Date of Award
Spring 1-1-2013
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
Nagurka, Mark L.
Second Advisor
Nagurka, Mark L.
Third Advisor
Johnson, Michelle J.
Abstract
TheraDrive is a low-cost robotic system for post-stroke upper extremity rehabilitation. This system uses off-the-shelf computer gaming wheels with force feedback to help reduce motor impairment and improve function in the arms of stroke survivors. Preliminary results show that the TheraDrive system lacks a robust mechanical linkage that can withstand the forces exerted by patients, lacks a patient-specific adaptive controller to deliver personalized therapy, and is not capable of delivering effective therapy to severely low-functioning patients.
A new low-cost, high-force haptic robot with a single degree of freedom has been developed to address these concerns. The resulting TheraDrive consists of an actuated hand crank with a compliant transmission. Actuation is provided by a brushed DC motor, geared to output up to 50 lbf (223 N) at the end effector. To enable safe human-machine interaction, a special compliant element was developed to function also as a failsafe torque limiter. A load cell is used to determine the human-machine interaction forces for use by the robot's impedance controller. The impedance controller renders a virtual spring that attracts or repels the end effector from a moving target that the human must track during therapy exercises. As exercises are performed, an adaptive controller monitors patient performance and adjusts the spring stiffness to ensure that exercises are difficult but doable, which is important for maintaining patient motivation. Experiments with a computer model of a human and robot show the adaptive controller's ability to maintain difficulty of exercises after a period of initial calibration.
Seven human subjects (3 normal, 4 stroke-impaired) were used to test this system alongside the original TheraDrive system in order to compare both systems. Data showed that the new system produced a larger change in normalized trajectory tracking error when assistance/resistance was added to exercises when compared to the original TheraDrive. Data also showed that adaptive control led subject performance to be closer to a desired level. Motivation surveys showed no significant difference in subject motivation between the two systems. When asked to choose a preferred system, stroke subjects unanimously chose the new robot.