JPS5922963B2 - Servo control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a servo control method using a photosensor as a position signal detector.

Conventionally, as a servo control method for positioning equipment, etc., a position signal detector also serves as a speed detection tachometer, and the position signal detector detects two position signals with 900 phase differences, and then inverts these to generate a four-phase signal. There is a known method in which signals are obtained and differentiated to produce a speed signal.

Fig. 1 shows a schematic block diagram of the same, in which 100 is a motor, and a position signal detector (sensor) is mounted on its rotating shaft.
101 is directly connected. The position signal detector 101 detects a pseudo sine wave signal containing two DC components with 900 phase differences, and amplifiers 102 and 103 cut off the DC components to become position signals A and B, respectively. Position signals A, B
are inverted by inverting amplifier circuits 104 and 105, and these signals A and B are sent to a differentiator 106 together with signals A and B, respectively.
, 107, 108, and 109, and are input to the speed signal and position pulse generation circuit 110. The circuit 110 sequentially samples the peak values of the input differential signals Λ', n', A', and B', and generates a speed signal whose amplitude increases and decreases approximately in proportion to the frequency of the position signal, that is, the speed of the 10 motors. Output. Further, the circuit 110 receives the signal B, creates a zero-crossing signal thereof, and supplies it to the command speed creation circuit 111 as a position pulse. Command speed signal generation circuit 1
Reference numeral 11 subtracts rotation distance information preset from an external device using a position pulse, and outputs a command speed signal at a predetermined level based on the position error. The speed signal and command speed signal thus obtained are input to an adder 112 to calculate the difference between the two, and the error signal is sent to an error signal amplifier 113.
is amplified and applied to the motor 100. As a result, the motor 100 rotates to obtain a speed corresponding to the command speed signal. By the way, let us consider a case where a photo sensor is used as a position signal detector of such a servo control method.

Generally, a photo sensor consists of a combination of a light-emitting diode and a light-receiving diode, but when the current of the light-emitting diode is kept constant and the output of the light-receiving diode is measured while changing the ambient temperature, approximately It fluctuates around 40%. Therefore, if such a photo sensor is used and a speed signal is created based on its output signal, the fluctuation in the output of the light receiving diode will appear as a speed error, making it impossible to expect accurate control. The present invention has been made in order to solve the above-mentioned problems, and stabilizes the output of a sensor against ambient temperature fluctuations, deterioration of light emitting diodes and light receiving diodes, etc. It is an object of the present invention to provide a highly reliable servo control system using a photo sensor that utilizes the sensor output as a reference voltage source for creating a command speed signal.

Hereinafter, the content of the present invention will be explained in detail with reference to Examples.

FIG. 2 shows an embodiment of the photo sensor section used in the present invention.

In FIG. 2a, 1 is a light emitting diode, and facing the light emitting diode are three light emitting diodes 2-1 and 2.
A photodiode array consisting of -2, 2-3 is arranged. The photodiode array 2 is, for example, a monolithic type, and has three elements 2-1, 2-2, 2-3.
have very similar electrical characteristics. A mirror 3 and a mask 4 are arranged between the light emitting diode 1 and the photodiode array 2, and among these, the light emitting diode 1,
The photodiode array 2 and mask 4 are fixed, and the mirror 3 rotates following the rotation of the motor. As shown in FIG. 2b, the mirror 3 has a disk shape, and optical slits are provided on its circumference by etching, with light passing portions 3-1 and light blocking portions spaced at equal intervals. It consists of 3-2. Further, as shown in FIG. 2c, the mask consists of an A slit 4-1, a B slit 4-2, which match the slit spacing of the mirror 3, and a C slit 4-3 through which light always passes. Slit 4-1 and B slit 4-2 are 9
0, out of phase. The light receiving element 2-1 on the photodiode array 2 receives the light passing through the A slit 4-1, and similarly, the light receiving element 2-2 receives the light passing through the B slit 4-2. The light receiving elements 2-3 each receive the light passing through the C slit 4-3. FIG. 3a shows the outputs of the light receiving elements 2-1, 2-2, and 2-3 when the mirror 3 is rotated in the direction of the arrow in FIG.
FIG. 3b shows the waveforms of position signals A and B obtained by extracting the alternating current components of the outputs of the light receiving elements 2-1 and 2-2. In the present invention, the outputs of the compensation light receiving elements 2-3 are measured by changing the temperature and aging of the outputs of the compensation light receiving elements 2-3. By stabilizing against changes, etc., the outputs of the position signal detection light receiving elements 2-1 and 2-2, that is, the position signals A and B in FIG. 1, are stabilized against temperature and changes over time, etc.
The present invention is characterized in that a reference voltage used as a command speed signal source for servo control is extracted from an output stabilizing circuit of the compensation light receiving element.

FIG. 4 is a block diagram of one embodiment of the stabilizing circuit which forms the main part of the present invention.

FIG. 4 is roughly divided into a feedback compensation circuit 10 for stabilizing the output of the light-receiving element 2-3 against temperature, changes over time, and voltage fluctuations, and an output detection circuit 20 for the light-receiving elements 2-1 and 2-2. , 30. The feedback compensation circuit 10 includes an inverting amplifier circuit 11 that amplifies the output of the light receiving element 2-3, a current amplification circuit 12 that drives the light emitting diode 1, and a current amplifying circuit 12 that amplifies the output of the light receiving element 2-3 and the light emitting diode 1.
A constant voltage circuit 13 that determines the current value of , a drift compensation circuit 14 that compensates for these current and temperature drifts, and a reference voltage circuit 15 that outputs a DC voltage that is a command speed signal source for servo control. The detection circuit 20 for the light receiving element 2-1 is made up of two stages of inverting amplifier circuits 21 and 22, and the bias setting is also performed in the inverting amplifier circuit 22 at the rear stage. The same applies to the detection circuit 30 for the light receiving element 2-2. In FIG. 4, the feedback compensation circuit 10 constantly feeds back the output of the light receiving element 2-3 that receives the light from the light emitting diode 1 to the current amplifier circuit 12 through the inverting amplifier circuit 11, and compares this with the output of the constant voltage circuit 13. However, when the output of the light receiving element 2-3 decreases due to temperature, voltage fluctuations, etc., the current of the light emitting diode 1 is increased,
Conversely, when the output of the light receiving element 2-3 increases, the current of the light emitting diode 1 is decreased, and furthermore, the drift of the current amplifier circuit 12 is compensated by the drift compensation circuit 14.

