JP2017000424A - Biological signal measurement device - Google Patents

Abstract

A biological signal measuring apparatus capable of preventing deterioration of an S / N ratio of a detected signal is provided. A biological signal measuring apparatus includes a light source, a first light receiving unit that receives light reflected from a user's body surface among light emitted from the light source, and a light source that is more lightly disposed than the user's body surface. Reflecting means that is provided in the vicinity and reflects the light emitted from the light source, a second light receiving means that receives the light reflected by the reflecting means, and the first light receiving means are reflected on the body surface of the user A first signal obtained by receiving light and a second signal obtained by the second light receiving means receiving light reflected by the reflecting means are obtained from each light receiving means and irradiated from the light source. Arithmetic means for performing a subtraction process for subtracting the value of the second signal from the value of the first signal in order to remove noise contained in the light to be transmitted. [Selection] Figure 3

Description

  Embodiments described herein relate generally to a biological signal measurement device.

  In recent years, wearable devices for health care have been widely used. In particular, wearable devices equipped with a pulse wave measurement function are gradually spreading. This pulse wave measurement function is realized by a non-invasive and simple method using, for example, a photoelectric volume pulse wave (PPG).

  There are two types of biological signal measuring devices (hereinafter also referred to as photoelectric pulse wave measuring devices) using photoelectric volumetric pulse waves, a transmission type and a reflection type. A transmissive photoelectric pulse wave measuring device is mounted with, for example, a fingertip or earlobe sandwiched between a light source and a photodetector of the device, and light that has been irradiated from the light source and passed through the finger or earlobe is detected by a photodetector. The pulse is measured by detecting.

  On the other hand, in the reflection type photoelectric pulse wave measuring device, the light source and the light detector are arranged on substantially the same plane, and the light emitted from the light source and reflected by the wearer's skin is detected by the light detector. . At this time, the amount of light detected by the photodetector repeatedly increases and decreases in synchronization with the blood flow, so the pulse is measured by measuring the time series peak point or rising point of the signal of the amount of light. Can do.

  In general, the reflection type photoelectric pulse wave measurement device has the advantage of less restrictions on the shape and mounting position compared to the transmission type photoelectric pulse wave measurement device, while the signal detected by the photodetector is There is an inconvenience that the S / N ratio is not so good.

JP 2009-11585 A JP 2006-102160 A

  The problem to be solved by the present invention is to provide a biological signal measuring apparatus capable of preventing the deterioration of the S / N ratio of a detected signal.

  According to the embodiment, the biological signal measuring apparatus includes a light source, a first light receiving unit, a reflecting unit, a second light receiving unit, and a computing unit. The first light receiving means receives light reflected from the surface of the user among the light emitted from the light source. The reflection means is provided at a position closer to the light source than the body surface of the user, and reflects light emitted from the light source. The second light receiving means receives the light reflected by the reflecting means. The computing means includes a first signal obtained by the first light receiving means receiving light reflected by the user's body surface, and light reflected by the second light receiving means by the reflecting means. To obtain the second signal obtained by receiving the light from each of the light receiving means and remove the noise included in the light emitted from the light source, from the value of the first signal A subtraction process for subtracting the signal value is executed.

The figure for demonstrating the outline | summary of a reflection type photoelectric pulse wave measurement. The figure for demonstrating the method of removing the fluctuation component of the light source in reflection type photoelectric pulse wave measurement. The figure which shows an example of a structure of the biosignal measuring device which concerns on 1st Embodiment. The figure which shows an example of arrangement | positioning of each part contained in the biological signal measuring device which concerns on the embodiment. FIG. 5 is a diagram illustrating an example of an arrangement different from that in FIG. The flowchart which shows an example of operation | movement of the calculating part contained in the biological signal measuring device which concerns on the embodiment. The figure which is a biological signal measuring device which concerns on the embodiment, Comprising: The figure which shows the structure of the biological signal measuring device of a structure different from the biological signal measuring device shown in FIG. The figure which is a biological signal measuring device which concerns on the embodiment, Comprising: The figure which shows the structure of the biological signal measuring device of another structure different from the biological signal measuring device shown in FIG. FIG. 9 is a diagram illustrating an example of an arrangement of each unit included in the biological signal measurement device illustrated in FIG. 8, which is the biological signal measurement device according to the same embodiment. FIG. 10 is a diagram illustrating an example of an arrangement different from FIG. The figure which shows an example of a structure of the biological signal measuring device which concerns on 2nd Embodiment. The figure for demonstrating the timing which turns on and off a light source, and the timing which acquires a 1st signal and a 2nd signal. The flowchart which shows an example of operation | movement of the biological signal measuring device which concerns on the embodiment. The flowchart which shows an example of operation | movement of the biological signal measuring device which is a biological signal measuring device which concerns on the same embodiment, and considers disturbance light. The figure for demonstrating the timing which turns on and off a light source, and the timing which acquires a 1st-3rd signal.

