Abstract:
Object 
     An object of the present invention is to provide a pressure-sensitive conductive yarn capable of detecting different biological information simultaneously when used as an electrode. 
     Means for Achieving the Object 
     A pressure-sensitive conductive yarn comprising a core yarn formed of an elastic yarn around which a winding yarn having conductivity is wound, wherein the winding yarn is a mixed yarn of a conductive fiber and a nonconductive fiber to cause variations in its electrical resistance with elongation or contraction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    (1) Field of the Invention 
         [0002]    The present invention relates to a pressure-sensitive conductive yarn and a garment for measuring biological information. 
         [0003]    (2) Description of the Related Art 
         [0004]    Biological information, e.g., respiration, heart rate, etc., is an important index for determining health conditions; however, known biological signal measurements require application of electrodes using gel, the wrapping of respiration bands, etc., causing great discomfort to the body. 
         [0005]    To eliminate such discomfort and facilitate daily health management, some attempts have been made to allow for the detection of biological information in a natural state by applying electrodes to a garment. For example, 
         [0000]    Patent Document 1 discloses providing electrodes formed of a conductive yarn on a garment to detect pulse signals. 
         [0006]    Patent Document 1: Japanese Unexamined Patent Publication No. 2005-525477 
       BRIEF SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
       [0007]    However, a known electrode made of a conductive yarn can detect only one kind of biological information from detected signals; therefore, another electrode is required to measure other biological information such as respiration signals, etc., together with pulse signals. However, this may cause discomfort during wear, and cost problems. 
         [0008]    An object of the present invention is to provide a pressure-sensitive conductive yarn that is capable of detecting different biological information simultaneously when used as an electrode, and further a biological information-measuring garment including the pressure-sensitive conductive yarn. 
       Means for solving the problem 
       [0009]    The object of the present invention can be achieved by a pressure-sensitive conductive yarn comprising a core yarn formed of an elastic yarn around which a winding yarn having conductivity is wound, wherein the winding yarn is a mixed yarn of a conductive fiber and nonconductive fiber to cause variations its electrical resistance with elongation or contraction. 
         [0010]    In the pressure-sensitive conductive yarn, it is preferable that the winding yarn be doubly wound around the core yarn, and that the first winding direction be opposite to the second winding direction. 
         [0011]    The object of the present invention can be achieved by a biological information-measuring garment including electrodes that are arranged on the garment formed of a nonconductive material in such a manner as to closely contact with the body, wherein the electrodes are formed of the pressure-sensitive conductive yarn. 
         [0012]    According to the biological information-measuring garment of the invention, a heart rate signal and respiration signal can be simultaneously extracted based on the output signals from the electrodes. 
       Effect of the Invention 
       [0013]    When the pressure-sensitive conductive yarn of the present invention is used as an electrode, different biological information can be detected at the same time. 
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING 
       [0014]      FIG. 1  is a schematic configuration view of one embodiment of the pressure-sensitive conductive yarn of the present invention. 
         [0015]      FIG. 2  is a graph showing an example of the relationship between the tension (load) on the winding yarn, and the resistance value. 
         [0016]      FIG. 3  is a configuration view of a measurement circuit used in the measurement shown in  FIG. 2 . 
         [0017]      FIG. 4  is a graph showing an example of the relationship between the load on the winding yarn and the elongation rate of the winding yarn. 
         [0018]      FIG. 5  is a graph showing the relationship between the elongation rate and the resistance value according to one embodiment of the pressure-sensitive conductive yarn. 
         [0019]      FIG. 6  is a schematic configuration view of one embodiment of the biological information-measuring garment of the present invention. 
         [0020]      FIG. 7  is a graph showing an example of the wave pattern of the output voltage detected from the biological information-measuring garment of  FIG. 6 . 
         [0021]      FIG. 8(   a ) is a graph showing an example of the measurement results of heart rate signals.  FIG. 8(   b ) is a graph showing an example of the reference signals of the heart rate signals. 
         [0022]      FIG. 9(   a ) is a graph showing an example of respiration signals.  FIG. 9(   b ) is a graph showing an example of the reference signals of the respiration signals. 
       EXPLANATION OF NUMERALS 
       [0000]    
       
           1 : Pressure-sensitive conductive yarn 
           2 : Core yarn 
           4 ,  6 : Winding yarn 
           10 : Biological information-measuring garment 
           12 : Garment body 
           14 , 16 : Different electrode 
           18 : GND electrode 
       
     
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Embodiments of the present invention will now be described with reference to the accompanying drawings. 
       Pressure-Sensitive Conductive Yarn 
       [0031]      FIG. 1  is a schematic configuration view of one embodiment of the pressure-sensitive conductive yarn of the present invention. As shown in  FIG. 1 , the pressure-sensitive conductive yarn  1  is formed by doubly winding the winding yarn  4 ,  6  around the core yarn  2  composed of elastic yarn such as polyurethane. The winding direction of the first winding yarn  4  is opposite that of the second winding yarn  6 . The pressure-sensitive conductive yarn  1  is produced by the same method as that of known double covering yarns. 
