D.C. Motor directional control

Abstract

A D.C. motor directional control in which relays switch the polarity of the D.C. voltage applied to the motor armature in order to obtain forward or reverse operation of the D.C. motor. A SCR is connected in the armature circuit to control the current of the armature circuit. A control circuit which includes a triggering circuit for the SCR is responsible for the sequential operation of the armature relay contacts and the firing of the SCR. Contacts on forward and reverse relays actuate a common relay, which in turn actuates the SCR triggering circuit. Either the forward or reverse relay must be actuated before the common relay will be actuated, therefore, the forward or reverse relay contacts in the armature circuit close before the common relay actuates the SCR triggering circuit. A delay circuit includes a capacitor connected in parallel with the forward and reverse relays. While the appropriate relay is actuated, the capacitor charges, and when the relay is deactivated, the capacitor discharges through the relay tending to hold it in an actuated state for a period of time. During this time period, the SCR commutates, shutting off the current in the armature circuit. The forward and reverse relay contacts in the armature circuit are not subject to the flow of current in the armature circuit at the time they are opening or closing and, therefore, need not be rated for make and break currents.

Dependencies are inferred from the claim text.