A Planetary Roller Screw Mechanism with Shaped Rollers for Converting Rotational Motion to Linear Motion

This paper describes design features and kinematics of a planetary roller-screw converter of the rotational motion of the nut to the linear motion of the screw. The rollers are shaped and have threads on the outer diameter. The mechanism design simplifies the process of thread grinding on the rollers after heat treatment. The main disadvantage of the «inverted» planetary roller-screw mechanism is the necessity to grind the internal thread in a long nut after thread hardening. The use of shaped rollers and nut made it possible to considerably simplify assembly in the axial direction. Due to gearing, the rollers and the nut rotate in one direction with almost the same tangential velocity on the contact surfaces. As the application of highly efficient linear actuators based on planetary roller-screw mechanisms is limited by production cost, reducing the cost becomes an important task. This can be achieved by using designs that do not involve expensive operations such as grinding internal threads, as part of their manufacturing process.

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