JPH08178950A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To provide a highly sensitive and durable dynamic quantity sensor that can measure a static acceleration, and is suitable for its scaling down and mass production and is excellent in temperature chracteristics. CONSTITUTION: A magnetostrictive layer 12 having a magnetostriction is stuck at the center of a substrate 11 and a half of the surface of the substrate 11 is fixed to the upper surface of a base 14-A. A coil 13 is wound around a part of the layer 12 and is fixed on a base 14-B. A detection circuit 15 converts the inductance of the coil into an electrical signal. When a stress is applied to the substrate 11, a compression stress or tensile stress is generated in the layer 12 and the permeability of the layer 12 is changed due to magnetostriction effect. As a result, the inductance of the coil 13 is changed and the change is detected as electrical signal by the circuit 15. Thanks to such a structure, the acceleration sensor that is highly sensitive and durable and capable of measuring static acceleration and has an excellent property suitable for scaling down and mass production.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor which can detect acceleration and stress with high sensitivity by using a magnetostrictive effect.

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization and cost reduction of electronic devices, further miniaturization, cost reduction and high sensitivity are required for acceleration sensors used in electronic devices. There is. Currently, piezoelectric sensors and semiconductor strain gauges are generally used as acceleration sensors used in electronic devices and moving bodies. The piezoelectric type uses a piezoelectric element in which an electric charge is generated on the surface when pressure is applied, and is a detection method that converts the applied force into a change in electric charge. The semiconductor strain gauge type utilizes the piezoresistive effect and is a method of detecting an applied force by a change in resistance.

[0003]

However, each of the above-described conventional acceleration sensors has its own problems. In the piezoelectric type acceleration sensor, electric charges do not appear on the surface unless vibration is applied to the piezoelectric body. That is, vibration of the piezoelectric body is indispensable for detecting acceleration, and static acceleration and stress cannot be measured. The main problem with the semiconductor strain gauge type sensor is that the temperature characteristics of the semiconductor are poor. In addition, since complicated processes and vacuum equipment are required for manufacturing,
Capital investment in manufacturing equipment is essential. The present invention is based on a new principle capable of solving the above-mentioned conventional problems, and is capable of detecting acceleration and stress with high sensitivity and measuring static acceleration, and is excellent in miniaturization, mass productivity, durability, and temperature characteristics. An object is to provide an acceleration sensor.

[0004]

In order to achieve the above object, an acceleration sensor of the present invention comprises a substrate that is deformed by receiving stress, and a magnetostrictive portion formed on at least a part of the substrate, At least one coil means for detecting a change in magnetic characteristics due to stress of a magnetic circuit including the magnetostrictive portion, at least one pedestal for fixing these, and a detection circuit for converting the inductance of the coil means into an electric signal. The stress is detected with high sensitivity as a change in magnetic characteristics.

Further, in the above construction, the coil means is
A configuration formed around at least a part of the magnetostrictive portion is preferable.

Further, in the above structure, it is preferable that the material of the pedestal is ferromagnetic and forms a closed magnetic circuit with the magnetostrictive portion.

Further, in the above construction, it is preferable that the material of the pedestal is non-conductive. Further, in the above configuration,
The difference in coefficient of thermal expansion between the magnetostrictive part material and the substrate material is ± 2pp
It is preferably within m.

In the above construction, it is preferable that the substrate material is nonmagnetic. Further, in the above structure, it is preferable that the magnetostrictive portion material is made of an amorphous alloy.

In the above structure, a magnetostrictive portion is provided,
A substrate having a deformed portion that is deformed by receiving stress, a non-deformed portion that is not deformed, and at least two that detect a change in magnetic characteristics of a magnetic circuit including the magnetostrictive portions of the deformed portion and the non-deformed portion. It is composed of a coil means and a detection circuit which converts the inductance of the coil means into an electric signal and outputs a differential signal. As a differential of the change in the magnetic characteristic of the coil means, the stress can be detected with good temperature characteristics. Characterize.

