Abstract: A low cost servo operated digital positioning system which utilizes a phase shift control circuit in combination with an encoder and servo circuit for driving a moveable element. The encoder generates a pair of signals A which may be equivalent to a sine signal A and a cosine signal A. The phase shift circuit multiplies signals from the encoder by a sine of a demand signal B and by a cosine of the demand signal B and produces a sine (A+B) signal and a cosine (A+B) signal. These sine and cosine shift signals are introduced into a servo circuit for control of a moveable element. By phase shifting these signals it is possible to substantially increase the overall number of positions to which a moveable member may be moved and thereby substantially increase the overall accuracy of a positioning system.

Abstract: Digital error correcting circuitry is disclosed which processes two analog output signals from an incremental position optical encoder to correct for both offset and amplitude errors. The peak amplitude values of the analog signals are stored in a digital storage register and are used to calculate bias signals of the proper polarity and amplitude to cancel the offset errors in each of the encoder signals. The peak amplitude values are also used to generate an amplitude correction factor which is applied to one of the encoder signals to correct the peak-to-peak amplitude of that signal so that it is equal to the peak-to-peak amplitude of the other encoder signal.