JPS61122721A - Servo control device - Google Patents

Abstract

PURPOSE:To include an error always in a small range and to reduce a quantized error as small as possible by changing a feedback variable in accordance with an objective acceleration value. CONSTITUTION:A comparator 13 applies the 1st control signal C1 to amplifiers of which amplification factors are variable 7a-9a when the output ¦a¦ of an absolute value circuit 12 is '0', i.e. when a unit 2 to be controlled is in the constant speed status, and applies the 2nd control signal C2 to the amplifiers 7a-9b when the output ¦a¦ is larger than '0', i.e. when in the accelerating or decelerating status. When the ¦a¦ is changed from an infinite value to zero, the control signal C2 is switched to the C1 after a prescribed time from the changing point of time. The amplifiers 7a-9a are set up to comperatively small feedback constants K1a, K2a and K3a when receiving the 1st control signal C1, and set up to comparatively large feedback constants K1b, K2b and K3b when receiving the 2nd control signal C2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a servo control device, and in particular, a function generating mechanism that generates a continuous target position and an actual position of a controlled object that follows the target value. The present invention relates to an improvement of a servo control device for a DC motor equipped with a servo mechanism that generates such a manipulated variable.

[Conventional technology]

FIG. 3 shows a block diagram of an example of a conventional servo control device. In FIG. 3, a servo control device 1 controls the speed or positioning of a controlled object 2 such as a rotor of a DC motor (hereinafter referred to as a DC motor), so that the DC motor moves to a specified speed or position. , a function generator 3 that generates a continuously changing target position r, and a difference e=r− between this target position and the actual position y of the DC motor 2.
It is equipped with a servo mechanism 4, ie, a feedback system, which works to make y zero. The servo mechanism 4 (feedback system) has a proportional operation, an integrator 5 to remove steady-state deviation, a differentiator 6 to keep the system stable, and a feedback constant to determine the strength of feedback. 3
It is equipped with amplifiers 7.8 and 9 having a constant gain of , and a zero-order hold circuit 10. By appropriately determining the feedpack constants of the amplifiers 7.8 and 9 depending on the purpose of control, it is possible to give the control system various characteristics. For example, kI, to! When the values of , and are set relatively small, the feedback is weakly applied, so that the position y of the DC motor 2 follows the target position r with a weak force.

Also, if kl, km, and kz are set relatively large, the feedback will be strong and the DC
The position y of the motor 2 follows the target position r, improving coordination.

In the conventional servo control device, these constants kl+kg,
The value of lcs is fixed, and feedback is applied strongly to the extent that the system does not become unstable, so that the position y of the DC motor 2 firmly follows the target position r.

[Problems to be solved by the invention]

However, since the position y of the DC motor is generally read using an incremental encoder or the like, a continuous position is not detected and the value is a discrete value. Therefore, the error e will not be detected unless the target value r and the actual position y deviate by at least the minimum unit of the encoder (hereinafter referred to as one unit). Therefore, when feedback is strongly applied, a manipulated variable U is added that strongly reduces the error to zero with an error of 1 unit, so the manipulated variable becomes an error of 6.
There is a large difference in the value of the manipulated variable U between when w Q and when e=±1, and this results in a pulse-like manipulated variable U.

FIG. 4 shows constants , , , k as in the above conventional example.

3 is a graph showing temporal changes in speed V, error e, and manipulated variable U when feedback is strongly applied by setting the value relatively large.

As shown in FIG. 4(a), it is assumed that the time differential of the target value r, that is, the target speed V, is changed in a trapezoidal manner to move the position of the DC motor 2 from a certain angle to another specified angle. to the feedback constant.

When k, , are made relatively large, the error e is very small, about ±5 units, as shown in Figure 4 (in Figure 4), but the feedback is strong (so the manipulated variable U becomes as shown in Figure 4 (C)). As shown, even a slight change in error causes a change with a large amplitude.Since the DC motor cannot follow such a pulse-like change in the manipulated variable U, unnecessary heat is generated in the DC motor. There is a problem that noise is generated due to the pulse of the manipulated variable U.

