| 摘要 |
495,901. Screw-and-nut gearing. ARCHDALE & CO., Ltd., J., and WRIGHT, 1. H. Aug. 12, 1937, No. 22160. [Class 80 (iii)] [Also in Group XXII] Means for eliminating backlash in the feed screws of milling machines and other machine tools comprises a feed screw b secured to the work-table a, two nuts c, d within a fixed bearing e, relatively opposed helical gears of slightly different speed ratios for rotating the nuts and a friction clutch between one of the gears and a source of motion which is common to both gears. To the nut c is secured a helical gear-wheel f abutting against a thrust face h at one end of the bearing e and meshing with a gear-wheel k coupled to a shaft j<1> through a lost-motion connection m, n. A helical gear-wheel g secured to the nut d abuts against the other end of the bearing through a ring of thrust balls i and meshes with a gear-wheel coupled to the shaft j through a friction clutch comprising an inner sleeve r secured to the wheel l, an outer member s secured to the shaft and intermediate plates t, u splined to the outer and inner members respectively and pressed together by a spring w. In operation, the shaft j<1> is driven through gearing o, p and as a result of the different speed ratios between the gears f, k and g, l, the nut d rotates faster than the nut c so that the nuts move in against the bearing until the clutch slips and both nuts rotate at the same speed. When the table is being returned, the clutch tends to be relieved of pressure and the nut d is driven by additional gears 3, 4 mounted on the nut and on the member s. In order to allow the table to be moved by hand while the above mechanism is stationary, the screw b is connected to the table through a releasable dog clutch 10, 11. |
