JP2001224568A - Adipometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a measurement with a current of more proper magnitude to a contact impedance having a magnitude of a wide range and precisely measure a body internal impedance under the batter condition of S/N ratio to determine the body fat quantity of a subject. SOLUTION: Both legs of the subject are brought into contact with electrodes 2a, 2b and 3a, an analog switch 8a is ON to connect a constant current controlling arithmetic amplifier 6 to an arithmetic control unit 9, a current is applied between the electrodes 2a and 2b or between the electrodes 3a and 2b, and the voltage generated in each current carrying between the electrodes is measured and inputted to the control unit 9. An analog switch 8b is ON to connect a current measuring arithmetic amplifier 10 to the arithmetic control unit 9, and each current value carried between the electrodes is measurement and inputted to the control unit 9. In the control unit 9, the internal impedance Zi is calculated by use of the voltage value and current value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring fat mass in the body by measuring the impedance value in the body by passing a current through the body of the subject.

[0002]

2. Description of the Related Art A conventional body fat mass measuring apparatus is shown in FIG. 5 as an explanatory diagram illustrating a body fat mass measuring apparatus 100 for measuring the body fat mass of a subject between both feet. A pair of current adding electrodes A ₁ and A ₂ and voltage measuring electrodes B ₁ ,
B ₂ is disposed, a constant current supply circuit 101 for supplying a constant current Ix to the current adding electrodes A ₁ , A ₂ is connected, and a body impedance of the body is connected to the voltage measuring electrodes B ₁ , B _2. A voltage measuring circuit 102 for measuring a voltage generated at both ends is connected and configured. In FIG. 5, the contact impedances including the tissue impedance around the tip of the foot between the sole surface of the subject and the current applying electrodes A ₁ and A ₂ are Z _S1 and Z _S2 , respectively. The contact impedances including the tissue impedance around the tip of the foot between the sole surface and the voltage measurement electrodes B ₁ and B ₂ are Z _S3 and Z _S4 , respectively, and the in-body impedance is Zi.

In the body fat measuring apparatus 100, the constant current supply circuit 101 includes an operational amplifier AMP1 and a reference resistor Rx. When a constant AC voltage Vi is applied to the input of the operational amplifier AMP1, the constant current supply circuit 101 outputs the constant current to the output of the operational amplifier AMP1. Each of the impedances Z _S1 and Z _S depends on the voltage that appears.
i, Z _S2 and the current Ix flowing through the path of the reference resistor Rx
Thus, the output voltage Vo is controlled such that the voltage generated across the reference resistor Rx is always equal to the input voltage Vi. This control operation is performed by the impedances Z _S1 , Zi, which are loads of the operational amplifier AMP1. If the magnitude of the sum of Z _S2 and the reference resistance Rx is within a certain range, the processing can be performed for an arbitrary magnitude value. Therefore, even if the contact impedances Z _S1 and Z _S2 and the magnitude of the impedance in the body differ for each subject, a current of a constant magnitude Ix = Vi / Rx is always applied to each impedance Z.
_{The current} flows through the paths of _S1 , Zi, _ZS2 and the reference resistor Rx.

[0004] The voltage generated in the body impedance Zi by the constant current Ix is equal to the voltage measurement electrodes B ₁ ,
Operational amplifier AMP2 is measured by the voltage measuring circuit 102 which are connected to the B ₂ via a resistor _R 1, _{R 2.} As for the voltage Vx generated in the impedance Zi in the body, if the resistance values of the resistors R ₁ and R ₂ are selected to be sufficiently larger than the impedance value in the body, almost current can flow toward the operational amplifier AMP2. Therefore, the operational amplifier AMP2 can amplify and output the voltage Vx = Zi · Ix to a gain K times almost accurately.

A CPU 106 is connected downstream of the voltage measurement circuit 102 via a rectifier circuit 103, a filter 104, and an A / D converter 105 in this order. Thus, the value of K · Vx output from the voltage measurement circuit 102 is rectified by the rectification circuit 103 and
After being smoothed by the A / D converter 04, it is digitized by the A / D converter 105 and input to the CPU 106. In the CPU 106, the values of the voltage Vi, the reference resistance Rx, and the gain K, which are given to the constant current supply circuit 101 in advance, are known, and the value of the current Ix is a fixed value.
The digital value of K · Vx is divided by K · Ix, and stored in a memory 107 connected to 106.
K · Vx / K · Ix = K · Zi · Ix / K · Ix = Zi
To calculate the in-body impedance Zi.

In the body fat mass measuring apparatus 100, the body impedance Z thus determined
i and the height, weight, sex,
Individual body information such as age and body fat mass can be obtained by substituting each value into an arithmetic expression with these measured values as parameters, which are obtained based on many experiments in advance. I have.

[0007] However, although the impedance Zi in the body varies from individual to individual, it is only about several hundred ohms and there is no significant difference. Apparatus 10
At 0, the output of the operational amplifier AMP1 is controlled so as to increase the value of the output voltage Vo as the contact impedance increases in order to maintain a constant current at the output of the operational amplifier AMP1.
Due to the nature of the above, the output can be output only up to about 95% of the power supply voltage applied to the operational amplifier AMP1. Therefore, when an impedance load of a certain magnitude or more is applied to the output of the operational amplifier AMP1, the output voltage is saturated and does not increase, so that the current supplied from the constant current supply circuit 101 does not become constant, and the body impedance Zi Measurement is impossible.

[0008] To cope with such a problem, a body fat mass measuring apparatus capable of measuring the impedance Zi in the body even when the contact impedance is large is disclosed in JP-A-11-118372 and JP-A-11-13872. 113
873 proposes this.

