Seismic sensor, earthquake detection method, and earthquake detection program

Abstract

A seismic sensor (10) comprises an acceleration acquiring unit (21), a direction angle calculating unit (23), a direction angle frequency distribution generating unit (24), and an earthquake determining unit (25). The acceleration acquiring unit (21) detects vibrations and acquires the accelerations of the vibrations. The direction angle calculating unit (23) calculates, for the accelerations acquired by the acceleration acquiring unit (21), the angle formed by the vector of each acceleration with reference to an origin on a predetermined coordinate plane. The direction angle frequency distribution generating unit (24) generates the frequency distribution of the angles calculated by the direction angle calculating unit (23). The earthquake determining unit (25) determines whether the vibrations are an earthquake on the basis of the angle frequency distribution created by the direction angle frequency distribution generating unit (24).

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 sensor disclosed in the above publication calculates the frequency of each axis (e.g., X and Y axes) of the acceleration sensor when analyzing the frequency of the acceleration measured by the acceleration sensor. This makes it difficult to analyze vibrations taking into account the vibration characteristics on both axes (e.g., X and Y axes), making it difficult to accurately determine whether an earthquake has occurred. An object of the present invention is to provide a seismic sensor, earthquake detection method, and earthquake detection program that can accurately determine whether a detected vibration is an earthquake or noise.

[0005] (Means for solving the problem) A seismic sensor according to a first aspect of the present invention includes an acceleration acquisition unit, an angle calculation unit, an angle frequency distribution generation unit, and an earthquake determination unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The angle calculation unit calculates the angle formed by the vector of each acceleration, based on an origin on a predetermined coordinate plane, for the accelerations acquired by the acceleration acquisition unit. The angle frequency distribution generation unit generates a frequency distribution of the angles calculated by the angle calculation unit. The earthquake determination unit determines whether the vibrations are an earthquake based on the angle frequency distribution created by the angle frequency distribution generation unit.

[0006] Here, the angle formed by the acceleration vector of the detected vibration with respect to the origin on the coordinate plane of the acceleration is calculated, and whether the vibration is an earthquake or not is determined based on the frequency distribution of the angle. Here, the predetermined coordinate plane means, for example, the XY plane, XZ plane, or YZ plane out of the three axes (X-axis, Y-axis, and Z-axis) of the 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.

[0007] The angle of an acceleration vector with respect to the origin on a given coordinate plane means, for example, the angle of the acceleration vector with respect to the X-axis when the starting point of the acceleration vector is aligned with the origin on the coordinate plane (XY plane). Normally, if the detected vibration is an earthquake, it will be characterized by vibrations in various directions on a substantially horizontal plane.

[0008] Therefore, this seismic sensor calculates the direction (directional angle) of the acceleration vector on a specified coordinate plane, generates its frequency distribution, and performs earthquake detection based on the frequency bias for each angle. This allows the sensor to detect the acceleration vector pointing in all directions, a characteristic of vibrations caused by earthquakes, using the frequency distribution of angles, thereby determining whether the vibration is an earthquake or not. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0009] The 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 the vibration is an earthquake if the angle frequencies are generally the same. As a result, if acceleration vectors pointing at all angles are detected to be generally the same from the frequency distribution of the generated angles, it can be determined that the characteristics match those of vibrations caused by an earthquake, and the vibration can be determined to be an earthquake.

[0010] The 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 the vibration is not an earthquake if there is a bias in the angle frequency for each angle. As a result, if a bias in the angle of the acceleration vector is detected from the frequency distribution of the generated angles, it can be determined that the characteristic matches the vibration due to noise other than an earthquake, and the vibration can be determined to be not an earthquake.

[0011] 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 calculates a coefficient of variation of the angle frequency from the average value and standard deviation of the angle frequency created by the angle frequency distribution generation unit, and determines that the vibration is an earthquake if the coefficient of variation is smaller than a predetermined threshold value. This makes it possible to easily determine whether the detected vibration is an earthquake by comparing the coefficient of variation calculated based on the average value and standard deviation of the angle frequency with the predetermined threshold value.

