JP2005270546A - Biological information measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological information measuring apparatus with which the living body information such as the pulse rate or the like can be measured with high accuracy while a size of an electrode terminal to sense a condition of contact with the skin is reduced to the utmost. <P>SOLUTION: When the biological information such as the pulse or the like is measured, an A electrode terminal 32 and a B electrode terminal 33 are brought into contact with the skin 31a of a living body 31. The A electrode terminal 32 is connected to an input terminal (a) of an inverter IC 34 and the B electrode terminal 33 is connected to a grounding electrode GND. The contact potential of the A electrode terminal 32 to the skin 31a is amplified by the inverter IC 34 and is taken out to an output terminal P1. At this time, an amplification factor of the inverter IC 34 is determined by the feedback resistance Rf so that the contact potentials of both the electrode terminals which are brought into contact with the skin 31a can be detected with a high potential level. Therefore, even though areas of the A electrode terminal 32 and the B electrode terminal 33 are made small, it is possible to detect with high accuracy whether a sensor unit to measure the biological information is brought into contact with the skin 31a or not so that the pulse or the like can be accurately measured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biological information measuring apparatus for measuring biological information of a human body, and more particularly, to a biological information measuring apparatus that measures biological information such as a pulse while being worn on a wrist such as a wristwatch.

  2. Description of the Related Art Conventionally, a biological information measuring apparatus that calculates biological information such as a pulse rate by irradiating a living body with light and receiving backscattered light has been widely used. Such an optical biological information measuring apparatus irradiates a living body with a light emitting element by attaching a sensor unit including a light emitting element (for example, a light emitting diode) and a light receiving element (for example, a photodiode) to the wrist of the living body. The light receiving element receives the backscattered light of the measured light, and can detect the amount of the backscattered light that changes according to the pulse. In particular, this type of biological information measuring device is configured to be a wristwatch and attachable to the user's wrist so that the user can easily carry it. In addition, when a user wraps around the wrist to measure a pulse or the like, the living body is configured so that even if the wrist is moved, the degree of close contact between the sensor unit and the wrist epidermis is kept constant and the biological information can be detected accurately. An information measuring device is also disclosed (for example, Patent Document 1).

  Furthermore, a technique for detecting whether or not the pulse sensor is in contact with the skin and stopping the measurement process of the pulse meter when the pulse sensor is not in contact with the skin and preventing useless use of the battery is disclosed. Has been. At this time, the method for detecting whether or not the pulse sensor is in contact with the skin is such that when the two electrode terminals are brought into contact with the skin and discharged, the voltage between both electrodes drops below a predetermined voltage (that is, 2 A method is used in which it is determined that the electrode terminal is in contact with the skin (for example, see Patent Document 2).

Usually, a pulse meter or the like detects whether or not the pulse sensor (sensor unit) is in contact with the skin with two electrode terminals, and calculates the pulse rate with an optical sensor when the pulse sensor is in contact with the skin. It is configured as follows. Therefore, since there are 3 to 5 sweat glands per 1 mm ² and sweating is active, the skin resistance is low, so the size of the electrode terminal is about 3 mm in diameter (that is, about 7 mm ² in surface area). If it carries out above, the contact state of skin can be detected reliably. At this time, the resistance value between the electrode terminals through the skin is 500 KΩ to 1 MΩ. In this way, fingertips with a lot of sweat glands, which are parts with low skin resistance, and body parts with reduced skin resistance due to sweating during exercise, etc. have a small contact resistance of the electrode terminals, so the electrode terminals with a small area However, it is possible to accurately detect whether the pulse sensor is in contact with the skin. However, when a pulse sensor is attached to the wrist or the like, the number of sweat glands is smaller than the fingertip and the skin resistance is high, so it is necessary to detect the contact state by increasing the area of the electrode terminal.
JP 2001-78973 A JP 2003-70757 A

However, a wristwatch-type pulsometer or the like in which a pulse sensor is brought into contact with a wrist or the like is small in size as a whole. Therefore, when the area of the electrode terminals is increased, the area occupied by the two electrode terminals is increased. In particular, the skin such as the arms, wrists, and abdomen has a small number of sweat glands. For example, the abdomen has about one sweat gland per 1 mm ² , so that the skin resistance inevitably increases. Furthermore, in elderly people, the ratio of impotence sweat sweat glands in the skin increases and skin resistance increases, so the contact state of the pulse sensor can be detected unless the electrode terminal area is further increased. I can't.

