Patent GB-635758-A (GB)
Title: Improvements in shaft positioning apparatus
IPC: H03J5/20
Filed: 1946-06-06
Abstract: 635,758. Electric switches. COLLINS RADIO CO. June 6, 1946, No. 17235. Convention date, Dec. 22, 1943. [Class 38 (v)] [Also in Group XXXVIII] In a mechanical shaft positioning device of the kind described in Specification 556,363, [Group XXXVIII], applicable to automatically tuned radio apparatus, a plurality of adjustable stop rings carried by a drum on the tuning shaft may be locked thereto, or released for individual adjustment, by dial operated control means which releasing action simultaneously disconnects the tuning shaft from the automatic drive means ; the stop rings and associated pawls are automatically disengaged by rotation of the tuning shaft on commencement of a tuning cycle but retain their normal locking association during setting-up ; and improved lost motion means are provided in the selector cam and selector switch drives so that neither is operated until the timing element has reached its terminal position, when drive is applied to the said elements to effect the desired selection after which they remain stationary for the remainder of the operational cycle. Construction.-A main tuning unit, Fig. 4, is worm geared to a motor driven lineshaft, Fig. 7 (not shown), which also drives a limit switch unit and a selector switch unit. The tuning unit shaft 10 directly positions a condenser or other tuning element and is coaxial with the free worm wheel 22 rigidly connected to gear 23 engaging gear 24, which drives a multi-turn lost-motion device embodying driving and driven members 24, 25 separated by washers 24a-f having 180 degrees spaced bent over interlocking ears, each successively engaged to rotate in turn, the driven member 25 rotating a selector cam drum having depressions 26a-l spaced helically round its periphery. Concentrically with shaft 10, a cup-shaped member 33 forms the outer element of a friction clutch co-operating with a plurality of friction shoes 33c-f, the ends of which are urged apart by springs to grip the inside of the drum 33a and which are engaged by a yoke 33g, Fig. 5, rigid with gear 22. The inward flange 33b retains the outward flange 14c of the locking drum 14 which carries a plurality of slotted rotatable stop rings 17a-l interspersed with washers keyed to the drum. Shaft 10 is manually rotatable by dial 16, concentric with which is a locking bar 15 operating a threaded stud 35 to urge a non- rotatable pressure member 36 against the movable end member 14a of the stop ring drum, so that rotation of the bar locks the stop rings. to the drum, which is in turn locked to the flange 33b of the cup-shaped member 33 clutched to gear 22. Each stop ring is associated with a pivoted pawl 18a-l, Fig. 2, spring-urged towards its stop ring and according to the position of the selector drum a selected pawl rides on the periphery of its stop-ring until the pawl head engages the slot therein to stop the ring and its drum. The pawl heads are angularly shaped to provide firm arrestment when the drum rotates clockwise, Fig. 2, but rise from the slot and trail on the ring periphery when the rotation is counterclockwise. The stop ring drum is arrested in either of its terminal positions by the engagement of the fixed lug 2 with the pawl 20. The limit switch, Fig. 8, is driven from the line shaft through a one turn lost-motion device, worm gear and a drum attached to the line shaft and encircled by a spring-loaded friction shoe 42 which throws over the spring- loaded switch-operating element 43 at the end of each cycle. The selector switch unit, Figs. 12, 13 (not shown), is driven through a multiturn lost-motion device identical with that of the selector drum, and has contacts, corresponding in number to the stop rings and pawls one of which is open circuited at a time by the switch rotor, the remainder being commoned thereto. Corresponding contacts are connected' to the contacts of a master switch 62, Fig. 14, which selects the required tuning position. Operation.-The master switch 62 is displaced from positional correspondence with the selector switch 51, and energizes the relay 61 from battery 70 to start the motor 71 to driving the main shaft and stop ring drum counterclockwise, Fig. 2, lifting the cam heads from their slots, until the shaft and drum are stopped in the terminal position. The clutch slips and the drive continues, taking up the lost motion in the selector drum and selector switch drives so that they rotate synchronically until the preselected switch contact is open-circuited, when the relay releases and the motor reverses. The stop ring drum is thus driven clockwise, Fig. 2, and the selector drum and switch remain standing in position, due to the lost-motion drive. The selected pawl rides on the periphery of its appropriate stop ring until its head drops into the slot therein, arresting the stop ring drum and drive-shaft in the selected position. The clutch slips and the motor runs until the limited switch 42 opens contacts 44, 46 at the terminal position, de-energizing the motor except for a small armature current through resistor 78 which keeps the selected stop ring in firm engagement with its arresting pawl. Switch 63 disables the automatic selection for manual control, while relay 64 and switch 65 furnish interlocking action preventing operation of the controlled radio apparatus while the tuning device is in operation, and vice versa. A particular stop ring is reset by selecting it to be engaged by its appropriate pawl and slackening the locking stud which releases the stop rings from the drum and disconnects the latter from the cup-shaped member clutched to the main tuning shaft. Thus the main shaft position corresponding to the stop ring may be manually reset by the dial without rotating the drive mechanism, after which the stop rings and drum are re-locked for normal operation. Alternative circuit elements such as crystals may be selected by a further switch ganged with the selector switch.