JPS6373308A - Servo control system - Google Patents

Abstract

PURPOSE:To perform positioning at high speed and with high accuracy, and to reduce and suppress the generation of motor noise, by supplying a gradually decreasing dither signal to a velocity loop only at time of deceleration of a motor. CONSTITUTION:After multiplying 23 the signal (b) of an oscillator 24 by the signal (c) of an envelope generator 22, amplifying 25 it, and adjusting a gain, the dither signal (f) is added on the entry of the velocity loop L2. By triggering 21 it corresponding to an angular velocity signal (a), the envelope generator 22 is started up. The grain is decreased in a low speed area because the characteristic of the velocity loop of a servo system has non-linearity. The shortage of the gain delays the stable rotation of the motor, and causes incomplete positioning. Generally speaking, the frequency area of a current loop is below 1kHz, and the frequency of the velocity loop is around 100Hz, and the frequency band area of an effective and appropriate dither signal is felt as the noise. Also, the current loop responds to the signal, and a reactive current flows, then the motor is heated. Therefore, the gain is increased by supplying the dither signal limiting only in the low speed area of the velocity loop. Thus, a servo characteristic can be improved, and fast and accurate positioning can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a servo control system that primarily performs position control.

[Conventional technology]

A conventional servo control system of this type is shown in FIG. In FIG. 5, ■ is an integrator that inputs the angular velocity command signal a and outputs the angle command signal; 2, 4, and 6 are subtractors;
is an adder, 5 and 7 are amplifiers with a gain of 1 and a gain of 2,
8 is a power element that outputs a current to drive the motor 9; 10 is a reducer for reducing the angular velocity of the motor; 1
1 is a rotating mechanism driven by the reducer 10; 12 is an angle detector that detects the angle of the rotating mechanism 11; 13 is a differentiator that differentiates the angle feedback signal output from the angle detector 12;
14 is an oscillator as a dither signal generator.

The control system shown in FIG. 5 includes a position loop LL, a speed loop L
2. By configuring the current loop L3 and applying a constant dither signal from the oscillator 14 to the speed loop L2, the motor 9, power element 8, amplifier 5.7, etc. (hereinafter referred to as "control element" as a common name) The deterioration of characteristics due to nonlinearity was improved.

Next, the operation of the servo control device shown in FIG. 5 will be schematically explained. The integrator 1 inputs the speed command signal a and outputs the angle command signal, and this angle command signal is sent to the angle detector 1 by the subtractor 2.
2 is subtracted from the angular feedback signal from 2 to become an angular deviation signal, that is, an angular velocity command signal, which is manually input to an adder 3. This angular velocity command signal is added to a dither signal from an oscillator 14, and subtracted from a differential signal obtained by differentiating the angular feedback signal by a subtracter 4, and is inputted to an amplifier 5 as an angular velocity deviation signal. The amplifier 5 outputs a torque command signal corresponding to the angular velocity deviation signal to the current loop L3. Current loop L3
outputs a current for driving the motor 9 in accordance with the torque command signal. The motor 9 is driven by this drive current, and rotates the rotating mechanism 11 via the reducer 10. Angle detector 12 detects the rotation angle of rotation mechanism 11 and outputs it to subtractor 2 and differentiator 13 as an angle feedback signal. In this way, the rotation angle, that is, the rotation position of the rotation mechanism 11 is controlled.

[Problem that the invention seeks to solve]

In the conventional servo control system described above, a dither signal is applied to the entire region in order to correct positioning defects caused by nonlinearity of the control element, particularly nonlinearity in the low speed region. For this reason, the dither signal is input to a high-speed region that is not originally required, and its vibration component generates motor noise, and the increase in reactive current causes the motor to generate more heat.

[Means for solving problems]

In order to solve these problems, the present invention provides an apparatus with a dither signal generator that applies a gradually decreasing dither signal to the speed loop only when the motor is decelerating.

[Effect]

In the present invention, a dither signal is added to the speed loop only in the low speed region.

〔Example〕

An embodiment of a servo control device according to the present invention is shown in FIG. In FIG. 1, 20 is a dither signal generator;
The dither signal generator 20 includes a trigger generator 21 . Envelope generator 22. It consists of a multiplier 231, an oscillator 24, and an amplifier 25 with a gain of 3. In FIG. 1, the same or equivalent parts as in FIG. 5 are given the same reference numerals.

