Model Reconfiguration Theory And Experiment Research Of Parallel Six-axis Force Sensor With Heavy-load Capacity

This thesis concentrates on the theoretical research, simulation and experiments on the parallel six-axis force sensor used for measuring heavy load. The systematic research work includes configuration synthesis, theoretical modeling, simulation analysis, theory of reconfigurable modeling, prototype design and experiments. The work provides theoretical foundations and design basis for the application of six-axis force sensor in heavy load fields.Firstly, configuration synthesis for the six-axis force sensor based on flexible-parallel mechanisms with heavy-load capacity is carried out and many reasonable configurations of six-axis force sensor are presented. The spoke structures based on flexible-parallel mechanism with mixture branches are selected as the research object in this thesis. With screw theory, the mathematical models of selected parallel six-axis force sensor with spoke structure are established and the feasibility of these configurations are discussed according to the force mapping matrix.Secondly, based on the deformation superposition principle in single flexible serial branch, the stiffness of flexible measuring branch is modeled. The stiffness matrices including flexible branch and weight-bearing branch are obtained. Then, the complete analytical stiffness model of six-axis force sensor with heavy load capacity is conducted based on the hypothesis theory of small deformation of flexible unit and the deformation compatibility condition of parallel mechanisms. Further, the analytical force model presenting the measurement principle of the proposed flexible-parallel mechanism is established.Then, the performances of six-axis force sensor with heavy-load capacity are explored by finite element simulation. The change rules between key parameters of the force sensor structure and the sensitivity of measurement are obtain and analyzed. An equivalent sensitivity index which is suitable for parallel six-axis force sensor with heavy-load capacity is proposed. Aiming at achieving higher measurement sensitivity, the structure of proposed six-axis force sensor is optimized based on the proposed sensitivity index. The three-dimensional model is calibrated virtually by the virtual prototype technology and its main performances are analyzed.Finally, the reconfiguration theory of measuring models of flexible-parallel six-axis force sensor with heavy-load capacity is researched. On the one hand, the stiffness model is rebuilt by numerical method considering the influence of heavy load on the initial configuration. On the other hand, faced with multi-task requirements, the reconfiguration theory for self-adapting measurement is proposed take advantages of flexible-parallel mechanisms with multiple constrains. The property of multiple measurement models which the redundant parallel mechanism based force sensor possesses is fully token advantage of and it provides the theoretical basis for the application of the sensor in the multi-stage measurement task. The prototype of spoke six-axis force sensor with mixture branches used for measuring heavy load is developed and manufactured, the calibration platform used for calibrate the prototype is established. The sensor prototype is calibrated on this platform and its key performances are tested.