The body fat measuring device described in Japanese Patent Application Laid-Open No. 11-13872 has substantially the same configuration as a conventional body fat measuring device, and further includes a constant current supply circuit 101.
The output voltage of the operational amplifier AMP1 is monitored by a comparator, and the value of the current Ix flowing through the paths of the impedances Z _S1 , Zi, Z _S2 and the reference resistor Rx is changed before the output of the operational amplifier AMP1 is saturated. It is configured to be. In addition, the conventional body fat mass measuring device 1
The same configuration as 00 is described using the same reference numerals,
Detailed description of the configuration is omitted.

According to the body fat measuring device, the output voltage of the operational amplifier AMP1 increases to maintain a constant current when the contact impedance between the subject and the current adding electrodes A ₁ and A ₂ increases. When Vo exceeds a preset value (slightly lower than the saturation output voltage) set in the comparator, the value of the reference resistor Rx is increased to decrease the value of the current Ix, and the output of the operational amplifier AMP1 is reduced. Are not saturated.

The method of increasing the value of the reference resistance Rx is based on the method of increasing the value of the reference resistance
Is implemented by a method of separating the parallel resistance of the portion by an analog switch. For example, if the value of the reference resistance Rx is 2
When the voltage is doubled, the voltage across the reference resistor Rx can be made equal to the voltage Vi by 1/2 of the conventional current value, so that the constant current value is Ix / 2. Assuming that the constant current value is Ix / 2, the output of the operational amplifier AMP1 can also be controlled with an output less than the saturation voltage value. Increase.

In this case, since the constant current value has dropped to Ix / 2, the voltage value Vx measured by the operational amplifier AMP2 of the voltage measuring circuit is input to the CPU as it is, and the calculation is performed using the current value Ix in the memory. Then, a body impedance value having a size of 1/2 is obtained. Therefore, by switching so that the gain resistance of the operational amplifier AMP2 is doubled in accordance with the switching, the normal impedance Zi in the body is obtained.

Subsequently, the above-mentioned Japanese Patent Application Laid-Open No. 11-113873 is disclosed.
The body fat mass measurement device described in the official gazette
A fixed value that is appropriately determined in advance by the subject to measure the
A voltage Va is applied, and by applying the voltage Va
End tissue impedance Z _S1, Z_S2And in the body
Current flowing through the path of impedance Zi and reference resistance Rx
Is measured.

In this body fat measuring device, a constant voltage Va is applied to the subject. However, if the total value of the impedance of the path is too small, a large current flows through the human body. Each impedance Z
_{Even when S1} and _ZS2 are 0 and Zi is small, Va / (Zi + R) is obtained by adding the impedance Zi in the body and the reference resistance Rx.
The reference resistor Rx is set so that x) does not exceed the specified current value. When the output current value fluctuating according to the total value of the impedance is Iy, the reference resistance R
The voltage Vy generated at both ends of x is represented by Vy = Rx · Iy, and this value is digitized and input to the CPU.

In the CPU, if the value of the reference resistance Rx is set in the memory in advance, (K ·
Zi · Iy / Vy) · Rx = (K · Zi · Iy / Rx ·
Iy) · Rx = K · Zi, and the value of the impedance Zi in the body can be obtained. When the contact impedance increases and the total impedance increases, the value of the current flowing through the path decreases according to the magnitude of the total impedance, but the output of the operational amplifier is saturated as described above. Can be prevented.

[0016]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open Nos.
Although the body fat mass measurement device described in Japanese Patent No. 3873 can measure a wide range of contact impedance, the impedance measurement in the body is performed using a lower current value as compared with a conventional body fat mass measurement device. Therefore, there is a problem that the measurement accuracy deteriorates and stable measurement cannot be performed. Hereinafter, the above-mentioned problems will be described in more detail with reference to design examples of the body fat mass measurement device described in each publication.

In the body fat mass measurement apparatus described in Japanese Patent Application Laid-Open No. 11-113872 (hereinafter referred to as Case 1), the tissue impedance around the tip of the foot is ignored, and the saturation voltage output of the operational amplifier AMP1 is set to 4. 8 V (Although an AC power supply is used, + and-signs are omitted from the numerical values.
The same applies to the following. ), The maximum allowable current flowing through the human body when the measurement circuit is defective is 2 mA, and the maximum current flowing through the human body during normal use is 1 mA. Therefore,
When a trouble occurs in the operational amplifier AMP1 and the output is saturated, the maximum current flowing through the body when the contact impedance is assumed to be 0 and the impedance in the body is assumed to be 0 is 2 mA, and the constant current value during normal current control is When it is set to 1 mA, the value of the reference resistor Rx is set to be 2.5 KΩ, and the voltage Vi applied to the operational amplifier AMP1 is 1 mA × 2.5 KΩ = 2.5V.

In the body fat mass measuring apparatus described in Japanese Patent Application Laid-Open No. 11-113873 (hereinafter referred to as Case 2), the maximum allowable current is 2 mA, as in Case 1, and the maximum current flowing through the human body during normal use is If designed at 1 mA, the value of the reference resistance Rx is 2.5 KΩ. When the impedance in the body of the subject in the standard state is 500Ω and the contact impedance is 100Ω for both electrodes, that is, 200Ω in total, the total value of the load (impedance) is represented by the reference resistance Rx
Is 3.2 KΩ together with the value of the constant voltage Va
Is Va = 1 mA × 3.2 KΩ = 3.2 V. In this case 2, the voltage Va is 3.2 V, and the reference resistance Rx is 2.
Since the impedance Zi is 5 K and the body impedance Zi is 0.5 KΩ, the value representing the current value Iy is given by: Iy = Va / (Rx + Zi + Z) = 3.2 / (3 + Z) where Z is the contact impedance. Then, as the contact impedance Z increases, it decreases so as to draw a hyperbola (see the dotted line in FIG. 6).

