JP2008206352A - Stepping motor drive controller and image forming apparatus therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stepping motor drive controller capable of controlling a stepping motor so that any excitation phase is chosen in a stopped position by counting a driving pulse in an excitation phase position upon starting/stopping the stepping motor. <P>SOLUTION: A microstep system enables changes in the frequency and the amplitude level of vibration generated under operating conditions to be inhibited in a load for drive and communication by applying a voltage and a current to the motor corresponding to the excitation phase position of the motor 502. Torque upon restarting the motor is kept constant by correcting the predicted phase of the microstep during a basic step upon stopping the motor 502 by the pulse count value of the motor counted by a counter 551. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a stepping motor drive control device that drives a rotary developer of an electrophotographic image forming apparatus such as a laser printer or a digital copying machine that forms an image by repeating charging, exposure, and development.

  As a structure for forming a full-color image by an electrophotographic method, there are a one-drum method, a four-drum method, etc., and a one-drum method further includes a one-drum batch transfer method. Since the 4-drum system is an expensive device, the 1-drum system is often adopted. In the one-drum system, a toner image for each color is formed on one photosensitive drum, and the toner image is transferred to a sheet via a transfer drum (or belt) facing the photosensitive drum. In this way, a full-color toner image is transferred onto the paper by four transfers. In order to form a toner image on the photosensitive drum, a rotary developing device in which developing devices of magenta, cyan, yellow, and black are provided on the circumference is used. When a toner image of a certain color is formed and transferred to a sheet or an intermediate transfer member, the rotary developing device rotates by a certain angle, and a toner image of the next color is formed. In the one-drum system, each color developer is moved and developed at a predetermined position of the photosensitive drum, so that the drive source of the rotary developer needs to perform accurate position control.

  In the one-drum type image forming apparatus, it is necessary to drive at high speed a rotating body having a large inertial mass and equipped with a developing device for each color called a rotary developing device. For this reason, there is a possibility that the rotating body vibrates with the start and stop of the driving of the rotary developer. The vibration affects the laser exposure system and causes a positional shift of the latent image formed on the photosensitive drum. When forming a color image in which development is performed for each of a plurality of colors, banding such as color shift and pitch unevenness occurs. There was a problem of causing it. This problem is caused by starting or stopping the rotary developer at the timing when an electrostatic latent image is generated on the photosensitive drum by an optical means such as a laser, and the vibration propagates to the optical system, and the scanning line interval is shifted. This is what leads to so-called banding. FIG. 7 shows a schematic diagram thereof. That is, when the rotation of the rotary developer is started or stopped (B1), the vibration at that time is transmitted to an optical system such as a laser scanner, the optical system vibrates (B2), and the vibration of the optical system shifts the scanning line interval. (B3) appears on the photosensitive drum. FIG. 6 shows a conceptual diagram of banding. That is, if there is no vibration, the scanning line interval is constant, but due to the vibration, the scanning line interval becomes narrower or wider than the no-vibration interval.

  As a drive source suitable for position control, a stepping motor that can be driven by open loop control is generally used for position control. Stepping motor driving methods mainly include (1) one-phase excitation method, (2) two-phase excitation method, and (3) 1-2-phase excitation method. In these methods, in order to obtain a stable output torque in the drive circuit of the stepping motor, a drive circuit using a constant current control circuit in which the current flowing in the exciting phase (or winding) is constant is known (for example, Non-patent document 1). An example of the circuit configuration of this constant current control method is shown in FIG. The drive circuit shown in FIG. 10 includes a phase excitation pattern generation circuit 300 and a constant current control circuit 200. The phase excitation pattern generation circuit 300 generates an on / off sequence for each phase (A, A *, B, B *) in accordance with the input drive pulse signal. The constant current control circuit 200 controls the winding current of the stepping motor to a constant current during the on period of each phase (A, A *, B, B *). In the constant current control circuit 200, current detection units 201A and 201B detect currents ia + ia * and ib + ib * flowing through the windings LA, LA * / LB / LB * flowing through the stepping motor 100. The PWM control 202A, 202B sets the on / off ratio based on 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 value by the current detection units 201A, 201B. Controlled pulse signals CA and CB are generated. By using the signals CA and CB as drive signals of the semiconductor switching elements SW_A, SW_A *, SW_B, and SW_B * connected to the respective windings as gates with the excitation patterns of the respective phases, the respective windings that flow within a predetermined driving period It is controlled so that the current becomes a substantially constant value.