[0012] 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 mean, median, and mode of the frequency distribution generated by the 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 angle frequency distribution.

[0013] 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 or not a vibration is an earthquake using any of the standard deviation, variance, skewness, and kurtosis of the frequency distribution generated by the 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, skewness, and kurtosis of the angle frequency distribution.

[0014] The seismic sensor according to a seventh 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 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.

[0015] 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, further comprising an activation determination unit that calculates the 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 that 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.

[0016] 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 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 cut-off signal to stop the supply of energy such as electricity or gas, or a warning signal to notify of danger.

[0017] An earthquake detection method according to a tenth aspect of the present invention includes an acceleration acquisition step, an angle calculation step, an 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 angle calculation step, angles formed by vectors of the accelerations acquired in the acceleration acquisition step with respect to an origin on a predetermined coordinate plane are calculated. In the angle frequency distribution generation step, a frequency distribution of the angles calculated in the angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake based on the frequency distribution of the angles created in the angle frequency distribution generation step.

[0018] Here, the angle formed by the acceleration vector of the detected vibration with respect to the origin on the coordinate plane of the acceleration is calculated, and whether the vibration is an earthquake or not is determined based on the frequency distribution of that angle. Here, the predetermined coordinate plane means, for example, the XY plane, XZ plane, or YZ plane out of the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor that measures acceleration.

[0019] The angle of an acceleration vector with respect to the origin on a given coordinate plane means, for example, the angle of the acceleration vector with respect to the X-axis when the starting point of the acceleration vector is aligned with the origin on the coordinate plane (XY plane). Normally, if the detected vibration is an earthquake, it will be characterized by vibrations in various directions on a substantially horizontal plane.

[0020] Therefore, this seismic sensor calculates the direction (directional angle) of the acceleration vector on a specified coordinate plane, generates its frequency distribution, and performs earthquake detection based on the frequency bias for each angle. This allows the sensor to detect the acceleration vector pointing in all directions, a characteristic of vibrations caused by earthquakes, using the frequency distribution of angles, thereby determining whether the vibration is an earthquake or not. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0021] An earthquake detection program according to an eleventh aspect of the present invention causes a computer to execute an earthquake detection method including an acceleration acquisition step, an angle calculation step, an 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 angle calculation step, angles formed by vectors of each acceleration, with reference to an origin on a predetermined coordinate plane, for the accelerations acquired in the acceleration acquisition step are calculated. In the angle frequency distribution generation step, a frequency distribution of the angles calculated in the angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake based on the frequency distribution of angles created in the angle frequency distribution generation step.

[0022] Here, the angle formed by the acceleration vector of the detected vibration with respect to the origin on the coordinate plane of the acceleration is calculated, and whether the vibration is an earthquake or not is determined based on the frequency distribution of the angle. Here, the predetermined coordinate plane means, for example, the XY plane, XZ plane, or YZ plane out of the three axes (X-axis, Y-axis, and Z-axis) of the 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.

[0023] The angle of an acceleration vector with respect to the origin on a given coordinate plane means, for example, the angle of the acceleration vector with respect to the X-axis when the starting point of the acceleration vector is aligned with the origin on the coordinate plane (XY plane). Normally, if the detected vibration is an earthquake, it will be characterized by vibrations in various directions on a substantially horizontal plane.

[0024] Therefore, this seismic sensor calculates the direction (directional angle) of the acceleration vector on a specified coordinate plane, generates its frequency distribution, and performs earthquake detection based on the frequency bias for each angle. This allows the sensor to detect the acceleration vector pointing in all directions, a characteristic of vibrations caused by earthquakes, using the frequency distribution of angles, thereby determining whether the vibration is an earthquake or not. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0025] A seismic sensor according to a twelfth aspect of the present invention includes an acceleration acquisition unit, an angle calculation unit, and an angle frequency distribution generation unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The angle calculation unit calculates the angle formed by the vector of each acceleration acquired by the acceleration acquisition unit, with the origin on a predetermined coordinate plane as the reference. The angle frequency distribution generation unit generates a frequency distribution of the angles calculated by the angle calculation unit.

