Method of producing mechanism for converting rotational motion into linear motion

A method for fabricating a rotational-to-linear motion conversion mechanism, the conversion mechanism including

• a pipe-shaped ring shaft having a female thread on its inner circumferential surface at its longitudinal center portion,
• a sun shaft disposed inside the ring shaft to extend coaxially with the ring shaft, the sun shaft having a male thread on its outer circumferential surface at its longitudinal center portion,
• a plurality of planetary shafts disposed between the outer circumferential surface of the sun shaft and the inner circumferential surface of the ring shaft to extend in the same direction as do the sun shaft and the ring shaft, each of the planetary shafts having a male thread on its outer circumferential surface at its longitudinal center portion, the male thread being mated with the female thread of the ring shaft and the male thread of the sun shaft,
• a first ring gear secured to an inner circumferential surface of a first longitudinal end portion of the ring shaft,
• a first sun gear integrated on an outer circumferential surface of a first longitudinal end portion of the sun shaft,
• a first planetary gear integrated on an outer circumferential surface of a first longitudinal end portion of the planetary shaft, the first planetary gear being mated with the first ring gear and the first sun gear,
• a second ring gear secured to an inner circumferential surface of a second longitudinal end portion of the ring shaft,
• a second sun gear secured to an outer circumferential surface of a second longitudinal end portion of the sun shaft, and
• a second planetary gear attached to an outer circumference of a second longitudinal end portion of the planetary shaft, to be circumferentially rotatable about its own axis and mated with the second ring gear and the second sun gear, the method comprising:
• fabricating a subassembly while each of the plurality of planetary shafts are being held in parallel to the sun shaft, wherein the subassembly includes (i) the sun shaft having the first and second sun gears, (ii) the planetary shaft having the first planetary gear, (iii) the ring shaft, and (iv) the having first and second ring gears, and
• mating a second planetary gear with the second sun gear and the second ring gear while the second planetary gear is being fitted over the outer circumferential surface of the second end portion of the planetary shaft in the subassembly.