Next, the operation of this device will be explained. In FIG. 1, an oscillation signal generated by an oscillator 24 is input to a multiplier 23. On the other hand, the envelope signal C generated by the envelope generator 22 is also input to the multiplier 23 . The envelope generator 22 includes a trigger generator 2 that prompts its activation in response to the angular velocity command signal a.
1 is connected. The output from multiplier 23 is sent to amplifier 2
5, the gain is adjusted and input by adder 3 to the entrance of velocity loop L2.

When a trapezoidal angular velocity command signal a as shown in FIG. output signal d
Perform a speed response as shown in .

When the trigger signal e shown in Fig. 2 (C1) is output from the trigger generator 21 at the moment when the angular velocity command signal a becomes lower than the predetermined speed in the deceleration region, the envelope generator 22 outputs the trigger signal e shown in Fig. 2 (dl). As shown, an envelope signal C that gradually decreases with a constant time constant is output.On the other hand, the oscillator 24 outputs
A rectangular wave oscillation signal as shown in FIG. 2+e) is always output. Therefore, the multiplier 23 outputs an oscillation signal that gradually decreases. The amplifier 25 is an adjuster for adjusting this oscillation signal to an optimum value for the servo system. The amplifier 25 outputs the input oscillation signal to the adder 3 as a dither signal f shown in FIG. 2ff).

Next, the reason why the dither signal improves the characteristics of the servo system will be described. In general, the characteristics of the speed loop in a servo system are such that the gain decreases in the low speed region, as shown by curve 30 in FIG. 3, due to the nonlinearity of the control element. Therefore, by applying a dither signal to the speed loop, the gain in the low speed region can be improved, as shown by curve 40.

Figure 4 shows the transient response of the servo system.
l indicates an angular velocity command signal. The angular velocity output signal shown in Fig. 4 (mountain) is the waveform when no improvement measures are taken, and an abnormality in the waveform due to lack of gain is seen in the 0 part.

This waveform abnormality delays the settling time of the motor, making high-speed positioning difficult and causing positioning errors. The angular velocity output signal shown in FIG. 4 fc) is the case where a dither signal is applied over the entire range, and the 0 part also has a good waveform.

Further, the angular velocity output signal shown in FIG. 4 (di) is that of this device, and has a good waveform as in the case of FIG. 4 (C1).

On the other hand, in order for the dither signal to work effectively, it must be in a frequency range to which the current loop of the servo system can respond, and must be in a frequency range to which the speed loop cannot respond. Generally, the frequency range of the current loop is 1 kHz or less, and the frequency range of the velocity loop is 100 kHz.
It is about Hz or less. Therefore, a suitable dither signal frequency would be 100 Hz - 1 kHz. This frequency band is in the audible range. In the case of a servo system that constantly provides a dither signal, the motor generates a sound at the frequency of this dither signal, which is perceived by humans as noise. Additionally, the current loop responds to this dither signal, causing a reactive current to flow and the motor to generate heat. Therefore, in this device,
By applying the dither signal only to the deceleration region, that is, the low speed region, the characteristics are improved, motor noise is reduced, and heat generation of the motor is also suppressed.

〔Effect of the invention〕

As explained above, by applying a gradually decreasing dither signal to the speed loop only when the motor is decelerating, the present invention enables positioning to be performed at high speed and high precision as in the past, while also reducing motor noise (and reducing motor noise). It has the effect of suppressing heat generation. Also, when applied to robots and NC machine tools, it has the effect of improving productivity.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the servo control system according to the present invention, Fig. 2 is a waveform diagram to explain its operation, Fig. 3 is a graph showing the effect of the dither signal, and Fig. 4 is A waveform diagram showing the effect of a dither signal, and FIG. 5 is a system diagram showing a conventional servo control system. DESCRIPTION OF SYMBOLS 1... Integrator, 2, 4.6... Subtractor, 3... Adder, 5.7.25... Amplifier, B... Power element, 9... Motor, 10... ...Reducer, 11... Rotating mechanism, 12... Angle detector, 13... Differentiator, 20
... Dither signal generator, 21 ... Trigger generator, 2
2... Envelope line generator, 23... Multiplier, 24...
oscillator.

Claims (1)

[Claims] A servo control system that performs position control, comprising a dither signal generator that applies a gradually decreasing dither signal to a speed loop only when the motor is decelerating.