JPH10201276A - Servo control device for scanner of image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanner control device of an image formation device wherein the drive signals for a motor are all turned for a certain period at forward/reverse switching to prevent a through current. SOLUTION: An H-type bridge circuit which rotates, in forward/reverse direction, a motor M31, a micro controller MC31 which performs rotation speed detection, speed calculation, and speed control with the detection signal of an encoder EC31, a detecting part CS31 which detects motor's current value and direction, and a feedback system wherein speed is controlled with a deviation of a motor current value and a target indication current value from a speed calculation result, and the target instruction current value is compared to the motor current value to control motor's rotation direction are provided. A value obtained by performing differential amplification with such value as motor current is voltage-transduced and such value as target indication current value is voltage-transduced is compared to such value as motor current is voltage-transduced at motor stop, and motor's current direction is judged with the obtained binary signal. Pulse generating means IC35 and IC36 which generate a constant or variable pulse signal, with changeover of binary signal level being as trigger, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which has a scanner which travels along a document image and reads image data from the document image, and which reciprocates the scanner by a motor. Thus, for example, the present invention can be applied to general techniques for performing speed control, position control, and the like using a DC servomotor.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, an original placed on a contact glass is irradiated with illumination light from a light source while scanning a scanner, and reflected light from the original image is captured as image data. An exposure process is performed by forming an image on a photoconductor. FIG. 3 schematically shows the image forming apparatus. In FIG. 3, below a contact glass 1 on which a document 2 is placed, a first scanner in which a light source 3 and a first mirror 4 are integrally mounted, and a second mirror 5 and a third mirror 6 are integrally mounted. A second scanner is provided, and an imaging lens 7 and a fixed fourth
A mirror 8, a fifth mirror 9, and a sixth mirror 10 are provided in this order, and a protective glass 11 and a photosensitive drum 12 are provided in this order on the optical path reflected by the sixth mirror 10.

In the first scanner, the light source 3 illuminates the original 2 in a slit shape while moving from left to right along the original 2 on the contact glass 1 at a constant speed V in FIG. The mirror 4 reflects in the horizontal direction.
The second mirror 5 and the third mirror 6 of the second scanner fold the reflected light from the first mirror 4 in the horizontal direction. The folded reflected light is reflected by the imaging lens 7, the fourth, fifth, and sixth mirrors 8, 9, and 10 and converges on the photosensitive drum 12, and the image of the original 2 is placed on the photosensitive drum 12. Tied. As described above, the first scanner moves along the document 2 at a constant speed V, and in synchronization with this, the second scanner moves from left to right at a speed of V / 2, and The optical path length to the drum surface is always kept constant. By rotating the photosensitive drum 12 in synchronization with the movement of the first and second scanners, image data is read from the original image and the same image as the original image is formed on the photosensitive drum 12. The first and second scanners are driven by a motor, and are returned to their original home positions when one scan is completed.

In order to read such image data, a scanner is driven in a forward / reverse direction using a DC servomotor. FIG. 4 shows an example of a servo control device in a scanner of a conventional image forming apparatus. In FIG. 4, a DC servo motor M1 has four MOS
The FETs Q1 to Q4 (hereinafter simply referred to as “Q1” and “Q2”) are connected to the middle point of an H-type bridge circuit. More specifically, a series circuit composed of Q1 and Q3 and a series circuit composed of Q2 and Q4 are connected between the power supply VMM and the ground, and between the connection point of Q1 and Q3 and the connection point of Q2 and Q4. The motor M1 is connected. Each Q1, Q
2, Q3, and Q4 each have a diode D that flows a current in a direction opposite to the direction of the current flowing through Q1, Q2, Q3, and Q4.
1, D2, D3, and D4 (hereinafter simply referred to as "D1" and "D2") are connected in parallel. Each Q1, Q
2, Q3 and Q4 are turned on by a command from a microcontroller (hereinafter referred to as "microcomputer") MC1 described later.
Off control is performed, and each control of forward / reverse rotation control, speed control, and stop is performed.

The microcomputer MC1 has two output ports P0 and P1 for setting the rotation direction of the motor M1,
It has a pulse width modulation (hereinafter referred to as "PWM") signal output port for performing speed control. Output ports P0, P1
Output on and off control the above Q1 and Q2, respectively. Outputs from the output ports P0 and P1 are also supplied to AND circuits IC3 and IC3 via inverters IC1 and IC2 respectively.
Input to IC4. The PWM signal is also input to each of the AND circuits IC3 and IC4, and the output ports P0,
The AND of the inverted signal of the output from P1 is taken, and the output of each of the AND circuits IC3 and IC4 is Q2 and Q4, respectively.
Is turned on and off.

