Speed control for d.c. motor

Claim 1

A speed control system for a d.c. motor comprising an amplifier (1) which, is depending on whether the sign of a difference voltage between a command voltage (Ei) and a negatively fedback voltage corresponding to the speed of the motor (4) is positive or negative, delivers a positively or negatively saturated output voltage (Ii) for controlling the armature current of the motor (4), the amplitude of said saturated voltage (Ii) being adjustable to a desired value, a proportional-integrating circuit (2) which receives a difference voltage between said output voltage (Iiand a voltage (Io) corresponding to the actual armature current of the motor (4) as its input, a power amplifier (3) which is formed by a chopper circuit operated with an operational period smaller than those corresponding to mechanical time constants of the motor portion, each operational period of said chopper circuit comprising a positive pulse and negative pulse, the relative durations of which are controlled by the output of said proportionalintegrating circuit (2) to supply an amplified armature current for the motor (4), and a gate circuit comprising a limiter (141), an upper limit discriminator (142), and a lower limit discriminator (143), all connected in parallel whereby the controllable range of the output voltage of the chopper circuit is further expanded stepwisely.