JP2019211608A - Image forming device - Google Patents

Abstract

To provide an image forming device with which it is possible to appropriately set the responsivity of a motor that rotates a rotary polygon mirror when a control unit sends a control signal in correspondence to the target revolution speed of the motor.SOLUTION: An image forming device A comprises: a control unit 50 for comparing the cycle of an FG signal with a cycle corresponding to the target revolution speed of a drive motor 106 and sending a control signal to a motor driver 202 so that the cycle of the FG signal equals the cycle corresponding to the target revolution speed of the drive motor and controlling the value of a drive current, thereby controlling the revolution speed of the drive motor 106; a gain setting circuit 204 for setting the responsivity of the drive motor 106 when the control unit 50 sends a control signal, the gain setting circuit 204 capable of setting a plurality of different responsivities; and the control unit 50 for switching the responsivity set by the gain setting circuit 204 in accordance with the target revolution speed of the drive motor 106.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  In an electrophotographic image forming apparatus, a light beam is deflected by a deflector having a polygon mirror (rotating polygon mirror) and a drive motor (motor), and the surface of the photoconductor is scanned by the deflected light beam to thereby perform photosensitivity. An optical scanning device that forms an electrostatic latent image on the body surface is mounted.

  In the rotational speed control of the drive motor, the control unit transmits an acceleration / deceleration signal that is a control signal according to the target speed, and controls the value of the drive current supplied from the motor driver to the drive motor. Control the rotation speed. Even when an acceleration / deceleration signal is transmitted from the control unit, the responsiveness of the drive motor varies depending on the configuration of the electric circuit that transmits the control signal. Here, in the configuration described in Patent Document 1, the drive motor is driven with a single circuit configuration regardless of the target rotational speed of the drive motor.

JP 2012-037578 A

  When setting the drive motor's rotational speed control, set the responsiveness according to the high-speed rotation when the target rotational speed of the drive motor is high, and set the responsiveness according to the low-speed rotation when the speed is low. It is desirable to set. This is because when the rotational speed of the drive motor is controlled based on the rotation detection signal output from the hall element, jitter is worsened if low-speed rotation is performed using a response setting that matches the target rotational speed. It is because it connects.

  Also, in the image forming apparatus, a configuration is known in which the target rotation speed of the drive motor is changed in accordance with changes in image forming conditions such as a change in the paper type or basis weight of the recording material. In the case of such a configuration, in the configuration described in Patent Document 1, the drive motor is driven with a single circuit configuration, so that it is difficult to set appropriate responsiveness according to the target rotational speed of the drive motor.

  Therefore, the present invention has been made in view of such a situation, and appropriately sets the responsiveness of the motor when the control unit transmits a control signal according to the target rotational speed of the motor that rotates the rotary polygon mirror. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes a light source, a photoconductor, and a rotating multi-plane that deflects a light beam emitted from the light source and scans the surface of the photoconductor. A mirror, a motor for rotating the rotary polygon mirror, a driving means for supplying a driving current to the motor to drive the motor, a period of a cycle corresponding to the rotation speed of the motor, detecting the rotation of the motor The rotation detection means for outputting a signal is compared with the period of the periodic signal and the period corresponding to the target rotational speed of the motor so that the period of the periodic signal becomes a period corresponding to the target rotational speed of the motor. In addition, a control signal is transmitted to the drive means to control the value of the drive current, thereby controlling a rotation speed of the motor, and the motor when the control unit transmits the control signal. Set responsiveness A setting circuit capable of setting a plurality of different responsivenesses, and switching means for switching the responsiveness set by the setting circuit in accordance with a target rotational speed of the motor. To do.

  According to the present invention, in the image forming apparatus, it is possible to appropriately set the responsiveness of the motor when the control unit transmits the control signal according to the target rotational speed of the motor that rotates the rotary polygon mirror.

