A Soft Four Degree-of-Freedom Load Cell Based on the Hall Effect

This paper presents the design of a soft four degree-of-freedom load cell that is robust and light-weight and can be integrated into robotic applications. The sensor measures three axes of force and a single axis of torque about the central axis. The sensor is comprised of a magnet suspended within an elastomer above two three-axis Hall effect sensors. As a load is applied, the magnet is displaced within the elastomer that results in changes in the magnetic flux density at the locations of the two Hall effect sensors. Experimental measurements of magnetic flux density within the area of interest were used to formulate analytical expressions to relate magnet field strength to the position of the magnet. The displacement and orientation measurements combined with the material properties of the elastomer are used to calibrate and calculate the applied load. The ability to measure the three degrees-of-freedom force and axial torque was evaluated with combined loading applied by a robotic arm. The decoupled results show the four degree-of-freedom load cell can distinguish three axes of force and one axis of torque with 6.9% average error for normal force, 4.3% and 2.6% average error for shear force in the Xand Y-axes, respectively. There was 8.6% average error for the torque.