In each of the body fat mass measuring devices (cases 1 and 2) designed under the conditions described above,
For a standard subject having a body impedance of 500Ω, the contact impedance Z is the amount of change in the measurement signal when the subject's fingers and toes are in various dry and wet states,
That is, FIG. 6 shows the relationship between the change in the measured current values Ix and Iy with respect to the change in the contact impedance between the sole surface of the subject and the measurement electrode. In FIG. 6, the vertical axis represents the current value flowing through the body, and the horizontal axis represents the total impedance value (Rx + Zi + Z). Since the subject may be wearing socks, the value of the contact impedance can be taken. Is set to be large. In the figure, the solid line represents Case 1, and the dotted line represents Case 2.

The point A in FIG. 6 (contact impedance Z = 20)
0Ω), the total impedance value is (2.5K +
0.5K + 0.2K) = 3.2 KΩ, and in case 1, the output of the operational amplifier is 3.2 V and the current value Ix flowing through the body maintains 1 mA. In case 2, the current value Iy is Iy = predetermined voltage / load = 3.2 /
A current of 3.2 K = 1 mA flows.

The middle point B (contact impedance 1.5K) in FIG.
Ω), the total impedance value is (2.5K +
0.5K + 1.5K) = 4.5KΩ, and in case 1, the set value of the converter is 4.5V.
The current value Ix flowing through the body maintains 1 mA. On the other hand, in case 2, the current value Iy is Iy = 3.2 / 4.5K = 0.711 mA because the total impedance value is 4.5 V.
It is.

A point C in FIG. 6 (a point whose contact impedance is sufficiently higher than the points B1 and B2;
KΩ), the constant current supply circuit of Case 1 cannot maintain a constant current of 1 mA, so that the current value is switched by the operation of a comparator installed in advance, and the target current value becomes 1
/2×Ix=0.5 mA. Note that this point C
Is a limit contact impedance value that can maintain a constant current of 0.5 mA. In this case, the load is 4.5 / 0.5 m because the operating voltage of the comparator is 4.5 V.
9 KΩ. Therefore, the contact impedance is 6 KΩ. Further, for a contact impedance larger than the point C, it is necessary to control the constant current Ix at 0.25 mA. On the other hand, in case 2, the total impedance value is 9 KΩ.
Therefore, the current value Iy is 3.2 / 9K = 0.356 m
A, and decreases along the hyperbolic shape of the above (Equation 1) as the contact impedance value increases.

According to the above case 1, when the contact impedance exceeds 1.5 KΩ, the output voltage exceeds 4.5 V, so that the comparator is activated, and the current value is suddenly reduced to half. The voltage signal output from the operational amplifier AMP2 also suddenly decreases to 、, and the measured current becomes double or 前後 before and after the point B, that is, the contact impedance becomes 1.5 KΩ, and the voltage is increased by the same ratio. The signal will also be different. Since the gain of the voltage measurement circuit is increased / decreased in inverse proportion to the increase / decrease ratio of the voltage signal, a constant measurement voltage is maintained even when the voltage signal changes.
Although the signal is sent to the D converter, the S / N ratio of the signal source is inversely proportional to the value of the current to be applied. There is a problem that the ratio changes.

If only one stage of switching is prepared for the reference resistor, the contact impedance is slightly larger than the point C in FIG. 6, that is, the operational amplifier is set to a saturation voltage (4.8 volts in the conventional example). Reached and the current value was 0.5
If the load condition exceeds 9.6 KΩ (a contact impedance value of 6.6 KΩ) that can limit mA, the operational amplifier AMP1 for constant current again saturates. This operational amplifier A
When MP1 saturates, the current of 0.5 mA cannot be maintained for further saturation of the contact impedance, and the measured current decreases, so that the voltage output value of the operational amplifier AMP2 decreases accordingly. However, in the arithmetic circuit, the arithmetic operation is performed assuming that the fixed current of 1 mA flows, so that there is a problem that the error of the impedance Zi in the body increases as the contact impedance increases. In order to avoid such a problem, it is necessary that the switching of the reference resistance by the operation of the comparator is set so that the current value at the point C becomes 1/4 of the original current value. Furthermore, in order to support a wide range of contact impedance,
There is a problem that a circuit capable of selecting a large number of reference resistances and a gain switching circuit of a large number of voltage measurement circuits are required, resulting in a high component cost.

As described above, the measured current value is previously set small so as not to saturate the operational amplifier AMP1 in preparation for an increase in the contact impedance. Therefore, the measurement with a small measured current value is always performed in a wide range of the contact impedance. However, there is a problem that the output signal from the operational amplifier AMP2 also becomes small and high-precision measurement cannot be performed. For example, the constant current value Ix is changed from 1.0 mA to 0.1
.. 0.9, 0.8, 0.7... at every mA and can be dealt with by performing measurement using the highest possible current value. However, the number of switching circuits increases and the circuit component cost increases. There is a problem.

Next, Case 2 is a case where the predetermined supply voltage is determined so that the current value at the point A at a contact impedance of 0.2 KΩ becomes a normal 1 mA, so that the contact impedance increases to 0.2 KΩ or more. However, since the impedance in the body can be obtained by the measurement current in the small direction from at least the proper current value of 1 mA, the range that can be measured by the proper current is narrow, and the high-precision measurement cannot be performed as in the case 1. is there.

