JP2012040241A - Electrocardiographic complex measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrocardiographic complex measuring device capable of correctly measuring the electrocardiographic complex of an occupant in human body motion in a vehicle.SOLUTION: The device incudes: a first electrode 2 which directly contacts the surface of skin of an occupant of a vehicle; a second electrode which is attached to a seat 11 of the vehicle and contacts the surface of the skin of the occupant through clothing; and an electrocardiographic complex calculating device 4 which processes an electric signal detected by the first electrode 2 and an electric signal detected by the second electrode to calculate a cardiographic complex. The second electrode consists of two capacitive coupling type electrodes 30, 31 which are different in contact area contacting the occupant. The electrocardiographic complex calculating device 4 uses two cardiographic complexes are calculated on the basis of the electric signals detected by each of the two capacitive coupling type electrodes 30, 31 to remove noises due to the body motion of the occupant which have mixed into the cardiographic complex, and specifies the cardiographic complex of the occupant from which the body motion noises are removed.

Description

  The present invention relates to an electrocardiogram waveform measuring apparatus for measuring an electrocardiogram waveform of a vehicle occupant.

  In daily life, automobiles are one of the indispensable means of transportation. However, with the widespread use of automobiles, traffic accidents caused by automobiles are increasing. In particular, in recent years, an increase in traffic accidents due to driver's snoozing driving has become remarkable. Therefore, in order to prevent traffic accidents due to the driver's snoozing driving, the driver's biological information is detected by a sensor, and the driver's awakening level is estimated using the detected biological information, thereby driving the driver while driving. Attempts have been made to monitor the state of arousal.

  For example, it has been conventionally performed to measure a driver's electrocardiogram waveform using an electrode for measuring the driver's body potential and analyze the measured electrocardiogram waveform to estimate the driver's arousal level. For this reason, research is being conducted on techniques for measuring the electrocardiogram waveform of a driver in a vehicle.

  As an example of an apparatus for measuring an electrocardiogram waveform in a vehicle, for example, an electrode is formed on the steering wheel of the vehicle to detect the potential of the driver's hand, and a capacitively coupled electrode is attached to the vehicle seat to determine the potential of the driver's buttocks. An electrocardiogram measuring device that detects and measures an electrocardiogram waveform from these potential differences is known (see, for example, Patent Document 1). According to the electrocardiogram waveform measuring apparatus described in Patent Document 1, it is possible to continuously and accurately grasp the electrocardiogram waveform of the driver who is driving.

JP 2010-46310 A

  However, as a result of further investigations by the present inventors on the electrocardiogram waveform measuring apparatus described in Patent Document 1, when the driving driver moves when measuring the electrocardiogram waveform, the body movement of the driver is affected. It was found that the accompanying noise (body motion noise) may be mixed into the measured electrocardiogram waveform. By removing the influence of this body motion noise from the electrocardiogram waveform, the measured electrocardiogram waveform can be made more accurate. Therefore, the electrocardiogram waveform measuring apparatus described in Patent Document 1 has room for further improvement. There is.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide an electrocardiogram waveform measuring apparatus capable of more accurately measuring an electrocardiogram waveform of a vehicle occupant.

  The object of the present invention is to provide a first electrode that is in direct contact with the skin surface of a vehicle occupant, a second electrode that is attached to a vehicle seat and is in contact with the skin surface of the occupant through clothing, and the first electrode. Electrocardiogram waveform calculating means for calculating an electrocardiogram waveform by processing the electric signal detected by the electrode and the electric signal detected by the second electrode, wherein the second electrode has different surface areas 2. The electrocardiogram waveform calculating means comprises two electrocardiogram waveforms calculated based on the electric signals detected by the respective capacitively coupled electrodes, and detects the occupant's body movement mixed in the electrocardiogram waveform. This is achieved by an electrocardiogram waveform measuring apparatus that removes the body motion noise caused and identifies the electrocardiogram waveform of the occupant from which the body motion noise is removed.

