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Direct kinematics with analytic solutions is critical to the real-time control of parallel mechanisms.Therefore,the type synthesis of a mechanism having explicit form of forward kinematics has become a topic of interest.Based on this purpose,this paper deals with the type synthesis of 1T2R parallel mechanisms by investigating the topological structure coupling-reducing of the 3UPS&UP parallel mechanism.With the aid of the theory of mechanism topology,the analysis of the topological characteristics of the 3UPS&UP parallel mechanism is presented,which shows that there are highly coupled motions and constraints amongst the limbs of the mechanism.Three methods for structure coupling-reducing of the 3UPS&UP parallel mechanism are proposed,resulting in eight new types of 1T2R parallel mechanisms with one or zero coupling degree.One obtained parallel mechanism is taken as an example to demonstrate that a mechanism with zero coupling degree has an explicit form for forward kinematics.The process of type synthesis is in the order of permutation and combination;therefore,there are no omissions.This method is also applicable to other configurations,and novel topological structures having simple forward kinematics can be obtained from an oriqinal mechanism via this method.