| 摘要 |
An assembly of a worm and a ball nut, with a multiplicity of antifriction balls rollably engaged therebetween and retained in preassigned relative positions by a tubular cage, to cause relative longitudinal displacement of either of the worm and the ball nut in response to the rotation of the other. At least one turn of the internal thread at the midportion of the ball nut differs in width from the other turns for preloading the balls on its opposite sides in the opposite axial directions of the worm with a view to minimal backlash between worm and ball nut. Also disclosed is a two-speed feed mechanism incorporating a wormshaft having first and second threaded portions with different leads on which are mounted first and second ball nuts, respectively, via caged, preloaded antifriction balls. The first ball nut is rotatably mounted to a stationary part via a bearing whereas the second ball nut is fastened to an object such as a worktable. One end of the wormshaft is straight-splined and received in a ball bushing which admits of axial motion of the wormshaft while being constrained to simultaneous rotation therewith. Thus, with the rotation of the wormshaft, the second ball nut travels linearly at either of two different speeds depending upon whether the first ball nut is restrained from rotation or coupled to the ball bushing for joint rotation therewith. |