If an error of 1 unit or less can be detected, there will be no large change in the manipulated variable U, but this is theoretically impossible with an incremental encoder, and an error of 1 unit is called a quantization error. That is,
When strong feedback is applied, due to the influence of quantization error,
Unnecessary heat and noise are generated in the DC motor.

In order to reduce the influence of quantization errors, feedback may be applied weakly. Figure 5 shows the speed V, error e, and time of the manipulated variable U when the feedback constant k l + is set relatively small and feedback is applied weakly in the conventional device shown in Figure 3. FIG.

As shown in Figure 5 (bl), while weak feedback is applied, the error e is about ±100 units even at constant speed, which is larger than when strong feedback is applied as shown in Figure 4 (bl). However, as shown in Fig. 5(C), the variation in the manipulated variable U is very small compared to the example in Fig. 4(C), so the DC motor can sufficiently follow this manipulated variable U, eliminating unnecessary Heat generation and noise are reduced.

However, if feedback is applied weakly, the DC motor 2 will follow the target position with a weak force, so if any disturbance is applied to the DC motor, the position of the DC motor will easily deviate from the target position and will not return to the target position. There is also the problem that it takes time.

Furthermore, if the feedback is weak, as shown in Figure 5), when the target speed V is changing, that is, when the target acceleration is not zero, a larger error e will appear than when the target acceleration is constant. There is a problem that there is a large difference between the position and the actual position.

An object of the present invention is to suppress the above-mentioned problem in a servo control device in which when feedback is applied weakly, the error from the target position becomes large, and when feedback is strongly applied, the influence of quantization error becomes large. The objective is to keep the error within a small range and reduce the quantization error as much as possible by changing the magnitude of the feedback depending on the magnitude of the target acceleration.

[Means for solving problems]

What is provided by the present invention is a servo control device that includes a function generating mechanism that generates a continuous target position and a servo mechanism that generates a vibration amount such that the actual position of a controlled object follows the target position. means for setting a feedback constant of the servomechanism to be relatively small when the acceleration at the target position generated by the function generating mechanism is smaller than a prespecified value; In this case, the servo control device is characterized by comprising means for setting a feedback constant of the servo mechanism to a relatively large value.

[For production]

The difference e between the target position r and the controlled object y becomes large immediately after starting the operation, immediately after changing from acceleration to constant speed, or immediately after changing from constant speed to deceleration. That is, immediately after the acceleration changes in a stepwise manner. Therefore, in these cases, by applying strong feedback, priority is given to reducing the error e over reducing the influence of the quantization error. Since the error e is originally small while moving at a constant speed or while stopping after positioning, feedback is weakly applied at this time to reduce the influence of the quantization error.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a servo control device according to the present invention. In FIG. 1, a servo control device 1
an integrator 5, a differentiator 6, included in the servo mechanism 4a of a.
The zero-order hold circuit 10 is the same as that in the conventional example shown in FIG. 3, and the difference from FIG. 3 is that in FIG. Accordingly, two types of feedback constants, large and small, are set, and an absolute value circuit 12 that takes the absolute value of the target acceleration a generated by the function generator 3a and a comparator 13 that compares this absolute value with a predetermined value ad are added. This is what is being done. In this embodiment, the predetermined value ad is adwQ.

When the output 1al of the absolute value circuit 12 is 0, the comparator 13
That is, in the constant speed state, the first control signal C1 is applied to the amplifiers 7a, 8a, and 9a with variable amplification factors, and the lal
is larger than zero, that is, in an acceleration or deceleration state, the second control signal C2 is sent to the amplifiers 7a18a% and 9a.
give to Furthermore, when fat changes from a finite value to zero, the control signal is immediately changed from 02 to C, depending on the change.
Instead of switching to , the switching is performed after a predetermined period of time from the time of the change, which is 50 m5ec in this embodiment. This is because even if the acceleration a returns to zero from a value other than zero, a large error may occur if the feedback is weakened immediately thereafter.

