JP2014124438A - Electrocardiographic measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrocardiographic measurement system that can precisely measure an electrocardiogram and can monitor changes in a contact state between a driver and a sensor.SOLUTION: An electrocardiographic measurement system comprises: two sheet electrodes 3 and 5 that are provided at a seat back of a vehicle; a steering electrode 7 that is provided at a steering wheel of the vehicle; a common mode feedback circuit 25 that feeds back a potential at an intermediate position 24 between the sheet electrodes 3 and 5 to the steering electrode 7; and voltage application means 33 that applies known AC voltage Vin from an input terminal of an operational amplifier 22 of the common feedback circuit 25 as a reference signal. The sheet electrodes 3 and 5 are connected to an operational amplifier 31, and the operational amplifier 31 is connected to a terminal CH1. An output of the operational amplifier 22 is connected to a terminal CH2. The system acquires an electrocardiographic signal and source impedance of the sheet electrodes 3 and 5 on the basis of CH1 and CH2.

Description

  The present invention relates to an electrocardiogram measurement system.

  An electrocardiogram measurement system that is mounted on a vehicle and measures the electrocardiogram of a driver has been proposed (see Patent Document 1). In this electrocardiogram measurement system, a signal GND is installed under the seat, and an electrocardiogram is detected by the differential between the steering electrode and the seat electrode.

JP 2009-142576 A

  As described above, the electrocardiogram measurement system described in Patent Document 1 has a configuration in which the steering electrode and the seat electrode are differentiated. However, when vehicle running noise increases, the method of superimposition is two electrodes. Therefore, even if differential, the noise reduction effect is small, and the electrocardiogram cannot be measured accurately.

  Moreover, although the accuracy of the electrocardiogram detection signal changes due to changes in the contact state of the driver with clothes, sweating, and movements during driving, there is no method for monitoring them and the risk of false detection is high.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an electrocardiogram measurement system capable of accurately measuring electrocardiograms and monitoring a contact state change between a driver and a sensor.

  The electrocardiogram measurement system of the present invention includes a sheet electrode A (3, 5, 203, 205, 207, 209) and a sheet electrode B (3, 5, 203, 205, 207, 209) provided on a vehicle seat. A steering electrode (7, 211) provided in the steering of the vehicle, and a feedback circuit (25, 239) that feeds back the potential between the seat electrode A and the seat electrode B to the steering electrode. The differential signal of the sheet electrode A and the sheet electrode B is taken out as an electrocardiogram signal. In addition, voltage application means (33, 251) for applying a predetermined AC voltage to the subject seated on the seat is provided, and the AC voltage is applied from the voltage application means and input to the subject. Based on the input signal and the output signals of the sheet electrode A and the sheet electrode B, the source impedance between the sheet electrode A and the person to be measured (hereinafter simply referred to as the source impedance of the sheet electrode A), and the sheet A source impedance between the electrode B and the measurement subject (hereinafter simply referred to as a source impedance of the sheet electrode B) is acquired.

  Since the electrocardiograph system of the present invention can reduce the source impedance between the human body and the GND by the feedback circuit, the human body potential can be accurately detected. Moreover, since common mode noise can be reduced and the signal is less likely to be saturated, the electrocardiogram can be accurately measured. Furthermore, since the electrocardiogram measurement system of the present invention performs differential operation between the seat electrode A and the seat electrode B, it is possible to cancel noise that is similarly superimposed on the seat electrode A and the seat electrode B when the vehicle travels.

  And furthermore, based on the input signal inputted to the person to be measured and the output signals of the sheet electrode A and the sheet electrode B, the source impedance of the sheet electrode A and the sheet electrode B can be accurately obtained, A decrease in electrocardiographic detection performance due to a change in the amount of clothes of the measurement subject or a change in the state of approach to the sheet electrode can be found.

  The voltage applying means may be configured to apply an AC voltage to the feedback circuit, and may acquire a signal input to the steering electrode as an input signal. The feedback circuit means a circuit that connects the position between the seat electrode A and the seat electrode B to the steering electrode. In the circuit, an AC voltage can be applied at various positions. It is conceivable to apply from the input terminal of the amplifier.

  In the electrocardiogram measurement system of the present invention, the voltage application unit may adjust the amplitude and / or frequency of the AC voltage based on the input signal, or the sheet electrode A and / or the frequency may be adjusted based on the input signal. Or it is good also as a structure provided with the adjustment means which adjusts the input impedance of the said sheet electrode B. FIG.

  If the potential of the input signal is saturated or very small, the source impedance cannot be captured. Therefore, with the above-described configuration, it is possible to suppress the saturation or minute potential of the input signal and always capture the source impedance.

  In addition, the code | symbol in the parenthesis described in this column and a claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is shown. It is not limited.

