JPS5913041B2 - Servo mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo mechanism used in automatic balancing instruments and the like.

Generally, as shown in FIG. 1, a servo mechanism amplifies the deviation between an input signal voltage Ei and a comparison voltage Ef using a servo amplifier 1, and then drives a servo motor 3 via a power amplifier 2 to generate the comparison voltage Ef. The brush of the slide resistance Rs of the potentiometer 4 is displaced to bring the deviation to zero.

Note that the voltage dividing circuit consisting of resistors R1 and R2 is used for range adjustment, and the instruction recording mechanism 5 is driven by the servo motor 3 to record the input signal voltage Ei as an instruction. In the servo mechanism configured in this manner, a filter 6 (a one-stage CR circuit is illustrated in the figure) is provided in the input circuit to attenuate noise superimposed on the input signal. . Moreover, the time constant of the filter 2 is selected to be large in order to obtain a large noise attenuation ratio. By the way, if the input circuit has a filter with a large time constant, it has the disadvantage that the input impedance decreases at high frequencies, and also has the disadvantage that the input circuit is restricted by the withstand voltage, leakage current, etc. of the filter 10 capacitor. be.
In addition, when the servo mechanism is configured as a multi-point system as shown in Fig. 2, and the input signals are sequentially switched using the changeover switch 7, there may be a situation where the input becomes open during the switching operation.
5 Ru. In this state, the input resistance seen from the servo amplifier 1 to the input circuit side changes significantly, so that the filter capacitor is charged with an abnormal voltage. This phenomenon becomes particularly noticeable when a direct-coupled DC amplifier is used as the servo amplifier 1 due to its bias current. This charging voltage maintains the voltage determined by the time constant of the filter even after switching to the next input, causing malfunction. Furthermore, instruments such as controllers and alarms are often connected in parallel to the servo mechanism, but the charging current transiently flows through the filter capacitor when the input signal changes or when the input is switched. This may cause disturbance to the instrument. To prevent this, it is necessary to provide filters on each instrument side, which has the disadvantage of complicating the overall configuration. The object of the present invention is to realize a novel 30 servo mechanism that does not have the above-mentioned drawbacks. That is, as shown in the embodiments of FIGS. 3 and 4, the present invention adds the output ε of the servo mechanism 1 and the comparison voltage Ef from the potentiometer 4 in an adder 8, and then adds the output to the servo amplifier via the filter 2. It is designed to return to the input 35 output side of 1. According to the present invention configured in this way, the gain of the servo amplifier 1 is sufficiently large, so that
Its output ε becomes, and the servo amplifier 1 receives the input signal Ei
Although it has high low-pass filter characteristics with respect to the comparison voltage Ef, it has a configuration that does not cause any delay with respect to the comparison voltage Ef.

Therefore, it is possible to obtain a large noise rejection ratio for the noise superimposed on the input signal voltage Z by using the filter 6 with a small time constant, and it is possible to obtain a high noise rejection ratio up to a relatively high frequency without reducing the input impedance due to the filter. It has an impedance. In addition, when the servo amplifier includes a large delay element like this, the servo system generally becomes extremely unstable, but as mentioned above, the servo system is structured so that no delay occurs in the comparison voltage Ef, so the stability of the servo system is not damaged. Further, in the case of a multi-point type, even if the input becomes open during the switching operation, the voltage of the filter 6 is the same as at zero equilibrium, so no malfunction occurs. 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 that the influence on instruments connected in parallel to the servo mechanism can be minimized on the input side of the instrument. It is possible to obtain characteristics equivalent to or better than when a filter is provided. Furthermore, since the servo amplifier 1 has low-pass filter characteristics as described above, 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 2 at the subsequent stage. Note that as the adder 8, an operational amplifier 0 is used as the adder 8, as shown in FIG.
P, the output ε of the servo amplifier 1 is applied to the negative phase input terminal (D) via the resistor R3, the comparison voltage Ef is applied to the positive phase input terminal (G), and the output of the operational amplifier 0P is connected to the resistor R4. If it is fed back to the negative phase input terminal (d) via
Gain adjustment can be made by selecting resistors R3 and R4. Also, in this case, operational amplifier 0P becomes a buffer amplifier, and the comparison voltage from potentiometer 4! can be extracted by converting the impedance. Note that the adder 8
A braking effect may be obtained by applying a voltage related to the rotation speed of the servo motor 3 to the servo motor 3. As explained above, according to the present invention, the output of the servo amplifier and the comparison voltage are added together and then fed back to the input side of the servo amplifier via a filter. , the configuration is such that there is no delay in the comparison voltage,
It is possible to eliminate the adverse effects of providing a filter with a large time constant in the input circuit without impairing the stability of the servo system.

[Brief explanation of the drawing]

1 and 2 are connection diagrams showing an example of a conventional servo mechanism, FIGS. 3 and 4 are connection diagrams showing an example of the servo mechanism of the present invention, and FIG. 5 is a connection diagram showing an example of the servo mechanism of the present invention. It is a connection diagram showing an example of. 1... Servo amplifier, 2... Power amplifier, 3...
Servo motor, 4... Potentiometer, 5... Instruction recording mechanism, 6... Filter, 7... Changeover switch, 8... Adder.

Claims (1)

[Claims] 1. A servo amplifier to which an input signal voltage is applied, an adder that adds the output of this servo amplifier and a comparison voltage, and the output of this adder is passed through a filter to the input side of the servo amplifier. A servo mechanism comprising means for differential feedback and means for driving a servo motor in response to the output of the servo amplifier to balance the comparison voltage with the input signal voltage.