Seismic sensor, earthquake detection method, and earthquake detection program

Abstract

A seismic sensor (10) comprises an acceleration acquisition unit (21), an interior angle calculation unit (23), an interior angle frequency distribution generation unit (24), and an earthquake determination unit (25). The acceleration acquisition unit (21) detects vibration and acquires acceleration of the vibration. For the acceleration acquired by the acceleration acquisition unit (21), the interior angle calculation unit (23) calculates an interior angle between two acceleration vectors that are continuous on a prescribed coordinate plane. The interior angle frequency distribution generation unit (24) generates a frequency distribution of the interior angle calculated by the interior angle calculation unit (23). On the basis of the frequency distribution generated by the interior angle frequency distribution generation unit (24), the earthquake determination unit (25) determines whether the vibration is from an earthquake.

Description

Earthquake sensor, earthquake detection method, and earthquake detection program

[0001] The present invention relates to a seismic sensor for detecting seismic motion, an earthquake detection method, and an earthquake detection program.

[0002] In recent years, seismic sensors have been used that are built into gas meters, electricity meters, distribution boards, outlets, etc., and that output a shutoff signal to shut off the supply of gas, electricity, etc. when they detect earthquake motion of a magnitude equal to or greater than a predetermined value (for example, seismic intensity 5+ or greater). For example, Patent Document 1 discloses a seismic sensor that outputs a shutoff signal when an index value indicating the magnitude of an earthquake is equal to or greater than a threshold value during an earthquake processing period following a determination period in an earthquake processing period, the seismic sensor including a continuing earthquake determination unit that determines the occurrence of an earthquake based on acceleration measured during the earthquake processing period, and a shutoff determination unit that prevents the output of a shutoff signal regardless of the index value when the continuing earthquake determination unit determines that an earthquake has not occurred.

[0003] Patent No. 6465257

[0004] However, the above-mentioned conventional seismic sensors have the following problems. Specifically, the seismic sensors disclosed in the above publications calculate the frequencies of the accelerations measured by the acceleration sensors along each axis (e.g., X and Y axes) of the acceleration sensors when analyzing the frequencies. This makes it difficult to analyze vibrations taking into account the vibration characteristics along both axes (e.g., X and Y axes), making it difficult to accurately determine whether an earthquake has occurred.

[0005] An object of the present invention is to provide a seismic sensor, an earthquake detection method, and an earthquake detection program that can accurately determine whether a detected vibration is an earthquake or noise.

[0006] (Means for solving the problem) A seismic sensor according to a first aspect of the present invention includes an acceleration acquisition unit, an interior angle calculation unit, an interior angle frequency distribution generation unit, and an earthquake determination unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The interior angle calculation unit calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit. The interior angle frequency distribution generation unit generates a frequency distribution of the interior angles calculated by the interior angle calculation unit. The earthquake determination unit determines whether the vibrations are an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit.

[0007] Here, for example, the interior angle between two consecutive acceleration vectors on a coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two consecutive acceleration vectors means the angle formed by the two acceleration vectors when the starting points of the two consecutive acceleration vectors are aligned with the origin over the elapsed time.

[0008] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of an acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration.Usually, when vibrations are caused by earthquakes, they are characterized by being low-frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0009] For this reason, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. As a result, if the interior angle between two consecutive acceleration vectors contains many acute-angle components and few obtuse-angle components, it can be determined that the characteristics of an earthquake match, and that the vibration is highly likely to be an earthquake. As a result, it can accurately determine whether the detected vibration is an earthquake or noise.

[0010] A seismic sensor according to a second aspect of the present invention is the seismic sensor according to the first aspect of the present invention, wherein the earthquake determination unit determines that vibration is an earthquake when the proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold. As a result, when the proportion of obtuse angle components, which are characteristic of noise such as daily vibrations, is smaller than a predetermined threshold in the frequency distribution of the interior angles of two consecutive acceleration vectors, the vibration can be determined to be an earthquake.

[0011] A seismic sensor according to a third aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, wherein the earthquake determination unit determines that vibration is not an earthquake if the proportion of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold. As a result, if the frequency distribution of the interior angles of two consecutive acceleration vectors contains more obtuse angle components, which are characteristic of noise such as daily vibrations, than a predetermined threshold, the vibration can be determined to be not an earthquake.

[0012] A seismic sensor according to a fourth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, wherein the earthquake determination unit determines whether or not a vibration is an earthquake using any of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit. This makes it possible to perform highly accurate earthquake determination by analyzing the characteristics of the detected vibration using any of the mean, median, and mode of the interior angle frequency distribution.

[0013] A seismic sensor according to a fifth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, wherein the earthquake determination unit determines whether or not a vibration is an earthquake using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit. This makes it possible to perform highly accurate earthquake determination by analyzing the characteristics of the detected vibration using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the interior angle frequency distribution.

[0014] A seismic sensor according to a sixth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, wherein the earthquake determination unit determines whether vibration is an earthquake or noise using the result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to angle. By weighting the frequency distribution according to angle so as to emphasize characteristic points of earthquakes or noise, it is possible to more accurately determine whether the detected vibration is an earthquake or noise.

[0015] A seventh aspect of the present invention is a seismic sensor according to the first or second aspect of the present invention, wherein the acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from the acceleration measured by the triaxial acceleration sensor, thereby extracting and acquiring acceleration components other than those in the gravity direction, thereby obtaining an acceleration vector on a predetermined coordinate plane.

