JPS6130514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo motor control device employing a closed loop method that improves the delay in response that occurs when the rotational direction of a DC motor is reversed.

Generally, a servo motor control device having a position feedback loop has a position feedback loop for controlling the rotational position of a DC motor 10 or the position of a mechanical movable part (not shown), as shown in FIG. In addition to the loop, a speed feedback loop for controlling the rotation speed of the DC motor 10 and a current feedback loop for controlling the motor current of the DC motor 10 are provided. In the current feedback loop, the deviation between the motor current I _d detected by the resistor 11 and the current command value I _s from the phase compensation circuit 12 is controlled to be zero, and in the speed feedback loop,
Motor speed v _d detected by speed detector 13 such as a speed generator and speed command value v from DA converter 14
The motor position ld detected by the position detector 15 such as a resolver or linear scale is controlled so that the deviation from _s becomes zero, and the position command value _l given from the command pulse generation circuit 16 is finally The motor position is controlled by a position feedback loop so that the difference from _s becomes zero. In addition, in the figure, 17 is an amplifier, and 18a to 18c are adders.

FIG. 2 is an electrical circuit diagram showing the conventional configuration of the adder 18b, phase compensation circuit 12, and adder _18c shown in FIG.
_R1 to _R5 constitute an adder 18b, and an operational amplifier
Q ₁ , resistors R ₆ to R ₉ and capacitor C ₁ constitute a phase compensation circuit 12, and operational amplifier Q ₃ and resistors R ₁₀ to _{R 13}
constituted the adder 18c.

By the way, in the conventional servo motor control device having the configuration shown in FIG. 2, the relationship between the motor current I and the motor speed v when the rotational direction of the DC motor is reversed is expressed as the monitor current I and the motor speed on the vertical axis. If v is plotted and time t is plotted on the horizontal axis with the origin at the time when the direction reversal command is input, the result will be, for example, curves 30i and 31v in FIG. 3.
Here, I ₀ is a value obtained by converting the friction torque of the machine into a motor current, and the illustrated example shows the case where t<0, that is, the rotation is stopped before the direction is reversed.

As can be seen from the figure, when a command pulse in the opposite direction is input at t=0, the motor current I shown by curve 30i gradually increases, but when the motor speed v shows by curve 31v, motor current I increases to +I ₀ The DC motor starts to rotate in reverse only when the motor current I exceeds + _I0 . That is, there is a time delay of _T1 after the command pulse in the opposite direction is input until the DC motor starts rotating in the reverse direction.

Such a time delay naturally appears as a numerical control machining error, and specifically, as shown in FIG. 4, a perfectly circular command pulse train is distributed, resulting in a perfect circle as shown by curve 40 in the same figure. However, since there is a delay in response when the direction of rotation is reversed, the actual shape of the cut object has a bulge as shown by curve 41 at the quadrant switching portion of arc cutting.

The present invention improves on these conventional drawbacks, and its purpose is to improve control accuracy by compensating for the response delay of the DC motor caused by frictional torque when the direction of the DC motor is reversed. According to the present invention, this purpose is achieved by utilizing the fact that the voltage that determines the current command value when the direction reversal signal is input is a voltage that is proportional to the friction torque. This is achieved by generating a compensation voltage and using this compensation voltage to quickly preset the voltage forming the command current value to a voltage corresponding to the frictional torque immediately after the direction reversal signal is input. Examples will be described in detail below.

FIG. 5 is a main part air transmission circuit diagram showing the configuration of the device according to the embodiment of the present invention, in which the same reference numerals as in _FIG . IN 2 is the input terminal to which the output of the adder 18b in Figure 1 is applied, IN ₂ is the input terminal to which the peak value set signal S ₁ is applied, IN ₃ is the input terminal to which the friction torque compensation signal S ₂ is applied, and OUT is the current command value I. _s to the adder 18c in FIG. 1, Q ₄ to _{Q 6} are operational amplifiers with the polarities shown, SW ₁ and SW ₂ are switching elements, and R ₁₄ to _{R 22}
is a resistor and C ₂ is a capacitor.

The device of this embodiment differs from the conventional device shown in FIG. 2 in that a compensation voltage generation circuit 50 and a response compensation circuit 51 are provided.

The compensation voltage generation circuit 50 generates a voltage that determines the current command value at that time, that is, the phase compensation circuit 1, when a rotation direction reversal signal of the DC motor is output from the command pulse generation circuit in the numerical control device.
2 output voltage (hereinafter referred to as command voltage) is detected,
It generates a compensation voltage Vc whose absolute value is almost equal to the command voltage and whose polarity is opposite, and it consists of an integrating circuit consisting of a resistor _R14 and a capacitor _C2 , a switching element _SW1 that controls its operation, and an operational amplifier.
It consists of Q ₅ , Q ₆ and a polarity inversion circuit consisting of resistors R ₁₅ to R ₁₇ .