1 is a schematic cross-sectional view of an image forming apparatus. It is a schematic diagram of an optical scanning device. It is a section schematic diagram of a deflector. It is a figure explaining the relationship between rotation of a drive motor, and the signal output from a Hall element. 1 is a block diagram illustrating a part of a system configuration of an image forming apparatus. It is the block diagram and circuit diagram which show the conventional control structure of a drive motor. It is a graph which shows the relationship between an acceleration signal, a deceleration signal, and the electric potential notified to a motor driver. It is the block diagram and circuit diagram which show the control structure of this embodiment of a drive motor. It is a table | surface which shows ON / OFF of the transistor of a gain setting circuit, and the relationship between an electrical resistance and a capacitor | condenser. It is a gain setting table according to the target rotation speed of a drive motor. It is a graph which shows the relationship between the rotation speed of a drive motor, and time after a drive motor starts a drive until it stabilizes at target rotation speed. It is a graph which shows the relationship between the rotation speed of a drive motor, and time after a drive motor starts a drive until it stabilizes at target rotation speed.

(First embodiment)
<Image forming apparatus>
The overall configuration of the image forming apparatus according to the first embodiment of the present invention will be described below together with the operation during image formation with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the component parts described below are not intended to limit the scope of the present invention only to those unless otherwise specified.

  The image forming apparatus A according to the present embodiment transfers a toner of four colors, yellow Y, magenta M, cyan C, and black K, to an intermediate transfer belt, and then transfers the image to a sheet to form an image. It is. In the following description, although the members using the toners of the respective colors are given subscripts Y, M, C, and K, the configuration and operation of each member are different except that the color of the toner used is different. Since they are substantially the same, subscripts are omitted as appropriate unless distinction is required.

  As shown in FIG. 1, the image forming apparatus A includes an image forming unit that transfers a toner image to a sheet to form an image, a sheet feeding unit that supplies the sheet toward the image forming unit, and a toner image on the sheet. A fixing unit for fixing the toner.

  The image forming unit includes a photosensitive drum 2 (2Y, 2M, 2C, 2K), a charger 3 (3Y, 3M, 3C, 3K) for charging the surface of the photosensitive drum 2, and a developing device 7 (7Y, 7M, 7C, 7K). Further, a primary transfer blade 6 (6Y, 6M, 6C, 6K), a cleaning blade 4 (4Y, 4M, 4C, 4K), an optical scanning device 5 (5Y, 5M, 5C, 5K), and an intermediate transfer unit 60 are provided.

  The intermediate transfer unit 60 includes an intermediate transfer belt 8, a secondary transfer roller 22, a secondary transfer counter roller 21, belt driving rollers 10 and 11, and a belt cleaner 12. The intermediate transfer belt 8 is an endless belt stretched around the belt drive rollers 10 and 11, and moves around in the direction of the arrow K 1 as the belt drive rollers 10 and 11 rotate.

  Next, an image forming operation will be described. First, when the control unit 50 shown in FIG. 5 receives the image forming job signal, the sheet S stacked and stored in the sheet stacking unit 17 by the feeding roller 18, the first transport roller 61, and the second transport roller 20 is transferred to the registration roller 16. Sent out. Next, the sheet S is sent to a secondary transfer portion formed by the secondary transfer roller 22 and the secondary transfer counter roller 21 after the timing is corrected by the registration roller 16.

  On the other hand, in the image forming unit, the surface of the photosensitive drum 2 is first charged by the charger 3. Thereafter, the optical scanning device 5 irradiates the surface of the photosensitive drum 2 of each color with a laser light beam L (LY, LM, LC, LK) in accordance with an image signal transmitted from an external device (not shown). 2 An electrostatic latent image is formed on the surface.

  Thereafter, toner of each color is attached to the electrostatic latent image formed on the surface of the photosensitive drum 2 by the developing device 7 to form a toner image on the surface of the photosensitive drum 2. The toner image formed on the surface of the photosensitive drum 2 is primarily transferred to the intermediate transfer belt 8 by applying a primary transfer bias to the primary transfer blade 6. As a result, a full-color toner image is formed on the surface of the intermediate transfer belt 8.

  Thereafter, the intermediate transfer belt 8 moves in the direction of the arrow K1, and the toner image is sent to the secondary transfer portion. Then, a secondary transfer bias is applied to the secondary transfer roller 22 in the secondary transfer portion, whereby the toner image on the intermediate transfer belt 8 is transferred to the sheet S.

