Design And Performance Resarch On A Novel 3-leg 6-DOF Parallel Manipulator

The development of the 6 degree of freedoms(DOF)parallel mechanisms with six legs is well-understood,most of which are Stewart mechanism and its similar mechanism in a real world application.However,using these mechanisms,it is easy to happen the interference among mechanical parts and singulars from the theoretical workspace.And the performances of the mechanism may be degenerated and the structure may be damaged.Thus,it is necessary further study for 6-DOF parallel mechanism with three legs.As an important enrichment in short leg of parallel mechanism,a special 6-DOF parallel manipulator have been developed.One of the advantages of this structure is that three translational and three rotational motions are decoupled,the end-effector position is only determined by three lengths of prismatic actuators,while the rotational angles are relative to all six inputs,so that it is easier to compute the end-effector position and orientation of the manipulator in inverse and forward kinematics.(1)Based on G_F sets,the 24 configurations of the 3-3T3R parallel mechanism,including position and orientation of the end-effector,are graphically displayed.Further more,a novel3-UP3R parallel mechanism with 6-DOFis selected as the best option.(2)The equations for the forward and inverse kinematics of a special 6-DOF parallel manipulator have been developed,and the solutions have been shown to be reducible to a first-degree polynomial equation and an eighth-degree polynomial equation.The degree of the equations is relatively smaller comparing to the existing methods,which reduce the computational burden.A numerical simulation is given to verify the algorithm,and the result implies that for a given set of input values,the manipulator can be assembled in at most eight different configurations.Based on those solutions,the configurations of the robot,including position and orientation of the end-effector,are graphically displayed.(3)One parameter design approach can easily find appropriate parameters that can make a robot with a smallest workspace include a predefined task workspace when a point with respect to the boundary of the maximal usable inscribed workspace is given.This method can improve the design efficiency and ensure that the robot has a small mechanical size possesses a large workspace volume,and meets in the light weight design requirements.An algorithm of optimal designing is introduced to find the smallest dimensional parameters of the proposed robot.Examples illustrate the design results,and a design stability index is introduced,which ensures that the robot remains a safe distance from the boundary of sits actual workspace.Finally,one prototype of the robot is developed based on this method?(4)Addressing the kinematics accuracy problem of the proposed new mechanism with three legs due to the location of the U joint errors,clearance and driving errors.According to the generalized kinematic mapping of motions in the workspace,the end-effector's exact output error bound for a standard deviation of the components can have a great influence on the pose(position and orientation)error.The stochastic results are presented;for considering both the location errors clearance and driving in the total simultaneous effect of the errors,the superposition principle is not suitable when any of the errors is considerably larger than the last two errors.The models can be built into the controller and used to compensate for the location of the U joint errors,clearance and driving errors.Experimental results show that the robot accuracy is improved and demonstrated the effectiveness of the proposed method.(5)The statics of the proposed mechanism is researched first and then the deformations of the links are introduced.And the stiffness model is formulated.The strength and rigidity design method about material characteristics,structure and dimensions of the component.A method for improving rigidity and stability in a novel 3-3T3R parallel mechanism is presented.