JP2006317327A - Position angle detection device and head motion tracker using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position angle detection device for obtaining an accurate angle and position by removing the influence of noise even when receiving a signal superposing electromagnetic noise. <P>SOLUTION: The position angle detection device comprises a reference signal generation part for generating an alternating current reference signal, a magnetic source for generating an alternating current magnetic field in a space by exciting a coil on the basis of the alternating current reference signal, a magnetic sensor for detecting the alternating current magnetic field at an arbitrary spot in the space in which the alternating magnetic field generates, a noise component extraction part for extracting a noise component included in a detection signal output from the magnetic sensor, a correction detection signal preparation part for generating a correction detection signal removing the noise component from the detection signal, and a position angle calculation part for calculating a position and angle of the magnetic sensor on the basis of the correction detection signal. The device finds the position and angle of an object attaching the magnetic sensor from the position and angle of the calculated magnetic sensor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an AC magnetic field type position angle detection device that obtains a position and an angle based on a detection signal of a magnetic sensor by detecting an AC magnetic field with a magnetic sensor.
The position angle detection device of the present invention is used, for example, in a head motion tracker that monitors a head movement by mounting a magnetic sensor on a helmet to detect the position and angle of the head.

The head motion tracker is used as a device for measuring the position and angle of the head of a head-mounted display device user in a virtual reality (VR) of a game machine or an actual aircraft.
For example, in the VR technology, the VR space is experienced by visually recognizing an image that changes according to the movement of the head of the person wearing the head-mounted display device. In this case, the head motion tracker is used to measure the position and orientation (angle) of the wearer's head and change the display image of the head-mounted display device in accordance with the measurement result. Yes.

  In addition, in order to avoid losing sight of the rescue target that was discovered in the rescue operation by the rescue flying boat, the aiming image displayed by the head-mounted display device is locked when the rescue target corresponds, and thereafter Measures the position and angle of the head, calculates the positional relationship with the locked rescue target, and displays it so that the display device wearer does not lose sight of the rescue target. In this case, when calculating the positional relationship with the rescue target, in addition to the latitude, longitude, altitude, and attitude of the aircraft, the position and angle of the head of the person wearing the head-mounted display device are calculated. It is necessary to measure, and a head motion tracker is used.

  One of the head motion trackers is an AC magnetic type (see, for example, Patent Document 1). This is because a magnetic sensor is fixed to a head-mounted display device or the like, an alternating magnetic field is generated in advance in a space area where the head-mounted display device or the like is used, and magnetic data (magnetic field at the current position) is detected by the magnetic sensor. By measuring the strength and direction as needed, the position and angle of the magnetic sensor, and thus the position and angle of the head-mounted display device or the like to which the magnetic sensor is fixed are calculated based on the measurement result.

  FIG. 8 is a diagram schematically showing a configuration of a head motion tracker in which a magnetic sensor of an AC magnetic position angle detection device is mounted on a helmet. The position angle detection device 100 includes a magnetic source 101 that generates an alternating magnetic field by three-axis coils directed to the X axis, the Y axis, and the Z axis orthogonal to each other, and a head-mounted type that a head motion tracker user attaches to the head. A display device 103, a magnetic sensor 104 including a three-axis pickup coil fixed to the head-mounted display device 103, and a control unit 105 that controls the magnetic source 101 and the magnetic sensor 104 are provided. The control unit 105 will be further described in terms of the control operation for each function. When the control for exciting the three-axis coil mounted on the magnetic source 101 to generate an AC magnetic field is performed, the control signal becomes an excitation signal for the three-axis coil. A position for calculating the position and angle of the magnetic sensor 104 at the current position from the reference signal generator 106 that generates the AC reference signal and the detection signal (magnetic field strength, direction of the magnetic field) when the magnetic sensor 104 detects the AC magnetic field. An angle calculation unit 107. One method of calculating the position and angle by the position angle calculation unit 107 is to obtain the position and angle of the magnetic sensor 104 at a point by theoretical calculation based on electromagnetic theory (calculation based on Biosaval's law). In another calculation method, magnetic field distribution in a space where an alternating magnetic field is generated is measured in advance to store magnetic mapping data, and magnetic data at the local point of the magnetic sensor 104 and stored magnetic mapping data are stored. The position and angle of the local point are calculated by comparison with.

