Design and Research of Plane-symmetric Bricard-like Mechanism

Abstract

Due to the ingenious geometric constraints of the spatial single-loop mechanism, Bennett mechanism and Bricard mechanism have been proposed and studied extensively. A new type of spatial mechanism can be constructed by connecting multiple anti-quadrilateral mechanisms by using revolute joints, which has the motion characteristics similar to a spatial single-loop mechanism. A spatial plane-symmetric Bricard-like mechanism similar to plane-symmetric Bricard mechanism is proposed. The Bricard-like mechanism is composed of two identical anti-quadrilateral units and one anti-parallelogram unit. According to the movement characteristics of the anti-quadrilateral unit, the Bricard-like mechanism can be simplified as a special spatial plane-symmetric mechanism with variable links' lengths. Then the degree of freedom and kinematic paths are further analyzed through the D-H parameters and the closure equations by considering the simplified spatial 6R mechanism with variable links' lengths. In addition, according to the kinematic paths, the motion mode is analyzed, and it is obtained that the mechanism can realize inward and outward motion, then can realize infinitely turnover. The feasibility conditions of infinitely turnover is analyzed, and the constraint conditions for constructing the infinitely turnover mechanism is obtained. Finally, a plane-symmetric Bricard-like mechanism is fabricated to verify the feasibility of the proposed method and the correctness of analysis.