JPS58165679A - Controller for linear servo motor - Google Patents

Abstract

PURPOSE:To stably control a linear servo motor without overshoot by differentiating a position voltage to add a nonlinear factor to the speed voltage for producing a damping in response to the speed at the operating time of an object to be controlled. CONSTITUTION:A block 25 differentiates a position voltage obtained by a potentiometer, outputs a speed voltage, and a block 26 applies a nonlinear factor to the speed voltage. An addition block 27 adds the position voltage and the speed voltage, and outputs as a negative feedback voltage of a servo system the sum. In this manner, when a linear servo motor is operated at a low speed, it is controlled in the state in the vicinity of critical brake and increases the gain of the speed damping at the high speed operating time, thereby preventing an overshoot.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a linear servo motor used in recorders, XY recorders, XY plotters, printers, etc.

Hereinafter, a conventional example and the present invention will be explained using an example of application to a recorder.

The servo system in a conventional recorder is basically constructed as shown in FIG. In the figure, 1 is a rotary servo motor, 2 is a steel wire, 3 is a pulley, 4 is a spring, 6 is a pen block, 6 is a contact brush, 7 is a potentiometer, 8 is a recording ben, and 9 is a guide rod. In this configuration, the rotational force generated by the rotary servo motor 1 is transmitted by the steel wire 2, and the pen block 6 is moved in the longitudinal direction of the guide rod 9. The pen block 6 supports a recording pen 8 and a contact brush 6, and the contact brush 6 slides in contact with a potentiometer 7, so that the position of the recording pen 8 is recognized by the potentiometer 7.

The pulley 3 suspends the steel wire 2, and the spring 4tIi applies tension to the steel wire 2. In the case of such a servo system, there are two major problems, which have limited the basic performance of the recorder. One of the problems is that there is a steel wire in the transmission system from the motor to the pen. Since the system includes the pulley 3, spring 4, etc., the transfer function of the system is very complicated, and a resonant system including unstable elements is likely to be formed. Therefore, the gain of the servo system cannot be increased beyond a certain level. Another problem is that the rigidity of the transmission system from the motor to the pen is low, and since the contact brush 6 is used for the potentiometer, there is a directivity (hysteresis) in its characteristics, so there is always a dead zone. exists.

Conventional recorders suffer from the two major problems mentioned above in terms of performance: poor linearity of plot lines, insufficient suppression of disturbances, lack of high-speed response, and poor plot quality due to dead zones. It had defects such as defects.

A block diagram of a well-known closed loop servo system for a servo motor is shown in FIG. In the figure, 1o is a rotary servo motor or a linear servo motor (hereinafter, unless otherwise specified, the term servo motor includes a linear servo motor), 011 is a potentiometer that recognizes the position of the servo motor 1o, and 12 is a potentiometer. 1 is a position voltage generation circuit that converts the obtained position information into position information (a voltage signal related to position, hereinafter referred to as position voltage), and 13 is a voltage signal proportional to speed for adding damping (hereinafter referred to as speed voltage). )
This is a speed voltage generation circuit that generates a speed voltage, and the speed voltage is usually obtained by differentiating the position voltage. 14 is an adder circuit that adds the speed voltage and the position voltage to obtain a negative feedback voltage for the servo system, and 16 calculates the difference between the negative feedback voltage and the input voltage (
The difference voltage obtained here will be referred to as an error voltage hereinafter. ),
A command voltage generating circuit 16 amplifies the error voltage to obtain a command voltage for the servo motor 10, and 16 is a drive circuit that supplies current to the servo motor 10 in accordance with the command voltage.

FIG. 3 is an external view of an example of a linear servo motor used in the present invention. In the figure, 17 is a bearing, 18 is a stator (also used as a guide rail), 19 is a linear servo motor body, and 20 is a sensor block equipped with a position sensor, in which an optical or magnetic sensor is used. 21 is a pen block that supports a recording pen, and 22 is a recording pen. Since the recording pen 22 is directly connected to the linear servo motor body 19 via the pen block 21, the movement of the linear servo motor directly corresponds to the movement of the drawing pen 22.