An encoder E is provided on the rotation output shaft of the motor M1.
C1 is attached, and a pulse signal corresponding to the rotation speed of the motor M1 is output from the encoder EC1, and this pulse signal is frequency-divided as a rotation speed signal by the frequency dividing circuit A1, and then input to the counter input port of the microcomputer MC1. Is done. The pulse signal from the encoder EC1 is composed of a plurality of phase signals having a phase shift corresponding to the forward and reverse rotation directions, and the rotation direction is detected by the output of the flip-flop circuit FF1 which is inverted according to the direction of the phase shift. , The rotation direction signal is input to the input port P2 of the microcomputer MC1.

As described above, the H-type bridge circuit composed of Q1, Q2, Q3, and Q4 constitutes a motor drive circuit that switches the current of the motor M1, and the microcomputer MC1 that controls the entire operation transmits the motor M1. PW for speed control
M signal and two P0 and P1 for setting the rotation direction
Signals are output, and the motor M1 is driven by these signals. The motor drive circuit outputs the two signals P0, P
As shown in the truth table in FIG. 4, the four combinations of 1 can form the forward rotation direction, the reverse rotation direction, the stop state, and the setting prohibited state. The forward rotation direction is a document reading direction (a direction from left to right in FIG. 3) by the scanner described with reference to FIG. 3, and the reverse rotation direction is a return operation for returning the scanner to its original position.

In the speed control, the period of the output pulse signal of the encoder EC1 attached to the shaft of the motor M1 is counted in the microcomputer MC1 to detect the rotation speed, and the detected rotation speed and a preset target rotation speed are detected. PI control is performed based on the deviation from the speed to change the duty ratio of the PWM signal. As a result, the duty ratio of the lower side Q3 or Q4 of the H-type bridge circuit changes, and the rotation speed of the motor M1 changes, so that control is performed so as to reach the target rotation speed. Speed control is interrupt processing by encoder signal,
Alternatively, high-speed processing is performed by a time interval interrupt processing of about several msec. This control is called full software servo, and all controls are implemented by software.

In scanner control of a high-speed copying machine, torque is reduced due to an increase in winding resistance due to heat generated by high-speed rotation of the motor, and the control becomes unstable. A constant current driving method using a circuit is used. An example of this is shown in FIG.

In FIG. 5, four MOSFETs Q1
The H-type bridge circuit constituted by 1, Q12, Q13, and Q14 is for rotating and driving the motor M11.
The motor M11 is connected between the connection point of Q1 and Q13 and the connection point of Q12 and Q14. Q11, Q12, Q1
D11, D12, D13, D1
4 are connected in parallel and in a direction in which a current flows in the opposite direction to the current flowing through Q11, Q12, Q13, and Q14.
D15 is interposed between Q11 and Q13 in the forward direction from Q11 to Q13, and Q12 is interposed between Q12 and Q14.
D17 is interposed in the forward direction from to Q14.
A motor current detecting resistor R11 is connected between the H-type bridge circuit and the ground, and the motor M
D16 is connected in the forward direction toward the connection point between D11 and D15, and D18 is connected in the forward direction from the ground to the connection point between the motors M11 and D17. The above resistor R
The voltage corresponding to the motor current detected by 11 is
The signal is input to the differential amplifier IC16 via the amplifier IC15.

The microcomputer MC11 determines the motor speed set in advance and the motor M1 detected by the encoder EC11.
The control target value is calculated as a current value based on the deviation from the speed of 1, and the current value that is the control target value is converted from a digital signal to an analog signal by D / A conversion to obtain a speed control value.
The difference between the speed control value and the detected motor current value is calculated by the differential amplifier IC16, and the difference is converted into a PWM signal by the comparator IC17 using a triangular wave, and the PWM signal corresponds to the duty ratio of the PWM signal. The motor is driven to control the speed.

In the example shown in FIG. 5, during normal rotation, when Q14 is on and Q11 is on by the PWM signal, current flows from the power supply VMM through Q11 to the motor M11, and D17,
It flows to the motor current detecting resistor R11 through Q14.
Therefore, the current can be converted into a voltage by the resistor R11 and a voltage value corresponding to the motor current value can be detected. When Q11 is turned off by the PWM signal, D16 is turned on by the back electromotive force of the motor M11, and the regenerative current becomes D17 and Q1.
4. Flow through R11 to ground, then from ground to D16 and back to motor M11. In this case, unlike the example shown in FIG. 4, the regenerative current generated when the PWM signal is off also flows through the motor current detecting resistor R11, so that an accurate motor current can be detected as a voltage value.

