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.

Additional Metadata
Keywords Calibration, compliant sensors, fiber-optic, Force, Force measurement, Force-Torque measurements, intensity modulation based, multi-axis force and torque sensor, Optical sensors, rehabilitation system, Torque, Torque measurement
Persistent URL dx.doi.org/10.1109/JSEN.2018.2856098
Journal IEEE Sensors Journal
Citation
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