JP5475873B2 - Geomagnetic detector - Google Patents

Description

  The present invention relates to a geomagnetism detection device in which a geomagnetic vector detected by a geomagnetic sensor is obtained as coordinate point data on a spherical coordinate, and in particular, after performing a calibration process for obtaining a coordinate point at the center of a spherical coordinate. The present invention relates to a geomagnetic detection device that can evaluate accuracy and calculation accuracy from a calculated value.

  A geomagnetism detection device using geomagnetic sensors arranged on three axes is used as an orientation sensor, an angular velocity sensor, or the like. In this geomagnetism detection device, when geomagnetism is detected by geomagnetic sensors arranged toward the X axis, the Y axis, and the Z axis orthogonal to each other, the geomagnetism vector is a coordinate point on a three-dimensional coordinate based on the detection output. Recognized as

  In this type of geomagnetism detecting device, at the time when the power is turned on, it is unclear at which position on the three-dimensional coordinates the geomagnetic vector appears due to the presence of the offset magnetic field and the influence of magnetic noise other than geomagnetism from the outside. Therefore, it is necessary to perform calibration processing to convert detected coordinate point data into data on three-dimensional coordinates centered on a predetermined origin.

  In the following Patent Document 1, it is pointed out that the azimuth data detected by the geomagnetic detection device appears on a coordinate system approximating an ellipse. It is described to compensate by converting to a ring.

  In Patent Document 2 below, as a method for obtaining a reference origin on a three-dimensional coordinate with a small amount of data, when three coordinate point data are obtained by detecting a plurality of geomagnetic vectors, three coordinate point data are obtained. An invention has been disclosed in which equidistant points are obtained and this point is used as a reference origin.

Japanese translation of PCT publication No. 7-507874 JP 2007-163389 A

  In the calibration process, it is necessary to detect a plurality of coordinate point data by rotating the geomagnetism detection device, and to calculate a reference origin of spherical coordinates using the coordinate point data.

  Therefore, in addition to variations in the sensitivity of the magnetic sensor and variations in the characteristics of the detection circuit, the calculation error due to the calibration process is added to the calculation result of the azimuth and the like, and is added to the calculation result of the azimuth. Accumulation of errors increases. Therefore, it is necessary to always evaluate how much error is included in the calculation result such as the orientation obtained after calibration.

  In addition, near the equator, it is necessary to calculate the azimuth from the projection vector obtained by projecting the geomagnetic vector onto the horizontal and horizontal coordinate planes, but the projection vector is short in regions where the latitude is high and the dip angle of the geomagnetic vector is large. Therefore, the ratio of the error to the calculated projection vector increases. In this case, it is further necessary to constantly evaluate how much error is included in the calculation result such as the direction.

  The present invention solves the above-described conventional problems, and enables calculation of how much error is included in the calculation result of coordinate point data after calibration, thereby accurately determining the reliability of the calculation result such as azimuth. The purpose is to provide a geomagnetism detection device that can be evaluated easily.

The geomagnetism detection device of the present invention has a geomagnetism detection unit in which three-dimensional detection coordinates are determined in advance, an acceleration sensor that detects the attitude of the geomagnetism detection unit, and a calculation unit,
When the X-axis sensor in which the absolute value of the detection output becomes a maximum value when the X direction of the three-dimensional detection coordinates is directed to the geomagnetism direction and the Y direction is directed to the geomagnetism direction A Y-axis sensor in which the absolute value of the detection output is a maximum value and a Z-axis sensor in which the absolute value of the detection output is a maximum value when the Z direction is directed to the geomagnetism direction are mounted,
The calculation unit obtains the direction of a geomagnetic vector based on the detection output as coordinate point data on a three-dimensional detection coordinate,
When obtaining a plurality of coordinate point data, a corrected spherical coordinate that minimizes an error from the plurality of coordinate point data and a coordinate point of the center of the corrected spherical coordinate on the three-dimensional detection coordinate are obtained, and The coordinate point data is converted into corrected coordinate point data on the corrected spherical coordinate having the center at the origin of the three-dimensional detection coordinates,
A deviation (δR) between a distance (ri) from the origin to a plurality of correction coordinate point data and a radius (R) of the correction spherical coordinate is obtained, and is perpendicular to the gravity vector obtained from the detection output of the acceleration sensor. The dip angle (I) from the X0-Y0 plane to the geomagnetic vector is obtained, and R · cosI and the deviation (δR) are used as evaluation criteria for detection accuracy or calculation accuracy.

