JP5937137B2 - Geomagnetic detector - Google Patents

Description

  The present invention relates to a geomagnetism detection device that detects geomagnetism using a magnetic sensor, and more particularly to a geomagnetism detection device that corrects an offset included in a geomagnetism vector detected by a magnetic sensor.

  An apparatus for detecting geomagnetism using a magnetic sensor to obtain a geographical orientation has been widely used in various navigation systems in the past, and in recent years, it is generally installed in portable electronic devices typified by mobile phones. It has come to be. Normally, a relatively strong magnetic field is generated in an electronic device in which a magnetic sensor is mounted from a magnet included in a speaker or a magnetic member magnetized by an external magnetic field. Therefore, a large magnetic field component inside the electronic device is superimposed on the detection value of the magnetic sensor together with a weak geomagnetic component. In order to obtain a geomagnetic component from the detection value of the magnetic sensor, it is necessary to remove the magnetic field component inside the electronic device by calibration.

  One known method of calibrating geomagnetism in a mobile phone is to rotate the mobile phone into a figure of 8 on a horizontal base. While detecting the detected value of the 2-axis (or 3-axis) magnetic sensor while rotating the cellular phone in this way, the locus of the circle (or spherical surface) in the two-dimensional coordinates (or three-dimensional coordinates) of the detected values. From this, a fixed magnetic vector (offset) that does not change due to the figure rotation is calculated. By subtracting this fixed magnetic vector (offset) from the detected value of the magnetic sensor, a geomagnetic vector is obtained.

  Incidentally, in recent years, small electronic devices (also called “wearables”) that are characterized by being worn directly on the body and used on a daily basis have attracted attention. When a geomagnetism detecting device is mounted on such an electronic device, the above-described calibration method using the figure-shaped rotation is difficult unless the electronic device is removed from the body. However, it is inconvenient if the removal is necessary for calibration, and the feature as “wearable” is impaired.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a geomagnetism detection device capable of correcting a fixed magnetic vector (offset) included in a magnetic detection value with a simple operation.

The geomagnetic detection device according to the present invention includes a magnetic sensor unit that detects, as magnetic coordinates, a combination of magnetic field strengths in a plurality of directions along a plurality of magnetic detection axes that are orthogonal to each other, and a plane that is stretched by the two magnetic detection axes. An angular velocity sensor for detecting an angular velocity around the one rotation detection axis, and a rotation around the one rotation detection axis based on the angular velocity around the one rotation detection axis detected by the angular velocity sensor. A rotation angle calculation unit that calculates an angle; two rotation angles around the one rotation detection axis calculated by the rotation angle calculation unit; and the magnetic sensor unit that detects the two rotation angles. A circle having the two magnetic coordinates on the circumference based on the two magnetic coordinates and having an arc that has the two magnetic coordinates at both ends. Central angle calculates the two center coordinates circle equal to the difference between the rotational angles, based on the center coordinates of the calculated, and a correction operation unit for correcting an offset of the geomagnetic vector representing said magnetic coordinates.
According to the above configuration, the two rotation angles around the one rotation detection axis calculated by the rotation angle calculation unit and the two detected by the magnetic sensor unit when the two rotation angles are provided. A circle having the two magnetic coordinates on the circumference based on the magnetic coordinates, and a center angle corresponding to an arc whose ends are the two magnetic coordinates is equal to the difference between the two rotation angles. Center coordinates are calculated. Based on the calculated center coordinates, the offset of the geomagnetic vector represented by the magnetic coordinates is corrected. Thereby, the offset of the geomagnetic vector can be corrected by a simple rotation operation around a single rotation detection axis.

Preferably, the angular velocity sensor unit may detect the other two angular velocities around two rotation detection axes parallel to the two magnetic detection axes. The correction calculation unit detects the one rotation detected by the rotation angle calculation unit when the other two angular velocities detected by the angular velocity sensor unit both continue to be smaller than a predetermined threshold value. The center coordinates may be calculated based on two rotation angles around the axis and two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided.
According to the above configuration, since the center coordinate is calculated based on the rotation angle calculated when the rotation is generated only around the one rotation detection axis, the accuracy of the center coordinate is improved. To do.

