Haptic Feedback Improvements for Prostheses

This project optimizes haptic system design parameters and more thoroughly evaluates the impact of a vibratory haptic system for prosthetics. Objectives include: (1) building a hardware and software test bed for non-invasive voluntary control of a prosthetic hand with vibratory haptic feedback, (2) optimizing the tactor application, (3) assessing the effectiveness of tactor vibratory feedback on cognitive loading interpretations, and (4) assessing perceptions of subjects regarding the actual use of haptic feedback. Specifically, Objective One involves the construction of a controlled box. Fingertip sensors on the thumb and index finger of a myoelectric arm convey pressure data to a microprocessor. Using a mapping algorithm, the processor generates a corresponding waveform that is sent to feedback devices (tactors) placed on the skin of the upper arm. Objectives Two through Four test the vibratory feedback on seven below-elbow amputees. Objective Two determines the best tactor location, vibration waveform, and time duration until deterioration in skin sensitivity occurs by measuring how well the subjects can sense a change in vibration frequency (as identified in previous work as a spectrum of interest). This information assists in determining when a resting period from vibrotactile stimulation is required to avoid over-stimulation of the skin. Objective Three tests the ability of the vibrotactile feedback to provide information on grasping force with the myoelectric hand. The myoelectric hand is controlled by the contraction intensity of the wrist extensor and flexor muscles as detected by electromyography electrodes. Trials use the myoelectric hand to grasp a plush ball at forty percent, sixty percent, and eighty percent of the subject’s maximum grasping force. Trials using vibrotactile feedback, visual feedback, and no feedback are compared. Objective Four requires the subjects to rate the system in terms of level of comfort, accuracy, user friendliness, level of discomfort, and overall usefulness in grasping activities.