[0010]

According to the structure of the present invention, the substrate having the magnetostrictive portion is deformed when subjected to acceleration and stress. This deformation causes a compressive stress or a tensile stress in the magnetostrictive portion. When stress is applied to the magnetostrictive portion, the magnetoelastic energy of the magnetostrictive portion changes. This change induces magnetic anisotropy in the stress direction of the magnetostrictive portion,
The magnetic permeability in the stress direction increases or decreases, and the magnetic characteristics of the magnetic circuit including the magnetostrictive portion change. As a result, the inductance of the coil means changes, and by converting this inductance change into an electric signal, it becomes possible to detect the stress as a change in magnetic characteristics. The magnetostriction effect is about 1000 times higher than that of the metal foil strain gauge, and the sensitivity is high, and the miniaturization is easy. Further, since the stress can be detected only by the deformation of the substrate, it is possible to detect the static acceleration without the need for vibration. Further, by forming the magnetostrictive portion as a part of the substrate, the material of the substrate itself can be arbitrarily selected. As a result, it is possible to arbitrarily select the substrate material suitable for performance and manufacturing such as temperature characteristics, resonance frequency, and sensitivity, and it is possible to improve durability without lowering sensitivity. Further, it is possible to manufacture by only forming the magnetostrictive portion on the substrate, which leads to mass productivity. As a result, it is possible to realize an acceleration sensor which has good sensitivity and durability, can measure static acceleration, and is suitable for downsizing and mass production.

Further, in the above, according to the preferable construction in which the coil means is formed around at least a part of the magnetostrictive portion, the change in the magnetic permeability due to the stress in the magnetostrictive portion causes a change in the inductance of the coil in a closed magnetic circuit. Therefore, the stress can be detected with high sensitivity.

Further, in the above, according to a preferable construction in which the material of the pedestal is ferromagnetic and forms a closed magnetic circuit with the magnetostrictive portion, a closed magnetic circuit is formed between the magnetostrictive portion and the pedestal, In addition to changes in the inductance of the coil means due to magnetostriction, changes in the magnetic circuit due to changes in the distance between the magnetostrictive portion and the pedestal can also be detected, leading to higher sensitivity. Further, the external magnetic field can be shielded, which leads to stabilization of the acceleration sensor.

Further, in the above, if the material of the pedestal is non-conductive, the pedestal can be mounted on the substrate of the electronic circuit as it is, leading to space saving and simplification of manufacturing.

Further, in the above, according to a preferred construction in which the difference in the coefficient of thermal expansion between the material of the magnetostrictive portion and the material of the substrate is within ± 2 ppm, the strain caused by the change in the length of the magnetostrictive portion and the substrate due to thermal expansion. Is reduced and the temperature characteristics are improved.

Further, in the above, according to the preferable configuration that the substrate material is non-magnetic, the magnetic characteristic of the coil means for detecting the change in the magnetic characteristic is determined only by the magnetostrictive portion, so that the change rate becomes large, It leads to higher sensitivity.

Further, in the above, according to a preferable construction in which the magnetostrictive portion material is made of an amorphous alloy,
The rigidity of the acceleration sensor can be improved by utilizing the strength of the amorphous alloy. Further, since the magnetostriction effect of the amorphous alloy is large, it is easy to increase the sensitivity of the acceleration sensor.

Further, in the above, a magnetostrictive portion is provided,
A substrate having a deformed portion that is deformed by receiving stress, a non-deformed portion that is not deformed, and at least two that detect a change in magnetic characteristics of a magnetic circuit including the magnetostrictive portions of the deformed portion and the non-deformed portion. According to the preferable configuration including the coil means and the detection circuit that converts the inductance of the coil into an electric signal and outputs the differential signal, the inductance change of the coil is differentiated to cancel the temperature change and the external noise. Therefore, an acceleration sensor having good temperature characteristics and stability can be realized.

