JPS61161988A - Servo motor drive device - Google Patents

Abstract

PURPOSE:To enable to always detect the prescribed motor drive current without influence of a switching noise by setting a timing for detecting a drive current near the end point in the output period of a pulse width modulation controller. CONSTITUTION:A drive current flowed to a motor drive circuit 3 is converted to a voltage by resistors R, R, and input to a differental amplifier 4, and an A/D converter 5. A microcomputer 1 servo-calculates so that a loop gain becomes constant on the basis of the output digital signal of the converter 5, and generates a drive command (a) to a PWM controller 2 on the basis of the signal. Here, the timing for reading the output digital signal of the converter 5 by the microcomputer 1 is near the end point of rear half of one period of the PWM signal. Thus, the constant motor drive current can be always detected without influence of a switching noise.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a servo motor drive device for driving a servo motor used in precision controlled devices such as machine tools and robots that utilize numerical control (NC). .

(Summary of the Invention) This invention prevents the detection timing of the motor drive current from being affected by switching noise superimposed on the motor drive current when the current minor loop of the servo motor drive control system is controlled by a microcomputer. This is to stabilize and facilitate the servo calculation to keep the loop gain constant.

(Background of the Invention) Servo motors are used in items that are precisely controlled, such as machine tools and robots that utilize numerical control (NC).

It is well known that the drive control system of this servo motor is provided with a current minor loop that operates so that the drive current of the servo motor is stabilized at a target value. We developed a method for controlling the loop using a microcomputer (unpublished).

That is, the current minor loop according to the present applicant is basically composed of a microcomputer, a pulse width modulation (PWM) control circuit, and a motor drive circuit.

The PWM control circuit receives a drive command from a microcomputer and generates a PWM signal having a constant pulse repetition frequency and different on-times.

The motor drive circuit is composed of, for example, a transistor bridge, and each arm of the bridge is appropriately controlled by the PWM signal to supply a drive current to the servo motor.

The microcomputer detects the drive current at appropriate intervals, performs servo calculations to keep the current minor loop constant, and issues the drive commands.The microcomputer also detects the drive current at appropriate intervals, performs servo calculations to keep the current minor loop constant, and issues the drive commands. (based on the information), operations such as change control of the drive command are performed.

By the way, when controlling the current minor loop with a microcomputer, one of the matters to be considered is the selection of the detection timing of the drive current.

That is, switching noise caused by the on/off operations of the transistors forming the bridge is superimposed on the drive current. The point of on-off operation is not the same point, but P
Since it changes depending on the WM signal, the superimposition position of the switching noise superimposed on the drive current also changes.

On the other hand, since the drive current has a sawtooth waveform, the detection timing is set to be always constant within one cycle (PWM cycle) of the PWM signal.

Therefore, the detection timing needs to be set at a time when the influence of switching noise can be ignored.

This invention was made based on such knowledge.

(Objective of the Invention) An object of the present invention is to enable detection of a constant motor drive current at all times without being affected by switching noise superimposed on the motor drive current.

(Structure and Effect of the Invention) In order to achieve the above object, a servo motor drive device according to the present invention includes a bridge circuit that controls a drive current supplied to a motor, and a switching circuit that constitutes each arm of the bridge circuit. A pulse width modulation control circuit that changes and outputs the width of a pulse signal that turns the element on and off at a constant cycle based on a drive command, and a servo calculation that detects the drive current controlled by the bridge circuit and performs a servo calculation so that the loop gain is constant. and a microcomputer that issues a surface drive command, and the timing at which the microcomputer detects the drive current is set near the end point of the output cycle of the pulse width modulation control circuit.

According to this configuration, a constant motor drive current can always be detected without being affected by switching noise superimposed on the motor drive current, and it is possible to stabilize and simplify the servo calculation that keeps the loop gain constant. can.

In other words, switching noise is superimposed on each peak point of the drive current forming a sawtooth wave, but the on-time of the switching element is set to within, for example, 90% of the first half of the output cycle of the pulse width modulation control circuit. The drive current is detected during the time when the switching element is off (the latter 10% of the output cycle of the pulse width modulation control circuit).

(Description of an Embodiment) FIG. 1 shows a servo motor drive device according to an embodiment of the present invention.

In the figure, this driving neck is equipped with a microcomputer 1.
, a pulse width modulation (PWM) control circuit 2, a drive circuit 3 that supplies a drive current to the servo motor M, a differential amplifier 4 that amplifies the detected drive current, and a circuit that converts the detected drive current into a predetermined digital signal. An analog-to-digital converter (A/D converter) 5 that feeds back to the microcomputer 1 forms a current minor loop.

