Stepping motor drive circuit for bi-directional rotation

Claim 1

An improved electrical drive circuit for a reversible stepping motor of the type having a coil and stator providing a magnetic circuit for a magnetized rotor having first poles adapted to cooperate with said magnetic circuit when electrical pulses are supplied from a voltage source, said circuit having means providing pulses of predetermined polarity and frequency to said coil for pre-determined intervals to step the rotor in forward or reverse direction, said rotor having second poles adapted to lock the rotor in stable equilibrium positions between steps when the coil is not activated, such stable positions being located such that less energy is required to step the rotor forward than in reverse; the improvement in said drive circuit comprising: a switching circuit adapted to provide a reverse switching cycle comprised of a first pulse portion initiating rotation in a forward direction and a second pulse portion applied at a predetermined time during rotation so as to cause a reverse electromagnetic torque to reverse rotation and move it in the opposite direction, at least one of said pulse portions comprised of a high frequency pulse train of pulses of the same polarity of those normally used to turn the rotor in the forward direction and of sufficiently high frequency to reduce the current which would otherwise flow through said coil.