[0016] The seismic sensor according to an eighth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, and further includes an earthquake scale calculation unit that, when the earthquake determination unit determines that an earthquake has occurred, determines whether the earthquake is equivalent to or greater than a predetermined seismic intensity. For example, when the earthquake scale is determined to be an upper 5 or greater, it is possible to determine that there is a risk of a fire, gas leak, or the like, and output a shutoff signal to stop the supply of energy such as electricity or gas, thereby improving the safety of the user.

[0017] The seismic sensor according to a ninth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, further comprising an activation determination unit that calculates vibration intensity from the results acquired by the acceleration acquisition unit, and, if the vibration intensity is equal to or greater than a predetermined magnitude, transitions from the power-saving mode to a measurement mode that consumes more power than the power-saving mode.As a result, by transitioning to the measurement mode, which performs earthquake determination processing using the vibration acceleration waveform, only when the detected vibration intensity is equal to or greater than a predetermined magnitude (e.g., equivalent to a seismic intensity of 4), it is possible to perform highly accurate earthquake determination while suppressing power consumption.

[0018] The seismic sensor according to a tenth aspect of the present invention is the seismic sensor according to the first or second aspect of the present invention, further comprising an output control unit that outputs a predetermined signal when the earthquake determination unit determines that an earthquake has occurred. As a result, for example, when an earthquake occurs, the output unit can output a cutoff signal to stop the supply of energy such as electricity or gas, or a warning signal to notify of danger.

[0019] An earthquake detection method according to an eleventh aspect of the present invention includes an acceleration acquisition step, an interior angle calculation step, an interior angle frequency distribution generation step, and an earthquake determination step. In the acceleration acquisition step, vibrations are detected and the acceleration of the vibrations is acquired. In the interior angle calculation step, the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane is calculated for the accelerations acquired in the acceleration acquisition step. In the interior angle frequency distribution generation step, a frequency distribution of the interior angles calculated in the interior angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step.

[0020] Here, for example, the interior angle between two consecutive acceleration vectors on a coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two consecutive acceleration vectors means the angle formed by the two acceleration vectors when the starting points of the two consecutive acceleration vectors are aligned with the origin over the elapsed time.

[0021] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of an acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration.Usually, when vibrations are caused by earthquakes, they are characterized by being low-frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0022] For this reason, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. As a result, if the interior angle between two consecutive acceleration vectors contains many acute-angle components and few obtuse-angle components, it can be determined that the characteristics of an earthquake match, and that the vibration is highly likely to be an earthquake. As a result, it can accurately determine whether the detected vibration is an earthquake or noise.

[0023] An earthquake detection program according to a twelfth aspect of the present invention causes a computer to execute an earthquake detection method including an acceleration acquisition step, an interior angle calculation step, an interior angle frequency distribution generation step, and an earthquake determination step. In the acceleration acquisition step, vibrations are detected and the acceleration of the vibrations is acquired. In the interior angle calculation step, the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane is calculated for the accelerations acquired in the acceleration acquisition step. In the interior angle frequency distribution generation step, a frequency distribution of the interior angles calculated in the interior angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step.

[0024] Here, for example, the interior angle between two consecutive acceleration vectors on a coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two consecutive acceleration vectors means the angle formed by the two acceleration vectors when the starting points of the two consecutive acceleration vectors are aligned with the origin over the elapsed time.

[0025] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of an acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration.Usually, when vibrations are caused by earthquakes, they are characterized by being low-frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0026] For this reason, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. As a result, if the interior angle between two consecutive acceleration vectors contains many acute-angle components and few obtuse-angle components, it can be determined that the characteristics of an earthquake match, and that the vibration is highly likely to be an earthquake. As a result, it can accurately determine whether the detected vibration is an earthquake or noise.

[0027] A seismic sensor according to a thirteenth aspect of the present invention includes an acceleration acquisition unit, an interior angle calculation unit, and an interior angle frequency distribution generation unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The interior angle calculation unit calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit. The interior angle frequency distribution generation unit generates a frequency distribution of the interior angles calculated by the interior angle calculation unit.

[0028] Here, for example, the vibration is analyzed by calculating the interior angle between two consecutive acceleration vectors on a coordinate plane of an acceleration sensor that acquires the vibration acceleration. Here, the interior angle between two consecutive acceleration vectors means the angle between the two consecutive acceleration vectors when their starting points are aligned with the origin over time.

[0029] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of an acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration.Usually, when vibrations are caused by earthquakes, they are characterized by being low-frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0030] For this reason, this seismic sensor analyzes vibrations based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. As a result, if the interior angle between two consecutive acceleration vectors contains many acute-angle components and few obtuse-angle components, it can be analyzed as matching the characteristics of an earthquake and determine that the vibration is highly likely to be an earthquake.

[0031] As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0032] (Effects of the Invention) The seismic sensor according to the present invention can accurately determine whether detected vibrations are earthquakes or noise.

