Mechanism for converting rotary motion into linear motion

A mechanism for converting rotary motion into linear motion, comprising a cylindrical-shaped or columnar-shaped rack rod, a holder member supported round the rack rod to be rotatable relative to the rack rod, and revolving rollers supported for rotation on the holder member,

• wherein the rack rod comprises a thread having a predetermined lead angle,
• an axial angle of each of the revolving rollers relative to an axis of the rack rod is larger than the lead angle of the thread of the rack rod,
• each of the revolving rollers is formed with a plurality of annular grooves on an outer peripheral surface thereof, and each annular groove has two-sided annular surfaces at least one of which meshes with a side flank of the thread of the rack rod, and
• meshing points of the at least one of two-sided annular surfaces and the side flank of the thread of the rack rod exist apart from the axis of the rack rod as viewed from a direction of a common perpendicular of the axis of the rack rod and the axis of the revolving roller,
• wherein each thread of the rack rod having a curvature that creates a line of connecting points of mesh between a right flank of each thread of the rack rod and each revolving roller, when each revolving roller rotates around the rack rod toward a direction in which the points of mesh occur at the right flank and a line of connecting points of mesh between a left flank of each thread of the rack rod and each revolving roller, when each revolving roller rotates around the rack rod toward a direction in which the points of mesh occur at the left flank, wherein the line of connecting points of mesh of the left flank and the line of connecting points of mesh of the right flank are parallel to each other and the axis of the rack rod.