WO2015045763A1 - 生体電気信号計測用回路 - Google Patents
生体電気信号計測用回路 Download PDFInfo
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- WO2015045763A1 WO2015045763A1 PCT/JP2014/073198 JP2014073198W WO2015045763A1 WO 2015045763 A1 WO2015045763 A1 WO 2015045763A1 JP 2014073198 W JP2014073198 W JP 2014073198W WO 2015045763 A1 WO2015045763 A1 WO 2015045763A1
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- bioelectric signal
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
- A61B5/6893—Cars
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0002—Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network
- A61B5/0004—Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network characterised by the type of physiological signal transmitted
- A61B5/0006—ECG or EEG signals
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/25—Bioelectric electrodes therefor
- A61B5/279—Bioelectric electrodes therefor specially adapted for particular uses
- A61B5/28—Bioelectric electrodes therefor specially adapted for particular uses for electrocardiography [ECG]
- A61B5/282—Holders for multiple electrodes
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/30—Input circuits therefor
- A61B5/302—Input circuits therefor for capacitive or ionised electrodes, e.g. metal-oxide-semiconductor field-effect transistors [MOSFET]
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/30—Input circuits therefor
- A61B5/307—Input circuits therefor specially adapted for particular uses
- A61B5/308—Input circuits therefor specially adapted for particular uses for electrocardiography [ECG]
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
- A61B5/7207—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
- A61B5/721—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7225—Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
Definitions
- the present invention relates to a bioelectric signal measurement circuit for measuring a bioelectric signal such as an electrocardiogram or an electroencephalogram through an electrostatic capacity.
- Patent Document 1 discloses one in which the capacitance between the measurement electrode and the subject is estimated from the area of the contact portion between the measurement electrode and the subject and the pressure applied to the contact portion.
- the electrostatic capacity of the clothes worn by the occupant (subject) varies depending on the material, volume, external pressure, and the factors applied.
- the technique described in Patent Document 1 cannot detect a change in capacitance due to the material, volume, etc. of the clothes worn by the occupant. Since the gain of the bioelectric signal changes according to the capacitance, there is a possibility that gain correction cannot be performed accurately unless the capacitance is correctly detected.
- the present invention pays attention to the above-mentioned problem, and the object of the present invention is to accurately detect and detect a capacitance between a biological composition and an input means for inputting a bioelectric signal generated by the biological composition. It is an object of the present invention to provide a bioelectric signal measurement circuit capable of correcting the gain of a bioelectric signal based on the capacitance obtained.
- a bioelectric signal is mixed with a reference signal, a capacitance between the biological composition and the input means is detected from the intensity of the reference signal, and based on the detected capacitance.
- the bioelectric signal gain was corrected.
- FIG. 3 is a control block diagram of the bioelectric signal measurement circuit according to the first embodiment.
- 1 is a schematic diagram of a vehicle seat of Example 1.
- FIG. 3 is a circuit diagram of an impedance conversion unit, a reference signal mixing unit, and a signal feedback unit according to the first embodiment.
- 3 is a flowchart showing a processing flow of an electrostatic capacitance measurement unit and a gain correction value calculation unit according to the first embodiment.
- FIG. 3 is a diagram illustrating an example of how to determine the intensity of a reference signal according to the first embodiment.
- 6 is a map showing the capacitance of the clothes with respect to the signal intensity of the reference signal of Example 1.
- 6 is a map showing an output gain of an impedance converter with respect to the capacitance of the clothes of Example 1.
- FIG. 1 is a schematic diagram of a vehicle seat of Example 1.
- FIG. 3 is a circuit diagram of an impedance conversion unit, a reference signal mixing unit, and a signal feedback unit according to the first embodiment
- FIG. 6 is a diagram illustrating a relationship between an output gain of an impedance converter and a frequency when gain correction is not performed in the first embodiment.
- FIG. 5 is a diagram illustrating a relationship between an output gain of an impedance converter and a frequency when gain correction is performed in the first embodiment.
- 6 is a control block diagram of a bioelectric signal measurement circuit according to Embodiment 2.
- FIG. FIG. 6 is a circuit diagram of an impedance converter, a reference signal mixer, a signal feedback unit, and a reference signal strength change unit according to the second embodiment.
- 10 is a flowchart showing a processing flow of a reference signal intensity set value calculation unit, a capacitance measurement unit, and a gain correction value calculation unit according to the second embodiment.
- FIG. 6 is a map showing the capacitance of the clothes with respect to the signal intensity of the reference signal of Example 2.
- 6 is a circuit diagram of an impedance conversion unit, a reference signal mixing unit, and a signal feedback unit of Example 3.
- FIG. 10 is a diagram illustrating gain characteristics of a reference signal output from an impedance conversion unit with respect to a frequency of the reference signal when the flattening function unit of Example 3 is not provided.
- FIG. 10 is a diagram illustrating a gain characteristic of a reference signal output from an impedance conversion unit with respect to a frequency of the reference signal when the flattening function unit of Example 3 is provided.
- FIG. 6 is a circuit diagram of an impedance conversion unit, a signal feedback circuit, a resonance suppression circuit, a reference AC signal strength analysis unit, and a reference AC signal supply circuit according to Example 4.
- FIG. 10 is a graph showing frequency gain characteristics of a signal output from the impedance converter of Example 4.
- 10 is a graph showing frequency gain characteristics of a signal output from the impedance converter of Example 4.
- FIG. 10 is a control block diagram of the bioelectric signal measurement circuit according to the fifth embodiment.
- 10 is a flowchart illustrating a processing flow of a capacitance measuring unit, a gain correction value calculating unit, and a reference signal generating unit of Example 5.
- 10 is a map showing a reference signal with respect to the capacitance of the clothes of Example 5.
- FIG. 10 is a graph showing a reference signal with respect to the capacitance of the clothes of Example 5.
- FIG. 10 is a control block diagram of a bioelectric signal measurement circuit of Example 6.
- 10 is a flowchart showing a flow of processing of a signal selection unit of Example 6.
- FIG. 10 is a control block diagram of the bioelectric signal measurement circuit of the seventh embodiment.
- FIG. 10 is a control block diagram of a bioelectric signal measurement circuit according to an eighth embodiment.
- FIG. 10 is a control block diagram of a bioelectric signal measurement circuit according to a ninth embodiment.
- FIG. 10 is a schematic diagram of a vehicle seat according to a ninth embodiment. It is a graph which shows the frequency output gain characteristic for every electrostatic capacitance of the clothes of Example 9.
- FIG. 10 shows an example of extremity guidance in Example 11.
- 14 is a graph showing an example of a change in capacitance between the electrode of Example 13 and a biological composition.
- FIG. 16 is a control block diagram of the bioelectric signal measurement circuit according to the fifteenth embodiment.
- Bioelectric signal measurement circuit 1 Bioelectric signal measurement circuit 2 electrodes (input means) 3 seats 6 Impedance converter 7 Reference signal mixing section 7a Flattening function section 8 Signal feedback section 9 Signal separator 10 Capacitance measurement unit 11 Gain correction value calculator 12 Bioelectric signal gain correction unit 13 Reference signal strength setting value calculator 14 Reference signal strength change section 16 Reference signal calculator (artifact calculation means) 18 Subtraction unit (artifact removal means) 19 Signal selector 20 Reliability Information Collection Department 24 Bioelectric signal measurement unit (Bioelectric measurement means) 25 External information sources (behavior estimation means) 27 Correlation evaluation section
- FIG. 1 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 inputs a bioelectric signal of the human body from the positive electrode 2p and the negative electrode 2n and outputs it as an electrocardiogram.
- Fig. 2 is a schematic diagram of the vehicle seat 3.
- a positive electrode 2p and a negative electrode 2n are provided separately on the left and right surfaces of the seat back 3a having the insulating property of the seat 3.
- a ground 2g is provided between the positive electrode 2p and the negative electrode 2n.
- Electrode 2 is made of metal materials such as gold, silver, copper, and nichrome, carbon-based materials such as carbon and graphite, particulate materials composed of semiconductors such as metals and metal oxides, acetylene-based, complex 5-membered ring systems, phenylene-based, It consists of conductive materials such as conductive polymer materials such as aniline.
- the bioelectric signal measurement circuit 1 has a gain correction unit 5 that corrects the gain according to the capacitance of the clothes worn by the occupant and an electrocardiogram generation unit 4 that generates an electrocardiogram from the signal after gain correction. is doing.
- the gain correction unit 5 includes a positive gain correction unit 5p that corrects the gain of the bioelectric signal input from the positive electrode 2p, and a negative gain correction unit 5n that corrects the gain of the bioelectric signal input from the negative electrode 2n.
- the gain correction unit 5 includes an impedance conversion unit 6, a reference signal mixing unit 7, a signal feedback unit 8, a signal separation unit 9, a capacitance measurement unit 10, a gain correction value calculation unit 11, and a bioelectric signal.
- FIG. 3 is a circuit diagram of the impedance conversion unit 6, the reference signal mixing unit 7, and the signal feedback unit 8.
- the impedance converter 6 detects the bioelectric signal input to the electrode 2.
- the impedance converter 6 includes a voltage follower circuit composed of an operational amplifier.
- the reference signal mixing unit 7 mixes and outputs the output of the impedance conversion unit 6 and the reference signal for measuring the capacitance of the clothes worn by the occupant.
- An AC signal is used as the reference signal. If a DC signal is used as the reference signal, the offset current of the voltage follower circuit of the impedance converter 6 is affected, and in some cases, the output current of the voltage follower circuit may be saturated.
- the frequency of the reference signal is desirably set to avoid the frequency band of 10 to 40 [Hz] of the R wave signal in order to avoid interference with the R wave signal of the electrocardiogram.
- a frequency signal fixed by an oscillation circuit such as a solid oscillator oscillation circuit, a CR oscillation circuit, or an LC oscillation circuit can be used, and a waveform shape programmed in a microcomputer is output by a D / A converter.
- the reference signal mixing unit 7 is composed of a circuit in which two inverting adder circuits are connected as shown in FIG. As a result, the output of the impedance converter 6 and the reference signal can be mixed.
- the signal feedback unit 8 is connected to the output side of the reference signal mixing unit 7.
- the signal feedback unit 8 is configured by a bootstrap circuit as shown in FIG. The output of the signal feedback unit 8 is fed back to the input side of the impedance conversion unit 6.
- the signal separation unit 9 includes a bandpass filter circuit that extracts a frequency band 10 to 40 [Hz] of an R wave of an electrocardiogram that is a bioelectric signal, and a bandpass filter circuit that extracts a frequency band other than the R wave. . Thereby, a bioelectric signal and a reference signal can be separated.
- FIG. 4 is a flowchart showing the flow of processing. Steps S1 and S2 are processes of the capacitance measuring unit 10, and steps S3 and S4 are processes of the gain correction value calculating unit 11.
- step S1 the signal strength of the reference signal is calculated.
- FIG. 5 is a diagram showing an example of how to obtain the strength of the reference signal. Here, three examples are shown as how to obtain the signal strength of the reference signal.
