JPH11101817A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrokinetic acceleration sensor which is compact and highly accurate. SOLUTION: This acceleration sensor includes a first sensor chamber R1 and a second sensor chamber R2 formed in a easing, an elastically deformable diaphragm 6 separating the first sensor chamber R1 and the second sensor chamber R2 , a permanent magnet (magnetic body) 5 shifting in accordance with an external acceleration thereby vibrating the diaphragm 6, and a detection coil 4a changing a magnetic field because of the shift of the permanent magnet 5. The permanent magnet is mounted to the diaphragm 6 at the first sensor chamber R1 , having a size ratio (major axis/minor axis) of a major axis extending in a vibration direction of the diaphragm 6 and a minor axis orthogonal to the major axis of not smaller than 1. The detection coil is set at an inner wall facing the diaphragm 6 at the first sensor chamber R1 and on the same axis as the permanent magnet 5. An acceleration is detected from an electromotive force generated by the change of the magnetic field of the detection coil 4a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for determining the speed and distance of a moving body.

[0002]

2. Description of the Related Art In recent years, a large number of sensors have come to be used in intelligent vehicles and the like, and in particular, the number of sensors for sensing the attitude, speed, direction, and the like of a moving object has been rapidly increasing. Among them, an acceleration sensor that obtains a speed or a distance by integrating an output signal is used as a very important sensor.

As an acceleration sensor, a mechanical vibration sensor called an electrodynamic type has been mainly used. FIG.
FIG. 3 schematically shows the configuration of an electrodynamic acceleration sensor.

[0004] As shown in the figure, the electro-dynamic acceleration sensor is composed of a combination of a seismic system vibration section 12 and an electro-dynamic transducer section 13 installed in a housing 11 and extracts mechanical vibration as an electric output. The vibration sensor is configured as described above.
The seismic-system vibrating part 12 includes a coil spring 14 and a mass part (weight) 9 that vibrates due to external acceleration, and the coil 4 is hung on the mass part 9. And
The coil 4 moves in the direction in which the coil spring 14 expands and contracts (Z direction) as the mass section 9 vibrates. Also,
The electrokinetic converter unit 13 having the permanent magnet 5 is provided with a high magnetic permeability material 7 in which the S pole is located inside the coil 4 and the N pole is located outside the coil 4. It moves in a direction crossing the magnetic flux of the magnetic permeability material 7. Then, the acceleration is obtained from the electromotive force generated in the coil 4 in proportion to the moving speed, and is a mechanical quantity-electric quantity converter.

[0005] However, recently, the mainstream of the acceleration sensor is gradually shifting from an electrodynamic type to a small-capacity type or a piezo type. This is because the user has begun to attach importance not only to performance but also to ease of handling, particularly downsizing. That is,
Since the above-mentioned electrodynamic acceleration sensor is structurally large and requires a large space, the measurement object on which the acceleration sensor is mounted is necessarily limited to a large object. On the other hand, in a capacitance type or piezo type acceleration sensor,
This is because an extremely small sensor can be formed by a structure processing method using a recent semiconductor process technology (hereinafter, simply referred to as “process technology”), so that the measurement target can be expanded to a small one.

As shown in FIG. 24, the capacitance type acceleration sensor has electrodes 10 arranged at two positions on a mass 9 and an opposing surface separated from the mass 9 by a very narrow gap. This structure has a structure for detecting a change in capacitance when the interval between the two electrodes 10 fluctuates due to the vibration of the mass portion 9 due to acceleration from the body. In addition, the piezo-type acceleration sensor
As shown in FIG. 25, diaphragm 6 supporting mass 9
A piezo element 8 is attached to a part of the piezo element, and detects a change in output of the piezo element 8 due to distortion of the diaphragm 6 when the mass section 9 is displaced by external acceleration.

Here, recently, there has been an electrokinetic acceleration sensor whose size has been reduced by using the semiconductor process technology. For example, Japanese Patent Application Laid-Open No. 5-142246 discloses an acceleration sensor in which a thin-film permanent magnet 5 is formed on a mass portion 9 by epitaxial growth, and a coil 4 is formed at a position facing the same, as shown in FIG. Have been. According to this acceleration sensor, when the thin film permanent magnet 5 vibrates together with the mass portion 9 due to external acceleration, a change in magnetic flux crossing the coil 4 is detected to determine the acceleration. The magnetization direction of the thin-film permanent magnet 5 at this time is the vibration direction of the magnet.

In the acceleration sensor, not only the miniaturization using the process technology as described above, but also the maintenance and improvement of its measurement performance (measurement accuracy, measurement band, etc.) have become extremely important themes. ing.