Hereinafter, embodiments will be described with reference to the drawings.
First, referring to FIG. 1, in the reflection type photoelectric pulse wave measuring apparatus, the principle that fluctuation of the light amount of the light source affects the S / N ratio of a signal obtained (detected) at the time of measurement. explain.

  Here, as shown in FIG. 1, the intensity of light emitted from the light source a1 at time t is P (t), and the photoelectric pulse wave measurement includes at least the light source a1 and the light receiving element (photodetector) a2. The skin reflectance at time t of the wearer (user) who wears the apparatus will be described as R (t).

  In general, although the reflectance R (t) of the skin is substantially constant, it changes minutely according to the amount of blood flowing through the skin (blood flow rate). Therefore, the reflectance R (t) of the skin is It can be expressed as

R (t) = R _DC + R _AC (t) (1)
In addition, _RDC shown to (1) Formula shows the fixed direct current | flow component which does not change, _RAC (t) shows the alternating current component which changes according to the blood flow rate which flows through skin.

As described above, when the light intensity is P (t) and the reflectance of the skin is R (t), the intensity of the signal obtained by the photoelectric pulse wave measuring device (light receiving element a2) at time t is It is proportional to Y ₁ (t) shown below.

Y ₁ (t) = P (t) × R (t) (2)
In the case of an ideal state, the intensity of light P (t) is constant, can be expressed as P _DC. Further, considering the above-described equation (1), the equation (2) can be modified as the equation (2) ′ described later.

Y ₁ (t) = P _DC × {R _DC + R _AC (t)}
= P _DC · R _DC + P _DC · R _AC (t) (2) ′
In the equation (2) ′ described above, the changing component (AC component) is P _DC · R _AC (t), which is proportional to the change in blood flow. That is, by observing (measuring) the AC component of the signal obtained by the photoelectric pulse wave measuring device, it is possible to observe (measure) the pulse wave signal corresponding to the blood flow.

  However, if it is assumed that the light intensity P (t) is not constant and has a minute fluctuation (noise), the light intensity P (t) can be expressed as the following equation (3). .

P (t) = P _DC + P _NOISE (t) (3)
In addition, P _DC shown in the equation (3) indicates a constant DC component that does not change, and P _NOISE (t) indicates a fluctuation component (noise) included in the light source a1. Here, considering the above equation (3), the above equation (2) can be rewritten as the following equation (4).

Y ₁ (t) = P (t) × R (t)
= {P _DC + P _NOISE (t)} × {R _DC + R _AC (t)}
= P _DC * R _DC + P _DC * R _AC (t) + P _NOISE (t) * R _DC + P _NOISE (t) * R _AC (t) (4)
In general, the fluctuation component P _NOISE (t) of the light source a1 is very small as compared with the direct current component P _DC, and the second term of the above-described equation (4) is sufficiently larger than the third and fourth terms. Therefore, it is considered that the AC component of Y ₁ (t) described above captures a pulse wave signal substantially corresponding to the blood flow.

However, according to a detailed examination by the inventor of the present application, the fourth term of the above-described equation (4) is negligibly small compared to the second term, but the third term is negligible compared to the second term. Although it was not small, it turned out to be a big noise factor in pulse wave measurement. For this reason, removing the noise shown in the third term of the equation (4) (in other words, removing P _NOISE (t) · R _DC from Y ₁ (t)) makes it possible to accurately measure the pulse wave. It becomes important in doing.

Hereinafter, with reference to FIG. 2, the principle for removing the noise shown in the third term of the above-described equation (4) (that is, the principle of the present invention) will be described. In FIG. 2, the reflectance of the object a3 is constant, and this reflectance is indicated by _RC . A part of the light emitted from the light source a1 is reflected by the object a3 having the reflectance R _C and detected by the second light receiving element a4. In this case, the intensity of the signal detected by the second light receiving element a4 is proportional to Y ₂ (t) shown below.

Y ₂ (t) = R _C × P (t) (5)
Here, considering the above equation (3), the equation (5) can be transformed into the following equation (5) ′.