Preferably, the magnetic sensor unit may detect a combination of the magnetic field strengths in directions along the first magnetic detection axis, the second magnetic detection axis, and the third magnetic detection axis orthogonal to each other as the magnetic coordinates. The angular velocity sensor unit includes an angular velocity around a first rotation detection axis that is the same as or parallel to the first magnetic detection axis, an angular velocity around a second rotation detection axis that is the same or parallel to the second magnetic detection axis, and An angular velocity around a third rotation detection axis that is the same as or parallel to the third magnetic detection axis may be detected. The rotation angle calculation unit may calculate at least a rotation angle around the first rotation detection axis and a rotation angle around the second rotation detection axis. The correction calculation unit is configured to detect the first rotation detection axis when the angular velocity around the second rotation detection axis and the angular velocity around the third rotation detection axis are both smaller than the threshold value. The center coordinate may be calculated based on two rotation angles around and the two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided. The correction calculation unit may detect the second rotation when both the angular velocity around the first rotation detection axis and the angular velocity around the third rotation detection axis continue to be smaller than the threshold value. The center coordinates may be calculated based on two rotation angles around the axis and two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided.

Preferably, the correction calculation unit selects two rotation angles having a difference larger than a predetermined angle from the series of rotation angles calculated by the rotation angle calculation unit, and selects the two rotation angles selected. The center coordinates may be calculated based on the difference and the two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided.
According to said structure, since the said 2 rotation angle used for calculation of the said center coordinate has a difference larger than a predetermined angle, the precision of the said center coordinate improves.

  According to the present invention, a fixed magnetic vector (offset) included in a magnetic detection value can be corrected by a simple operation according to the detection result of the acceleration sensor.

It is a figure which shows the external appearance of the spectacles type electronic device by which the geomagnetism detection apparatus which concerns on this embodiment is mounted. FIG. 1A shows an appearance example of a spectacle-type electronic device, and FIG. 1B shows detection axes of geomagnetism and angular velocity in a geomagnetism detection device. It is a figure which shows an example of a structure of the geomagnetic detection apparatus which concerns on this embodiment. It is a figure for demonstrating the locus | trajectory of the magnetic coordinate in a 3-axis coordinate system. It is the figure which projected the locus | trajectory of the magnetic coordinate shown in FIG. 3 on XY plane. It is a figure for demonstrating the method of calculating the center coordinate of a circle. It is a flowchart for demonstrating operation | movement of the geomagnetism detection apparatus which concerns on this embodiment. It is a 1st flowchart for demonstrating a calibration process. It is a 2nd flowchart for demonstrating a calibration process.

Hereinafter, electronic devices according to embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating the external appearance of a spectacle-type electronic apparatus equipped with a geomagnetism detection device according to an embodiment of the present invention. The eyeglass-type electronic device shown in FIG. 1 includes a front portion 1 located on the front surface (face) of the head, two temple portions 2 located on the side surface (the temple) of the head, and the front portion 1 and the temple portion. And two hinges 3 for foldably connecting the two.

  The front unit 1 includes left and right eyeglass lenses 7, two rims 4 that hold the eyeglass lenses 7, and a bridge 5 that connects the two rims 4. The bridge 5 is formed of, for example, resin, and a circuit board on which electronic circuit components such as sensors (10, 20, 30) and a control unit 40 of a geomagnetism detection device described later are mounted inside the bridge 5. 6 is accommodated. A display unit 8 that projects an image in the user's field of view is disposed in a partial region of the spectacle lens 7. The display unit 8 is a transmissive display using, for example, a half mirror. Audio output units 9A and 9B are mounted on the end portions of the left and right temple portions 2 near the ears. The audio output units 9A and 9B include, for example, a speaker that transmits sound to the eardrum by bone conduction.

FIG. 2 is a diagram illustrating an example of a geomagnetism detection device in the eyeglass-type electronic device illustrated in FIG. 1.
For example, as shown in FIG. 2, the geomagnetism detection device according to the present embodiment includes a magnetic sensor unit 10, an angular velocity sensor unit 20, an acceleration sensor unit 30, and a control unit 40.

The magnetic sensor 10 is a sensor that detects a magnetic field, and is configured using, for example, a magnetoresistive effect element such as a GMR element, a Hall element, or a magnetic impedance element. The magnetic sensor unit 10 detects magnetic field strengths in directions along a plurality of detection axes (two axes and three axes) orthogonal to each other. Here, as an example, the magnetic field strengths in the directions along the three axes (X axis, Y axis, and Z axis) shown in FIG. 1A are detected.
In the following description, a combination of magnetic field strengths in directions along three axes (X axis, Y axis, and Z axis) may be referred to as “magnetic coordinates M” in a three-axis coordinate system.