For example, if the number of active sweat glands and ² per 0.2 pieces 1mm in the wrist, wrist area 15 mm ² becomes the number of active sweat glands of 1mm ² per fingertip is equivalent to three, the result is the wrist When the electrode terminal is brought into contact with the electrode terminal, an electrode terminal having an area 15 times larger than the area of the fingertip is required. In other words, since the size of the electrode terminal at the fingertip usually requires a diameter of about 3 mm (surface area of about 7 mm ² ), the area of the electrode terminal at the wrist needs to be 7 mm ² × 15 = 105 mm ^2. Specifically, two electrode terminals having a diameter of 11.6 mm are required.

  Adhering such a large electrode terminal to the wrist is a major obstacle to downsizing a wristwatch-type pulse meter. In other words, it is difficult to enlarge the electrode terminal in a wristwatch-type pulsometer attached to the wrist, and it is necessary to devise it so that it can be stored in the pulsometer device as an electrode terminal of a correspondingly small size. is there. However, in the conventional technique disclosed in Patent Document 2, the contact state is detected unless the area of the electrode terminal is increased from the operation of the contact detection circuit that detects the contact state of the electrode terminal with the skin. Sensitivity cannot be increased. In other words, the conventional technique cannot eliminate the trade-off relationship between reducing the electrode terminal and increasing the contact state detection sensitivity. In other words, a biological information measuring device such as a pulsometer cannot be reduced in size unless the electrode terminal is reduced. However, since the conventional technology cannot accurately detect the contact state if the electrode terminal is reduced, it is reduced in size and weight. Is hindering their needs.

  The present invention has been made in view of the above-described problems, and the electrode terminal for detecting the contact state with the skin can be made as small as possible to measure biological information such as a pulse with high accuracy. An object of the present invention is to provide a living body information measuring apparatus.

  The living body information measuring device of the present invention was created to achieve the above-described object, and the living body is irradiated with light from the sensor unit, and the sensor unit receives backscattered light from the living body. A biological information measuring device for measuring information, comprising: two electrode terminals for detecting whether or not a sensor unit is in contact with a living body; and detection of a first electrode terminal of the two electrode terminals An electrode-type contact detecting means is provided, comprising an inverting amplifier that amplifies the potential with respect to the ground potential of the second electrode terminal.

  According to the present invention, the weak contact detection voltage when the electrode terminal contacts the living body's skin is amplified by the CMOS inversion type amplifier. Thereby, even if the area of the electrode terminal is reduced (that is, even if the skin resistance is high), it is possible to detect with high accuracy whether the sensor unit of the biological information measuring device is in contact with the living body.

  In the biological information measuring device of the present invention, the feedback resistance Rf of the inverting amplifier is the output voltage Vout of the sensor unit, the skin resistance value between the first electrode terminal and the second electrode terminal is Rs, When the contact detection threshold voltage when the first electrode terminal and the second electrode terminal are in contact with the living body is Vs, it is a value obtained by Rf> Rs {(Vout−Vs) / Vs}. And

  According to the present invention, even if the electrode area of the two electrode terminals is small and the skin resistance is high, if the feedback resistance Rf of the inverting amplifier is set to be equal to or higher than the resistance value obtained by the above formula, the inverter IC The contact detection voltage can be increased by increasing the amplification factor. Therefore, even if the area of the electrode terminal is small, the contact state of the sensor unit can be detected with high accuracy, so that the biological information measuring device can be further reduced in size.

