JPH04259872A - How to correct the magnetic field measurements of a 3-axis magnetometer - Google Patents

Abstract

PURPOSE:To enable simple and precise detection of an orthogonal-axis magnetic field component value by determining a correction factor on the basis of an output voltage of each detection axis of a triaxial magnetometer in arbitrary five attitudes which are obtained by rotation at known angles in geomagnetism. CONSTITUTION:A triaxial magnetometer 1 wherein sensors 1a being capable of measuring a magnetic field component value in a uniaxial direction are arranged so as to be orthogonal substantially to three axes of a rectangular coordinate system is fitted to a hexahedron, and this is mounted on a base stage 3. The base stage 3 is disposed on a horizontal plane and further fixed in a space so that the X axis of the magnetometer 1 is directed substantially to the northeast of geomagnetism, and output voltages caused by the geomagnetism in the directions of three axes at a prescribed position are measured by the sensors 1a. Next, the magnetometer 1 is rotated five times by predetermined rotational angles around a reference axis, the output voltages in the directions of three axes at each changed position by the rotational angle are measured and inputted to a prescribed arithmetic formula containing unknown correction factors regarding the sensitivity, offset and orthogonal property of the detection axis of each sensor 1a, and thereby the correction factors and determined. By these correction factors, the exact strength of a magnetic force at an arbitrary position can be measured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a magnetometer with a magnetic field strength of 3
The present invention relates to a method for correcting detected magnetic field errors that occur when the sensitivities and offsets of each detection axis are different and when the detection axes are not magnetically orthogonal to each other when measuring axis component values.

0002

2. Description of the Related Art Even if three sensors capable of measuring magnetic field component values in one axial direction are prepared as shown in FIG. 1 and are mechanically orthogonal to each other, they are not necessarily orthogonal to each other magnetically. The conventional method of correcting this magnetic orthogonality is to install a magnetic field generating coil system in a magnetically shielded space with a precise and uniform magnetic field whose magnitude and direction are known, and then A rotating table that can be rotated in a plane related to the rotation table is used, and a 3-axis magnetometer is attached to the rotating table, and the orthogonality is corrected by adjusting the detection axis and measuring the angle that produces the maximum (or minimum) of the measured value. ing. Furthermore, the sensitivity and offset of each detection axis were corrected based on the known magnetic field generated by the coil system.

0003

[Problem to be solved by the invention] In the conventional three-axis magnetometer, it was necessary to align the magnetic detection axis of the sensor for detecting the magnetic force component with the three orthogonal axes of X, Y, and Z axes. . In this case, a magnetic field generating coil system is provided in the magnetically shielded space, and the magnitude and direction of the generated magnetic field are known with precision and uniformity, and a rotary table that can rotate in a plane related to the coil system is used, A 3-axis magnetometer is attached to the rotary table, and while measuring the output value, the sensitivity and offset of each detection axis are adjusted based on the known magnetic field generated by the coil system, and the detection sensor is used to keep the orthogonality error within the tolerance. Adjust the placement direction by trial and error. For this reason, there are disadvantages in that it requires complicated and highly accurate equipment and a large amount of adjustment time, and that it is difficult to ensure accuracy because the magnetic field generating coil system itself includes errors.

0004

[Means for Solving the Problem] A three-axis magnetometer is constructed by arranging three sensors that can measure magnetic field component values in one axis direction and are arranged almost orthogonally to each other, and is used to measure X, Y, and Z values at a predetermined position.
When measuring the magnetic field strength in the orthogonal coordinate system, first, a sensor measures the output voltage due to the earth's magnetism in the three directions of X, Y, and Z at a predetermined position. Next, this three-axis magnetometer as a whole is sequentially rotated five times by a predetermined rotation angle around the reference axis, and each time the X
, Y, and Z directions. These measured values are input into predetermined arithmetic expressions including unknown correction coefficients for the sensitivity, offset, and orthogonality of the detection axis of each sensor, and these arithmetic expressions are solved to obtain the correction coefficients. Thereafter, the measurement value at an arbitrary position is inputted into an arithmetic expression including the obtained correction coefficient, and the result is outputted as the magnetic field strength.

