Magnetic adhesive force monitoring system for magnetic wheeled robot

1. A magnetic adhesion force monitoring system, comprising:

a magnetic field sensor measuring a stray field portion of a total magnetic field emitted by a magnetic wheel that is magnetically adhered to a ferromagnetic structure, the magnetic wheel being on a robot, the stray field portion including a portion of the total magnetic field redirected by the ferromagnetic structure; and

a controller determining a change in a magnetic adhesion force of the magnetic wheel to the ferromagnetic structure based on a change in the measured stray field portion of the total magnetic field,

wherein the magnetic field sensor includes a first magnetic field sensor at a first predefined angle relative to an axis of the magnetic wheel, and a second magnetic field sensor at a second predefined angle relative to the axis of the magnetic wheel, wherein the first predefined angle is different than the second predefined angle; and

wherein the controller further determines an angular contact point of the magnetic wheel with the ferromagnetic structure relative to the axis of the magnetic wheel while in motion based on an empirical model representing a relation of a known contact point of the magnetic wheel and the ferromagnetic structure, and respective first and second stray field portion measurements with the first and second magnetic field sensors while in motion.

2. The system of claim 1 , wherein an increase in the stray field portion indicates a reduction in the magnetic adhesion force.

3. The system of claim 1 , further comprising a biasing magnet proximate a location of the magnetic field sensor to reduce the stray field portion toward the magnetic field sensor.

4. The system of claim 1 , wherein the robot is a magnetic crawler robot.

5. The system of claim 4 , wherein the magnetic field sensor includes a plurality of magnetic field sensors positioned about the magnetic wheel, each magnetic field sensor measuring the stray field portion of the total magnetic field about the magnetic wheel that is redirected by the ferromagnetic structure.

6. The system of claim 4 , wherein the magnetic crawler robot includes a plurality of magnetic wheels, each magnetic wheel including at least one magnetic field sensor positioned thereabout to measure the stray field portion of the total magnetic field about the respective magnetic wheel that is redirected by the ferromagnetic structure.

7. The system of claim 4 , wherein the controller is further configured to detect an obstacle in a path of the magnetic wheel based on the measured stray field portion.

8. The system of claim 4 , wherein the controller is further configured to detect contamination on the magnetic wheel based on the magnetic adhesion force.

9. The system of claim 4 , wherein the controller is further configured to:

determine whether the magnetic adhesion force is outside of a safe operating level for the magnetic crawler robot; and

in response to the magnetic adhesion force being outside the safe operating level, create an unsafe signal for a motor controller of the magnetic crawler robot.

10. The system of claim 4 , wherein the magnetic field sensor is radially outward of a circumference of the magnetic wheel.

11. The system of claim 4 , wherein the controller further determines the magnetic adhesion force of the magnetic wheel to the ferromagnetic structure based on an empirical model representing the stray field portion versus the magnetic adhesion force.

12. The system of claim 11 , wherein the ferromagnetic structure includes a ferromagnetic body and a coating thereon, and the empirical model is created by measuring the stray field portion versus the magnetic adhesion force over a range of coating thicknesses for a given ferromagnetic body thickness.

13. A magnetic crawler robot, comprising:

a chassis having a plurality of magnetic wheels thereon, each magnetic wheel configured to magnetically adhere the chassis to a ferromagnetic structure;

a magnetic field sensor measuring a stray field portion of a total magnetic field emitted by at least one selected magnetic wheel, the stray field portion including a portion of the total magnetic field redirected by the ferromagnetic structure; and

a controller determining a change in a magnetic adhesion force of the magnetic wheel to the ferromagnetic structure based on a change in the measured stray field portion of the total magnetic field,

wherein the magnetic field sensor includes a first magnetic field sensor at a first predefined angle relative to an axis of the magnetic wheel, and a second magnetic field sensor at a second predefined angle relative to the axis of the magnetic wheel, wherein the first predefined angle is different than the second predefined angle; and

wherein the controller further determines an angular contact point of the magnetic wheel with the ferromagnetic structure relative to the axis of the magnetic wheel while in motion based on an empirical model representing a relation of a known contact point of the magnetic wheel and the ferromagnetic structure, and respective first and second stray field portion measurements with the first and second magnetic field sensors while in motion.

14. The magnetic crawler robot of claim 13 , further comprising a motor controller to control at least one motor on the chassis that is configured to drive at least one of the plurality of magnetic wheels.

15. The magnetic crawler robot of claim 14 , wherein the controller is configured to:

determine whether the magnetic adhesion force is outside of a safe operating level for the magnetic crawler robot; and

in response to the magnetic adhesion force being outside the safe operating level, create an unsafe signal for the motor controller of the magnetic crawler robot.

16. A method, comprising:

measuring a stray field portion of a total magnetic field emitted by a magnetic wheel while the magnetic wheel is magnetically adhered to a ferromagnetic structure, the stray field portion including a portion of the total magnetic field redirected by the ferromagnetic structure; and

identifying a change in a magnetic adhesion force of the magnetic wheel to the ferromagnetic structure based on a change in the measured stray field portion of the total magnetic field,

wherein the measuring includes measuring using a magnetic field sensor includes a first magnetic field sensor at a first predefined angle relative to an axis of the magnetic wheel, and a second magnetic field sensor at a second predefined angle relative to the axis of the magnetic wheel, wherein the first predefined angle is different than the second predefined angle; and

wherein the identifying includes determining using a controller that further determines an angular contact point of the magnetic wheel with the ferromagnetic structure relative to the axis of the magnetic wheel while in motion based on an empirical model representing a relation of a known contact point of the magnetic wheel and the ferromagnetic structure, and respective first and second stray field portion measurements with the first and second magnetic field sensors while in motion.

17. The method of claim 16 , further comprising determining the magnetic adhesion force of the magnetic wheel to the ferromagnetic structure based on an empirical model representing the stray field portion versus the magnetic adhesion force.

18. The method of claim 17 , wherein the ferromagnetic structure includes a ferromagnetic body and a coating thereon, and

further comprising creating the empirical model by measuring the stray field portion versus the magnetic adhesion force over a range of coating thicknesses for a given ferromagnetic body thickness.

19. The method of claim 16 , further comprising determining an angular contact point of the magnetic wheel with the ferromagnetic structure relative to an axis of the magnetic wheel, the determining of the angular contact point including:

with the magnetic wheel magnetically adhered to the ferromagnetic structure in a stationary position having a known contact point of the magnetic wheel with the ferromagnetic structure, measuring the stray field portion over a range of angles of the magnetic field sensor about the axis of the magnetic wheel, to create an empirical model of the stray field portion measurements to angular position of the magnetic field sensor relative to the axis of the magnetic wheel;

during movement of the magnetic wheel over the ferromagnetic structure while magnetically adhered thereto, determining the contact point of the wheel by:

first measuring the stray field portion of the total magnetic field with a first magnetic field sensor at a first predefined angle relative to a fixed reference radius of the axis of the magnetic wheel,

second measuring the stray field portion of the total magnetic field with a second magnetic field sensor at a second predefined angle relative to the fixed reference radius of the axis of the magnetic wheel, and

using the empirical model to calculate the contact point of the magnetic wheel with the ferromagnetic structure using the first and second stray field portion measurements.