This paper introduces the fabrication of a six degreeof- freedom force and torque sensor based on fiber-optic sensing technology and its novel calibration methodology. The sensor is cost-effective, lightweight and flexible with a large force and torque measurement range suitable for biomechanics and rehabilitation systems particularly when a wearable sensing system is desired. Six fiber-optic sensing elements are used to detect three main forces Fx, Fy, Fz and three main torques Tx, Ty, Tz. Sensor data was collected by applying dynamic forces and torques with various magnitudes, directions and frequencies and compared with measurements obtained from a standard force and torque reference. The proposed calibration procedure is intended to reduce errors stemmed from a nonlinear forcedeformation relationship and to increase the estimation speed by splitting the calibration into two estimation models: a linear model, based on a standard Least Squares Method (LSM) to estimate the linear portion; and a nonlinear Decision Trees model (DT) to estimate the residuals. Both models work simultaneously as a single calibration system named Least Squares Decision Trees LSDT. Using LSDT, the estimation speed increased by 55.17% and the Root Mean Square Errors (RMSE) reduced to 0.53%. In comparison, each model separately had a root mean square errors of 1.26% and 4.70% for DT and LSM, respectively.

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IEEE Sensors Journal
Department of Mechanical and Aerospace Engineering

Al-Mai, O. (Osama), Ahmadi, M, & Albert, J. (2018). Design, Development and Calibration of A Lightweight, Compliant 6-Axis Optical Force/Torque Sensor. IEEE Sensors Journal. doi:10.1109/JSEN.2018.2856098