(A) is a block diagram which shows the electrocardiogram measurement system of 1st Embodiment, (B) is a block diagram which shows the electrocardiogram measurement system of 2nd and 3rd embodiment. 3 is a circuit diagram illustrating an equivalent circuit of the electrocardiogram measurement circuit 1. FIG. 3 is a functional block diagram illustrating an electrocardiogram / impedance simultaneous detection unit 52. FIG. It is a graph which shows the simulation result of F1 (s) at the time of changing the source impedance of a sheet electrode, and F2 (s). It is a flowchart which shows the process sequence of the electrocardiogram detection process of 1st Embodiment. It is a flowchart which shows the process sequence of the electrocardiogram and impedance real-time detection process of 1st Embodiment. It is a flowchart which shows the process sequence of the applied voltage adjustment process of 1st Embodiment. It is a flowchart which shows the process sequence of the input impedance adjustment process of 1st Embodiment. It is a flowchart which shows the process sequence of the electrocardiogram detection availability determination process of 1st Embodiment. 3 is a circuit diagram showing an equivalent circuit of an electrocardiogram measurement circuit 201. FIG. It is explanatory drawing showing arrangement | positioning of a sheet electrode when the sheet | seat of a driver is seen from a front direction. It is a functional block diagram explaining the electrocardiogram / impedance simultaneous detection unit 252. It is a flowchart which shows the process sequence of the electrocardiogram detection process of 2nd Embodiment. It is a flowchart which shows the process sequence of the electrocardiogram and impedance real-time detection process of 2nd Embodiment. It is a flowchart which shows the process sequence of the electrode selection process of 2nd Embodiment. 3 is a circuit diagram showing an equivalent circuit of an electrocardiogram measurement circuit 301. FIG. It is a flowchart which shows the process sequence of the electrocardiogram detection process of 3rd Embodiment. It is a flowchart which shows the process sequence of the circuit structure determination process of 3rd Embodiment. It is a flowchart which shows the process sequence of the electrode selection process of 3rd Embodiment. It is explanatory drawing showing the relationship between the source impedance of a seat electrode, the driving | running | working state of a vehicle, and ON / OFF of a feedback circuit.

Embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
1. Configuration of the electrocardiogram measurement system As shown in FIG. 1A, the electrocardiogram measurement system of the present embodiment includes an electrocardiogram measurement circuit 1, an A / D converter 51, a CPU 61, an operation switch 71, and a sensor. And a group 73, which is a system mounted on a vehicle.

  The electrocardiogram measurement circuit 1 is an analog circuit, and the analog output signal of the electrocardiogram measurement circuit 1 is digitally converted by the A / D converter 51, and the CPU 61 performs a predetermined output according to the signal and the electrocardiogram measurement circuit. 1 is controlled. The operation switch 71 is a switch for switching on / off the operation of the entire electrocardiogram measurement system. The sensor group 73 includes a temperature sensor and a humidity sensor that measure the temperature and humidity in the vehicle compartment, a speed sensor that measures the traveling speed of the vehicle, and the like.

  The configuration of the electrocardiogram measurement circuit 1 will be described with reference to FIG. FIG. 2 is a circuit diagram showing an equivalent circuit of the electrocardiogram measurement circuit 1. The electrocardiogram measurement circuit 1 includes two seat electrodes 3 and 5 provided on the back portion of the vehicle seat and a steering electrode 7 provided on the steering of the vehicle.

The sheet electrodes 3 and 5 are reference capacitive coupling electrodes. The sheet electrodes 3 and 5 are examples of the sheet electrode A and the sheet electrode B in the present invention.
An impedance converter 9 is connected to the sheet electrode 3, and an impedance converter 11 is connected to the sheet electrode 5. The impedance converters 9 and 11 are composed of operational amplifiers 13a and 13b and resistors 15a and 15b, respectively. The impedance converters 9 and 11 are configured so that the resistance values of the resistors 15a and 15b can be changed according to the control signal of the CPU 61. The impedance converters 9 and 11 are an example of adjusting means in the present invention.

The impedance converters 9 and 11 are connected to the operational amplifier 31, and the operational amplifier 31 is connected to the terminal CH1. The potential output from this terminal CH1 is F1 (s).
The seat electrode 3 and the seat electrode 5 are connected via resistors 21 and 23 having the same resistance value, and the potential at the intermediate position 24 between the resistors 21 and 23 is controlled by the common mode feedback circuit 25 by the steering electrode 7. Has been fed back.

  The common mode feedback circuit 25 includes operational amplifiers 17 and 22, resistors 18, 19, and 20. Further, voltage application means 33 is provided for applying a known alternating voltage Vin (in this embodiment, 0.2 V, 100 Hz) as a reference signal from the input terminal of the operational amplifier 22. The output of the operational amplifier 22 is connected to the terminal CH2. The potential output from this terminal CH2 is defined as F2 (s).

2. Detection of ECG and seat electrode source impedance A driver (person to be measured) sits on the vehicle seat and holds the steering wheel. At this time, the back portion of the driver is in contact with the sheet electrodes 3 and 5. The driver's hand contacts the steering electrode 7. Since the output of the electrocardiogram signal is different due to the difference in the position of the sheet electrodes 3 and 5, the differential signal of the sheet electrodes 3 and 5 is taken out from the terminal CH1 as the electrocardiogram signal of the driver. At this time, an intermediate potential between the seat electrodes 3 and 5 is fed back to the steering electrode 7. Further, an input signal input to the driver is taken out from the terminal CH2.

  The A / D converter 51 and the CPU 61 constitute an electrocardiogram / impedance simultaneous detection unit 52. Specifically, the electrocardiogram / impedance simultaneous detection unit 52 includes an AD detection unit 53, a frequency separation unit 54, an electrocardiogram signal acquisition unit 55, and an impedance calculation unit 56, as shown in FIG.

The AD detection unit 53 performs digital conversion (A / D detection) on the signals of CH1 and CH2.
The frequency separation unit 54 includes a band-pass filter 54a that extracts a 15 to 35 Hz electrocardiographic signal from the CH1 signal, and a band-pass filter 54b that extracts an applied frequency (Vin) signal from the CH1 and CH2 signals. ,have. The band pass filters 54a and 54b are configured to apply a filter by digital processing, but may be configured to detect A / D by performing filter processing with an analog circuit.

  The electrocardiogram signal acquisition unit 55 extracts an electrocardiogram signal from the output signal of the bandpass filter 54a. The electrocardiogram signal acquisition unit 55 is an example of an electrocardiogram acquisition unit in the present invention, and is substantially constituted by the CPU 61.

