JPH06351276A - Drive circuit for dc servo motor - Google Patents

Abstract

PURPOSE:To allow reduction of effective current by setting the constant current at a high level at the time of rising of a DC servo motor and setting the constant current at a low level at the time of constant speed operation. CONSTITUTION:When the output ACCEL-P from an acceleration control section 8 is H (acceleration), a comparator 17a connected with an AND gate (AN) 18a is selected. When the current flowing through the coil of a motor 14 is lower than the reference levels 27, 8A being set by resistors 16a, 16b, the combination of power transistors(Tr) 12a, 12d or 12b, 12c is turned ON and otherwise the power transistors Tr12a-12d are entirely turned OFF. When the output ACCEL-O from the acceleration control section 8 is L(other than acceleration), a comparator 17b connected with an AN 18b is selected and the Tr 12a-12d are controlled with reference levels 10, 8A being set by resistors 16c, 16d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a DC servo motor.

[0002]

2. Description of the Related Art A conventional drive circuit for a DC servo motor will be described with reference to FIGS. 3, 4, 5, 6, and 7. FIG.

In FIG. 3, reference numeral 1 denotes a microcomputer unit, which sequentially reads data for controlling a DC servo motor (hereinafter referred to as a motor) stored in a ROM 4 and executes a command, and a CPU 2 which executes the command. R to freely read and write the data required to perform
An AM5, a timer 6 for generating a motor reference speed clock, and an I / O port 3 for the CPU 2 to output data to or from peripheral elements. ing. The data output from the microcomputer unit 1 is input to the servo motor control unit 7 including the acceleration control unit 8, the constant speed control unit 9, and the driver control unit 10, and the motor drive signal generated by the motor control unit 7 is It is transmitted to the driver 11 and drives the motor 14.

The acceleration controller 8 includes a counter 20, inverters 21a and 21b, and S as shown in FIGS.
-R flip-flops 22a and 22b and AND gates 23a and 23b.

When + 5V is supplied, the signal RESET-
N becomes “L” at the TTL level and then becomes “H” (hereinafter, “L” and “H” are all at the TTL level). Further, since SERVO ROT-P is at "L" level, the flip-flops 22a and 22b are initialized and the output Q is at "H" level.

Output signal ACCEL of AND gate 23b
-P is "L" at this point. When the signal SERVO ROT-P from the I / O port 3 changes from "L" to "H", the output signal ACCEL-P of the AND gate 23b also changes from "L" to "H".

On the other hand, since the counter 20 is a 1/256 frequency divider circuit, 128 clocks of 499.2 KHZ-N are used.
When counted, the output is inverted from "L" to "H" or "H" to "L". In time (1 /
499.2 KHZ) × 128 = 256 μsec.

The SERVO ENC-P generated by the rotation of the motor 14 is the reset signal of the counter 20, and the counter 20 is reset every time the SERVO ENC-P is generated, and the output signal of the counter 20 becomes It becomes "L".

When the SERVO ENC-P becomes "L", the counter 20 starts counting. Figure 5 is SERV
An example in which the acceleration ends because the rotation of the motor 14 reaches a constant speed (encoder pulse cycle 256 μsec) at the time when three O ENC-Ps are received.

When SERVO ROT-P becomes "H", the output ACCEL-P of the AND gate 23b becomes "H".
become.

First, when the first SERVO ENC-P is generated, the counter 20 is reset and the output signal becomes "L". The flip-flop 22a is SERVO
Since the counter 20 counts up before the ENC-P is input, the S input is once "L", so the Q output is "L".

The D input of the flip-flop 22b is "L".
Is triggered by the SERVO ENC-P, the Q output becomes "H", and the output of the AND gate 23b ACCEL-P
Remains "H".

Next, the second SERVO ENC-P is set to 1
When the second SERVO ENC-P is generated with a delay of 256 μsec or more, the counter 20 displays 449.2 KH.
Since the number of Z clocks is 128, the output signal is "H". Therefore, the flip-flop 22a
Q output of the flip-flop 22 remains "L".
The Q output of b is "H", and the output signal ACCEL-P of the AND gate 23b remains "H".

