Update marker system for naviagtion of an automatic guided vehicle

• US 5,191,528 A
• Filed: 10/24/1990
• Issued: 03/02/1993
• Est. Priority Date: 06/28/1990
• Status: Expired due to Term

• 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): Lall, Parshotam S.
• Assistant Examiner(s): PARK, COLLIN
• Application Number:
  US07/602,609
• Time in Patent Office: 860 Days
• Field of Search: 364/424.02, 364/449, 364/571.04, 364/577, 364/474.31, 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 determined 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 improved accuracy for ascertaining an estimate of a lateral position of an automatically guided vehicle at a predetermined area on a route of the vehicle comprising:

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

sensor means comprising a plurality of magnetic-field sensors on the vehicle in a linear array and means for calibrating said sensors to null each sensor offset before the vehicle passes near the magnet, each of said sensors in combination with said calibrating means producing a search variable representing sensed magnetic field strength;

means for pre-storing a plurality of predetermined patterns of magnetic field strength as a function of distance from the center of a magnetic field to a precalibrated sensor on the vehicle;

interpolation means for receiving and processing said search variables, including means for computing a mean estimated lateral position of said magnetic field center relative to said vehicle based upon interpolation of each value of each search variable within said stored predetermined pattern;

means for communicating said estimated lateral position for use by said automatically guided vehicle.

2. Apparatus as in claim 1 and wherein

said means for pre-storing a predetermined pattern of magnetic field strength as a function of distance from the magnet comprises memory means for storing a lookup table;

and

said means for computing comprises;

means for identifying a sensor group comprising a sensor having the largest search variable and a sensor having the next-largest search variable adjacent the sensor having the largest search variable;

program means for providing a measurement of distance between the magnet and each sensor of said group;

means for receiving said measurement of distance for computing an estimated lateral position of said magnet relative to said vehicle based upon a composite of said distances.

3. Apparatus as in claim 2 and wherein

said distance measurement receiving means comprise means for computing an estimated lateral position of said magnet relative to said vehicle by averaging the measurements of lateral position derived from each sensor of said group.

4. Apparatus as in claim 3 and wherein

said means for computing the lateral position of said magnet relative to said vehicle further comprise means for calculating a running average of a plurality of computations of the estimated lateral position of said magnet relative to said vehicle whereby the estimate of lateral position of said magnet to said vehicle is improved.

5. Apparatus for improved accuracy for ascertaining an estimate of a lateral position of an automatically guided vehicle at a predetermined area on a route of the vehicle comprising:

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

a plurality of magnetic-field sensors on the vehicle in an array, each sensor producing an electrical signal comprising a magnitude which decreases as distance between the sensor and the center of the magnetic field increases;

means for receiving and processing said signals comprising means for precalibrating each sensor signal as the vehicle travels between magnets and means for identifying a sensor group comprising a sensor having the greatest calibrated signal strength and a sensor having the next-greatest calibrated signal strength on a side adjacent to the sensor having the greatest calibrated signal strength;

program means for providing a plurality of measurements comprising each distance between the center of the magnetic field and each sensor of said group, based on the calibrated signal strength of each sensor;

means for receiving said measurements of distance and for computing an estimated lateral position of said magnetic field center relative to said vehicle based upon a composite of said measurements;

means for communicating said estimated lateral position for use by said automatically guided vehicle.

6. Apparatus as in claim 5 and wherein

said receiving and computing means further comprise means for calculating a running average from a plurality of computations of estimated lateral position of said magnet relative to said vehicle whereby the running average estimate of the estimated lateral position of said magnet to said vehicle is improved relative to the measurement of each single computation of estimated lateral position.

