JPS595921B2 - Servo Seigyohoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo control scheme for controlling the velocity or relative position between two relatively movable members.

The position servo control method will be described below as an example. As is well known, this type of servo control system requires position and velocity signals of the movable member.

However, conventionally, the position signal of a movable member is inductosyn,
Although the speed signal is detected by a photo sensor, etc., the speed signal is generally detected by a speed generator installed separately from the position detector. There was a problem. As a method to solve this problem, some methods have been proposed to obtain a speed signal by differentiating a position signal detected by a position detector. (See US Pat. No. 3,839,665). However, this method detects two position signals with different phases, and
These position signals are each inverted, and the position of the movable member is detected using a total of four position signals, which is difficult in terms of simplifying the circuit configuration. The present invention has been developed in view of the above-mentioned circumstances, and is a servo that can easily obtain a speed signal from one position signal, for example, without deteriorating accuracy compared to a system that obtains a speed signal from two position signals. The objective is to provide a control method.

Hereinafter, the content of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

The control is such that the movable member is initially driven at the maximum speed, and thereafter, each time the movable member passes a predetermined position, it is gradually decelerated and stopped at the target position. Figure 3 shows its speed characteristics. In the case of the speed servo system, the movable member simply rotates at a constant speed following the commanded speed, and the principle of control is the same. In FIG. 1, reference numeral 10 denotes a motor for driving a controlled object, and a position detector 11 is directly connected to the rotating shaft of the motor. The position detector 11 is composed of an inductosin, a photosensor, etc., and generates a single-phase signal (hereinafter referred to as a position signal) whose frequency is proportional to the amount of deviation of the motor 10 per unit time. This position signal may be either a sine wave or a triangular wave, but here a sine wave is used. When using an inductosin as the position detector 11, the detector 11 is usually coupled with a high frequency oscillator 12.
The output of is modulated. By passing the output of the position detector 11 through a demodulator 13 and a frequency characteristic compensation circuit 14, a nearly perfect sine wave position signal whose frequency is proportional to the rotational speed of the motor 10 and whose peak value is kept approximately constant is obtained. A is obtained. The position signal A is inverted by the signal inverting circuit 15, and a signal A having a phase difference of 1800 with respect to the position signal A is obtained. FIG. 4a shows the waveforms of the position signals A (solid line) and A (dashed line). The output of the frequency characteristic compensation circuit 14, that is, the position signal A, is given to a differentiating circuit 17, and a signal A' obtained by differentiating the position signal A is obtained.

Similarly, the output of the signal inverting circuit 15, ie, the position signal A, is applied to a differentiating circuit 20 to obtain a differentiated signal N. FIG. 4b shows the waveforms of the differential signals A' (solid line) and A' (broken line). now,
Let the position signal A be, then its differential signal is N (however,
C. R is a differential constant).