The indication of the direction of rotation is the same as in the example shown in FIG. In the speed control, a control target value is calculated as a current value based on a deviation between a predetermined motor speed and a speed of the motor M11 detected by an encoder EC11 connected to the motor M11, and the control target value is calculated by D / A conversion. Is converted into a digital signal to obtain a control value. The difference between the current value, which is the control target value, and the detected motor current value is calculated by the differential amplifier IC 16, and this difference is used to generate a PWM signal by the comparator IC 17 using a triangular wave. The motor is driven accordingly to control the speed. At the time of reverse rotation, Q13 is turned on and Q12 is turned on by the PWM signal.
Is on, current flows from VMM through Q12 to motor M
11, and flows to the motor current detecting resistor R11 through D15 and Q13. Therefore, the current can be converted into a voltage by the resistor R11 and a voltage value corresponding to the motor current value can be detected. When Q12 is turned off by the PWM signal,
D18 is turned on by the back electromotive force of the motor M11, and the regenerative current flows through D15, Q13 and R11 to the ground,
The motor returns to the motor M11 from the ground through D18.

In the example shown in FIG. 5, the direction of rotation is selected by the output ports P0 and P1 of the microcomputer MC11. As shown in FIG. 6, the forward rotation direction instruction of the motor is:
From the start-up of the scanner to the end of document reading, and from the reversing brake at the time of return deceleration to the stop of the scanner, the reverse rotation direction instruction is predetermined from the reversing brake at the end of document reading to the end of return acceleration and return constant-speed running. . That is, the direction of the current flowing through the motor is determined in advance, and the speed is controlled by adjusting the current in accordance with the direction of the PWM signal.

As can be seen from FIG. 6, the scanner of the high-speed copying machine is realized by increasing the speed at the time of return, and is driven at a speed approximately four to seven times the speed at the time of document reading. . When stopping the scanner by decelerating from the maximum speed at the time of return, the rotation direction of the motor is reversed during deceleration and the reverse brake is used, but the problem here is that when switching the rotation direction the motor The excessive electromechanical voltage causes excessive braking, resulting in an unexpectedly low speed. The control attempts to reduce the motor current to compensate for this speed drop, that is, the excessive reverse braking amount.However, even if the control target value is set to zero, the excessive reverse braking amount cannot be corrected. Will occur. Therefore, the scanner vibrates at the time of return deceleration, generating abnormal noise, and variations in the stop position due to the instability of the scanner speed due to the vibration. Also, when using a DC motor with a large induced voltage or when the sliding load of the scanner is large, there is a limit to accurately set the acceleration for return deceleration, and the scanner must be stopped at the target acceleration. May be difficult.

In order to solve such a problem, the present inventor has studied a constant current driving method capable of detecting the current and direction of the current flowing through the motor and automatically switching the direction of the current flowing through the motor. . An example is shown in FIG.

In FIG. 7, four MOSFETs Q2
1, Q22, Q23, Q24 (hereinafter simply "Q21""Q
22) is connected to a DC drive for driving a scanner of an image forming apparatus such as a copying machine.
The current flowing through the servomotor M21 is switched, and the motor M21 is connected to the middle of the H-type bridge circuit. More specifically, a series circuit including Q21 and Q23 and Q22 and Q2 are connected between the power supply VMM and the ground.
4 are connected, and a motor M21 is connected between a connection point between Q21 and Q23 and a connection point between Q22 and Q24. Each of the diodes D21, D22, and D24 passes a current in the opposite direction to the current flowing through the Q21, Q22, Q23, and Q24.
23 and D24 (hereinafter simply referred to as “D21” and “D22”) are connected in parallel. Each Q21, Q2
2, Q23 and Q24 are on / off controlled by a command from the microcomputer MC21, and each control of forward / reverse rotation control, speed control and stop is performed.

Between the connection point of Q21 and Q23 and the motor M21, a Hall current detector CS21 is connected in series with the motor M21 as means for detecting the motor current value and the current direction. The Hall current detector CS21 detects a magnetic flux generated in proportion to the current in a non-contact manner by a combination of a magnetic core and a Hall element, converts the current into a voltage, and outputs the voltage. FIG. 8 shows an example of the characteristic. As shown in FIG. 8, when no current flows through the motor, that is, when the motor is in a stopped state, the output voltage is OV, and when the current is a positive current (tentatively, the motor is in the normal rotation direction), the positive output voltage is changed to a negative current ( (Suppose the direction of motor reverse rotation)
In the case of, a negative output voltage is generated. This output voltage is a value proportional to the current. Therefore, the motor current value and the direction of the current can be detected by checking whether the output voltage of the Hall current detector CS21 is 0 V and the polarity of the output voltage. The polarity of the value obtained by converting the control target current value into a voltage is determined in accordance with the polarity of the Hall current detector CS21, such that the plus side is the motor normal rotation direction and the minus side is the motor reverse rotation direction.