  The angular velocity sensor 20 is a sensor that detects an angular velocity when the spectacles-type electronic device moves. For example, a minute mechanism member (moving body) formed on a semiconductor chip by MEMS technology is moved, and the mechanism member is rotated by rotation. The detection signal of the angular velocity according to the Coriolis force generated in is output. The acceleration sensor 10 detects angular velocities around a plurality of detection axes (two axes and three axes) orthogonal to each other. Here, as an example, it is assumed that angular velocities V around the three axes (X axis, Y axis, and Z axis) shown in FIG. 1A are detected.

  The acceleration sensor 30 is a sensor that detects acceleration acting on the spectacle-type electronic device, and converts, for example, a distance by which a minute mechanism member formed on a semiconductor chip by MEMS technology is displaced against a spring force into an electric signal. By doing so, a signal corresponding to the acceleration is output. The acceleration sensor 10 detects accelerations in directions along a plurality of detection axes (two axes and three axes) orthogonal to each other. Here, as an example, the angular velocities G in the directions along the three axes (X axis, Y axis, and Z axis) shown in FIG. 1A are detected.

  The control unit 40 processes sensor signals (M, V, G) output from the magnetic sensor unit 10, the angular velocity sensor unit 20, and the acceleration sensor unit 30, respectively, and calculates geomagnetism and direction. The control unit 40 includes, for example, a computer having a CPU and a memory, a dedicated logic circuit, and the like.

  The control unit 40 includes a data buffer 41, a rotation angle calculation unit 42, a correction calculation unit 43, an azimuth calculation unit 44, a display control unit 45, and an audio control unit 46 as functional processing blocks.

  The data buffer 41 stores the magnetic coordinate M data detected by the magnetic sensor unit 10 and the angular velocity V data detected by the angular velocity sensor unit 20 in the order of detection. The data buffer 41 stores a series of a predetermined number of data groups including the latest data in order, like the FIF0 type buffer, for example, and discards the oldest data every time new data is stored. The data buffer 41 stores the magnetic coordinate M data and the angular velocity M data detected at the same timing as a group of data.

  The rotation angle calculation unit 42 calculates the rotation angle θ around each axis based on the angular velocity V around each axis detected by the angular velocity sensor unit 20. For example, the rotation angle calculator 42 calculates the rotation angle θ around each axis by time-integrating the angular velocity V around each axis. The timing at which the rotation angle calculation unit 42 starts time integration of the angular velocity V is arbitrary. Therefore, the rotation angle θ obtained as a calculation result of the rotation angle calculation unit 42 represents a relative rotation angle with the rotation angle in an arbitrary posture at the arbitrary timing as a reference (zero). By calculating the difference between the rotation angle θ calculated at a certain time and the rotation angle θ calculated at another time, the angle rotated during that time is obtained.

  The correction calculation unit 43 includes two rotation angles θ around one axis calculated by the rotation angle calculation unit 42 and two magnetic coordinates detected by the magnetic sensor unit 10 when the two rotation angles θ are included. Based on (A, B), a circle (S2) having the two magnetic coordinates (A, B) on the circumference, the arc having both ends of the two magnetic coordinates (A, B) The center coordinate (P) of the circle (S2) whose corresponding center angle is equal to the difference (α) between the two rotation angles θ is calculated (see FIG. 5 for the sign). Further, the correction calculation unit 43 corrects the offset of the magnetic vector represented by the magnetic coordinates detected by the magnetic sensor 10 based on the calculated center coordinates (P).

FIG. 3 is a diagram for explaining the locus of magnetic coordinates in a three-axis coordinate system.
The three-axis coordinate system shown in FIG. 3 represents the magnetic intensity in each of the X axis, the Y axis, and the Z axis fixed on the eyeglass-type electronic device. “O” in FIG. 3 indicates the origin of the coordinate system, and “M” indicates one magnetic coordinate in the coordinate system. When the entire eyeglass-type electronic device is rotated in an arbitrary direction, the magnetic coordinates M move on the spherical surface S1 in FIG.