From equations 1) and (2) above, it can be seen that the instantaneous value of the differential signal A'' when the position signal A is zero is proportional to the angular velocity ω of the position signal A. Naturally, the angular velocity ω is Therefore, by detecting the zero-crossing signal of the position signal A and sampling the differential signal N using this, it is possible to obtain a speed signal corresponding to the rotation speed of the motor 10.Position signal The same applies to the signal A and its differential signal N, which have a phase difference of 180 degrees with respect to A.
In FIG. 1, 16 is a zero-crossing detection circuit that creates a zero-crossing x signal of the position signal A, and 18 is an analog gate circuit that samples the differential signal N using the output pulse of the zero-crossing detection circuit 16. Similarly, 19 is a zero-crossing detection circuit that creates a zero-crossing signal of the position signal A, and 21 is an analog gate circuit that samples the differential signal 8 using the output pulse of the zero-crossing detection circuit 19. That is, analog gate circuits 18, 21
The peak values of only the positive polarity components of the differential signals A' and N, which differ in phase by 1800 degrees, are output. The outputs of analog gate circuits 18 and 21 are stored in capacitor 22.
The voltage of this capacitor 22 is proportional to the rotational speed of the motor 10, but the voltage is
Since it is obtained by charging the peak values of the differential signals A and N for the sampling time determined by the pulse width of the output pulse 9, the time from one sampling to the next is almost constant regardless of the movement of the motor 10. kept at the same potential. Further, the capacitor 22 has a large impedance, and the impedance is converted by the amplifier 23. in this case,
The input impedance of the amplifier 23 is finite, and
The output voltage of capacitor 22, including other leakage currents, discharges over time. Due to these, the output voltage of the capacitor 22 does not accurately reflect the actual speed of the motor 10, but this can be solved by inserting the compensation circuit 25. That is, the compensation circuit 25 has a built-in voltage source that generates a constant voltage, and by superimposing the voltage obtained by inverting the output of the amplifier 23 with the inverter 24 and applying it again to the capacitor 22, the leakage can be suppressed. The current is compensated. Further, the compensation circuit 25 receives a signal voltage representing the magnitude of the drive current of the motor 10 from the motor side. The compensation circuit 25 superimposes this signal voltage on the previous voltage and supplies it to the capacitor 22. As is easily understood, the above signal voltage is dependent on the acceleration/deceleration of the motor 10 and 1
By supplying this to the capacitor 22, a speed voltage responsive to the actual speed of the motor 10 can be obtained from the capacitor 22. 3c and d are the output pulses of the zero-crossing detection circuits 16 and 19, and e is the output pulse of the motor 10.
The drive current, f, represents the output voltage of the capacitor 22, that is, the speed signal. Note that details of the compensation circuit 25 will be described later. On the other hand, the peak value of the output A of the inverter 15 is output by the output circuit 29, and the position timing signal is detected.

This position timing signal is sent to a subtraction counter 30. An initial value is set in the subtraction counter 30 through the signal line L1, and its contents are counted down each time a position signal is applied. The above initial value specifies the so-called homing position of the movable member driven by the motor 10, and the contents of the counter 30 indicate the distance of the movable member from the homing position. The contents of the counter 30 are taken into the command speed setting circuit 34. The command speed setting circuit 34 generates a level voltage whose level decreases step by step every time the counter 30 indicates a predetermined value (that is, each time the movable member moves a predetermined distance), and outputs the voltage to the analog comparison circuit as a speed command signal. Supply to 27. Note that 33 is a voltage generating section for generating a level voltage used in the command speed setting circuit 34. The other input of the analog comparison circuit 27 is the actual speed signal of the motor 10 provided through the capacitor 22, the amplifier circuit 23, and the switching circuit 26. These speed command signals and actual speed signals are compared in an analog comparison circuit 27 to detect the difference between the two, and the error signal is passed through an amplifier circuit 28 to the motor 10.
given to. The speed of the motor 10 is controlled so that the error signal becomes zero, that is, the actual speed signal matches the speed command signal. In this way, the motor 10 is initially driven at its highest speed and then gradually reduced by level switching of the speed command signal until the content of the counter 30 reaches zero when it enters the homing region.

When the counter 30 becomes zero, the gate 31 is driven and a homing detection signal is sent out from the gate 31. This homing detection signal is applied to the switching circuit 26, and as a result,
A differential signal N obtained by the differentiating circuit 17 instead of the output voltage of the capacitor 22 passes through the switching circuit 26 and is applied to the analog comparing circuit 27 as the actual speed signal of the motor 10.
Further, the homing detection signal is also given to the switching circuit 32,
Position signal A is directly given to analog comparison circuit 27 as a speed command signal. Therefore, in the homing region, the motor 10 decelerates following the position signal A, and the position signal A
It stops when becomes zero. In this homing area,
The position signal A used as a speed command signal is within ±1/4 cycle of the stop position. Figure 2 shows capacitor 22.
, the amplifier circuit 23, the inverter 24, and the compensation circuit 25.

