JPH06213921A - Magnetic fluid type acceleration sensor - Google Patents

Abstract

PURPOSE:To improve measuring sensitivity of a magnetic fluid type acceleration sensor for detecting acceleration by using a permanent magnet and magnetic fluid. CONSTITUTION:A magnetic fluid type acceleration sensor comprises a housing 11, permanent magnets 16a-16d provided in the housing 11 to be displaced corresponding to acceleration to be applied to the housing 11, magnetic fluids 17a-71d for displaceably holding the magnets 16a-16d in the housing 11, and a Hall element 18 so arranged as to be opposed to the magnets 16a-16d to generate an acceleration signal corresponding to the displacement, wherein the fluids 17a-17d are arranged at positions opposed to the housing 11 of the magnets 16a-16d. Further, the sensor comprises a flow preventive member 19 provided near the opposed position of the magnets 16a-16d to the element 18 to prevent the fluids 17a-17d from flowing to the opposed positions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid type acceleration sensor, and more particularly to a magnetic fluid type acceleration sensor for detecting acceleration using a permanent magnet and a magnetic fluid.

[0002]

2. Description of the Related Art Conventionally, as an acceleration sensor using a magnetic fluid, there is one disclosed in Japanese Patent Application Laid-Open No. 2-205775. The magnetic fluid type acceleration sensor disclosed in the above publication is a housing formed by a main housing in which a substantially cylindrical space whose one end face is open is formed inside, and a sub-housing which closes this open one end face. A magnetic fluid is filled in the inside, and a permanent magnet is floated in the magnetic fluid. The permanent magnet has a ring shape and is magnetized with 8 poles in the radial direction.

Further, a hall element is arranged at the central position of the main housing, and the hall element is arranged so as to be located at the center of the permanent magnet when the ring-shaped permanent magnet is arranged inside the housing. Has been done. Therefore, the Hall element has a structure facing the inner wall of the permanent magnet.

The permanent magnet is displaced according to the acceleration applied to the magnetic fluid type acceleration sensor, and the Hall element detects a change in the magnetic field caused by the acceleration, whereby the strength of the applied acceleration is detected. Was there.

FIGS. 5A and 5B are model diagrams for explaining the principle of acceleration measurement of the magnetic fluid type acceleration sensor having the above-mentioned configuration. As shown in the figure, the permanent magnet 3 is configured to be displaceable in the housing 1 and floated on the magnetic fluid 2 (shown in satin), so that the permanent magnet 2 is attached to the permanent magnet 2 via the housing 1. When the acceleration A acts,
In the housing 1, the permanent magnet 3 corresponds to the above acceleration and x
Displace in the direction. At this time, the magnetic fluid 2 has magnetic stickiness or elastic force (just the spring 6 and the damper 7 in the magnetic field).
It produces the effect like. Hereinafter, since this elastic force acts as a magnetic elastic force, the permanent magnet 3 is displaced against this magnetic elastic force (see FIG. 5A).
The reference numeral 8 indicates the isobar of the magnetic fluid 2.)

On the other hand, a Hall element 4 is arranged at a position facing the permanent magnet 3. Therefore, when the permanent magnet 3 is displaced according to the applied acceleration, a change in the magnetic field applied to the Hall element 4 occurs, and since this change in the magnetic field corresponds to the acceleration, the acceleration applied from the output of the Hall element 4 is measured. can do.

[0007]

According to the magnetic fluid type acceleration sensor having the above-mentioned conventional structure, it is possible to prevent bubbles from being generated due to the rocking of the magnetic fluid, and it is possible to detect the acceleration with high accuracy.

On the other hand, in the magnetic fluid type acceleration sensor having the above-mentioned structure, a ring-shaped permanent magnet is arranged in a floating state in a substantially cylindrical space filled with the magnetic fluid formed in the housing. Therefore, the magnetic fluid also wraps around the magnetic pole on the side facing the Hall element of the permanent magnet. This will be described with reference to FIG.

