JP3729301B2 - Servo control device in scanner of image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo control device in a scanner of an image forming apparatus that is driven by a motor along a document image to reciprocate and reads image data from the document image. For example, speed control and position control using a DC servo motor. It can be applied to all technologies for performing the above.
[0002]
[Prior 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 the scanner, and reflected light from the document image is captured as image data. An image is formed on the photoreceptor. An outline of this image forming apparatus is shown in FIG. In FIG. 3, below the contact glass 1 on which the document 2 is placed, a first scanner in which the light source 3 and the first mirror 4 are integrally attached, and a second mirror 5 and a third mirror 6 are integrally attached. The second scanner is provided, and an imaging lens 7, a fixed fourth mirror 8, a fifth mirror 9, and a sixth mirror 10 are provided in this order on the light path reflected by the third mirror 6. A protective glass 11 and a photosensitive drum 12 are provided in this order on the reflected light path.
[0003]
The first scanner illuminates the document 2 in a slit shape while moving from left to right in FIG. 3 along the document 2 on the contact glass 1 at a constant speed V, and the first mirror 4 reflects the reflected light. Reflects horizontally. 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 document 2 is formed 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. 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 home positions when one scan is completed. In place of the photosensitive drum 12, a photoelectric conversion element such as a CCD is arranged at an image forming position by the lens 7 to read image data of an original, and an image is applied to the photosensitive drum while driving a semiconductor laser or the like in accordance with the image data. Some are designed to form.
[0004]
In order to read such image data, the first and second scanners are driven in forward and reverse directions using a DC servo motor. FIG. 4 shows the forward and reverse operations of the scanner and the motor that drives the scanner. As shown in FIG. 4, when the scanner driving motor is rotated forward for reading to start the scanner, the scanner immediately rises to the original reading speed and moves at a constant speed to read the original. When the document reading is completed, the drive motor is driven in the reverse direction, and the scanner is returned to the home position. In this return operation, in order to return the scanner as quickly as possible, the document is accelerated immediately in the reverse direction to several times the original reading speed after completion of the original reading, and is returned at a constant speed while maintaining the high speed after acceleration. The motor is decelerated by a forward current flowing from a predetermined position near the motor, and the scanner is stopped by stopping energization of the motor at the home position.
[0005]
As can be seen from FIG. 4, the speed of the copying machine can be increased by increasing the speed at the time of return of the scanner. The scanner is returning twice as fast. When decelerating from the maximum speed at the time of return and stopping the scanner, the reversing brake is used by reversing the motor rotation direction at the time of deceleration. However, the problem here is that excessive braking is applied due to the back electromotive force of the motor when the rotational direction is switched, resulting in a reduction in speed more than expected. In the motor control, the motor current is reduced to compensate for this speed reduction, that is, the excessive reverse brake amount, but the excessive reverse brake amount is corrected even if the current value that is the control target value is set to zero. The case where it is not possible will occur. For this reason, the scanner vibrates at the time of return deceleration, so that an abnormal noise is generated or the stop position varies due to unstable scanner speed due to vibration. Also, when using a DC motor with a large induced voltage or when the scanner has a large sliding load, there is a limit to setting the return deceleration acceleration accurately, and the scanner must be stopped at the target acceleration. May be difficult.
[0006]
In order to solve such a problem, the present inventors examined a constant current driving method capable of automatically switching the direction of the current flowing through the motor by detecting the current and direction flowing through the motor. As a result, the circuit shown in FIG. 5 was developed. However, this circuit is not known.
[0007]
In FIG. 5, an H-type bridge circuit comprising four MOS FETs Q31, Q32, Q33, and Q34 (hereinafter simply referred to as “Q31” and “Q32”) drives a scanner of an image forming apparatus such as a copying machine. The current to be supplied to the DC servo motor M31 is switched, and the motor M31 is connected in 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 source VMM and the ground, and the motor is connected between the connection point of Q31 and Q33 and the connection point of Q32 and Q34. M31 is connected. In each of Q31, Q32, Q33, and Q34, diodes D31, D32, D33, and D34 (hereinafter simply referred to as “D31” and “D32”) that pass a current in a direction opposite to the direction of the current flowing through Q31, Q32, Q33, and Q34. Are connected in parallel). Each of Q31, Q32, Q33, and Q34 is ON / OFF controlled in a constant current control circuit by a value obtained by converting a target instruction current value from a microcontroller (hereinafter referred to as “microcomputer”) 30 into a voltage, forward / reverse rotation control, speed Control and stop control are performed.
[0008]
Between the connection point of Q31 and Q33 and the motor M31, a current sensor 40 for detecting a motor current value and a current direction is connected in series with the motor M31. The current sensor 40 includes, for example, a Hall current detector, 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. 6, when no current flows through the motor, that is, when the motor is stopped, the output voltage OV. When the current is positive (assuming that the motor is in the forward rotation direction), the positive output voltage is changed to the negative current ( If the motor reverse direction is assumed), 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 current sensor 40 is 0V and the polarity of the output voltage. The polarity of the value obtained by converting the control target command current value into the voltage is determined in accordance with the polarity of the current sensor 40 so that the plus side is the forward motor rotation direction and the minus side is the motor reverse rotation direction.
[0009]
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 whose phase shift direction differs 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. In addition, a flip-flop circuit 32 is provided that inverts depending on the phase shift direction of the multiple-phase signals from the encoder EC31. The rotation direction is detected by the output of the flip-flop circuit 32, and the rotation direction signal is input to the input port P2 of the microcomputer 30. To be input.
