Application of Screw Theory to the Analysis of Instant Screw Axis of Vehicle Suspension System

This paper proposes a method using screw theory to find the twist of a rigid body of a mechanism. For this, a geometric method to determine the screws and reciprocal screws associated with kinematic joints and links is introduced. This geometric method provides a simple way to find the wrenches acting upon a rigid body of a mechanism using the joint types and positions. Then, the twist which is reciprocal to the wrenches is determined to find the instant screw axis and pitch of the body. The proposed method is applied to planar mechanisms and spatial suspension mechanisms. For planar mechanisms, the method finds the instant center of velocity as the point in the plane of planar motion intersected by the instant screw axis. Using the proposed method, the instant screw axes and pitches are determined for the bump-rebound motion and steering motion of the double wishbone, McPherson strut, and 5-SS multi-link type suspension mechanisms. The numerical results agree with findings of previous researches.