[0033] 1 is a control block diagram showing the configuration of a seismic sensor according to one embodiment of the present invention. FIG. 2 is a functional block diagram generated within the seismic sensor of FIG. 1. FIG. 3 is a graph showing the acceleration on a horizontal plane (XY plane) of seismic vibrations detected by the seismic sensor of FIG. 1. (a) is a diagram showing an example of two consecutive acceleration vectors in the seismic vibration of FIG. 3. (b) is a diagram showing the interior angle of the two acceleration vectors in (a) with the origin aligned at the origin. (c) is a graph showing the frequency distribution of the interior angle in (b). FIG. 1 is a graph showing the acceleration on a horizontal plane (XY plane) of noise vibrations detected by the seismic sensor of FIG. 1. (a) is a diagram showing an example of two consecutive acceleration vectors in the daily vibrations (noise) of FIG. 5. (b) is a diagram showing the interior angle of the two acceleration vectors in (a) with the origin aligned at the origin. (c) is a graph showing the frequency distribution of the interior angle in (b). (a) is a graph showing the acceleration on a horizontal plane (XY plane) of seismic vibrations detected by the seismic sensor. 2. (b) is a graph showing the frequency distribution of the interior angles of the acceleration of (a). (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (high frequency) vibrations detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angles of the acceleration of (a). (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (same frequency) vibrations detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angles of the acceleration of (a). (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (linear motion) vibrations detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angles of the acceleration of (a). A flowchart showing the processing flow of an earthquake detection method executed by the seismic sensor of FIG. 2. As an example of earthquake determination using the mode, mean, or median of the interior angle frequency distribution generated by a seismic sensor according to another embodiment of the present invention, (a) is a graph showing the interior angle frequency distribution when the detected vibration is an earthquake. Graphs (b) and (c) show the frequency distribution of noise interior angles. As an example of an interior angle frequency distribution generated by a seismic sensor according to yet another embodiment of the present invention, (a) is a graph showing a case where the detected vibration is an earthquake. (b) is a graph showing weights for positively and negatively weighting earthquake features and noise features, respectively, for the interior angle frequency distribution in (a).10A is a graph showing an example of an interior angle frequency distribution generated by a seismic sensor according to yet another embodiment of the present invention, in which (a) is a graph showing a case where the detected vibration is noise, and (b) is a graph showing weights for positively and negatively weighting earthquake features and noise features, respectively, for the interior angle frequency distribution in (a).

[0034] A seismic sensor according to one embodiment of the present invention will be described below with reference to FIGS. 1 to 11. In this embodiment, more detailed explanation than necessary may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art. Furthermore, the applicant provides the accompanying drawings and the following explanation to enable those skilled in the art to fully understand the present invention, and does not intend for them to limit the subject matter recited in the claims.

[0035] (1) Configuration of the Seismic Sensor 10 As shown in FIG. 1, the seismic sensor 10 according to this embodiment includes an acceleration sensor 11, a controller 12, and a memory 13.

[0036] The acceleration sensor 11 is, for example, an acceleration sensor using a piezoelectric element or an acceleration sensor that detects electrostatic capacitance between electrodes. The acceleration measured (also called "sampled") by the acceleration sensor 11 is output to the controller 12. The acceleration sensor 11 also has virtual three-dimensional axes (X-axis, Y-axis, and Z-axis), and detects acceleration along each of the axes and outputs the detected acceleration to the controller 12.

[0037] The controller 12 is, for example, a general-purpose integrated circuit that acquires the acceleration measured by the acceleration sensor 11 at a predetermined period, detects the occurrence of an earthquake based on the acquired acceleration, and calculates an index value indicating the magnitude of the earthquake. The controller 12 also operates in two different modes, active mode and sleep mode, depending on the situation.

[0038] The sleep mode is a mode in which the controller 12 operates with limited functionality, such as halting command execution while accepting interrupts and halting clock supply. This sleep mode can reduce power consumption more than the active mode. The active mode is a mode in which the controller performs processing to determine whether detected vibrations are earthquakes or noise, and calculates an index value indicating the magnitude of an earthquake.

[0039] The functional blocks (see FIG. 2) generated when the CPU in the seismic sensor 10 reads the earthquake detection program stored in the memory 13 will be described in detail later. The memory 13 is a temporary storage means such as a RAM (Random Access Memory) or a non-volatile memory such as an EPROM (Erasable Programmable Read Only Memory), and stores, for example, the acceleration measured by the acceleration sensor 11 and threshold values ​​used for earthquake detection.

[0040] The memory 13 may be a memory built into the acceleration sensor 11 or the controller 12. The output unit 14 is, for example, an output terminal included in the controller 12, and when the controller 12 determines that an earthquake has occurred, information indicating the occurrence and magnitude of the earthquake is output to another device via the output unit 14. When an earthquake of a predetermined magnitude or greater is detected, the output unit 14 outputs, for example, a cutoff signal to an external device to stop the supply of energy such as electricity or gas.

[0041] (2) Functional blocks of the seismic sensor 10 As shown in Fig. 2, the seismic sensor 10 includes an acceleration acquisition unit 21, a vibration intensity classification and activation determination unit 22, an interior angle calculation unit 23, an interior angle frequency distribution generation unit 24, an earthquake determination unit 25, an earthquake magnitude calculation unit 26, an output control unit 27, an offset adjustment unit 28, and a memory unit 29. These functional blocks shown in Fig. 2 are configured by the controller 12 receiving acceleration data acquired from the acceleration sensor 11 and reading a program stored in the memory 13.