Y ₂ (t) = R _C × {P _DC + P _NOISE (t)}
= R _C · P _DC + R _C · P _NOISE (t) (5) '
Since the reflectance R (t) of the skin and the reflectance _RC of the object a3 are different values, there is a difference between the above Y ₁ (t) and the above Y ₂ (t). Therefore, by multiplying an appropriate coefficient α by Y ₂ (t) and subtracting this from Y ₁ (t), the noise shown in the third term of the above-mentioned equation (4) can be removed. It becomes like this. That is, the noise shown in the third term of the above-described equation (4) can be removed by performing the following equation (6). Note that the fourth term of the above-described equation (4) is sufficiently smaller than the second term of the equation (4) and can be ignored here.

Y ₁ (t) −αY ₂ (t) = {P _DC · R _DC + P _DC · R _AC (t) + R _DC · P _NOISE (t)} − α {R _C · P _DC + Rc · P _NOISE (t) }
= P _DC * R _{DC- [} alpha] R _C * P _DC + P _DC * R _AC (t) + R _DC * P _NOISE (t)-[alpha] R _C * P _NOISE (t)
_{= (P DC · R DC -αR} C · P DC) + P DC · R AC (t) + {R DC -αR C} P NOISE (t) ··· (6)
At this time, if the coefficient α is R _DC / _RC , the third term of the above-described equation (6) is zero, so that the component (alternating current component) that changes Y ₁ (t) −αY ₂ (t) Becomes only P _DC · R _AC (t), and noise P _NOISE (t) caused by fluctuation included in the light amount of the light source a1 can be removed.

However, it is assumed that the reflectance _{RC of the} object a3 is not constant and has a component ΔR _C (t) that fluctuates with time, and this ΔR _C (t) has a magnitude that cannot be ignored. Then, the reflectance R _C (t) of the object a3 at time t can be expressed as follows.

R _C (t) = R _C + ΔR _C (t) (7)
In this case, the above-described expression (5) can be rewritten as an expression (8) described later.

Y ₂ (t) = {R _C + ΔR _C (t)} × P (t)
= {R _C + ΔR _C (t)} × {P _DC + P _NOISE (t)}
= R _C · P _DC + R _C · P _NOISE (t) + P _DC · ΔR _C (t) + ΔR _C (t) · P _NOISE (t) (8)
Along with this, the above-described equation (6) can also be rewritten as the following equation (9).

Y ₁ (t) −αY ₂ (t) = {P _DC · R _DC + P _DC · R _AC (t) + R _DC · P _NOISE (t)} − α {R _C · P _DC + R _C · P _NOISE (t ) + P _DC · ΔR _C (t) + ΔR _C (t) · P _NOISE (t)}
_{= (P DC · R DC -αR} C · P DC) + P DC · R AC (t) + {R DC -αR C -αΔR C (t)} P NOISE (t) -αP DC · ΔR C (t) ... (9)
According to the above equation (9), the term _{relating to} P _NOISE (t) cannot be made zero by a constant value of α unlike the above equation (6). In other words, thus applied as _{{R DC -αR C -αΔR C (} t)} P NOISE (t) is the fluctuation component is the third term of equation (9).

Considering the above, it can be seen that keeping the reflectance _RC of the object a3 constant is important in removing noise caused by fluctuations in the amount of light contained in the light source a1. In addition to the constant reflectance _RC , the positional relationship between the light source a1 and the object a3 that reflects a part of the light emitted from the light source a1, and further the light receiving elements a2 and a4 is kept constant. It is also important that

  Below, the biological signal measuring device which considered the principle demonstrated above is demonstrated.

<First Embodiment>
FIG. 3 is a diagram illustrating an example of a functional configuration of the biological signal measuring apparatus 10 according to the first embodiment. As shown in FIG. 3, the biological signal measuring apparatus 10 includes a light source 101, a reflection unit 102, a first light receiving unit 103, a second light receiving unit 104, a calculation unit 105, and the like.

  The light source 101 irradiates light on the skin of the wearer wearing the biological signal measuring apparatus 10 and the reflection unit 102. For the light source 101, for example, a light emitting diode (LED) or the like is used. As light emitted from the light source 101, for example, light having a wavelength of 500 nm to 600 nm is used. Note that the wavelength of light emitted from the light source 101 is not limited to 500 nm to 600 nm, and may be, for example, an infrared ray of about 1000 nm.

