Optimal Design And Comparison Study Of Constraint Performance For Two Kinematic Identical Parallel Manipulators With 2R1T Dofs

Due to the broad application prospects,parallel manipulators(PMs)with two rotational and one translational(2R1T)degrees of freedom(DOFs)are always the focus topic in field of kinematic of machinery and industry.In this paper,two PMs with 2R1 T dofs are studied to demonstrate a complete research system for kinematics identical mechanisms(KIMs),which is from the derivation of KIMs to motion/force transmission performance evaluation and optimal design based on transmission performance of KIMs,and then finally to comparison study on conatraint ability among KIMs.The study is significant which can not only help to avoid some repetitive work in the field,but also provide more configuration choices for the design of PMs in the practical applications of Engineering.Firstly,taking the 2RPU+UPR PM as the research object,this paper explains the evolution principle of KIMs in detail and proposes a unified form of the principle in mathematical expressions.Based on the evolution principle,many parallel manipulators with different configurations are derived.Secondly,the concept of motion/force transmission indices is introduced.The motion/force transmission performance of the 2RPU+UPR PM and it's KIMs are considered on the basis of local transmission index and transmission performance atlas of them are proposed.According to geometric constraint,parameters design space of the 2RPU+UPR PM and it's KIMs is obtained.Optimal design based on the global transmission index and good transmission orientation workspace of the PM is performed in the parameters design space.Aafterwards,motion/force constraint indices of non-overconstrained parallel manipulators are introduced.Some problems exist in the process of solving the input constraint index(ICI)and physical meaning of the input constraint index are discussed.Inspired by the way of motion/force transmission performance evaluation of redundant actuated PMs,this paper proposed an approach to solve the output constraint index(OCI)of overconstraint PMs.Performance atlases of OCI for the 2RPU+UPR PM and it's KIMs are presented under optimized physical dimensions.Global constraint indices of PMs are calculated to compare the constraint ability among them.At last,based on the research route about KIMs expressed by this paper,an asymmetric 3PRS PMs is taken as an example to review and verify the route.For the asymmetric 3PRS PMs and its KIMs,the motion/force transmission ability of them is evaluated and optimal design based on transmission performance is performed,and then the conatraint performance among the asymmetric 3PRS and it's KIMs is compared for providing a reference for configuration selection finally.