Study on friction modeling for sizable Stewart platform-based force/torque sensor

To further improve the precision of sizable Stewart platform-based force/torque sensor with general spherical joints in existing manufacture and calibration techniques, substituting spherical joints with three equivalent revolute joints, the paper presents the friction model of sizable parallel 6-axis force sensor with Stewart structure based on the screw theory and theory of influence coefficient. The friction influence matrix and the expressions of type I/II errors are deduced, which indicate the effect of joint-friction upon precision of measurement. Then, the graphs of type I/II errors of the parallel 6-axis force sensor under different external forces and frictional coefficient are plotted and the rule how the joint- friction affect the measuring precision is analyzed. Thus, the powerful basis and method are raised for the improvement of the precision of sizable Stewart platform-based force/torque sensor with general spherical joints.