  The impedance calculation unit 56 calculates the source impedance of the sheet electrode 3 and the driver and the source impedance of the sheet electrode 5 and the driver based on the output signal of the bandpass filter 54b. Hereinafter, the source impedance refers to the source impedance between the electrode and the driver. The impedance calculation unit 56 is an example of a source impedance acquisition unit in the present invention, and is substantially constituted by the CPU 61.

  An outline of a source impedance calculation method will be described below. As described above, when the potential of the terminal CH1 is the transfer function F1 (s) and the potential of the CH2 is the transfer function F2 (s), the following equations 1 and 2 are obtained. The source impedance of the sheet electrode 3 is C11, and the source impedance of the sheet electrode 3 is C21. The resistance value of the resistor 15a is R12, the resistance value of the resistor 15b is R22, the resistance value of the resistor 18 is R34, and the resistance value of the resistor 19 is R33.

  In addition, A, B1, and B2 in the above formulas 1 and 2 are represented by the following formulas (formula 3 to formula 5).

  In the above equation, A has a low-pass filter configuration with the contact resistance R31 between the hand and the steering electrode, and the human body and GND C41. B1 and B2 are the input parts of the human body and the seat boat electrode, and the source impedances C11 and C21 and the input impedances R12 and R22 have a high-pass filter configuration, respectively.

  The relationship between F1 (s), F2 (s) and C11, C21 based on the above formulas 1 and 2 is shown in FIGS. 4A and 4B show the potential with respect to the source impedance of C11 when the source impedances of C11 and C21 are equal and when they are unbalanced (when the errors of C11 and C21 are 5 pF and 10 pF). It is a result of simulation. As shown in FIG. 4A, the potential difference of F1 (s) increases if C11 and C21 are unbalanced. On the other hand, as shown in FIG. 4B, F2 (s) reflects the absolute values of C11 and C21, and it can be seen that the influence of imbalance is small.

  Then, B1 + B2 indicating an absolute value and B1-B2 indicating unbalance can be calculated from the simultaneous equations using Expressions 1 and 2 shown in Expressions 6 and 7.

  In this way, the source impedances C11 and C21 of the sheet electrodes 3 and 5 can be estimated by monitoring F1 (s) and F2 (s) acquired from the terminals CH1 and CH2.

  By the way, the source impedance changes according to the amount of clothes of the driver. Therefore, the driver's clothing amount (inclusion between the human body and the electrode) was changed, F1 (s) and F2 (s) were obtained, the source impedances of C11 and C21 were calculated, and the behavior was confirmed. Here, the calculation is performed assuming that the contact state between the sheet electrode and the driver is good and the source impedance is C11 = C21. As a result, as shown in Table 1, it was confirmed that the source impedance increased as the thickness increased. The inclusions are L: Leather, T: T-shifts, Y: Y-shifts, J: Jacket, C: Coat.

3. Processing by CPU 3-1. Electrocardiogram Detection Process The electrocardiogram detection process executed by the CPU 61 will be described based on the flowchart shown in FIG. This process is started when the operation switch 71 is turned on and power is supplied to the entire electrocardiogram measurement system including the CPU 61.

  In this process, first, the applied voltage is initially set (S1). The applied voltage is set according to environmental information in the vehicle measured by a temperature sensor, a humidity sensor, or the like. For example, since the source impedance tends to be low due to light and high humidity in summer, and the source impedance tends to be high due to thick and low humidity in winter, the initial value is adjusted in advance according to the temperature and humidity conditions.

  Next, it is determined whether or not the measurement command is on (operation switch 71 is on) (S2). If the measurement command is OFF, that is, if OFF is selected by the operation switch (S2: NO), this process ends.

  On the other hand, if ON is selected (S2: YES), an electrocardiogram / impedance real-time detection process is performed (S3), and the electrocardiogram signal and the source impedance of the sheet electrode are detected simultaneously. Subsequently, an applied voltage adjustment process is performed (S4), and then an input impedance adjustment process is performed (S5). With these processes, the source impedance can be acquired well in S3. Next, an electrocardiogram detection possibility determination process is performed (S6). Details of the processes of S3 to S6 will be described later.

After S6, the process returns to S2. While the measurement command is on, the processes of S3 to S6 are repeated. If the driver operates the operation switch 71 and the measurement command is turned off, the process is terminated.
3-2. Electrocardiogram / impedance real-time detection process The electrocardiogram / impedance real-time detection process executed by the CPU 61 will be described based on the flowchart shown in FIG. This process is executed in S3 of the electrocardiogram detection process.

  In this process, first, A / D detection of CH1 and CH2 is performed (S11). Here, the analog output information of CH1 and CH2 accumulated for a certain time is converted into digital information. Next, frequency separation is performed (S12). Here, a signal of 15 to 35 Hz is extracted from the CH1 signal, and a signal of an applied frequency (Vin) (for example, a signal of 90 to 110 Hz) is extracted from the CH1 and CH2 signals.

  Next, an electrocardiogram signal is acquired based on the signal of 15 to 35 Hz extracted in S12 among the CH1 signals (S13). Next, the source impedance of the sheet electrodes 3 and 5 is calculated based on the signals of the applied frequencies of CH1 and CH2 extracted in S12 (S14). Thereafter, this process is terminated and the process returns to the electrocardiogram detection process.

3-3. Applied Voltage Adjustment Processing The applied voltage adjustment processing executed by the CPU 61 will be described based on the flowchart shown in FIG. This process is executed in S4 of the electrocardiogram detection process. In this process, the voltage applied by the voltage applying unit 33 is adjusted so that the F2 (s) potential detected in CH2 falls within a predetermined range. From the above formulas 1 and 2, if the F2 (s) potential is saturated or very small, the source impedance cannot be satisfactorily captured. Therefore, the F2 (s) potential is controlled between the thresholds t1 and t2 by adjusting the applied voltage.

