Patent GB-1388573-A (GB)
Title: Motor apparatus
IPC: H02P6/32
Filed: 1972-02-08
Abstract: 1388573 Control of brushless motors SONY CORP 8 Feb 1972 [13 Feb 1971] 5866/72 Heading H2J [Also in Divisions G3 and H3] A control system for a brushless motor having windings 2a, 2b, 2c fed with full-wave rectified current through respective pairs of silicon controlled rectifiers 4a, 4a<SP>1</SP>; 4b, 46<SP>1</SP>; 4c, 4c<SP>1</SP> comprises a permanent magnet 5 coupled to the rotor 1 and controlling saturable transformers 6a, 6b, 6c to cause each to pass high frequency firing signals to respective rectifier pairs 4a, 4a<SP>1</SP>; 4b, 4b<SP>1</SP>; 4c, 4c<SP>1</SP> for a predetermined period of each rotor rotation, the rotor also being coupled to a tachometer 20 whose output signal is compared in a circuit 18 with a desired speed reference signal to produce an error signal for varying the firing point of each rectifier pair. Each saturable transformer, such'as 6a in Fig. 2, is adjacent to a yoke 12 carrying a bias coil 13 responsive to the speed error signal and comprises portions 8a, 8b responsive to the magnetic field of the magnet 5 to cause portions 9a, 9b to saturate and so transfer high frequency signals from winding 10a to 11a for the predetermined period, which is also controlled by the error signal to determine the nature of the motor torque, namely accelerating or braking. As shown in Fig. 4, the actual and reference speed signals are applied to a differential amplifier circuit 18, whose output feeds a diode bridge 19 supplying one winding 22a of a modulator 15 having a second winding 22b fed with a sawtooth signal from an oscillator 17. Modulator 15 is similar in construction and operation to the arrangement shown in Fig. 2 and has a saturable core 23 carrying an input winding connected to a high frequency oscillator 16 and an output winding supplying through amplifier 14 the windings 10a, 10b, 10c of the transformers 6a, 6b, 6c. The flux produced by windings 22a, 22b is combined, Fig. 7 (not shown), to periodically saturate the core 23 and so supply blocks of high frequency signals to the amplifier 14, the width of the blocks being dependent on the value of the error signal, Figs. 6A, 6B and 6C (not shown), whereby the start of each block relative to each half cycle of the A.C. supplied from transformer 3 to the rectifiers is varied, Fig. 6D (not shown). Hence the firing point of each rectifier pair is varied with respect to the rectified half cycles supplied during the predetermined period, whereby the value of the motor torque is varied with the value of the error signal. The latter is also fed to a polarity-determining circuit 24 controlling a bias source 25 for the coils 13 of the yokes 12 of transformers 6a, 6b, 6c, whereby a positive or negative bias is applied to the coils according to whether the speed is below or above the reference value, the positive bias causing the windings to be energized in a sequence 2a, 2b, 2c to produce an accelerating torque and the negative bias producing a 180 degree phase shift of the predetermined period for each transformer 6a, 6b, 6c, Fig. 3 (not shown), whereby the windings are energized in a sequence 2a, 2b, 2c to produce a braking torque. The direction of motor rotation may be reversed by use of the 180 degree phase shift of the predetermined period, typical waveforms for both directions being discussed, Figs. 5A ... 5I (not shown).