  For example, the geomagnetic detection device of the present invention obtains a deviation (δθ) of the azimuth angle (θ) based on the ratio of R · cosI and the deviation (δR), and detects the deviation (δθ) with detection accuracy or calculation. It is used as an accuracy evaluation standard.

  The present invention is provided with a display device that displays map information at a position where a geomagnetism detection unit is arranged. When the display device rotates, the map information is changed with a change in azimuth angle (θ). Can be switched by a predetermined angle, and the angle can be switched according to the deviation (δθ) of the azimuth angle (θ).

  In the present invention, Fi is calculated by Equation 1, xc, yc, zc and a, b, c that minimize J are obtained, and the corrected spherical coordinate and its center position are calculated (xc, yc, zc are , The coordinate point of the center of the corrected spherical coordinate in the three-dimensional detection coordinates, and a, b, and c are coefficients based on the sensitivity of the X-axis sensor, Y-axis sensor, and Z-axis sensor).

Alternatively, the previous number system 2 calculates the Fi, xc where J is minimized, yc, seeking zc and R, to calculate a correction spherical coordinates and the center position (xc, yc, zc is the three-dimensional detection The coordinate point of the center of the corrected spherical coordinate in coordinates, and R is the radius of the corrected spherical coordinate).

  The geomagnetism detecting device of the present invention performs a correction process for obtaining corrected spherical coordinate and corrected coordinate point data, and then calculates a corrected spherical coordinate after calculation by calculating a deviation of the corrected coordinate point data with reference to the corrected spherical coordinate. The correction coordinate point data can be evaluated.

  Therefore, when the deviation is large, the data obtained at that time can be deleted or ignored, or the user can be informed that the data has a large error. Alternatively, the calibration process can be restarted immediately. Further, when the map information is displayed on the display device and the direction of the map information is switched according to the movement of the geomagnetism detection device, the angle at which the direction of the map information is switched is changed according to the degree of error in the calculation result. It becomes possible.

The circuit block diagram of the geomagnetism detection device of the embodiment of the present invention, Explanatory drawing showing the processing operation of the data buffer, Explanatory drawing of the X-axis sensor, the Y-axis sensor and the Z-axis sensor provided in the geomagnetism detection unit, Explanatory drawing showing spherical coordinate and coordinate point data before correction on the three-dimensional detection coordinate, Explanatory drawing showing the calculation of the dip angle, Explanatory drawing which shows the correction spherical coordinate and correction coordinate point data which have a center in the origin of a three-dimensional detection coordinate, Explanatory drawing showing how to find the deviation of azimuth Explanatory diagram showing the switching operation of the map information display screen,

  A geomagnetism detecting device 1 according to an embodiment of the present invention shown in FIG. 1 is mainly used as an orientation sensor, and includes a geomagnetism detecting unit 2 and a three-axis acceleration sensor 8.

  As shown in FIG. 3, in the geomagnetic detection device 1, the X1, Y1, and Z1 axes, which are reference axes orthogonal to each other, are determined as fixed axes. Three-dimensional detection coordinates are determined by the X1 axis, the Y1 axis, and the Z1 axis. The geomagnetism detection device 1 is mounted on a portable device or the like, and can move freely in space while maintaining the orthogonal relationship between the X1 axis, the Y1 axis, and the Z1 axis of the three-dimensional detection coordinates.

  As shown in FIG. 3, the X-axis sensor 3 is fixed along the X1 axis, the Y-axis sensor 4 is fixed along the Y1 axis, and the Z-axis sensor is fixed along the Z1 axis. Has been. The X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor 5 are all configured by GMR elements (giant magnetoresistance effect elements). The GMR element is composed of a pinned magnetic layer and a free magnetic layer made of a soft magnetic material such as a Ni—Co alloy or a Ni—Fe alloy, and a nonmagnetic material such as copper sandwiched between the pinned magnetic layer and the free magnetic layer. And a conductive layer. An antiferromagnetic layer is laminated below the pinned magnetic layer, and the magnetization of the pinned magnetic layer is pinned by exchange coupling between the antiferromagnetic layer and the pinned magnetic layer.