  The reflection unit 102 is provided at a position closer to the light source 101 than the wearer's skin, and reflects light emitted from the light source 101 toward the second light receiving unit 104. That is, the reflection unit 102 causes the second light receiving unit 104 to reflect the light emitted from the light source 101 before reaching the wearer's skin. The reflecting part 102 is preferably formed of a material having a constant reflectance, an opaque and rigid material, and having a specular reflection characteristic. Specifically, opaque plastic or the like is used for the reflecting portion 102.

  The first light receiving unit 103 receives light reflected from the skin of the wearer wearing the biological signal measuring device 10 among the light emitted from the light source 101. The signal obtained by receiving the light reflected by the skin is subjected to processing such as filtering through an analog front end (AFE) circuit, for example, and after the DC component and unnecessary high frequency components of the signal are removed Are output to the arithmetic unit 105.

  The second light receiving unit 104 receives the light reflected by the reflecting unit 102 among the light emitted from the light source 101. The signal obtained by receiving the light reflected by the reflecting unit 102 is subjected to processing such as filtering through an AFE circuit, for example, as in the first light receiving unit 103, so that the DC component of the signal or unnecessary After the high frequency component is removed, it is output to the calculation unit 105. Note that the frequency characteristics of the AFE circuit are preferably the same as those of the AFE circuit provided in the first light receiving unit 103.

  The computing unit 105 is constituted by, for example, a microcomputer with a built-in A / D converter. When the calculation unit 105 acquires (captures) signals from each of the first light receiving unit 103 and the second light receiving unit 104, the calculation unit 105 performs a subtraction process according to the above-described equation (6) to obtain the light amount of the light source 101. Noise (noise) due to the included 1 / F noise is removed, and a pulse wave time-series signal with a high S / N ratio is calculated.

  Note that the positional relationship (specifically, distance and angle) of the light source 101, the reflecting unit 102, the first light receiving unit 103, and the second light receiving unit 104 is maintained substantially constant. Specifically, as shown in FIG. 4, the light source 101, the first light receiving unit 103, and the second light receiving unit 104 are disposed on the same printed circuit board PCB, and the reflecting unit 102 is disposed on the printed circuit board PCB. By being arranged on the arranged spacers SP, the mutual positional relationship is kept substantially constant. Note that the reflection unit 102 may be directly bonded onto the printed circuit board PCB as long as a position where the light emitted from the light source 101 can be reflected toward the second light receiving unit 104 can be secured.

  Further, as shown in FIG. 5, the reflection unit 102 may also serve as a housing of the biological signal measurement device 10. In this case, the light irradiated from the light source 101 and the light reflected by the skin of the wearer of the biological signal measuring device 10 are placed at a position facing the light source 101 and the first light receiving unit 103 as shown in FIG. A transparent window W that is transparent is provided. At both ends of the transparent window W, a reflecting portion 102 and a casing SC that also serve as a casing are provided. The transparent window W is provided at the upper center of the light flux distribution of the light source 101 so that a large amount of light emitted from the light source 101 reaches the skin of the wearer of the biological signal measuring device 10. Is preferred.

  Here, an example of the operation of the arithmetic unit 105 included in the biological signal measuring apparatus 10 configured as described above will be described with reference to the flowchart of FIG. Here, it is assumed that the frequency characteristics of the AFE circuits provided in each of the first light receiving unit 103 and the second light receiving unit 104 are the same.

First, the calculation unit 105 acquires (captures) the first signal output from the first light receiving unit 103, and the value Y ₁ of the first signal provided in the calculation unit 105 is not shown in the memory. (Step S1). In the following, it is assumed that the value of the first signal acquired for the i-th time is denoted as Y ₁ (i).

Subsequently, the calculation unit 105 acquires (captures) the second signal output from the second light receiving unit 104, and the value Y2 of the _second signal provided in the calculation unit 105 is not illustrated. Record in the memory (step S2). In the following, it is assumed that the value of the second signal acquired for the i-th time is denoted as Y ₂ (i).

  Next, the calculation unit 105 determines whether the first signal and the second signal have been acquired from the first light receiving unit 103 and the second light receiving unit 104 a predetermined number of times (here, N times). Determine (step S3). When it is determined that the number of times the first signal and the second signal are acquired is less than N times (NO in step S3), the process returns to step S1 and the process in step S1 is executed again. To do.

On the other hand, when it is determined that the number of acquisitions of the first signal and the second signal is N (YES in step S3), the memory (not illustrated) of the calculation unit 105 includes N signals related to the first signal. Y ₁ (i) (where i = 1, 2,..., N) and N values Y ₂ (i) relating to the second signal (where i = 1, 2,... , N) are recorded. The calculation unit 105 determines (calculates) the coefficients a and b using these values so that X given by the equation (10) described later is minimized (step S4). Note that the determination of the coefficients a and b by the process of step S4 is a general optimization problem, and a known method may be used.

