Dc motor reversing system including protective features responsive to reversing selector and to dynamic breaking current

Claim 1

In a braking and reversing system for a reversible motor having a motor winding operative to reverse the motor upon the reversal of power supplied thereto, the combination of: A. a controlled power supply including AC input terminals for the reception of AC, first and second DC output terminals, and AC to DC conversion means including controlled rectifiers for converting said AC to DC and providing an adjustable DC output at said DC output terminals; B. a selector switch including a plurality of switch sections, each of said switch sections including a plurality of positions defining run and brake positions for said motor; C. first and second of said switch sections each having first and second terminals connected to opposite sides of said motor winding, and a third terminal which is selectively connectable to either of the first and second terminals of the same switch section; D. first circuit means for connecting the first DC output terminal to the third of the first switch section; E. second circuit means for connecting the second DC output terminal to the third terminal of the second switch section; F. a discharge path connected across the third terminals of the first and second switch sections for discharging stored energy of said motor winding; said discharge path having a freewheeling unidirectional circuit portion connected across said DC output terminals and poled in the same direction as said controlled rectifiers, said discharge path including in series therein a controlled switching device; G. a braking and sensing circuit operatively connected across said motor and including a dynamic braking resistor, controlled bilateral switching means which when conductive is operable to pass dynamic braking current from said motor winding through said resistor, and brake current sensing means operable in a first mode in response to flow of dynamic braking current, and in a second mode in the absence of dynamic braking current flow; H. means for rendering said bilateral switching means conductive in response to said selector switch being moved from a run to a brake position, once rendered conductive said bilateral switching means maintaining conduction until the motor substantially stops and braking current drops to substantially zero regardless of the position of said selector switch; I. means for preventing said power supply from supplying an output in response to said selector switch being moved from a run to a brake position and in response to operation of the brake current sensing means in its first mode; and J. means for rendering said controlled switching device nonconductive in response to the selector switch being moved from a run to a brake position and in response to operation of the brake current sensing means in its first mode.