JP3809599B2 - Accelerometer - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an acceleration sensor capable of detecting a change in acceleration in the direction of gravity, for example, a fall sensor or a seismic sensor capable of detecting a vertical shake of an earthquake and outputting a signal corresponding to the magnitude of the shake. It is.
[0002]
[Prior art]
There are few conventional accelerometers that can see the acceleration change in the direction of gravity in particular, but those that use inertial elements such as metal spheres and piezoelectric elements and contact mechanisms, for example, semiconductors There are things that use.
[0003]
[Problems to be solved by the invention]
However, a combination of an inertia element, a piezoelectric element, and a contact mechanism has a problem that the structure becomes complicated in order to detect both an increase and a decrease in acceleration in the direction of gravity. In other words, gravitational acceleration of 1G is always applied in the direction of gravity, and in order to detect a change in acceleration, the inertia element is always held against gravity by a spring or beam, etc. The inertial element must be structured to be movable in the vertical direction with a sufficient stroke to drive the mechanism or the like and to sufficiently displace the semiconductor detector. Further, the structure must be such that the inertial element does not move due to the lateral acceleration or that the contact mechanism or the detection unit is not driven. In particular, a combination of contact mechanisms cannot obtain the amount of change in acceleration as a continuous signal.
[0004]
Furthermore, in order to obtain a sensitivity capable of reliably detecting an acceleration change of 1 G or less as a sensor, it is necessary that the detection portion has a structure that generates a necessary displacement at an acceleration of 1 G or less. However, the impact acceleration that the sensor instantaneously receives during normal handling at the time of manufacture and installation may range from several G to several tens of G. When the sensor detection part is structured as described above, the strength point of view In addition, there is a possibility of destruction due to impact during handling. Therefore, it is necessary to handle the sensor with care, which causes a reduction in efficiency during manufacturing and handling. Although some have a buffer mechanism for protecting the detection portion against overload, there is a problem that the structure is complicated and the cost is increased.
[0005]
Therefore, there is a demand for a sensor that can be easily handled, is small, and can obtain a continuous signal corresponding to the magnitude of acceleration.
[0006]
[Means for Solving the Problems]
Therefore, in the acceleration sensor of the present invention, a sealed housing is constituted by a cylindrical housing closed at one end and a lid plate fixedly fixed to the open end of the housing, and a conductive liquid is enclosed in the sealed container. In addition, a thin tube having a predetermined inner diameter is fixed at the center inside the container so as to be substantially perpendicular to the conductive liquid and so that one end of the thin tube is immersed in the conductive liquid. The thin tube has an electrode along its longitudinal direction. The liquid level of the conductive liquid rises due to capillary action in the capillary tube, and a change in the contact area with the electrode due to a change in the position of the liquid surface in the capillary tube is output as a resistance value change. It is characterized by.
[0007]
This acceleration sensor uses the fact that the liquid surface position of the liquid rising in the capillary tube changes due to capillary action when the acceleration in the direction of gravity changes, and this change in the liquid surface position is detected by the electrode and liquid provided in the capillary tube. The acceleration change in the direction of gravity can be measured by detecting the change in the resistance value due to the change in the contact area.
[0008]
Further, in the acceleration sensor according to claim 2, a plurality of electrodes insulated from each other are fixed to the lid plate, and these electrodes are respectively fixed to the inner peripheral surface of the thin tube along the longitudinal direction thereof. A change in the position of the liquid surface in the narrow tube is output as a change in resistance value between the electrodes.
[0009]
In this acceleration sensor, the acceleration change in the gravitational direction can be measured by detecting the change in the liquid surface position as a change in resistance value between a plurality of electrodes provided in the narrow tube. Further, by providing a plurality of electrodes in the narrow tube, the distance between the electrodes is reduced, and a liquid having a relatively high specific resistance value can be used.
[0010]
The acceleration sensor according to claim 3 is characterized in that an orifice having an opening area smaller than the cross-sectional area of the thin tube is provided in the vicinity of the tip where the liquid of the thin tube enters and exits.
