Assembly precision prediction for planar closed-loop mechanism in view of joint clearance and redundant constraint

The assembly process for planar closed-loop mechanisms is full of complexity and uncertainty due to joint clearance, link coupling and probable redundant constraint. In order to ensure assembly precision, an algorithm of predicting accuracy for planar closed-loop mechanisms in view of joint clearance and redundant constraint is proposed. Firstly by analyzing the assembly process of a planar fivebar closed-loop mechanism, three components of single-fixed, two-connected and redundant-inserted links are proposed to describe the assembly process of arbitrary planar closed-loop mechanisms which is regarded as successive stacking of those components. Then error models of those components are established based on the linear kinematics and principle of virtual work. Subsequently, an algorithm of precision prediction for planar closed-loop mechanisms is constructed by combining those error models. Finally the extendible support structure of the SAR antenna is used as the numerical example to verify the validity and generality of the proposed algorithm.