Dead reckoning vehicle location using a solid state rate gyro

A solid state rate sensor based on the principle of inertia modulation has been evaluated for use in a dead reckoning vehicle location system using sparse signposts. The sensor consisted of a small, simply supported steel bar caused to vibrate at its resonant frequency. Rotation of the bar about its longitudinal axis induces vibration in a plane orthogonal to the driven motion whose magnitude is linearly related to the rotation rate and, upon integration, angular displacement. This output, together with distance-travelled estimates from the vehicle odometer was used to provide a semi-continuous estimate of vehicle position relative to a known initial location and heading. Cumulative errors due to sensor inaccuracies and drift were corrected by means of a grid of simulated radio sign-posts spaced at approximately half mile intervals over the test area. Field test of the experimental system yielded a worst case location error of 212 ft. at the 95% confidence level. Location accuracies of 134 ft./95% were obtained when corrections based on map trends were employed.