Abstract: The direction of rotation of a three-phase voltage is determined by simultaneous reading of counters triggered by the respective phase zero crossings. Such determination is used in an AC motor drive to dispense of using a tachometer.

Abstract: A synchronous motor drive includes an inverter gating control system using three counters wherein two counters respond to 180.degree. apart zero crossings for providing units of time in terms of clock units, and the third counter is at a computed time interval preset with a count to be counted down to derive the remaining time which is to elapse until a predetermined firing angle is reached, at which time firing of the thyristor of the inverter is triggered.

Abstract: In accordance with the present invention, a single line-frequency sync signal is used to derive cosine-crossover type gating angle reference waves, each with additional phase shifting accounting for phase shifts introduced by the system, such as the power transformers associated with the several thyristors in the sequence. A common variable voltage control signal and comparator are used to apply the various gating signals to the thyristor multiplexer and driver circuits. A plurality of switches controlled by the firing logic circuit establishes the order of selection between the cosine reference waves to be generated.

Abstract: The invention relates to process control in general and to numerical control machining in particular. A programmable digital controller is associated with a digital motion control unit in which are stored numerical data for point-to-point operation of a machine tool, for instance a grinder. The motion control unit is of the incremental type and generates command pulses which are applied to a stepping motor. Numerical data are stored defining desired displacement, velocity and sign of travel, and dress compensation. A feedback loop with the machine tool provides corrective pulses when the command pulses sent are not in exact relation with the increments of displacement effectively imparted on the tool. The programmable controller can be coupled to a plurality of motion control unit controlling one or more machine tools, or axes, and it is performing sequence control in relation to industrial process as well.