JPS59103113A - Positioning servo control system - Google Patents

Abstract

PURPOSE:To perform the positioning with high accuracy and high reliability and to decrease the setting time by detecting an error between a target position and the present position with sampling of a prescribed cycle and having comparison and calculation to decide whether each error is within an allowance range. CONSTITUTION:The position of a stage 6 is decided by a servo motor 5 of a positioning servo controller, and the value of a position detector 7 is read to an electronic computer 1. The computer 1 calculates the difference epsilon(t) to the command value, and this difference value is converted into an analog signal by a D/A converter 2 and applied to a servo amplifier 3. Then the motor 5 is driven by the output of the amplifier 3, and at the same time the output of a tachogenerator 4 connected directly to the shaft of the motor 5 is fed back to the amplifier 3. Then the error between the target position and the present position is sampled and detected at prescribed cycle time points t0, t1, t2-. Then the computer 1 performs comparison and calculation to decide whether each error epsilon(t) is within an allowance range + or -epsilonP. Thus it is possible to perform positioning with high accuracy and high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a positioning servo control system.

[Prior art]

In the conventional positioning servo control system, as shown in the typical positioning error characteristic diagram in Figure 1, the error signal ε(1)
However, with respect to the preset tolerance range of ±61, at the time tpl when 1ε(t)1≦εl first becomes,
The positioning was completed.

However, the target positioning tolerance becomes highly accurate,
For example, in a setting such as ε2≦1μm, if there is a disturbance such as external vibration, and the time until it settles continues for a long period of time, the error signal ε(1) will initially fall within the tolerance range of ±62. If the positioning is completed at the moment when the position is entered "p2'fr", then the tolerance range ±
There was a problem in that the accuracy could not be guaranteed because it sometimes deviated from the value of 62.

[Purpose of the invention]

An object of the present invention is to provide a positioning servo control system that eliminates the drawbacks of the prior art described above and can perform highly accurate (for example, error of 1 μm or less) positioning with high reliability. [Summary of the Invention] The configuration of the positioning servo control system according to the present invention is such that, in a positioning servo device having a feedback control function using digital arithmetic processing, an error between a target position and a current position is detected by sampling at a predetermined period, and an allowable error range is set in advance to a desired value. , and compare and calculate whether each error is within the allowable error range.
Control and processing are performed such that a determination of completion of positioning is made based on the fact that each error is continuously within the allowable error range for a predetermined number of times or more.

If it is not possible to determine whether positioning is complete within the specified time from when the error first enters the preset tolerance range, the tolerance range should be relaxed completely and reset, and the positioning should be retried. The aim is to increase the probability of success in positioning and improve its reliability.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of an example of a positioning servo device that implements the positioning servo control method according to the present invention, and FIG. 3 is a time chart thereof.

Here, 1 is an electronic computer (CPU) related to feedback control using digital arithmetic processing, 2 is a D/A converter (D/'A), 3 is a servo amplifier (PA), and 4 is
A tacho generator, 5 a servo motor, 6 a stage, and 7 a position detector.

In this embodiment, the stage 6 is positioned by the servo motor 5.

The value of the position detector 7 is read by the electronic computer 1, which calculates the difference ε(1) from the command value, converts this into an analog signal by the D/A converter 2, and then sends it to the servo amplifier 3. give.

A servo motor 5 driven by the output of the servo amplifier 3 is directly connected to a tacho generator 4 coaxially for speed feedback, and its output is directly connected to the servo motor 5 which is driven by the output of the servo amplifier 3.
This provides localized feedback to the system, contributing to improved responsiveness.

Figure 3(a) shows the error between the position of the stage 6 and the target value from when the target position is given until it settles. I'm keeping it. The sampling and calculation of the error ε(1) is shown in Figure 3 (b
) is performed by the electronic computer 1 at a predetermined calculation cycle shown in FIG. The sampling period may be a period shorter than a time that can faithfully detect the temporal change within a range that does not cause any practical problems, depending on the response characteristics of the positioning servo control.