[0010]
The microcomputer 30 calculates a control target value as a current value based on a deviation between a preset motor speed and the speed of the motor M31 detected by the encoder EC31, converts the current value that is the control target value into a voltage value, and outputs it. To do. This voltage value is converted from a digital signal to an analog signal by the D / A converter 31 to obtain a target instruction current value. The target command current value and the motor current value detected by the current sensor 40 are input to the differential amplifier IC33, and the difference between the target command current value and the motor current value is calculated. Further, the difference calculation signal between the target command current value and the motor current value is calculated by calculating the difference between the motor current when the motor is stopped by the differential amplifier IC35, that is, the difference between 0V and the output of the differential amplifier IC35. Is binarized by the comparator IC36. The binary signal is fed back to determine the forward / reverse rotation of the motor M31. The inverted signal S1 of the binary signal by the inverter IC37 controls the on / off of the Q33, and the binarization is performed. Signal S2 controls Q34 on and off.
[0011]
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, a calculation signal for the difference between the target indicated current value and the motor current value, The absolute value of the difference from the value obtained by voltage-converting the motor current at the stop is calculated. This absolute value signal is compared with the triangular wave output from the triangular wave generating circuit 33 by the comparator IC 34, and a PWM signal is output. This PWM signal is input to the NAND circuits 34 and 35. The NAND circuit 34 also receives the inverted signal S1 of the binarized signal, and the NAND circuit 35 receives the binarized signal S2. The PWM signal performs speed control 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.
[0012]
The operation of the above circuit example at the time of scanner return will be described. In FIG. 5, the control target command current value during the return constant speed operation is a negative value. At this time, the binarized signals S1 and S2 in the example shown in FIG. 5 are S1 = “H” level and S2 = “L”. Since the motor is rotating in the reverse direction at the level, when Q33 is on and Q32 is on with the PWM signal, the motor M31 passes through the power supply VMM through Q32 and passes through the motor M31, the current sensor 40, and Q33 to the ground. Is flowing. When Q32 is OFF in the PWM signal, the regenerative current flows from the motor M31 to the ground through the current sensor 40 and Q33, and returns to the motor M31 through D34. At this time, the output voltage of the current sensor 40 is negative.
[0013]
When the scanner reaches the return deceleration position, the target command current value is set to a positive value in order to decelerate using the reverse brake. As a result, S1 = “L” level and S2 = “H” level are set, so that the motor is automatically switched to the normal rotation direction, and the direction of the current is reversed. During energization in the forward direction of the motor, when Q34 is on and Q31 is on with a PWM signal, the motor M31 passes through the power supply VMM through Q31, and the current flows to the ground through the current sensor 40, the motor M31 and Q34. ing. Further, when Q31 is OFF in the PWM signal, a current flows from the motor M31 through Q34 to the ground, and returns to the motor M31 through D33 and the current sensor 40.
[0014]
Here, when the direction of the current is switched, an excessive torque is generated due to the counter electromotive voltage of the motor M31, the reverse brake amount becomes larger than the control operation amount, and the speed rapidly decreases. At this time, since a current exceeding the control target current value flows to the motor M31, S1 = “H” level, S2 = “L” level, the energization direction is switched to the motor reverse rotation direction, and the reverse motor brake amount is released. Perform the action. In this way, by providing means for automatically switching the direction of the current flowing to the motor according to the target instruction current value, the current value actually flowing in the motor, and the direction of the current, it is possible to appropriately control the sudden speed change. This prevents the occurrence of vibration at the time of scanner deceleration, prevents variations in the scanner stop position due to vibration, and improves the margin for setting the control speed profile.
[0015]
As described above, in the servo control device in the scanner of the image forming apparatus shown in FIG. 5, the direction of the current flowing through the motor is set to the bipolar voltage value obtained by converting the motor current into voltage and the bipolar value obtained by converting the target instruction current value into voltage. The value obtained by differentially amplifying the voltage value of the motor and the 0 V obtained by converting the motor current when the motor is stopped are compared, and the direction of the current flowing to the motor through the H-type bridge circuit is determined by the binary signal obtained as a result. It is decided automatically.
[0016]
In addition, the amount of current that flows to the motor is the value obtained by differentially amplifying the bipolar voltage value obtained by converting the motor current into voltage and the bipolar voltage value obtained by converting the target command current value into voltage, and the motor current when the motor is stopped. An absolute value of a difference from 0 V that has been converted into voltage is generated, and a PWM signal is generated by comparing the absolute value with a triangular wave, and this is used as a control amount for the motor speed. The amount of current flowing through the motor is determined.
[0017]
Further, in the speed control, the rotational speed is calculated in the microcomputer 30 by the encoder EC31 attached to the motor shaft, PI control is performed based on the deviation between the calculated rotational speed and a preset target rotational speed, and the target indicated current value Is controlled so as to reach the target rotational speed. This speed control is performed at high speed by an interrupt process using an encoder signal or a time interval interrupt process of about several milliseconds.
[0018]
According to the servo control device in the scanner of the image forming apparatus shown in FIG. 5, the control for the rapid speed change is appropriately performed to prevent the occurrence of vibration at the time of scanner deceleration and to prevent the variation in the stop position of the scanner due to the vibration. be able to.
However, the value detected by the current sensor 40 when the motor is stopped and converted into a voltage is not completely 0V, but has a slight offset value, so that the motor does not actually rotate immediately after the start of driving. Nevertheless, the motor current is detected as flowing in the forward or reverse direction, and the speed is indicated. In other words, according to the above-described technique, when the motor current immediately after the start of driving is 0 A, a very small voltage value is actually output even though the value converted to voltage must be 0 V. In some cases, the motor control accuracy at the start of driving may be reduced. Further, if the current sensor 40 has a minute offset value as described above, this offset value causes a reduction in motor control accuracy even during motor driving.
[0019]
Therefore, the present inventors have proposed a servo control device in which means for detecting the output value of the current sensor when the motor is stopped is added to the servo control device shown in FIG. This is the invention described in the specification and drawings attached to the application of Japanese Patent Application No. 9-35791, and its embodiment is shown in FIG. This is because the difference between the output value of the current sensor when the motor is stopped and the ideal voltage value when the motor current is 0 A is added, and a means for recognizing the value as the offset voltage value of the current sensor is added. The voltage value is corrected as the center value of the target instruction voltage of the motor speed when the image forming apparatus is turned on or while the motor is stopped. The servo control device in the scanner of the image forming apparatus shown in FIG. 7 will be specifically described below.
