JPS63156206A - Servo controller - Google Patents

Abstract

PURPOSE:To improve the positioning precision and eliminate unnecessary oscillation due to steady disturbance by providing a switch, which selects a digital servo system or an analog servo system, and a switch changeover control circuit. CONSTITUTION:A switch 23 is switched to select a digital servo system 31 by a switch changeover control circuit 25 until the difference between the command value which a function generating part 41 designates based on a target value and the present value of a control object 11 is within a minimum pulse interval of digital pulses DP, and the switch 23 is switched to select an analog servo system 32 after said difference is within the minimum pulse interval for a prescribed time, and the control object 11 is servo-controlled in this manner. Thus, a high positioning precision is obtained by the digital servo control until the object reaches the target position, and the control is quickly converged and oscillation is eliminated by the analog servo control after the object approaches the target position.

Description

Detailed Description of the Invention [Summary] A servo control device using an encoder that outputs a first sinusoidal signal and a second sinusoidal signal having a phase shift of 90” with respect to the first sinusoidal signal, the a digital servo system that forms digital pulses from first and second sinusoidal signals and performs servo control using the digital pulses;
an analog servo system that processes a signal obtained by adding and subtracting the sinusoidal signals of the above to form an analog position signal that changes linearly with a constant slope between adjacent digital pulses, and performs servo control using this signal. , by operating the digital servo system until the control deviation falls within the minimum pulse interval of the digital pulses, and operating the analog servo system after the control deviation continuously falls within the minimum pulse interval. , improves the positioning accuracy of the target position, speeds up convergence to the target position, and eliminates unnecessary vibrations at the target value 1.

[Industrial application field]

The present invention relates to a servo control device.

A servo control device is an essential component in the field of robots or NC machine tools, and the performance of this servo control device determines the quality of the performance of the robot or NC machine tool. In general, servo control is broadly classified into analog control and digital control, each of which has its advantages and disadvantages. The present invention proposes a mixed type servo control device of analog control and digital control.

[Conventional technology]

FIG. 5 is a block diagram showing an example of a conventional digitally controlled servo control device. In the servo control device 10, 11 is a controlled object, for example, a DC motor, and an encoder 12 is provided in conjunction with this. Encoder 12
is composed of two signals, a first sinusoidal signal S1 and a second sinusoidal signal S1.
The digital pulse generator 13 sends out a sinusoidal signal S2, which is converted into a digital pulse DP by the digital pulse generator 13. This digital pulse DP is applied to the digital servo controller 14, which gives a digital servo control output to the controlled object 11 and guides it to the target position (the details of the signals Sl and S2 will be described later).

FIG. 6 is a block diagram showing an example of a conventional analog control type servo control device. Note that in the servo control device 20, the same components are shown with the same reference numerals or symbols throughout the drawings, and the first sinusoidal signal Sl and the second sinusoidal signal S2 from the encoder 12 are
The digital pulse generator 13 generates a digital pulse D.
After being converted to P, the counter 14 increments (steps). Furthermore, after the deviation between the target value (digital data specifying the target position) and the current value is determined, the digital/analog converter 15 converts it into an analog signal. Since this analog signal is a signal that changes stepwise, it is necessary to smooth it out. Therefore, the first and second signals S1 and S2 are added by an adder 16 and subtracted by a subtracter 17, and then added to an analog position signal generator 18, where a linear signal is generated with a constant slope between the digital pulses DP. An analog position signal AP that changes as follows is generated.

This analog position signal AP is then superimposed on the step-like signal from the converter 15 to form a smooth analog waveform. This is added to the controlled object 11 via the analog servo controller 19 and guided to the target position.

When the digital servo control device 1o and the analog servo control device 20 described above are compared, the digital device 10 is superior to the analog device 20 in the following points.

(b) Positioning accuracy is high because the target position is accessed digitally.

(b) Since the analog type device 20 is mainly composed of an operational amplifier, it has the disadvantage that problems such as offset and drift occur and the work to adjust them is complicated. It is not present in the shaped device 10.

(c) Various control variations can be easily realized by introducing a function generator using software or a dedicated (c) function generator.

(d) The servo control system can be easily changed just by changing the software.

[Problem that the invention seeks to solve]

The digital type servo controller 10 is superior to the analog type in the above-mentioned respects. However, since the digital servo control device 10 is controlled using digital pulses as a basic unit, so-called quantization errors are inevitable. Therefore, control is no longer possible between the digital pulse corresponding to the target position and the digital pulses adjacent thereto (on the left and right). Moreover, within this minimum pulse interval (resolution is determined), it is not known where the controlled object 11 is. Therefore, only when the controlled object 11 shifts for some reason and goes out of the minimum pulse interval, deviation from the target position is detected (a pulse is generated), and control to return it to its original position is activated.