The motor M21 is provided with an encoder EC21 which generates a pulse signal of a plurality of phases which is a pulse signal corresponding to the rotation of the motor M21 and whose phase shift direction differs depending on the rotation direction. The pulse signal from the encoder EC21 is used as a rotation speed signal by the microcomputer MC21.
Is input to the counter input port. Further, a flip-flop circuit FF21 is provided which inverts according to the direction of the phase shift of the plurality of phase signals from the encoder EC21, the rotation direction is detected by the output of the flip-flop circuit FF21, and the rotation direction signal is input to the input port P2 of the microcomputer MC21. To be entered.

The microcomputer MC21 calculates a control target value as a current value based on a deviation between a preset motor speed and the speed of the motor M21 detected by the encoder EC21, and converts the control target value current value to a voltage value. Convert and output. This voltage value is converted from a digital signal to an analog signal by the D / A converter DAC 21 to obtain a control target value. The current value, which is the control target value, and the motor current value detected by the Hall current detector CS21 are the differential amplifier I
The difference is input to C21 and the difference between the control target value and the motor current value is calculated. In addition, the difference signal between the control target value and the motor current value is calculated as the difference between the voltage obtained by converting the motor current when the motor is stopped by the differential amplifier IC22, that is, 0 V. The output of the differential amplifier IC22 is Comparator IC23
Is binarized. The binarized signal is fed back to determine the forward / reverse rotation of the motor M21. An inverted signal S21 of the binarized signal by the inverter IC24 controls ON / OFF of the Q23, and the binarized signal S22 is Q
24 is turned on and off.

The output of the differential amplifier IC22 is full-wave rectified by an absolute value circuit A22 having an operational amplifier IC27 and another operational amplifier IC28, and an operation signal of a difference between the control target value and the motor current value is calculated. Then, the absolute value of the difference from the value obtained by voltage conversion of the motor current when the motor is stopped is calculated. This absolute value signal is compared with the triangular wave output from the triangular wave generation circuit A21 by the comparator IC29, and a PWM signal is output. This PWM signal is output to the NAND circuit IC2.
5, input to the IC 26. The NAND circuit IC25 also receives the inverted signal S21 of the binary signal, and the NAND circuit IC26 receives the binary signal S22.
The PWM signal changes the duty ratio of Q21 and Q22 on the upper side (current inflow side) of the H-type bridge circuit that rotationally drives the motor M21 to perform speed control.

The operation at the time of scanner return in the above circuit example will be described. 7, the control target current value during the return constant speed operation is a negative value. At this time, the binarized signals S21 and S22 in the example shown in FIG.
1 = “H” level, S22 = “L” level, and the motor is in the reverse direction. When Q23 is on and the PWM signal turns on Q22, the motor M21 is supplied from the power supply VMM through Q22 to the motor M21, Hall current detector CS2
1, and current is flowing to ground through Q23.
When Q22 is off by the PWM signal, the motor M21
Regenerative current from the Hall current detector CS21 and Q2
3 to ground and back to motor M21 through D24. At this time, the Hall current detector CS
The output voltage of 21 is negative.

When the scanner reaches the return deceleration position,
In order to decelerate using the reverse brake operation, the control target current value is set to plus. Thereby, S21 =
The "L" level, S22 = "H" level, automatically switch to energization in the motor normal rotation direction, and the direction of the current is reversed. During energization in the motor normal rotation direction, Q24 is on and P
When Q21 is turned on by the WM signal, the motor M21 passes through the power supply VMM through Q21 and passes through the Hall current detector CS2.
1. Current is flowing to ground through motor M21 and Q24. When Q21 is turned off by the PWM signal, a current flows from the motor M21 to the ground through the Q24, and then returns to the motor M21 through the D23 and the hall current detector CS21.

Here, when the direction of the current is switched,
Excessive torque is generated by the back electromotive voltage of the motor M21,
The reverse braking amount becomes larger than the control operation amount, and the speed rapidly decreases. At this time, a current larger than the control target current value flows to the motor M21, so that S21 = “H” level and S22 = “L” level, the energizing direction is switched to the motor reverse direction, and the reverse motor brake amount is released. Perform the operation. In this way, by providing a means for automatically switching the direction of the current flowing to the motor according to the control instruction current value and the current value and the current direction of the current actually flowing to the motor, it is possible to appropriately control the rapid speed change. In this way, vibration during deceleration of the scanner is prevented, variations in the stop position of the scanner due to vibration are prevented, and the margin for setting the control speed profile is improved.