  In this process, first, it is determined whether or not the F2 (s) potential is a predetermined threshold value t1 or more and t2 or less (S21). If it is t1 or more and t2 or less (S21: YES), this process is terminated. Return to the electrocardiogram detection process. If the F2 (s) potential is less than t1 (S22: YES), there is a possibility that the sensitivity is insufficient, and therefore processing for increasing the applied voltage amplitude or decreasing the applied frequency is performed (S23). If the F2 (s) potential is not less than t1, that is, if the F2 (s) potential exceeds t2 (S22: NO), there is a possibility of saturation, and therefore processing for lowering the applied voltage amplitude or raising the applied frequency is performed. Perform (S24). Thereafter, this process is terminated and the process returns to the electrocardiogram detection process. Note that the adjustment of the applied voltage amplitude and the applied frequency in S23 and S24 may be only one or both.

3-4. Input Impedance Adjustment Processing The input impedance adjustment processing executed by the CPU 61 will be described based on the flowchart shown in FIG. This process is executed in S5 of the electrocardiogram detection process. In this process, the input impedance is adjusted so that the F2 (s) potential is within a predetermined range. The adjustment of the input impedance is executed by the impedance converters 9 and 11 according to a control signal from the CPU 61.

  In this process, first, it is determined whether or not the F2 (s) potential is not less than a predetermined threshold value t1 and not more than t2 (S31). If it is not less than t1 and not more than t2 (S31: YES), the process is terminated and the heart is finished. Return to the power detection process. If the F2 (s) potential is less than t1 (S32: YES), the input impedance is lowered because there is a possibility of insufficient sensitivity (S33). If the F2 (s) potential is not less than t1, that is, if the F2 (s) potential exceeds t2 (S32: NO), the input impedance is increased because there is a possibility of saturation (S24). Thereafter, the process returns to the electrocardiogram detection process.

3-5. ECG detection availability determination processing The ECG detection availability determination processing executed by the CPU 61 will be described based on the flowchart shown in FIG. This process is executed in S6 of the electrocardiogram detection process. This process is a process of presenting to the driver that it is not suitable for electrocardiogram detection when the source impedance is larger than a predetermined threshold, such as when the contact (approach) state between the sheet electrode and the driver's body is poor.

  In this process, first, it is determined whether or not the source impedance of the two sheet electrodes 3 and 5 is less than a predetermined threshold value (S41). If both are less than the predetermined threshold (S41: YES), this process is terminated and the process returns to the electrocardiogram detection process. The predetermined threshold here is a value of the source impedance that allows a large electrocardiogram signal to be acquired by sufficiently approaching the driver and the sheet electrode.

  On the other hand, if either one of the sheet electrodes 3 and 5 has a source impedance equal to or higher than a predetermined threshold value (S41: NO), an electrocardiographic detection impossibility is presented (S42). Specifically, for example, a speaker or a display (display device) mounted on a vehicle is caused to output a voice or an image indicating that “correct the posture because an electrocardiogram cannot be detected properly”. Thereafter, the process returns to the electrocardiogram detection process.

4). Effects produced by the electrocardiogram measurement system The electrocardiogram measurement system according to the present embodiment has a GND electrode (steering electrode 7) that is resistively coupled to the steering side that can reduce the source impedance relatively without using clothes, and is arranged on the seat side. Capacitively coupled sheet electrodes 3 and 5 for detecting an electrocardiogram are arranged, and a potential is obtained by feeding back the potential obtained from the sheet electrodes 3 and 5 to the human body via the steering electrode 7. The electrocardiogram measurement circuit 1 takes out a differential signal between the sheet electrode 3 and the sheet electrode 5 from the terminal CH1 as an electrocardiogram signal.

  As a result, the source impedance between the human body and GND can be reduced, and the human body potential can be accurately detected. Therefore, common mode noise is reduced, and the electrocardiogram can be measured without saturating the signal. Further, since differential is performed between the seat electrodes 3 and 5 in the vicinity of the seat, it is possible to cancel the noise that is similarly superimposed when the vehicle travels.

  And simultaneously with acquiring an electrocardiogram signal, it is possible to accurately acquire the source impedance of the sheet electrodes 3 and 5 based on the input signal input to the driver's body and the output signals of the sheet electrodes 3 and 5. It is possible to detect a decrease in electrocardiographic detection performance due to a change in the amount of clothes of the measurement subject or a change in the state of proximity to the sheet electrode.

  From Equations 1 and 2, the higher the frequency is, the less the transfer function change associated with the source impedance is observed. On the other hand, when the frequency is too low, F2 (s) saturates when the source impedance is high. There is a possibility that.

  However, in the electrocardiogram detection system of this embodiment, the frequency and amplitude of the applied signal can be adjusted and the input impedance can be adjusted so that F2 is not saturated and the change in the source impedance can be captured. In addition to setting the initial value of the applied signal in accordance with the temperature and humidity conditions in the vehicle, a source impedance monitor that can cope with a wide range of environmental conditions and clothing state (impedance) ranges becomes possible.

  By the way, as for the frequency of the input signal Vin applied to the human body, it is desirable to avoid an electrocardiographic frequency of 15 Hz to 35 Hz in order to separate it from the electrocardiographic signal. By setting Vin to be in the range of 40 to 200 Hz, it is easy to observe a change in transfer function accompanying a change in source impedance, which is convenient.

