JPH0251703A - Numerical controller - Google Patents

Abstract

PURPOSE:To perform the working under the highly accurate position follow-up control by correcting the speed command value of a servo motor based on the secondary delay signal received from an ideal position computing element. CONSTITUTION:The position command signal inputted to an ideal position computing element 7 is compared with the ideal position given from an integrator 11 via a subtractor 8. The deviation of the comparison is outputted as an ideal speed command via an amplifier 9. Then a computing element 10 operates an ideal speed in consideration of the primary delay and sent to the integrator 11. The ideal positions accumulated by the integrator 11 are turned into a secondary delay signal to the position command signal. While the deviation of a closed loop is obtained by the feedback and compared with a deviation E via a subtractor 12. Then the difference obtained from the comparison is multiplied by the correction gain via an amplifier 13 and then added to a speed command via an adder 14. As a result, the fluctuation of the position loop gain caused by the wear of a servo motor, etc., can be corrected. Thus the highly accurate working is ensured based on the position command signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a numerical control device for a machine tool, etc., and particularly relates to position tracking control provided with a correction means for tracking a moving object to be controlled with high precision. It is something.

[Prior Art] Fig. 2 is a block diagram showing an example of a closed loop control system in a normal numerical control device. In the figure, (Xc) is a position command, (1) is a position command (Xc) and a position detector. (6
) and perform subtraction to obtain the deviation (E)
(2) is an amplifier that amplifies the deviation (E) and outputs the speed command (Vc), and (3) drives the servo motor (4) according to the input speed command (Vc). A speed controller that controls the output, (5) a processing machine in which, for example, a processing tool is moved or a processing table on which a workpiece is placed is moved by driving the servo motor (4), and (6) is a processing machine that moves a processing tool or a processing table on which a workpiece is placed. This is a position detector that detects the position of the above-mentioned moving body in the processing machine (5).

In the control system configured as above, position command (Xc)
and the position detection signal fed back from the position detector (6), the subtractor (1) calculates the deviation (
E) is output, and this deviation (E) is amplified in the amplifier (2) to output a speed command (We) that determines the driving speed of the servo motor (4). The speed controller (3) outputs a drive control signal for the servo motor (4) based on the speed command (Vc), and this control signal drives the servo motor (4) to control the processing of the processing machine (5). The tool, processing table, etc. are moved, and the position detector (6) sequentially feeds back changes in the movement position to generate a position command (X
e) and is controlled in a closed loop so that the deviation (E) becomes 0.

[Problems to be Solved by the Invention] The control system of the conventional numerical control device configured as described above suffers from loss, which is a drawback of closed-loop control systems, especially when controlling processing machines that require high-precision position control. If the control operation cannot fully respond to mechanical characteristics such as motion, *friction, stiffness, and inertia, problems such as deterioration of the accuracy of the machined shape and the formation of protrusions when switching quadrants during arc cutting may occur. If the loop gain is increased in the speed controller (3) as a countermeasure to this, there is a problem that the control system may oscillate depending on the increase in gain.

This invention was made in order to solve the above-mentioned problems, and improves the follow-up ability of position control by improving the above-mentioned drawbacks of the closed-loop control system. The purpose is to obtain a numerical control device.

C: Means for Solving Problem S] The numerical control device according to the present invention drives a movable body in a processing machine that is a controlled object by a servo motor based on a position command signal, and uses a detected position signal of the movable body and A closed loop control system that operates to reduce the deviation from the position command signal to O, and an ideal position calculator that calculates an ideal position signal that is a second-order delayed signal with respect to the position command signal based on the position command signal. A correction amount proportional to the difference between the deviation between the position command signal and the ideal position signal and the deviation of the closed loop control system is added to the drive speed command signal of the servo motor.

[Operation] By correcting the drive speed command signal of the servo motor in this invention, defects in control operation due to lost motion, friction, etc. in the controlled object are improved, there is no fear of oscillation in the control system, and the tracking ability of position control is improved. let

Embodiment FIG. 1 is a block diagram showing the configuration of a control system in a numerical control device according to an embodiment of the present invention.
Since (1) to (6) are the same or corresponding parts to those with the same reference numerals in FIG. 2 showing the conventional example, a description of the structure will be omitted.

(7) is an ideal position calculator, which includes a subtracter (8) that compares the position command (Xc) and the ideal position signal (Xf) and outputs the deviation (El), and an amplifier that amplifies the deviation (El). (9
), a first-order lag calculator (■0) that gives the output (Vcl) of the amplifier (9) a delay equivalent to the theoretical time delay due to the speed loop, and the ideal speed (vl) that is the output thereof are accumulated to calculate the ideal It is composed of an integrator (11) that outputs the position (XI). (12) is the deviation (E
) and the above deviation (El) and outputs the difference E-Ei, (13) is an amplifier that multiplies the difference E-21 by a correction gain, and (14) is the output of the amplifier (14). This is an adder that adds to the speed command signal (Vc) which is the output of the amplifier (2).

In the control system of the numerical control device according to the present invention configured as described above, the position command signal (Xc) input to the ideal position calculator (7) is fed back to the integrator (11).
The subtracter (8) compares the ideal position (xl) which is the output of the subtractor (8), and outputs the deviation (El).

This deviation (El) is determined by the amplifier (2) in the amplifier (9).
) is amplified with the same gain as the ideal speed command (Vc i
) is output, and the next first-order lag calculator (10) calculates the ideal speed m) taking into account the first-order lag l/l+Ts based on the theoretical speed loop time constant T, and inputs it to the integrator (11). . The ideal position (X
l) becomes a second-order delayed signal with respect to the position command signal (Xe), and this signal is fed back to the subtractor (8) to perform the above subtraction, and the deviation in this closed loop (El
) is obtained.

On the other hand, the deviation (El) is input to the subtracter (12), where it is compared with the deviation (E), and the obtained difference E-E i is input to the amplifier (13), where it is multiplied by the correction gain. The output is added to the speed command (Vc), which is the output of the amplifier (2), in an adder (14). In other words, processing machines (
If the actual position (X) of the processing tool, processing table, etc. to be moved in step 5) advances, for example, from the ideal position (xi), the value of the speed command (Vc) is decreased, and conversely, the actual position If (X) is delayed, speed command (Vc)
It will work to increase the value of .

The above operations cause torque ripple in the motor.

By correcting fluctuations in the position loop gain caused by lost motion, friction, etc. of the mechanical device, highly accurate machining can be performed based on the position command signal (Xc).

[Effects of the Invention] As described above, according to the present invention, in order to prevent operational errors caused by lost motion frictional resistance of the controlled object, based on the second-order delay signal obtained by the ideal position calculator, Since the configuration is configured to correct the speed command value of the servo motor that drives the controlled object, there is no fear of oscillation in the control system, and there is an effect that machining can be performed using highly accurate position follow-up control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a control system of a numerical control device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the configuration of a control system of a conventional numerical control device. In the figure, (Xc) is a position command, (+), (8)
, (12) is a subtractor, (4) is a servo motor, (5
) is the controlled object, (6) is the position detector, and (7) is the ideal position detector. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] In a closed-loop position tracking control system, a moving body to be controlled is driven by a servo motor based on a position command signal, a detected position signal of the moving body is fed back, and the position command is operated based on a deviation from the position command signal. Based on the signal, an ideal position signal that is a second-order delayed signal of this position command signal is calculated, and a correction amount proportional to the difference between the deviation between this ideal position signal and the position command signal and the deviation of the closed loop control system is calculated. A numerical control device comprising a control system configured to calculate the amount of correction and add the calculated correction amount to a drive speed signal of the servo motor.