GB1154141A - Improvements in and relating to Electro-Motive Apparatus. - Google Patents

Abstract

1,154,141. Control of stepping motors. NATIONAL RESEARCH DEVELOPMENT CORP. 9 Jan., 1967 [10 Jan., 1966], No. 1131/66. Heading H2J. A servo system comprises a stepping motor 13 and has error indicator 23 whose output represents the magnitude and sense of a difference in the angular positions of shafts 21, 24. Signals from a device 17, which detects the angular position of rotor 11, are combined with signals from the indicator 23 whereby field coils 14, 15, 16, are energized in sequence to turn the rotor in a direction tending to reduce the error. A signal from branch A of the detector 17 is amplified, rectified, and the resultant pulses are then fed to a bi-stable device 34 producing signals of opposite sign which tend to drive the rotor in one direction or the other. A servo amplifier 35 receives the error signal from the indicator 23 and is also connected to a sawtooth generator 36, the outputs on leads 47, 46, representing the sum and difference respectively of the error and sawtooth signals. These resultant signals are fed through resistors 37, 38, to diodes 39, 40, which also receive the signals from the device 34. The combined signals are isolated by the diodes, amplified, and then applied to trigger circuit 44 having a constant output when its input exceeds a given level, but providing no output below that level. During time intervals when the circuit 44 is effective, amplifier 18 energizes the field coil 14. The operation of branches B, C, of the detector 17 and similar to that of the branch A. When the sense of the servo error signal changes, the signals on lines 46, 47, are interchanged to reverse the motor. As the error signal increases in magnitude, the duration of the pulses passed by the trigger circuit 44 is increased. In a modification, the generator 36 may be replaced by a sine wave generator. The detector 17 may comprise a metal disc which is mounted on shaft 12 and has an asymmetric shape with regard to its axis of rotation. High frequency currents are produced in the disc by means of a fixed ring which is supplied from a H.F. source and is capacitively coupled with the disc. As the disc is rotated, pulses are cyclically induced in metal strips which are circumferentially spaced around the axis of rotation. In an alternative form of detector 17, the shaft 12 carries a flat ring which is divided into magnetic and non-magnetic parts. Iron cores carrying coils are spaced symmetrically around the ring, each core having a central coil which is fed with alternating-current, and two outer coils which are connected in opposition.