In this operation example, it is assumed that the frequency characteristics of the AFE circuits provided in each of the first light receiving unit 103 and the second light receiving unit 104 are the same as described above. When the frequency characteristics of the AFE circuits provided in each of the light receiving unit 103 and the second light receiving unit 104 are different, the above equation (10) is replaced with the equation (10) ′ described later, resulting in a difference in frequency characteristics. This can reduce the effect that occurs.

  Note that Δi shown in the above equation (10) ′ is the time when the first light receiving unit 103 receives the light emitted from the light source 101 and passes through the AFE circuit, and the light emitted from the light source 101 to the reflecting unit 102. The second light receiving unit 104 receives the reflected light and is a value indicating an average difference from the time for passing through the AFE circuit, and is recorded in advance in a memory (not shown) provided in the arithmetic unit 105. It shall be.

Returning to the description of FIG. When the calculation unit 105 determines the coefficients a and b by the process of step S4 described above, the calculation unit 105 performs a subtraction process based on the expression (11) described later, and the time series Y _S (i) ( However, i = 1, 2,..., N) is calculated (step S5).

Y _S (i) = Y ₁ (i) − {aY ₂ (i) + b} (11)
As described above, the frequency characteristics of the AFE circuits provided in each of the first light receiving unit 103 and the second light receiving unit 104 are different, and the coefficients a and b are determined using the above equation (10) ′. In such a case, the influence caused by the difference in frequency characteristics can be reduced by replacing the above-described expression (11) with the expression (11) ′ described later.

Y _S (i) = Y ₁ (i) − {aY ₂ (i + Δi) + b} (11) ′
Returning to the description of FIG. Thereafter, the calculation unit 105 outputs the calculated time series Y _S (i) of the signal from which noise is removed (step S6), and ends the processing here. Note that the output destination of the signal time series Y _S (i) may be outside the biological signal measuring apparatus 10, a memory (not shown) provided in the biological signal measuring apparatus 10, or the biological signal measurement. It may be a module or the like that can execute a pulse rate detection process that is separately installed in the apparatus 10.

  According to the first embodiment described above, since the arithmetic unit 105 capable of executing the processing shown in FIG. 6 is provided, it is caused by 1 / F noise included in the light amount of light emitted from the light source 101. The noise of the photoelectric pulse wave signal can be effectively removed. Moreover, since the positional relationship among the light source 101, the reflecting unit 102, the first light receiving unit 103, and the second light receiving unit 104 is kept constant as shown in FIGS. 4 and 5, the reflecting unit 102 is irradiated. The intensity of the emitted light is not affected by the minute movement of the wearer of the biological signal measuring apparatus 10, and as a result, the photoelectric pulse wave caused by 1 / F noise included in the amount of light emitted from the light source 101. Signal noise can be effectively removed. Further, the calculation unit 105 is configured to reduce the influence caused by the phase difference between the first signal output from the first light receiving unit 103 and the second signal output from the second light receiving unit 104. Therefore, even if the frequency characteristics of the AFE circuits provided in the first light receiving unit 103 and the second light receiving unit 104 are different, noise can be removed with high accuracy.

  In the present embodiment, the calculation unit 105 executes a process for determining a coefficient and a subtraction process after acquiring a predetermined number (N times) of signals. For example, by using an LSM adaptive filter, The subtraction process may be executed every time one signal is captured.

  In the present embodiment, as shown in FIG. 3 described above, the reflection unit 102 that reflects the light emitted from the light source 101 toward the second light receiving unit 104 is provided. As shown in FIG. 4, a configuration in which a light guide unit 102 ′ is provided instead of the reflection unit 102 may be used.

  The light guide unit 102 ′ guides (guides) a part of the light emitted from the light source 101 not toward the skin of the wearer of the biological signal measuring device 10 but toward the second light receiving unit 104. It is. The light guide portion 102 ′ is made of a light transmissive material and further a rigid material. For example, it may be formed of a material such as an optical fiber, or may be formed of a resin such as transparent plastic. The light guide 102 'is preferably formed of a material having a higher refractive index than air. If the material cannot be formed of a material having a refractive index higher than that of air due to production costs, the surface of the light guide unit 102 ′ is coated with a light-shielding property so that light other than the light source 101 (for example, external The light guide 102 ′ may be formed by making it difficult for light from the light to enter the light guide 102 ′.