[0026] Here, the angle formed by the acceleration vector with respect to the origin on the coordinate plane of the detected vibration acceleration is calculated, and a frequency distribution of the angle is generated. Here, the predetermined coordinate plane means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the 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.

[0027] The angle of an acceleration vector with respect to the origin on a given coordinate plane means, for example, the angle of the acceleration vector with respect to the X-axis when the starting point of the acceleration vector is aligned with the origin on the coordinate plane (XY plane). Normally, if the detected vibration is an earthquake, it will be characterized by vibrations in various directions on a substantially horizontal plane.

[0028] Therefore, this seismic sensor calculates the direction (directional angle) of the acceleration vector on a specified coordinate plane and generates its frequency distribution. This allows the sensor to detect the acceleration vector pointing in all directions, a characteristic of earthquake vibrations, using the frequency distribution of angles, thereby determining whether the vibration is an earthquake or not. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0029] (Effects of the Invention) The seismic sensor according to the present invention can accurately determine whether detected vibrations are earthquakes or noise.

[0030] 1 is a control block diagram showing the configuration of a seismic sensor according to one embodiment of the present invention. A functional block diagram generated within the seismic sensor of FIG. 1. A diagram showing the direction angle of an acceleration vector calculated in the direction angle calculation unit of FIG. 2. A graph showing the acceleration on a horizontal plane (XY plane) of earthquake vibrations detected by the seismic sensor of FIG. 1. (a) is a graph showing the angles of the acceleration vectors in the earthquake vibrations of FIG. 4, divided into the first, second, third, and fourth quadrants. (b) is a graph showing the frequency distribution of the angles of the acceleration vectors. A graph showing the acceleration on a horizontal plane (XY plane) of daily life vibrations (noise) detected by the seismic sensor of FIG. 1. (a) is a graph showing the angles of the acceleration vectors in the daily life vibrations (noise) of FIG. 4, divided into the first, second, third, and fourth quadrants. (b) is a graph showing the frequency distribution of the angles of the acceleration vectors. A flowchart showing the processing flow of an earthquake detection method performed by the seismic sensor of FIG. 2. As an example of earthquake determination using the mode, mean, or median of the frequency distribution of direction angles generated by a seismic sensor according to another embodiment of the present invention, (a) is a graph showing the frequency distribution of direction angles when the detected vibration is an earthquake. (b) is a graph showing the frequency distribution of direction angles when the detected vibration is noise. As an example of earthquake determination using the variation (standard deviation, variance) relative to the mode of the frequency distribution of direction angles generated by a seismic sensor according to yet another embodiment of the present invention, (a) is a graph showing the frequency distribution of direction angles when the detected vibration is an earthquake. (b) is a graph showing the frequency distribution of direction angles when the detected vibration is noise. As an example of earthquake determination using the kurtosis of the frequency distribution of direction angles generated by a seismic sensor according to yet another embodiment of the present invention, (a) is a graph showing the frequency distribution of direction angles when the detected vibration is an earthquake. (b) is a graph showing the frequency distribution of direction angles when the detected vibration is noise.

[0031] A seismic sensor according to one embodiment of the present invention will be described below with reference to Figures 1 to 8. Note that in this embodiment, more detailed explanation than necessary may be omitted. For example, detailed explanations of already 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.

[0032] Furthermore, the applicant provides the accompanying drawings and the following description to enable those skilled in the art to fully understand the present invention, and they are not intended to limit the subject matter described in the claims.

[0033] (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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] (2) Functional blocks of the seismic sensor 10 As shown in Figure 2, the seismic sensor 10 includes an acceleration acquisition unit 21, a vibration intensity classification / activation determination unit 22, a direction angle calculation unit (angle calculation unit) 23, a direction angle frequency distribution generation unit (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.