[0020]
In the example shown in FIG. 7, the analog / digital converter 50 is added to the example shown in FIG. 5 as means for detecting the output value of the current sensor when the motor is stopped. The description will focus on the converter 50, and the same components as those in the other example shown in FIG. 5 will be denoted by the same reference numerals, and redundant description will be avoided as much as possible. In FIG. 7, the output of the motor current sensor 40 branches from the input to the negative terminal of the differential amplifier IC33, is converted into a digital signal by the analog / digital converter 50, and is input to the microcomputer 30 via the data bus. Is done. As will be apparent from the description of the operation described later, the microcomputer 30 detects the output value when the motor is stopped from the detection output of the current sensor 40 input via the analog / digital converter 50, and this output value and the motor Means is provided for taking a difference from an ideal voltage value at a current of 0 A and recognizing the value as an offset voltage value of the current sensor. The microcomputer 30 also has means for correcting the offset voltage value as the center value of the target instruction voltage of the motor speed when the image forming apparatus is turned on or stopped.
[0021]
Now, the power of the image forming apparatus is turned on, and after the initial setting of each part is completed, the detection output of the current sensor 40 is read. The output of the current sensor 40 is converted into a voltage value proportional to the motor current, and this voltage value is input to the microcomputer 30 via the analog / digital converter 50. At this time, since the motor is not driven yet, when the detection output of the current sensor 40 is input to the microcomputer 30, the voltage value, that is, the output value when the motor drive is stopped is detected. The output of the current sensor 40 when the motor current is 0 A is ideally 0 V as shown in FIG. 6, but in reality, since the current sensor 40 has an offset, the recognition means in the microcomputer 30 is
Actual output value when the motor is stopped-Ideal output value when the motor is stopped = Offset voltage value
The offset voltage value is calculated from the output value when the motor driving is stopped and the ideal output value 0 V when the motor is stopped, and recognized.
[0022]
The offset voltage value calculated by the above equation is output in addition to the target command voltage that is proportionally output according to the target command current calculated based on the motor current 0A, that is, no offset voltage. Here, it is assumed that the calculated offset voltage is 0.5 V, for example. Immediately after the start of motor driving, the offset means 0.5V is added to the target instruction voltage by the correcting means in the microcomputer 30, and "target instruction voltage + 0.5V" is output from the data bus. This “target instruction voltage + 0.5V” is input to the positive terminal of the differential amplifier IC33, and the output value of the current sensor 40 is directly input to the negative terminal of the differential amplifier IC33, and thus 0.5V is input in this case. . In this manner, the output of the differential amplifier IC33 is a calculation result obtained by subtracting the output value of the current sensor 40 = 0.5V from the output from the data bus = (target instruction voltage + 0.5V). This calculation formula is shown below.
(Target instruction voltage + 0.5V)-(0.5V) = Target instruction voltage value
[0023]
Eventually, the calculation result is the “target instruction voltage”, so that the offset voltage value of the current sensor 40 is canceled. Thereafter, normal processing similar to that described with reference to FIG. 5 is performed, and rotation direction control and rotation speed control are performed.
[0024]
As another operation example, the output value of the current sensor 40 is read, the offset voltage value of the current sensor 40 is calculated according to the above-described equation, and the offset voltage value is added to the target instruction voltage value to be corrected. Or, normal processing may be performed. In short, every time the driving of the motor is finished and the motor driving is stopped, the output value of the current sensor 40 is read, an offset voltage value is calculated, and the target command voltage value is corrected by this offset voltage value. Is to be updated. For example, if the scanner drive is performed and the output value of the current sensor 40 newly read when the motor is stopped after the end of the scanner drive is 0.6V, the offset voltage value of the current sensor 40 is 0.6V. In the scanner drive, 0.6 V is added to the target instruction voltage value output from the data bus.
[0025]
With this setting, immediately after starting the next scanner drive, the output from the data bus = (target instruction voltage + 0.6 V) is input to the positive terminal of the differential amplifier IC33, and the current sensor is connected to the negative terminal of the differential amplifier IC33. The output value 0.6V is directly input from 40. The output of the differential amplifier IC33 is an amplification of the calculation result of the following equation.
(Target instruction voltage + 0.6V) -0.6V = Target instruction voltage
[0026]
As described above, even if the current sensor 40 has an offset voltage, and the offset voltage fluctuates due to temperature fluctuations or changes with time, the offset voltage value of the current sensor 40 is used as the center value of the target instruction voltage of the motor speed. Since the correction means is provided during the stop of driving, the offset voltage value which is the difference between the output value of the current sensor 40 when the motor is stopped and the ideal output value of the current sensor 40 when the motor is stopped after the end of the scanner driving. Thus, the correction value is updated, and accurate motor control can be performed in each scanner drive. In addition, accurate motor control can be performed even with the current sensor 40 having a high offset voltage value and large variations.
[0027]
According to the example shown in FIG. 7, even when a current sensor having the characteristics shown in FIG. 8 is used, when the output voltage range from the DAC output port is 0 V to 5 V, the offset of the current sensor is reduced by the processing described above. It can be detected and corrected. In the characteristics of the current sensor shown in FIG. 8, the output voltage value is 2.5 V when the motor current is 0 A, and the offset is detected and corrected with reference to 2.5 V. That is, an offset voltage value that is a difference between an actual output value when the motor is stopped and an ideal output value (2.5 V) when the motor is stopped is calculated. Further, according to the offset voltage value, Make corrections.