  A magnetic vector “OM” from the origin O to the magnetic coordinate M is a magnetic vector represented by the magnetic coordinate M in the three-axis coordinate system shown in FIG. As shown in FIG. 3, this magnetic vector “OM” is composed of a magnetic vector “OP” from the origin O toward the central coordinate P of the spherical surface S <b> 1 and a magnetic vector “PM” from the central coordinate P toward the magnetic coordinate M. It is a thing. The magnetic vector “OP” is based on a magnetic field generated inside the spectacles-type electronic device, and is a fixed vector that does not change no matter how the spectacles-type electronic device is rotated, that is, an offset. On the other hand, the magnetic vector “PM” is based on a magnetic field external to the spectacle-type electronic device, that is, the geomagnetism. When the spectacle-type electronic device is rotated with respect to the external magnetic field, the direction of the magnetic vector “PM” also corresponds to this. Rotate. Thus, since the vector representing the direction of geomagnetism is the magnetic vector “PM”, it is necessary to calculate the center coordinate P. Therefore, the correction calculation unit 43 calculates the center coordinate P from the locus of the magnetic coordinate M as described below.

FIG. 4 is a diagram in which the trajectory of the circle S2 of the magnetic coordinates M shown in FIG. 3 is projected on the XY plane.
When the spectacles-type electronic device is rotated only around the Z axis while the rotation on the Y axis and the Z axis is stopped, the locus of the magnetic coordinates M becomes a circle S2 as shown in FIG. For example, when the coordinate system of the eyeglass-type electronic device is set as shown in FIG. 1, the rotation only around the Z-axis corresponds to a simple operation of simply swinging the neck in the lateral direction. As shown in FIG. 5, the center coordinates P of the circle S2 as shown in FIG. 4 are the coordinates of the two points A and B on the circumference of the circle S2 and an arc having the two points A and B as both ends. It can be calculated from the corresponding central angle α.

FIG. 5 is a diagram for explaining a method of calculating the center coordinate P of the circle S2.
The two magnetic coordinates on the circumference of the circle S2 are “A” and “B”, the X coordinate component and the Y coordinate component of the magnetic coordinate A are “Xa” and “Ya”, the X coordinate component of the magnetic coordinate B and the Y coordinate The coordinate components are “Xb” and “Yb”. In this case, the slope E of the straight line L1 passing through the two magnetic coordinates “A” and “B” is expressed by the following equation.

  Further, if the magnetic coordinate located between the two magnetic coordinates “A” and “B” is “C” and the X coordinate component and the Y coordinate component of the magnetic coordinate C are “Xc” and “Yc”, this “ Xc "and" Yc "are each represented by the following equations.

  The center coordinate P of the circle S2 is located on a straight line L2 that passes through the intermediate magnetic coordinate C and intersects perpendicularly to the straight line L1. Assuming that the X coordinate component and the Y coordinate component of the central coordinate P are “Xp” and “Yp”, since “Xp” and “Yp” satisfy the relationship of the linear equation of the straight line L2, the following equation is established.

  On the other hand, the magnetic vector “PA” going from the central coordinate P to the magnetic coordinate A and the magnetic vector “PB” going from the central coordinate P to the magnetic coordinate B are expressed as follows using the coordinate display.

  When the central angle α corresponding to the arc having the magnetic coordinates A and B at both ends is used, the following relationship is established by the cosine theorem.

  The denominator and numerator in Equation (7) are each expressed by the following equations.

  From the relationship between Expression (4) and Expressions (7) to (9), the center coordinates P (Xp, Yp) can be calculated based on the magnetic coordinates A and B and the center angle α.

  The correction calculation unit 43 calculates the X coordinate component and the Y coordinate component (Xp, Yp) of the center coordinate P by such a method. Note that the correction calculation unit 43 uses a method based on rotation only about the X axis, for example, as with the above-described method based on rotation only about the Z axis, for the Z coordinate component (Zp) of the center coordinate P. The Y coordinate component and the Z coordinate component (Yp, Zp) of the center coordinate P are calculated. When the coordinate system is set as shown in FIG. 1, rotation only around the X axis corresponds to a simple operation of simply swinging the neck in the vertical direction. When the center coordinate P is calculated by two methods in this way, two calculation results are obtained as the Y coordinate component (Yp). For example, the correction calculation unit 43 finally calculates an average value of the two calculation results. It may be determined as a Y coordinate component (Yp).

