Study On Platform-configurable And Foldable 3-UPU Parallel Mechanism

The parallel mechanism has been developing for many years since its birth,and it has derived 6,5,4,3 branches and other types of parallel mechanism.Among the researches on the three-branch parallel mechanism,most of the papers set the mechanism with regular triangle platform the as a default condition.There are not so much research on the influence to the performance of the mechanism when the mechanism is designed with an arbitrary triangle platform.In view of this phenomenon,this paper takes the 3-UPU parallel mechanism as an example to analyze the influence on the performance of the mechanism when changing the shape and size of the platform.A novel 3-UPU parallel mechanism with configurable platform is proposed.The DOF of the mechanism was analyzed with the method of screw theory.The global mobility of the mechanism is proved,and the method of changing the shape of the platform without changing the DOF of the mechanism is derived.The influence on the workspace of the mechanism is analyzed when changing the shape and size of the platform,and the rule of influence is found.Based on the rule,two method of increasing the workspace of the mechanism is proposed.Based on the Hervé and Bricard over-constrained mechanisms,the planar and space auxiliary mechanism for changing the size of the platform are designed,so that the 3-UPU parallel mechanism could obtain a larger workspace with only two additional DOF.The property of the Threefold-symmetric Bricard mechanism is analyzed.The fullyexpanded shape and the mechanism is obtained by the D-H method.A foldable 3-UPU parallel mechanism is designed based on the Threefold-symmetric Bricard mechanism,greatly reduced the space occupation of the mechanism,and made a great benefit to the transportation and carry of the mechanism.