JP3462017B2 - Servo control device in scanner of image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo control device for an image forming apparatus having a scanner which runs along an image of a document and reads image data from the image of the document and which is reciprocated by a motor. Then, for example, the present invention can be applied to general techniques for performing speed control, position control, etc. using a DC servo motor.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a document placed on a contact glass is irradiated with illumination light from a light source while scanning a scanner, and reflected light from the document image is captured as image data. An exposure process is performed by forming an image on the photoconductor. An outline of this image forming apparatus is shown in FIG. In FIG. 4, below the contact glass 1 on which the original 2 is placed, a first scanner in which a light source 3 and a first mirror 4 are integrally attached, and a second mirror 5 and a third mirror 6 are integrally attached. A second scanner is provided, and an imaging lens 7 and a fixed fourth lens are provided on the optical path reflected by the third mirror 6.
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 the left to the right in FIG. 4 along the original 2 on the contact glass 1 at a constant speed V, and the reflected light is reflected by the first light. The mirror 4 reflects in the horizontal direction.
The second mirror 5 and the third mirror 6 of the second scanner return the reflected light from the first mirror 4 in the horizontal direction. The reflected light that has been returned is reflected by the imaging lens 7, the fourth, fifth, and sixth mirrors 8, 9 and 10 and converges on the photosensitive drum 12, so that the image of the original 2 is transferred onto the photosensitive drum 12. Tied together. 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, from the surface of the document 2 to the photoconductor. 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 DC servomotor is used to drive the scanner in forward and reverse directions. FIG. 5 shows an example of a servo control device in a scanner of a conventional image forming apparatus. In FIG. 5, the DC servo motor M1 has four MOS
It is connected to the middle point of an H-type bridge circuit composed of FETs Q1 to Q4 (hereinafter simply referred to as "Q1" and "Q2"). 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
Diodes D, 2, Q3, Q4, which flow a current in the opposite direction to the current flowing in Q1, Q2, Q3, 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 on / off controlled by a command from a micro controller (hereinafter referred to as "microcomputer") 20, which will be described later, and forward / reverse rotation control, speed control, and stop control are performed.

The microcomputer 20 has two output ports P0 and P1 for setting the rotation direction of the motor M1 and a pulse width modulation (hereinafter referred to as "PWM") signal output port for speed control. Outputs from the output ports P0 and P1 control ON / OFF of Q1 and Q2, respectively. The outputs from the output ports P0 and P1 are also input to the AND circuits 23 and 24 via the inverters 21 and 22, respectively. Each AND circuit 23, 24 also has the above PWM
A signal is input and ANDed with the inverted signal of the output from the output ports P0 and P1.
The output of 4 controls ON / OFF of Q2 and Q4.

An encoder E is provided on the rotation output shaft of the motor M1.
C1 is attached, a pulse signal corresponding to the rotation speed of the motor M1 is output, and this pulse signal is frequency-divided by the frequency dividing circuit 25 as a rotation speed signal, and then the microcomputer 20
Is input to the counter input port of. 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 26 which is inverted depending on the direction of the phase shift. The rotation direction signal is input to the input port P2 of the microcomputer 20.

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 20 that controls the overall operation controls the operation of the motor M1. PWM for speed control
A signal and two P0 and P1 signals for setting the rotation direction are output, and the motor M1 is driven by these signals. The motor drive circuit is configured to operate the two signals P0 and P1.
As described in the truth table in FIG. 1, the forward rotation direction, the reverse rotation direction, the stopped state, and the setting prohibited state can be created by the four combinations according to. The forward rotation direction is the document reading direction (direction from left to right in FIG. 4) of the scanner described with reference to FIG. 4, and the reverse rotation direction is the return operation of returning the scanner to the original position.

In the speed control, the cycle of the output pulse signal of the encoder EC1 attached to the shaft of the motor M1 is counted in the microcomputer 20 to detect the rotation speed, and the detected rotation speed and a preset target rotation are set. 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 Q3 or Q4 on the lower side of the H-type bridge circuit changes, the rotation speed of the motor M1 changes, and control is performed so as to reach the target rotation speed.
The speed control is performed at high speed by interrupt processing by an encoder signal or time interval interrupt processing of about several msec. This control is called full software servo, and all control is performed by software.

