JP5299663B2 - Body motion detection sensor and body motion detection method - Google Patents

Description

  The present invention relates to a body motion detection sensor and a body motion detection method using a piezoelectric film, for example, a body motion detection sensor for detecting respiration of a subject by connecting a piezoelectric film bent into a curved shape to a band member. And a body motion detection method.

  Conventional body motion detection means can be broadly classified into (a) a current flowing through a sensor to measure a change in electrical resistance, and (a) a device to measure a change in voltage generated in a piezoelectric body due to body motion.

(A) The former is a method in which a current is passed in a state where a strain gauge (a thin tube in which a conductive substance such as carbon particles is injected) is wound around the body, and a voltage change is measured, or a coil in which a thin conductor is sewn on a band. It measures the change in inductance of the sensor.
However, it has been pointed out that there are safety problems associated with passing current around the body and noise effects on other devices. In order to solve this problem, a sensor that monitors respiration by detecting a change in band length has been proposed (Patent Document 1).
However, the sensor disclosed in Patent Document 1 measures the physical expansion and contraction of the band length itself, and has a problem in accuracy.

(A) Since the latter needs to bend in the piezoelectric material, an elastic film-shaped material is used as the piezoelectric material. As the piezoelectric film, a piezoelectric ceramic or a piezoelectric ceramic thin film made of PVDF (Polyvinylidene fluoride film), barium titanate, lead zirconate titanate (PZT), or the like is used. There has been proposed a method and a device for detecting timing of minutes by monitoring muscle activity using PVDF (Patent Document 2).
In addition, there is a band-type respiration sensor using a piezoelectric film that incorporates the idea of Patent Document 2. FIG. 1 shows a usage mode of a band-type respiration sensor using a conventional piezoelectric film. A piezoelectric film 2 is provided in the central portion of the band 1 and is a mechanism for detecting whether respiration is accurately performed by measuring an output voltage generated by a change in the amount of deflection of the portion.

However, when the band is wound around the chest or abdomen, it is necessary to wind the band tightly in order to cause the piezoelectric film to bend, the patient is uncomfortable, the band is easily displaced, and the piezoelectric film In order to cause bending, a material that does not expand and contract is used for the band 1, which further deteriorates the wearing feeling.
In addition, due to the structure in which only a part of the abdomen / chest movement causes the piezoelectric film to bend, there is little change in voltage, and the output electrical signal is small (catalog value 700μV), so noise accompanying changes in body position There was a problem that stable recording could not be obtained due to noise caused by heartbeat.
In addition, the use of two bands wrapped around the chest and abdomen increases the detection accuracy, but the feeling of wearing is worse than that of a single band, and the body is visually bound. The patient's psychological burden was great.

Therefore, the present inventor follows the expansion and contraction movement of a stretchable member that is composed of a piezoelectric film bent in a bridge shape and a stretchable member that is shorter than the piezoelectric film connecting both ends of the piezoelectric film. And the body motion detection sensor in which the bending of a piezoelectric film changes and the body motion monitoring system using the same were proposed (patent document 3).
JP 2001-17409 A Japanese Patent Publication No. 63-501196 Japanese Patent No. 4405344

The body motion detection sensor disclosed in Patent Document 3 has room for improvement from the viewpoint of miniaturization. FIG. 1 is a drawing for explaining a photograph and characteristics of a prototype of a body motion detection sensor disclosed in Patent Document 3. The body motion detection sensor disclosed in Patent Document 3 requires a thickness (height) for bending the piezoelectric film due to its structure. In order to increase the stroke, it is necessary to increase the deflection, but with this, an increase in the size of the body motion detection sensor is inevitable.
In addition, when the circuit unit is stacked on the sensor unit, the overall thickness is further increased. Therefore, there is a limitation in layout design, for example, the sensor unit and the circuit unit are separated from each other.

  In order to solve the above problems, an object of the present invention is to provide a body motion detection sensor and a body motion detection method using a piezoelectric film, which have a structure with high detection accuracy and can be miniaturized.

A first aspect of the present invention is a body movement detection sensor that detects body movement by an output voltage generated by expansion and contraction of a piezoelectric film, a cover member that houses the piezoelectric film, and a longitudinal direction that accompanies the body movement of the subject. a band member to be stretchable in a winding member (4), and engagement times member (5), and a elastic member Ru wound engages the winding member and Kakarikai member, a piezoelectric film first wound end to the winding member is constructed by connecting the second end of the piezoelectric film to the end portion of the band member, arising voltage piezoelectric film expands and contracts by the winding member is rotated It is a body motion detection sensor.
The second invention is characterized in that, in the first invention, the second end portion of the piezoelectric film and the circuit portion are laminated.

