Development of a 3-DOF exoskeleton for rehabilitation and training of human wrist in combination with a virtual interface

Abstract

Rehabilitation therapies produce positive outcomes by recovering the lost brain plasticity after a cerebrovascular accident or stroke; such therapies can be applied by physiotherapists with the assistance of rehabilitation devices; among these devices, robots have shown the capability of providing consistent and measurable routines for long periods. In the physiotherapy process, the upper limbs are the first parts of the body to receive rehabilitation by playing a key role in performing activities of daily living (ADL) again. In that sense, wrist rehabilitation robots are the most common device with that purpose. The thesis presented herein describes the development of an exoskeleton robot for wrist rehabilitation with three degrees of freedom (DOFs). It was designed to have the capability of proving the forces and ranges of motion required to generate wrist rehabilitation routines. The device DOFs consist of three rotational joints in series, allowing the user to effectuate the natural wrist movements: pronation/supination, flexion/extension, and radial/ulnar deviation. The exoskeleton joints are actuated directly by quasi-direct drive actuators that provide sufficient torque and speed at each DOF to replicate wrist ADLs movements. Actuator's low inertia and low friction allow the joints to be back-drivable, enhancing the transparency of the device. Robust state feedback control algorithms are implemented to achieve position control and trajectory tracking at each DOF without implementing the system's mathematical model. System characterization is obtained through the frequency response and static friction tests over each joint. The effect of the robot dynamics on the user was measured by analyzing the kinematic data of healthy participants when performing wrist movements when using and not the exoskeleton, validating the transparency of the exoskeleton joints by observing smooth velocity profiles when using the device. Finally, a pilot test is performed to demonstrate the capability of interacting with a two-dimensional virtual interface (VI) through the wrist movements performed over the exoskeleton, validating the possibility of future implementation of game-based therapies to encourage participants to perform wrist movements for their rehabilitation. The obtained results provide meaningful data demonstrating the potential of the developed exoskeleton to be used as a wrist rehabilitation device.