JP2008228987A - Biological state detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a time needed for detection of biological information, such as a heartbeat of a living body object while improving the detection accuracy of the biological information. <P>SOLUTION: A biological state detecting apparatus 10 comprises: a biological sensor unit 11 for detecting heartbeat or a state amount related to the heartbeat (biological information); a transformation processing part 23 for performing Fourier transformation of a detection signal of the biological sensor unit 11 in a prescribed period with cutout interval Δt; a biological information detection part 24 for detecting the biological information from a frequency waveform generated by the transformation processing part 23; a prediction value calculation part 26 for calculating a predicted heart rate Bp from a detection result of the biological information in the past; and a cutout interval setting part 27 for calculating the cutout interval Δt(s) = (60/bp)x(2+α) on the basis of a prescribed coefficient α in the ranges of 0 to 1, and a predicted heart rate Bp((60s)<SP>-1</SP>). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a biological state detection device.

2. Description of the Related Art Conventionally, for example, an apparatus that detects the occupant's body temperature, blood pressure, pulse, or the like from a sensor provided on a vehicle seat and acquires the occupant's biological information is known (see, for example, Patent Document 1).
Further, conventionally, for example, a device is known that performs Fourier transform on a biological signal of a subject to be inspected and outputs each frequency component for each of a plurality of different predetermined periods, and detects biological information such as breathing and heartbeat for each frequency component. (For example, refer to Patent Document 2).
JP 2000-99867 A JP 2000-300529 A

By the way, in the apparatus according to the above prior art, when detecting biological information, high-speed detection is performed by Fourier transform in a relatively short period, and detection is performed with high accuracy by Fourier transform in a relatively long period. When these multiple detection results are displayed, due to the high-precision detection process, rapid detection becomes difficult, and the multiple detection results are displayed so that these detection results can be quickly displayed. It may be difficult to recognize and evaluate.
The present invention has been made in view of the above circumstances, and provides a biological state detection device capable of reducing the time required for detection while improving the detection accuracy of biological information such as a heartbeat of a biological object. It is aimed.

  In order to solve the above problems and achieve the object, the biological state detection apparatus according to the first aspect of the present invention is a state quantity detection unit (for example, an embodiment) that detects a state quantity related to the state of a biological object. Fourier transform means (for example, conversion in the embodiment) which outputs a frequency component by Fourier transforming each state element signal detected by the state quantity detection means in a predetermined period. A processing unit 23 and a cut-out interval setting unit 27), and biological information detection means (for example, the biological information detection unit 24 in the embodiment) that detects biological information of the biological object based on the frequency component, The Fourier transform means can change the predetermined period based on the biological information detected in the past by the biological information detection means.

Furthermore, in the biological state detection device according to the second aspect of the present invention, the Fourier transform means sets Δt (s), which is the predetermined period, to α, which is a predetermined coefficient that is greater than or equal to zero and less than or equal to 1, and the biological information detection By a predetermined formula (Δt = (60 / Bp) × (2 + α)) using a predicted value Bp ((60 s) ⁻¹ ) of biological information in the next process based on the biological information detected in the past by the means. Set.

According to the biological state detection device of the first aspect of the present invention, when the signal of the state quantity detected by the state quantity detection unit is Fourier-transformed, feedback processing based on biological information detected in the past by the biological information detection unit Since the time domain of Fourier transform is set by, the time domain becomes excessively long in order to improve detection accuracy, or the time domain is excessively shortened in order to shorten the time required for detection. It can be prevented that the accuracy cannot be ensured.
Furthermore, according to the biological state detection device according to the second aspect of the present invention, a predetermined mathematical formula (Δt = (60 / Bp) × (2 + α)) and a predetermined period (2 + α) with a predetermined period of Fourier transform. A certain Δt (s) changes according to the predicted value Bp ((60s) ⁻¹ ) of the biological information, and the time domain of Fourier transform is appropriately set according to the biological information detected in the past.
The predetermined period (2 + α) is 2 or more and 3 or less depending on α, which is a predetermined coefficient of 0 or more and 1 or less. For example, if it is less than 2, the time domain of Fourier transform becomes excessively short and the error increases. For example, if it is larger than 3, the error increases due to the fluctuation component of the biological information.