  The correction calculation unit 43 determines that rotation has occurred only around the Z axis or only around the X axis based on the detection result of the angular velocity sensor unit 20. For example, when the correction calculation unit 43 determines rotation only around the Z axis, the angular velocity around the other two axes (angular velocity around the X axis, angular velocity around the Y axis) is set to a predetermined threshold value. If any of the angular velocities is lower than a predetermined threshold value, it is determined that the motor rotates only about the Z axis. Further, when determining the rotation only around the X axis, the correction calculation unit 43 compares the angular velocity around the Y axis and the angular velocity around the Z axis with a predetermined threshold value, and both angular velocities are predetermined. If it is lower than the threshold value, it is determined that the motor is rotating only around the X axis.

  Further, when the correction calculation unit 43 calculates the center coordinate P using the difference α between the two magnetic coordinates A and B and the two rotation angles θ as described above, the difference α between the two rotation angles θ is predetermined. The data satisfying the condition larger than the angle is used for calculating the center coordinate P. That is, the correction calculation unit 43 selects two rotation angles θ having an angle difference α larger than a predetermined angle from the series of rotation angles θ calculated by the rotation angle calculation unit 42, and selects the selected two rotation angles θ. Based on the difference α of the rotation angle θ and the two magnetic coordinates (A, B) detected by the magnetic sensor unit 10 when the two rotation angles θ are present, the center coordinate P is calculated. As described above, since the distance between the two magnetic coordinates (A, B) is increased by using data with a condition that the difference α between the two rotation angles θ is larger to some extent, as shown in FIG. An error in calculating P can be suppressed.

When the center coordinate P is calculated in this way, the correction calculation unit 43 corrects the offset of the geomagnetic vector represented by the magnetic coordinate M detected by the magnetic sensor unit 10 based on the center coordinate P. Specifically, the correction calculation unit 43 calculates the magnetic coordinate M ′ whose offset is corrected by subtracting each coordinate component of the center coordinate P from each coordinate component of the magnetic coordinate M. This corresponds to the coordinate conversion for moving the origin O in FIG.
The above is the description of the correction calculation unit 43.

Returning to FIG.
The azimuth calculation unit 44 calculates the azimuth based on the magnetic coordinates M ′ corrected by the correction calculation unit 43 and the direction of gravitational acceleration obtained in the acceleration sensor unit 30. The magnetic coordinate M ′ corrected by the correction calculation unit 43 indicates the direction of geomagnetism viewed from the coordinate system set on the glasses-type electronic device, and the coordinate system set on a plane parallel to the ground. Is not the direction of geomagnetism. Therefore, the azimuth calculation unit 44 sets the geomagnetic vector on a plane parallel to the ground by rotating and converting the geomagnetic vector indicated by the magnetic coordinate M ′ based on the direction of the gravitational acceleration obtained in the acceleration sensor unit 30. After conversion into a vector in the coordinate system, the azimuth angle indicated by the vector is calculated.

  The display control unit 45 is a block that controls display of video on the display unit 8, and generates a video signal supplied to the display unit 8, for example. When the correction calculation unit 43 calculates the central coordinate P described above, the display control unit 45 rotates only around the Z axis (neck swinging motion) or rotates only around the X axis (neck rotation). The display unit 8 displays an image for giving an instruction to the user to perform (vertical swing operation).

  The audio control unit 46 is a block that controls the output of audio in the audio output units 9A and 9B. For example, the audio control unit 46 generates an audio signal to be supplied to the audio output units 9A and 9B. When the correction calculation unit 43 calculates the center coordinate P described above, the voice control unit 46 rotates only around the Z axis (neck swinging motion) or rotates only around the X axis (neck rotation). The sound output unit 9A, 9B outputs a sound that gives an instruction to the user to perform a vertical swing operation.

  Here, the operation of the geomagnetism detecting device having the above-described configuration will be described with reference to FIGS.

  FIG. 6 is a flowchart for explaining the operation of calculating the azimuth based on the detection result of geomagnetism in the geomagnetism detection device according to the present embodiment. The operation shown in FIG. 6 is repeatedly executed at regular time intervals when the azimuth is continuously calculated, for example, during navigation.

