Research On Kinematics Analysis Method Of Parallel Mechanism Based On Basic Branch Chain Configuration

Parallel mechanism has always been the focus of mechanism research.Compared with serial mechanism,it has the advantages of high accuracy and flexibility,and is widely used in aerospace,medicine,intelligent manufacturing and other fields.Among them,the kinematics research of parallel mechanism is an extremely important part,which plays a decisive role in the performance and application of parallel mechanism.At present,the research method is still the direct kinematics analysis of the parallel mechanism as a whole,which has the problems of complex analysis and non-generality of the method.In order to solve this problem,the kinematics analysis method of parallel mechanism is studied from the point of the branch chain,which is the basic unit of parallel mechanism.To put forward new analysis methods or improve existing methods can not only enrich the theoretical research content of parallel mechanism kinematics,but also have important significance for the practical application of parallel mechanism and the development of industrial technology.In this paper,from the point of the basic branch chain of parallel mechanism,the DOF analysis method,position analysis method,workspace analysis method and singularity analysis method of parallel mechanism are studied.Firstly,the geometric method for DOF analysis of parallel mechanisms is studied.The basic branch chains of parallel mechanisms are constructed and their geometric constraints are analyzed.In the analysis of DOF,all the branch chains of the parallel mechanism are dismantled and the geometric constraints of the branch chains are obtained according to the relationship between the branch chains and the basic branch chains.Then the geometric constraints of the parallel mechanism are analyzed,and the restricted motions are obtained.Finally,the DOF of the mechanism is analyzed.Secondly,the position analysis method of parallel mechanism is studied.In the aspect of inverse displacement analysis,the inverse displacement equation of each driving pair’s branch chain is established by coordinate transformation,and then the inverse displacement equation group of parallel mechanism is obtained.According to the structure or motion characteristics of parallel mechanism,the additional constraint equation of mechanism is deduced and substituted into the inverse displacement equation group,and the final form of inverse displacement solution is obtained.In the aspect of forward displacement analysis,based on the angle of branch chain,the numerical and analytical methods of forward displacement analysis are studied,and the analysis process is summarized.Then,the analytical method of workspace analysis for parallel mechanism is studied.Firstly,the inverse displacement equations are formally transformed,the influencing factors are input,and the boundary equation of each branch chain position workspace is established by analytic method.Then,the position workspaces of all branch chains are intersected and the position workspace of parallel mechanism is obtained.Finally,the global workspace of the parallel mechanism is obtained by merging all the position workspaces of the parallel mechanism.Finally,the singularity analysis method of parallel mechanism is studied.Based on the idea that each branch chain is subject to geometric constraints and the driving pair is locked and transformed into geometric constraints,the singularity judgment and the construction of singularity type of parallel mechanism are carried out by using the knowledge of linear geometry,and the singularity distribution characteristics are analyzed.In this paper,the method of kinematics analysis based on basic branch chains is used and several typical parallel mechanisms are taken as examples to analyze and verify the validity and feasibility of the method of kinematics analysis of parallel mechanisms from the perspective of basic branch chains.