  Next, the sheet S to which the toner image has been transferred is subjected to heating and pressure processing in the fixing device 26, whereby the toner image on the sheet S is fixed to the sheet S. Thereafter, the sheet S on which the toner image is fixed is discharged to the discharge tray 25 by the discharge roller 24.

  The toner remaining on the photosensitive drum 2 after the primary transfer is scraped off by the cleaning blade 4 and removed. Similarly, the toner remaining on the intermediate transfer belt 8 after the secondary transfer is scraped off and removed by the belt cleaner 12.

<Optical scanning device>
Next, the configuration of the optical scanning device 5 will be described.

  FIG. 2 is a schematic diagram of the optical scanning device 5. As shown in FIG. 2, the optical scanning device 5 includes two laser diodes (hereinafter referred to as LDs) 101 (101a and 101b) as a light source that emits a laser light beam L modulated in accordance with an image signal, and a collimator lens 102. And a cylindrical lens 104. Further, it has a deflector 110 having an aperture stop 103, a polygon mirror 105 (rotating polygon mirror) and a drive motor 106 (motor), a toric lens 107, a diffractive optical element 108, a mirror 113, and a BD sensor 114. In FIG. 2, one of the two LDs 101 is omitted.

  The toric lens 107 is a lens having an fθ characteristic, and has different refractive indexes in the main scanning direction and the sub-scanning direction. Both the front and back lens surfaces of the toric lens 107 in the main scanning direction are aspherical.

  The diffractive optical element 108 is an optical component having an fθ characteristic, and is a long diffractive portion having different magnifications in the main scanning direction and the sub-scanning direction.

  The BD sensor 114 (reference signal output means) detects the laser light beam L emitted from the LD 101 and outputs a BD signal. The BD signal is used as a reference signal serving as a reference for determining an image writing timing to the photosensitive drum 2 in the main scanning direction and a scanning cycle of the photosensitive drum 2.

  Regarding the operation at the time of image formation, first, the laser light beam L emitted from the LD 101 is converted into a parallel light beam by the collimator lens 102, and then the light beam width is limited through the aperture stop 103. Is incident on. The cylindrical lens 104 has a predetermined refractive power only in the sub-scanning direction, and forms the laser light beam L on the reflection surface 105a of the polygon mirror 105 as an elliptical image that is long in the main scanning direction.

  Next, the laser light beam L is deflected while being reflected by the reflecting surface 105 a as the polygon mirror 105 is rotated by the drive motor 106. The laser beam L deflected by the polygon mirror 105 first enters the BD sensor 114 via the mirror 113. At this time, the image writing timing to the photosensitive drum 2 is determined based on the BD signal output from the BD sensor 114. Next, the laser light beam L deflected by the polygon mirror 105 passes through the toric lens 107 and the diffractive optical element 108 and forms a spot image on the surface of the photosensitive drum 2.

  In this way, the optical scanning device 5 scans the photosensitive drum 2 with the laser light beam L to form an electrostatic latent image. Specifically, the angle at which the laser beam L is deflected is changed by the rotation of the polygon mirror 105, and the spot image formed by the laser beam L is scanned in the main scanning direction. The spot image formed by the laser light beam L is scanned in the sub-scanning direction by rotating the photosensitive drum 2.

<Deflector>
Next, the configuration of the deflector 110 will be described.

  FIG. 3 is a schematic cross-sectional view of the deflector 110. As shown in FIG. 3, the drive motor 106 of the deflector 110 includes a rotor 120 having a permanent magnet 212, a stator 215 having a stator coil 215a and a stator core (not shown).

  When driving the deflector 110, first, a drive current is supplied from the motor driver 202 mounted on the substrate 213 to the stator coil 215a. As a result, an electromagnetic force is generated between the stator coil 215a and the permanent magnet 212, and the rotor 120 rotates about the shaft 210 as a rotation axis. As the rotor 120 rotates in this way, the polygon mirror 105 and the shaft 210 rotate together with the rotor 120. That is, the motor driver 202 (driving means) drives the driving motor 106 by supplying a driving current to the stator coil 215a.

