JPS62204318A - Servo controller - Google Patents

Abstract

PURPOSE:To enable a servo system to respond stably to a wide changing range of feed speed between a low speed and a high speed, by switching the loop gain so that the degree of deviation produced in response to the feed speed is changed. CONSTITUTION:The deviation degree epsilon3 is calculated by a deviation counter 2 between the synchronized input command signal 13 and position feedback signal 14. An address of a ROM 15 is designated by the degree epsilon3 and an output bit pattern is read out so that the speed command signal (e) corresponding to the deviation degree at that time point is delivered by a D/A converter 4. The data on the bit pattern read out of the ROM 15 is held temporarily by a latch circuit 16 and converted into the prescribed voltage (e) by the converter 4. Thus the overall loop gain of a servo system is automatically switched against the command feed speed by incorporating the ROM 15 and the latch circuit 16 into the servo system. Therefore it is possible to control stably the revolution of a servo motor in a wide range between an extremely high and low feed speeds.

Description

[Detailed description of the invention] (Technical field) ・5. This invention is a method that determines the characteristics of the servo control system.
This relates to a method of setting gain.

(Prior art and its problems) In recent years, as digital processing speeds up, positioning control using a digital servo control method using a DC servo motor is becoming mainstream.

FIG. 7 shows an example of the configuration of this system, where 1 is a synchronous circuit, 2 is a deviation counter, and 3 is a positional deviation amount.

4 is a digital-to-analog (hereinafter referred to as D/A) converter, 5 is a servo amplifier, 6 is a DC servo motor, 7 is a DC tacho generator, 8 is an optical rotary encoder,
9 is an X-Y table drive mechanism.

10 is an input command signal, and 11 is a speed feedback signal.

12 is a position feedback signal.

In the pulse train of the input command signal 10, the number of pulses has position information, and the pulse frequency has information on the table feed speed. The input command signal 10 and the position feedback signal 12 are used as a reference clock (not shown) within the synchronization circuit 1.
It is synchronized and output to the deviation counter 2. The deviation counter 2 is an up/down counter, and by inputting a synchronized input command signal to the up side and a synchronized position feedback signal to the down side, the deviation amount is output. . This is the position deviation amount 3
This is converted by a D/A converter 4 to obtain an analog voltage corresponding to the magnitude of the deviation amount, and inputted to the servo amplifier 5 as a speed command voltage. In the servo amplifier 5, due to the deviation between the speed command voltage and the speed feed bank signal 11,
Drive the servo motor 6. The purpose of such a speed control system is to increase the responsiveness of the speed loop in the servo system as much as possible since the inertia of the table drive mechanism 9 affects it. Speed feedback is applied as a method to reduce the speed. In the example shown in FIG. 7, the DC tacho generator 7 is directly connected to the servo motor shaft.

A tacho generator 7 generates a voltage proportional to the rotation speed of the servo motor 60, and outputs a speed feedback signal 11.

In the position control system, the servo motor 6 is controlled by an encoder 8 directly connected to the servo motor shaft, similar to the tachogenerator.
A position feedback signal 12 is generated and fed back using the zero rotation amount as a digital pulse signal train.

The encoder is a kind of analog-to-digital converter that has a circular disk with slits arranged on its circumference and converts the light passing through the slits into an electrical signal and outputs a pulse train. Therefore, the number of slits determines the resolution of the servo system.

In the closed loop system as described above, the servo motor rotates until the positional deviation amount 3 becomes zero, and the point at which it becomes zero, that is,
When the input command signal 1o and the position feed bank amount become equal, it stops and the positioning operation is completed.

A block diagram using transfer functions is shown in FIG. 2 in order to analyze the characteristics of such a servo system. In reality, the transfer function is even higher-order, but approximation using a quadratic system generally poses no problem in practice.

In Fig. 2, ε is the positional deviation amount, 1 is the D/A conversion gain, 2 is the servo amplifier gain, 3 is the servo motor gain, TM is the time constant of the servo motor, and 4°K is the tacho generator. and the feedback gain of the encoder. S is a Laplace operator.

Open loop transfer function G in Figure 2. (S) is expressed by the following equation.

'9~Eng J9 This -cyclic transfer function G. If FIG. 2 is rewritten using (S), it can be expressed as shown in FIG. 3, and the relationship between the deviation amount E(S) and the input command R(S) is expressed by the following equation.

E(S)=1+. . (8) R(S) Considering a speed input like a ramp function as an input, R(
S ) " s, and the deviation amount in the steady state at this time is expressed as. This K is the loop gain of the entire servo system, and the relationship of the above equation is shown in Figure 4. As is clear from this, the loop gain The larger the gain value.

Although the amount of deviation, that is, the tracking error, can be reduced and the responsiveness can be improved, on the other hand, oversheeting is more likely to occur, which poses a problem in terms of stability.

Also, when the table feed rate is extremely low.

When K is large, the amount of deviation becomes small, and it is conceivable that it becomes less than the resolution of the servo system. In this case, the followability is so good that the rotating shaft of the servo motor exhibits intermittent movement.

Furthermore, when high-speed feeding is performed in a system with a high loop gain, the amount of deviation is small, but the impact when stopping is large.

There were problems such as having an adverse effect on the table drive mechanism and generating resonance in the mechanical system.

(Purpose) This invention aims to maintain a constant proportional relationship (fourth
It is characterized by the fact that the loop gain can be switched to change the degree of deviation that can occur depending on the feed rate, taking into account the characteristics of the 9 mechanical system (see figure).The purpose is to The goal is to make the servo system respond stably to changes in feed speed over a wide range of speeds.