  The X-axis sensor 3 detects a component of the geomagnetic vector facing the X1 direction, and the magnetization direction of the pinned magnetic layer is fixed in the PX direction along the X1 axis. The direction of magnetization of the free magnetic layer responds to the direction of geomagnetism. When the magnetization direction of the free magnetic layer is parallel to the PX direction, the resistance value of the X-axis sensor 3 is minimized, and when the magnetization direction of the free magnetic layer is opposite to the PX direction, the resistance value of the X-axis sensor 3 is maximized. become. Further, when the magnetization direction of the free magnetic layer is orthogonal to the PX direction, the resistance value is an average value of the maximum value and the minimum value.

  In the magnetic field data detection unit 6 shown in FIG. 1, the X-axis sensor 3 and the fixed resistance are connected in series, and a voltage is applied to the series circuit of the X-axis sensor 3 and the fixed resistance. The voltage between the resistors is taken out as the detection output of the X1 axis. When a magnetic field directed in the X1 direction is not applied to the X-axis sensor 3, or when a magnetic field orthogonal to PX is applied, the detection output of the X1-axis becomes a midpoint potential.

  When the entire geomagnetism detector 2 is tilted and the fixed direction PX of the magnetization of the pinned magnetic layer of the X-axis sensor 3 is set to the same direction as the geomagnetic vector V, the magnetic field component applied to the X-axis sensor 3 becomes a maximum value. The detected output of the X1 axis at this time becomes a maximum value on the plus side with respect to the midpoint potential. Conversely, when the fixed direction PX of the magnetization of the fixed magnetic layer of the X-axis sensor 3 is directed opposite to the geomagnetic vector V, the reverse magnetic field component applied to the X-axis sensor 3 has a maximum value. At this time, the detection output of the X1 axis has a maximum value on the minus side with respect to the midpoint potential.

  Each of the Y-axis sensor 4 and the Z-axis sensor 5 is also connected to a fixed resistor in series, and a voltage is applied to the Y-axis sensor 4 or a series circuit of the Z-axis sensor 5 and the fixed resistor. Is taken out as a detection output of the Y1 axis or the Z1 axis.

  When the fixed direction PY of the magnetization of the fixed magnetic layer of the Y-axis sensor 4 is set in the same direction as the geomagnetic vector V, the Y1-axis detection output has a maximum value on the plus side with respect to the midpoint potential. If the fixed direction PY of the magnetization of the fixed magnetic layer of the Y-axis sensor 4 is directed opposite to the geomagnetic vector V, the Y1-axis detection output becomes a maximum value on the minus side with respect to the midpoint potential. Similarly, when the fixed direction PZ of the magnetization of the fixed magnetic layer of the Z-axis sensor 5 is set to the same direction as the geomagnetic vector V, the detection output of the Z1-axis becomes a maximum value on the plus side with respect to the midpoint potential. When the fixed direction PZ of the magnetization of the fixed magnetic layer of the Z-axis sensor 5 is directed opposite to the geomagnetic vector V, the detection output of the Z1-axis becomes a maximum value on the minus side with respect to the midpoint potential.

  If the magnitude of the geomagnetic vector V is constant, the detection outputs from the X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor 5 are all of the absolute value of the plus side maximum value and the minus side maximum value. The absolute value is the same.

  As the X-axis sensor 3, a positive detection output and a negative detection output are obtained depending on the direction of the geomagnetic vector, and the absolute value is the same between the maximum value of the positive detection output and the maximum value of the negative detection output. If it becomes, it can also be comprised with geomagnetic sensors other than a GMR element. For example, a Hall element or MR element that can detect only the positive magnetic field intensity along the X1 axis and a Hall element or MR element that can detect only the negative magnetic field intensity may be combined and used as the X-axis sensor 3. Good. The same applies to the Y-axis sensor 4 and the Z-axis sensor 5.

  As shown in FIG. 1, the detection outputs of the X axis, the Y axis, and the Z axis detected by the magnetic field data detection unit 6 are given to the calculation unit 10. The arithmetic unit 10 includes an A / D converter, a CPU, a clock circuit, and the like. According to the measurement time of the clock circuit of the calculation unit 10, the detection outputs of the X axis, the Y axis, and the Z axis detected by the magnetic field data detection unit 6 are intermittently sampled in a short cycle and read out to the calculation unit 10. . Each detection output is converted into a digital value by the A / D conversion unit provided in the calculation unit.

  A memory 7 is connected to the CPU constituting the arithmetic unit 10. In the memory 7, software for arithmetic processing is programmed and stored. The arithmetic processing of the arithmetic unit 10 is executed by the software.