  In a preferred embodiment of the present invention, each capacitively coupled electrode is formed of a conductive cloth in which conductive yarn or conductive fiber yarn is woven.

  In a further preferred embodiment of the present invention, among the capacitively coupled electrodes, an electrode having a relatively small surface area is arranged so as to be surrounded by an electrode having a larger surface area.

  In a further preferred aspect of the present invention, the first electrode is attached to a steering wheel.

  According to the electrocardiogram waveform measuring apparatus of the present invention, it is possible to accurately measure the electrocardiogram waveform of a vehicle occupant even if the vehicle occupant moves due to body movement during driving.

It is a figure showing a schematic structure of an electrocardiogram waveform measuring device concerning one embodiment of the present invention. It is a figure which shows the structure of the example which attached the 1st electrode to the steering wheel. It is a figure which illustrates the composition which attaches the 2nd electrode to the seat of vehicles. It is a figure which shows the structure of the 2nd electrode of other embodiment. FIG. 2 is a circuit diagram of FIG. 1. It is a measurement figure of the original electrocardiogram waveform obtained by each electrode in a resting state. It is a measurement figure of the original electrocardiogram waveform obtained by each electrode under the body movement of a driver. It is an electrocardiogram waveform of a driver from which body motion noise is removed. It is sectional drawing which shows the structure of an active electrode. It is a figure which shows the virtual circuit structure formed by other embodiment. It is sectional drawing which shows the other structure of an active electrode.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of an electrocardiogram waveform measuring apparatus 1 according to an embodiment of the present invention. The electrocardiogram waveform measuring apparatus 1 in the illustrated example includes, as main components, a first electrode 2 and a second electrode 3 having conductivity, and an electrocardiogram waveform calculating apparatus 4. In the following description, the electrocardiogram waveform measuring apparatus 1 will be described as an apparatus for measuring an electrocardiogram waveform of a driver of a vehicle. However, the electrocardiogram waveform measuring apparatus according to the present invention can be applied to passengers other than the driver. .

  The first electrode 2 is an electrode for directly contacting the driver's skin surface and detecting the body potential of the driver, and is formed of, for example, a chromium plating resin. As shown in FIG. 2, the first electrode 2 is attached to, for example, the outer peripheral surface of the vehicle steering wheel 10. However, the present invention is not limited to this, and the first electrode 2 may be attached to another place that the driver frequently touches, such as a shift lever. Further, when measuring the electrocardiogram waveform of an occupant other than the driver, it is preferable that the first electrode 2 is attached to, for example, an operation unit provided at the upper part of the center console or inside the door. The first electrode 2 is connected to the ground terminal 12.

  The second electrode 3 is not in direct contact with the driver's skin, but is in contact with the driver's skin with the driver's clothes used as a dielectric and sandwiching the clothes as the dielectric. The second electrode 3 is attached to the vehicle seat 11 to form virtual capacitors 32 and 33 (shown in FIG. 5) between the driver's buttocks and the second electrode 3 and the driver's buttocks. It functions as a capacitively coupled electrode for detecting the body potential of the driver by capacitive coupling between the two.

  The second electrode 3 is composed of two capacitively coupled electrodes of different sizes, has a relatively small surface area and a small contact area that contacts the driver, and a relatively large surface area that contacts the driver. It is comprised with the large sized electrode 31 with a large contact area. Signal electrodes 32A and 33A are connected to the electrodes 30 and 31, respectively, and the potentials of the capacitively coupled electrodes 30 and 31 that change according to changes in the body potential of the driver are transmitted to the electrocardiogram waveform calculation device 4. .

  FIG. 3 is a diagram illustrating a mode in which the second electrode 3 is attached to the vehicle seat 11. For example, as shown in FIG. 3A, the second electrode 3 may be configured by a plate electrode 34 inserted between the skin 11 </ b> A of the seat 11 and the cushion 11 </ b> B. Moreover, as shown to FIG. 3 (B), you may be comprised by the net-like electrodes 35, such as a metal fiber knitted on the skin 11A of the sheet | seat 11. As shown in FIG.

