Mechanical screw transmission

Abstract

A low-friction light-load mechanical transmission for converting between rotary and linear motion, comprising a screw shaft having a helical thread groove, and a nut body having a radially movable socket member in which there is received a thread-engaging ball. The socket member has a circular load surface surrounding a circumference of the ball, and a second load surface centrally located with respect to the circular load surface and displaced laterally therefrom. The second load surface of the socket member engages the ball along a relatively small area thereof. The helical thread groove is characterized by a pair of co-extensive, helical troughs, each trough being partially circular in cross section. The troughs intersect one another adjacent the root of the thread groove, each trough having a radius of curvature slightly greater than the radius of the ball. The arrangement is such that for a given direction of relative axial movement between the nut body and screw shaft, the ball has a relatively small area of contact with the surface of only one trough, at a point on the ball which is substantially aligned with but opposite to the resultant of the forces existing between the ball and the socket member. The socket member is resiliently backed by a single, bowed snap ring which locks into an annular groove in the nut body. The transmission finds use in ticket printers, X-ray camera shutters, and kindred light-duty devices.

Dependencies are inferred from the claim text.