A third invention is a body motion detection method for detecting body motion by an output voltage generated by expansion and contraction of a piezoelectric film, and is connected to the cover member that houses the piezoelectric film and the body motion of the subject. a band member to be stretchable in the longitudinal direction, the winding member (4) has a engaging times member (5), and a elastic member wound member and Ru wound engaged in Kakarikai member, a piezoelectric film One end is wound around the winding member, and the second end of the piezoelectric film is connected to the end of the band member. When the winding member is rotated, the piezoelectric film expands and contracts and voltage is applied. the resulting Ru body motion detection sensor, mounted on the subject by the band member is a body motion detecting method and detecting the body movement.
A fourth invention is characterized in that, in the third invention, the body motion detection sensor is attached to a chest of a subject to detect respiration.

According to the present invention, since the piezoelectric film can be stored compactly in the cover member, it is possible to realize a small body motion detection sensor and a body motion detection method using the same.
In addition, since the piezoelectric film does not directly touch the body, it is possible to suppress noise caused by changes in body position and noise caused by heartbeat.

The body motion detection sensor according to the present invention measures a change in voltage generated by a bent piezoelectric film due to body motion of a subject.
In the body motion detection sensor according to the present invention, the piezoelectric film can be stored compactly in the cover member that constitutes the sensor unit, and therefore, the circuit unit and the sensor unit can be arranged in an overlapping manner.

The piezoelectric film is housed in the cover member in a bent state. One end of the piezoelectric film is connected to a band member inserted into the cover member, and is expanded and contracted as the subject moves. For example, when attached to the chest or abdomen, the air in the lungs is exhaled during inhalation and the chest circumference / retraction becomes smaller, the piezoelectric film pulled by the band member contracts, and conversely, air in the lungs during inspiration. When the chest circumference / reincarnation becomes larger by being sucked, the piezoelectric film is pulled and stretched.
In the body motion detection sensor of the best mode, the piezoelectric film is housed in the cover member in a substantially U shape or wound around a columnar member, so that the cover member can be made thin. it can. In any of the modes, a sufficient stroke can be secured and a high output can be obtained. However, in the former mode, the forward voltage may be canceled by the reverse voltage, so the latter mode. Is more preferable.
Since the piezoelectric film is housed in the cover member, even if the sensor portion is attached to the chest, the film is not directly brought into close contact with the body, so that noise due to the heartbeat can also be suppressed.

  The material of the piezoelectric film is not particularly limited as long as it exhibits a piezo effect, but a material that is light and flexible is preferable in order to enhance the wearing feeling. Piezoelectric ceramics such as PZT are well known as piezo materials, but PVDF, which is lightweight, flexible and has good workability, is a preferred material. PVDF has a feature that it has a very wide response band and is difficult to have a specific resonance frequency. Since PVDF is not suitable for use in a high temperature environment, a thin film or a thick film using a piezoelectric ceramic is used when it is used in such an environment.

  The piezoelectric film is preferably protected against noise by shielding with a conductive cloth tape. Conductive cloth tape can be a general one used for shielding electromagnetic waves and static electricity of electronic equipment, shielding of signal cables and connectors, and the adhesive surface is also conductive and conductive even when bonded. A shielding effect can be obtained.

  In the body motion sensor of the present invention, since the piezoelectric film is a capacitor, ideally, the voltage remains output if there is no discharge. For example, when PVDF is used, the voltage is large and becomes several volts or more. At the time of discharging, the differential characteristics can be obtained by converting the discharge current into a voltage via a resistor. Here, according to the type and shape (size and thickness) of the piezoelectric film to be used, the resistor can output a voltage as high as possible and obtain a signal having a necessary frequency. Choose the best one.

The body motion detection sensor according to the present invention is connected to a measurement circuit such as a charge amplifier or FET (field drop transistor), and converts the charge amount induced in the piezoelectric film into a voltage signal. By passing through the measurement circuit, it can be output only when the piezoelectric film charge is induced, so it can be made less susceptible to noise caused by changes in body position and noise from the heartbeat. Judgment can be made instantly.
The analog voltage signal of the measurement circuit is converted into a digital signal (A / D conversion), output on the screen, and transmitted to a dedicated program of the computer, where the presence or absence of body movement is determined. When the voltage signal is below the reference value, it is counted that there is no body movement, and when there is no body movement for a certain period of time, an alarm can be issued to notify the abnormality. In order to realize a portable monitor system, it is preferable to use a small charge amplifier as the measurement circuit.