In the AC magnetic type head motion tracker, an origin and a coordinate system as a reference of a position are determined in advance, and a reference direction as a reference of a direction is determined in advance. Specifically, the XYZ coordinate system is defined with the position of the magnetic source as the origin, and the X-axis direction is defined as the reference direction.
Then, based on the detection signal from the magnetic sensor, by the calculation method described above, the positional coordinate information of X, Y, and Z, which is the amount of positional movement from the coordinate origin (center of the magnetic source 101) to the magnetic sensor 104, and the magnetic sensor Angle information of the azimuth direction (rotation with respect to the X axis), the elevation direction (rotation with respect to the Y axis), and the roll direction (rotation with respect to the Z axis), which are angular movement amounts with respect to the reference direction, are obtained from these position angle information The head-mounted display device to which the magnetic sensor is fixed, and the position and angle of the head are obtained.
JP 2002-81904 A

In an AC magnetic position angle detector, various signal lines may be provided around a magnetic source or a magnetic sensor. When current signals such as ON and OFF signals flow through these signal lines, a sudden change in current occurs, and electromagnetic noise is generated accordingly.
When electromagnetic noise is generated in a space where the magnetic source and the magnetic sensor exist, the influence also reaches an alternating magnetic field. For example, when a sine wave is generated as an AC reference signal and an AC magnetic field having a sine wave waveform is generated from a magnetic source, if electromagnetic noise is superimposed on the sine wave waveform, the magnetic sensor will generate a pulse-like noise on the sine wave waveform. A signal with a superimposed waveform (see FIG. 2) is received, and a position and an angle are calculated based on a detection signal including a noise component.

For this reason, the signal level of the detection signal when the position angle calculation unit calculates the current position and angle of the magnetic sensor from the detection signal changes by the amount of noise, and the accuracy of the calculated position and angle decreases. The output value may become unstable.
In such a case, it is possible to reduce the influence of noise by sampling the detection signal in time series and performing moving average processing, but in that case, the original signal itself is also averaged, The responsiveness becomes dull.

  Accordingly, an object of the present invention is to provide a position angle detection device capable of obtaining an accurate position and angle by removing the influence of noise even when a signal on which electromagnetic noise is superimposed is received. To do.

  The position angle detection device of the present invention made to solve the above problems includes a reference signal generation unit that generates an AC reference signal, and a magnet that generates an AC magnetic field in space by exciting a coil based on the AC reference signal. A source, a magnetic sensor for detecting an alternating magnetic field at an arbitrary point in a space where an alternating magnetic field is generated, a noise component extracting unit for extracting a noise component included in a detection signal output from the magnetic sensor, and a detection signal A correction detection signal generation unit that generates a correction detection signal from which noise components have been removed, and a position angle calculation unit that calculates the position and angle of the magnetic sensor based on the correction detection signal, and the calculated position and angle of the magnetic sensor From this, the position and angle of the object to which the magnetic sensor is attached are obtained.

According to this invention, the magnetic source generates an alternating magnetic field in the surrounding space based on the alternating current reference signal generated by the reference signal generator. The magnetic sensor is disposed at an arbitrary point in the space where the alternating magnetic field is generated, detects the alternating magnetic field at that point, and outputs a detection signal.
When some noise occurs and a noise component is included in the detection signal, the noise component extraction unit extracts the noise component included in the detection signal. Then, the correction detection signal creation unit performs an operation for removing a noise component from the detection signal, and generates a correction detection signal. The position angle calculation unit calculates the position and angle based on the correction detection signal from which the noise component has been removed.

  According to the present invention, even if electromagnetic noise is included in the signal detected by the magnetic sensor, the position and angle can be calculated with the corrected detection signal from which the noise component has been removed, so the accuracy and stability are excellent. Position and angle information can be obtained.

