JP2004336847A - Motor controller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the control of a stepping motor so as not to affect a formed image by lessening the vibration at rotation stoppage when driving/stopping a load with large inertia, such as a rotating developing machine of a color image forming apparatus. <P>SOLUTION: This image forming apparatus reduces vibration in a low-speed region and at stoppage, by switching a current control value at decelerating drive into a current value lower than the drive current value required in a fixed-speed region, within a range where the angular acceleration at deceleration is not lower than a specified value; and moreover in a fixed-voltage control region, when driving the rotating developing machine with a stepping motor and accelerating the stepping motor in fixed-current control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to control of a driving source for driving a load having a large inertia such as a developing device in an image forming apparatus used for a laser printer, a digital copying machine, or the like.
[0002]
[Prior art]
As a method of obtaining a full-color image using the electrophotographic method,
(1) A sheet is held on a transfer drum (or belt), and toner images are sequentially formed by rotating a magenta, cyan, yellow, and black colors on an image carrier such as a photosensitive drum by rotating a rotary developing device. A one-drum system in which four colors are transferred four times to obtain a full-color image in which four colors are superimposed,
(2) A full-color image is obtained by superimposing four colors by forming and developing a latent image for each color on each photoconductor and transferring the latent image to each sheet. Drum system,
(3) Magenta, cyan, yellow, and black colors are sequentially formed on the photoreceptor by rotating a rotary developing device to form toner images. Further, four-color images are formed on an intermediate transfer body such as a transfer drum (or belt). Are sequentially formed, and then, a one-drum collective transfer method in which four colors are transferred at once by contacting the paper,
Etc.
[0003]
In the above three methods, the method (2) has a high copy speed but is costly in terms of configuration. Therefore, the methods (1) and (3) are adopted for medium and low speed machines. Often.
[0004]
As a driving source used in the devices of the methods (1) and (3), it is necessary to move a developing device of each color to perform a developing process at a predetermined position on a photoconductor, so that accurate position control is performed. Is required.
[0005]
Generally, DC servo motors and stepping motors are well known as drive sources suitable for position control. However, the former is very expensive due to its configuration, and requires a DC motor, that is, a brush mechanism. Since there is also a problem in terms of noise and durability, a stepping motor that can be driven by open loop control without using feedback for positioning control is often used.
[0006]
As the drive system of the stepping motor, there are mainly known a (1) one-phase excitation system, (2) a two-phase excitation system, and (3) a 1-2-phase excitation system. Further, as a control method capable of obtaining a stable output torque in these driving methods, a driving circuit using a constant current control circuit for making a current flowing in a phase (or a winding) to be excited constant is known.
[0007]
As a circuit configuration of this constant current control system, as shown in FIG. 1 in general (for example, see Non-Patent Document 1), a motor according to the above-mentioned systems (1) to (3) according to an input drive pulse signal. Excitation pattern generation circuit 300 for generating an on / off sequence signal (A, A *, B, B *) of each phase (LA, LA *, LB, LB *), and each phase defined by the phase excitation pattern generation circuit 300 A constant current control circuit 200 for controlling the winding current of the stepping motor to a constant current during the ON period of (LA, LA *, LB, LB *). In the constant current control circuit 200, the current detection units 201A and 201B detect currents ia + ia * and ib + ib * flowing through the respective phases LA, LA *, LB, and LB * (or windings) of the stepping motor 100. The output voltage of the reference voltage generation circuit 203 set so that the current of each phase becomes a specified current value and the detection values of the current detection units 201A and 201B are input to PWM control circuits 202A and 202B, and PWM control is performed. Pulse signals CA and CB whose on / off ratios are controlled are generated from the circuits 202A and 202B. The logical product of these signals (A, A *, B, B *, CA, CB) is used as a driving signal for the semiconductor switching elements SW_A, SW_A *, SW_B, SW_B * connected to each winding. By doing so, the current of each winding flowing within the predetermined driving period is controlled to be substantially constant.
