JPS5869483A - Controller for scanning drive motor - Google Patents

Abstract

PURPOSE:To reduce the ordinary error at the time of controlling at constant speed operation by applying a bias current to cancel the viscous force based on a signal corresponding to the target or actual speed of a motor to the motor, thereby ignoring the viscous force. CONSTITUTION:When an exposure mirror for a copying machine is repeatedly and recirculatingly driven, a feedback control system of the PLL type including a phase comparator 6, a charge pump circuit 7 and a loop filter 8, and an analog feedback control system including a D/A converter 17, a frequency divider 11 and an f/v converter 13 are selected by a switch circuit, thereby controlling a motor 1. At this time, the output of the converter 17 is connected through a switch SWA'' to a servo amplifier 3 to apply the bias current for cancelling the viscous force to the motor 1 separately from a signal of the filter 8. Accordingly, the influence of the viscous force can be eliminated to shorten the rising time, thereby reducing the error.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a scanning drive motor that repeatedly drives objects such as an exposure mirror of a copying machine, an image reading head of a facsimile machine, and a recording head of a printer back and forth.

In a scan drive motor, it is preferable that the time from startup to stabilization at a constant speed is as short as possible. In general motor control, phase locked loop
PLL (hereinafter abbreviated as PLL) type constant velocity control is known, but since there is a delay in the loop filter, it takes a long time to enter the constant velocity control mode from startup. Conventionally, a voltage at a certain level is applied to the motor drive circuit as an energizing signal at startup, and during this time the loop filter is charged so that its output voltage reaches the constant speed instruction level during constant speed control, and the motor speed or When the starting energization time reaches a predetermined value, the output of the loop filter is switched and applied to the motor drive circuit (for example, Japanese Patent Laid-Open No. 54-35312). According to this, startup to a predetermined speed is quick, there is no problem such as large hunting occurring when switching to constant speed control mode, and the rise time from start to constant speed control is short.

By the way, when performing this type of motor control, a common problem is the frictional force of the sliding parts, bearings, etc. of the scanning mechanism, and various measures have been proposed as countermeasures for this frictional force. (Patent Application No. 19537-1983). However, in addition to frictional force, viscous force also exists in the scanning mechanism, and the viscous force increases in proportion to the scanning speed. If the viscous force becomes too large to ignore compared to the frictional force, the rise time from start to constant velocity control becomes longer, and the steady-state error during constant velocity control increases, resulting in a decrease in accuracy.

In order to reduce the latter steady-state difference, the loop gain of the control circuit must be increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a scan drive motor that requires a small loop gain during constant velocity control of a control system (CPLL) and has a short rise time.

In order to achieve the above object, the present invention applies a bias current necessary to cancel the viscous force to the motor separately from the output signal of the loop filter, based on a signal corresponding to the target motor speed or the actual motor speed. Apply. This generates a driving force in the motor that counteracts the viscous force, and the PL
In the L system, since the viscous force is ignored, the steady-state error during constant velocity control can be reduced and the rise time can be shortened without increasing the loop gain.

When the frictional force of the scanning mechanism driven by the motor is large (and/or when the loop gain is small), a large torque is required from the motor. The phase difference is stabilized at a value corresponding to the frictional force, and the output voltage of the loop filter is stabilized from a zero level to a certain level (vf) on the motor speed increasing side. Therefore, in this case, when switching from startup to constant speed control, the motor temporarily decelerates and then speeds up until the loop filter output reaches V (a temporary oscillation occurs. Therefore, according to the present invention, In a preferred embodiment, the motor drive circuit is provided with an additional force applying means for energizing the motor current to overcome the frictional force of the driven system at least in constant velocity control mode.In other words, at least in constant velocity control mode The motor current required to substantially equalize the phase difference at a specified speed is instructed to a motor drive circuit separate from the PLL control system.As a modification, the output of the loop filter is Set to the above-mentioned additional voltage.

