JP2002297242A - Method for improving accuracy of position control system and position controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the control accuracy of a position control system by canceling the offset of a D/A converter and an A/D converter. SOLUTION: In this position control system for controlling the position of a motor 10 by combining a position controller 1B for outputting a speed command through a D/A converter 5 with a speed controller 20 for inputting the speed command through an A/D converter 6, the inputs of the D/A converter 5 are sampled the prescribed number of times in a state that the motor 10 is stopped and averaged and added to the output of a position controller 4 arranged in the position controller 1B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the position control accuracy of a position control system having an analog speed command interface.

[0002]

2. Description of the Related Art The prior art of a position control system having an analog speed command interface will be described with reference to FIG. In the figure, reference numeral 10 denotes a servomotor, and 11 denotes an encoder connected to the servomotor 10 to detect its rotation. Reference numeral 20 denotes a servo driver for controlling the speed of the servo motor 10, that is, a speed control device.
Is a motion controller that controls the position of the camera, that is, a position control device. The servo driver 20 includes an A / D converter 6, an adder / subtractor 7, a speed controller 8, a power converter 9, and a pulse output unit 12. The motion controller 1 includes a position target 2, an adder / subtractor 3, Position controller 4,
It comprises a D / A converter 5 and a counter 13.

In such a configuration, the servo driver 20 operates as follows. When an analog speed command is given to the A / D converter 6, it is converted into a digital signal,
This signal and the speed signal detected by the encoder 11 are subtracted by the adder / subtractor 7. The result is input to the speed controller 8 to control the speed. A command signal of the speed controller 8 is supplied to the power converter 9 to output a drive current to the servomotor 10. In this way, the servo motor 10
It rotates according to the speed command given to the D converter 6. In the motion controller 1, when the position target 2 outputs a position command of the servomotor 10, the rotation position of the servomotor 10 is subtracted by the adder / subtractor 3. The rotational position of the servo motor 10 is signal-processed and detected by the pulse output device 12 of the servo driver 20 and the counter 13 of the motion controller 1. The position controller 4 to which the output of the adder / subtractor 3 has been input controls the position and outputs a speed command. The speed command is converted into an analog signal by the D / A converter 5 and becomes the output of the motion controller 1. As described above, since the motion controller 1 and the servo driver 20 form a speed control loop and a position control loop doubly, the rotational position of the servo motor 10 rotates according to the position command of the position target 2.

[0004]

However, since the D / A converter 5 and the A / D converter 6 generally have an offset, it is difficult to control the speed according to the speed command output from the motion controller 1. But similarly, position target 2
Is not controlled according to the position command output by the controller, but the position is controlled to be shifted from the target position by a distance corresponding to the offset of the D / A converter 5 and the A / D converter 6. is there. Further, since these offsets generally vary depending on the temperature, apparently, there is no reproducibility of the speed deviation and the position deviation, and it is not easy to correct the offset in advance. Further, even if the correction can be made, the temperature changes depending on the use condition, so that the offset is again caused, and there has been a problem that high-precision position control cannot be performed. An object of the present invention is to cancel such an offset and improve the control accuracy of the position control system.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a position control device for outputting a speed command via a D / A converter and inputting the speed command via an A / D converter. In a position control system for controlling the position of a motor in combination with a speed control device, the D / D
The input of the A converter is sampled a predetermined number of times, averaged, added to the output of the position controller provided in the position controller, and the offset between the D / A converter and the A / D converter is canceled. It is characterized by: This cancels the offset between the D / A converter and the A / D converter.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a position control device that implements the method of the present invention. The components shown in FIG.
1B is a motion controller obtained by adding a circuit which is a feature of the present invention to the motion controller 1 of FIG. 2,
That is, it is a position control device. In the figure, 14 is a measurement timing switch, 15 is a position controller output buffer, 16 is an averaging circuit, 17 is a correction output timing,
18 is an adder / subtractor. Measurement timing switch 14
Transmits the signal of the adder / subtracter 18 to the position controller output buffer 15 only when receiving the command. The command is given by a sequence circuit (not shown) provided in the motion controller 1B in synchronization with the clock of the sequence circuit. The position controller output buffer 15 amplifies and outputs the input signal. The averaging circuit 16 calculates and outputs an average value of the signals input a predetermined number of times. After the averaging circuit 16 completes the averaging operation, the corrected output timing 17 is output by the sequence circuit in synchronization with the clock. To illustrate such a situation, for example, when the sequence circuit detects that the servomotor 10 is in the stopped state, it gives a command to the measurement timing switch 14 to sample the output of the adder / subtractor 18 for 20 clocks. The position controller output buffer 15 outputs the data, the averaging circuit 16 performs the averaging operation, and outputs the average data to one input terminal of the adder / subtracter 18.

