Patent GB-916592-A (GB)
Title: Improvements in or relating to step-by-step electric motors
IPC: H02K7/065
Filed: 1959-05-28
Abstract: 916,592. Rotary distributers. HARRIS, J. T. (Kohlhageu, W.). May 28, 1959, No. 18258/59. Class 38 (5). [Also in Groups XVIII, XXVI and XXXV] A commutation device for an electric motor comprises a conductive plate 68, Fig. 5, supported by pillars 70 from the plate 18 and carrying an insulation plate 64 to which are fixed three wire brushes 52 which co-operate with a commutator 54 mounted on a shaft 100 and comprising two conductive elements 88, an insulating core 90, and end pieces 92, 94. The inner end of a spiral spring 104, Fig. 5, is fixed to a collet on the rotor shaft 42 and its outer end is anchored to a bracket 112 secured to the end piece 94 of the commutator. The shaft 100 is the sweep seconds shaft of a timepiece movement controlled by a pin pallet lever escapement. The arrangement is such that the rotor is periodically moved 60 degrees to further wind the preloaded spring 104 and then stops; the spring 104 unwinds to drive the escapement controlled train and the commutator which after a predetermined angular rotation changes the motor field connections to cause the rotor to advance 60 degrees and again wind the spring 104. A stop-arm determines the rest position of the rotor on current failure. Instead of the commutator comprising three stationary brushes and two rotating commutator segments it may comprise three stationary commutator segments and two brushes mounted on a rotary insulated disc, Fig. 9 (not shown). The rotor is advanced in 30 degree steps instead of 60 degree steps if the commutation device is constructed to provide alternating overlapping and non-overlapping commutation by having the insulating segments 102, Fig. 12, extend over 30 degrees and the conducting segments 88 extending over 130 degrees. Where the brushes are on a rotating member and the commutator segments are stationary this alternating overlapping and non-overlapping action may be obtained by forming the brushes as shown in Fig. 18 with projections spaced by 30 degrees. The commutator segments 88 may be overlapped, Fig. 24, to produce the same effect. The spring 104 is wholly or in part of bimetallic construction so as to maintain a uniform torque output despite temperature changes. Temperature compensation may be obtained by a bimetallic arm 198, Fig. 29, fixed to a collet 106b and having a depending curb pin 202 or being connected to the inner end of the spring 104b. A second spiral spring 210, Fig. 31, fixed to a collet 218 having a lost motion connection with the collet 106d of the spring 104d may be used for temperature compensation. Instead of temperature compensation being effected by influencing the action of the spring 104d a bimetallic arm 230, Fig. 35, may be so disposed as to act on the rotary plate 64f carrying the commutator brushes. There may be a lost motion connection between the arm 230 and the plate 64f so that compensation is only effected when the temperature rises above and/or falls below a particular value. To prevent return movement of the rotor 14 upon current failure due to dirt particles &c., a spring-loaded detent 194, Fig. 40, acting on a disc 192 on the rotor shaft may be provided. A ratchet and detent pawl could be used for the same purpose, in this case the detent may be controlled by a relay coil.