JP6833372B2 - Image forming device - Google Patents

Description

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

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

The image forming apparatus is required to control the peripheral speed (surface speed) at which the surface of the photoconductor moves and the peripheral speed (surface speed) at which the surface of the intermediate transfer member moves at a constant speed. This is because the laser beam for forming an electrostatic latent image on the photoconductor scans the photoconductor at a predetermined timing. For example, if the surface speed of the photoconductor changes, the pitch of the scanning lines changes, the length of the image changes, and the density of the image on the photoconductor changes. Further, in an image forming apparatus that superimposes and transfers an image for each color formed by a plurality of image forming portions on an intermediate transfer body in order to form a full-color image, the relative position of the image for each color is used. Misalignment will occur and the color will change. Therefore, in order to control the surface speed of the photoconductor and the surface speed of the intermediate transfer body, the image forming apparatus executes feedback control based on, for example, the output of the encoder.

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

By the way, in an image forming apparatus in which the peripheral speed of the photoconductor and the peripheral speed of the intermediate transfer body are controlled to different speeds, the friction coefficient of the photoconductor and the intermediate transfer body depends on the internal temperature of the image forming apparatus and the number of prints. May change. During the formation of the image, the developer is supplied to the nip for transferring the image on the photoconductor to the intermediate transfer body, so that even if the friction coefficient of the photoconductor or the intermediate transfer body changes, the photosensitivity is exposed. The surface velocity of the body or intermediate transfer is controlled to the target velocity. However, the load of the motor for driving the photoconductor and the intermediate transfer body suddenly changes at the timing of changing from the state in which the developer is not interposed in the nip to the state in which the developer is present in the nip. Therefore, there is a possibility that the rotation speed of the motor becomes uncontrollable. This timing occurs, for example, immediately after starting the rotational drive of the photoconductor or the intermediate transfer body in order to form an image. In a state where the rotation speed of the motor cannot be controlled, the above-mentioned image defects occur.

Therefore, the peripheral speed of the photoconductor and the intermediate transfer are reduced so that the difference between the load of the motor when the developer is supplied to the nip and the load of the motor when the developer is not supplied to the nip is 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 acquires the drive signal of the motor while supplying the developer to the nip part and switching the speed command value of the motor, and switches the speed command value of the motor without supplying the developer to the nip part. Get the drive signal of. 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 speed command value of the motor is determined based on the drive signal of the motor.

Japanese Unexamined Patent Publication No. 2016-1268

However, the difference in peripheral speed is controlled so that the difference between the load of the motor when the developer is supplied to the nip and the load of the motor when the developer is not supplied to the nip is reduced. However, there was a possibility that the speed of the intermediate transcript would fluctuate. This is because the frictional force between the photoconductor and the intermediate transfer body increases, and the surface speed of the intermediate transfer body changes depending on the rotation speed of the photoconductor. If the surface speed of the intermediate transfer body cannot be controlled to the target speed, for example, the length of the image will change or the density of the image on the intermediate transfer body will be uneven.
In particular, when a monochromatic image is formed with a plurality of photoconductors in contact with the intermediate transfer body, the photoconductor and the intermediate transfer body other than the photoconductor on which the monochromatic image is formed are formed even while the monochromatic image is being formed. No developer is supplied to the nip between the and. Therefore, when a monochromatic image is formed in a state where a plurality of photoconductors are in contact with the intermediate transfer body, the surface speed of the intermediate transfer body cannot be controlled to the target speed.

Therefore, an object of the present invention is to prevent the rotation speed of the intermediate transfer member from becoming uncontrollable in the mode of forming a monochromatic image.

The image forming apparatus of the present invention includes a first photosensitive member on which an electrostatic latent image is formed, and a first developer carrying member rotates while carrying a black developer, on the first photoreceptor A first image forming means for developing the electrostatic latent image with the black developer, a first motor for rotating the first photoconductor, and a second photoconductor on which an electrostatic latent image is formed. A second image forming means that has a second developer carrier that carries a color developer and rotates, and develops the electrostatic latent image on the second photoconductor using the color developer. , A second motor that rotates the second photoconductor, and an intermediate transfer body to which the black image developed on the first photoconductor and the color image developed on the second photoconductor are transferred. a third motor for rotationally driving the intermediate transfer member, prior Symbol a transfer unit that transfers the image transferred to the intermediate transfer member to the sheet, the first photoreceptor and the intermediate transfer member contacts and said second 2 A first state in which the photoconductor and the intermediate transfer body are in contact with each other, and a second state in which the first photoconductor and the intermediate transfer body are in contact with each other and the second photoconductor and the intermediate transfer body are separated from each other. preparative to the second photosensitive member and the contact and separation means for controlling the positional relationship between the intermediate transfer member, prior Symbol first motor rotational speed and the second motor rotation speed and that control control means when have the contact and separation unit, when the black monochrome image is formed on the sheet, to control the positional relationship based on the type of the sheet, wherein, the black in the first state When a monochromatic image is formed on the sheet, information on the load of the third motor is acquired while the rotation of the first developer carrier is stopped and the intermediate transfer body is rotating, and the second It is characterized in that whether or not to change the rotational speed of the motor is controlled based on the above information.

According to the present invention, it is possible to prevent the rotation speed of the intermediate transfer member from becoming uncontrollable in the mode of forming a monochromatic image.

The block diagram of the image forming apparatus. Explanatory drawing of development processing. Explanatory drawing of development processing. Configuration diagram of the control system. An illustration of a test image. Explanatory drawing of the drum drive part. Explanatory drawing of the intermediate transfer body drive part. An explanatory diagram of a change in load torque according to the number of sheets to be passed. The figure which shows the relationship between the dynamic friction force and the speed difference. A flowchart showing a rotation speed adjustment process. An explanatory diagram of a change in load torque according to the number of sheets to be passed. (A) and (b) are explanatory views of the operation of the image forming apparatus according to the image forming mode. Flowchart in black image formation mode.

Hereinafter, embodiments will be described in detail with reference to the drawings.

