Update marker system for navigation of an automatic guided vehicle

Abstract

An improved accuracy position and direction updating system for use with an automatic guided vehicle that navigates by dead reckoning. Permanent magnets providing detectable position indicators are mounted in the floor and may be at widely spaced locations such as fifty feet apart along the route of the vehicle. A row of Hall sensors is transversely mounted on the vehicle. The sensors detect the lateral location of each floor magnet relative to the vehicle as the vehicle passes over the magnet. Sensors are precalibrated, correcting for errors in sensor null voltage readings due to changes in sensor characteristics due to causes comprising aging and temperature. Data from five sensors that are closest to the magnet are correlated with a stored pattern of magnetic field and their position data are averaged to determine a first estimate of the lateral or first dimensional position of the vehicle. A running average is calculated from sequentially acquired estimates to improve the results. Such precalibration and averaging provides an improved accuracy of the lateral or first dimensional position measurement between the array of Hall sensors and the magnet. A high frequency measurement of the time at which the signals from the row of sensors reaches a peak value, which is the time that the row of sensors arrives at the magnet, provides an improved second dimensional position measurement. More than one magnet is read concurrently to provide position and bearing information during one processing cycle.