In scanner control of a high-speed copying machine, torque is reduced due to increase in winding resistance due to high-speed control and heat generation at high-speed motor rotation, and control becomes unstable. A constant current drive method using a circuit is used. Examples of this are shown in FIGS. 6 and 8.

In the example shown in FIG. 6, a motor current detecting resistor R11 is added to that shown in FIG. 5, and the current flowing through the resistor R11 is converted into a voltage to detect the voltage value corresponding to the motor current value. The duty ratio of the PWM signal is changed according to the voltage value to control the motor speed. More specifically, a motor current detection resistor R11 is added between the H-type bridge circuit composed of Q11, Q12, Q13 and Q14 and the ground, and the current flowing through this resistor R11 is converted into a voltage by the resistor R11. The voltage value corresponding to the motor current value is detected, and the detected voltage is the amplifier IC11.
It is amplified by and is input to the capacitor C11 via the analog switch IC15. Capacitor C
Reference numeral 11 indicates a peak hold of the voltage of the resistor R11, and this peak value is input to the differential amplifier IC13 via the buffer amplifier IC12. The microcomputer 20
The rotation speed of the motor M11 is calculated by the signal from the encoder EC11, the target instruction current value is calculated from the calculation result, and this is converted into an analog signal and input to the differential amplifier IC13. The differential amplifier IC13 outputs the deviation between the target instruction current value and the current value of the motor M11 replaced with the peak-held voltage. This deviation is compared with the triangular wave output from the triangular wave generating circuit 29 in the comparator IC14, and the PWM signal is output. As described above, the PWM signal changes the duty ratios of the lower side Q13 and Q14 of the H-type bridge circuit that rotationally drives the motor M11 so that speed control is performed.

FIG. 7 shows a signal waveform of each circuit portion in the normal rotation in the example shown in FIG. Q11 is turned on during forward rotation, PW
When Q14 is turned on by the M signal (section indicated by A in FIG. 7), current flows from the power supply VMM through Q11 to the motor M11.
To the current detecting resistor R11 through Q14. The resistor R11 converts the current into a voltage and detects the voltage value corresponding to the motor current value. When Q14 is off due to the PWM signal (section shown by B in FIG. 7), a counter electromotive force is generated in the motor M11, and a regenerative current passes through the power source VM through D12.
M, the power source VMM returns to the motor M11 through Q11, and no motor current flows through the resistor R11. Therefore, the current flowing through the motor M11 can be detected only when the PWM signal is on. As a countermeasure against this, in the example of FIG. 6, when Q14 is turned on by the PWM signal, the analog switch IC15 is turned on, and the voltage detected by the resistor R11 is peak-held by the capacitor C11. The voltage of C11 is used as the one corresponding to the motor current. As an example similar to that shown in FIG. 6, there is one described in JP-A-8-9681.

In the example shown in FIG. 6, the instruction of the rotation direction is selected by the output ports P0 and P1 of the microcomputer 20. As shown in FIG. 2, the forward rotation direction instruction is from the start-up of the scanner to the end of the original reading and from the reverse brake at the time of deceleration of the return to the stop of the scanner, and the reverse direction instruction is from the reverse brake at the end of the original reading to return acceleration and return. It is predetermined that the end of high-speed running. As described above, the preset motor speed and encoder EC
The control target value is calculated as a current value by the deviation from the speed of the motor M11 detected by 11, and the current value which is the control target value is converted by D / A conversion from a digital signal to an analog signal to obtain a speed control target value. To do. The difference between the current value, which is the control target value, and the detected motor current value is calculated by the differential amplifier I.
Computation is performed by C13, and the comparator I
A PWM signal is generated by C14, and the motor M11 is driven according to the duty ratio of this PWM signal to control the speed.

