Patent GB-1366904-A (GB)
Title: Circuit for driving an electric pulse motor
IPC: H02P8/12
Filed: 1971-10-08
Abstract: 1366904 Control of stepping motors FUJITSU Ltd 8 Oct 1971 [19 Oct 1970 20 Oct 1970 (2)] 46922/71 Heading H2J [Also in Division G3] A control circuit for a stepping motor having exciting coils 2 ... 6 supplied from a D.C. source VB comprises respective driving circuits 7 ... 11 for each coil and an exciting control circuit 19 fed with positive or negative signals at terminals CW, CCW and providing output signals a ... e to control the driving circuits 7 ... 11, each of which includes means to alternately connect and disconnect the coil to and from the source VB during the period of application of the control signal to the driving circuit and means to ensure that the time for which the coil is first supplied with D.C. voltage is longer than the time of the or each subsequent supply of D.C. to the coil. In a typical operation for the period of a control signal, the first supply pulse substantially corresponds to a step operation and the subsequent pulses to a stop operation and the first pulse has an amplitude and period greater than the subsequent pulses, which are controlled so that their mean value is maintained constant, Fig. 1 (not shown). This method of supplying the motor prevents hunting arising from the intrinsic vibration of the motor. Each driving circuit, for example 7, includes a transistor switch 23, a current detecting resistance 24, an integrating circuit 25 and a gate 21, the time constant of the circuit 25 being chosen so that, after a comparatively long time of closure of the switch 23, the current is interrupted at a predetermined value by the switch which is then cycled to maintain the current at the predetermined mean value. The circuit diagram of the basic driving circuit is described, Fig. 3 (not shown), together with the operation for two successive control signal periods, Fig. 4 (not shown). Figure 11 shows a modification of the basic driving circuit, wherein application of the voltage VB before the appearance of a control signal at terminal 26, causes capacitors 50, 60 and 61 to charge and transistor 33 to become conductive. Application of the control signal turns transistors 29, 33 and 36, 38 respectively on, off and on to produce current in the motor coil 2 and discharge of capacitors 50, 60 and 61. Subsequent conduction of a diode 63 turns transistors 33 and 36, 38 respectively on and off and causes capacitors 50, 60 to charge. Current pulses of constant mean value are then produced by cycles, each of which includes the charging of capacitor 60 via 61, 63 by the voltage surge following the first current interruption, discharge of circuit 60, 64, switching of transistor 33, 36, 38, discharge of capacitor 61 and further switching of transistors 33, 36, 38. The current detecting resistor 59 may be replaced or augmented by a varistor or a thermistor. Typical voltage and current waveforms for the circuit are described, Fig. 12 (not shown). Variation of the mean current with the frequency of the control signal is discussed, Fig. 9 (not shown), and a modification is described, Fig. 10 (not shown), wherein a voltage inversely proportional to the frequency is produced and used to modify the feedback from the current detecting resistor and hence the mean value of the current. Various forms of the spark killer circuits 12...16 of Fig. 2A are described, Figs. 13, 15, 18 and 19 (not shown), together with a discussion of the variation of the spark voltage with the exciting current, Fig. 14 (not shown).