Next, the third SERVO ENC-P is 2
256μ after the occurrence of the second SERVO ENC-P
When it occurs within sec, the counter 20 displays the second S
256 after being reset by ERVO ENC-P
Since it is within μsec, set the clock of 499.2KHZ to 1
Since the number is not 28, the output signal is "L" and the output signal of the inverter 21a remains "H".

Therefore, since the Q output of the previous flip-flop 22a remains "H", SERVO ENC-P
At the rising edge of, the Q output of the subsequent flip-flop 22b is inverted to "L", and ACCEL-P becomes "L". Then, once the Q output of the subsequent flip-flop 22b becomes "L", the output signal of the AND gate 23a always becomes "L". Therefore, unless the SERVO ROT-P becomes "L", The Q output remains "L".

By the above operation, the SERVO ROT-
After P becomes "H" and the motor 14 starts to rotate, SE
The output signal of the ACCEL-P holds the "H" level until the pulse interval of the RVO ENC-P becomes less than 256 .mu.sec, and the driver control unit 10 is notified that the acceleration is in progress.

Next, the operation of the constant speed controller 9 will be described with reference to FIG.

As described above, the motor 14 is the SERVO.
It is accelerated until the pulse interval of ENC-P becomes 256 μsec. Then, once the pulse interval reaches 256 μsec, the acceleration control ends, and the control is controlled by the phase difference between the reference clock SLEW CLK-P output from the microcomputer unit 1 and the SERVO ENC-P rotation signal from the motor 14. Reference clock SLEW CLK
Compared to -P, the SERVO E of the rotation signal of the motor 14
SLEW-P is generated by the delay amount (phase difference) of NC-P.

Next, the driver control unit 10 and the driver 11 shown in FIG. 3 will be described. Driver controller 10
The motor 1 output from the microcomputer unit 1
4 FWD-P for determining normal rotation and reverse rotation, ACCEL-P of acceleration control signal output from the acceleration control unit 8, constant speed control signal SLEW-P output from the constant speed control unit 9 and output from the comparator 17a CUR of current limit signal
RENT LIMIT-P is input. For example,
FWD-P is "H", CURRENT LIMIT-P
Is “L” and ACCEL-P or SLEW-P is “H”, FWD DRV U-P and FWD D
Since the output signal of RV L-P becomes "H", both power transistors 12a and 12d are turned on, and the motor 1
An electric current flows through 4 in the direction of the arrow.

Further, when the output signal FWD-P from the microcomputer unit 1 becomes "L", RVS DRV
Only the output signals of L-P and RVS DRV U-P become "H", both power transistors 12b and 12c are turned on, and a current flows in the motor 14 in the opposite direction of the arrow.

Since this circuit is an H-bridge circuit which is generally used for controlling the motor 14, detailed description thereof will be omitted.

When a current flows through the motor 14, a current also flows through the current detection resistor 13 and a voltage is generated across the current detection resistor 13. This voltage increases in proportion to the increase in the current flowing through the motor 14.

The motor 1 is connected to the negative input of the comparator 17a.
Resistors 16a, 1 for determining the upper limit of the current flowing through
6b is connected. One end of the current detection resistor 13 is connected to the positive input, and the voltage generated at both ends of the current detection resistor 13 when a current flows through the motor 14 is input. When the upper limit value of the current passed through the motor 14 is A, the current detection resistor 1
The voltage that appears across both ends of A is
Resistance value). If the values of the resistors 16a and 16b are determined so that this value is equal to 5 × (resistance value of the resistor 16b) / {(resistance value of the resistor 16a) + (resistance value of the resistor 16b)}, the motor 14 is determined. When the flowing current is smaller than A, the output of the comparator 17a becomes "L", and when it becomes larger than A, it becomes "H". The output signal CURRENT LIMIT-P of the comparator 17a is input to the driver control unit 10 and the current detection resistor 13
When the value of the current flowing in is greater than the upper limit A, C
URRENT LIMIT-P becomes “H”, and the output signal FWD DRV U-P from the driver control unit 10
FWD DRV L-P, RVS DRV U-P, R
VS DRV LP is all "L", power transistors 12a, 12b, 12c, 12d are turned off,
The electric current stops flowing to the motor 14. When the current flowing through the motor 14 becomes smaller than the upper limit value A, the power transistor is turned on again.

As described above, the current flowing through the motor 14 is controlled to be constant so as not to exceed the upper limit value A.