[0018]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a configuration diagram of an acceleration sensor according to a first embodiment. FIG. 2 is a view of FIG. 1 viewed from the direction A (upward). The configuration of the acceleration sensor of this embodiment will be described below with reference to these drawings.

In this embodiment, the substrate 11 has a thickness of 50.
By etching a titanium thin plate of μm, the long side is 13 mm,
It is molded into a short side of 5 mm, and is heat-treated to remove internal stress. The magnetostrictive layer 12 is formed by the quenching piece roll method and has a thickness of 20 μm Fe—Cr—Si—.
By etching the B-based amorphous alloy film, the long side 12
mm, short side 4 mm, and heat treated to remove internal stress. This magnetostrictive layer 12 has a positive saturation magnetostriction constant of +22 ppm. The coil 13 is φ0.06
The coated copper wire having a diameter of 100 mm is wound around 100 times, and the coated copper wire is fixed with an adhesive. The pedestal is made of aluminum and has a length of 20 mm, a width of 13 mm, and a height of 5 mm, and a cuboid (pedestal 14-A) has a length of 10 mm, a width of 13 mm, and a height of 2.
It has a structure having a rectangular parallelepiped (pedestal 14-B) of mm. The detection circuit 15 includes a power supply, a high frequency oscillator, a filter, an amplifier, a rectification circuit, and a DC / AC conversion circuit. In this embodiment, the amplification factor of the output amplifier is 10 times,
The amplitude of the high frequency wave flowing through the coil 13 was 4 [V], and the frequency was 16 k [Hz].

The deformed portion has a cantilever structure, and the magnetostrictive layer 12 is fixed to the central portion of the substrate 11 as shown in FIG. To fix, apply a resin adhesive to the entire surface of one side of the magnetostrictive layer 12, and then apply 3 in a constant temperature layer at a temperature of 190 ° C.
After inserting for a while, the resin adhesive was cured, and then taken out and allowed to cool at room temperature. As shown in FIG. 2, the substrate 11 has bisectors in the long side direction taken along the line BB ′ of the pedestal 14-B.
Aligned with the sides, half of the surface of the substrate 11 was fixed to the upper surface of the pedestal 14-B. To fix the substrate 11 and the pedestal 14-B, an adhesive was applied to the upper surface of the pedestal 14-B and fixed at room temperature. The coil 13 is formed around the magnetostrictive layer 12, is arranged so as not to contact the substrate 11 and the magnetostrictive layer 12, is fixed to the pedestal 14-A, and these are used as a sensor unit. To fix the coil 13 and the pedestal 14-A, an adhesive was applied to the coil 13 and fixed at room temperature. Two ends of the copper wire of the coil 13 are the detection circuit 1
5 and converts the inductance of the coil into an electric signal.

The sensor unit is fixed to the inside of the magnetic shield made of a soft magnetic material with an adhesive in order to avoid the influence of the earth magnetism and the external magnetization by the magnet of the vibrator. This sensor unit was attached to a vibrator and measured.

The direction of acceleration is the direction normal to the surface of the substrate 11. The range of applied acceleration is 0 [G] to 50
[G], the frequency of the sine wave is 0 [Hz] to 3000 [H]
z].

Finally, the result of the characteristic measurement will be described. 0 when stress is applied in the direction normal to the surface of the substrate 11
0.5 [V] / in all ranges from [G] to 50 [G]
The output of [G] having high sensitivity, stability, and high linearity was obtained. Further, when the frequency is changed in the range of 0 [Hz] to 3000 [Hz], the frequency is changed from the static state of 0 [Hz] to the resonance frequency (1460 [Hz] in this embodiment). An output with good frequency characteristics that did not depend was obtained. Further, the reproducibility was good, and the same output was obtained even after 50 repeated measurements. Moreover, even if a load equivalent to 500 [G] was applied, it was not damaged and high durability was confirmed.