[0009]

As a conventional electrodynamic acceleration sensor, there is a so-called servo acceleration sensor which aims at high-accuracy measurement. This is a combination of the displacement detection function and the internal drive function.When relative displacement occurs in the mass section due to external acceleration, the displacement signal from the displacement detection section is fed back to the internal drive section, and the mass section is driven by the drive function. It has a structure in which it is returned to a position close to the original position and is controlled so that the inertia force and the driving force of the mass portion are balanced. The signal actually taken out is such that the current to the drive unit that generates this balancing force is handled as the output of the servo-type acceleration sensor, and the detection accuracy is high and the mass of the mass unit is large regardless of the magnitude of the external acceleration. Since the vibration can be made very small, there is an advantage that the measurement band can be widened.

However, since the servo type acceleration sensor is expensive and large, similarly to other types of electrodynamic type acceleration sensors, the measurement target is limited to a large type.

Therefore, in order to simultaneously achieve miniaturization and high performance of the acceleration sensor, it is necessary to use the process technology and to incorporate a servo mechanism as described above.

However, the acceleration sensor has some problems for each type as follows.

First, the conventional capacitance type and piezo type acceleration sensors do not have a driving function inside, and the measurement accuracy is limited.

Second, in a capacitance type acceleration sensor,
From the measurement principle, it is necessary to narrow the electrode interval, and the amount of electrode displacement is limited to this narrow electrode interval. Therefore, the allowable measurement band for external acceleration is such that the electrode displacement is within the electrode interval. It is limited to the range.

Third, in the case of a piezo-type acceleration sensor, it is necessary to separately perform temperature compensation because the detection characteristics are affected by the pyroelectric effect of the piezo element due to an external temperature change. Further, a special manufacturing process is required, such as a firing process for forming the piezo element itself.

Fourth, Japanese Patent Application Laid-Open No.
The acceleration sensor disclosed in Japanese Patent No. 2246 has no internal driving function, and the demagnetizing field of the thin-film permanent magnet 5 is extremely high, so that it is hardly magnetized in the thickness direction even when magnetized. is there.

Here, the demagnetizing field refers to the magnetic field strength inside the magnetic material that is uniquely determined by the shape and size of the permanent magnet in the direction in which the magnetic pole is formed. The direction is a direction in which a magnetic field opposite to the magnetic field due to the magnetization of both ends of the magnet is generated, and the magnitude is represented by the following equation.

H _d = −N * I / μ ₀ (H _d : demagnetizing field, N: demagnetizing factor, I: magnetization intensity,
mu _0: initial permeability) From this equation, the strength of the more demagnetizing field H _d demagnetizing factor N is you move closer to 1 approaches to the magnetization of the magnetic field intensity I, cancel each other because the magnetization direction is the magnetic field opposite Therefore, the function of the permanent magnet is extremely reduced. That is, there is a high possibility that the magnet hardly functions as a permanent magnet.

FIG. 27 is a graph showing the relationship between the shape anisotropy and the demagnetizing factor N. As can be seen from the graph, when the shape ratio (major axis / minor axis) λ of the magnetic material is 1 or less, the demagnetizing field N increases rapidly, so that the demagnetizing field also increases. Therefore, as a result, the function as a magnetic pole decreases, and the magnetic field to the outside decreases sharply.

For example, when the shape ratio (major axis / minor axis) λ is 1 /
If it is less than 10, the demagnetizing factor N becomes 0.8 or more, and the strength of the magnetic field is reduced to 20% or less of the magnitude due to the original magnetization. In other words, in a thin film permanent magnet,
Since the demagnetizing field coefficient becomes extremely high, it becomes difficult to magnetize the permanent magnet in the film thickness direction, and it becomes impossible to obtain a sufficient magnetic field intensity necessary for signal detection as an acceleration sensor. In particular, the epitaxial method (gas layer growth method) is a typical example of a manufacturing method for forming a uniform film, and the more uniform the film, the closer the demagnetizing factor due to the shape becomes closer to the theoretical value. Forming the magnet becomes more difficult.

In the case of a conventional electrodynamic acceleration sensor as shown in FIG. 23, the magnetic field strength between the permanent magnet 5 and the magnetic poles NS formed of the high magnetic permeability material 7 is highly uniform, and external vibration As a result, a good signal waveform of electromotive force generated when the coil 4 crosses this magnetic field with little distortion in proportion to external vibration can be obtained. However, even if a small amount of output signal is obtained with the structure shown in FIG. 26 using a process technology for the purpose of miniaturization, the displacement at the position where the coil 4 and the permanent magnet 5 are offset by a certain distance is obtained. May be distorted depending on the positional relationship between the coil 4 and the permanent magnet 5. This is because the amount of magnetic flux traversing the coil 4 is not proportional to the amount of movement of the magnet, so that accurate acceleration cannot be obtained.