Hereinafter, a biological state detection device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
The biological state detection device 10 according to the present embodiment is, for example, as shown in FIG. 1, the biological information of a vehicle occupant (for example, physical information that is the basis for grasping the whole body state as a vital sign of the occupant, Among the heart beats (heartbeat), respiration rate, blood pressure, body temperature, etc.), for example, a biosensor unit 11 is provided for detecting a heartbeat or a state quantity related to the heartbeat. The biosensor unit 11 is, for example, a vehicle seat 12. A cable-type first piezoelectric element 14 provided in the seat cushion 13, a cable-type second piezoelectric element 16 provided in the seat back 15 of the vehicle seat 12, and a processing device 17. Configured.
The processing device 17 includes a filter processing unit 21, a waveform region extraction unit 22, a conversion processing unit 23, a biological information detection unit 24, a biological information storage unit 25, a predicted value calculation unit 26, and a cutting interval. And a setting unit 27.

  Each of the piezoelectric elements 14 and 16 is, for example, a cable-type piezoelectric element, and the two first piezoelectric elements 14 arranged inside the seat cushion 13 are from the occupant's buttocks and thighs that contact the seat cushion 13. A second vibration disposed on the inside of the seat back 15 is detected by detecting a temporal change of minute vibrations transmitted to the occupant's skin surface acting on the seat cushion 13 (for example, periodic pressure fluctuation related to the pulsation of the occupant's heart). The piezoelectric element 16 changes with time of minute vibrations transmitted from the back of the occupant in contact with the seat back 15 to the skin surface of the occupant acting on the seat back 15 (for example, periodic pressure fluctuations related to the heartbeat of the occupant). Is detected.

  The filter processing unit 21 of the processing device 17 uses, for example, a bandpass filter or the like from a detection signal obtained as time series data by the piezoelectric elements 14 and 16, for example, a predetermined frequency bandwidth, for example, the natural frequency of the human body (for example, 4 The waveform components in the band including ˜8 Hz are extracted and output to the waveform region extraction unit 22.

  The waveform area extraction unit 22 sets a predetermined time interval (for example, 6 s) set in advance with respect to the waveform component extracted by the filter processing unit 21, or a cutout interval output from the cutout interval setting unit 27. A waveform region corresponding to Δt (s) is extracted and output to the conversion processing unit 23.

  The conversion processing unit 23 decomposes the waveform region extracted by the waveform region extraction unit 22 into frequency components by, for example, orthogonal transformation such as Fourier transform, and generates a waveform indicating temporal changes in the occupant's body pressure or minute vibrations on the body surface. Then, it is converted into a frequency waveform indicating the frequency distribution and output to the biological information detection unit 24.

  The biological information detection unit 24 corresponds to a multiple frequency having, as a fundamental frequency, a frequency corresponding to a fundamental wave component of biological information such as a heartbeat that is a detection target by pattern matching on the frequency waveform generated by the conversion processing unit 23, for example. A pattern waveform composed of each waveform component corresponding to the frequency component to be processed, that is, the harmonic component is generated. A pattern waveform that best approximates the frequency waveform output from the conversion processing unit 23 is detected from among the plurality of pattern waveforms, and the detection target is based on the frequency of each waveform component constituting the pattern waveform. Detect biological information such as heartbeats.

  For example, when biometric information such as a heartbeat is a detection target, the biometric information detection unit 24 detects each heart rate for each of a plurality of appropriate heart rates within a predetermined range (for example, 30 to 180 times / minute). A pattern waveform including a waveform component having a frequency (for example, a fundamental frequency, a harmonic component, etc.) corresponding to the frequency and an amplitude corresponding to the envelope waveform of the frequency waveform output from the conversion processing unit 23 is generated. Then, the degree of matching between each pattern waveform and the frequency waveform generated by the conversion processing unit 23 is evaluated by an evaluation function such as a distance function. For example, a pattern waveform having a minimum distance (dB) is converted into a frequency waveform. It is determined that the approximation is best, and the heart rate corresponding to this pattern waveform is set as the biological information that is the detection target.

The biological information storage unit 25 stores a history of biological information detected by the biological information detection unit 24.
The predicted value calculation unit 26 extracts data having a predetermined reliability from the detection result of the past biometric information stored in the biometric information storage unit 25. For example, the predicted value calculation unit 26 uses the average value of these data in the next detection process. A predicted value of biological information, for example, a predicted heart rate Bp (bpm: (60 s) ⁻¹ ) is calculated.

