Abstract
This thesis presents the design, development, and control of a two-degree-of-freedom (2 DOF) spherical 5-bar thumb exoskeleton to augment the FINGER rehabilitation robot, which assists the index and middle fingers individually in a naturalistic curling motion. The thumb module expands the capabilities of FINGER, allowing for broader proprioceptive training and assessment of hand function. The 5-bar spherical mechanism was synthesized by minimizing the distance error between the output of the mechanism and the digitized trajectories (recorded from multiple healthy subjects utilizing a motion-capture system). The optimization of the spherical 5-bar included constraints for symmetry and cost-function penalties for poor manipulability. For evaluation, the fit and function of the device was tested on multiple healthy and post-stroke individuals. A proportional-derivative (PD) force controller with gravity and friction compensation was implemented to reduce resistance to motion.
A novel impedance controller with varying directional gains was implemented without a reference trajectory to reduce the apparent inertia and damping of the thumb exoskeleton, increasing the robot’s transparency, and facilitating free motion over the mechanism’s workspace. The controller successfully renders the prescribed dynamic behavior isotopically on the robot. The performance of the controller in rendering the prescribed dynamics was analyzed through a regression model based on the forces of interaction measured by the F/T sensor during free motion. Gain-reducing splines and the force saturation function are implemented to ensure stability and prevent the application of large forces during collisions with objects, collisions with the actuator hard stops, and accidental contact of the sensor with the user, therapist or with other links. The experimental results show that the impedance controller significantly reduces impedance to subject-initiated motion and renders the apparent inertia and apparent damping very close to the prescribed value. The directional gains facilitate the smooth motion of the thumb over the workspace. The added stability from the gain-reducing splines and the saturation functions allows the use of larger gains, making the impedance controller perform better at low speeds and small contact forces.
Next, the complete FINGER2.0 (hardware upgraded FINGER robot with the thumb exoskeleton) system was integrated with the game environment, similar to GuitarHero©. Modifications were included to make the game system more intuitive, and a new set of protocols was designed to assess finger/thumb proprioception. Protocols included different game modes which can modulate the level of assistance provided by the robot during the game.