[0028]
[Problems to be solved by the invention]
The present invention is a further improvement of the servo control device in the scanner of the image forming apparatus that brings about the excellent effects studied so far. In other words, with the conventional technology, it is necessary to recognize the output value of the current sensor that detects the motor current by taking it into an analog / digital converter or a microcomputer incorporating an analog / digital converter. There was a difficulty in using a converter or using analog / digital input / output ports of a microcomputer.
[0029]
Therefore, the present invention holds the output value of the current sensor when the motor is stopped as an offset value without using the analog / digital converter or the analog / digital input / output port of the microcomputer, and uses this output value as a target indication voltage. It is an object of the present invention to provide a servo control device in a scanner of an image forming apparatus that can correct a value and perform accurate motor control.
[0030]
The present invention also holds the output value of the current sensor as an offset value when the motor is stopped, and corrects the target instruction voltage value by this output value so that the correction is made according to the circuit configuration, thereby reducing the software load. An object of the present invention is to provide a servo control device in a scanner of an image forming apparatus that can reduce and always perform accurate motor control.
[0031]
Furthermore, the present invention automatically corrects the target command voltage even if the current sensor has a different reference value by adding a simple process to the holding means that holds the output value of the current sensor when the motor is stopped as an offset value. It is an object of the present invention to provide a servo control device in a scanner of an image forming apparatus that can always perform accurate motor control.
[0032]
[Means for Solving the Problems]
According to the first aspect of the present invention, in a scanner of an image forming apparatus that reciprocates along a document image by a motor and reads image data from the document image, the motor is driven to rotate forward and backward by a signal for determining the motor speed and a signal for determining the rotation direction. An H-type bridge circuit, a current sensor that detects a current flowing through the motor and converts it into a voltage value, a current direction detection unit that detects the direction of the current flowing through the motor, an encoder attached to the motor shaft, A microcontroller that performs a rotation speed calculation and speed control of the motor by a detection signal, a target instruction voltage value proportional to a target instruction current value from the speed calculation result, and a value obtained by converting the motor current detected by the current sensor into a voltage; And a binary signal obtained as a result of comparison by the above comparator through an H-type bridge circuit. A feedback circuit that automatically determines the direction of the current flowing to the data, holding means for holding the output value of the current sensor every time the motor is stopped, and when the motor is driven and when the motor is stopped according to the driving state of the scanner. A scanner enable signal that outputs a different signal is input as an on / off control signal of the first switch connected to the holding means, and an inverted signal of the scanner enable signal is input to the second switch connected to the holding means. By inputting as an on / off control signal, the first switch is turned on when the motor is stopped, and the offset voltage value, which is a voltage value corresponding to the motor current value at that time, is held in the holding means, and the motor is driven when the motor is driven. When the second switch is turned on and the motor stops just before the offset voltage value held by the holding means, Converts the output value of the current sensor voltage, the voltage value from the target instruction voltage value obtained by inverting the polarity of the converted voltage Subtraction And an arithmetic circuit that automatically generates a target instruction voltage value.
[0033]
The invention according to claim 2 is the invention according to claim 1, When the motor is stopped, a value equal to the center value of the current sensor is output from the microcontroller port as the target instruction voltage for the motor speed, and this target instruction voltage is automatically corrected by the unique offset voltage value of the current sensor. Correction means for inputting to the holding means It is characterized by having.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments 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 the drawings. In addition, the same code | symbol was attached | subjected to the same component as the component of the circuit example shown in FIG. 5, FIG.
In FIG. 1, an H-type bridge circuit comprising four MOS FETs Q31, Q32, Q33, and Q34 (hereinafter simply referred to as “Q31” and “Q32”) drives a scanner of an image forming apparatus such as a copying machine. The current to be supplied to the DC servo motor M31 is switched, and the motor M31 is connected in 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 source VMM and the ground, and the motor is connected between the connection point of Q31 and Q33 and the connection point of Q32 and Q34. M31 is connected. In each of Q31, Q32, Q33, and Q34, diodes D31, D32, D33, and D34 (hereinafter simply referred to as “D31” and “D32”) that pass a current in a direction opposite to the direction of the current flowing through Q31, Q32, Q33, and Q34. Are connected in parallel). Each of Q31, Q32, Q33, and Q34 is ON / OFF controlled in a constant current control circuit by a value obtained by converting a target instruction current value from a microcontroller (hereinafter referred to as “microcomputer”) 30 into a voltage, forward / reverse rotation control, speed Control and stop control are performed.
[0036]
A current sensor 40 is connected in series with the motor M31 between the connection point of Q31 and Q33 and the motor M31. The current sensor 40 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. 6. When no current flows through the motor, that is, when the motor is stopped, the output voltage is OV, and when the current is positive (assuming that the motor is in the forward rotation direction), the output is positive. When the voltage is a negative current (assuming the motor reverse direction), 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 current sensor 40 is 0V and the polarity of the output voltage. The polarity of the value obtained by converting the control target current value into the voltage is determined in accordance with the polarity of the current sensor 40 so that the plus side is the forward motor rotation direction and the minus side is the motor reverse rotation direction. Thus, the current sensor 40 functions as a current sensor that detects the motor current value, and also functions as a current direction detection unit that detects the direction of the current flowing through the motor M31.
[0037]
The characteristics of the current sensor 40 shown in FIG. 6 are ideal characteristics. When the motor is stopped and the motor current is 0 A, the output voltage of the current sensor 40 is 0V. However, the actual current sensor 40 has few such ideal characteristics. Rather, the motor current is 0 A, and a voltage value offset from the ideal output voltage value 0 V when the motor is stopped is output. There are many things. Therefore, in order to cope with the offset of the current sensor 40, for example, a peak hold circuit is added as the holding means 55 for holding the output value of the current sensor 40, and the output value when the motor is stopped and the target held by the holding means 55 are added. A function of automatically correcting the target instruction voltage value by calculating the instruction voltage value with an arithmetic circuit is provided. This point will be described later in detail.