  Moreover, as shown in FIG. 4, you may make it comprise the 2nd electrode 3 with the electrically conductive cloth woven using the electrically conductive thread or electrically conductive fiber thread. Conductive yarn refers to conductive yarn made by twisting fine single wires such as copper, silver, and stainless steel with fiber. Conductive fiber yarn refers to fine yarn such as polyester with copper This refers to a fiber thread that has been plated with silver or gold and twisted with other threads. By constituting the second electrode 3 with the flexible conductive cloth electrode 36, the second electrode 3 comes into close contact with the buttocks of the driver.

  The second electrode 3 shown in FIG. 4 is composed of 25 conductive cloth electrodes 36 having substantially the same size (surface area). In this embodiment, 21 conductive cloth electrodes 36B among them are electrically connected. Are connected to each other to form a large electrode 31, and the remaining four conductive cloth electrodes 36A are electrically connected to form a small electrode 30. The small electrode 30 is disposed so as to be surrounded by the large electrode 31, whereby the small electrode 30 and the large electrode 31 are closely adjacent to each other, and the details will be described later. The effects given to the two electrodes 30 and 31 are similar. In addition, arrangement | positioning of the small electrode 30 and the large electrode 31 is not restricted to this, For example, both may be arranged in parallel. Further, the size of the small electrode 30 and the large electrode 31 can be appropriately changed by changing the number of the conductive cloth electrodes 36A and 36B.

  FIG. 5 is a circuit diagram showing an equivalent circuit of FIG. Ground terminals 12 and 12 are connected to the signal lines 32A and 33A via resistors 40 and 40, respectively. As a result, a virtual circuit using the driver's body potential as an input is formed. This circuit configuration functions as a high-pass filter or a band-pass filter.

  The electrocardiogram waveform calculation device 4 includes voltage followers 42 and 42, capacitors 43 and 43, amplification circuits 44 and 44, a microcomputer 45, and a storage device 46. Note that these configurations can be replaced by an operational amplifier or the like.

  Signal lines 32A and 33A are connected to the input terminal (+ side) 42A of each voltage follower 42, and the potentials of the small electrode 30 and the large electrode 31 are respectively input as electric signals. Further, the feedback from the output terminal 42 </ b> C of the voltage follower 42 is input to the input terminal (− side) 42 </ b> B of each voltage follower 42. With the above configuration, each voltage follower 42 can transmit electric signals from the small electrode 30 and the large electrode 31 to the output terminal 42C while suppressing the input of current.

  Each capacitor 43 realizes the function of a high-pass filter or a band-pass filter together with the resistors 41 and 41. The amplifying circuits 44 and 44 amplify the electric signal from which the low frequency component is cut by each capacitor 43 and the resistor 41 and output the amplified electric signal to the microcomputer 45.

  The microcomputer 45 calculates an electrocardiogram waveform by processing each electric signal input from each amplifier circuit 44. Here, when the driver is in a resting position while driving, the waveform shape of the electrocardiogram waveform calculated is substantially accurate as shown in FIG. 6 (in FIG. 6, the upper stage is The electrocardiogram waveform by the large electrode 31 and the electrocardiogram waveform by the small electrode 30 are respectively shown in the lower part). In contrast, when the driver's body moves during driving due to the driver's accelerator or brake operation, the driver's body movement causes the driver's skin (buttock) and the second electrode 3 to move. The contact state between the body and the body (contact pressure between the living body and the electrode) fluctuates, and this becomes a large noise (body motion noise) and is mixed into the electrocardiogram waveform. Therefore, as shown in FIG. 7, if the driver's body moves during driving, it may become impossible to measure an accurate electrocardiogram waveform (in FIG. 7, the upper stage is formed by the large electrode 31. An electrocardiogram waveform, and the lower part shows an electrocardiogram waveform by the small electrode 30).