In case 1, the constant current supply circuit 101
The output signal of the operational amplifier AMP1 is AC, and the AC signal is a sine wave until the output voltage of the operational amplifier AMP1 reaches saturation. After the saturation, the peak of the sine wave is sliced by the saturation voltage. Becomes These output signals are half-wave or full-wave rectified by the rectifier circuit 103,
The signal is input to the filter 104 and is smoothed.
5 is integrated.

The output voltage of the filter 104 is 50 KHz, 0.0 irrespective of whether the input waveform is a sine wave or a saturated sine wave.
Since it contains a ripple component having a period of 2 msec, this portion becomes a non-linear factor as compared with a flat DC signal.
In the case where the wave shape of the voltage signal applied to the impedance is a sine wave and a sine wave sliced by a saturation voltage, the peak value of the voltage measurement value generated in the body at that time is proportional to the impedance in the body, and the filter has a waveform. Since there is a difference in the transient response waveform, the integral value KVi after the A / D conversion of the input signal of the transient response wave differs depending on the waveform shape. In order to obtain the impedance in the body, the integral KVi is divided by the fixed value Ix stored in the memory 107 in advance. Therefore, when the output of the operational amplifier AMP1 is not saturated and when it is saturated, the actual body Even if the internal impedances Zi are equal, the same measured value cannot be obtained. Therefore, there is a problem that the measurement result of the impedance Zi in the body is different due to a change in the contact impedance in the subject or the same person having the same impedance in the body, and stable measurement cannot be performed.

The present invention has been made in order to solve such a problem. The present invention has been made so that the S / N ratio can be measured with a more appropriate current for a wide range of contact impedances. It is an object of the present invention to provide a body fat mass measuring device that measures the impedance in the body with high accuracy under a condition with a better ratio and obtains the body fat mass of the subject.

[0030]

Means for Solving the Problems and Functions / Effects In order to achieve the above-mentioned object, a body fat mass measuring device according to the present invention comprises: (a) a body fat mass measuring device for measuring fat mass in a body; A) a current applying means for passing a current through at least the body of the subject; and (b) a total value of loads present in a current supply path by the current applying means within a predetermined range.
It is characterized by comprising: current control means for controlling the current value to be a constant value; and (c) current measurement means for measuring a value of a current flowing through the current path.

In the present invention, the current is applied at least into the body of the subject by the current applying means, and the current value is controlled by the current control means so that the total value of the loads existing in the current path is within a predetermined range. The current value flowing through this current path is measured by current measuring means. In this way, the impedance in the body of the subject is determined using the current value under the best condition for the impedance measurement in the body at least to be conducted through the body, that is, the current value measured by the current measuring means. The body fat mass of the subject is measured using the internal impedance.

According to the present invention, when the total value of the load exceeds a value at which the current value can be kept constant by the current control device due to, for example, an increase in the contact impedance generated between the current application device and the body. In this case, the value of the current flowing in the body is measured by the current measuring means, and the impedance in the body is obtained using the current value at that time. Therefore, there is no need to provide a complicated switching circuit, and the impedance in the body can be measured with a higher measured current value in response to a change in the total value of the subject's load as compared to the conventional body fat mass measurement device. It is possible to perform highly accurate and stable measurement under the optimum condition of the S / N ratio.

In the present invention, further, voltage measuring means for measuring a voltage generated in the current path, and measured voltage information obtained from the voltage measuring means and measured current information obtained from the current measuring means are used. It is preferable that the apparatus further comprises an arithmetic circuit for calculating an in-body impedance value existing in the body of the subject by calculation.

In the present invention, the arithmetic circuit includes:
Preferably, the impedance value in the body is obtained using an arithmetic expression including a division between the measured voltage information and the measured current information. By using such an arithmetic expression, a non-linear factor such as a ripple component included in the measured voltage information and a non-linear factor such as a ripple component included in the measured current information are canceled out. This has the effect that a stable impedance in the body can be obtained irrespective of whether the impedance is set to a constant value or not.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific embodiment of the body fat measuring device according to the present invention will be described with reference to the drawings.

FIG. 1A shows a measurement circuit diagram for measuring the body fat mass of a subject using the body fat mass measurement device according to the first embodiment of the present invention.

In the body fat amount measuring apparatus 1 of the first embodiment, three electrodes 2a, 2b, 3a are provided on the upper surface of the measuring table W, and the electrodes 2a, 2b are
Is arranged so that the electrode 3a is stepped on the heel side, and the electrode 2b is stepped on the toe side.

FIG. 1 (b) shows that a person to be measured has electrodes 2a and 2a.
An explanatory diagram illustrating a state in which steps b and 3a are stepped on is shown. Contact impedances R _2a , R _2a , between the feet of the subject and the electrodes 2a, 2b, 3a, respectively.
R _2b and R _3a are generated, and tissue impedances Z _2a , Z _2b and Z _3a around the tip of the foot around the sole are generated. In the drawing, the impedance in the body existing between both feet to be measured is represented as Zi.

The electrodes 2a, 2b, 3a are each connected to a current supply circuit (corresponding to a current applying means in the present invention) 5 via an analog switch 4 (4a, 4b, 4c).
It is connected to the. This current supply circuit 5 receives a voltage Vo of a certain magnitude from a non-inverting input terminal and receives a voltage Vo.
And a constant current control operational amplifier (corresponding to a current control means and a voltage measurement means in the present invention) for outputting a current, and a resistance value for measuring a current connected to the inverting input terminal of the constant current control operational amplifier 6. Rs reference resistor 7.