[0005]

[Embodiment] To explain the present invention in detail based on the drawings, in FIG. 2, reference numeral 1 denotes three sensors 1a capable of measuring magnetic field component values in one axis direction as shown in FIG. A three-axis magnetometer is arranged such that the axis, Y axis, and Z axis are almost orthogonal to each other. 2 is a hexahedron made of a dice-shaped non-magnetic material with excellent perpendicular accuracy; The three-axis magnetometer 1 is removably attached to one surface 2A with bolts (not shown), while the remaining five surfaces are connected to each other at predetermined positions with reference to two pin holes 2a, 2a, respectively. Pin holes 2a'2a' are drilled at positions rotated by a known angle, and a total of four pin holes are drilled on each surface. Reference numeral 3 denotes a reference stand made of a flat plate, and on this reference stand there are pins 3a, 3 that engage with the pin holes 2a, 2a of the hexahedron 2.
A is attached.

Now, as shown in FIG.
It is attached to the facepiece 2, and then fitted onto the pins 3a, 3a of the reference stand 3 so that the three-axis magnetometer 1 is positioned at the top, matching the pin holes 2a, 2a of the hexahedron. The reference stand 3 prepared in this manner is placed on a horizontal surface, and further fixed in space so that the X-axis of the three-axis magnetometer 1 points approximately toward the northeast of the earth's magnetic field. This state is referred to as "posture 1".

[0007] Three of the ridgelines of the hexahedron in "Posture 1"
3 shown in FIG. 3 approximately parallel to each axis (non-orthogonal) of the axial magnetometer 1.
Let us assume a spatially fixed coordinate system XrYrZr in which the ridge lines (orthogonal) are the Xr, Yr, and Zr axes. 3 in a space-fixed coordinate system
The direction cosines of the X, Y, and Z axes of the axial magnetometer 1 are expressed as X(
Lx Mx Nx), Y (Ly My Ny)
, Z(Lz Mz Nz). Furthermore, if the Xr, Yr, and Zr axis components of the earth's magnetism in a fixed space coordinate system are Hex, Hey, and Hez, respectively, then the magnetic fields Hsx, Hsy, and Hsy applied to the X, Y, and Z axes of the 3-axis magnetometer are
and Hsz are expressed by Equation 1.

[Math. 1] Magnetic fields Hsx, Hs applied to the 3-axis magnetometer 1 in Equation 1
y and Hsz are actually the magnetometer output voltage Vsx1,
It is measured as Vsy1 and Vsz1. Typically,
The relationship between the applied magnetic field and the output voltage is linear, Ax, Ay
, Az are sensitivity correction coefficients (constants), and Bx, By, and Bz are offset correction coefficients (constants).

[Math 2]

[Math 3]

[Math 4]

[0008] Furthermore, there are relationships between the direction cosines as shown in Equations 5 to 7.

[Math 5]

[Math 6]

[Equation 7] Therefore, from the relationship between Equations 2 to 7, the unknowns included in Equation 1 are Mx, Nx, Ly, Ny, Lz, Mz, Hex, He
They are 15: y, Hez, Ax, Bx, Ay, By, Az, and Bz.

[0009] Here, if Equation 8 is replaced with Equation 22 and Equation 1 is rewritten, Equation 23 is obtained. However, always Formula 2
4 to Equation 26.

[Math. 8]

[Math. 9]

[Math. 10]

[Math. 11]

[Math. 12]

[Math. 13]

[Math. 14]

[Math. 15]

[Math. 16]

[Math. 17]

[Math. 18]

[Math. 19]

[Math. 20]

[Math. 21]

[Math. 22]

[Math. 23]

[Math. 24]

[Math. 25]

[Math. 26]

In order to obtain the above-mentioned 15 unknowns, the hexahedron is rotated by +90 degrees around the Zr axis from "Posture 1" (referred to as "Posture 2"), and the 3-axis magnetometer is If the output voltages are Vsx2, Vsy2, and Vsz2, Equation 27 holds true.