[0008]
However, in the above-mentioned methods (1) and (3), it is necessary to drive a rotary body having a large mass and inertia at high speed and having a developing unit for each color, which is called a rotary developing unit due to its configuration. Vibration of the rotating body due to the stop affects the laser exposure system, causing a displacement of a latent image formed on the photosensitive body, and causing color misregistration and pitch unevenness when forming a color image that requires a development process using a plurality of colors. However, there is a problem that banding such as the above occurs remarkably. This is at a timing when an electrostatic latent image is generated on the photosensitive drum by an optical means such as a laser. By starting and stopping the rotary developing device (FIG. 8: B1), the vibration is transmitted to the laser exposure meter. When the light propagates (FIG. 8: B2), the scanning interval in the sub-scanning direction shifts, and a streak called banding appears (FIG. 8: B3). FIG. 7 shows a conceptual diagram.
[0009]
FIG. 7 shows a state where a line-shaped latent image is formed, and the left side of the figure is an enlarged view of the formed latent image. When normal latent image formation is performed, line-shaped latent images are formed at regular intervals in the sub-scanning direction.
[0010]
However, when banding occurs due to the start and stop of the rotary developing device, linear latent images that should be originally at regular intervals become irregular at regular intervals.
[0011]
This banding does not occur unless the rotating developing device is started and stopped at the timing when the electrostatic latent image is being generated. It is necessary to start and stop the rotary developing device even during the generation of, and it is important to improve this problem.
[0012]
A stepping motor is also used for the driving source motor for reasons such as cost and simplicity of the positioning control. However, the disadvantage of the stepping motor is that the torque characteristics depend on the frequency, Vibration and noise.
[0013]
Therefore, in the conventional example, in the laser exposure system, the vibration of the laser unit is detected in advance by detecting means such as a vibration sensor, and the laser is vibrated in the opposite phase, the angle of the mirror of the optical system is controlled, and the light exposure is performed. Methods such as controlling the rotation speed of a drum have been proposed.
[0014]
In addition, the drive source uses a method that allows different current values to be set according to the number of revolutions for vibration and noise countermeasures, and uses an encoder that detects the number of revolutions of the motor to maintain a constant error with the rotation speed command value. A method of performing optimal control of the current value so as to be within the value has been proposed. However, there is a problem that the vibration sensor and the rotation detection device as described above must be attached, which increases the cost and increases the size of the device. There were problems such as conversion.
[0015]
The advantage of using a stepping motor as described above is that control can be performed in an open loop, but the advantage is lost in the above-described optimal control by control in a feedback loop. .
[0016]
As a countermeasure for reducing the vibration of the stepping motor, by setting the drive current to an optimum value, overshoot / undershoot with respect to the moving position of the rotor during the step operation can be reduced as shown in FIG. It is known that vibration and noise can be reduced by using the method (for example, see Patent Documents 1 to 4).
[0017]
However, when setting this current, when performing acceleration / deceleration driving as shown in FIG. 10, the generated torque of the motor must be set in consideration of the torque during acceleration / deceleration. Even when the setting is changed, the setting is limited to a constant speed region (see Patent Document 1) or is performed only during acceleration or deceleration (see Patent Documents 2 and 3). The part concerning the current change and its oscillation was not discussed. It has also been proposed to suppress the vibration by changing the current setting during acceleration / deceleration in an analog manner (see Patent Document 4). However, as a method of defining the torque, the current setting is based on a general definition. Is what you do.
[0018]
[Non-patent document 1]
"Stepping Motor and Microcomputer Control", Hisashi Mishiro and Akira Sugawara, Sogo Denshi Publishing, 1994, Chapter 7.3 [Patent Document 1]
JP 07-075386 A [Patent Document 2]
JP-A-1-205182 [Patent Document 3]
JP-A-2-190368 [Patent Document 4]
JP-A-63-262098
[Problems to be solved by the invention]
Generally, a torque value required for a stepping motor is defined as follows.