  When a stepping motor is employed as a drive source, there are disadvantages such as the torque characteristics of the motor depending on the frequency and vibration / noise during low frequency driving. There are also the following problems.

In general, the equation of motion for a rotating object is
T = J * (ω1-ω0) / t (1)
It is represented by The applied torque is T [Nm], the application time of torque T is t [s], the moment of inertia of the rotating object is J [kgm2], the initial angular velocity is ω0 [rad / s], and the angular velocity after the change is ω1 [rad]. / S]. In this case, the kinetic energy change ΔK is
ΔK = J * (ω12−ω02) / 2 (2). Here, assuming that the angular acceleration ω ′ (= dω / dt) and the displacement angle θ,
(Ω12−ω02) = 2ω′θ (3)
Because
ΔK = J * (ω12−ω02) / 2 = Tθ (4)
It is expressed.

  Thus, when the amount of change in angular velocity increases or when the torque supplied from the drive motor to the load increases, the amount of change in kinetic energy increases, resulting in increased vibration and noise. . In particular, when the inertia moment of the load is larger, the increase in kinetic energy is inevitably larger than when the moment of inertia is small even if the change in the angular velocity is constant. Therefore, there arises a problem that vibration and noise are also increased.

  In order to improve the vibration at the time of driving peculiar to these stepping motors, the μSTEP (microstep) driving method is adopted instead of the above-described driving method. Reduction of motor vibration by the micro-step drive method is achieved by dividing the basic step angle, that is, by reducing ΔK in the equation (4) or by reducing the harmonic component of the generated torque by making the drive current sinusoidal. .

In the micro-step drive system, the basic step angle (2-phase: 1.8 degrees, 5-phase: 0.72 degrees, etc.) defined by the motor structure is electrically connected to each winding LA / LA * / (LB / LB). *) Further control with the current ratio. By doing so, the basic step angle is subdivided such as 1/4, 1/8,... Of the basic step angle. A step (step angle) obtained by dividing a basic step (basic step angle) is referred to as a microstep (microstep angle). Such a driving method in units of microsteps is called a microstep driving method. FIG. 11 shows an example of the current command value of each winding at the time of the micro step which is 1/8 of the basic step. By setting the current command value as shown in FIG. 11 for the A phase and the B phase as the constant current command values in FIG. 10, microstep drive control is realized. The current ratio of each microstep is determined from a sine function, and by subdividing the microstep, the current waveform flowing in each winding approaches the shape of a sine wave.
Naoshi Mijo and Atsushi Sugawara, “Stepping Motor and Microcomputer Control”, Chapter 7.3, General Electronic Publishing, 1994

  The problem here is that the motor torque generated during the operation of each microstep in the microstep drive is not necessarily constant due to the mechanical and electrical factors of the motor.

  13 shows a relationship between each phase current and generated torque in a 4-split microstep, and FIG. Thus, within one basic step, the torque varies for each microstep. As a result of the torque fluctuation, the generated vibration level also changes every 1 microstep drive.

  For this reason, there is no problem with driving in basic steps, but in a system that drives gears in microsteps, if the generated torque of the motor at startup and stop varies depending on the phase, the motor and transmission system The vibrations generated in the are different. This becomes more conspicuous when a large inertia element such as a rotary developing device is rotationally driven. This leads to the fact that the frequency and amplitude of vibration generated during the formation of the latent image differ from color to color, which may cause banding and image degradation in the image.