  A Hall element 211 is mounted on the substrate 213. The hall element 211 (rotation detection means) detects the rotation of the drive motor 106 and outputs a periodic signal having a period corresponding to the rotation speed of the drive motor 106.

  FIG. 4A is a schematic diagram of the drive motor 106. As shown in FIG. 4A, magnetic poles S1 to S4 and N1 to N4 are arranged on the permanent magnet 212 of the drive motor 106 at substantially equal intervals in the rotation direction. The drive motor 106 is a three-phase motor having U-phase, V-phase, and W-phase coils as the stator coil 215a.

  FIG. 4B is a diagram for explaining the relationship between the rotation of the drive motor 106 and the signal output from the Hall element 211. As shown in FIG. 4B, when the drive motor 106 rotates, the magnetic poles in the vicinity of the Hall element 211 are sequentially switched. At this time, the Hall element 211 outputs a signal corresponding to the magnitude of the magnetic flux density of each magnetic pole. This signal is digitally processed and input to the control unit 50 as an FG signal which is a pulse signal.

<Control unit>
Next, an outline of the system configuration of the image forming apparatus A will be described.

  FIG. 5 is a block diagram illustrating a part of the system configuration of the image forming apparatus A. As shown in FIG. 5, the image forming apparatus A includes a control unit 50 including a CPU 51, a ROM 52, and a RAM 53. The control unit 50 is connected to an EEPROM 140, a laser driver 130, a motor driver 202, a BD sensor 114, a thermistor 200, and the like.

  The laser driver 130 supplies drive current to the LD 101 and controls the amount of laser light beam L emitted from the LD 101. Here, when the light amount control of the laser light beam L is performed, the laser driver 130 controls the drive current that flows through the LD 101 so that the output of a photodiode (not shown) attached to the LD 101 becomes a predetermined value. This is called APC control (APC: Auto Power Control). The APC control cannot be performed at the timing when the laser light beam L scans the image area on the photosensitive drum 2, and is therefore performed at the timing of the non-image area.

  The control unit 50 transmits to the laser driver 130 a light amount control signal for setting the light amount of the laser light beam L, image data for drawing an image, a control signal for switching the control mode, and the like. Since the laser driver 130 drives the two LDs 101, the control signal is composed of 3 bits of CTRL0, CTRL1, and CTRL3.

  Note that the number of control signals is determined by the number of operation modes of the laser driver 130. The operation modes are the APC mode, the OFF mode, the image mode, and the like of the LD 101a and LD 101b. Note that when the number of laser light beams L increases in accordance with the number of LDs 101, the number of APC modes also increases, so the number of control signals also increases.

  The motor driver 202 supplies a drive current to the drive motor 106 based on the motor control signal transmitted from the control unit 50 to rotate the deflector 110. The hall element 211 detects the rotation of the drive motor 106 and transmits an FG signal to the control unit 50.

  The control unit 50 compares the FG signal with a cycle corresponding to the target rotational speed of the drive motor 106, and sends a motor to the motor driver 202 so that the cycle of the FG signal becomes a cycle corresponding to the target rotational speed of the drive motor 106. Transmit control signals. As a result, the control unit 50 controls the drive motor 106 so as to achieve the target rotation speed. The control unit 50 can detect the rotational speed of the drive motor 106 by counting the FG signal with a counter (not shown) inside the CPU 51.

  Here, in the present embodiment, the control unit 50 divides the FG signal, and transmits the control signal to the motor driver 202 so that the divided FG signal has a cycle corresponding to the target rotational speed of the drive motor 106. . Specifically, as shown in FIG. 4B, the control unit 50 divides the FG signal by 8, and the FG signal detected from the same magnetic pole S1 corresponds to the target rotational speed of the drive motor 106. The control signal is transmitted so as to have a cycle to be performed. As a result, the drive motor 106 can be controlled in one rotation cycle, so that the accuracy of speed control of the drive motor 106 can be improved even when the magnetic pole arrangement intervals are slightly non-uniform.