23 is a wire harness.

Compared to Figure 1, which uses a rotary servo motor explained as an example of a conventional recorder, the features of this linear servo motor are that the transmission system from the motor to the recording pen is very simple, and the rigidity is also low. That's a high point. This is advantageous in increasing the gain of the servo system. Increasing the gain of the servo system increases the ability to suppress disturbances, and can be expected to improve the performance of the recorder, such as improving the linearity of plot lines and input followability. Of course, the dead zone can also be made smaller.

However, if the gain of the servo system is high, problems arise due to the nonlinearity of the circuit. The nonlinearity of the circuit includes constraints (clip) due to power supply voltage, constraints on motor output (limits on drive current), and the like. When the gain of the servo system is high, when the error voltage exceeds a certain value, the circuit enters the saturation region, which means that the operation of the servo motor cannot be sufficiently controlled just by satisfying the Nyquist stability condition. The input voltage given to the recorder is -15 position voltage is Ex.

When the speed voltage is Ev and the error voltage is Em, the following equation holds true. −Em=Ein−(E!10Ev)・・・・・・Mountain song・
(1) When Em is positive, the servo motor is in a positive acceleration section, and when - is negative, the servo motor is in a negative acceleration section (deceleration section). Now, when a step waveform signal with a large amplitude is applied to the input of the recorder, the linear servo motor starts moving toward the target position, but if the negative feedback gain of the closed loop is high, the linear servo motor will move until it approaches the target position. Most of the time, circuits operate in the saturation region. When the linear servo motor enters the deceleration zone near the target position, the motor command voltage, which is an amplified version of the error voltage, gives a command to the motor drive circuit to generate an appropriate braking force, but the current that can flow through the motor is Due to restrictions, the necessary braking force cannot be obtained. Therefore, the linear servo motor passes the target position and overshoots, and the error voltage caused by the deviation from the target position occurs.
The operation is to return to the target position and settle.

In the case of a recorder that uses a conventional rotary servo motor, as mentioned earlier, the gain of the servo system cannot be increased, so the control is mostly performed within the linear region and is based on the Nyquist stability condition. If designed, it could be controlled stably, but in order to perform stable control without overshoot while taking advantage of the characteristics of a linear servo motor, control in a nonlinear region is required.

In view of the above points, the present invention is an improvement of the speed voltage generation circuit. Basically, the position voltage is converted into speed information, and a speed voltage is generated to provide appropriate damping according to the speed.

FIG. 4 shows the most basic circuit example for realizing the conventional speed voltage generation circuit 13, in which the operational amplifier 23. 'A differential circuit is formed using a resistor and a capacitor.' FIG. 5 shows the frequency characteristics of FIG. 4.

This transfer function is expressed as follows.

However, A is a gain, T is a time constant, and S is a Laplace transform constant.

The reason why the high frequency region in FIG. 6 has a flat characteristic is that components in this region are often unnecessary and harmful to control.

The concept of obtaining a speed voltage using such a method and combining and adding it with a position voltage is completely equivalent to the concept of performing phase lead compensation using a so-called lead-lag filter. The lead-lag element gives the position voltage the frequency characteristic shown in FIG. 6, but if the speed voltage and position voltage created in FIG. 4 are combined and added, exactly the same conclusion can be obtained.

In the explanation of this conventional example, the position voltage and the speed voltage are only considered separately.

The present invention adds a nonlinear element to the speed voltage so that when the linear servo motor operates at low speed, it satisfies the Nyquist condition as in the past and is always controlled in a state close to critical damping. When the motor is moving near the target position at high speed, a large speed voltage is suddenly generated to prevent overshoot and stabilize the motor.

FIG. 7 is a block diagram showing an example of the configuration of the speed voltage generation circuit 13 used in the present invention. In the figure, 26 is the position differential (
In other words, it is a block that provides a speed voltage, and 26 is a block that provides a nonlinear element to this speed voltage. 2
7 is an addition block that adds the position voltage and speed voltage.

