Friction drive mechanism for converting a rotational movement into an axial movement, or vice versa

A friction drive mechanism for converting a rotational movement into an axial movement, or vice versa, and comprising a friction assembly cooperating with a driving means and a load, respectively, said friction assembly comprising a smooth shaft, at least two axially displaced sets of roller members, each set comprising at least four roller members, a holder surrounding said shaft and journalling said rolling members to be equally spaced around said shaft in external frictional engagement therewith and to be rotatable around axes having the same inclination to, but not intersecting the axis of said shaft, the points of engagement between the rolling memers of each set and the shaft remaining substantially in a common plane normal to the axis of said shaft, said holder being made in two parts each carrying two roller members of each set of roller members, and clamping means being provided for connecting said two holder parts with a tension sufficient to secure frictional engagement between said rolling members and said shaft, said clamping means comprising interconnected first and second portions engaging each of the two holder parts in a manner so as to be pivotable relative thereto about a respective pivot axis transverse to the axis of said shaft, only one of said portions being fixed relative to said driving means or said load, whereas the other portion has no firm connection with said driving means or said load, whereby in the absence of an axial load said clamping means assumes a neutral position with both of said pivot axes extending substantially in the same plane normal to the axis of said shaft, while in the presence of an axial load, the clamping means will be turned out from said neutral position to reduce the separation of the two holder parts.