(Second Embodiment) FIG. 3 is a configuration diagram of an acceleration sensor according to a second embodiment. FIG. 4 is a side view of FIG. 3 viewed from the B direction (lateral direction). Hereinafter, the acceleration sensor of this embodiment will be described with reference to these drawings. In this embodiment, the structure of the substrate 11 and the magnetostrictive layer 12,
The material and manufacturing process are the same as those in the first embodiment, and the cantilever structure and manufacturing process are also the same. Coil 23-
A and the coil 23-B are the same as the coil 13 and the material of the first embodiment,
The manufacturing process is the same. Pedestal 24 is ferrite E
It is the core. 50 μm of the surface 24-A of the pedestal 24 with a file
It does not interfere with the vibration of the substrate 11. The detection circuit 25 includes a power supply, a high-frequency oscillator, a filter, an amplifier, a rectifier circuit, a DC / AC converter circuit, and a differential circuit, and converts the inductances of the coil 23-A and the coil 23-B into an electric signal, Motion is detected. The measurement conditions are the same as in Example 1.

In the substrate 11, the bisector in the long side direction is the surface 24.
Align so as to match the center line BB ′ of −B, and face 24-B,
It was fixed by an adhesive on the surface 24-C. With this configuration, a closed magnetic circuit including the magnetostrictive layer 12 and the ferromagnetic body 24 is formed. The coil 23-A includes the surface 24-B and the surface 24 of the magnetostrictive layer 12.
It is formed around a part between −C, is arranged so as not to contact the substrate 11 and the magnetostrictive layer 12, and is fixed to the pedestal 24. The coil 23-B is formed around a portion of the magnetostrictive layer 12 between the surface 24-A and the surface 24-B, and the substrate 11,
It is arranged so as not to contact the magnetostrictive layer 12, and is fixed to the pedestal 24. Coil 23-A, coil 23-B and pedestal 2
The fixing of No. 4 is the same as that of the first embodiment. The two ends of the copper wire of the coil 23-A and the two ends of the copper wire of the coil 23-B are the detection circuit 2
5, the inductance of the coil is converted into an electric signal, and the differential is output, thereby canceling the influence of temperature change and the like.

The acceleration application method and the acceleration measurement method are the same as in the first embodiment. The operation is performed by the same magnetostrictive effect as in Example 1, in addition to the change in the magnetic characteristics of the closed magnetic circuit due to the increase or decrease in the magnetic permeability of the magnetostrictive layer 12, and the change in the magnetic circuit due to the change in the distance of the magnetostrictive layer 12-face 24-A. A change in the inductance of the coil 23-B due to the change will also be detected. This coil 2
The change in the inductance of 3-B and the change in the inductance of the coil 23-A were converted into an electric signal by the detection circuit 25, and the difference was used as an output.

Finally, the result of characteristic measurement will be described. When the measurement was performed under the same conditions as in Example 1, 0 [G] to 5
A stable and highly linear output was obtained with a high sensitivity of about 2.4 times that of Example 1 of 1.2 [V] / [G] in all ranges up to 0 [G]. In addition, 0 [Hz] to 3000 [Hz]
When the frequency is changed in the range up to, the resonance frequency is changed from the static state of 0 [Hz] (160 in the second embodiment).
In the range of 0 [Hz]), an output with good frequency characteristics independent of frequency was obtained. The resonance frequency was increased in Example 2 because the length of the vibrating portion of the cantilever was changed due to the difference in the mounting position. (In Example 2, since the long side bisectors are aligned with the center of the surface 24-B,
The same results as in Example 1 were obtained in terms of reproducibility and durability as well (the vibration part of the cantilever was short).