(Image forming device)
FIG. 1 is a configuration diagram of an image forming apparatus of the present embodiment. The image forming apparatus 100 forms an image by an electrophotographic method. The image forming apparatus 100 includes image forming units 1200Y, 1200M, 1200C, and 1200K for forming an image for each of the colors Y (yellow), M (magenta), C (cyan), and K (black). The image forming unit 1200Y, 1200M, 1200C, 1200K is a tandem system arranged on the intermediate transfer body 24. Primary transfer rollers 23Y, 23M, 23C, 23K are provided at positions facing each other with the intermediate transfer body 24 interposed therebetween, corresponding to the image forming portions 1200Y, 1200M, 1200C, 1200K. An image detection sensor 1004 for detecting a toner image (image) formed on the intermediate transfer body 24 is arranged in the vicinity of the intermediate transfer body 24. The image forming apparatus 100 includes a secondary transfer roller 29 and a fixing device 25. In the following description, Y, M, C, and K at the end of the reference numerals represent the colors of the images to be formed, and are not added when it is not necessary to distinguish the colors.

The image forming unit 1200 of each color has the same configuration, and includes a photosensitive drum 10, a charger 21, an exposure device 22, a developer 1, and a drum cleaner 26. Since the photosensitive drum 10K of the image forming unit 1200K that forms a black image is also used when forming a monochrome image in addition to the full-color image, the photosensitive drums 10Y and 10M of other colors are considered in consideration of the product life. The drum diameter is formed larger than 10C.

The photosensitive drum 10 is a drum-shaped photosensitive member, and is a rotating object that rotates about a drum axis. The charger 21 uniformly charges the surface of the photosensitive drum 10. The exposure device 22 forms an electrostatic latent image by irradiating the charged surface of the photosensitive drum 10 with a laser beam modulated based on the image data. The developer 1 develops an electrostatic latent image to form a toner image on the surface of the photosensitive drum 10. The developer 1Y forms a yellow toner image on the photosensitive drum 10Y with a yellow developer. The developer 1M forms a magenta toner image on the photosensitive drum 10M with the magenta developer. The developer 1C forms a cyan toner image on the photosensitive drum 10C with a cyan developer. The developer 1K forms a black toner image on the photosensitive drum 10K with a black developer.

The developer 1 contains a two-component developer containing a non-magnetic toner and a carrier having low magnetization and high resistance. The non-magnetic toner is composed of an appropriate amount of a binder resin such as a styrene resin or a polyester resin, a colorant such as carbon black or dye, a pigment, a mold release agent such as wax, or a charge control agent. The toner can be produced by a conventional method such as a pulverization method or a polymerization method.
The toner is triboelectricly charged with the low magnetization and high resistance carriers in the developer 1. The charged toner adheres to the electrostatic latent image on the photosensitive drum 10 when the development bias potential is applied. As a result, the electrostatic latent image is developed. In this embodiment, the toner is negatively charged. The developer 1 is replenished with toner from the toner replenishment tank 20.

The toner image formed on the photosensitive drum 10 is transferred to the intermediate transfer body 24 by the primary transfer roller 23. The photosensitive drum 10 and the intermediate transfer pair 24 form a nip portion for transferring a toner image. The toner remaining on the photosensitive drum 10 after transfer is removed by the drum cleaner 26. The intermediate transfer body 24 is an image carrier composed of an endless belt member, and rotates clockwise in FIG. 1. By rotating the intermediate transfer body 24, the toner image is transferred in the order of the photosensitive drum 10Y, the photosensitive drum 10M, the photosensitive drum 10C, and the photosensitive drum 10K. The intermediate transfer body 24 transfers the transferred toner image to the secondary transfer roller 29 by rotation. The toner image formed on the intermediate transfer body 24 is transferred to the sheet 30 by the secondary transfer roller 29. The toner remaining on the intermediate transfer body 24 after transfer is removed by the transfer body cleaner 28. After the toner image is transferred, the sheet 30 is transferred to the fixing device 25 by the secondary transfer roller 29. The fuser 25 fixes the toner image on the sheet 30. The sheet 30 for which image formation is completed in this way is discharged from the fixing device 25 to the outside of the image forming apparatus 100.

(Development processing)
2 and 3 are explanatory views of the developing process by the developing device 1. The surface of the photosensitive drum 10 is charged to a negative potential Vd by the charger 21. The potential (exposure portion potential) VL of the portion of the photosensitive drum 10 on which the electrostatic latent image is formed is static-free from the potential Vd to the 0 [V] side. The potential Vd is, for example, -700 [V], and the exposed potential VL is, for example, -200 [V].

The developer 1 conveys the contained developer containing the negatively charged toner to the vicinity of the photosensitive drum 10 by the developer carrier 8. The development bias potential Vdc applied to the developer carrier 8 during development is a potential between the potential Vd and the exposure portion potential VL, and is, for example, −550 [V]. Due to the negative development bias potential Vdc, the negatively charged toner on the developer carrier 8 has a portion of the exposed portion potential VL that is relatively close to the positive potential than the potential Vd on the surface of the photosensitive drum 10 and the development bias potential Vdc. Fly to. As a result, an amount of toner corresponding to the development latent image potential Vcont, which is the difference between the development bias potential Vdc and the exposure portion potential VL, adheres to the photosensitive drum 10. The density of the toner image is determined according to the amount of toner adhering to the photosensitive drum 10. Therefore, the image density can be adjusted by adjusting the developing latent image potential Vcont. The negative electrode toner that has flown onto the photosensitive drum 10 is transferred to the intermediate transfer body 24 by the pressure and electric field between the primary transfer roller 23 and the intermediate transfer body 24. At this time, the primary transfer bias potential Vtr1 having the opposite polarity to the toner is applied to the primary transfer roller 23. For example, the primary transfer bias potential Vtr1 is +1500 [V].

(Control system)
FIG. 4 is a configuration diagram of a control system of the image forming apparatus 100 having such a configuration. The control system is built in the image forming apparatus 100. The image forming apparatus 100 performs an image forming process by controlling the operation of each part by a control system.

The control system mainly controls the operation of the image forming apparatus 100 by the controller 1001. The controller 1001 includes a CPU (Central Processing unit) 1000 as a main control unit. The CPU 1000 controls the operation of each part by reading a computer program from a memory (not shown) and executing the program. The controller 1001 includes a speed setting controller 1002, a color resist controller 1003, an image drawing controller 1100Y, 1100M, 1100C, 1100K, and output torque detection units 45Y, 45M, 45C, 45K, 45B. The controller 1001 is connected to the image detection sensor 1004, the image forming unit 1200Y to 1200K, and the speed control unit 1300Y to 1300K, 1400. The speed control units 1300Y to 1300K are connected to the drum drive motors 41Y to 41K. The speed control unit 1400 is connected to the intermediate transfer body drive motor 42.

