JP3414931B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which a scanner is reciprocally moved by a drive motor to read image information from a document, and more particularly to improvement of reading accuracy when reading image information and simplification of a drive circuit. Is.

[0002]

2. Description of the Related Art An image forming apparatus for reciprocating a scanner by a stepping motor to read image information of a document is disclosed in, for example, Japanese Patent Laid-Open No. 6-110137. This device adopts the PID control system and makes the gain of the feedback control system variable so as to correct the speed of the stepping motor.

The control of the servo motor that drives the scanner is usually performed using a microcomputer. For example, when controlling the drive of the DC servo motor, as shown in FIG.
The microcomputer 3 sends forward / reverse rotation commands CW and CCW to the power amplifier 65 having a bridge circuit to control the forward / reverse rotation of the servo motor 1. Further, a pulse amplitude modulation method is adopted for speed control of the servo motor 1. That is, the microcomputer 3 calculates the control target value as a current value from the difference between the predetermined target speed and the speed of the servo motor 1 detected by the rotary encoder 2 connected to the servo motor 1, and causes the DA converter 4 to calculate the control target value. send. The DA converter 4 converts a current value, which is a control target value, from a digital signal into an analog signal and outputs the analog signal to the control unit 6. The control unit 6 calculates the difference between the current value, which is the control target value, and the current value actually sent to the servomotor 1 from the amplifier 62 by the differential amplifier 61, and outputs this difference from the triangular wave generator 63. The pulse width is modulated by the pulse width modulator 64 using a triangular wave to generate a pulse width pulse having a pulse width proportional to the difference between the current value as the control target value and the current value actually flowing in the servo motor 1. Part 6
5 is output to match the current value flowing in the servo motor 1 with the control target value.

When the microcomputer 3 inputs the A-phase and B-phase signals of the rotary encoder 2 via the flip-flop circuit 7 and detects the forward rotation and the reverse rotation of the servomotor 1, the scanner reads the original. And when the scanner finishes reading the original and returns to the home position. When the scanner reads the original, the servo motor 1 is driven at a low speed, and when the scanner returns to the fixed position, the servo motor 1 is driven at a high speed.

[0005]

There is a speed difference of 5 to 8 times between the motor speed when the scanner reads a document and the motor speed when the scanner returns, and the speed is higher when returning. , A large acceleration is required when the return is accelerated and a return is decelerated, and a large current is required for the motor. On the other hand, when reading a document, the motor rotates at a low speed, so that the current is made small, and since it depends on the reading accuracy of the scanner, it is necessary to finely control the current value for rotating the motor at a constant speed.

In order to control all the current values of these motors, considering fine control of low-speed and constant-speed rotation, a high-cost and high-bit D / A converter is required, and the control becomes complicated.

The present invention has been made in order to eliminate such disadvantages, and uses an 8-bit class inexpensive DA converter without using a high-bit and expensive DA converter. It is another object of the present invention to provide an image forming apparatus that simplifies the circuit and enables stable scanner control.

[0008]

SUMMARY OF THE INVENTION An image forming apparatus according to the present invention is reciprocating while operating at a low speed during a document reading operation.
And after moving at a constant speed and reading is completed,
The scanner moves at a high speed during operation, the drive motor for conveying the scanner, the sensor that monitors the forward or reverse rotation of the drive motor and the rotation speed of the drive motor, and the predetermined motor. A microcomputer that compares the target value of the rotation speed with the speed of the drive motor monitored by the sensor, calculates the target current value from the difference, and sends a signal instructing the target current value and the rotation direction of the motor as a digital signal. , A D-A converter that converts a digital signal that is the target current value sent from the microcomputer into a target current value that is an analog signal, and the target current value sent from the D-A converter and the drive that actually flows to the drive motor In an image forming apparatus having a control unit that controls the rotation speed of a drive motor by comparing currents, an output signal is output after an analog signal output of a D-A conversion unit. Has a part, the target current value scanner
Smaller than the reference value set in advance by the operation pattern of
It is characterized in that the output range of the output range unit is reduced during the read operation and the output range of the output range unit is increased during the return operation in which the target current value is larger than the reference value.

Further, it is preferable that the output range section reduces the output range when the sensor detects the forward rotation of the drive motor and increases the output range when the sensor detects the reverse rotation of the drive motor.