Note that either one of the processes of S4 and S5 in FIG. 5 can adjust F2 (s). Therefore, it is not always necessary to execute both, and the adjustment may be performed using only one of them.
Further, in the present embodiment, the configuration in which the operation signals of the sheet electrodes 3 and 5 are acquired by CH1, but CH1a and CH1b that acquire the output signals of the sheet electrodes 3 and 5 shown in FIG. May be. Similarly, CH2 may be configured to acquire a potential at a position different from that in FIG. 2 as long as it is a signal to which Vin is applied and is an input signal input to the driver.

  Moreover, although the electrocardiogram measurement system of this embodiment is mounted on a vehicle, a part of its constituent elements, for example, a device corresponding to the CPU 61 is disposed outside the vehicle, and transmits and receives signals by wireless communication. May be configured to execute.

Note that the CPU 61 is an example of a device that controls the entire system. For example, another device such as a PC may be used, or a configuration in which distributed processing is performed by a plurality of CPUs may be used.
<Second Embodiment>
1. Configuration of ECG Measurement System As shown in FIG. 1B, an electrocardiogram measurement system according to this embodiment includes an electrocardiogram measurement circuit 201, an A / D converter 261, a CPU 263, an operation switch 71, and a sensor. A group 73; The electrocardiogram measurement circuit 201 is an analog circuit, and the analog output signal of the electrocardiogram measurement circuit 201 is digitally converted by the A / D converter 261, and the CPU 263 outputs a predetermined output in accordance with the signal and the electrocardiogram measurement circuit. 201 is controlled. The electrocardiogram measurement circuit 201 acquires signals from CH1 to CH7. The operation switch 71 and the sensor group 73 have the same configuration as in the first embodiment.

  The configuration of the electrocardiogram measurement circuit 201 will be described with reference to FIGS. FIG. 10 is a circuit diagram showing an equivalent circuit of the electrocardiogram measurement circuit 201. FIG. 11 is an explanatory diagram showing the arrangement of sheet electrodes when the driver's sheet 214 is viewed from the front. The electrocardiogram measurement circuit 201 includes four seat electrodes 203, 205, 207, and 209 provided on the back portion of the vehicle seat 214, and two steering electrodes 211 and 213 provided on the steering of the vehicle. The arrangement of the sheet electrodes 203, 205, 207, and 209 on the sheet 214 is as shown in FIG.

  The sheet electrodes 203, 205, 207, 209 and the steering electrode 211 are reference capacitive coupling electrodes. Impedance converters 215, 217, 219, 221, and 223 are connected to the sheet electrodes 203, 205, 207, and 209 and the steering electrode 211, respectively. The impedance converters 215, 217, 219, 221, and 223 are each composed of an operational amplifier 225 and a resistor 227.

  The sheet electrode 203 is connected to the terminal CH3, the sheet electrode 205 is connected to the terminal CH4, the sheet electrode 207 is connected to the terminal CH5, and the sheet electrode 209 is connected to the terminal CH6. The steering electrode 211 is connected to the terminal CH7.

  The sheet electrodes 203, 205, 207, and 209 are connected to the two multiplexers 229 and 231, respectively. The output of the multiplexer 229 and the output of the multiplexer 231 are input to the operational amplifier 232, and the output of the operational amplifier 237 is connected to the terminal CH1. The operations of the multiplexers 229 and 231 are controlled according to the control signal of the CPU 263. Of the sheet electrodes 203, 205, 207, and 209, two sheet electrodes set as outputs in the multiplexers 229 and 231 are examples of the sheet electrode A and the sheet electrode B in the present invention.

  The output of the multiplexer 229 and the output of the multiplexer 231 are connected via resistors 233 and 235 having the same resistance value, and the potential at the intermediate position 237 between the resistors 233 and 235 is controlled by the common mode feedback circuit 239 by the steering electrode. 213 is fed back. The common mode feedback circuit 239 includes operational amplifiers 241 and 249 and resistors 243, 245, and 247.

  Further, voltage application means 251 for applying a known alternating voltage Vin (in this embodiment, 0.2 V, 100 Hz) as a reference signal from the input terminal of the operational amplifier 249 is provided. The output of the operational amplifier 249 is connected to the terminal CH2.

2. Detection of Electrocardiogram and Source Impedance of Sheet Electrode In the electrocardiogram measurement system of this embodiment, an A / D converter 261 and a CPU 263 constitute an electrocardiogram / impedance simultaneous detection unit 252. Specifically, the electrocardiogram / impedance simultaneous detection unit 252 includes an AD detection unit 253, a frequency separation unit 254, an electrocardiogram signal acquisition unit 255, and an impedance calculation unit 256, as shown in FIG.

The AD detection unit 253 performs digital conversion (A / D detection) on the signals of CH1 to CH7.
The frequency separation unit 254 includes a bandpass filter 254a that extracts a 15 to 35 Hz signal from the CH1 signal, a bandpass filter 254b that extracts an applied frequency (Vin) signal from the CH1 and CH2 signals, and CH3 to CH7. A band-pass filter 254c that extracts a signal having an applied frequency (Vin) from the signal. The band-pass filters 254a, 254b, and 254c are filtered by digital processing, but A / D may be detected by filtering with an analog circuit.

  The electrocardiogram signal measurement unit 255 extracts an electrocardiogram signal from the output signal of the bandpass filter 254a. The electrocardiogram signal acquisition unit 255 is an example of an electrocardiogram acquisition unit in the present invention, and is substantially constituted by the CPU 263.

  The impedance calculation unit 256 calculates the source impedance of any two of the sheet electrodes 203, 205, 207, and 209 based on CH1 and CH2 based on the output signal of the bandpass filter 254b, and the output of the bandpass filter 254c. And a function of calculating the source impedance of each of the sheet electrodes 203, 205, 207, and 209 based on the signal. The impedance calculation unit 256 is an example of a source impedance acquisition unit in the present invention, and is substantially configured by the CPU 263.

