Patent GB-1184624-A (GB)
Title: Electric Motor Drive Unit.
IPC: H02K29/10
Filed: 1968-09-12
Abstract: 1,184,624. Motor driving arrangements; protection systems. BENDIX CORP. 12 Sept., 1968 [26 Sept., 1967], No. 43418/68. Headings H2A and H2K. [Also in Division F2] A drive unit comprises an electromagnetic motor and an epicyclic gear where the armature of the motor is attached to a ring gear which is toothed on its internal and external periphery and eccentrically mounted to co-operate with an output member and stationary member respectively. The armature is rotated by sequential excitation of electromagnets arranged concentric with the stator. Construction.-Stator 14 comprises a laminated core with salient poles each wound with an individual coil C1-C16 and energized in a sequence controlled by light sensitive SCR's, S1-S4, which are mounted around and illuminated through an aperture in a drum driven from the output shaft 24 of the unit through step-up gearing 46, 48. The stator assembly also includes stationary members 20 which have internal teeth at 22 co-operating with outer teeth 42 on ring gear 34 which is attached to armature 18 of the motor. Output member 24 has external teeth 30 which cooperate with inner teeth 40 on ring gear 34. Stator 40, stationary members 20 and output member 24 are concentrically mounted about axis 32 while ring gear 34 and armature 18 are concentrically mounted about axis 38, displaced from axis 32, and are free to move radially when rotated in bearings 44. The ring gear has less teeth 42 than the stationary member and more teeth 40 than the output member and on rotation meshes at diametrically opposite points with these co-operating members. Circuit operation.-The coils C1-C16 are connected in groups of four with one coil from each 90 degree sector of the stator present in each group and, for reversible operation, each light sensitive SCR is connected to two power switching trigger circuits T in each respective group. The supply to each group of coils 75-78 passes through a current limiting circuit 72 which can be controlled by current control circuit 74. In operation when light sensitive SCR, S1 is illuminated, the trigger circuit T associated with the SCR in the circuit of C3 or C15 will be made conductive depending on whether the directional control associated with each trigger circuit is set for clockwise or counter-clockwise rotation. The aperture in the light shield is large enough for four adjacent rectifiers to be illuminated at the same time, thus, as the screen rotates, the next four coils are energized. The oscillator 66 supplies a voltage, having a period shorter than the shortest " on time " of any coil, to the cathode of the light sensitive SCR's so that they switch off when not illuminated. Normal commutating capacitors and diodes are provided to ensure the coil switches are turned off correctly. The current control 74 and limiting stage 72, Figures 8 and 9 (not shown), provides a semiconductor switch in series with the supply, which semi-conductor is made non-conductive when the current exceeds a predetermined level and after a delay imposed by an RC network is again made conductive. The automatic control can be over-ridden by the network in stage 74 which can render the above semi-conductor non-conductive in accordance with the setting of a potentiometer to control the speed of the motor.