[0011]
According to this acceleration sensor, the orifice suppresses the rapid flow of the liquid when the liquid enters and exits the capillary tube, and attenuates the kinetic energy, so that the natural frequency of the liquid can be maintained even when the acceleration sensor receives repeated vibration acceleration. A sensor in a high frequency range that is unnecessary especially when used as a seismic sensor by preventing coincidence with the frequency of vibration acceleration, suppressing the occurrence of resonance phenomenon accompanying it, and suppressing the movement speed of liquid. It is possible to suppress the generation of noise signals caused by daily vibrations other than earthquakes.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The acceleration sensor of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of the acceleration sensor, and FIG. 2 is a sectional view taken along the line AA in FIG. This acceleration sensor 1 has a substantially cylindrical metal housing 2 closed at one end and a disk-shaped metal cover plate 3, and the cover plate 3 has a peripheral edge at the opening side end of the housing 2. An airtight container is configured by being closely fixed to each other by resistance welding or the like. Here, the housing 2 and the cover plate 3 are not necessarily made of metal, and may be made of resin or ceramics as long as the liquid-tightness is reliably maintained.
[0013]
A through-hole 3A is provided in the center of the cover plate 3, and two electrodes 4A and 4B are inserted into the through-hole 3A and insulated from each other by an electrically insulating material 5 such as glass. It is fixed. A predetermined conductive liquid 6 is sealed inside the sealed container of the lid plate 3. The conductive liquid 6 is not only conductive but also needs to maintain the required fluidity in the temperature range in which the acceleration sensor is used. For example, the specific resistance value is relatively low like methyl alcohol or ethyl alcohol. Alcohols can be used, and liquids in which a conductive material such as lithium nitrate is dissolved in a liquid having a relatively high specific resistance such as esters such as methyl propionate and ethyl propionate can be used. Of course, it is needless to say that the conductivity may be adjusted by dissolving a conductive material in alcohols.
[0014]
In the center of the container, an electrically insulating thin tube 7 is provided so as to be perpendicular to the liquid surface of the conductive liquid 6 in a normal posture. By arranging in this way, the narrow tube 7 is positioned on the central axis of the container, and even when the sensor container is slightly inclined, the liquid level at the position of the central thin tube does not change. The material of the thin tube 7 is required to be a glass or engineering plastic such as PPS that does not dissolve partly or entirely by the conductive liquid 6 and does not alter the liquid, has a small contact angle with the liquid, and does not penetrate the liquid. It is preferable to use (polyphenylene sulfide) resin or PEEK (polyether ether ketone) resin.
[0015]
An orifice 7C having a diameter smaller than the inner diameter of the hollow portion 7A is provided at the opening of the hollow portion 7A located at the lower end 7B of the thin tube 7, and the conductive liquid 6 enters and exits the hollow portion 7A from here. Here, the orifice 7C, which is the opening, faces directly below and the hollow portion 7A extends in the direction of gravity, so that the liquid 6 moves laterally in the container 2 due to an earthquake roll or impact applied to the acceleration sensor 1. In this case, the liquid hardly enters or leaves the hollow portion 7A. Further, in the narrow tube, the liquid is hardly biased due to the acceleration in the lateral direction due to the surface tension of the liquid, so that the sensor can reliably detect the change in the acceleration in the vertical direction, that is, the gravity direction. Further, at least one notch 7E is provided in the upper end portion 7D of the narrow tube 7 that is in contact with the cover plate 3, so that the gas in the container does not hinder the inflow / outflow of the conductive liquid 6 into the hollow portion 7A. The hollow portion 7A can freely enter and exit.
[0016]
Further, the electrodes 4A and 4B are provided along the longitudinal direction of the inner wall of the hollow portion 7A, and the conductive liquid 6 flowing into the hollow portion 7A through the orifice 7C conducts between the electrodes 4A and 4B. Put it in a state. In this embodiment, a leg 7F is provided at the lower end 7B and supports the narrow tube 7 by contacting the bottom surface of the housing 2. However, the upper end 7D of the narrow tube is fixed to the cover plate 3 by a method such as adhesion. For example, the leg portion 7F may be omitted.