  In the living body information measuring device of the present invention, the light emitting circuit for irradiating the living body with the light emitting element and the light receiving for detecting whether the sensor unit is in contact with the living body by receiving the backscattered light from the living body. And an optical contact detector configured by a circuit. In other words, the detection by the electrode-type contact detection means is easily affected by the moisture of the living body, and the detection light intensity depends on the state of the living body in the detection by the optical contact detection means that determines the presence or absence of the contact of the living body from the change in the detection light intensity Because it changes, there is a possibility that it may be affected by the state of the living body, but by using both the electrode-type contact detection means and the optical contact detection means as in this invention, it is possible to make contact with high accuracy by compensating for the disadvantages of both. The state can be detected. In other words, in the detection of the contact state by either one of the methods, it may be determined that it is not mounted even if it is mounted, or it may be determined that it is mounted even if it is not securely mounted. The contact state can be accurately and reliably detected by detecting the contact state in combination with the optical contact detection unit and the optical contact detection unit.

  In the living body information measuring device of the present invention, the optical contact detection means measures living body information together. In other words, since biological information is detected by a sensor unit including a light emitting circuit and a light receiving circuit, if the light emitting circuit and the light receiving circuit are directly used as an optical contact detection means to detect a contact state, the circuit configuration is further simplified. can do.

  In the biological information measuring device of the present invention, a pulse is measured as biological information. That is, according to the biological information measuring device of the present invention, even when applied to a watch-type pulse meter attached to a wrist or the like, it is possible to accurately detect a contact state with the wrist and measure a pulse or the like with high accuracy. it can.

  According to the biological information measuring apparatus of the present invention, since the weak contact detection voltage when the electrode terminal comes into contact with the skin of the living body is amplified by the CMOS inverter IC, even if the area of the electrode terminal is reduced, the sensor Whether or not the unit is in contact with the living body can be accurately detected. At this time, if the feedback resistance Rf of the inverter IC is set to a desired resistance value based on the calculation formula, the amplification factor of the inverter IC can be increased, so that the area of the electrode terminal can be further reduced. As a result, the wristwatch-type biological information measuring apparatus can be further reduced in size.

  Further, according to the biological information measuring apparatus of the present invention, by using both the electrode-type contact detection means and the optical contact detection means, the contact state can be detected with high accuracy while making up for the disadvantages of both. For example, the detection by the electrode type contact detection means is easily influenced by the moisture of the living body, and the detection light intensity depends on the state of the living body in the detection by the optical contact detection means for judging the presence or absence of the contact of the living body from the change in the detection light intensity. However, by using both methods, it is possible to detect the contact state with high accuracy by making up for the disadvantages of both. In addition, since biological information is detected by a sensor unit including a light emitting circuit and a light receiving circuit, the circuit configuration can be further simplified by using the light emitting circuit and the light receiving circuit as they are for the optical contact detection means. If such a biological information measuring device is applied to a clock-type pulse meter or the like, the pulse meter can be further reduced in size and weight.

  Hereinafter, embodiments of a biological information measuring device according to the present invention will be described in detail with reference to the drawings. First, an outline of the biological information measuring device according to the present invention will be described. In the following description, in order to facilitate understanding, a case where the biological information measuring device is a pulse meter will be described, but the present invention is not limited to the biological information measuring device.

  The pulse meter according to the present invention is equipped with a sensor unit including a light emitting element and a light receiving element on a wrist of a living body, and the light receiving element receives the back scattered light of the light irradiated to the living body by the light emitting element, Although the pulse is measured by detecting the amount of light, this technique is the same as the prior art. In the present invention, the electrode terminal for detecting the contact state of the pulse meter with the skin is made as small as possible, and the contact voltage indicating the contact state with the skin is amplified by an amplifier in which the CMOS inverter IC is linearly operated. It is characterized by being configured to detect the contact state with the skin with high accuracy. Hereinafter, the sensor that detects the contact state with the electrode terminal in this manner is referred to as an electrode-type contact detection sensor (electrode-type contact detection means). Furthermore, the contact state to the skin is detected by backscattered light from the skin using an optical sensor having a light emitting element and a light receiving element. Hereinafter, the sensor that detects the contact state with the skin using the optical sensor in this manner is referred to as an optical contact detection sensor (optical contact detection means). That is, in the pulse meter of the present invention, the contact state of the pulse sensor with the skin is detected with high accuracy using the electrode type contact detection sensor and the optical contact detection sensor.