  The arithmetic unit 10 performs arithmetic processing based on software. The X1 axis detection output, the Y1 axis detection output, and the Z1 axis detection output converted into digital data are subjected to calculation processing by the calculation unit 10, and the coordinates on the three-dimensional detection coordinates of X1-Y1-Z1 shown in FIG. It is converted into point data Di (xi, yi, zi) and stored in the data buffer (buffer memory) 11 shown in FIG. The coordinate point data Di sampled and calculated in a short cycle in synchronization with the clock circuit is given to the storage unit 11a of the data buffer 11. Each time the coordinate point data Di is given to the storage unit 11a, the coordinate point data Di obtained before that is sequentially sent from the storage unit 11a to 11m, and the coordinate point data Di of the storage unit 11m at the final stage is discarded. While the geomagnetism detection device 1 is operating, the latest data is continuously read from the magnetic field data detection unit 6 at regular intervals, and the calculated coordinate point data Di is sequentially stored in the data buffer 11.

  As shown in FIG. 1, the geomagnetic detection device 1 is provided with a triaxial acceleration sensor 8. The triaxial acceleration sensor 8 detects accelerations in directions along the X1 axis, the Y1 axis, and the Z1 axis, and the detection output is given to the posture detection unit 9. In the posture detection unit 9, the gravitational acceleration vector A shown in FIG. 5 is calculated from the accelerations in the directions along the X1 axis, the Y1 axis, and the Z1 axis, and the information is given to the calculation unit 10.

  As shown in FIG. 4, when the geomagnetism detection unit 2 is placed anywhere on the earth, the detection output xi is obtained from the X-axis sensor 3 of the geomagnetism detection unit 2, and the detection output yi is obtained from the Y-axis sensor 4. Thus, a detection output zi is obtained from the Z-axis sensor 5. In the calculation unit 10 shown in FIG. 2, coordinate point data Di (xi, yi) indicating the direction of the geomagnetic vector V on the three-dimensional detection coordinates of the X1-Y1-Z1 axes from the detection outputs xi, yi, zi of the respective axes. , Zi) is calculated.

  When the measurement location is the northern hemisphere, the geomagnetic vector V is incident at a predetermined dip angle toward the horizon. Therefore, as shown in FIG. 4, in the three-dimensional detection coordinates having the X1-Y1-Z1 axes, the geomagnetic vector V faces the center Oc of the spherical coordinate G1 before calibration, and the direction of the geomagnetic vector V is the geomagnetic vector V Is expressed as coordinate point data Di (xi, yi, zi) on the spherical coordinate G1 with the absolute value of.

  The coordinate point data Di (xi, yi, zi) are obtained one after another for each sampling period (i = 1, 2, 3, 4,...) And stored in the data buffer 11 in order. The plurality of coordinate point data Di (xi, yi, zi) is distributed on the surface of the spherical coordinate G1.

  At the time when the power is turned on and the detection operation is disclosed, the coordinates (xc, yc, zc) of the center Oc of the spherical coordinate G1 are unknown, and the shape and radius of the spherical coordinate G1 are also unknown. The positional deviation between the origin O of the three-dimensional detection coordinate having the X1-Y1-Z1 axis and the center Oc of the spherical coordinate G1 is caused by the influence of an external magnetic field other than geomagnetism, the X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor. 5 is an offset amount due to sensitivity variation and noise from the circuit.

  Therefore, the calculation unit 10 performs the following calibration process when a plurality of coordinate point data Di (xi, yi, zi) is obtained.

  The calculation unit 10 recognizes the spherical coordinate G1 before calibration shown in FIG.

  xc, yc, zc are the coordinates of the center Oc of the spherical coordinate G1 in the three-dimensional detection coordinates of the X1-Y1-Z1 axes. a is a coefficient related to the sensitivity of the X-axis sensor 3, b is a coefficient related to the sensitivity of the Y-axis sensor 4, and c is a coefficient related to the sensitivity of the Z-axis sensor 5. When the sensitivities of the X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor 5 coincide with each other with high accuracy, Equation 3 is a sphere equation. Actually, there is a difference in sensitivity between the X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor 5, and the circuit to which each sensor is connected also varies. It becomes an equation such as a sphere.