Accordingly, an object of the present invention is to provide a small and highly accurate electrodynamic acceleration sensor.

[0023]

To solve this problem, an acceleration sensor according to the present invention comprises a first sensor chamber and a second sensor chamber formed in a casing, a first sensor chamber and a second sensor chamber. A dimension ratio between an elastically deformable diaphragm partitioning the second sensor chamber, a major axis attached to the diaphragm in the first sensor chamber and extending in the vibration direction of the diaphragm, and a minor axis orthogonal to the major axis; (Long axis / short axis) is set to 1 or more, a magnetic body displaced by external acceleration to vibrate the diaphragm, and an inner wall facing the diaphragm in the first sensor chamber and provided coaxially with the magnetic body. A detection coil whose magnetic field changes due to the displacement of the magnetic material, and configured to detect acceleration from an electromotive force generated by the change in the magnetic field of the detection coil.

As a result, the demagnetizing field is suppressed and the waveform distortion of the detection signal is reduced, so that a small and highly accurate electrodynamic acceleration sensor can be obtained.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a first sensor chamber and a second sensor chamber formed in a casing, a first sensor chamber and a second sensor chamber. And a dimension ratio of a major axis attached to the diaphragm in the first sensor chamber and extending in the vibration direction of the diaphragm and a minor axis orthogonal to the major axis (long axis / short axis). A magnetic body that is displaced by an external acceleration to vibrate the diaphragm, and an inner wall facing the diaphragm in the first sensor chamber and is provided coaxially with the magnetic body.
A detection coil whose magnetic field changes due to the displacement of the magnetic material; and an acceleration sensor that detects acceleration from an electromotive force generated by the change in the magnetic field of the detection coil. Since the number is reduced, a small and high-precision electrodynamic acceleration sensor can be obtained.

According to a second aspect of the present invention, in the first aspect, a dimensional ratio of a distance a from the end surface of the magnetic material to the detection coil to the detection coil and a radius b of the detection coil is used. An acceleration sensor in which (b / a) is 1.5 to 4, which has an effect that waveform distortion of a detection signal due to displacement of a magnetic material is more effectively suppressed.

According to a third aspect of the present invention, in the first or the second aspect of the invention, the acceleration is such that the magnetic material is attached to the diaphragm so that the same mass distribution is provided on both sides of the diaphragm. This is a sensor, and even if acceleration is applied in the direction intersecting the original vibration direction of the diaphragm, there is no moment to displace the magnetic material in that direction. Has the effect that distortion of the detection signal caused by the displacement can be prevented.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the first sensor chamber or the second sensor chamber is located at a position facing the vibration plate, and is provided with a magnetic material. A magnetic field corresponding to the electromotive force from the detection coil is generated coaxially, and the acceleration sensor is provided with a drive coil for driving the displaced magnetic body in the direction of the normal position. Since it is very small, it has an effect that acceleration can be measured in a wide band.

According to a fifth aspect of the present invention, there is provided the first sensor chamber and the second sensor chamber formed in the casing, and the first sensor chamber and the second sensor chamber are separated from each other. The dimensional ratio (long axis / short axis) of a deformable diaphragm, a major axis attached to the diaphragm in the first sensor chamber and extending in the vibration direction of the diaphragm, and a minor axis orthogonal to the major axis is 1 The magnetic member is attached to a magnetic body that vibrates the diaphragm by being displaced by an external acceleration, a position corresponding to the magnetic body of the diaphragm in the second sensor chamber, and a position facing the position. A pair of electrodes whose capacitances change due to the displacement of the first sensor chamber and an inner wall facing the diaphragm in the first sensor chamber and provided coaxially with the magnetic body, and a magnetic field corresponding to the capacitance of the electrodes is generated; Drive the displaced magnetic body in the direction of the normal position. A displacement signal is detected from a change in the capacitance of the electrode, and a signal is fed back to the drive coil so as to stop the vibration of the magnetic body based on the displacement. This is an acceleration sensor in which the current value flowing through the coil for use is an output corresponding to the acceleration, which has the effect of reducing the waveform distortion of the detection signal and enabling the measurement of the acceleration in a wide band.

According to a sixth aspect of the present invention, in accordance with the first aspect of the present invention, the magnetic body is an acceleration sensor that is a permanent magnet or an electromagnet, and the magnetic body is always a constant detection type. It has an effect that a magnetic field can be secured.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the inner wall of the first sensor chamber to which the magnetic body is attached and the inner wall are opposed to the inner wall. An acceleration sensor in which at least one of the inner walls is coated with a highly magnetically permeable material, which reduces the resistance of the entire magnetic circuit and reduces magnetic flux leakage to the outside, thereby improving the measurement efficiency. Has the effect of being able to.

