Update marker system for navigation of an automatic guided vehicle

• US 5,216,605 A
• Filed: 10/29/1992
• Issued: 06/01/1993
• Est. Priority Date: 06/28/1990
• Status: Expired due to Fees

• Current Assignee: HK Systems Incorporated (KION GROUP AG)
• Original Assignee: Eaton-Kenway Incorporated
• Inventors: Whatcott, Gary L., Yardley, James V., Bloomfield, Bryan A.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): PARK, COLLIN
• Application Number:
  US07/968,555
• Time in Patent Office: 215 Days
• Field of Search: 364/424.02, 364/449, 180/167, 180/168, 180/169, 318/580, 318/587
• US Class Current: 701/23
• CPC Class Codes: G05D 1/0261 using magnetic plots
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00

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.

Claims

1. Apparatus for ascertaining a directionally independent time of arrival of an automatically guided vehicle at a predetermined area on a preselected vehicle route, said apparatus comprising:

a stationary magnet mounted on the route to provide a sensible unipolar magnetic field that diminishes with increasing distance from the center of said field;

sensor means comprising a plurality of magnetic-field sensors on the vehicle in a sensor array transversely disposed relative to direction of vehicle travel and means for calibrating each sensor as the vehicle travels between magnets, each sensor in combination with said calibrating means producing a search variable having a magnitude dependent upon distance between the sensor and the center of the magnetic field;

means for repeatedly receiving and for processing said search variables as the sensors approach and pass through the magnetic field, including program means for discerning when the search variables start to diminish after rising to a peak magnitude;

means for terminating operation of said processing means when said discerning means indicate the magnitudes of the search variables have started to diminish after rising to the peak;

means for signalling to said automatically guided vehicle when the search variables have risen to said peak.

2. A method for concurrently ascertaining, with improved accuracy, a time of arrival of a vehicle at a magnet relative, comprising the following steps:

(a) providing a stationary magnet mounted in predetermined orientation to a preselected vehicle route to provide a separably sensible unipolar magnetic field;

(b) providing an array of magnetic-field sensors on the vehicle, the array of sensors being transversely disposed to direction of travel of the vehicle;

(c) providing a means for programmably interpolating and storing position related data;

(d) calibrating measurement outputs of said sensors to null sensor offset before the vehicle passes sensibly near each magnetic field thereby calculating a search variable for each measurement output;

(e) sensing presence of the magnetic field emanating from said magnet to end the calibrating step and begin a search variable magnitude comparative process;

(f) as a part of the comparative process, identifying by search variable magnitude, a separate sensor group which centrally comprises a sensor having the largest search variable;

(g) determining whether measurements of search variables from the sensor group have reached a peak, if not, continue by proceeding to step (f), otherwise continue by proceeding to step (h);

(h) terminating the interpolation process immediately after a peak of the search variables within the sensor group is detected, whereby said time of arrival is communicated to the vehicle.