Image forming device

Abstract

To solve the problem in which: in place of a technique to superimpose a torque load, a method for increasing the inertia of a drive train is proposed; however, the method reduces speed control responsiveness.SOLUTION: An image forming apparatus can be provided which can apply optimal brake torque at a predetermined timing in an image forming operation, and can ensure responsiveness required for speed control, extend its life, and reduce unnecessary power consumption.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus having an image carrier on which a toner image is formed. [Background technology]

[0002] In an electrophotographic image forming apparatus, in order to stabilize image quality (suppress color registration and uneven density), speed control is performed to set the angular speed or peripheral speed of the photoconductor and transfer body, which are image carriers, to a predetermined target value.

[0003] Among image carriers, the transfer body in particular comes into contact with various components (rollers, recording materials, etc.), which means there are many factors that cause load fluctuations. These load fluctuations destabilize the speed control, which in turn degrades image quality.

[0004] In order to solve the above problems, a configuration has been proposed as prior art (1) in which a torque limiter is connected to the drive shaft to apply a predetermined torque through mechanical friction in order to suppress load fluctuations (Patent Document 1), and a method has been proposed as prior art (2) in which the torque of the image carrier is detected and a contact member is controlled based on the detection results (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-215774 A [Patent Document 2] JP 2012-255912 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the torque limiter proposed in the prior art (1) above generates torque through mechanical wear, making it difficult to extend its lifespan. In addition, while the recording paper is being transported, unnecessary torque is applied to the rotational operation, which requires additional power consumption and leads to an increase in the size of the drive motor.

[0007] Even in the case of the prior art (2), the connection of the brake torque generating means using the vibration mechanism requires securing installation space, which results in an increase in cost due to the larger size of the device.

[0008] As an alternative to the above-mentioned method of superimposing torque loads, a method of increasing the inertia of the drive train has been proposed, but this method has the problem of reducing speed control responsiveness.

[0009] In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of ensuring the responsiveness required for speed control, extending the life of the apparatus, and reducing unnecessary power consumption. [Means for solving the problem]

[0010] In order to solve the above problems, an image forming apparatus according to the present invention comprises: In an image forming apparatus having a photoconductor on which a toner image is formed and a transfer body onto which the toner image formed on the photoconductor is transferred, a first motor that drives a transfer body driving rotor that drives the transfer body; A second motor connected to the shaft of the transfer member driving rotor. Ta and , a current control circuit electrically connected to a coil of the second motor and configured to change a current flowing through the coil of the second motor in response to an electromotive force generated in the coil of the second motor in synchronization with the rotation of the transfer body driving rotor; A third motor that drives the photoconductor; a first speed detection means for detecting a rotation speed of the transfer body driving rotor; A second speed detection means for detecting a rotation speed of the photoconductor; A transfer rotor that comes into contact with and separates from the transfer body; a fourth motor for moving the transfer rotator relative to and away from the transfer body; a control means for controlling the speed of the first motor based on a detection result from the first speed detection means, and for controlling the speed of the third motor based on a detection result from the second speed detection means; the control means controls the current control circuit so that, in a state in which the transfer body is driven by the first motor, a current caused by the electromotive force flows through a coil of the second motor before the transfer rotating body comes into contact with the transfer body, and so that, after the transfer rotating body comes into contact with the transfer body, a current caused by the electromotive force does not flow through the coil of the second motor. It is characterized by: Effect of the Invention

[0011] According to the present invention, it is possible to provide an image forming apparatus that can ensure the responsiveness required for speed control, extend the life of the apparatus, and reduce unnecessary power consumption. [Brief description of the drawings]

[0012] [Figure 1] Overall configuration of an image forming apparatus [Diagram 2] Control block diagram of the present invention [Diagram 3] 1 is a control flow chart showing the present invention; [Figure 4] Timing chart showing the present invention [Diagram 5] Block diagram of a coil current control circuit according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a color image forming apparatus according to the present invention will be described with reference to the drawings.

[0014] Fig. 1 is a schematic cross-sectional view of a tandem type color image forming apparatus according to an embodiment of the present invention. This apparatus is configured with image forming units (100A, 100B, 100C, 100D) for each color of yellow (Y), magenta (M), cyan (C), and black (K), and in each image forming unit, photosensitive drums 101A-101D, which are image carriers, rotate in the direction of arrow R in the figure, and their surfaces are charged to a uniform potential by primary chargers 102A-102D, and laser scanning units 103A-103D, which use semiconductor lasers as light sources, irradiate them with lasers to form electrostatic latent images on the drum surfaces based on image data.