FIG. 6 is a plan view of the magnetic fluid type acceleration sensor with the sub-housing removed, in which 1 is a main housing (1a is an outer wall and 1b is an inner wall) and 2 is a magnetic fluid. Reference numeral 3 is a permanent magnet, and 4 is a Hall element. In the conventional magnetic fluid type acceleration sensor, since the permanent magnet 3 is floated on the magnetic fluid 2 as described above, it is necessary to provide an inner wall to prevent the magnetic fluid 2 from coming into contact with the Hall element 4. . Therefore, the permanent magnet 3 and the Hall element 4 are inevitably separated from each other.
The magnetic fluid 2 is the inner wall 3a of the ring-shaped permanent magnet 3.
The magnetic fluid 2 is also present in a portion where the inner wall 1b of the main housing 1 and the inner wall portion 3a of the permanent magnet 3 are separated from each other because the magnetic fluid 2 flows into the inner wall 1b.

As described above, the magnetic fluid 2 has a magnetic elastic force. Therefore, when the permanent magnet 3 is displaced due to acceleration, the inner wall 1b of the main housing 1 and the permanent magnet 3 are thus displaced.
The magnetic elastic force also acts on the portion separated from the inner wall portion 3a. It is known that the strength of the magnetic elastic force increases as the distance between the inner wall 1b and the inner wall portion 3a (magnetic pole) decreases, and therefore the permanent magnet 3 is smoothly displaced in accordance with the applied acceleration. To the main housing 1
It is necessary to largely separate the inner wall 1b and the inner wall portion 3a of the permanent magnet 3 from each other.

Further, in the structure in which the permanent magnet 3 is floated on the magnetic fluid 2, the inner wall portion 3a is inevitably provided between the permanent magnet 3 and the Hall element 4 so that the magnetic fluid 2 does not come into contact with the Hall element 4.
Must be provided, which also causes the distance between the permanent magnet 3 and the Hall element 4 to be separated.

However, focusing on the measurement sensitivity of the Hall element 4, the larger the change in the magnetic flux density applied to the Hall element 4, the higher the measurement sensitivity. Therefore, from the viewpoint of improving the measurement sensitivity, it is necessary to dispose the permanent magnet 3 and the Hall element 4 close to each other.

As described above, in the conventional magnetic fluid type acceleration sensor, the measurement sensitivity is lowered when the permanent magnet 3 is smoothly displaced in accordance with the applied acceleration, and the permanent magnet 3 is permanently changed when the measurement sensitivity is improved. There is a problem in that the smooth displacement of the magnet 3 is hindered, resulting in a decrease in measurement sensitivity.

The present invention has been made in view of the above points, and a magnetic fluid type acceleration in which the measurement sensitivity is improved by preventing the magnetic fluid from flowing into the magnetic detection sensor side of the permanent magnet. It is intended to provide a sensor.

[0015]

In order to solve the above-mentioned problems, according to the present invention, a housing made of a non-magnetic material and a structure which is provided in the housing and is displaced in accordance with an acceleration applied from the outside. A magnet, a magnetic fluid that holds the magnet in the housing in a displaceable manner, and a magnetic detection sensor that is arranged so as to face the magnet and that generates an acceleration signal corresponding to the displacement of the magnet. In the magnetic fluid type acceleration sensor provided with, the magnetic fluid is arranged at a position facing the housing of the magnet, and the magnetic fluid flows into the facing position in the vicinity of the facing position facing the magnetic detection sensor of the magnet. It is characterized in that a flow-in prevention member for preventing the flow is provided.

[0016]

By providing the flow-in prevention member for preventing the magnetic fluid from flowing into the facing position as described above,
Since the magnetic fluid does not exist between the magnet and the magnetic detection sensor, the magnetic elastic force does not act between them, and the magnet is displaced with good responsiveness according to the applied acceleration. Further, since there is no magnetic fluid between the magnet and the magnetic detection sensor, the magnet and the magnetic detection sensor can be arranged close to each other. Therefore, the measurement sensitivity of the magnetic fluid type acceleration sensor can be improved.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. 1 and 2 show a magnetic fluid type acceleration sensor 10 which is an embodiment of the present invention. FIG. 1 is a horizontal sectional view of the magnetic fluid type acceleration sensor 10, and FIG. 2 is a vertical sectional view of the magnetic fluid type acceleration sensor 10.