[0040] 2, each of the functional blocks is configured by the controller 12 receiving acceleration data acquired from the acceleration sensor 11 and reading a program stored in the memory 13. The acceleration acquisition unit 21 acquires measurement data of acceleration in the X-axis, Y-axis, and Z-axis measured at a predetermined cycle by the acceleration sensor 11. The acceleration acquisition unit 21 normally acquires measurement data of acceleration measured repeatedly at a relatively low speed (i.e., at a relatively large measurement cycle).

[0041] When performing such low-speed acceleration sampling, 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, so the controller 12 operates in the sleep mode with limited functionality, thereby reducing power consumption.

[0042] 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.

[0043] 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.

[0044] 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 stored in the memory unit 29, and if the acceleration value exceeds the activation threshold, transitions from power saving mode to measurement mode (activates the seismic sensor 10). The vibration intensity discrimination and activation determination unit 22 also 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 power saving mode to measurement mode, which consumes more power than power saving mode (activates the controller 12).

[0045] Here, the vibration intensity classification process performed by the vibration intensity classification / 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 storage unit 29. The direction angle calculation unit (angle calculation unit) 23 calculates the angle (direction angle) of the acceleration vector based on the origin on a predetermined coordinate plane (e.g., XY plane) for the acceleration acquired by the acceleration acquisition unit 21 (see FIG. 3 ).

[0046] Here, the predetermined coordinate plane refers to, for example, the 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. Furthermore, the angle of the acceleration vector based on the origin refers to the angle of the acceleration vector with respect to the X-axis, as shown in Fig. 3, for example, when the starting point of the acceleration vector is aligned with the origin on the coordinate plane (XY plane).

[0047] Specifically, when the vibration detected by the 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 (a substantially horizontal plane) as shown in Fig. 4. Here, when the direction angle calculation unit 23 classifies the angles (direction angles) that the acceleration vector based on the origin makes with respect to the X axis among the accelerations in the XY plane in Fig. 4 into the first, second, third, and fourth quadrants, the accelerations are arranged almost evenly in each quadrant as shown in Fig. 5(a).

[0048] The direction angle frequency distribution generator (angle frequency distribution generator) 24 generates a frequency distribution of the angle (direction angle) that the acceleration vector based on the origin makes with respect to the X-axis, as shown in FIG. 5(b). At this time, if the detected vibration is an earthquake as shown in FIG. 4, the frequency distribution will be approximately uniform because vibrations caused by earthquakes distribute acceleration in various directions. On the other hand, if the vibration detected by the acceleration sensor 11 is not an earthquake, the vibration caused by noise such as daily vibrations will be characterized as generating acceleration in an approximately constant direction in the XY plane (approximately horizontal plane), as shown in FIG.

[0049] Here, when the direction angle calculation unit 23 classifies the angles (direction angles) that an acceleration vector based on the origin makes with respect to the X axis among the accelerations in the XY plane in Fig. 6 into the first, second, third, and fourth quadrants, the angles tend to be concentrated in the first and third quadrants, resulting in a bias, as shown in Fig. 7(a). The direction angle frequency distribution generation unit 24 generates a frequency distribution of the angles (direction angles) that an acceleration vector based on the origin makes with respect to the X axis, as shown in Fig. 7(b).

[0050] At this time, if the detected vibration is noise as shown in Fig. 6, the direction of acceleration is concentrated in one direction due to noise-induced vibration, resulting in a bias in the frequency distribution, such as a peak at a certain angle. In other words, when the detected vibration is an earthquake and when it is something other than that (multiple types of noise), different acceleration distributions and angle frequency distributions of directional angles are generated on a predetermined coordinate plane.

[0051] That is, if the detected vibration is an earthquake, it will contain components in various frequency bands in all directions on the XY plane, as shown in Fig. 4. Therefore, the frequency distribution generated by the direction angle frequency distribution generator 24 will be approximately uniform over the entire angle range of 0° to 180°, as shown in Fig. 5(b), with little bias. On the other hand, if the detected vibration is not an earthquake but high-frequency vibration noise, as shown in Fig. 6, two consecutive acceleration components will be linear on the XY plane and will contain components in high frequency bands.