[0025]

As shown in FIG. 7 which shows the drive signal and the current waveform flowing through the motor 14 during acceleration and constant speed operation of the motor 14, during acceleration, that is, when ACCEL-P is "H". , If the current flowing through the motor 14 exceeds the upper limit value A, the CURR of the output signal of the comparator 17a
The ENT LIMIT-P becomes "H", and the power transistors 12a, 12b, 12c, 12d are turned off to prevent current from flowing to the motor 14.

Further, during constant speed operation, the current flowing through the motor 14 does not exceed the upper limit value A, but since the coil resistance of the motor 14 is extremely small, the SLEW-P output from the constant current control unit 9 is changed. Motor 1 for different pulse widths
The rate of change in the value of the current flowing in 4 tends to increase, and the current waveform is unstable. That is, the variation in the torque generated by the motor 14 becomes large, and the rotation fluctuation is likely to become large.

Further, since the upper limit value A of the current is determined at the time of acceleration requiring a large motor torque, a large current tends to flow even during constant speed operation, and heat generation of the motor and abrasion of the brush are likely to occur. There is.

The object of the present invention is to eliminate the drawbacks of the prior art and to supply a sufficient current to generate the required torque of the DC servomotor, while reducing the effective current of the current flowing in the coil to reduce the variation of the generated torque. The object of the present invention is to provide a drive circuit for a DC servo motor that can reduce the rotational fluctuation of the DC servo motor, suppress heat generation, reduce brush wear, and improve the reliability of the motor by making them uniform.

[0029]

Attention is paid to the fact that the required operating torque (current flowing through the coil) of the DC servo motor may be smaller at constant speed than at startup, and it is constant at startup of the DC servo motor. The relationship between the operation mode of the DC servo motor and the current flowing through the coil is devised so that the current setting value is increased and the constant current setting value is decreased at constant speed.

[0030]

According to the present invention, the effective current flowing through the coil of the DC servomotor can be reduced by adding a simple circuit.

Further, when the DC servomotor is rotated, the current flowing through the motor is averaged, so that the variation in the torque generated by the motor is reduced, the rotational fluctuation is suppressed, and accurate control is possible.

Furthermore, since the spike current is suppressed, the brush life is extended and the reliability of the motor is improved.

[0033]

Embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram of a constant current control system of a DC servo motor showing an embodiment of the present invention. FIG. 2 is a timing chart of the drive signal and the motor current waveform in FIG.

In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals, and the description of the common parts will be omitted. The improvement from the prior art is that it has two constant current control circuits 24a and 24b.
The circuit can be switched depending on the signal level of CCEL-P.

In this embodiment, the constant current set value is 27.8A.
In addition, the comparator 17b and the resistors 16c and 16d are added so that the constant current setting value of 10.8A can be set.

The signal ACCEL-P indicating that the motor 14 is in the accelerating state and the signal inverted by the inverter 15 are input to the AND gates 18a and 18b, respectively, and further, via the OR gate 19, the driver control unit. Connected to 10. That is, when the output signal ACCEL-P from the acceleration control unit 8 is "H" (servo motor acceleration), the comparator 17a connected to the AND gate 18a is selected. When the current flowing through the coil of the motor 14 is smaller than the reference value 27.8A set by the resistors 16a and 16b, the power transistors 12a and 12
O in combination of d or 12b, 12c
N becomes possible and the current flowing through the coil is larger than 27.8 A, the power transistors 12a, 12b, 12
All of c and 12d are turned off.

The output signal ACC from the acceleration control unit 8
When EL-P is "L" (except during servo motor acceleration), the comparator 17b connected to the AND gate 18b is selected, and the power transistors 12a, 12b, 12c,
12d is the reference value 1 set by the resistors 16c and 16d
Controlled by 0.8A.

That is, the AC output from the acceleration control unit 8
The constant current set value can be switched by the CEL-P signal.

Next, the timing chart of FIG. 2 will be described.

To start the motor 14, the SERVO ROT-P signal is output from the I / O port 3 at "H" and the FWD-P that determines the motor rotation direction is output at either "H" or "L". To do. Here, FWD-P is shown as “H”. When acceleration starts, the ACCEL-P signal becomes "H". When the ACCE LP signal becomes "H", the output signal EW from the driver control unit 10
D DRV U-P and FWD DRV L-P are "H"
Then, the power transistors 12a and 12d are turned on and current flows in the motor 14 in the direction of the arrow.