In each drawing, reference numeral 11 denotes a housing made of a non-magnetic material, which is composed of a main housing 12 and a sub housing 13. Main housing 12
Has a cylindrical shape, and has four magnet housings 14a inside thereof.
14d are formed, and the Hall element housing portion 15 is formed in the central portion thereof.

The magnet accommodating portions 14a to 14d are rectangular parallelepiped grooves, and the hall element accommodating portion 15 is a cylindrical groove.
The magnet storage portions 14a to 14d are hall element storage portions 15
Is formed so as to extend in the radial direction with respect to the center, and each of the magnet accommodating portions 14a to 14d is 90 degrees apart from the center position.
They are formed so as to be spaced apart from each other (they are formed in a cross shape as a whole). Further, each of the magnet housing portions 14a to 14d is formed so as to be continuous with the hall element housing portion 15.

Further, 16a to 16d are permanent magnets,
In this embodiment, four rod-shaped dipole magnets are used. The permanent magnets 16a to 16d are housed in magnet housing portions 14a to 14d formed in the main housing 12. Therefore, the permanent magnets 16a to 16d are also arranged in a cross shape in a state of being separated from each other by 90 degrees with respect to the center position.

As mentioned above, the permanent magnets 16a to 16d are used.
Is a magnet housing portion 14a formed in the main housing 12.
˜14d, the magnet storage parts 14a to 14d.
Is formed larger than the size of the permanent magnets 16a to 16d, so that the permanent magnets 16a to 16d can be displaced in the magnet accommodating portions 14a to 14d in the directions shown by the arrows in the drawings in the attached state. . Further, the magnetic fluids 17a to 17d are filled in the inner portions of the magnet storage portions 14a to 14d on the side opposite to the hall element storage portion 15 by using, for example, a dispenser, and the permanent magnets 16a to 1 are provided.
6d is connected to one end portions 16a- _{1 to} 16d- ₁ .

As described above, the magnetic fluids 17a to 17d are
In the magnetic field, magnetic stickiness and elastic force (magnetic elastic force) act. Therefore, when acceleration is applied to the magnetic fluid acceleration sensor 10, the permanent magnets 16a to 16d are
Is configured to be displaced in the magnet storage portions 14a to 14d in the direction indicated by the arrow in the figure against the magnetic elastic force of the magnetic fluids 17a to 17d.

A hall element 18 is arranged at the center of the hall element housing portion 15. This Hall element 18 is the other end 16a _{-2 of the} permanent magnets 16a to 16d.
It is arranged so as to face ~ 16d _-2 . Therefore, acceleration is applied to the magnetic fluid acceleration sensor 10 and the permanent magnet 1
When 6a to 16d are displaced in the directions shown by the arrows in the figure, the magnetic field applied to the Hall element 18 changes according to the displacement amount of the permanent magnets 16a to 16d.

This change in the magnetic field is caused by the magnetic fluid acceleration sensor 10
Since it corresponds to the magnitude and direction of the acceleration applied to, the state of the acceleration applied to the magnetic fluid acceleration sensor 10 can be detected by the output of the Hall element 18.

On the other hand, a flow-in prevention member 19, which is a feature of the present invention, is disposed in the vicinity of the end portions 16a _{-2 to} 16d _-2 of the permanent magnets 16a to 16d facing the Hall element 18. As shown in FIG. 3 in addition to FIGS. 1 and 2, the flow-in prevention member 19 has an annular shape, and the permanent magnets 16a to 16d have insertion holes 20a to 20d formed in the side wall of the flow-in prevention member 19. It is configured to be inserted through 20d.