  The control unit 40 detects the strength of the surrounding magnetic field based on the magnetic field strength data detected by the magnetic sensor unit 10 (ST10), and whether or not the magnetic field detection result is abnormal based on the detection result. Is determined (ST15). For example, the control unit 40 calculates the magnitude of the geomagnetic vector indicated by the magnetic coordinates M ′ corrected by the correction calculation unit 43, and based on whether the magnitude of the geomagnetic vector is within a predetermined normal range, The presence or absence of abnormality in the magnetic field detection result is determined. When it is determined that there is no abnormality in the magnetic field detection result, the control unit 40 calculates an azimuth in the azimuth calculation unit 44 (ST20).

  When it is determined in step ST15 that the magnetic field is abnormal, the control unit 40 performs a calibration process in which the correction calculation unit 43 recalculates the offset correction center coordinates P (ST25). After the calibration process, the control unit 40 determines the reliability of the recalculated center coordinate P (ST30). For example, the control unit 40 corrects a plurality of magnetic coordinates stored in the data buffer 41 based on the recalculated center coordinates P, and calculates the magnitudes of the magnetic vectors indicated by the corrected magnetic coordinates, A variation (standard deviation or the like) in the magnitudes of the calculated magnetic vectors is calculated. Since the corrected magnetic vectors are ideally on the same spherical surface, their lengths are equal. A large variation in the length of the magnetic vector indicates that the reliability of the center coordinate P is low. For example, the control unit 40 further calculates a ratio between the calculated variation in the length of the magnetic vector and the average value of the magnetic vectors, and if the ratio is not included in a predetermined normal range, the reliability of the center coordinate P is Judged to be lower than the standard. When it is determined that the reliability of the center coordinate P is lower than the reference, the control unit 40 performs the calibration process of step ST25 again, and when it is determined that the reliability of the center coordinate P is equal to or higher than the reference, the control unit 40 performs step ST20. Then, the azimuth calculation unit 44 calculates the azimuth.

7 and 8 are flowcharts for explaining the calibration process (ST25).
When shifting to the calibration process, the control unit 40 collects the data of the magnetic coordinates M detected by the magnetic sensor unit 10 and the data of the angular velocity V detected by the angular velocity sensor unit 20 as a set of data at the same time. The process of sequentially saving the data buffer 41 as a group is started. The rotation angle calculation unit 42 starts calculation of the rotation angle θ around each axis, and together with the data of the magnetic coordinates M and the data of the angular velocity V detected at the same time, the data buffer 41 as a group of data. (ST100). Note that if the detection data is stored in the data buffer 41 or the rotation angle θ is already being calculated, step ST100 may be omitted.

  When the calibration process is started, the display control unit 45 displays on the display unit 8 an image for giving an instruction to the user so as to perform a rotation operation only around the Z axis (a neck swinging operation). The voice control unit 46 also outputs voice giving similar instructions at the voice output units 9A and 9B (ST105).

  When the rotation operation starts in accordance with the video or audio guidance, the correction calculation unit 43 initializes the minimum rotation angle θmin and the maximum rotation angle θmax (ST110), and determines whether the rotation operation only around the Z axis is performed. (ST115). For example, the correction calculation unit 43 compares the angular velocity around the X axis and the Y axis with a predetermined threshold value, and makes a determination based on the comparison result. When the rotation operation only around the Z axis is not performed, the correction calculation unit 43 returns to step ST110, and when the rotation operation only around the Z axis is performed, the correction calculation unit 43 performs the minimum rotation angle θmin and the maximum rotation angle. θmax is updated (ST120). The correction calculation unit 43 compares the latest rotation angle θ calculated by the rotation angle calculation unit 42 with the minimum rotation angle θmin and the maximum rotation angle θmax, respectively, and if the latest rotation angle θ is smaller than the minimum rotation angle θmin, The latest rotation angle θ is stored as a new minimum rotation angle θmin, and when the latest rotation angle θ is larger than the maximum rotation angle θmax, the latest rotation angle θ is stored as a new maximum rotation angle θmax.

  The correction calculator 43 calculates a difference (| θmax−θmin |) between the minimum rotation angle θmin and the maximum rotation angle θmax, and determines whether or not the difference is greater than a predetermined threshold value TH1 (ST125). When the difference does not exceed the threshold value TH1, the correction calculation unit 43 returns to step ST115 and determines whether or not the rotation operation only around the Z axis is continued. On the other hand, when the difference is greater than the threshold value TH1, the correction calculation unit 43 and two pairs of rotation angles θ whose angle difference α is greater than the threshold value TH1 and the corresponding magnets (belonging to the same data group). A pair of coordinates M is acquired from the data buffer 41 (ST130). When the rotation angle θ pair of the angle difference α and the magnetic coordinate M pair are acquired from the buffer 41, the correction calculation unit 43 calculates the center coordinate P based on these (ST135). Then, the correction calculation unit 43 determines whether the number of central coordinates P calculated so far has reached a predetermined number (ST140). If the predetermined number has not yet been reached, the process returns to step ST115 and repeats the above-described processing. . When the calculated number of center coordinates P reaches a predetermined number, the correction calculation unit 43 calculates an average value (average of each coordinate component) of the predetermined number of center coordinates P (ST145).

