Comparison of Tone compensation and Spring assistance for hand rehabilitation in HEXORR.

Robotic rehabilitation techniques have the capacity to provide high dosage therapy without the labor burden of conventional methods. The most effective means of using robots to retrain function is not yet known, though many studies now support providing assistance to movement while the user actively participates in that movement. In this study, we compare, in three chronic stroke subjects, a novel Tone assistance mode to a Spring assistance method commonly used in other robots. The Tone mode provides assistance comparable to the subject's own resistance to extension while Spring mode provides a spring-like force to pull the subject to the target. All three subjects produced larger finger movements with robotic assistance, but they also produced much more positive work with the Tone assistance compared to the Spring assistance. This demonstrates that subjects were actively driving the movements in Tone mode to a greater extent than in Spring mode. Two out of three subjects showed similar results in the thumb. In the third subject, work was comparable across all modes. With Tone assistance, subjects produced movement and torque profiles more similar to that of Unassisted movement than Spring-assisted movement for both fingers and thumb. These results suggest that providing assistance tailored to the user's own tone profile may be an effective means of enhancing range of motion to ultimately enable gains in hand function.