The allowable error range ±ε, which is considered to be the completion of positioning, is set in advance in the storage section of the electronic computer 1, and is the error range between the current position read from the position detector 7 and the target value ε(
t) Calculate 'e and allowable error ε.

When 1ε(t)1≦62 is obtained, positioning is considered complete.

However, if the positioning is completed immediately after this condition is satisfied, the current position reading and the 9 sampling points may fall within the error range ±ε, as in the case shown in Figure 3 (1)). There is a danger that the

Therefore, in order to improve reliability, positioning is truly completed only when the error 1ε (month≦ε) is satisfied during n consecutive current position samplings.By doing this, for example, , as in the example shown in Fig. 3, at the sampling point of time t0, it is true that 1ε(t)
1≦ε, but at the next sampling time t1, 1ε
(t) I>ε.

In such a case, even if the target value is reached at time t0, it is possible to avoid determining that positioning is complete at time io at which the positioning accuracy cannot reach the target value at subsequent times.

For example, if n-4, time t4 in FIG.
Since 1ε(t)l≦ε holds for all four consecutive points starting from 5 r 16 + t7, it is assumed that positioning is completed at time t7.

If the value of n is too large, the time required for positioning will be too long, and even if it is small, it will not be possible to remove the influence of disturbances, so it is necessary to choose the value optimally according to practical requirements. There is.

As described above, a highly reliable positioning servo can be realized, but in some cases, two modes of positioning, coarse positioning and fine positioning, may be performed by the same servo mechanism.

If the same control as the above-mentioned precision positioning is performed in coarse mode, it will require unnecessary settling time, so in this case, the tolerance 6. The above problem can be solved by setting the dog within a range that does not cause any practical problems.

Next, for precision mode positioning, the tolerance ε.

When the positioning is very small, the servo system may not operate stably due to nonlinear phenomena such as load fluctuations or backlash, which may have different coefficients of friction depending on the location of stage 6 and the performance of the stage mechanical system. Otherwise, the positioning may not be completed indefinitely due to oscillation.

Therefore, in order to avoid this kind of thing, the electronic computer 1
starts a timer for a predetermined time for timeout processing from the time when the target tolerance range 1ε(t)1≦ε first becomes true (t in Fig. 3), and positioning is completed within the predetermined time. If the positioning is not completed, it is assumed that the positioning cannot be performed again, and the positioning is retried, for example, from the direction opposite to the direction in which the initial positioning is started.

In this case, after detecting that positioning is impossible, first the stage 6 is roughly moved to the vicinity of the target position, and then precise positioning is performed from that position to the target position again. Since the accuracy of the coarse movement is not critical, it can be performed extremely coarsely and at high speed.

By performing the above retry, the probability of success in positioning can be increased, so that the reliability of positioning can be significantly improved.

〔Effect of the invention〕

As described above in detail, according to the present invention, remarkable effects can be obtained in increasing the precision and significantly improving the reliability of the positioning servo device. Further, by setting the target error to a desired optimum value in a conductive manner, there is an effect that the settling time can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a typical positioning error characteristic diagram, Fig. 2 is a block diagram of an example of a positioning servo device for implementing the positioning servo control method according to the present invention, and Fig. 3 is its time chart. . 1... Electronic computer, 2... D/A converter, 3...
Servo amplifier, 4... Tacho generator, 5... Servo motor, 6... Stage, 7... Position detector. Agent Patent attorney Kosaku Fukuda (and 1 other person) Kaya 1 Figure 2 6 εtt), Z 3rd attorney

Claims (1)

[Claims] 1. In a positioning servo device having a feedback control function using digital arithmetic processing, an error between a target position and a current position can be detected by sampling at a predetermined period, and an allowable error range can be set in advance to a desired value. Then, it compares and calculates whether each error falls within the allowable error range, and determines that positioning is complete when each error falls within the allowable error range a predetermined number of times or more consecutively. A positioning servo control system that is characterized by control and processing. 2. In the item described in claim 1, if it is not possible to determine whether positioning is complete within a predetermined time from when the error first enters the preset tolerance range, the tolerance range shall be changed. A positioning servo control method that relaxes, resets, and retries positioning.