[0042] The acceleration acquisition unit 21 acquires measurement data of acceleration in the X-axis, Y-axis, and Z-axis measured by the acceleration sensor 11 at a predetermined cycle. The acceleration acquisition unit 21 typically acquires measurement data of acceleration repeatedly measured at a relatively low speed (i.e., at a relatively long measurement cycle). When performing acceleration sampling at such a low speed, the controller 12 basically operates in a sleep mode (standby state or power-saving mode) with low power consumption. In the standby state, the acceleration sensor 11 is in an operating state where it samples at a low speed, and therefore the controller 12 operates in a sleep mode with limited functionality, thereby reducing power consumption.

[0043] Furthermore, when the acceleration acquisition unit 21 acquires vibrations greater than a threshold value preset in the memory unit 29, the acceleration sensor 11 repeatedly measures acceleration at a higher speed (i.e., at a relatively short cycle) than during low-speed sampling. During such high-speed sampling, the controller 12 operates in sleep mode or active mode. Note that when the earthquake determination unit 25 (described later) and other units execute processing, the controller 12 operates in active mode (measurement mode). The transition from power-saving mode to measurement mode is called activating the seismic sensor 10.

[0044] The measurement mode is an operating state in which high-speed sampling is performed, and the controller 12 may operate in a sleep mode with limited functionality, or in an active mode with maximum computing power. In the measurement mode, the sampling period is shortened and the controller 12 switches from the sleep mode to the active mode, resulting in greater power consumption than in the power-saving mode.

[0045] Furthermore, the acceleration acquisition unit 21 acquires acceleration on a coordinate plane (e.g., the XY plane) by extracting acceleration in a non-gravity direction from the acceleration measured by the three-axis acceleration sensor 11. The vibration intensity discrimination and activation determination unit 22 is a function of the acceleration sensor 11, which compares the acceleration value acquired by the acceleration acquisition unit 21 with an activation threshold value stored in the memory unit 29, and if the acceleration value exceeds the activation threshold value, transitions from the power saving mode to the measurement mode (activates the seismic sensor 10).

[0046] Furthermore, the vibration intensity discrimination / activation determination unit 22 calculates the vibration intensity from the measurement results of the acceleration acquisition unit 21, and if the vibration intensity is equal to or greater than a predetermined magnitude, transitions from the power saving mode to a measurement mode that consumes more power than the power saving mode (activates the controller 12). Here, the vibration intensity discrimination process performed by the vibration intensity discrimination / activation determination unit 22 is implemented by filtering the acceleration values ​​acquired by the acceleration acquisition unit 21. At this time, the filtered acceleration is stored in the memory unit 29.

[0047] The interior angle calculation unit 23 calculates the interior angle between two consecutive acceleration vectors on a predetermined coordinate plane (e.g., an XY plane) for the acceleration acquired by the acceleration acquisition unit 21. Here, the predetermined coordinate plane refers to, for example, a substantially horizontal XY plane formed by the X-axis and Y-axis among the X-axis, Y-axis, and Z-axis of the acceleration sensor 11. The interior angle between two consecutive accelerations refers to the interior angle between two acceleration vectors connecting three consecutive acceleration points on the coordinate plane acquired over time. The interior angle between two acceleration vectors refers to the angle formed by the two vectors when the starting points of the two consecutive acceleration vectors are aligned with the origin.

[0048] Specifically, when the vibration detected by acceleration sensor 11 is an earthquake, the vibration caused by the earthquake is characterized by, for example, vibration that generates acceleration in all directions in the XY plane of the X, Y, and Z axes of acceleration sensor 11 or in the horizontal plane, as shown in Fig. 3. Here, as shown in Fig. 4(a), the interior angle calculation unit 23 extracts two acceleration vectors A and B connecting three consecutive points from the accelerations in the XY plane in Fig. 3, and calculates the interior angle as the angle formed by the two acceleration vectors with the starting points of the two acceleration vectors aligned with the origin, as shown in Fig. 4(b).

[0049] The interior angle frequency distribution generator 24 generates a frequency distribution of the interior angle formed by two consecutive acceleration vectors, as shown in Figure 4(b). If the detected vibration is an earthquake, as shown in Figure 3, the vibration is low-frequency, contains various frequency components, and vibrates in various directions on the horizontal plane, resulting in a circular motion on the horizontal plane. Therefore, the interior angle between the two consecutive acceleration vectors is often an acute angle and rarely an obtuse angle. Therefore, the interior angle frequency distribution generated by the interior angle frequency distribution generator 24 peaks at around 20 degrees (part A) and decreases in frequency as the angle increases (part B), as shown in Figure 4(c).

[0050] In the graph of Fig. 4(c), when the interior angle between two consecutive acceleration vectors is 0° (part C), this means that the detected vibration is linear motion and that vibration that is not characteristic of an earthquake is occurring. On the other hand, when the vibration detected by acceleration sensor 11 is not an earthquake, it is characteristic of vibration caused by noise such as everyday vibration, and will be vibration that generates acceleration in a substantially fixed direction in the XY plane of the X, Y, and Z axes of acceleration sensor 11 or in the horizontal plane, as shown in Fig. 5.

