Gravity Compensation Strategy Of 3-R(?)S Parallel Manipulator With Horizontal Layout

In order to meet the demands of large/complex component manufacture for the high-efficient manufacturing equipment in the aircraft and automotive industry, and pay attention on the gravity compensation issues of parallel manipulators with horizontal layout, this thesis carries out the gravity compensation strategy of a 3-R(?)S parallel manipulator with horizontal layout, which includes the inverse position analysis, the analysis of the gravitational influence to the parallel manipulator deformation, design and parameter optimization of passive gravity compensation device, evaluation of the gravity compensation consequence, design of active gravity compensation device, etc. The following contributions have been made.Inverse position analysis and compliance modelling of 3-R(?)S parallel manipulator. The inverse position analysis is carried out based upon the closed-loop vector method. According to the relative motion and gravity distribution of components, the 3-R(?)S parallel manipulator with horizontal layout is decomposed into 3-R(?)S limbs and the end effector. By means of the linear superposition, the compliance model of the parallel manipulator is formulated.The analysis of gravitational influence to the parallel manipulator deformation. The gravity mapping model is formulated by using the virtual work principle. The distribution of the manipulator deformation in the workspace caused by gravity is achieved by the combination of the compliance model and the gravity mapping model, and then the conclusion is made that the gravity compensation is necessary.Design and parameter optimization of passive gravity compensation device. According to the static analysis, the gravity compensation device is designed based upon the helical tension springs, and its parameters are optimized by taking the minimum of the potential energy fluctuation within the workspace as the objective function and subjecting to several constraints. It is concluded that the gravity compensation strategy is valid by comparing the results before and after implementing the gravity compensation.Design of active gravity compensation device. The displacement compensation device is introduced to improve the passive gravity compensation device. According to the each spring variation, the installation positions of the displacement compensation devices is determined, and then its displacement parameters are optimized by taking the minimum of the parallel manipulator deformation under given trajectory. Finally, the 3D structure design of the displacement compensation device is established by using Solidworks.The above research work provides theoretical and technological support for the realization of the gravity compensation for 3-R(?)S parallel manipulator with horizontal layout, which can also lay a solid foundation for the gravity compensation of similar parallel manipulators.