JPH06186248A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide an acceleration sensor wherein its constitution is simple, it is influenced little by an error signal due to a sound pressure and it can be used under high-humidity surroundings. CONSTITUTION:A first metal sheet 11 which is provided with an electret film on one face and a second metal sheet 12 which is faced with the electret film 14 on the first metal sheet by keeping a slight gap 20 are installed. One out of the first and second metal sheets 11, 12 is arranged so as to be capable of being shaken and moved by a vibration, and a hole by which both faces of the metal sheet capable of being shaken and moved are made to communicate is formed. An electric signal is taken out from the first metal sheet, and the acceleration of a vibrating object is detected. At least the face, of the second metal sheet 12, which is faced with the electret film 14 by keeping the slight gap 20 is insulation-treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for obtaining, for example, a motional feedback signal from a motional feedback type speaker, and for an industrial instrument such as an electronic musical instrument or the like, which requires a small and high-performance vibration detector. Regarding the acceleration sensor.

[0002]

2. Description of the Related Art As an acceleration sensor of this type, the applicant previously provided the one shown in FIG. 17 (see Japanese Patent Application No. 61-157597).

That is, in FIG. 17, reference numeral 1 is a thin case made of a conductive metal, and a first metal plate 2 is arranged inside the case 1. The bottom surface 1c of the case 1 of the metal plate 2
An electret film 3 is formed on the surface facing (constituting the second metal plate). From the other side of the metal plate 2,
The lead wire 4 is led out and used as a first electrode. The lead wire 4 is led out to the outside from the through hole 1b of the upper surface 1a of the case 1.

The metal plate 2 is locked in the case 1 with a predetermined gap between the upper surface 1a and the lower surface 1c of the case 1 by ring-shaped spacers 5 and 6 made of insulating rubber or the like. The sensor is, for example, the diaphragm 8 of the speaker.
When attached to the metal plate 2, the metal plate 2 vibrates following the vibration of the diaphragm 8. From the metal plate 2,
The lead wire 7 is led out and used as a second electrode. The gap g between the electret film on one surface of the metal plate 2 and the lower surface 1c of the case 1 is, for example, 30 μ to 100 μ.

In this acceleration sensor, the diaphragm 8
When the metal plate vibrates, the metal plate 2 vibrates accordingly, and the size of the gap g between the electret film 3 and the lower surface 1c of the case 1 changes. Therefore, the electrostatic capacitance formed by the electret film 3 and the lower surface 1c of the case 1 changes according to the vibration, and thus the change in the electrostatic capacitance can be detected as a voltage change to detect the acceleration.

[0006]

The above-described acceleration sensor has achieved its function sufficiently, but since it is attached to the speaker diaphragm, when abnormal vibration such as split vibration occurs in the speaker diaphragm, When using a plurality of speaker units, an error signal due to the sound pressure may be slightly generated when exposed to the high sound pressure generated by other units.

Further, with the expansion of the industrial field in which this type of acceleration sensor is used, there has been a demand for use under severe conditions where the humidity exceeds 90%. As described above, in the above configuration of the acceleration sensor, the first,
The interval between the second metal plates is optimally 20 μ to 100 μ in order to optimize the acceleration detection sensitivity and to set the low cutoff frequency sufficiently low. For the same reason, the insulation resistance between the metal plate (first metal plate) 2 and the lower surface 1c (second metal plate) of the case 1 is set to several tens MΩ.
It is desirable to set the above.

However, when the acceleration sensor is used under the high humidity conditions as described above, dew condensation may occur between the two metal plates 2 and 1c facing each other with a narrow space. In this case, the two metal plates are short-circuited, and an abnormal signal may be generated in the output.

In view of the above points, the present invention provides an acceleration sensor that can detect acceleration more stably and satisfactorily by making use of the characteristics of the acceleration sensor that can detect acceleration satisfactorily with the simple structure of the previous invention. With the goal.

[0010]

The acceleration sensor of the present invention corresponds to an embodiment shown in FIG. 1 which will be described later, and a first metal plate 11 having an electret film 14 on one surface and the first metal plate 11. Electret film 14 of metal plate 11
Second metal plate 1 facing each other with a slight gap between and
2 and the first electrically connected to the first metal plate 11
Electrode 24 and a second electrode 25 electrically connected to the second metal plate 12, and either one of the first and second metal plates 11 and 12 can be swung by vibration. And a hole 16 is provided so as to connect at least the gap on one side of the swingable metal plate and the space on the other side, and the first electrode and the second electrode It is characterized in that the acceleration is detected from the electric signal change between the electrodes.