  Further, the amount of toner consumed and supplied for each color developing device built in the rotary developing device is not constant, and there is also a problem of weight deviation caused by the deviation amount of the center of gravity position of each developing device. The mutual influence between the problem of deviation and the fluctuation of the motor output torque is not negligible. For example, if each developer unit is used as a mass point, and the moment generated by the relationship between the mass and the operating point acts in the direction to assist the torque required by the load on the drive side, the required torque amount is Decrease. Conversely, when acting in the direction of assisting the load torque side, the required torque amount on the drive side increases. As described above, due to the deviation in weight, the load torque varies depending on the phase of the rotary developer, and the required torque on the drive side also varies. As a result of changes in load torque and motor torque during operation, the amount of change in kinetic energy at startup and stop always changes. As shown in FIG. 13, the relationship between the current and the generated torque changes the generated torque due to the phase current at each microstep position, and the angular acceleration during the microstep operation also differs. That is, there is a problem that the amount of vibration generated is not constant. FIG. 14 shows the set values (A0 to A3, B0 to B3) of each phase current and the change in angular velocity at the time of four-divided microstep drive.

  As another countermeasure for reducing the vibration of the stepping motor, the drive current is set to an optimum value so that overshoot and undershoot with respect to the moving position of the rotor are reduced during the step operation as shown in FIG. There is. When this current is set, when performing acceleration / deceleration driving as shown in FIG. 9, the torque generated by the motor must be set in consideration of the torque at the time of acceleration reduction. In addition, it is necessary to consider the vibration element due to the torsion spring component provided in the drive system, and a sufficient margin must be provided.

  As described above, when a rotating body having a large moment of inertia such as a rotary developer is controlled to rotate with a precise phase by a stepping motor driven by microsteps, the torque varies depending on the rotational phase of the motor and the rotating body, and the frequency and It causes vibrations with different amplitudes. The vibration is difficult to control because the frequency and amplitude differ depending on the rotational phase of the motor and the rotating body.

  The present invention has been made in view of the above-described conventional example, and operates in at least one of driving and transmission and a load portion by making the excitation phase position constant at the time of starting and stopping the stepping motor or any one of them. It is an object of the present invention to provide a stepping motor drive control device that suppresses changes in the frequency and / or amplitude level of vibrations that sometimes occur.

In order to achieve the above object, the present invention comprises the following arrangement. That is, a stepping motor drive control device of a microstep driving system that drives the stepping motor in units of microsteps obtained by dividing a basic step driven by a basic step angle of the stepping motor into a predetermined number,
A driving circuit for driving the stepping motor by a microstep method;
Detecting means for detecting a timing at which a load rotationally driven by the stepping motor reaches a predetermined rotational phase;
A counter for specifying which microstep in the basic step of the stepping motor the timing detected by the detection means;
A pulse for driving the stepping motor in units of the microsteps is sent to the drive circuit, and the stepping motor is driven in a certain number of microsteps based on the timing detected by the detection means. Drive control means for stopping the rotational phase of the load at a predetermined phase;
The drive control unit corrects the fixed number so that the stepping motor stops at a rotation phase in units of basic steps when the stepping motor is driven based on the order of the microsteps specified by the counter.

  With the above configuration, the excitation phase position when starting and stopping the stepping motor is always kept constant, so that changes in the frequency and amplitude level of vibrations that occur during operation in the drive, transmission, and load sections are suppressed. It becomes possible to do.

[First Embodiment]
An image forming apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 15 is a block diagram showing a main part of a full-color printer as an example of the image forming apparatus according to the present invention, and FIG. 1 is a schematic diagram showing the configuration of a color image rotating developer. In the one-drum electrophotographic image forming apparatus according to this embodiment, the rotary developing unit is rotationally driven by a stepping motor. In particular, the microstep drive system in which the drive control of the stepping motor is controlled in units of microsteps obtained by dividing the basic steps into a predetermined number is adopted.