The color resist controller 1003 controls the operation of the image detection sensor 1004 according to the control of the CPU 1000, and adjusts the image forming controllers 1100Y to 1100K according to the detection result of the image detection sensor 1004. The speed setting controller 1002 adjusts the rotation speeds of the photosensitive drums 10Y to 10K and the intermediate transfer body 24 according to the control of the CPU 1000.

The image-creating controller 1100Y controls the operation of the image forming unit 1200Y in response to the control of the CPU 1000. The image-creating controller 1100M controls the operation of the image forming unit 1200M in response to the control of the CPU 1000. The image-creating controller 1100C controls the operation of the image forming unit 1200C in response to the control of the CPU 1000. The image-creating controller 1100K controls the operation of the image forming unit 1200K in response to the control of the CPU 1000.

The speed control unit 1300Y is a drive control unit that controls the operation of the drum drive motor 41Y in response to the control of the speed setting controller 1002. The drum drive motor 41Y rotationally drives the photosensitive drum 10Y. The speed control unit 1300Y inputs a PWM (Pulse Width Modulation) signal representing the load torque of the drum drive motor 41Y to the output torque detection unit 45Y. The output torque detection unit 45Y transmits a PWM signal to the speed setting controller 1002. The speed control unit 1300Y controls the load torque of the drum drive motor 41Y so that the photosensitive drum 10Y rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

The speed control unit 1300M is a drive control unit that controls the operation of the drum drive motor 41M in response to the control of the speed setting controller 1002. The drum drive motor 41M rotationally drives the photosensitive drum 10M. The speed control unit 1300M inputs a PWM signal representing the load torque of the drum drive motor 41M to the output torque detection unit 45M. The output torque detection unit 45M transmits a PWM signal to the speed setting controller 1002. The speed control unit 1300M controls the load torque of the drum drive motor 41M so that the photosensitive drum 10M rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

The speed control unit 1300C is a drive control unit that controls the operation of the drum drive motor 41C in response to the control of the speed setting controller 1002. The drum drive motor 41C rotationally drives the photosensitive drum 10C. The speed control unit 1300C inputs a PWM signal representing the load torque of the drum drive motor 41C to the output torque detection unit 45C. The output torque detection unit 45C transmits a PWM signal to the speed setting controller 1002. The speed control unit 1300C controls the load torque of the drum drive motor 41C so that the photosensitive drum 10C rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

The speed control unit 1300K is a drive control unit that controls the operation of the drum drive motor 41K in response to the control of the speed setting controller 1002. The drum drive motor 41K rotationally drives the photosensitive drum 10K. The speed control unit 1300K inputs a PWM signal representing the load torque of the drum drive motor 41K to the output torque detection unit 45K. The output torque detection unit 45K transmits a PWM signal to the speed setting controller 1002. The speed control unit 1300K controls the load torque of the drum drive motor 41K so that the photosensitive drum 10K rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

The speed control unit 1400 is a drive control unit that controls the operation of the intermediate transfer body drive motor 42 in response to the control of the speed setting controller 1002. The intermediate transfer body drive motor 42 rotationally drives the intermediate transfer body 24. The speed control unit 1400 inputs a PWM signal representing the load torque of the intermediate transfer body drive motor 42 to the output torque detection unit 45B. The output torque detection unit 45B transmits a PWM signal to the speed setting controller 1002. The speed control unit 1400 controls the load torque of the intermediate transfer body drive motor 42 so that the intermediate transfer body 24 rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

(Image formation processing)
When image forming processing is continuously performed on two sheets 30, the image forming apparatus 100 performs pre-rotation processing, image drawing processing, inter-paper processing, and post-rotation processing.

The pre-rotation process is a process of putting the drive units of the drum drive motors 41Y to 41K, 42 and the like and the high voltage member such as the charger 21 into a stable operating state in order to execute the image drawing. In the pre-rotation process, the photosensitive drum 10 and the intermediate transfer body 24 are driven. Since the photosensitive drum 10 and the intermediate transfer body 24 have a large inertia, it takes a predetermined time, for example, 500 milliseconds, from the start of driving to reach the target rotation speed (target speed) and operate at a stable and constant speed. is there. Details of driving the photosensitive drum 10 and the intermediate transfer body 24 will be described later. After the photosensitive drum 10 and the intermediate transfer body 24 operate stably at a constant speed, a charging bias is applied to the charger 21. The primary transfer bias potential Vtr1 is applied according to the timing at which the charged portion on the photosensitive drum 10 passes through the position of the primary transfer roller 23. The drive unit of the developer carrier 8 and the development bias potential Vdc should have a desired rotation speed and a desired potential before the electrostatic latent image formed on the photosensitive drum 10 approaches the developer carrier 8. Just do it. However, in order to prevent deterioration of the developer, it is desirable that the drive unit of the developer carrier 8 and the development bias potential Vdc reach a desired rotation speed and a desired potential at the latest possible timing.

The image forming process is a process of forming a toner image on the photosensitive drum 10 and transferring it to the intermediate transfer body 24. In the image forming process, the surface of the charged photosensitive drum 10 is exposed to laser light from the exposure device 22 to form an electrostatic latent image. The developer 1 visualizes the electrostatic latent image with toner. The primary transfer roller 23 transfers the toner image formed on the photosensitive drum 10 to the intermediate transfer body 24.

The paper-to-paper process is a process in which each drive unit and high-voltage member are operated in a minute gap formed between the first and second sheets without performing the image drawing process.

The post-rotation process represents a process of stopping each drive unit and high voltage member. In the post-rotation process, the exposure device 22, the charging device 21, the driving unit of the developer carrier 8, the developing bias potential Vdc, the primary transfer bias potential Vtr1, and the charging bias are stopped in this order, and then the photosensitive drum 10 and the intermediate transfer body 24 are stopped. Stop the rotation of.

(Color resist adjustment processing)
The image forming apparatus 100 performs a color resist adjusting process for correcting the forming position of the toner image on the photosensitive drum 10 by detecting the position of the test image formed on the intermediate transfer body 24 with the image detection sensor 1004. The color resist adjustment process is performed according to an instruction from the user, when the image forming apparatus 100 is installed, after forming an image on a predetermined number of sheets, or at a set predetermined timing. The color resist adjustment process corrects the shift in the formation position of the toner image due to the manufacturing variation of the image forming apparatus 100 and the change over time in the toner image formation position due to environmental changes such as temperature rise in the machine.