  Hereinafter, embodiments of a pulse meter applied to the present invention will be described in detail with reference to the drawings. 1A and 1B are a perspective view and a cross-sectional view of a pulse meter applied to the present invention, wherein FIG. 1A is a front view, FIG. 1B is a back view, and FIG. . As shown in FIG. 1, the pulsometer 1 is configured to be worn on the wrist of a human body by a wristband 2. Further, as shown in FIG. 1A, a liquid crystal display unit 3 for displaying various information such as date, time, and pulse rate is provided on the surface of the pulsometer 1, and time adjustment is provided on the side surface. Various button switches 4 for switching display modes and the like are provided. Moreover, as shown in FIG.1 (b), the rectangular sensor unit 5 is provided in the substantially center part on the back surface (namely, surface which contacts a wrist) of the pulsometer 1. FIG. The sensor unit 5 is covered with transparent glass, and an LED (Light Emitting Diode) 7 that is a light emitting element and a photodiode 8 that is a light receiving element are mounted therein as shown in FIG. Yes. In addition, a pair of electrode terminals 6 protrude from both sides of the sensor unit 5 in the longitudinal direction.

  When the pulsometer 1 configured as shown in FIG. 1 is worn on the wrist and a predetermined operation is performed by the button switch 4, the pair of electrode terminals 6 detects the contact state with the skin. Here, when it is detected that the contact is normal, light from the LED 7 which is a light emitting element of the sensor unit 5 is irradiated to the skin. The irradiated light is absorbed and scattered by tissues such as fat and muscle in the living body, hemoglobin in blood, and the like, and the back scattered light is received by the photodiode 8 which is a light receiving element. As a result, the photodiode 8 outputs an electrical signal corresponding to the amount of received light. Although the amount of absorption by tissues such as fat and muscle does not change much, the amount of hemoglobin in the blood changes according to the pulsation because the amount of hemoglobin changes due to pulsation. Therefore, as a result, the pulse meter 1 can calculate the pulse rate from the output signal of the photodiode 8 and display it on the liquid crystal display unit 3.

  Next, the configuration of the pulse meter 1 applied to the present invention will be described in more detail. FIG. 2 is a block diagram schematically showing a circuit configuration of a pulse meter applied to the present invention. The pulsometer 1 detects a CPU (Central Processing Unit) 11 that performs various arithmetic processes, a contact sensor 12 that is a pair of electrode terminals for contacting the skin, and a state of contact with the skin by the pair of electrode terminals at a voltage level. A contact state detection circuit 13, a pulse sensor 14 for detecting a pulse signal corresponding to the pulse rate by an optical signal, a pulse detection circuit 15 for converting the pulse signal detected by the pulse sensor 14 to a voltage level, and the voltage level converted to a voltage level Filter circuit 16 for removing noise contained in the pulse signal, amplification circuit 17 for amplifying the voltage level of the pulse signal, A / D conversion means for converting the voltage level of the contact state with the skin and the voltage level of the pulse signal into digital values 18. Input means such as an oscillation circuit 19 for generating a timing signal for driving the pulse sensor 14, an input button pressed by the user 0, a communication means 21 serving as a communication interface between the CPU 11 and the outside, a drive signal generating means 22 for generating a drive signal for the pulse sensor 14 based on a timing signal generated by the oscillation circuit 19, and a pulse for driving the pulse sensor 14 The sensor driving circuit 23 includes a display unit 24 that displays a pulse rate or the like by liquid crystal, an illumination unit 25 that illuminates the display unit 24, and a notification unit 26 that notifies abnormality information. The CPU 11 includes a calculation unit 11a that executes a pulse rate calculation process, a time measurement unit 11b that counts the time for counting the pulse rate, and a storage unit 11c that includes a ROM, a RAM, and the like. Each of these elements is connected by a bus.

  The function of each component will be described in more detail. In the CPU 11, the calculation means 11a executes a pulse signal detection process and a pulse rate calculation process based on the time count by the time measuring means 11b. These processing programs are stored in the storage unit 11c. Further, when the pulse signal detection process and the pulse rate calculation process are executed based on the button operation of the input means 20, the CPU 11 expands the corresponding processing program stored in the storage means 11c, and executes each process. Is temporarily stored in the storage unit 11c (for example, information on the calculation result of the pulse rate or information indicating that there is no contact). The CPU 11 also has a function of causing the display unit 24 to display the processing contents temporarily stored in the storage unit 11c.