At least the first of the second metal plates 12
An insulating layer 15 made of a material having an insulating property such as polyimide is provided on the surface of the surface facing the metal plate 11.

[0012]

When the acceleration sensor of the present invention having the above-mentioned structure is attached to the vibrating object, the first metal plate 1 is made swingable.
Either the first metal plate 12 or the second metal plate 12 vibrates as the vibrating body vibrates, the distance between the electret film 14 and the second metal plate 12 changes, and the static electricity formed by the electret film 14 and the second metal plate 12 changes. The capacitance changes according to this vibration.

Further, the pressure difference generated on both sides of the swingable metal plate due to the sound pressure entering from the outside is neutralized by the communication holes provided in the metal plate, and the first and second metal plates due to the sound pressure. No change in the interval occurs.

Therefore, by extracting the voltage signal from the first metal plate 11 having the electret film 14, only the acceleration can be detected, and a stable and good acceleration detection output without error signal due to sound pressure can be obtained with a simple structure. be able to.

At least the first of the second metal plates 12
By providing the insulating layer 16 on the surface of the metal plate 11 facing the surface of the electret film 14, even if dew condensation occurs,
It is possible to prevent a rapid change in the resistance value between the electret film 14 and the second metal plate 12, and it is possible to detect acceleration with stability against humidity.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the acceleration sensor according to the present invention will be described below with reference to the drawings. The acceleration sensor of the present invention is an electrostatic acceleration detection device using an electret as in the previously proposed invention.

FIG. 1 shows an acceleration sensor 1 according to the first embodiment.
It shows a configuration of 0. Accelerometer 1 of this example
0 is configured by arranging the first and second metal plates 11 and 12 in the cylindrical case 13 made of a conductive metal. In this example, the second metal plate 12 is attached to the case 13
Is arranged so as to face the lower surface side of the first metal plate 11
Opens a slight gap 20 with the second metal plate 12,
It is arranged above the second metal plate 12. The gap between both metal plates 11 and 12 is set to 20 μ to 100 μ.

In the first metal plate 11, the electret film 14 is formed on the lower surface facing the second metal plate 12, and the lead wire 21 is soldered on the upper surface. The lead wire 21 is led out from above the case 13 to form a first electrode terminal 24. An insulating fixing member 19 is provided in order to maintain a sufficient distance so that the first metal plate 11 and the conductive case 13 do not come into contact with each other.

The second metal plate 12 is the acceleration sensor 10
The thickness is sufficiently smaller than that of the first metal plate 11 so that the member 23 swings in response to the vibration of the member 23 to detect the vibration. For example, the thickness of the second metal plate 12 is 50 μ.

The second metal plate 12 has a ring-shaped spacer 18 for keeping a sufficient distance from the lower surface of the case 13,
It is sandwiched by a ring-shaped spacer 17 having an insulating property of, for example, 20 μ to 100 μ for maintaining the appropriate gap 20 with the first metal plate 11, and is arranged so as to face the first metal plate 11. It

The second metal plate 12 is provided with holes 15 for communicating both sides thereof, and the first and second metal plates 11 and 12 are provided.
The space between the second metal plate 12 and the lower surface of the case 1 is made to communicate with each other. Further, on the upper surface of the second metal plate 12 facing the first metal plate 11,
For example, the insulating layer 15 made of polyimide or the like is provided with a thickness of, for example, about 6 μ. Then, the second metal plate 12 and the case 13
The spacer 18 provided between the lead wire 22 and the outer surface of the case 13 is made of a conductive metal such as brass.
Is soldered to derive the second electrode terminal 25 electrically connected to the second metal plate 12.

The sensor output of the acceleration sensor 10 constructed as described above is taken out as a voltage. Therefore, an example of the sensor output take-out circuit is configured as shown in FIG.

That is, the first terminal 24 connected to the first metal plate 11 is connected to the gate of the FET 31, and the F
The drain of ET31 is connected to terminal 34. Also, FE
The source of T31 is connected to the case 13, that is, the second metal plate 12 via the resistor 32, and the second terminal 25.
And to the terminal 35. In addition, FET
The connection point between 31 and the resistor 32 is connected to the terminal 36 via the capacitor 33. Then, a DC voltage having an appropriate voltage is supplied between the terminals 34 and 35. Terminal 36 and terminal 3
5 is connected so as to detect the voltage value between these terminals 36 and 35. The voltage value between the terminals 36 and 35 becomes an acceleration detection output.

