The Type Synthesis Of 2R1T And 2T1R 3-DOF Redundant Actuated Parallel Mechanism Based On The Atlas Method

In some applications like complex surface milling with high stiffness,high precision and high dexterity,drilling rivets that need to compensate for instantaneous impact,welding with high precision and large working space,and logistics handling applications with large load-carrying capacity,good dynamic characteristics and good adaptability,2R1 T and 2T1 R 3 degrees of freedom redundant actuators are required.In this paper,two methods for type synthesis of redundant parallel mechanisms are proposed from two perspectives based on atlas method.This method is simple,systematic and has clear physical meaning.Then the type synthesis and instantaneous analysis of 2R1 T and 2T1 R 3-DOF redundant actuated parallel mechanisms are carried out by using the two proposed methods.The main contents are as follows:Firstly,the atlas method and the geometric principle of Grassmann line were briefly introduced.A method of type synthesis of redundant actuated parallel mechanisms with redundant branches based on Atlas method is proposed,and 2R1 T and 2T1 R redundant actuated parallel mechanisms are classified according to their motion characteristics.Secondly,the type synthesis of the first and second kind of 2R1 T 3-DOF redundant actuated parallel mechanisms is carried out by using the proposed method.According to the principle of branch chain constraint allocation,it can be divided into seven schemes.Each scheme can obtain 12,67,96,0,12,48,and 16 configurations respectively,and a total of 251 configurations are synthesized;and the instantaneous analysis of the synthesized mechanism is carried out by the atlas method.It is found that the synthesized mechanisms of scheme 1 and scheme 2 are instantaneous.An improved method of coaxial placement with a pair of parallel force constraints is proposed to eliminate the instantaneity of the mechanisms.Thirdly,the type synthesis of the first and second kind of 2T1 R 3-DOF redundant actuated parallel mechanisms is carried out by using the proposed method.According to the principle of branch chain constraint allocation,it can be divided into twenty-five schemes.In this paper,scheme 5 is taken as an example for type synthesis and instantaneous analysis.Taking scheme 6 as an example,this paper introduces an extended thinking for obtaining the second type of 2T1R3 DOF redundant actuated parallel mechanisms,and their type synthesis and instantaneous analysis are completed.Finally,based on the atlas method,a type synthesis method of redundant actuated parallel mechanisms with redundant branched chains and closed-loop units is proposed.Two kinds of 2R1 T redundant actuated parallel mechanisms with closed-loop units and one kind of 2T1 R redundant actuated parallel mechanisms with few branched chains and closed-loop units are taken as examples,and type synthesis is carried out by choosing one of the constraint allocation schemes of three types of mechanisms respectively based on the atlas method.238,92 and 15 new configurations were obtained respectively.The instantaneous analysis of typical representative parallel mechanisms is also carried out.