FIG. 1 shows an embodiment of the present invention. This embodiment controls the reciprocating drive of a cartridge equipped with an exposure lamp and mirror of a copying machine, and a home position is set in front of the exposure area, and the photosensor of the initial position detector 23 is placed there. has been done. In the overview, the carriage starts from the home position and is driven forward to the exposure area.
During this drive, the control device IO counts the output pulses AC of the rotary encoder 2 connected to the scanning drive motor 1 (to be more precise, the output pulses of the multiplexer curtain 2), and when the forward drive reaches a specified width, the carriage is driven backward, and the carriage is returned to the home position. The reciprocating drive is performed until the position is exceeded, and the amount control device 10 for this reciprocating drive operates the analog switches sw8', SWA'', and SW.
A, 8WB, SWC, SWD and 8WB are opened and closed, and the output polarity of the positive/inverting amplifier 16 is switched and controlled. The entire device includes a pulse oscillator OSC, a counter 4. Output gate 5. Speed designation latch/reference pulse generator 1 consisting of register 19 and decoder 20 Phase comparator 6.
Charge pump circuit7. Loop filter 8. A switch circuit consisting of analog switches 8WA' and 8WA-8WC, a servo amplifier 3 (motor drive circuit), and a rotary encoder 2 constitute a PLL feedback control system. A speed designation latch/analog target value generation circuit consisting of a converter 17 and a register 18, and a frequency division counter 1
1. Ma/l/multiplexer 12° frequency-voltage converter 13
An analog feedback control system is composed of a digital processing/analog feedback circuit including a positive/inverting amplifier 14, a differential amplifier 15, and a phase compensation circuit 21. These PLL type feedback control system and analog feedback control system use analog switch SW.
A', 8WA-8WC, and a switch circuit composed of swg select and connect to the servo amplifier 3. Also,
The drive of the carriage from the backward scanning stop position to the home position is performed by the initial position detector 2 including the above-mentioned photosensor.
3 and a phase compensation circuit 22, and this home position drive control system is also selectively connected to the servo amplifier 3 via the aforementioned switch circuit.

In this embodiment, the output end of the D/A converter 17, which is a viscous force insect trapping means, is connected to the servo amplifier 3 via an aerolog switch S-kai 8''.

First, the PLL feedback control system will be explained. Data specifying the speed is latched in the register 19, and the data is converted into a count output selection signal by the decoder 2o and applied to the output gate 5. The counter 4 counts the output pulses (pulse C) of the pulse oscillator O8c, and outputs a pulse with a period twice that of the pulse C and a duty of 50% to the O output terminal, and a pulse C to the 1 output terminal. A pulse with a period 4 times the period of pulse C and 8 times the period of 1+1 is output to the 2 output terminal, and a pulse with a period twice the period of pulse C is output to the i output terminal. The output gate 5 applies the pulse at the count output end specified by the selection signal from the decoder 20 to the phase comparator 6 as a speed reference pulse R. Note that the counter 4 may be a preset counter for block operation, and its borrow signal may be applied to the preset terminal, and the output of the register 19 may be provided to the preset input terminal.

In this case, output gate 5 and decoder 20 can be omitted.

The output pulse of the rotary encoder 2, that is, the motor rotation synchronization pulse V is applied to the phase comparator 6. The configuration of the phase comparator 6, charge pump circuit 7 and loop filter 8 is shown in FIG. 2, and the input/output of the comparator 6 and charge pump circuit 7 is shown in FIG. The phase comparator 6 is the third
As shown in the figure, when the phase of the rotation synchronization pulse V lags behind the speed reference pulse, a low-level pulse U is output for the period corresponding to the delay, and when the phase of the rotation synchronization pulse V is ahead, A low level pulse D is output for the advance period.