A situation where the offset is canceled under the above configuration will be described. Servo motor 1
It is assumed that 0 is in a stop state at a certain point after repeating predetermined acceleration / deceleration, and an offset remains. In this case, the position command of the position target 2 and the value detected and fed back become the same, the output of the adder / subtractor 3, that is, the position deviation becomes zero, and the output of the position controller 4 also becomes zero. However, if there is an offset between the D / A converter 5 and the A / D converter 6, the output of the A / D converter is not zero, so that the speed of the servo motor 10 is not zero, and the servo motor 10 rotates and deviates from the target position. . The rotation of the servomotor 10 stops at A /
This is the time when the output of the D converter 6 becomes zero.
This is when the input of the / A converter 5 is not zero, that is, when the input of the position controller is not zero. When the position is shifted and stopped as described above, the sequence circuit operates, the measurement timing switch 14 is operated, sampling is performed a predetermined number of times, averaged, and output from the correction output timing 17. The signal output from the correction output timing 17 is equal to the output of the position controller 4 when the position is shifted and stopped, and this is the signal resulting from the offset between the D / A converter 5 and the A / D converter 6. Therefore, by adding to the output of the position controller 4 by the adder / subtractor 18, the stop at the position where the output of the position controller 4 becomes zero can be achieved. That is, the position where the output of the adder / subtractor 3 is zero,
In other words, it is possible to stop at a position where the position command of the position target 2 is equal to the position of the servomotor 10 detected by the encoder 11, so that the position can be controlled to the position according to the command.

[0008]

As described above, according to the present invention, D /
Since the output of the position controller during the stop of the servomotor caused by the offset of the A converter and the A / D converter is detected and corrected at the output of the position controller, as a result, the offset of the two converters is corrected. Cancellation can be performed, and the control accuracy of the position control system can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a position control device of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional position control device.

[Explanation of symbols]

 1, 1B Motion controller 2 Position target 3, 7 Adder / subtractor 4 Position controller 5 D / A converter 6 A / D converter 8 Speed controller 9 Power converter 10 Servo motor 11 Encoder 12 Pulse output device 13 Counter 14 Measurement Timing switch 15 Position controller output buffer 16 Averaging circuit 17 Correction output timing

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H03M 1/10 H03M 1/10 B

Claims (6)

[Claims] A position for controlling the position of a motor by combining a position control device for outputting a speed command via a D / A converter and a speed control device for inputting the speed command via an A / D converter. In the control system, the output of the position controller provided in the position control device is signal-processed, and the speed command is corrected.
A method for improving the accuracy of a position control system, wherein an offset between an A / A converter and the A / D converter is canceled. 2. The method according to claim 1, wherein the correction is performed when the motor is stopped. 3. The method according to claim 1, wherein the correction is performed by sampling the input of the D / A converter a predetermined number of times, averaging the input, and adding the result to the output of the position controller.
3. A method for improving the accuracy of a position control system according to item 1. 4. A servo motor, detecting means for detecting a rotational speed and a rotational position of the servo motor, a speed control device for controlling a speed of the servo motor when a speed command is received via an A / D converter, In a position control system including a position control device that outputs a speed command to the speed control device via an A converter, a subtractor that compares a position command with a position detection signal of the detection unit, and inputs a signal of the subtractor A position controller that performs position control by performing an operation, an adder that receives an output of the position controller as one input, a D / A converter that performs D / A conversion on an output of the adder, and an output of the adder. And an offset compensating circuit for performing signal processing by inputting at a predetermined timing, wherein an output of the offset compensating circuit is used as another input of the adder. 5. The position control device according to claim 4, wherein said predetermined timing is set to a motor stopped state. 6. The position control device according to claim 4, wherein the offset compensation circuit samples the signal a predetermined number of times, performs an averaging process, and performs the signal processing.