JPH0124037B2 - - 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, position signals of movable members are detected using inductosyn, photosensors, etc.
Since the speed signal is generally detected by a speed generator provided separately from the position detector, there have been problems such as response deterioration due to increased inertia load and increased cost. 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, inverts each position signal, and detects the position of the movable member using a total of four position signals, which simplifies the circuit configuration. There are some difficulties in terms of compatibility.

Therefore, the present applicant has proposed a servo control method that detects a speed signal using only one position signal without degrading the accuracy compared to the above-mentioned method that obtains a speed signal using two position signals. (Gan No. 50-143485, Special Publication No. 59-5921). this is,
In response to the movement of the movable member, a first signal whose frequency is proportional to the amount of displacement of the movable member per unit time is generated, and a second signal is generated by differentiating the first signal.
and detecting a zero-crossing point of the first signal and sampling the second signal using the zero-crossing point detection signal, and an amplitude peak of the second signal obtained by the sampling. The value is held in a capacitor, and the voltage held in the capacitor is used as an actual speed signal.

An object of the present invention is to compensate for the leakage current of the capacitor in the servo control method, and to obtain a voltage from the capacitor that faithfully responds to the actual speed of the motor that drives the movable member. The purpose is to improve accuracy. Hereinafter, one embodiment of the present invention will be described 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 inductosyn, a photosensor, etc., and generates a periodic position signal of only one phase whose frequency is proportional to the eccentric position of the motor 10 per unit time. This position signal may be either a sine wave or a triangular wave, but a sine wave is used here. When using an inductosyn as the position detector 11, a high frequency oscillator 12 is usually coupled to the detector 11, so that the output of the detector 11 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 a signal inversion circuit 15, and a signal having a phase difference of 180° with respect to the position signal A is obtained. FIG. 4a shows the waveforms of the position signals A and .

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 signal inversion circuit 15
The output, that is, the position signal, is also given to the differentiating circuit 20 to obtain a differentiated signal '. Figure 4b shows the differential signal.
The waveforms of A′ and ′ are shown. Now, if the position signal A is A=Esin ωt (1), then its differential signal A' is A'=ωCRE cos ωt (2) (where C and R are differential constants). From the above equations (1) and (2), 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 corresponds to the rotational speed of the motor 10. Therefore, detecting the zero crossing signal of the position signal A,
By sampling the differential signal A' in this manner, a speed signal corresponding to the rotational speed of the motor 10 can be obtained. The same holds true for the signal having a phase difference of 180° with respect to the position signal A and its differential signal'. In FIG. 1, 16 is a zero-crossing detection circuit that creates a zero-crossing signal of the position signal A, and 18 is an analog gate circuit that samples the differential signal A' with 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, and 21 is an analog circuit that samples the differential signal' with the output pulse of the zero-crossing detection circuit 19.
It is a gate circuit. That is, the analog gate circuits 18 and 21 output differential signals having a phase difference of 180°.
The peak values of only the positive polarity components of A′ and ′ 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, and the voltage changes over the peak value of the differential signals A',' for a sampling time determined by the pulse width of the output pulses of the zero-crossing detectors 16 and 19. Since it is obtained by charging, it is kept at approximately the same potential from one sampling to the next, regardless of the movement of the motor 10. 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 the capacitor 22, including other leakage currents, discharges over time. With these, the capacitor 22
The output voltage of the compensation circuit 2 does not accurately reflect the actual speed of the motor 10.
This is solved by inserting 5. That is, the compensation circuit 25 has a built-in voltage source that generates a constant voltage, and the output of the amplifier 23 is connected to the inverter 2.
By superimposing the voltage inverted in step 4 and applying it again to the capacitor 22, the leakage current can be compensated for. Further, the compensating rotation 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 has a one-to-one correspondence with the acceleration/deceleration of the motor 10, and by supplying this to the capacitor 22, the capacitor 22 responds to the actual speed of the motor 10. Speed voltage is obtained. Figure 3 c and d
is the output pulse of the zero-crossing detection circuits 16 and 19, e is the drive current of the motor 10, and f is the output voltage of the capacitor 22, that is, the speed signal.

On the other hand, the peak value of the output of the inverter 15 is filtered by a Schmitt circuit 29, and a 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 sent. The above initial value specifies the so-called homing position of the movable member driven by the motor 10.
The content of indicates 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. In addition, 33 is a command speed setting circuit 34
This is a voltage generator for generating level voltages used in 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. The speed command signal and the actual speed signal are compared by an analog comparator circuit 27 to detect the difference between them, and the error signal is provided to the motor 10 through an amplifier circuit 28. 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, the differential signal A' obtained by the differentiating circuit 17 instead of the output voltage of the capacitor 22 passes through the switching circuit 26 and is passed through the analog comparison circuit as the actual speed signal of the motor 10. Given to 27. Further, the homing detection signal is also given to the switching circuit 32, and the position signal A is directly given to the analog comparator circuit 27 as a speed command signal. Therefore, in the homing region, the motor 10 decelerates following the position signal A, and stops when the position signal A becomes zero. In this homing region, the position signal A used as the speed command signal is ±1/4 cycle of the stop position.

FIG. 2 shows a specific example of the capacitor 22, amplifier circuit 23, inverter 24, and 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 R ₁ , R ₂ , R ₃ and an operational amplifier 25' is used. A constant voltage V _C is applied to input resistor R ₁ , and inverter ₂ is applied to input resistor R 2.
4, and _a voltage _V1 representing the drive current of the motor 10 is applied to the input resistor _R3 . The value of the drive current of the motor 10 is
It can be easily detected by connecting a resistor in series with the armature winding 10 and detecting the terminal voltage.

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 becomes simpler.

As described above, according to the servo control method according to the present invention, a speed signal that almost faithfully responds to the actual speed of the movable member can be detected from only one position signal, which simplifies the circuit and therefore reduces costs. This also has the effect of realizing highly accurate servo control.

[Brief explanation of drawings]

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 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, 12 ... Demodulator, 14 ... Frequency characteristic compensation circuit, 15 ... Inverter, 16, 1
9... Zero-crossing detection circuit, 17, 20... Differentiation circuit, 18, 21... Analog gate circuit, 22
... Capacitor, 23 ... Amplification 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, 3
3...Level voltage generation section, 34...Command speed setting circuit.

Claims (1)

[Scope of Claims] 1. The difference between an actual speed signal representing the actual speed of a motor that drives a movable member and a speed command signal representing the speed that the motor should take is calculated, and the motor is adjusted so that the difference becomes zero. A servo system for controlling the speed of a movable member by driving a first servo whose frequency is proportional to the eccentric position of the movable member per unit time in response to the movement of the movable member.
generating a signal and differentiating the first signal to obtain a second signal, detecting a zero-crossing point of the first signal, and generating the second signal using the zero-crossing point detection signal. In a servo control method in which the amplitude peak value of the second signal obtained by sampling is held in a capacitor, and the voltage held in the capacitor is used as the actual speed signal, the output voltage of the capacitor is inverted. obtain a first voltage from a voltage source that generates a constant voltage, detect a driving current of the motor, obtain a third voltage corresponding to the driving current, A servo control method characterized in that the first, second, and third voltages are superimposed and applied to the capacitor again.