  The calibration process is performed in order to obtain the values of xc, yc, zc and a, b, c in Equation 3. If there is no variation in the plurality of obtained coordinate point data Di (xi, yi, zi) and each coordinate point data Di appears in the same spherical coordinate (coordinates such as a spherical surface or an elliptical sphere) G1, a plurality of obtained xi, Substituting the respective values of yi, zi (i = 1, 2, 3, 4,...) into x, y, z in Equation 3, and solving the simultaneous equations, xc, yc, zc and a, The values of b and c can be obtained.

  However, actually, there is a variation in each coordinate point data Di (xi, yi, zi). Therefore, as shown in Equation 4 below, the equation of Equation 3 is expressed by Fi, and the values of xc, yc, zc and a, b, c that minimize J that is 1/2 of the cumulative value of the square of Fi Find the value. That is, an equation of a spherical surface or an elliptical sphere having the smallest error from a plurality of coordinate point data Di is obtained by the least square method.

  In order to simplify the equation of Fi in the above equation 4, a, b, and c are represented by the following equation 5. In Equation 5, the coefficient a related to the sensitivity of the detection output of the X-axis sensor 3 is R, Ay represents the coefficient b related to the sensitivity of the detection output of the Y-axis sensor 4 as a ratio to a, and Az is the ratio of the Z-axis sensor 5 A coefficient c relating to the sensitivity of the detection output is expressed as a ratio to a. Using R, Ay, and Az to represent Fi and J in Equation 4, Fi ′ and J ′ in Equation 6 below.

  Then, the values of xc, yc, zc and R, Ay, Az when J ′ is minimum are obtained. As shown in Equation 7 below, J ′ is partially differentiated with unknowns of xc, yc, zc and R, Ay, Az, and the simultaneous equations obtained by partial differentiation are solved. The values of xc, yc, zc and R, Ay, Az when ′ becomes minimum can be obtained.

ただし、

である。

However,

It is.

  Since Equation 7 is a nonlinear simultaneous equation, it cannot be solved by a general solution, but can be obtained by iterative calculation using a numerical solution method such as the Gauss-Newton method.

  Alternatively, it is also possible to obtain the values of xc, yc, zc and R, Ay, Az after transforming Fi ′ in Expression 6 into the linear equation shown in Expression 9 below without performing the above iterative calculation. .

  Each unknown and unknown equation in Equation 9 is expressed as Equation 10 below.

  When Fi ′ and J ′ are rewritten using Equation 10, the following Equation 11 is obtained.

  When J ′ in Equation 11 is partially differentiated by unknown numbers a1, a2, a3, a4, a5, and a6 and set to 0, the following simultaneous equations of Equation 12 are obtained.

  When Expression 12 is expressed by a determinant, the following Expression 13 is obtained.

  Since the determinant is a linear simultaneous equation including unknown numbers a1, a2, a3, a4, a5, and a6, it can be solved by numerical analysis such as Gaussian elimination. This numerical analysis eliminates the need for iterative calculation as in the case of solving the nonlinear equation shown in Equation 7, so that a solution can be obtained in a relatively short time in a CPU or the like.

  By solving the unknown numbers a1, a2, a3, a4, a5, a6, xc, yc, zc and R, Ay, Az can be obtained as shown in the following formula 14.

  Further, when there is no variation in the sensitivity of the X-axis sensor 3, the Y-axis sensor 4, and the Z-axis sensor 5, or when it is desired to simplify the calculation while ignoring the variation in sensitivity of each sensor, the spherical coordinate G1 shown in FIG. Can be expressed by Equation 15 below. Equation 15 is a spherical equation.

  Since the unknown numbers in this case are only xc, yc, zc, and R, the calculation can be simplified compared with obtaining the unknown numbers xc, yc, zc and a, b, c in Equation 3. R is a radius from the center Oc of the spherical coordinate G1 shown in FIG. 4 and corresponds to the absolute value of the geomagnetic vector.

  The unknown numbers xc, yc, zc and R in Formula 15 are calculated in the same manner as the calculation of the unknown number of Formula 3 as follows. In the following, Expression 16 corresponds to Expression 4, and Expressions 17 and 18 correspond to Expressions 7 and 8. Expressions 19, 20 and 21 correspond to Expressions 9, 10 and 11. Expressions 22 and 23 correspond to Expressions 12 and 13.

  By the above calculation, unknown numbers xc, yc, zc and R can be obtained as shown in Expression 24.

  The calibration process is performed when the geomagnetism detecting device 1 is started after the power is turned on and a predetermined number of coordinate point data Di (xi, yi, zi) is obtained thereafter. Or it is performed regularly.