  In FIG. 15, a photoreceptor (photosensitive drum) 1 as an image carrier is rotated in the direction of arrow A by a motor (not shown). A developing unit 13 and a cleaner unit 12 are disposed around the photoreceptor 1. The developing unit 13 includes three color developing units 13Y, 13M, 13C and a black developing unit 14 for full color development. The color developing units 13Y, 13M, 13C, and 14 develop the latent images on the photoreceptor 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 the arrow R by the drive motor for each color, and the developing unit of the color is aligned so as to contact the photoreceptor 1. This position is the development position. The developing roller of the black developing unit 14 is always in contact with the photoreceptor 1 and controls the development of black toner by controlling the high-voltage bias for black development.

  The toner images of the respective colors developed on the photosensitive member 1 are sequentially transferred to the belt 2 as an intermediate transfer member by the transfer unit 10 and the four color toner images are superimposed. The belt 2 is stretched around rollers 17, 18, 19 and 20. Among these, the roller 17 functions as a driving roller that is coupled to a driving source (not shown) and drives the belt 2. The rollers 18 and 20 function as tension rollers that adjust the tension of the belt 2. The roller 19 functions as a backup roller for the transfer roller 21 as a secondary transfer portion. 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.

  The recording paper drawn from the recording paper cassette 23 to the conveyance path by the pickup roller 24 is fed to a nip portion, that is, a contact portion between the secondary transfer portion 21 and the belt 2 by a pair of rollers 25 and 26. The toner image formed on the belt 2 is transferred onto the recording paper at this nip portion, thermally fixed by the fixing portion 5 and discharged outside the apparatus.

  In the color printer configured as described above, an image is formed as follows. First, a voltage is applied to the charging unit 7 to uniformly negatively charge the surface of the photoreceptor 1 with a predetermined charging unit potential. Subsequently, exposure is performed by the exposure unit 8 including a laser scanner so that the charged image portion on the photosensitive member 1 has a predetermined exposure unit potential, and a latent image is formed. The exposure unit 8 is turned on / off based on the image signal to form a latent image corresponding to the image.

  A developing bias set in advance for each color is applied to the developing roller such as the developing unit 13Y, and the latent image is developed with toner when passing through the position of the developing roller, and visualized as a toner image. The toner image is transferred to the belt 2 by the transfer unit 10 and further transferred to the recording paper by the secondary transfer unit 21 and then fed to the fixing unit 5. In full-color printing, toners of four colors are superimposed on the belt and then transferred onto the recording paper. The toner remaining on the photoconductor 1 is made to be easily charged by the preliminary cleaning unit, and is removed and collected by the cleaner unit 12. Finally, the photoconductor 1 is uniformly removed by the charge eliminating unit (not shown). The charge is removed to near 0 volts to prepare for the next image forming cycle.

  The image forming timing of the color printer is controlled with reference to 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.

  Between the backup roller 19 and the tension roller 20, a reflective sensor 36 for detecting the reference position is disposed. The reflective sensor 36 detects a marking such as a reflective tape provided at the end of the outer peripheral surface of the belt 2 and outputs an I-top signal.

  The peripheral length of the photoreceptor 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 photoreceptor 1 rotates an integer during one revolution of the belt 2 and returns to the same state as before one revolution of the belt. Therefore, the intermediate transfer belt 2 makes four revolutions and has four colors. When toner images are superimposed, it is possible to avoid color misregistration due to uneven rotation of the photoreceptor 1.

  In such an intermediate transfer type image forming apparatus, after detecting the I-top signal, the charging unit 7 starts forming a latent image in accordance with the image signal after a predetermined time has elapsed. In addition, since the photosensitive member 1 rotates an integer number of times during one rotation of the belt 2 and the rotational phase of the photosensitive member 1 with respect to the rotational phase of the belt 2 is constant, a toner image is always formed on the belt 2 at the same position. Is done.

