Research on Type Synthesis and the Method of Choosing Optimum of a Family of Spatial Translational Parallel Robots
|School||Zhejiang University of Technology|
|Course||Mechanical and Electronic Engineering|
|Keywords||Spatial Translational Parallel Robots Type Synthesis Choosing Optimum Actuated Layouts Conjugate Subgroups Conjugate Submanifolds Maximal Regular Dexterous Workspace|
In the recent ten years,the type synthesis research of the lower-mobility parallel robot mechanism（LmPRM）has a larger evolvement.Many systematic methods of the type topological synthesis were proposed,thus a lot of topological limbs were disclosed.However,the number of the LmPRM is very poor in the actual applications.The reasons of baffling their wide application have many aspects, hereinto includes:（ⅰ）since the variety of mechanism type,difficult to select an optimal mechanism solution for a operation task;（ⅱ）the performance indices depend on their topological limb types,the actuated layouts,and design parameters, such that their design is a difficult task.The former is comparison and choosing optimum of LmPRMs.Another is optimal design of parameters of the mechanism. In the dissertation,the each mechanism of a family of spatial translational parallel robots（STPR）is constructed firstly by means of group theory and differential geometry.Then,a systemic method is proposed to solve the problem of their choosing optimum.The goal is find an optimal mechanism solution for a prescribed operation task.Following jobs are carried out:Firstly,in order to construct fully a family of STPR mechanisms,and to depict uniquely and distinctly each mechanism.Carry out orderly three jobs:（ⅰ）The usable topological limbs of a family of STPR mechanisms are enumerated.All these limbs have an actuated prismatic joint fixed in the base.They are classified into three categories:the type of T（3）subgroup,X（z）subgroup,and T（3）·U（O,ω1,ω2）submanifold,by means of their output motion types;（ⅱ）According to the number of absolute directions of the three-vector-system,then the actuated layout problem of a family of STPR are analyzed systematically.Their six kinds of actuated layouts are obtained,and coordinate-free description of each kind of actuated layout is given too.（ⅲ）Introduce the concept of conjugate subgroup and conjugate submanifold,and a novel theoretical method is proposed to construct a whole STPR mechanism here according to assembly condition of corresponded topological limb.Based on these researches,a full theoretical method is established, which is an applicable to determine all possible STPR mechanisms of anyone usable topological limb.Finally,this family of STPR mechanisms is determined one by one.Each mechanism in the family is depicted by means of the type of its topological limb,the actuated layout,and the structure parameter.Then,a systemic method for choosing optimum is proposed.For a prescribed operation task,an optimal mechanism solution is found from this family of STPR through the proposed method.The global conditioning index,the global stiffness index,and the space utilized rate index of each STPR are considered in our criterion of the choosing optimum.Some pivotal processes are investigated to serve as higher efficiency of the choosing optimum:（ⅰ）A kind of uniform method is proposed to analyze the kinematic problems of this family of STPR.Additional, the kinematic analysis software is designed to avoid analyzing singular mechanism and the vast symbol operation;（ⅱ）A set of numerical algorithms is proposed to determine the reachable and the dexterous workspaces and their boundaries,and the maximal regular dexterous workspace of encasing inside the accessible;（ⅲ） Based on this,two kinds of optimal design problems are converted into the unconstrained nonlinear optimal problems,and are solved.Finally,in order to obtain the result of the choosing optimum with a numerical form,an operation task is defined,four different criterions of the choosing optimum are considered,and four cases of results are presented by means of the proposed approach through the subfamily of PRPaR STPR acted as an example. The validity and comprehensiveness of results of the dissertation are validated through comparing with other results in the correlative literatures.