  As a result of the calibration process, the coordinate position (xc) of the center Oc of the spherical coordinate G1 where the coordinate point data Di (xi, yi, zi) shown in FIG. , Yc, zc). In addition, each constant that determines the shape of the spherical coordinate G1 that is a spherical surface or an elliptical sphere becomes clear. After the calibration process, the constants for determining the coordinate position of the center Oc and the shape of the spherical coordinate G1 are held in the memory in the calculation unit 10. The coordinate point data Di (xi, yi, zi) obtained thereafter is corrected using constants stored in the memory.

  The equation of the spherical coordinate G1 is defined by Equation 3, and when the unknowns xc, yc, zc and R, Ay, Az are obtained in Equation 14, the coordinate points xi, The corrected coordinate point data Di ′ (xi ′, yi ′, zi ′) is obtained by substituting yi and zi into the following equation (25).

(Equation 25)
xi '= xi-xc
yi ′ = Ay · (yi−yc)
zi '= Az. (zi-zc)

  When the equation of the spherical coordinate G1 is defined by Equation 15 and the unknowns xc, yc, zc and R are obtained in Equation 24, the coordinate points xi, yi, zi of the coordinate point data Di obtained after the calibration processing are obtained. The corrected coordinate point data Di ′ (xi ′, yi ′, zi ′) can be obtained by substituting into the following equation (26).

(Equation 26)
xi '= xi-xc
yi '= yi-yc
zi '= zi-zc

  As shown in FIG. 5, the corrected coordinate point data Di ′ (xi ′, yi ′, zi ′) corrected by the calibration process has a center Oc at the origin O of the three-dimensional detection coordinates of the X1-Y1-Z1 axes. It is expressed as a coordinate point on the corrected spherical coordinate G0 that is a mathematically accurate spherical shape. The radius of the corrected spherical coordinate G0 is R. This R corresponds to R used in Equations 5 and 15, and is a value determined based on the sensitivity of the X-axis sensor 3.

  Since the center of the corrected spherical coordinate G0 coincides with the origin O of the three-dimensional detection coordinates of the X1-Y1-Z1 axes, the corrected coordinate point data Di ′ (xi ′, yi ′, zi) appearing in the corrected spherical coordinate G0. ′) And the detection output of the triaxial acceleration sensor 8 shown in FIG. 1, the dip angle I of the geomagnetic vector can be obtained.

  FIG. 5 shows a gravitational acceleration vector A detected by the triaxial acceleration sensor 8. Further, the geomagnetic vector obtained from the corrected coordinate point data Di ′ (xi ′, yi ′, zi ′) when the geomagnetic detection device 1 is stopped in the same attitude in space is indicated by M.

  As shown in the following Equation 27, the relative angle α of both vectors can be obtained from the inner product of the gravitational acceleration vector A and the geomagnetic vector M at rest, and by subtracting 90 degrees from α, the geomagnetic vector M The dip angle I can be obtained.

  FIG. 6 shows the three-dimensional correction coordinates of the X0-Y0-Z0 axis corrected so that the gravitational acceleration vector A is directed to the negative of the Z axis. In the three-dimensional correction coordinates, the X0-Y0 plane coincides with the direction of the horizontal plane. When the measurement location is the northern hemisphere, the geomagnetic vector M is shown in an orientation having an angle I (positive angle) I on the plus side from the X0-Y0 plane.

  Next, evaluation of detection accuracy or calculation accuracy after the calibration process is performed as follows.

  After the calibration process, a plurality of correction coordinate point data Di ′ (xi ′, yi ′, zi ′) appearing on the correction spherical coordinate G0 on the three-dimensional correction coordinate shown in FIG. 6 and the origin O of the three-dimensional correction coordinate The distance ri is calculated by the following equation (28). In the following Expression 29, a deviation δR between the obtained distance ri and the radius R of the corrected spherical coordinate is obtained.

  The calculation unit 10 can evaluate detection accuracy or calculation accuracy based on a ratio between the radius R and the deviation δR. However, detection accuracy or calculation accuracy can be evaluated with higher accuracy by the following calculation.

  The geomagnetic vector M is projected onto the X0-Y0 plane of the three-dimensional correction coordinates, and the angle between the projected vector and the X0 axis is obtained. This angle is the azimuth angle θ. Here, the larger the dip angle I of the geomagnetic vector M, the shorter the projected vector projected on the X0-Y0 coordinate plane. As a result, the ratio of the deviation δR expressed by Equation 29 to the projection vector increases, the detection accuracy or calculation accuracy decreases, and the measurement error of the azimuth angle θ increases.

