JPS5845725B2 - Servo amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulation type servo amplifier suitable for use in automatic balancing instruments and the like.

In general, a modulation type servo amplifier device drives a servo motor by converting the difference between a DC input signal and a comparison voltage into an AC signal using a modulator, and then amplifying the signal.

A filter is provided in the input circuit to attenuate power frequency noise superimposed on the DC input signal.

Moreover, the time constant of the filter is selected to be large in order to obtain a large noise attenuation ratio.

However, if the input circuit includes a filter with a large time constant, there is a drawback that the input impedance decreases at high frequencies, and there is also the drawback that the input circuit is restricted by the withstand voltage, leakage current, etc. of the filter capacitor.

Furthermore, when using a servo amplifier in a multi-point automatic balancing instrument, the input may become open during the process of switching the input signal with a changeover switch, and the input resistance changes significantly, causing an abnormal voltage to charge up the filter capacitor. be done.

This charging voltage maintains the voltage determined by the time constant of the filter even after switching to the next input, which may cause malfunction.

Furthermore, automatic balancing instruments are often connected in parallel with instruments such as controllers and alarms, but when an input signal changes or an input is switched, a transient charging current flows through the filter capacitor. Therefore, disturbance may be given to the instruments connected in parallel.

For this reason, it is necessary to provide filters for each of the instruments connected in parallel, which has the disadvantage of complicating the overall configuration.

Furthermore, in recent modulation-type servo amplifiers, direct-coupled amplifiers such as linear [C] are often used as the main amplifier.

By the way, when a direct-coupled amplifier is used as a high-gain AC amplifier, the direct-coupled amplifier is usually provided with a bias stabilization circuit that applies negative feedback in the DC and low frequency regions.

However, such a bias stabilization circuit causes a delay in the phase of the signal, and as a result, the gain of the servo system (
motor torque and speed) decrease.

Moreover, this phenomenon is particularly noticeable in high-gain amplifiers, and is therefore a major hindrance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel modulation-type servo amplification device that does not have the above-mentioned drawbacks.

FIG. 1 is a connection diagram showing an embodiment of the device of the present invention.

In the figure, 11 and 12 are signal input terminals to which the DC input signal E is applied, and the terminal 12 is connected to the common line l.

2 is a circuit for generating a comparison voltage Er, and the figure shows a potentiometer consisting of a stabilized DC power supply R8 and a slide resistor R8.

3 is a modulator, which has two input terminals a, b and two output terminals c, d, one input terminal (al) is applied with a DC input signal E, and the other input terminal is A feedback voltage Ef is applied.

Sl, S2. S3. S4 is a switching element constituting the modulator 3, Sl is connected between input/output terminals a and c, S2 is connected between a and d, S3 is connected between terminals a and c, and s4 is connected between input and output terminals a and d.

d, respectively.

And switches s1j s4 and S2. S3 is AC power supply e
It is excited so that it alternately turns on and off in synchronization with the frequency f.

Therefore, the output terminals c and d of the modulator 3 are supplied with alternating current signals e1. Generate e2.

4 is a high-gain differential input direct-coupled DC amplifier, which is a linear IC
is shown consisting of OPl, whose input terminals -,
-1 and the difference between the AC signals el and e2 from the modulator 3 is amplified to produce a rectangular wave AC signal e3 as shown in FIG. 2C.
Output.

The frequency of this AC signal e3 is the same as the power supply frequency f, and the amplitude and phase correspond to the magnitude and polarity of the difference between the DC input signal voltage Ei and the feedback voltage Ef.

In short, the modulator 3 and the differential amplifier 4 form a balanced modulation circuit.

Reference numeral 5 denotes a synchronous rectifier circuit, which includes a linear C0P2 and a switch S5 connected between its input terminal terminal and the common line 1.

The input terminals + and -1 of the linear LCOP2 are connected to the output terminal of the differential amplifier 4 via resistors R1 and R2, respectively, and a feedback resistor R3 is connected between the output terminal and the input terminal -.

Switch S5 is switch S2 . It is excited to repeat on/off in synchronization with S3, and when the switch S5 is turned on, the linear FCOP2 becomes an inverting amplifier, and when it is turned off, it becomes a non-inverting amplifier.

Therefore, if the values of the resistors R2 and R3 are chosen to be equal, the linear C0P2 converts the AC signal e3 from the differential amplifier 4 into a DC signal E1 and outputs it.

6 is an adder, which consists of a linear C0P3.

Potentiometer 2 at the input terminal of linear C0P3
The brush of the slide resistor R3 is connected to the input terminal -, and the output terminal of the synchronous rectifier circuit 5 is connected via the resistor R4.

Further, a feedback resistor R5 is connected between the output terminal and the input terminal - of the linear LCOP3.