         [0032]    The winding yarn  4 ,  6  is a mixed yarn of a conductive fiber such as stainless steel fiber and a nonconductive fiber such as polyester fiber; for example, those described in Japanese Unexamined Patent Publication No. 2003-20538 are preferably used. When a large amount of tension is exerted on the winding yarn  4 ,  6  having such properties, the density of the conductive fiber becomes large, resulting in low electrical resistance. In contrast, when a small amount of tension is exerted on the winding yarn, the density of the conductive fiber becomes small, resulting in high electrical resistance. That is, the electrical resistance value varies with changes in the tension on the winding yarn  4 ,  6 . 
         [0033]      FIG. 2  is a graph showing an example of the relationship between the tension (load) on the winding yarn and the resistance value, and shows the measurement results of five winding yarns. As a winding yarn, a yarn having a blending ratio of 70/30 (polyester fiber/stainless fiber) was used. With the winding yarn (300 mm) having a weight at the end, changes in the resistance value of the winding yarn were measured using the measurement circuit of  FIG. 3 . In  FIG. 3 , VCC indicates a constant voltage (5V); R 1 , metal film resistor (1 kΩ); and Rx, resistance of the subject winding yarn. The resistance value of Rx was calculated based on the output voltage (Vout) obtained when the VCC was divided by R 1  and Rx. Water was used as a weight, and increased in 5 g increments up to 150 g. The measurement of “Vout” was conducted using a portable oscilloscope (ZR-MDR 10, produced by OMRON Corporation) at a sampling rate of 200 Hz. 
         [0034]    As shown in  FIG. 2 , when the weight of the load is about 40 g or less, the resistance values of all of the winding yarns are significantly decreased as the load increases. This indicates that there is a correlation between the tension acting on the winding yarn and the resistance value. In contrast, when the weight of the load is 40 g or more, almost no change was observed in the resistance values of the winding yarns. This indicates that the measurement of the resistant value does not help to uniquely determine the weight of the load. 
         [0035]      FIG. 4  is a graph showing an example of the relationship between the load acting on the winding yarn and the elongation rate of the winding yarn. The elongation rate is defined based on the natural length of the winding yarn. When the load has a good correlation with the resistance value, i.e., when the weight of the load is 40 g or less, the elongation rate is as small as 1% or less, as shown in  FIG. 4 . Therefore, when a winding yarn alone is used as an electrode, it is difficult to accurately extract biological signals that can be detected from body movements associated with respiration or the like. 
         [0036]    On the other hand, in the pressure-sensitive conductive yarn  1  of the present embodiment, the winding yarn  4 ,  6  having the aforementioned properties is wound around the core yarn  2  composed of an elastic yarn. Therefore, even when the large amount of tension resulting from body movements acts on the pressure-sensitive conductive yarn  1  to greatly elongate the core yarn  2 , the elongation of the winding yarn  4 ,  6  wound around the core yarn can be relatively suppressed. Accordingly, the entire elongation of the pressure-sensitive conductive yarn  1  can be detected as a small deformation of the winding yarn  4 ,  6 , which allows for an accurate detection of biological signals associated with respiratory body movements or the like. 
         [0037]      FIG. 5  is a graph showing an example of the relationship between the elongation rate and the resistance value according to the pressure-sensitive conductive yarn  1  of the present embodiment. The pressure-sensitive conductive yarn  1  had an initial length of 100 mm, and the elongation rate was measured up to 20% in 4% increments. The resistance value was measured in the same manner as in the measurement of the winding yarn alone described above, and the test was conducted three times for the same pressure-sensitive conductive yarn  1 . As shown in  FIG. 5 , the resistance value was continuously changed until the elongation rate achieved 20%. This indicates that the pressure-sensitive conductive yarn of the present invention can detect a more significant elongation rate change as a resistance value change, compared to the results of the winding yarn alone, as shown in  FIGS. 2 and 4 . 
         [0038]    In the pressure-sensitive conductive yarn  1  of the present embodiment, the winding yarns  4 , 6 , each having a different winding direction, are wound around the core yarn  2 , which cancels out the torque, resulting in a stable yarn. Further, due to the variations in the contact density of the winding yarns  4 ,  6 , the pressure-sensitive conductive yarn  1  of the present invention has a higher sensitivity than the pressure-sensitive conductive yarn having a single winding yarn. However, the winding yarn may be singly wound around the core yarn. In this case also, biological signals associated with body movements can be detected by suppressing the elongation of the winding yarn relative to the core yarn. 
         [0039]    Further, by employing the covering structure in which a material having stretch properties is used as the core yarn  2 , the stretch properties of the core yarn  2  is stabilized, which reduces hysteresis and provides the winding yarn  4 ,  6  with a length enough for the entire deformation. Thereby, the winding yarn  4 ,  6  can be utilized in a stable deformation range, which allows for a stable detection compared to when the winding yarn  4 ,  6  is utilized alone without the core material  2 . 