When the start of the color resist adjustment process is instructed, the controller 1001 starts driving the intermediate transfer member 24 and starts the image forming process of the test image. FIG. 5 is an example diagram of a test image. The test images 702Y, 702M, 702C, and 702K of each color are continuously formed at the detection position of the image detection sensor 1004 on the intermediate transfer body 24 in the direction of rotation of the intermediate transfer body 24. The image detection sensor 1004 continuously detects the test images 702Y, 702M, 702C, and 702K according to the rotation of the intermediate transfer body 24.

The color resist controller 1003 detects the relative positions of the test images 702Y, 702M, 702C, and 702K at the timing when the image detection sensor 1004 detects the test images 702Y, 702M, 702C, and 702K. When the test images 702Y, 702M, 702C, and 702K of each color pass through the detection position of the image detection sensor 1004 (two-dot chain line in FIG. 5), the interval between the test images 702Y, 702M, 702C, and 702K is calculated from the passing timing. Will be done. For example, Lys and Lms in FIG. 5 represent the positions of the test images 702Y and 702M in the main scanning direction (direction orthogonal to the rotation direction of the intermediate transfer body 24), and the large and small test images 702Y and 702M of each color. The relative positional relationship in the main scanning direction is calculated.

Further, from Lym in FIG. 5, which is the relative difference between the average values of the two passing portions of the test images 702Y and 702M, the relative positions in the sub-scanning direction (rotation direction of the intermediate transfer body 24) of each patch. The relationship is calculated. In this way, the relative positional relationship of the test images 702Y, 702M, 702C, and 702K of each color is calculated.

The test images 702Y, 702M, 702C, and 702K of each color as shown in FIG. 5 are combined into one set, and a plurality of sets of test images 702Y, 702M, 702C, and 702K are formed to calculate the positional relationship. Various disturbances are applied to the test images of each set, and minute variations in the image formation position occur. By averaging the positional relationships calculated from the plurality of sets of test images, the positional relationships of the test images 702Y, 702M, 702C, and 702K can be accurately detected.

The color resist controller 1003 repeats such a series of processes until a positional relationship is acquired from a predetermined number of test image sets. When the acquisition of a predetermined number of positional relationships is completed, the color resist controller 1003 averages the relative positional deviations of the images of each color by the test images 702Y, 702M, 702C, and 702K, and corrects the average positional deviations. Calculate the adjustment value. The color resist controller 1003 adjusts the exposure timing of the laser beam by the exposure device 22 based on the calculated color resist adjustment value.

(Rotation speed control of photosensitive drum 10 and intermediate transfer body 24)
FIG. 6 is an explanatory view of a drum driving unit that rotationally drives the photosensitive drum 10. The drum drive unit includes a motor gear 31, a first speed detection unit 32, a second speed detection unit 33, an encoder 34, and a drum drive gear 35, and is driven by the drum drive motor 41. The rotation speed of the drum drive motor 41 is controlled by the speed control unit 1300.

By driving the drum drive motor 41, the driving force is transmitted to the drum shaft 101 of the photosensitive drum 10 via the motor gear 31 and the drum drive gear 35. As a result, the photosensitive drum 10 rotates. The encoder 34 is provided on the drum shaft 101. The first speed detection unit 32 and the second speed detection unit 33 monitor the rotation of the encoder 34. The first speed detection unit 32 and the second speed detection unit 33 count the rotation speed of the photosensitive drum 10 as a pulse. The first speed detection unit 32 and the second speed detection unit 33 input the rotation speed of the photosensitive drum 10 as the first and second speed detection signals to the speed control unit 1300. The speed control unit 1300 generates a PWM signal, which is a drive command, in response to the first and second speed detection signals and inputs the PWM signal to the drum drive motor 41, so that the rotation speed of the photosensitive drum 10 becomes constant at the target speed. Feedback control is performed.

The speed control unit 1300 also inputs the PWM signal to the output torque detection unit 45. The PWM signal represents the electric power required to drive the photosensitive drum 10, and is a signal related to the load torque of the drum drive motor 41. The load torque of the drum drive motor 41 represents the load torque of the photosensitive drum 10. Further, the rotation speed of the photosensitive drum 10 is set to be faster than the rotation speed of the intermediate transfer body 24, for example, 0.15% faster.

FIG. 7 is an explanatory diagram of an intermediate transfer body driving unit that rotationally drives the intermediate transfer body 24. The intermediate transfer body drive unit includes a motor gear 36, a first speed detection unit 37, a second speed detection unit 38, an encoder 39, an intermediate transfer body drive roller 40, and a drive gear 400, and is driven by the intermediate transfer body drive motor 42. To. The rotation speed of the intermediate transfer body drive motor 42 is controlled by the speed control unit 1400.

By driving the intermediate transfer body drive motor 42, the driving force is transmitted to the intermediate transfer body drive roller 40 via the motor gear 36 and the drive gear 400. The intermediate transfer body drive roller 40 is a rotating member that rotates the intermediate transfer body 24 by being rotationally driven. The encoder 39 is provided on the intermediate transfer body drive roller 40. The first speed detection unit 37 and the second speed detection unit 38 monitor the rotation of the encoder 39. The first speed detection unit 37 and the second speed detection unit 38 count the rotation speed of the intermediate transfer body drive roller 40 as a pulse. The first speed detection unit 37 and the second speed detection unit 38 input the rotational speed of the intermediate transfer body drive roller 40 to the speed control unit 1400 as first and second speed detection signals. The speed control unit 1400 generates a PWM signal, which is a drive command, in response to the first and second speed detection signals and inputs the PWM signal to the intermediate transfer body drive motor 42, so that the rotation speed of the intermediate transfer body drive roller 40 is targeted. Feedback control is performed so that the speed becomes constant.

The speed control unit 1400 also inputs the PWM signal to the output torque detection unit 45B. The PWM signal represents the electric power required to drive the intermediate transfer body 24, and is a signal related to the load torque of the intermediate transfer body drive motor 42. The load torque of the intermediate transfer body drive motor 42 represents the load torque of the intermediate transfer body 24.