[0051] As shown in Fig. 6(a), the interior angle calculation unit 23 extracts two acceleration vectors A and B connecting three consecutive points from the accelerations on the XY plane in Fig. 5, and calculates the angle formed by the two acceleration vectors with the starting points of the two acceleration vectors aligned with the origin as the interior angle, as shown in Fig. 6(b). The interior angle frequency distribution generation unit 24 generates a frequency distribution of the interior angle formed by two consecutive acceleration vectors shown in Fig. 6(b).

[0052] In this case, if the detected vibration is noise such as a non-earthquake vibration as shown in Figure 5, it has the characteristic of moving along a substantially constant straight line, so the interior angle between two consecutive acceleration vectors is often near 0° or an obtuse angle, and rarely an acute angle. Therefore, the interior angle frequency distribution generated by the interior angle frequency distribution generator 24 is a graph as shown in Figure 6(c), with many angles near 0° (part A), few acute angles (part B), and the frequency increasing as the angle becomes larger (part C).

[0053] Here, different acceleration distributions and interior angle frequency distributions are generated on a predetermined coordinate plane depending on whether the detected vibration is an earthquake or not (multiple types of noise). That is, when the detected vibration is an earthquake, it contains components of various frequency bands in all directions on the XY plane, as shown in Fig. 7(a). Therefore, the frequency distribution generated by the interior angle frequency distribution generator 24, as shown in Fig. 7(b), has a high frequency of acute angles and a low frequency of obtuse angles, similar to Fig. 4(c).

[0054] On the other hand, if the detected vibration is not an earthquake but high-frequency vibration noise, two consecutive acceleration components on the XY plane will be linear and contain high-frequency components, as shown in Fig. 8(a). Therefore, the frequency distribution generated by the interior angle frequency distribution generator 24 will have a high frequency of obtuse angles near 0° and a low frequency of acute angles, as shown in Fig. 8(b).

[0055] Furthermore, if the detected vibration is not an earthquake but vibration noise with approximately the same frequency, it will contain approximately circular acceleration components on the XY plane, as shown in Fig. 9(a). Therefore, the frequency distribution generated by the interior angle frequency distribution generator 24 will have a particularly high frequency of certain angles, as shown in Fig. 9(b). Furthermore, if the detected vibration is not an earthquake but linear motion noise, two consecutive acceleration components on the XY plane will be linear components, as shown in Fig. 10(a).

[0056] For this reason, the frequency distribution generated by the interior angle frequency distribution generator 24 has a high frequency of angles near 0° and obtuse angles, and a low frequency of acute angles, as shown in Figure 10(b). Here, a characteristic feature that appears as a characteristic of earthquakes is, for example, that the interior angle formed by two consecutive acceleration vectors is often an acute angle. Specifically, because earthquake vibrations are always vibrating in various directions, the frequency distribution of the interior angle formed by two consecutive acceleration vectors is high for acute angles and low for obtuse angles.

[0057] Therefore, in the seismic sensor 10 of this embodiment, since a characteristic of earthquakes is that the interior angle between two consecutive acceleration vectors is often an acute angle, if the frequency distribution of the interior angles is detected to be high at acute angles, the vibration is determined to be an earthquake; otherwise, the vibration is determined to be noise. The earthquake determination unit 25 determines whether the vibration is an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. That is, if the proportion of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold, as shown in FIG. 7(b), the earthquake determination unit 25 determines that the vibration is not an earthquake. Furthermore, if the proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold, as shown in FIG. 7(b), the earthquake determination unit 25 determines that the vibration is an earthquake.

[0058] The earthquake determination unit 25 may also determine whether or not the vibration is an earthquake using any one of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit 24. Furthermore, the earthquake determination unit 25 may also determine whether or not the vibration is an earthquake using any one of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit 24.

[0059] As a result, in order to avoid erroneously determining that noise with a frequency distribution having a peak at an acute angle, similar to the characteristics of earthquakes, as an earthquake as shown in Fig. 9(b), for example, when kurtosis is greater than a predetermined threshold, noise of approximately the same frequency as shown in Fig. 9(a), in which a specific angle becomes prominently high, can be determined as vibration that is not an earthquake. When the earthquake determination unit 25 determines that there is an earthquake, the earthquake magnitude calculation unit 26 determines whether the earthquake is equivalent to or greater than a predetermined seismic intensity.

[0060] Furthermore, after the earthquake magnitude calculation unit 26 determines that the detected vibrations are an earthquake and starts calculating an index indicating the magnitude of the earthquake, if an acceleration waveform that can be considered to be an impact is detected, the earthquake magnitude calculation unit 26 calculates the magnitude of the earthquake by excluding the acceleration waveform. The output control unit 27 controls the output of a signal from the output unit 14, which outputs a predetermined signal, depending on whether the magnitude of the earthquake calculated by the earthquake magnitude calculation unit 26 is equivalent to or greater than a predetermined seismic intensity.

[0061] Here, the predetermined signal output from output unit 14 includes, for example, a shutoff signal transmitted to an external device such as an electricity supply device or a gas supply device in order to stop the supply of energy such as electricity or gas. When earthquake determination unit 25 determines that the vibration detected by acceleration acquisition unit 21 is noise, offset adjustment unit 28 adjusts the offset amount of the acceleration waveform in accordance with the magnitude of the noise. Then, offset adjustment unit 28 adjusts the offset amount of the acceleration waveform in accordance with the determination result of earthquake determination unit 25.