At this time, the permanent magnets 16a to 16d are configured to be inserted in the insertion holes 20a to 20d in a liquid-tight state. Further, since the flow-in prevention member 19 is formed of a flexible non-magnetic material such as rubber, for example, by providing the flow-in prevention member 19, the housing 11 is provided.
It does not cause a magnetic field change inside and does not hinder the displacement of each of the permanent magnets 16a to 16d corresponding to the acceleration. The flow-in prevention member 19 is used for the permanent magnet 1
6A to 16d are mounted in the housing 11 so as to be positioned inside the Hall element housing portion 15.

Next, the operation of the flow-in prevention member 19 having the above structure will be described.

As shown in FIGS. 1 and 2, the flow-in prevention member 19 includes permanent magnets 16a to 16d in the housing 1.
It is configured so as to be located inside the Hall element housing portion 15 in a state of being attached to the No. On the other hand, the magnetic fluid acceleration sensor 10
When acceleration is applied to the permanent magnets 16a to 16
Since d is displaced in the direction shown by the arrow in the figure, the magnetic fluids 17a to 17d are displaced by the displacements in the magnet housing portions 14a to 14d.
It is conceivable that it flows out toward the Hall element housing portion 15 through the gap formed between the permanent magnets 16a to 16d.

Assuming that the magnetic fluid acceleration sensor 10 having the above-described structure is not provided with the flow-in prevention member 19, the magnetic fluids 17a to 17a, which flow out, are discharged.
17d enters between the Hall element 18 and the end portions 16a _{-2 to} 16d _-2 of the permanent magnets 16a to 16d, and the Hall element 1
8 and the permanent magnets 16a to 16d are magnetically short-circuited, and the Hall element 18 does not function effectively.

Further, the Hall element 18 and the end portions 16a _-2 to 1
When the magnetic fluids 17a to 17d enter between 6d- ₂ and
The magnetic elastic force of the magnetic fluids 17a to 17d acts between the Hall element 18 and the permanent magnets 16a to 16d, and the permanent magnets 16a to 16d do not move smoothly, resulting in a displacement corresponding to the applied acceleration. become unable.

However, by providing the flow-in prevention member 19, the magnetic fluids 17a to 17d are displaced by the displacement of the permanent magnets 16a to 16d so that the gaps formed between the magnet storage portions 14a to 14d and the permanent magnets 16a to 16d are formed. Even if the magnetic fluids 17a to 17d flow out toward the passage hall element accommodating portion 15, the magnetic fluids 17a to 17d that flow out are blocked by the flow-in prevention member 19 and do not flow into the inner position (opposite position) of the flow-in prevention member 19.

Therefore, the end portions 16a _{-2 to} 16d _-2 of the permanent magnets 16a to 16d can be brought close to the Hall element 18. Therefore, the magnetic fields of the permanent magnets 16a to 16d applied to the Hall element 18 can be strengthened,
The measurement sensitivity of the magnetic fluid type acceleration sensor 10 can be improved. In addition, the hall element 18 and the permanent magnets 16a ...
Since the magnetic fluids 17a to 17d do not enter between the magnetic fluids 17a to 17d and the permanent magnet 1d.
A magnetic elastic force is applied to the end portions 16a _{-1 to} 16d _-1 of 6a to 16d. That is, the magnetic fluids 17a to 17
Since the magnetic elastic force of d acts only on the one ends 16a _{-1 to} 16d _-1 of the permanent magnets 16a to 16d, the permanent magnets 16a to 16d are the magnetic fluid acceleration sensor 1
It is displaced with a high responsiveness to the acceleration applied to 0, which also improves the measurement sensitivity.

FIG. 4 is a diagram showing a comparison between the Hall element output of the magnetic fluid acceleration sensor 10 according to the present invention and the Hall element output of the conventional magnetic fluid acceleration sensor when the same acceleration is applied. As shown in the figure, the Hall element output of the magnetic fluid acceleration sensor 10 according to the present invention is about three times as large as the Hall element output of the conventional magnetic fluid acceleration sensor. It is understood that the sensor 10 can improve the measurement sensitivity.