  The thermistor 200 (temperature detection means) is arranged inside the image forming apparatus A, detects the temperature of the environment, and outputs it to the control unit 50. The EEPROM 140 stores adjustment values unique to the optical scanning device 5 such as the light amount, the writing position for each surface of the polygon mirror 105, and the magnification for each surface.

<Conventional drive motor acceleration / deceleration control>
Next, conventional acceleration / deceleration control of the drive motor 106 will be described.

  FIG. 6 is a block diagram (FIG. 6A) and a circuit diagram (FIG. 6B) showing a conventional control configuration of the drive motor 106. In FIG. As shown in FIG. 6, the control unit 50 monitors the rotation state of the drive motor 106 with the FG signal, and either the acceleration signal ACC or the deceleration signal DEC is used as a motor control signal so that the drive motor 106 reaches the target rotation speed. Is output.

  The acceleration signal ACC and the deceleration signal DEC are received by the charge pump circuit 201 and notified to the motor driver 202 as a potential V1 indicating a voltage level via the gain setting circuit 203. The motor driver 202 reflects the notified potential V <b> 1 on the drive current to the drive motor 106.

  The charge pump circuit 201 is connected to the control unit 50 and the gain setting circuit 203, includes a transistor Tr1 and a transistor Tr2, and is grounded on the emitter side of the transistor Tr2. The gain setting circuit 203 is connected to the charge pump circuit 201 and the motor driver 202, and includes an electric resistance R1 and a capacitor C1 and is grounded.

  When the acceleration signal ACC is input to the charge pump circuit 201, only the transistor Tr1 is turned on, a current flows through the path L1, charges are charged in the capacitor C1, and the potential V1 rises. On the other hand, when the deceleration signal DEC is input to the charge pump circuit 201, only the transistor Tr2 is turned on, the charge charged in the capacitor C1 is released through the path L2, and the potential V1 drops. The potential V1 is notified to the motor driver 202 and converted into a drive current of the drive motor 106.

  FIG. 7 is a graph showing the relationship between the acceleration signal ACC, the deceleration signal DEC output from the control unit 50, and the potential V1 notified to the motor driver 202. Here, the graph shown in FIG. 7B is a graph in the case where the electrical resistance R1 of the gain setting circuit 203 is smaller than the graph shown in FIG.

  As shown in FIG. 7, when the acceleration signal ACC is input to the charge pump circuit 201, the potential V1 increases, and when the deceleration signal DEC is input to the charge pump circuit 201, the potential V1 decreases. Further, when the electric resistance R1 of the gain setting circuit 203 is small, a larger amount of current flows with respect to the input of the acceleration signal ACC to the charge pump circuit 201 than when the electric resistance R1 is large, and the potential V1 increases rapidly. Similarly, when the deceleration signal DEC is input, the potential V1 drops rapidly.

  That is, when the electric resistance R1 in the gain setting circuit 203 is large, the response of the drive motor 106 when a control signal is input from the control unit 50 is lowered, and when the electric resistance R1 is small, the response is high. This can also be seen from the fact that the time constant τ in the RC circuit is τ = RC. Note that the potential V1 rises by the amount determined by the capacitor C1 included in the gain setting circuit 203. That is, when the capacitor C1 is charged, the potential V1 does not change even when the acceleration signal ACC is input.

  FIG. 11 is a graph showing the relationship between the rotational speed of the drive motor 106 and the time from when the drive motor 106 starts driving until it stabilizes at the target rotational speed. Here, the graph shown in FIG. 11B is a graph in the case where the electrical resistance R1 of the gain setting circuit 203 is smaller than the graph shown in FIG.

  As shown in FIG. 11, after starting driving, the drive motor 106 accelerates according to the acceleration signal ACC output from the control unit 50 based on the FG signal, and then reaches the target rotational speed. At this time, the inclination (θ1, θ2 shown in FIG. 7) when the drive motor 106 accelerates to the target rotational speed, that is, the response of the drive motor 106 increases as the electrical resistance R1 of the gain setting circuit 203 decreases. Further, the maximum value of this inclination is determined by the capacitance of the capacitor C1.

