Fiber Bragg Gratings Sensor System for Kinematic and Dynamic Assessment in Lower Limb Robotic Rehabilitation

This article presents the development and application of a fiber Bragg grating (FBG)-based sensor system for dynamic and kinematics assessment of an exoskeleton for lower limb rehabilitation. The exoskeleton has 2 degree-of-freedom, one at the knee joint and the other for the ankle joint, which is positioned on a chair for robotic-assisted rehabilitation of both joints. The proposed FBG-based sensor system includes an FBG array for the strain distribution assessment along the exoskeleton structure, which is used for the human-robot interaction assessment. In addition, FBG accelerometers and inclinometers are positioned on the knee and ankle joints (respectively) of the exoskeleton for the kinematic analysis of such device. The angle characterization tests indicated a root mean squared error (RMSE) for angle assessment of 3.17° and 1.64° for knee and ankle joints, respectively, which results in a relative errors of 3.96% and 6.07% considering the range of movement of both joints. Moreover, the strain sensors indicated a determination coefficient of 0.999 for FBGs 1 and 2. Thereafter, the sensor system is applied on the knee and ankle joint angle measurements as well as the human-robot interaction via strain distribution along the structure. In this case, the tests with a user indicate the variations in knee and ankle joints within the range of movement applied by the exoskeleton’s controller. Furthermore, the interaction forces between the user and the exoskeleton are evaluated using the strain distribution along the exoskeleton structure.