Research On 4-DOF Parallel Mechanisms Symbol Group And Topology Synthesis Method

In the field of modern mechanism research,with the advantages of high rigidity,good precision,and no accumulation of errors,the parallel mechanism are received great attention from scholars.In recent years,with the widespread use of parallel mechanisms in industry,it has been found that the total stiffness may be increased by hybrid limbs when the parallel mechanism has more basic links.In addition,through the auxiliary kinematic chain structure,the load capacity of the mechanism can also be increased.At present,the parallel mechanism models in application are relatively scarce.Therefore,it has a very important theoretical and practical value to study the structure of parallel mechanism design.The topology synthesis of mechanism is an important stage in the design of parallel mechanism configuration,and it is also a key problem to be solved in mechanical innovation design.Based on the associated linkages,symbol groups,arrays,contracted graphs and topology graphs,the configuration synthesis method of parallel robot and mechanism is studied.Using this method,the structure synthesis of 4-DOF parallel mechanism is also studied.The main research in this paper is as follows:(1)Based on the modified degrees of freedom G-K formula,this paper studys the associated linkages theory of the closed-loop mechanism.It deduces the computational results from the relationship between the basic links,redundant restraint and degree of freedom of the associated linkages with redundant constraint.Finally,the formula for calculating the basic links in the associated linkages are deduced.(2)A new characterization method of describing the contracted graph of parallel mechanism is proposed.Starting from revealing the basic rules of the contracted graph(the type and number of the basic links and the mutual connection between the links),the concept of the characteristic string and the connection substring is defined and the rules are formulated.These rules are the basis for developing the program algorithm.(3)On the basis of research on the theory of associated linkage and the description method of the contracted graph,the problem of isomorphic recognition of graphs in the process of contracted graph synthesis is deeply analyzed and the solution is proposed.Firstly,prior to the synthesis of the contracted graph,the isomorphic arrangement of basic links in the same set of associated linkage is cleared;then,after ensuring that the arrangement of basic links is not isomorphic,the characteristic string and the connection substring are generated.According to the rules,the arrays describing the same or isomorphic contracted graph are deleted,which can delete most of the same or isomorphic contracted graph;finally,according to the graph theory,the isomorphic graphs are identified when drawing the contracted graphs.(4)Based on the proposed contracted graph description method,the algorithm development is carried out,and the automatic synthesis system for the contracted graphs of parallel and closed-loop mechanism is designed.The aspects of the content are achieved: automatic derivation and display of associated linkages,automatic recognition and deletion of isomorphic arrangement of basic links,automatic generation and display of characteristic string and connection substring,automatic recognition and deletion of isomorphic characteristic string and connection substring,as well as the automatic synthesis and drawing of contracted graph.(5)The configuration synthesis of 4-DOF parallel mechanism is studied.The concept of digital topology graph and characteristic array is put forward,and the digital topology graph synthesis with more number of basic links is studied.At the same time,the derivation and synthesis process is illustrated by examples.On this basis,the configuration synthesis research on spatial 4-DOF parallel mechanism is carried out.