[0062] The offset adjustment performed by the offset adjuster 28 detects noise components contained in the measured acceleration as offset components, such as changes in the measurement value caused by changes in the seismic sensor 10 over time, changes in the measurement value caused by temperature changes, and changes in the measurement value caused by a change in the direction of gravitational acceleration relative to the seismic sensor 10 when the installed seismic sensor 10 is tilted for some reason. Specifically, the offset adjuster 28 calculates, as offset components, the median of the maximum and minimum values ​​of the acceleration determined to be noise, or the average value of the acceleration. The memory unit 29 stores, for example, acceleration data acquired by the acceleration acquisition unit 21 or acceleration data after filtering, interior angle data calculated by the interior angle calculation unit 23, frequency distribution data generated by the interior angle frequency distribution generator 24, determination results from the earthquake determination unit 25, and offset component data used by the offset adjuster 28.

[0063] <Earthquake Detection Method> The earthquake detection method using the seismic sensor 10 of this embodiment will be described below with reference to the flowchart shown in FIG.

[0064] That is, in step S11, the acceleration acquisition unit 21 of the seismic sensor 10 acquires the acceleration measured by the acceleration sensor 11. Next, in step S12, the interior angle calculation unit 23 calculates two consecutive acceleration vectors from the accelerations of the three consecutive points acquired in step S11. Next, in step S13, the interior angle calculation unit 23 calculates the interior angle of the two consecutive acceleration vectors calculated in step S12 using an inner product or a cross product.

[0065] Next, in step S14, the interior angle frequency distribution generating unit 24 counts up the frequency (number of times) of the interior angles calculated in step S13. Next, in step S15, it is determined whether or not to end the vibration determination process. If it is to be ended, the process proceeds to step S16, and if it is not to be ended, the process returns to step S11 and the subsequent processes are repeated.

[0066] Next, in step S16, the interior angle frequency distribution generator 24 calculates the total number of frequencies of the interior angles counted up in step S14. Next, in step S17, the interior angle frequency distribution generator 24 calculates the total number of frequencies of interior angles that are 90° or greater (obtuse angles) out of the total number of frequencies of interior angles calculated in step S16. Next, in step S18, the interior angle frequency distribution generator 24 calculates the proportion of obtuse angles to the total (total number of frequencies of 90° or greater (obtuse angles) / total number of frequencies of each interior angle).

[0067] Next, in step S19, the earthquake determination unit 25 determines whether the following relational expression (1) is satisfied: Percentage of obtuse angles<Predetermined threshold value (1) If relational expression (1) is satisfied, the process proceeds to step S20, where the earthquake determination unit 25 determines that the frequency distribution of the interior angles formed by two consecutive acceleration vectors, which is a characteristic of noise, has a low percentage of obtuse angles, making it highly likely that an earthquake has occurred, and the process ends. On the other hand, if relational expression (1) is not satisfied, the process proceeds to step S21, where the earthquake determination unit 25 determines that the vibration has a high percentage of obtuse angles, which is a characteristic of noise, making it highly unlikely that an earthquake has occurred, and the detected vibration is determined to be not an earthquake (it is noise), and the process ends.

[0068] <Major Features> As shown in FIG. 2 , the seismic sensor 10 of this embodiment includes an acceleration acquisition unit 21, an interior angle calculation unit 23, an interior angle frequency distribution generation unit 24, and an earthquake determination unit 25. The acceleration acquisition unit 21 detects vibrations and acquires the vibration acceleration. The interior angle calculation unit 23 calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane based on the acceleration acquired by the acceleration acquisition unit 21. The interior angle frequency distribution generation unit 24 generates a frequency distribution of the interior angles calculated by the interior angle calculation unit 23. The earthquake determination unit 25 determines whether the vibration is an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. As a result, if the interior angle of two consecutive acceleration vectors has many acute angle components and few obtuse angle components, it can be determined that the angle matches the characteristics of an earthquake and that the vibration is likely to be an earthquake. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0069] [Other Embodiments] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention.

[0070] (A) In the above embodiment, the present invention has been described as being implemented as a seismic sensor and an earthquake detection method. However, the present invention is not limited to this. For example, the present invention may be implemented as an earthquake detection program that causes a computer to execute the earthquake detection method using the seismic sensor described above.

[0071] This earthquake detection program is stored in a memory (storage unit) installed in the seismic sensor, and a CPU loads the earthquake detection program stored in the memory and causes the hardware to execute each step. More specifically, the CPU loads the earthquake detection program and executes the acceleration acquisition step, interior angle calculation step, interior angle frequency distribution generation step, and earthquake determination step described above, thereby achieving the same effects as those described above. The present invention may also be realized as a recording medium storing the earthquake detection program.

[0072] (B) In the above embodiment, an example was described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two consecutive acceleration vectors is less than a predetermined threshold. However, the present invention is not limited to this.

[0073] For example, the earthquake determination unit may be configured to determine whether or not a detected vibration is an earthquake using any of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit. Specifically, as shown in FIG. 12( a), the earthquake determination unit may be configured to determine that the vibration is an earthquake when an angle having a frequency (mode) greater than the mean frequency is an acute angle. Also, as shown in FIG. 12( a), the earthquake determination unit may be configured to determine that the vibration is an earthquake when an angle having a frequency greater than the median frequency is an acute angle. Alternatively, as shown in FIG. 12( a), the earthquake determination unit may be configured to determine that the vibration is an earthquake when the mode of frequency is an acute angle.