(Friction of the contact portion between the photosensitive drum 10 and the intermediate transfer body 24)
FIG. 8 is an explanatory diagram of a change in load torque according to the number of sheets to be passed (the number of sheets in which an image is formed) at the contact portion between the photosensitive drum 10 and the intermediate transfer body 24.

The frictional force of the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 differs depending on whether or not a toner image is formed on the photosensitive drum 10. When a toner image is formed on the photosensitive drum 10, the toner intervenes in the contact portion between the photosensitive drum 10 and the intermediate transfer body 24, so that the speed difference in rotation speed between the photosensitive drum 10 and the intermediate transfer body 24 However, the frictional force hardly changes. When the toner image is not formed on the photosensitive drum 10, the toner does not intervene in the contact portion between the photosensitive drum 10 and the intermediate transfer body 24, so that the rotation speed difference between the photosensitive drum 10 and the intermediate transfer body 24 When is generated, it greatly affects the frictional force. The greater the speed difference, the greater the frictional force.

As shown in FIG. 8, when a toner image is formed on the photosensitive drum 10, the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 is changed according to aging, for example, the number of sheets to be passed (the number of sheets on which the image is formed). There is little change in frictional force, and there is little fluctuation in load torque. Therefore, the change in the duty ratio of the PWM signal is small. When the toner image is not formed on the photosensitive drum 10, the frictional force between the photosensitive drum 10 and the intermediate transfer body 24 and the contact portion increases with the aging, and the load torque increases. The duty ratio of the PWM signal decreases as the load torque increases. The increase in load torque causes control divergence due to the fact that the intermediate transfer body 24 is finally pulled and the load torque is no longer generated. The photosensitive drum 10 becomes a load weight due to an increase in load torque.

The developer 1 supplies toner to the photosensitive drum 10 in accordance with the rotation of the developer carrier 8 during development even when only a small amount of toner is contained therein. Therefore, in order to minimize the consumption of toner, it is required to rotate the developer carrier 8 only for the minimum time required for image formation. Specifically, the developer carrier 8 starts rotating at a timing immediately before image formation after the photosensitive drum 10 and the intermediate transfer body 24 rotate, and stops rotating immediately after the image formation is completed. Therefore, the developer carrier 8 is often driven in a state where the toner image is not formed on the photosensitive drum 10. When the developer carrier 8 is rotated, controlled divergence of the intermediate transfer body 24 and load weight of the photosensitive drum 10 may occur.

By increasing the speed difference between the rotational speeds of the photosensitive drum 10 and the intermediate transfer body 24, the frictional force of the contact portion increases. The frictional force between objects includes static frictional force and dynamic frictional force. The frictional force associated with the speed difference is the dynamic frictional force. When the speed difference between the objects is large to some extent, the dynamic friction force is constant without being affected by the speed difference. However, the speed difference between the photosensitive drum 10 and the intermediate transfer body 24 is usually about 1% at the maximum. Therefore, the dynamic friction force between the photosensitive drum 10 and the intermediate transfer body 24 changes under the influence of the speed difference. FIG. 9 is a diagram showing the relationship between such dynamic friction force and speed difference. In a device such as the image forming apparatus 100 in which the speed difference between the photosensitive drum 10 and the intermediate transfer body 24 is small, the dynamic friction force increases due to the large speed difference.

(Speed adjustment processing of the photosensitive drum 10 and the intermediate transfer body 24)
FIG. 10 is a flowchart showing an adjustment process of the rotation speed of the photosensitive drum 10.

The controller 1001 waits until the instruction to start the image forming process is acquired (S11). The controller 1001 that has acquired the instruction to start the image forming process starts the image forming process. The controller 1001 starts the image drawing process (S12). As a result, each part of the image forming apparatus 100 is driven, and for example, the photosensitive drum 10 and the intermediate transfer body 24 start rotating. At this time, the developer carrier 8 also starts rotating, and a small amount of toner is supplied to the photosensitive drum 10 regardless of the development bias potential Vdc. When the toner adheres to the photosensitive drum 10 and reaches the intermediate transfer body 24, the frictional force at the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 is reduced. While the developer carrier 8 is being driven in this way, the frictional force between the photosensitive drum 10 and the intermediate transfer body 24 is reduced, so that the influence of the load torque is suppressed, and the photosensitive drum 10 and the intermediate transfer body 24 are moved. Stable drive control.

Upon completion of the image drawing process or paper-to-paper processing, the controller 1001 stops the operation of the developer 1 (S13). As a result, the rotation of the developer carrier 8 is also stopped. The controller 1001 waits until the developer carrier 8 is completely stopped and all the supplied toner reaches the intermediate transfer body 24 via the photosensitive drum 10 (S14). The standby time is determined based on the drum diameter of the photosensitive drum 10, the position of the developer carrier 8, and the rotation speed of the photosensitive drum 10. Further, the time for the toner to reach the intermediate transfer member 24 in all the image forming portions 1200Y to 1200K is the time until the toner in the most upstream image forming portion 1200Y passes through the position of the most downstream image forming portion 1200K. .. For example, in this embodiment, it takes about 1.5 seconds.

The controller 1001 acquires a PWM signal representing the load torque of the intermediate transfer body 24 by the output torque detection unit 45B (S15). The details of the PWM signal acquisition process will be described later. The controller 1001 stores the acquired PWM signal in a predetermined memory (S16). The stored PWM signal is used as a backup value. The memory stores up to 30 PWM signals. When the 31st and subsequent PWM signals are acquired, the controller 1001 updates the memory with the latest value at any time. The number of PWM signals stored does not have to be 30 as long as the amount is sufficient to determine the load state.

The controller 1001 calculates the average value of the duty ratios of the PWM signals stored in the memory by the speed setting controller 1002 and compares them with the threshold value (S17). The controller 1001 repeatedly executes the processes S12 to S16 until the average value becomes larger than the threshold value (S17: N). As a result, the state of the load torque is monitored at each timing when the toner runs out from the photosensitive drum 10 and the intermediate transfer body 24.

When the average value becomes larger than the threshold value (S17: Y), the controller 1001 determines that the load state of the intermediate transfer member 24 may cause control divergence. In this case, the controller 1001 changes the target speed of the rotation speed of the photosensitive drum 10 by the speed setting controller 1002 (S18). In the present embodiment, the drum diameter is different between the color (chromatic) photosensitive drums 10Y, 10M, 10C and the black (achromatic) photosensitive drum 10K. Since the drum diameters are different, changing the target speed causes a shift in the writing position when forming the electrostatic latent image. Therefore, the speed setting controller 1002 adjusts the writing position by setting different target speeds for the photosensitive drums 10Y, 10M, 10C and the photosensitive drum 10K in consideration of the difference in drum diameter (S19). The controller 1001 may separately execute the above-mentioned color resist adjustment in parallel with the change of the target speed.