  The contact state detection circuit 13 is a circuit for converting the contact signal detected by the contact sensor 12 into a voltage level and detecting whether or not the pulsometer 1 is reliably in contact with the skin. That is, the circuit detects the contact state by amplifying the signal level when the pair of contact terminals contact the skin.

  The pulse sensor 14 is a sensor configured such that a photodiode, which is a light receiving element, detects backscattered light emitted from an LED, which is a light emitting element, toward the skin. The pulse detection circuit 15 is a circuit that converts an optical signal caused by backscattering detected by a light receiving element (photodiode) of the pulse sensor 14 into a voltage level. The filter circuit 16 is a circuit that removes noise included in the optical signal due to backscattering of the voltage level output from the pulse detection circuit 15. The amplifying circuit 17 is a circuit that amplifies the optical signal caused by backscattering input from the pulse detecting circuit 15 to a predetermined magnification indicated by the CPU 11 and outputs the amplified signal to the A / D converting means 18. The A / D conversion means 18 is a circuit that converts an optical signal caused by backscattering from an analog signal to a digital signal and transmits it to the CPU 11. Then, the CPU 11 determines whether or not the pulse meter 1 is in contact with the skin based on the signal from the contact sensor 12, and performs the pulse rate counting process based on the signal from the pulse sensor 14.

  Next, the contact state detection circuit 13 applied to the present invention in order to reduce the electrode terminal of the contact sensor 12 will be described. For example, as disclosed in Patent Document 2, the conventional contact state detection circuit detects the contact potential level of two electrode terminals that are in contact with the skin, and both of the contact potential levels become Low. Sometimes, the circuit configuration is such that the output of the NOR circuit becomes High and the contact state is detected. For this reason, unless the area of the electrode terminal is relatively large, the potential level cannot be set low when contacting the skin. As a result, the state of contact with the skin is detected unless the area of the electrode terminal is increased. I can't.

  However, in the present invention, a standard logic CMOS inverter IC (unbuffered type) is provided so that the skin resistance can be reliably detected even if the area of the electrode terminal in contact with the skin is reduced (that is, the skin resistance is high). ) Is used for linear operation. That is, the operating point when the feedback resistor Rf is inserted into the CMOS inverter IC and not mounted (Rs = ∞) is Vs = Vout. This voltage can be expressed as a power supply voltage Vcc / 2. That is, the detection voltage is also determined by determining the operating point based on the balance between the feedback resistance Rf and the skin resistance Rs. By making the feedback resistance Rf high, even if the area of the electrode terminal is small and the skin resistance is high, the contact state can be detected with high accuracy.

  FIG. 3 is an example of a contact state detection circuit used in the pulse meter of the present invention. In FIG. 3, an A electrode terminal 32 that is in contact with the skin 31a of a living body 31 is connected to an input terminal a of a CMOS inverter IC (hereinafter simply referred to as an inverter IC) 34 via a protective resistor R1. The other B electrode terminal 33 in contact with the skin 31a of the living body 31 is connected to the ground electrode GND through a protective resistor R2. Further, the output terminal b of the inverter IC 34 is connected to the input terminal a of the inverter IC 34 via the feedback resistor Rf and the capacitor Cf. With such a configuration of the amplifier circuit, a voltage amplified to a desired level is output to the output terminals P1 and P2.

  The amplification factor of the inverter IC 34 is determined by the feedback resistor Rf. The larger the feedback resistor Rf, the higher the amplification factor. However, when the feedback resistor Rf is infinite, a hunting phenomenon or the like is caused and the circuit becomes unstable. On the other hand, when the feedback resistance Rf is set to a high resistance of 100 MΩ or more, the voltage at the output terminal b (that is, the output terminal P1) of the inverter IC 34 can be amplified to about ½ of the power supply voltage Vcc. That is, as shown in FIG. 3, when the A electrode terminal 32 and the B electrode terminal 33 having a small area are connected to the input gate (input terminal a) and the ground electrode GND of the inverter IC 34, the skin resistance Rs becomes ∞, and the output voltage Becomes the same voltage level as the operating voltage, and when the electrode terminals 32 and 33 are brought into contact with the skin 31a of the living body 31, the skin resistance Rs ≦ 120 MΩ, and the operating point of the input gate (input terminal a) of the inverter IC 34 is lowered. In this case, the output terminal b (that is, the output terminal P1) of the inverter IC 34 can be set to a high level up to a potential close to the power supply voltage. Thus, by using the contact state detection circuit by the inverter IC 34 as shown in FIG. 3, the contact state to the skin can be reliably detected even when the A electrode terminal 32 and the B electrode terminal 33 having a small area are used. Is possible.