[0015] The electrostatic latent images on the photosensitive drums 101A to 101D are developed by the developing devices 104A to 104D to become toner images, and the toner images of each color are sequentially transferred to the intermediate transfer belt 107 at a primary transfer section where the primary transfer rollers 105A to 105D and the photosensitive drums 101A to 101D to which a high voltage is applied rub against each other via the intermediate transfer belt 107. The toner images of each color superimposed on the intermediate transfer belt 107 are conveyed to the secondary transfer section 108, where the four toner images are collectively transferred onto the recording material P that is fed from a paper feed conveying section 130 including a paper feed cassette and conveyed through a vertical path conveying section 131 and a registration conveying section 132. The registration conveying section 132 has a mechanism (registration correction mechanism) (not shown) that moves the recording material P to a predetermined conveying position so that the recording material P is conveyed parallel to the toner images on the intermediate transfer belt.

[0016] The secondary transfer unit 108 comprises a pressure section made up of an upper roller 108U and a lower roller 108L, and the lower roller 108L has a contact / separation mechanism (details will be described later). A high pressure is applied to the lower roller 108L for transferring the toner image onto the recording material P. The upper and lower rollers 108U and 108L which form the secondary transfer nip are driven to rotate in synchronization with the drive of the intermediate transfer belt 107. (The arrows on each roller and roller shaft connecting member indicate the rotation direction of each member.)

[0017] Reference numerals 106A to 106D denote drum cleaners that remove toner remaining on the surfaces of the photosensitive drums 101A to 101D, and reference numeral 112 denotes a belt cleaner that removes toner remaining on the intermediate transfer belt 107.

[0018] The recording material P onto which the four-color toner image has been transferred collectively in the secondary transfer section 108 is transported to a fixing device 109, where the unfixed toner image is thermally fixed by rotating bodies such as upper and lower rollers of the fixing device 109, and then the recording material P is discharged to a discharge tray 120 via a discharge conveying section 110.

[0019] Here, the intermediate transfer belt 107 is stretched around a plurality of rollers and driven by rotating a drive roller 121 serving as a transfer body driving rotor.

[0020] As shown in FIG. 1, there are various load fluctuation factors on the intermediate transfer belt 107, such as when the upper and lower rollers 108U, 108L contact and separate in the secondary transfer portion, and when a recording material enters the secondary transfer portion. These load fluctuations become unstable factors when controlling the speed of the intermediate transfer belt 107.

[0021] Therefore, it is effective to apply the present invention to the drive unit of the intermediate transfer belt 107, and the details thereof will be described below with reference to the drawings. Figure 2 is a control block diagram when the present invention is applied to the intermediate transfer belt drive unit.

[0022] 2, a control unit 200 having a CPU 250 and a memory 251 performs drive control of the present invention and also performs sequence control of the entire image forming apparatus. The memory 251 stores setting values ​​such as control parameters that the CPU 250 applies to the above-mentioned control.

[0023] The intermediate transfer belt drive roller 121 is driven by a first motor 211 via a gear 202. An encoder (speed detection means) 203 detects the rotation speed of the intermediate transfer belt drive roller 121. A CPU 250 controls the speed of the intermediate transfer belt drive roller 121 by driving the first motor 211 with a control signal: Sig_D1 based on the detection result: Sig_S1 of the encoder 203.

[0024] A second motor 212 according to the present invention is connected to the shaft of the intermediate transfer belt driving roller 121, and the coil of the motor is electrically connected to a current control circuit 230. In this embodiment, the second motor 212 will be described using a two-phase motor composed of a magnet rotor 220 and two-phase coils 221a and 221b. The motor current control circuit 230 is composed of transistors 223a and 223b that switch between energizing and de-energizing the coils 221a and 221b in response to a control signal Sig_D2 from the CPU 250, and resistors 222a and 222b that limit the current flowing through the coils 221a and 221b. When the driving roller 121 rotates, the magnet rotor 220 of the second motor 212 rotates in synchronization with the rotation, and the torque generates a current due to electromotive force in the coils 221a and 221b (arrows Sa and Sb in the figure). This current is a magnet Rotor Because the current flows in a direction that hinders the rotation of 220, it can be used as a braking torque for the rotating body, and the braking torque can be changed by changing the current value (details will be described later).

[0025] The photosensitive drums 101A to 101D are connected to gears 204A to 204D, respectively, and driven by third motors 213A to 213D, respectively. Encoders 205A to 205D detect the speeds of the photosensitive drums 101A to 101D. The CPU 250 drives the third motors 213A to 213D with a control signal: Sig_D2 based on the detection results of the encoders 205A to 205D, thereby controlling the speeds of the photosensitive drums 101A to 101D.

