Dc servomotor system

Abstract

An automatic motion or position control DC servomotor system in which a load-driving axis driven by a DC motor to be controlled in one rotary mechanism is rotated synchronously with, or following the rotation of, a reference axis manually operated or driven by another DC motor. The system comprises a position signal generator producing first sine- and cosine-wave signals corresponding to an angle of rotation of the controlled load-driving axis; a command signal generator producing second sine- and cosine-wave signals corresponding to an angle of rotation of the reference axis; an arithmetic unit processing the first and second sine- and cosine-wave signals and providing a sine-wave feedback voltage output signal; and a driver circuit amplifying the feedback voltage signal and providing a thus amplified signal to the DC motor driving the load-driving axis. When the reference axis is driven by another DC motor, the command signal generator may be a second position signal generator. The command signal and position signal generators each consists of a combination which preferably comprises a sine-cosine potentiometer. The DC servomotor system is suitably applicable to a sewing machine in such manner that the rotating hook shaft is driven by a first DC motor and the arm shaft by a second DC motor, the first DC motor being controlled synchronously with the second one under closed-loop feedback control as stated above.