  Next, the correction calculation unit 43 calculates a predetermined number of center coordinates P by a rotation operation only around the X axis, and obtains an average value thereof (ST150 to ST190). Since these steps ST150 to ST190 are the same processing as already described ST105 to ST145, description thereof will be omitted.

  In this way, the average value of the center coordinates P by the rotation operation only around the Z axis (the neck swinging operation) and the average value of the center coordinates P by the rotation operation only around the X axis (the neck vertical swing operation). When the value is obtained, the correction calculation unit 43 determines the coordinates of the center coordinate P in the three-axis coordinate system based on the average value (ST195). Since the Y coordinate component Yp is obtained at the average value of the two central coordinates P, for example, the correction calculation unit 43 determines the average of the two Y coordinate components Yp as the final Y coordinate component Yp.

  As described above, according to the geomagnetism detection device according to the present embodiment, the two rotation angles θ around the single rotation detection axis calculated by the rotation angle calculation unit 42 and the two rotation angles θ are calculated. Based on the two magnetic coordinates A and B detected by the magnetic sensor unit 10 when they have a circle having the two magnetic coordinates A and B on the circumference, the two magnetic coordinates A and B A center coordinate P of a circle in which the center angle corresponding to the arc having both ends of is equal to the difference α between the two rotation angles θ is calculated. Based on the calculated center coordinate P, the offset of the geomagnetic vector represented by the magnetic coordinate M detected by the magnetic sensor unit 10 is corrected. As a result, the offset of the geomagnetic vector included in the detection value of the magnetic sensor is corrected by a rotation operation within a certain angular range around a single axis, instead of the complicated figure-eight rotation as in the conventional mobile phone. be able to. For example, offset correction can be performed with very simple movements such as side and vertical movements of the neck, so when this geomagnetism detector is mounted on a wearable device, it is necessary to bother to remove it from the body for offset correction. It is possible to provide high convenience without losing the characteristics of wearable devices.

  In addition, according to the geomagnetism detection device according to the present embodiment, the rotational operation is performed only around one rotation detection axis, and the angular velocity around the other two rotation detection axes is a predetermined threshold value. The center coordinate P is calculated using the rotation angle around one rotation detection axis after the determination is made and the determination result is obtained. Thereby, since the data used for calculation of the center coordinate P is acquired in a state where the rotation operation is reliably performed only around one rotation detection axis, the center coordinate P can be calculated more accurately. .

  Further, according to the geomagnetism detecting device according to the present embodiment, the center coordinate P is calculated using the two rotation angles θ in which the angle difference α is larger than the predetermined threshold value TH1, and therefore the center coordinate P is more accurately determined. Can be calculated.

  As mentioned above, although embodiment of this invention was described, this invention is not limited only to embodiment mentioned above, Various modifications are included.

  In the embodiment described above, the case where the detection axes of the magnetic sensor unit 10 are three axes (X axis, Y axis, Z axis) is described as an example, but the present invention is not limited to this. In another embodiment of the present invention, the detection axis of the magnetic sensor unit may be two axes.

  In the above-described embodiment, the case where the detection axis of the magnetic sensor unit 10 and the detection axis of the angular velocity sensor unit 20 coincide is described as an example, but the present invention is not limited to this. At least one detection axis of the angular velocity sensor unit may be an axis orthogonal to the plane on which the two detection axes of the magnetic sensor unit are stretched. For example, the detection axes (X ′ axis, Y ′ axis, Z ′ axis) of the angular velocity sensor unit may be shifted in parallel to the detection axes (X axis, Y axis, Z axis) of the magnetic sensor unit.