Further, since the magnetic fluid acceleration sensor 10 has a structure in which the magnets 17a to 17d are provided only around the one ends 16a- _{1 to} 16d- ₁ of the permanent magnets 16a to 16d, the conventional magnets floating in the magnetic fluid are used. The amount of the magnetic fluids 17a to 17d used can be reduced as compared with the magnetic fluid acceleration sensor having the configuration, and the cost of the magnetic fluid acceleration sensor 10 can be reduced. Along with this, the vacuum filling work of magnetic fluid in the housing, which was conventionally required, becomes unnecessary,
Assembling work of the magnetic fluid acceleration sensor 10 can be facilitated.

Further, in the conventional magnetic fluid acceleration sensor, when a strong magnetic force is desired, as shown in FIG. 7, four anisotropic magnets 5a to 5d are attached to each other and used as a ring shape. The arrow in the figure (A) indicates magnetic orientation). This configuration has a special shape, and the magnets 5a ...
A large number of steps are required for processing and adhering 5d, so that the product cost increases. However, since the magnetic fluid acceleration sensor 10 uses the rod-shaped permanent magnets 16a to 16d having a simple shape, it is possible to reduce the cost required to create the permanent magnets 16a to 16d, and eventually the magnetic fluid acceleration sensor 10 can be manufactured. Product cost can be reduced.

Although the flow-in prevention member 19 is provided near the position where the permanent magnets 16a to 16d face the hall element 18 in the above-described embodiment, the position of the flow-in prevention member is limited to this. However, the magnetic fluid may be arranged at another position as long as it can prevent the magnetic fluid from flowing into a position facing each Hall element of each permanent magnet. A configuration to be installed can be considered.

[0037]

As described above, according to the present invention, by providing the inflow prevention member for preventing the magnetic fluid from flowing into the position where the magnet and the magnetic detection sensor face each other, the magnetic fluid is provided between the magnet and the magnetic detection sensor. Since the fluid does not exist, the magnetic elastic force does not act between the two, the magnet is displaced with a high response in response to the applied acceleration, and the magnetic force between the magnet and the magnetic detection sensor is high. Since there is no fluid, it is possible to dispose the magnet and the magnetic detection sensor in proximity to each other, and thus it is possible to improve the measurement sensitivity of the magnetic fluid type acceleration sensor.

[Brief description of drawings]

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

FIG. 2 is a vertical sectional view of a magnetic fluid acceleration sensor according to an embodiment of the present invention.

FIG. 3 is an enlarged perspective view showing a flow-in prevention member.

FIG. 4 is a diagram showing the Hall element output of the magnetic fluid acceleration sensor according to the present invention in comparison with the Hall element output of the conventional magnetic fluid acceleration sensor.

FIG. 5 is a diagram for explaining a measurement principle of a conventional magnetic fluid acceleration sensor.

FIG. 6 is a diagram showing an example of a conventional magnetic fluid acceleration sensor.

FIG. 7 is a diagram for explaining an example of a permanent magnet used in a conventional magnetic fluid acceleration sensor.

[Explanation of symbols]

 10 Magnetic Fluid Acceleration Sensor 11 Housing 12 Main Housing 13 Sub Housing 14a to 14d Magnet Storage Section 15 Hall Element Storage Section 16a to 16d Permanent Magnet 17a to 17d Magnetic Fluid 18 Hall Element 19 Inflow Prevention Member 20a to 20d Insertion Hole

Claims (1)

[Claims] 1. A housing made of a non-magnetic material, a magnet disposed inside the housing and arranged to be displaced in response to an externally applied acceleration, and the magnet being displaced inside the housing. A magnetic fluid type acceleration sensor comprising: a magnetic fluid that is held as much as possible; and a magnetic detection sensor that is arranged so as to face the magnet and that generates an acceleration signal corresponding to the displacement of the magnet. The magnetic fluid is arranged at a position facing the magnetic sensor, and a flow-in prevention member for preventing the magnetic fluid from flowing into the facing position is provided near the facing position of the magnet facing the magnetic detection sensor. Characteristic magnetic fluid type acceleration sensor.