  Therefore, the calculation unit 10 obtains Rhorizontal by the following equation 30. Rhorizontal corresponds to the plane radius from the Z0 axis of the latitude line Ha where the corrected coordinate point data Di ′ of the geomagnetic vector M appears in the corrected spherical coordinate G0 shown in FIG.

  By using the ratio of the deviation δR obtained in Equation 29 and Rhorizontal obtained in Equation 30 as a reference, it is possible to evaluate detection accuracy or calculation accuracy with high accuracy. It can be considered that the ratio of the deviation δR to the plane radius Rhorizontal obtained in Equation 30 corresponds to the ratio of error to the detected value of the geomagnetic vector. Therefore, the higher the latitude at which the corrected coordinate point data Di appears, the greater the ratio of the error component to the detected value of the geomagnetic vector.

  Next, since it is considered that the ratio of the error component to the measured value of the measured geomagnetic vector is directly reflected as the ratio of the error component to the measured value of the azimuth angle θ, in the following Expression 31, the plane of the latitude line Ha The deviation δθ of the azimuth angle θ is obtained from the radius Rhorizontal and the deviation δR.

  FIG. 7 is a projection of the corrected spherical coordinate G0 shown in FIG. 6 onto a plane passing through the equator line H0. As shown in Equation 31, it is assumed that the ratio between the plane radius Rhorizontal of the latitude line Ha and the deviation δR appears as the deviation δθ of the azimuth angle θ at the same ratio. From the ratio of this azimuth angle θ and its deviation δθ, the detection accuracy or calculation accuracy can be evaluated with high accuracy.

  In the calculation unit 10, when the ratio of the deviation δR to the plane radius Rhorizontal of the latitude line Ha exceeds a predetermined ratio, or when the ratio of the deviation δθ to the azimuth angle θ exceeds a predetermined ratio, the detection accuracy or calculation For example, it is possible to perform a process of re-calibrating the calibration using a plurality of coordinate point data Di stored in the data buffer 11 at the time when it is determined that the accuracy is lowered.

  Alternatively, the calculation unit 10 may monitor the ratio of the deviation δθ to the azimuth angle θ, calculate the reliability of the azimuth angle θ in% based on the ratio, and display the reliability on a display device such as a portable device. Good. Alternatively, when the ratio of the deviation δθ to the azimuth angle θ is large, the data of the azimuth angle θ may be ignored as having low reliability.

  Next, when the geomagnetism detecting device 1 is provided with means for detecting the current position such as a GPS device, map data corresponding to the current position is extracted from the memory 7 and displayed on the display device 15 as shown in FIG. The map information can be displayed on the display screen 15a.

  In this device, the orientation of the map information displayed on the display screen of the display device 15 is switched according to the information on the azimuth angle θ obtained by the calculation. For example, when the geomagnetism detection device 1 is mounted on a portable device, if the person holding the portable device rotates and changes the orientation of the display device 15, the orientation of the map information displayed on the display screen Are switched in stages.

  FIG. 6 shows the relationship between the direction of the display screen 15a and the display direction of the map information. When the portable device is facing north (N), north (N) of the map information is directed in front of the display screen 15a. When the mobile device is turned counterclockwise and turned to the northwest (NW), the map information displayed on the display screen 15a is turned clockwise, and the northwest of the map information is directed in front of the display screen 15a. Further, when the portable device is directed to the west (W), the map information displayed on the display screen 15a rotates in the clockwise direction, and the west of the map information is directed in front of the display screen 15a.

  In the geomagnetic detection device 1 having such a function, the map information displayed on the display screen 15a according to the ratio of the deviation δR to the plane radius Rhorizontal of the latitude line Ha or the ratio of the deviation δθ to the azimuth angle θ. The division angle when rotating is switched. When the ratio of the deviation δR to the plane radius Rhorizontal of the latitude line Ha is large, or when the ratio of the deviation δθ to the azimuth angle θ is large, the number of divisions when the map information is rotated when the portable device is rotated is calculated. Reduce the direction of the map information so that it does not rotate unless it is rotated by a large angle. Conversely, when the ratio is small, the number of divisions is increased, and the direction of the map information is switched when rotated at a small angle.