-Motor required torque during acceleration = acceleration torque + friction torque Acceleration torque = (load inertia moment + motor inertia moment of motor) x angular acceleration-Motor required torque during deceleration = deceleration torque-friction torque deceleration torque = (load inertia Moment + moment of inertia of the rotor of the motor) x angular acceleration. That is, if the change pattern of the angular velocity during acceleration is the same as that during deceleration as described above, the acceleration torque and the deceleration torque have the same value, and the required torque is the friction load. The general definition was that the deceleration time was reduced by the minute. For this reason, the drive current must be set to be substantially the same during acceleration and deceleration.
[0020]
SUMMARY OF THE INVENTION An object of the present invention is to improve a drive stop shock effective as a banding countermeasure without imposing a cost increase factor such as a sensor in order to solve the above-described problems.
[0021]
[Means for Solving the Problems]
In order to solve the above-described problems, a motor control device of the present invention includes a stepping motor that drives a load, a constant current control circuit that controls the stepping motor with a constant current, and a switch that switches a current value in the constant current control circuit. Circuit, and the switchable period of the current value at the time of deceleration of the stepping motor by the constant current control circuit, the angular acceleration at the time of deceleration of the stepping motor is a predetermined value or more, within the constant voltage control region It is characterized by being within a certain period.
[0022]
An image forming apparatus according to the present invention is an image forming apparatus having a rotary developing device provided with a plurality of color component developing devices for developing a latent image formed on a photoreceptor, wherein the rotary developing device is provided. It is characterized by being rotationally driven by the motor control device according to any one of (1) to (5).
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
Hereinafter, an image forming apparatus according to a first exemplary embodiment of the present invention will be described with reference to the drawings.
[0024]
FIG. 9 is a main part configuration diagram of a full-color printer as an example of the image forming apparatus according to the present invention. In FIG. 9, a photoconductor 1 as an image carrier is rotated in the direction of arrow A by a motor (not shown). Around the photoconductor 1, a developing unit 13 and a cleaner device 12 are arranged.
[0025]
The developing unit 13 includes four developing devices 13Y, 13M, 13C, and 13K for full-color development. The developing devices 13Y, 13M, 13C, and 13K develop the latent images on the photoconductor 1 with yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively. When developing each color of Y, M, and C, the developing unit 13 is rotated in the direction of arrow R by the stepping motor shown in FIG. 1, and the developing device of the color is aligned so as to contact the photoconductor 1. .
[0026]
The toner images of each color developed on the photoreceptor 1 are sequentially transferred to a belt 2 as an intermediate transfer body by a transfer device 10, and four color toner images are superimposed. The belt 2 is stretched around rollers 17, 18, 19, 20. Among these, the roller 17 is coupled to a drive source (not shown) and functions as a drive roller for driving the belt 2. The rollers 18 and 20 function as tension rollers for adjusting the tension of the belt 2. The roller 19 functions as a backup roller for the transfer roller 21 as a secondary transfer device.
[0027]
A belt cleaner 22 is provided at a position facing the roller 17 with the belt 2 interposed therebetween, and residual toner on the belt 2 is scraped off by a blade.
[0028]
The recording paper pulled out from the recording paper cassette 23 to the transport path by the pickup roller 24 is fed to the nip portion, that is, the contact portion between the secondary transfer device 21 and the belt 2 by the pair of rollers 25 and 26. The toner image formed on the belt 2 is transferred onto the recording paper at the nip portion, is thermally fixed by the fixing device 5, and is discharged out of the device.
[0029]
In the color printer having the above configuration, an image is formed as follows. First, a voltage is applied to the charging device 7 to uniformly negatively charge the surface of the photoreceptor 1 at a predetermined charging portion potential. Subsequently, exposure is performed by an exposure device 8 including a laser scanner so that the charged image portion on the photoconductor 1 has a predetermined exposure portion potential, and a latent image is formed. The exposure device 8 forms a latent image corresponding to an image by turning on and off based on the image signal.
