Method for automatic recognition of a mobile magnetic object

Patent metadata

Field	Value
Publication number	US-9703001-B2
Application number	US-201314443755-A
Country	US
Kind code	B2
Filing date	Nov 12, 2013
Priority date	Nov 20, 2012
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

An automatic recognition method includes the calculation of an error representative of the difference between an estimate of the values of the magnetometer measurements when the positions, orientations and amplitudes of the magnetic moments of the P dipoles are equal to those determined, and the values of the magnetometer measurements taken. There is the selection of another system of equations linking each measurement of a triaxial magnetometer to the position, orientation and amplitude of the magnetic moment of P′ magnetic dipoles. The method includes the calculation of at least one distinctive feature of the object presented from the position, orientation, or amplitude of the magnetic moment of each dipole determined with the system of equations that minimizes the error calculated. The method includes the recognition of the magnetic object presented if the calculated distinctive features correspond to those of a known object, otherwise the lack of recognition of this object.

First claim

The invention claimed is:

1. A method for automatic recognition of a mobile magnetic object presented in front of an array of magnetometers having N triaxial magnetometers mechanically connected to each other without any degree of freedom for maintaining a known distance between each of these magnetometers, where N is an integer greater than or equal to five, said method comprising
a) when the magnetic object is presented in front of the array of magnetometers, causing each of the magnetometers to measure the amplitude of the magnetic field along each of the measurement axes thereof,
b) determining, from the magnetometer measurements, the positions, orientations and amplitudes of the magnetic moments of P magnetic dipoles, where P is an integer greater than or equal to one and less than or equal to N/2, wherein determining comprises solving a predetermined system of equations linking each measurement of a triaxial magnetometer of the array to the positions, orientations, and amplitudes of the magnetic moments of P distinct magnetic dipoles,
c) calculating an error representative of the difference between: an estimate of the values of the magnetometer measurements when the positions, orientations and amplitudes of the magnetic moments of the P dipoles are equal to those determined in step b), and the values of the magnetometer measurements taken in step a),
d) selecting another system of equations linking each measurement of a triaxial magnetometer to the position, orientation and amplitude of the magnetic moment of P′ magnetic dipoles, where P′ is a natural integer different from P, then the repetition of steps b) and c) with the other system of equations,
e) automatically selecting the system of equations that minimizes the error calculated in step c) and calculating at least one distinctive feature of the object presented from the position or orientation or amplitude of the magnetic moment of each dipole determined in step b) with the automatically selected system of equations that minimizes the error calculated in step c),
wherein the distinctive feature is selected from a first group, if the number of magnetic dipoles in the system of equations that minimizes the error calculated in step c) is strictly greater than one,
wherein the distinctive feature is selected from a second group otherwise,
wherein the first group consists of the relative position of the P magnetic dipoles with respect to each other, the orientation of the magnetic moments of the P magnetic dipoles with respect to each other, the amplitudes of the magnetic moments of the P dipoles or the relative amplitudes of the magnetic moments of the P magnetic dipoles with respect to each other, and the number of magnetic dipoles identified in the magnetic object presented, and
wherein the second group consists of: the amplitude of the magnetic moment of the dipole, and the number of magnetic dipoles identified in the magnetic object presented,
f) comparing each distinctive feature calculated in step e) with a corresponding prerecorded distinctive feature for a known object, and
g) recognizing the magnetic object presented if the calculated distinctive features correspond to those of the known object, otherwise recognizing the lack of recognition of the object.

2. The method as claimed in claim 1 , wherein the number P of magnetic dipoles is systematically strictly greater than one.

3. The method as claimed in claim 1 , wherein solving the system of equations comprises implementing an estimation algorithm capable of solving a nonlinear system of equations.

4. A manufacture comprising a tangible and non-transitory computer-readable medium having encoded thereon instructions that, when executed by an electronic computer, implement steps c) through g) of the method of claim 1 .

5. An apparatus for automatic recognition of a mobile magnetic object, said apparatus comprising:—
(a) an array of magnetometers, said array comprising N triaxial magnetometers mechanically connected to each other without any degree of freedom for maintaining a known distance between each of these magnetometers, where N is an integer greater than or equal to five, and —an electronic computer programmed for:
b) determining, from the magnetometer measurements, the positions, orientations and amplitudes of the magnetic moments of P magnetic dipoles, where P is an integer greater than or equal to one and less than or equal to N/2 by solving a predetermined system of equations linking each measurement of a triaxial magnetometer of the array to the positions, orientations and amplitudes of the magnetic moments of P distinct magnetic dipoles,
c) calculating an error representative of the difference between:
an estimate of the values of the magnetometer measurements when the positions, orientations and amplitudes of the magnetic moments of the P dipoles are equal to those determined in step b), and
the values of the magnetometer measurements used in step b),

d) selecting another system of equations linking each measurement of a triaxial magnetometer to the position, orientation and amplitude of the magnetic moment of P′ magnetic dipoles, where P′ is a natural integer different from P, then repeating steps b) and c) with the other system of equations,
e) automatically selecting the system of equations that minimizes the error calculated in step c) and calculating at least one distinctive feature of the object presented from the position or orientation or amplitude of the magnetic moment of each dipole determined in step b) with the system of equations that minimizes the error calculated in step c),
wherein the distinctive feature is selected from a first group
if the number of magnetic dipoles in the system of equations that minimizes the error calculated in step c) is strictly greater than one and wherein the distinctive feature is selected from a second group otherwise wherein the first group consists of
the relative position of the P magnetic dipoles with respect to each other, the orientation of the magnetic moments of the P magnetic dipoles with respect to each other,
the amplitudes of the magnetic moments of the P dipoles or the relative amplitudes of the magnetic moments of the P magnetic dipoles with respect to each other, and
the number of magnetic dipoles identified in the magnetic object presented,
and wherein the second group consists of
the amplitude of the magnetic moment of the dipole, and
the number of magnetic dipoles identified in the magnetic object presented,

f) comparing each distinctive feature calculated in step e) with a corresponding prerecorded distinctive feature for a known object, and
g) recognizing the magnetic object presented if the calculated distinctive features correspond to those of the known object, and otherwise reporting a failure to recognize the object.

6. The apparatus of claim 5 , wherein said mobile magnetic object comprises a plurality of permanent magnets having different powers, and wherein the ratio between the power of the strongest permanent magnet of the object and the power of the weakest permanent magnet of the object is less than five.

7. The method of claim 1 , wherein repetition of steps b) and c) with the other system of equations is carried out using the same magnetic measurements as the ones used for the previous iteration of steps b) and c).

Assignees

• Commissariat à{grave over ( )}l'énergie atomique et aux énergies alternatives
• Commissariat L Energie Atomique Et Aux Energies Alternatives

Inventors

• Hautson Tristan
• Aloui Rabeb
• Aloui Saifeddine
• Jobert Timothée

Classifications

• G01R33/0094

  Sensor arrays · CPC title

• G01V3/081 Primary

  the magnetic field is produced by the objects or geological structures (characterised by the method of magnetic field measurement G01R33/00) · CPC title