Servo systems

Abstract

A servo control system comprising, in a feedback loop, means for providing an error signal representing the difference between desired and actual conditions of a controlled system, and means responsive to said error signal to produce a control signal for the controlled system; the control system also comprising means for injecting a predetermined disturbance signal into the loop, and means responsive to a comparison of said disturbance signal and a loop response signal for varying gain in said loop.

What we claim is: 
     
       1. A servo control system comprising a feedback loop including means for supplying an error signal representing the difference between actual and desired conditions of a controlled system, means responsive to the error signal to produce a control signal for said controlled system, means for applying to the feedback loop discrete signals each comprising a first excursion of one polarity providing a disturbance signal and a second excursion of opposite polarity to substantially cancel the effects of the disturbance signal on the system, means for extracting from the loop a loop response signal, comparison means for comparing the disturbance signal and the loop response signal and means responsive to the output of the comparison means to vary the gain in the feedback loop. 
     
     
       2. A system according to claim 1, wherein said disturbance signal is applied at regular intervals, and further comprising means, connected between the comparing means and the gain varying means, for sampling the means for comparing at instants related to those intervals. 
     
     
       3. A system according to claim 2, further including means for supplying a pulse train, and wherein the means for applying discrete signals includes means for differentiating said supplied pulses so as to provide a bipolar signal having said first excursion of one polarity and said second excursion of opposite polarity. 
     
     
       4. A system according to claim 3 wherein said means for differentiating said supplied pulses is a capacitor to said comparison means for applying thereto said signals of one polarity. 
     
     
       5. A system according to claim 4 wherein said connecting means includes a gating circuit operative to close first and second input paths to said comparitor, said gating circuit being operative in response to the pulses of said pulse train. 
     
     
       6. A system according to claim 5 wherein said first input path establishes the connection between said capacitor and a first input of said comparison means and said second input path establishes a connection between the point in said loop where the loop response signal is extracted and a second input of said comparison means. 
     
     
       7. A system according to claim 3 wherein the gain varying means includes an integrator coupled to the output of said comparison means and an amplifier controlled by the output of the integrator. 
     
     
       8. A system according to claim 7 wherein said control signal producing means includes an amplifier. 
     
     
       9. A method of controlling a servo loop, comprising the steps of injecting a discrete temporary disturbance signal of predetermined short duration into a loop output control signal, said temporary disturbance signal corresponding to the positive excursion of a differentiated pulse signal of predetermined rate and duration synchronously detecting a corresponding loop response signal comparing the disturbance signal and a loop response signal extracted from the loop and varying overall loop gain in accordance with an output signal derived from a comparison between said disturbance signal and the loop response signal.