[0074] (C) In the above embodiment, an example was described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two consecutive acceleration vectors is less than a predetermined threshold. However, the present invention is not limited to this.

[0075] For example, the earthquake determination unit may be configured to determine whether an earthquake has occurred based on the degree of variation in angles when the standard deviation, variance, and coefficient of variation of the frequency in the frequency distribution are within predetermined thresholds. Specifically, the standard deviation, variance, and coefficient of variation represent the degree of variation in the distribution, and smaller values ​​indicate less variation. Furthermore, vibrations caused by earthquakes are characterized by the fact that the variation around the most frequent angle is neither extremely large nor extremely small.

[0076] Therefore, as shown in Figure 12(b), if there is extremely little variation around the most frequent angle, the vibration can be determined to be noise. Similarly, as shown in Figure 12(c), if there is extremely large variation in the frequency distribution of interior angles, the vibration can be determined to be noise. Furthermore, the earthquake determination unit may be configured to determine an earthquake when the skewness of the frequency in the frequency distribution of interior angles is equal to or greater than a predetermined threshold (e.g., 0). The skewness is equal to or greater than 0 when the frequency distribution of interior angles is biased to the left (high frequency of acute angles), and equal to or less than 0 when it is biased to the right (high frequency of obtuse angles). Therefore, earthquake determination can be performed by setting the predetermined threshold to 0.

[0077] The earthquake determination unit may also be configured to determine an earthquake when the kurtosis of the frequency in the frequency distribution of interior angles is equal to or less than a predetermined threshold. Here, kurtosis represents the degree of sharpness (degree of variation) in the frequency distribution of interior angles, with larger kurtosis representing less variation. Thus, when the kurtosis of the peak in the frequency distribution of interior angles is within the threshold, the degree of variation in angles is determined to be small, and the vibration can be determined to be an earthquake. On the other hand, for example, as shown in FIG. 12( b), when the kurtosis of the frequency distribution of interior angles is large, it can be determined that the angle is close to the characteristic of noise, with a large deviation, and the vibration can be determined to be noise.

[0078] (D) In ​​the above embodiment, an example was described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two consecutive acceleration vectors is less than a predetermined threshold. However, the present invention is not limited to this.

[0079] For example, the earthquake determination unit may be configured to focus on the fact that in the frequency distribution of interior angles, the frequency is high around 20 to 50° as a characteristic of earthquakes, and the frequency is high around 0° and above 150° as a characteristic of noise, and to assign a positive weight to the frequency of interior angles between about 20 to 50° and a negative weight to the frequency of about 0° and above 150°, and perform earthquake determination depending on whether the sum is positive or negative.

[0080] Specifically, when the detected vibration is an earthquake as shown in Fig. 13(a), the earthquake determination unit assigns a positive weight to the frequency of interior angles of approximately 20 to 50°, and a negative weight to the frequency of interior angles of approximately 0° and approximately 150° or greater, and calculates the sum from 0 to 180°, as shown in Fig. 13(b). As a result, when the sum is positive, it is determined that the characteristics of an earthquake are more strongly expressed than the characteristics of noise, and the vibration can be determined to be an earthquake.

[0081] On the other hand, when the detected vibration is noise as shown in Fig. 14(a), the earthquake determination unit assigns a positive weight to the frequency of interior angles of approximately 20 to 50°, and a negative weight to the frequency of angles of approximately 0° and approximately 150° or greater, and calculates the sum from 0 to 180°, as shown in Fig. 14(b). As a result, when the sum is negative, it is determined that the characteristics of noise are more strongly expressed than the characteristics of an earthquake, and the vibration can be determined to be noise.

[0082] (E) In the above embodiment, the XY plane of the acceleration sensor 11 is used as the predetermined coordinate plane to calculate the interior angle between two consecutive acceleration vectors. However, the present invention is not limited to this. For example, the predetermined coordinate plane set for calculating the interior angle between two consecutive acceleration vectors may be the XZ plane or the YZ plane of the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor. Alternatively, it may be a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration along the three axes of the acceleration sensor that measures acceleration.

[0083] (F) In the above embodiment, an example was described in which the seismic sensor 10 includes an earthquake determination unit 25 that performs earthquake determination based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. However, the present invention is not limited to this. For example, the seismic sensor may be configured to analyze the detected vibrations but not perform earthquake determination. In this case, the frequency distribution generated by the interior angle frequency distribution generation unit may be transmitted to an external device (e.g., an external server device), and the external device may perform earthquake determination, thereby achieving the same effect as described above.

[0084] <Notes> The seismic sensor according to the first invention comprises an acceleration acquisition unit that detects vibrations and acquires the acceleration of the vibrations; an interior angle calculation unit that calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane based on the acceleration acquired by the acceleration acquisition unit; an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit; and an earthquake determination unit that determines whether the vibrations are an earthquake or not based on the frequency distribution generated by the interior angle frequency distribution generation unit.

[0085] A seismic sensor according to a second invention is the seismic sensor according to the first invention, wherein the earthquake determination unit determines that the vibration is an earthquake if the proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold.A seismic sensor according to a third invention is the seismic sensor according to the first or second invention, wherein the earthquake determination unit determines that the vibration is not an earthquake if the proportion of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold.

