Development of a long lead miniature differential screw drive mechanism

Abstract

This paper proposes a method for machining a miniature Gaudi-screw and nut for a miniature differential drive mechanism with an ultra-small diameter and ultra-long lead based on a square cross-section. A miniature Gaudi-screw with a square cross-section of 2 mm on one side, a 10 mm lead (57.9 degrees slope angle), a total length of 40 mm (aspect ratio 20), and a square cross-section of right and left helix nuts are developed. First, the geometry of the proposed Gaudi-screw and the reasons why it is suitable for miniaturization are explained. Then, the configuration and kinematics of the mechanism using the Gaudi-screw as a two-input, two-output differential screw mechanism are described in preparation for the operation verification experiment. Next, the minimum radii of curvature of the Gaudi-screw and nut surfaces are derived using three-dimensional surface geometry, and the ball end mill tip diameters for cutting the miniature Gaudi-screw and nut are calculated. For the machining of long miniature Gaudi screws with small diameters, a machining method that suppresses deformation during machining due to machining reaction forces are proposed, and the results of actual machining using a 5-axis NC machine are shown. In addition, a parting and assembling method for miniature nuts are proposed, and the results of actual machining are shown. A prototype of an experimental device to motorize the miniature Gaudi differential screw mechanism was fabricated, and its operations were verified.

Keywords

• differential screw drive mechanism
• mechanical design mechanics
• surface geometry
• micro machining