       Biological Information-Measuring Garment 
       [0040]    The pressure-sensitive conductive yarn  1  as mentioned above is formed into a woven or knitted fabric to produce a sheet-like electrode. A biological information-measuring garment can be obtained by sewing the electrode on a garment. 
         [0041]      FIG. 6  is a schematic configuration view of the biological information-measuring garment according to one embodiment of the present invention. The biological information-measuring garment  10  shown in  FIG. 6  is used for measuring heart rate and respiration at the same time, and is provided with two different electrodes  14 ,  16  and a GND electrode (indifferent electrode)  18  inside the garment body  12 . It is preferable that the garment body  12  be in the form of a T-shirt composed of a nonconductive material such as highly elastic polyurethane, and have a certain level of stretch properties so that the provided electrodes  14 ,  16 , and  18  are easily attached to the body. 
         [0042]    The different electrodes  14 ,  16  are provided on the right clavicular region and left subcostal region, respectively, according to the bipolar lead II of an ECG system, and the GND electrode  18  is provided on the left clavicular region. The different electrode  14  placed on the right clavicular region, different electrode  16  placed on the left subcostal region, and GND electrode  18  are all woven fabrics made of the pressure-sensitive conductive yarn  1  of  FIG. 1 , and are fixed to the garment body  12  by sewing or the like. The size of the different electrodes  14 ,  16  is, for example, about 60×30 (mm). 
         [0043]    To reduce the effects of noise from commercial power supplies, knitted fabrics or the like composed of the pressure-sensitive conductive yarn  1  may be provided as shields on the front side of the garment body  12  at the regions corresponding to the different electrodes  14  and  16 . Further, to ensure the adhesion between the user&#39;s body and each of the different electrodes  14 ,  16 , and GND electrode  18 , an elastic body such as urethane foam may be inserted between the garment body  12  and each of the different electrodes  14 ,  16  and GND electrode  18 . However, such shields and elastic bodies are not essential for the present invention. 
         [0044]    With the subject wearing the biological information-measuring garment  10  of  FIG. 6 , the output voltage, which is the potential difference of the different electrodes  14  and  16  based on the GND electrode  18 , was measured. The gain was set to ×510, and a primary high pass filter (HPF) having a cutoff frequency of 0.05 Hz and a fourth-order low pass filter (LPF) having a cutoff frequency of 30 Hz were used. An example of the output voltage is shown in  FIG. 7 . The output voltage was measured using a portable oscilloscope (ZR-MDR 10, produced by OMRON Corporation). It is possible to enter the value of the output voltage in the wristwatch-type information processing device to display and store it. 
         [0045]    The output voltage shown in  FIG. 7  includes a heart rate signal based on the electrocardiogram, as well as a respiration signal emitted from respiratory trunk movements. Specifically, when the elongation or contraction of the different electrode  16  on the left subcostal region causes a small deformation on the winding yarn  4 ,  6 , the baseline oscillates due to the differential motion with the different electrode  14  on the right clavicular region. Using this information, respiration can be detected. 
         [0046]    In conducting the measurement, heart rate signals were extracted by filtering the output voltage by HPF at 0.8 Hz while respiration signals were extracted by LPF at 0.8 Hz. The separated heart rate signals and respiration signals are shown in  FIG. 8(   a ) and  FIG. 9(   a ), respectively. 
         [0047]    At the same time, the reference signals of each of the heart rate signals and respiration signals were measured. A disposable electrode (Blue Sensor, produced by Ambu) and a respiration pick-up (AP-C022, produced by Futami ME) were used for detecting the reference signals of the heart rate and that of the respiration, respectively. The signals are simultaneously measured and recorded using a Polymate (AP1524, produced by TECH).  FIG. 8(   b ) and  FIG. 9(   b ) show the heart rate reference signals and respiration reference signals, respectively. 
         [0048]    The comparison between  FIGS. 8(   a ) and ( b ), and the comparison between  FIGS. 9(   a ) and ( b ) reveal that both of the heart rate signals and respiration signals have wave patterns similar to those of the reference signals, indicating that the biological information-measuring garment  10  of the present embodiment can detect a heart rate signal and respiration signal at the same time. 
         [0049]    In the biological information-measuring garment  10  of the present embodiment, the location and the number of electrodes are not particularly limited, and can be suitably changed depending on the subject biological information and measurement principal, such as electromyography and brain waves. Further, the form of the garment body  12  on which the electrodes are attached is not limited to T-shirts, and any garment or clothing accessory can be selected in accordance with the location of the electrodes. In the present embodiment, the both electrodes are formed using the pressure-sensitive conductive yarn of the present invention; however, only one side of the electrodes, i.e., the electrode placed on the region elongated and contracted by body movements, may be formed of the pressure-sensitive conductive yarn of the present invention. 
         [0050]    In addition to the known biological signal measurements using an electrode, the biological information-measuring garment of the present invention can simultaneously detect biological signals that result from body movements, such as respiration, movement of the shoulder joints, leaning of the trunk, movement of the neck by feeling of fullness or swallowing, etc. Therefore, the present invention is particularly appropriate for this purpose.