According to an eighth aspect of the present invention, in the first aspect of the present invention, there is provided an acceleration sensor according to any one of the first to sixth aspects, wherein the entire inner wall of the first sensor chamber is covered with a high magnetic permeability material. The sensor has the effect of further reducing the magnetic circuit resistance and further improving the measurement efficiency.

According to a ninth aspect of the present invention, in accordance with the first aspect of the present invention, there is provided an accelerometer wherein the entire inner wall of the second sensor chamber is covered with a highly permeable material. The sensor has the effect of further reducing the magnetic circuit resistance and further improving the measurement efficiency.

A tenth aspect of the present invention is the acceleration sensor according to the seventh, eighth or ninth aspect, wherein the high magnetic permeability material is an alloy of Fe-based, Ni-based or Co-based.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

(Embodiment 1) FIG. 1 is a partially cutaway perspective view showing an acceleration sensor according to Embodiment 1 of the present invention, and FIG. 2 is an enlarged sectional view showing a part of the acceleration sensor of FIG. Figure,
3 is a sectional view showing the acceleration sensor of FIG. 1 in a stationary state, FIG. 4 is a sectional view showing the acceleration sensor of FIG. 1 to which acceleration is applied, and FIG. 5 is a detection coil and a driving coil in the acceleration sensor of FIG. Explanatory drawing showing an example of the mounting structure of FIG.
Is an explanatory view showing another example of the mounting structure of the detection coil and the driving coil in the acceleration sensor of FIG. 1, FIG. 7 is a cross-sectional view showing a modification of the acceleration sensor of FIG. 1, and FIG. 8 is an acceleration sensor of FIG. FIG. 9 is an explanatory view showing a positional relationship between a permanent magnet and a detection coil in the acceleration sensor shown in FIG. 1, and FIG. 10 is a sectional view showing displacement and detection of a permanent magnet in the acceleration sensor shown in FIG. FIG. 11 is a graph showing the relationship between the output signal of the coil and the output signal of the detection coil. FIG. 11 shows the relationship between the displacement of the permanent magnet and the output signal of the detection coil when the dimensional ratio between the permanent magnet and the detection coil is changed in the acceleration sensor of FIG. FIG. 12 is a graph schematically showing the relationship between the dimensional ratio of the permanent magnet-detection coil and the relative electromotive force ratio in the acceleration sensor of FIG. 1, and FIG. 13 is a graph in which the dimensional ratio of the permanent magnet-detection coil is 1 0.5-4.0 Maximum electromotive graph showing the change in the range, 14 permanent magnets - is a graph showing the relationship between the dimension ratio and the relative electromotive force of the detecting coil.

As shown in FIG. 1, in the acceleration sensor according to the present embodiment, a casing is constituted by three laminated substrates, that is, a protective substrate 1, a support substrate 2, and a coil substrate 3. As shown in detail in FIGS. 3 and 4, the support base 2 and the coil substrate 3 are provided inside the casing.
Thus, a first sensor chamber R ₁ is formed, and a _second sensor chamber R ₂ is formed by the protection substrate 1 and the support base 2.
Further, between the first sensor chamber R ₁ and the second sensor chamber R ₂ , an elastically deformable diaphragm 6 that partitions the sensor chambers R ₁ and R ₂ is provided integrally with the support base 2. Have been.

The protection substrate 1, the support substrate 2, and the coil substrate 3 are formed by using the etching method or the film formation method of the above-described process technology. Are joined. Then, by the second space of the sensor chamber R _2, it is prevented from the vibration plate 6 is damaged and deformed beyond its limit displacement by excessive external acceleration. The diaphragm 6 is formed by forming the inside of the support substrate 2 into a thin film by a structure processing method such as an etching method of a process technique.

As shown in FIG. 2, at the center of the diaphragm 6 facing the first sensor chamber, a permanent magnet (magnetic material) 5 serving as a mass portion of the acceleration sensor is formed by a process technique. That is, after the permanent magnet 5 has formed the diaphragm 6,
For example, it is formed on the diaphragm 6 by plating or vapor deposition, and is magnetized in a strong magnetic field. When acceleration is applied from the outside, the permanent magnet 5 is displaced and the diaphragm 6 is vibrated. The permanent magnet 5 has a shape in which the long axis extends in the vibration direction Z of the diaphragm 6, and by adopting such a shape, a demagnetizing field is suppressed and a necessary magnetization amount as a magnet is secured.

