Patent GB-643858-A (GB)
Title: Improvements in shaft positioning apparatus
IPC: H03J5/20
Filed: 1947-02-14
Abstract: 643,858. Stopping shafts in predetermined positions. COLLINS RADIO CO. Feb. 14, 1947, No. 4388. Convention date, April 12, 1946. [Class 80(ii)] [Also in Group XL(c)] The invention of Specification 632,782 is improved by (i) replacing each of the three-armed pawls by two pawls, one a stop pawl and the other a secondary pawl for holding the operative stop pawl out of engagement with its respective stop ring until the tuning shaft has reached the final partial revolution of its setting, (ii) providing means for holding all of the stop pawls from engagement with their respective stop rings during the initial homing of the tuning shaft, (iii) providing means including a clutch rendering the manual tuning knob effective only when the stoprings have been loosened as for presetting thereof, (iv) providing separate terminal stops for the tuning shaft' for automatic and manual tuning. The circuit arrangements for controlling the driving motor, Fig. 5 (not shown) and the selective positioning of the multi-turn tuning shaft are similar to that of Specification 632,782. As shown, the individual stop rings 28, Fig. 1, normally locked to the tuning shaft 25, co-operate with respective spring-biassed stop pawls 29 pivoted about shaft 30, and each stop pawl co-operates with a pivotal secondary pawl 32 the ends 32b, 32c of which co-act respectively with the corresponding selector cam 35 and secondary turns determining cam 36. As in the prior mentioned Specification the selector cam shaft is set during the " homing" movement of the motor 20, to bring the notch in the appropriate selector cam 35 opposite the end 32b of the associated secondary pawl 32. Thereafter, during the reverse rotation of the motr, the selector cams 35 remain stationary, and after a predetermined number of revolutions of the tuning shaft 25, the appropriate secondary cams 36 rotates sufficiently to permit clockwise rocking of the associated secondary pawl 32 to the position shown in Fig. 3. The associated stop pawl 29 is thereby rocked by its biassing spring into engagement with the periphery of the corresponding stop ring 28 and, after the subsequent partial revolution of the shaft 25 locks the stop ring and hence the tuning shaft in the selected position. Presetting of stop cams; manual tuning, Fig. 9. The stop rings 28 are mounted between spacer rings 50 on a drum 48 splined to the tuning shaft 25, and normally locked frictionally to the drum by a pressure member 53 urged to the right by a thumbscrew 52 threaded into the tuning shaft 25 as in the prior Specification. When the nut 52a is loosened to release the stop rings, as for presetting, one element 54b of a dog clutch 54 is spring-urged to the left to engage the element 54a when manual tuning may be effected through the knob 55a, gearing 56, 57, 58 and the clutch 54. Locking of stop pawls during homing, Fig. 7. During the homing movement of the motor the secondary cam shaft 63 rotates anti-clockwise. A sleeve 69a driven frictionally thereby rotates from the normal position shown in Fig. 7 to the position Fig. 8 (not shown) where a sleeve extension 69b engages a shaft 70. A hook-shaped member 67 is thereby released and rocked by a biassing spring 68 to a position where it engages over the ends 32d of all the secondary cams 32 whereby all of the stop pawls 29 are held from engagement with their corresponding stop cams during homing, the secondary cams being released when the motor reverses, when the sleeve 69a through its other extension 69b rocks the member 67 to the Fig. 7 position. Terminal stops for tuning shaft rotations, Fig. 7. During automatic tuning, stopping of the tuning shaft at its terminal positions is effected by a projection 49a on the terminal stop ring 49, secured concentrically with the stop rings on shaft 25, engaging one or other of the ends 58a. 58b of the terminal stop pawl 58. During the intermediate rotations of the tuning shaft the pawl 58 is held in an intermediate inoperative position by spring bias and is moved into operative position by a spring-actuated link 59 lost-motion connected through a pin 60 to a pivotal sector plate, Fig. 6 (not shown) driven by the turns determining secondary cam shaft, during the last revolution of the shaft 25. During manual tuning terminal stopping is required at positions prior to those used during automatic tuning and is effected by the ends 65a. 65b of a plate 65 integral with the stop pawl 58 engaging projections 55b, 55c, 55d on the manual tuning shaft 55. Specification 556,363, [Group XXXVIII], also is referred to.