Method for estimating an angular deviation between the magnetic axis and a reference axis of a magnetic object
View Patent ↗A method for estimating an angular deviation between a reference axis of a magnetic object and a magnetic axis co-linear to a magnetic moment of the magnetic object, including: a) positioning the magnetic object facing at least one magnetometer; b) rotating the magnetic object about the reference axis; c) measuring, during the rotating, the magnetic field, using the magnetomenter; and d) estimating the angular deviation from the magnetic field measurements.
1. A method for estimating an angular deviation between a reference axis of a magnetic object and a magnetic axis co-linear to a magnetic moment of the magnetic object in order to sort the magnetic object, comprising:
a) positioning the magnetic object at a fixed position facing at least one magnetometer configured to measure a magnetic field in presence of the magnetic object, the magnetic object remaining at the fixed position during the estimation of the angular deviation;
b) rotating the magnetic object about the reference axis while maintaining the magnetic object at the fixed position;
c) measuring, using the magnetometer, the magnetic field at different instants of a measurement duration during the rotating of the magnetic object while the magnetic object is maintained at the fixed position;
d) estimating the angular deviation from the measurements of the magnetic field;
e) comparing the angular deviation with a threshold value; and
f) sorting the magnetic object based a result of the comparison of the angular deviation and the threshold value,
wherein the magnetic object is a cylindrical magnet having an axis of symmetry, the reference axis being the axis of symmetry of the cylindrical magnet, and
wherein the d) estimating comprises:
d1) identifying a minimum magnetic field, and a maximum magnetic field, from the measurements of the magnetic field; and
d2) computing the angular deviation from the identified minimum and maximum magnetic fields, and from geometric parameters representing the position of the magnetometer relative to the magnetic object.
2. The method as claimed in claim 1 , wherein, during the d1) identifying, the minimum and maximum magnetic fields are respectively identified from the minimum and maximum values of the norm of the measurements of the magnetic field.
3. The method as claimed in claim 1 , wherein the geometric parameters are coordinates and distance of the magnetometer relative to the magnetic object, in a plane passing through the reference axis and containing the magnetometer.
4. The method as claimed in claim 1 , wherein the angular deviation is computed from a coefficient equal to the ratio of the norm of the vector formed from the subtraction of the minimum and maximum magnetic fields to the norm of the vector formed from the addition of the minimum and maximum magnetic fields, and from the geometric parameters.
5. The method as claimed in claim 1 , wherein the angular deviation is computed from the following equation:
α
_
=
tan
-
1
(
(
B
max
d
-
B
min
d
B
max
d
+
B
min
d
)
·
(
r
2
z
2
+
(
z
2
-
d
2
/
a
)
2
r
2
z
2
+
(
r
2
-
d
2
/
a
)
2
)
)
,
wherein d is distance between the magnetometer and the magnetic object, z and r are coordinates of the magnetometer relative to the magnetic object along an axis, respectively parallel and orthogonal to the reference axis, and wherein a is a predetermined coefficient, and wherein B max and B min correspond to maximum and minimum magnetic field values respectively.
6. The method as claimed in claim 1 , wherein, during the b) rotating, the magnetic object completes at least one rotation about the reference axis.
7. The method as claimed in claim 1 , wherein the at least one magnetometer comprises at least three axes for detecting the magnetic field, the detection axes being non-parallel to each other.
8. The method as claimed in claim 1 , wherein the at least one magnetometer is a single tri-axis magnetometer.
9. The method as claimed in claim 1 , wherein the at least one magnetometer is positioned outside the reference axis or outside the perpendicular to the reference axis passing through the magnetic object.
10. The method as claimed in claim 1 , wherein the at least one magnetometer is positioned relative to the magnetic object at a coordinate z along an axis parallel to the reference axis and at a coordinate r along an axis orthogonal to the reference axis, such that the coordinate z is greater than or equal to the coordinate r.
11. A method for characterizing a magnetic object having an angular deviation between a reference axis of the magnetic object and a magnetic axis co-linear to a magnetic moment of the magnetic object, comprising:
implementing the method for estimating the angular deviation as claimed in claim 1 ;
computing an amplitude of the magnetic moment associated with the magnetic object, from the estimated angular deviation, of the identified maximum magnetic field, and from the geometric parameters.
12. The method as claimed in claim 11 , wherein the amplitude of the magnetic moment is computed from the ratio between the no'iu of the maximum magnetic field and the norm of a magnetic field, for a unitary amplitude of the magnetic field, expressed analytically using the following equation:
B
^
max
d
(
α
_
,
r
,
z
)
=
b
d
5
(
-
sin
(
α
_
)
d
2
a
+
sin
(
α
_
)
r
2
+
cos
(
α
_
)
rz
-
cos
(
α
_
)
d
2
a
+
cos
(
α
_
)
z
2
+
sin
(
α
_
)
rz
)
,
wherein α is the previously estimated angular deviation, d is distance between the magnetometer and the magnetic object, z and r are coordinates of the magnetometer relative to the magnetic object along an axis, respectively parallel and orthogonal to the reference axis, and wherein a and b are predetermined coefficients.
13. A device for estimating an angular deviation between a reference axis of a magnetic object and a magnetic axis co-linear to a magnetic moment of the magnetic object, comprising:
at least one magnetometer configured to measure, at each measurement instant of a duration, a magnetic field disrupted by the magnetic object;
a retention and rotation component configured to retain the magnetic object in a determined position facing the at least one magnetometer and of rotating the magnetic object along its reference axis;
a processor configured to implement the method as claimed in claim 1 .
14. A non-transitory computer readable information recording medium, comprising instructions for implementing the method as claimed in claim 1 , the instructions being able to be executed by a processor.
15. The method according to claim 1 , further comprising rejecting the magnetic object if the angular deviation is greater than the threshold value.