Next, the example shown in FIG. 8 will be described. In the example shown in FIG. 6, when the PWM signal is off, the regenerative current of the motor does not flow in the motor current detection resistor, and this is compensated by peak holding. However, in the example shown in FIG. The regenerative current also flows through the motor current detection resistor. In FIG. 8, four MOs
The H-type bridge circuit composed of S-FETs Q21, Q22, Q23 and Q24 is for rotating and driving the motor M21. The motor M21 is connected between the connection point of Q21 and Q23 and the connection point of Q22 and Q24. Has been done. Q2
1, Q22, Q23, and Q24 have D21 and D2, respectively.
2, D23, D24 in parallel and Q21, Q22, Q2
3, Q24 is connected in the opposite direction. Q21 and Q2
During the period of 3, D25 in the forward direction from Q21 to Q23
, And D27 is interposed between Q22 and Q24 in the forward direction from Q22 to Q24. A motor current detecting resistor R2 is provided between the H-type bridge circuit and the ground.
1 is connected to the motors M21 and D25 from the ground.
D26 is connected in the forward direction toward the connection point with and, and D28 is connected in the forward direction from the ground toward the connection point between the motors M21 and D27.

The voltage corresponding to the motor current detected by the resistor R21 is input to the differential amplifier IC23 via the amplifier IC21. The microcomputer 20 calculates a control target value as a current value based on the deviation between the preset motor speed and the speed of the motor M21 detected by the encoder EC21, and the current value, which is the control target value, is converted into a digital signal by D / A conversion. Is converted into an analog signal and used as the speed control value. The difference between this speed control value and the detected motor current value is calculated by the differential amplifier IC23, and this difference is converted into a PWM signal by the comparator IC24 using a triangular wave.
The motor is driven according to the duty ratio of the M signal to control the speed.

In the example shown in FIG. 8, when Q24 is on during normal rotation and Q21 is on due to the PWM signal, current flows from the power supply VMM to the motor M21 through Q21, and D27,
It flows to the motor current detection resistor R21 through Q24.
Therefore, the resistor R21 can convert the current into a voltage and detect the voltage value corresponding to the motor current value. When Q21 is off by the PWM signal, D26 is turned on by the back electromotive force of the motor M21, and the regenerative current is D27, Q2.
4 and R21 to flow to the ground, and from the ground to D26 to return to the motor M21. In this case, unlike the example shown in FIG. 6, since the regenerative current generated when the PWM signal is off also flows through the motor current detection resistor R21, an accurate motor current can be detected as a voltage value.

The instruction of the rotation direction 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 the speed of the motor M21 detected by the encoder EC21 connected to the motor M21, and the control target value is calculated by D / A conversion. Is converted into a digital signal and used as 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 IC23, and a PWM signal is generated by the comparator IC24 using the triangular wave and this difference is used as the duty ratio of this PWM signal. The motor is accordingly driven to control the speed. During reverse rotation, Q23 turns on, and Q22
When is on, the current flows from VMM through Q22 to motor M
21 to the motor current detecting resistor R21 through D25 and Q23. Therefore, the resistor R21 can convert the current into a voltage and detect the voltage value corresponding to the motor current value. When Q22 is off by the PWM signal,
The back electromotive force of the motor M21 turns on D28, and the regenerative current flows through D25, Q23, and R21 to the ground,
Return from the ground to the motor M21 via D28. The following operation is the same as the example shown in FIG.

[0017]

The servo control device in the scanner of the conventional image forming apparatus described above is shown in FIG.
As described above, the operation of the scanner is determined, and the rotation direction of the motor is determined according to the operation of the scanner. In other words, the direction of the current passed through the motor is determined in advance, and the speed is controlled by adjusting the current according to the PWM signal in that direction.