The microcomputer 1 performs servo calculations based on the output digital signal of the A/D converter 5 so that the loop gain is constant, and based on this, issues a drive command a to the PWM control circuit 2, as well as main control (not shown). The drive command a is changed and controlled in accordance with control commands (based on speed information and position information) input from the device at predetermined intervals.

The PWM control circuit 2 receives the drive command a and generates a PWM signal having a constant pulse repetition frequency and different on-times.

The drive circuit 3 includes four FETs 31, 32 in this example.
．． It is composed of 33 and 34 bridges, and a PWM signal from the PWM control circuit 2 is input to the gate of each FET.

That is, in this drive circuit 3, FET31.3
Either one of the pair of FETs 32 and 34 is controlled, and a drive current is supplied to the servo motor M in a predetermined direction.

For example, when supplying a drive current to the servo motor M in the direction of the arrow shown in the figure, a pair of FETs 31 and 33 is used, and the FE
T33 is turned on, and at the same time, FET31 is turned on and off using a PWM signal as shown in FIG. 2(a).

Then, ideally, the drive current flowing to the servo motor M is the inductance of the servo motor M and the regenerative diode 3.
5.35 results in a sawtooth wave as shown in FIG. 2(C).

However, the drive current that actually flows through the servo motor M is the second
As shown in Figure (b), noise (d) is superimposed on each peak point of the sawtooth wave. This noise (d) is FE
This is due to the delay time when T performs a switching operation.

In this way, the drive current flowing through the motor drive circuit 3 is converted into voltage by the resistors R, R, and is input to the differential amplifier 4.

The differential amplifier 4 amplifies the detected voltage to a predetermined level and outputs it to the A/D 5.

The A/D 5 converts the output analog voltage of the differential amplifier 4 into a predetermined digital signal, and outputs this to the microcomputer 1 as a feedback input.

As is clear from the above explanation, the microcomputer 1 takes in the output of the A/D 5 and performs servo calculations to keep the loop gain of the current minor loop constant, but the timing at which the output of the A/D 5 is read is affected by switching noise ( In the case of the superimposed position (d), errors will occur in the servo calculation.

In the example of the operation explained above, since the amplitude of the pulse width of the PWM signal that turns on and off the FET 31 is varied, the switching noise superimposed on the drive current within one output cycle of the PWM control circuit 2 is The superimposition position also changes variously, as shown in FIG.

FIG. 3 shows that within one output cycle of the PWM control circuit 2, P
The case where the duty ratio of the WM signal increases in the order of (a), (b), and (c) is shown.

In the figure, if the timing at which microcombination 1-1 reads the output digital signal of A/D 5 is point A or point 8, it may not be possible to detect the correct current value due to the influence of switching noise (2). Recognize.

Therefore, in this invention, the timing at which the output digital signal of the A/D 5 is read is controlled by the switching noise (2).
The point in time was set to avoid the superimposed position of .

In the example shown in Figure 3, microcomputer 1 has an A/D
The timing for reading the output digital signal of 5 is shown in the same figure (
The zero point is shifted further back from the superimposition position of the switching noise (d) shown in c).

In other words, PWM! The IJ control circuit 2 does not operate independently of the microcomputer 1, but is configured so that each cycle starts upon receiving the activation signal C from the microcomputer 1, and the duty ratio of the PWM signal is in the second half of one cycle. There should be a time domain in which switching noise is not superimposed on the

Specifically, the duty ratio of the PWM signal is 0 to about 9.
The hardware configuration of the PWM control circuit 2 is set so that it is within 0%.

The timing at which the microcomputer 1 reads the output digital signal of the A/D 5 is set near the end point of the second half of one cycle.

Therefore, in this invention, the microcomputer 1
As the operation, a start command C is output to the PWM control circuit 2 along with the drive command a, the elapsed time after outputting the start command C is monitored, and after a predetermined time (for example, 90% of one cycle elapsed time), It reads the output digital signal of the A/D 5 and then outputs the drive command a and the start command C to the PWM control circuit 2 again.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a servo motor drive device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram illustrating how switching noise is superimposed on the drive current of the servo motor.
FIG. 3 is a waveform diagram showing how the position of superimposition of the switching noise changes. 1...Microcomputer 2...PWM control circuit 3...Drive circuit a of servo motor M...Drive command C...Start command

Claims (1)

[Claims] (1) A bridge circuit that controls the drive current supplied to the servo motor, and a pulse width modulation that changes and outputs the width of the pulse signal that turns on and off the switching elements that make up each arm of the bridge circuit at a constant cycle based on the drive command. a control circuit; and a microcomputer that detects the drive current controlled by the bridge circuit, performs servo calculation so that the loop gain is constant, and issues the drive command, the microcomputer detects the drive current. A servo motor drive device characterized in that the timing is set near an end point within an output cycle of the pulse width modulation control circuit.