Uncertainty Analysis of a Force and Torque Sensor Calibration Machine Utilizing Electromagnetic Actuation

Six-axis force and torque (F/T) sensors are integral to automatic machinery applications. To meet stringent accuracy requirements, these sensors necessitate precise calibration prior to deployment. A calibration machine using electromagnets and load cells to generate six-axis referenced forces and torques for sensor calibration is proposed. Three primary sources of uncertainty—load cell repeatability, temperature drift, and fabrication tolerance of the calibration machine—have been analyzed. Among these, geometric errors because of fabrication tolerance were identified as the most significant source of uncertainty. Mathematical models were developed to quantitatively analyze the error forces and torques induced by the geometric errors after fabrication. The uncertainty budgets for each of the six axes were comprehensively discussed. Experiments verified the uncertainties of the prototype, with the mean repeatability and relative error of the calibration machine, referenced to a commercialized calibrated F/T sensor, found to be 0.259% and 0.185%, respectively.