The cut-out interval setting unit 27 uses the following mathematical formula (1) based on the predicted value of the biological information calculated by the predicted value calculation unit 26, for example, the predicted heart rate Bp, and a predetermined coefficient α that is greater than or equal to zero and less than or equal to 1 next time. In this process, the data extraction time width for setting the waveform region extracted by the waveform region extraction unit 22, that is, the extraction interval Δt (s) is calculated.
In the following formula (1), the predetermined value (2 + α) is 2 times (2 cycles) which is the minimum number of beats necessary for calculating the heart rate, and increases the certainty of heart rate calculation. A value that fluctuates according to a predetermined coefficient α between 3 times (3 cycles) that is the number of pulsations. For example, if a value less than 2 is used instead of the predetermined value (2 + α), the time domain of Fourier transform Becomes excessively short and increases the detection error of the biological information. For example, if a value larger than 3 is used instead of the predetermined value (2 + α), the error increases due to the fluctuation component of the biological information.

For example, as shown in FIGS. 2 (a) and 2 (b), in an appropriate waveform P indicating the time change of the detection signals (voltage values) output from the piezoelectric elements 14 and 16, the number of beats is one (1). According to the waveform region extracted by the cut-out interval Δt (s) corresponding to (period), only the envelope waveform EV of less than one period is obtained.
On the other hand, for example, as shown in FIGS. 2C and 2D, according to the waveform region extracted by the cut-out interval Δt (s) corresponding to two beats (two cycles), An envelope waveform longer than at least one period is obtained, and extracted, for example, by a cutting interval Δt (s) corresponding to three beats (three periods) as shown in FIGS. 2 (e) and 2 (f). According to the waveform region, an envelope waveform longer than at least two periods is obtained.

The biological state detection device 10 according to the present embodiment has the above-described configuration. Next, based on the operation of the biological state detection device 10, in particular, detection signals output from the piezoelectric elements 14 and 16, heartbeats and the like. Processing for detecting biological information will be described.
Note that the following processing is performed, for example, when the vehicle encounters an accident, when an occupant protection device such as an air bag device is activated, or when detecting the drowsiness or determining the degree of arousal from the appropriate control device. It is executed when a detection request is output.
First, for example, in step S01 shown in FIG. 3, a detection signal of a time change of the occupant's body pressure or minute vibrations on the body surface detected by the piezoelectric elements 14 and 16 is acquired.

In step S02, a waveform component having a predetermined frequency bandwidth including the natural frequency (eg, 4 to 8 Hz) of the human body is extracted from the acquired detection signal, and a predetermined time is set as an initial value for the cut interval Δt. An interval (for example, 6 s) is set.
In step S03, a waveform region corresponding to the cutting interval Δt is extracted.
In step S04, the extracted predetermined waveform component is decomposed into frequency components by, for example, orthogonal transformation such as Fourier transform, and the waveform of the time series data is converted into a frequency waveform of frequency distribution.

  And in step S05, the pattern waveform comprised by the harmonic component corresponding to the multiple frequency which makes the frequency corresponding to each appropriate value a fundamental frequency for every some appropriate value with respect to biometric information, such as a heartbeat which is a detection target, The pattern waveform that best approximates the frequency waveform is detected from the multiple pattern waveforms, and the interval between the peak positions of each waveform component that makes up this pattern waveform, that is, the frequency difference at each peak position, is detected. Based on this, biological information (for example, heart rate) that is a detection target is detected.

In step S06, the detection result of the biological information is stored.
In step S07, it is determined whether there is an end instruction.
If the determination result is “YES”, the series of processes is terminated.
On the other hand, if this determination is “NO”, the flow proceeds to step S08.
In step S08, it is determined whether or not there is data having a predetermined reliability among the detection results of the stored biological information.
In this determination process, for example, an average value is calculated from a population of heart rate obtained in the past for a predetermined time (for example, about 1 minute), and the difference between the average value and the detection result is within a predetermined range, for example, ± If it is 20 (bpm: (60 s) ⁻¹ ) or the like, it is determined that a predetermined reliability is obtained.
If this determination is “NO”, the flow returns to step S 03 described above.
On the other hand, if this determination is “YES”, the flow proceeds to step S 09.

In step S09, based on the detection result of the biological information having a predetermined reliability, the predicted value of the biological information in the next detection processing, for example, the predicted heart rate Bp (bpm: (60s) ^{− 1} ) is calculated.
In step S10, the cut-out interval Δt (s) in the next process is calculated by the above formula (1), and the process returns to the above-described step S03.