The amplifiers 7a, 8a, and 9a have relatively small feedback constants when receiving the first control signal CI;
a, Kza, and a, and when receiving the second control signal C1, relatively thick feedback constants are set to +b, Kzb-, and 3b.

FIG. 2 is a graph showing an example of the servo control operation by the servo control device shown in FIG.

In FIG. 2(a), the target value r generated by the function generator 3 is changed so that the velocity V becomes trapezoidal, as in the conventional example shown in FIG. 4(a), and y= The DC motor, which is stationary at point o, is moved to the final target position y = 50000 for positioning.

As shown in Figure 2(C), the acceleration period and subsequent 5
0++sec, that is, between 0 and 130w5ec,
Deceleration period and subsequent 501115eC% or 628
Between m5ec and 764m5ec, the feedback is strong, K+b = 66.6, K! b
=332, K3b-999. Otherwise, weak feedback will occur, and the feedback constant will be +
a = 0.833, Kza = 18.2+ to 3a-
It is 233. However, the sampling period is IKHz,
The transfer function Gp(31) of the motor to be controlled is Y(31664 Gp(Sl= □ Mi □ U(313'') U(S): Laplace transform of the manipulated variable U.

As you can see by comparing Figure 2 with Figure 4, 130m5
While applying weak feedback between ec and 628m5ec, as shown in Figure 2 ('b), the error e is about ±10 units even in a constant speed state, compared to the conventional example shown in Figure 4 (bl). However, as shown in Figure 2 (C1), the fluctuation in the manipulated variable U is very small compared to the conventional example in Figure 4 tc+, so the DC motor can sufficiently follow this manipulated variable U, making it unnecessary. This reduces heat generation and noise.

On the other hand, 0~130 and 628m5ec~3764m5
The feedback is strong (because it depends on the second
Although the manipulated variable U shown in the figure (C1) is more influenced by the quantization error than that in Figure 5 TC, the error e is smaller.

In the above embodiment, the feedback constant 1°k, .
When is larger than ad+, the feedback constant becomes,
Increase the feedback constant to 3 or more levels, such as increasing , , , and further increasing , , , and when lal becomes larger than ad. It is also possible to switch.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, in the servo control device, when the absolute value of the target acceleration of the controlled object is less than or equal to a predetermined value, the quantization error is reduced and the object moves smoothly. When the absolute value of is greater than or equal to the predetermined value,
Strong feedback allows target position r and actual position Wy
This reduces the generation of unnecessary heat and noise during the movement of the controlled object, and also prevents the stability of the control system from being impaired by disturbances at the stopped position.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a servo control device according to the present invention, FIG. 2 is a graph showing an embodiment of the operation of the device shown in FIG. 1, and FIG. 3 is an example of a conventional servo control device. FIG. 4 is a graph showing the operation of the device when strong feedback is applied in the conventional example shown in FIG. 3, and FIG. 5 is a graph showing the operation of the device when weak feedback is applied in the conventional example shown in FIG. It is a graph showing the operation. 1a... Servo control device, 2... Controlled object, 3a...
...Function generator, 4a...Servo mechanism, 5...
・Integrator, 6...differentiator, ? a, 8a, 9
a...Amplifier, "...Target position, y...Actual position, e...Error, U...Manipulated amount,
a...Target acceleration, ad...Predetermined value,
12... Absolute value circuit, 13... Comparator.

Claims (1)

[Claims] 1. In a servo control device equipped with a function generation mechanism that generates a continuous target position and a servo mechanism that generates a manipulated variable such that the actual position of a controlled object follows the target position, the function generation mechanism means for setting a feedback constant of the servo mechanism to be relatively small if the generated acceleration at the target position is smaller than a prespecified value; A servo control device comprising means for setting a relatively large feedback constant.