JPH06230027A - Acceleration sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a small and highly accurate acceleration sensor capable of simultaneously detecting acceleration in three axes. [Structure] A support member 2 made of a soft magnetic material and having displacement degrees of freedom in three axial directions, a permanent magnet 1 supported by the support member 2, and a circumference of the permanent magnet 1 are surrounded to change a magnetic flux. It is characterized by comprising magnetic field sensors 4a to 4d for detecting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small, lightweight acceleration sensor capable of detecting acceleration in three dimensions.

[0002]

2. Description of the Related Art Conventionally, a small and lightweight sensor has been required for detecting a collision of an automobile, and a sensor for detecting displacement due to acceleration of a spring-supported object as a change in capacitance or a piezoelectric element has been used. The one that detects stress strain as a piezo voltage has been used.

All of them detect acceleration in one axis direction, and in order to detect acceleration in three-dimensional directions, it is necessary to use the detecting elements in combination with three axes. On the other hand, there are basically three
Since it is necessary to detect the axial acceleration, a mechanical gyro using a top that rotates at high speed is generally used.

When a rotational angular velocity is applied to a vibrating object, Coriolis force is applied in the direction perpendicular to the vibration.

Fc = 2m × V × ωp where Fc: Coriolis force, m: mass, V: velocity, ω
There is also a piezoelectric gyro that utilizes the occurrence of p: angular velocity to detect the Coriolis force with a piezoelectric element.

[0005]

However, in the mechanical gyro used for controlling the attitude of the airplane and the like, in order to improve the accuracy, it is inevitable that the mass of the top is increased to accelerate the rotation speed, and the size is reduced. It is difficult. Further, the piezoelectric gyro is used for car navigation, a four-wheel steering system, a camera shake prevention, etc., but it is difficult to downsize the vibrator.

Further, there is a capacitance-changing type accelerometer that detects the minute unit due to acceleration as a capacitance change by adding a mass to one of the two electrodes constituting the capacitance and supporting it by a spring. However, since the impedance of the sensor portion is high in capacitance, it is weak against external noise, and the connection distance to the detection circuit is limited, which poses a serious problem. In view of the above-mentioned problems of the conventional technique, the present invention provides a small-sized acceleration sensor capable of high-accuracy and simultaneously detecting acceleration in three axial directions.

[0007]

The solution to the above problems can be achieved by adopting the novel characteristic constitutional means listed below the present invention. That is, a first feature of the present invention is that a support member made of a soft magnetic material and having three degrees of freedom of displacement, a permanent magnet supported by the support member, and a periphery of the permanent magnet are surrounded. An acceleration sensor including a magnetic field sensor that detects a change in magnetic flux.

A second feature of the present invention is an acceleration sensor in which the soft magnetic material forming the support member of the acceleration sensor in the first feature has a magnetostriction constant set to near zero.

A third feature of the present invention is that the first or second
The magnetic field sensor having the above-mentioned feature is an acceleration sensor formed by surrounding one end of each permanent magnet at regular intervals of 90 ° on the same circle.

A fourth feature of the present invention is that the permanent magnets of the first, second or third features are integrally formed in a rectangular shape at one extreme and in a pyramidal regular pyramid at the other extreme. It is an acceleration sensor.

A fifth feature of the present invention is that the first, second, and
The support member according to the third or fourth feature has a base end that is cantilevered and an intermediate portion that is formed in a spiral shape,
It is an acceleration sensor that connects the tips that are concentrated in the center with a permanent magnet mounting piece.

[0012]

Since the present invention adopts the above-mentioned means,
Since the magnetic circuit has an almost closed magnetic circuit structure, it has high resistance to external magnetic field noise, like a ring-shaped magnetic head having a similar magnetic circuit structure. Further, since the magnetic field noise itself is smaller than the electric field noise in the natural world, it becomes easier to use even in a place where there is much electromagnetic noise, as compared with an acceleration sensor using a piezoelectric element or capacitance change.

