JP2692733B2 - Accelerometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerometer that measures a heartbeat using an acceleration detector, and
Of order to be able to measure the heart rate, it was to separate the output component of the acceleration detector due to pulsation of the output signal component and cardiac acceleration detector due to come dynamic body with a simple structure < This is related to the improvement of the second.

[0002]

2. Description of the Related Art Conventionally, a heart rate is measured in order to know a person's health condition. An electrocardiograph for detecting an electrocardiogram and a photoelectric detector are attached to a finger as a heart rate monitor used for this measurement. A heart rate meter that detects a pulse wave from a light transmission amount and an acceleration heart rate meter that detects a pulse wave by attaching an accelerometer to a body surface are known. Unlike the electrocardiograph, the accelerometer is not required to attach electrodes to the body surface and is relatively easy to wear on the body. Further, unlike a heart rate monitor in which a photoelectric detector is mounted on a finger, the mounting position of the detector is not limited to a fingertip or the like, and the heart rate of a working person can be measured without hindering the operation. For this reason, the acceleration heart rate meter is suitable as a heart rate meter for knowing the physical condition of the worker in the work environment. However, during the operation, a component caused by the movement or utterance of the worker is included in the output of the acceleration detector. Therefore, if the output is used as it is to measure the heartbeat, accurate measurement cannot be performed.

Therefore, Japanese Patent Laid-Open No. 5-5950 discloses that
A first acceleration detector arranged near the body surface of the subject and detecting acceleration including vibration of the body surface; and a first acceleration on the opposite side of the body surface of the first acceleration detector. A second acceleration detector attached to a position facing the detection and detecting the acceleration, and interposed between the first and second acceleration detectors, and detects the vibration of the first acceleration detector accompanying the vibration of the body surface. A medium that absorbs and suppresses transmission of the vibration to the second acceleration detector; and a signal processing unit that outputs a signal about a heartbeat based on a difference between output values of the first and second acceleration detectors. A heart rate monitor equipped with a heart rate monitor has been proposed.

In the heart rate monitor according to this proposal, the first acceleration detector detects not only the heartbeat but also the acceleration component caused by body motion and the like, while preventing the transmission of vibration of small amplitude such as the vibration accompanying the heartbeat. The second detector attached to the first accelerometer via the above-described medium detects only acceleration of vibration having a large amplitude such as body motion. Then, the signal processing unit extracts only the acceleration component accompanying the heartbeat based on the difference between the outputs of the two detectors, and detects the heartbeat. Note that, as a specific example of the signal processing unit, the above publication discloses a method for removing noise caused by a sound component included in the output value difference between the two acceleration detectors together with the heartbeat as a result of being absorbed together with the heartbeat by the medium. Also, there is disclosed one that cuts high-frequency components such as audio components with a low-pass filter.

[0005]

However, the heart rate monitor according to the above proposal requires two acceleration detectors, which are expensive parts. In addition, the difference between the output values of the two acceleration detectors is taken to remove the acceleration component of vibrations other than the heartbeat, such as body motion, so in order to satisfactorily remove such an extra acceleration component. Is a problem that it is necessary to strictly match the characteristics of the two acceleration detectors or to strictly adjust, for example, a differential amplifier for obtaining the difference between the output values in accordance with the characteristics of the two detectors. Points are left.

The present invention has been made in view of the above problems, and its object is to accurately measure a heartbeat.
Because of the separation of the output component of the acceleration detector caused by the output signal component and a heart rate acceleration detector caused by machinery movement of the body
It is an object of the present invention to provide an acceleration heart rate monitor that can be performed with a simple configuration.

[0007]

In order to achieve the above object, the present invention provides an acceleration signal due to the pulsation of the heart.
And an acceleration detector capable of obtaining a sharp pulse waveform, and a bandpass filter for extracting a signal of a specific frequency band from the output signal of the acceleration detector, and the signal extracted by the bandpass filter is An accelerometer for measuring a heartbeat using the bandpass filter, comprising:
Up to a predetermined frequency in the range of 0 to 40 hertz
It is characterized by using a low-side attenuation range .

[0008]

[ Operation ] Acceleration under various working conditions by the present inventors
The following facts were found as a result of the measurement of the degree signal and its analysis.
Was. That is, the acceleration signal due to the movement of the body accompanying the work
Signal is predominant in the low frequency range of a few hertz and
Attenuates toward higher frequencies. Meanwhile, the heart beat
The resulting acceleration signal has a sharp pulse-like waveform.
Therefore, the component exists over a wide frequency band. So
Here, in the accelerometer of the present invention ,
Obtain a sharp pulse-like waveform as the resulting acceleration signal
It is mounted an acceleration detector body may, by the acceleration detector detects the acceleration due to vibrations in the body due to the heartbeat. The output of the acceleration detector is too long and also include acceleration components of the dynamic vibration by moving the other to the body of the vibration in the body due to the heartbeat. The extra minute acceleration component of this, except in a band pass filter. That is, 20 to 40 hertz
Attenuation range on the low frequency side up to a predetermined frequency within the range of ruts
More band-pass filter that, to sufficiently attenuate the acceleration signal component caused by the movement of the body caused by the working.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram of the acceleration heart rate meter according to the present embodiment.
First, the overall outline will be described. The acceleration heart rate meter of this embodiment includes an acceleration sensor 101, an amplifier 102 that amplifies an acceleration signal from the acceleration sensor, and the amplifier.
A bandpass filter 103 that attenuates components other than a predetermined frequency band of the signal amplified by 102, and a heartbeat detecting means 201 to which the signal from the bandpass filter 103 is input. The acceleration sensor 101 is
For example, a strain gauge type acceleration sensor that is attached to the surface of the human chest or the like and that utilizes the fact that the impedance of the sensor is proportional to the acceleration can be used. The amplifier 102 amplifies the acceleration signal from the acceleration sensor 101 to a signal level that is not easily affected by electrical noise, as shown in a waveform example a in FIG. The band pass filter 103 is an amplifier
This is for attenuating components other than a predetermined frequency band of the signal amplified by 102 . This will be described in detail later. The heartbeat detecting means 201 is an absolute value means 301,
Smoothing means 302, threshold value generating means 304 and comparator 3
03.