3. Processing by CPU 3-1. Electrocardiogram Detection Process The electrocardiogram detection process executed by the CPU 263 will be described based on the flowchart shown in FIG. In addition, since there are many processes common to the process of FIG. 5 in 1st Embodiment, it abbreviate | omits description about the same process using the same code | symbol.

  When the measurement command is ON (S2: YES), an electrocardiogram / impedance real-time detection process is performed (S7), an applied voltage adjustment process is performed (S4), an input impedance adjustment process is performed (S5), and an electrode selection process is performed. Perform (S8). Thereafter, the process returns to S2. Details of the processes of S7 and S8 will be described later.

3-2. Electrocardiogram / impedance real-time detection process The electrocardiogram / impedance real-time detection process executed by the CPU 263 will be described based on the flowchart shown in FIG. This process is executed in S7 of the electrocardiogram detection process of FIG. In this process, first, AD detection of CH1 to CH7 is performed (S51), and then frequency separation is performed (S52). Here, a 15-35 Hz signal is extracted from the CH1 signal, and an applied frequency (Vin) signal is extracted from the CH1 and CH2 signals. Further, a signal having an applied frequency (Vin) is extracted from the signals of CH3 to CH7.

  Next, an electrocardiogram signal is acquired based on the 15 to 35 Hz signal extracted in S52 among the CH1 signals (S53). Next, based on the signal of the applied frequency of CH1 and CH2 extracted in S52, the source impedance of the sheet electrode set by the multiplexers 229 and 231 at that time is calculated, and the signals of CH3 to CH7 are also calculated. Based on this, the source impedances of the seat electrodes 203, 205, 207, 209 and the steering electrode 211 are calculated (S54). The sheet electrode switching setting by the multiplexers 229 and 231 is performed in S63 of an electrode selection process described later. After the process of S54, the process returns to the electrocardiogram detection process.

3-3. Electrode Selection Process The electrode selection process executed by the CPU 263 will be described based on the flowchart shown in FIG. This process is executed in S8 of the electrocardiogram detection process. This process is a process of selecting and setting an appropriate sheet electrode having a source impedance smaller than a predetermined threshold from the four sheet electrodes in order to increase the accuracy of electrocardiogram detection.

  In this process, first, it is determined whether or not the source impedance of the two currently set electrodes is less than a predetermined threshold value (S61). The two currently set electrodes here are sheet electrodes set in S63 below. Any initial setting may be used. For example, the sheet electrodes 203 and 205 may be used. If the sheet electrode is less than the predetermined threshold value in S61 (S61: YES), this process is terminated and the process returns to the electrocardiogram detection process.

  On the other hand, if any one of the two sheet electrodes is equal to or greater than the predetermined threshold (S61: NO), it is determined whether or not there are two or more electrodes having a source impedance less than the predetermined threshold among the four sheet electrodes. Determine (S62). In addition, the source impedance of the sheet electrode set by the multiplexers 229 and 231 is calculated as two source impedances calculated based on the signals of CH3 to CH6. May be used.

  In S62, if there are two or more electrodes whose source impedance is less than the predetermined threshold (S62: YES), the multiplexers 229 and 231 are switched so that the output of CH1 becomes a combination of two electrodes having the lowest source impedance. The setting is changed to (S63). Thereafter, the process returns to the electrocardiogram detection process.

  On the other hand, if there are not two or more electrodes whose source impedance is less than the predetermined threshold value (S62: NO), an indication that the electrocardiogram cannot be detected is given (S64). This process is the same as S42 in FIG. Thereafter, the process returns to the electrocardiogram detection process.

4). Effects produced by the electrocardiogram measurement system The electrocardiogram measurement system according to the present embodiment has the same effects as the electrocardiogram measurement system according to the first embodiment, and further, the source impedance of the four sheet electrodes and the driver. Based on the above, it is possible to selectively use a sheet electrode suitable for electrocardiogram signal measurement. Moreover, since a sheet electrode having a relatively low source impedance can be selected and used, the electrocardiogram can be measured more accurately.

  In addition, said effect is equipped with the seat electrode selection means which equips the vehicle seat with three or more seat electrodes, and selects two sheet electrodes used for electrocardiogram measurement based on the source impedance of each seat electrode and the person being measured. Any configuration may be used.

<Third Embodiment>
The electrocardiogram detection system according to the present embodiment is different from the electrocardiogram detection system according to the second embodiment only in part of the circuit configuration of the electrocardiogram measurement circuit and the processing by the CPU. Only the part will be described, and the description of the same part will be omitted.

1. Configuration of electrocardiogram measurement system FIG. 16 shows an electrocardiogram measurement circuit 301 of the present embodiment. A switch 271 that can be switched on / off is provided between the steering electrode 213 and the common mode feedback circuit 239. In addition, a switch 273 that can be switched on / off is provided between the voltage applying unit 251 and the input terminal of the operational amplifier 249. When the switches 271 and 273 are both off, the switches 271 and 273 are short-circuited, and a reference signal can be output to the steering electrode 213 therefrom.

2. Processing by CPU 2-1. Electrocardiogram Detection Process The electrocardiogram detection process executed by the CPU 263 will be described based on the flowchart shown in FIG. In addition, since there are many processes in common with the process of FIG. 5 in 1st Embodiment, and the process of FIG. 13 in 2nd Embodiment, it abbreviate | omits description about the same process using the same code | symbol.

  If the measurement command is on (S2: YES), it is determined whether the feedback circuit is on (S81). On / off of the feedback circuit is set in S84 described later. If the feedback circuit is on (S81: YES), an electrocardiogram / impedance real-time detection process is performed (S7), an applied voltage adjustment process is performed (S4), an input impedance adjustment process is performed (S5), and an electrode selection process is performed. Perform (S82). This electrode selection process is a process of selecting and setting an appropriate sheet electrode from the four sheet electrodes, and details will be described later. Thereafter, the process proceeds to S84.