7. Apparatus for improved accuracy for ascertaining an estimate of a lateral position and a time of arrival of an automatically guided vehicle at a predetermined area on a route of the vehicle comprising:

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

sensor means comprising a plurality of magnetic-field sensors on the vehicle in a sensor array 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 receiving and processing said search variables, including means for identifying a group comprising a sensor having the greatest search variable magnitude and a sensor adjacent the sensor having the greatest search variable magnitude having the next-greatest search variable magnitude;

program means for calculating a measurement of distance between the center of the magnetic field and a reference position on the vehicle;

means receiving each said measurement of distance for computing an estimated lateral position of said magnet relative to said reference position on said vehicle based upon a composite comprising a running average of each of distance measurements;

means for repeatedly receiving and for processing said search variables as the sensor array approaches and passes over said magnet, including second program means for discerning when the magnitudes of the search variables start to diminish after rising to a peak;

means for terminating said computing means when said discerning means detect a peak value of said search variables whereat said running average is said estimated lateral position;

means for outputting said estimated lateral position when the signals have risen to said peak as the array passes over the magnet whereby information as to estimated lateral position and time of arrival at said magnet is provided, for use by said automatically guided vehicle.

8. Apparatus for ascertaining an estimated lateral position of an automatically guided vehicle at a predetermined area on a route of the vehicle with improved accuracy, said apparatus comprising:

(a) 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;

(b) means for pre-storing a predetermined pattern of magnetic field strength as a function of distance from the center of the magnetic field;

(c) sensor means comprising an array of magnetic-field sensors transversely disposed to direction of vehicle travel and means for calibrating said sensors as the vehicle travels between sensible magnetic fields, each sensor in combination with said calibrating means producing a search variable calibrated to precisely represent magnetic field strength;

(d) correlation means for receiving and for processing said search variables, including means for computing an estimated lateral position of said magnet relative to said vehicle based upon interpolation involving said search variables and said stored predetermined pattern.

9. Apparatus as in claim 8 and wherein said means for pre-storing a predetermined pattern of magnetic field strength as a function of distance from the center of the magnetic field comprises a computer memory for storing a lookup table.

10. Apparatus as in claim 8 and wherein

said means for pre-storing a predetermined pattern of magnetic field strength as a function of distance from the center of the magnetic field comprises memory means for storing a lookup table;

said means for computing the estimated lateral position of said magnet relative to said vehicle based upon correlation between said search variables and said stored predetermined pattern comprise;

means for identifying within the array a sensor group comprising a sensor having the largest search variable and a sensor adjacent the sensor having the largest search variable having the next-largest search variable;

program means for providing a measurement of distance between the center of the magnetic field and each sensor of said group, based upon the magnitude of the search variable of each sensor;

means receiving said measurements of distance for computing an estimated lateral position of said magnetic field center relative to said vehicle based upon a respective composite of said measurements.

11. Apparatus as in claim 10 and wherein

said means receiving said measurements of distance for computing the estimated lateral positions of said magnet relative to said vehicle comprise means for computing the said estimated lateral positions by at least one means for averaging the measurements of lateral position derived from each sensor of said group, for the array of sensors.

12. Apparatus for improved accuracy for ascertaining an estimated lateral position and bearing of an automatically guided vehicle at a predetermined area on a route of the vehicle comprising:

at least two stationary magnets mounted in predetermined orientation to the route to provide a plurality of separably sensible unipolar magnetic fields, each magnetic field decreasing in strength as distance increases from the center of said magnetic field;

sensor means comprising a plurality of magnetic-field sensors on the vehicle in an array transversely disposed to direction of travel of the vehicle and means for calibrating to null each sensor offset as the vehicle passes between magnets, each sensor in combination with said calibrating means producing a search variable representing measured magnetic field strength;

means for pre-storing a plurality of predetermined unipolar patterns of magnetic field strength as a function of distance from the center of the magnetic field to a sensor on the vehicle;

interpolation means for receiving and for processing said search variables, including means for computing a mean estimated lateral position of each of said centers of magnetic fields relative to a fixed site on said vehicle based upon interpolation of said stored predetermined pattern relative to each search variable;

means for communicating said estimated lateral positions for use by said automatically guided vehicle wherein vehicle bearing is calculated from said plurality of positions.

