusting unit 821 adjusts the formation timing of the electrostatic latent image according to the set value. This is an example of means. Such color shift correction by the first adjustment unit 821 is executed at intervals shorter than the execution interval of the original color shift correction. Therefore, it is expected that such a serious color shift correction has not occurred, and a simple correction that does not form a patch image will be sufficient.

As described with reference to FIG. 1 and the like, the primary charger 21 is an example of a charging means for uniformly charging the photoconductor drum 10. The exposure device 22 is an example of an exposure means for forming an electrostatic latent image by exposing a uniformly charged photoconductor drum 10. The primary transfer roller 23 is an example of the primary transfer means for primary transfer of the toner image carried on the photoconductor drum 10 to the intermediate transfer body 24. The secondary transfer roller 29 is an example of a secondary transfer means for secondary transfer of the toner image primary transferred to the intermediate transfer body 24 to the sheet P. The fixing device 27 is an example of fixing means for fixing the toner image secondarily transferred to the sheet P. The CPU 800 is an example of control means for controlling the primary charger 21, the exposure device 22, the motor M3, the motor M2, and the motor M4. The image sensor 14 is an example of a measuring means for measuring the formation position of a measurement image (patch image) formed on the intermediate transfer body 24. When the execution condition for executing the correction process for forming the measurement image and correcting the image formation position is satisfied, the second adjustment unit 822 executes the color shift correction using the patch image. That is, the second adjusting unit 822 controls the exposure device 22 to form an electrostatic latent image corresponding to the patch image, and the developing sleeve 8 develops the electrostatic latent image to form the patch image. Further, the second adjusting unit 822 first transfers the patch image to the intermediate transfer body 24 by the primary transfer roller 23, causes the image sensor 14 to measure the formation position of the patch image, and causes the electrostatic latent image according to the formation position of the patch image. Adjust the formation timing of. The second statistical unit 804 is an example of the second statistical means for obtaining the average value of the differences of M (eg, 30) stored in the storage device 850 as statistical values. The second statistics unit 804 may obtain M differences from the M first information and the M second information stored in the storage device 850. When the color shift correction execution condition is satisfied, the second determination unit 812 determines whether the average value of the M differences is equal to or greater than the second threshold value. When the average value of the M differences becomes equal to or greater than the second threshold value, the speed determination unit 805 determines the set value of the rotation speed of the motor M3 according to the average value of the M differences so that the difference becomes smaller.

The second adjusting unit 822 adjusts the formation timing of the electrostatic latent image based on the patch image after the set value of the rotation speed of the motor M3 is changed to the set value determined by the speed determining unit 805. When the rotation speed is changed, the color shift is also affected. Therefore, by executing the color shift correction after the rotation speed is changed, the color shift will be corrected more accurately.

In addition, M (example: 30 pieces)> N (example: 5 pieces). The execution interval of the color shift correction accompanied by the patch image is a relatively long interval. Therefore, the variation in the measurement results can be reduced by obtaining the average value using more measurement results. On the other hand, in order to detect a sudden increase in rotational torque, it is necessary to pay attention to the change in rotational torque in a shorter period of time. However, we would like to reduce the variation in measurement results if possible. Therefore, N is selected as a natural number smaller than M.

In principle, the rotation speed is also adjusted at the timing of color shift correction accompanied by the patch image. Therefore, by setting the second threshold value (example: 2%) to be smaller than the first threshold value (example: 10%), the rotation speed is adjusted with a high probability at the timing of color shift correction accompanied by the patch image. Let's be like that. If the difference in rotational torque is small enough, the rotational speed adjustment may be omitted to further reduce downtime.

The load parameter measured by the load measuring unit 801 may be a duty ratio (eg, PWM duty) of a pulse width-modulated drive signal supplied to the motor M3 or the motor M4. The drive circuit 830 adjusts the PWM duty so that the target speed is achieved. If the frictional force acting between the photoconductor drum 10 and the intermediate transfer body 24 increases, the load applied to the motor M3 increases, and the PWM duty must also increase. In this way, the PWM duty correlates with the frictional force. In addition, installing a device that directly measures the frictional force increases the manufacturing cost. Therefore, by measuring the PWM duty instead of the frictional force, it is possible to observe the frictional force inexpensively and accurately.