In general, the deviations mentioned above are unlikely to occur. This is because, due to the inherent mechanical friction (for example, bearing friction) of the controlled object, once the controlled object has stopped at the target position, it will not leave there unless there is an external force. However, in recent years, there has been a strong demand for improvement in the response of servo control systems, and the above-mentioned mechanical friction etc. tends to be close to zero. In this case, even if the controlled object 11 settles within the minimum pulse interval, it easily deviates from it and is pulled back again, which is repeated, resulting in vibration. When the object to be controlled is a DC motor, such vibration causes the motor to generate heat, generates noise, and also becomes a hindrance to precise transportation work, processing work, etc.

The present invention has been made in view of these points, and an object of the present invention is to propose a servo control device that can eliminate harmful vibrations at a target position while maintaining good positioning accuracy of a digital servo. .

[Means for solving problems]

FIG. 1 is a principle block diagram of a servo control device according to the present invention. A switch 23 is provided in the servo control device 30, and one end of the switch 23 is connected to a digital servo system (
13, 21) 31, and the other end is connected to the analog servo system (16, 17, 18, 22) 32. 2
1 is a digital servo controller having at least a function generating section 41 therein, and 22 is an analog servo controller. The outputs from these controllers 21 and 22 are connected to the switch 2
3 is determined by the switch changeover control circuit 25.

[For production]

Until the difference between the command value specified by the function generator 41 based on the target value and the current value of the controlled object 11, that is, the control deviation, falls within the minimum pulse interval of the digital pulses DP,
The switch 23 is connected to the upper contact, and the controlled object 11 is servo-controlled by the digital servo system. After the control deviation is continuously within the minimum pulse interval for a predetermined time, the switch 23 is connected to the lower contact, and the analog The control object 11 is servo-controlled by a servo system. As a result, the target position is reached with high positioning accuracy by digital servo control, and after approaching the target position, it is quickly converged there, and the harmful vibrations mentioned above are eliminated by analog servo control.

〔Example〕

FIG. 2 is a diagram showing a specific example of the servo control device according to the present invention. Further, FIG. 3 is a waveform diagram of signals appearing in each part of FIG. 2, and the following description will be made with reference to both figures. First, the first and second sinusoidal signals S1 from the encoder (E) 12
and s2 are as shown in columns (1) and (2) of FIG. 3, respectively, and are out of phase with each other by 90°. The encoder 12 is made of, for example, a disk, and rotates in conjunction with a motor (M) 112 within the controlled object 11. A first slit group consisting of a large number of slits is provided at equal intervals along the circumference of the disk, and a first sinusoidal signal S1 is obtained from a corresponding photocoupler (arranged to sandwich the slits). A second group of slits is further provided in the disk, and a second group of slits
The first slit group is provided slightly closer to the center of the disk than the first slit group, and at an angle shifted from each slit in the first slit group, and a second sine wave signal s2 is obtained from the corresponding photocoupler. These signals St and S2 are respectively applied to a first comparator (CMP) 131 and a second comparator (CMP) 132 in the digital pulse generator 13, and are converted into rectangular wave signals P1 and P2 (the third
(Columns (3) and (4) in the figure). The rectangular wave signals P1 and P2 are applied to the phase discriminator 134, where they are converted into digital pulses DP (minimum pulse interval MIN) shown in FIG. 3 (6) IM, and the mutual phases of these signals P1 and P2 are checked. Then, it is determined whether the motor 112 is rotating in the forward direction or in the reverse direction. For example, if Pl appears before P2, it means that the motor is rotating in the normal direction, and if Pl appears before P2, it means that the motor is rotating in the reverse direction.

If the rotation is in the normal direction, the counter 211 in the digital servo controller 21 is counted up by the digital pulse DP, while if it is in the reverse rotation, the counter 211 is counted down. The count value of the counter 211 is calculated by the microprocessor (MP[I
) 212, where the deviation between the target value and the current value is calculated. The microprocessor 212 includes a function generator 41 (usually realized by software processing, but may also be configured by hardware) and a normal PID (
Proportional Integral Diff
erentia1) type compensator 42 (which can be software or hardware) and a control deviation detection section 43, which will be described later. The deviation between the above target value and the current value (obtained from the counter 211 based on the digital pulse DP) is actually the command value specified by the function generator 41 (command value curve C1 in FIG. 4(A)). The difference between the current value (see current value curve C2 in FIG. 4(A)), that is, the control deviation (see control deviation ER in FIG. 4(C)), is added to the compensator 42 and is added to the digital/analog (D
/A) After converting it into an analog control signal with the converter 213, it is transmitted to the power amplifier (AMP) 11 in the controlled object 11 via the switch 23 (the switch 23 is now in the upper contact).
1 to guide the motor 112 to the target position.