  In the embodiment described above, the central coordinates are calculated in two ways: a condition in which the rotation operation is performed only around the Z axis, and a condition in which the rotation operation is performed only around the X axis. It is not limited to. For example, when the geomagnetism component in the Z-axis direction can be ignored, the calculation of the center coordinates may be omitted under the condition that the rotation operation (the vertical swing operation of the neck) is performed only around the X-axis.

  In the above-described embodiment, the example in which the geomagnetism detection device is mounted on the eyeglass-type electronic device is given, but the present invention is not limited to this. That is, the geomagnetism detection device of the present invention can be mounted on various electronic devices (cell phones, smartphones, tablets, notebook computers, portable game machines, game machine controllers, wearable devices).

DESCRIPTION OF SYMBOLS 1 ... Front part, 2 ... Temple part, 3 ... Hinge, 4 ... Rim, 5 ... Bridge, 6 ... Circuit board, 7 ... Eyeglass lens, 8 ... Display part, 9 ... Audio | voice output part, 10 ... Magnetic sensor part, 20 DESCRIPTION OF SYMBOLS ... Angular velocity sensor part, 30 ... Acceleration sensor part, 40 ... Control part, 41 ... Data buffer, 42 ... Rotation angle calculation part, 43 ... Correction calculation part, 44 ... Direction calculation part, 45 ... Display control part, 46 ... Voice control Part, M, A, B: magnetic coordinates, P: center coordinates, θ: rotation angle, θmin: minimum rotation angle, θmax: maximum rotation angle, V: angular velocity, G: acceleration.

Claims (3)

A magnetic sensor unit that detects, as magnetic coordinates, a combination of magnetic field strengths in a plurality of directions along a plurality of magnetic detection axes orthogonal to each other;
An angular velocity sensor that detects an angular velocity around one rotation detection axis perpendicular to a plane on which the two magnetic detection axes are stretched;
A rotation angle calculation unit that calculates a rotation angle around the one rotation detection axis based on an angular velocity around the one rotation detection axis detected by the angular velocity sensor unit;
Based on the two rotation angles around the one rotation detection axis calculated by the rotation angle calculation unit and the two magnetic coordinates detected by the magnetic sensor unit when having the two rotation angles. Calculating a center coordinate of a circle having the two magnetic coordinates on the circumference and having a center angle corresponding to an arc having both ends of the two magnetic coordinates equal to the difference between the two rotation angles; A correction calculation unit that corrects an offset of the geomagnetic vector represented by the magnetic coordinates based on the calculated center coordinates ,
The angular velocity sensor unit detects the other two angular velocities around two rotation detection axes parallel to the two magnetic detection axes;
The correction calculation unit detects the one rotation detected by the rotation angle calculation unit when the other two angular velocities detected by the angular velocity sensor unit both continue to be smaller than a predetermined threshold value. A geomagnetism detection device that calculates the center coordinate based on two rotation angles around an axis and two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided. . The magnetic sensor unit detects a combination of the magnetic field strengths in directions along the first magnetic detection axis, the second magnetic detection axis, and the third magnetic detection axis orthogonal to each other as the magnetic coordinates;
The angular velocity sensor unit includes an angular velocity around a first rotation detection axis that is the same as or parallel to the first magnetic detection axis, an angular velocity around a second rotation detection axis that is the same or parallel to the second magnetic detection axis, and Detecting angular velocities around a third rotation detection axis that is the same as or parallel to the third magnetic detection axis;
The rotation angle calculation unit calculates at least a rotation angle around the first rotation detection axis and a rotation angle around the second rotation detection axis;
The correction calculation unit is
When the angular velocity around the second rotation detection axis and the angular velocity around the third rotation detection axis are both less than the threshold value, the two rotation angles around the first rotation detection axis And calculating the center coordinates based on the two magnetic coordinates detected by the magnetic sensor unit when having the two rotation angles,
When the angular velocity around the first rotation detection axis and the angular velocity around the third rotation detection axis continue to be less than the threshold value, two rotation angles around the second rotation detection axis 2. The geomagnetic detection device according to claim 1 , wherein the center coordinates are calculated based on the two magnetic coordinates detected by the magnetic sensor unit when the two rotation angles are provided. The correction calculation unit selects two rotation angles having a difference larger than a predetermined angle from the series of rotation angles calculated by the rotation angle calculation unit, and the difference between the selected two rotation angles; geomagnetism detection device according to claim 1 or 2, wherein said calculating the said center coordinates based on two of said magnetic coordinates detected in the magnetic sensor section when having the two rotation angles.