  The intensity of light guided to the second light receiving unit 104 by the light guide unit 102 ′ and received by the second light receiving unit 104 is reflected by the reflecting unit 102 and received by the second light receiving unit 104. Therefore, the same effect as described above can be obtained. That is, the noise of the photoelectric pulse wave signal due to the 1 / F noise included in the amount of light emitted from the light source 101 can be effectively removed.

  Furthermore, if the second light receiving unit 104 is provided at a position where it can directly receive light emitted from the light source 101, as shown in FIG. 8, the reflecting unit 102 and the light guide unit 102 ′ are not provided. It doesn't matter. In this case, the second light receiving unit 104 is a printed circuit board different from the printed circuit board PCB1 on which the light source 101 and the first light receiving unit 103 are provided, for example, as shown in FIG. Are arranged on a printed circuit board PCB2 provided between the two. As shown in FIG. 9, the positional relationship between the portions 101, 103, 104 is kept constant by a rigid spacer SP, a board connector, or the like.

  Further, as a specific configuration in which the second light receiving unit 104 directly receives the light emitted from the light source 101, for example, the configuration shown in FIG. 10 can be considered in addition to the configuration shown in FIG. Here, the case where the 2nd light-receiving part 104 is arrange | positioned on the flexible substrate FCB is illustrated. Even in the configuration shown in FIG. 10, the positional relationship between the portions 101, 103, and 104 is kept constant by the rigid spacer SP or the like.

  Thus, even when the second light receiving unit 104 directly receives the light emitted from the light source 101, the intensity of the light received by the second light receiving unit 104 is reflected by the reflecting unit 102, Since there is a proportional relationship with the intensity of light received by the second light receiving unit 104, the same effect as described above can be obtained. That is, the noise of the photoelectric pulse wave signal due to the 1 / F noise included in the amount of light emitted from the light source 101 can be effectively removed.

<Second Embodiment>
FIG. 11 is a diagram illustrating an example of a configuration of the biological signal measurement device 10 according to the second embodiment. In addition, about the structure which has the same function as 1st Embodiment, the same code | symbol is attached | subjected and the detailed description shall be abbreviate | omitted. In the second embodiment, the biological signal measuring device 10 is further provided with a control unit 106 in addition to the light source 101, the reflection unit 102, the first light receiving unit 103, the second light receiving unit 104, and the calculation unit 105. Will be described.

  The light source 101 irradiates light toward the skin of the wearer of the biological signal measuring apparatus 10 and the reflection unit 102 as in the first embodiment described above, but the timing at which light is emitted by the control unit 106 described later. And the timing to turn off is controlled.

  The first light receiving unit 103 and the second light receiving unit 104 are light reflected by the skin of the wearer of the biological signal measuring device 10 or light reflected by the reflecting unit 102, as in the first embodiment. Is received, and a signal obtained thereby is output to the arithmetic unit 105, but an AFE circuit that does not include a general AFE circuit that executes a filtering process or has a very fast response. Are installed.

  When the calculation unit 105 receives an input of timing information indicating the timing at which the light source 101 is caused to emit light from the control unit 106, which will be described later, the calculation unit 105 synchronizes with the timing indicated by the timing information, A process of acquiring (capturing) the signal output from the light receiving unit 104 is executed. Note that it is preferable that the A / D converter used for the process of acquiring the signal has a resolution of 16 bits or more.

  The control unit 106 acquires the timing at which the light source 101 emits light (in other words, the timing at which the light source 101 emits light) and the signal output from the first light receiving unit 103 and the second light receiving unit 104 by the calculation unit 105. It has a function to control the timing (to capture).

For example, as shown in FIG. 12, the control unit 106, a light source 101 to emit light (lighting) at the timing of _{t A,} the acquisition of the first signal outputted from the first light receiving portion 103 at the timing of _{t B} to execute the calculation unit 105, the acquisition of the second signal is performed to the operation unit 105 that is output from the second light receiving section 104 at the timing of t _C, so as to turn off the light source 101 at the timing of t _D, various Control timing.

  Here, an example of the operation of the biological signal measuring apparatus 10 configured as described above will be described with reference to the flowchart of FIG.

  First, the control unit 106 causes the light source 101 to emit light (turns on), and outputs timing information that notifies the arithmetic unit 105 that the light source 101 has emitted light (step S11).

Subsequently, when receiving the input of timing information output from the control unit 106, the calculation unit 105 acquires the first signal output from the first light receiving unit 103 according to the timing indicated by the timing information. (Acquisition) and record the value Y1 of the _first signal in a memory (not shown) provided in the calculation unit 105 (step S12).