[0017]
Here, the resistance value between the electrodes is determined by the distance between the electrodes, the specific resistance value of the conductive liquid, and the contact area between the electrode and the conductive liquid. Of these, the distance between the electrodes and the specific resistance value of the liquid do not change due to acceleration, so the change in resistance value is determined by the contact area between the electrode and the conductive liquid, that is, the amount of liquid rise due to capillary action.
[0018]
The relationship between the acceleration due to this capillary phenomenon and the amount of rise in the liquid level will be described. Assuming that the cross-sectional shape of the hollow portion 7A of the thin tube 7 is a circle, the increase amount h of the conductive liquid 6 due to capillary action is r, the liquid density is ρ, the liquid surface tension is γ, and the contact angle is If θ and acceleration in the direction of gravity are g,
h = 2γ cos θ / rρg
It becomes. Here, for example, when a thin tube is made of glass and methyl alcohol is used as the conductive liquid, since the contact angle is almost 0 °, cos θ can be regarded as 1, so that substantially h = 2γ / rρg.
It becomes. Here, the surface tension γ, the density ρ, and the radius r of the hollow portion 7A are constants, whereas the acceleration g is a variable, and the steady gravitational acceleration g ₀ and other accelerations g in the gravitational direction. ₁ is the sum, that is, g = g ₀ + g ₁ . When the sensor as seen from here is subjected to acceleration g ₁ value of the acceleration g of gravity direction increases or decreases, the liquid level in response to the acceleration change moves. As the liquid level moves, the contact area between the electrodes 4A and 4B provided on the thin tube 7 and the conductive liquid 6 changes, and the resistance value between the electrodes changes accordingly. The magnitude of acceleration can be reliably detected from the increase / decrease of the resistance value.
[0019]
In this example, the lower end 7B of the narrow tube 7 is provided with an orifice 7C having a diameter smaller than the inner diameter of the hollow portion 7A. The purpose is to obtain a damping effect on the flow of the conductive liquid 6. This point will be described with reference to FIGS. These graphs show the relationship between the vibration frequency and the maximum resistance change between the electrodes when a constant sinusoidal acceleration in the direction of gravity is applied to the sensor. FIG. 3 shows an orifice in the narrow tube. FIG. 4 is a graph in the case where an orifice is provided at the tip of the thin tube when the hollow portion is passed through to the lower end without being provided.
[0020]
When acceleration (or deceleration) in the gravitational direction is applied to the sensor, the liquid in the capillary tube moves up and down in response to the change in acceleration to change the resistance value between the electrodes. For example, in the example with a 2 mm inner diameter tube measured in the graph of FIG. 3, the resistance value between the electrodes is 390 kΩ when stationary, but when the acceleration of a sinusoidal wave of 1 Hz is applied with a size of 200 gal The resistance value between the electrodes is 290 to 510 kΩ, and the maximum value of the resistance value change from the stationary state is 120 kΩ.
[0021]
By the way, when the liquid flows into the narrow tube, the movement of once flowing over the balance position due to inertia and backflowing to return to the original is repeated, so that vibration occurs in the liquid flow. However, for example, when this sensor is used as a drop sensor, the acceleration applied from the outside is not repeated, so that the vibration of the liquid is attenuated by friction with the electrode, the wall surface, etc. and converges immediately.
[0022]
However, when repeated vibration acceleration is applied, if the vibration of the liquid is synchronized with the applied vibration acceleration, the vibration of the liquid may not be converged and may be amplified conversely. For example, in order to inspect the characteristics as a seismic sensor, if a vibration acceleration of a sine wave is continuously applied to the sensor in the direction of gravity as a substitute for seismic waves, the resonance frequency near the resonance frequency determined by the diameter of the hollow part or the viscosity of the liquid With respect to vibration, the vertical movement of the liquid increases, and the resistance value change between the electrodes increases.
[0023]
For example, in the example of FIG. 3 in which the diameter of the thin tube is 2 mm, the resonance frequency of the liquid exists in the vicinity of the vibration frequency of 5 to 6 Hz. The fluctuation is about twice that of the case where the vibration frequency is 1 Hz, and the resistance value changes as shown by the curve 11 in FIG. For this reason, even if the vibration acceleration actually applied does not reach the predetermined magnitude, the change in the resistance value of the sensor may reach the predetermined value, and the determination device driven by the signal from the sensor may malfunction. There is. Even when an actual seismic wave is applied, the seismic wave is synthesized from vibrations of several frequency components, so if the seismic wave contains a frequency component close to the resonance frequency of the sensor, the liquid will resonate and be output. The value will increase.
