Patent GB-817642-A (GB)
Title: Improvements in or relating to shaft-positioning mechanisms
IPC: F16D71/04
Filed: 1956-12-07
Abstract: 817,642. Stopping shafts in predetermined positions. PHILIPS ELECTRICAL INDUSTRIES Ltd. Dec. 7, 1956 [Dec. 12, 1955], No. 37480/56. Class 80 (2). In electrically-operated shaft positioning  means in which the axial displacement of a projection, on a travelling nut, in a groove in one wall of a cylinder carrying adjustable stops determines the ultimate angular movement of the shaft, whilst on passing from one predetermined position to another the projection is axially removed from the groove to allow relative rotation of the nut and the cylinder for selection of another groove having another adjustable stop contacted by the projection on reversal of the screw spindle for the nut, means are provided such that the shaft is pre-adjusted to a position situated within a sector forming part of the maximum possible angle of rotation, the location of the sector being determined by the pre-adjustment, and it being possible to select other sectors which may or may not overlap, whilst a reduction gear is provided for driving the shaft and the screw spindle. A shaft 50 to be positioned is rotated by an electric motor on a shaft 57 connected through an overload coupling 55 of the type described in Specification 799,816, driving a shaft 53 carrying a worm 52 meshing with a worm-wheel 51 on the shaft 50. The shaft 53 has a screw-thread of coarse pitch 54 and carries a gear 60 freely mounted between a disc 58 of magnetic material and an adjusting disc 59, the gear 60 having an axial pin 61. A cylinder 62 freely rotatable about the shaft 53 has internal and external longitudinal grooves 63, 64 in which adjustable stops 65, 66 are arranged. The cylinder also has a current collector 67 coacting with sliding contacts 68, a toothed rim on the collector 67 being engageable with an electrically controlled arresting device 80. A gear 72, meshing with the gear 60, is rigidly fixed to a shaft 70 together with a collar 74. The shaft 70 has a fine thread 71 on which travels a nut 77 having projecting teeth 78 meshing with the grooves 64 of the cylinder 62 and also able to engage the stops 66. The thread 54 carries a nut 75 having a projection 76 engageable with the stops 65 in the internal grooves 63, and a collar of magnetic material 79. To obtain a desired position of the shaft 50 an electrical contact selector (not shown) is set. This energizes the driving motor through a reversing relay to rotate the shaft 57 in a direction to move the nut 75 to the right until it is free of the cylinder 62 and the magnetic collars 58, 79 engage. The nut then starts to rotate together with the gear 60 and pin 61 and rotates, through gear 72, the shaft 70 to screw the nut 77 to the right until it abuts the collar 74. The teeth 78 then drive the cylinder 62 until the collector 67 has reached a predetermined position when the appropriate contact 68 causes reversal of the motor and engagement of the locking device 80. With the cylinder 62 held, the nut 77 moves to the left until one tooth 78 abuts the stop 66, this prevents further rotation of shaft 70, gear 72, and gear 60. At this moment the shaft 50 has reached the end of a predetermined sector within which the final position of the shaft 50 lies. The gear 60 slips on the shaft 53 and the nut 75, against the action of the magnetic coupling 58, 79, moves to the left until the projection 76 engages the stop 65. The shaft 50 is now adjusted in the correct position and overload coupling 55 operates to switch off switch 56 to stop the driving motor. The shafts 70, 53 may have manual controls and the teeth 78 may be replaced by a Geneva mechanism. In a second embodiment the shaft 70 and its associated components are omitted and a second electrical collector is provided to ensure that the driving-shaft reverses when the correct sector has been reached. In this embodiment the sliding nut projection engages with grooves in the outer surface of the cylinder. Specifications 758,603 and 817,641 also are referred to.