Patent GB-794708-A (GB)
Title: Improvements in or relating to shaft-positioning mechanisms
IPC: G05D3/12
Filed: 1956-11-23
Abstract: 794,708. Stopping shafts in predetermined positions. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 23, 1956 [Nov. 26, 1955], No. 35904/56. Class 80 (2). A shaft positioning mechanism comprises the adjusting members, one of which determines the end of a sector of the total angle of rotation and the other determines, in the opposite direction of rotation, the position from the end of the sector of the first member, the drive to the members being such that the speed of the second member is greater than the speed of the first member. A shaft 1, to be positioned, is rigid with a worm-wheel 2 having a pin 3 free in a slot 7 occupying an angle of a little over 10 degrees, the slot being formed in a current collector 4, of conducting material, pivoted on the shaft 1. The collector 4 has a small sector 5 of non-conducting material subtending an angle of less than 10 degrees. Thirty-six fixed contacts 6 are arranged with equal spacings to bear on the collector 4 and a contact 9 is also slidably connected to the inside of the connector. A worm 8, driving the wheel 2, is rigid with a shaft 10 carrying a skew gear 11 driving an auxiliary member 12 driving a ratchet-wheel 15 through a friction coupling 12a. The auxiliary member 12 has a pin 14 forming with a pawl 19 a onerevolution one-way clutch between the member 12 and the ratchet-wheel 15. The ratchet-wheel has fifty notches 16 uniformly spaced on the circumference and engageable by a pawl 26 controlled by an electromagnet 28 ; the pawl 26 also closing a switch 29 when disengaged from the wheel 15. Rigid with the wheel 15 is a second collector 22 having a non-conductive sector 23 and fifty sliding contacts 24. The shaft 10 is rotatable by a reversible electric motor 31 driving through an overload coupling 30 actuating a switch 32. Two manually-actuated selectors 34, 40 having small conductive sectors 36, 42 and sliding contacts 38, 44 connected to the sliding contacts 6, 24 respectively provide the position selecting means. To select a position of the shaft 1 the selector 34 is turned to provide the sector in which the chosen position lies, and the selector 40 is turned to give the position within that sector. Movement of the selector 34 causes energization of a reversing relay 33 to start the motor 31 to drive the members 2 and 12 in an anti-clockwise direction. When the position selected by the member 40 is reached by the collector 22, the non-conducting sector 23 causes interruption of the current and release of the pawl 26 by the electromagnet 28, with the member 15 then held the wheel 12 continues to rotate by virtue of the slipping coupling 12a. When the collector 2, driven by the pin-and-slot 3, 7, reaches its selected position the reversing relay 33 becomes de-energized and the direction of the motor reverses, to drive the collector 2 and member 12 in a clockwise direction. Since the gear ratio of the worm and wheel 8, 2 and skew gears 11, 12 is such that one revolution of the gear 12 is equivalent to the angle of the sector of the pin-and-slot connection 3, 7, the wheel 12 can rotate in a clockwise direction to allow adjustment of the shaft 1 within the sector, until the pin 14 contacts the pawl 19 on the ratchet-wheel 15 held in the selected position by the pawl 26. This stops the shaft 10, with the shaft 1 in the selected position, and the overload torque trips the switch 30 to stop the motor 31. In the embodiment described the number of possible positions of shaft 1 is 1800, these positions may be varied in number according to the number of contacts 38, 44 and may similarly vary in angular position from equal spacing. If the controlled apparatus is driven from the shaft 10 it becomes possible to position the apparatus shaft in a number of complete rotations.