  For example, when the map information on the display screen 15a shown in FIG. 8 is switched in 36 divisions when the geomagnetism detection device 1 rotates once along the horizon, the direction of the map information every time the geomagnetism detection device 1 rotates 10 degrees. Is switched. In this case, if the deviation δθ is about 10 degrees, there is a possibility that chattering in which the map information on the screen is switched to the fluttering may occur although the geomagnetic detection device 1 is not rotating. Therefore, when the deviation δθ is about 10 degrees, for example, when the geomagnetism detecting device 1 rotates once along the horizon, it is divided into 18 parts so that the direction of the map information is not switched unless the rotation angle becomes 20 degrees. Thus, chattering can be prevented and map information can be displayed stably.

  Therefore, the rotation angle θd of the geomagnetism detecting device 1 when the direction of the map information is switched is preferably 2 · δθ ≦ θd.

Thereby, even when the ratio of the deviation θR to the azimuth angle θ is large, the map information displayed on the display screen 15a can be stabilized. For example, the map information displayed on the display screen 15a has the azimuth angle θ. It becomes possible to solve problems such as fine fluctuations following the variation of the calculation value.

DESCRIPTION OF SYMBOLS 1 Geomagnetism detection apparatus 2 Geomagnetism detection part 3 X-axis sensor 4 Y-axis sensor 5 Z-axis sensor 6 Magnetic field data detection part 7 Memory 10 Calculation part 8 3-axis acceleration sensor 11 Data buffer G1 Spherical coordinate G0 Correction spherical coordinate X1-Y1-Z1 Three-dimensional detection coordinates X0-Y0-Z0 Three-dimensional correction coordinates Di Coordinate point data Di 'Correction coordinate point data

Claims (5)

It has a geomagnetism detection unit whose three-dimensional detection coordinates are determined in advance, an acceleration sensor that detects the attitude of the geomagnetism detection unit, and a calculation unit,
When the X-axis sensor in which the absolute value of the detection output becomes a maximum value when the X direction of the three-dimensional detection coordinates is directed to the geomagnetism direction and the Y direction is directed to the geomagnetism direction A Y-axis sensor in which the absolute value of the detection output is a maximum value and a Z-axis sensor in which the absolute value of the detection output is a maximum value when the Z direction is directed to the geomagnetism direction are mounted,
The calculation unit obtains the direction of a geomagnetic vector based on the detection output as coordinate point data on a three-dimensional detection coordinate,
When obtaining a plurality of coordinate point data, a corrected spherical coordinate that minimizes an error from the plurality of coordinate point data and a coordinate point of the center of the corrected spherical coordinate on the three-dimensional detection coordinate are obtained, and The coordinate point data is converted into corrected coordinate point data on the corrected spherical coordinate having the center at the origin of the three-dimensional detection coordinates,
A deviation (δR) between a distance (ri) from the origin to a plurality of correction coordinate point data and a radius (R) of the correction spherical coordinate is obtained, and is perpendicular to the gravity vector obtained from the detection output of the acceleration sensor. A geomagnetic sensing device characterized in that an dip angle (I) from a plane X0-Y0 to a geomagnetic vector is obtained, and R · cosI and the deviation (δR) are used as evaluation criteria for detection accuracy or calculation accuracy.   The deviation (δθ) of the azimuth angle (θ) is obtained based on the ratio between R · cosI and the deviation (δR), and the deviation (δθ) is used as an evaluation criterion for detection accuracy or calculation accuracy. The geomagnetic detection device described. A display device that displays map information at a position where the geomagnetism detection unit is arranged is provided, and when the display device rotates, the orientation of the map information is predetermined according to a change in azimuth angle (θ). The geomagnetic detection device according to claim 2, wherein the angle can be switched in accordance with a deviation (δθ) of the azimuth angle (θ). The number 1 follows, calculates the Fi, xc where J is minimized, seeking yc, zc and a, b, and c, calculates a correction spherical coordinates and the center position (xc, yc, zc is a coordinate point of the center of the correction spherical coordinates in three dimensions detecting coordinates, a, b, c are, X-axis sensor, Y-axis sensor, a coefficient based on the sensitivity of the Z-axis sensor) any of claims 1 to 3 The geomagnetic detection device according to the above.

The number 2 follows, calculates the Fi, xc where J is minimized, yc, seeking zc and R, to calculate a correction spherical coordinates and the center position (xc, yc, zc is the three-dimensional position coordinate The geomagnetic detection device according to any one of claims 1 to 3 , wherein R is a radius of the corrected spherical coordinate.

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