Hereinafter, details of the present invention will be described with reference to examples, but the present invention is not limited to these examples. Example 1 is a reference example.

  In order to realize a small body motion detection sensor, the body motion detection sensors of Comparative Example 1 and Example 1 were prototyped, and using these sensors, human respiration was monitored.

(Comparative Example 1)
As shown in FIG. 2, the sensor of Comparative Example 1 was configured by sticking a piezoelectric film 2 made of a PVDF film to a silicon spiral tube 7. The input impedance was 10 KΩ, and a power supply noise removal and high frequency noise removal circuit was used for the external circuit for measurement. Here, a power supply noise filter (50 Hz and 60 Hz notch filter) and a high frequency cut filter are used.
The thickness of the piezoelectric film 2 is 28 μm, and the size is 16 mm × 73 mm. The electrode size is 12 mm × 62 mm.
The respiration measurement result (female A) by the sensor of Comparative Example 1 is as shown in FIG. In Comparative Example 1, since a large output could not be obtained, signal amplification is necessary. In the configuration of Comparative Example 1, since the direction in which the piezoelectric film 2 expands and contracts is reversed up and down, it is assumed that the reverse voltage is generated in the upper and lower directions, and the forward voltage is canceled.

Example 1
In the sensor of Example 1, as shown in FIG. 4, the piezoelectric film 2 made of PVDF film is bent into a substantially U shape, one end thereof is fixed to the inner surface 11 of the cover member by the fixing member 23, and the other end is fixed. The band member 32 and the elastic member 3 are connected via the member 24. The elastic member 3 is fixed to the inner surface 12 in the cover member by a fixing member 25. The input impedance was 10 KΩ, and a power supply noise removal and high frequency noise removal circuit was used for the external circuit for measurement.
The thickness of the piezoelectric film 2 is 28 μm, and the size is 16 mm × 73 mm. The electrode size is 12 mm × 62 mm.
The cover member was made of an acrylic plate having a thickness of 0.5 mm.

When the subject breathes, the band member 32 is pulled in the direction of the arrow, and a stroke of L1 is obtained. As shown in FIG. 5, the respiration measurement result (female A) of the sensor of Example 1 has a larger output than that of Comparative Example 1.
Moreover, since the sensor of Example 1 can take a long stroke compared with the sensor which concerns on patent document 3, there are few burdens to a test subject and there are also less noise compared with-. The reason why noise is reduced is that the respiration signal has a very long period (low frequency), and a signal with a short period (high frequency) than the respiration signal can be said to be noise due to vibration. This is thought to be due to this.

  In addition, the results of measurement with the sensor of Example 1 attached to the subject and riding in a passenger car are FIG. 6 (female A) and FIG. 7 (male B). It was confirmed that a practical output could be obtained even in a running passenger car by mounting the sensor of this example. From this, it can be said that according to the sensor of the present embodiment, it is possible to monitor the breathing state of the driver.

The sensor of Example 2 is configured by winding a piezoelectric film 2 made of a PVDF film around a columnar winding member 4 as shown in FIG. The winding member 4 and the columnar engaging member 5 are engaged by an elastic member 6, and the winding member 4 is pulled (right direction in FIG. 8) and loosened by the band member 32 (left direction in FIG. 8). ) To turn back and forth. And when the winding member 4 rotates, the piezoelectric film 2 expands and contracts and a voltage is generated.

In the sensor of this example, two types of winding members 4 were prepared and respiration was measured. The input impedance was 10 KΩ, and a power supply noise removal and high frequency noise removal circuit was used for the external circuit for measurement. FIG. 9 shows the measurement results when the winding member 4 has a radius of 4 mm as ch1 and the radius of 10 mm as ch2.
The thickness of the piezoelectric film 2 is 28 μm, and the size is 16 mm × 73 mm. The electrode size is 12 mm × 62 mm.
From the measurement results in FIG. 9, it was confirmed that a larger output can be obtained when the radius of the winding member is smaller .
In addition, in the structure of a present Example, compared with the case where a piezoelectric film is comprised in a U-shape, since a voltage does not arise in the reverse direction on both sides of a U-shaped trough part, higher output can be obtained.
In addition, the sensor of the first embodiment can obtain an output approximately twice or more that of the sensor according to Patent Document 3.