In the above description, the target speed of the rotation speed of the photosensitive drum 10 is changed, but the target speed of the rotation speed of the intermediate transfer member 24 may be changed. When the rotation speed of the intermediate transfer member 24 is changed, the image area is enlarged or reduced. Therefore, when the enlargement / reduction of the image area is unacceptable, it is necessary to adjust the image pattern, for example.

The PWM signal acquisition process of the intermediate transfer body 24 in S15 will be described. In the present embodiment, the speed control unit 1400 samples and averages the first detection speed and the second detection speed 36 times at intervals of 8 milliseconds in about 300 milliseconds, thereby averaging the PWM of the intermediate transfer body 24. Generate a signal. When driving the intermediate transfer body 24, the PWM signal of the intermediate transfer body 24 changes due to the influence of load fluctuations of the intermediate transfer body driving unit and the like. Since the speed control unit 1400 can know the degree of such an influence by analyzing the PWM signal by FFT (Fast Fourier Transform), it is possible to generate the PWM signal accurately by canceling the most influential value. it can. The controller 1001 acquires the PWM signal generated in this way by the output torque detection unit 45.

When acquiring the PWM signal of the photosensitive drum 10, the speed control unit 1300 generates the PWM signal by the same process. The above sampling time is set so that the photosensitive drum 10 makes one rotation in about 300 milliseconds. The sampling time can be set short when priority is given to reducing downtime or when the number of acquisitions of PWM signals is increased. The load torque may be obtained from at least one of the photosensitive drum 10 and the intermediate transfer body 24.

The main factors that generate the load torque when the intermediate transfer body 24 is driven are the frictional force due to the photosensitive drum 10 and the frictional force due to the transfer body cleaner 28. In the present embodiment, the load torque (PWM signal) of the intermediate transfer body 24 is measured in a state where the toner does not intervene in the intermediate transfer body 24 and the developing device 1 is stopped.

The load torque of the intermediate transfer body 24 changes depending on whether the transferred toner 28 includes the removed toner or not. In order to stabilize the rotation speed of the intermediate transfer body 24, the photosensitive drum 10 is rotated faster than the intermediate transfer body 24. In this case, the frictional force between the photosensitive drum 10 and the intermediate transfer body 24 may cause the photosensitive drum 10 to pull the intermediate transfer body 24 and reduce the load torque of the intermediate transfer body 24. Therefore, it is desirable to acquire the load state of the intermediate transfer body 24 when the load of the transfer body cleaner 28 is small.

When toner is included in the transfer body cleaner 28, the frictional force between the intermediate transfer body 24 and the transfer body cleaner 28 is reduced, so that the load torque of the intermediate transfer body 24 is reduced. Therefore, the controller 1001 acquires the load torque (PWM signal) of the intermediate transfer body 24 in a state where the toner does not intervene in the intermediate transfer body 24 and the toner is included in the transfer body cleaner 28. In the present embodiment, there is a time in which these two conditions are met for about 2 seconds. Since the sampling time is about 300 milliseconds, it is a sufficient time to acquire the PWM signal.

In the present embodiment, the photosensitive drum 10 is set to rotate faster than the intermediate transfer body 24, but conversely, the intermediate transfer body 24 is set to rotate faster than the photosensitive drum 10. The same is true. However, it is desirable to acquire the load of the intermediate transfer body 24 at the timing when the transfer body cleaner 28 does not include the toner.

The change in the load torque of the intermediate transfer body 24 when the target speed of the photosensitive drum 10 is changed by the rotation speed adjustment process as described above will be described. FIG. 11 is an explanatory diagram of a change in load torque according to the number of sheets to be passed in the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 in this case. Even when the frictional force of the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 is large or the frictional force increases with aging, the intermediate transfer body 24 is stable without controlled divergence. Can be driven.

In this embodiment, the controller 1001 acquires the load torque as a PWM signal for controlling the drum drive motor 41 and the intermediate transfer body drive motor 42. Instead of this, the controller 1001 may acquire the load torque by the input current to the drum drive motor 41 and the intermediate transfer body drive motor 42, which are also substantially proportional to the load torque characteristics.

(Acquisition of load torque of photosensitive drum 10)
When the load torque of the photosensitive drum 10 becomes large, controlled divergence of the photosensitive drum 10 may occur. In this case, the controller 1001 also acquires the load torque of the intermediate transfer body 24 and the load torque of the photosensitive drum 10.

When acquiring the load torque of the photosensitive drum 10, if there is no toner in the photosensitive drum 10 of the target image forming unit 1200, the load torque is acquired regardless of the other image forming unit 1200. Is possible. Since the controller 1001 can acquire the toner in the time required for the photosensitive drum 10 of the target image forming unit 1200 to be free of toner, the acquisition timing can be increased.

The main factors that generate the load torque when the photosensitive drum 10 is driven are the frictional force due to the intermediate transfer body 24 and the frictional force due to the drum cleaner 26. In the present embodiment, the load torque (PWM signal) of the photosensitive drum 10 is measured in a state where the developer 1 is stopped and toner does not intervene in the photosensitive drum 10.

The load torque changes depending on whether the removed toner is included in the drum cleaner 26 or not. In order to stabilize the rotation speed of the photosensitive drum 10, the photosensitive drum 10 is rotated faster than the intermediate transfer body 24. In this case, it is desirable to acquire the load torque of the photosensitive drum 10 when the load torque (friction force) of the drum cleaner 26 is larger.

When the toner is included in the drum cleaner 26, the frictional force between the photosensitive drum 10 and the drum cleaner 26 is reduced, so that the load torque of the photosensitive drum 10 is reduced. Therefore, the controller 1001 acquires the load torque (PWM signal) of the photosensitive drum 10 in a state where the toner does not intervene in the photosensitive drum 10 and the toner is not included in the drum cleaner 26. When the load torque of the intermediate transfer body 24 is also acquired at the same time, the controller 1001 acquires the load torque just before the toner is not included in the transfer body cleaner 28.

