JP2006340820A - Body motion sensing sensor, and body motion monitoring system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a body motion sensing sensor using a piezoelectric film, of which the sensing precision is high, and in addition, of which the fitting feeling is good, and to provide a body motion monitoring system using the body motion sensing sensor. <P>SOLUTION: This body motion sensing sensor is constituted of the piezoelectric film which is made to warp into a bridge shape, and a stretchable member which connects both ends of the piezoelectric film and is shorter than the piezoelectric film. For the body motion sensing sensor, the warpage of the piezoelectric film changes following the stretching/contracting motion of the stretchable member which comes into contact with a subject. The body motion monitoring system has a signal converting means, and a body motion judging means which judges the presence/absence of a body motion based on an analogue signal. In this case, the signal converting means converts an electric load induced by the body motion sensing sensor into a voltage signal, and converts the voltage signal into the analogue signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensor and system for detecting body movement, and more particularly to a body movement detection sensor using a piezoelectric film with high detection accuracy and good wearing feeling, and a body movement monitoring system using the same.

  Conventional body motion detection means can be broadly classified into one that passes a current through a sensor and measures a change in electrical resistance, and one that measures a change in voltage generated in a piezoelectric body due to body motion.

The former is a method of measuring the voltage change by passing a current with a strain gauge (a thin tube infused with a conductive material such as carbon particles) wrapped around the body, or the inductance of a coil sensor in which a thin conductor is sewn to the band. It is to measure the change of.
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).

The latter needs to bend in the piezoelectric body, so that an elastic film-shaped one is used as the piezoelectric body. 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 the timing of minutes by monitoring muscle activity using PVDF (Patent Document 2).
JP 2001-17409 A Japanese Patent Publication No. 63-501196

The invention disclosed in Patent Document 1 measures the physical expansion and contraction of the band length itself, and has a problem in accuracy.
On the other hand, there is a band-type respiration sensor using a piezoelectric film, which incorporates the idea of Patent Document 2 above. 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 part 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 deflection amount of the part.
FIG. 2 shows a cross-sectional view of this state. By tightly wrapping the band 1 around the chest and abdomen, the piezoelectric film 2 as the sensor part is brought into close contact with the body, and the piezoelectric film 2 is pulled during inspiration. The voltage is generated by loosening at the time of exhalation.

  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 that only the movement of the abdomen and chest causes the piezoelectric film to bend, the resulting voltage change is small, and the output electrical signal is small (catalog value 700μV), so noise due to changes in body position There was a problem that stable recording could not be obtained due to noise caused by heartbeat.

  By using two bands wrapped around the chest and abdomen, the detection accuracy will be higher, but the feeling of wearing will be worse compared to one band, and the body will also be visually bound Therefore, the psychological burden on the patient was great.

  There is also a method of sticking a piezoelectric film directly to the body with a double-sided tape, etc., but the feeling of wearing was bad and patient discomfort was high. In addition, there is a problem that since the generated deflection is small, the output electric signal is small.

  In order to solve the above-mentioned problems, an object of the present invention is to provide a body motion detection sensor using a piezoelectric film and a body motion monitoring system using the same with high detection accuracy and good wearing feeling.

According to the present invention, a piezoelectric film for detecting body movement and a member that expands and contracts with body movement are made into separate structures, and the piezoelectric film is bent in a bridge shape, thereby obtaining high detection accuracy without impairing the wearing feeling. It was possible.
That is, the first invention is composed of a piezoelectric film bent in a bridge shape and a member that can be expanded and contracted shorter than the piezoelectric film that connects both ends of the piezoelectric film, and is capable of expanding and contracting the expandable member that contacts the subject. It is a body motion detection sensor that follows and changes the deflection of the piezoelectric film.
According to a second aspect, in the first aspect, the surface of the piezoelectric film is covered with a conductive cloth tape.
A third invention is characterized in that, in the first or second invention, the piezoelectric film is polyvinylidene fluoride.
According to a fourth aspect of the present invention, there is provided any one of the first to third body motion detection sensors, a signal conversion unit that converts the charge induced by the body motion detection sensor into a voltage signal and converts the voltage signal into an analog signal, and the analog signal. It is a body movement monitoring system which has a body movement determination means which determines the presence or absence of a body movement based on this.
A fifth invention is characterized in that, in the fourth invention, the signal conversion means is constituted by a charge amplifier unit, and the body movement determination means is constituted by an MPU (Micro Processing Unit).