[0024]
Therefore, in the acceleration sensor 1 of the embodiment, as shown in FIGS. 1 and 2, the orifice 7C having an opening area smaller than the cross-sectional area of the hollow portion 7A is provided at the lower end 7B of the thin tube 7, so The inflow speed and outflow speed of the liquid 6 are slowed down, and the kinetic energy of the liquid 6 is deprived and the vibration is attenuated at the time of entering and exiting, so that resonance hardly occurs. In the embodiment, an orifice 7C having a diameter of 1 mm is provided at the lower end of a hollow portion having a diameter of 2 mm, and the liquid 6 is configured to enter and exit the hollow portion 7A through the orifice 7C. The damping effect increases as the vibration frequency increases, that is, as the moving speed of the liquid increases. Therefore, by providing an orifice, the amount of change in resistance value is not significantly affected at a low vibration frequency as shown in FIG. A damping effect can be obtained for vibration frequencies of 5 Hz or more that are affected by resonance.
[0025]
The frequency component of the seismic wave is mainly 10 Hz or less, particularly 1 to 5 Hz. However, by providing the orifice, it is possible to suppress the occurrence of resonance due to the vibration component in this frequency region and to make the detection sensitivity almost constant. . Therefore, it is possible to always obtain a stable sensitivity to earthquake vibrations. In addition, life vibrations other than earthquakes are mainly at a high frequency exceeding 10 Hz and are usually sufficiently higher than the natural frequency due to liquids, so their movements are sufficiently suppressed. For example, if a seismic device hits an object or human body When an impact is applied, there is a case where the vibration becomes large compared with the vibration of the earthquake, and the suppression may be insufficient. However, since the movement of the liquid is more effectively attenuated by providing an orifice, the signal from the sensor hardly changes for high-frequency vibrations. The possibility of recognition decreases.
[0026]
As described above, the thin tube provided with the orifice has been described. However, for example, when detecting acceleration other than repetitive vibrations such as a drop sensor, there is no possibility that the liquid will resonate and the orifice need not be provided. Further, the orifice may be omitted by changing the diameter of the hollow portion of the narrow tube or adjusting the viscosity of the liquid to move the resonance frequency to a low region or a high region where there is no practical problem.
[0027]
In the above-described example, a case where a plurality of electrodes are provided on the cover plate and each electrode is disposed in a thin tube made of an electrical insulator has been described. However, for example, the narrow tube itself can be used as one electrode. This example will be described with reference to FIG. The same parts as those in the above example are denoted by the same symbols, and detailed description thereof is omitted.
[0028]
The acceleration sensor 21 includes a metal housing 2 and a lid plate 23 to form a sealed container. A conductive terminal 24, which is an electrode, is inserted into the through hole 23 </ b> A of the lid plate 23 and is sealed and fixed by the electrically insulating filler 5. A conductive thin tube 27 made of metal or the like is disposed in the center of the housing 2, and this thin tube 27 is conductively fixed by welding a fixing portion 27 </ b> A to the bottom surface of the housing 2. The fixed portion 27A at the lower end of the thin tube 27 is provided with a liquid inflow hole 27B, and the conductive liquid 6 flowing in from this rises in the thin tube 27 by capillary action. Further, the conductive terminal 24 is inserted and fixed at the center of the thin tube 27 so as to be located at a predetermined distance from the inner wall of the thin tube. In this embodiment, an electrically insulating cap 28 is fixed to the front end of the conductive terminal 24 inside the container for positioning. A gap through which the conductive liquid 6 can flow is provided between the periphery of the cap 28 and the inner wall of the thin tube 27, and this gap also serves as an orifice.