- signal strength is obtained by performing a discrete Fourier transform on the reference signal (FIG. 5 (a)).
- low-pass filter processing is performed to obtain signal strength in time series (FIG. 5 (b)).
- the signal intensity is obtained in a time series by performing a peak-to-peak correction process after the root mean square of the reference signal (FIG. 5 (c)).
- step S2 the capacitance of the clothes is calculated from the signal intensity of the reference signal.
- FIG. 6 is a map showing the capacitance of the clothes with respect to the signal intensity of the reference signal.
- step S2 the capacitance of the clothes is calculated using the map of FIG.
- step S3 the output gain of the impedance converter 6 is calculated from the calculated capacitance.
- FIG. 7 is a map showing the output gain of the impedance converter 6 with respect to the capacitance of the clothes.
- step S3 the output gain of the impedance converter 6 is calculated using the map of FIG.
- step S4 a gain correction value is calculated according to the calculated output gain.
- the signal strength calculation of the reference signal in step S1 is also implemented as software, but it may be configured from an analog circuit that can perform the same processing using a detection circuit or the like.
- the bioelectric signal gain correction unit 12 corrects the gain of the bioelectric signal input from the signal separation unit 9 with the gain correction value input from the gain correction value calculation unit 11.
- the bioelectric signal gain correction unit 12 is configured by combining an amplification circuit and an attenuation circuit that can set an input signal at an arbitrary magnification.
- the electrocardiogram generation unit 4 receives the bioelectric signal after gain correction from the gain correction unit 5.
- the positive and negative bioelectric signals are filtered and amplified, respectively, and the difference between the processed positive and negative signals is taken as an electrocardiogram.
- Example 1 the output of the impedance converter 6 and the reference signal for measuring the capacitance of the clothes were mixed, and the mixed signal was returned to the impedance converter 6.
- the occupant side is also ground, and the reference signal also flows to the occupant side.
- the capacitance of the clothes becomes a factor for dividing the reference signal, and the signal strength of the reference signal changes according to the capacitance.
- the reference signal is separated from the signal output from the impedance converter 6, and the capacitance of the clothes can be obtained from the signal intensity of the reference signal. Then, by correcting the gain to a predetermined value set in advance, a change in the gain of the bioelectric signal due to a change in the capacitance of the clothes can be suppressed.
- FIG. 8 is a diagram showing the relationship between the output gain of the impedance converter 6 and the frequency when gain correction is not performed.
- FIG. 8 shows the gain according to the frequency when the capacitance (Cp, Cn) of the clothes is 110 [pF] (shown by a solid line) and 10 [pF] (shown by a broken line). From Fig.
- the difference in gain due to capacitance can be eliminated by incorporating the above relationship into a software program as a database or calculation formula in advance in a microprocessor.
- the target value of the output gain of the gain correction unit 5 is 0 [dB]
- the capacitance of the clothes is 10 [pF] What is necessary is just to correct
- the target value of the output gain of the gain correction unit 5 is not limited to 0 [dB] and may be set arbitrarily.
- FIG. 9 is a diagram showing the relationship between the output gain of the impedance converter 6 and the frequency when gain correction is performed.
- FIG. 9 shows the gain according to the frequency when the capacitance (Cp, Cn) of the clothes is 110 [pF] (shown by a solid line) and 10 [pF] (shown by a broken line). From Fig. 9, the capacitance is 110 [pF] and 10 [pF] in the R wave region (10 to 40 [Hz]) of the electrocardiogram after gain correction. The gain difference has been eliminated.
- the electrode 2 is installed on the seat back 3a of the vehicle seat 3. Therefore, if an occupant is seated on the seat 3, a bioelectric signal can be measured.
- a bioelectric signal cannot be measured if the occupant releases his hand from the handle.
- the occupant basically sits on the seat 3, and in Example 1, the bioelectric signal of the occupant during the ride can always be measured.
- An electrode 2 for inputting a bioelectric signal emitted by an occupant (biological composition), an impedance conversion unit 6 for impedance conversion of the bioelectric signal input by the electrode 2, and an output signal of the impedance conversion unit 6
- the reference signal mixing unit 7 that mixes the reference signal for measuring the capacitance between the occupant and the electrode 2 (clothing), and the output signal of the reference signal mixing unit 7 is fed back to the impedance conversion unit 6
- the electrostatic capacity is calculated from the signal feedback unit 8, the signal separation unit 9 that separates the bioelectric signal and the reference signal from the output signal of the impedance conversion unit 6, and the intensity of the reference signal input from the signal separation unit 9.
- the electrode 2 is installed on the vehicle seat 3. Therefore, it is possible to always measure the bioelectric signal of the occupant in the vehicle.
- FIG. 10 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 according to the second embodiment is different from the bioelectric signal measurement circuit 1 according to the first embodiment in that a reference signal strength set value calculation unit 13 and a reference signal strength change unit 14 are provided.
- the processing contents of the capacitance measuring unit 10 are different.
- the configuration different from that of the first embodiment is mainly described, and the same configuration as that of the first embodiment is denoted by the same reference numeral and the description thereof is omitted.
- FIG. 11 is a circuit diagram of the impedance conversion unit 6, the reference signal mixing unit 7, the signal feedback unit 8, and the reference signal strength changing unit 14.
- the impedance conversion unit 6, the reference signal mixing unit 7, and the signal feedback unit 8 are almost the same as the circuit shown in FIG. However, two terminals for inputting the reference signal of the reference signal mixing unit 7 are provided, and the resistance of each terminal is different. That is, the resistance R11 on one terminal side is 10 [k ⁇ ], and the resistance R1 on the other terminal side is 1 [k ⁇ ].
- the reference signal strength changing unit 14 is a switch circuit that selects which input terminal of the reference signal mixing unit 7 inputs the reference signal. Which input terminal is selected is determined according to an intensity setting value obtained by a reference signal intensity setting value calculator 13 described later.
- the reference signal strength setting value calculation unit 13 inputs the reference signal from the signal separation unit 9, and sets the signal strength of the reference signal input to the reference signal mixing unit 7 according to the signal strength of the input reference signal (strength setting value).
- the capacitance measuring unit 10 calculates the capacitance of the clothes according to the signal intensity of the reference signal using a map according to the intensity setting value.
- FIG. 12 is a flowchart showing the flow of processing.
- Steps S11, S12, and S13 are processing of the reference signal strength setting value calculation unit 13
- steps S14 and S15 are processing of the capacitance measurement unit 10
- step 16 is processing of the gain correction value calculation unit 11. Note that the process of the gain correction value calculation unit 11 in step S16 performs the same process as the process in the first embodiment (steps S3 and S4 in FIG. 4).
- the reference signal strength set value calculation unit 13, the capacitance measurement unit 10, and the gain correction value calculation unit 11 are software installed in a microprocessor having an A / D converter.
- step S11 the signal strength of the reference signal is calculated.
- the signal intensity is calculated in the same manner as the process in step S1 of FIG.
- step S12 it is determined whether or not the calculated signal strength of the reference signal is within the measurement range of the capacitance measuring unit 10. If the signal strength is within the measurement range, the process proceeds to step S14. Control goes to step S13.
- Step S13 changes the signal strength setting value (strength setting value) of the reference signal input to the reference signal mixing unit 7.
- the intensity setting value may be set in multiple steps or steplessly, but in Example 2, it is set in two steps, large and small. If the strength setting value is set to a large value, the input terminal provided with the resistor R1 is selected in the reference signal strength changing unit 14, and if the strength setting value is set to a small value, the resistor R11 in the reference signal strength changing unit 14 is selected. The input terminal provided with is selected.
- step S14 the capacitance of the clothes is calculated from the signal intensity of the reference signal.
- FIG. 13 is a map showing the capacitance of the clothes with respect to the signal intensity of the reference signal.
- two maps are provided depending on whether the intensity setting value is large or small. That is, when the intensity setting value is large and the input terminal of the resistor R11 is selected in the reference signal intensity changing unit 14, the map indicated by the dotted line in FIG. 13 is selected. Further, when the strength setting value is small and the input terminal of the resistor R1 is selected in the reference signal strength changing unit 14, the map indicated by the solid line in FIG. 13 is selected.
- step S15 the capacitance of the clothes is calculated using the selected map.
- step S16 the gain correction value is calculated as in the first embodiment.
- the reference signal strength set value calculation unit 13 determines whether the signal strength of the reference signal input from the signal separation unit 9 is within a range in which the capacitance can be measured by the capacitance measurement unit 10. Judgment was made. Then, when it is outside the measurable range, the intensity setting value is changed to change the signal intensity of the reference signal input to the reference signal mixing unit 7.
- the signal intensity of the reference signal input to the capacitance measuring unit 10 can be set appropriately, and the capacitance can be measured with high accuracy.
- the reference signal strength changing unit 14 is configured by a switch circuit that selects which input terminal of the reference signal mixing unit 7 is input with the reference signal. Therefore, the signal intensity of the reference signal input to the reference signal mixing unit 7 can be changed with a simple configuration.
- a reference signal strength changing unit 14 that changes the strength of the reference signal input to the reference signal mixing unit 7 according to the set reference signal strength, and the capacitance measuring unit 10 is connected to the signal separating unit 9
- the capacitance is calculated from the intensity of the input reference signal and the intensity of the reference signal set by the reference signal intensity set value calculator 13. Therefore, the signal intensity of the reference signal input to the capacitance measuring unit 10 can be set appropriately, and the capacitance can be measured with high accuracy.
- the reference signal intensity changing unit 14 performs the intensity of the reference signal input to the reference signal mixing unit 7 by changing the constant of the electronic circuit in the reference signal mixing unit 7. Therefore, the signal intensity of the reference signal input to the reference signal mixing unit 7 can be changed with a simple configuration.
- Example 3 The bioelectric signal measurement circuit 1 of the third embodiment is partially different from the bioelectric signal measurement circuit 1 of claim 1 in the configuration of the reference signal mixing unit 7.
- the configuration different from that of the first embodiment is mainly described, and the same configuration as that of the first embodiment is denoted by the same reference numeral and the description thereof is omitted.
- FIG. 14 is a circuit diagram of the impedance conversion unit 6, the reference signal mixing unit 7, and the signal feedback unit 8.
- the reference signal mixing unit 7 is provided with a flattening function unit 7a at the input portion of the reference signal.
- the flattening function unit 7a is an RC series circuit in which a resistor R11 and a capacitor C1 are connected in series.
- FIG. 15 is a diagram illustrating the gain characteristic of the reference signal output from the impedance converter 6 with respect to the frequency of the reference signal when the flattening function unit 7a is not provided.
- the frequency of the reference signal deviates from a desired value due to variations in temperature characteristics and individual characteristics, a deviation also occurs in the gain of the reference signal output from the impedance converter 6 as shown in FIG.
- the flattening function unit 7a is provided to flatten the gain change according to the frequency change of the reference signal.