  As described above, in the electrocardiogram waveform measurement using the capacitive coupling type electrode as the second electrode 3, it is not necessary to directly apply the second electrode 3 to the driver's skin, so the driver's electrocardiogram waveform is measured without restriction. Although it is possible, measurement of the driver's electrocardiogram waveform may be impossible due to the body movement of the driver while driving. Therefore, even if the driver's body movement occurs during driving, it is necessary to measure an accurate electrocardiogram waveform from which the influence of the body movement noise is removed. The present inventors have different sizes as the second electrode 3. It has been found that by using two capacitively coupled electrodes, it is possible to remove the influence of body motion noise from a calculated electrocardiogram waveform (hereinafter referred to as “original electrocardiogram waveform”).

  In other words, since the electrical signal obtained from the second electrode 3 in the resting state is mostly due to the electrocardiogram signal (ECG signal) inside the driver's body, it is possible to measure the electrocardiogram waveform with high accuracy. Therefore, referring to FIG. 6, if the original electrocardiogram waveform obtained from the large electrode 31 and the original electrocardiogram waveform obtained from the small electrode 30 are compared, the shape of the basic waveform is the same. It was confirmed that the waveform output V of the original electrocardiogram waveform obtained from the electrode 31 has a larger value than the waveform output V of the original electrocardiogram waveform obtained from the small electrode 30. That is, if ECG is a waveform output based on an electrocardiogram signal inside the driver's body (potential difference between R wave and S wave; hereinafter referred to as “electrocardiogram waveform output”)> ECG1 (ECG waveform output by large electrode 31)> ECG2 ( ECG waveform output by the small electrode 31), that is, ECG1 / ECG2> 1 was confirmed.

  This is because the waveform output V (ECG1, ECG2) of the original electrocardiogram waveform in the resting state is proportional to the capacitance value of the capacitors 32, 33 formed between the electrodes 30, 31 and the buttocks of the driver. However, since the capacitance value is proportional to the contact area of the electrodes 30 and 31 with the driver's buttocks, the size of the electrodes 30 and 31 is considered to be proportional to the waveform output V (ECG1 and ECG2) of the original electrocardiogram waveform. It is done.

  On the other hand, the electrical signal obtained from the second electrode 3 under the body movement of the driver is a mixture of the above-mentioned electrocardiogram signal (ECG) with body movement noise caused by the body movement of the driver. Referring to FIG. 7, if the original electrocardiogram waveform obtained from the large electrode 31 and the original electrocardiogram waveform obtained from the small electrode 30 are compared, the basic waveform shape is the same, but the original electrocardiogram waveform obtained from the large electrode 31 is the same. It was confirmed that the waveform output V of the electrocardiogram waveform has a smaller value than the waveform output V of the original electrocardiogram waveform obtained by the small electrode 30. That is, assuming that waveform output based on body motion noise (hereinafter referred to as “noise waveform output”) is Noise, ECG1 + Noise1 (noise waveform output by large electrode 31) <ECG2 + Noise2 (noise waveform output by small electrode 30). confirmed. Thus, the present inventors have found that the influence of body movement noise on the electrocardiogram waveform is larger in the small electrode 30 than in the large electrode 31, that is, Noise1 <Noise2 (Noise1 / Noise2 <1). It was.

  As described above, the knowledge that the ratio of ECG waveform output (ECG1 / ECG2) and the ratio of noise waveform output (Noise1 / Noise2) detected based on the difference in size between the electrodes 30 and 31 are not the same magnification. Based on the above, it was found that the influence of body motion noise can be removed from the original electrocardiogram waveform by arithmetically processing the original electrocardiogram waveform obtained from the large electrode 31 and the small electrode 30 having different sizes.

  Specifically, the original ECG waveform obtained from the large electrode 31 in the sitting position is compared with the original ECG waveform obtained from the small electrode 30 (see FIG. 6), and the cross-correlation coefficient between the two original ECG waveforms is calculated. To do. Thus, the time when the cross-correlation coefficient is maximized is found, and the time difference between the original electrocardiogram waveform obtained by the large electrode 31 and the original electrocardiogram waveform obtained by the small electrode 30 is calculated using the time τ when the cross correlation coefficient is maximized. . In the illustrated example, the time difference τ is τ = 0.005 seconds.

