Patent ID: 8162794

Claim:
A rotation/linear motion conversion mechanism, comprising: an annular shaft provided with a space extending in an axial direction therein, the annular shaft including an internally threaded portion and first and second annular gears, the annular gears being internal gears; a sun shaft arranged inside the annular shaft, the sun shaft including an externally threaded portion and first and second sun gears, the sun gears being external gears; and a plurality of planetary shafts arranged around the sun shaft, each planetary shaft including an externally threaded portion and first and second planetary gears, the planetary gears being external gears, wherein the externally threaded portion of each planetary shaft is engaged with the internally threaded portion of the annular shaft and with the externally threaded portion of the sun shaft, each first planetary gear is engaged with the first annular gear and with the first sun gear, each second planetary gear is engaged with the second annular gear and with the second sun gear, and wherein the conversion mechanism converts rotational motion of one of the annular shaft and the sun shaft into linear motion of the other one of the annular shaft and the sun shaft along the axial direction through sun-and-planet motion of the planetary shafts, and wherein the planetary shafts are configured to permit relative rotation between the first planetary gear and the second planetary gear.