In addition, the calculation unit 105 acquires (captures) the second signal output from the second light receiving unit 104 according to the timing indicated by the timing information that has received the input, and the value Y _{2 of} the second signal. Is recorded in a memory (not shown) provided in the calculation unit 105 (step S13).

  Next, the control unit 106 turns off the light source 101 (step S14). When the light source 101 is turned off, the calculation unit 105 acquires the first signal and the second signal from the first light receiving unit 103 and the second light receiving unit 104 a predetermined number of times (here, N times). It is determined whether or not (step S15). If it is determined that the number of times the first signal and the second signal are acquired is less than N (NO in step S15), the process returns to the process in step S11 and the process in step S11 is executed again. To do.

  On the other hand, when it is determined that the number of acquisitions of the first signal and the second signal is N (YES in step S15), the same process as the process in step S4 shown in FIG. 6 described above is executed. (Step S16).

  Since the subsequent processes of steps S17 and S18 are the same as the processes of steps S5 and S6 shown in FIG. 6 described above, detailed description thereof is omitted here.

  In the present embodiment, the calculation unit 105 acquires the first signal output from the first light receiving unit 103 and the timing for acquiring the second signal output from the second light receiving unit 104. A slight deviation (approximately several milliseconds or less) occurs. However, since noise included in the amount of light emitted from the light source 101 has a very low frequency, a shift of about several milliseconds does not affect the above-described operation.

  According to the second embodiment described above, the control unit 106 that can control the timing at which the light source 101 emits light and the timing at which signals output from the first light receiving unit 103 and the second light receiving unit 104 are acquired. Further, the lighting time of the light source 101 can be shortened, and the average value of current consumption can be lowered. In addition, an A / D converter capable of simultaneous sampling, a sample hold circuit, and the like are not required, and the arithmetic unit 105 can be configured with only a multiplexer and one A / D converter, so that the circuit scale can be reduced. .

  Here, a method for reducing the influence of not only noise included in the amount of light emitted from the light source 101 but also light from the outside will be described with reference to the flowchart of FIG. Note that the processing in steps S21 to S24 shown in FIG. 14 is the same as the processing in steps S11 to S14 described above, and thus detailed description thereof is omitted here.

Processing in step S21~S24 are executed, when the light source 101 is turned off at timing _{t D} shown in FIG. 15, the control unit 106 outputs the timing information indicating that the light source 101 is turned off to the arithmetic unit 105. When the calculation unit 105 receives an input of timing information indicating that the light source 101 output from the control unit 106 is extinguished, the calculation unit 105 outputs the third light output from the first light receiving unit 103 according to the timing indicated by the timing information. Is acquired (captured), and the value Y _1d of the third signal is recorded in a memory (not shown) provided in the calculation unit 105 (step S25). In the following, it is assumed that the value of the third signal acquired for the i-th time is denoted as Y _1d (i). Since the third signal is obtained by the light received by the first light receiving unit 103 when the light source 101 is turned off, that is, at the timing t _E shown in FIG. 15, Y _1d (i) This value does not include the component of light emitted from the light source 101, but includes only the component of disturbance light.

  Next, the calculation unit 105 determines whether or not the first to third signals have been acquired from the first light receiving unit 103 and the second light receiving unit 104 a predetermined number of times (here, N times). (Step S26). When it is determined that the number of times the first to third signals have been acquired is less than N (NO in step S26), the process returns to step S21 described above, and the process in step S21 is executed again.

On the other hand, when it is determined that the number of times the first to third signals are acquired is N (YES in step S26), the memory (not shown) of the calculation unit 105 stores N values related to the first signal. Y ₁ (i) (where i = 1, 2,..., N) and N values Y ₂ (i) for the second signal (where i = 1, 2,..., N) ) And N values Y _1D (i) (where i = 1, 2,..., N) relating to the third signal. The calculation unit 105 determines (calculates) the coefficients a ₁ , a ₂ , and b using these values so that X given by the equation (12) described later is minimized (step S27). Note that the determination of the coefficients a ₁ , a ₂ , and b by the processing in step S27 is a general optimization problem, and a known method may be used.

When calculating the coefficients a ₁ , a ₂ , and b by the processing in step S27 described above, the arithmetic unit 105 performs subtraction processing based on the equation (13) described later, and the time series Y _{S of the} signal from which noise has been removed. (I) (where i = 1, 2,..., N) is calculated (step S28).