When the target value is reached as guided by the command value curve C1, the switch changeover control circuit 25, which operates in response to signals from lines 214 and 215, switches the contact of the switch 23 to the lower contact. Here, control is switched from the digital servo system 31 to the analog servo system 32. Generally, servo control involves overshoot near the target value. Immediately switching to the analog servo system 32 in this overshoot state will result in two inconveniences. First, under the analog servo control described with reference to FIG. 3, the braking force is weaker than in the case of digital servo control, and the braking force does not quickly converge to the target position. This is because if the braking force is increased, oscillation will occur. Second, under analog servo control, which will be explained with reference to FIG. 3, when entering overshoot,
In fact, this is because a force that promotes this overshoot acts (on the left side of the target position DS in column (9) of Fig. 3, a force e that promotes the overshoot acts, and the force e that promotes the overshoot acts only after exceeding DS). (The force e that suppresses the shoot does not work).

Therefore, a switch changeover control circuit 25 is provided to continue to leave control to the digital servo system 31 under an overshoot condition, and to switch to the analog servo system 32 after determining that the condition has been overcome. The operation of this control circuit 25 will be described later.

The first stage of the analog servo system 32 inputs the first and second sinusoidal signals St and S2, and adds them together (S1
+S2) and subtraction (Sl -S2).

These are performed by an adder 16 and a subtracter 17, and an addition signal P4 and a subtraction signal P5 ((7) and (8) in FIG.
) column). Note that S1+32 is 5 inches (θ+45°
), the signal P4 leads Sl by 45 degrees, while 5L-32 has sinθ-cosθ=-5
in (θ-45°), the signal P5 is delayed by 45° from f-th Sl. These signals P
4 and P5, each slope portion is used, so in columns (7) and (8) of FIG. 3, each slope portion is represented by a thick line. Since the slope portions alternately change symmetrically in slope, all these slope portions are aligned in one direction to obtain a waveform as shown in column (9) of FIG. 3. This becomes the analog position signal AP. This signal AP is a signal that changes linearly with a constant slope between the minimum pulse intervals (M I N ) of the digital pulses DP.

Each slope portion of the addition signal P4 and the subtraction signal P5 is converted into an analog position signal AP by exclusive OR (E
XOR) gate 24, selector 181, and inverting non-inverting device 1
Due to the function of 82. First, the output P3 of the EXOR gate 24
is as shown in column (5) in Figure 3.

Comparing signals PI, P2, and output P3, it is found that signal P2 is at "H" (high) level and output P3 is at H level.
When the level is high, the slope part of the signal P4 is inverted, and the signal P2 is H level and the output P3 is L'' (low).
Is it a signal when it's level? It can be seen that if the slope portions of 5 are inverted, all the slopes become the same as in the signal AP. Therefore, the selector 181 selects each slope portion of the signal P4 or P5, and the inverting/non-inverting device 182 inverts the slope portion each time the signal P2 becomes "H" level.

Based on the analog position signal AP thus obtained, the analog servo controller 22 (D(differentia1
)-P (example of proport 1ona 1) type is shown) to perform analog servo control and power amplifier 1
11 to drive a motor 112. In this case, the center of the signal AP corresponding to the target position becomes the true target position DS.

On the left side of DS, a positive force e pushing toward DS acts, and DS
On the right side, a negative force e acts to pull it back toward DS,
Harmful vibrations are eliminated by constantly balancing these with DS.

FIG. 4 is a graph used to explain the operation of FIG.
) is a curve C1 representing the command value from the function generator 41;
C2, which shows a curve C2 representing the current value of the controlled object 11, always changes to follow 01. (B) is the command value curve C
This is the target speed to satisfy condition 1. After accelerating from time to, the vehicle travels at a constant speed, decelerates, and then reaches the target position at time t1. (C) is the control deviation ER, which corresponds to the deviation between the curve C1 and the curve C2 in (A).

