Patent GB-1502676-A (GB)
Title: Stepping motor control system
IPC: H02P8/00
Filed: 1975-04-28
Abstract: 1502676 Control of stepping motors INTERNATIONAL BUSINESS MACHINES CORP 28 April 1975 [2 May 1974] 17466/75 Heading H2J [Also in Division G3] In a stepping motor control system a data store stores a plurality of delay times which are accessed in a predetermined manner in timed relationship with feedback pulses derived from the rotor movement so that the motor windings are energized according to these pulses delayed by associated accessed delay times. As shown in Fig. 1, a motor 1 has four bifilar windings and a time disc 3 driven by the rotor and associated with a pulse former 5 to provide the feedback pulses to a switching circuit 7. This circuit receives command signals at 8, addresses a motion data table 11, which stores the delay times, and provides phase switching signals a and b (90 degrees out of phase) in accordance with the delay times, for application to the driver circuits 17A and 17B and to the driver circuits 18A and 18B via inverters 19A and 19B. Chopped current limiters 12A and 12B and controls 13A and 13B are provided to limit the current flow in the windings dependent upon the magnitude of current flow in the drivers or upon the signal DR and DE present on lines 15 and 16. Signal DR requires a high winding current for high speed running and signal DE requires a low holding current in the windings for holding the rotor in its set position. As described, the accessed delay times are entered into downward counting counters in the circuit 7, the counters being operated by clock pulses and when the count reaches zero a motor advance pulse is produced from which are derived the signals a and b. The drive circuits are described with reference to Figs. 9-11 (not shown) and one form of chopped current limiter is described with reference to Fig. 13 (not shown). In an alternative embodiment, Fig. 14 (not shown), each winding is formed by two coils which can be connected to the drive circuit singly, in series or in parallel. This is designed such that the decrease of current in the windings and thus the decrease of motor torque with rising frequency of stepping of the motor is reduced so that the torque is substantially constant over a large range of speed. The control system and delay times can be such as to provide a nominal acceleration curve, a nominal steady speed, and a nominal deceleration curve, so that operation over a selected number of steps will involve an acceleration along part of the acceleration curve and a deceleration along part of the deceleration curve with possibly an intermediate period at the steady speed. This may be under control of a microprogram. Another possibility is to provide in the data store sets of delay times, each set being appropriate for a particular process of motion, e.g. starting over 5 steps, acceleration over 10 steps, motion at a steady speed over 20 steps, deceleration over 8 steps and stopping over 2 steps. Again this may be vunder control of a microprogram. The delay times may be sufficiently long that a motor advance pulses derived from a feedback pulse may overlap one or two succeeding feedback pulses.