Position control system comprising a digital algebraic adder circuit

Abstract

A system for controllably driving a motor to place a movable element at a position indicated by a command signal from an external source produces, in response to a phase staggered incremental position signal pair, one and the other of two position pulse sequences at a time depending on an instantaneous angular velocity of the motor. Responsive to the command signal and the position pulses, a mode signal is produced to indicate a position control mode while a position error is within a predetermined range and otherwise a velocity control mode. Likewise, a signal is produced that represents at least one reference angular velocity and the position error during the respective modes. Responsive to the position pulses alone, gate pulses are produced either with two different pulse widths depending on the modes or with a single pulse width. During presence of each gate pulse and dependent on the sense of the instantaneous angular velocity indicated by the position pulses, a digital algebraic adder circuit calculates an algebraic sum of the reference angular velocity or the position error and a reference feedback value, which may either be memorized in the system or supplied from the source and may take two digital values depending on the modes. A digital signal representative of the sums and either the reference angular velocity or the position error during presence and absence, respectively, of the gate pulses is converted to an analog signal, which is smoothed and amplified to provide a motor drive signal.