Therefore, the output of the light-receiving element 2-3 is determined by the gain of the first-stage inverting amplifier circuit 11 and the voltage value of the constant voltage circuit 13, and fluctuations in the output can be suppressed to several percent or less. As explained in FIG. 2, the light-receiving elements 2-1 and 2-2 are formed integrally with the light-receiving element 2-3, for example, of a monolithic type, and since they receive light from the same light emitting diode 1, the light-receiving elements The outputs of 2-1 and 2-2 are the compensation light receiving element 2.
It will be stabilized in the same way as the -3 output. That is, the position signals A and B of the detection circuits 20 and 30 vary only within the error of the feedback compensation circuit 10. Therefore, for example, if the blocks 101 to 103 in FIG. 1 are replaced with the configuration shown in FIG. 4, the position signals A and B will be extremely stable against changes in temperature and time. Also, at this time, if the reference voltage of the command speed signal generation circuit 111, that is, the command speed signal source, is obtained from the reference voltage circuit 15 that takes in the output of the inverting amplifier circuit 11 shown in FIG.
fluctuations are relatively negligible. Furthermore, the detection circuits 20, 3
If a signal obtained by inverting the output of the reference voltage circuit 15 is used as the zero bias, bias fluctuations can also be reduced. A specific example of the circuit shown in FIG. 4 is shown in FIG.

In FIG. 5, parts corresponding to those in FIG. 4 are designated by the same symbols and surrounded by broken lines. The stability of the circuit shown in FIG. 5 is expressed by the stability of the output voltage V2-3 of the compensation light-receiving element 2-3, and is expressed by the following equation. Here, Vz is the voltage of Zener-diode ZD, VBE is the base-emitter voltage of drift compensation transistor TR-2, and VBE is
is a transistor TR- that constitutes the current amplification circuit 12;
1, G is the gain of amplifier AMP-1. That is, Vz is a constant voltage, which is current-amplified by the amplifier AMP-4 and the transistor TR-3.

The base-emitter voltage VBE of the transistor TR-1 is an error item for the voltage V2-3, and increases with the current and decreases with the rise in temperature. Transistor TR-2
The base-emitter voltage VBE has the role of removing the above fluctuation term, and if elements with the same characteristics are used for transistors TR-1 and TR-2, the above fluctuation element can be almost ignored.
In other words, the voltage V2-3 in equation (1) is approximately Vz/G, takes a constant value regardless of temperature, and is stable. Note that similar results can be obtained even if a diode is used as the compensation transistor TR-2. As can be seen in Fig. 3, the output signals of the light-receiving elements 2-1 and 2-2 are output at a negative voltage with respect to the ground potential, and have an alternating current component superimposed on a direct current component.
The alternating current components have a phase difference of 90 currents from each other. The outputs of the light receiving elements 2-1 and 2-2 are sent to amplifiers AMP-5 and AMP.
After amplification at the amplifier AMP-7, a bias is set at the center of the alternating current component using the potentiometers VR-1 and VR-2 to which the output of the amplifier AMP-2 is supplied.
When amplified by MP-8, position signals A and B are obtained. or,
A reference voltage used as a command speed signal source for servo control is taken out from amplifier AMP-3. As is clear from the above description, according to the present invention, in servo control that uses a differentiated position signal of a photo sensor as a speed signal and a DC voltage as a command speed signal, the photo sensor output is At the same time, the servo control can be stabilized by taking out the DC reference voltage, which should be the source of the commanded speed signal, from within the photo sensor compensation circuit and reducing the relative fluctuation difference between the speed signal and the commanded speed signal.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the general configuration of the servo control system, Fig. 2 is a single example of a photo sensor section applied to the method of the present invention, Fig. 3 is an output waveform diagram of the photo sensor, and Fig. 4 is a diagram of the present invention. FIG. 5 is a specific circuit diagram of FIG. 4.

Claims (1)

[Claims] 1. Connecting a position signal detector to the rotating shaft of the motor, obtaining a position signal whose frequency follows the speed of the motor using the position signal detector, and differentiating the position signal to generate a speed signal; In a servo control system that controls the rotation of the motor by comparing the speed signal with a command speed signal, a light source, a signal detection light receiving element, a compensation light receiving element, the output of the compensation light receiving element and a constant voltage source are provided. a current amplification circuit for light intensity compensation that compares the output with the light receiving element for compensation and controls the current of the light source according to output fluctuations of the light receiving element for compensation; and a signal amplification circuit that amplifies the output of the light receiving element for signal detection and uses it as a position signal. circuit, a person extracts a reference voltage from the light amount compensation current amplification circuit to use as a command speed signal source, and compares a command speed signal of the command speed signal source with a speed signal obtained from the position signal. A servo control method characterized by reducing relative fluctuation differences. 2. The servo control method according to claim 1, wherein the output of the detection light receiving element is biased at a level based on the output of the compensation light receiving element.