Mechanism for converting rotational motion to linear motion

A rotational-to-linear motion conversion mechanism, comprising:

• a rack rod including thread formed on its outer peripheral face;
• a holder member provided on the outer periphery of the rack rod, rotating about the rack rod and moving in the axis direction;
• and
• revolving rollers rotatably supported in the holder member, each having ring-shaped grooves formed in its outer peripheral face to be engaged with the thread, and placed at an axis angle with respect to a center axis of the rack rod to allow the ring-shaped grooves to be engaged with the thread formed on the rack rod,
• wherein only one of contact faces of the thread with each of the ring-shaped grooves in an engagement site of the thread and the ring-shaped groove is formed as a convex face having different curvatures in a radial direction.

A method for manufacturing a rotational-to-linear motion conversion mechanism including:

• a rack rod including thread formed on its outer peripheral face;
• a holder member provided on the outer periphery of the rack rod, rotating about the rack rod and moving in the axis direction;
• and
• revolving rollers rotatably supported in the holder member, each having ring-shaped grooves formed in its outer peripheral face to be engaged with the thread, and placed at an axis angle with respect to a center axis of the rack rod to allow the ring-shaped grooves to be engaged with the thread formed on the rack rod,
• the method comprising the steps of:
• setting curvatures on a thread section outline in an engagement site of the thread and the ring-shaped groove to be larger in a portion of the thread section outline close to the inner periphery of the thread than the curvature in proximity to the engagement site;
• and
• sweeping and grinding the section outline along a thread spiral of the rack rod to form thread of the rack rod.