As can be seen from FIG. 2, 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 of about 4 to 7 times the speed at the time of reading the original. . The problem here is to stop the scanner by decelerating from the maximum speed on return,
When decelerating, the reversing brake is used by reversing the rotation direction of the motor, but when this rotation direction is switched, excessive braking is applied due to the back electromotive force of the motor, resulting in unexpected speed reduction. That is. The control tries to reduce the motor current in order to compensate for this speed decrease, that is, the excessive reversal brake amount, but when the current value that is the control target value is set to zero, the excessive reversal brake amount cannot be corrected. Will occur. For this reason, the scanner vibrates during deceleration of the return, causing abnormal noise,
Variations in the stop position occur due to unstable scanner speed due to 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 setting the acceleration for return deceleration accurately, and stop the scanner at the intended acceleration. Can be difficult.

In view of the above problems, the present invention automatically switches the direction of the current flowing to the motor when the difference between the motor current and the control target current value at the time of deceleration of the return becomes large, and the agility is improved. 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 various controls and obtain appropriate scanner running performance.

[0020]

The invention according to claim 1 is
Servo control in a scanner of an image forming apparatus that has a scanner that runs along a document image and reads image data from the document image, and causes the scanner to reciprocate by a motor
In the device , a pulse width modulation signal that determines the motor speed and
An H-shaped bridge circuit that drives the motor to rotate forward and backward according to the direction of the current flowing to the motor, an encoder attached to the motor shaft, and a microcontroller that performs motor rotation speed detection, speed calculation, and speed control by the detection signal of this encoder. And a detector for detecting the current value flowing in the motor and its current direction, and a difference signal between the target instruction current value from the speed calculation result and the motor current value.
The pulse width modulation signal is generated from the absolute value of the
And a feedback system for controlling the rotation direction of the motor by determining the direction of the current flowing through the motor by comparing the target instruction current value with the motor current value. .

According to a second aspect of the present invention, in the first aspect of the invention, the feedback system for determining the direction of the current flowing through the motor and controlling the motor rotation direction controls the motor current within the feedback of the constant current control circuit. A value obtained by differentially amplifying the voltage-converted value and the value obtained by voltage-converting the target instruction current value,
The motor current when the motor is stopped is compared with a voltage-converted value, and the binary signal obtained as a result is used to automatically determine the direction of the current passed through the H-type bridge circuit.

According to a third aspect of the present invention, in the second aspect of the present invention, a value obtained by differentially amplifying a value obtained by converting the voltage of the motor current and a value obtained by converting the target instruction current value by voltage, and the motor current when the motor is stopped. The absolute value of the difference from the voltage converted value is generated, the pulse width modulation signal is generated by comparing this absolute value with the triangular wave, and this is used as the control amount of the motor speed. It is characterized in that the amount of current flowing through the bridge circuit is determined.

[0023]

DETAILED 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.
Four MOS FETs Q31, Q32, Q33, Q34
The H-type bridge circuit composed of (hereinafter simply referred to as “Q1” and “Q2”) switches the current supplied to the DC servo motor M31 for driving the scanner of the image forming apparatus such as a copying machine. A motor M31 is connected in the middle of the mold bridge circuit. More specifically, the power source V
A series circuit composed of Q31 and Q33 and a series circuit composed of Q32 and Q34 are connected between the MM and the ground.
The motor M31 is connected between the connection point of 1, Q33 and the connection point of Q32, Q34. Each Q31, Q32, Q3
3 and Q34, these Q31, Q32, Q33, Q3
The diodes D31, D32, D33, D34 (hereinafter simply referred to as "D1") that pass a current in the direction opposite to the direction of the current flowing in
(Displayed as "D2") are connected in parallel.
Each Q31, Q32, Q33, Q34 is on / off controlled by a command from the microcomputer 30, and forward / reverse rotation control, speed control, and stop control are performed.

Between the connection point of Q31 and Q33 and the motor M31, a hall current detector 40 is connected in series with the motor M31 as means for detecting the motor current value and the current direction. The Hall current detector 40 detects a magnetic flux generated in proportion to the current in a non-contact manner by a combination of a magnetic iron core and a Hall element, converts the current into a voltage, and outputs the voltage. An example of the characteristic is shown in FIG. As shown in FIG. 3, when no current is flowing in the motor, that is, when the motor is stopped, the output voltage is OV, and when the current is a positive current (provisionally, the motor is in the forward rotation direction), the positive output voltage is a negative current ( If the motor is rotated in the reverse direction), a negative output voltage is generated. This output voltage has 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 40 is 0V 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 40 so that the positive side is the motor forward direction and the negative side is the motor reverse direction.

