Designing a Vibrotactile Biofeedback Prosthesis

Shi, Sam 1, 2 ; Leineweber, Matt 1 ; Andrysek, Jan 1, 2

1. Bloorview Research Institute, Holland Bloorview Kids Rehabilitation Hospital 2. Institute of Biomaterials and Biomedical Engineering, University of Toronto

Introduction: Individuals with lower-limb amputation suffer loss of awareness of limb orientation and movement, which limits the utility of their prostheses. Vibrotactile biofeedback systems have been explored to compensate for their sensory loss, by using small vibrating motors to provide feedback on gait and balance parameters. However, the application of vibrotactile feedback to lower-limb prostheses is still in the preliminary stages, with no systems currently exist commercially. This project aims to inform the design of a vibrotactile biofeedback lower-limb prosthesis, through first building a testing prototype, and then using it to study how varying design parameters affects user’s perception to vibration.

Methods: A mock socket has been made to test key design parameters on able-bodied individuals, while mimicking a real prosthetic interface. Nine different experimental conditions of different vibration intensities and vibrating motor placements were tested. For each condition, accelerometers measure vibration at the prosthesis/limb interface at specified distances away from the vibrating motor. User’s perception to vibration is implied from measured vibration amplitudes.

Results: Below are observations from the amplitude vs. distance graphs:

• When motor is placed between liner/skin and liner/socket, vibrations propagate with decreasing amplitude for 3cm, then reach a steady-state.

• When motor is placed at outer side of socket, vibrations propagate throughout the measured distance, but absolute amplitudes are much lower.

• Higher vibration intensity results in higher absolute amplitude throughout the measured distance.

• In addition to accelerometer measurements, subjects report adaptation to vibration after 3-5 seconds.

Discussion and Conclusions: It can be implied from the results that higher vibration intensity may be better perceived. The desired vibrating motor placements are liner/skin or liner/socket. Distance between vibration motors should be at least 3cm to avoid interference. Vibration duration should be no longer than 3-5 seconds. In conclusion, all of the four key design parameters affect vibration amplitude and propagation at the prosthesis/limb interface. However, we are not certain that vibration amplitude and propagation correlate with user’s perception to vibration. Future experiments will be performed to measure subjects’ response time and accuracy to vibration.