Here, as the amplifier circuit 23 and the inverter 24, operational amplifiers with stable operation are used. Further, as the compensation circuit 25, an analog adder circuit consisting of input resistors Rl, R2, R3 and an operational amplifier 25' is used. A constant voltage Vc is applied to the input resistor R1.
However, the output voltage Vs of the inverter 24 is applied to the input resistor R2, and the voltage VI indicating the drive current of the motor 10 is applied to the input resistor R3. The value of the drive current of the motor 10 can be easily detected by connecting a resistor R9 in series with the armature winding 10 and detecting the terminal voltage thereof. In FIG. 2, the current i supplied from the operational amplifier 25' to the input example of the amplifier circuit 23 via the resistor R6 is represented by .

Here, if R2=R4 and R8-R7, then the equation (1) is obtained. The first term on the right side of equation (2) is determined by the constant voltage Vc and the resistors Rl, R6, and R4, and the capacitor 22
This is to compensate for the leakage current.

The second term on the right side of equation (2) is the speed correction current determined by the voltage V1 proportional to the current flowing through the motor 10 and the resistors R3, R6, and R4.

That is, the voltage change v that occurs at the input section of the amplifier circuit 23 due to the second term on the right side of equation (2) is as follows, and is proportional to VI-t.

On the other hand, the rotational speed of the motor 10dθ is Dt, where K is the motor torque constant, and is also proportional to It.

Therefore, the fine speed signal from one hold of a certain speed (peak value of the amplitude of the differential signal) to the next hold is corrected by equation (2). As described above, in the embodiment shown in Fig. 1, the movable member is initially driven at the maximum speed and then gradually decelerated to stop at the target position. However, the movable member is simply rotated at a constant speed following the commanded speed. In this case, there is no need for a function to measure the moving distance of the movable member, and it is clear that the configuration shown in FIG. 1 is simpler.

As described above, according to the servo control method of the present invention, a speed signal that almost faithfully responds to the actual speed of the movable member can be easily obtained even from a single position signal, simplifying the circuit and reducing costs. It is measured.

Of course, the illustrated configuration is merely one example, and it goes without saying that the configuration can be modified without departing from the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the servo control system according to the present invention, FIG. 2 is a diagram showing a specific example circuit configuration of a part thereof, and FIG. 3 is a diagram showing an example of the operating characteristics of FIG. 1. FIG. 4 is a time chart of signal waveforms at various parts in FIG. 1. 10... Motor, 11... Position detector, 12... High frequency oscillator, 13... Demodulator, 14... Frequency characteristic compensation Circuit, 15...
...Inverter, 16,19...Zero crossing detection circuit, 17,20...Differentiating circuit, 18,21
...Analog gate circuit, 22...
Capacitor, 23... Amplifier circuit, 24...
...Inverter, 25... Compensation circuit, 26...
... Signal switching circuit, 27 ... Analog comparison circuit, 28 ... Amplification circuit, 29 ... Schmitt circuit, 30 ... Counter, 31 ...・・・
...AND circuit, 32...Switching circuit, 33.
... Level voltage generation section, 34 ... Command speed setting circuit.

Claims (1)

[Claims] 1. Taking the difference between an actual speed signal representing the actual speed of the movable member and a speed command signal representing the speed the movable member should take,
In a servo control method that controls the speed of the movable member so that the difference becomes zero, a first signal whose frequency is proportional to the eccentric position of the movable member per unit time in response to the movement of the movable member. and differentiating the first signal to obtain a second signal, detecting a zero crossing point of the first signal, and using the zero crossing point detection signal to obtain the second signal.
A servo control system characterized in that the second signal obtained by sampling is held at an amplitude peak value, and the held voltage is used as the actual speed signal. 2. The servo control method according to claim 1, wherein the amplitude peak value of the second signal obtained by sampling is held by a capacitor. 3. The servo control method according to claim 2, wherein a predetermined voltage is superimposed on the output voltage of the capacitor and applied again to the capacitor to compensate for a voltage drop due to leakage current of the capacitor. method.