100 ... image forming device, 10 ... photoconductor drum, M3 ... motor, 8 ... developing sleeve, M2 ... motor, 24 ... intermediate transfer member, M4 ... motor, 801 ... load measuring unit 801, 850 ... storage device, 811 ... One judgment unit, 805 ... Speed determination unit

Claims (6)

Photoreceptor and
An exposure means that exposes the photoconductor to form an electrostatic latent image,
A developing means having a developer carrier that supports and rotates a developer and develops the electrostatic latent image on the photoconductor using the developer supported on the developer carrier.
An intermediate transfer body to which an image visualized by development by the developing means is transferred, and
A transfer means for transferring the image from the intermediate transfer body to the sheet,
A photoconductor motor that rotates the photoconductor and
An intermediate transfer motor that rotates the intermediate transfer,
Motor control that controls the photoconductor motor so that the rotation speed of the photoconductor becomes the photoconductor target speed, and controls the intermediate transfer body motor so that the rotation speed of the intermediate transfer body becomes the intermediate transfer body target speed. Means and
In the first state in which the photoconductor, the intermediate transfer body, and the developer carrier are rotating, the first information regarding the load of the photoconductor motor is acquired, the rotation of the developer carrier is stopped, and the developer carrier is rotated. In the second state in which the photoconductor and the intermediate transfer body are rotating, the second information regarding the load of the photoconductor motor is acquired, and whether or not the target speed of the photoconductor is changed is determined by the first information and the first information. It has a control means for controlling based on two pieces of information.
When the predetermined condition regarding the number of sheets on which the image is formed is satisfied while the image is formed on a plurality of sheets while the photoconductor, the intermediate transfer body, and the developer carrier are rotated. The control means is an image forming apparatus characterized in that the rotation of the developer carrier is stopped to acquire the second information. The image forming apparatus according to claim 1, wherein the predetermined condition is satisfied each time the number of the images formed on the plurality of sheets reaches a predetermined number. The first information is the duty of the PWM signal supplied to the photoconductor motor in the first state.
The image forming apparatus according to claim 1, wherein the second information is a duty of a PWM signal supplied to the photoconductor motor in the second state. Photoreceptor and
An exposure means that exposes the photoconductor to form an electrostatic latent image,
A developing means having a developer carrier that supports and rotates a developer and develops the electrostatic latent image on the photoconductor using the developer supported on the developer carrier.
An intermediate transfer body to which an image visualized by development by the developing means is transferred, and
A transfer means for transferring the image from the intermediate transfer body to the sheet,
A photoconductor motor that rotates the photoconductor and
An intermediate transfer motor that rotates the intermediate transfer,
Motor control that controls the photoconductor motor so that the rotation speed of the photoconductor becomes the photoconductor target speed, and controls the intermediate transfer body motor so that the rotation speed of the intermediate transfer body becomes the intermediate transfer body target speed. Means and
In the first state in which the photoconductor, the intermediate transfer body, and the developer carrier are rotating, the first information regarding the load of the intermediate transfer body motor is acquired, the rotation of the developer carrier is stopped, and the developer carrier is stopped. In the second state in which the photoconductor and the intermediate transfer body are rotating, the second information regarding the load of the intermediate transfer body motor is acquired, and whether or not to change the target speed of the photoconductor is referred to the first information. It has a control means for controlling based on the second information.
When the predetermined condition regarding the number of sheets on which the image is formed is satisfied while the image is formed on a plurality of sheets while the photoconductor, the intermediate transfer body, and the developer carrier are rotated. The control means is an image forming apparatus characterized in that the rotation of the developer carrier is stopped to acquire the second information. The image forming apparatus according to claim 4 , wherein the predetermined condition is satisfied each time the number of the images formed on the plurality of sheets reaches a predetermined number. The first information is the duty of the PWM signal supplied to the intermediate transfer motor in the first state.
The image forming apparatus according to claim 4 , wherein the second information is a duty of a PWM signal supplied to the intermediate transfer motor in the second state.

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