For higher sensitivity detection, the output circuit of the sensor output is constructed as shown in FIG. That is, the resistor 37 is connected between the terminal 34 and the drain of the FET 31. The connection point between the drain of the FET 31 and the resistor 37 is connected to the terminal 3 via the capacitor 38.
Connect to 6. Also in the case of this example, the connection for detecting the voltage value between the terminals 36 and 35 is the same as the example of FIG.

In addition, the circuit (FE
(T31, resistors 32, 37, capacitor 33, etc.), or a circuit board 40 in which a part of the circuit is incorporated may be integrally incorporated in the case 13 of the acceleration sensor 10 as shown in FIG. it can.

The detection circuit of the acceleration sensor according to the present invention is not limited to the circuits shown in FIGS. 2 and 3, and may be a circuit using FETs, transistors, integrated circuits, etc. which are generally known for capacitance type detectors. It goes without saying that the purpose can be achieved.

By configuring the acceleration sensor 10 of this example as described above, it is possible to detect the acceleration corresponding to the vibration of the member 23 to which the acceleration sensor 10 is attached. That is, the case 13 of the acceleration sensor 10
Between the first metal plate 11 and the electret film 14 arranged inside the chamber, a charge having a capacity corresponding to the size of the gap between the electret film 14 and the second metal plate 12 formed by the spacer 17 is generated. Exists. Therefore, when the member 23, which is going to detect vibration, vibrates, the second metal plate 12
Vibrates following the vibration of the member 23, the gap 20 with the electret film 14 changes, and the amount of charge changes. Then, by extracting this charge amount with the gate of the FET 31, the change in this charge amount becomes a change in the voltage value, and the acceleration can be detected by detecting the change in the voltage value.

Since the acceleration can be detected by the electret film 14 in this manner, the charge capacity that is not influenced by magnetism is detected, and the detection signal is not influenced by magnetism or is influenced by sound pressure. Not good sensor output signal can be obtained.

The acceleration sensor 10 of this example has a first metal plate 11 having an electret film 14 on one surface.
Since the spacer 17 that creates the optimum gap and the second metal plate 12 are simply arranged in the case 13, the structure is simple and the manufacturing cost is low, and the structure is thin and lightweight.
Furthermore, since the amount of change in capacitance can be adjusted by the material and thickness of the second metal plate 12, and the capacitance can be changed by changing the thickness of the spacer 17, the selection can be made by these selections. The detection characteristics of acceleration can be freely selected.

Further, as described above, the acceleration is detected as a change in capacitance, so that the first metal plate 11 and the second metal plate 12 can be efficiently extracted as a change in voltage.
It is necessary to keep the resistance value between the metal plate and the metal plate 12 as high as possible, and if dew condensation occurs between the metal plates, minute water droplets bond the electret film 14 and the second metal plate 12 with a low resistance value.

However, in the above example, the second
On the surface of the metal plate 12 facing the first metal plate 11, a material having a high insulating property such as polyimide is used as the insulating layer 16
For example, since it is formed to have a thickness of 6μ, even in the high humidity environment where dew condensation occurs, even if a minute water droplet is formed in a minute gap of 20μ to 100μ between the electret film 14 and the second metal plate 12, Since the resistance of the insulating layer 16 enters in series with the resistance value, the decrease in the insulation resistance can be suppressed to a slight extent, and the generation of an abnormal signal due to the decrease in insulation due to water droplets can be prevented. That is, a good acceleration detection signal can be obtained even in a severe environment with high humidity.

In the experiments conducted by the inventors, similar effects were obtained when epoxy resin or polyester resin was used as the insulating material for the insulating layer 16 in addition to polyimide. Moreover, as a means for forming the insulating layer 16 on the second metal plate 12,
The same effect was obtained by both the method of applying a liquid insulating material and the method of adhering a sheet-shaped insulating material. The insulating layer 16 may be formed by printing or any other method.

In the above example, the insulating layer 16 has a thickness of 6 μ. However, if pinholes are taken into consideration, even if the insulating layer 16 is formed thinner, a sufficient effect can be obtained, and vibration of the second metal plate 12 can be obtained. It is also possible to form a thick film within the range not limited.

In the embodiment shown in FIG. 1, the case 13 has an upper surface opened, but as shown in FIG.
The lower surface 13a, the side surface 13b, and the upper surface 13c may be covered with a hole 26 through which the lead wire 21 is drawn.