[0025]

The servo control device in the scanner of the conventional image forming apparatus described above is shown in FIG.
As described in the above example, since the current flowing through the motor is automatically switched, a through current may flow through the H-type bridge circuit at the time of switching between forward and reverse rotations, and the motor drive circuit may be destroyed by an overcurrent.

In view of the above-mentioned problems of the prior art, the present invention adds a circuit that turns off all the drive signals of the motor for a certain period of time when switching between forward and reverse rotations, thereby preventing the drive circuit from being destroyed due to a through current. It is an object of the present invention to provide a servo control device in a scanner of an image forming apparatus that can perform the above-described operations.

[0027]

According to the first aspect of the present invention,
In a servo control device in a scanner of an image forming apparatus, an H-type bridge circuit that drives a motor forward and reverse by a pulse width modulation signal that determines a motor speed and a signal that determines a rotation direction; an encoder attached to a motor shaft; Detection signal of the motor by the detection signal of
A microcontroller that performs speed calculation and speed control,
A detection unit for detecting a current value flowing in the motor and its current direction; performing speed control based on a deviation between the target command current value from the speed calculation result and the motor current value; and further controlling the target command current value and the motor current value. And a feedback system that determines the direction of the current flowing to the motor based on the comparison result and controls the motor rotation direction. This feedback system converts the motor current into a voltage in the feedback of the constant current control circuit. The value obtained by differentially amplifying the value obtained by voltage-converting the target instruction current value and the value obtained by voltage-converting the motor current when the motor is stopped are compared, and the resulting binary signal is supplied to the motor. A pulse generating means for generating a constant or variable pulse signal triggered by the switching of the binary signal level; Characterized in that it.

According to a second aspect of the present invention, in the first aspect of the invention, at the time of switching of the current direction automatically determined by the current direction determining means, it is determined by a pulse signal generated by the pulse generating means. There is provided a means for turning off the driving of the motor for a certain period of time, and the switching of the drive control signal from the off state to the on state of the H-type bridge circuit is delayed.

According to a third aspect of the present invention, in accordance with the second aspect of the present invention, H is controlled by the delayed drive control signal.
It is characterized in that only one of the current inflow side and the current outflow side of the type bridge circuit is turned off for a certain time.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a servo control device in a scanner of an image forming apparatus according to the present invention will be described below with reference to FIGS. In FIG. 1, four MOSFETs Q31, Q32, Q33,
The H-type bridge circuit consisting of Q34 (hereinafter simply referred to as "Q31" and "Q32") switches the current supplied to the DC servomotor M31 that drives the scanner of the image forming apparatus such as a copying machine. The motor M31 is connected to the middle of the H-type bridge circuit. More specifically, a series circuit consisting of Q31 and Q33 and a series circuit consisting of Q32 and Q34 are connected between the power supply VMM and the ground, and a motor is connected between the connection point of Q31 and Q33 and the connection point of Q32 and Q34. M31 is connected. Each Q31, Q3
2, Q33 and Q34 have these Q31, Q32 and Q3
3. Diodes D31, D32, D33 and D34 (hereinafter simply referred to as "D31" and "D32") for passing a current in the opposite direction to the current flowing through Q34 are connected in parallel. Each of Q31, Q32, Q33, Q34 is on / off controlled by a command from the microcomputer MC31,
Each control of forward / reverse rotation control, speed control, and stop is performed.

Between the connection point of Q31 and Q33 and the motor M31, a Hall current detector CS31 is connected in series with the motor M31 as means for detecting the motor current value and the current direction. The Hall current detector CS31 detects a magnetic flux generated in proportion to the current in a non-contact manner by a combination of a magnetic core and a Hall element, converts the current into a voltage, and outputs the voltage. An example of the characteristic is as shown in FIG. 8. When no current is flowing through the motor, that is, when the motor is stopped, the output voltage is OV, and when the current is positive (tentatively, the motor is in the normal rotation direction), the output is positive. When the voltage is a negative current (assuming the motor is in the reverse direction), a negative output voltage is generated. This output voltage is a value proportional to the current. Therefore, the Hall current detector CS31
By checking whether the output voltage is 0 V and the polarity of the output voltage, the motor current value and the direction of the current can be detected. The polarity of the value obtained by converting the control target current value into a voltage is determined in advance in accordance with the polarity of the hall current detector CS31, with the plus side being the motor normal rotation direction and the minus side being the motor reverse rotation direction.

