JPS61198310A - Position controller - Google Patents

Abstract

PURPOSE:To improve the positioning precision by giving a hysteresis to the output/input characteristic of a servo amplifier. CONSTITUTION:If a position command xC having a value larger than that of a present position (x) of a load 3, the load 3 is fed forward with respect to (x) coordinate because an initial positional deviation DELTAx is smaller than '0', and a servo amplifier 1 is operated in accordance with an arrow (a) with respect to the input/output characteristic according as the load 3 approaches a target position of DELTAx=0, and a driving force F which a driving device 2 gives to the load 3 is reduced gradually. The load 3 is stopped in the position where the driving force F and the force of friction of the load 3 are balanced near the target position, and the positional deviation DELTAx gives a positioning stop error. If such adjustment is performed by an output voltage VOS that the driving force given from the driving device 2 to the load 3 is equal to the force of friction of the load 3, the positioning stop error is adjusted to zero because the driving force F and the force of friction are balanced for DELTAx=0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a position control device, and particularly to a position control device suitable for arbitrarily adjusting a positioning/stopping error of a load with respect to a position command.

[Background of the invention]

Conventionally, in a position control device that performs precise positioning that requires a positioning nu of about 1 μm, as shown in FIG.
a servo amplifier 1 that amplifies the deviation Δχ between the position command XC and the current position X to drive the drive device 2;
A drive device 2 that drives a load 3 to a target position by the output of
A closed-loop position control consisting of here,
In order to reduce the positioning error caused by the frictional force existing in the load 3, for example, as proposed in Japanese Patent Application No. 59-65785, the servo amplifier 10 has a servo amplifier 10 with a broken line characteristic sound as its input/output characteristics as shown in the figure. Are known.

This method also generates an offset driving force that counters the frictional force of the load using the polygonal input/output characteristics of the servo amplifier. For example, as shown in Fig. 6, when the frictional force of the load is (b), the target position Δx If the input/output characteristics of the servo amplifier are set so that the driving force is exactly balanced with the frictional force at =Q, the load will change to the target position with time t in response to the frictional force (b) as shown in Figure 7(b). It stably converges toward Δx=0. However, the magnitude of the frictional force of the load varies depending on the location of the load and changes over time, for example, as shown in Figure 6 (a) and (
Variations occur as shown in C).

For example, when the frictional force is larger than the offset driving force as shown in Figure 6(a), the load stabilizes toward the position where the driving force and frictional force are balanced with respect to the target position as shown in Figure 7(a). Converge. - If the friction is smaller than the offset driving force as shown in Figure 6 (C), the gain of the driving force is very high at the position where the driving force and frictional force are balanced, that is, Δx = 0, so the load will be reduced as shown in Figure 7 (C). ), the target position becomes the center of hunting, resulting in instability.

Therefore, if an attempt is made to bring the stopping error close to zero by adjusting the input/output characteristics of the servo amplifier, there is a problem that the system becomes unstable.

[Purpose of the invention]

An object of the present invention is to provide a position control device that improves positioning accuracy while keeping the entire gain control system within a sufficiently stable range.

[Summary of the invention]

The reason why a gain is necessary to improve positioning accuracy is that even near the target position where the positional deviation is minute, it occurs due to the driving force that moves the load against the frictional force. The invention is to keep the gain of the servo amplifier within a range where the control system is sufficiently stable, and by adding hysteresis to the special training, it is sufficient to move the load against the frictional force even when the positional deviation is zero. The fact that we were able to generate driving force
This is the gist of it.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, the entire structure includes a drive device 2 such as a servo motor that drives a load 3 such as a moving table, a position detector 4 such as a laser interferometer that detects the current position of the load 3, and a position detector 4 that detects the current position of the load 3. It is composed of a servo amplifier 1 that amplifies the positional deviation ΔX and drives the drive device 2. Here, the input/output characteristics of the servo amplifier 1 are provided with hysteresis characteristics as shown in the figure, and the gain slope of the input/output characteristics is set within a range in which the entire position control system is stable.