  Next, the original electrocardiogram waveform obtained by the large electrode 31 and the original electrocardiogram waveform obtained by the small electrode 30 under the driver's body movement are compared (see FIG. 7), and the region where the influence of the body movement noise occurs (see FIG. 7). In the example shown, the ratio of the waveform outputs V of both original electrocardiogram waveforms is calculated in the region from 3.2 seconds to 7.0 seconds. In this embodiment, the maximum values of the peak and bottom amplitude values in each original electrocardiogram waveform are compared, and the waveform output V (ECG1 + Noise1) of the original electrocardiogram waveform obtained from the large electrode 31 and the original electrocardiogram obtained from the small electrode 30 are compared. A ratio α ((ECG1 + Noise1) / (ECG2 + Noise2)) with the waveform output V (ECG2 + Noise2) of the waveform was calculated. In the illustrated example, the ratio α is α = 0.52. Note that the method of calculating the ratio α of the waveform outputs V of both original ECG waveforms is not limited to the above-described method, and the average value of the amplitude values of the original ECG waveforms in the region where the influence of body motion noise occurs is obtained. It can be calculated by various methods such as comparison.

  Finally, the difference between the waveform output V (ECG1 + Noise1) of the original ECG waveform obtained from the large electrode 31 and the waveform output V (ECG2 + Noise2) of the original ECG waveform obtained from the small electrode 30 is calculated based on the following formula (1). Thus, the waveform output ECG of the electrocardiogram waveform of the driver from which the influence of the body motion noise is removed is derived. That is, in the following formula (1), the waveform outputs Noise 1 and Noise 2 based on body motion noise are sufficiently larger than the waveform outputs ECG 1 and ECG 2 based on the electrocardiogram signal, so the ratio α is as shown in the following formula (2). Can be approximated.

  Using the above formula (2), the above formula (1) can be approximated as the following formula (3).

  Thus, according to the electrocardiogram waveform measuring apparatus 1 of the present embodiment, it is possible to measure an electrocardiogram waveform from which the influence of body motion noise has been removed even if the driver moves due to an accelerator operation or a brake operation during driving. It has become.

  The microcomputer 45 samples the electrocardiogram waveform of the driver measured by the above method at a predetermined period and stores it in the storage device 46 as time series waveform data. The storage device 46 is, for example, a flash memory. By displaying and printing the electrocardiogram waveform stored in the storage device 46, it is possible to check the electrocardiogram waveform during the operation of the driver.

  As described above, according to the electrocardiogram waveform measuring apparatus 1 having the above-described configuration, the electrocardiogram waveform during the driving of the driver can be continuously measured. That is, it is extremely rare that the driver does not touch the first electrode 2 at all during driving, and as long as the driver is seated on the seat 11, the second is composed of the capacitively coupled electrode attached to the seat 11. This is because the body potential of the driver can be continuously detected by the electrode 3.

  In addition, since it is not necessary to apply the second electrode 3 directly to the driver's skin, the driver's electrocardiogram waveform can be measured without restriction.

  Furthermore, the electrocardiogram waveform of the driver can be accurately measured. That is, when an electrocardiogram waveform is obtained as a second electrode 3 by using one capacitively coupled electrode, body motion noise caused by a driver's body motion during driving may be mixed into the measured electrocardiogram waveform. Measurement of an electrocardiogram waveform may be difficult. In the present embodiment, an electrocardiogram waveform is measured using two capacitively coupled electrodes (small electrode and large electrode) 30, 31 having different sizes (surface areas) as the second electrode 3, and the two electrocardiogram waveforms thus measured are measured. Thus, the influence of body motion noise mixed in the electrocardiogram waveform can be removed. Thereby, even if a driver's body movement occurs during driving, the electrocardiogram waveform of the driver can be accurately measured.

  As mentioned above, although one Embodiment of this invention was described, the specific aspect of this invention is not limited to the said embodiment. For example, as the second electrode 3, an active electrode 5 in which a capacitively coupled electrode and an amplifier circuit are integrally formed can be used. Other configurations, that is, the first electrode 2, the microcomputer 45, and the storage device 46 are the same as those in the first embodiment.