The charge pump circuit 7 outputs a negative constant level voltage -VCC while the pulse U is at a low level, and outputs a positive constant level voltage -+-Vcc while the pulse D is at a low level. During high level, it outputs zero level voltage. In other words, if there is no phase shift, the output of the charge pump 7 will be at zero level, and if there is a phase shift, it will be delayed and increase as the output progresses.

becomes a negative level. The loop filter 8 integrates the output voltage of the charge pump circuit 7, and the integrated voltage is set to zero level while the analog switch SWD is closed. While this analog switch 8WD is open, a voltage LP obtained by integrating the output CP of the charge pump circuit 7 is output from the loop filter 8 to the analog switch 8WA, and when this switch SWA is closed, it is applied to the servo amplifier 3. In addition, as described later, in constant velocity control mode,
The control device 10 controls the switches SW A' and SW
A'', SWA and SWC are closed, and the servo amplifier 3 has a bias current command voltage E (, P L L control voltage LP) for generating torque that overcomes the frictional force.
, an analog feedback voltage (error signal), and a target speed signal for generating a torque counteracting the viscous force are applied in a superimposed manner (addition). Therefore, the output LP of the loop filter B increases the motor current if the phase lags, and decreases the motor current if the phase leads, depending on the phase difference of the rotation synchronizing pulse V with respect to the reference pulse R. If it is, the motor current cannot be changed.

Next, the analog feedback control system will be explained.

In this embodiment, the carriage return (double drive) is driven at high speed only by an analog feedback control system. Rotation synchronization pulse A of rotary encoder 2
, B (phase difference between B and human being π/2) are applied to the forward/reverse judgment circuit 9, where the pulse A is applied.

The direction of rotation of the motor 1 is determined from the phase difference between the signals B, and the forward/reverse determination circuit 9 outputs a direction signal CW/CLW with a low level "o" for forward rotation and a high level "1" for reverse rotation. It is applied to the inverting amplifier 14 and the control device 10. Career
Prior to the second exposure scan (forward drive), the control device IO latches speed instruction data in the registers 19 and 18, instructs the positive/inverting amplifier 16 to output positive polarity, and causes the multiplexer 12 to output the rotation synchronization pulse A. Since the command is given, the motor 1 rotates in the forward direction and the forward/reverse judgment circuit 9 turns to a low level "
0'' is applied to the positive inverting amplifier 14 and its switch swg is opened, so that the analog voltage (plus) corresponding to the speed instruction data, that is, the target speed signal (plus) is applied to the positive input terminal of the differential amplifier from the positive inverting amplifier 16. On the other hand, the f/V conversion voltage of the rotation synchronizing pulse A, that is, the speed feedback signal, is applied from the positive inverting amplifier 14 with positive polarity to the negative input terminal of the differential amplifier 15, and the difference between the target speed signal and the speed feedback signal is A signal indicating , that is, an error signal is output from the differential amplifier 15 and applied to the phase compensation circuit 21 . The phase compensation circuit 21 is a well-known circuit composed of a lead/lag circuit that suppresses overshoot at the rising edge, and applies a control voltage obtained by adding overshoot correction to the error signal to the servo amplifier 3 via the switch SWC. The control device 1O determines an exposure scan stop point based on the scan width instruction data inputted in advance to the control device 10, and sequentially inputs the data in the register 18 at a predetermined timing from before the stop point so that the carriage is returned at the stop point. Replace it with one that shows a smaller value. This is done by counting the rotation synchronizing pulse A from the home position and timing with the count value.

This causes deceleration and the speed drops rapidly.

When the pulse person count value reaches the value associated with the scanning width instruction data, the control device 10 sets the positive/inverting amplifier 16 to the negative output (applies a high level l"■"), and sends a control signal to the multiplexer 12. The multiplexer 12 is divided and counted, with the value "1".

the return speed data is latched into the register 18. As a result, the current direction of the motor 1 is reversed, and the motor 1 starts rotating in reverse. When the motor 1 reverses, the output of the forward/reverse determination circuit 9 becomes “1” and the forward/invert amplifier 14
At this point, switch SWE is closed and its output is inverted to a negative level.

In this return drive, the division pulse of the rotation synchronization pulse A (output of the counter 11) is applied to the f/v converter 13, so assuming that the target speed signal is at the same level as during exposure scanning, The return speed is n of the exposure scanning speed.
times (n=output pulse period of frequency division counter 11/pulse person period=frequency division ratio).