The motor M31 is provided with an encoder EC31 that generates a pulse signal of a plurality of phases which is a pulse signal corresponding to the rotation of the motor M31 and has a phase shift direction which differs depending on the rotation direction. The pulse signal from the encoder EC31 is used as a rotation speed detection signal by the microcomputer MC.
It is input to 31 counter input ports. Further, a flip-flop circuit FF31 is provided which inverts according to the direction of the phase shift of the multi-phase signal from the encoder EC31, the rotation direction is detected by the output of the flip-flop circuit FF31, and the rotation direction signal is input to the input port P2 of the microcomputer MC31. To be entered.

The microcomputer MC31 calculates a control target value as a current value based on a deviation between a preset motor speed and a speed of the motor M31 detected by the encoder EC31, and converts the current value as the control target value to a voltage value. Convert and output. This voltage value is converted from a digital signal to an analog signal by the D / A converter DAC 31 to obtain a control instruction current value. The voltage corresponding to the control instruction current value and the voltage converted value of the motor current detected by the Hall current detector CS31 are input to the differential amplifier IC31, and the difference between the control instruction current value and the motor current value is calculated. Is done. The difference signal between the control instruction current value and the motor current value is calculated as the difference between the value obtained by converting the motor current when the motor is stopped and the motor current when the motor is stopped, that is, 0 V, by the differential amplifier IC32.
The output of 32 is binarized by a comparator IC33.

The binarized signal is input to the monostable multivibrators IC35 and IC36, and the rising and falling edges of the binarized signal are used as a trigger to output "L" from the multivibrator IC35 and IC36.
A level signal is output. Multivibrator IC3
5, The output pulse of IC 36 is input to AND circuit IC 37, and the output is input to AND circuits IC 38 and IC 39. An AND circuit IC38 receives an inverted signal S31 of the above-mentioned binarized signal from the inverter IC34,
The output signal S11 controls on / off of the Q33 through a bridge removing circuit A31. The binarized signal S32 is input to the AND circuit IC39, and the output signal S22 controls ON / OFF of the Q34 through the bridge removing circuit A32.

The output of the differential amplifier IC32 is full-wave rectified by an absolute value circuit A33 having an operational amplifier IC312 and another operational amplifier IC313, and an operation signal of a difference between the control instruction current value and the motor current value is obtained. And the absolute value of the difference between the value and the value obtained by voltage conversion of the motor current when the motor is stopped is calculated. This absolute value signal is compared with the triangular wave output from the triangular wave generation circuit A34 by the comparator IC 314, and a PWM signal is output. This PWM signal is input to the NAND circuits IC310 and IC311. The NAND circuit IC310 also has the reverse drive signal S3 after the motor drive signal S11 has passed through the bridge removal circuit A31.
11 is input, and the forward drive signal S322 after the motor drive signal S22 has passed through the bridge removal circuit A32 is input to the NAND circuit IC311. The PWM signal is used to control the speed by changing the duty ratio of Q31 and Q32 on the upper side (current inflow side) of the H-type bridge circuit that rotationally drives the motor M31.

Next, the operation of the embodiment shown in FIG. 1 will be described. A circuit including the differential amplifier IC31, the differential amplifier IC32, and the comparator IC33 performs speed control based on a deviation between the target instruction current value and the motor current value, and further compares the target instruction current value with the motor current value. A feedback system that determines the direction of the current flowing to the motor based on the comparison result and controls the motor rotation direction is configured. The feedback system includes a value obtained by converting the motor current into a voltage and a target instruction current in the feedback of the constant current control circuit. The value obtained by differentially amplifying the value obtained by voltage-converting the value is compared with the value obtained by voltage-converting the motor current when the motor is stopped, and the resulting binary signal determines the direction of the current flowing to the motor. It constitutes direction determining means. That is, the differential amplifier IC31 in the constant current control circuit differentially amplifies the current value as the control target value and the detected motor current value, and this differential amplified signal and no current flow in the motor. At this time, that is, the signal when the current detector is OV in the motor stopped state is differentially amplified by the differential amplifier IC32, and this value is binarized by the comparator IC33 with respect to the OV in the motor stopped state.
Switching between the normal rotation direction and the reverse rotation direction is automatically performed by two signals of the binarized signal S32 and the signal S31 obtained by inverting the polarity of the binarized signal S32 by the inverter IC34.

Next, the means for determining the control operation amount and controlling the motor speed includes a signal indicating a difference between a current value as a control target value and the detected current value, and a signal indicating that no current is flowing through the motor, A signal obtained by differentially amplifying the signal when the motor is stopped and the signal when the current detector is OV is applied to a full-wave rectifier circuit A33.
Takes an absolute value for the OV in the motor stopped state.
This signal and the triangular wave are compared by the comparator IC314, and PW
An M signal is generated, and the PWM signal and the automatically determined rotation direction instruction signal are used to generate a Q3 signal of the H-type bridge circuit.
1 or Q32 is on / off controlled to supply a current corresponding to the duty ratio of the PWM signal to the motor M31 to control the speed of the motor M31.