[0030]
A developing bias preset for each color is applied to the developing roller of each color of the developing device 13, and the latent image is developed with toner when passing through the position of the developing roller and is visualized. The toner image is transferred to the belt 2 by the transfer device 10, further transferred to the recording paper by the secondary transfer device 21, and then sent to the fixing device 5. During full-color printing, four color toners are superimposed on a belt and then transferred to recording paper. The toner remaining on the photoreceptor 1 is electrostatically cleaned by a preliminary cleaning device, and is removed and collected by a cleaner device 12. Finally, the photoreceptor 1 is removed by a static eliminator (not shown). The charge is uniformly removed to around 0 volts to prepare for the next image forming cycle.
[0031]
The image forming timing of the color printer is controlled based on a predetermined position on the belt 2. The belt 2 is stretched around rollers including a driving roller 17, tension rollers 18 and 20, and a backup roller 19, and a predetermined tension is applied by the tension rollers 18 and 20.
[0032]
A reflection sensor 36 for detecting a reference position of the belt 2 is disposed between the backup roller 19 and the tension roller 20. The reflection type sensor 36 detects a marking on a reflection tape or the like provided at an end of the outer peripheral surface of the belt 2 and outputs an I-top signal indicating a reference of an image formation start timing.
[0033]
The outer peripheral length of the photoconductor 1 and the peripheral length of the belt 2 are in an integer ratio represented by 1: n (n is an integer). With this setting, the photoconductor 1 rotates an integer while the belt 2 makes one revolution, and returns to the same state as before the one revolution of the belt, so that when the four colors are superimposed on the intermediate transfer belt 2, In this case (the belt makes four revolutions), it is possible to avoid color shift due to uneven rotation of the photoconductor 1.
[0034]
In the intermediate transfer type image forming apparatus as described above, after the I-top signal is detected, the charging device 7 starts latent image formation in accordance with the image signal after a predetermined time has elapsed. Further, as described above, while the belt 2 makes one rotation, the photoconductor 1 rotates an integer and returns to the same state as before the one rotation of the belt, so that a toner image is always formed on the belt 2 at the same position.
[0035]
The color image is copied onto the recording paper through the above-described process. However, the problem here is that when the rotary developing unit is driven, especially for each color due to vibration generated by inertia at the time of stoppage, This is the displacement of the latent image formation during the latent image formation. When the latent image forming position is shifted, the position of the developed toner image is shifted, which causes color shift when four color toner images are superimposed, and pitch unevenness caused by a change in pixel interval. In the following, in order to improve the shock at the time of stopping the rotary developing device which causes these color shifts, the setting method of switching the drive current at the time of deceleration and changing the drive current to a value lower than at the time of acceleration and at the constant speed is described. Will be described.
[0036]
FIG. 1 is a block diagram of a drive circuit of a power regenerating type stepping motor for driving the rotary developing device 13 shown in FIG. 9, and its operation is to perform constant current control as described in the related art. FIG. 2 is a diagram showing an acceleration / deceleration drive profile of a stepping motor and a switching timing of a constant current control value of a drive current.
[0037]
In FIG. 1, reference numeral 100 denotes a stepping motor,
As described above, the value of the torque required for the stepping motor is generally defined as follows.
-Motor required torque during acceleration = acceleration torque + friction torque Acceleration torque = (load inertia moment + motor inertia moment of motor) x angular acceleration-Motor required torque during deceleration = deceleration torque-friction torque deceleration torque = (load inertia (Moment + moment of inertia of rotor of motor) x angular acceleration If the change pattern of angular velocity during acceleration is the same as that during deceleration as described above, acceleration torque and deceleration torque have the same value, and required torque is the friction load of the motor. Since the general definition is that the deceleration time becomes smaller by the minute, the drive current must be set to be almost the same during acceleration and deceleration.