(Third Embodiment) FIG. 5 is a side view of an acceleration sensor according to a third embodiment. Hereinafter, the acceleration sensor of the present embodiment will be described with reference to this drawing. In this embodiment, the substrate 11, the magnetostrictive layer 12 have the same configuration, material, and manufacturing process as in the first embodiment, and the cantilever configuration and manufacturing process are also the same. For the coils 33-A and 33-B, the pedestal 34 is made of the material of the coil 13 of the first embodiment.
It is wound around and is fixed between the pedestal and the clothing conducting wire with an adhesive. The pedestal 34 is the same in material and manufacturing process as the pedestal 24 in the second embodiment. The structure, material, and manufacturing process of the detection circuit 25 are the same as those in the second embodiment. The measurement conditions are the same as in Example 1.

The structure of the substrate 11, the pedestal 34, etc., excluding the coil, is the same as that of the second embodiment. The coil 33-A is formed around a part of the pedestal protrusion 34-A and is fixed to the pedestal 34. With this configuration, the coil can be wound cheaply and the sensor unit can be easily manufactured. Coil 3
3-B is formed around a part of the pedestal protrusion 34-B and is fixed to the pedestal 34. Coil 33-A,
The fixing of the coil 33-B and the pedestal 34 is the same as that of the first embodiment. The configuration of the coil-detection circuit is similar to that of the second embodiment.

The acceleration applying method and the measuring method are the same as in the first embodiment. The operation is similar to that of the second embodiment, but the coil 33-A includes the magnetostrictive layer 12 to the pedestal protrusion 34-A to the pedestal 3.
The change in the magnetic characteristics of the closed magnetic circuit between 4 and the pedestal protrusion 34-C is detected. Similarly, the coil 33-B includes the magnetostrictive layer 12, the pedestal protrusion 34-B, the pedestal 34, and the pedestal protrusion 34.
The change in the magnetic characteristics of the closed magnetic circuit between −C is detected.
In addition, in order to evaluate the temperature characteristics, Examples 1, 2, 3
The sensor unit of No. 1 was put in a constant temperature layer, and acceleration measurement was performed in the range of −30 ° C. to 80 ° C. for comparison.

Finally, the result of characteristic measurement will be described. When the measurement was performed under the same conditions as in Example 1, 0 [G] to 5
A stable and highly linear output was obtained with a high sensitivity of 0.9 [V] / [G] in all ranges up to 0 [G]. Also,
When the frequency is changed in the range of 0 [Hz] to 3000 [Hz], it depends on the frequency in the range from the static state of 0 [Hz] to the resonance frequency (1600 [Hz] in the second embodiment). An output with good frequency characteristics was obtained. The sensitivity of the third embodiment is lower than that of the second embodiment because the coil is wound around the pedestal 34, and thus the rate of change in the inductance due to the magnetostrictive layer of the inductance is reduced. Also in terms of reproducibility and durability, the same results as in Example 1 were obtained.

Further, in the measurement of the temperature characteristics, the sensor of Example 1 had an error of several% in sensitivity at a high temperature of 50 ° C. to 80 ° C., but the sensors of Examples 2 and 3 were −30 ° C. to 80 ° C. No change in sensitivity appeared in the range of ° C, and it was confirmed that the temperature characteristics were improved.

The shapes of the substrate 11, the magnetostrictive layer 12, the coil 13, and the pedestal 14 in the first embodiment are not limited to those described above, and it is obvious that other shapes will be similar sensors.

In Examples 1, 2, and 3 described above, the magnetostrictive layer 12 is fixed to the substrate 11, but it is clear that the same sensor can be obtained even if a part of the substrate 11 has magnetostriction. .

Although the Fe-Cr-Si-B type amorphous alloy is used as the magnetostrictive layer 12 in Examples 1, 2 and 3, the same sensor is constructed by using other ferromagnetic layers having magnetostriction. It is obvious that you can.

In the first, second and third embodiments described above, the substrate 1
Although titanium is used as the material 1, it is obvious that a similar sensor can be constructed with other materials.