However, the return speed can be determined by the data latched into the register 18 upon return. In any case, the return speed is faster than the exposure scanning speed, so in the return, it becomes difficult for the control device 10 to perform timing control based on the rotation synchronization pulse count and the count value. Therefore, in return, the frequency-divided pulses are counted and the timing is controlled using the counted value. That is, the return width is determined from the exposure scanning width, the return stop point is set to a position beyond the home position, and the data in the register 8 is sequentially changed to a smaller value as the return stop point is approached.

Next, the exposure scan control and return scan control of the entire embodiment shown in FIG. 1 will be explained, mainly focusing on the control operation of the control device 10. First, an outline of the timing is shown in Table 1.

Table 1: 8! !11 W W W W 8 通璋L6= When the device power is turned on, the control device 10 sets the analog switches 8WB and SWD to close, and sets the other analog switches to open. As a result, servo amplifier 3
The output distortion of the phase compensation circuit 22 is applied to the input terminal of the phase compensation circuit 22. The phase compensation circuit 22 has the same configuration as 21, and the output of the detector 23 is at a predetermined positive level while the photosensor of the initial position detector 23 is not detecting a carriage, and becomes zero level when a carriage is detected. Therefore, if the carriage is out of the home position in the return direction, the motor 1 is driven to rotate in the normal direction and the carriage is stopped when it reaches the home position. If the carriage is out of the home position in the exposure scanning direction, the motor 1 is driven in the forward direction, the carriage moves in the exposure scanning direction, a limit switch (not shown) is closed near the limit position, and the control device In response to this, the IO controls the stop and switches to the return scanning mode shown in Table 1 and described below. In the return scanning mode, the carriage stops slightly past the home position, and then the mode is switched to the same timing mode as when the power is turned on, and the output of the phase compensation circuit 22 drives the hole motor l in the forward direction, and the carriage returns to the home position. positioned in position. The control device 1O is composed of an LSI such as a microcomputer, and when a start signal is given, it reads and holds the speed instruction data and scanning width instruction data given from the outside, and stores the speed instruction data in registers 18 and 19. and starts counting the scan width instruction data to the scan width count value (pulse count value). At this rise, a signal obtained by performing phase compensation on the output of the differential amplifier 15 is applied to the servo amplifier 3, the motor 1 is controlled in analog feedback speed to suppress overshoot, and the analog switch 8WD in the loop filter 8 is applied to the servo amplifier 3. It is closed, and the integrated voltage of the loop filter 8 is set to zero level. Incidentally, at the time of this rise, the switch SW ``man'' may be turned on to apply torque to the motor to counteract the frictional force. When the count value of the output pulse (pulse A) of the multiplexer 12 reaches a predetermined value, the control device 10 switches to the constant velocity control mode. In this constant velocity control mode,
The switch 8WD of the loop filter 8 is opened, and the servo motor 1 receives the PLL control signal LP and the friction force compensation signal E.
f, a target velocity signal Ev for viscous force compensation, and an analog feedback error signal are added and applied. In constant velocity control mode, the motor speed almost matches the target speed, and the analog feedback error signal level is low.
The contribution rate of the PLL control signal LP is large, and the rotation synchronization pulse A
Fine speed control is performed by matching the phase of (V) with the reference pulse R. During constant velocity control, viscous force and frictional force proportional to the speed act, but since the current to provide the necessary torque is passed through the servo amplifier 3, PLL control is used to keep the steady-state error during constant velocity control small. The loop gain required for the system becomes smaller. In switching from the rise mode to the constant velocity control mode, the integrated voltage of the loop filter 8 is set in advance to the zero level when the phases match by the switch 8WD. Therefore, phase lock is quickly performed after entering constant velocity control mode, and the target velocity is accurately stabilized.