- FIG. 16 is a diagram showing the gain characteristic of the reference signal output from the impedance converter 6 with respect to the frequency of the reference signal when the flattening function unit 7a is provided. As shown in FIG. 16, the gain characteristic of the reference signal is flattened in a frequency band from about 10 [Hz] to about 1 [kHz], and the gain changes little even if the frequency of the reference signal is slightly shifted. Therefore, the capacitance can be measured with high accuracy.
- the reference signal mixing unit 7 has a flattening function unit 7a set so that the gain characteristic of the reference signal output from the impedance conversion unit 6 is flattened with respect to the frequency change of the reference signal. did. Therefore, the gain characteristic of the reference signal is flattened with respect to the frequency change of the reference signal, so even if the frequency of the reference signal slightly deviates from the desired value, the gain change can be reduced and the capacitance can be measured with high accuracy. can do.
- the bioelectric signal measurement circuit 1 of the fourth embodiment is partially different from the bioelectric signal measurement circuit 1 of claim 1 in the configuration of the signal feedback unit 8.
- the resonance suppressing unit 15 is provided.
- the configuration different from that of the first embodiment is mainly described, and the same configuration as that of the first embodiment is denoted by the same reference numeral and the description thereof is omitted.
- FIG. 17 is a circuit diagram of the impedance conversion unit 6, the reference signal mixing unit 7, the signal feedback unit 8, and the resonance suppression unit 15.
- the signal feedback unit 8 includes two resistors R2, R3 connected in series in the circuit connected to the input terminal of the impedance conversion unit 6 and the ground, and the resistors R2, R3 and the output terminal of the impedance conversion unit 6. It is composed of a capacitor C2 and a resistor R4 that are directly connected in the circuit to be connected. That is, the resistor R4 is added to the configuration of the signal feedback unit 8 of the first embodiment.
- the resonance suppression unit 15 includes a capacitor Cin and a switch SW.
- the switch SW switches between a circuit that passes through the capacitor Cin and a circuit that does not pass through the capacitor Cin in accordance with the reference signal intensity calculated by the capacitance measuring unit 10.
- a circuit that passes through the capacitor Cin is selected.
- a circuit that does not pass through the capacitor Cin is selected.
- the signal feedback unit 8 is connected between the two resistors R2 and R3 connected in series in the circuit connecting the input terminal of the impedance conversion unit 6 and the ground, and the two resistors R2 and R3. And a capacitor C1 and a resistor R4 connected in series in a circuit connecting the output terminal of the impedance converter 6 and the impedance converter 6.
- FIG. 18 shows the frequency of the signal output from the impedance converter 6 when the capacitance Cc of the clothes is 10 [pF] (FIG. 18 (a)) and 100 [pF] (FIG. 18 (b)). It is a graph showing a gain characteristic. Fig. 18 shows the characteristics when the resistance values of resistors R2 and R3 are both 51 [M ⁇ ], the resistance value of resistor R4 is 20 [k ⁇ ], and the capacitance of capacitor C2 is 470 [pF]. , Set to a value that can be used as a chip component. FIG. 18 shows a state where a circuit that does not pass through the capacitor Cin is selected in the resonance suppression unit 15.
- FIG. 19 shows the frequency of the signal output from the impedance converter 6 when the electrostatic capacitance Cc of the clothes is 10 [pF] (FIG. 19 (a)) and 100 [pF] (FIG. 19 (b)). It is a graph showing a gain characteristic. Note that in FIG. 19, the resistance values of resistors R2 and R3 are both 51 [M ⁇ ], the resistance value of resistor R4 is 20 [k ⁇ ], the capacitance of capacitor C1 is 470 [pF], and the capacitance of capacitor Cin Indicates the characteristics when 10 [pF], and is set to a value that can be used as a chip component.
- FIG. 18 shows a state in which a circuit passing through the capacitor Cin is selected in the resonance suppression unit 15.
- the resonance suppression unit 15 when the capacitance Cc of the clothes is relatively high (100 [pF]), a frequency gain without resonance can be obtained by the capacitor Cin. Then, when the capacitance Cc of the clothes is relatively low (10 [pF]), a circuit that does not pass through the capacitor Cin can be used, and a decrease in gain due to the capacitor Cin can be avoided.
- the signal feedback unit 8 includes two resistors R2 and R3 connected in series in a circuit connecting the input terminal of the impedance conversion unit 6 and the ground, and a reference between the two resistors R2 and R3.
- the capacitor C2 and the resistor R4 connected in series in the circuit connecting the output terminal of the signal mixing unit 7 and when the capacitance measured by the capacitance measuring unit 10 is larger than a predetermined value
- a capacitor Cin is provided in series between the electrode 2 and the input terminal of the impedance converter 6. Therefore, it is possible to obtain a stable frequency gain characteristic with a high value regardless of the electrostatic capacitance of the clothes, and it is possible to stably measure a bioelectric signal even in a vibration environment.
- Example 5 The bioelectric signal measurement circuit 1 of the fifth embodiment is different from the bioelectric signal measurement circuit 1 of claim 1 in that a reference signal calculation unit 16, a filter / amplification unit 17, and a subtraction unit 18 are provided.
- the configuration different from that of the first embodiment is mainly described, and the same configuration as that of the first embodiment is denoted by the same reference numeral and the description thereof is omitted.
- FIG. 20 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 inputs a bioelectric signal of the human body from the positive electrode 2p and the negative electrode 2n and outputs it as an electrocardiogram.
- the reference signal calculation unit 16 is software installed in a microprocessor having an A / D converter.
- FIG. 21 is a flowchart showing the flow of processing. Steps S1 and S2 are processing of the capacitance measuring unit 10, steps S3 and S4 are processing of the gain correction value calculating unit 11, and step S5 is processing of the reference signal calculating unit 16. The processing in steps S1 to S4 is the same as that described in the first embodiment with reference to FIG.
- a reference signal (voltage) Vref ′ is calculated from the calculated capacitance.
- FIG. 22 is a map showing a reference signal Vref ′ with respect to the capacitance of the clothes.
- the reference signal Vref ′ is calculated using the map of FIG.
- the reference signal Vref ′ has a substantially inversely proportional relationship with the capacitance.
- the filter / amplifier 17 performs a filtering process and an amplification process on the bioelectric signal, respectively, so as to be a signal suitable for electrocardiogram measurement.
- the filter / amplifier unit 17 can be realized as an electronic circuit composed of a general-purpose analog IC. Then, it is converted into a digital signal by the A / D converter connected to the microprocessor (bioelectric signal Vsig).
- the subtractor 18 subtracts the reference signal (voltage) Vref from the bioelectric signal (voltage) Vsig output from the filter / amplifier 17 and outputs the subtracted signal as a bioelectric signal (voltage) Vsig ′.
- RMS represents the root mean square.
- the electrocardiogram generation unit 4 receives the bioelectric signal Vsig ′ from the subtraction unit 18.
- the electrocardiogram is obtained by taking the difference between the positive and negative bioelectric signals Vsig ′.
- the electrocardiogram generation unit 4 also performs filtering processing and amplification processing.
- the electrocardiogram generation unit 4 since the filtering process and the amplification process are performed in the filter / amplifier unit 17, the electrocardiogram generation unit 4 does not perform the filtering process and the amplification process.
- Example 5 the artifact (reference signal Vref) was calculated from the change in the capacitance of the clothes, and the artifact was removed from the bioelectric signal input from the electrode 2. Thereby, the artifact mixed in the bioelectric signal due to the change in the capacitance of the clothes can be removed, and the measurement accuracy can be improved.
- Example 5 The effect of Example 5 will be described below.
- the reference signal calculation unit 16 (artifact calculation means) that calculates the artifact superimposed on the bioelectric signal in the electrode 2 from the change in capacitance calculated by the capacitance measurement unit 10 and the signal separation unit 9 output
- a subtracting unit 18 (artifact removing means) for subtracting the calculated artifact from the bioelectric signal. Therefore, artifacts mixed in the bioelectric signal due to the change in the capacitance of the clothes can be removed, and the measurement accuracy can be improved.
- FIG. 23 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 according to the sixth embodiment is different from the bioelectric signal measurement circuit 1 according to the fifth embodiment in that a signal selection unit 19 is provided.
- the configuration different from the first and fifth embodiments will be mainly described, and the same components as those in the first and fifth embodiments will be denoted by the same reference numerals and the description thereof will be omitted.
- the signal selection unit 19 is software installed in the microprocessor.
- the signal sorting unit 19 inputs the bioelectric signal Vsig before subtraction correction in the subtraction unit 18 and the bioelectric signal Vsig ′ after subtraction correction, and selects one of the signals to generate an electrocardiogram Output to part 4.
- FIG. 24 is a flowchart showing a process flow of the signal selection unit 19.
- step S11 the root mean square (RMS (Vsig)) of the bioelectric signal Vsig before subtraction correction in the subtraction unit 18, and the root mean square (RMS (Vsig ′) of the bioelectric signal Vsig ′ after subtraction correction )).
- the root mean square of the bioelectric signal received for a predetermined time or a predetermined number of times is calculated.
- step S12 it is determined whether RMS (Vsig ') is greater than RMS (Vsig) .When RMS (Vsig') is larger, the process proceeds to step S13, and when RMS (Vsig ') is smaller. The process ends. In step S13, Vsig is substituted as Vsig 'and the process is terminated. That is, the bioelectric signal Vsig before subtraction correction is input to the difference means 4.
- RMS (Vsig) and RMS (Vsig ′) indicate variations in the bioelectric signal Vsig before the subtraction correction and variations in the bioelectric signal Vsig ′ after the subtraction correction.
- the variation of the bioelectric signal is mainly caused by an artifact mixed in the bioelectric signal due to a change in the capacitance of the clothes when the occupant moves.
- the RMS (Vsig ') being larger than the RMS (Vsig) indicates that the movement of the occupant is small and the artifact is not mixed in the bioelectric signal Vsig before the subtraction correction.
- the setting accuracy of the reference signal Vref is low, and artifacts are mixed into the bioelectric signal by subtraction correction, indicating that the accuracy is low.
- RMS (Vsig ′) being equal to or lower than RMS (Vsig) indicates that artifacts are reduced by subtraction correction and the accuracy of the bioelectric signal is improved.
- the signal selection unit 19 in the signal selection unit 19, the voltage variation of the bioelectric signal Vsig ′ after the subtraction correction of the reference signal Vref (artifact) by the subtraction unit, and the bioelectric signal Vsig before the subtraction correction of the reference signal Vref The bioelectric signal having the smaller variation is selected by comparing with the variation of the voltage.
- Example 6 The effects of Example 6 will be described below.
- the voltage variation of the bioelectric signal after the artifact subtraction by the subtracting unit 18 (artifact removal means) is compared with the voltage variation of the bioelectric signal before the artifact subtraction.
- a signal sorting unit 19 for selecting an electrical signal is provided. Therefore, artifacts mixed in the bioelectric signal can be reduced and measurement accuracy can be increased.
- FIG. 25 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 according to the sixth embodiment is different from the bioelectric signal measurement circuit 1 according to the sixth embodiment in that a reliability information collection unit 20 is provided.