  When the rotation speed of the drive motor 106 reaches the vicinity of the target rotation speed, the control unit 50 controls the drive motor 106 to be stabilized at the target rotation speed while repeatedly outputting an acceleration / deceleration signal. At this time, the response of the drive motor 106 to the motor control signal changes sensitively when the electric resistance R1 of the gain setting circuit 203 is small, and insensitive when it is large. For this reason, when the electric resistance R1 of the gain setting circuit 203 is large, the drive motor 106 is more stable than when it is small.

  Thus, if the resistance value of the electric resistance R1 of the gain setting circuit 203 is too large and the responsiveness of the drive motor 106 becomes too low, it takes time until the drive motor 106 reaches the target rotational speed with respect to the acceleration signal ACC. It takes too much. Further, if the resistance value of the electric resistance R1 of the gain setting circuit 203 is too small and the responsiveness of the drive motor 106 becomes too high, the rotational speed of the drive motor 106 changes rapidly with respect to the motor control signal, and the rotational speed oscillates. Jitter deteriorates without becoming stable at the target rotational speed. Therefore, the gain setting circuit 203 needs to set an appropriate value of the electric resistance R1 and the capacitance of the capacitor C1 with respect to the target rotational speed of the drive motor 106.

<Acceleration / deceleration control of drive motor of this embodiment>
Next, acceleration / deceleration control of the drive motor 106 of this embodiment will be described.

  FIG. 8 is a block diagram (FIG. 8A) and a circuit diagram (FIG. 8B) showing the control configuration of the drive motor 106 according to this embodiment. Here, the gain setting circuit 204 shown in FIG. 8 has the same function as the gain setting circuit 203 shown in FIG.

  As shown in FIG. 8, in the control configuration of this embodiment, the control unit 50 and the gain setting circuit 204 are directly connected. The gain setting circuit 204 includes a plurality of transistors Tr10 and Tr11, a plurality of electric resistors R10 and R11, and a plurality of capacitors C20 and C21, and is grounded. In this embodiment, the value of the electric resistance R10 is 10 kΩ, the value of the electric resistance R20 is 20 kΩ, the capacity of the capacitor C20 is 0.0075 μF, and the capacity of the capacitor C21 is 0.017 μF. The gain setting circuit 204 can set the responsiveness of a plurality of different drive motors 106 by switching ON / OFF of the transistors Tr10, 11, 20, and 21 by the control unit 50. The other control configuration is the same as the conventional control configuration shown in FIG.

  Thereby, the control part 50 can switch ON / OFF of transistor Tr10,11,20,21, and can select an appropriate thing from the setting of the response of several different drive motors 106. FIG. That is, as shown in FIG. 9A, for example, when the control unit 50 switches the setting to the gain G1, the transistors Tr10 and Tr20 are turned on and the transistors Tr11 and 21 are turned off. As a result, as shown in FIG. 9B, the gain setting circuit 204 includes the electric resistance R10 and the capacitor C20, and the time constant at this time is 0.075 msec. Similarly, when the control unit 50 switches the setting to the gain G2, the transistors Tr11 and Tr20 are turned on and the transistors Tr10 and Tr21 are turned off. As a result, the gain setting circuit 204 includes the electric resistance R11 and the capacitor C20, and the time constant at this time is 0.150 msec. Similarly, when the control unit 50 switches the setting to the gain G3, the time constant becomes 0.170 msec, and when the setting is switched to the gain G4, the time constant becomes 0.340 msec.

  As a result, with respect to the gains G1 to G4, the time constant becomes G4> G3> G2> G1. Therefore, the response of the motor driver 202 is G1> G2> G3> G4. That is, the gain setting circuit 204 can change the time constant of the RC circuit by changing the combination of the electric resistances R10, 11 and the capacitors C20, 21 in the circuit. Since the time constant of the RC circuit corresponds to the speed at which the motor driver 202 responds after the control unit 50 outputs the control signal, the image forming apparatus according to the present embodiment uses a combination of the electric resistors R10 and 11 and the capacitors C20 and 21. By changing, it is possible to set at what response speed the drive motor 106 is accelerated / decelerated with respect to the acceleration signal ACC and the deceleration signal DEC. Further, the control unit 50 switches the responsiveness of the drive motor 106 set by the gain setting circuit 204 according to the target rotational speed of the drive motor 106 as a switching unit. Note that the timing at which the control unit 50 switches the responsiveness of the drive motor 106 is preferably performed when the rotational speed of the drive motor 106 is changed in accordance with a change in image quality or a change in paper type.

