JPS5854402B2 - 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, in a servo mechanism, as shown in FIG. 1, a deviation between an input signal voltage Ei and a comparison voltage Ef is amplified by a servo amplifier 1, and then a servo motor 3 is driven via a power amplifier 2.
The brush of the slide resistance Rs of the potentiometer 4 that generates the comparison voltage Ef is displaced to bring the deviation to zero.

The voltage dividing circuit consisting of resistors R3 and R4 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.

In a servo mechanism having such a configuration, a filter circuit 6 (a two-stage CR open circuit is illustrated in the figure) is provided in the input circuit to attenuate commercial frequency noise superimposed on the input signal. There is.

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

By the way, if the input circuit has a filter circuit with a large time constant, it has the disadvantage that the input impedance decreases at high frequencies.It also has the disadvantage that the input circuit is restricted by the withstand voltage, leakage current, etc. of the capacitor of the filter circuit. .

Further, when the servo mechanism is configured as a multi-point type and the input signals are sequentially switched using a changeover switch, there is a situation where the input becomes open during the process of the switching operation.

In this state, the input resistance seen from the servo amplifier to the input circuit side changes significantly, so the capacitor of the filter circuit is charged with an abnormal voltage.

This phenomenon becomes particularly noticeable when a direct-coupled DC amplifier is used as the servo amplifier, depending on its bias current.

Even after switching to the next input, this charging voltage maintains the voltage determined by the time constant of the filter circuit, 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 capacitor of the filter circuit 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 present invention adds the output of the servo amplifier and the comparison voltage using an adder, and then returns the output to the input side of the servo amplifier.
By providing the adder with filter characteristics, a new servo mechanism without the above-mentioned drawback Φ is realized.

That is, in the present invention, as shown in the embodiment shown in FIG.
servo amplifier 1 which is divided by resistors R and R6 and applied to
The output ε of the servo amplifier 1 is added to the comparison voltage Ef from the potentiometer 4 (non-inverting input terminal) and fed back to the input side of the servo amplifier 1 so as to be differential with the input signal Ei. , connect the output terminals of OP*OP to resistors R7 and R8.
and connected to the reference point via capacitor q, and resistor R7
, R8 is connected to the input terminal (Y) of OP via a resistor R0 to give the adder 7 filter characteristics.

According to the present invention configured in this way, since the gain of the servo amplifier 1 is sufficiently large, the transfer function G(S) between the input signal voltage Ei(S) and the output ε(S) of the servo amplifier 1 is as follows. A good noise attenuation ratio can be obtained with a small time constant for commercial frequency noise superimposed on the input signal Ei.

Further, the input impedance of the servo amplifier 1 is not lowered by the adder 7, and has a high input impedance up to a relatively high frequency.

In addition, in the case of a multi-point type, even if the human power becomes open during the switching operation, the output of the adder 1 does not change at all at zero equilibrium, so no malfunction occurs.

Furthermore, when the input signal changes or when the input is switched, the capacitor C3
Since the charging current that flows transiently can be reduced and the time constant can be shortened, the effect on instruments connected in parallel to the servo mechanism can be reduced to a level that is equal to or better than when a filter is installed at the input of each instrument. Obtainable.

On the other hand, the transfer function Gf between the comparison voltage Ef and the output ε of the servo amplifier 1 can be set to a leading characteristic by selecting the resistance value such that Rather, the damping characteristics can be improved.

In the above description, the capacitor C3 is connected to the reference point, but if a small polar capacitor is used as C3, it may be connected to an appropriate power source.

Further, the filter characteristics of the adder 7 are not limited to those in the embodiment, and can be configured to have desired characteristics as necessary.

Furthermore, if the output of the adder 7 is configured to be fed back to the input side of the servo amplifier 1 via the filter circuit 6 as shown in FIG. 3, the noise attenuation ratio can be further improved and the damping characteristics can be improved. can.

As explained above, in the present invention, the output of the servo amplifier and the comparison voltage are added by the adder and fed back to the input side of the servo amplifier, and the adder has filter characteristics, so the servo system The adverse effects of providing a filter in the input circuit can be removed without compromising stability.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram showing an example of a conventional servo mechanism, Fig. 2 is a connection diagram showing an embodiment of the servo mechanism of the present invention, and Fig. 3 is a connection diagram showing another embodiment of the servo mechanism of the present invention. It is. 1... Servo amplifier, 2... Power amplifier, 3... Servo motor, 4... Potentiometer, 5... Instruction recording mechanism, 6...
... Filter circuit, 7 ... Adder, OP ... Operational amplifier.

Claims (1)

[Claims] 1. A servo amplifier to which a human input signal voltage is applied, an operational amplifier to which the output of this servo amplifier is applied to an inverting input terminal, and a comparison voltage is applied to a non-inverting input terminal, and a connection between the output terminal of this operational amplifier and a reference point. It has a series circuit of connected first and second resistors and a capacitor, and a resistor that feeds back the voltage at the connection point of the first and second resistors of this series circuit to the inverting input terminal of the operational amplifier, and has filter characteristics. a circuit for outputting the difference between the output of the servo amplifier and the previous comparison voltage; means for differentially applying the output voltage of the circuit to the input side of the servo amplifier with respect to the input signal voltage; and means for driving a servo motor accordingly to balance the comparison voltage with the input signal voltage.