[0052] 7B, the frequency distribution generated by the direction angle frequency distribution generator 24 is highly biased, with the 70 degree angle being prominent in the angle range of 0 to 180 degrees. Therefore, since earthquakes are characterized by the direction angles of acceleration vectors being generally uniform, the seismic sensor 10 of this embodiment determines whether the vibration is an earthquake or not depending on whether it detects that the frequency distribution of direction angles is generally uniform.

[0053] Specifically, the earthquake determination unit 25 determines whether or not the vibration is an earthquake based on the frequency distribution of direction angles generated by the direction angle frequency distribution generation unit 24. That is, the earthquake determination unit 25 determines that the vibration is an earthquake when the frequency of angles in the frequency distribution of direction angles is generally the same as shown in Fig. 5(b). On the other hand, the earthquake determination unit 25 determines that the vibration is noise rather than an earthquake when the frequency distribution of direction angles shows a bias in the frequency of angles for each angle as shown in Fig. 7(b).

[0054] Here, the earthquake determination unit 25 calculates the coefficient of variation of the angle frequency from the average value and standard deviation of the angle frequency created in the direction angle frequency distribution generation unit 24, and determines that the vibration is an earthquake if the coefficient of variation is smaller than a predetermined threshold. The coefficient of variation is calculated using the following relational expression: Coefficient of variation of angle frequency = Standard deviation of angle frequency / Average value of angle frequency. The earthquake determination unit 25 may also use any of the average value, median value, or mode value of the frequency distribution created in the direction angle frequency distribution generation unit 24 to determine whether the vibration is an earthquake.

[0055] When the earthquake determination unit 25 determines that an earthquake has occurred, the earthquake scale calculation unit 26 determines whether the earthquake has a seismic intensity of at least a predetermined level. After the earthquake determination unit 25 determines that the detected vibrations are an earthquake and starts calculating an index indicating the magnitude of the earthquake, if the earthquake scale calculation unit 26 detects an acceleration waveform that can be considered to be an impact, it calculates the magnitude of the earthquake by excluding the acceleration waveform.

[0056] 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 equal to or greater than a predetermined seismic intensity. Here, the predetermined signal output from the output unit 14 includes, for example, a cutoff signal sent 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.

[0057] When the earthquake determination unit 25 determines that the vibration detected by the acceleration acquisition unit 21 is noise, the offset adjustment unit 28 adjusts the offset amount of the acceleration waveform according to the magnitude of the noise. The offset adjustment unit 28 then adjusts the offset amount of the acceleration waveform according to the determination result of the earthquake determination unit 25. The offset adjustment performed by the offset adjustment unit 28 detects noise components contained in the measured acceleration as offset components, such as changes in measurement values ​​that occur due to changes in the seismic sensor 10 over time, changes in measurement values ​​that occur due to temperature changes, and changes in measurement values ​​that occur when the orientation of the installed seismic sensor 10 is tilted for some reason and the direction of gravitational acceleration relative to the seismic sensor 10 changes. Specifically, the offset adjustment unit 28 calculates, for example, the median of the maximum and minimum values ​​of the acceleration determined to be noise or the average value of the acceleration as the offset component.

[0058] The memory unit 29 stores, for example, acceleration data acquired by the acceleration acquisition unit 21 or acceleration data after filtering processing, direction angle data calculated by the direction angle calculation unit 23, frequency distribution data generated by the direction angle frequency distribution generation unit 24, the judgment results of the earthquake judgment unit 25, and offset component data used in the offset adjustment unit 28.

[0059] <Earthquake Detection Method> The earthquake detection method using the seismic sensor 10 of this embodiment will be explained below using the flowchart shown in Figure 8. That is, in step S11, the acceleration acquisition unit 21 of the seismic sensor 10 acquires the acceleration measured by the acceleration sensor 11.