Further, a buffer is provided between the output range section and the control section, and the buffer stops transmission of impedance fluctuation when the output range is switched in the output range section to perform impedance matching of the input line of the control section. good.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a digital signal which is a target current value of a servo motor sent from a microcomputer for controlling a servo motor which drives a scanner is converted into a target current which is an analog signal. An output range unit is provided at the output stage of the DA converter for converting the value. The output range section has a comparator, a switch, and a shunt resistance. Then, the comparator compares the target current value that determines the rotation speed of the motor with a predetermined reference value, and when the operation of the scanner is reading and the target current value is smaller than the reference value, the switch is turned on. At the time of return, when the target current value is larger than the reference value, the switch is turned off to switch the shunt resistance, and the output range width of the DA converter is apparently switched.

In the output range section, a switch is turned on and off in the rotation direction of a motor for driving the scanner,
When the scanner scans the original, the output range width of the DA converter is apparently reduced, and when the scanner is in the return operation, the output range width of the DA converter is apparently increased, and the original is read. The rotation speed of the motor during reading is kept constant, and the rotation speed of the motor is rapidly accelerated during the return operation.

A buffer is provided between the output range section and the control section, and the buffer is composed of a voltage follower circuit using an operational amplifier, and an impedance variation caused by switching the shunt resistance in the output range section is a motor. To prevent the voltage fluctuation due to impedance fluctuation and the waveform distortion of the target current value.

[0014]

1 is a block diagram of a drive control unit of a drive motor for carrying a scanner according to an embodiment of the present invention. As shown in the figure, the drive control unit of the drive motor includes a sensor 2 for monitoring forward or reverse rotation, which is the rotation direction of the motor 1 for carrying the scanner, and a rotation speed of the motor 1, and a predetermined motor 1 The target value of the rotation speed is compared with the speed of the motor 1 monitored by the sensor 2, the target current value is calculated from the difference, and a signal instructing the target current value and the rotation direction of the motor 1 is sent as a digital signal. Microcomputer 3, a D-A converter 4 for converting a digital signal, which is a target current value sent from the microcomputer 3, into a target current value, which is an analog signal, and an output range unit located after the D-A converter 4. 5
And the rotation direction of the motor 1 sent from the sensor 6 and the control unit 6 that controls the rotation speed of the motor 1 by comparing the target current value sent from the output range unit 5 with the current actually flowing in the motor 1. The voltage of low level at the time of forward rotation and high level at the time of reverse rotation is received by the microcomputer 3 by the switching operation by receiving the signal of
It has a flip-flop circuit 7 for inputting to.

The output range section 5 includes a comparator 52 and a switch S.
W and shunt resistors R1 and R2. The comparator 52 compares the reference value 51 of the rotation speed of the motor 1 determined by the operation pattern of the scanner with a target current value that determines the rotation speed of the motor 1, and turns on / off the switch SW. Shunt resistance R1
Is connected in series to the output stage of the DA converter 4, and the shunt resistor R2 is connected between the resistor R1 and the ground via the switch SW.

In describing the operation of the drive control unit configured as described above, first, the operation of the reading optical system will be described with reference to the schematic diagram of the reading optical system of the analog copying machine shown in FIG. .

As shown in FIG. 2, a scanner optical system 10 is provided below the contact glass 9 on which the original 8 is placed. The scanner optical system 10 includes a light source 21, a reflection plate 22, a first scanning unit 20 having a first mirror 23, and a second scanning unit 3 having a second mirror 31 and a third mirror 32.
0, an imaging lens 14, a fourth mirror 15, and a dustproof glass 16. The speed V1 of the first scanner section 20 and the speed V2 of the second scanner 30 of the scanner optical system 10 are set so that the optical path length reflected from the original 8 does not change during scanning.
It is reciprocally driven in the sub-scanning direction at a speed ratio of 2: 1. Then, the driving motor 1 is used for the first scanning unit 20 and the second scanning unit 3.
When 0 is driven in the sub-scanning direction indicated by arrow A, the original 8
The surface is exposed and scanned, and the image of the original 8 is read to form an image on the drum-shaped photoconductor 11. When the first scan unit 20 and the second scan unit 30 return to the home position after the reading of the image of the document 8 is completed, the image of the document 8 is not read and the first scan unit 20 and the second scan unit 30 are not read. Moves. In the digital copying machine, the image data read when the first scanning unit 20 and the second scanning unit 30 are driven in the sub-scanning direction indicated by arrow A is stored as valid data.