[0086] A seismic sensor according to a fourth invention is the seismic sensor according to any one of the first to third inventions, wherein the earthquake determination unit determines whether or not the vibration is an earthquake using any of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit.A seismic sensor according to a fifth invention is the seismic sensor according to any one of the first to fourth inventions, wherein the earthquake determination unit determines whether or not the vibration is an earthquake using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit.

[0087] A seismic sensor according to a sixth aspect of the present invention is the seismic sensor according to any one of the first to fifth aspects of the present invention, wherein the earthquake determination unit determines whether the vibration is an earthquake or not using the result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to the angle.A seismic sensor according to a seventh aspect of the present invention is the seismic sensor according to any one of the first to sixth aspects of the present invention, wherein the acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from the acceleration measured by the triaxial acceleration sensor.

[0088] The seismic sensor according to an eighth invention is the seismic sensor according to any one of the first to seventh inventions, further comprising an earthquake magnitude calculation unit that, when the earthquake determination unit determines that an earthquake has occurred, determines whether the earthquake is equivalent to or greater than a predetermined seismic intensity. The seismic sensor according to a ninth invention is the seismic sensor according to any one of the first to eighth inventions, further comprising an activation determination unit that calculates the intensity of the vibration from the results acquired by the acceleration acquisition unit, and, when the intensity of the vibration is equal to or greater than a predetermined magnitude, transitions from a power saving mode to a measurement mode that consumes more power than the power saving mode.

[0089] The seismic sensor of the tenth invention is a seismic sensor of any one of the first to ninth inventions, further comprising an output control unit that outputs the specified signal when the earthquake determination unit determines that an earthquake has occurred.

[0090] The seismic sensor of the present invention has the effect of being able to accurately determine whether detected vibrations are earthquakes or noise, and is therefore widely applicable to various devices that analyze vibrations such as earthquakes.

[0091] REFERENCE SIGNS LIST 10 Seismic sensor 11 Acceleration sensor 12 Controller 13 Memory 14 Output unit 21 Acceleration acquisition unit 22 Vibration intensity classification and activation determination unit (activation determination unit) 23 Interior angle calculation unit 24 Interior angle frequency distribution generation unit 25 Earthquake determination unit 26 Earthquake magnitude calculation unit 27 Output control unit 28 Offset adjustment unit 29 Storage unit

Claims

1. A seismic sensor comprising: an acceleration acquisition unit that detects vibrations and acquires the acceleration of the vibrations; an interior angle calculation unit that calculates the interior angle of two consecutive acceleration vectors on a specified coordinate plane based on the acceleration acquired by the acceleration acquisition unit; an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit; and an earthquake determination unit that determines whether the vibrations are an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit.

2. The seismic sensor according to claim 1, wherein the earthquake determination unit determines that the vibration is an earthquake if the proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold value.

3. The seismic sensor according to claim 1 or 2, wherein the earthquake determination unit determines that the vibration is not an earthquake if the proportion of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold value.

4. The seismic sensor according to claim 1 or 2, wherein the earthquake determination unit determines whether the vibration is an earthquake or not using any of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit.

5. The seismic sensor of claim 1 or 2, wherein the earthquake determination unit determines whether the vibration is an earthquake or not using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit.

6. The seismic sensor according to claim 1 or 2, wherein the earthquake determination unit determines whether the vibration is an earthquake or not by using the result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to the angle.

7. The seismic sensor according to claim 1 or 2, wherein the acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from the acceleration measured by the three-axis acceleration sensor.

8. The seismic sensor according to claim 1 or 2, further comprising an earthquake magnitude calculation unit that, when the earthquake determination unit determines that an earthquake has occurred, determines whether the earthquake is of a predetermined seismic intensity or greater.

9. A seismic sensor as described in claim 1 or 2, further comprising an activation determination unit that calculates the intensity of the vibration from the results acquired by the acceleration acquisition unit, and when the intensity of the vibration is equal to or greater than a predetermined magnitude, transitions from a power saving mode to a measurement mode that consumes more power than the power saving mode.

10. A seismic sensor as described in claim 1 or 2, further comprising an output control unit that outputs the specified signal when the earthquake determination unit determines that an earthquake has occurred.

11. An earthquake detection method comprising: an acceleration acquisition step of detecting vibrations and acquiring the acceleration of the vibrations; an interior angle calculation step of calculating the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane for the acceleration acquired in the acceleration acquisition step; an interior angle frequency distribution generation step of generating a frequency distribution of the interior angles calculated in the interior angle calculation step; and an earthquake determination step of determining whether the vibrations are an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step.

12. An earthquake detection program that causes a computer to execute an earthquake detection method, comprising: an acceleration acquisition step of detecting vibrations and acquiring the acceleration of the vibrations; an interior angle calculation step of calculating the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane for the accelerations acquired in the acceleration acquisition step; an interior angle frequency distribution generation step of generating a frequency distribution of the interior angles calculated in the interior angle calculation step; and an earthquake determination step of determining whether the vibrations are an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step.

13. A seismic sensor comprising: an acceleration acquisition unit that detects vibrations and acquires the acceleration of the vibrations; an interior angle calculation unit that calculates the interior angle of two consecutive acceleration vectors on a specified coordinate plane based on the acceleration acquired by the acceleration acquisition unit; and an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit.

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