- the configuration different from the first and sixth embodiments will be mainly described, and the same configuration as the first and sixth embodiments will be denoted by the same reference numerals and the description thereof will be omitted.
- the reliability information collection unit 20 collects information on the variation of the bioelectric signal Vsig after the subtraction correction in the subtraction unit 18 for each electrode.
- the variation of the bioelectric signal Vsig can be obtained from the root mean square RMS (Vsig) of the bioelectric signal Vsig.
- the variation of the bioelectric signal is mainly caused by an artifact mixed in the bioelectric signal due to a change in the capacitance of the clothes when the occupant moves. After the subtraction correction is performed in the subtracting unit 18, the artifacts are removed due to the change in capacitance, and thus the variation in the bioelectric signal should be small. However, the variation in the bioelectric signal after subtraction correction may increase due to factors such as low setting accuracy of the reference signal Vref.
- the electrocardiogram generated from the bioelectric signal of the portion with large variation has low accuracy, and the electrocardiogram accuracy can be determined from the variation of the bioelectric signal.
- the reliability information collection unit 20 By collecting the accuracy of the electrocardiogram in the reliability information collection unit 20, it is possible to select the electrocardiogram in subsequent processing. For example, if the process requires an electrocardiogram with high accuracy, only an electrocardiogram with high accuracy may be selected and used. If the process requires a lot of data even if the accuracy is somewhat low, it is relatively low. An electrocardiogram may be used.
- the reliability information collecting unit 20 is provided for collecting information on the voltage variation of the bioelectric signal after the artifact subtraction by the subtracting unit 18 (artifact removing unit) of each electrode 2. Therefore, the reliability information of the electrocardiogram can be added together with the electrocardiogram and sent to subsequent processing.
- FIG. 26 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit 1 according to the eighth embodiment is different from the bioelectric signal measurement circuit 1 according to the seventh embodiment in that a correlation evaluation unit 27 is provided.
- a correlation evaluation unit 27 is provided in the seventh embodiment.
- configurations different from the first and seventh embodiments are mainly described, and the same configurations as the first and seventh embodiments are denoted by the same reference numerals and description thereof is omitted.
- the correlation evaluation unit 27 calculates the correlation between the reference signals Vref of each electrode 2.
- the calculated correlation information is collected by the reliability information collection unit 20.
- the correlation between the reference signals Vref may be obtained using a correlation function or the like.
- the electrocardiogram generation unit 4 takes the difference between the positive and negative bioelectric signals Vsig ′ to form an electrocardiogram. If the correlation between the positive-side reference signal Vref and the negative-side reference signal Vref is high, the ECG error after differential processing is small and a highly accurate ECG can be generated. On the other hand, if the correlation between the positive-side reference signal Vref and the negative-side reference signal Vref is low (especially in the case of inverse correlation), artifacts appear in the ECG after differential processing, and the ECG accuracy is low. Become.
- the reliability information collection unit 20 can also collect the reliability of the electrocardiogram based on the correlation of the reference signal Vref.
- Example 8 The effect of Example 8 will be described below.
- a correlation evaluation unit 27 for calculating the correlation of the reference signal Vref (artifact) calculated in the reference signal calculation unit 16 provided corresponding to the plurality of electrodes 2 is provided. Therefore, the reliability of the electrocardiogram can be calculated from the reference signal Vref, and the reliability information of the electrocardiogram can be added together with the electrocardiogram and sent to the subsequent processing.
- Example 9 Bioelectric signal measurement circuit
- the bioelectric signal measurement circuit 1 of the ninth embodiment is different from the bioelectric signal measurement circuit 1 of claim 1 in that an electrode selection unit 26 and a bioelectric signal switching unit 23 are provided.
- two electrodes, the positive electrode 2p and the negative electrode 2n, are provided as the electrode 2 in addition to the ground 2g, but the difference in Example 9 is that two or more electrodes are provided.
- the configuration different from that of the first embodiment is mainly described, and the same configuration as that of the first embodiment is denoted by the same reference numeral and the description thereof is omitted.
- FIG. 27 is a control block diagram of the bioelectric signal measurement circuit 1.
- the bioelectric signal measurement circuit inputs bioelectric signals of the human body from the electrodes 21, 22, ..., 2n and outputs them as an electrocardiogram.
- FIG. 28 is a schematic diagram of the vehicle seat 3.
- the electrode 2 is installed on the surface of the seat back 3a having the insulating property of the seat 3 and the seat cushion 3b.
- Electrode 2 is made of metal materials such as gold, silver, copper, and nichrome, carbon-based materials such as carbon and graphite, particulate materials composed of semiconductors such as metals and metal oxides, acetylene-based, complex 5-membered ring systems, phenylene-based, It consists of conductive materials such as conductive polymer materials such as aniline.
- the bioelectric signal measurement circuit 1 measures the bioelectric signal generated from the human body and the capacitance of the clothes worn by the occupant, and processes and outputs the input bioelectric signal, and a gain correction unit 5;
- a bioelectric signal measurement unit 24 that selects and measures the bioelectric signal output by each gain correction unit 5;
- the gain correction unit 5 is provided according to each of the electrodes 21, 22,..., 2n, but since the configuration is the same, the following description will be made without distinction.
- the gain correction unit 5 includes an impedance conversion unit 6, a reference signal mixing unit 7, a signal feedback unit 8, a signal separation unit 9, a capacitance measurement unit 10, a gain correction value calculation unit 11, and a bioelectric signal.
- a gain correction unit 12. The configuration of each part is the same as in the first embodiment.
- the bioelectric signal measurement unit 24 includes an electrocardiogram generation unit 4 that generates an electrocardiogram from the bioelectric signal, an electrode selection unit 26 that selects a bioelectric signal used in the electrocardiogram generation unit 4, and a circuit according to the selected bioelectric signal. And a bioelectric signal switching unit 23 for switching.
- the electrode selection unit 26 calculates the output gain of the impedance conversion unit 6 from the capacitance of the clothes calculated by the capacitance measurement unit 10 provided corresponding to each electrode 2.
- FIG. 7 is a map showing the output gain of the impedance converter 6 with respect to the capacitance of the clothes. The output gain is expressed as a ratio of the signal intensity output from the impedance converter 6 to the signal intensity of the bioelectric signal emitted from the human body.
- the electrode selection unit 26 selects the bioelectric signal having the highest output gain and the next highest bioelectric signal among the bioelectric signals having an output gain greater than a predetermined value.
- FIG. 29 is a graph showing frequency output gain characteristics for each capacitance of clothing. As shown in FIG. 29, the output gain increases as the capacitance increases.
- the electrode selection unit 26 selects from the electrodes 2 to which a bioelectric signal having an output gain greater than a predetermined value (for example, greater than ⁇ 20 [dB]) is input.
- a predetermined value for example, greater than ⁇ 20 [dB]
- the magnitude determination of the output gain may be performed by the output gain in the range of 10 to 40 [Hz] of the R wave frequency band of the electrocardiogram.
- the bioelectric signal switching unit 23 switches the circuit so that the bioelectric signal output from the bioelectric signal gain correction unit 12 corresponding to the bioelectric signal selected by the electrode selection unit 26 is input to the electrocardiogram generation unit 4.
- the electrocardiogram generation unit 4 inputs the bioelectric signal output from the bioelectric signal gain correction unit 12 corresponding to the selected electrode 2.
- the input bioelectric signal is subjected to filtering processing and amplification processing, respectively, and the difference between the processed positive signal and negative signal is taken as an electrocardiogram.
- Example 9 the capacitance of the clothes in contact with each electrode 2 is calculated, and the output gain of the impedance conversion unit 6 is calculated from the calculated capacitance. A bioelectric signal having an output gain larger than a predetermined value is detected. Thereby, since a bioelectric signal with a high output gain can be measured, measurement accuracy can be improved.
- the bioelectric signal having the largest output gain and the next largest bioelectric signal are measured. Therefore, since a bioelectric signal with a higher output gain can be measured, measurement accuracy can be improved.
- Example 9 The effect of Example 9 is described below.
- (11) From the impedance conversion unit 6 for the bioelectric signal generated by the biological composition from the plurality of electrodes 2 (input means) for inputting the bioelectric signal generated by the biological composition and the capacitance calculated by the capacitance measuring unit 10 A bioelectric signal measurement unit 24 (bioelectric measurement means) that calculates a bioelectric signal gain to be output and measures a bioelectric signal having a gain larger than a predetermined value is provided. Therefore, since a bioelectric signal with a high output gain can be measured, the measurement accuracy can be increased.
- the bioelectric signal measuring unit 24 measures the bioelectric signal having the largest gain and the next largest bioelectric signal among bioelectric signals having a gain greater than a predetermined value. Therefore, since a bioelectric signal having a higher output gain can be measured, the measurement accuracy can be increased.
- the bioelectric signal measuring unit 24 measures the bioelectric signal having the largest gain and the next largest bioelectric signal among bioelectric signals having a gain larger than a predetermined value.
- the bioelectric signal selection method is different. Since the configuration other than the bioelectric signal selection method is the same as that of the ninth embodiment, the description thereof is omitted.
- the bioelectric signal measuring unit 24 measures two bioelectric signals having the smallest gain difference among bioelectric signals having a gain larger than a predetermined value. Thereby, an error can be reduced when the ECG generation unit 4 performs difference processing, and measurement accuracy can be increased.
- the bioelectric signal measuring unit 24 measures two bioelectric signals having the smallest gain difference among bioelectric signals having a gain larger than a predetermined value. Therefore, the error can be reduced when performing the difference process, and the measurement accuracy can be increased.
- the bioelectric signal measuring unit 24 measures the bioelectric signal having the largest gain and the next largest bioelectric signal among bioelectric signals having a gain larger than a predetermined value.
- the selection method of the bioelectric signal is different. Since the configuration other than the bioelectric signal selection method is the same as that of the ninth embodiment, the description thereof is omitted.
- the bioelectric signal measuring unit 24 the bioelectric signal is measured in accordance with the first, second, and third inductions of the limb guidance among bioelectric signals having a gain greater than a predetermined value.
- Limb guidance is a method of observing bioelectric signals generated from the heart.
- the first lead attaches a + electrode on the left hand and a-electrode on the right hand.
- the second lead attaches a + electrode to the left foot and a-electrode to the right hand.
- the third lead attaches a + electrode to the left foot and a-electrode to the left hand.
- FIG. 30 shows an example of limb guidance.
- Example 11 since the electrodes are provided on the sheet 3, the electrodes cannot be directly attached to the left hand, the right hand, and the left foot, but the limb guidance is realized by using the electrodes closest to the respective positions. Of the limb leads, the waveform is most clearly depicted in the second lead, followed by the first lead and finally the third lead.
- the bioelectric signal corresponding to the second induction is selected and measured.
- the bioelectric signal corresponding to the first induction is selected and measured.
- the bioelectric signal corresponding to the third lead is selected and measured.