[0060] Next, in step S12, the direction angle calculation unit 23 calculates an acceleration vector from the acceleration acquired in step S11. Next, in step S13, the direction angle calculation unit 23 calculates an angle (direction angle) of the acceleration vector calculated in step S12 with respect to the origin. Next, in step S14, the direction angle frequency distribution generation unit 24 counts up the frequency (number of times) of the direction angle of the acceleration vector calculated in step S13.

[0061] Next, in step S15, it is determined whether or not the vibration determination process is to be ended. If it is to be ended, the process proceeds to step S16. If it is not to be ended, the process returns to step S11 and the subsequent processes are repeated. Next, in step S16, the direction angle frequency distribution generator 24 calculates the average value of the frequencies of the direction angles counted up in step S14.

[0062] Next, in step S17, the direction angle frequency distribution generation unit 24 calculates the standard deviation of the frequencies of the direction angles counted up in step S 14. Next, in step S18, the direction angle frequency distribution generation unit 24 calculates the coefficient of variation of the frequencies of the direction angles based on the average values ​​and standard deviations of the frequencies of the direction angles calculated in steps S15 and S16.

[0063] Next, in step S19, the earthquake determination unit 25 determines whether the following relational expression (1) is satisfied: Coefficient of variation<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 deviation in the frequency of the direction angles is small and a variety of direction angles are observed because the coefficient of variation is smaller than the threshold value, so that the possibility of an earthquake is high, 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 deviation in the frequency of the direction angles is large and the frequency of the direction angles is biased in one direction, so that the possibility of an earthquake is low, and the detected vibration is determined to be not an earthquake (it is noise), and the process ends.

[0064] <Major Features> As shown in Fig. 2, the seismic sensor 10 of this embodiment includes an acceleration acquisition unit 21, a direction angle calculation unit 23, a direction angle frequency distribution generation unit 24, and an earthquake determination unit 25. The acceleration acquisition unit 21 detects vibrations and acquires the acceleration of the vibrations. The direction angle calculation unit 23 calculates the angle formed by the vector of each acceleration, with respect to an origin on a predetermined coordinate plane, for the accelerations acquired by the acceleration acquisition unit 21. The direction angle frequency distribution generation unit 24 generates a frequency distribution of the angles calculated by the direction angle calculation unit 23. The earthquake determination unit 25 determines whether the vibrations are an earthquake based on the frequency distribution of angles created by the direction angle frequency distribution generation unit 24.

[0065] This allows us to use the frequency distribution of angles to detect that the acceleration vector points in all directions, which is a characteristic of vibrations caused by earthquakes, and determine whether the vibrations are earthquakes or not. As a result, we can accurately determine whether the detected vibrations are earthquakes or noise.

[0066] [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.

[0067] (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.

[0068] 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, direction angle calculation step, direction 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.

[0069] (B) In the above embodiment, an example has been described in which the earthquake determination unit 25 performs earthquake determination based on the coefficient of variation of the frequency of the direction angle calculated from the average value and standard deviation in the frequency distribution generated by the direction angle frequency distribution generation unit 24. However, the present invention is not limited to this.

[0070] For example, the earthquake determination unit may be configured to determine whether the detected vibration is an earthquake using any of the mean, median, and mode of the frequency distribution generated by the angle frequency distribution generation unit. Specifically, as shown in Figure 9(a), the average (or median) of the calculated acceleration vector angle over the entire range from 0° to 180° is compared with the mode of the acceleration vector angle, and if the two values ​​are close, it is determined that the variation in the frequency distribution of the acceleration vector angle is small, and the vibration can be determined to be an earthquake.

[0071] On the other hand, as shown in Figure 9(b), the average value (or median) of the calculated acceleration vector angle over the entire range of 0° to 180° is compared with the most frequent value of the acceleration vector angle, and the greater the difference between the two values, the greater the variation in the frequency distribution of the acceleration vector angle, and the vibration can be determined to be noise rather than an earthquake.