The shape ratio (long axis / short axis) λ between the long axis of the permanent magnet 5 and the short axis orthogonal to the long axis is 1 or more. This is because, as shown in FIG. 27 already described, when the shape ratio (major axis / minor axis) λ is less than 1, a sharp increase in the demagnetizing factor N is confirmed. This is because the magnetization intensity (effective magnetization intensity) that can generate a magnetic field outside of the above is reduced to 70% or less. The amount of displacement of the permanent magnet 5, which is the mass of a small acceleration sensor manufactured using the process technology, is extremely small. If the amount of displacement is small, the electromotive force generated in a detection coil described later decreases. Therefore, if the effective magnetic field strength of the permanent magnet 5 is not sufficiently ensured, a sufficient detection signal may not be obtained. However, the shape ratio λ
Is 1, the demagnetizing factor N is about 0.30, and the shape ratio λ is desirably 2 or more in order to secure a sufficient effective magnetization intensity.

[0041] on the coil substrate 3 is an inner wall that faces the vibrating plate 6 of the first sensor chamber R ₁ includes a detection coil 4a of the magnetic field is changed by the displacement of the permanent magnet 5, the magnetic field of the detecting coil 4a Magnet 5 that generates a magnetic field corresponding to the electromotive force excited by the change in
And a driving coil 4b for driving the driving coil in the direction of the normal position. These coils 4a and 4b are installed coaxially with the permanent magnet 5. Then, the electromotive force generated in the detection coil 4a is detected in accordance with the displacement amount and the displacement direction of the permanent magnet 5, and the acceleration is obtained from the detected electromotive force. Also,
By driving the permanent magnet 5 by the driving coil 4b as described above, the amount of displacement of the permanent magnet 5 can be made very small, and acceleration can be measured in a wide band.

Detection coil 4a and drive coil 4b
Is installed, for example, as shown in FIGS.
In FIG. 5, the detection coil 4a is located on the outside,
b is arranged inside. In FIG. 6, the detection coil 4a and the drive coil 4b are arranged in a double spiral shape, and have a common ground. Here, in FIG. 5 and FIG.
4b are electrodes connected to both ends. Note that the driving coil 4b may not be provided as the acceleration sensor.

Here, the displacement of the permanent magnet 5 will be described. In a stationary state where no external acceleration is applied,
As shown in FIG. 3, the permanent magnet 5 is not displaced, and thus the diaphragm 6 is not deformed. When acceleration is applied, as shown in FIG. 4, the diaphragm 6 is elastically deformed, and the permanent magnet 5 is relatively displaced in the Z direction in the figure. The electromotive force required for signal detection is obtained by the displacement of the permanent magnet 5 changing the magnetic field crossing the coil 4.

As shown in FIGS. 7 and 8, including other embodiments to be described later, the inside of the acceleration sensor may be coated with a high magnetic permeability material 7 made of, for example, permalloy (Fe--Ni alloy). it can. In the case shown in FIG.
Diaphragm 6 is an inner wall which is mounted in the permanent magnet 5 of the sensor chamber R _1, and the coil 4 opposite to the vibration plate 6
The inner walls to which a and 4b are attached are covered with a high magnetic permeability material 7. By coating with the high magnetic permeability material 7 in this manner, the resistance of the magnetic circuit is reduced, and the efficiency of driving and detection by the coils 4a and 4b can be increased. Also, in the case shown in FIG. 8, first entire inner wall of the sensor chamber R ₁ it is coated with a high magnetic permeability material 7. In this case, the resistance of the magnetic circuit is further reduced, and the measurement efficiency is further improved. In the case shown in FIG. 7, only one of the inner wall on the mounting side of the permanent magnet 5 and the inner wall on the mounting side of the coils 4a and 4b may be coated with the high magnetic permeability material 7. Further, the inner wall of the second sensor chamber R ₂ may be covered with the high magnetic permeability material 7. As the high magnetic permeability material 7, an Fe-based, Ni-based or Co-based alloy or the like can be used.

Here, the relationship between the permanent magnet 5 and the detection coil 4a will be described. In FIG. 9, the distance from the tip of the permanent magnet 5 to the detection coil 4a is a, the radius of the detection coil 4a is b, and the dimensional ratio is b / a. Also,
One-sided amplitude of the permanent magnet 5 is assumed to be c. The detection coil 4
The radius of “a” refers to the distance from the center of the thick winding portion to the center of the coil as shown in FIG.

FIG. 10 is a graph showing the relationship between the displacement of the permanent magnet 5 and the output signal from the detection coil 4a as relative values, and the phase between the two. Ideally, the displacement and the phase of the output signal have a sine wave shape having a phase difference of 90 degrees from each other, as shown in this figure. However, in practice, depending on the positional relationship between the distance a from the end face of the permanent magnet 5 to the coil plane and the coil average radius b, a phase shift occurs in the signal waveform and the waveform is distorted. ing.