- the bioelectric signal measurement unit 24 is input from the bioelectric signal input from the electrode 2 closest to the left foot of the biocomposition and the electrode 2 closest to the right hand among the bioelectric signals having a gain greater than a predetermined value.
- the bioelectric signal input from the electrode 2 closest to the left hand of the biological composition and the closest to the right hand When the bioelectric signal input from the electrode 2 is measured (first induction) and the bioelectric signal cannot be measured by the first induction, the bioelectric signal input from the electrode 2 closest to the left foot of the biological composition, The bioelectric signal input from the electrode 2 closest to the left hand was measured (third induction). Therefore, measurement accuracy can be improved by using a bioelectric signal having a clearly drawn waveform.
- the bioelectric signal measuring unit 24 measures the bioelectric signal having the largest gain and the next largest bioelectric signal among bioelectric signals having a gain larger than a predetermined value.
- the bioelectric signal selection method is different. Since the configuration other than the bioelectric signal selection method is the same as that of the ninth embodiment, the description thereof is omitted.
- the bioelectric signal measuring unit 24 measures a bioelectric signal having the highest SN ratio and a bioelectric signal having the next highest SN ratio among bioelectric signals having a gain greater than a predetermined value. Thereby, the noise in the bioelectric signal to measure is small, and measurement accuracy can be improved.
- the bioelectric signal measuring unit 24 measures a bioelectric signal having the highest SN ratio and the next highest bioelectric signal among bioelectric signals having a gain greater than a predetermined value. Therefore, the noise in the bioelectric signal to be measured can be reduced, and the measurement accuracy can be increased.
- the bioelectric signal measuring unit 24 selects a bioelectric signal to be measured by each selection method from bioelectric signals having a gain greater than a predetermined value.
- the gain of the bioelectric signal being selected becomes smaller than a predetermined value by the selection method of the ninth to twelfth embodiments, another bioelectric signal is selected on the way. Since the configuration other than the bioelectric signal selection method is the same as that of the ninth embodiment, the description thereof is omitted.
- Example 13 the determination whether or not to select another bioelectric signal is not performed by directly using the change in gain, but the capacitance between the electrode 2 to which the bioelectric signal is input and the biological composition is used. This is done using the change.
- FIG. 31 is a graph showing an example of a change in capacitance between the electrode 2 and the biological composition.
- FIG. 31 shows a change in capacitance between an electrode (electrode A) and another electrode (electrode B) as an example and the biological composition.
- the bioelectric signal input by the electrode A is selected and measurement is performed.
- the time t when the electrostatic capacitance between the electrode A and the biological composition is less than or equal to the predetermined value is shorter than the predetermined time, the bioelectric signal input by the electrode A is continuously selected. That the electrostatic capacity is equal to or less than the predetermined value indicates that the gain of the bioelectric signal is equal to or less than the predetermined value described in the ninth embodiment.
- the bioelectricity inputted by another electrode B whose capacitance between the biological composition and the biological composition is greater than the predetermined value Select a signal.
- a new bioelectric signal may be selected based on each selection method described in the ninth to twelfth embodiments. Thereby, even when the gain temporarily decreases, the bioelectric signal can be stably measured without reselecting the bioelectric signal. On the other hand, when the gain is steadily decreasing, measurement accuracy can be improved by measuring other bioelectric signals.
- the bioelectric signal measurement unit 24 when the time during which the capacitance between the electrode 2 receiving the bioelectric signal used for measurement and the biocomposition is lower than a predetermined value is equal to or longer than a predetermined time The bioelectric signal input from another electrode 2 is measured. Therefore, even when the gain temporarily decreases, the bioelectric signal can be stably measured without reselecting the bioelectric signal. On the other hand, when the gain is steadily decreasing, measurement accuracy can be improved by measuring other bioelectric signals.
- Example 14 In Example 13, when the gain of the selected bioelectric signal is smaller than a predetermined value, another bioelectric signal is selected on the way. In Example 14, when another bioelectric signal is selected, the bioelectric signal whose output gain change amount is smaller than a predetermined value is selected. Since the configuration other than the bioelectric signal selection method is the same as that of the ninth embodiment, the description thereof is omitted.
- Example 14 the determination as to whether or not to select another bioelectric signal is not performed by directly using the amount of change in gain, but the electrostatic capacitance between the electrode 2 that receives the bioelectric signal and the biological composition is used. This is done using the amount of change in capacitance. That is, a history of changes in capacitance of clothes in contact with each electrode 2 is recorded, and a bioelectric signal input from the electrode 2 whose capacitance change amount is smaller than a predetermined value is selected. Thereby, possibility of re-selecting again can be made small, and a bioelectric signal can be measured stably.
- the bioelectric signal measurement unit 24 stores a history of changes in capacitance between the biological composition and each electrode 2, and is input from another electrode 2 in which the change in capacitance is smaller than a predetermined value. The measured bioelectric signal was measured. Therefore, the possibility of re-selection can be reduced, and the bioelectric signal can be stably measured.
- Example 15 In Example 14, the history of capacitance change was recorded. In Example 15, the behavior of the occupant (or the clothes worn by the occupant) was estimated, and the change in capacitance was estimated from the estimated behavior.
- FIG. 32 is a control block diagram of the bioelectric signal measurement circuit 1.
