JPH06161559A - Position controller - Google Patents

Abstract

PURPOSE:To improve the accuracy of contour control by performing stick motion correction without the effect of plus and minus pulse vibrations in the position controller constituting a numerical controller. CONSTITUTION:This position controller provided with friction correction is equipped with a dead zone setting part 14 with respect to a velocity command and a dynamic characteristic model 15 for a position command signal, and an output from the dynamic characteristic model is used for an input to a decision equipment 11 to decide the code of a friction correcting current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control device used for an NC machine tool or a robot, and more particularly to a system for suppressing stick motion occurring at a quadrant switching point of arc machining.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional position control system having friction correction. In FIG. 2, the first
The adder 1 receives the position command signal and the position feedback signal and outputs the difference between them to the accumulator 2. The accumulator 2 accumulates the difference between the position command signal and the position feedback signal for each unit time, and outputs the position deviation amount that is the accumulation result to the first multiplier 3. The first multiplier 3 multiplies the output of the accumulator 2 by a gain K ₁ that determines the responsivity of position control to generate a speed command signal. Reference numeral 4 denotes a second adder, which inputs a speed command signal and a speed feedback signal obtained by differentiating a position feedback signal by a differentiator 10 with time, and outputs a difference between them to the speed control unit 5. The speed control unit 5 inputs the speed deviation output from the second adder 4 and controls the rotation speed of the motor 8 so that the speed deviation becomes zero. The third adder 6 inputs the output of the speed control unit 5 and the friction correction current which is the output of the second multiplier 13, and outputs the sum thereof as a torque current command to the current control unit 7. The current controller 7 is a motor 8
Apply the torque current command current to the. The encoder 9 detects the rotational position of the motor and outputs the motor movement amount in pulse units. The differentiator 10 time-differentiates the output from the encoder 9 and outputs it to the second adder 4 as a speed feedback signal. The determiner 11 determines the sign of the speed command, and is +1 until the sign changes from negative to positive and becomes negative again.
Is output to the second multiplier 13 until the sign changes from positive to negative and becomes positive again. The friction correction current parameter setter 12 sets the absolute value of the torque current value corresponding to the static friction force of the mechanical system. The second multiplier 13 multiplies the friction correction current parameter value by the output of the determiner 11, and outputs it as a torque current command to the third adder 6. The above is the outline of the position control device having friction correction.

As an example, consider FIG. 3, which is the response when the rotation direction of the motor changes from the CW direction to the CCW direction during circular interpolation. Here, the speed command has a time constant of 1 with respect to the position command when the dynamic characteristics of the speed controller are omitted.
There is a delay of / K. During the rotation in the CW direction, the dynamic frictional force is working, and the current command I _d is generated. At the switching point A of the rotation direction from CW to CCW, the speed becomes once 0, and thus the static friction force acts.

Due to the static friction force and the time delay required for reversing the sign of the dynamic friction force, if friction correction is not used, a velocity response of results in a shape error.
The shape error due to this stick motion causes the roundness to deteriorate. The current command at this time is. When the friction correction is used, the output from the determiner 11 is, the friction correction current I _d is added to the current command, and the current command becomes. As a result, the speed response of the motor becomes as follows, and it is possible to reduce the stick motion at the rotation direction switching point and improve the roundness.

[0005]

However, in general, in this type of position control system, vibration of ± pulse intervals, which is the minimum unit of position feedback signal pulses, can occur when the motor is stopped. That is, when some kind of disturbance acts, the motor is controlled to return to the original position, so that a kind of limit cycle may occur around the stop position.

Usually, such a one-pulse vibration has a small amplitude and is often attenuated by the influence of friction of a mechanical system, so that it does not cause a problem so much. However, in the conventional position control device, ± 1 pulse signal is given to the judging device. Is input, the friction correction current is output in the direction of accelerating the rotation of the motor, and the vibration increases as compared with the case where the friction correction is not used, and there is a drawback that oscillation occurs depending on the machine.

In view of the above-mentioned drawbacks, a technical object of the present invention is to provide a position control device capable of suppressing mechanical vibration even when inputting ± 1 pulse signals.

[0008]

According to the present invention, there is provided a first adder which compares a motor rotation command amount with a position feedback signal from an encoder of the motor and outputs a difference between them, and the first adder. An accumulator for accumulating and outputting the output of the adder, a first multiplier for multiplying the output of this accumulator by a gain and outputting as a motor speed command, and a speed command and a speed feedback are input and the difference between them is input. The second adder that outputs and the speed deviation that is the output of this second adder
A speed control unit for controlling to, a current control unit for supplying a torque current command, which is the output of the speed control unit, to the motor, and a determiner that determines the sign change of the input signal and outputs the same sign as the speed command, A friction correction current parameter unit that sets an absolute value of a torque current value corresponding to the static friction force of the mechanical system, a second multiplier that multiplies the output from the determination unit and the friction correction current parameter, and a second A third adder that adds the output from the multiplier to the output of the speed control unit and outputs it to the current control unit, and a speed command as an input to the determination unit, and a predetermined dead zone is set for the input. A dead zone setting unit is provided.