Next, the operation of the above circuit at the time of scanner return will be described with reference to FIG. In FIG. 1, the control instruction current value during the return constant speed operation is a negative value. At this time, the binarized signals S31 and S32 in the embodiment shown in FIG.
Since "H" level, S32 = "L" level and the motor is in the reverse rotation direction, Q33 is on and PWM signal Q3
2 is on, the motor M31 is connected to the power supply VMM by Q3.
2, a current flows to the ground through the motor M31, the Hall current detector CS31, and the Q33. Also,
When Q32 is off by the PWM signal, current flows from the motor M31 to the ground through the Hall current detector CS31 and Q33, and returns to the motor M31 through D34. At this time, the output voltage of the Hall current detector CS31 is negative.

When the scanner reaches the return deceleration position,
In order to decelerate using the reverse brake operation, the control instruction current value is set to plus. As a result, as shown in FIG. 2, S31 = “L” level and S32 = “H” level, and the current is automatically switched to the forward direction of the motor, and the direction of the current is reversed. At this time, the multivibrator I
A pulse generating means including C35 and IC36 generates a pulse signal of a fixed time width triggered by the switching of the levels of the binary signals S31 and S32, and the AND circuit IC3
7, IC38, IC39, bridge removal circuit A31, A
32, the forward drive signal S322 changes to “H” level after a certain time from when the reverse drive signal S311 goes to “L” level. Is turned off for a certain period of time to prevent a through current flowing through Q32 and Q34.

During energization in the forward rotation direction of the motor, when Q34 is on and Q31 is on by a PWM signal, the motor M31 passes through the power supply VMM through Q31, and the Hall current detector CS
Current flows to ground through 31, motor M31, and Q34. When Q31 is turned off by the PWM signal, a current flows from the motor M31 to the ground through the Q34, and returns to the motor M31 through the D33 and the hall current detector CS31.

Here, when the direction of the current is switched,
Excessive torque is generated by the back electromotive voltage of the motor M31,
The reverse braking amount becomes larger than the control operation amount, and the speed rapidly decreases. At this time, a current larger than the control instruction current value flows to the motor M31, so that S31 = “H” level, S32 = “L” level, and the energizing direction is switched to the motor reverse direction to release the reverse brake amount. I do. At this time, the multivibrator ICs 35 and I
The pulse generating means including C36 generates the binary signal S31,
A constant pulse signal S30 triggered by the switching of the level of S32 is generated, and the reverse drive signal S311 changes to "H" level after a certain time from when the forward drive signal S322 changes to "L" level. When switching from forward rotation to reverse rotation, the power supply to the motor is turned off for a certain period of time,
A through current flowing through Q31 and Q33 is prevented.

As is clear from the above description, according to the embodiment as shown in FIG. 1, the current is automatically supplied to the motor according to the control instruction current value and the current value and direction of the current actually flowing in the motor. The means for switching the direction of the current, that is, the forward direction or the reverse direction of the motor, is provided, so that the control for the rapid change in speed can be appropriately performed, and the switching of the direction of the motor drive current is constant as a trigger. A pulse generating means for generating a pulse signal is provided, and the circuit is configured to turn off the driving of the motor for a certain period of time corresponding to the pulse signal. Therefore, it is possible to prevent a through current flowing through the motor driving circuit, The drive circuit can be prevented from being broken, and the reliability of the circuit can be improved.

In the embodiment shown in FIG. 1, when the H-type bridge circuit switches from off to on, the upper stage (current inflow side) and the lower stage (current outflow side) of the H-type bridge circuit
In both cases, the configuration is switched from off to on with a delay of a fixed time. However, only one of the upper and lower stages of the H-type bridge circuit may be switched from off to on with a delay for a fixed time. For example, when the binary signals S31 and S32 shown in FIGS. 1 and 2 rise or fall, a fluttering phenomenon similar to a chattering phenomenon may occur. In the case where the multivibrators IC35 and IC36 are not provided, if the fluttering phenomenon occurs, the MOS-FET constituting the H-type bridge circuit and the buffer amplifier on the input side thereof cannot follow the fluttering phenomenon, and the H-type bridge circuit does not follow the fluttering phenomenon. The upper and lower circuits may be turned on at the same time and a through current may flow through the motor. Further, if the time required for the fluttering phenomenon to settle out exceeds the delay time caused by the pulse signal S30, a through current will flow through the motor. In the embodiment shown in FIG. If the fluttering phenomenon occurs when the signals S31 and S32 are switched, the multivibrator ICs 35 and 36 are reset each time the signals S31 and S32 flap, and the delay is again delayed for a predetermined time from the reset point, so that a through current flows through the motor. Never. As described above, the delay time due to the pulse signal S30 is basically constant, but is substantially a binary signal S31,
The result is the same as that changed by the fluttering of S32. In the claims, "constant or" variable "pulse signal" means this.