  The color image is copied onto the recording paper through the above process. Here, the problem is the positional deviation of the latent image formation when the latent image formation for each color is caused by the vibration generated at the time of rotation of the rotary developing unit or the like, especially at the stop. When the latent image forming position is shifted, the developed toner image is shifted, and when the four colors are superimposed, the color shift and the pitch unevenness caused by the change in the pixel interval are caused. As described above, this problem is basically due to the release of the kinetic energy accumulated in the load, in this case the inertial moment of the rotary developer, and the vibration generated by the released energy is as described above. Propagation to the laser exposure system is the main factor.

  Here, if the moment of inertia is J and the angular velocity is ω, the energy K of the rotating body is given by the rotational energy K = J * ω2 / 2. Thus, the rotational energy K is defined as being proportional to the square of the angular velocity of the rotating body. Therefore, to reduce this energy, it is important to reduce the angular velocity.

  By adopting the micro-step driving method, the driving angle of one step becomes smaller than that of the prior art, and this change in rotational energy is also suppressed. Further, as described above, the torque generated in the motor changes depending on the excitation phase position. In this case, if there is a rattling element such as a backlash in the drive gear portion, as shown in FIG. Will increase or decrease.

  Here, as shown in FIG. 1, the developing unit includes a rotary developing unit 500 including developing units (Y, M, C, K) for each color, a drive motor 502, a home position sensor 501, and an HP flag. 510 and a control circuit 550. A home position sensor (referred to as HP sensor) 501 includes an optical sensor having a light emitting element and a light receiving element, and determines the home position of the rotary developing device 500. An HP flag 510 reflecting plate or the like, which indicates a reference position at which the HP sensor 501 detects the position of the rotary developing device 500. The control circuit 550 controls the driving amount of the motor 502 and performs positioning control based on the output from the HP sensor 501. The control circuit 550 is configured such that an excitation phase to be given to the stepping motor 502 is determined by a reset signal (not shown) at the time of startup or the like. The drive circuit 552 has the basic configuration shown in FIG. However, the constant current command value is not constant, and the current value changes for each microstep according to the phase of the microstep, for example, as shown in FIG. Since the motor 502 cannot always secure a torque for holding the load when the power is off, the phase of the photoreceptor 1 may change while the power is off. Therefore, normally, positioning control for returning the transfer belt to the home position is performed at the time of activation or at a predetermined timing. In this case, the position where the sensor 501 detects the HP flag 510 provided on the rotary developer side is used as a reference, and the transfer belt and the rotary developer 500 are rotated at a rotational phase by stopping at a position driven by a predetermined amount of movement. Is returned to the home position.

  However, since the driving amount of the motor until the sensor 501 detects the HP flag 510 is not fixed, that is, the rotational phase of the stopped driving motor 502 is unknown, the excitation phase cannot be determined. Therefore, in the present embodiment, a pulse counter 551 that counts the number of pulses sent from the control circuit 550 to the motor drive circuit 552 is provided. Further, the number of digits of the pulse counter 551 is used as the division number of the basic step. In this example, since the basic step is divided into 8 micro steps, the number of digits of the pulse counter 551 is 3 bits. The pulse counter 551 is a counter indicating which phase is in the basic step. That is, the pulse counter 551 is reset when the phase of the microstep shown in FIG. 13 or the like is 0, and is counted up in synchronization with the drive pulse. Assuming that the upper limit value of the counter is the number of microsteps (7 in FIG. 13) constituting the basic step, the pulse counter 551 is the microstep in the basic step when the sensor 501 detects the HP flag 510. Will be identified.