[0072] (C) In the above embodiment, an example has been described in which the earthquake determination unit 25 performs earthquake determination based on the coefficient of variation of the frequency of the direction angle calculated from the average value and standard deviation in the frequency distribution generated by the direction angle frequency distribution generation unit 24. However, the present invention is not limited to this.

[0073] 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 and variance of the frequency in the frequency distribution are within a predetermined threshold. Specifically, the standard deviation and variance represent the degree of variation in the distribution, and a smaller value indicates less variation. Furthermore, vibrations caused by earthquakes are characterized by the fact that the variation is neither extremely large nor extremely small around the angle of the most frequent value.

[0074] Specifically, as shown in Figure 10(a), when the frequency of other angles is close to the most frequent value of the calculated acceleration vector angle (directional angle) in the entire range of 0° to 180°, it is determined that the variation in the frequency distribution of the acceleration vector angle is large, and the vibration can be determined to be an earthquake. On the other hand, as shown in Figure 10(b), the more the frequency of other angles is farther from the most frequent value of the calculated acceleration vector angle (directional angle) in the entire range of 0° to 180°, it is determined that the variation in the frequency distribution of the acceleration vector angle is small, and the vibration can be determined to be noise rather than an earthquake.

[0075] (D) In ​​the above embodiment, an example has been described in which the earthquake determination unit 25 performs earthquake determination based on the coefficient of variation of the frequency of the direction angle calculated from the mean value and standard deviation in the frequency distribution generated by the direction angle frequency distribution generation unit 24. However, the present invention is not limited to this. For example, the earthquake determination unit may be configured to determine whether the detected vibration is an earthquake using the kurtosis of the frequency distribution generated by the angle frequency distribution generation unit.

[0076] Here, the kurtosis in the frequency distribution of angles generated by the direction angle frequency distribution generator 24 refers to the degree of peaking (variation) of the normal distribution in the frequency distribution graph. In other words, high kurtosis in a normal distribution means that the frequency of a particular angle is exceptionally high, which corresponds to the linear vibrations seen in noise such as daily vibrations. As a result, as shown in Figure 11(a), if the kurtosis of the calculated acceleration vector angle is small over the entire range from 0° to 180°, it can be determined that the variation in the frequency distribution of the acceleration vector angle is small, and the vibration can be determined to be an earthquake.

[0077] On the other hand, as shown in Figure 11(b), if the kurtosis of the calculated acceleration vector angle is large throughout the range of 0° to 180°, it can be determined that the variation in the frequency distribution of the acceleration vector angle is small, and the vibration can be determined to be noise rather than an earthquake.

[0078] (E) In the above embodiment, an example was described in which the XY plane of the acceleration sensor 11 was used as a predetermined coordinate plane and the angle of the acceleration vector with respect to the origin was calculated. However, the present invention is not limited to this.

[0079] For example, the predetermined coordinate plane set for calculating the angle of the acceleration vector may be the XZ plane or the YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor, or may be, 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.

[0080] (F) In the above embodiment, an example was described in which the seismic sensor 10 was equipped with the earthquake determination unit 25 that determines whether an earthquake has occurred based on the frequency distribution generated by the direction angle frequency distribution generation unit 24. However, the present invention is not limited to this.

[0081] For example, the seismic sensor may be configured to analyze the detected vibrations but not determine whether an earthquake has occurred. In this case, the frequency distribution generated by the angle frequency distribution generator is transmitted to an external device (for example, an external server device), and the external device performs earthquake determination, thereby achieving the same effect as described above.

[0082] <Note> The seismic sensor of the first invention comprises an acceleration acquisition unit that detects vibrations and acquires the acceleration of the vibrations; an angle calculation unit that calculates the angle formed by the vector of each acceleration based on an origin on a predetermined coordinate plane for the accelerations acquired by the acceleration acquisition unit; an angle frequency distribution generation unit that generates a frequency distribution of the angles calculated by the angle calculation unit; and an earthquake determination unit that determines whether the vibrations are an earthquake or not based on the frequency distribution of the angles created by the angle frequency distribution generation unit.