The motor M31 is provided with an encoder EC31 for generating pulse signals of a plurality of phases which are pulse signals corresponding to the rotation of the motor M31 and have different phase shift directions depending on the rotation direction. The pulse signal from the encoder EC31 is input to the counter input port of the microcomputer 30 as a rotation speed signal. Also, the encoder EC
A flip-flop circuit 26 that inverts depending on the direction of the phase shift of the signals of multiple phases from 31 is provided, and the rotation direction is detected by the output of the flip-flop circuit 26.
The rotation direction signal is input to the input port P2 of the microcomputer 30.

The microcomputer 30 uses a preset motor speed and the motor M3 detected by the encoder EC31.
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 into a voltage value and output. This voltage value is converted from a digital signal to an analog signal by the D / A converter 31 and used as a control target value. The current value that is the control target value and the motor current value detected by the hall current detector 40 are input to the differential amplifier IC33, and the difference between the control target value and the motor current value is calculated. Further, as for the calculation signal of the difference between the control target value and the motor current value, the difference between the value obtained by voltage-converting the motor current when the motor is stopped, that is, 0 V is calculated by the differential amplifier IC35, and the output of the differential amplifier IC35 is calculated. It is binarized by the comparator IC36. This binary signal is fed back to the motor M31
Of the binarized signal is inverted by the inverter IC 37 to turn on Q33.
It is turned off, and the binarized signal S2 turns on and off the Q34.

The output of the differential amplifier IC35 is full-wave rectified by an absolute value circuit 38 having an operational amplifier 36 and another operational amplifier 37, and an arithmetic signal of the difference between the control target value and the motor current value is obtained. The absolute value of the difference between the motor current when the motor is stopped and the voltage converted from the motor current is calculated. This absolute value signal is compared with the triangular wave output from the triangular wave generating circuit 33 in the comparator IC34, and the PWM signal is output. This PWM signal is input to the NAND circuits 34 and 35. The NAND circuit 34 also receives the inversion signal S1 of the binarized signal, and the NAND circuit 35 receives the binarized signal S1.
2 is input. The PWM signal controls the speed by changing the duty ratio of Q31 and Q32 on the upper 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. The circuit including the differential amplifier IC33, the differential amplifier IC35, and the comparator IC36 constitutes a constant current control circuit that automatically determines the direction of the current flowing through the motor M31. The differential amplifier IC33 in the constant current control circuit differentially amplifies the current value which is the control target value and the detected motor current value, and when this differential amplified signal and no current is flowing to the motor, That is, the signal when the current detector = OV in the motor stopped state is differentially amplified by the differential amplifier IC35, and this value is binarized by the comparator IC36 with respect to the OV in the motor stopped state. The binarized signal S2 and the signal S1 in which the binarized signal S2 is inverted in polarity by the inverter IC 37 automatically switch between the normal rotation direction and the reverse rotation direction.

Next, the means for controlling the motor speed by determining the control manipulated variable is used when the signal of the difference between the current value which is the control target value and the detected current value and the current is not flowing through the motor, that is, The full-wave rectification circuit 38 takes the absolute value of the signal differentially amplified with the signal when the current detector = OV in the motor stopped state with respect to OV in the motor stopped state. This signal and the triangular wave are compared by the comparator IC34 to generate a PWM signal, and the PWM signal and the automatically determined rotation direction instruction signal are used to turn on / off the Q31 or Q32 of the H-type bridge circuit. The motor M31 is 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 during return deceleration will be described. In FIG. 2, the control target current value during the return constant velocity operation is a negative value. At this time, the binarized signals S1 and S2 in the embodiment shown in FIG. 1 are S1 = “H” level, S2 = “ At "L" level, the motor is running in the reverse direction. Therefore, when Q33 is ON and the PWM signal is Q32, the motor M31 passes from the power source VMM through Q32 to the motor M31, the hall current detector 40, and Q33. Current is flowing to the ground. In addition, Q3 with PWM signal
When 2 is off, Hall current detector 4 from motor M31
A current flows to ground through 0, Q33, and then returns to the motor M31 through D34. At this time, the output voltage of the Hall current detector 40 is negative.