(Means and effects for solving other problems)
In the above invention, the noise component extraction unit may extract the noise component by comparing the waveform of the detection signal with the waveform of the reference signal.
The AC magnetic field generated from the magnetic source is generated by exciting the coil based on the AC reference signal, and thus has a waveform similar to the AC reference signal. The signal intensity of the detection signal detected by the magnetic sensor is also different, but the waveform itself has a waveform similar to an alternating magnetic field. Therefore, the waveform of the detection signal originally has a waveform similar to the AC reference signal, and if the waveform is different from the similar shape, it is determined that the noise component is superimposed on that portion. Can do.
Therefore, a noise component can be extracted by comparing the waveform of the detection signal of the magnetic sensor with the waveform of the AC reference signal.

In the above invention, the noise component extraction unit may extract the noise component based on the fluctuation characteristics of the peak value of the AC waveform included in the waveform of the detection signal.
The detection signal output from the magnetic sensor has an AC waveform similar to the AC reference signal. Although the AC reference signal is modulated or not, it has a sine wave or regular periodicity based on the sine wave. Therefore, the detection signal also has a sine wave or regular periodicity based on the sine wave. When electromagnetic noise is superimposed on the detection signal, the peak value of the noise location changes abruptly compared to the peak value of the peaks and valleys of the AC waveform based on the sine wave of the detection signal. The fluctuation characteristics of the value are monitored, and a noise component is extracted as noise is superimposed when it is determined as “abrupt change”. Various methods can be used to monitor whether the fluctuation characteristics are “rapid changes”, but one is to extract the peak values of individual peaks and valleys of the AC waveform included in the waveform of the detection signal. Compared with the peak value immediately before (or after) the peak value, if the peak fluctuation range exceeds a predetermined threshold fluctuation range (for example, ± 10% of the previous peak value), it is judged as noise and extracted. There is a way to do it. As another monitoring method, there is a method in which a differential value of a detection signal is calculated, and when a differential coefficient value exceeds a predetermined threshold, it is determined as a noise component and extracted.

In the above invention, the correction detection signal creation unit may create a correction detection signal from which a noise component has been removed by replacing a portion of the detection signal where noise is superimposed with interpolation data.
As a result, a signal estimated to be detected when the noise component is not superimposed can be obtained as a correction detection signal, so that the position and angle can be accurately calculated.

Further, a head motion tracker according to another aspect of the present invention, which is made from another viewpoint, is configured to detect the position and angle of the helmet by mounting the magnetic sensor of the above-described position angle detection device on the helmet.
According to the present invention, a head motion tracker capable of calculating an accurate position and angle even when electromagnetic noise occurs can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of a position angle detection device 10 according to an embodiment of the present invention. The position angle detection device 10 includes a magnetic source 11, a magnetic sensor 14 attached to a helmet 13, and a control unit 20 that is connected to and controls the magnetic source 11 and the magnetic sensor 14.
The magnetic source 11 has a triaxial coil 12 oriented in the directions of the X axis, the Y axis, and the Z axis orthogonal to each other, and 3 based on an AC reference signal generated by a reference signal generation unit 21 described later. By repeating the operation of exciting the shaft coil 12 for each of the X, Y, and Z axes, three types of alternating magnetic fields (AC magnetic fields) that are temporally resolved are repeatedly generated in the surrounding space.
The magnetic sensor 14 has the same triaxial coil 16 as that of the magnetic source 11, and an AC magnetic field generated by exciting one of the three axial coils 12 of the magnetic source 11 is converted into the three axes of the magnetic sensor 14. Similarly, the AC magnetic field generated when each of the coils 16 is detected and the remaining two axes of the three-axis coil 12 are excited is similarly detected. Is output as a detection signal of the magnetic sensor 14 for one measurement (at one point in time). Note that, as long as no noise is superimposed on these nine measurement data, the waveform shape is the same as that of the AC reference signal and has a similar shape with different signal strengths.

The control unit 20 is constructed by a so-called computer system including hardware devices such as a CPU, ROM, RAM, and HDD, and further, software necessary as a position angle detection device is stored in the storage area thereof. In addition, by loading these software, various functions necessary for position angle detection are realized.
In order to explain the function executed by the control unit 20 using the magnetic source 11 and the magnetic sensor 14, the control unit 20 is divided into functional blocks. The control unit 20 includes a reference signal generation unit 21, noise extraction, and the like. The unit 22 includes a correction detection signal generation unit 23 and a position angle calculation unit 24.