According to the present invention, high detection accuracy can be obtained without impairing the wearing feeling, and the piezoelectric film does not touch the body directly like conventional products, so that noise caused by changes in body position and noise due to heartbeat are suppressed. Detection accuracy is high. Therefore, since it is not necessary to perform filtering by an expensive device (for example, polysomnography (PSG)), it can be configured at a low cost, and a fine signal can be prevented from being overlooked by filtering.
In addition, by adjusting the length of the telescopic member, it can be used from infants to adults regardless of body shape and age, and it is not necessary to wrap the band tightly around the body, so the wearing feeling is not impaired and the body is bound. The apparent psychological burden of being taken can be minimized. High detection accuracy and simple configuration make it suitable for miniaturization and portability.

The sensor according to the present invention includes a piezoelectric film that is bent in a bridge shape and a member that can be expanded and contracted shorter than the piezoelectric film that connects both ends of the piezoelectric film.
For example, when it is attached to the chest or abdomen, the chest circumference / reconstruction is reduced by exhaling air in the lungs during exhalation, so that the expansion rate of the elastic member 3 is small, and the piezoelectric film 2 is a high bridge as shown in FIG. It becomes a shape. On the contrary, since the chest circumference / reincarnation becomes larger by inhaling air into the lungs during inhalation, the elongation rate of the elastic member 3 becomes large, and the piezoelectric film 2 has a low bridge shape as shown in FIG.
As described above, the sensor according to the present invention has a larger change in the voltage generated due to the larger deflection change in the piezoelectric film than the conventional product as shown in FIG. Is possible. In addition, since the piezoelectric film is not in direct contact with the body, noise due to heartbeat can also be suppressed.

  In the sensor according to the present invention, it is output only when a change is applied to the piezoelectric film, and this output is generated by inducing charges at both ends of the piezoelectric film. Since the sensor is a capacitor having electrodes on both sides of the piezoelectric film, ideally, the voltage remains output unless electric charges are discharged from the electrodes at both ends. For example, in the case of PVDF, 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. Note that the resistance is adjusted according to the size and thickness of the PVDF to be used so that an output with a voltage as high as possible can be obtained and a signal having a necessary frequency can be obtained.

  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 also has the characteristics that the response band is extremely wide and it 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.

  As shown in FIG. 8, the piezoelectric film is preferably shielded with a conductive cloth tape to take measures against noise. 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.

The 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 amount of charge 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.
Subsequently, the analog voltage signal of the measurement circuit is converted into a digital signal (A / D conversion), output on the liquid crystal screen, and transmitted to a dedicated program of the computer, where the presence or absence of body movement is determined. That is, when the voltage signal is below the reference value, it is counted as no body movement, and when no body movement continues for a certain period of time, an alarm is issued to notify the abnormality (see FIG. 5).
Since the measurement circuit outputs a sufficiently large voltage, there is no need for subsequent amplification.

In order to realize a portable monitor system, it is preferable to use a small charge amplifier as the measurement circuit and an MPU (Micro Processing Unit) as the computer, and an MPU is, for example, a PIC (Peripheral Interface Controller). It is done. The PIC is a so-called one-chip microcomputer having all of the CPU, ROM, RAM, and I / O in the chip, and is characterized by low cost and low power consumption.
On the other hand, it is preferable to use an FET as the measurement circuit in order to obtain a configuration without cost. At this time, in order to ensure an appropriate input impedance, it is necessary to consider the filter effect due to the element capacity (C) and input resistance (R) of the piezoelectric film.
The details of the present invention will be described with reference to examples, but the present invention is not limited to these examples.

  Respiration monitoring was performed using both a conventional sensor and a sensor according to the present invention (hereinafter referred to as “sensor of Example 1”). The configuration and measurement results of the respiratory monitoring system using each sensor are as follows.

1. Constitution
(1) Conventional sensor Piezoelectric film: PVDF
Input impedance: 1MΩ
External circuit for measurement: Charge amplifier (NEC Sanei 6D07) [High-pass filter passes 15Hz or less, low-pass filter passes 0.15Hz or more, and time constant is set to 1 second]
(2) Sensor of Example 1 Piezoelectric film: PVDF
Elastic member: Rubber band Input impedance: 1 MΩ
External circuit for measurement: Charge amplifier (NEC Sanei 6D07) [No filter setting]

2. Measurement Result The measurement result of the conventional sensor is as shown in the left diagram of FIG. 6. The output was as low as about 5 mv and there was a lot of noise. As shown in the figure on the right, the cardiac signal output is about 15 mv, and the S / N ratio obtained by dividing the respiratory signal by the cardiac signal is 1 or less. Therefore, it is necessary to perform filtering to remove the cardiac signal.
By amplifying the voltage signal with the amplifying device, only changes in the entire circumference of the chest and abdomen that occur when breathing (differential characteristics of the respiratory signal) can be directly measured. By measuring only the signal accompanying the change in this way, it can be instantaneously determined that there is no apnea if there is no output.