  Next, specific examples will be described. FIG. 4 is an actual measurement characteristic diagram showing the transition of the wearing time of the electrode terminal and the skin resistance value. In FIG. 4, the horizontal axis indicates the wearing time of the electrode terminals, and the vertical axis indicates the skin resistance value (MΩ). The skin resistance value at the time of wearing was about 2-3 MΩ, and the initial resistance value was immediately after exercise, so the skin resistance value was minimized. The skin resistance value does not increase so much until about 80 minutes after wearing, but thereafter, the skin resistance value increases with time and reaches about 20 MΩ as the state becomes normal.

Thus, when the skin resistance of a living body is actually measured using an electrode terminal, it is distributed over a wide range with a considerably high resistance of 6 to 24 MΩ / cm ² depending on the activity of the living body. Therefore, the resistance value of the electrode terminal detection target is set to 28.8 MΩ / cm ² , which is a 20% increase of the maximum distributed resistance value of 24 MΩ / cm ² , and the contact state detection circuit in FIG. It was.

  As an example, when the size of the two electrode terminals (the A electrode terminal 32 and the B electrode terminal 33) is 0.6 cm wide × 0.4 cm long, and the distance between the electrode centers in the width direction is 2 cm, The skin resistance value Rs is Rs = 28.8 MΩ × (2 / 0.6) = 96 MΩ. On the other hand, the condition that the output terminal b of the inverter IC34 in FIG. 3 is at a high level is that the voltage at the input terminal a of the inverter IC34 (that is, the high level threshold voltage Vs) is 0.55V when the power supply voltage Vcc is 3.1V. It becomes.

  On the other hand, the feedback resistance Rf of the inverter IC 34 in FIG. 3 can be obtained by the following equation (1).

Vs> Vcc × {Rs / (Rf + Rs)} (1)
Here, since the power supply voltage Vcc is 3.1 V, the skin resistance value Rs is 96 MΩ, and the high level threshold voltage Vs is 0.55 V, Rf> Rs {(Vcc−Vs) / Vs} = 96 MΩ from Equation (1). X {(3.1-0.55) /0.55} = 445 MΩ.

  That is, if 500 MΩ is used as the actual resistance value of the feedback resistor Rf of the inverter IC 34 shown in FIG. 3, the output terminal when the two electrode terminals (A electrode terminal 32 and B electrode terminal 33) are in contact with the skin 31 a of the living body 31. A high level signal can be reliably output from P1. In the contact state detection circuit of FIG. 3, the overcurrent protection resistors R1 and R2 are 10 MΩ, and the oscillation prevention capacitor Cf is 47 μF.

  FIG. 5 is an actual measurement characteristic diagram showing the mounting state of the electrode terminals when the contact state detection circuit of FIG. 3 is used. In FIG. 5, the horizontal axis represents time (10 Sec / div), and the vertical axis represents the output voltage (0.5 V / div) of the inverter IC. That is, when the electrode terminal is not attached near time zero, the output voltage of the inverter IC indicates 1.6 V. However, when the electrode terminal is attached at time 10 Sec, the output voltage of the inverter IC becomes 3.1 V and is at a high level. Is shown. Furthermore, if the electrode terminal is not attached when time 70Sec has passed, the output voltage of the inverter IC becomes 1.6V again. In this way, the high level can be reliably detected when the electrode terminal is mounted.