[0083] 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 the vibration is an earthquake if the frequencies of the angles are generally the same.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 the vibration is not an earthquake if there is a bias in the frequencies of the angles for each angle.

[0084] The seismic sensor of the fourth invention is a seismic sensor of any one of the first to third inventions, wherein the earthquake determination unit calculates a coefficient of variation of the angle frequency from the average value and standard deviation of the angle frequency created by the angle frequency distribution generation unit, and determines that the vibration is an earthquake if the coefficient of variation is smaller than a predetermined threshold value.

[0085] 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 mean, median, and mode of the frequency distribution generated by the angle frequency distribution generation unit.A seismic sensor according to a sixth invention is the seismic sensor according to any one of the first to fifth inventions, wherein the earthquake determination unit determines whether or not the vibration is an earthquake using any of the standard deviation, variance, skewness, and kurtosis of the frequency distribution generated by the angle frequency distribution generation unit.

[0086] The seismic sensor according to a seventh invention is the seismic sensor according to any one of the first to sixth 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 an eighth invention is the seismic sensor according to any one of the first to seventh 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.

[0087] The seismic sensor of the ninth invention is a seismic sensor of any one of the first to eighth inventions, further comprising an output control unit that outputs the specified signal when the earthquake determination unit determines that an earthquake has occurred.

[0088] 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.

[0089] 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 Direction angle calculation unit (angle calculation unit) 24 Direction angle frequency distribution generation unit (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 angle calculation unit that calculates the angle formed by the vector of each acceleration, based on an origin on a predetermined coordinate plane, for the accelerations acquired by the acceleration acquisition unit; an angle frequency distribution generation unit that generates a frequency distribution of the angles calculated by the angle calculation unit; and an earthquake determination unit that determines whether the vibrations are an earthquake or not, based on the frequency distribution of the angles created by the 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 frequency of the angles is generally the same.

3. The seismic sensor according to claim 1 or 2, wherein the earthquake determination unit determines that the vibration is not an earthquake if there is a bias in the frequency of the angles for each angle.

4. The seismic sensor of claim 1 or 2, wherein the earthquake determination unit calculates a coefficient of variation of the angle frequency from the average value and standard deviation of the angle frequency created by the angle frequency distribution generation unit, and determines that the vibration is an earthquake if the coefficient of variation is smaller than a predetermined threshold value.

5. 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 angle frequency distribution generation unit.

6. A seismic sensor as described in 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, skewness, and kurtosis of the frequency distribution generated by the angle frequency distribution generation unit.

7. 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.

8. 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.

9. The seismic sensor according to claim 1 or 2, further comprising an output control unit that outputs the predetermined signal when the earthquake determination unit determines that an earthquake has occurred.

10. An earthquake detection method comprising: an acceleration acquisition step of detecting vibrations and acquiring the acceleration of the vibrations; an angle calculation step of calculating the angle formed by the vector of each acceleration, based on an origin on a predetermined coordinate plane, for the accelerations acquired in the acceleration acquisition step; an angle frequency distribution generation step of generating a frequency distribution of the angles calculated in the angle calculation step; and an earthquake determination step of determining whether the vibrations are an earthquake or not, based on the angle frequency distribution created in the angle frequency distribution generation step.

11. 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 angle calculation step of calculating the angle formed by the vector of each acceleration, with reference to an origin on a predetermined coordinate plane, for the accelerations acquired in the acceleration acquisition step; an angle frequency distribution generation step of generating a frequency distribution of the angles calculated in the angle calculation step; and an earthquake determination step of determining whether the vibrations are an earthquake or not, based on the angle frequency distribution created in the angle frequency distribution generation step.

12. A seismic sensor comprising: an acceleration acquisition unit that detects vibrations and acquires the acceleration of the vibrations; an angle calculation unit that calculates the angle formed by the vector of each acceleration, based on an origin on a specified coordinate plane, for the acceleration acquired by the acceleration acquisition unit; and a frequency distribution generation unit that generates a frequency distribution of the angles calculated by the angle calculation unit.

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