<< Total length and number of turns of piezoelectric film >>
The total length of the piezoelectric film is determined based on the stroke that needs to be measured. For example, when measuring human respiration, if there is a change of 50 mm in the chest, the total length of the piezoelectric film needs to be 50 mm or more.
Further, from the experimental results so far, the circumference of the winding member with respect to the stroke (the size of the radius) is configured such that the circumference of the winding member is 2 to 4 times the stroke of the measured object. It has been found preferable.
As the circumference of the winding member becomes shorter (the radius becomes smaller), the change in the piezoelectric film becomes larger. Therefore, it is preferable to configure the winding member to have a small diameter and increase the number of windings, and at least the piezoelectric film shrinks. In this case, the winding member is wound around one or more times. However, there is a minimum radius for winding the piezoelectric film (similar to deterioration when the optical fiber is set to a radius less than the catalog value), and this differs depending on the specifications of the piezoelectric film. It is. From the experimental results so far, it was found that 3 to 4 mm is the minimum radius in the configuration of this example. This value seems to be related to the thickness of the piezoelectric film and the material and thickness of the material for insulating and protecting the piezoelectric film.

  The sensor unit 1 of the present embodiment can be configured to be thin due to its structure. And as shown in FIG. 10, it is possible to comprise the whole magnitude | size of a body movement detection sensor compactly by overlapping a circuit part. That is, by configuring the substantially L-shaped sensor portion 1 in which the portion where the columnar members 4 and 5 are not installed is thin, and arranging the circuit portion 40 in the thin portion, the overall size of the body motion detection sensor is increased. This makes it possible to make the device compact.

The present invention can be used for monitoring human body movements, and for example, can be used for monitoring respiratory breathing of artificial respiratory users and patients who have a risk of sudden attacks. Since the configuration is simple and suitable for miniaturization and portability, for example, it is expected to be used in home ventilation therapy for muscular dystrophy patients.
It can also be used in a dozing detection system that monitors the breathing state of a vehicle driver.
Note that it may be used not only for humans but also for monitoring body movements of animals, for example, for use in monitoring the delivery timing of animals.

It is drawing for demonstrating the photograph and characteristic of the prototype of the body motion detection sensor disclosed by patent document 3. FIG. It is a photograph of the prototype of the body motion detection sensor of Comparative Example 1. It is drawing which shows the respiration measurement result (female A) by the body movement detection sensor of the comparative example 1. It is a schematic block diagram of the body movement detection sensor of Example 1. It is drawing which shows the respiration measurement result (female A) by the body movement detection sensor of Example 1. FIG. It is drawing which shows the respiration measurement result (female A) in the vehicle by the body movement detection sensor of Example 1. FIG. It is drawing which shows the respiration measurement result (male B) in the vehicle by the body movement detection sensor of Example 1. FIG. It is a schematic block diagram of the body movement detection sensor of Example 2. It is drawing which shows the respiration measurement result by the body movement detection sensor of Example 2. FIG. It is explanatory drawing of the arrangement | positioning relationship between the body movement detection sensor of Example 2, and a circuit part.

Explanation of symbols

1 Sensor part (cover member)
The inner surface of the second piezoelectric film 3 elastic member 4 spirally wound member 5 engaging rotary member 6 elastic members 7 spiral tube 11 cover member (first inner surface)
12 Inner surface of cover member (second inner surface)
21 First end portion 22 of piezoelectric film 22 Second end portions 23 to 26 of piezoelectric film Fixing members 31 and 32 Band member 40 Circuit portion

Claims (4)

In the body motion detection sensor that detects body motion by the output voltage generated by the expansion and contraction of the piezoelectric film,
A cover member for housing the piezoelectric film is connected to the cover member, and the band member to be stretchable in the longitudinal direction due to body motion of the subject, the winding member (4), and engagement times member (5), wound and a elastic member Ru wound engaging members and Kakarikai member,
The first end of the piezoelectric film is wound around the winding member, and the second end of the piezoelectric film is connected to the end of the band member. The piezoelectric film expands and contracts when the winding member rotates. body motion detection sensor in which the voltage arising in.   The body motion detection sensor according to claim 1, wherein the second end portion of the piezoelectric film and the circuit portion are laminated. A body motion detection method for detecting body motion by an output voltage generated by expansion and contraction of a piezoelectric film,
A cover member for housing the piezoelectric film is connected to the cover member, and the band member to be stretchable in the longitudinal direction due to body motion of the subject, the winding member (4), and engagement times member (5), wound and a elastic member Ru wound engaging members and Kakarikai member, wound around a first end of the piezoelectric film to the winding member, connecting the second end of the piezoelectric film to the end portion of the band member body movement to be constructed, the body motion detection sensor voltage piezoelectric film expands and contracts is arising by winding member rotates, attached to the subject by the band member, and detecting the body movement Detection method.   The body motion detection method according to claim 3, wherein the body motion detection sensor is attached to a chest of a subject to detect respiration.