  Hereinafter, the stop-time control operation will be described with reference to FIGS. The pulse counter 551 is configured to be reset by a reset signal input in synchronization with power-on or the like. Here, a setting table of the pulse counter 551 is shown in FIG. As a function, not only the above-described reset function but also an enable signal is provided so that the counter operation can be turned on and off as necessary. The pulse counter 551 is mapped to the CPU memory or IO space of the control circuit 550. Specifically, a 3-bit signal ROT_CNT_COUNTER indicating the value of the pulse counter 551 is assigned to the address 601650 shown in FIG. Further, a signal ROT_CNT_LATCH_MODE (2 bits), a signal ROT_CNT_EDGE_MODE (1 bit), and a signal ROT_CNT_ENB (1 bit) are allocated to the address 601652. Of course, these signals are signals between the control circuit 550 and the pulse counter 551. The signal ROT_CNT_LATCH_MODE is a flag for designating the timing at which the counter value is latched. The initial value is latched at 0 at the falling edge of the HP sensor signal, 1 at the rising edge, and otherwise at both timings. The signal ROT_CNT_EDGE_MODE indicates that the edge of the clock for driving the counter falls when it is 0 and rises when it is 1. The signal ROT_CNT_ENB is a counter enable signal. A clock signal ROT_CLK is input to the pulse counter 551 from the control circuit 500. The pulse counter 551 also receives a detection signal ROT_HP from the HP sensor.

  The operation of the control circuit 550 is realized by a software control flow as shown in FIGS. 4A and 4B. 4A and 4B are procedures of a program executed by a CPU built in the control circuit 550, and are recorded in, for example, a ROM. FIG. 4A shows a process of waiting for an interrupt generated by the HP flag 510 after starting the home position operation. FIG. 4B is a processing routine for performing correction pulse setting up to the stop position by interrupt processing after the HP flag 510 is detected.

  The pulse counter 551 is reset when the power is turned on, and as shown in FIG. 2, the counter value is loaded with the initial value 0 and waits in that state. A home position search start command is input to the control circuit 550 from the image forming apparatus. The control circuit 550 loads the pulse number setting (38400 in this example) and the self-starting frequency (4000 pps (pulse / second) in this example) from the predetermined storage position as parameters for searching for the momo position (S401). The control circuit 550 starts sending pulses to the motor drive circuit 552 at a self-starting frequency of 4000 pps (S402) When the pulse sending is started, the control circuit 550 waits for an interrupt from the HP sensor (S403).

  Since the pulse counter 551 is a 3-bit period counter, 0 to 7 are repeatedly counted (ROT-COUNT in FIG. 2). When the HP sensor 501 detects the edge of the HP flag 510, the pulse counter 551 latches the count value at that time. Since the signal from the HP sensor is also input to the control circuit 550 as an interrupt signal, the interrupt process (FIG. 4B) is activated when the interrupt occurs. 4B, first, the value ROT_CNT_COUNTER of the pulse counter 551 is read to determine the number of correction pulses (corresponding to a certain number of claims 1) (S411). The number of correction pulses is a remainder from the number of divisions of the basic step−the read counter value−the number of movement steps. The number of movement steps is the number of steps (the number of micro steps) by which the motor is driven until the movement to the home position after the edge of the HP flag 510 is detected. When the excitation phase of the motor at the home position is set to 0, if the number of movement steps after HP sensor detection is not divisible by the number of divisions of the basic step, the motor stops in the middle of the basic step. A value indicating the excitation phase in the stopped state is (the remainder with respect to the number of movement steps). For example, if the number of movement steps is 1333 and the number of divisions of the basic step is 8, the remainder obtained by dividing 1333 by 8 is 5, so that “the remainder with respect to the number of movement steps” is 5. That is, in this example, the number of correction pulses is 8−pulse counter value−5 = 3−pulse counter value.

  If the correction pulse number is obtained, the correction pulse number is added to the movement step number 1333 from the position where the HP flag is detected by the HP sensor 502 (referred to as the HP sensor position) to the home position to correct the correction pulse number. The number of movement steps is obtained (S412).

