Sensor system and method for use with an automated guided vehicle (AGV)

• US 8,751,147 B2
• Filed: 08/02/2011
• Issued: 06/10/2014
• Est. Priority Date: 08/03/2010
• Status: Active Grant

• Current Assignee: Fori Automation Incorporated (Lincoln Electric Holdings Incorporated)
• Original Assignee: Fori Automation Incorporated (Lincoln Electric Holdings Incorporated)
• Inventors: Colwell, Dean
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): GOLDMAN, RICHARD A
• Application Number:
  US13/196,354
• Publication Number:
  US 20120197477A1
• Time in Patent Office: 1,043 Days
• Field of Search: None
• US Class Current: 701/408
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G05D 1/0212 with means for defining a desired trajectory involving a plurality of land vehicles G05D1/0287

Abstract

A sensor system for use with an automated guided vehicle (AGV) includes a plurality of sensor units electronically coupled to a sensor control module via parallel communications. Each sensor unit may include a sensor array having a plurality of sensor elements, a conditioning circuit having one or more filter/amplifiers, and a conversion circuit. The sensor control module may be configured to communicate with other AGV components via serial communications. The sensor system is capable of obtaining and storing sensor readings with or without associated offset values and can use the sensor readings to determine the center of a magnetic field using methods that require relatively little processing power. A method of calibrating the sensor system may include determining and storing offset values for a plurality of sensor elements and may be performed with the sensor system installed or uninstalled to the AGV.

Claims

1. A method for operating a sensor system for an automated guide vehicle (AGV), comprising the steps of:

(a) providing a sensor system having a plurality of magnetic sensor elements that interact with a magnetic indicating system that is laid out on the ground and follows a pre-determined path;

(b) obtaining sensor readings for each of the magnetic sensor elements;

(c) storing the sensor readings for each of the magnetic sensor elements at a memory device; and

(d) using a known location of each of at least some of the magnetic sensor elements on the sensor system along with the stored sensor readings associated with the at least some of the magnetic sensor elements to determine a center of field value that represents the center or centroid of a corresponding magnetic field produced by the magnetic indicating system, wherein, for each of the at least some magnetic sensor elements, the known location of the sensor elements is weighted with the magnitude of the associated stored sensor reading.

2. The method of claim 1, wherein step (d) further comprises using the stored sensor readings and the following equation to determine the center of field value:

3. The method of claim 2, wherein the center of field value equation only uses sensor readings (mn) that are greater than a threshold value so that the number of sensor elements included in the calculation (N) is less than the total number of sensor elements of the sensor system.

4. The method of claim 1, wherein steps (b)-(d) are part of a periodic process, and the method further comprises the steps of:

interrupting the periodic process to perform one or more of the following functions;

a calibration function, a read sensor function, or an analyze readings function; and

resuming the periodic process following completion of the one or more functions.

5. The method of claim 4, wherein the step of interrupting the periodic process includes performing the analyze readings function, and the analyze readings function includes one or more of the following:

determining the presence or absence of a magnetic field, determining the width of a magnetic field, determining minimum and/or maximum strengths of a magnetic field, determining the direction of a magnetic field, determining the presence or absence of a location marker, or determining the number of maxima and/or minima strengths of a magnetic field.

6. The method of claim 4, wherein the step of interrupting the periodic process includes performing the read sensor function, and the read sensor function uses one or more of the following:

identification of a sensor board;

identification of a sensor sweep direction;

identification of a magnetic field polarity;

identification of a sensor reading threshold value;

or identification of a minimum magnetic field width threshold value.

7. The method of claim 1, further comprising the step of:

establishing a sensor reading threshold value, wherein only sensor readings that are above the threshold value are used in the center of field value equation.

8. The method of claim 7, further comprising the steps of:

providing the sensor system so that the sensor elements are spaced along at least a portion of the lateral width of the AGV from a leftmost sensor element to a rightmost sensor element; and

consecutively obtaining sensor readings for each of the sensor elements in a sensor sweep direction that is either from the leftmost sensor element to the rightmost sensor element or from the rightmost sensor element to the leftmost sensor element.

9. The method of claim 8, further comprising the steps of:

defining a first edge of the corresponding magnetic field at the location of the first sensor element in the sensor sweep direction that has a sensor reading above the sensor reading threshold value; and

defining a last edge of the corresponding magnetic field at the location of the last sensor element in the sensor sweep direction that has a sensor reading above the sensor reading threshold value.

10. A method for operating a sensor system for an automated guide vehicle (AGV), comprising the steps of:

(a) providing a sensor system having an array of magnetic sensor elements that interact with a magnetic indicating system that is laid out on the ground and follows a pre-determined path;

(b) obtaining sensor readings for the magnetic sensor elements;

(c) storing the sensor readings for the magnetic sensor elements at a memory device; and

(d) calculating a center of field value that represents the center or centroid of a corresponding magnetic field by;

determining a first edge of the magnetic field during the sensor reading sweep of step (b), wherein the first edge is associated with the sensor element that first exceeds a predetermined threshold, and

then determining a second edge of the magnetic field during the sensor reading sweep of step (b), wherein the second edge is associated with the sensor element that last exceeds the predetermined threshold,

wherein the calculation of the center of field includes a weighting calculation of a range of the sensor elements, wherein the weighting calculation uses a known location on the sensor system, the sensor readings for each of the range of sensor elements, and known locations for each of the range of sensor elements,

wherein the range includes the sensor element firstly exceeding the predetermined threshold, the sensor element lastly exceeding the predetermined threshold, and all the sensors elements therebetween.

11. The method of claim 10, wherein step (b) further comprises either sweeping the array from a leftmost sensor element to a rightmost sensor element or sweeping the array from the rightmost sensor element to the leftmost sensor element.

12. The method of claim 10, wherein the calculating step (d) further comprises using the following equation to determine the center of field value:

13. The method of claim 12, wherein the calculating step (d) uses less than the total number of sensor elements of the sensor system.

14. The method of claim 10, wherein steps (b)-(d) are part of a periodic process, and the method further comprises the steps of:

interrupting the periodic process to perform one or more of the following functions;

a calibration function, a read sensor function, or an analyze readings function; and

resuming the periodic process following completion of the one or more functions.

15. The method of claim 14, wherein the step of interrupting the periodic process includes performing the analyze readings function, and the analyze readings function includes one or more of the following:

determining the presence or absence of a magnetic field, determining the width of a magnetic field, determining minimum and/or maximum strengths of a magnetic field, determining the direction of a magnetic field, determining the presence or absence of a location marker, or determining the number of maxima and/or minima strengths of a magnetic field.

16. The method of claim 14, wherein the step of interrupting the periodic process includes performing the read sensor function, and the read sensor function uses one or more of the following:

identification of a sensor board;

identification of a sensor sweep direction;

identification of a magnetic field polarity;

identification of a sensor reading threshold value;

or identification of a minimum magnetic field width threshold value.

17. The method of claim 10, wherein the predetermined threshold is statically or dynamically configurable.

18. The method of claim 10, wherein step (a) further comprises providing the sensor system so that the sensor elements are spaced along at least a portion of the lateral width of the AGV from a leftmost sensor element to a rightmost sensor element.