Study On A Six-AXIS Accelerometer Based On Stewart Platform

In the course of grasping objects by the dexterous hands of humanoid robot, the inertial force caused by the spacial acceleration imposed on the hands will affect the grasping robustness. The spacial acceleration need to be measured so as to calculate the position and attitude of the carrier with the method of integration the spacial acceleration in inertial navigation systems. And there is an urgent need of six-axis accelerometers in the other fields such as weapons guidance, car collision and sports. Nevertheless, it is difficult to fabricate the elastic element to simultaneously sense the three linear accelerations and three angular accelerations with the method of placing the sensing elements along the x, y, and z-orthogonal decomposition. With the development of parallel mechanism, the structural features of Stewart platform provide a new approach to study on a six-axis accelerometer. Using the compliant mechanism based on Stewart plarform as elasitc element,This paper studied a six-axis accelerometer on the theory and calibration experiment in order to solve the key science questions such as parallel mechanism not used as the elastic element of sensor with small range because of high rigidity causing low singal to noise(S/N) and the structural errors by the solid model instead of the simplified theoretical model affecting sensor measurement accuracy, and provide a theoretical basis and experimental guidance for study on the six-axis accelerometer. Research the following:(l)Based on the definition of the static model for the six-axis accelerometer, the mathematic static model of sensor war established with the method of the physical model of solution space and changed3D nondimensional parameters into2D by the conversion formulas. According to the method of vector product and theory of parallel mechanism, acceleration Jacobian matrix was detailedly deduced and expressed by the nondimensional parameters.(2)Based on deviding the errors affecting measurement accuracy into basic errors associated with the acceleration Jacobian matrix and impact errors associated with the output strain matrix of the elastic leg, this paper analyzed the impact law caused by the errors affecting measurement accuracy and factors affecting S/N of sensor. And then, the sensor performance indexes were difined such as the static and dynamic characteristics, especially in isotropy and sensitivity characteristics expressed by nondimensional parameters of simplified theoretical model.(3)The performance atlases were drawn and used to express the relationship among all kinds of indexes to theoretical parameters based on the definition of isotropy and sensitivity characteristics. Then, the single-objective optimization functions and multi-objective optimization functions were constructed so as to optimize the theoretical parameters, and the results were compared with those obtained by other optimization methods.(4)In order to solve the questions such as the structural errors by the solid model instead of the simplified theoretical model affecting sensor measurement accuracy and he limitations of modeling methods for compliant parallel mechanism, the finite element method of numerical solution was utilized to study the structural rigidy affecting measurement accuracy and dynamic characteristics of the sensor. Taking the contradictions bring by structural rigidy affecting measurement accuracy and dynamic characteristics into account, this paper presented to optimize the solid model parameters by orthogonal test and extreme difference analysis.(5)So as to solve the questions such that parallel mechanism not used as the elastic element of sensor with small range because of high rigidity causing low singal to noise(S/N), the method of stress concentration factor was applied to study the elastic element structure based on the redefinition stress concentration factor in order to establish the mathematic model for he elastic element structure with the method of Muskhelishvili. According to the method of stress concentration factor, this paper presented a structure of elastic element with double cantilever beam, constructed force model and calculated by the finite element method.(6)Based on the anslysis mechanism of coupling errors for the six-axis acclelerometer with Stewart platform, this paper studied the decoupling method, designed the measuring system for sensor based on the prototype processed, calibrated the measurement accuracy by calibration experiment and,finally, silmulated dynamic characteristics.