The electrodes 2a and 3a are connected to the output terminal of the constant current control operational amplifier 6 via the analog switches 4a and 4c, respectively, and the electrode 2b is connected to the constant terminal via the analog switch 4b. It is connected to the inverting input terminal of the operational amplifier 6 for current control. The ON / OFF of the analog switches 4a to 4c is controlled, and a path (hereinafter, referred to as a first path) including the inside of the body of the person to be measured and configured by the electrodes 2b and 3a and the current supply circuit 5, and the person to be measured The current I flows through a path (hereinafter, referred to as a second path) including the inside of the body and including the electrodes 2b and 2a and the current supply circuit 5. The first path includes contact impedance R _3a , foot tip tissue impedance Z _3a , body impedance Zi,
There are impedances of the foot tip tissue impedance Z _2b , the contact impedance R _2b, and the reference resistance Rs, and the second path includes the contact impedance R _2a , the foot tip tissue impedance Z _2a , the foot tip tissue impedance Z _2b , and the contact There is an impedance _R2b and an impedance Rs of the reference resistor 7.

FIG. 2 is a graph showing the characteristics of the current supply circuit 5, that is, the relationship between the value I of the current flowing through each path and the total value of the impedances present in each path. According to the current supply circuit 5, the current value I flowing through the path is kept constant until the total impedance value of each path is within a predetermined range, that is, until the output voltage Vo of the constant current control operational amplifier 6 reaches a saturation value. Thus, the output voltage Vo is controlled. When the output voltage Vo of the constant current control operational amplifier 6 exceeds the saturation value, as the total impedance value increases,
The current value I draws a hyperbola and decreases. When the output saturation value of the constant current control operational amplifier 6 used in this embodiment is, for example, 4.8 V, the current value I is I = 4.8 / Za with respect to the total impedance Za of each path. (Expression 2) Therefore, the current I shown in FIG. 2 can always obtain a higher or the same current value as the current I of the case 1 and the case 2 shown in FIG.

A current measuring operational amplifier 10 is provided between the inverting input terminal of the constant current controlling operational amplifier 6 and the reference resistor 7 for measuring a voltage generated across the reference resistor 7 by the current I. A current measuring circuit (corresponding to a current measuring means in the present invention) 11 is provided.
Since the resistance value Rs of the reference resistor 7 is known, the value of the current I can be obtained from the measured voltage value of the operational amplifier 10 for current measurement. The constant current control operational amplifier 6
Is set to a voltage value that satisfies Vi = Rs · I (where I is a constant current value before the output voltage Vo is saturated).

An output terminal of the constant current control operational amplifier 6 and an output terminal of the current measurement operational amplifier 10 are respectively connected via analog switches 8a and 8b to an arithmetic control unit (corresponding to an arithmetic circuit in the present invention). 9, a voltage signal Vo output from the constant current control operational amplifier 6 and a voltage (voltage generated across the reference resistor 7) signal V output from the current measurement operational amplifier 10.
r is ON / OF of the analog switches 8a and 8b, respectively.
F is switched and transmitted to the arithmetic and control unit 9.

FIG. 3 is a block diagram showing a specific configuration of the arithmetic and control unit 9. The arithmetic and control unit 9 includes a rectifier circuit 12 for converting an AC voltage signal output from the constant current control operational amplifier 6 or the current measuring operational amplifier 10 into a DC signal, and a DC signal connected to the rectifier circuit 12. Low-pass filter 13 for smoothing voltage signal
An A / D converter 14 connected to the low-pass filter 13 for digitizing an analog signal; and an I / O circuit 15 for receiving a digital signal from the A / D converter 14. The circuit 15 includes a CPU (corresponding to an arithmetic circuit in the present invention) 16 for calculating the body fat mass of the subject based on various data, and personal data (age, height, weight, sex) of the subject. A key switch 17 for inputting and a display 18 for displaying the amount of body fat (or body fat percentage) are connected to each other. The CPU 16 has a ROM / RA for storing various data.
An M memory (hereinafter, referred to as a memory) 19 is connected.

The CPU 16 calculates the in-body impedance Zi based on the output voltages Vo and Vr output from the constant current control operational amplifier 6 and the current measuring operational amplifier 10, respectively. The body fat amount (or body fat percentage) is calculated based on the internal impedance Zi and the personal data input from the key switch 17 and displayed on the display 18. Further, the CPU 16 includes the analog switches 4a to 4c, 8
The on / off control signals for the switches a, b are output to the analog switches 4a to 4c, 8a, 8b through the I / O circuit 15.

The body fat measuring device 1 configured as described above
In the method, both feet of the subject are connected to the electrodes 2a, 2b, 3
a, the analog switches 4b and 4c are
Connection impedance R when ON_3a, Around the tip of the foot
Tissue impedance Z_3a, Body impedance Z
i, tissue impedance Z around the tip of the foot_2b, Connection in
Peedance R_2b, The first path including the reference resistor 7 is formed.
Connected when the analog switches 4a and 4b are ON.
Impedance R_2a, Tissue impedance around tip of foot
Z_2a, Tissue impedance Z around the tip of the foot_2b, Connection
Impedance R _2b, The second path including the reference resistor 7 is shaped
Is done. Also, the analog switch 8a is turned on.
The operational amplifier 6 for constant current control is connected to the arithmetic and control unit 9.
When the analog switch 8b is turned on, the ammeter
The measurement operational amplifier 10 is connected to the arithmetic and control unit 9.

Next, when the analog switches 4b and 4c are turned on, the measurement mode 1 is set, and when the analog switches 4a and 4b are turned on, the measurement mode 2 is set. 6 and the voltage signal V output from the current measuring operational amplifier 10
o and Vr will be described.