13. Apparatus for concurrently ascertaining an estimated lateral position of at least two magnets relative to a vehicle with improved accuracy, said apparatus comprising:

at least two stationary magnets mounted in predetermined orientation to a predetermined vehicle route to provide a plurality of separably sensible unipolar magnetic fields;

sensor means comprising a plurality of magnetic-field sensors on the vehicle in an array disposed transverse to direction of vehicle travel and means for calibrating to null each sensor offset before each sensor passes sensibly near a magnet, each of said sensors in combination with the calibrating means producing a search variable representing measured magnetic field strength of each magnet;

means for pre-storing a plurality of predetermined patterns of magnetic field strength as a function of distance from the center of a sensed magnetic field to a precalibrated sensor on the vehicle;

interpolation means for receiving and processing said search variables, including means for computing a mean estimated lateral position of each of said centers of magnetic fields relative to said vehicle based upon interpolation of each search variable within a pattern of magnetic field strength selected from said stored predetermined patterns;

means for identifying a first sensor group comprising a sensor having the largest search variable and a sensor, adjacent the sensor having the largest search variable, having the next-largest search variable for a first sensed magnet;

means for identifying a second sensor group comprising a sensor having the largest search variable and a sensor, adjacent the sensor having the largest search variable, having the next-largest search variable for a second sensed magnet;

program means for providing a measurement of distance between the center of the magnetic field of the first magnet and each sensor of said first group based upon the search variable of each precalibrated sensor of said first group;

program means for providing a measurement of distance between the center of the magnetic field of the second magnet and each sensor of said second group based upon the search variable of each precalibrated sensor of said second group;

means receiving all of said measurements of distance for computing the estimated lateral position of the center each said magnetic field relative to said vehicle based upon a composite of said distances.

14. A method for concurrently ascertaining, with improved accuracy, an estimated position of a magnet relative to a vehicle, 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 an interpolation process;

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

(g) interpolating to calculate an estimated lateral position of the center of the magnetic field relative to each sensor;

(h) averaging calculated positions as derived from each sensor search variable relative to a position on the sensor array and therefrom to the vehicle whereby an estimate of vehicle position relative to said magnet is determined;

(i) determining whether measurements of search variables have reached a peak, if not, continue by proceeding to step (f), otherwise continue by proceeding to step (j);

(j) terminating the interpolation process immediately after a peak of the magnetic field is detected, whereby said estimate is a final estimated position of the magnet relative to the vehicle.

15. A method for concurrently ascertaining an estimated position of each of at least two magnets relative to a vehicle with improved accuracy, comprising the following steps:

providing at least two stationary magnets mounted in predetermined orientation transversely disposed to direction of travel along a predetermined vehicle route to provide a plurality of separably sensible unipolar magnetic fields;

providing an array of magnetic-field sensors on the vehicle, said array being transversely disposed to directions of vehicle travel;

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

calibrating said sensors to null sensor offset before the vehicle passes sensibly near a magnet;

sensing presence of the magnetic field emanating from at least one of said magnets to begin an interpolation process;

setting a first group active flag;

identifying by signal strength, a first sensor group for the magnet concurrently sensed, the first group centrally comprising a sensor having the greatest calibrated signal;

cyclicly, interpolating to calculate an estimated lateral position of the magnet sensed by the first group relative to each sensor selected for use in the first sensor group and averaging calculated positions as derived from each first group sensor relative to a position on the sensor array and therefrom to the vehicle whereby a first measured vehicle position relative to the first magnet is determined;

terminating the interpolation steps for the first magnet immediately after a peak of the magnetic field of the first magnet is detected;

sensing presence of a second magnetic field emanating from a second magnet;

setting a second group active flag;

identifying by signal strength, a second sensor group for the second magnet, the second group centrally comprising a sensor having the greatest signal;

cyclicly, interpolating to calculate the estimated lateral position of the magnet sensed by the second group relative to each sensor selected for use in the second sensor group and averaging calculated positions as derived from each second sensor group relative to the position on the sensor array and therefrom to the vehicle whereby a second measured vehicle position relative to the second magnet is determined;

terminating the interpolation steps for the second magnet immediately after a peak of the magnetic field of the second magnet is detected;

upon terminating each interpolation, resetting each respective group active flag whereafter a final first and a second measured vehicle position is determined relative to each magnet.