Theory And Experimental Research Based On Over-constrained Orthogonal-Parallel Six Axis Force Sensor

With the rapid development of aerospace capabilities,the need of accuracy and large range of six-axis force/torque sensor has grown in importance.The parallel six-axis force/torque sensor has many obvious advantages,such as good stiffness and a symmetric and compact structure,which have resulted in widespread usage of this mechanism in the design of large range six-dimensional force sensor configurations.The orthogonal parallel six-axis force sensor is an improved based on the six-dimensional force sensor,which have considerable advantages,such as simple mapping and large range.This paper studies the theoretical analysis and experimental research on the over-constrained parallel six-axis force sensor.The main contents of this paper are as fllows:Based on screw theory,the structure of orthogonal parallel six-axis force sensor and characteristics are introduced,two types of over constrained orthogonal parallel six-axis force sensor configuration is proposed.Branch decoupling characteristics,load-sharing characteristics,range-limited and self-coupling output characteristics are put forward.The influence relationship between sensor parameters and performance indicators is discussed by the numerical simulation.The static equilibrium equation of the proposed sensor is established,the deformation of the pretightening-force and the deformation of the generalized external force are separated and expressed,then the displacement coordination equation is established.The expression of mapping relationship between generalized external force and branching force is derived considering the friction force of each branch.The displacement coordination equation is established by using the force method under the condition that the branch stiffness of the six-dimensional force sensor is difference,and the expression of the static branch force is obtained by using the superposition principle.On this foundation,the measurement model under the condition that the branch stiffness of the six-dimensional force sensor is generated under a tensile or compressive is derived,and the measurement model of the over-constrained orthogonal parallel six-axis force sensor is further obtained.The influence of branch stiffness on the branch output of the sensor is analyzed by numerical example.The ball decoupling measurement branch structure is designed and applied to develop the twelve branch orthogonal parallel six-axis force sensor and the eight branch orthogonal parallel six-axis sensor,then the calibration loading device is developed.The data acquisition system is set up and the data acquisition program is developed.Finally,the loading calibration experiment is carried out,and the calibration matrix and error matrix of the sensor are obtained through experiments.The error and performance of two kinds of sensor prototype are analyzed and compared by experiment data,which verifies the rationality of the design of ball decoupling structure,and a double-linear mapping model is used to correct the sensor error.The experiment is carried out to verify the measurement accuracy of the eight branch orthogonal parallel six-axis force sensor.