[0038]
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 whose phase shift direction differs 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 detection signal. In addition, a flip-flop circuit 32 that reverses depending on the phase shift direction of a plurality of phase signals from the encoder EC31 is provided, and the rotation direction signal of the motor M31 is detected by the output of the flip-flop circuit 32, and the rotation direction signal is output from the microcomputer 30. The signal is input to the input port P2.
[0039]
The microcomputer 30 calculates a control target value as a current value based on a deviation between a preset motor speed and the speed of the motor M31 detected by the encoder EC31, converts the current value that is the control target value into a voltage value, This voltage value is output from the DAC output port. This output is set in the range of −5 V to +5 V corresponding to the output voltage range of the current sensor 40. The output from the output port is input to the digital / analog converter 31 via the data bus, and the converted analog signal is input to the differential amplifier IC33 as the target instruction current value Iref. The differential amplifier IC33 also receives the output value IΔmot of the current sensor 40 when the motor is stopped, which is held by the holding means 55, which will be described in detail later, and the target instruction current value Iref and the current value when the motor is stopped. A difference (Iref−IΔmot) from IΔmot is calculated, and the target command current value Iref is automatically corrected with the current value IΔmot when the motor is stopped. Further, the target command current value (Iref−IΔmot) corrected by the current value IΔmot when the motor is stopped is different from the motor current value Imot input via the analog switch SW2 (described later) by the differential amplifier IC33 ( Iref−IΔmot−Imot) is calculated.
[0040]
The calculation output of the differential amplifier IC33 is a value obtained by converting the motor current when the motor is stopped by the differential amplifier IC35, that is, a difference from 0V, and the output of the differential amplifier IC35 is binarized by the comparator IC38. . The binary signal is fed back to determine the forward / reverse rotation of the motor M31. The inverted signal S1 of the binarized signal by the inverter IC37 is Q33 and Q32 via the NAND circuit 34. On / off control is performed, and the binarized signal S2 controls Q34 and Q31 via the NAND circuit 35, respectively. The input / output values of the differential amplifiers IC31, IC33, and IC35 are expressed as current values, but are actually values converted into voltage values corresponding to the current values.
[0041]
The microcomputer 30 has a control terminal P1. The control terminal P1 is connected to the plus input terminal of the comparator IC 40, and is an output port of a scanner enable signal that outputs an “H” signal when the motor M31 is driven and an “L” signal when the motor M31 is stopped. It has become. The output signal of the control terminal P1 is also input as an on / off control signal to the analog switch SW1, and an inverted signal of the output signal of the control terminal P1 by the inverter IC39 is input as an on / off control signal to the analog switch SW2. The The analog switch SW1 is off when the output signal of the control terminal P1 is “H”, and is on when the output signal of the control terminal P1 is “L”. The analog switch SW2 is off and “H”. When turned on.
[0042]
The comparator IC40 is an open collector output together with comparators IC34 and IC39 described later. A voltage of 3 V is always input to the negative input terminal of the comparator IC40.
When the motor is driven, an “H” signal is output from the control terminal P1, and the comparator IC 40 compares the “H” signal input to the positive input terminal with the 3V of the negative input terminal. Since it is an open collector, the output of the comparator IC 40 is cut off, and a triangular wave signal from the comparator IC 34, which will be described later, is directly input to the NAND circuit 34 to drive the motor.
When the motor is stopped, an “L” signal is output from the control terminal P1, and the comparator IC 40 compares the “L” signal at the plus input terminal with the 3V at the minus input terminal, and outputs a 0V signal. Since the 0V signal is input to the NAND circuits 34 and 35, the Q31 and Q32 are turned off, and the motor M31 is stopped.
[0043]
When the motor is driven, that is, when the control terminal P1 is “H”, the analog switch SW1 is turned off and the analog switch SW2 is turned on, and the connection of the current sensor 40 to the holding means 55 is cut off, while the output of the current sensor 40, Therefore, the output of the current sensor 40 when the motor is driven is input to the negative input terminal of the differential amplifier IC33.
Further, when the motor is stopped, that is, when the control terminal P1 is “L”, the analog switch SW1 is turned on and the analog switch SW2 is turned off, so that the output of the current sensor 40, that is, the output of the current sensor 40 when the motor is stopped is held by the holding means 55. On the other hand, the connection of the output of the current sensor 40 to the negative input terminal of the differential amplifier IC33 is cut off. The holding means 55 comprising a peak hold circuit has a function of holding the input voltage and outputting it with the polarity reversed.
[0044]
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 is corrected with a target instruction current value Iref corrected by the current value IΔmot when the motor is stopped. The absolute value of the difference between the calculation signal (Iref−IΔmot−Imot) of the difference from the motor current value Imot and the value obtained by converting the motor current when the motor is stopped, that is, 0V, is calculated. This absolute value signal is compared with the triangular wave output from the triangular wave generating circuit 33 by the comparator IC 34, and a PWM signal is output. This PWM signal is input to the NAND circuits 34 and 35. The NAND circuit 34 also receives the inverted signal S1 of the binarized signal, and the NAND circuit 35 receives the binarized signal S2. The PWM signal performs speed control 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.
[0045]
Next, the operation of the above embodiment will be described. The circuit from the differential amplifier IC31 to the differential amplifiers IC33, IC35, and the comparator IC36 basically compares the target instruction current value with the motor current value, and determines the direction of the current flowing to the motor based on the comparison result. A feedback system that controls the motor rotation direction is configured, and this feedback system includes a difference value between a value obtained by converting the motor current value into a voltage and a value obtained by converting the target command current value into a voltage within the feedback of the constant current control circuit. The current direction determining means for comparing the reference value and determining the direction of the current flowing through the motor based on the binary signal obtained as a result of the comparison. Switching between the forward direction and the reverse direction of the motor M31 is automatically performed by the two signals of the binary signal S2 and the signal S1 obtained by reversing the polarity of the binary signal S2 by the inverter IC37.