In the present embodiment, the photosensitive drum 10 is set to rotate faster than the intermediate transfer body 24, but conversely, the intermediate transfer body 24 is set to rotate faster than the photosensitive drum 10. The same is true. However, it is desirable to acquire the load torque of the intermediate transfer body 24 at the timing when the drum cleaner 26 includes the toner.

Even when the frictional force of the contact portion between the photosensitive drum 10 and the intermediate transfer body 24 is large or the frictional force increases with aging, the photosensitive drum 10 is controlled and diverged. It can be driven stably without any problems.

(Image formation mode)
The image forming apparatus 100 can set an image forming mode for forming a color image (multicolor image) and an image forming mode for forming an image (monochromatic image) with a single black color. Since a high-speed color image forming apparatus for offices is often used in an image forming mode in which an image is formed with a single black color, the durability of the configuration for forming a black image (image forming unit 1200K) becomes high. ing. In this case, the image forming apparatus 100 is provided with a configuration for forming a color image (image forming units 1200Y, 1200M, 1200C) so as not to deteriorate. The controller 1001 (CPU 1000) is a mode control means for controlling the image forming unit 1200 by setting the image forming apparatus 100 in the image forming mode instructed by a print job or the like.

FIG. 12 is an explanatory diagram of the operation of the image forming apparatus 100 according to the image forming mode. Here, the relationship between the photosensitive drum 10 and the intermediate transfer body 24 according to the image formation mode is shown. FIG. 12A shows the relationship between the photosensitive drum 10 and the intermediate transfer body 24 in the image forming mode for forming a color image. FIG. 12B shows the relationship between the photosensitive drum 10 and the intermediate transfer body 24 in the image forming mode in which an image is formed in a single black color.

An upstream tension roller 51 is provided between the primary transfer roller 23Y and the intermediate transfer body drive roller 40. A downstream tension roller 52 is provided between the primary transfer roller 23C and the primary transfer roller 23K. The primary transfer rollers 23Y, 23M, 23C, the upstream tension roller 51, and the downstream tension roller 52 are movable in a direction away from the photosensitive drums 10Y, 10M, and 10C. The controller 1001 moves the primary transfer rollers 23Y, 23M, 23C, the upstream tension roller 51, and the downstream tension roller 52 according to each image formation mode.

In the image forming mode for forming a color image (multicolor image), the primary transfer rollers 23Y, 23M, 23C, and the upstream tension roller 51 move to the photosensitive drums 10Y, 10M, and 10C. As a result, the photosensitive drums 10Y, 10M, 10C, and 10K come into contact with the intermediate transfer body 24. In the image formation mode for forming a black monochromatic image, the primary transfer rollers 23Y, 23M, 23C, and the upstream tension roller 51 are separated from the photosensitive drums 10Y, 10M, and 10C, and the downstream tension roller 52 is the photosensitive drum 10. Move to the side. As a result, the photosensitive drum 10K comes into contact with the intermediate transfer body 24, and the photosensitive drums 10Y, 10M, and 10C are separated from the intermediate transfer body 24.

In the case of the image formation mode for forming a black monochromatic image (monochromatic image) (FIG. 12B), the holding force between the photosensitive drum 10K and the primary transfer roller 23K is secondary depending on the type of sheet forming the image. The effect of transfer shock may appear in the image. For example, if the basis weight of the sheet is ^{less than 150 [g / m 2} ], the controller 1001 has the photosensitive drums 10Y, 10M, and 10C separated from the intermediate transfer body 24 as shown in FIG. 12 (b). Form a black monochromatic image. When the basis weight of the sheet is 150 [g / m ² ] or more, the controller 1001 has the photosensitive drums 10Y, 10M, 10C and the primary transfer roller 23Y, as shown in FIG. 12A, regardless of the image formation mode. , 23M, 23C sandwich the intermediate transfer body 24. At this time, the photosensitive drums 10Y, 10M, and 10C rotate idle. That is, the rotation of the developer carrier 8 of the developers 1Y, 1M, and 1C is stopped.

Therefore, toner is not supplied to the photosensitive drums 10Y, 10M, and 10C, and the frictional force between the photosensitive drums 10Y, 10M, and 10C and the intermediate transfer body 24 increases. Since the drum cleaners 26Y, 26M, 26C do not include toner, the frictional force between the drum cleaners 26Y, 26M, 26C and the photosensitive drums 10Y, 10M, 10C also increases. Therefore, there is a possibility that controlled divergence may occur in any of the photosensitive drums 10Y, 10M, 10C and the intermediate transfer body 24.

In order to avoid this, the controller 1001 monitors the PWM signal of the intermediate transfer body 24 so that the load torque does not become a value at which control divergence may occur, as shown in the flowchart shown in FIG. The controller 1001 changes the target speed of the rotational speeds of the photosensitive drums 10Y, 10M, and 10C when the load torque exceeds a threshold value at which there is a possibility of divergence. The controller 1001 acquires the load characteristics when the toner is not present in the photosensitive drums 10Y, 10M, and 10C in advance, and based on this, the rotation of the photosensitive drum 10 in the image forming mode of forming a black monochromatic image. Determine the target speed for speed. At this time, the rotation speed of the photosensitive drum 10K for forming the black image is not changed. When only the specific photosensitive drum 10K forms an image in this way, the rotation speeds of the other photosensitive drums 10Y, 10M, and 10C can be changed to change the rotation speeds of the other photosensitive drums 10Y, 10M, 10C, and the intermediate transfer body 24. Prevents control divergence.

An image forming mode in which the image forming apparatus 100 forms a black monochromatic image in a state where the photosensitive drums 10Y, 10M, 10C, and 10K are in contact with the intermediate transfer body 24 belt will be described with reference to the flowchart of FIG. When forming a black monochrome image, the CPU 1000 reads a program stored in a memory (not shown) and executes the process of the flowchart of FIG.