When the count value of the rotation synchronization pulse reaches the value associated with the scan width instruction data, the control device switches the analog switch to the exposure scan stop mode shown in Table 1, and sequentially performs the exposure scan with timing based on the count value of the rotation synchronization pulse. , update the data in register 18 to a smaller value [exposure scan stop mode], then change the switch to the return mode shown in Table 1, reload register 1B with the data loaded at the start of exposure scan, and set the return width. 1/n+ of the width
The output pulses of the multiplexer 12 (output pulses of the branch counter 11) are counted as α. On the right, α corresponds to the width (calculated from the output pulse of the C counter 11) that exceeds the home position.

When the remainder of the return reaches a predetermined value, the control device 10
sequentially updates the data in the register 18 to a smaller value (return stop mode) and then switches the switch to the standby mode shown in Table 1. At the time of this switching, the carriage has passed the home position, so when switching to the timing mode, the motor 1 is driven forward by the output (plus) of the phase compensation circuit 22, and the carriage is driven by the photo sensor of the initial position detection circuit 23. When the position (home position) is reached, the output of the phase compensation circuit 22 becomes zero level, and the motor 1 stops.

In this embodiment, since the start-up is slow if only the PLL type motor side division is used, the start-up is made faster by analog feedback control. Furthermore, in constant velocity control, the analog feedback system is used as is, and frictional force and viscous force are corrected separately from the PLL control system to reduce the necessary loop gain of the PLL control system and stabilize the control system. .

FIG. 4 shows a block stage of another embodiment of the present invention.
A positive inverting amplifier as the v converter 13! The actual speed signal BR is applied to the servo amplifier 3 from the output terminal of 4. In addition, a positive inverting amplifier 2 is configured to provide a bias current instruction to cause the motor to generate torque that overcomes the frictional force.
It is turned on and off by the servo amplifier CW/CLW via 4. An overview of the timing in this example is shown in Table 2.

The difference in timing from the previous embodiment is that the switch SWA' is closed even during return. In this embodiment, during exposure scanning, the switch SWF is opened and a positive frictional force correction voltage is output to the output terminal of the positive/inverting amplifier 24.
During return operation, the switch 8WF is closed and a negative frictional force correction voltage is output to the output terminal of the positive/inverting amplifier 24. Therefore, when the switch SWA' is closed in either forward scanning or backward scanning, friction is applied to the motor 1. A bias current flows to counteract the force. Since the actual speed signal (voltage) BR is proportional to the frequency of the pulse corresponding to the actual rotational speed of the motor 1, the bias current is sufficient to cause the motor 1 to generate a torque counteracting the viscous force, as in the previous embodiment. It flows into servo amplifier 3.

As described above, according to the present invention, even in high-speed scanning control where viscous force is a problem, a PLL is required to reduce steady-state errors during constant velocity control and perform control with high accuracy.
The loop gain of the control system can be reduced and the rise time required to reach the target speed can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a detailed configuration of a part of the same, and FIG. 3 is a time diagram showing input and output signals of the phase comparator 6 and charge pump circuit 7 FIG. 4 is a block diagram showing another embodiment of the present invention. 1: Servo motor 2: Rotary encoder 3: Servo amplifier

Claims (3)

[Claims] (1) Equipped with a phase comparator, a charge pump circuit, a loop filter, a motor drive circuit, and a switching circuit for constant speed control at startup 1. When the motor starts and shifts to constant speed control, the output of the loop filter is transferred to the motor drive circuit. A scan drive that compares the phases of a rotation synchronization pulse that is applied and synchronized with the rotation of the motor and a comparison reference pulse with a period corresponding to a specified speed, and controls the motor speed by increasing or decelerating it according to the phase difference. The motor control device is configured to include a viscous force correction means for generating a viscous force correction signal corresponding to at least one of a target speed of the motor and an actual motor speed, and to apply a signal from the correction means to a motor drive circuit. A control device for a scan drive motor, characterized in that: (2) A control device for a scanning drive motor according to claim 1, wherein the viscous force correction means is a D/A converter that converts digital information corresponding to a designated speed into an analog signal. (3) The control device for a scan drive motor according to claim 1, wherein the viscous force correction means is a converter that converts the frequency of a pulse signal having a frequency proportional to the rotational speed of the motor into voltage or current. .