In Embodiments 1, 2, and 3 above, the detection circuit 15 is composed of a power supply, a high-frequency oscillator, a filter, an amplifier, a rectifier circuit, and a DC / AC converter circuit. However, other inductances are converted into electric signals. It is obvious that a similar sensor can be configured by a circuit (for example, a circuit that uses a multivibrator and converts a phase delay of an input signal into an electric signal).

Although the acceleration range is set to 0 [G] to 50 [G] in the first, second, and third embodiments, the same applies as long as the substrate 11 is elastically deformed in other ranges. It is clear that the output of

Although the frequency range is set to 0 [Hz] to 3000 [Hz] in the first, second, and third embodiments, similar outputs can be obtained in other ranges as long as the resonance frequency is lower than the resonance frequency. Is obvious.

The shapes of the substrate 11, the magnetostrictive layer 12, the coil 23-A, the coil 23-B, and the pedestal 24 in the second embodiment are not limited to the above-mentioned ones. It is clear that

In Embodiments 2 and 3 above, ferrite is used as the pedestal 24, but it is natural that a similar sensor can be constructed by using other ferromagnetic materials.

The shapes of the substrate 11, the magnetostrictive layer 12, the coil 33-A, the coil 33-B, and the pedestal 34 in the third embodiment are not limited to those described above, and other shapes may be used as the same sensor. It is clear that

[0044]

According to the present invention, a substrate that is deformed by receiving a stress, a magnetostrictive portion formed on at least a part of the substrate, and a magnetic characteristic due to stress of a magnetic circuit including the magnetostrictive portion. At least 1 to detect changes in
High sensitivity, high durability, and static acceleration utilizing the magnetostrictive effect, which are composed of one coil means, at least one pedestal for fixing them, and a detection circuit for converting the inductance of the coil means into an electric signal. It provides an acceleration sensor that can measure the temperature, is suitable for miniaturization and mass production, and has excellent temperature characteristics.

[Brief description of drawings]

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

FIG. 2 is a top view of FIG. 1 viewed from the direction A.

FIG. 3 is a configuration diagram of an acceleration sensor according to a second embodiment of the present invention.

FIG. 4 is a side view seen from the direction B in FIG.

FIG. 5 is a side view of an acceleration sensor according to a third embodiment of the present invention.

[Explanation of symbols]

 11 substrate 12 magnetostrictive layer 13 coil 14-A pedestal 14-B pedestal 15 detection circuit

Claims (8)

[Claims] 1. A substrate which is deformed by receiving stress,
A magnetostrictive portion formed on at least a part of the substrate, and at least one coil means for detecting a change in magnetic characteristics due to stress of a magnetic circuit including the magnetostrictive portion;
An acceleration sensor comprising at least one pedestal for fixing these and a detection circuit for converting the inductance of the coil means into an electric signal. 2. The acceleration sensor according to claim 1, wherein the coil means is formed around at least a part of the magnetostrictive portion. 3. The acceleration sensor according to claim 1, wherein the pedestal material is ferromagnetic and forms a magnetostrictive portion and a closed magnetic circuit. 4. The acceleration sensor according to claim 1, wherein the pedestal material is non-conductive. 5. The acceleration sensor according to claim 1, wherein the difference in coefficient of thermal expansion between the magnetostrictive portion material and the substrate material is within ± 2 ppm. 6. The acceleration sensor according to claim 1, wherein the substrate material is non-magnetic. 7. The acceleration sensor according to claim 1, wherein the magnetostrictive portion material is an amorphous alloy. 8. A substrate having a magnetostrictive portion, the substrate having a deformable portion that is deformed by receiving stress, a non-deformable portion that is not deformed, and the magnetostrictive portion of each of the deformable portion and the non-deformable portion. It is composed of at least two coil means for detecting a change in the magnetic characteristic of the magnetic circuit and a detection circuit for converting the inductance of the coil means into an electric signal and outputting the change in the magnetic characteristic of the coil means due to stress as a differential signal. An acceleration sensor characterized by the above.