[Formula 27] In a posture rotated by +90 degrees around the Xr axis from “Posture 2” (referred to as “Posture 3”), the output voltages are Vsx3, Vsy
3, and Vsz3, Equation 28 holds true.

[Formula 28] In a posture rotated by +90 degrees around the Zr axis from “Posture 3” (referred to as “Posture 4”), the output voltages are Vsx4, Vsy
4, and Vsz4, Equation 29 holds true.

[Formula 29] In a posture rotated +90 degrees from “Posture 4” to the Xr axis (referred to as “Posture 5”), the output voltages are Vsx5, Vsy
5, and Vsz5, Equation 30 holds true.

[Formula 30] From Equations 23 and 27, 15 equations are obtained from Equation 30, and by solving them by numerical solution of nonlinear simultaneous equations, unknowns X1 to X15 can be obtained. From this, as a correction for the 3-axis magnetometer, the output voltage of the 3-axis magnetometer is set to Vsx, V
When sy and Vsz, the correct orthogonal 3 is obtained by formula 31.
The axial components Hx, Hy, and Hz are determined.

[Math. 31]

For example, each axis magnetic field component value Hx', Hy before correction as shown in FIG. 4 in a uniform magnetic field with a true total magnetic force of 474 mG
', Hz', total magnetic force value Ht', total magnetic force fluctuation value △Ht'
In Table 1, the corrected magnetic field component values Hx, H as shown in FIG.
y, Hz, total magnetic force value Ht, and total magnetic force variation value △Ht as the second
Shown in the table. Here, the values are obtained when the 3-axis magnetometer is rotated approximately 360 degrees in 45 degree increments around the horizontal line. Although the ideal value of the total magnetic force value is constant, as shown in Table 1, the total magnetic force fluctuation before correction △Ht ' was 16.58 mG, but as shown in Table 2, the total magnetic force variation ΔHt after correction is 0.18 mG, which is approximately 100 times more accurate.

0012

[Effects of the Invention] As described above, the present invention allows rotation at a known angle in the earth's magnetism without requiring complicated and highly accurate equipment or adjusting the assembled three-axis magnetometer. By simply measuring the output voltage of each detection axis of the 3-axis magnetometer in any of the 5 orientations obtained, it is possible to obtain extremely simple and accurate orthogonal axis magnetic field component values. This has the effect of suppressing fluctuations in the total magnetic force value to a very small level.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing detection axes of a three-axis magnetometer.

FIG. 2 is an explanatory diagram of tools used for measurement.

FIG. 3 is an explanatory diagram of a spatially fixed coordinate system.

FIG. 4 is a block diagram for detecting each axis magnetic field component value and total magnetic force value using a conventional method.

FIG. 5 is a block diagram for detecting each axis magnetic field component value and total magnetic force value using the present invention.

[Explanation of symbols]

1 3-axis magnetometer 1a sensor 2 Hexahedron ３　　　　Standard stand

[Table 1]

[Table 2]

Claims (1)

[Claims] Claim 1: A 3-axis magnetometer consisting of three sensors that can measure magnetic field component values in one axis direction and arranged almost orthogonally to each other, which measures the magnetic field in an X, Y, Z orthogonal coordinate system at a predetermined position. To measure the strength, first each sensor measures the output voltage due to the earth's magnetism in the three directions of X, Y, and Z at a predetermined position, and then this 3-axis magnetometer as a whole is rotated at a predetermined angle around the reference axis. Rotate it five times in sequence, measure the output voltage in the X, Y, and Z directions at each rotation angle change position each time, and use these measured values to make unknown corrections for the sensitivity, offset, and orthogonality of each sensor's detection axis. The correction coefficients are obtained by inputting them into predetermined calculation formulas including the coefficients, and then by inputting the measured values at arbitrary positions into the calculation formula including the calculated correction coefficients. A method for correcting a magnetic field measurement value of a three-axis magnetometer, characterized in that the result is output as magnetic field strength.