[0044]

According to the first aspect of the present invention, the direction of the current automatically flowing to the motor, that is, the normal rotation direction of the motor, depends on the control target current value and the current value and the current direction of the current actually flowing through the motor. A means that can switch between the reverse direction and the reverse direction is provided, so that control for a sudden change in speed can be appropriately performed, and a pulse that generates a constant or variable pulse signal triggered by switching of the motor drive current direction is triggered. When the motor drive circuit is turned on / off or switched between the normal rotation direction and the reverse rotation direction, the current flowing through the motor drive circuit is interrupted for a time corresponding to the pulse signal, thereby providing the motor drive circuit. Can be prevented.

According to the second aspect of the present invention, there is provided an H-type bridge circuit having means for turning off the motor for a predetermined time determined by the pulse signal generated by the pulse generating means when the current direction is switched. Since the switching of the drive control signal from OFF to ON is delayed, it is possible to prevent a through current flowing through the motor drive circuit with a simple configuration, thereby preventing damage to the motor drive circuit and preventing circuit breakage. Reliability can be improved.

According to the third aspect of the present invention, only one of the current inflow side and the current outflow side of the H-type bridge circuit is turned off for a predetermined time by the delayed drive control signal. Can be simplified, and the number of components can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a servo control device in a scanner of an image forming apparatus according to the present invention.

FIG. 2 is a timing chart showing an operation of a servo control device in the scanner of the image forming apparatus.

FIG. 3 is a front view schematically illustrating an example of a scanner of the image forming apparatus.

FIG. 4 is a circuit diagram illustrating an example of a servo control device in a scanner of a conventional image forming apparatus.

FIG. 5 is a circuit diagram showing another example of a servo control device in a scanner of a conventional image forming apparatus.

FIG. 6 is a timing chart illustrating an operation of the scanner of the image forming apparatus.

FIG. 7 is a circuit diagram showing an example of a servo control device in a scanner of an image forming apparatus which is not known but has been studied so far.

FIG. 8 is a graph showing current-output voltage characteristics of a Hall current detector that can be used in the embodiment of the present invention.

[Explanation of symbols]

M31 Motor Q31 MOS • FET composing an H-type bridge circuit Q32 MOS • FET composing an H-type bridge circuit Q33 MOS • FET composing an H-type bridge circuit Q34 MOS • FET composing an H-type bridge circuit EC31 Encoder IC31 Difference Dynamic amplifier IC33 Comparator MC31 Microcontroller A33 Absolute value circuit A34 Triangular wave generation circuit CS31 Hall current detector for detecting current value and current direction IC35 Pulse generation means IC36 Pulse generation means

Claims (3)

[Claims] 1. A scanner for an image forming apparatus which runs along a document image and reads image data from the document image, and reciprocates the scanner by a motor, comprising: a pulse width modulation signal for determining a motor speed; An H-type bridge circuit that drives the motor forward and reverse according to a signal that determines the rotation of the motor; an encoder attached to the motor shaft; a microcontroller that detects the rotation speed of the motor, calculates the speed, and controls the speed based on the detection signal of the encoder; And a detection unit for detecting a current value flowing in the motor and a current direction thereof, and performing speed control based on a deviation between the target command current value from the speed calculation result and the motor current value. Compare and determine the direction of current flowing to the motor based on the comparison result to control the motor rotation direction A feedback system, wherein the feedback system differentially amplifies a value obtained by voltage-converting the motor current and a value obtained by voltage-converting the target instruction current value in the feedback of the constant current control circuit; The motor current is compared with a value obtained by converting the voltage of the motor current, and a current direction determining means for determining a direction of a current flowing to the motor based on a binary signal obtained as a result, wherein the switching of the binary signal level is used as a trigger. A servo control device in a scanner of an image forming apparatus, comprising: a pulse generating means for generating a fixed or variable pulse signal. 2. A means for turning off the motor for a predetermined time determined by a pulse signal generated by the pulse generating means when the current direction automatically changed by the current direction determining means is switched, 2. The servo control device for a scanner of an image forming apparatus according to claim 1, wherein the switching of the drive control signal from OFF to ON of the H-type bridge circuit is delayed. 3. The driving control signal delayed as described above,
3. The servo control device according to claim 2, wherein only one of the current inflow side and the current outflow side of the H-type bridge circuit is turned off for a predetermined time.