Among these, the reference signal generation unit 21 performs control to generate an AC reference signal having a sine wave waveform based on a built-in clock of the CPU.
The noise extraction unit 22 performs control to extract a noise component from the detection signal D. The noise extraction unit 22 of the present embodiment includes a signal comparison unit 25 that compares the detection signal D from the magnetic sensor 14 with the AC reference signal E, and compares two signal waveforms as shown in FIG. Thus, it is determined whether or not the waveforms of the detection signal D and the AC reference signal E have a similar shape. Specifically, the difference is calculated by expanding and reducing the signal level so that the signal strength of one is the same as the signal strength of the other. If there is a significant difference, noise is generated in the portion where the difference has occurred. Is determined to be superimposed. If there is no difference, it is determined that there is no noise component.

  The correction detection signal generation unit 23 performs control to generate a correction detection signal obtained by removing a noise component from the detection signal. FIG. 3 is an enlarged view of a portion in which a noise component is superimposed in the detection signal. The detection signal is AD-converted and digitized for processing in the control unit 20, and is a set of discrete measurement points. Among each measurement point, the measurement point (may be a plurality of points) extracted as a noise superimposed portion by the noise extraction unit 22 is deleted. Then, interpolation data is calculated by interpolating using data of measurement points on both sides adjacent to the deleted point, and a correction detection signal using the interpolation data is generated instead of the deleted measurement point. As described above, the three-axis coil 12 and the three-axis coil 16 output a total of nine sets of measurement data as detection signals of the magnetic sensor 14 for one measurement (at one point in time for one point). However, for each of these nine pieces of measurement data, a noise component is removed and a set of interpolated data becomes a correction detection signal.

  The position angle calculation unit 24 performs control to calculate the position and angle of the magnetic sensor 14 at the point where the magnetic sensor 14 exists based on the correction detection signal calculated by the correction detection signal generation unit 23. The position and angle are calculated by associating an actual measurement value based on the corrected detection signal with a theoretical value obtained by theoretical calculation based on electromagnetic theory (calculation based on Biosaval's law). Alternatively, as another calculation method, measured data for each place in the space is stored in advance as a database, and the position and angle are calculated by associating this with the current correction detection signal data.

Next, the processing procedure of the position angle measurement by the position angle detection device 10 will be described using the flowchart of FIG.
The position angle detector 10 is activated to excite the three-axis coil 12 of the magnetic source 11 based on the AC reference signal E to generate an AC magnetic field. The magnetic field data at the location where the magnetic sensor 14 currently exists is detected, and the detection signal D is stored (S101).
The stored detection signal D is compared with the AC reference signal E to determine whether the two waveforms are similar (S102). When it is determined that they are similar, the process proceeds to S104, and when it is determined that they are not similar, the process proceeds to S103.
If it is determined that they are not similar, noise is superimposed, so that a corrected detection signal is created for the portion where the noise is superimposed and the noise is deleted and interpolated, and the process proceeds to S104 (s103). ).

Subsequently, an operation for calculating the position and angle of the magnetic sensor 14 is performed based on the detection signal or the correction detection signal (S104).
By executing the above arithmetic processing, the position and angle can be obtained based on the measurement data from which noise is deleted.

(Embodiment 2)
FIG. 5 is a block diagram showing a configuration of a position angle detection device 30 according to another embodiment of the present invention. In FIG. 5, the same structural parts as those shown in FIG.
In this position angle detection device 30, the noise extraction unit 22 includes a threshold comparison unit 26 instead of the signal comparison unit 25 as shown in FIG. 1. The threshold comparison unit 26 determines whether or not it is a noise component based on whether or not the fluctuation of the peak value of the AC waveform included in the detection signal exceeds the threshold.
That is, in the case of a non-modulated sine wave as shown in FIG. 6A and the case of a modulated sine wave (modulation by a window function) as shown in FIG. The allowable fluctuation range of the peak value of the waveform is set to ± 10% of the previous peak value (when the threshold is set to ± 10% of the previous peak value). It is determined that
The processing by the correction detection signal generation unit 23 and the position angle extraction unit 24 after the noise component is extracted is the same as in the first embodiment.

