Digital servo comprising means for controlling driving energy in response to droop

Claim 1

A digital servo system for causing displacement of a controlled member by means of a motor driven by a driving signal produced in response to input pulses and a direction command signal, said member being moved towards a commanded position identified by the instantaneous number of said input pulses accumulated in compliance with the sign specified by said direction command signal, said system comprising alarm signal means mechanically coupled to said member and responsive to said input pulses and said direction command signal for producing an alarm signal assuming a first value when the difference between the instantaneous actual position of said member and the instantaneous commanded position is within a prescribed range, said alarm signal assuming a second value when said difference falls outside of said range, wherein the improvement comprises: control signal means responsive to said alarm signal for producing a control signal containing control pulses of a predetermined pulse rate when said alarm signal assumes said first value, said control signal containing no control pulses when said alarm signal assumes said second value, reversible counter means responsive to command pulses, a sign signal, and said control signal for reversibly accumulating therein the number of said command pulses in compliance with the sign specified by said sign signal when said control signal contains no control pulses and for changing the number accumulated therein towards zero in compliance with the control pulses if contained in said control signal, thereby producing a counter output signal representative of the number accumulated therein, and driving signal means supplied with said control signal and said counter output signal for producing said Driving signal, the control pulses contained in said control signal providing said input pulses, said counter output signal providing said direction command signal by the sign of the number accumulated in said reversible counter means and also providing control on said driving signal in compliance with the absolute value of the number accumulated in said reversible counter means.