Patent GB-1068972-A (GB)
Title: Improvements in or relating to self regulating stepping motors
IPC: H02K37/04
Filed: 1966-01-04
Abstract: 1,068,972. Electric selective signalling. INTERNATIONAL BUSINESS MACHINES CORPORATION. Jan. 4, 1966 [Jan. 6, 1965], No. 258/66. Heading G4H. A stepping motor control system produces pulses having parameters dependent on the rotational speed of the motor rotor and energizes the motor windings in response to these pulses. As described, four stator windings (I, II, III, IV) can be energized in pairs to position the rotor (34), which has five pole positions, in any one of 20 positions. A disc (50) on the rotor shaft has a ring of 20 slots at 18 degree intervals sensed by two photo-cells (P1, P2) 9 degrees apart, and a ring of five slots each 36 degrees long and spaced with 36 degree gaps between them. The latter slots are sensed by two photo-cells (P3, P4) 18 degrees apart. When a go flip-flop (106) is set, the outputs of the second pair of photo-cells (P3, P4) are passed by AND gates (98, 100), which received them in true or inverted (102, 104) form depending on the state of a direction flip-flop (116). The outputs of the AND gates (98, 100) are passed directly and through inverters (112, 114) to the stator windings, to accelerate the rotor in the direction specified by the direction flip-flop (116). The number of steps required is preset in a register (131) and compared (126) with a count (124) of the pulses from the first two photo-cells (P1, P2). Equality indicates the mid-point and causes the direction flip-flop (116) to be switched, so that the rotor now starts to decelerate though continuing to rotate in the same direction due to inertia. At the desired end-point, a comparison (134) between the register (131) and a count (132) of the pulses from the first photo-cell (P1) will indicate equality, producing an end-point signal which resets the go flip-flop (106) thereby disabling the AND gates mentioned (98, 100) and energizing the stators with restore-hold signals derived from the second pair of photo-cells (P3, P4, 144, 140, 142) instead. Ideally the rotor will be stationary when the end-point signal is produced, having been decelerated to rest arid not yet having started to move in the opposite direction. In case friction or load conditions cause the rotor to come to rest before the endpoint, the length of the pulses from the first photo-cell (P1) is monitored (150) and at rest is sufficient to cause an undershoot flip-flop (158) to be set. This causes each subsequent pulse from the first photo-cell (P1) to switch the direction flip-flop (116) causing acceleration and deceleration alternately in successive steps until the end-point is reached when the endpoint signal appears as before. The go flipflop (106) through a delay (156) prevents the undershoot flip-flop (158) from being set as the rotor starts from rest at the beginning of operation. The alternate acceleration' and deceleration during undershoot correction may occur at halfstep intervals instead, by using the outputs from both the first two photo-cells (P1, P2) to switch the direction flip-flop (116). This reduces vibration otherwise caused at the end-point after an odd number of undershoot correction steps. Overshoot circuitry similar to the undershoot circuitry may be provided, or braking means. If the number of steps required is so large that the rotor reaches maximum velocity before the mid-point, the circuitry for producing the midpoint indication may be disabled and the deceleration started a predetermined fixed number of steps before the desired end-point.