This deviation appears as an overshoot O8 near the target value. Generally, when high-speed response is required, the occurrence of overshoot O8 is unavoidable. In this case, there are usually discrete points where the control deviation ER is zero (ER=O). For example, time t2 in (C). t3.
It is as shown by t4 etc. The switch 23 in FIG.
Originally, the role is to switch from the digital servo system 31 to the analog servo system 32 when the control deviation ER falls within the minimum pulse interval MIN, but simply ER=O
If the switching is executed at , the above-mentioned two problems (inability to quickly converge to S and promotion of overshoot) will occur.

Therefore, the switch changeover control circuit 25 shown in FIG.
It is assumed that the switch 23 is switched to the analog servo system 32 after waiting until after time t4 in Figure (C) (waiting for O3 to subside). This switch switching control circuit 2
5 can be composed of, for example, an AND gate 251 and a counter 252, as shown in FIG. Counter 252 counts clock CLK from clock source 26. In addition,,
As the clock source 26, the digital servo controller 21
It is economical to use the sampling clock generator that was originally needed.

The counter 252 outputs “H3 (hi)” to its clear terminal CLR.
jh) When a level signal is input, the contents are cleared to zero and the clock CLK starts counting. When the constant value has been counted, a carry signal CR is generated. The signal CR switches the switch 23 (31-32), and in the present invention, a value corresponding to a predetermined time is set as the constant value. The predetermined time is, for example, the time from t2 to t4 in FIG. 4(C), which corresponds to the time during overshoot, and the optimum value is selected in advance for each controlled object.

In order for the counter 252 to be cleared, it is necessary to confirm that the control stage has reached O3 in FIG. 4(A).

First, a signal (“H”) indicating that the command value of the function generator 41 has become constant is received from the line 214, and a signal (“H”) indicating that the control deviation ER has become zero (ER=0) is received from the line 214. H") is received from the line 215 and when the two match, the AND gate 251 sends a clear signal to the counter 252. Such an AND operation is required for curves C1 and C1 in FIG. 4(A). This is because there is a state in which ER=0 even when C2 rises, and in order to ignore these, a signal from line 214 indicating that the command value has become constant (reached the target value) is also sent. need to be included in the conditions.

〔Effect of the invention〕

As described above, according to the present invention, a servo control device is realized that utilizes the advantage of high accuracy provided by digital servo control while overcoming the disadvantage of generating harmful vibrations by using analog servo control.

[Brief explanation of the drawing]

Fig. 1 is a principle block diagram of a servo control device according to the present invention, Fig. 2 is a diagram showing a specific example of a servo control device according to the present invention, and Fig. 3 is a waveform diagram of signals appearing in various parts of Fig. 2. , FIG. 4 is a graph used to explain the operation in FIG. 2, FIG. 5 is a block diagram showing an example of a conventional digital control type servo control device, and FIG. 6 is an example of a conventional analog control type servo control device. FIG. 11... Controlled object, 12... Encoder,
13... Digital pulse generator, 18... Analog position signal generator, 21... Digital servo controller, 22... Analog servo controller, 23... Switch, 25... Switch switching control Circuit, AP...Analog position signal, DP...Digital pulse, ER...Control deviation, MIN...Minimum pulse interval, S1, S2...Sine wave signal. Ub Waveform diagram of signals present in each part of Fig. 2 Fig. 3 1011 Time diagram 4 used to explain the operation of Fig. 2

Claims (1)

[Claims] 1. A first sinusoidal signal (S1) and a second sinusoidal signal (S2) whose phase is shifted by 90° from the signal (S1) according to the amount of movement of the controlled object (11). an encoder (12) that outputs a digital pulse (DP); a digital pulse generator (13) that receives the first and second sinusoidal signals (S1, S2) as input and outputs a digital pulse (DP); Digital servo control that servo-controls the controlled object (11) so that the control deviation (ER) between the current value obtained based on (DP) and the command value specified by the function generator (41) is zero. A device (21) receives the signal obtained by adding and subtracting the first and second sinusoidal signals (S1, S2) from each other as input, and calculates the minimum pulse interval (MI) of the adjacent digital pulses (DP).
an analog position signal generator (18) that generates and outputs an analog position signal (AP) that changes linearly with a constant slope between
an analog servo controller (22) that servo-controls the controlled object (11) based on P); and either an output from the digital servo controller (21) or an output from the analog servo controller (22). a switch (23) that selects one and applies the voltage to the controlled object (11); and the control deviation (ER) is equal to the minimum pulse interval (MIN).
The switch (23) is connected to the digital servo controller (21) side until the control deviation (ER) approaches the minimum pulse interval (MIN), and it is detected that the state in which the control deviation (ER) is within the minimum pulse interval (MIN) continues for a predetermined period of time. and a switch switching control circuit (25) for connecting the switch (23) to the analog servo controller (22).