FIG. 11 is a graph showing the relationship between the phase and the electromotive force in a state where the phase shift is generated by changing the dimensional ratio (b / a). Here, the phase shift means that the phase difference between the maximum value and the minimum value in one cycle deviates from 180 degrees.

The level of this phase shift is the output ratio between E90 (electromotive force at 90 degrees of phase) and Emax (maximum electromotive force in one cycle), that is, how much Emax / E90 has changed from 1. Can predict the level of waveform distortion. Here, Emax / E90 is defined as a relative electromotive force ratio.

FIG. 12 is a graph showing the relationship between the dimensional ratio (b / a) on the horizontal axis and the relative electromotive force ratio Emax / E90 on the vertical axis. From this graph, it is found that when the dimensional ratio (b / a) is less than 1.5, the relative electromotive force ratio Emax / E
A sharp rise of 90 can be seen. Therefore, when the dimensional ratio (b / a) is less than 1.5, waveform distortion due to a sudden phase shift occurs. This indicates that the dimensional ratio (b / a) needs to be 1.5 or more. From the figure, the dimensional ratio (b / a) is
It can be seen that the waveform distortion increases little by little even at 4.0 or more. Therefore, from the viewpoint of waveform distortion, it is necessary to select the dimensional ratio (b / a) in the range of 1.5 to 4.0.

Next, a case will be described in which consideration is made from the viewpoint of the maximum electromotive force Emax. FIG. 13 is a graph schematically showing a change in the maximum electromotive force Emax when the phase shift is small, that is, when the dimensional ratio (b / a) is in the range of 1.5 to 4.0. As can be seen from the figure, as the dimensional ratio (b / a) increases, that is, when the distance a between the tip of the permanent magnet 5 and the detection coil 4a is constant, the detection coil 4a
It can be seen that the maximum electromotive force Emax decreases as the radius b increases.

A more detailed expression of this relationship is:
FIG. In this figure, the horizontal axis represents the dimensional ratio (b / a), and the vertical axis represents the change in the maximum electromotive force Emax in terms of the relative electromotive force. Here, the relative electromotive force is Emax (b /
a = 1.5) is a relative value of the electromotive force based on the output.

Since the amplification factor of the electric circuit used for signal processing is at most about 1000 times, it is 1/100 of the dimensional ratio (b / a) = 1.5 obtained in FIG.
It is considered that up to about 0 is a signal processing range that can be handled at a time. Then, the dimensional ratio (b / a) = 1.5 in FIG.
The dimension ratio at which the relative electromotive force ratio becomes 0.001 is 4.0
Therefore, it is appropriate to select the range of the upper limit of the dimensional ratio (b / a) up to 4.0 from the viewpoint of the maximum output as in the case of the evaluation using the phase shift.

Therefore, the dimensional ratio (b / a) = 1.5 to
If the dimensional relationship between the detection coil 4a and the permanent magnet 5 is set to a predetermined value within the range of 4.0, a signal with less waveform distortion (phase shift) and good processing can be obtained.

(Embodiment 2) FIG. 15 is a perspective view showing a partially cutaway acceleration sensor according to Embodiment 2 of the present invention.
FIG. 16 is a sectional view showing a part of the acceleration sensor of FIG. 15 in an enlarged manner.

[0055] In the acceleration sensor of this embodiment, in place of the permanent magnet, a high permeability material 15a attached to the first diaphragm 6 facing the sensor chamber R _1, the second sensor chamber R ₂ (Magnetic material) 15 comprising an electromagnet coil 15b attached to the opposite surface of the diaphragm 6 corresponding to the highly permeable material 15a.

As described above, the electromagnet 15 can be used as the magnetic material. In the embodiment described later, the electromagnet 15 can be used instead of the permanent magnet 5.

(Embodiment 3) FIG. 17 is a perspective view showing an acceleration sensor according to Embodiment 3 of the present invention, partially cut away.
FIG. 18 is an enlarged sectional view showing a part of the acceleration sensor of FIG.

[0058] In the acceleration sensor of this embodiment, the position corresponding to the permanent magnet 5 of the vibration plate 6 in the second sensor chamber R _2, and to the position facing the position is, the permanent magnets 5
A pair of electrodes 10 whose capacitances are changed by the displacement of the electrodes are respectively attached.

A magnetic field corresponding to the capacitance of the electrode 10 is generated on the inner wall of the first sensor chamber R ₁ facing the diaphragm 6 and coaxially with the permanent magnet 5. 5 is provided in the direction of the normal position.