That is, a feedback circuit 5 is interposed between the load 3 and the servo amplifier 1, and this feedback circuit 5 controls the offset output voltage Vos of the servo amplifier according to the magnitude of the frictional force F' of the load 3. It looks like this. For example, the value of the frictional force F' of the load 3 is obtained by detecting the driving current of the driving device 2 such as a servo motor, and the offset driving force due to the offset output voltage ■o11 of the servo amplifier overcomes the frictional force F' of the load 3. The output voltage V o of the servo amplifier is adjusted according to the magnitude of the frictional force F' so that
sk control. Further, the offset output voltage V o sO value in a state where the input to the servo amplifier 1 is zero, that is, the positional deviation ΔX is zero, can be arbitrarily adjusted. Next, its operation will be explained.

First, a position command x with a value larger than the current position tx of the load 3 is given.
Consider the case where c is given. In this case, the initial positional deviation Δx (0) causes the load 3 to be driven in the positive direction of the The drive device 2 operates along the arrow (a) on the input/output characteristics of the servo amplifier 1, and the drive device 2
The driving force FFi applied to the drive force FFi gradually becomes smaller. Since the gain gradient of the servo amplifier 1 at this time is set within a range in which the position control system is stable, hunting and oscillation do not occur. Then, near the target position, the load 3 stops at a position where the driving force F and the frictional force of the load 3 are exactly balanced.
The positional deviation ΔX at the stop position gives the positioning stop error. Here, the offset output voltage V of servo amplifier 1
Let us consider a case where the sO value is arbitrarily adjusted. Vo
Offset driving force dz negative Wa given from the drive device 2 to the load 3 by s.

If adjusted to be equal to the frictional force, the positional deviation Δx
Since the driving force F and the frictional force are balanced at =O, the positioning and stopping error can be adjusted to zero. Furthermore, if the offset driving force is adjusted to be larger than the frictional force of load 3, the positioning and stopping error can be reduced to Δx ) O, that is,
It can be adjusted so that it stops at a position that is too far from the target position, and conversely, if it is adjusted so that the offset driving force is smaller than the frictional force of load 3, the positioning stop error can be reduced to Δx (O
That is, it can be adjusted so that it stops at a position that is short of the target position.

Next, the current position tx of load 3 is also smaller than the position command x.
(, is given. In this case, the initial position deviation ΔX>0, the load 3 is driven in the negative direction of the As time progresses, the input/output characteristics of the servo amplifier 1 shown in FIG. The positioning and stop error can be arbitrarily adjusted by adjusting the offset output voltage Vost41![ft of the servo amplifier 1 in exactly the same way as in the case of forward direction feed except that the signs of the driving force F and positional deviation ΔX are reversed. becomes possible.

The reason why the load can be stopped at the target position in such a relationship will be explained. By adding hysteresis to the input/output characteristics of servo amplifier 1, υ, position deviation ΔX
The relationship between the driving force F and the driving force F is shown in FIG. In FIG. 8, when the frictional force of the load 3 and the offset power +1 are equal as shown in (h), the load stably converges toward the target position Δx=Q as shown in FIG. 9(b). Considering the case without a feedback circuit, the difference in the location of the load and changes over time can cause
Even when the frictional force changes, the system always operates within a stable range due to the balance with the driving force, which has a constant gain slope set within a stable range, so the load operation is As shown in FIGS. 9(a) and 9(c), even if a positioning error occurs, it converges stably without hunting. Next, by providing a feedback circuit, the offset driving force is controlled so as to cancel out the frictional force of the load, so that even if there are variations in the frictional force from place to place or over time, the frictional force is always maintained as shown in Figure 8 (b). As shown in FIG. 9(b), the load can be stably converged and the positioning error can be brought close to zero, as shown in FIG. 9(b).

