Tilt Determination in MEMS Inertial Vestibular Prosthesis

[+] Author and Article Information
Marc. S. Weinberg1

 Draper Laboratory, Cambridge, MAmweinberg@draper.com

Conrad Wall

 Massachusetts Eye and Ear Infirmary, Boston, MA and Harvard Medical School, Boston, MA

Jimmy Robertsson

 Massachusetts Eye and Ear Infirmary, Boston, MA

Edward O’Neil, Robert Fields

 Draper Laboratory, Cambridge, MA

Kathleen Sienko

 Massachusetts Eye and Ear Infirmary, Boston, MA and Massachusetts Institute of Technology, Cambridge, MA


Corresponding author. Draper Laboratory, Mail Stop 37, 555 Technology Square, Cambridge, MA, 02139, 617.258.2308.

J Biomech Eng 128(6), 943-956 (May 08, 2006) (14 pages) doi:10.1115/1.2378922 History: Received April 01, 2005; Revised May 08, 2006

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.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

The vestibular function. Only one of six inertial sensors (otoliths and semicircular canals) on one side is shown. The X indicates a break in the neural path

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Figure 2

Tactor coding: (a) tactor locations, (b) the schedule of tilt activation versus tilt magnitude, (c) an example where forward and backward activate only the forward-most and backward-most columns of tactors

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Figure 3

Major components of the wearable device to show mounting locations. Also shown is the laboratory computer that communicates wirelessly with the wearable device

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Figure 4

Inverted pendulum model of standing person

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Figure 5

Single-axis tilt estimation: (a) block diagram (b) the estimated tilts for a 1-deg step change in actual tilt are shown for the gyro, accelerometer, and combined (indicated) channels (simulation)

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Figure 6

Two-axis, motion sensor test station equipped for thermal sensitivity testing. The horizontal cylinders drive outer gimbal rotation axis. The vertical cylinder below the station rotates inner table axis. The system under test in inside the cubic, electrically heated thermal enclosure mounted on the inner axis. Seen behind the test station and connected by insulated flexible tubes is the cooler, which enables operation to below −40°C

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Figure 7

ISA misaligned 0.1rad about x, roll (peak −0.9rad) and pitch (peak −1rad) motion. Solid line is actual, dashed is estimated, and dotted is difference

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Figure 8

ISA misaligned 0.1rad about x, 1rev∕s rotation (turn to right) about vertical. Solid line is actual, dashed is estimated, and dotted is difference

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Figure 9

No misalignments, no inputs. Gyro noise is white, 1000deg∕h over 50Hz bandwidth (0.01s sampling), and accelerometer noise is white, 0.01g over 50Hz

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Figure 10

Test results of higher performance six-axis system for various roll angles. Input and estimated angles are plotted and are very close to one another

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Figure 11

Sequential tilt performance index (TPI) scores from one subject’s sensory organization test (SOT) runs during computerized dynamic posturography testing. The SOT 5 (circles) has distorted proprioceptive and no vision inputs. The SOT 6 (squares) has distorted proprioceptive and visual inputs. TIP=1∕rms center of pressure sway and is scored zero if the subject falls during a run.

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Figure 12

Pitch and roll angles for a subject having normal balance function (A) without and (B) with VTTF. In both cases, the subject is standing on a platform that is driven by a signal that moves it randomly in the horizontal plane. Spectral analyses (C–F) of the motions shown in A and B, respectively. Panels C and E, respectively, show pitch and roll power without VTTF, while panels D and F show pitch and roll with VTTF display

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Figure 13

The rms of the resultant tilt estimate for one subject across all trials

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Figure 14

Average of the two subjects’ normalized rms of the resultant tilt vector for the first block of no-tactor trials, the VTTF trials, and the last block of no-tactor trials. Error bars represent the standard deviation across averaged trials



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