As described above, the electrode 1 is used instead of the detection coil.
0 may be used. (Embodiment 4) FIG. 19 is a sectional view showing an acceleration sensor according to Embodiment 4 of the present invention, and FIG. 20 is a comparative view for explaining the operation of the acceleration sensor of FIG.

As shown in FIG. 19, in the acceleration sensor of the present embodiment, the permanent magnets 5 are attached to the diaphragm 6 so that the same mass distribution is provided on both sides of the diaphragm 6.

When the permanent magnet 5 is attached so as to hang down from the lower part of the diaphragm 6, as shown in FIG. There is a possibility that the permanent magnet 5 receives a relatively large moment. Then, the detection signal is distorted and the measurement accuracy is adversely affected.

However, when the permanent magnet 5 is mounted as shown in FIG. 19, the position of the center of gravity of the permanent magnet 5 matches the mounting position of the diaphragm 6, so that no moment is generated in the permanent magnet 5 by external acceleration. And a good detection signal can be taken out.

(Embodiment 5) FIG. 21 is a sectional view showing an acceleration sensor according to Embodiment 5 of the present invention.

In the present embodiment, the driving coil 4
b is provided on the second sensor chamber and the permanent magnet 5 and coaxially position opposite to the vibration plate 6 in R _2. The driving coil 4b can also be arranged in this way.

The driving coil 4b and the detecting coil 4
a may be arranged reversely to the case shown in the figure. Alternatively, both may be used as detection coils, and the differential output of both coils may be taken out.

Further, as shown in FIG. 22, such a coil separation structure can be applied to an acceleration sensor attached to the diaphragm 6 such that the permanent magnets 5 have the same mass distribution on both sides of the diaphragm 6. Can be applied.

[0068]

As described above, according to the present invention, since the demagnetizing field is suppressed and the waveform distortion of the detection signal is reduced, it is possible to obtain a small and highly accurate electrodynamic acceleration sensor. Effects can be obtained.

The dimensional ratio (b / a) of the distance a from the detection coil side end surface of the magnetic material to the detection coil and the radius b of the detection coil is set to 1.5 to 4, so that the magnetic material The effective effect that the waveform distortion of the detection signal due to the displacement of the detection signal is more effectively suppressed is obtained.

By mounting the magnetic body on the diaphragm so that the same mass distribution is provided on both sides of the diaphragm, distortion of the detection signal caused by displacement of the magnetic body in a direction different from the original displacement direction can be prevented. An effective effect is obtained.

By providing a driving coil for driving the magnetic body displaced by the acceleration in the direction of the normal position, the amount of displacement of the magnetic body becomes very small, so that it is possible to measure the acceleration in a wide band. Effective effects can be obtained.

By covering the inner walls of the first sensor chamber and the second sensor chamber with a highly magnetically permeable material, the resistance of the entire magnetic circuit is reduced and the leakage magnetic flux to the outside is reduced, so that the measurement efficiency is improved. An effective effect of being able to do so is obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a part of the acceleration sensor of FIG. 1;

FIG. 3 is a sectional view showing the acceleration sensor of FIG. 1 in a stationary state;

FIG. 4 is a sectional view showing the acceleration sensor of FIG. 1 to which acceleration has been applied;

FIG. 5 is an explanatory view showing an example of a mounting structure of a detection coil and a driving coil in the acceleration sensor of FIG. 1;

FIG. 6 is an explanatory view showing another example of the mounting structure of the detection coil and the driving coil in the acceleration sensor of FIG. 1;

FIG. 7 is a sectional view showing a modification of the acceleration sensor of FIG. 1;

FIG. 8 is a sectional view showing another modification of the acceleration sensor of FIG. 1;

FIG. 9 is an explanatory diagram showing a positional relationship between a permanent magnet and a detection coil in the acceleration sensor of FIG. 1;

10 is a graph showing a relationship between a displacement of a permanent magnet and an output signal of a detection coil in the acceleration sensor of FIG.

11 is a graph schematically showing the relationship between the displacement of the permanent magnet and the output signal of the detection coil when the dimensional ratio between the permanent magnet and the detection coil is changed in the acceleration sensor of FIG.

12 is a graph showing a relationship between a dimensional ratio of a permanent magnet and a detection coil and a relative electromotive force ratio in the acceleration sensor of FIG. 1;

FIG. 13: The dimensional ratio of the permanent magnet to the detection coil is 1.5 to
Graph showing a change in maximum electromotive force in the range of 4.0

FIG. 14 is a graph showing a relationship between a permanent magnet-detection coil dimensional ratio and a relative electromotive force.

FIG. 15 is a perspective view showing the acceleration sensor according to the second embodiment of the present invention in a partially broken manner.