[0048] In the measurement mode 1, the analog switches 8a, 4b, Vo ₁ appears on the output voltage of the constant current control operational amplifier 6 when the ON and 4c, a current flowing through the output load when the _{I 1,} Vo ₁ = (R _3a + Z _3a + Zi + Z _2b + R _2b + Rs) · I ₁ (Expression 3) The output voltage Vo ₁ represented in this manner is digitized through the rectifier circuit 12, the smoothing circuit 13, and the A / D converter circuit 14, and is read into the CPU 16. Note that the output voltage Vo ₁ is equal to the constant current control operational amplifier 6.
Until the reach the saturation output voltage value, the current I ₁ is controlled to be constant, measuring also the output voltage Vo ₁ is over the saturated output voltage value continues.

Thereafter, the analog switches 4a and 4c are
Continued N state, when Vr ₁ the output voltage of the current measuring operational amplifier 10 when the ON analog switch 8b to the analog switch 8a to _{OFF, Vr 1 = Rs · I} 1 ... and (Equation 4) Can be represented. The output voltage Vr represented in this manner
₁ is digitized through each circuit and C
It is read into the PU16.

Next, in the measurement mode 2, Vo ₂ appears in the output voltage of the constant current control operational amplifier 6 when the analog switches 8a, 4a, 4b are turned on, and the current flowing through the output load is I ₂ . Then, Vo ₂ = (R _2a + Z _2a + Z _2b + R _2b + Rs) · I ₂ (Expression 5) The output voltage Vo ₂ represented in this manner is digitized through the rectifier circuit 12, the smoothing circuit 13, and the A / D converter circuit 14, and is read into the CPU 16. When the output load related to the constant current control operational amplifier 6 is small, the constant current control is established, so that I ₁ = I _2. Therefore, the output load increases and the output of the constant current control operational amplifier 6 is saturated. In this case, since constant current control is not established, I ₁ ≠
The I _2.

Thereafter, the analog switches 4a and 4b are
Continued N state, when Vr ₂ the output voltage of the current measuring operational amplifier 10 when the ON analog switch 8b to the analog switch 8a to _{OFF, Vr 2 = Rs · I} 2 ... (Expression 6) Can be represented. The output voltage Vr represented in this manner
₂ is digitized through each circuit and C
It is read into the PU16. The value Rs of the reference resistor 7 is set in advance so that the currents I ₁ and I ₂ become optimal for human measurement during the constant current control by the constant current control operational amplifier 6. It is stored in the memory 19.

It is assumed that the electrodes 2a and 3a have a sufficiently large area so that all contact surfaces of the feet can make contact with each other, and that R _2a ≒ R _3a is established between both contact impedances. Further, it is assumed that the energization routes in the measurement mode 1 and the measurement mode 2 are substantially the same, and the tissue impedance Z _2a ≒ Z _3a around the tip of the foot is established.

Therefore, R _3a + Z _3a + Z _2b + R
_{2b + Rs = R 2a + Z} 2a + Z 2 b + R 2b + Rs =
Putting it as Zt, Vo ₁ can be expressed as Vo ₁ = (Zt + Zi) · I ₁ (Equation 7), and Vo ₂ can be expressed as Vo ₂ = Zi · I ₂ (Equation 8).

From the above (Equation 4) and (Equation 7), Zt + Zi = Vo ₁ / I ₁ = (Vo ₁ / Vr ₁ ) · Rs (Equation 9), and (Equation 6) and (Equation 9) 8), Zt = Vo ₂ / I ₂ = (Vo ₂ / Vr ₂ ) · Rs (Expression 10) Therefore, the impedance Zi in the body
Is expressed as Zi = {(Vo ₁ / Vr ₁ ) − (Vo ₂ / Vr ₂ )} · Rs (Equation 11) from (Equation 9) and (Equation 10).

Since Rs is a known value according to this operation equation (Equation 11), the impedance Zi in the body is obtained. Using the in-body impedance Zi obtained in this way and the personal data input in advance by the key switch 17, the CPU 16 determines the body fat mass (or body fat percentage) of the subject and displays it on the display 18. Is done.

According to the present embodiment, a wide range of contact impedance values can be handled, and even if the output of the constant current control operational amplifier 6 is saturated, the current continuously decreases in accordance with the magnitude of the total impedance value. And body impedance Zi
Measurement, it is not necessary to provide a complicated switching circuit or saturation detection circuit, etc., as compared with the conventional body fat mass measurement device (Case 1 and Case 2), the change in the contact impedance of the subject is reduced. Correspondingly, the impedance in the body can be measured with a higher measured current value, and the measurement accuracy is not affected even if the output of the operational amplifier for constant current control is saturated. Thus, the subject and the electrodes 2a, 2b,
3a, contact impedances R _2a , R _2b , R
There is an effect that stable measurement can be performed under the optimum condition of the S / N ratio from the normal value to the high value of _3a .

Further, according to the present embodiment, the arithmetic expression (expression
In 11), Vo₁/ Vr₁And Vo ₂/ Vr₂Toariso
The output of the operational amplifier 10 for current measurement of the denominator and the numerator
Both the output of the operational amplifier 6 for constant current control and the rectifier circuit
12, the filter 13, the CP through the A / D conversion circuit 14.
Division is performed using the value read into U16.
Therefore, the gain of each of these circuits has temperature drift, etc.
However, it is possible to obtain a stable measurement value.