[0026] In addition, the lower roller 108L is configured to be raised and lowered in order to contact and separate from the upper roller 108U in the secondary transfer portion 108, and a fourth motor 214, which is the driving source thereof, is connected to a gear 212 and a driving cam 213 and synchronizes with the rotation of the driving cam 213. The contact and separation mechanism is necessary for the following reasons: first, to facilitate removal of the recording material when a jam (recording material jam) occurs in the nip portion, and second, to prevent the toner image for adjustment from being transferred to the lower roller 108L when the toner image is formed. Here, the contact position and separation position are defined as a predetermined angle set in advance from the reference phase of the cam 213 on which the HP sensor 230 is installed. During the contact and separation operation of the secondary transfer portion, the CPU 250 controls the movement amount of the first motor 201 based on the signal of the HP sensor 230.

[0027] Next, the control of the present invention executed by the control unit 200 will be described with reference to a control flowchart (FIG. 3) and a timing chart (FIG. 4). The control flowchart shown in FIG. 3 is executed by the CPU 250 in the control unit 200, and the control unit 200 operates based on the setting values ​​stored in the memory 251.

[0028] In the timing chart of FIG. 4, the first row from the top indicates (1) the speed of the photosensitive drums 101A-101, the second row indicates (2) the speed of the intermediate transfer belt, the third row indicates (3) the torque on the intermediate transfer belt drive roller shaft, the fourth row indicates (4) the nip state of the upper and lower rollers in the secondary transfer section, and the fifth row indicates the state of the coil current control of the second motor 212 that generates the brake torque of the present invention.

[0029] Next, a description will be given based on the control flow chart shown in FIG.

[0030] When the image forming apparatus is in a standby state, the CPU 250 of the control unit 200 keeps the lower roller 108L in the separated position, and keeps the transistors 223a and 223b off (coil open state) so that no current flows through the coils 221a and 221b of the second motor 212 for generating braking torque (a state in which no braking torque is generated) (S300).

[0031] When an operation request for an image forming job is made (S301), first, in order to start the rotational operation of the photosensitive drums 101A to 101D and the intermediate transfer belt 107 of the image forming unit, the acceleration of the first motor 211 and the third motor 213A to 213D is started (S302, timing t1 in FIG. 4). The first motor 211 and the third motor 213 are accelerated to preset target speeds: VtDRM and VtITB. At this time, the target speed VtITB of the intermediate transfer belt 107 and the target speed VtDRM of the photosensitive drums 101A to 101D are set to have a predetermined peripheral speed difference. This is to prevent vibration at the nip portions where the photosensitive drums 101A to 101D and the intermediate transfer belt 107 come into contact with each other. In the present invention, the target speed VtDRM of the photosensitive drums 101A to 101D is set to be faster than the target speed of the intermediate transfer belt drive roller 121 (VtDRM>VtITB).

[0032] Then, after the photosensitive drums 101A-101D and the intermediate transfer belt 107 reach the target speeds VtDRM and VtITB, that is, after the acceleration is completed (S303, timing t2 in FIG. 4), the control signal Sig_D2 turns on the transistors 223a and 223b in the motor current control circuit 230 to energize the coils 221a and 221b of the second motor 212, thereby applying a brake torque to the intermediate transfer belt drive roller 121 (S304). The speed VtDRM of the photosensitive drums 101A-101D is set so that the speed VtITB of the intermediate transfer belt drive roller 121 is set to be high, and the lower secondary transfer roller 108L is in a separated state, so that the load torque on the intermediate transfer belt drive roller 121 is in a light load state. If the speed is controlled in this state, the rotation operation is likely to become unstable. Therefore, by implementing the present invention, it is possible to prevent a light load state of the intermediate transfer belt drive roller 121 and stabilize the speed control. Also, the resistance value is set in advance so that a current value at which an appropriate brake torque can be applied is obtained.

[0033] Next, the CPU 250 starts driving the fourth motor 214 to move the secondary transfer lower roller 108L to a position where it contacts the upper roller 108U as preparation for starting the image forming operation (S305, timing t3 in FIG. 4). Then, if the cam phase detection signal: Sig_S4 from the HP sensor 230 is detected within a predetermined time, the motor is moved a preset amount and then stopped (S307). If it is not detected within the predetermined time, the user of the image forming apparatus is notified of the contact operation error (S320).