FIG. 16 is an enlarged sectional view showing a part of the acceleration sensor of FIG. 15;

FIG. 17 is a perspective view showing an acceleration sensor according to a third embodiment of the present invention, partially cut away;

FIG. 18 is an enlarged sectional view showing a part of the acceleration sensor of FIG. 17;

FIG. 19 is a sectional view showing an acceleration sensor according to a fourth embodiment of the present invention.

20 is a comparative diagram for explaining the operation of the acceleration sensor of FIG.

FIG. 21 is a sectional view showing an acceleration sensor according to a fifth embodiment of the present invention.

FIG. 22 is a sectional view showing an example of menopause of the acceleration sensor of FIG. 21;

FIG. 23 is a schematic diagram showing a configuration of a conventional electrodynamic acceleration sensor.

FIG. 24 is a sectional view showing a conventional capacitance type acceleration sensor.

FIG. 25 is a sectional view showing a conventional piezo-type acceleration sensor.

FIG. 26 is a cross-sectional view showing an electrodynamic acceleration sensor created by using a semiconductor process technology.

FIG. 27 is a graph showing the relationship between shape anisotropy and demagnetizing factor N

[Explanation of symbols]

4a Detection coil 4b Driving coil 5 Permanent magnet (magnetic material) 6 Diaphragm 7 High permeability material 10 Electrode 15 Electromagnet (magnetic material) R ₁ First sensor room R ₂ Second sensor room

Claims (10)

[Claims] A first sensor chamber and a second sensor chamber formed in a casing; an elastically deformable diaphragm partitioning the first sensor chamber and the second sensor chamber; The dimensional ratio (long axis / short axis) of a major axis attached to the diaphragm in the first sensor chamber and extending in the vibration direction of the diaphragm and a minor axis orthogonal to the major axis is 1 or more. A magnetic body displaced by the acceleration of the vibrating plate to vibrate the diaphragm; and an inner wall opposed to the diaphragm in the first sensor chamber and provided coaxially with the magnetic body, and a magnetic field is generated by the displacement of the magnetic body. An acceleration sensor, comprising: a detection coil that changes; and detecting acceleration from an electromotive force generated by a change in a magnetic field of the detection coil. 2. A dimensional ratio (b / a) of a distance a from an end face of the magnetic body to the detection coil to the detection coil and a radius b of the detection coil is 1.5 to 4. The acceleration sensor according to claim 1, wherein: 3. The acceleration sensor according to claim 1, wherein the magnetic body is attached to the diaphragm so that the same mass distribution is provided on both sides of the diaphragm. 4. A magnetic field corresponding to an electromotive force from the detection coil at a position facing the diaphragm in the first sensor chamber or the second sensor chamber and coaxial with the magnetic body. 4. The acceleration sensor according to claim 1, further comprising a driving coil for driving the generated and displaced magnetic body in a direction of a normal position. 5. A first sensor chamber and a second sensor chamber formed in a casing; an elastically deformable diaphragm partitioning the first sensor chamber and the second sensor chamber; The dimensional ratio (long axis / short axis) of a major axis attached to the diaphragm in the first sensor chamber and extending in the vibration direction of the diaphragm and a minor axis orthogonal to the major axis is 1 or more. A magnetic body displaced by the acceleration of the vibrating plate to vibrate the diaphragm; and a magnetic body attached to a position corresponding to the magnetic body of the diaphragm in the second sensor chamber and a position facing the position. A pair of electrodes whose capacitances change due to the displacement of the magnetic field provided on the inner wall of the first sensor chamber facing the diaphragm and coaxial with the magnetic body, and corresponding to the capacitance of the electrodes Is generated and displaced A driving coil for driving the magnetic body in the direction of a normal position, detecting a displacement signal from a change in capacitance of the electrode, and sending a signal to the driving coil to return the displacement to the normal position. An acceleration sensor for detecting acceleration from a current value when fed back. 6. The acceleration sensor according to claim 1, wherein the magnetic body is a permanent magnet or an electromagnet. 7. An inner wall of the first sensor chamber to which the magnetic body is attached and at least one of an inner wall opposed to the inner wall is coated with a highly magnetically permeable material. The acceleration sensor according to claim 1. 8. The apparatus according to claim 1, wherein the entire inner wall of said first sensor chamber is coated with a high magnetic permeability material.
The acceleration sensor according to any one of claims 6 to 6. 9. The apparatus according to claim 1, wherein the entire inner wall of said second sensor chamber is coated with a highly permeable material.
The acceleration sensor according to any one of claims 1 to 8. 10. The high-permeability material is an Fe-based, Ni-based, or Co-based alloy.
Or the acceleration sensor according to 9.