Study Of A Novel Parallel Piezoelectric Six-dimensional Heavy Force/Torque Sensor On Axis

The huge heavy-load manipulators are foundational equipment in machine industry chain. They not only represent the national extreme manufacturing capability and level, but also affect national economy and national construction projects. They are key devices which are needed in precise manufacture of large structure in fields of nuclear power, shipbuliding, chemical engineering, national defense. In working process of huge heavy-load manipulators, the loads can usually reach 100kN to 100MN, and have multi-degree characteristics. Measurement of six-dimensional force/moment and real-time force feedback are foundation to realize coordinated operation control and force compliance control on huge industrial robots. And they are also important to planning and adjusting forge process. At present, heavy force sensor can only measure one dimensional force. However, the measurement range of existing multi-dimensional force sensor can not satisfy requirement of heavy force value.This work is supported by a grant from the Major State Basic Research Development Program of China (973 Program) (No.2006CB705406). The main reaserch of this paper is to measure six-dimensional force in condition of huge heavy load. The concrete work is shown as followingFirstly, based on piezoelectric effect, the measuring method of multi-point supporting six-dimensinal heavy force is present. The mapping relationships between number of supporting points and six-dimensional heavy force to be measured are established. Configuration database of multi-point supporting six-dimensional heavy force sensor and responding decoupling algorithem are constructed. According to dynamic measurement requirement of six-dimensional force on huge heavy-load manipulator's gripper, the installation position of six-dimensional heavy force sensor is determined. Piezoelectric quartz is chosen as force sensing element to realize real-time measurement. The relationship between supporting points and spatial six-dimensional force is deduced. In order to investigate the validity of the proposed method, the FEM analysis and the experiments of piezoelectric six-dimensional force sensor is put forward with two kind's different spatial arrangement, and characteristic tests of the piezoelectric six-dimensional force sensor are performed. The results of experiment are consistent with theoretical and FEM analysis. The square arrangement based on four-point supporting structure is vertified to be better for measurement of six-dimensional force on axis. Secondly, the method for measurement of six-dimensional heavy force based on parallel structure principle is researched. According to parallel concente shunt principle, the parallel load distribution principle of piezoelectric six-dimensional force sensor based on four-point supporting structure is presented. The six-dimensional force sensor is rigidity connected with parallel bearing axis, so small part load of six-dimensional force/torque is translated to six-dimensional force/torque sensor. The measurement of six-dimensional heavy force/torque can be received by the mapping relationship between six-dimensional force/torque and load distribution force. The load distribution ratios are analyzed and calculated in vertical, horizontal, torque, moment directions. The main parameters which influence load distribution are obtained and analyzed. The feasibility and effectiveness of six-dimensional heavy force are verified by parallel load distribution principle and method.Thirdly, a novel non-assembly four-point supporting piezoelectric six-dimensional force sensor is designed with advantages of high-rigidity and high linearity. The preload project of this kind sensor is researched, and the influence of preload force on sensor is analyzed. The model of parallel piezoelectric six-dimensional heavy force sensor is set up, and the static and dynamic characteristics are analyzed by ANSYS software. By using scale as constraint conditions and improving the sensitivity as the main objective, structural parameters of four-point supporting six-dimensional heavy force sensor are optimized by single-factor method. The dynamic response characteristic of the sensor is studied. The mapping relationship between structure and dynamic characteristic is built.Fourth, method of static calibration on parallel piezoelectric six-dimensional force sensor is deeply researched. Novel calibration equipment for parallel force sensor is designed. Measurement platform for the sensor is built. According to measurement requirement and actural installation condition, tightening technology of surface friction based on distensible principle is presented. Tightening equipment for the sensor to fix on axis is put forward to solve fixation of six-dimensional force sensor and force transfer problem.Fifth, the static and dynamic calibrations on the optimal designed four-point supporting six-dimensional heavy force sensor are made. And then its calibrated matrix is obtained after static calibration experiment. Six signals can be decoupled by calibration matrix. Measurement performances in each direction can be obtained. The factors which affect on measurement performance of parallel piezoelectric six-dimensional are analyzed. The method of dynamic calibration is researched, and dynamic calibration experiment is dsigned. The result of experiment shows this kind six-dimensional force sensor has good force mesuring performance, and can realize measurement of spatial external force. The value of linearity error and repeatability error are all less than 1%, and the interference errors are less than 5%. The first natural frequency in three directions are all more than 2 kHz, and can satisfy required measuring requirement of huge heavy-load manipulator(1 kHz).The force sensor has reference value for the development of six-dimensional heavy force measuring technology by using piezoelectric as force sensing element. It can be widely used in extreme environments for real-time accurate measurement of multi-dimensional time-varying large loads. It can also provide important technical support to improve manufacturing precision and production efficiency of large and complex components. Meanwhile it has important practical value for upgrading Chinese huge heavy load manufacturing equipments with capabilities of high-precision, high efficiency, energy-saving manufacturing capacity and level of engineering.