[0034] After the contact operation is normally completed, the control signal: Sig_D2 turns off the coil current of the second motor 212, thereby turning off the application of the brake torque to the intermediate transfer belt drive roller 107. When the lower secondary transfer roller 10L is brought into contact, the roller is driven by the intermediate transfer belt 107, so the torque of the intermediate transfer belt drive roller 121 is increased. Therefore, by opening the coils 221a and 221b at this timing and turning off the brake torque, the power required for the drive motor 211 can be reduced.

[0035] In this state, the control signals Sig_D1, Sig_D2 are changed to maintain the intermediate transfer belt drive roller 121 and the photosensitive drums 101A-101D at the target speeds VtDRM, VtITB, thereby controlling the speeds of the first motor 211 and the third motor 213, and performing image formation operation (S309).

[0036] Then, when there is a stop request such as the end of the image forming operation (S310), the coil current of the second motor 212 is turned on by the control signal: Sig_D2 (S311), and the first motor 211 and the third motor 213 start to decelerate (S312, timing t4 in FIG. 4) and stop (S313, timing t5 in FIG. 4) in a state where a brake torque is generated. This prevents the load from becoming lighter due to the deceleration torque, and also enables vibration suppression when stopped. After that, the fourth motor 214 is driven to move the lower secondary transfer roller 108L to the separation position (S314, timing t6 in FIG. 4), and if the detection signal: Sig_S4 from the HP sensor 230 is detected within a predetermined time, the operation is terminated normally. If it is not detected within the predetermined time, the user of the image forming apparatus is notified of the contact operation error (S320).

[0037] In this embodiment, in the current control circuit 230, resistors 222a, 224b and transistors 223a, 223b are connected one each to the coils 221a, 221b of the second motor 212. However, as shown in FIG. 5, by connecting transistors 223a, 225a and resistors 222a, 222b of different values ​​to the coil 221a, and connecting transistors 223b, 225b and resistors 222b, 224b of different values ​​to the coil 221b, it is possible to change (switch) the magnitude of the brake torque to be applied.

[0038] Therefore, for example, it is possible to set the brake torque applied before the secondary transfer roller 108L comes into contact with the roller 108L and the brake torque applied before the deceleration operation starts to have different magnitudes.

[0039] As described above, according to the present invention, it is possible to provide an image forming apparatus that can apply an optimal brake torque at a predetermined timing during an image formation operation, thereby ensuring the responsiveness required for speed control, extending the life of the apparatus, and reducing unnecessary power consumption. [Explanation of symbols]

[0040] 107 Intermediate transfer belt 121 Intermediate transfer belt drive roller 203 Encoder 205 Encoder 211 Drive motor 212 Second Motor 213 3rd Motor 230 Motor current control circuit 250 CPU

Claims

1. In an image forming apparatus having a photoconductor on which a toner image is formed and a transfer body onto which the toner image formed on the photoconductor is transferred, a first motor that drives a transfer body driving rotor that drives the transfer body; a second motor connected to the shaft of the transfer body driving rotor; a current control circuit electrically connected to a coil of the second motor, and changing a current flowing through the coil of the second motor in response to an electromotive force generated in the coil of the second motor in synchronization with the rotation of the transfer body driving rotor; A third motor that drives the photoconductor; a first speed detection means for detecting a rotation speed of the transfer body driving rotor; a second speed detection means for detecting a rotation speed of the photoconductor; A transfer rotor that comes into contact with and separates from the transfer body; a fourth motor for moving the transfer rotor relative to and away from the transfer body; a control means for controlling the speed of the first motor based on a detection result from the first speed detection means, and for controlling the speed of the third motor based on a detection result from the second speed detection means, The control means controls the current control circuit so that, when the transfer body is driven by the first motor, a current caused by the electromotive force flows through the coil of the second motor before the transfer rotating body contacts the transfer body, and so that a current caused by the electromotive force does not flow through the coil of the second motor after the transfer rotating body contacts the transfer body.

2. The image forming apparatus described in Claim 1, characterized in that the control means controls the current generated by the electromotive force to flow through the coil of the second motor during the deceleration period before the transfer body drive rotor and the photosensitive body stop, and controls the current control circuit so that no current flows through the coil of the second motor when the transfer body drive rotor and the photosensitive body stop.

3. the current control circuit has a switch element connected to the coil, 3. The image forming apparatus according to claim 1, wherein the control means prevents current from flowing through the coil by turning off the switch element.

4. the current control circuit includes a resistor connected to the coil and a switch element that changes a resistance value of the resistor, 3. The image forming apparatus according to claim 2, wherein the control means controls the current control circuit so that a value of a current flowing through the coil of the second motor due to the electromotive force before the transfer rotating body contacts the transfer body is different from a value of a current flowing through the coil of the second motor due to the electromotive force during the deceleration period.

Images