Screw and nut transmission mechanism

Claim 1

Screw and nut mechanism for converting a movement of rotation into a movement of translation, and vice versa, comprising a screw member and a mating nut member having a common axis, each of said members having at least one peripheral helical groove, which grooves define together at least one helical channel having two ends, a train of balls of predetermined diameter engaged in said helical channel for transmitting forces between said members, at least one substantially straight keyway in the outer peripheral surface of said nut member, said keyway extending parallel to the common axis of said numbers and having side walls spaced apart a width distance, and a floor intermediate said side walls, said keyway having depth in the radial direction less than one-half of said diameter of said balls, an elongated key having side walls spaced apart a width distance corresponding to that of said keyway, and intermediate said side walls a bottom surface including therein a longitudinal channel having cross-section permitting passage of said balls, said key being secured in said keyway with the bottom surface and groove therein facing and adjacent said floor of the keyway, said groove and floor defining a partial ball-recirculation passage including two ends, and connection means for interconnecting the ends of said passage with the ends of said helical channel.