- an external information unit 25 is connected to the electrode selection unit. From the external information unit 25, accelerator pedal operation information, brake pedal operation information, steering wheel steering information, vehicle behavior control device, information from a navigation system, and the like are input by CAN communication.
- the behavior of the vehicle is estimated from an accelerator pedal operation, a brake pedal operation, a vehicle behavior control device, and the like, and the behavior of the occupant (clothing) accompanying the change in the behavior of the vehicle is estimated.
- the behavior of the vehicle is estimated using information from the navigation system, and the behavior of the occupant (clothing) accompanying the change in the behavior of the vehicle is estimated. Thereby, possibility of re-selecting again can be made small, and a bioelectric signal can be measured stably.
- Example 15 The effects of Example 15 will be described below.
- An external information unit 25 (behavior estimation means) for estimating the behavior of the occupant (biological composition) is provided, and the bioelectric signal measurement unit 24 estimates and estimates the change in capacitance from the occupant behavior.
- a bioelectric signal input from another electrode 2 having a capacitance change amount smaller than a predetermined value is measured. Therefore, the possibility of re-selection can be reduced, and the bioelectric signal can be stably measured.
- the external information unit 25 estimates the occupant's behavior using information from the navigation system. Therefore, the possibility of re-selection can be reduced, and the bioelectric signal can be stably measured.
- the external information unit 25 estimates the occupant's behavior using the operation information for operating the vehicle. Therefore, the possibility of re-selection can be reduced, and the bioelectric signal can be stably measured.
- the present invention is not limited to the configuration of the above embodiment, and may have other configurations.
- the signal strength calculation of the reference signal in step S1 of the first embodiment is implemented as software, but may be configured from an analog circuit that can perform the same processing using a detection circuit or the like.
- the capacitance measuring unit 10 is configured by software installed in a microprocessor, but may be configured by an analog circuit.
- the reference signal strength changing unit 14 is configured by a switch circuit, but the magnitude of the signal strength itself of the input reference signal may be changed.
- the flattening function unit 7a of the third embodiment may be applied to the reference signal mixing unit 7 of the second embodiment.
- a capacitor may be provided in series with the resistors R11 and R1.
- the switch SW of the resonance suppression unit 15 switches between a circuit that passes through the capacitor Cin and a circuit that does not pass through the capacitor Cin.
- a plurality of capacitors Cin having different capacities may be provided and switched between two or more stages.
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Abstract
Description
本発明は、上記問題に着目されたもので、その目的とするところは、生体組成と、生体組成が発する生体電気信号を入力する入力手段との間の静電容量を正確に検出し、検出した静電容量に基づいて生体電気信号の利得補正をすることができる生体電気信号計測回路を提供することである。
2 電極(入力手段)
3 シート
6 インピーダンス変換部
7 基準信号混合部
7a 平坦化機能部
8 信号帰還部
9 信号分離部
10 静電容量計測部
11 利得補正値演算部
12 生体電気信号利得補正部
13 基準信号強度設定値演算部
14 基準信号強度変更部
16 参照信号演算部(アーチファクト算出手段)
18 減算部(アーチファクト除去手段)
19 信号選別部
20 信頼性情報収集部
24 生体電気信号計測部(生体電気計測手段)
25 外部情報源(挙動推定手段)
27 相関性評価部
[生体電気信号計測用回路]
図1は生体電気信号計測用回路1の制御ブロック図である。生体電気信号計測用回路1は、正電極2p、負電極2nから人体の生体電気信号を入力し、心電図として出力する。
図3は、インピーダンス変換部6、基準信号混合部7、信号帰還部8の回路図である。
インピーダンス変換部6は、電極2に入力された生体電気信号を検出する。インピーダンス変換部6は、図3に示すように、オペアンプからなるボルテージフォロア回路から構成されている。
基準信号混合部7は、インピーダンス変換部6の出力と、乗員が着用している衣服の静電容量を計測するための基準信号とを混合させて出力する。
信号帰還部8は、基準信号混合部7の出力側に接続されている。信号帰還部8は、図3に示すようにブートストラップ回路により構成されている。信号帰還部8の出力は、インピーダンス変換部6の入力側に帰還されている。
信号分離部9は、生体電気信号である心電図のR波の周波数帯10~40[Hz]を取り出すバンドパスフィルタ回路と、R波以外の周波数帯を取り出すバンドパスフィルタ回路とから構成されている。これにより、生体電気信号と基準信号とを分離することができる。
静電容量計測部10および利得補正値演算部11は、A/D変換器を有するマイクロプロセッサに搭載されたソフトウェアである。
図4は処理の流れを示すフローチャートである。ステップS1,S2は静電容量計測部10の処理、ステップS3,S4は利得補正値演算部11の処理である。
ステップS4では、算出した出力利得に応じて利得補正値を算出する。
生体電気信号利得補正部12は、信号分離部9から入力した生体電気信号の利得を、利得補正値演算部11から入力した利得補正値により補正を行う。生体電気信号利得補正部12は、入力した信号を任意の倍率に設定できる増幅回路や減衰回路を組み合わせて構成している。
心電図生成部4は、利得補正部5から利得補正後の生体電気信号を入力する。正側と負側の生体電気信号をそれぞれフィルタリング処理および増幅処理を行い、処理後の正側の信号と負側の信号との差分を取って心電図としている。
乗員は衣服を着用した状態でシート3に着座するため、電極2と人体との間に静電容量(Cp,Cn)を有する衣服が介在することとなる。衣服の静電容量は、衣服の材質、体積、外部からの圧力といった要因により変化する。生体電気信号の利得は静電容量に応じて変化するため、静電容量を正しく検出できなければ利得補正を正確に行うことができない。また、正側の静電容量Cpと負側の静電容量Cnとが異なると、心電図生成部4において各処理後の正側の信号と負側の信号との差分を取ったのちの信号は誤差を含むこととなる。
(1) 乗員(生体組成)が発する生体電気信号を入力する電極2(入力手段)と、電極2が入力した生体電気信号をインピーダンス変換するインピーダンス変換部6と、インピーダンス変換部6の出力信号と、乗員と電極2との間(衣服)の静電容量を計測するための基準信号とを混合させる基準信号混合部7と、基準信号混合部7の出力信号を、インピーダンス変換部6に帰還させる信号帰還部8と、インピーダンス変換部6の出力信号から、生体電気信号と基準信号とを分離する信号分離部9と、信号分離部9から入力した基準信号の強度から、静電容量を算出する静電容量計測部10と、静電容量計測部10が算出した静電容量に基づいて、生体電気信号の利得補正値を演算する利得補正値演算部11と、利得補正値に基づいて生体電気信号の利得補正を行う生体電気信号利得補正部12と、を有するようにした。
よって、乗員が着用している衣服の静電容量を正確に求めることができ、静電容量に応じて変化する生体電気信号の利得を所定値に補正することができる。したがって、生体電気信号から正確な心電図を得ることができる。
よって、車両に乗車中の乗員の生体電気信号を常に計測することができる。
[生体電気信号計測用回路]
図10は生体電気信号計測用回路1の制御ブロック図である。実施例2の生体電気信号計測用回路1は、実施例1の生体電気信号計測用回路1に対して、基準信号強度設定値演算部13と、基準信号強度変更部14を設けた点、また静電容量計測部10の処理の内容が異なる。実施例2では実施例1と相違する構成について中心に記載し、実施例1と同じ構成については同一の符号を付して説明を省略する。
図11は、インピーダンス変換部6、基準信号混合部7、信号帰還部8および基準信号強度変更部14の回路図である。インピーダンス変換部6、基準信号混合部7、信号帰還部8は、実施例1の図3で示す回路とほぼ同じである。ただし、基準信号混合部7の基準信号を入力する端子が二つ設けられており、それぞれの端子の抵抗が異なっている。すなわち、一方の端子側の抵抗R11は10[kΩ]であり、他方の端子側の抵抗R1は1[kΩ]である。
基準信号強度変更部14は、基準信号を基準信号混合部7のどちらの入力端子に入力するかを選択するスイッチ回路である。どちらの入力端子を選択するかは、後述する基準信号強度設定値演算部13で求めた強度設定値に応じて決定する。
基準信号強度設定値演算部13は信号分離部9から基準信号を入力し、入力した基準信号の信号強度に応じて、基準信号混合部7に入力する基準信号の信号強度を設定する(強度設定値)。
ステップS16では、実施例1と同様に利得補正値を演算する。
静電容量計測部10に入力される基準信号の信号強度が小さいとA/D変換後の分解能が悪化し、静電容量の計測精度が劣化する。一方、信号強度が大きいとA/D変換器の入力範囲を超えてしまい、静電容量の計測が行えなくなる。
(3) 信号分離部9から入力した基準信号の強度から、基準信号混合部7に入力する基準信号の強度を設定する基準信号強度設定値演算部13と、基準信号強度設定値演算部13が設定した基準信号の強度に応じて、基準信号混合部7に入力する基準信号の強度を変更する基準信号強度変更部14と、を有し、静電容量計測部10は、信号分離部9から入力した基準信号の強度と、基準信号強度設定値演算部13が設定した基準信号の強度と、から静電容量を算出するようにした。
よって、静電容量計測部10に入力される基準信号の信号強度を適切に設定することができ、静電容量を高精度に計測することができる。
よって、簡単な構成で基準信号混合部7に入力する基準信号の信号強度を変更することができる。
[生体電気信号計測用回路]
実施例3の生体電気信号計測用回路1は、請求項1の生体電気信号計測用回路1に対して、基準信号混合部7の構成が一部異なる。実施例3では実施例1と相違する構成について中心に記載し、実施例1と同じ構成については同一の符号を付して説明を省略する。
図14は、インピーダンス変換部6、基準信号混合部7、信号帰還部8の回路図である。基準信号混合部7は、基準信号の入力部に平坦化機能部7aを設けた。平坦化機能部7aは図14に示すように、抵抗R11とコンデンサC1とを直列に接続したRC直列回路である。
図15は、平坦化機能部7aを設けていないときの基準信号の周波数に対するインピーダンス変換部6から出力される基準信号の利得特性を示す図である。温度特性や個体特性のバラツキにより基準信号の周波数が所望する値からずれていたときには、図15に示すようにインピーダンス変換部6から出力される基準信号の利得にもずれが生じる。
(5) 基準信号混合部7は、インピーダンス変換部6から出力される基準信号の利得の特性が、基準信号の周波数変化に対して平坦化するように設定した平坦化機能部7aを有するようにした。
よって、基準信号の利得特性が基準信号の周波数変化に対して平坦化するため、基準信号の周波数が所望の値から多少ずれたとしても利得の変化を小さくでき、静電容量を高精度に計測することができる。
[生体電気信号計測用回路]
