Abstract: The rotor speed of a three phase induction motor is detected by a two channel pulse tachometer, which generates per revolution of the rotor 384 signals that are summed with a slip rate command signal in the first of two successive digital counters. The counters divide the 384 signals/revolutions by 192, thereby producing a four bit counter output which cycles twice per revolution of the rotor. The four bit output is decoded by a read-only memory which produces six output signals each half revolution of the rotor. The read-only output signals are applied to an inverter circuit which controls the gating of the SCR's in the lines of the stator winding of the motor. Gating circuits associated with the counters prevent undesirable simultaneous triggering of count up and down terminals, respectively, on the counters. Also balanced choke coils are employed in two of the stator winding leads between the inverter and the rectifier which supplies DC current to the inverter-controlled SCR's.

Abstract: When a stacker motor slows down before stopping or reversing, it generates an error signal the polarity of which is detected by a sensing circuit which is optically coupled to a motor reversing circuit. If the detected error signal is positive, a first set of LED's in the sensing circuit are illuminated and trigger associated photo-sensitive transistors in the reversing circuit, which in turn energize selected pairs of back-to-back SCR's to connect the lines of a polyphase power source in a "forward" drive direction to the windings of the stacker motor in question, so that the motor is driven in a forward direction. When the error signal is negative, different LED's in the sensing circuit are illuminated and energize different transistors in the reversing circuit so that the motor is driven in the opposite or reverse direction. Inhibiting devices are employed in the reversing circuit to prevent undesirable shorting out of lines upon sudden motor reversal.