[0046]
Control of the motor speed is as follows. The differential amplifier IC35 differentially amplifies the output of the differential amplifier IC33 and the voltage of the reference value, and the output signal of the differential amplifier IC35 is compared with the voltage of the reference value by the full-wave rectifier circuit 38. An absolute value is taken. The absolute value signal is compared with the triangular wave generated by the triangular wave generating circuit 33 by the comparator IC 34 to generate a PWM signal. The PWM signal and the rotation direction instruction signal are used to generate Q31 or Q32 of the H-type bridge circuit. Is turned on / off, and a current corresponding to the duty ratio of the PWM signal is supplied to the motor M31 to control the speed of the motor M31.
[0047]
In addition to the operation described above, the embodiment of the present invention is devised so that even if the current sensor 40 has an offset voltage value, the motor control accuracy is not reduced by the offset voltage. Hereinafter, the operation will be described.
The output value from the current sensor 40 when the motor is stopped is an offset value as can be seen from the above description. When the motor is stopped, the signal of the control terminal P1, which is the scanner enable signal of the microcomputer 30, is “L”. Therefore, the analog switch SW2 is turned off and the analog switch SW1 is turned on. An offset voltage value, which is a voltage value corresponding to the motor current value, is input to the holding means 55, and this voltage value is held. A value IΔmot obtained by reversing the polarity of the offset value is output from the holding means 55 and input to the negative input terminal of the differential amplifier IC31.
[0048]
When the motor is driven, the signal of the control terminal P1 of the microcomputer 30 is “H”, so the analog switch SW1 is turned off and the analog switch SW2 is turned on. The offset voltage value held by the holding means 55 is input to the negative input terminal of the differential amplifier IC31. The differential amplifier IC31 calculates the difference between the target command current value Iref output from the microcomputer 30 and converted by the digital / analog converter 31 and the offset value IΔmot, thereby obtaining the target command current value Iref as the offset value IΔmot. To correct and output. The corrected target instruction current value Iref is input to the positive input terminal of the differential amplifier IC33, and the differential amplifier IC33 is input to the negative input terminal via the target instruction current value Iref and the analog switch SW2. The difference from the motor current value (current value at the time of driving the motor) Imot from 40 is calculated and output.
[0049]
For example, assume that the output of the current sensor 40 when the motor is stopped, that is, the offset value is 0.5V. The offset value 0.5V is held in the holding means 55 when the signal of the control terminal P1 is “L” and the analog switch SW1 is turned on when the motor is stopped. When the motor is driven, since the signal of the control terminal P1 is “H”, the analog switch SW1 is turned off and the analog switch SW2 is turned on. The motor current detected by the current sensor 40 is the negative input terminal of the differential amplifier IC33. Is input. The holding means 55 inverts the held offset value of 0.5 V and inputs −0.5 V to the negative input terminal of the differential amplifier IC31. If the value obtained by voltage-converting the target command current Iref is, for example, 3V, 3V is input from the microcomputer 30 to the positive input terminal of the differential amplifier IC31 via the digital / analog converter 31. The differential amplifier IC31 outputs 3.5V by calculation with the inversion value -0.5V. This 3.5 V becomes the target instruction voltage corrected in consideration of the offset value of the current sensor 40.
[0050]
Hereinafter, as described above, speed control by generation of the PWM signal, and forward / reverse control and stop control by the output of the comparator IC 38 are performed.
As described above, according to the embodiment shown in FIG. 1, even if the current sensor 40 has an offset voltage, and the offset voltage fluctuates due to a temperature variation or a change over time, the offset voltage value of the current sensor 40 can be reduced. Is held by the holding means 55, and the target instruction voltage of the motor speed is corrected by the offset voltage value when the motor is driven. Therefore, even if the current sensor 40 has an offset, accurate motor control can be performed in each scanner drive. It can be carried out. Even if the offset voltage value of the current sensor 40 is large or the offset voltage value of each current sensor 40 varies greatly, the target instruction voltage is corrected according to the offset voltage value, so that accurate motor control is performed. be able to. Furthermore, the offset correction of the current sensor 40 is performed by hardware using the holding means 55 such as a peak hold circuit, the differential amplifier IC31, etc., and the processing by software is not required, so the burden of software is reduced. There is also an advantage that it is possible to reduce and always perform accurate motor control.
[0051]
In the embodiment shown in FIG. 1, the current sensor 40 uses 0V as a reference value as shown in FIG. 6, but the reference value of the current sensor deviates greatly from 0V. For example, as shown in FIG. The output voltage value when the motor current is 0 A is 2.5 V, and even if the 2.5 V is the central value, the central value 2 of the current sensor 40 is used as the target instruction voltage for the motor speed when the motor is stopped. The present invention can be applied by outputting a value equal to 0.5 V from the port of the microcontroller 30. Then, the value obtained by converting the motor control target instruction current at the time of driving the motor into a voltage is set to a voltage of 2.5 to 5 V if the target instruction current is positive (this is assumed to be the normal rotation direction of the motor). If it is negative, the voltage is set to 0 to 2.5 V (this is set as the motor reverse direction), and the polarity of the current sensor 40 is adjusted to match the output voltage of 2.5 to 5 V in the normal direction. The output voltage of 5V is set as the reverse direction. FIG. 2 shows another embodiment of the present invention corresponding to a current sensor having the characteristics shown in FIG.
