Feedback control system for linear position transducer

Apparatus for electronically correcting errors in the position information output signals from a pair of photodetectors used in a linear motion position transducer having light parameters subject to variation, the output signals from one of said photodetectors being phase displaced from the output signals from the other of said photodetectors by a phase angle .phi. in the range 0<.phi.<180.degree., said apparatus comprising:

• a light source having a selectively variable energy source;
• a light modulating shutter mechanism interposed between said light source and said photodetector pair;
• a summing circuit coupled to said photodetectors for continuously algebraically summing the instantaneous values of said photodetector output signals to produce a combined variable amplitude signal therefrom, said summing circuit including a pair of buffer amplifiers each having an input coupled to the output of a different one of said photodetectors, and a summing amplifier having an input connected to said buffer amplifier outputs and an output carrying said combined signal;
• an error signal generation circuit for sampling the peak positive value of said combined signal and for generating an error signal representative of the difference between said peak value and a reference signal having a preselected value representative of a desired value of said light parameters, said circuit having an input connected to said summing circuit output and an output carrying said error signal;
• and
• a correction signal generation circuit for applying a correction signal to said light source input proportional to said error signal to reduce said error signal to zero, said circuit having an input connected to said error signal circuit output and an output connected to said light source input.