When the scanner reaches the return deceleration position,
The control target current value is set to positive in order to decelerate using the reverse brake operation. As a result, S1 = "L"
The level, S2 = “H” level, is automatically switched to energization in the motor forward direction, and the direction of the current is reversed.
During energization in the forward direction of the motor, when Q34 is turned on and Q31 is turned on by the PWM signal, the power source VMM is supplied to the motor M31.
Through Q31, Hall current detector 40, motor M3
1 and current is flowing to ground through Q34. When Q31 is off by the PWM signal, the motor M31
Through Q34 to ground, and D3
3. Return to the motor M31 through the hall current detector 40.

Here, when the direction of the current is switched,
Excessive torque is generated by the back electromotive force of the motor M31,
The reverse braking amount becomes larger than the control operation amount, and the speed drops rapidly. At this time, since an electric current larger than the control target electric current value flows into the motor M31, S1 = “H” level,
At S2 = “L” level, the energization direction is switched to the motor reverse rotation direction, and the operation of releasing the reverse motor brake amount is performed.

As is apparent from the above description, according to the embodiment shown in FIG. 1, the current is automatically supplied to the motor according to the control target current value, the current value actually flowing in the motor and the direction of the current. Since the means for switching the direction of the electric current, that is, the forward rotation direction or the reverse rotation direction of the motor is provided, it is possible to appropriately execute the control for the rapid speed change. Also, when a DC motor with a large induced voltage is used to set the acceleration or deceleration when decelerating the return, or when the sliding load of the scanner is large, the direction of the current during the deceleration operation is set to the scanner target speed. It constantly changes to satisfy the condition, and the forward and reverse energization control is performed, so that flexible acceleration or deceleration can be set.

With the above control, it is possible to prevent vibration during return deceleration, and to prevent variations in the stop position caused by unstable scanner speed due to vibration, and further increase the degree of freedom in setting the speed profile and increase the control margin. The degree improves.

[0035]

According to the first aspect of the present invention, a servo control is provided in a scanner of an image forming apparatus which has a scanner which runs along an original image image and reads image data from the original image. In the device , the pulse width modulation signal that determines the motor speed and the motor
An H-type bridge circuit that drives the motor to rotate normally and reversely according to the direction of the flowing current, an encoder attached to the motor shaft, and a microcontroller that performs motor rotation speed detection, speed calculation, and speed control by the detection signal of this encoder, A detector for detecting the current value flowing in the motor and its current direction, a difference signal between the target instruction current value and the motor current value from the speed calculation result is generated, and the difference signal is cut off.
The pulse width modulation signal is generated from the logarithmic value to control the speed of the motor , and the target instruction current value and the motor current value are compared, and the direction of the current flowing to the motor is determined by the comparison result to determine the motor rotation direction. Since it has a feedback system for controlling, it is possible to appropriately execute control with respect to a rapid speed change of the scanner. For example, when the difference between the motor current and the control target current value at the time of deceleration of the scanner's return becomes large, the direction of the current flowing to the motor can be automatically switched to prevent the deceleration effect from becoming too effective. As a result, agile control can be executed and proper scanner running performance can be obtained.

According to the second aspect of the present invention, the feedback system for determining the direction of the current flowing through the motor and controlling the motor rotation direction is provided in the feedback of the constant current control circuit.
A binary signal obtained as a result of comparing the voltage-converted value of the motor current and the differential-amplified value of the target instruction current value with the voltage-converted value of the motor current when the motor is stopped. As a result, the direction of the current flowing to the motor is automatically determined through the H-type bridge circuit, so it is processed at high speed in the current feedback circuit of the hardware, and even if the speed change is faster than the soft control cycle. Sufficient support will be provided and appropriate control will be possible.

