Patent GB-783853-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B23Q15/24
Filed: 1954-07-20
Abstract: 783,853. Control of A.C. motors. GENERAL ELECTRIC CO., Ltd., and BRYER, R. F. July 20, 1955 [July 20, 1954], No. 21136/54. Class 38 (3). A film cassette holder 4 for use in serial radiography is mounted on a carriage 6 movable from a position in front of a loading aperture 2 to one of a number of positions in front of an exposure aperture 3, the carriage being driven by a split phase motor 18 through a chain 16. The carriage is located in the selected exposure position by a tongue 13 engaging the appropriate one of lugs A, B, C, D on a tubular sleeve 9 which slides on a rod 11. Successive rotational movements of the rod 11 are produced by an electro-magnetic device 19 so that the lugs corresponding to a sequence of predetermined exposure positions are moved to their operative positions in turn. When the tongue 13 engages the corresponding lug the sleeve 9 is moved to operate switches S20, S27; further movement of the sleeve operating switches S21, S25, before being brought to rest by end stop 12. To initiate movement of the carriage from the loading-position, switch S24 is actuated to energize relay CD/6 switches S28, S29 completing the circuit when the cassette holder is correctly positioned in relation to the selector rod 11. A holding circuit for the relay is established through a switch S25, which, in its operated position, completes a circuit for preparing the radiographic apparatus for an exposure. Closure of contact CD6 energizes the motor 18 which 'has windings W18, W19, the winding W18 being connected in series with capacitor C4. When the motor speed reaches a given value, a motor-driven generator G actuates relay MC/2 and contact MC1 is changed over. Actuation of the switch S20 reverses the connections of the capacitor to the windings of the motor which decelerates, and, as the motor slows down, the relay MC/2 is released so that the contact MC1 reconnects capacitor C4 in series with winding W18 and the motor is again energized for forward rotation but at a reduced value due to the resistor R6. Switch S25 is then actuated to prepare the apparatus for an exposure and switch. S21 prepares a circuit for reversing the motor. The stand-still torque of the motor maintains the selector sleeve 9 against the end stop 12. After switch S22 has been actuated for exposure of the film, the switch S24 is re-set for return movement of the carriage whereby relay CD/6 is de-energized and contacts CD2, CD3 reverse the connection of motor winding W18. When the tongue 13 strikes a lug 14 on the selector sleeve 9, the switch S21 completes the decelerating circuit through relay contact MC1 which had been previously operated during the acceleration period of the motor. Switch S25 energizes the device 19, except when switch S26 is open, and this device turns the selector rod through a predetermined angle so that the next lug in the sequence is operatively positioned. If one exposure only is to be made the winding W20 of the device 19 is not energized when the carriage is returned towards the loading position owing to the opening of switch S26. Operation of the control relay MC/2 then re-connects the resistor R6 in the motor circuit for movement at low speed back to the loading-position, switch S20 preparing a circuit for forward operation and switch S27 breaking the motor circuit. Specification 783,851 is referred to.