As described above, the driving current of the motor 1 and the operating speed of the scanner optical system 10 during the reading operation for reading the image of the original by the scanner optical system 10 and the returning operation for returning to the home position are shown in FIG. It is as shown in the operating speed diagram. That is, since the first scanning unit 20 and the second scanning unit 30 are moved at a low speed and a constant speed during the reading operation, the driving current value of the motor 1 required at the time t1 of the reading start is about 2 to 4 amperes. When reading the original 7, t2 is 1
It is about ampere. However, since the processing speed becomes faster when the first scanning unit 20 and the second scanning unit 30 are moved at a high speed during the return operation after the reading is completed, a considerable acceleration occurs at the acceleration time t3 and the deceleration time t5 during the return operation. Required, the drive current value of the motor 1 is 10
You need more than amperes.

Since the drive current value of the motor 1 changes in accordance with the operation pattern of the scanner optical system 10 in this way, the reference value 5 of the output range section 5 of the drive control section of the motor 1 is 5
1 is determined by the operation pattern of the scanner optical system 10, and when the target current value is smaller than the reference value 51, the range is decreased, and when the target current value is large, the range is increased and D-
The apparent resolution of the A converter 4 is changed. That is, the comparator 52 of the output range unit 5 is used by the microcomputer 3
The target current value of the motor 1 sent from the motor 1 is compared with the reference value 51, and when the scanner optical system 10 is in the reading operation and the target current value of the motor 1 is smaller than the reference value 51, the switch SW.
Turn on. When the switch SW is turned on, the shunt resistor R2 is connected between the output line of the target current value of the DA converter 4 and the ground, so that the target current value shunted by the resistance ratio of the shunt resistors R1 and R2 passes through R2. Flows to the ground.
As a result, the target current value flowing in the input stage of the control unit 6 is reduced, and the apparent output range of the DA converter 4 can be reduced. When the scanner optical system 10 is in the return operation and the target current value of the motor 1 is larger than the reference value 51, the switch SW is turned off. When the switch SW is turned off, the shunt resistance R2 is disconnected from the line of the target current value, so that all target current values output from the DA converter 4 flow into the input stage of the control unit 6. As a result, the apparent output range of the DA converter 4 can be increased.

The resolution X per bit of the D-A converter 4 is X = Imax / (2N-), where N is the number of bits of the D-A converter 4 and Imax is the maximum current consumption of the motor 1.
Determined in 1). For example, when a 10-bit D / A converter is used to control the current of the motor 1 having a maximum of 15 amperes, the resolution is about 15 milliamperes per bit. When the 8-bit D / A converter 4 is used, the resolution is 59 milliamperes per bit, and 1
The resolution per bit is four times lower than that of a 0-bit DA converter. Therefore, in order to finely control the current of about 1 amp when reading the original 8 by using the 8-bit DA converter 4, the shunt resistance R of the output range unit 5 is used.
By dividing the target current value by 1 and R2 to 1/4 and increasing the apparent resolution, it is possible to use a 10-bit DA converter.

In this way, when the control target current value of the motor 1 is larger than the reference value 51 in the output range section 5, the width of the output range is increased, and when the control target current value of the motor 1 is smaller than the reference value 51. By reducing the width of the output range, it is possible to obtain an apparent resolution equivalent to that of the 10-bit D / A converter even if the 8-bit class inexpensive D / A converter 4 is used. The running stability of 10 can be maintained.

In the above embodiment, the output range of the D / A converter 4 is changed by the control target current value of the scanner optical system 10 in the output range unit 5. However, the output range of the output range unit 5 is switched to rotate the motor 1. By detecting and switching the direction, the scanner optical system 10 can be made to travel more reliably at the time of reading and at the time of returning.

FIG. 4 shows an example in which the output range of the output range section 5 is switched by detecting the rotation direction of the motor 1.
As shown in FIG. 4, in the output range section 5, the switch SW is turned on by the forward rotation signal of the motor 1 sent from the flip-flop circuit 7, and turned off by the reverse rotation signal. Thus, even if the inexpensive 8-bit class DA converter 4 is used, the output of the DA converter 4 is detected when the scanner optical system 10 detects the forward rotation of the motor 1 when reading the original 8. The scanner optical system 10 can be stably transported by making the range apparently small and finely controlling the target current value. When the scanner optical system 10 detects the reverse rotation of the motor 1 when the scanner 8 finishes reading the original 8 and returns to the home position, the output range of the DA converter 4 is increased to increase the target current value. Thus, the scanner optical system 10 can be transported at high speed. Also, the microcomputer 3
Since the output range switching control and the port for the output range switching signal are not required, the control and the circuit can be simplified.