[0052]
Hereinafter, the embodiment shown in FIG. 2 will be described. Most of the embodiment is the same as the embodiment shown in FIG. 1, and the current sensor 40 and the analog in the embodiment shown in FIG. The differential amplifier IC45 is inserted between the switch SW1, the detection signal of the current sensor 40 is input to the positive input terminal of the differential amplifier IC45, and the digital / analog conversion from the microcomputer 30 to the negative input terminal of the differential amplifier IC45. The point that the target indicated current value output via the device 31 is input is
Only different. The differential amplifier IC45 calculates the difference between the detected value of the current sensor 40 and the target indicated current value. When the analog switch SW1 is turned on when the motor is stopped, the current sensor 40 is detected when the motor is stopped. The difference between the value and the target command current value is calculated and the result is held in the holding means 55 comprising a peak hold circuit. In the case of the current sensor 40 having the characteristics shown in FIG. 8, the target instruction current value when the motor is stopped, and thus the center value of the target instruction current value, is set to 2.5V in accordance with the center value 2.5V. The differential amplifier IC45 calculates and outputs the difference between the center value of 2.5 V and the actual detection value of the current sensor 40 when the motor is stopped, that is, the offset voltage value of the current sensor 40 with respect to the center value. The offset voltage value is held by the holding means 55. The processing of the signal output from the holding means 55 and the subsequent signal processing circuit are configured in the same manner as in the embodiment shown in FIG.
[0053]
Next, the operation of the embodiment shown in FIG. 2 will be described focusing on the differences from the embodiment shown in FIG. When the motor is driven, that is, when the scanner enable signal output from the control terminal P1 of the microcomputer 30 is “H”, the analog switch SW1 is turned off, the analog switch SW2 is turned on, and the connection of the current sensor 40 to the holding means 55 is cut off. On the other hand, the output of the current sensor 40, that is, the output of the current sensor 40 when the motor is driven is input to the negative input terminal of the differential amplifier IC33.
When the motor is stopped, that is, when the control terminal P1 is “L”, the analog switch SW1 is turned on and the analog switch SW2 is turned off. The difference between the output of the current sensor 40 at this time, that is, the actual output of the current sensor 40 when the motor is stopped and the target indicated current value Iref, that is, the offset value of the current sensor 40 is calculated by the differential amplifier IC45, and this offset value is calculated. The signal is input to and held by the holding means 55 via the analog switch SW1. On the other hand, the connection of the output of the current sensor 40 to the negative input terminal of the differential amplifier IC33 is cut off. The holding means 55 has a function of outputting the held signal with the polarity reversed, as in the above-described embodiment.
[0054]
When the motor is driven, the analog switch SW1 is turned off and the analog switch SW2 is turned on as described above, and the offset value of the current sensor 40 held by the holding means 55 is input to the negative input terminal of the differential amplifier IC31. . The differential amplifier IC31 calculates the difference between the target command current value Iref and the offset value IΔmot, thereby correcting the target command current value Iref with the offset value IΔmot and outputting the result. The corrected target instruction current value Iref is input to the positive input terminal of the differential amplifier IC33, and the differential amplifier IC33 is input to the negative input terminal via the target instruction current value Iref and the analog switch SW2. The difference from the motor current value (current value at the time of driving the motor) Imot from 40 is calculated and output.
[0055]
For example, assume that the output value of the current sensor 40 when the motor is stopped is 2.6V. When the motor is stopped, the reference value (center value) 2.5 V of the target instruction current value is output from the DAC port of the microcomputer 30, and the differential amplifier IC 45 has the reference value 2.5 V and the current sensor 40 when the motor is stopped. An output value of 2.6 V is calculated, and the calculation result of 0.1 V is output as the offset value of the current sensor 40 and held in the holding means 55. The holding means 55 inverts the offset value and outputs -0.1V. When the motor is driven, the signal of the control terminal P1 of the microcomputer 30 is “H”, the analog switch SW1 is turned off, and the SW2 is turned on. The voltage value corresponding to the motor current at the time of driving detected by the current sensor 40 is applied to the analog switch SW2. Then, it is input to the differential amplifier IC33. During this time, the holding means 55 holds the above 0.1V. Assuming that the target instruction voltage output from the DAC port of the microcomputer 30 when driving the motor is, for example, 4V, the differential amplifier IC31 calculates the target instruction voltage 4V and -0.1V from the holding means 55 to calculate the target The command voltage is automatically corrected and 4.1V is output. This 4.1 V becomes the target instruction voltage in consideration of the offset value of the current sensor 40. Thereafter, similarly to the embodiment shown in FIG. 1, speed control, forward rotation, reverse rotation, and stop control of the motor M31 are performed.
[0056]
As described above, according to the embodiment shown in FIG. 2, the output value of the current sensor 40 when the motor is stopped, that is, the center value of the current sensor 40 is used as the reference value of the target instruction voltage. Since the reference value of the target instruction voltage to be output is automatically corrected by the inherent offset value of the current sensor 40 and the differential amplifier IC 45 is provided as a correction means for inputting to the holding means 55, the current sensor 40 is provided with the differential amplifier IC 45. Even if there is an offset voltage, even if the offset voltage fluctuates due to temperature fluctuations or changes over time, the target instruction voltage is corrected to an appropriate value according to the characteristics of the individual current sensors 40, so that each time the scanner is driven, Thus, it is possible to perform proper motor control. Further, even if there are large variations in the offset voltage values of the individual current sensors 40, the same effects as those of the embodiment shown in FIG. 1 can be obtained, such as accurate motor control.
[0057]
In the embodiment shown in FIGS. 1 and 2, motor speed control by PWM control is performed by Q31 and Q32 on the upper stage (current inflow side) of the H-type bridge circuit, but the lower stage (current outflow side) ) Q33 and Q34.
In the embodiment described above, the center value of the current sensor 40 is 0 V or 2.5 V. However, the center value of the current sensor 40 is arbitrary, and the target instruction voltage output from the port of the microcomputer 30 is set. Is set to be equal to the central value of the current sensor 40. Even if there is an offset in the output value of the current sensor when the motor is stopped with respect to the reference value of the target instruction voltage set in this way, according to the embodiment shown in FIG. Thus, the target command voltage is automatically corrected and accurate motor control is performed.
