Patent GB-615539-A (GB)
Title: Improvements in shaft positioning apparatus
IPC: H03J5/20
Filed: 1946-01-09
Abstract: 615,539. Electric selective signalling systems. DEHN, F. B. (Collins Radio Co.). Jan. 9, 1946, No. 826. [Class 40 (i)] In a mechanical shaft positioning device applicable to tuning radio apparatus, a drum disposed on the motor driven primary drive shaft carries a plurality of angularly adjustable axially spaced stops, co-operating with a similar number of axially aligning stops, helically disposed on a second drum which is mounted on a ratchet-controlled countershaft rotatable by the motor in one direction only to assume one of a plurality of positions, determinable by a master switch through a selective electric control system so that a stop on the second drum engages a corresponding stop on the first drum to arrest and retain the primary shaft in one of a plurality of pre-set positions. Prior art of Specification No. 556,363 is referred to. In Figs. 3 and 4 a motor driven worm or gear-wheel 100 meshes with gear-wheel 21 which drives primary shaft 10 through a slipping clutch wherein a stud. 23 engages a friction shoe 24 pressed against clutch drum 15a by surrounding annular spring 25, the clutch drum being integral with a drum 15 mounted on the primary shaft and encircled by loose stop rings 16a-d bearing stops 16a<SP>1</SP>-d<SP>1</SP>, fast spacer rings 17a-d, and a fast terminal ring 18 bearing a stop 18<SP>1</SP> which engages stud 20 to define the terminal positions of rotation of the drum. The loose rings may be clamped after adjustment by screw member 19. Gearwheel 21 meshes gear-wheel 22 and drives a countershaft 26 through a device comprising pins 22a, 28a, and dog 35, which introduces more than one full revolution of lost motion into the drive between the gear 22 and the countershaft 26, which is limited to clockwise rotation by a four-position ratchet-wheel 31 engaged by a spring detent, 'and carries a second composite drum around which stops 29a<SP>1</SP>-d<SP>1</SP> are helically disposed at equal intervals in axial alignment with the stops of drum 15. Shaft 26 also operates a rotary fourposition switch 36, Fig. 8, such that the rotary member thereof open circuits one contact at a time, the remainder being commoned to the rotary member. Corresponding contacts of switch 36 are connected to the contacts of a master selector switch 37. On displacement of the arm of this switch from positional coincidence with the arm of switch 36, relay 38a is energized to operate the motor 43, which drives primary shaft 10 and drum 15 in a counterclockwise direction until stop 18<SP>1</SP> engages stud 20 to arrest the drum in its terminal position. The slipping clutch allows the gear-wheel 21 to rotate gear-wheel 22 in a clockwise direction to overcome the lost motion and then to rotate countershaft 26, its top drum, and the rotary switch 36 until the contact of the latter corresponding to that selected by the master switch 37 is open circuited. Relay 38a releases, the motor first stops and then re-starts in the reverse direction, through a rotary limit switch which may be of the kind described in Specification No. 556,363. Drum 15 and shaft 10 rotate in a clockwise direction, until one of the adjustable stops, e.g. 16a<SP>1</SP>, abuts on a stop on the countershaft drum, e.g. 29a<SP>1</SP>, which has been placed in the appropriate position by movement of the drum under control of the master selector switch 37. The countershaft 26 is prevented from rotating counterclockwise by the ratchet mechanism, and drum 15 stops, while the slipping clutch and the lost motion device allow the gear-wheels 21, 22 to rotate until the limit switch is operated by rotatable member 39a, and the motor circuit is broken after the drive has rotated by an amount corresponding to one revolution of drum 15 from its terminal position. On repositioning the master selecter switch 37, the system performs a similar cycle appropriately to reposition the shaft 10. Single-turn shaft positioning devices of the type described may be used in combination with multi-turn units, for example in turning a radio transmitter.