Here, the absolute value means 301 converts the polarities of the acceleration signals that take positive and negative values, for example, to take only positive values, as shown in the waveform example c in FIG.
The smoothing means 302 smoothes a fine change in the acceleration signal converted into unipolar by the absolute value means 301, as shown in a waveform example c in the figure. The comparator 303 compares the smoothed signal with a predetermined threshold value from the threshold value generating means 304. This threshold value is lower than the peak value of the acceleration due to the heartbeat and higher than the noise of the circuit and the like, and is set so that the heartbeat can be detected. And
As shown in the waveform example e in the figure, the comparator 303 outputs, for example, a logical value "1" when the value of the signal input is larger than the value of the threshold value input, and otherwise, for example, a logical value "
It is configured to output 0 ". This comparator 303
Is used for the measurement of the time interval of heartbeats and the measurement of the number of heartbeats per minute by the time interval measuring means (not shown).

[0011] Next, describes the two-fold the band-pass filter 103 which forms the main part of this embodiment. As a result of the measurement and analysis of the acceleration signal under various working conditions, the following facts were revealed. 1. Since the acceleration signal due to the heart beat has a sharp pulse-like waveform, its component exists over a wide frequency band. FIG. 2 shows the shape of the spectrum. 2. The acceleration signal caused by the movement of the body accompanying the work is dominant in a low frequency band of about several hertz, and is attenuated toward higher frequencies. FIG. 3 shows the shape of the spectrum of the acceleration signal in which the component resulting from the movement of the body is mixed. 3. The acceleration signal due to utterance usually exists in the frequency region of about 70 hertz or higher. FIG. 4 shows the shape of the spectrum of an acceleration signal in which a component caused by utterance is mixed.

In this embodiment, based on the above facts, the pass band of the band pass filter 103 is set as follows. That is, the frequency of the lower limit of the pass band is set to a frequency at which the acceleration signal due to the movement of the body accompanying the work is sufficiently attenuated, and the frequency of the upper limit of the pass band is set to be lower than the frequency range defined by the acceleration signal due to utterance. As a result, it is possible to extract the acceleration component caused by the pulsation of the heart while reducing the unnecessary acceleration component caused by the movement of the body and vocalization accompanying the work, and the heartbeat can be detected accurately. .

In FIG. 5, the horizontal axis represents the lower limit of the pass band of the band pass filter 103, and the vertical axis represents the upper limit frequency of the pass band of the band pass filter 103. Is a contour display of. As is clear from this figure, the lower limit of the pass band of the band pass filter 103 is set to 20 Hz to 4 Hz.
When the upper limit frequency of the pass frequency band is set within the range of 0 hertz and within the range of 30 hertz to 50 hertz, it is possible to detect the heartbeat relatively accurately.

The bandpass filter having the above characteristics can be constructed by a circuit as shown in FIG. 6 using, for example, an operational amplifier. Further, as shown in FIG. 7, it may be configured by a circuit in which a low pass filter F1 at the front stage and a high pass filter F2 at the rear stage are connected in cascade. The center frequency fc of the bandpass filter of the circuit of FIG. 6 and Q representing the sharpness of resonance are R1 // R2 which is the combined resistance of the resistors R1 and R2.
It will be as shown below. On the other hand, the cutoff frequency fc1 of the low-pass filter F1 and the Q that determines the cutoff characteristic in the circuit of FIG. 7 are as follows. Further, the cutoff frequency fc2 and the cutoff characteristic Q of the high-pass filter F2 in the circuit of FIG. 7 are as follows.

[0015]

According to the acceleration heart rate monitor of the present invention, with a simple configuration as compared with the heart rate monitor proposed in Japanese Patent Laid-Open 5-5950 JP above, the acceleration detector due to movement of the body
Accelerometer output due to output signal components and heart beat
There is an excellent effect that the force component can be separated .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a schematic configuration of an acceleration heart rate meter according to an embodiment.

FIG. 2 is a graph showing a shape of a spectrum of an acceleration signal caused by a heart beat.

FIG. 3 is a graph showing a shape of a spectrum of an acceleration signal in which an acceleration signal caused by a motion of a body accompanying work is mixed.

FIG. 4 is a graph showing a shape of a spectrum of an acceleration signal mixed with an acceleration signal caused by utterance.

FIG. 5 is a graph showing the relationship between the characteristics of the bandpass filter and the ratio (percentage) of correct detection of heartbeat.

FIG. 6 is a circuit diagram showing a configuration example of a bandpass filter.

FIG. 7 is a circuit diagram showing another configuration example of a bandpass filter.

[Explanation of symbols]

 101 acceleration sensor 102 amplifier 103 band pass filter 201 heartbeat detecting means

Claims (1)

(57) [Claims] 1. An acceleration signal resulting from a heart beat,
An acceleration detector capable of obtaining a sharp pulse waveform and a bandpass filter for extracting a signal of a specific frequency band from the output signal of the acceleration detector are provided, and the signal extracted by the bandpass filter is used. An acceleration heart rate meter for measuring a heartbeat , comprising:
Low frequency down to a certain frequency in the range of Hertz to 40 Hertz
An acceleration heart rate monitor characterized by using an attenuation range on the range side .