[0038]
However, when the moment of inertia of the load is large, the accumulated rotational energy can be used at the time of deceleration. At this time, the change amount dErot of the rotational energy for each step is expressed by the following equation.
[0039]
Erot = 1/2 * Irot * (ωn ＾ 2−ωn + 1 ＾ 2)
Here, ωn: the angular velocity at the n-th step The torque Trot generated by the change in the kinetic energy is Trot · θstep = Erot (θstep: step angle of the stepping motor)
Because
Trot = Erot / θstep
And the torque Tmot actually acting on the stepping motor as the driving source is Tmot = deceleration torque + Trot
Since the action direction of the deceleration torque and Trot is opposite, the torque by Trot is reduced.
[0040]
The result is shown in FIG. FIG. 3 shows the case where the ratio of the inertia of the motor rotor to the load inertia is 1: 2. The graph shown as “+ load energy” indicates the torque actually required by the motor. The same can be derived from the fact that the sum of the kinetic energy due to friction torque and the kinetic energy of the rotary developing device becomes the required torque of the motor. Thus, as shown in FIG. 3 (motor: load inertia ratio = 1: 2) and FIG. 4 (motor: load inertia ratio = 1: 2), the torque at the time of deceleration depends on the inertia ratio between the motor rotor and the load. Is reduced in comparison with the required torque during acceleration.
[0041]
However, as a range in which this relationship is established and the current can be switched, the following conditions must be established as shown in FIG.
(1) Angular acceleration (dω / dt) is above a specified value. (2) ωr ≧ ωm
here,
ωr: Angular velocity ωm on the deceleration curve when the drive torque is reduced to zero from the constant-speed rotation state of the rotary developing device as a load ωm: Actually specified motor drive speed (3) ωm ≧ ωc
here,
ωc: angular velocity at which the constant current operation region and the constant voltage operation region are switched The above condition (3) is a condition provided as a limit when the constant current set value of the motor is switched.
[0042]
This is because, in the constant voltage operation region, even when the constant current set value is changed, the current supplied to the winding is not forcibly changed, and a magnetic field change due to a sudden change in current does not occur. Therefore, generation of unnecessary vibration can be suppressed.
[0043]
In FIG. 1, the switching of the current setting is performed by the current level switching circuit 400 changing the output voltage level of the reference voltage generating circuit 203 according to a current setting change signal from a controller (not shown). Specifically, a circuit is used that changes the voltage dividing ratio of the reference voltage using a semiconductor switch element such as a transistor.
[0044]
In the case where a rotational torque is applied to the motor by the rotational energy of the rotary developing device side, in the drive circuit shown in FIG. Regeneration is performed.
[0045]
This operation will be described below with reference to the schematic diagram of the stepping motor shown in FIG.
(1) When A-phase is on and A * -phase is off: A current flows through the A-phase winding in the direction of the arrow shown in the figure, and a magnetic field is generated in the direction shown in the figure to attract the magnetic poles of the rotor. Generate force.
(2) When the A-phase is off and the A * -phase is also off: The current flowing in the A-phase winding flows through the A * -phase winding in the direction shown in FIG. Power is regenerated to the side.
[0046]
At this time, if an external force is applied to the rotor of the motor and the amount of the magnetic flux from the magnetic poles of the rotor interlinking the magnetic path cross section of the A * phase winding is displaced, the direction in which the magnetic flux does not change, that is, the rotation in the figure, When the rotor magnetic pole is displaced in the direction, it acts in a direction in which the amount of current regenerated to the power supply increases.
[0047]
FIG. 6 shows a result measured in an actual driving device. As shown in the figure, at the time of deceleration, it is confirmed that the amount of regenerative current increases due to the torque acting on the motor rotor side from the rotary developing device side, and that the input current is on the negative side. Has also occurred.