The filter 13 has a resistance R and a capacitance C
Of the first order delay circuit having a period of 2t ₁Half-wave AC signal
When the rectified signal is input, the operational amplifier for constant current control
6 is pulsed with a peak value Vo, and the electrodes 3a and 2b
Is applied to the body, the applied voltage
Of the voltage signal generated at both ends of the contact Z
Impedance Z_3a, Z_2b, Body impedance Z
i and the total impedance Za of the reference resistor 7 and the body
Wave height divided by the ratio to the internal impedance Zi
It is obtained as a pulsed signal of value Ei. This signal
Output voltage of the filter 13 when input to the filter 13
The voltage between both ends of a certain capacitor C is expressed as E₁Then E₁= Ei · (1-e^-X) In addition, during the pulse rest period, the charge becomes t.₁It was discharged for sec
Output voltage E of the filter 13₂Is E₂= Ei · (1-e^-X) ・ E^-X  It is expressed as Note that X in the formula is X = t₁/ CR.
Therefore, pulse input after a sufficiently long time has elapsed
The output of the filter 13 is E_n= Ei · [(1-e^-X) / ｛1-
(E^-X)²｝] And E_{n + 1}= En ・ e^-X  The ripple is repeated between and. In the above equation,
If the term in [] representing the answer is g (t), the output of the filter
Signal Eo₁Is Eo₁= Ei · g (t) = (Zi / Za) / Vo · g
(T). Further, after the output of the A / D converter 14, the integration is performed.
∫Eo₁Dt = (Zi / Za) Vo∫g (t)
dt. The integration time values above and below the symbol ∫ are omitted.
You. Similarly, the applied voltage is also applied to both ends of the reference resistor 7.
Wave height divided by the ratio of total dance value Za and reference resistance 7
A pulse-like voltage of value Es is obtained, and the same rectification
The output signal after passing through the path 12 and the filter 13 is the same
を 持 つ Eo ・ dt = Es∫∫g (t) ・ dt = (Rs / Z
a) · Vo · ∫g (t) · dt. The signal in both equations is
After a sufficiently long response time for the time constant
It is read and digitized during the interval and divided in the arithmetic circuit.
∫g (t) · dt related to the transient response
Both are equal and offset by the numerator denominator, the value of Rs is known
Therefore, the information inside the body
Peedance Zi can be determined.

Therefore, according to the arithmetic expression (Equation 11), the error due to the smoothed ripple waveform, that is, the non-linear factor is canceled regardless of the relaxation of the voltage waveform and the unsaturated shape. For this reason, the constant current control operational amplifier 6 is always connected regardless of the saturation / unsaturation of the constant current control operational amplifier 6 and the output saturation voltage value differs depending on the characteristics of the operational amplifier used. By measuring the output voltage according to the magnitude of the total impedance value of the first path or the second path and the value of the current flowing through the first path or the second path, the constant current control region of the constant current control operational amplifier 6 is measured. The body impedance Zi can be determined in such a manner that the saturation region is used continuously.

Next, the body fat measuring device 20 according to the second embodiment will be described. FIG. 4A shows a measurement circuit diagram when measuring the body fat mass of the subject using the body fat mass measurement device 20.

In the body fat measuring device 20 of the second embodiment, four electrodes 22a, 22b,
23a and 23b are provided, the electrodes 22a and 22b are stepped on by one foot of the subject, and 23a and 2b are
3b, so that the electrodes 22a, 22
3a is stepped on the heel side, and the electrodes 22b, 2
3b is disposed so as to be stepped on the toe side.

FIG. 4 (b) shows that the person to be measured has electrodes 22a,
The state in which steps 22b, 23a, and 23b are stepped on will be described.
FIG. Both feet of the subject and each electrode 22
a, 22b, 23a, 23b
Impedance R_22a, R _22b, R_23a, R
_23bAs well as around the tip of the foot around the sole
Woven impedance Z_22a, Z_22b, Z_23a, Z
_23bHas occurred. Note that both feet you want to measure in the figure
The impedance in the body that exists between is represented as Zi
You.

The electrodes 22a and 23a receive a voltage signal Vi of a predetermined magnitude from a non-inverting input terminal and receive a voltage V
A constant current control operational amplifier that outputs o (corresponding to a current application unit and a current control unit in the present invention) 24
And a reference resistance 25 having a resistance value Rs connected to the inverting input terminal of the constant current control operational amplifier 24. The current control operational amplifier 24 is configured such that the current I flows through a path formed through the body of the subject by the electrode 22a connected to its inverting input terminal and the electrode 23a connected to its output terminal. The output voltage Vo is controlled so that Vi = Rs · I is satisfied at the input. When the output voltage Vo exceeds the output saturation voltage value of the current control operational amplifier 24, the constant current I cannot be maintained, and a hyperbolic curve is drawn as the total impedance value in the path increases. The current will decrease. (See Fig. 2)

On the other hand, the electrodes 22b and 23b are connected to a resistor 29 having a resistance value larger than the total impedance value.
a and 29b via the electrodes 22b and 23b, respectively.
It is connected to the inverting / non-inverting input terminals of a measuring operational amplifier (corresponding to a current measuring means and a voltage measuring means in the present invention) 30 for measuring a voltage generated therebetween and outputting a voltage signal. The output terminal of the measurement operational amplifier 30 is connected to the arithmetic and control unit 9 that calculates the body fat mass of the subject using the measured voltage. Since the arithmetic and control unit 9 is the same as that of the first embodiment, a detailed description thereof will be omitted.