[0058]
According to the first aspect of the present invention, in a scanner of an image forming apparatus that reciprocates along a document image by a motor and reads image data from the document image, the motor is rotated forward and backward by a signal for determining a motor speed and a signal for determining a rotation direction. An H-type bridge circuit to be driven; a current sensor that detects a current flowing through the motor and converts it into a voltage value; a current direction detection unit that detects a direction of the current flowing through the motor; an encoder attached to the motor shaft; A microcontroller that performs motor rotation speed calculation and speed control based on the detection signal of the encoder, a target instruction voltage value proportional to a target instruction current value from the speed calculation result, and a motor current detected by the current sensor converted into a voltage A comparator for comparing the values, and an H-type bridge circuit based on a binary signal obtained as a result of comparison by the comparator A feedback circuit that automatically determines the direction of the current flowing to the motor, holding means that holds the output value of the current sensor every time the motor is stopped, and when the motor is driven and when the motor is stopped according to the driving state of the scanner. And a second switch connected to the holding means and an inverted signal of the scanner enable signal. The scanner enable signal that outputs a different signal is input as an on / off control signal of the first switch connected to the holding means. When the motor is stopped, the first switch is turned on, and the offset voltage value corresponding to the motor current value at that time is held in the holding means. When the motor is stopped just before the second switch is turned on and the offset voltage value held by the holding means It converts the output value of the definitive the current sensor voltage, a voltage value obtained by inverting the polarity of the converted voltage from the target instruction voltage value Subtraction Therefore, the current sensor has an offset voltage, and even if this offset voltage fluctuates due to temperature fluctuations or changes over time, etc. The offset voltage value of the current sensor can be held by the holding means, and by correcting the target instruction voltage value by the offset voltage value of the held current sensor, accurate motor control can be performed in scanner driving.
In addition, when the motor stops, the output value of the current sensor is held as an offset value, and when the target instruction voltage value is corrected by this output value, the correction is made according to the circuit configuration, thereby reducing the software load. An intended object of providing a servo control device in a scanner of an image forming apparatus capable of always performing accurate motor control can be achieved.
[0059]
According to the invention of claim 2, in the invention of claim 1, When the motor is stopped, a value equal to the center value of the current sensor is output from the microcontroller port as the target instruction voltage for the motor speed, and this target instruction voltage is automatically corrected by the unique offset voltage value of the current sensor. Correction means for inputting to the holding means Therefore, even if there is an offset voltage in the current sensor and this offset voltage fluctuates due to temperature fluctuations or changes over time, the target indication voltage is corrected to an appropriate value according to the characteristics of each current sensor. Thus, accurate motor control can be performed in scanner driving. Even if there is a large variation in the offset voltage values of the individual current sensors, accurate motor control can be performed.
[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 circuit diagram showing another embodiment of a servo control device in the scanner of the image forming apparatus according to the present invention.
FIG. 3 is a front view schematically showing an example of a scanner of the image forming apparatus.
FIG. 4 is a timing chart showing the operation of the scanner of the image forming apparatus.
FIG. 5 is a circuit diagram showing an example of a servo control device in a scanner of an image forming apparatus that has been studied so far although it is not publicly known.
FIG. 6 is a graph showing an example of current vs. output voltage characteristics of a current sensor used in a servo control device in the scanner of the image forming apparatus.
FIG. 7 is a circuit diagram showing another example of a servo control device in a scanner of an image forming apparatus that has been studied until now, although it is not publicly known.
FIG. 8 is a graph showing an example of current vs. output voltage characteristics of a current sensor used in a servo control device in the scanner of the image forming apparatus.
[Explanation of symbols]
M31 motor
Q31 MOS-FETs that make up an H-type bridge circuit
Q32 MOS-FETs that make up an H-type bridge circuit
Q33 MOS-FETs that make up an H-type bridge circuit
Q34 MOS ・ FET that constitutes an H-type bridge circuit
EC31 encoder
IC33 differential amplifier
30 microcontroller
33 Triangular wave generator
38 Absolute value circuit
40 Current sensor
IC35 differential amplifier
IC36 comparator
IC45 differential amplifier as correction means
55 Holding means

Claims (2)

In a scanner of an image forming apparatus that reciprocates along a document image by a motor and reads image data from the document image,
An H-type bridge circuit for driving the motor to rotate forward and backward by a signal for determining the motor speed and a signal for determining the rotation direction;
A current sensor that detects the current flowing through the motor and converts it into a voltage value;
A current direction detector for detecting the direction of the current flowing through the motor;
An encoder attached to the motor shaft;
A microcontroller for calculating and controlling the rotational speed of the motor based on the detection signal of the encoder;
A comparator that compares a target instruction voltage value proportional to a target instruction current value from the speed calculation result and a value obtained by converting the motor current detected by the current sensor into a voltage;
A feedback circuit that automatically determines the direction of a current flowing through the H-type bridge circuit through a binary signal obtained as a result of comparison by the comparator;
Holding means for holding the output value of the current sensor every time the motor is stopped;
According to the driving state of the scanner, a scanner enable signal that outputs different signals when the motor is driven and when the motor is stopped is input as an on / off control signal for the first switch connected to the holding means, and the scanner By inputting an inverted signal of the enable signal as an on / off control signal of the second switch connected to the holding means, the first switch is turned on when the motor is stopped, and a voltage value corresponding to the motor current value at that time Is held in the holding means, the second switch is turned on when the motor is driven, and the output value of the current sensor at the time of the motor stop immediately before being the offset voltage value held in the holding means is the voltage. It is converted into a voltage value obtained by inverting the polarity of the converted voltage to be subtracted from the target instruction voltage value An operation circuit for automatically generating a target instruction voltage value,
A servo control device in a scanner of an image forming apparatus.   When the motor is stopped, a value equal to the center value of the current sensor is output from the microcontroller port as the target instruction voltage for the motor speed. 2. The servo control apparatus for a scanner of an image forming apparatus according to claim 1, further comprising correction means for correcting and inputting to the holding means.

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