Therefore, the linear IC0P3 has the synchronous rectification circuit output E1
and the comparison voltage Er are added to output a voltage E2 of E1 +E r (where R4>R5).

This output voltage E2 is passed through the filter circuit 7 to the feedback voltage E2.
f and is applied to the input terminal of the modulator 3.

As the filter circuit 7, resistors R6t R7, RB2
Rg O and capacitor c1. A CR circuit consisting of c2 is shown.

In this way, the synchronous rectifier circuit 5, the adder 6, and the filter circuit 7 form the feedback circuit of the differential amplifier 4.
The output e3 of the differential amplifier 4 has a ratio of 4 to the DC input signal voltage Ei.
1 It corresponds to the difference from the reference voltage Er -(-Ei-Ef) and is 5Gf.

However, Gf is a transfer function of the filter circuit 7.

The output e3 of the differential amplifier 4 is applied to the control coil 911 of the servo motor 9 via the power amplifier 8.

Since the servo motor 9 has an excitation coil 92 connected to the AC power source e via the phase shift capacitor C3, the servo motor 9 rotates in forward and reverse directions depending on the magnitude and phase of the output e3 of the differential amplifier 4.

The amount of rotation of the servo motor 9 is transmitted to the brush of the slide resistor R8 of the potentiometer 2, and the comparison voltage Er is changed to bring the output e3 of the differential amplifier 4 to zero balance.

As described above, in the present invention), the AC output e3 of the differential amplifier 4 is converted into DC by the synchronous rectifier circuit 5 to obtain the comparison voltage Er.
Since the differential amplifier 4 has high low-pass filter characteristics with respect to the DC input signal Ei, it produces a delay with respect to the comparison voltage Efl. It has no configuration.

Therefore, a large noise rejection ratio can be obtained by using a filter with a small time constant compared to the noise l superimposed on the DC input signal voltage Ei, and high impedance can be maintained up to relatively high frequencies without reducing the input impedance due to the filter. have

In addition, when the main amplifier includes a large delay element like this, the servo system generally becomes extremely unstable, but as mentioned above, the comparison voltage ErI is configured so that no delay occurs, so the stability of the servo system is not damaged.

Furthermore, when used in a multi-point automatic balance instrument, even if the input becomes open during the switching process, the voltage of the filter 7 will remain the same as at zero balance, so no malfunction will occur.

Furthermore, the charging current that transiently flows through the filter capacitor when the input signal changes or when the input is switched can be reduced, and the time constant can be shortened, so the influence on the instruments connected in parallel can be minimized. The size can be made as small as or more than the case where filters are provided on each side.

Furthermore, since the differential amplifier 4 has low-pass filter characteristics, its characteristics can be changed significantly by selecting filter constants.

Therefore, good damping characteristics can be obtained by selecting a damping constant in accordance with the response of the servo system and further providing nonlinearity to the power amplifier 8 at the subsequent stage.

Next, the DC component of the output of the differential amplifier 4 is transferred to the synchronous rectifier circuit 5.
After converting the AC current of the power supply frequency f to the modulator 3I via the adder 6 and filter 7, it is converted back to DC and fed back to the differential amplifier 4I, thereby stabilizing the bias. .

In this way, a circuit that negatively feeds back the signal component is used without providing a separate bias stabilization circuit, so
Obstacles caused by the bias stabilizing circuit I can be removed, and the number of circuit components can be reduced.

Although the above example uses an AC two-phase servo motor, in a servo system using a DC servo motor, the output of the synchronous rectifier circuit 5 may be amplified in power to drive the DC servo motor. .

As explained above, according to the present invention, a novel servo amplification device without the drawbacks of conventional modulation type servo amplification devices can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing one embodiment of the device of the present invention, and FIG. 2 is an explanatory diagram of its operation. 1L12... Signal input terminal, 2... Comparison voltage generation circuit, 3... Modulator, 4... Differential amplifier, 5... Synchronous rectifier circuit, 6... Adder, 7...・Filter, 8・
...Power amplifier, 9...Servo motor.

Claims (1)

[Claims] 1. A DC input signal, a circuit that generates a comparison voltage to be compared with this DC input signal, and 2.
One of the switches in the set alternately applies the DC input signal to the input terminals of the differential amplifier, and the other switch applies the feedback voltage alternately to the input terminals of the differential amplifier. an output terminal of the amplifier; a circuit that outputs a voltage obtained by modulating the difference between the DC input signal and the feedback voltage; an adder that synchronously rectifies the output of the differential amplifier and adds it to the comparison voltage; and the adder. A servo amplifier comprising: means for obtaining the feedback voltage by passing the output of the differential amplifier through a filter; and a servo motor that is driven in accordance with the output of the differential amplifier and has means for changing the comparison voltage.