Next, the position angle measurement processing procedure by the position angle detection device 30 will be described with reference to the flowchart of FIG.
The position angle detection device 30 is activated to excite the three-axis coil 12 of the magnetic source 11 based on the AC reference signal E to generate an AC magnetic field. The magnetic field data at the location where the magnetic sensor 14 is present and the time point are detected, and the detection signal D is stored (S201).
The AC peak values included in the stored detection signal D are sequentially extracted, and it is determined whether or not the fluctuation of the peak value exceeds ± 10% of the previous peak value (S202). When it is determined that it does not exceed, the process proceeds to S204, and when it is determined that it exceeds, the process proceeds to S203.
When it is determined that the noise is exceeded, the noise is superimposed, so that the noise is deleted by executing the same processing as the processing described in FIG. 3 for the portion where the noise is superimposed. A correction detection signal interpolated together is created, and the process proceeds to S204 (s203).

Subsequently, a calculation for calculating the position and angle of the magnetic sensor 14 is performed based on either the detection signal or the correction detection signal (S204).
By executing the above arithmetic processing, the position and angle can be obtained based on the measurement data from which noise is deleted.
In the present embodiment, the threshold for peak fluctuation is determined by comparison with the previous peak, but the present invention is not limited to this. For example, since the differential coefficient of the detection signal reflects the peak position in the detection signal, the peak fluctuation characteristic can be monitored by monitoring the differential coefficient of the detection signal.

  In the first and second embodiments, the magnetic sensor 11 of the position angle measuring device is mounted on a helmet (head motion tracker), but the mounting location is not limited to the helmet. By attaching to a measuring object that moves, the movement of the measuring object can be monitored.

  INDUSTRIAL APPLICABILITY The present invention can be used for an AC magnetic type position angle detection device. For example, it can be used as a head motion tracker by being mounted on a helmet.

The block diagram which shows the structure of the position angle detection apparatus which is one Embodiment of this invention. The figure explaining a detection signal and an alternating current reference signal. The figure explaining deletion of a noise component, and substitution to interpolation data. The flowchart in one Embodiment of this invention. The block diagram which shows the structure of the position angle detection apparatus which is other one Embodiment of this invention. The figure explaining a detection signal. The flowchart in other one Embodiment of this invention. The block diagram which shows the structure of the conventional position angle detection apparatus.

Explanation of symbols

10: Position angle detector 11: Magnetic source 12: Triaxial coil (transmission side)
13: Helmet 14: Magnetic sensor 16: 3-axis coil (receiving side)
20: Control unit 21: Reference signal generation unit 22: Noise extraction unit 23: Correction detection signal generation unit 24: Position angle calculation unit 25: Signal comparison unit 26: Threshold comparison unit

Claims (5)

A reference signal generator for generating an AC reference signal;
A magnetic source that generates an alternating magnetic field in space by exciting a coil based on an alternating current reference signal;
A magnetic sensor for detecting an alternating magnetic field at any point in the space where the alternating magnetic field is generated;
A noise component extraction unit that extracts a noise component included in the detection signal output from the magnetic sensor;
A correction detection signal creating unit for generating a correction detection signal obtained by removing a noise component from the detection signal;
A position angle calculator that calculates the position and angle of the magnetic sensor based on the correction detection signal,
A position and angle detection device that obtains the position and angle of an object to which a magnetic sensor is attached from the calculated position and angle of the magnetic sensor. The position angle detection device according to claim 1, wherein the noise component extraction unit extracts a noise component by comparing a waveform of the detection signal with a waveform of the AC reference signal. The position angle detection device according to claim 1, wherein the noise component extraction unit extracts a noise component based on a fluctuation characteristic of a peak value of an AC waveform included in the waveform of the detection signal. 2. The position angle detection apparatus according to claim 1, wherein the correction detection signal creation unit creates a correction detection signal from which a noise component has been removed by replacing a portion of the detection signal where noise is superimposed with interpolation data. A head motion tracker, wherein the magnetic sensor of the position angle detection device according to claim 1 is mounted on a helmet to detect the position and angle of the helmet.

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