Patent GB-1477255-A (GB)
Title: Stepping motor drive circuit
IPC: H02P8/16
Filed: 1975-06-30
Abstract: 1477255 Control of stepping motors QUME CORP 30 June 1975 [5 July 1974] 27599/75 Heading H2J Apparatus for supplying a relatively high voltage and a relatively low voltage to a plurality of associated devices, e.g. the phase windings of a multi-phase stepping motor, comprises a control signal generator 16 for generating a mode control signal and a plurality of pairs of polarity control signals, and a source selector 13 having a plurality of control signal inputs individually coupled to different ones of control signals from the generator, a pair of voltage inputs respectively coupled to a relatively high voltage source 12 and a relatively low voltage source 14, and a plurality of pairs of voltage outputs 15a-15n for coupling said high voltage source or said low voltage source to the outputs in dependence upon the mode control signal, the voltage polarity on the outputs being determined by the polarity control signals. In the described arrangement, the high voltage source is coupled in the stepping mode of the motor and the low voltage source is coupled in the rest mode. The control signal generator 16, Fig. 2 (not shown), provides pairs of polarity control signals in which the signals in each pair are complementary and the signals of adjacent pairs are phase displaced by a fixed amount, e.g. 90 degrees. The mode control signal is a two level signal which is high in the stepping mode and low in the rest mode. In Fig. 4, which shows the source selector 13, the phase windings 11a and 11b of a two-phase stepping motor are shown. The winding 11a is connected in circuit with four transistors 50, 51, 65, 70 as shown, the bases of those transistors being connected to the outputs of respective inverting AND gates 53, 55, 67, 72 which receive the FA, FA and mode HOLD control signals as shown. The winding 11b is connected in an identical circuit, control signals FB and FB being applied and being phase displaced by 90 degrees with respect to the signals FA and FB. With FA high, FA low and mode signal in the stepping mode (high), transistors 50 and 70 and switched on and current flows from the voltage source V H , through transistor 50, winding 11a from left to right and transistor 70 to ground. With FA low and FA high, transistors 51 and 65 are switched on and current flows in the opposite direction through the winding 11a. When mode signal goes low (rest mode), if FA is high and FA is low, transistor 70 is rendered conductive and current flows from low voltage source V L , through adjustable resistor 60, diode 57, winding 11a and transistor 70 to ground. If FA is low and FA is high, transistor 65 is rendered conductive and current flows in the opposite direction through winding 11a via adjustable resistor 61, diode 59 and transistor 65 to ground. The winding 11b is energized in the same manner, but phase displaced 90 degrees from that of winding 11a. In some applications, the mode control signal may comprise a periodic pulse train consisting of a plurality of uniformly spaced pulses of substantially identical width in order to reduce the average current through the windings.