| 摘要 |
548,957. Screw-and-nut gearing. ARCHDALE & CO., Ltd., J., and WRIGHT, I. H. July 3, 1941, No. 8407. [Class 80 (iii)] Consists in means for eliminating backlash ir screw-and-nut gearing fox moving the slides of machine tools. A cutter b acts upon work d on a slide a to which is secured a screw c prevented from rotating by clutch elements e, f. A pair of rotatable nuts g, h on the screw are supported by fixed stationary bearings i. The nut g has a pair of ball thrust bearings j, whilst the nut h has a pair of thrust friction bearings k such that endwise force on the screw in either direction cannot cause rotation of the nut. Formed on or secured to the nuts are a pair of helical toothed pinions m. n which engage corresponding pinions o, p on a driving shaft q adapted to be rotated by gear wheels r. The teeth of the pinions m, o are of moderate helical angle, but the teeth of the pinions n, p are of relatively large angle, but both sets of pinions are of the same hand. The thrust bearings j, k are situated between opposite sides of their respective pinions and the corresponding bearings. The shaft q is free to move axially to an extent determined by stops s, such endwise movement being derived from the interactions of the helical pinions or from fluid-pressure actuated plungers t or springs. These are only brought into action preparatory to a cutting operation and are not in operation during idle movements of the slide. The pinion o is secured to the shaft q, but the pinion p is mounted thereon with a lost motion connection v. Initial rotation of shaft q causes it to move to the left, due to the action of pinions o, m which will be rotated, this endwise movement 'being arrested by the stop s before the lost motion v is wholly taken up. Rotation of shaft q to take it up wholly causes sufficient relative motion of nuts g, h to bring them closely but not tightly against the ball and friction thrust bearings j, k. If now a plunger t is caused to exert pressure on the left-hand end of shaft q, the latter tends to move to the right against the force of interaction of the pinions m, o and n, p, but so long as a thrust of high value is exerted on the slide a no such endwise movement occurs. If and when this thrust falls sufficiently, the shaft moves endwise causing the nuts to be screwed closer together thus creating on the bearings j. k a pressure that will prevent sudden forward movement of the slide. If the thrust on the slide again becomes large, the effect of plunger t is overcome and the pressure on the bearings reduced. If cutting takes place with movement of the slide in the opposite direction, the nuts are forced against the other or outer pair of bearing surfaces. |
