Realization of a fiber-optic force-torque sensor with six degrees of freedom

Abstract

Multi-axial force and torque sensing is of importance for robot control and many force-feedback applications. Minimal invasive robotic surgery (MIRS) is a possible field of application of force and torque sensors with up to six degrees of freedom. Although these sensors are not yet employed in current commercial MIRS systems, extensive work has been carried out on the development of these sensors. Some of their issues are related to their electric working principle: they are limited in performance by thermal noise, need electric power inside the patient and are not usable under influence of strong magnet fields (e. g. in MRI machines). One possible alternative is seen in fiber optic force torque sensors, since the signal demodulation may be located in some distance to the actual sensor and they also do not have to include any magnetic material. This article presents a fiber optic force and torque sensor with six degrees of freedom. The general setup resembles a Stewart Platform, whereas its connecting beams are formed by the fiber itself, and the element creating stiffness may be of arbitrary form. Only a single fiber is needed to extract all six parameters since they are measured on six multiplexed fiber Bragg grating sensors. We demonstrate how the sensor is realized and show results of torque measurements with variable load.