1,175,896. Control of stepping motors. INTERNATIONAL BUSINESS MACHINES CORP. 10 March, 1967 [28 March, 1966], No. 11271/67. Heading H2J. [Also in Division H3] A stepping motor, e.g. driving the carriage of a printer, is supplied with a predetermined number of pulses at a variable, e.g. steadily increasing, frequency. The pulses are produced by a relaxation oscillator controlled by the voltage on a capacitor which is charged at an adjustable rate (Fig. 2, not shown) and are supplied to a counter having outputs connected to A, A, B, B to sequentially switch transistors T9 ... T12 supplying the halves of motor phase windings A and B. At a predetermined count, e.g. six, two further pulses, delayed 1.6 and 2.6 ms. respectively, are sent which, due to their delay, have a braking effect on the motor. The pulses then cease and the circuit to ground is opened at transistor T13 by a "pedestal drive" signal derived from logic circuits (Fig. 1, not shown). D.C. then flows through whichever phase is energized from + 48V. to + 38V. through diode D1 or D2 to "lock" the motor. A signal is generated (at 65, Fig. 1), when the motor is running and indication is given if this is absent when it should be present.
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