[0048]
Under the load conditions having the above relationship, the drive current of the stepping motor at the time of deceleration can be reduced as compared with the time of acceleration. Experimentally confirmed results show that in the acceleration / deceleration drive pattern shown in FIG. 3, in a device having a configuration in which the inertia ratio between the motor rotor and the rotary developing device is about 1: 2, even if the torque margin is set to 1.5 as the drive current, the acceleration is increased. The current at the time of deceleration could be reduced to 1.5 A at the current of 4 A at the time of deceleration. In addition, the surplus energy stored in the rotary developing device can be regenerated to the power input side, which saves power even for methods such as current switching only at the end of deceleration, and only at the time of stop. However, there is an advantage that the step vibration can be reduced in a low-speed region.
[0049]
This enables effective banding correction in a color copier equipped with a rotary developing device.
[0050]
INDUSTRIAL APPLICABILITY The present invention is effective not only for the rotary developing device of the image forming apparatus but also for an apparatus for controlling the driving / stop of a load having a large inertia.
[0051]
【The invention's effect】
According to the present invention, when decelerating the driving of the load, the driving current can be reduced while the rotational energy stored in the inertia of the load is regenerated to the power supply side, and the shock at the time of stopping the driving of the load can be reduced. Became.
[Brief description of the drawings]
FIG. 1 is a constant current drive circuit of a stepping motor.
FIG. 2 is a setting diagram of a current switchable range.
FIG. 3 is a diagram showing torque characteristics.
FIG. 4 is a diagram showing torque characteristics.
FIG. 5 is a schematic diagram illustrating the operation of a stepping motor.
FIG. 6 is a diagram showing a power supply voltage / input current characteristic during actual operation of the motor.
FIG. 7 is a diagram showing an outline of banding.
FIG. 8 is a schematic diagram of a vibration propagation path.
FIG. 9 is a diagram illustrating an operation response characteristic of a stepping motor depending on a drive current.
FIG. 10 is a diagram for explaining required torque during acceleration / deceleration driving.
FIG. 11 is a schematic sectional view of an image forming apparatus having a rotary developing device configuration.
[Explanation of symbols]
13 rotary developing device 100 stepping motor 200 constant current control circuit 400 current level switching circuit

Claims (6)

A stepping motor for driving a load,
A constant current control circuit that controls the stepping motor with a constant current;
A switching circuit for switching a current value in the constant current control circuit,
A period during which the constant current control circuit can switch the current value at the time of deceleration of the stepping motor, within a period during which the angular acceleration at the time of deceleration of the stepping motor is equal to or more than a predetermined value and within the constant voltage control region. A motor control device, characterized in that: The predetermined value of the angular acceleration is a natural deceleration curve due to a friction load when the drive by the stepping motor is cut off from a state where the load is being rotated at a constant speed at a predetermined speed and the torque transmission amount becomes zero. 2. The motor according to claim 1, wherein the angular velocity on ω _m (t) is equal to an angular velocity on an angular velocity curve (ω _r (t)) defined as a driving pattern of the stepping motor. 3. Control device. 2. The energy is regenerated on the power supply side via the other phase when one of the first phase and the second phase of one winding of the stepping motor is turned off. 3. Motor control device. 2. The motor control device according to claim 1, wherein a current value after switching by the switching circuit is lower than a current value required at the time of acceleration and at a constant speed of the stepping motor. 2. The motor control according to claim 1, wherein the ratio of the inertia of the load to the inertia of the stepping motor is twice or more, and the driving current at the time of deceleration of the stepping motor is less than half the driving current at the time of acceleration. apparatus. An image forming apparatus having a rotary developing device provided with a plurality of color component developing devices for developing a latent image formed on a photoconductor,
An image forming apparatus, wherein the rotary developing device is driven to rotate by the motor control device according to claim 1.

Images