  In the above example, the number of correction pulses with respect to the counter value when the edge of the HP flag 510 is detected is set as shown in the table of FIG. In FIG. 3, a latch count value 301 is a value of a pulse counter at a timing when the HP sensor 501 outputs a detection signal. This pulse counter value is a value that specifies the number of micro steps in the basic step of the stepping motor, that is, the order of the micro steps in the basic step. The phase of the motor when the motor is driven to the home position by driving the 1333 step (microstep) motor based on this timing is the corrected non-stop phase position 302. This value is a remainder obtained by adding the latch count value 301 to 1333 which is the number of movement steps and dividing the result by the number of divisions of the basic step (here, 8). The number of correction pulses is the number of microsteps to drive the motor from the corrected non-stop phase position 302 to the stop phase position during driving in one basic step. If the number of correction pulses, that is, “3-latch count value” is added to the number of movement steps 1333 from the HP sensor position to the home position, the number becomes a multiple of the division number of microsteps. Therefore, when the drive motor 502 is driven by “3-latch count value” +1333 steps obtained by adding the correction pulse number from the HP sensor position, the rotational phase of the drive motor 502 at the stop position matches the stop position at the time of basic step drive. . That is, the driving torque of the motor at the home position can be made constant. In this way, when the number of microsteps to drive the stepping motor is converted into the number of basic steps, the latch count value specified by the pulse counter is calculated from the deviation from the basic step boundary (the number of microsteps that is insufficient). Subtract. The value obtained by subtraction is the number of correction pulses. By driving the motor by microstep driving by a value (correction value) added to the number of microsteps to be driven (1333 in this example), the stop position of the motor after rotation is the boundary of the basic step. Match.

  In the table shown in FIG. 3, a case where the correction pulse is a positive integer (reference numeral 303) and a case where both the positive and negative are indicated (reference numeral 304) are displayed. Any value may be used depending on the stop accuracy of the stop position.

  If the corrected moving step number is obtained, the control circuit 550 drives the drive motor by the number of microsteps (that is, outputs a clock (S413), and then stops supplying the clock to stop the motor. Then, the signal ROT_CNT_ENB is set to the low level to reset the pulse counter 551 (S414).

  In this way, in the home position search operation flow, the correction pulse is set by the interrupt process, and the continuous operation is performed with the stop position corrected so that it becomes the predetermined phase excitation position (that is, the position of the basic step unit). It will be. For this reason, the rotation phase of the stepping motor at the home position is a phase determined in units of basic steps, and the stop torque and start torque of the drive motor 502 at the home position are constant.

  This example will be described with reference to FIG. In FIG. 2, when a signal ROT_HP is input from the HP sensor 501, the value of the pulse counter 501 is latched. Since the latch count value at this time is 5, the number of correction pulses is 3-5 + 1333 = 1331. However, in FIG. 2, the operation “−” is an operation (modulus operation) that obtains a positive integer with 8 as a modulus, so that 3−5 = 6 and the number of correction pulses is 1339. That is, after the 1333 microstep motor is driven to the home position, the position that is further driven by 8 steps is set as the corrected home position.

By the control operation as described above, it is possible to determine the excitation phase position when the stepping motor driven by the microstep method is stopped. That is, the phase of the microstep of the drive motor can be kept constant when the rotary developing device is stopped (naturally when restarting). Thereafter, when the rotary developer is rotated 30 degrees and 60 degrees in order to change the color of the toner to be developed, the number of pulses for the rotation is a multiple of 8, so that the same excitation phase position is always obtained. It becomes. Therefore, it is possible to suppress banding due to a change in the vibration generation level. When the rotary developing device 500 makes one round, the drive motor 502 is rotated an integral number of times to return to the original rotational phase.
[Modification]
As described above, there are some image forming apparatuses in which the rotation is not 30 degrees or 60 degrees and the number of pulses is not a multiple of 8, or the relationship between the rotation phase of the rotary developer and the phase of the drive motor is not constant. Let's go. In such a case, not only the home position operation but also a mark similar to the aforementioned HP flag 510 for identifying the position is attached to the position of each color developer on the rotary developer. The ROT_HP signal is also generated when these marks are detected. The control circuit 550 executes the processes of FIGS. 4A and 4B. However, after the HP_ROT interruption, the number of steps for driving the motor is determined according to the stop position of the developing unit for each color.