  On the other hand, if the feedback circuit is off (S81: NO), an electrocardiogram / impedance real-time detection process is performed (S83). Here, the source impedance of each corresponding seat electrode and steering electrode 211 is calculated based on the signals of the terminals CH3 to CH7, and an electrocardiographic signal is acquired based on one of the CH3 to CH6 (single end mode). Subsequently, an electrode selection process is performed (S82). After this electrode selection process, the process proceeds to S84. Subsequently, a circuit configuration determination process is performed (S84), and the process returns to S2. Details of the electrode selection process and the circuit configuration determination process will be described later.

2-2. Circuit Configuration Determination Processing The circuit configuration determination processing executed by the CPU 263 will be described based on the flowchart of FIG. This process is executed in S84 of the electrocardiogram detection process.

  In this process, first, it is determined whether or not there are two or more sheet electrodes 203 to 209 calculated from the signals of CH3, CH4, CH5, and CH6, the source impedance of which is smaller than an arbitrary threshold (S91). If there are two or more (S91: YES), it is determined whether or not the traveling speed of the vehicle is 0 km / h or more (running) (S92). When it is 0 Km / h or more (S92: YES), the process proceeds to S94.

  On the other hand, if two or more electrodes are not present in S91 (S91: NO), or if SK is 0 Km / h (S92: NO), whether the source impedance of CH7 is greater than a predetermined threshold value or not Is determined (S93). When it is larger than the predetermined threshold (S93: YES), the process proceeds to S94, and when it is equal to or smaller than the predetermined threshold (S93: NO), the process proceeds to S95.

  In subsequent S94, the switches 271 and 273 are both turned on to turn on the feedback circuit. On the other hand, in S75, both the switches 271 and 273 are turned off, the switches 271 and 273 are short-circuited, and the feedback circuit is turned off. After these processes, this process is terminated and the process returns to the electrocardiogram detection process.

2-3. Electrode Selection Process The electrode selection process executed by the CPU 263 will be described based on the flowchart shown in FIG. This process is executed in S82 of the electrocardiogram detection process. This process is a process of selecting an appropriate electrode having a source impedance larger than a predetermined threshold from the four electrodes in order to increase the accuracy of electrocardiogram detection.

  In this process, first, it is determined whether or not the source impedance of two or more electrodes is less than a predetermined threshold (S111). If there are not two or more sheet electrodes whose source impedance is less than the predetermined threshold (S111: NO), an indication that electrocardiogram detection is impossible is made (S112). This process is the same as S42 in FIG. Thereafter, this process is terminated, and the process returns to the electrocardiogram detection process.

  On the other hand, if there are two or more sheet electrodes whose source impedance is less than the predetermined threshold (S111: YES), it is determined whether there are three or more such electrodes (S113). If there are not three or more electrodes whose source impedance is less than the predetermined threshold (S113: NO), the multiplexers 229 and 231 are switched to change the setting to a combination of two electrodes whose source impedance is less than the predetermined threshold (S114). This process is terminated.

  On the other hand, if there are three or more electrodes whose source impedance is less than the predetermined threshold value (S113: YES), a CH pair having a predetermined high priority is selected, and the multiplexers 229 and 231 are switched to the CH pair, and two electrodes are selected. The combination setting is changed (S115).

The selection criterion is that the arrangement direction of the pair of sheet electrodes in the selected pair of CHs matches the predetermined high-priority guidance direction as much as possible. For example, the priority of guidance can be as follows. CH3, 4, 5, and 6 correspond to sheet electrodes 203, 205, 207, and 209, respectively.
First priority: right upper and lower left CH pairs in induction II (CH3-CH4, CH5-CH6)
Second priority: In the third lead, the upper left and lower left CH pairs (CH4-CH6)
3rd priority: Left and right CH pair (CH4-CH5) in the same way up and down in lead I
Fourth priority: upper right, lower right CH pair (CH3-CH5)
After S115, the process returns to the electrocardiogram detection process.

3. Effects produced by the electrocardiogram measurement system The electrocardiogram measurement system of the present embodiment has the same effects as the first embodiment and the second embodiment.

  Further, the feedback circuit ON state and the feedback circuit OFF state can be switched according to the source impedance of each seat electrode and the steering electrode 211 and the traveling state of the vehicle. FIG. 20 shows the relationship between the source impedance of each seat electrode and steering electrode 211, the running state of the vehicle, and the on / off state of the feedback circuit.

  The source impedance of the sheet electrode set as the output of CH1 by switching the multiplexers 229 and 231 is less than a predetermined threshold value (both the sheet electrodes are in sufficient contact with the driver), and the vehicle is running In the state, the electrocardiogram is measured with the feedback circuit on. In addition, when both of the set source impedances of the seat electrodes are equal to or lower than a predetermined threshold, the vehicle is stopped, and the source impedance of the steering electrode 211 is equal to or higher than the predetermined threshold, Measure electricity. In these cases, the same effects as those of the first and second embodiments are obtained.

  Further, when two or more seat electrodes having a source impedance smaller than a predetermined threshold do not exist or when the vehicle is running and the source impedance of the steering electrode 211 is less than an arbitrary threshold, the feedback circuit is off. Measure ECG in single-ended mode. This is due to the following reason.