  FIG. 9 is a cross-sectional view showing the configuration of the active electrode 5. The active electrode 5 has an operational amplifier 51 mounted as an amplifier circuit on one surface of the substrate 50, and a capacitive coupling made of, for example, a flat copper plate on the other surface of the substrate 50 opposite to the operational amplifier 51. A mold electrode 52 is mounted. The capacitively coupled electrode 52 and the operational amplifier 51 are connected by a leading wire (not shown) inserted into a through hole (not shown) formed in the substrate 50. A shield electrode 53 is attached to the same surface of the substrate 50 as the operational amplifier 51 to eliminate the influence of the electric field on the operational amplifier 51 and maintain physical strength. The substrate 50 is covered with, for example, an insulating resin such as an epoxy resin, and most of the substrate 50 is sealed in the mold resin 54 so that troubles such as a short circuit do not occur in other parts other than the capacitive coupling electrode 52. It has become. Note that at least the surface 52A of the capacitively coupled electrode 52 is not resin-molded and is exposed to the outside.

  FIG. 10 is a diagram showing a virtual circuit configuration formed by the above configuration. In the figure, Vs is a potential difference in the driver's body (potential difference between the hand and the buttocks). CE is the capacity of a virtual capacitor formed by the driver body and the capacitively coupled electrode 52. Rg is a resistance for discharging static electricity caused by the body movement of the driver body. Cg is the capacity of a virtual capacitor formed by the capacitively coupled electrode 52 and the shield electrode 53. Rop and Cop are the input resistance and input capacitance of the operational amplifier 51, respectively.

  The gain G (S) of the virtual circuit configuration is given by the following equation (4). As shown by this equation, this circuit configuration functions as a high-pass filter, and its cutoff frequency is determined by four parameters CE, Cg, Cop, and Rg.

  According to the present embodiment, since the operational amplifier 51 and the capacitive coupling electrode 52 are integrated, more compact hardware can be realized. The active electrode 50 may be configured without the shielding electrode 53. Further, as shown in FIG. 11, the entire substrate 50 including the capacitively coupled electrode 52 and the operational amplifier 51 may be molded with an epoxy resin. According to this, since the capacitively coupled electrode 52 is completely enclosed in the mold resin 54, the capacitively coupled electrode 52 is less likely to deteriorate due to aging due to external force, wear, etc., and affect measurement accuracy. Also, you can get a long life.

DESCRIPTION OF SYMBOLS 1 ECG waveform measuring device 2 1st electrode 3 2nd electrode 4 ECG waveform calculation device 10 Handle 11 Sheet 30 Small electrode 31 Large electrode

Claims (4)

A first electrode in direct contact with the skin surface of a vehicle occupant;
A second electrode attached to the vehicle seat and in contact with the occupant's skin surface through clothing;
Electrocardiogram waveform calculating means for processing an electric signal detected by the first electrode and an electric signal detected by the second electrode to calculate an electrocardiogram waveform;
The second electrode is composed of two capacitively coupled electrodes having different contact areas that contact the passenger,
The electrocardiogram waveform calculating means removes body motion noise caused by the body motion of the occupant mixed in the electrocardiogram waveform by using two electrocardiogram waveforms calculated based on the electric signals detected by the capacitive coupling electrodes. An electrocardiogram waveform measuring device that identifies an electrocardiogram waveform of an occupant from which body motion noise has been removed.   2. The electrocardiogram waveform measuring apparatus according to claim 1, wherein each capacitively coupled electrode is configured by a conductive cloth woven with conductive yarns or conductive fiber yarns.   The electrocardiogram waveform measuring apparatus according to claim 1 or 2, wherein an electrode having a relatively small area among the capacitively coupled electrodes is disposed so as to be surrounded by an electrode having a larger area.   The electrocardiogram waveform measuring apparatus according to claim 1, wherein the first electrode is attached to a steering wheel.

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