[0029]
When the acceleration in the gravitational direction changes in this acceleration sensor, the inflow amount of the conductive liquid in the capillary tube 27 due to capillary action changes as in the above example. As a result, the resistance value between the conductive terminal 24 and the thin tube 27 via the conductive liquid 6 varies, so that a drop, vibration, or the like can be detected from this variation.
[0030]
In this embodiment, the thin tube 27 is conductively fixed to the center of the bottom surface of the housing 2. However, for example, the fixing portion 27A is fixed to the metal portion of the cover plate 23, and the conductive terminal is positioned at a predetermined distance at the center. You may make it do.
[0031]
In this embodiment, when the positional relationship between the conductive terminal and the narrow tube can be ensured and the orifice is not required, the cap 28 serving as the positioning and the orifice can be omitted. For example, if the other electrode is arranged at a position where there is no influence of capillary action in the sealed container, or if the second conductive terminal is directly fixed to a metal thin tube and led out of the housing as an electrode to the outside The housing and the cover plate do not necessarily need to be conductive.
[0032]
【The invention's effect】
In this acceleration sensor, utilizing the fact that the liquid surface position of the liquid rising in the capillary tube changes due to capillary action as the acceleration in the gravity direction increases or decreases, an electrode is placed in the capillary tube and the conductive liquid is used as the liquid. Thus, acceleration change in the gravitational direction can be detected as a continuous resistance value change between the electrodes according to the change amount of the liquid surface position in the narrow tube. In addition, since liquid is used as an inertial body, it is possible to detect acceleration changes of 1 G or less, while the detector is destroyed by impact acceleration of several G to several tens of G that may be received during assembly or other handling. It is possible to provide a sensor that is not performed.
[0033]
In addition, by providing an orifice with an opening area that is at least smaller than the cross-sectional area of the thin tube near the tip where the liquid flows in and out of the thin tube, this orifice suppresses the flow rate of liquid flowing into and out of the thin tube, and at the same time attenuates kinetic energy and accelerates. Even when the sensor receives repeated vibration acceleration, the occurrence of a liquid resonance phenomenon at a specific vibration frequency can be suppressed. In addition, by suppressing the moving speed of the liquid, it is possible to reduce the sensitivity of the sensor in the high frequency area, which is unnecessary especially when used as a seismic sensor, and to suppress the generation of signals caused by life vibrations other than earthquakes. .
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing the structure of an acceleration sensor according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA of the acceleration sensor in FIG. 1. FIG. FIG. 4 is a graph showing the relationship between the vibration frequency of the electrode and the resistance change between the electrodes. FIG. 4 is a graph showing the relationship between the vibration frequency and the resistance change between the electrodes when an orifice is provided in the thin tube of the acceleration sensor of the present invention. ] Vertical sectional view showing the structure of another embodiment of the acceleration sensor of the present invention [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 2: Acceleration sensor 2: Housing 3, 23: Cover plate 4: Electrode 5: Insulating filler 6: Conductive liquid 7: Narrow tube 7A: Hollow part 7C: Orifice 24: Conductive terminal (electrode)
27: Capillary tube (electrode)

Claims (3)

A cylindrical housing closed at one end;
A sealed container is configured with a lid plate that is closely fixed to the open end of the housing,
A conductive liquid is sealed in the sealed container,
In addition, a narrow tube having a predetermined inner diameter is fixed to the center inside the container so as to be substantially perpendicular to the conductive liquid and so that one end thereof is immersed in the conductive liquid.
The tubule is provided with electrodes along its longitudinal direction,
The conductive liquid has a higher liquid level than the surroundings due to capillary action in the capillary tube,
An acceleration sensor characterized in that a change in contact area with the electrode due to a change in position of the liquid surface in the narrow tube is output as a change in resistance value. A plurality of electrodes insulated from each other are fixed to the cover plate,
These electrodes are each fixed to the inner peripheral surface of the thin tube along its longitudinal direction,
2. The acceleration sensor according to claim 1, wherein a change in position of the liquid level in the narrow tube is output as a change in resistance value between the electrodes. The acceleration sensor according to claim 1 or 2, wherein an orifice having an opening area smaller than at least a cross-sectional area of the thin tube is provided in the vicinity of a tip where the liquid of the thin tube enters and exits.

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