FIG. 6 shows another embodiment of the acceleration sensor of the present invention. In this example, only the first metal plate 41 is arranged in the conductive case 43, and the case 4
The lower surface 42 of 3 is used as a second metal plate. And the 1st metal plate 41 is arrange | positioned in the case 43 so that it may vibrate according to the vibration of the member which detects a vibration.

The first metal plate 41 is made of a thin metal plate such as a stainless steel plate of 50 μ, for example, and the electret film 44 is formed on the lower surface thereof. In addition, this first metal plate 41
A hole 45 communicating with the upper and lower sides is opened in the electret film 44. On the other hand, an insulating layer 46 is formed on the lower surface 42 of the case 43. Then, the first metal plate 41 on which the electret film 44 is formed is arranged in the case 43 so as to vibrate following the vibration of the member that detects vibration.

That is, the first metal plate 41 includes a spacer 47 for forming an optimum gap between the electret film 44 and the lower surface 42 of the case 43, and the first metal plate 4
The position is fixed by a fixing member 49 having an insulating property provided between the upper surface of 1 and the case 43, and is arranged in the case 43. The lower surface of the case 43 is made sufficiently thick and strong.

In this example, the first metal plate 41 is made swingable, and an insulating layer 46 is formed on the lower surface 42 of the case facing the surface of the electret film 44 formed on the metal plate 41. Acceleration is detected by the change in the electrostatic capacitance of the opposing surface formed by the electret film 44 and the case lower surface 42.

FIG. 7 shows still another example of the embodiment of the present invention. In this example, as shown in FIG.
1 is a metal plate similar to the examples of FIGS. 1, 4 and 5 with an electret film 54 formed on one side, but the lower surface 52 of the case 53 is sufficiently thinner than the first metal plate 51. Form. Then, a communication hole 53 with the external space is opened in the lower surface 52 of the case 53, and the lower surface 52 of the case is shown in FIG.
This is also used as the second metal plate in the example of FIG. 4 and constitutes an acceleration sensor for detecting the vibration of the lower surface 52 of the case. 5
Reference numerals 7 and 58 are a spacer and a fixing member. In addition, also in the example of FIG. 6 and FIG.
Similar to the case 13 in the above example, the upper surface may be covered.

Further, as another embodiment, FIG. 8 and FIG.
The modification of the example of is shown. In this example, the case 13 is made of an insulating material such as ceramic, and a through hole 60 is formed in the side surface of the case 13. Then, the lead wire 22 soldered to the second metal plate 12 is pulled out through the through hole 60, and the fixing member 19 having an insulating property and the spacer 18 shown in FIG. 1 are omitted.

Still another embodiment is shown in FIGS. In this example, a groove 61 is provided on the inner side surface of the case 13, and the spacers 17 and 18 are, as shown in FIG.
A portion corresponding to the position of the groove 61 is cut out so that the space between the upper gap 20 of the swingable metal plate 12 and the lower surface of the metal plate 12 and the lower surface 13c of the case 13 communicates with each other. In this way, the generation of the error signal due to the sound pressure is suppressed.

Communication holes 15 and 4 provided in the swingable metal plate shown in FIGS. 1, 4, 5, 6, 7, 8 and 9.
As shown in FIG. 11, the holes 55 and 55 can be round holes 71. Reference numeral 70 is a swingable metal plate.

However, the communication holes 15, 45, 55 provided in the swingable metal plate may have various other shapes. For example, a plurality of cutout holes 7 as shown in FIG.
Similar effects could be confirmed with the one provided with No. 2 or with the metal plate 70 having a plurality of round holes 73 as shown in FIG. Further, as shown in FIG. 14, the metal plate 70 may be formed of a metal plate having mesh holes. In addition, it goes without saying that the shape of the communicating hole can be freely selected.

Next, referring to FIG. 15, in the acceleration sensor having the structure shown in FIG. 5, the second metal plate 12 has a diameter of 9 mm and a communication hole 15
An example of characteristics when manufactured by using a stainless steel plate having a diameter of 2 mm and a thickness of 50 μ is shown. Fh0 shown in FIG. 15 is a peak peculiar to a material having a high resonance sharpness, such as a metal, which appears in the resonance frequency of the swingable second metal plate 12. In applications where this peak is a problem, the thickness of the insulating layer 16 described above is formed thicker, or by forming an insulating layer on both surfaces of the second metal plate 12, the metal plate is damped and the apparent appearance is reduced. The resonance sharpness can be lowered, and can be controlled, for example, like fh1 in FIG.