The electrodes 22b and 23b and the resistor 29
a and 29b are connected to the analog switch 27, respectively.
The analog switches 27a and 27b are disposed, and the voltage is measured by the measuring operational amplifier 30 when the analog switches 27a and 27b are ON. However, the current I almost flows to the measuring operational amplifier 30 side by the resistors 29a and 29b. Imaginary points P and Q in the body excluding the contact impedance and the tissue impedance around the tip of the foot.
The voltage between them (the voltage generated across the body impedance Zi) is measured as a differential voltage.

The inverting input terminal of the constant current controlling operational amplifier 24 and the inverting input terminal of the measuring operational amplifier 30 are connected via an analog switch 27c, and the analog switch 27c is turned on. When the analog switches 27a and 27b are turned off, the voltage generated across the reference resistor 25 is measured by the measuring operational amplifier 30. Since the value Rs of the reference resistor 25 is known from the measured voltage value, the value of the current flowing in the path is obtained.

The body fat measuring device 2 configured as described above
In the case of 0, both feet of the subject are
b, 23a, and 23b, the analog switches 27a to 27c are sequentially turned on and off by the output signal of the CPU 16 of the arithmetic and control unit 9 to change the voltage generated at both ends of the impedance Zi in the body. The measurement and the measurement of the voltage generated at both ends of the reference resistor 25 are performed. That is, the analog switches 27a and 27b are turned on.
By turning off the analog switch 27c as a state, a voltage generated at both ends of the impedance Zi in the body is measured, and the analog switches 27a and 27b are turned off.
When the analog switch 27c is turned on in the FF state, the voltage generated across the reference resistor 25 is measured.

The value of the current flowing through the path is I₃To be
And the analog switches 27a and 27b are turned on.
In this case, the voltage Vo output from the operational amplifier 30 for measurement₃
Is Vr₃= Zi · I₃  When the analog switch 27c is turned on.
Vr output from the operational amplifier 30 for measurement
₄Is Vr₄= Rs · I₃  And the output voltage Vr₃, Vr₄Is the rectification cycle
Through the path 12, the smoothing circuit 13, and the A / D conversion circuit 14.
It is digitized and read into the CPU 16.

The value Rs of the reference resistor 25 is stored in the memory 1 in advance.
9, and the CPU 16 calculates the impedance Zi in the body by Zi = (Vr ₃ / Vr ₄ ) · Rs (Equation 12) regardless of the current value I ₃ . The body fat amount (or body fat percentage) is obtained based on the thus obtained value of the impedance Zi in the body based on the personal data input from the key switch 17 as in the first embodiment, and is displayed on the display 18. Is done.

In this embodiment, during the constant current control by the constant current control operational amplifier 24, the value Rs of the reference resistor 25 is set in advance so that the current value I becomes an optimal value for human measurement. Even when the contact impedance increases and the output voltage of the constant current control operational amplifier 24 saturates, the body impedance is measured with the measurement current that gradually decreases from the optimal constant current value according to the size of the load. Therefore, measurement can always be performed under preferable conditions compared with the conventional method from the viewpoint of the S / N ratio.

In this embodiment, since the output voltages Vr ₃ and Vr ₄ are divided, even if the gains of the rectifier circuit 12, the smoothing circuit 13, and the A / D converter circuit 14 have drifts, It can be offset and no special correction process is required.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a measurement circuit diagram (a) when a body fat mass of a subject is measured using a body fat mass measurement device according to a first embodiment of the present invention, and an explanation for explaining a measurement state; FIG.

FIG. 2 is a diagram illustrating characteristics of the current supply circuit according to the present embodiment.

FIG. 3 is a block diagram illustrating a specific configuration of an arithmetic and control unit according to the embodiment;

FIG. 4 is a measurement circuit diagram (a) and an explanatory diagram (b) illustrating a measurement state when measuring the body fat mass of a subject using the body fat mass measurement device of the second embodiment. It is.

FIG. 5 is an explanatory view illustrating a conventional body fat mass measurement device.

FIG. 6 is an explanatory diagram for explaining a conventional problem.

[Explanation of symbols]

1,20 body fat measuring device 2a, 2b, 3a, 22a, 22b, 23a, 23b
Electrodes 4a, 4b, 4c, 8a, 8b, 27a, 27b
Analog switch 5 Current supply circuit 6, 24 Constant current control operational amplifier 7, 25 Reference resistor 9 Operation control device 10 Current measurement operational amplifier 11 Current measurement circuit 12 Rectifier circuit 13 Low pass filter 14 A / D converter 15 I / O Circuit 16 CPU 17 Key switch 18 Display 19 Memory 29a, 29b Resistance 30 Operational amplifier for measurement

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G028 AA01 BC07 CG08 DH05 DH13 FK01 GL07 HN10 HN11 LR02 MS03 4C027 AA06 CC01 DD03 EE03 FF00 KK03 KK05

Claims (3)

[Claims] An apparatus for measuring fat mass in a body for measuring the amount of fat in the body, comprising: (a) a current applying means for passing a current through at least the body of a subject; and (b) an energizing path by the current applying means. Current control means for controlling the current value to be a constant value within a predetermined range, and (c) current measuring means for measuring a value of a current flowing through the current path. An apparatus for measuring fat mass in a body, comprising: 2. A voltage measuring means for measuring a voltage generated in the current path, and a voltage to be measured using measured voltage information obtained from the voltage measuring means and measured current information obtained from the current measuring means. 2. The body fat mass measurement device according to claim 1, further comprising: a calculation circuit for calculating an impedance value in the body existing in the body of the person by calculation. 3. The body fat measurement device according to claim 2, wherein the arithmetic circuit obtains an impedance value in the body using an arithmetic expression including a division of the measured voltage information and the measured current information.