Y _S (i) = Y ₁ (i) − {a ₁ · Y ₂ (i + Δi) + a ₂ · Y _1d (i) + b} (13)
Thereafter, the calculation unit 105 executes the same process as in step S6 described above (step S29), and ends the process here.

  According to this, it is possible to reduce not only the noise included in the light amount of light emitted from the light source 101 but also the influence of disturbance light, and it is possible to measure the photoelectric pulse wave signal with higher accuracy.

  According to at least one embodiment described above, the reflection type photoelectric pulse is provided because it has a configuration capable of reducing the influence of noise caused by 1 / F noise included in the amount of light emitted from the light source 101. It is possible to prevent the deterioration of the S / N ratio of the signal detected by the photodetector of the wave measuring device (in other words, the light receiving element of the biological signal measuring device 10), thereby realizing highly accurate pulse measurement. it can.

  Note that the processing of the present embodiment can be realized by a computer program. Therefore, the computer program can be installed and executed on a computer through a computer-readable storage medium storing the computer program. Similar effects can be easily realized.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Biological signal measuring device, 101 ... Light source, 102 ... Reflection part, 102 '... Light guide part, 103 ... 1st light-receiving part, 104 ... 2nd light-receiving part, 105 ... Calculation part, 106 ... Control part.

Claims (9)

A light source;
A first light receiving means for receiving light reflected from the body surface of the user among the light emitted from the light source;
Reflecting means provided at a position closer to the light source than the body surface of the user and reflecting light emitted from the light source;
A second light receiving means for receiving the light reflected by the reflecting means;
By receiving the first signal obtained by the first light receiving means receiving the light reflected on the surface of the user's body and the second light receiving means receiving the light reflected by the reflecting means. The obtained second signal is obtained from each of the light receiving means, and the value of the second signal is subtracted from the value of the first signal in order to remove noise included in the light emitted from the light source. A biological signal measuring device comprising: a calculation means for executing a subtraction process. A light source;
A first light receiving means for receiving light reflected from the body surface of the user among the light emitted from the light source;
A light guide means for connecting the light source and the second light receiving means, and guiding the light emitted from the light source to the second light receiving means;
Second light receiving means for receiving light guided by the light guide means;
The first light receiving means receives the first signal obtained by receiving the light reflected on the body surface of the user, and the second light receiving means receives the light guided by the light guiding means. In order to remove the noise contained in the light irradiated from the light source, and to obtain the second signal obtained from the light receiving means, the value of the second signal from the value of the first signal A biological signal measuring device comprising: an arithmetic means for performing a subtraction process for subtracting. A light source;
A first light receiving means for receiving light reflected from the body surface of the user among the light emitted from the light source;
A second light receiving means that is provided at a position closer to the light source than the user's body surface and directly receives light emitted from the light source;
A first signal obtained by the first light receiving means receiving light reflected from the body surface of the user, and a second light receiving means directly receiving the light emitted from the light source; The obtained second signal is obtained from each light receiving means, and the value of the second signal is subtracted from the value of the first signal in order to remove noise contained in the light emitted from the light source. A biological signal measuring device comprising: a calculation means for executing a subtraction process. Further comprising control means for controlling the timing at which the light source emits light and the timing at which the computing means obtains a signal;
The control means includes
4. The arithmetic unit is controlled to acquire the first signal and the second signal in synchronization with the timing at which the light source is caused to emit light intermittently. The biological signal measuring device according to any one of the above. The first light receiving means includes
At the timing when the light source is turned off, further receiving light from the outside,
The control means includes
The said calculating means is controlled to synchronize with the timing which turned off the said light source, and the said 1st light-receiving means acquires the 3rd signal obtained by receiving the light from the outside. Biological signal measuring device. The computing means is
A time series of the first signal obtained by acquiring a predetermined number of signals from each of the light receiving means and acquiring the first signal by the predetermined number of times from the first light receiving means, and the second light receiving The coefficient used at the time of the said subtraction process is determined from the time series of the said 2nd signal obtained by acquiring the said 2nd signal by the said predetermined number of times from a means. The biological signal measuring device according to item. The computing means is
4. The biological signal measuring apparatus according to claim 1, wherein a coefficient used at the time of the subtraction process is determined based on an LSM algorithm every time a signal is acquired from each light receiving unit. The computing means is
The biological signal measuring device according to claim 1, wherein the subtraction process is executed based on a phase difference between the first signal and the second signal. The reflecting means is
The biological signal measuring device according to claim 1, wherein the biological signal measuring device is formed as a part of a housing of the biological signal measuring device.

Images