  In the pulse meter of the present invention, the contact state to the skin can be detected using the optical contact detection sensor in combination with the contact state detection circuit using the electrode type contact detection sensor as described above. That is, in the optical contact detection sensor, the contact state to the skin is detected by the backscattered light from the skin using an optical sensor including a light emitting element and a light receiving element. In this way, by using the electrode-type contact detection sensor and the optical contact detection sensor in combination, the contact state of the pulse sensor with the skin can be detected with higher accuracy.

  FIG. 6 is an example of a light emission circuit diagram in the optical contact detection sensor applied to the pulse meter of the present invention. Since the light emitting circuit of FIG. 6 is a circuit that is generally used, a detailed description thereof is omitted. However, a constant current is always supplied regardless of fluctuations in the power supply voltage and the like so that the light emission amount of the LED 11 is constant. A current amplifier circuit is used. That is, the power supply voltage Vcc is made constant by the Zener diode DZ11, and the emitter bias resistor R12 in the transistor Tr11 in the amplification stage is kept constant via the operational amplifier 35. As a result, a constant current flows between the collector and emitter of the transistor Tr11 regardless of the fluctuation of the power supply voltage Vcc. Therefore, the LED 11 can emit light with a constant light amount by passing a constant current regardless of the fluctuation of the power supply voltage Vcc. That is, since the LED 11 irradiates the skin with a certain amount of light, the light receiving circuit described later can receive stable backscattered light. In this way, the detection accuracy of the contact state with the skin is increased.

  FIG. 7 is an example of a light receiving circuit that receives backscattered light from the LED 11 in the light emitting circuit of FIG. Since the light receiving circuit of FIG. 7 is a circuit that is generally used, detailed description thereof is omitted, but the backscattered light of the light from the LED 11 of FIG. 6 is received by the photodiode PD21. In other words, when the photodiode PD21 receives light by applying a reverse bias voltage to the junction, the photocurrent Id flows from the cathode of the photodiode PD21 toward the anode. Then, by amplifying the photocurrent Id by the transistor Tr21, a contact detection current I1 proportional to the amount of light received by the photodiode PD21 can be extracted from the output terminal P21.

  That is, FIG. 6 and FIG. 7 will be described together. When light is emitted from the LED 11 in the light emitting circuit of FIG. 6 to the skin, the backscattered light from the skin is received by the photodiode PD21 in the light receiving circuit of FIG. Thereby, the light receiving circuit outputs the contact detection current I1 obtained by amplifying the photocurrent Id of the backscattered light from the output terminal P21. In this way, it can be detected by the optical contact detection sensor whether or not the pulse meter is securely attached to the skin.

  FIG. 8 is another example of a light receiving circuit that receives backscattered light of light irradiated on the living body from the LED 11 in the light emitting circuit of FIG. In the circuit of FIG. 8, the photocurrent Id of the backscattered light received by the photodiode PD31 is amplified by the transistor Tr33 to extract the contact detection current I2. By applying a logic signal to D31 and D32, it is possible to select the switching resistors R35 and R36 for the path through which the contact detection current I2 flows. That is, current-voltage conversion is performed, and the output voltage becomes the terminal P31 and the terminal N31. That is, it is possible to switch the amplification degree according to the amount of backscattered light. Further, the optical contact detection means for detecting the wearing state is a combination of the light emitting circuit and the light receiving circuit used in the pulse sensor as they are without providing the light emitting circuit and the light receiving circuit shown in FIGS. May be.

  FIG. 9 is a flowchart showing a flow of processing for detecting the contact state of the pulse sensor with the skin using the electrode-type contact detection sensor and the optical contact detection sensor. First, when a pulse meter is worn on the wrist and a predetermined button switch is pressed, a wearing detection mode is entered and detection of the wearing state is started (step S1). Next, it is determined whether or not the contact state is detected by the detection by the electrode type contact detection sensor (step S2). Here, if the detection result by the electrode type contact detection sensor is in the contact state (Yes in step S2), it is further determined whether or not the detection by the optical contact detection sensor is in the contact state (step S3). Here, if the detection result by the optical contact detection sensor is in a contact state (Yes in step S3), it is determined that the pulse meter is attached to the wrist (step S4). That is, when it is detected that both the electrode-type contact detection sensor and the optical contact detection sensor are in contact with each other, it is determined that the pulse meter is attached to the wrist.