  In the state where the source impedance of two or more sheet electrodes is not smaller than a predetermined threshold, the electrocardiogram cannot be measured accurately. In this state, since the contact state of the seat electrodes 203, 205, 207, and 209 is considered to be not equivalent, the vehicle noise superimposed on each seat electrode is different, and even if the two seat electrodes are differentiated. Noise may not be reduced. In this state, the single-ended mode is more likely to measure the electrocardiogram accurately.

  When the source impedances of two or more seat electrodes are both equal to or lower than a predetermined threshold, the vehicle stops, and the source impedance of the steering electrode 211 is lower than the predetermined threshold, the feedback circuit is turned off. ECG is measured in single-ended mode. This is because the noise is considered to be less if the vehicle is stopped, and the single-ended mode that can be detected with only one electrode is more effective than the feedback circuit on state that requires two electrodes to be in contact. This is because the electrocardiogram detection rate is improved.

  In addition, said effect is realizable by providing the electrocardiogram measurement system with the feedback determination means which determines ON / OFF of a feedback circuit based on the source impedance between a sheet electrode and a to-be-measured person. Thereby, the measurement method of an electrocardiogram can be selected according to various situations.

  As the feedback determination means, for example, at least one of the source impedance between the sheet electrode A and the person to be measured and the source impedance between the sheet electrode B and the person to be measured is higher than a predetermined threshold. As a condition, there is one that turns off the feedback circuit. By providing such feedback determination means, the electrocardiogram cannot be accurately measured by the differential signal of the sheet electrode A and the sheet electrode B (for example, at least one of the sheet electrode A and the sheet electrode B is measured). In a state where the person is not sufficiently in close contact with the person, the feedback circuit is turned off, and the electrocardiogram can be measured, for example, in a single end mode.

  Further, for example, it comprises means for obtaining the source impedance between the steering electrode and the person to be measured, and noise information obtaining means for obtaining noise information representing the amount of noise of the vehicle, and the feedback determining means comprises the steering electrode The feedback circuit can be turned off on condition that the source impedance is equal to or less than a predetermined threshold and the amount of noise represented by the noise information is equal to or less than the predetermined threshold.

  That is, when the source impedance of the steering electrode is equal to or lower than a predetermined threshold and the amount of noise represented by the noise information is equal to or lower than the predetermined threshold, the differential signal of the seat electrode A and the seat electrode B is not used (for example, Since the electrocardiogram may be accurately measured (by using the single end mode), the feedback circuit is turned off.

  The noise information is information related to the amount of noise derived from the vehicle engine (or motor) or the running state. The noise information includes, for example, the speed of the vehicle (for example, whether the vehicle is stopped), the rotational speed of the engine or motor (for example, whether the engine or motor is stopped), or the like. When the vehicle is traveling, noise is larger than when the vehicle is stopped. Further, when the engine (or motor) is rotating, noise becomes larger than when the engine is stopped.

  For example, when the source impedance of the sheet electrode is less than a predetermined threshold value and the amount of noise represented by the noise information exceeds the predetermined threshold value, the feedback determination unit can turn on the feedback circuit. Even when the amount of noise exceeds a predetermined value, it is possible to cancel the noise by turning on the feedback circuit and making a difference between the sheet electrode A and the sheet electrode B.

  For example, when the feedback circuit is turned off, an electrocardiographic signal can be taken out from one of the sheet electrode A and the sheet electrode B (measurement in a single end mode).

DESCRIPTION OF SYMBOLS 1 ... Electrocardiogram measurement circuit, 3 ... Sheet electrode, 5 ... Sheet electrode, 7 ... Steering electrode, 22 ... Operational amplifier, 25 ... Common mode feedback circuit, 31 ... Operational amplifier, 33 ... Voltage application means, 55 ... Electrocardiogram signal acquisition part 56 ... Impedance calculation unit 61 ... CPU 201 ... Electrocardiogram measurement circuit 203 ... Sheet electrode 205 ... Sheet electrode 207 ... Sheet electrode 209 ... Sheet electrode 211 ... Steering electrode 213 ... Steering electrode 214 ... Sheet, 229 ... Multiplexer, 231 ... Multiplexer, 239 ... Common mode feedback circuit, 249 ... Operational amplifier, 251 ... Voltage application means, 255 ... ECG signal acquisition unit, 255 ... ECG signal measurement unit, 256 ... Impedance calculation unit, 263 ... CPU, 271 ... switch, 273 ... switch, 301 Electrocardiographic measurement circuit

Claims (4)

A sheet electrode A (3, 5, 203, 205, 207, 209) and a sheet electrode B (3, 5, 203, 205, 207, 209) provided on a vehicle seat;
Steering electrodes (7, 211) provided on the steering of the vehicle;
A feedback circuit (25, 239) for feeding back a potential between the seat electrode A and the seat electrode B to the steering electrode;
Voltage application means (33, 251) for applying a predetermined AC voltage to the measurement subject seated on the seat;
Electrocardiographic acquisition means (61, 263) for taking out a differential signal of the sheet electrode A and the sheet electrode B as an electrocardiographic signal;
Based on the input signal to which the AC voltage is applied from the voltage application means and input to the person to be measured, and the output signals of the sheet electrode A and the sheet electrode B, the sheet electrode A and the person to be measured A source impedance acquisition unit (61, 263) for acquiring a source impedance between the sheet electrode B and a source impedance between the sheet electrode B and the person to be measured. The voltage applying means applies the AC voltage to the feedback circuit,
The electrocardiogram measurement system according to claim 1, wherein the input signal is a signal input to the steering electrode. The electrocardiogram measurement system according to claim 1 or 2, wherein the voltage application unit adjusts the amplitude and / or frequency of the AC voltage based on the input signal. The adjustment means (9, 11) for adjusting the input impedance of the sheet electrode A and / or the sheet electrode B based on the input signal is provided. The electrocardiogram measurement system described in 1.