First, the CPU 1000 sets the image forming mode of the image forming apparatus 100 to the black monochromatic image forming mode (S21). In the process of S21, the CPU 1000 sets the target speeds of the photosensitive drums 10Y, 10M, 10C, and 10K in the speed control units 1300Y, 1300M, 1300C, and 1300K, and sets the target speed of the intermediate transfer body 24 in the speed control unit 1400. Set. Then, the CPU 1000 causes the image forming unit 1200K to form a black monochromatic image based on the image data (S22). After completing the formation of the black image based on the image data, the CPU 1000 causes the image forming unit 1200K to stop the rotation of the developer carrier 8 (S23), waits for a predetermined time (S24), and then waits for a predetermined time (S24). The PWM signal value of 42 is acquired (S25). In the process of S25, the CPU 1000 acquires the PWM signal transferred from the output torque detection unit 45B. The output torque detection unit 45B inputs a PWM signal representing the load torque of the intermediate transfer body drive motor 42 to the CPU 1000 as a PWM signal value of the intermediate transfer body drive motor 42. This PWM signal value is stored in the memory (S26).

Next, the CPU 1000 determines whether or not the PWM signal value is larger than the threshold value (S27). Here, when the peripheral speed of the intermediate transfer body 24 changes depending on the rotation speed of the photosensitive drums 10Y, 10M, 10C, and 10K, the load torque of the intermediate transfer body drive motor 42 gradually decreases. That is, the PWM signal value detected by the output torque detection unit 45B decreases. In the process of S27, the CPU 1000 compares the PWM signal value with the threshold value, and if the PWM signal value is smaller than the threshold value, it is determined that the load torque of the intermediate transfer body drive motor 42 is gradually decreasing.

If the PWM signal value is smaller than the threshold value in the process of S27, the CPU 1000 reduces the rotation speed of the photosensitive drums 10Y, 10M, and 10C in order to reduce the load on the intermediate transfer body 24 (S28). In the process of S28, the CPU 1000 changes the setting of the target speed in the speed control units 1300Y, 1300M, and 1300C so that the rotation speeds of the photosensitive drums 10Y, 10M, and 10C are reduced by a predetermined value. Then, the CPU 1000 determines whether or not the image data of the color image has been transferred (S29). If the image data of the color image is not input, the CPU 1000 shifts to the process of S22.

Further, in the process of S27, if the PWM signal value is equal to or higher than the threshold value, the CPU 1000 shifts to the process of S29 without changing the rotation speeds of the photosensitive drums 10Y, 10M, and 10C. In the process of S29, when the image data of the color image is input, the CPU 1000 determines whether or not the target speeds of the photosensitive drums 10Y, 10M, and 10C have been changed. That is, in the process of S28, it is determined whether or not the target speed of the rotation speed of the photosensitive drums 10Y, 10M, and 10C is changed. In order to form a color image when the target speed is not changed, the CPU 1000 sets the image forming mode of the image forming apparatus 100 to the color image forming mode.

On the other hand, in the process of S28, when the target speed of the rotation speeds of the photosensitive drums 10Y, 10M, and 10C is changed, the CPU 1000 adjusts the writing position (S31). It is desirable that the controller 1001 keeps the target speed of the rotation speeds of the photosensitive drums 10Y, 10M, and 10C as they are when shifting to the image forming mode for forming a color image. This is because the frictional force between the drum and the belt is maintained in an increased state even when the color image formation mode is entered. In this case, the rotation speeds of the photosensitive drums 10Y, 10M, and 10C are different from the rotation speeds of the photosensitive drums 10K. In order to correct this, the controller 1001 adjusts the color resist as described above, and changes the writing position of the electrostatic latent image to the photosensitive drum 10 by the exposure device 22. As a result, the deviation of the formation position of the toner image due to the deviation of the rotation speed is corrected.

As described above, the image forming apparatus 100 can appropriately set the optimum target speed even when the rotation speed of the photosensitive drum 10 is changed by the processing according to the image forming mode. The photosensitive drum 10 and the intermediate transfer body 24 are stably driven without controlled divergence regardless of the frictional force between the photosensitive drum 10 and the intermediate transfer body 24.

Claims (4)

It includes a first photosensitive member on which an electrostatic latent image is formed, and a first developer carrying member rotates while carrying a black developer, the black electrostatic latent image on the first photoconductor The first image forming means for developing with the developer of
The first motor that rotates the first photoconductor and
And a second photosensitive member on which an electrostatic latent image is formed, and a second developer carrying member that rotates carrying the color developer, the color of the electrostatic latent image on said second photosensitive body A second image forming means for developing with the developer of
A second motor that rotates the second photoconductor and
An intermediate transfer body to which the black image developed on the first photoconductor and the color image developed on the second photoconductor are transferred, and
A third motor for rotating driven the intermediate transfer member,
A transfer unit that transfers the image transferred to prior Symbol intermediate transfer member to a sheet,
The first state in which the first photoconductor and the intermediate transfer body are in contact with each other and the second photoconductor and the intermediate transfer body are in contact with each other, and the first photoconductor and the intermediate transfer body are in contact with each other. A contact separating means for controlling the positional relationship between the second photoconductor and the intermediate transfer body in the second state in which the second photoconductor and the intermediate transfer body are separated from each other.
Before SL has a that control means controls the rotational speed of the second motor and the rotation speed of the first motor, and
When a black monochromatic image is formed on a sheet, the contact separation means controls the positional relationship based on the type of the sheet.
The control means said that when a black monochromatic image is formed on the sheet in the first state, the rotation of the first developer carrier is stopped and the intermediate transfer body is rotating. It is characterized in that information on the load of the second motor is acquired and whether or not to change the rotation speed of the second motor is controlled based on the information.
Image forming device. The contact separation means is characterized in that when the sheet on which a black monochromatic image is formed is a sheet having a basis weight larger than a predetermined basis weight, the positional relationship is controlled to the first state.
The image forming apparatus according to claim 1. The information is the duty ratio of the PWM signal supplied to the third motor.
Wherein if the duty ratio of the PWM signal is less than the threshold value, and wherein the Rukoto reduces the rotational speed of the second motor,
The image forming apparatus according to claim 1 or 2. A detection means for detecting test images of different colors formed on the intermediate transfer body, and
Further having an adjusting means for adjusting the relative positional relationship of the images of different colors based on the detection result of the detecting means.
The adjusting means is the first when a superposed image in which a black image and a color image are superimposed is formed on the sheet after the rotation speed of the second motor is changed based on the information by the control means. The test image is formed by the image forming means 1 and the second image forming means, the detection means detects the test image, and the black image formed by the first image forming means and the first image are formed. It is characterized in that the relative positional relationship with the color image formed by the image forming means of 2 is adjusted based on the detection result of the detecting means .
The image forming apparatus according to any one of claims 1 to 3.