実施例4の生体電気信号計測用回路1は、請求項1の生体電気信号計測用回路1に対して、信号帰還部8の構成が一部異なる。また実施例4では、共振抑制部15を設けた。実施例4では実施例1と相違する構成について中心に記載し、実施例1と同じ構成については同一の符号を付して説明を省略する。
図17はインピーダンス変換部6、基準信号混合部7、信号帰還部8、共振抑制部15の回路図である。
共振抑制部15は、コンデンサCinとスイッチSWとから構成されている。スイッチSWは静電容量計測部10が算出した基準信号強度に応じて、コンデンサCinを経由する回路とコンデンサCinを経由しない回路とを切り換える。基準信号強度により乗員が着用している衣服の静電容量が大きいと判断されたときにはコンデンサCinを経由する回路が選択される。また、衣服の静電容量が小さいと判断されたときにはコンデンサCinを経由しない回路が選択される。
安定的な生体電気信号の計測を行うためには大型なリード線型の抵抗器やコンデンサを用いて電子回路を構成することが必要である。一方、装置の小型化や低コスト化を実現するためにリード線型の抵抗器やコンデンサに代えてチップ型の部品を使うことが考えられる。しかし、チップ型の部品の場合、耐圧特性や寸法の制約から抵抗値や静電容量がリード線型のものよりも小さい。そのため、周波数利得特性に共振点が生じてしまい、特に振動が発生する環境化において生体電気信号を計測する場合、計測が不安定になる問題があった。
実施例4の効果を以下に述べる。
(6) 信号帰還部8は、インピーダンス変換部6の入力端子とグラウンドとを接続する回路内に直列に接続された二つの抵抗器R2,R3と、二つの抵抗器R2,R3の間と基準信号混合部7の出力端子とを接続する回路内に直列に接続されたコンデンサC2および抵抗器R4とを有し、静電容量計測部10が計測した静電容量が所定値よりも大きいときに、電極2とインピーダンス変換部6の入力端子との間にコンデンサCinを直列に設けた。
よって、衣服の静電容量の高低に関わらず、高い値で安定的な周波数利得特性を得ることができ、振動環境下においても安定的に生体電気信号の計測を行うことができる。
[生体電気信号計測用回路]
実施例5の生体電気信号計測用回路1は、請求項1の生体電気信号計測用回路1に対して、参照信号演算部16、フィルタ/増幅部17、減算部18を設けた点で異なる。実施例5では実施例1と相違する構成について中心に記載し、実施例1と同じ構成については同一の符号を付して説明を省略する。
図21は処理の流れを示すフローチャートである。ステップS1,S2は静電容量計測部10の処理、ステップS3,S4は利得補正値演算部11、ステップS5は参照信号演算部16の処理である。
ステップS1~ステップS4の処理は、実施例1で図4を用いて説明したものを同じであるため、説明を省略する。
フィルタ/増幅部17は、生体電気信号をそれぞれフィルタリング処理および増幅処理を行い、心電図計測に適切な信号とする。フィルタ/増幅部17は、汎用アナログICより構成された電子回路として実現できる。そしてマイクロプロセッサに接続されたA/D変換器においてデジタル信号に変換される(生体電気信号Vsig)。
減算部18では、フィルタ/増幅部17から出力された生体電気信号(電圧)Vsigから参照信号(電圧)Vrefを減算して、減算後の信号を生体電気信号(電圧)Vsig'として出力する。なお、減算部18では、参照信号Vref'を用いて生体電気信号Vsigを減算するときの誤差ΔV=RMS(Vsig-Vref)が最小となるように参照信号Vrefを決定する。参照信号Vref=α・Vref'としてαが決定される。ここでRMSは二乗平均平方根を示す。
心電図生成部4は、減算部18からの生体電気信号Vsig'を入力する。正側と負側の生体電気信号Vsig'の差分を取って心電図としている。実施例1では心電図生成部4において、フィルタリング処理および増幅処理も行っていた。実施例5ではフィルタリング処理および増幅処理は、フィルタ/増幅部17において行われているため、心電図生成部4ではフィルタリング処理および増幅処理を行っていない。
乗員は衣服を着用した状態でシート3に着座するため、電極2と人体との間に静電容量(Cp,Cn)を有する衣服が介在することとなる。衣服の静電容量は、衣服の材質、体積、外部からの圧力といった要因により変化する。つまり、車両の振動等により乗員が動くと衣服の静電容量も変化する。静電容量が変化するたびに電荷の移動が発生するため、生体電気信号に電荷の移動によるノイズが発生することとなる。このノイズをアーチファクトと称する。アーチファクトとは、生体電気信号に混入する生体電気信号以外の信号を総称したものである。アーチファクトが混入すると心電図を正確に計測することができない。
実施例5の効果を以下に説明する。
(7) 静電容量計測部10が算出した静電容量の変化から電極2において生体電気信号に重畳するアーチファクトを算出する参照信号演算部16(アーチファクト算出手段)と、信号分離部9が出力した生体電気信号から、算出したアーチファクトを減算する減算部18(アーチファクト除去手段)と、を設けた。
よって、衣服の静電容量の変化による生体電気信号へ混入したアーチファクトを除去することができ、計測精度を高めることができる。
[生体電気信号計測用回路]
図23は生体電気信号計測用回路1の制御ブロック図である。実施例6の生体電気信号計測用回路1は、実施例5の生体電気信号計測用回路1に対して、信号選別部19を設けた点が異なる。実施例6では実施例1および実施例5と相違する構成について中心に記載し、実施例1および実施例5と同じ構成については同一の符号を付して説明を省略する。
信号選別部19はマイクロプロセッサに搭載されたソフトウェアである。信号選別部19は、減算部18において減算補正される前の生体電気信号Vsigと、減算補正された後の生体電気信号Vsig'とを入力して、どちらか一方の信号を選択して心電図生成部4に出力する。
ステップS11では、減算部18において減算補正される前の生体電気信号Vsigの二乗平均平方根(RMS(Vsig))と、減算補正された後の生体電気信号Vsig'の二乗平均平方根(RMS(Vsig'))とを算出する。なお、所定時間または所定回数受信した生体電気信号の二乗平均平方根を算出する。
ステップS13では、Vsig'としてVsigを代入して処理を終了する。すなわち、差分手段4には減算補正される前の生体電気信号Vsigが入力される。
RMS(Vsig)とRMS(Vsig')は、それぞれ減算補正される前の生体電気信号Vsigのばらつき、減算補正された後の生体電気信号Vsig'のばらつきを示す。生体電気信号のばらつきは、主に乗員が動くときの衣服の静電容量の変化により生体電気信号に混入するアーチファクトが原因となる。
これにより、生体電気信号に混入するアーチファクトを低減し、計測精度を高めることができる。
実施例6の効果について、以下に説明する。
(8) 減算部18(アーチファクト除去手段)によるアーチファクトの減算後の生体電気信号の電圧のばらつきと、アーチファクトの減算前の前記生体電気信号の電圧のばらつきとを比較し、ばらつきが小さい方の生体電気信号を選択する信号選別部19を設けた。
よって、生体電気信号に混入するアーチファクトを低減し、計測精度を高めることができる。
[生体電気信号計測用回路]
図25は生体電気信号計測用回路1の制御ブロック図である。実施例6の生体電気信号計測用回路1は、実施例6の生体電気信号計測用回路1に対して、信頼性情報収集部20を設けた点が異なる。実施例7では実施例1および実施例6と相違する構成について中心に記載し、実施例1および実施例6と同じ構成については同一の符号を付して説明を省略する。
信頼性情報収集部20は、減算部18において減算補正された後の生体電気信号Vsigのばらつきの情報を各電極毎に収集する。生体電気信号Vsigのばらつきは、生体電気信号Vsigの二乗平均平方根RMS(Vsig)により求めることができる。
生体電気信号のばらつきは、主に乗員が動くときの衣服の静電容量の変化により生体電気信号に混入するアーチファクトが原因となる。減算部18において減算補正された後は、静電容量の変化によりアーチファクトが除去されているため、生体電気信号のばらつきは小さいはずである。しかし、参照信号Vrefの設定精度が低いなどの要因により減算補正後の生体電気信号のばらつきが大きくなることがある。
実施例7の効果について以下に説明する。
(9) 各電極2の減算部18(アーチファクト除去手段)によるアーチファクトの減算後の生体電気信号の電圧のばらつきの情報を収集する信頼性情報収集部20を設けた。
よって、心電図とともにその心電図の信頼性の情報を付加して後続の処理に送ることができる。
[生体電気信号計測用回路]
図26は生体電気信号計測用回路1の制御ブロック図である。実施例8の生体電気信号計測用回路1は、実施例7の生体電気信号計測用回路1に対して、相関性評価部27を設けた点が異なる。実施例7では実施例1および実施例7と相違する構成について中心に記載し、実施例1および実施例7と同じ構成については同一の符号を付して説明を省略する。
相関性評価部27は、各電極2の参照信号Vref同士の相関性を算出する。算出した相関性の情報は、信頼性情報収集部20において収集される。参照信号Vref同士の相関性は、相関関数などを用いて求めれば良い。
心電図生成部4では正側と負側の生体電気信号Vsig'の差分を取って心電図としている。正側の参照信号Vrefと負側の参照信号Vrefとの相関が高ければ差分処理後の心電図の誤差は小さく高精度な心電図を生成できる。一方、正側の参照信号Vrefと負側の参照信号Vrefとの相関が低ければ(特に逆相関のときは)、差分処理後の心電図にはアーチファクトが強調されて現れるため、心電図の精度は低くなる。
信頼性情報収集部20では、参照信号Vrefの相関による心電図の信頼性も収集することができる。
実施例8の効果について以下に説明する。
(10) 複数の電極2に対応して設けた参照信号演算部16において算出した参照信号Vref(アーチファクト)の相関性を算出する相関性評価部27を設けた。
よって、参照信号Vrefから心電図の信頼性を算出し、心電図とともにその心電図の信頼性の情報を付加して後続の処理に送ることができる。
[生体電気信号計測用回路]
実施例9の生体電気信号計測用回路1は、請求項1の生体電気信号計測用回路1に対して、電極選択部26、生体電気信号切替部23を設けた点で異なる。また、実施例1では電極2としてグランド2gの他に正電極2p、負電極2nの2つの電極を設けていたが、実施例9では2つ以上の電極を設けた点で異なる。実施例9では実施例1と相違する構成について中心に記載し、実施例1と同じ構成については同一の符号を付して説明を省略する。
利得補正部5は各電極21,22,…,2nに応じて設けられているが、構成は同じであるため、以下では区別せずに説明する。
利得補正部5は、インピーダンス変換部6と、基準信号混合部7と、信号帰還部8と、信号分離部9と、静電容量計測部10と、利得補正値演算部11と、生体電気信号利得補正部12とを有している。各部の構成は実施例1と同様である。
生体電気信号計測部24は、生体電気信号から心電図を生成する心電図生成部4と、心電図生成部4で用いる生体電気信号を選択する電極選択部26と、選択した生体電気信号に応じて回路を切り換える生体電気信号切替部23とを有している。
電極選択部26は、各電極2に対応して設けた静電容量計測部10が算出した衣服の静電容量からインピーダンス変換部6の出力利得を算出する。図7は、衣服の静電容量に対するインピーダンス変換部6の出力利得を示すマップである。出力利得は、人体から発する生体電気信号の信号強度に対するインピーダンス変換部6から出力される信号強度の比として表わされる。
生体電気信号切替部23は、電極選択部26により選択された生体電気信号に対応する生体電気信号利得補正部12から出力された生体電気信号を心電図生成部4に入力するように回路を切り換える。
心電図生成部4は、選択された電極2に対応する生体電気信号利得補正部12から出力された生体電気信号を入力する。入力された生体電気信号をそれぞれフィルタリング処理および増幅処理を行い、処理後の正側の信号と負側の信号との差分を取って心電図としている。
乗員は衣服を着用した状態でシート3に着座するため、電極2と人体との間に静電容量(C1,C2,…,Cn)を有する衣服が介在することとなる。衣服の静電容量は、乗員の着座姿勢によって各電極2と接触している衣服の静電容量は異なる。
衣服の静電容量が小さいと、人体(生体組成)が発している生体電気信号に対して、インピーダンス変換部6から出力される生体電気信号の利得が小さくなる。利得が小さくなりすぎると生体電気信号の計測精度が悪化する恐れがあった。
これにより、出力利得の高い生体電気信号を計測することができるため、計測精度を高めることができる。
これにより、出力利得がより高い生体電気信号を計測することができるため、計測精度を高めることができる。
実施例9の効果を以下に記載する。
(11) 生体組成が発する生体電気信号を入力する複数の電極2(入力手段)と、静電容量計測部10が算出した静電容量から、生体組成が発する生体電気信号に対するインピーダンス変換部6から出力される生体電気信号の利得を計算し、利得が所定値よりも大きい生体電気信号を計測する生体電気信号計測部24(生体電気計測手段)と、を設けた。
よって、出力利得の高い生体電気信号を計測することができるため、計測精度を高めることができる。
よって、出力利得がより高い生体電気信号を計測することができるため、計測精度を高めることができる。
実施例9では、生体電気信号計測部24において、利得が所定値よりも大きい生体電気信号のうち、利得が最も大きい生体電気信号と次に大きい生体電気信号を計測するようにした。実施例10では、生体電気信号の選択方法が異なる。生体電気信号の選択方法以外の構成は実施例9と同じであるため、説明は省略する。
生体電気信号計測部24において、利得が所定値よりも大きい生体電気信号のうち、利得差が最も小さい二つの生体電気信号を計測するようにした。
これにより、心電図生成部4において差分処理を行う際に誤差を小さくすることができ、計測精度を高めることができる。
実施例10の効果について以下に記載する。
(13) 生体電気信号計測部24は、利得が所定値よりも大きい生体電気信号のうち、最も利得差が小さい二つの生体電気信号を計測するようにした。
よって、差分処理を行う際に誤差を小さくすることができ、計測精度を高めることができる。
実施例9では、生体電気信号計測部24において、利得が所定値よりも大きい生体電気信号のうち、利得が最も大きい生体電気信号と次に大きい生体電気信号を計測するようにした。実施例11では、生体電気信号の選択方法が異なる。生体電気信号の選択方法以外の構成は実施例9と同じであるため、説明は省略する。
これにより、明瞭に描かれる波形の生体電気信号を用いることにより計測精度を高めることができる。
実施例11の効果について以下に述べる。
(14) 生体電気信号計測部24は、利得が所定値よりも大きい生体電気信号のうち、生体組成の左足に最も近い電極2から入力された生体電気信号と、右手に最も近い電極2から入力された生体電気信号を計測(第二誘導)し、第二誘導による生体電気信号の計測が行えないときには、生体組成の左手に最も近い電極2から入力された生体電気信号と、右手に最も近い電極2から入力された生体電気信号を計測(第一誘導)し、第一誘導による生体電気信号の計測が行えないときには、生体組成の左足に最も近い電極2から入力された生体電気信号と、左手に最も近い電極2から入力された生体電気信号を計測(第三誘導)するようにした。
よって、明瞭に描かれる波形の生体電気信号を用いることにより計測精度を高めることができる。