In addition, the response compensation circuit 51 operates to immediately make the command voltage almost equal to the compensation voltage immediately after inputting a command to reverse the rotational direction of the DC motor, and performs a calculation to amplify the difference between the command voltage and the compensation voltage Vc. It consists of an amplifier Q ₆ and a switching element SW ₂ that operates to feed back its output to the input side of the phase compensation circuit 12.

FIG. 6 is a diagram showing signal waveforms of various parts when the apparatus illustrated in the fifth figure is operated, and the operation of the apparatus illustrated in the fifth figure will be described in detail below with reference to the figure.

When a direction reversal signal as shown, for example, in FIG. 6A is output from the command pulse generation circuit, a control circuit (not shown) determines the time at which the rising edge almost coincides with the rising edge of the direction reversing signal, as shown in FIG. 6B, for example. width
A peak value set signal _S1 of _T2 is generated.

This peak value set signal _S1 is applied to the switching element _SW1 of the compensation voltage generating circuit 50, and turns on the switching element _SW1 for a time _T2 . As a result, the capacitor C ₂ is charged by the command voltage at that time, and the compensation voltage Vc of the opposite polarity, which is almost equal in absolute value to the command voltage, is at the output of the operational amplifier Q ₅ as approximately τ = C ₂ × R ₁₄ . Appears as a time constant. Therefore, the time width T ₂ of the peak value set signal S ₁ is set to 2τ~
If set to about 3τ, the compensation voltage generation circuit 5
0, a compensating voltage of opposite polarity having substantially the same absolute value as the command voltage is obtained, for example as shown in C in FIG. 6, and this compensating voltage is maintained even after switching element _SW1 is turned off.

Next, a control circuit (not shown) controls, for example, the sixth
As shown in Figure D, a friction torque compensation signal _S2 with a time width _T3 that rises approximately at the time of the fall of the peak value set signal _S1 is generated, and this signal is applied to the switching element _SW2 of the response compensation circuit 51. Make this conductive. As a result, the command voltage is feedback-controlled to be approximately equal to the compensation voltage Vc by the output of the operational amplifier _Q6 which amplifies the difference between the command voltage and the compensation voltage Vc. (However, if the opposite direction is reversed, it will rise quickly) as shown in
Become something to do. Here, the compensation speed of the command voltage can be freely changed by adjusting the value of the resistor _R22 .

Changes in motor current I and motor speed when the rotational direction of the DC motor is reversed in this embodiment device are as shown, for example, in curves 32i and 33v in FIG. Since the friction torque I ₀ is exceeded, the motor speed curve 33v also rises earlier, and the motor reversal delay time T ₄ is significantly improved. Note that the reversal delay time T ₄ can be freely changed by adjusting the value of the resistor R ₂₂ .

As can be seen from the above description, the present invention provides a method in which when a command to reverse the rotational direction of the DC motor is input from the command pulse generation circuit, the absolute value of the current command value is approximately equal to the command voltage that determines the current command value at that time. In addition, a compensation voltage of opposite polarity is generated in a compensation voltage generation circuit, and this compensation voltage is used to immediately make the command voltage almost equal to the voltage corresponding to the reverse side friction torque immediately after the direction reversal signal is input. Since the voltage corresponding to the friction torque is quickly compensated, the delay in the servo system due to the friction torque can be significantly improved. Therefore, if the present invention is applied to a servo motor control device of a numerical control device, it will be very effective to improve processing accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the general configuration of a servo motor control device having a position feedback loop, Fig. 2 is a main part electric circuit diagram showing the structure of a conventional servo motor control device, and Fig. 3 is a block diagram showing the general configuration of a servo motor control device having a position feedback loop. Figures 2 and 5 are diagrams showing changes in motor current I and motor speed v when the apparatus shown in Figures 2 and 5 are operated, and Figure 4 is a diagram illustrating the influence of response delay upon direction reversal on machining. , FIG. 5 is an electrical circuit diagram of a main part of the apparatus according to the embodiment of the present invention, and FIG. 6 is a diagram showing signal waveforms of various parts when the apparatus shown in FIG. 5 is operated. 10 is a DC motor, 12 is a phase compensation circuit, 13
15 is a speed detector, 15 is a position detector, 16 is a command pulse generation circuit, 17 is an amplifier, 18a to 18c are adders, 50 is a compensation voltage generation circuit, and 51 is a response compensation circuit.

Claims (1)

[Claims] 1. In a servo motor control device adopting a closed-loop method that controls a DC motor according to a command value given from a command pulse generation circuit of a numerical control device, when a direction reversal signal is input from the command pulse generation circuit, a compensation voltage generation circuit that generates a compensation voltage that is approximately equal in absolute value and opposite in polarity to the command voltage that determines the current command value; A servo motor control device comprising: a response compensation circuit that responds immediately after inputting a direction reversal signal to a voltage approximately equal to a voltage corresponding to reverse friction torque.