  Moreover, if the detection result by the electrode-type contact detection sensor is not in a contact state in step S2 (No in step S2), it is determined that the pulse meter is not worn on the wrist (step S5). Furthermore, even if the detection result by the electrode contact detection sensor is in the contact state in step S2, if the detection result by the optical contact detection sensor is not in the contact state in step S3 (No in step S3), the pulse meter is placed on the wrist. It is determined that it is not attached (step S6). In the flowchart of FIG. 9, the detection by the electrode contact detection sensor is performed first and the detection by the optical contact detection sensor is performed later. However, the detection by the optical contact detection sensor is performed first, and the electrode contact detection sensor is performed. Detection may be performed later.

  In other words, the detection by the electrode type contact detection sensor is easily affected by moisture of the living body, and the detection light intensity depends on the state of the living body in the detection by the optical contact detection sensor that determines the presence or absence of the living body contact from the change in the detection light intensity. Although it may change, it may be influenced by the state of the living body, but the contact state can be detected with higher accuracy by using both the electrode type contact detection sensor and the optical contact detection sensor. In other words, in the detection of the contact state by either one of the methods, it may be determined that it is not attached even if it is attached, or it may be determined that it is attached even if it is not securely attached. It is desirable to detect a contact state using both an electrode-type contact detection sensor and an optical contact detection sensor.

It is the perspective view and sectional drawing of a pulse meter applied to this invention, (a) is a front view, (b) is a back view, (c) is AA sectional drawing of (b). It is a block diagram which shows roughly the circuit structure of the pulse meter applied to this invention. It is an example of the contact state detection circuit used for the pulse meter of this invention. It is an actual measurement characteristic figure which shows transition of the mounting time of an electrode terminal, and skin resistance value. It is an actual measurement characteristic figure which shows the mounting state of the electrode terminal when the contact state detection circuit of FIG. 3 is used. It is an example of the light emission circuit diagram in the optical contact detection sensor applied to the pulse meter of this invention. FIG. 7 is an example of a light receiving circuit that receives backscattered light from an LED 11 in the light emitting circuit of FIG. 6. FIG. It is another example of the light receiving circuit which receives the backscattered light of the light from LED11 in the light emitting circuit of FIG. It is a flowchart which shows the flow of the process which detects the contact state to the skin of a pulse sensor using an electrode-type contact detection sensor and an optical contact detection sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pulse meter 2 Wristband 3 Liquid crystal display part 4 Button switch 5 Sensor unit 6 Electrode terminal 7 LED (light emitting element)
8 Photodiode 31 Living body 31a Skin 32 A electrode terminal 33 B electrode terminal 34 Inverter IC
35 Operational amplifier DZ11 Zener diode LED11 LED
Tr11, Tr21, Tr31, Tr32, Tr33 Transistors PD21, PD31 Photodiode

Claims (5)

A biological information measuring device that measures biological information by irradiating light to a living body from a sensor unit, and the sensor unit receives backscattered light from the living body,
Two electrode terminals for detecting whether the sensor unit is in contact with the living body;
An inverting amplifier for amplifying the detection potential of the first electrode terminal of the two electrode terminals with respect to the ground potential of the second electrode terminal;
A biological information measuring device comprising an electrode-type contact detecting means configured by the above. The feedback resistor Rf of the inverting amplifier is
The output voltage Vout of the sensor unit, the skin resistance value between the first electrode terminal and the second electrode terminal are Rs, and the first electrode terminal and the second electrode terminal are in contact with the living body. When the contact detection threshold voltage is Vs,
Rf> Rs {(Vout−Vs) / Vs}
The biological information measuring apparatus according to claim 1, wherein the biological information measuring apparatus is a value obtained by: Furthermore, a light emitting circuit for irradiating the living body with a light emitting element;
A light receiving circuit that receives backscattered light from the living body and detects whether the sensor unit is in contact with the living body;
The biological information measuring device according to claim 1, further comprising an optical contact detection unit configured by:   The biological information measuring apparatus according to claim 3, wherein the optical contact detection means also measures the biological information.   The biological information measuring apparatus according to claim 1, wherein a pulse is measured as the biological information.

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