Article

The iMachine is a spring-loaded turntable used to measure inertial properties of
irregularly shaped rigid bodies, specifically manual wheelchairs. We used a
Newton-Euler approach to calculate wheelchair mass and center of mass (CM)
location from static force measurements using load cells. We determined the
moment of inertia about the vertical axis from the natural frequency of the
system in simple harmonic motion. The device was calibrated to eliminate the
effects of platform components on measurement error. For objects with known
inertial properties, the average relative error of the mass and the CM
coordinates (x and y) were 0.76%, 0.89%, and 1.99%, respectively. The resolution
of the moment of inertia calculation depends on the ratio of test piece inertia
to system inertia, such that the higher the ratio, the more accurate the
measurements. We conducted a Gage Repeatability and Reproducibility (Gage R&R)
test using three manual wheelchairs measured three times by three operators; the
results showed that over 90% of the variance in inertia was caused by differences
in the wheelchairs being measured. Gage R&R analysis indicated that measurement
system operation was acceptable using criteria from the Automobile Industry
Action Group for both inertia and mass measurements.

Langue : ANGLAIS