[0013]

Embodiments of the present invention will be described with reference to the drawings. Figure 1
Is a perspective view for explaining the overall structure of this embodiment, and FIG.
It is a II-II line sectional view.

In the figure, A is the acceleration sensor of this embodiment, 1
Is a permanent magnet in which the lower S pole is a cuboid and the upper N pole is a pyramidal quadrangular pyramid, 2 is a symmetrical spiral bidirectional support spring which is a support member for ensuring the freedom of movement of the permanent magnet 1 in the three axial directions, Substrate, 4a to 4d are magnetic pole bars, 5a to 5d are detection coils,
6a to 6d are drive coils, 7a to 7d are magnetic pole rod support blocks, 8 is a permanent magnet mounting piece, 9 is a base, and 9a is a recess. The X-axis and the Y-axis indicated by the solid arrow in FIG.
The axis is a coordinate axis for convenience of description.

The support spring 2 is made of a soft magnetic material whose magnetostriction constant is set to near zero, for example, a NiFe alloy or a CoZr type amorphous foil. Magnetic pole bar support block 7a
Are connected via ~ 7d. Magnetic pole rods 4a arranged in the orthogonal direction with their inner ends facing the same circle in the plane.
4d is made of a soft magnetic material and is connected to the support spring 2 via the pole bar support blocks 7a to 7d and the substrate 3.

The acceleration sensor A according to this embodiment has a magnetic pole bar 4
The permanent magnet 1 and the space are inserted in the magnetic circuit formed by a to 4d and the support spring 2. Permanent magnet 1
The magnetic flux generated from the magnetic poles enters from the inner ends of the adjacent magnetic pole rods 4a to 4d, and the magnetic pole rod support blocks 7a to 7d and the support spring 2 are generated.
Of the permanent magnet 1. Pole stick 4
An alternating current is applied to the drive coils 6a to 6d around which a to 4d are wound.

The acceleration sensor A of this embodiment has such a specific embodiment, and its operation will be described below with reference to the drawings. First, when the permanent magnet 1 is displaced integrally with the permanent magnet mounting piece 8 due to the swing of the support spring 2, each magnetic pole bar 4a is moved.
Since the distance between ~ 4d and the permanent magnet 1 changes, each pole bar 4
The amount of magnetic flux flowing in a to 4d changes.

Since the magnetic pole rods 4a to 4d are excited by an alternating current, the change in the magnetic flux changes the operating point of the soft magnetic material forming the magnetic pole rods 4a to 4d, and thus the magnetic pole rod 4a.
The output of the detection coils 5a to 5d wound near the inner ends of 4d to 4d shows the second harmonic component of the frequency of the drive current that would not be generated without the magnetic flux.

The operation of the magnetic pole rods 4a to 4d will be described below with reference to the magnetization curves and the like. FIG. 3 is a graph illustrating the operation of each magnetic pole rod 4a to 4d in this embodiment.
In the following, the magnetic pole rod 4a will be described as an example.
It goes without saying that the magnetic pole rods 4b to 4d exhibit the same operation.

First, FIG. 3A is a graph showing the magnetization curve of the magnetic pole material used for the magnetic pole rod 4a. The horizontal axis represents the applied magnetic field and the vertical axis represents the magnetization of the material. 4a indicates that magnetization in the magnetic field direction occurs. There is a maximum value for the magnetization amount of the magnetic material depending on the material. Further, the magnetic permeability μ represented by the slope of the curve in the figure is
In the case of the present embodiment, since the soft magnetic material is used, it is considerably high.

FIG. 3B shows the time-varying output magnetic flux in the pole bar 4a. Since the voltage detected by the detection coil 5a is the time change of the magnetic flux due to the Maxwell's principle of electromagnetic induction, this time differential waveform appears.

FIG. 3 (c) is a graph showing the temporal change of the magnetic field applied to the magnetic pole material of the magnetic pole bar 4a. A waveform drawn by a solid line is a magnetic field generated by a sinusoidal current artificially applied to the magnetic pole material by the drive coil 6a from the outside. The dotted line shown in FIG. 3C shows the magnetic field when the external magnetic field, which is the measurement target, is applied.

The detection of such a magnetic field change is based on the same principle as a fluxgate type magnetic field sensor widely used as a highly sensitive magnetic field sensor, and a block diagram of the fluxgate type magnetic field sensor is shown in FIG. In the figure, B is a flux gate type magnetic field sensor, 10
Is an oscillator, 11 is an amplifier, 12 is a frequency multiplier, 13 is a magnetic core of high magnetic permeability such as permalloy, 13a is a primary coil which plays the same role as the drive coils 6a to 6d of this embodiment,
Reference numeral 13b is a secondary coil that plays the same role as the detection coils 5a to 5d of the present embodiment, 14 is a phase converter, 15 is a band pass filter (BPF), and 16 is a phase detector.

The operation of the fluxgate type magnetic field sensor B is as follows. First, the high-permeability magnetic core 13 and the primary / secondary coil 13
When a and 13b are wound and a sinusoidal current is passed to the primary coil 13a side, the output induced to the secondary coil 13b side due to the saturation characteristic loses symmetry when a magnetic field is applied from the outside,
The output will include harmonics. When even-order harmonics are extracted from this harmonic and the magnitude and phase thereof are examined, an output indicating the magnitude and direction of the external magnetic field proportional to the external magnetic field is obtained, so that the magnetic field sensor has high sensitivity.

By applying the same principle as this fluxgate type magnetic field sensor B and comparing the second harmonic components of each axis in the plane, it becomes possible to detect in what direction and how much the permanent magnet 1 has moved. For example, referring to FIG. 1, if the permanent magnet 1 moves to the arrow side of the X axis, the pole bar 4a
Output increases and the output of the pole bar 4b decreases. The outputs of the magnetic pole rods 4c and 4d arranged in the Y-axis direction do not change.

As described above, 2 in the XY plane shown in FIG.
The dimensional movement can be obtained by comparing the output differences of 4a and 4b, 4c and 4d, which are sets of magnetic pole rods installed in the respective X-axis and Y-axis directions. Also, the displacement in the Z-axis direction is
Since the magnetic flux amount changes regardless of any magnetic pole, the detection coil 5a wound around each magnetic pole rod 4a, 4b, 4c, 4d,
The displacement can be detected by comparing the in-phase components of 5b, 5c and 5d.

Since the above-described processing is processing of electric signals, it is not necessary to mount it on the sensor portion, and the capacitance type acceleration which detects the electric capacitance change by changing the electrode gap by the same minute displacement. Since the output impedance is lower than that of the meter, it is extremely easy to separate the sensor part and the signal processing part with a long cable or the like.

In this case, since the sensor portion may be only the portion shown in FIG. 1, it can be constructed very simply. In addition, since the sensor portion does not use an element sensitive to temperature change such as a semiconductor element, it has a feature that the operating temperature range is wide.

When the permanent magnet 1 is placed in free space, only a small magnetic field can actually be generated due to demagnetization due to its own magnetization. Therefore, in order to increase sensitivity, a large permanent magnet is taken into consideration in consideration of the demagnetization. Although a magnet is required, in the present embodiment, since the magnetic flux of the permanent magnet 1 is circulated by the soft magnetic material that is the material of the support spring 2, the magnetic resistance at the time of circling can be made extremely low, so that it is permanent. A small magnet 1 is sufficient.

Since the support spring 2 is also flexed to support the minute displacement of the permanent magnet 1, the soft magnetic material as its constituent material is also stressed. In general, the soft magnetic characteristics change when stress is applied, but in this embodiment, there is no problem because a material having a magnetostriction constant of almost zero is used as the constituent material of the support spring 2.

Further, the soft magnetic material has a slightly lower Young's modulus than the ordinary spring material, but since the mass of the magnet is small, it is possible to sufficiently increase the mechanical resonance. If, for example,
To obtain a higher Young's modulus, a hard metal such as titanium may be laminated on the soft magnetic material by plating or the like.

Next, the manufacturing method of this embodiment will be described. The acceleration sensor A of this embodiment can be manufactured by assembling individual parts, but it can also be integrally processed from the beginning by a thin film forming technique such as photolithography or sputtering.

That is, like the thin-film magnetic head and the like, the support spring 2 material is formed and patterned on the substrate 3 such as silicon, and then the permanent magnet 1 is formed on the permanent magnet mounting piece 8. The magnetic pole bar 4 is then flattened with a soluble resist.
a-4d, each detection coil 5a-5d, each drive coil 6
a to 6d are formed. Then, the soluble resist may be dissolved and removed, and further the silicon under the support spring 2 may be removed by anisotropic etching.

On the contrary, first, the magnetic pole rods 4a to 4d, the detection coils 5a to 5d, and the drive coils 6a to 6d are formed, then flattened with a soluble resist, the permanent magnet 1 is formed, and then flattened again. Then, by removing the flattening resist at the end, an acceleration sensor A having a shape just like that of FIG. 1 is completed. Furthermore, according to the thin film forming technique, it is extremely easy to stack the soft magnetic material and the hard metal to realize the optimum mechanical characteristics of the support spring 2.

[0035]

As described above, according to the present invention, accelerations in the three axial directions can be detected at the same time, and it is possible to provide a small-sized and highly accurate acceleration sensor at a wide operating temperature at low cost. Demonstrate excellent utility and economy.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating the overall structure of an acceleration sensor of the present invention.

2 is a sectional view taken along line II-II in FIG.

3 (a), (b), (c) are characteristic graphs for explaining the magnetic operation of the same magnetic pole bar, respectively.

FIG. 4 is a block diagram showing a configuration of a fluxgate type magnetic field sensor.

[Explanation of symbols]

 A ... Acceleration sensor B ... Fluxgate type magnetic field sensor 1 ... Permanent magnet 2 ... Support spring 2a ... Cantilever base end 2b ... Tip 3 ... Substrate 4a-4d ... Magnetic pole bar 5a-5d ... Detection coil 6a-6d ... Drive coil 7a 7d ... Magnetic pole rod support block 8 ... Permanent magnet mounting piece 9 ... Base 9a ... Recessed portion 10 ... Oscillator 11 ... Amplifier 12 ... Frequency multiplier 13 ... Magnetic core 13a ... Primary coil 13b ... Secondary coil 14 ... Phase converter 15 ... Band pass filter (BPF) 16 ... Phase detector

Claims (5)

[Claims] 1. A support member made of a soft magnetic material and having three degrees of freedom of displacement, a permanent magnet supported by the support member, and a magnetic field surrounding the periphery of the permanent magnet to detect a change in magnetic flux. An acceleration sensor comprising a sensor and. 2. The acceleration sensor according to claim 1, wherein the soft magnetic material forming the support member has a magnetostriction constant set to near zero. 3. The acceleration sensor according to claim 1, wherein the magnetic field sensors are arranged so that one end faces a permanent magnet, and the magnetic field sensors are surrounded by 90 degrees at regular intervals on the same circle. 4. The acceleration sensor according to claim 1, wherein the permanent magnet is integrally formed with one extreme in a rectangular parallelepiped shape and the other extreme in a pyramidal regular pyramid shape. 5. The supporting member has a base end that is cantilevered and a middle portion that is formed in a spiral shape, and that the front ends that are concentrated in the center are connected by a permanent magnet mounting piece. , 2, 3 or 4 acceleration sensor.