  In this way, the number of motor drive steps is corrected so that the phase of the microstep of the drive motor 550 at the stop position of the rotary developing device 550 is constant during the operation of moving the developing portions of the respective colors to the development positions. This makes it possible to always have the same excitation phase position.

  Furthermore, in the case of a system in which the amount of misalignment due to the correction pulse is a problem, the vibration level is controlled to the same level by variably controlling the drive voltage / drive current level according to the excitation phase position at the time of stop. It is possible.

  In the present invention, the rotary developing device is described as an example of the load, but the present invention is not limited to this. In other words, the present invention can be applied when a stepping motor driven by a microstep method is used as a drive source and a load that suppresses vibration and requires precise positioning is driven.

  Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) consisting of a single device even if it is applied to a system composed of a plurality of devices (eg, a host computer, interface device, reader, printer, etc.). You may apply. Another object of the present invention is to supply a recording medium recording a program code for realizing the functions of the above-described embodiments to a system or apparatus, and the system or apparatus computer reads out and executes the program code stored in the storage medium. Is also achieved. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention.

It is a figure which shows the rotation developing device structure of embodiment. It is a figure which shows the pulse correction control operation specification of embodiment. It is a figure which shows the correction | amendment pulse table of embodiment. It is a figure which shows the control flow of embodiment. It is a figure which shows the control flow of embodiment. It is a figure which shows the function setting table | surface of a pulse counter. It is a banding outline figure. It is a schematic diagram of a vibration propagation path. It is a figure which shows the operation response characteristic by the drive current of a stepping motor. It is a general explanatory view of required torque during acceleration / deceleration driving. It is a figure which shows the constant current drive circuit of a stepping motor. It is a figure which shows the electric current command value at the time of microstep drive. It is a figure which shows the electric current and output torque at the time of 1/8 micro step drive. It is a figure which shows the electric current and output torque at the time of 1/4 micro step drive. It is a figure which shows the step response characteristic at the time of 1/4 micro step drive. 1 is a diagram illustrating an image forming apparatus.

Claims (5)

A stepping motor drive control device of a microstep drive system that drives the stepping motor in units of microsteps obtained by dividing a basic step driven by a basic step angle of a stepping motor into a predetermined number,
A driving circuit for driving the stepping motor by a microstep method;
Detecting means for detecting a timing at which a load rotationally driven by the stepping motor reaches a predetermined rotational phase;
A counter for specifying which microstep in the basic step of the stepping motor the timing detected by the detection means;
A pulse for driving the stepping motor in units of the microsteps is sent to the drive circuit, and the stepping motor is driven in a certain number of microsteps based on the timing detected by the detection means. Drive control means for stopping the rotational phase of the load at a predetermined phase;
The drive control means corrects the fixed number so as to stop at a rotation phase in units of basic steps when the stepping motor is driven based on the order of microsteps specified by the counter. Stepping motor drive control device.   The drive control means corrects the fixed number by adding a value obtained by subtracting a value specified by the counter to the fixed number from the predetermined number that is the divided number of the basic step. The apparatus according to claim 1.   The apparatus according to claim 1, wherein the detection unit detects a timing at which one of a plurality of predetermined rotation phases for the load is reached. The load is a rotary developing device for color images included in a one-drum electrophotographic image forming apparatus,
The predetermined rotation phase is such a rotation phase that the color developing unit of the rotating developer reaches the developing position of the photosensitive drum by driving the stepping motor by the predetermined number of microsteps from the rotation phase. The device according to claim 1, wherein the device is a device.   5. An image forming apparatus, wherein the rotary developing device is rotationally driven by the stepping motor drive control device according to claim 4.

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