| Due to the characteristic of the cylindrical internal surface grinding,this thesis proposed a family of symmetrical parallel mechanisms.The proposed mechanisms have two sides,and each side is a parallel mechanism which can performance the machining task.In the machining process,one side of the proposed mechanisms is the driving mechanism,which can drive the moving platform along the desired trajectory.The other side is the passive mechanism,which can support the moving platform.Based on its structural characteristic,the proposed manipulators are the redundancy parallel mechanisms.Based on the redundancy structure,the driving force of each motion can be decreased.At the same time,the loading capacity,stiffness and accuracy of the moving platform can be improved.The end-effector is connected to the two moving platforms with revolute joints.In this case,the end-effector can move along the desired trajectory,and its static stiffness can be improved.Thus,the mechanism can complete the grinding task,accurately.Firstly,based on screw theory,20 planar and 12 spatial symmetrical parallel mechanism are designed.Due to the practical situation and the form of the limb,the double parallel mechanism has been chosen as the following research objective.Secondly,the kinematics model of the proposed mechanism has been established.The position solution of the proposed mechanism has been performed,and the Jacobian matrix has been calculated.Next,the workspace,singularity and static stiffness of the proposed mechanism have been obtained.Thus,the effect which caused by the possible existing errors both of length and actuator have been analyzed.Next,the dynamics model of the proposed mechanism has been calculated.And the driving forces of each motion have been obtained.The difference of the driving forces between the two sides and one side of the proposed mechanism has been analyzed.Based on ADAMS,the theoretical and emulation results have been verified.The driving force under different working modes have been obtained,which can be regarded as the theoretical foundation for different tasks.And the multi-objective optimization has been processed by regarding the workspace and stiffness as the fitness functions.Finally,due to the above theory and results,the virtual model of the novel double parallel mechanism has been established.By combing ADAMS and MATLAB,error compensation of the proposed mechanism has been performed.In the overall workspace,the trajectory of the end-effector has been planned under special working mode.And the simulation results verified the correctness of the kinematics and dynamics model.Therefore,the proposed mechanism can meet the design requirement. |
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