FIG. 16 shows the output frequency characteristic (A) of the acceleration sensor shown in FIG. 5 with respect to the sound pressure, and the second metal plate 12 of the acceleration sensor shown in FIG. The output frequency characteristic (B) with respect to the sound pressure of what replaced with what vapor-deposited metal is shown. As shown in the figure, the unnecessary signal with respect to the sound pressure can be improved by 50 dB or more at the maximum.

As described above, in the present invention, the thickness of either the first metal plate or the second metal plate is increased or the material is changed to strengthen one of them intentionally. You can select a metal plate that can swing. It can also be intentionally selected by combining a strong material with the metal plate on the side to be fixed.

[0047]

As described above, according to the acceleration sensor of the present invention, by extracting an electric signal from the metal plate having the electret film, it is possible to detect the acceleration with a simple structure and to swing the first sensor. The influence of sound pressure can be eliminated by providing a communication hole in the metal plate or the second metal plate. Further, by forming an insulating layer on the metal surface side facing the electret film, it is possible to suppress the generation of a noise signal due to dew condensation that occurs in a high humidity environment or the like, and there is an advantage that stable acceleration can be detected.

[Brief description of drawings]

FIG. 1 is a sectional view of the configuration of an embodiment of an acceleration sensor according to the present invention.

FIG. 2 is a circuit configuration diagram of an embodiment of a detection circuit of the acceleration sensor according to the present invention.

FIG. 3 is a circuit configuration diagram of another embodiment of the detection circuit of the acceleration sensor according to the present invention.

FIG. 4 is a sectional view of the configuration of an embodiment in which a detection circuit is incorporated in the acceleration sensor according to the present invention.

FIG. 5 is a sectional view of the configuration of another embodiment of the acceleration sensor according to the present invention.

FIG. 6 is a sectional view of the configuration of another embodiment of the acceleration sensor according to the present invention.

FIG. 7 is a sectional view of the configuration of another embodiment of the acceleration sensor according to the present invention.

FIG. 8 is a sectional view of the configuration of another embodiment of the acceleration sensor according to the present invention.

FIG. 9 is a sectional view of the configuration of another embodiment of the acceleration sensor according to the present invention.

10 is a diagram showing an example of a configuration of a main part of the example of FIG.

FIG. 11 is a front view of an embodiment of the swingable metal plate of the acceleration sensor according to the present invention.

FIG. 12 is a front view of another embodiment of the swingable metal plate of the acceleration sensor according to the present invention.

FIG. 13 is a front view of another embodiment of the shape of the swingable metal plate of the acceleration sensor according to the present invention.

FIG. 14 is a front view of another embodiment of the swingable metal plate shape of the acceleration sensor according to the present invention.

FIG. 15 is an example of an output-frequency characteristic diagram in which the detection output of the acceleration sensor according to the present invention is measured.

FIG. 16 is an example of a sound pressure output-frequency characteristic diagram showing the effect on the error signal due to the sound pressure of the acceleration sensor according to the present invention.

FIG. 17 is a sectional view of the configuration of an example of the acceleration sensor proposed previously.

[Explanation of symbols]

 11, 41, 51 First metal plate 12, 42, 52 Second metal plate 13, 43, 53 Case 14, 44, 54 Electret film 15, 45, 55 Communication hole 16, 46, 56 Insulating layer 17, 47 , 57 Spacer 20 Gap 24, 25 Electrode terminal

Claims (5)

[Claims] 1. A first metal plate having an electret film on one surface, and a second metal plate facing each other with a slight gap between the electret film of the first metal plate and the first metal plate. A first electrode electrically connected to the metal plate, and a second electrode electrically connected to the second metal plate, wherein one of the first and second metal plates is It is arranged so as to be swingable by vibration, and at least a hole is provided so as to connect the above-mentioned gap on one surface side of this swingable metal plate and the space on the other surface side to each other. An acceleration sensor configured to detect acceleration from a change in an electric signal between an electrode and a second electrode. 2. The acceleration sensor according to claim 1, wherein the swingable metal plate is provided with a hole penetrating the metal plate. 3. The acceleration sensor according to claim 1, wherein a peripheral member of the swingable metal plate is provided with a hole that connects the gap on one side of the metal plate and the space on the other side. 4. The acceleration sensor according to claim 1, wherein an insulating layer is provided on at least a surface side of the second metal plate facing the electret film surface. 5. The acceleration sensor according to claim 1, wherein the second metal plate is swingable, and an insulating layer is provided on the second metal plate to dampen the resonance of the second metal plate.