実施例9では、生体電気信号計測部24において、利得が所定値よりも大きい生体電気信号のうち、利得が最も大きい生体電気信号と次に大きい生体電気信号を計測するようにした。実施例12では、生体電気信号の選択方法が異なる。生体電気信号の選択方法以外の構成は実施例9と同じであるため、説明は省略する。
実施例12の効果について以下に述べる。
(15) 生体電気信号計測部24は、利得が所定値よりも大きい生体電気信号のうち、SN比が最も高い生体電気信号と次に高い生体電気信号を計測するようにした。
よって、計測する生体電気信号内のノイズが小さくでき、計測精度を高めることができる。
実施例9から実施例12では、生体電気信号計測部24において、利得が所定値よりも大きい生体電気信号の中からそれぞれの選択方法によって計測する生体電気信号を選択していた。実施例13では、実施例9から実施例12の選択方法により選択中の生体電気信号の利得が所定値より小さくなったときには、途中で別の生体電気信号を選択するようにした。生体電気信号の選択方法以外の構成は実施例9と同じであるため、説明は省略する。
これにより、利得が一時的に低下したときにも生体電気信号を選択し直すことがなく、安定して生体電気信号を計測することができる。一方、利得が定常的に低下しているときには、他の生体電気信号を計測することで計測精度を高めることができる。
実施例13の効果について説明する。
(16) 生体電気信号計測部24は、計測に用いている生体電気信号を入力している電極2と生体組成との間の静電容量が所定値を下回る時間が所定時間以上となったときには、別の電極2から入力された生体電気信号を計測するようにした。
よって、利得が一時的に低下したときにも生体電気信号を選択し直すことがなく、安定して生体電気信号を計測することができる。一方、利得が定常的に低下しているときには、他の生体電気信号を計測することで計測精度を高めることができる。
実施例13では、選択中の生体電気信号の利得が所定値より小さくなったときには、途中で別の生体電気信号を選択するようにした。実施例14では、別の生体電気信号を選択する際に、生体電気信号の出力利得変化量が所定値よりも小さいものを選択するようにした。生体電気信号の選択方法以外の構成は実施例9と同じであるため、説明は省略する。
これにより、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
実施例14の効果について以下に説明する。
(17) 生体電気信号計測部24は、生体組成と各電極2との間の静電容量の変化の履歴を記憶し、静電容量の変化量が所定値よりも小さい別の電極2から入力された生体電気信号を計測するようにした。
よって、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
実施例14では静電容量の変化の履歴を記録していた。実施例15では乗員(または乗員が着用している衣服)の挙動を推定して、推定した挙動から静電容量の変化を推定するようにした。
これにより、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
実施例15の効果について以下に説明する。
(18) 乗員(生体組成)の挙動を推定する外部情報部25(挙動推定手段)を設け、生体電気信号計測部24は、推定し乗員の挙動から静電容量の変化を推定し、推定した静電容量の変化量が所定値よりも小さい別の電極2から入力された生体電気信号を計測するようにした。
よって、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
よって、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
よって、再び選択をし直す可能性を小さくすることができ、安定して生体電気信号を計測することができる。
以上、本発明は上記実施例の構成に限らず、他の構成であっても構わない。
例えば、実施例1のステップS1の基準信号の信号強度算出もソフトウェアとして実装しているが、検波回路などを用いて同様な処理を行えるアナログ回路から構成しても良い。
実施例2では基準信号強度変更部14をスイッチ回路により構成したが、入力する基準信号の信号強度自体の大きさを変えるようにしても良い。
また実施例3の平坦化機能部7aを実施例2の基準信号混合部7に適用するようにしても良い。その場合、抵抗R11,R1に直列にコンデンサを設ければ良い。
例えば、実施例4では、共振抑制部15のスイッチSWは、コンデンサCinを経由する回路とコンデンサCinを経由しない回路とを切り換えるようにしている。しかし、容量の異なるコンデンサCinを複数設けて二段階以上に切り換えるようにしても良い。
Claims (20)
- 生体組成が発する生体電気信号を入力する入力手段と、
前記入力手段が入力した生体電気信号をインピーダンス変換するインピーダンス変換手段と、
前記インピーダンス変換手段の出力信号と、前記生体組成と前記入力手段との間の静電容量を計測するための基準信号とを混合させる基準信号混合手段と、
前記基準信号混合手段の出力信号を、前記インピーダンス変換手段に帰還させる信号帰還手段と、
前記インピーダンス変換手段の出力信号から、前記生体電気信号と前記基準信号とを分離する信号分離手段と、
前記信号分離手段から入力した前記基準信号の強度から、前記静電容量を算出する静電容量計測手段と、
に基づいて、前記生体電気信号の利得補正値を演算する利得補正値演算手段と、
前記利得補正値に基づいて前記生体電気信号の利得補正を行う生体電気信号利得補正手段と、
を有することを特徴とする生体電気信号計測用回路。 - 請求項1に記載の生体電気信号計測用回路において、
前記信号分離手段から入力した前記基準信号の強度から、前記基準信号混合手段に入力する前記基準信号の強度を設定する基準信号強度設定値演算手段と、
前記基準信号強度設定値演算手段が設定した前記基準信号の強度に応じて、前記基準信号混合手段に入力する前記基準信号の強度を変更する基準信号強度変更手段と、
を有し、
前記静電容量計測手段は、前記信号分離手段から入力した前記基準信号の強度と、前記基準信号強度設定値演算手段が設定した前記基準信号の強度と、から前記静電容量を算出することを特徴とする生体電気信号計測用回路。 - 請求項2に記載の生体電気信号計測用回路において、
前記基準信号強度変更手段は、前記基準信号混合手段に入力する前記基準信号の強度を、前記基準信号混合手段内の電子回路の定数を変更することで行うことを特徴とする生体電気信号計測用回路。 - 請求項1ないし請求項3のいずれか1項に記載の生体電気信号計測用回路において、
前記基準信号混合手段は、前記インピーダンス変換手段から出力される前記基準信号の利得の特性が、前記基準信号の周波数変化に対して平坦化するように設定した平坦化機能部を有することを特徴とする生体電気信号計測用回路。 - 請求項1ないし請求項4のいずれか1項に記載の生体電気信号計測用回路において、
前記信号帰還手段は、前記インピーダンス変換手段の入力端子とグラウンドとを接続する回路内に直列に接続された二つの抵抗器と、前記二つの抵抗器の間と前記基準信号混合手段の出力端子とを接続する回路内に直列に接続されたコンデンサおよび抵抗器とを有し、
静電容量計測手段が計測した前記静電容量が所定値よりも大きいときに、前記入力手段と前記インピーダンス変換手段の入力端子との間にコンデンサを直列に設けたことを特徴とする生体電気信号計測用回路。 - 請求項1ないし請求項5のいずれか1項に記載の生体電気信号計測用回路において、
前記静電容量計測手段が算出した前記静電容量の変化から前記入力手段において前記生体電気信号に重畳するアーチファクトを算出するアーチファクト算出手段と、
前記信号分離手段が出力した前記生体電気信号から、算出した前記アーチファクトを減算するアーチファクト除去手段と、
を設けたことを特徴とする生体電気信号計測用回路。 - 請求項6に記載の生体電気信号計測用回路において、
前記アーチファクト除去手段による前記アーチファクトの減算後の前記生体電気信号の電圧のばらつきと、前記アーチファクトの減算前の前記生体電気信号の電圧のばらつきとを比較し、ばらつきが小さい方の生体電気信号を選択する信号選択手段を設けたことを特徴とする生体電気信号計測用回路。 - 請求項6または請求項7に記載の生体電気信号計測用回路において、
各電極の前記アーチファクト除去手段による前記アーチファクトの減算後の前記生体電気信号の電圧のばらつきの情報を収集する信頼性情報収集手段を設けたことを特徴とする生体電気信号計測用回路。 - 請求項6ないし請求項8のいずれか1項に記載の生体電気信号計測用回路において、
複数の入力手段に対応して設けた前記アーチファクト算出手段において算出した前記アーチファクトの相関性を算出する相関性評価手段を設けたことを特徴とする生体電気信号計測用回路。 - 請求項1ないし請求項9のいずれか1項に記載の生体電気信号計測用回路において、
前記入力手段を複数備え、
前記静電容量計測手段が算出した前記静電容量から、前記生体組成が発する生体電気信号に対する前記インピーダンス変換手段から出力される生体電気信号の利得を計算し、前記利得が所定値よりも大きい生体電気信号を計測する生体電気計測手段を設けたことを特徴とする生体電気信号計測用回路。 - 請求項10に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、前記利得が所定値よりも大きい前記生体電気信号のうち、前記利得が最も大きい前記生体電気信号と次に大きい前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項10に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、前記利得が所定値よりも大きい前記生体電気信号のうち、最も利得差が小さい二つの前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項10に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、前記利得が所定値よりも大きい前記生体電気信号のうち、
前記生体組成の左足に最も近い前記入力手段から入力された前記生体電気信号と、右手に最も近い前記入力手段から入力された前記生体電気信号を計測(第二誘導)し、
前記第二誘導による前記生体電気信号の計測が行えないときには、前記生体組成の左手に最も近い前記入力手段から入力された前記生体電気信号と、右手に最も近い前記入力手段から入力された前記生体電気信号を計測(第一誘導)し、
前記第一誘導による前記生体電気信号の計測が行えないときには、前記生体組成の左足に最も近い前記入力手段から入力された前記生体電気信号と、左手に最も近い前記入力手段から入力された前記生体電気信号を計測(第三誘導)することを特徴とする生体電気信号計測用回路。 - 請求項10に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、前記利得が所定値よりも大きい前記生体電気信号のうち、SN比が最も高い前記生体電気信号と次に高い前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項10ないし請求項14のいずれか1項に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、計測に用いている前記生体電気信号を入力している前記入力手段と前記生体組成との間の前記静電容量が所定値を下回る時間が所定時間以上となったときには、別の前記入力手段から入力された前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項15に記載の生体電気信号計測用回路において、
前記生体電気計測手段は、前記生体組成と前記各入力手段との間の静電容量の変化の履歴を記憶し、前記静電容量の変化量が所定値よりも小さい前記別の入力手段から入力された前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項15に記載の生体電気信号計測用回路において、
前記生体組成の挙動を推定する挙動推定手段を設け、
前記生体電気計測手段は、推定した前記生体組成の前記挙動から前記静電容量の変化を推定し、推定した前記静電容量の変化量が所定値よりも小さい前記別の入力手段から入力された前記生体電気信号を計測することを特徴とする生体電気信号計測用回路。 - 請求項17に記載の生体電気信号計測用回路において、
前記挙動推定手段は、ナビゲーションシステムからの情報を用いて前記生体組成の挙動を推定することを特徴とする生体電気信号計測用回路。 - 請求項17に記載の生体電気信号計測用回路において、
前記挙動推定手段は、車両を操作する操作情報を用いて前記生体組成の挙動を推定することを特徴とする生体電気信号計測用回路。 - 請求項1ないし請求項19のいずれか1項に記載の生体電気信号計測用回路において、
前記入力手段を、車両のシートに設置したことを特徴とする生体電気信号計測用回路。
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JP2015539051A JP6025187B2 (ja) | 2013-09-25 | 2014-09-03 | 生体電気信号計測用回路 |
EP14848590.7A EP3050501A1 (en) | 2013-09-25 | 2014-09-03 | Circuit for measuring bioelectric signal |
US15/023,698 US20160228063A1 (en) | 2013-09-25 | 2014-09-03 | Circuit for measuring a bioelectric signal |
CN201480052731.9A CN105578956A (zh) | 2013-09-25 | 2014-09-03 | 生物电信号测量用电路 |
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CN104757962A (zh) * | 2015-04-13 | 2015-07-08 | 深圳市飞马与星月科技研究有限公司 | 心电检测电路的感抗调节电路及心电检测设备 |
JP2016214388A (ja) * | 2015-05-15 | 2016-12-22 | テイ・エス テック株式会社 | 車両用シート |
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JP2020058001A (ja) * | 2018-10-04 | 2020-04-09 | 株式会社豊田中央研究所 | バッファ回路 |
JP2021016404A (ja) * | 2019-07-17 | 2021-02-15 | 学校法人立命館 | 心電図計測システム |
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CN104757962A (zh) * | 2015-04-13 | 2015-07-08 | 深圳市飞马与星月科技研究有限公司 | 心电检测电路的感抗调节电路及心电检测设备 |
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US20160228063A1 (en) | 2016-08-11 |
CN105578956A (zh) | 2016-05-11 |
EP3050501A1 (en) | 2016-08-03 |
JP6025187B2 (ja) | 2016-11-16 |
JPWO2015045763A1 (ja) | 2017-03-09 |
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