  The measurement result of the sensor of Example 1 is as shown in the left diagram of FIG. 7. The output was about 60 mv, about 12 times that of the conventional sensor, and there was little noise. As shown in the figure on the left, the output of the heart signal after amplification is as low as about 12 mV, and the S / N ratio obtained by dividing the respiratory signal by the heart signal is as large as 5, so the heart signal need not be removed. This is probably because the piezoelectric film does not directly contact the body.

As shown in FIG. 9, the sensor of this example is formed by sandwiching polyvinylidene fluoride with an electrode and protecting the surface with a polyester laminate, attaching a conductive cloth tape to the surface, and connecting it to GND of a coaxial cable. The charge amplifier was manufactured using NO12-1 (36 mm x 17.5 mm x 4 mm), a charge amplifier unit made by Toyonobu Electronics, in order to reduce size and cost. The charge amplifier used in Example 1 was 130 mm × 50 mm × 255 mm, but in this example, it could be realized on a palm-sized substrate (about 50 mm × about 50 mm) (see FIG. 10).
In addition, as a circuit for determining the presence or absence of breathing, a collection circuit prepared based on a base board kit for PIC16F87 series, which is a PIC made by Akizuki Denshi, was used (see FIG. 11).
With the above configuration, portable respiratory monitoring can be realized without using a personal computer. If a more expensive customized IC is used, further high performance and downsizing can be achieved.

The flow of respiratory signal measurement in the monitoring system having the above configuration is as follows.
(1) Input the output of the piezoelectric film sensor to the charge amplifier.
(2) The charge amplifier converts the charge amount into a voltage signal.
(3) Bias the output of the charge amplifier by about + 2.5V and input it to the analog input pin of PIC16F877.
(4) Convert analog signals to digital signals by A / D conversion of PIC.
(5) A signal is output to the liquid crystal display and data is transmitted to the personal computer via the RS232C cable.
(6) Make apnea judgment in PIC, and if it is judged as apnea by the process of Fig. 5, the LED connected to B6 pin of PIC is made to emit light. The reference voltage was 2.6V and the reference time was 300 counts.

When a respiratory waveform in a healthy person was measured with a sensor without a conductive cloth tape and a sensor with a conductive cloth tape, a remarkable noise removal effect could be confirmed as shown in FIG. Similarly, when the waveforms of apneas in healthy subjects were measured, the sensor with a conductive cloth tape measured the heartbeat as the signal was constant at a bias voltage (approx. + 2.5V) immediately after stopping breathing. (See FIG. 13).
Since the A / D converter of the PIC used in this embodiment can only input 0 to 5 V, 2.5 V (0 to 5 V) is used to measure the respiratory signal output to the plus side and the minus side. The middle voltage was the bias voltage.

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.
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.

This is a usage mode of a band-type respiration sensor using a conventional piezoelectric film. It is sectional drawing at the time of band type respiration sensor using a conventional type piezoelectric film. It is a side view at the time of contraction of the body movement detection sensor concerning the present invention. It is a side view at the time of extension of a body movement detection sensor concerning the present invention. It is a flowchart of the body movement detection process which concerns on this invention. It is the output measurement result of the sensor for conventional respiration monitors. It is an output measurement result of the sensor for respiratory monitors concerning Example 1. FIG. It is explanatory drawing of the structure of a conductive cloth tape. It is a side view of the piezoelectric film shielded with the conductive cloth tape. FIG. 6 is an explanatory diagram of a charge amplifier according to a second embodiment. It is explanatory drawing of the respiration determination circuit which concerns on Example 2. FIG. It is the measurement result at the time of the breathing concerning Example 2. It is a measurement result at the time of apnea concerning Example 2.

Explanation of symbols

1 Band 2 Piezoelectric film 3 Elastic member

Claims (5)

  The piezoelectric film is composed of a piezoelectric film bent in a bridge shape and a member that can be expanded and contracted shorter than the piezoelectric film that connects both ends of the piezoelectric film. Body motion detection sensor that changes.   The body motion detection sensor according to claim 1, wherein the surface of the piezoelectric film is covered with a conductive cloth tape.   The body motion detection sensor according to claim 1, wherein the piezoelectric film is polyvinylidene fluoride.   The body motion detection sensor according to any one of claims 1 to 3, a signal conversion means for converting the electric charge induced by the body motion detection sensor into a voltage signal, and converting the voltage signal into an analog signal; A body movement monitoring system having body movement judging means for judging presence or absence. 5. The body movement monitoring system according to claim 4, wherein the signal conversion means is constituted by a charge amplifier unit, and the body movement determination means is constituted by an MPU (Micro Processing Unit).