6 DOF force and torque sensor for micro-manipulation applications

This paper presents the design, fabrication and characterization of a piezoresistive 6 degrees of freedom (DOF) force and torque sensor to be used in micro-manipulation. The device has been fabricated with an IC-compatible process and contains 24 piezoresistors as sensing elements. Its partly asymmetric mechanical structure consists of 7 suspended beams providing force sensing functionality on a probing area, which includes a calibration structure. Thanks to this asymmetrical structure, micro-manipulation tools such as micro-grippers or probes can be easily implemented in the same substrate as the sensor, replacing the probing area. The geometry of the beams and the location of the piezoresistors in the structure are designed using finite element modeling to provide independent force measurements (i.e. low crosstalk) and high sensitivity, with limited geometrical size. The mechanical structure is 3 mm × 1.5 mm × 0.03 mm in size and its first resonance frequency is estimated to be 4500 Hz, as computed with a dynamical analysis. A calibration of the device is experimentally performed, and a linear regression model is fitted to the calibration data to extract the forces and torques from the resistance variations detected in the piezoresistors. The data acquisition system is programmable, allowing for dynamic adjustments of the trade-offs between noise levels, uncertainty and bandwidth. Depending on the axis, the linear range of the sensor reaches 4-30 mN in forces and 4-50 μN m in torques. During on-line measurements, noise levels up to 13-27 μN/Hz0.5 and 11-43 nN m/Hz0.5 were observed respectively, for forces and torques.