(Example) In the case of the configuration shown in Fig. 1, the deviation ε and the feed rate υ are
As shown in the figure, there is a proportional relationship with loop gain K as the slope.9 In the present invention, the speed range is divided, and for each divided range, the value of K, that is, the feed rate υ given by the slope by the command signal, is divided into three. It is divided into sections, and the magnitude of the loop gain (gradient) is changed in each section. That is, 0〈υ
In the low-speed section υ, the gain is set to a small value to prevent the servo system from responding too quickly and causing intermittent movement in the servo motor's shaft rotation. In the next speed section υ1〈υkuυ2, the so-called practical speed section, the loop gain is set thick (K'') in order to minimize the follow-up delay and improve responsiveness.Furthermore, the high-speed section υ2〈υ In this case, the loop gain is set to a small value <r> in order to suppress the impact force and resonance effect in the mechanical system.At this time, the follow-up delay, that is, the amount of deviation is large (although this is due to the usage conditions as a device). It is sufficient to set the loop gain within a range that allows for an acceptable amount of deviation.

Next, a method for imparting the characteristics shown in FIG. 5 to the servo system will be explained.

As mentioned above, the loop gain is expressed by the following equation.

K is the D/A conversion gain, K2. K3. K4.
K5 is a servo amplifier gain, a servo motor gain, a tacho generator gain, and an encoder gain, respectively.

The latter four gain constants are all determined by the performance of the hardware constituting the servo system, and are difficult to control variably.

Ichimanjima is the D/A conversion gain, and the speed command voltage e (voH) to the servo amplifier corresponding to the deviation amount ε [chu]
The output is expressed as =-Cm/vol t ] ε, and is expected to have a gain that is easy to control.

In other words, to make the loop gain ′.

Just set '1' to satisfy. Similarly, to set the loop gain to K", K"', use 'l', 4'
All you have to do is set it.

FIG. 6 shows this relationship. In quadrant ■ of FIG. 6, the speed command voltage C corresponding to the deviation amount ε is determined,
In the second quadrant, the rotation speed N (rpm or rad/5ee) of the servo motor corresponding to the speed command voltage e is determined.

Therefore, if the contents of quadrant Ⅰ in Fig. 6 can be incorporated into the servo system, the loop gain K will depend on the feed rate υ.
This can be considered equivalent to automatically switching. One method of incorporating this gain characteristic in the first quadrant into a servo system will be explained with reference to FIG.

In Fig. 1, 13 and 14 are synchronized input command signals and position feedback signals, respectively, and the deviation counter 2
The deviation amount ε is calculated as follows.

15 is the deviation amount pair as shown in the first quadrant of Figure 6! ROM for converting and storing the relationship between speed command voltages as data
It is. That is, D/A conversion is performed to specify the address of the ROM using the value of the deviation amount 3 and output the data at that address, that is, the speed command voltage e corresponding to the deviation amount at that time, using the D/A converter. Read the output bit pattern to the device. The read bit pattern data is temporarily held in the latch circuit 16 and converted to a predetermined voltage e by the D/A converter.

Although this series of conversion processing may be performed at a processing speed that is slightly faster than the pulse period corresponding to the maximum feed speed, a sufficient speed can be obtained using a commercially available digital IC or D/A converter.

By incorporating the above-mentioned ROM and latch circuit into the servo system, as shown in Fig. 5, the loop gain becomes Kl/l when the command feed speed is υ2 and υ.
Therefore, the loop gain of the servo system is automatically switched according to the commanded feed rate.

In the method described above, since the relationship between the amount of deviation and the speed command voltage is stored in the ROM in advance, there is a restriction in terms of the degree of freedom. Therefore, it is also possible to use a RAM that can be written to during operation without using a ROM, and to specify the gain characteristics as appropriate from a microcomputer.

(Effects) The servo control device according to the present invention automatically switches the loop gain of the entire servo system in response to the commanded feed rate, so it can stably control the rotation of the servo motor over a wide speed range from extremely low feed speeds to high speed feed speeds. can. Moreover, the increase in hardware is only about the same as ROM or RAM and its peripheral circuits, making it cost-effective.

[Brief explanation of drawings]

FIG. 7 is a block diagram of a conventional servo control device, FIGS. 2 and 3 are block diagrams of servo system transfer functions, and FIG. 4 is a gain characteristic of the conventional configuration. It is a block. 2: deviation counter, 3: deviation amount, 4: D/A converter, 5: servo amplifier, 6: servo motor, 7: tacho generator, 8: encoder, 15: ROM. Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) Detecting the X-Y table drive mechanism that is subject to position control, the servo motor that serves as the power source for the table mechanism, table feed speed information, and table position information,
Compares the magnitude of the speed detector and position detector that generate the feedback signal with the position feedback signal and the input signal that commands movement to the target position, and drives the servo motor with an electric signal corresponding to the deviation. In a closed-loop servo control device consisting of a servo amplifier, a memory element is incorporated into the closed-loop system that stores the position deviation vs. feed speed characteristics in advance so that the magnitude of the loop gain can be switched according to the feed speed. A servo control device characterized by a non-linear relationship between quantity and feed rate. (2) Detecting the X-Y table drive mechanism that is subject to position control, the servo motor that serves as the power source for the table mechanism, table feed speed information, and table position information;
Compare the magnitude of the speed detector and position detector that generate the feedback signal with the position feedback signal and the input signal that commands movement to the target position, and drive the servo motor with an electric signal corresponding to the deviation. In the case of a control system in which the change in feed rate given by an input command signal is extremely large in a closed-loop servo control device consisting of a servo amplifier, the loop gain to be set by a microcomputer is calculated from the change in feed rate, and the closed-loop system 1. A servo control device that operates a servo system by setting gain characteristics in a writable memory element incorporated in the servo control device.