  Thus, the control unit 50 can switch the four responsivenesses of the gains G1 to G4 according to the target rotational speed of the drive motor 106. Therefore, even when the drive motor 106 is driven at a plurality of target rotational speeds, the drive motor 106 can be driven with appropriate responsiveness.

  In addition, even when the drive motor 106 is driven at a plurality of target rotation speeds, the drive motor 106 can be driven with an appropriate responsiveness setting. Therefore, a common drive motor 106 can be mounted between the image forming apparatuses A having different productivity. This can lead to cost reduction.

<Setting example of drive motor response>
Next, an example of setting the responsiveness of the drive motor 106 when the drive motor 106 has three target rotation speeds of 15000 rpm, 30000 rpm, and 50000 rpm will be described.

  FIG. 10 is a responsiveness table set according to the target rotational speed of the drive motor 106. Here, G1 to G4 in FIG. 10 indicate the gains G1 to G4 shown in FIG. That is, the gain G1 is set to have a higher responsiveness of the drive motor 106 than the gain G4. This gain setting table is stored in the ROM 52 in advance.

  As shown in FIG. 10, in the present embodiment, the control unit 50 switches the response of the drive motor 106 according to the stop time of the drive motor 106 and the environmental temperature in addition to the target rotational speed of the drive motor 106. That is, the control unit 50 refers to a table in which the target rotational speed of the drive motor 106, the environmental temperature detected by the thermistor 200, and the ON / OFF settings of the transistors Tr10 to 21 in the gain setting circuit 204 are associated. Switch responsiveness. This is due to the following reason.

  That is, oil is generally applied to the shaft 210 that is the rotation shaft of the drive motor 106 in order to reduce rotational friction. The viscosity of this oil depends on the environmental temperature, and is high at low temperatures and low at high temperatures. Further, the load torque of the drive motor 106 changes depending on the viscosity of the oil. If the load torque is large with respect to the response of the drive motor 106, the start-up of the drive motor 106 becomes slow, but the jitter is small, but if the load torque is small, the start-up is quick. However, the jitter increases.

  Therefore, as in this embodiment, in addition to the target rotation speed of the drive motor 106, the response of the drive motor 106 is selected according to the stop time of the drive motor 106 and the environmental temperature. Specifically, in a low temperature environment where the viscosity of oil is high, the drive current is set larger than in a high temperature environment where the viscosity is low, and the response of the drive motor 106 is set high. As a result, it is possible to suppress the jitter caused by the change in the viscosity of the oil and to activate the drive motor 106 satisfactorily.

  FIG. 12 is a graph showing the relationship between the rotational speed of the drive motor 106 and the time from when the drive motor 106 starts driving until it stabilizes at the target rotational speed. Here, the graph shown in FIG. 12B is a graph in the case where the electrical resistance R1 of the gain setting circuit 203 is larger than that in the graph shown in FIG.

  As shown in FIG. 12A, when the maximum rotation speed from when the drive motor 106 starts driving to when it stops is 110% or more (predetermined or higher) compared to the target rotation speed, the overshoot amount Can be said to be large. For this reason, it can be determined that the responsiveness of the drive motor 106 set by the gain setting circuit 204 is too high. Therefore, the control unit 50 lowers the setting of the table by one rank according to the target rotational speed. For example, when the setting at the start of driving of the drive motor 106 is the gain G2, the control unit 50 rewrites the table to the gain G3 that is lower by one rank. Note that the threshold value for rewriting the table is not a relative value with respect to the target rotation speed of the drive motor 106 as in this embodiment, but may be a fixed value when the maximum rotation speed of the drive motor 106 is 33000 rpm or more.