Thus, for example, even when the predetermined coefficient α is set to 1 and the predetermined period (2 + α) is fixed to 3 (period), for example, output from each of the piezoelectric elements 14 and 16 shown in FIGS. Like the appropriate waveform P indicating the time change of the detected signal (voltage value), the cut-out interval Δt (s), that is, the time domain of the Fourier transform is the predicted heart rate Bp (bpm: (60s) ⁻¹ ). It will change accordingly.
For example, when the average heart rate is 64 (bpm: (60 s) ⁻¹ ) as in the embodiment shown in FIG. 5, the extraction interval is detected with respect to the detection signals obtained from the piezoelectric elements 14 and 16. As can be seen from the detection error of the heart rate when Δt is changed over 1 to 10 (s), the extraction interval Δt = 3, that is, the number of beats corresponds to about 2.8 times (cycle) For example, if the extraction interval is less than Δt = 2, that is, if the number of pulsations is less than about 1.9 times (cycles), the time domain of Fourier transform becomes excessively short and the detection error of biological information increases. For example, if the value is larger than the extraction interval Δt = 3, that is, if the number of pulsations is larger than 3 (periods), the error increases due to the fluctuation component of the biological information.

As described above, according to the biological state detection device 10 according to the present embodiment, when the waveform indicating the time change of the detection signals (voltage values) output from the piezoelectric elements 14 and 16 is Fourier transformed in the past. Since the Fourier transform time domain, that is, the extraction interval Δt (s) is set by feedback processing using the detected biometric information, the time domain of the Fourier transform becomes excessively long in order to improve the detection accuracy of the biometric information. It is possible to prevent the time required for detecting biometric information from being shortened, and the time domain of Fourier transform from becoming excessively short, so that the desired detection accuracy of biometric information cannot be ensured.
Further, in the above formula (1) for setting the cutting interval Δt (s), by setting the predetermined period (2 + α) to 2 or more and 3 or less, for example, the time domain of the Fourier transform becomes excessively short and the error increases. For example, it is possible to prevent the error from increasing due to the fluctuation component of the biological information, and appropriately set the time domain of the Fourier transform.

  In the above-described embodiment, the piezoelectric elements 14 and 16 are provided. However, the present invention is not limited to this, and an appropriate pressure-sensitive element that detects temporal changes in the body pressure of the occupant or the minute vibrations on the body surface is used. There may be.

It is a block diagram of the biological condition detection apparatus which concerns on embodiment of this invention. 2A to 2F are diagrams showing a waveform P of a detection signal (voltage value) output from each piezoelectric element and an envelope waveform EV corresponding to the cut-out interval Δt. It is a flowchart which shows operation | movement of the biological condition detection apparatus which concerns on embodiment of this invention. 4A and 4B are diagrams showing the predicted heart rate Bp and the cut-out interval Δt of the waveform P of the detection signal (voltage value) output from each piezoelectric element. With respect to the waveform of the detection signal (voltage value) output from each piezoelectric element when the average heart rate is 64 (bpm: (60 s) ⁻¹ ), the cutting interval Δt is set to 1 to 10 (s). It is a figure which shows the detection error of the heart rate when making it change.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Living body state detection apparatus 14 1st piezoelectric element (state quantity detection means)
16 Second piezoelectric element (state quantity detection means)
23 Conversion processing unit (Fourier transform means)
24 Biological information detection unit (biological information detection means)
27 Cutting interval setting unit (Fourier transform means)

Claims (2)

State quantity detection means for detecting a state quantity relating to the state of the biological object;
Fourier transform means for Fourier-transforming a signal of the state quantity detected by the state quantity detection means in a predetermined period and outputting a frequency component;
Biological information detection means for detecting biological information of the biological object based on the frequency component,
The biological state detection apparatus, wherein the Fourier transform means can change the predetermined period based on the biological information detected in the past by the biological information detection means. In the next processing based on the biological information detected in the past by the biological information detecting means, the Fourier transforming means sets Δt (s), which is the predetermined period, to α, which is a predetermined coefficient not less than zero and not more than 1. The predetermined mathematical formula (Δt = (60 / Bp) × (2 + α)) using the predicted value Bp ((60 s) ⁻¹ ) of the biological information of
The biological state detection device according to claim 1, wherein the biological state detection device is set according to claim 1.

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