The block 26 that provides the nonlinear element has a gain of 1 in the region where the speed is small, but the gain becomes 1 or more when the speed exceeds a certain speed. In other words, at low speeds, there is no effect of nonlinear elements, and control is performed in a state close to critical damping, and only at high speeds, the gain of speed damping increases due to the influence of nonlinear elements, resulting in early braking It becomes possible to generate force.

FIG. 8 is a wiring diagram showing the speed voltage generating circuit 13 shown in FIG. 7 in more detail. In the figure, 28 is a block that provides a position differential (that is, velocity) voltage, which corresponds to 26 in Figure 7, and includes an operational amplifier 31 and resistors R1, R2, R3.
and a capacitor C for differentiation. 2
9 is a block that provides a nonlinear element to the speed output of this block 28, and corresponds to 26 in FIG. It is composed of: Reference numeral 30 denotes an addition block for synthesizing and adding the position voltage and the velocity voltage given nonlinearity, and corresponds to 27 in FIG. This is operational amplifier 3
3 and resistors R7, R8, and R9.

Although the specific embodiment shown in FIG. 8 has a very simple configuration, it has many excellent features as described below.

(1) By adding a nonlinear element, the gain of the servo system can be set high. Therefore, the linearity of the recording line is improved, and the ability to suppress disturbances can be strengthened.

(2) Stable damping can be obtained even during high-speed response, eliminating overseat. (3) Optimal control close to critical damping when operating at low speed near the target position. can be realized, and especially by applying the present invention, this control will not be adversely affected.

(4) Since it can be realized with a simple circuit, there is no disadvantage in terms of cost.

As described above, according to the present invention, it is possible to realize a high-performance recorder that takes advantage of the many excellent features of a linear servo motor while compensating for its drawbacks.

It goes without saying that the present invention is not necessarily limited to recorders, but is generally applicable to devices that require linear motion and that use a closed-loop servo system to which a linear servo motor can be applied.

[Brief Description of the Drawings] Figure 1 is a perspective view of main parts of a linear feed mechanism of a recording pen of a conventional recorder, Figure 2 is a block diagram of a conventional closed loop servo system, and Figure 3 is a diagram of a linear feed mechanism of a recording pen of a conventional recorder. FIG. 4 is a diagram showing a configuration example of a conventional speed voltage generation circuit, FIGS. 5 and 6 are gain-frequency characteristic diagrams,
FIG. 7 is a block diagram of an example of a speed voltage generating circuit used in the present invention, and FIG. 8 is a wiring diagram showing a specific example of the configuration of FIG. 7. 10... Servo motor, 11... Potentiometer, 12... Position voltage generation circuit,
13... Speed voltage generation circuit, 14...
Addition circuit, 15... Command voltage generation circuit, 16.
... Drive circuit, 22 ... Routing pen, 25
, 28...Block that provides position differential voltage (velocity voltage), 26.29...Block that provides nonlinear elements, 27.30...Addition block, 31, 32.33...Operation amplifier, 34゜3
5...Diode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure 6 Figure 7

Claims (1)

[Claims] A potentiometer that is configured to position a linearly moving controlled object using a closed-loop servo system and that recognizes the position of the controlled object, and a position that generates a position voltage according to the position information obtained from this potentiometer. a voltage generation circuit, a speed voltage generation circuit that differentiates the position voltage to obtain a speed voltage for applying damping according to the speed of the object to be controlled, and an adder circuit that adds the speed voltage and the position voltage. and a command voltage generation circuit that obtains a motor command voltage by taking and amplifying the difference between the output voltage and the input voltage of the adder circuit, and a drive circuit that converts the motor command voltage into a motor drive current, and A control device for a linear servo motor, wherein the speed voltage generation circuit includes a nonlinear element that imparts nonlinearity to the speed voltage.