Research On The Theory Of A Kind Of Limited-dof-freedom Parallel Manipulator With Composite Driving And Constrained Branch

Limited-degree-of-freedom(limited-DOF) parallel manipulators have many advantages, for example higher opposite stiffness, less active legs, larger workspace,stronger loading ability, simple structure, easily control and so on. It is different with the traditional 6 freedom degrees parallel manipulators, limited-DOF parallel manipulators lie in the structure constraints, it cause to produce constraint force/wrench in legs. To make sure stress, accuracy of manipulator, and to choose suit manipulators, the question of active-constrain force/wrench must be solved. We construct composite active legs to reduce number of active legs, reasonably assign legs and distribute error, raise kinematic accuracy of limited-DOF parallel manipulators.Stiffness is one of important performance sign, so stiffness and deformations analysis is very important for limited-DOF parallel manipulators.In this thesis, a statics vector analytical approach is proposed for determining poses of the active/constrained wrench and analyzing statics problem of limited-DOF parallel manipulators. 21 types of acceptable legs with linear or rotational actuator is summarized, the poses of the active/constrained wrench exerted on the various acceptable legs are determined by the statics vector analytical approach. Design adjustable type parallel manipulators linear legs, convert 3 kinds of pair, transform parallel manipulators types. A 6×6 Jacobain matrices and a statics equation are derived for solving active/constrained wrench of many limited-DOF parallel manipulators. The active/constrained wrench 3-DOF 3-RRPRR parallel manipulators and 4-DOF2-SPS+2-SPR parallel manipulators are solved by statics vector analytical approach.A method is proposed to solve the active-constrained force of some limited-DOF parallel manipulators with SPR-type active legs by using the CAD variation geometric.By the example of 3-SPR parallel manipulators, 2-SPS+2-SPR parallel manipulators,and 4SPS+SPR parallel manipulators, they have 3-5 DOF with SPR-type active legs.Firstly we construct their motion simulation mechanisms, and then construct their force simulation mechanisms, solve their active-constrained wrench matrices and active-constrained force. Thus we can certify the method is feasible to solve the active-constrained force of some limited-DOF parallel manipulators with SPR-typeactive legs by using the CAD variation geometric.A 3-leg 5-DOF 2-SPS+UPU parallel manipulator with UPU-type composite active leg and a 3-leg 4-DOF 2-SPS+PUP parallel manipulator with PUP-type composite active leg are proposed, Influence of kinematics and statics are analyzed systematically by composite active leg. For kinematic accuracy is raised, we construct UPU and PUP composite active leg. By considering the active/constrained wrench, the6×6 Jacobian matrices and 6 layer 6×6 Hessian matrices are solved, and model of displacements, velocity, accelerations are established and statics analysis. 2 kinds of parallel manipulator are analyzed by motion simulation, and compare analytic results with motion simulation results.Elastic deformations of active/constrained leg of 3-SPS+UP and 3-UPS+RRPR limited-DOF parallel manipulators are solved by basing on the active/constrained wrench. The compliance matrices of active/constrained legs are solved. Based on the6×6 Jacobian and compliance matrices of active/constrained legs, total stiffness matrices and elastic deformations of the limited-DOF parallel manipulators are solved.Elastic deformations of moving platform’s centre is analyzed, and compare analytic results with finite element simulation results by establishing finite element simulation model of 2 kinds of limited-DOF parallel manipulators. The influence of the constrained wrench on the stiffness and elastic deformations of the limited-DOF parallel manipulators is analyzed.