  Also, as shown in FIG. 12B, when the maximum number of rotations from when the drive motor 106 starts driving to when it stops is 101% or less (predetermined or less) compared to the target number of rotations, overshooting occurs. It can be said that the amount is small. For this reason, it can be determined that the response of the drive motor 106 set by the gain setting circuit 204 is too low. Therefore, the control unit 50 increases the setting of the table by one rank according to the target rotational speed. For example, when the setting at the start of driving of the drive motor 106 is the gain G2, the control unit 50 rewrites the table to the gain G1 that is higher by one rank. Note that the threshold value for rewriting the table is not a relative value with respect to the target rotation speed of the drive motor 106 as in the present embodiment, but may be a fixed value when the maximum rotation speed of the drive motor 106 is 30300 rpm or less.

  If it is determined that the gain rank is increased in the state of the gain G1, the table remains the gain G1. Similarly, if it is determined that the gain rank is lowered in the state of the gain G4, the table remains the gain G4. The timing for rewriting the table is updated before the start of the next image forming job.

  As described above, the control unit 50 determines the gain setting circuit according to the difference between the target rotation speed of the drive motor 106 and the maximum rotation speed of the drive motor 106 from when the drive motor 106 starts driving to when it stops. The response of the drive motor 106 set by 204 is switched. As a result, it is possible to optimize the responsiveness of the drive motor 106 in response to variations in the durability of the drive motor 106, changes in the amount of oil applied to the shaft 210, variations in rotational properties caused by tolerances of members during manufacture, and the like. it can.

2 ... Photoreceptor drum (photoreceptor)
50 ... Control unit (switching means)
101 ... Laser diode (light source)
105 ... Polygon mirror (rotating polygon mirror)
106: Drive motor (motor)
200 ... Thermistor (temperature detection means)
202 ... Motor driver (driving means)
204... Gain setting circuit 211... Hall element (rotation detection means)
A: Image forming apparatus ACC: Acceleration signal (control signal)
DEC ... Deceleration signal (control signal)

Claims (6)

A light source;
A photoreceptor,
A rotating polygon mirror that deflects the light beam emitted from the light source and scans the surface of the photoreceptor;
A motor for rotating the rotary polygon mirror;
Drive means for driving the motor by supplying a drive current to the motor;
Rotation detection means for detecting rotation of the motor and outputting a periodic signal having a period according to the rotation speed of the motor;
By comparing the period of the periodic signal with the period corresponding to the target rotational speed of the motor, a control signal is sent to the driving means so that the period of the periodic signal becomes a period corresponding to the target rotational speed of the motor. A controller that controls the rotational speed of the motor by transmitting and controlling the value of the drive current;
A setting circuit for setting the responsiveness of the motor when the control unit transmits the control signal, and a setting circuit capable of setting a plurality of different responsiveness;
Switching means for switching the responsiveness set by the setting circuit in accordance with the target rotational speed of the motor;
An image forming apparatus comprising:   2. The setting circuit is a circuit including an electric resistance and a capacitor, and sets responsiveness of a plurality of different motors by changing a value of the electric resistance and a capacitance of the capacitor. The image forming apparatus described in 1. The setting circuit includes a plurality of transistors, a plurality of electric resistors, and a plurality of capacitors.
The switching unit is set by the setting circuit by switching the electrical resistance and the capacitor included in the setting circuit when transmitting the control signal by switching ON / OFF of the plurality of transistors. The image forming apparatus according to claim 2, wherein the responsiveness of the motor is switched. A temperature detecting means for detecting the temperature;
The switching means switches the responsiveness of the motor set by the setting circuit based on the target rotational speed of the motor and the temperature detected by the temperature detecting means. The image forming apparatus according to claim 1.   The switching means switches the responsiveness set by the setting circuit so that when the temperature detected by the temperature detecting means is low, the responsiveness of the motor is higher than when the temperature is high. Item 5. The image forming apparatus according to Item 4.   The control unit divides the periodic signal and transmits the control signal to the driving unit so that the divided periodic signal has a period corresponding to a target rotational speed of the motor. Item 6. The image forming apparatus according to any one of Items 1 to 5.

Images