GB1025021A - Indexing drive mechanism - Google Patents

Abstract

1,025,021. Toothed gearing. ENGLISH ELECTRIC CO. Ltd. July 3, 1962 [July 5, 1861], No. 24339/61. Headings F2L and F2Q. In mechanism allowing a worm-driven wheel 11, Fig. 1, to be locked in any one of a number of index positions, particularly for a nuclear reactor fuelling mechanism, the worm 10, engaging rollers 12 on the wheel 11, is longitudinally divided into two parts 13, 14 which co-operate to present to a roller 12 either a normal helical groove 17 extending over one and a quarter turns or, when part 14 has been shifted axially to align grooves 16 and 17, to present a part helical groove which as a 60- degree portion 18 of zero pitch providing a dwell in the drive. In a practical embodiment the parts 13, 14 (Fig. 4) are coupled for rotation by a pin 31, and the axial shifting of the part 14 is obtained by radially projecting an appropriate roller 28 or 27 into the path of respective cams 26, 25 (Fig. 2, not shown), cut into the surface of the part 14. In operation, using the normal helical groove 17, the wheel 11 is continuously rotated until the desired index station is approached. While the roller 12 still engages the part 13 the roller 27 is projected into the path of cam 25 so that the part 14 is moved axially to allow the roller 12 to enter the zero-pitch portion 18 and thus stop the wheel 11 accurately in the required index position. The worm 10 is then stopped. A block 36 on the end of a fixed spindle 34 projecting into the worm 10 has on one side portions 36A, 36B which co-operate with an inward projection 14B on the part 14 to prevent any axial movement thereof except when it is clear of the rollers 12.