According to the third aspect of the invention, the value obtained by differentially amplifying the value obtained by converting the voltage of the motor current and the value obtained by converting the voltage of the target instruction current value, and the value obtained by converting the voltage of the motor current when the motor is stopped are used. The absolute value of the difference is generated, a pulse width modulation signal is generated by comparing this absolute value with the triangular wave, and this is used as the control amount of the motor speed, and is supplied to the motor through the H-type bridge circuit according to this control amount. Since the amount of current is determined, the direction of the current flowing to the motor is automatically determined,
The control of the manipulated variable may be performed only in one of the plus side and the minus side of the H-type bridge circuit, and can be realized by a simple full-wave circuit. Further, the conversion into the pulse width modulation signal can be realized by a simple circuit by using the absolute value.

[Brief description of 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 the operation of the scanner of the image forming apparatus.

FIG. 3 is a graph showing current vs. output voltage characteristics of the Hall current detector used in the embodiment of the present invention.

FIG. 4 is a front view schematically showing an example of a scanner of the image forming apparatus.

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

FIG. 6 is a circuit diagram showing another example of a servo control device in a scanner of a conventional image forming apparatus.

FIG. 7 is a timing chart showing an operation of each unit of the above servo control device.

FIG. 8 is a circuit diagram showing still another example of the servo control device in the scanner of the conventional image forming apparatus.

[Explanation of symbols]

M31 Motor Q31 MOS-FET Q31 H-type bridge circuit MOS-FET Q32 H-type bridge circuit MOS-FET Q33 H-type bridge circuit MOS-FET Q34 H-type bridge circuit MOS-FET EC31 Encoder IC36 Comparison 30 Micro controller 33 Triangular wave generating circuit 38 Absolute value circuit 40 Hall current detector for detecting current value and current direction

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02P 5/00-5/26 H02P 7/00-7/34 G03G 15/04 G05D 3/12

Claims (3)

(57) [Claims] 1. A scanner of an image forming apparatus , comprising a scanner that runs along an original image image and reads image data from the original image, and reciprocates the scanner by a motor .
In the servo control device , the pulse width modulation signal that determines the motor speed and the electric current that flows to the motor.
An H-type bridge circuit that drives the motor to rotate forward and backward depending on the direction of the flow, 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 signals of the encoder, current flowing through the and the detector for detecting the current direction, and generates a difference signal between the target command current value and the motor current value from the speed calculation result, the more the absolute value of the difference signal
Generate a pulse width modulation signal to control the speed of the motor ,
Further comparing the target command current value and the motor current value, the scanner of the image forming apparatus characterized by comprising a feedback system for controlling the rotating direction of the motor to determine the direction of the current flowing to the motor according to the comparison result Servo control device. 2. A feedback system for determining a direction of a current flowing through a motor and controlling a motor rotation direction, wherein a value obtained by converting a motor current into a voltage and a value obtained by converting a target instruction current value into a voltage within a feedback of a constant current control circuit. The value obtained by differentially amplifying is compared with the value obtained by converting the voltage of the motor current when the motor is stopped, and the binary signal obtained as a result automatically determines the direction of the current flowing to the motor through the H-bridge circuit. The servo control device in the scanner of the image forming apparatus according to claim 1, wherein the servo control device is determined. 3. An absolute value of a difference between a value obtained by voltage-converting a motor current, a value obtained by differentially amplifying a value obtained by voltage-converting a target instruction current value, and a value obtained by voltage-converting the motor current when the motor is stopped is generated. , A pulse width modulation signal is generated by comparing this absolute value with a triangular wave, and this is used as the control amount of the motor speed,
3. The servo control device in the scanner of the image forming apparatus according to claim 2, wherein the amount of current flowing through the motor through the H-type bridge circuit is determined according to the control amount.