Tilt determination in MEMS inertial vestibular prosthesis.
BACKGROUND: There is a clear need for a prosthesis that improves postural stability in the balance impaired. Such a device would be used as a temporary aid during recovery from ablative inner-ear surgery, a postural monitor during rehabilitation (for example, hip surgery), and as a permanent prosthesis for those elderly prone to falls. METHOD OF APPROACH: Recently developed, small instruments have enabled wearable prostheses to augment or replace vestibular functions. The current prosthesis communicates by vibrators mounted on the subject's trunk. In this paper we emphasize the unique algorithms that enable tilt indication with modestly performing micromachined gyroscopes and accelerometers. RESULTS: For large angles and multiple axes, gyro drift and unwanted lateral accelerations are successfully rejected. In single-axis tests, the most dramatic results were obtained in standard operating tests where balance-impaired subjects were deprived of vision and proprioceptive inputs. Balance-impaired subjects who fell (into safety restraints) when not aided were able to stand with the prosthesis. Initial multiaxis tests with healthy subjects have shown that sway is reduced in both forward-back and sideward directions. CONCLUSIONS: Positive results in initial testing and a sound theoretical basis for the hardware warrant continued development and testing, which is being conducted at three sites.