Braun, Leopold., Hamburg, Gary M., and Braun, Leopold.
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A variable reluctance motor wound for two-phase excitation is excited with single phase pulses, whereby the de-energization of one phase coil aids in the energization of the succeeding (and preceding) phase coil, in which a phase coil that is about to be de-energized is energized for a short period with maximum excitation energy power in order that the decay from that maximum power level, upon advance of the stepping motor, induces, by transformer action, an aiding voltage in the next succeeding phase coil so as to increase the speed of excitation of that next succeeding phase coil.
A stepping motor is driven with extended pulses producing an effective excitation intermediate to the single phase and the dual phase operations. The unique drive circuit creates a series of drive pulses for each motor phase so that each pulse slightly overlaps the drive pulse of the next adjacent phase. Thus, since each previous phase is still providing torque while the current in the next phase is being built up, the torque characteristics are improved, and the extended pulses are terminated before the subsequent phase is energized so that excessive power consumption is avoided. In closed loop systems, a fixed duration overlap provides the improved speed-torque characteristic at high speeds where the overlap is a large percentage of the drive pulse, while at lower speeds (such as when the motor is accelerating) where power consumption is greatest, the overlap is a smaller percentage of the drive pulse hence minimizing the increase in power consumption. This type of operation maximizes slew speed while conserving power consumption at low speeds. In open loop systems, using extended drive pulses increases the torque over that provided by single phase excitation, and the duration of the overlap may be adjusted so that large overlaps occur only where the torque needs are greatest (at times of acceleration, for example) while small overlaps occur where torque requirements are low (during constant speed operation, for example), thus minimizing the total overall power consumption.