At this time, the ACCEL-P signal is "H".
Since the comparator 17a connected to the AND gate 18a is selected, the constant current setting value is 27.8A (corresponding to A in FIG. 2), and the current flowing through the coil is 27.8A constant. Kept in.

When the interval between the encoder pulses from the motor 14 is within 256 μsec, the ACCEL-P signal becomes "L" and the start-up is completed.

Next, the motor 14 uses the encoder pulse SE
Constant speed control is performed by SLEW-P generated by the phase difference between RVO ENC-P and SLEW CLK-P output from the microcomputer unit 1.

At this time, since the ACCE LP signal is "L", the comparator 17b connected to the AND gate 18b is selected. Therefore, the constant current setting value is 1
0.8A (corresponding to B in FIG. 2), and the current flowing through the coil is kept constant at 10.8A.

As described above, at the time of startup when the required operating torque is large (the current that must be supplied to the motor 14 is large), the constant current set value is set to 27.8 A, and the required operating torque is small (the motor 14 must be supplied). At constant speed, switch the constant current setting value to 10.8A.

In this embodiment, since the effective current during constant speed rotation is reduced and the peak value is suppressed to 10.8 A, the heat generation of the motor is suppressed by eliminating the spike current, and the brush wear is suppressed. It was reduced and the reliability of the motor could be improved. Further, since the torque generated by the motor can be made uniform, the rotation fluctuation can be reduced.

[0047]

According to the present invention, the effective current flowing through the coil of the DC servo motor can be reduced by adding a simple circuit. Therefore, the motor which has been required to be forcibly cooled by an external cooling fan or the like. However, the need for an external cooling fan is eliminated and the current consumption is reduced, so that the power supply can be downsized and the cost can be reduced.

Further, when the DC servo motor is rotated, the current flowing through the DC servo motor is averaged, so that the variation in the torque generated by the motor is reduced, the rotational fluctuation is suppressed, and accurate control is possible.

Further, since the spike current is suppressed, the brush life is extended and the reliability of the motor is improved.

[Brief description of drawings]

FIG. 1 is an embodiment of a drive circuit for a DC servo motor according to the present invention.

FIG. 2 is an explanatory diagram showing a drive signal and a current waveform of a DC servo motor in the drive circuit of FIG.

FIG. 3 is a drive circuit of a conventional DC servo motor.

FIG. 4 is an acceleration control circuit.

FIG. 5 is a timing chart showing the movement of the acceleration control circuit.

FIG. 6 is a timing chart showing the movement of the constant speed control unit.

7 is an explanatory diagram showing a drive signal and a current waveform of a DC servo motor in the drive circuit of FIG.

[Explanation of symbols]

8 is an acceleration control unit, 9 is a constant speed control unit, 10 is a driver control unit, 12a, 12b, 12c and 12d are power transistors, 13 is a current detection resistor, 14 is a DC servo motor, and 24a and 24b are constant current control circuits. Indicates.

Claims (2)

[Claims] 1. An acceleration control unit for accelerating a DC servo motor based on rotation information based on an encoder pulse from the DC servo motor, a reference speed clock of the DC servo motor, and an encoder pulse are compared, and a speed control feedback is used. The operating conditions of the DC servo motor driving power transistor are controlled by a constant speed control unit that performs constant speed control, control signals from the acceleration control unit and the constant speed control unit, and a DC servo motor rotation direction instruction signal from the microcomputer unit. The driver control unit that determines the DC servo motor driving power transistor, the circuit that detects the current flowing in the coil of the DC servo motor, the power transistor is turned off when the current value exceeds a certain level, and the current flowing in the coil of the DC servo motor DC servo motor consisting of a constant current control circuit that keeps the A drive circuit for a DC servo motor, wherein the drive circuit has a plurality of constant current control circuits having different current detection levels. 2. The constant current control circuit is switched and used according to each operation mode such as acceleration and constant speed of the DC servo motor to change the current flowing through the coil of the DC servo motor according to the operation mode. The drive circuit for the DC servo motor according to claim 1.