In the above device, the shunt resistance R of the output range section 5 is
Scanner optical system 10 by connecting or disconnecting 2
However, by connecting or disconnecting the shunt resistor R2, the impedance fluctuates, and the voltage fluctuation and the waveform of the target current value are distorted. Therefore, stable traveling control of the scanner optical system 10 is adversely affected.

Therefore, a buffer section 40 is provided at the subsequent stage of the output range section 5 shown in FIG. 5, and the buffer section 40 is composed of a voltage follower circuit using an operational amplifier, and the output range section 5 connects or disconnects the shunt resistance R2. It prevents the fluctuation of the impedance that occurs from time to time from being transmitted to the input stage of the control unit 6.

As described above, by inserting the buffer 40 between the output range section 5 and the control section 6 to prevent the impedance variation from being transmitted to the input stage of the control section 6, the scanner optical system 10 with high accuracy can be obtained. Control can be achieved.

An amplifier 62 for the detected current in the control unit 6
It is advisable to insert a shock absorber 41 in the output stage as in the above case.

[0028]

As described above, according to the present invention, the target current value for determining the rotation speed of the motor in the output range section is compared with a predetermined reference value, and the target current value is the reference value when the scanner is reading. If it is smaller, the output range of the output range unit is reduced, and if the target current value is greater than the reference value when the scanner operation is returning, the output range of the output range unit is increased to output the output range of the DA converter. Since the width is apparently switched, the traveling of the scanner optical system can be kept stable.

Further, from the direction of rotation of the motor for driving the scanner, the width of the output range of the DA converter is apparently reduced when the scanner reads the original, and when the scanner is in the return operation, DA is output. Since the width of the output range of the converter is set to be apparently large, the rotation speed of the motor when reading a document can be kept constant and the rotation speed of the motor can be rapidly accelerated during the return operation.
The reading operation can be performed stably and the reading processing speed can be improved. Further, since the output range switching control by the microcomputer and the port for the output range switching signal and the like are not required, the control and the circuit can be simplified.

Since a buffer is inserted between the output range section and the control section to prevent the transmission of impedance fluctuation to the input section of the control section, the voltage fluctuation and the waveform of the target current value are distorted. It is possible to eliminate defects and control the scanner optical system with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a drive control unit of a drive motor that conveys a scanner according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an outline of a reading optical system.

FIG. 3 is an operation speed diagram of a drive motor showing a relationship between a drive current and a rotation speed.

FIG. 4 is a configuration diagram of a drive control unit of a drive motor according to a second embodiment.

FIG. 5 is a configuration diagram of a drive control unit of a drive motor according to a third embodiment.

FIG. 6 is a configuration diagram of a drive control unit of a drive motor of a conventional example.

[Explanation of symbols]

1 drive motor 2 sensors 3 Microcomputer 4 DA converter 5 Output range section 6 control unit 7 Flip-flop circuit 40 shock absorber 61 Differential amplifier 62 amplifier 63 triangular wave generator 64 pulse width modulator 65 Power amplifier

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Claims (3)

(57) [Claims] 1. When reading a document while reciprocating ,
Moves at a low speed and at a constant speed, and
During the return operation, the scanner moves at high speed, the drive motor for transporting the scanner, the sensor for monitoring the forward or reverse rotation of the drive motor and the rotation speed of the drive motor, and the predetermined motor A microcomputer that compares the target value of the rotation speed with the speed of the drive motor monitored by the sensor, calculates the target current value from the difference, and sends a signal instructing the target current value and the rotation direction of the motor as a digital signal. , A D-A converter that converts a digital signal that is the target current value sent from the microcomputer into a target current value that is an analog signal, and the target current value sent from the D-A converter and the drive that actually flows to the drive motor In an image forming apparatus having a control unit that compares the currents and controls the rotation speed of the drive motor, the analog signal output of the D-A conversion unit is output to the latter stage. With a force range section, the target current value can be adjusted according to the operation pattern of the scanner.
An image forming apparatus characterized by decreasing the output range of the output range unit during a reading operation smaller than a predetermined reference value and increasing the output range of the output range unit during a return operation in which the target current value is larger than the reference value. . Wherein said output range section is smaller output range when detecting the forward rotation of the drive motor in the sensor, characterized in that to increase the output range when it detects the reverse rotation of the drive motor in the sensor according The image forming apparatus according to item 1. 3. A buffer is provided between the output range section and the control section, and the buffer stops transmission of impedance variation when the range is switched in the output range section and impedance matching of an input line of the control section. The image forming apparatus according to claim 1, wherein: