JPH0290061A - Two-dimensional acceleration sensor - Google Patents

Abstract

PURPOSE:To secure excellent durability and to make it possible to ensure the detection of acceleration in the direction of multiple axes without the effect of rotation by omitting mechanical contact and sliding parts in a simple constitution comprising magnetic fluid and a permanent magnet. CONSTITUTION:A permanent magnet 5 is moved to a position where receiving acceleration is balanced with magnetic viscoelasticity generated by a magnetic fluid 4 between a returning-force generating member and the poles of the magnet 5. The displacement in said movement occurs in the directions of multiple axes along the directions of the poles of the magnet 5. The displacement is detected with a magnetism detecting means. An acceleration computing means computes the acceleration based on the detected signal. A rotation preventing member is provided so as to face a part between the poles of the magnet 5. Therefore, magnetic viscoelasticity which suppresses the rotary motion of the magnet 5 acts between the high density part of the fluid 4 in the vicinity of the poles and the rotation preventing member. Since the rotation of the magnet 5 is prevented in this way, only the displacement of the magnet 5 caused by the acceleration can be detected positively without the effect of the displacement of the poles caused by the rotation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a two-dimensional acceleration sensor that detects acceleration in multiple axes on a two-dimensional plane, for example, detects acceleration in two axes of a vehicle, front and back and left and right. It is effective when used as a two-dimensional acceleration sensor.

[Conventional technology]

Conventionally, as a device for detecting acceleration of multiple axes with a single sensor, for example, Japanese Patent Laid-Open No. 163972/1984 has been proposed. This device also seals a magnetic fluid between two concentric spherical shells, holds the inner sphere in a floating position within the outer sphere, and detects the position of the inner sphere as it moves in response to acceleration.

[Problem to be solved by the invention]

However, conventional sensors require one pair of electromagnets per axis to hold the inner sphere in a free-flowing manner, and a contact-type potentiometer must be used to detect the position of the inner sphere. . Therefore, the structure is complicated and there are problems with durability, etc.

Therefore, the present invention has a simple PJ configuration and mechanical contact/
It is an object of the present invention to provide a two-dimensional acceleration sensor capable of detecting acceleration of multiple axes within a two-dimensional plane without a sliding part.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a large number of Ef! a permanent magnet having a pole; a non-magnetic housing having a space for enclosing the magnetic fluid and the permanent magnet; and within the space of the housing, each magnetic pole of the permanent magnet is separated by a predetermined distance in the direction of the reference mark. Returning force generating members provided oppositely to each other and opposing magnetic poles of the permanent magnets with a distance smaller than the distance between the permanent magnet and the returning force generating member within the space of the housing. a rotation prevention member provided as a magnet, a magnetic detection means provided close to a magnetic pole of the permanent magnet; It is characterized by comprising an acceleration calculation means for determining the acceleration acting on the permanent magnet based on a signal from the magnetic detection means.

(Function) According to the above configuration, the permanent magnet receives acceleration and
The restoring force generating member moves to a position where the magnetorheological force generated by the magnetic fluid between the magnetic pole of the permanent magnet is balanced. Displacement due to this movement occurs in multiple axial directions along the magnetic pole direction of the permanent magnet, and this displacement is detected by the magnetic detection means. Further, the acceleration calculation means calculates acceleration based on this detection signal.

Here, the rotation prevention member is provided facing between the magnetic poles of the permanent magnet with a distance smaller than the distance between the permanent magnet and the restoring force generating member, so that the magnetic fluid near the magnetic poles is A magnetorheological force that suppresses the rotational movement of the permanent magnet acts between the high-density portion and the rotation prevention member. This prevents the permanent magnet from rotating, so that only the displacement of the permanent magnet due to acceleration can be reliably detected without being affected by the displacement of the magnetic poles due to rotation.

〔Effect of the invention〕

As described above, the present invention has a simple structure using a magnetic fluid and a permanent magnet, and since there is no mechanical contact or sliding part, good durability can be ensured. Moreover, since rotation of the permanent magnet can be prevented, accelerations in multiple axis directions can be reliably detected without being affected by rotation.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described based on the drawings.

FIG. 1 is a 1-yellow sectional view of the first embodiment, a sectional view taken along the line A--A in FIG. 2, and FIG. 2 is a longitudinal sectional view of the first embodiment.

Reference numeral 1 denotes a main housing made of aluminum, which has at least two pairs of opposing depressions 2a and 2c, 2b and 2d, and forms a substantially cylindrical space 2 with one end open on the inside. Reference numeral 3 denotes a sub-housing made of aluminum, which is fixed to the main housing 1 by screws -1la, llb in order to close the open end surface of the cylindrical space 2. The screws 11a and llb are made of non-magnetic material.

A small hole 7 is formed in the subhousing 3 so as to be concentric with the cylindrical axis of the cylindrical space 2 so as to communicate the cylindrical space 2 with an external space. A magnetic fluid 4 is, for example, one in which ultrafine particles such as manganese zinc ferrite are dispersed in isoparaffin, and is enclosed in the cylindrical space 2 together with a permanent magnet 5.

Reference numeral 5 denotes a disk-shaped permanent magnet magnetized in the radial direction, the number of magnetic poles of which is equal to the number of depressions (2a to 2d) in the cylindrical space 2, and the thickness thereof is slightly shorter than the depth of the cylindrical space 2.

The recesses 2a to 2d are composed of two side surfaces, one of which is a restoring force generating portion 2b-- which is provided facing each other at a predetermined distance in the normal direction of each magnetic pole (N, S) of the permanent magnet 5. 1, the apparent density of the magnetic fluid 4 is large in the vicinity of the magnetic pole of the permanent magnet 5, so a 6n viscoelastic force acts between the restoring force generating portion and each magnetic pole of the permanent magnet. The permanent magnet 5 moves in the direction of the majority axis of each magnetic pole until the magnetorheological force and the acceleration received by the permanent magnet 5 are balanced, and then come to rest. Moreover, each &f pole (N) of the permanent magnet 5 is placed in the recess.

S) There are anti-rotation parts 2b to 2 that face the intermediate part in the normal direction and are provided at a distance smaller than the distance between the restoring force generating part and the magnetic pole of the permanent magnet.

This has the effect of preventing rotational movement of the permanent magnet 5, as will be described later.

The magnetic fluid 4 is injected through the small hole 7 of the sub-housing 3, sealed with a rubber plug 8, and then sealed and fixed with a cap 9. Reference numeral 10 denotes an O-ring, which is provided between the main housing 1 and the sub-housing 3. 12
Hall elements a to 12d are recesses L3a to L3a provided on the outside of the main housing I so as to face the recesses 2a to 2d of the main housing 1 at a constant distance.
It is adhesively fixed to 13d.

Reference numeral 14 denotes a print plate made of glass epoxy, which is fixed to the main housing 1 with non-magnetic screws 15, and each terminal of the Hall elements 12a to 12d is soldered. 16 is a processing circuit section, which is formed on the print plate 14.

Reference numeral 17 denotes an iron shield cover, which is fixed to the main housing l by screws 22a and 22b (not shown). 18 is a shield plate, screw 19
It is fixed to the shield cover 17 by a to 19c. The shield cover 7 and the shield cover 18 constitute the outer shape of this sensor.

Reference numeral 20 denotes a rubber grommet, which is fixed in a hole 23 provided on the side surface of the shield cover 17, and a lead wire bundle 21 from the processing circuit 16 is led out through this grommet 20.

Figure 3 shows a block diagram of the circuit system.

The lead wire bundle 21 taken out from the processing circuit 16 is connected to terminals 37.3B and 39.40 of the processing circuit 16. 39 is connected to a power source, and 40 is connected to ground. The Hall elements 12a to 12d are connected to a power source 39 and a ground 40, respectively.

31 to 36 are differential amplifiers, respectively.

Two output terminals of the Hall element 12a are connected to an input terminal of a differential amplifier 31. Two output terminals of the Hall element 12c are connected to an input terminal of the differential amplifier 32. The output terminals of the differential amplifiers 31 , 32 are connected to the input terminals of an amplifier 35 , and the output terminals of the amplifier 35 are connected to a terminal 37 of the processing circuit 16 .

Similarly, the two output terminals of the Hall element 12b are connected to the input terminal of the differential amplifier 330, the two output terminals of the Hall element 12d are connected to the input terminal of the differential amplifier 34, and the output terminals of the differential amplifier 33, 34 are connected. The terminal is connected to the input terminal of the differential amplifier 2S36, and the output terminal of the differential amplifier 36 is connected to the terminal 38 of the processing circuit 16.

Reference numeral 100 denotes an external arithmetic circuit, which is composed of a mean square circuit 103 and an arithmetic circuit 104. The external arithmetic circuit 100 may be a well-known one, for example, a vector function or division function of Burr-Brown's multi-function converter (model 4302).

Input terminals 101 and 102 of the external arithmetic circuit 100 are connected to output terminals 37 and 38 of the processing circuit 16 via a lead wire bundle 21. Input terminals 101 and 102 are mean square circuit 1
03 and an arithmetic circuit 104. The output terminal of the mean square circuit 103 is connected to the output terminal 105 of the external arithmetic circuit 00, and the output terminal of the division port 8104 is connected to the external arithmetic circuit 1.
It is connected to the output terminal 106 of 00.

Next, its operation will be explained based on the above configuration.

In this device, a permanent magnet 5 placed in a magnetic fluid 4 attracts the magnetic fluid 4, and the permanent magnet 5
The two-dimensional displacement of the permanent magnet 5 according to the acceleration is realized by utilizing the position adjustment phenomenon that occurs between the magnetic fluid 4 and the housing (1, 3) that houses the magnetic fluid 4, and by detecting the displacement, it is stabilized. This method performs two-dimensional acceleration detection.

A permanent magnet 5 magnetized with multiple poles in the radial direction floats in the 6i magnetic flow 4. This is because the apparent density of the magnetic fluid 4 becomes larger where the magnetic field gradient is larger, that is, closer to the magnetic pole. At this time, an acceleration a is generated in the plane direction of the disk-shaped permanent magnet 5.
When this is applied, an inertial force acts on the permanent magnet 5, causing it to move within the main housing l. As the permanent magnet 5 moves, the apparent density of the magnetic fluid 4 near the outer circumferential wall of the cylindrical space 2 of the main housing 1 increases at positions close to the magnetic poles of the permanent magnet 5 and decreases at positions far from the magnetic poles of the permanent magnet 5. Viscoelastic restoring force works. The permanent magnet 5 stands still at the equilibrium point between this restoring force and the inertial force. Therefore, the permanent magnet 5
If the position in the cylindrical space 2 is detected, the acceleration a
A signal corresponding to can be obtained. Hall elements 12a to 12d are used to detect the position of the magnet 5.

However, when the magnet 5 rotates, it is affected by it and cannot be separated from the acceleration signal. In order to prevent this permanent magnet 5 from rotating, depressions 2a to 2d are provided in the cylindrical space 2. This is to utilize the magnetorheological properties also in the rotational direction. The magnetic field generated by the permanent magnet 5 has a cylindrical distribution centered near each magnetic pole on the side surface of the magnet. Therefore,
By providing the recesses 2a to 2d in the normal direction of the magnetic poles and forming the cylindrical space 2 so that there is a relatively small gap in the normal direction between the magnetic poles, when the magnet 5 tries to rotate,
High apparent density part and abundance of magnetic fluid 4 near the magnetic pole 23
The magnetorheological force acting between the side surface portion (2b-2) of 2d and 2d acts as a return torque to the permanent magnet 5.

Therefore, the permanent magnet 5 is prevented from rotating within the cylindrical space 2, and is only allowed to move linearly in the direction of the depression within the horizontal plane.

Further, the cylindrical magnet 5 moves within the cylindrical space 2 in the axial direction of the cylinder. This is to provide sensitivity only to horizontal acceleration.

To realize this, the distance between both bottom surfaces of the cylindrical magnet 5 and both bottom surfaces of the cylindrical space 2 is compared to the distance between the outer peripheral surface of the cylindrical magnet 5 and the inner surface of the recesses 2a to 2d of the cylindrical space 2. , by setting it sufficiently small. This utilizes the fact that the above-mentioned magnetic field distribution near the magnetic pole is spatially distributed not only in the side surface of the magnet but also in the direction of the bottom surface. In other words, by making the distance between both bottom surfaces of the cylindrical magnet 5 and both bottom surfaces of the cylindrical space 2 sufficiently small, the high apparent density portion of the magnetic fluid 4 near the magnetic poles fills the axial gap between the magnet and the housing. , the movement of the permanent magnet 5 in response to axial acceleration is suppressed.

As described above, in the configuration of the multipolar magnet 5 and the magnetic fluid 4 enclosed in the cylindrical space 2, the same number of depressions as the magnetic poles of the magnet are provided in the inner cylindrical space 2 facing the magnetic poles, and the permanent magnet By setting the length of the cylindrical space in the non-magnetic pole surface direction of the permanent magnet 5 to be slightly longer than the length of the permanent magnet 5, the following three effects can be obtained.

(1) The permanent magnet 5 stably floats in the magnetic fluid 4 within the cylindrical space 2.

(2) The permanent magnet 5 receives a centripetal restoring force due to magnetorheological elasticity.

(3) Permanent magnet 5 does not rotate.

Therefore, the position of the permanent magnet, and more specifically the position of each magnetic pole, is uniquely determined with respect to acceleration in the horizontal plane.

Therefore, by detecting the magnetic pole position using a magnetic field detection means such as a Hall element, the applied acceleration can be determined.

A specific example will be explained using FIGS. 1 and 3. 1st
In Fig. 3), the y-axis is taken in the direction of the depressions 2a-2c, and the y-axis is taken in the direction of the depressions 2b-2d. The illustrated case is a four-pole magnet in which both the magnetic poles of the permanent magnet 5 in the χ-axis direction are S poles, and the magnetic poles in the y-axis direction are N poles. This device has an acceleration A as shown in Fig. 1(b).
When , the main power degree a is added. Acceleration a is acceleration A
are vectors that have the same magnitude and point in opposite directions. If the weight of the magnet 5 is m, the inertial force F acting on the magnet 5 is F
= can be expressed as ・m−a. Here, k is a constant determined by various conditions. Also, the magnetoelastic force F
2 has the opposite direction and the same magnitude as the inertial force F1.

Here, in the horizontal section of the cylindrical space 2, the center is set as the origin, and the center position of the magnet 5 when the magnetoelastic force F and the inertial force F1 are in a plane is P(χ.

y), when the amount of movement of the magnet 5 is small, Fzl=
The relationship kz·Jz"+y" is established. Here, k
! is a constant. Therefore, IF.

(z, y)=(k・la l・cos θ, −1 asin θ), and if you know the magnet position (χ, y), you can know the applied acceleration.

Therefore, as shown in FIG. 1(a), the Hall elements 12a to 1
2d is placed facing the magnetic pole. Hall element 12a,
12c faces the S pole of the magnet 5, and is arranged so that the positive output increases when the S pole approaches each other. Further, the Hall elements 12b and 12d are arranged so as to face the ON pole of the magnet 5, and to increase their positive output when the N pole approaches each other. Therefore, for example, when the magnet 5 moves horizontally in the χ-axis direction as shown in FIGS. 1(a) and 1(b), the Hall element 12a and the magnetic pole S approach each other, and the output of the Hall element 12a increases. At the same time, the output of the Hall element 12c becomes small. The Hall element output voltage is approximately inversely proportional to the square of the distance between the Hall element and the magnetic poles.

Therefore, by obtaining a differential output between the Hall elements 12a and 12c, when the amount of magnet movement is small, it is possible to obtain an output voltage that is approximately proportional to the χ direction component of the magnet position. Similarly, the Hall element 12b.

By obtaining a differential output of 12d, it is possible to obtain an output voltage approximately proportional to the y-direction component of the magnet position. Differential output voltage Vx of Hall elements 12a and 12c obtained in this way
and the differential output vy of the Hall elements 12b and 12d each have a value corresponding to the center position (χ, y) of the permanent magnet 5.

Also, by providing differential output, high gain, good linearity, and temperature compensation can be achieved.

Therefore, as shown in FIG. 3, the external processing circuit 100 calculates 1. / V X” + degree a
The latter represents the direction tanθ of the acceleration a.

Incidentally, the processing circuit 16 shown in FIG. 3 will be briefly mentioned. Hall elements 12a-12d are coupled to a stabilized power source via terminal 39. The output of the Hall element 12a is
obtained via a differential amplifier 31 and similarly ball element 1
Outputs 2b-12d are obtained via differential amplifiers 32-34. A differential output of the outputs of the differential amplifiers 31 and 32 is obtained via a differential amplifier 35 and connected to a terminal 37. Further, differential outputs of the outputs of the differential amplifiers 33 and 34 are obtained via a differential amplifier 36 and connected to a terminal 38.

Therefore, the configuration is such that the output voltage Vx is obtained from the terminal 37 and the output voltage vy is obtained from the terminal 38.

The amount of magnetic fluid 4 sealed in the cylindrical space 2, that is, the volume obtained by subtracting the volume of the permanent magnet 1 from the volume of the cylindrical space 2, is the total amount of magnetic fluid that the permanent magnet 1 can hold in a free state. Preferably, they are equal.

Here, the total amount of tR magnetic fluid that the permanent magnet 1 can hold in a free state is the total amount of magnetic fluid that adheres to the permanent magnet 1 when the permanent magnet 1 is inserted into the magnetic fluid at room temperature and normal pressure and pulled out. means. If the volume is determined to be larger than this amount, a dead zone will occur in the permanent C8 stone movement amount with respect to acceleration. If set to a small value, the amount of movement relative to acceleration will be reduced,
This is because sensitivity decreases.

FIG. 4 shows the effect of the Hall element 12 on the magnitude of the applied acceleration.
a, 12. Similarly, the differential output Vx of Hall elements 12b and 12c is shown in FIG.
al ·sin θ is shown, and the solid line shows the actual measured value obtained from the acceleration sensor.

Next, the configuration of the second embodiment will be explained in detail. Portions having the same configuration or similar functions as those in the first embodiment are designated by the same reference numerals, and explanations thereof will be omitted.

The first embodiment used recesses (2a to 2d) having a return force generating part and a rotation prevention part, but in the second embodiment,
Each part was separated into two parts to facilitate construction.

First, each magnetic pole of the permanent magnet 5 (S, N, S, N
Returning force generating walls 1 a - 1 d are provided opposite in the normal direction of ), and these returning force generating walls 1 a - 1 d are formed integrally with the main housing 1 . In addition, Hall elements 12a-12 are provided in the return force generating walls 1a-1d, respectively.
A space is formed in which d can be stored. Further, in the normal direction of the intermediate portion of each magnetic pole of the permanent magnet 5, rotation prevention walls 3a to
3d, and the rotation prevention walls 3a to 3d are formed integrally with the subhousing 3. For the rotation prevention walls 3a to 3d, wall surfaces having a component in the normal direction to the permanent magnet 5 are effective in order to prevent the permanent magnet 5 from rotating.

These return force generating walls 1a-1d and rotation prevention walls 3a-3d
, and the magnetorheological force of the magnetic fluid 4 around the permanent magnet 5, the permanent magnet 5 can be moved in two axes directions, up and down and left and right in FIG. 6, and the rotation of the permanent magnet 5 itself is as follows. Since rotation is prevented by the rotation prevention walls 3a to 3d, in the second embodiment as well, the Hall elements 12a to 12d are not affected by the output change caused by the 50 rotations of the permanent magnet, and can only prevent the displacement of the permanent tn stone 5 due to acceleration. Can be detected reliably.

In the above-mentioned embodiment, the number of magnetic poles of the permanent magnet and the number of depressions in the cylindrical space are shown as four (two sets facing each other), but as long as there are two or more sets, it does not matter how many times.

Further, although a Hall element is used as an example of the magnet position detecting means, other magnetic detecting means such as a magnetoresistive element or a coil may be used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention, FIG. 2 is a cross-sectional view of the first embodiment, FIG. 3 is a circuit diagram showing an electric circuit of the embodiment, and FIGS. The figure is a characteristic diagram showing the output characteristics of the acceleration sensor, FIG. 6 is a cross-sectional view showing the second embodiment, and FIG.
The figure is a longitudinal sectional view showing the second embodiment. 1... Main housing, 2... Space, 2a to 2d
... recess, 3 ... subhousing, 4 ... magnetic fluid, 5 ... permanent magnet, 12a-12d ... Hall element, la - 1d ... return force generating wall, 3a - 3d.
...Anti-rotation wall. Representative Patent Attorney Takashi Okabe

Claims (1)

[Scope of Claims] A magnetic fluid; a permanent magnet having a large number of magnetic poles; a non-magnetic housing having a space for enclosing the magnetic fluid and the permanent magnet; restoring force generating members provided facing each other at a predetermined distance in the normal direction of each magnetic pole; and a distance within the space of the housing that is smaller than the distance between the permanent magnet and the restoring force generating member. a rotation preventing member provided oppositely between the magnetic poles of the permanent magnet, and a rotation preventing member provided oppositely between the magnetic poles of the permanent magnet; A two-dimensional acceleration sensor comprising: a magnetic detection means provided in close proximity to the permanent magnet; and an acceleration calculation means for calculating acceleration acting on the permanent magnet based on a signal from the magnetic detection means.