Further, according to the present invention, in the above position control device, a position characteristic is input, and a dynamic characteristic model for estimating and outputting a dynamic characteristic with respect to a current instruction is input to the judging device, and this dynamic characteristic model is input. A position control device is obtained which is characterized by using the output of the characteristic model.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram of the position control device of the present invention. The same parts as those in FIG. 2 are denoted by the same symbols.

The first embodiment has a dead zone setting section 14 in addition to the conventional control system shown in FIG. The dead zone setting unit 14 receives the speed command as an input, and outputs the code to the determiner 11 only when the input speed command signal pulse number has a value exceeding the arbitrarily set dead zone.

This dead band width is ± 1 of the feedback signal.
It is possible to prevent the sign change of the friction correction current following ± 1 pulse vibration by setting the fluctuation width of the speed command larger than the fluctuation range of the pulse vibration, for example, 2 pulses. Further, if the dead zone is about several pulses, the original friction correction effect is hardly affected.
As a result, friction correction can be made effective without being affected by ± 1 pulse vibration at the time of stop.

Next, in the second embodiment, the determiner 1
The input signal 1 is characterized by the point that the position command is the basis instead of the speed command and that the position command has the dynamic characteristic model 15. The increase of ± 1 pulse vibration at the stop, which is a problem of the conventional control method, is caused by the input of the position feedback signal due to disturbance or the like, and as a result, the speed command is generated. It is stable without output.

Therefore, by inputting the position command to the determiner 11, it is possible to avoid an increase in ± 1 pulse vibration due to friction correction. The actual current command has a time delay with respect to the position command because of the dynamic characteristics of the position loop determined by the gain K _{1 of the} multiplier and the dynamic characteristics of the speed control unit. The dynamic characteristic model 15 corrects these dynamic characteristics with respect to the position command.
By inputting the output of 1 to the determination device 11, the friction correction can be applied in accordance with the actual current command.
As an example of the dynamic characteristic model, the characteristic of the position loop in which the dynamic characteristic of the speed control unit is omitted, that is, the first-order delay of the time constant 1 / K can be used. Further, when the dynamic characteristics of the speed control unit actually become a problem, the timing of friction correction can be adjusted by finely adjusting the time constant of the dynamic characteristic model.

[0016]

As described above, the position control device of the present invention has the dead zone setting section for the speed command, so that the friction correction is effective without being affected by ± 1 pulse vibration at the time of stop. You can do it.

Further, in the position control device of the present invention, the dynamic characteristic model output of the position command signal is used as an input to the judging device for judging the sign of the friction correction current, so that ±
It is possible to make the friction correction effective without being affected by one-pulse vibration and corresponding to the actual current command.

Therefore, according to the present invention, the friction correction can be correctly applied even when there is ± 1 pulse vibration at the time of stop due to disturbance or the like, the stick motion at the quadrant switching point at the time of arc cutting is reduced, and the perfect circle The cutting accuracy can be improved.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing a speed response at a quadrant switching point when a conventional position control device is used.

[Explanation of symbols]

 1 1st adder 2 accumulator 3 1st multiplier 4 2nd adder 5 Speed control part 6 3rd adder 7 Current control part 8 Motor 9 Encoder 10 Differentiator 11 Determinator 12 Friction correction current parameter 13 Second Multiplier 14 Dead Zone Setting Section 15 Dynamic Model

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G05B 19/19 P 9064-3H

Claims (2)

[Claims] 1. A first adder for inputting a motor rotation command amount and an actual motor rotation amount for each unit processing time and outputting a difference between them, and an accumulator for accumulating the output of the first adder. A first multiplier that multiplies the position deviation, which is the output of the accumulator, by a gain and outputs the result as a motor speed command; a speed control unit that controls the rotation speed of the motor according to the motor speed command; and a current command. To the motor, an encoder that detects the rotational position of the motor and outputs the motor movement amount in pulse units, a determiner that determines and outputs the sign of the motor speed command, and a determiner from the determiner. A second multiplier that multiplies the output of the filter by a friction correction current parameter,
A position control device having a second adder for adding the multiplication result of the second multiplier to a current command, and performing a friction correction, wherein a dead band setting for setting a predetermined dead band at the input of the judging device. A position control device having a section. 2. The position control device according to claim 1, wherein
A position control device characterized by using a dynamic characteristic model for inputting the position command and estimating and outputting a dynamic characteristic corresponding to a current command, and using an output of the dynamic characteristic model as an input of the judging device.