Patent GB-758603-A (GB)
Title: Improvements in or relating to shaft-positioning devices
IPC: A23L13/40
Filed: 1954-07-14
Abstract: 758,603. Stopping shafts in predetermined positions NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. July 14, 1954 [July 14, 1953; March 11, 1954; March 11, 1954], No. 20626/54. Class 80(2) [Also in Group XXV] A device for positioning a shaft 10, adjusting, e.g. a radio capacitor or machinetool part, within 360 degrees of rotation, comprises a nut 56 traversing a 10-start coarse pitch screw-thread 11 on the shaft 10, and having an arm 58 axially slidable in any selected one of a number (50 shown) of longitudinal slots 59, Figs. 1 and 4, inside a fixed hollow cylinder 7 centred about the shaft 10, each slot having an adjustable abutment screw 62, the end of which arrests the nut 56 in an axial position corresponding to the required setting of the shaft 10. The shaft 10 is turned by an electric motor 17 through spur and worm gear 18, 19, 34, 35, the worm-shaft 22 of which can yield axially against a spring (Fig. 2, not shown), when the shaft is arrested, to maintain firm contact of the arrested surfaces, and also to switch off the motor supply. During a setting cycle the motor 17 first drives the shaft 10 in one direction until the nut-arm 58 overlies the required slot 59, whereupon the motor is automatically reversed and the shaft 10 screws the nut 56 until the arm 58, moving along the slot 59, is stopped by the corresponding screw. Slot selection is by a selector disc 66 which is freely mounted on the shaft 10 and carries 'five insulated peripheral contact segments 81, Fig. 12, tracking ten fixed brushes 77 such that in each of the fifty positions of adjustment of the selector disc 66 a different combination of five of the brushes 77 contacts the segments 81, the remaining five brushes being on insulating segments. The brushes 77 are connected to ten similar brushes 87, grouped around a remotely positioned control disc 86, having conducting segments 90 complementary to those of the selector disc 66. The selector and control discs 66, 86 are themselves connected to a D.C. supply AB, the former directly, the latter through a relay winding 100, which is thus only energized when the selector disc 66 occupies that particular one of its fifty evenly spaced positions corresponding to the selected one of the fifty control disc settings. A complete sequence of movement of the shaft 10 from one set position to another is as follows. The control disc 86 is turned manually to a position corresponding to the position the selector disc 66 will occupy in relation to that cylinder slot 59 to be effective in the final positioning, such turning energizing the relay winding 100 which changes-over the contacts 101 and so directly supplies the armature 17 of the permanent-magnet field motor 17, from the D.C. main AB, for clockwise (from above) rotation of the shaft 10 independently of the switch 103 which is closed by the initial clockwise rotation of the motor allowing the wormshaft loading spring to expand. The clockwise rotation of the shaft 10 screws the nut 56 upwards until its arm 58 leaves the cylinder slot 59 and enters a gap between two pins 74, Figs. 1 and 5, depending from the selector disc 66, whereupon axial movement of the nut is arrested and the nut turns with the shaft 10, taking with it the selector disc 66 by its pins 74. When the nut-arm 58 overlies that one of the cylinder slots 59 which is to be effective, the selector disc contacts 81 break the circuit of the relay 100, permitting the motor reversing contacts 101 to return to the position shown for anti-clockwise rotation of the shaft 10. In this direction rotation of the selector disc 66 is prevented by a one-way detent pawl 69 engaging one of fifty positioning ratchet teeth on the disc 66, so that the nut 56, held from rotation by the selector disc pins 74, is forced to screw downwards and enter its arm 58 into the selected cylinder slot 59, in which it continues its downward travel until arrested at the final setting point by abutment on the screw 62 of that slot. The shaft 10 is now finally positioned but the motor runs on, compressing the wormshaft loading spring until the axial movement of the worm-shaft 22 actuates, through a cam groove (Fig. 3, not shown), the switch 103, cutting off motor current, but leaving the shaft-arresting surfaces 58, 62 still under the constant stress of the spring. To reduce clearance errors the abutment surfaces on the nut arm 58 and screw end 62 are respectively chiselshaped and convex. To permit adjustment of the arresting screws 62, the shaft 10 can be declutched from the worm-wheel 35 by withdrawing a knob 43 to retract a diametral clutch-key 38 into an idle recess 44, whereupon the shaft 10 can be turned through a knob 50 having a friction connection with a scale-plate 46 fast on the shaft. The screws 62 are rendered self-retaining in their adjusted positions either by outwardly biasing their split ends 63, or by pairs of diametral nylon pins 64 at right angles bearing on the internal thread. Two methods of producing the slotted cylinder 7 are described. In one the cylinder is formed by stacking slotted brass plates; in the other by rolling up a brass strip (Fig. 11, not shown), having transverse slots which finally become trapezium shaped and of such dimensions as to require no drilling prior to tapping the threads for the adjusting screws.