FIG. 2 shows a block diagram of another embodiment of the present invention. What is different from FIG. This was achieved using virtual reality (VR). In FIG. 2, if the output saturation voltage of the comparator 23 is Vsit, and it is attenuated by a factor of 2 (k<1) by the variable resistor R, then the comparator 23 and the variable resistor Since the servo amplifier 21 is in a positive feedback form due to the positive feedback provided by the servo amplifier 21, the input/output characteristics of the servo amplifier 21 exhibit hysteresis characteristics as shown in FIG. Therefore, by adjusting the variable resistor VR and changing the value of k, the offset output voltage of the servo amplifier 21 vo s
% In addition, the offset driving force of the drive device 2 can be adjusted as desired.

Now, when the variable resistor VR is adjusted so that the frictional force of load 3 and the offset driving force are equal, the result is (a) in Fig. 3.
Suppose that we have the characteristics shown in . The positioning and stopping error at this time is zero, but if the variable resistor VR, t is adjusted so that the value of k becomes larger, its characteristics become thicker than V o s as shown in Figure (b). As a result, the offset driving force becomes sharper, causing the load to stop after passing the target position.Conversely, if the variable resistor VR' is adjusted to decrease the value of k, its characteristics will be as shown in the same figure (C ) as shown in Vos
becomes smaller and the offset driving force becomes smaller, so the load comes to stop before the target position.

However, if this variable resistor is adjusted to an appropriate value by the output of the feedback circuit 5 to which the output from the load 3 is input, the load can be stably stopped at a predetermined position.

FIG. 4 shows a block diagram of still another embodiment of the present invention. What differs from FIG. 2 is that a stop error control signal generator 4 is used instead of the variable resistor VFLO constituting the servo amplifier.
3, a variable amplification amplifier 42 whose amplification degree changes depending on the output of the stop error control signal generator 43 is used.

That is, instead of manually adjusting the magnification k of the variable resistor VR in order to adjust the stop error of the load 3 in FIG. 2, in this embodiment, the stop error control signal generator 43
By changing the output of the variable amplification amplifier 42 and changing the amplification degree of the variable amplification amplifier 42, the load stoppage error can be adjusted. Therefore, according to this embodiment, there is an effect that the load positioning/stopping error can be arbitrarily adjusted by the electric signal.

〔Effect of the invention〕

According to the present invention, the servo amplifier has hysteresis input/output%.
Since the driving force offset amount of the driving device can be arbitrarily adjusted with all the features, the positioning accuracy can be completely improved while keeping the gain within a range where the control system is sufficiently stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the position control device according to the present invention, FIG. 2 is a block diagram showing another embodiment of the position control device according to the present invention, and FIG. 3 is a block diagram showing the position control device according to the present invention. FIG. 4 is a block diagram showing still another embodiment of the position control device according to the present invention, and FIG. 5 is a diagram showing the input/output characteristics of a servo amplifier according to another embodiment of the device. A block diagram showing an example, FIGS. 6 and 7 are explanatory diagrams showing the drawbacks of the conventional position control device, and FIGS. 8 and 9 are explanatory diagrams showing the effects of the position control device according to the present invention. 1.21.41... Servo amplifier, 2... Drive device, 3... Load, 4... Position detector, 22... Differential amplifier, 23... Comparator, 42... - Variable gain amplifier, 43...stop error control signal generator.

Claims (1)

[Claims] 1. A drive device that drives a load, a position detector that detects the current position of the load, and a servo amplifier that amplifies the deviation between a position command and the current position of the load to drive the drive device. 1. A position control device characterized in that the input/output characteristics of the servo amplifier have hysteresis characteristics. 2. The position control device according to claim 1, wherein the servo amplifier comprises a differential amplifier, a comparator inserted into a feedback loop of the differential amplifier, and a variable resistor. 3. The servo amplifier has a differential amplifier, a comparator inserted into the feedback loop of the differential amplifier, a stop error control signal generator, and a variable amplification degree such that the amplification degree changes depending on the output of the stop error control signal generator. The position control device according to claim 1, characterized in that it comprises an amplifier.