GB1374625A - Motor control arrangement - Google Patents

Abstract

1374625 Pulse lengthening and delay circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 22 Oct 1971 [27 Oct 1970] 49140/71 Heading H3T [Also in Division H2] A brushless D.C. motor, having windings 1-4 controlled by respective transistors 16 switched by corresponding control circuits 8, 9, 13, 14, 15 responsive to a rotor-position indicator 6, 7, is provided with one or more delay circuits which generate pulses having a duration determined by the time constant(s) of the delay circuit(s) in response to the output pulses of the control circuits, the arrangement producing resultant pulses which control the transistors 16 and which are variable in phase and/or length in dependence on the time constant(s). In a first embodiment, Figs. 3 and 4 (not shown), the base of each transistor 16 is connected to a delay circuit having a differentiator and a monostable length which is added to the end of the control circuit pulse. In another embodiment Figs. 5 and 6 (not shown), the delay circuit is responsive to the outputs of two control circuits and further includes an inverting stage, so that the trigger output pulse is produced at the start of the control circuit pulse which is reduced in length by the trigger pulse. The embodiment shown in Fig. 7, has a delay circuit 31 generally similar to that of Fig. 3 (not shown) and a delay circuit 41 generally similar to that of Fig. 5 (not shown), those circuits respectively adding to and subtracting from the control circuit pulse to produce a lengthened pulse phase displaced therefrom, Fig. 8 (not shown). The time constants of the delay circuits 31, 41 may be varied by respectve signals V D , V S proportional to the motor torque and speed, which signals vary the resistance of respective transistors 40<SP>1</SP>, 40 controlling the (unreferenced) monostable trigger circuit of circuit 31 and the monostable trigger circuit 22, 23, 27, 28 of the circuit 41. The input 19 of the circuit 31 is connected to the transistor 35 of the inversion stage of the circuit 41. In a modification, Fig. 9 (not shown), this stage is omitted and both delay circuits are responsive to the start of the control circuit pulse to produce respective addition and subtraction pulses, the resultant of which controls the transistor 16. A. modification of Fig. 9 (not shown), makes the circuit 31 controllable by the circuit 41, so that the subtraction pulse is produced by the start of the control circuit pulse and the addition pulse by the end of the subtraction pulse, the former pulse being applied to the transistor 16. Typical pulse waveforms for these modifications are discussed, Fig. 10 (not shown), and it is explained how the permanent magnet brushless motor may be given torque/ speed characteristics similar to those of a D.C. shunt motor having variable field speed control. In further embodiments, Figs. 11 and 13 ,(not shown) logic elements are used to combine the pulses, and the delay circuit pulse produced by one control circuit may be combined with the output pulse of another control circuit. If the delay pulse is dependent on the motor speed, it may be arranged for the delay and control circuit pulses to overlap only at speeds above a predetermined value, Fig. 12 (not shown), whereby the motor is started at full torque and the torque/speed reationship is subsequently stabilized above this value. The use of logic elements enables the pulses to be divided into a plurality of sub-pulses, Fig. 14 (not shown).