Instantaneous Mobility and Constraint of a 3-PPS Parallel Mechanism

Jing-Shan Zhao, Fulei Chu, Li-Ping Wang and Zhi-Jing Feng

ABSTRACT: This paper investigates the mobility and constraint of a spatial parallel mechanism whose end-effector has three degrees of freedom. The novelty of the mechanism is that its end-effector should output two rotations and one translation with 3-PPS kinematic chains. In this paper, the degree of freedom of an end-effector of a mechanism and the number of actuations required to control the end-effector are defined, individually. And then, the exponential product procedure to analyze the twists and wrenches of a kinematic chain is deduced in one fixed Cartesian coordinate system. The mobility and constraint of the end-effector are addressed from the viewpoint of instantaneous free motions and the number of actuations needed to control it. Actuation scheme analysis indicates that the degree of freedom of an end-effector and the number of independent actuations needed to uniquely control the end-effector should not be ambiguously represented by one concept such as the general mobility of a mechanism.

KEYWORDS: Mobility, Constraint, Spatial Mechanism, Endeffector, and Kinematic Chain

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