Calibration of the pose parameters between coupled 6-axis F/T sensors in robotics applications

This paper presents a new method for calibrating the pose parameters between two coupled 6-axis F/T sensors. The pose parameters include translational and rotational parameters defining the full coordinate transformation between the F/T sensors. The sensor 1 was fixed mount in the robot's flange and the sensor 2 was relocatable i.e. it was mounted arbitrarily on the last link of the robot after the wrist mount sensor. The novelty of our work is in the procedure for solving the translational pose parameters by means of contact point locations solved from systems of linear 3D-torque equations. In the calibration the operator exerts a series of diverging forces on the guiding handle which results in different amount of torque with respect to the coordinate frames of the F/T sensors depending on the respective contact point locations. The acquired forces and torques in the both sensor frames are input to the calibration function which outputs the full pose of the sensor 2 with respect to sensor 1. The influence of the sensor signal noise and the deviation of contact point location as well as unintended wrenching of the handle to the calibration accuracy were evaluated with numerical simulations in MATLAB. The performance of the calibration procedure was demonstrated with the real system including commercially available F/T sensors and medium sized industrial KUKA robot. The experiments verify the achievable calibration accuracy was in the level of ±20 mm and ±5° and in line with the simulation results.