JPH0674965A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide a compact and lightweight acceleration sensor having high reliability and environmental compatibility by using the dynamics amount sensitivity of magnetic fluid, and also the the interaction of magnetism and light for a detecting section. CONSTITUTION:This sensor has magnetic fluid 1 movably housed in a case 2, magnets 3 and 4 laid in such a way as clamping the fluid 1 and giving a magnetic field gradient in the movable direction of the fluid 1, an illuminant for projecting light, and the first deflection plate 6 laid between the illuminant 5 and fluid 1. In addition, the sensor is provided with an analyzer 10 for detecting light intensity, the second deflection plate 8 laid between the fluid 1 and the analyzer 10, and having a deflection plane roughly orthogonal with the deflection plane of the first deflection plate 6, and an acceleration computation means to calculate acceleration from the output of the analyzer 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to a small and lightweight acceleration sensor used for attitude control and motion control in a moving body such as an automobile.

[0002]

2. Description of the Related Art An acceleration sensor for detecting an applied acceleration based on the amount of movement of a magnetic fluid has no mechanically movable parts or supporting parts as its characteristic. Therefore, the reliability of acceleration detection is improved and the structure thereof is improved. Can be made smaller and lighter. As such an example, Japanese Patent Laid-Open No. 60-1333
There is number 70.

Japanese Unexamined Patent Publication (Kokai) No. 60-133370 discloses a device in which the displacement of a magnetic fluid due to acceleration is detected by a differential transformer or a magnetic generation coil. There is also a structure in which detection is performed by a magnetic detection element (hall element, magnetic resistance element). However, the configuration in which these magnetic changes are detected as they are is likely to be affected by an external magnetic field or an external electromagnetic wave, and is difficult to use in a poor electromagnetic environment.

Japanese Utility Model Laid-Open No. 1-180664 discloses a conventional metal strain gauge that detects a displacement of a plate member due to movement of a magnetic fluid due to acceleration without detecting a magnetic change. Here, a magnetic fluid is used for temperature compensation. However, the detection of the displacement of the plate member by the metal strain gauge has a problem in terms of reliability and reduction in size and weight as described above.

On the other hand, as an acceleration sensor using light, there is a sensor which detects displacement of a light source in a viscous liquid by an optical position detecting device, as in Japanese Utility Model Laid-Open No. 63-150376. However, similar to the above, there are problems in terms of reliability and reduction in size and weight.

[0006]

DISCLOSURE OF THE INVENTION The present invention uses a mechanical quantity sensitivity of a magnetic fluid and an interaction of magnetism and light in a detection part, so that the acceleration sensor has high reliability and environmental resistance, and is small and lightweight. I will provide a.

[0007]

In order to solve this problem, the acceleration sensor of the present invention has a magnetic fluid arranged so as to be movable in the acceleration direction and a gradient of magnetic field orientation density in the acceleration direction. A magnetic field applying means for applying an external magnetic field to the magnetic fluid, a light incident means for making light linearly polarized in a direction substantially perpendicular to the magnetic field of the magnetic fluid enter the magnetic fluid, and an output after passing through the magnetic fluid. A light detection unit that detects the emitted light and an acceleration calculation unit that calculates the acceleration from the detected change in the emitted light are provided. Here, the light detecting unit includes a separating unit that separates the light having a polarization plane different from the polarization plane of the incident light from the emitted light, and a light intensity detecting unit that detects the intensity of the light having the separated polarization plane. .

Further, the acceleration sensor of the present invention comprises a magnetic fluid movably housed in a case, and a magnet which is disposed so as to sandwich the magnetic fluid and which gives a magnetic field gradient in the movable direction of the magnetic fluid. A light source for injecting light, a first polarizing plate arranged between the light source and the magnetic fluid, an analyzer for detecting light intensity, and arranged between the magnetic fluid and the analyzer, A second polarization plate having a polarization plane substantially orthogonal to the polarization plane of the first polarization plate, and an acceleration calculation means for calculating acceleration from the output of the analyzer are provided. Here, the acceleration calculating means includes a table that stores the relationship between the light intensity detected by the analyzer and the acceleration.

[0009]

First, the measurement principle of the acceleration sensor of the present invention will be briefly described. In the present invention, an external magnetic field is applied to the magnetic fluid so that a magnetic gradient can be created, and a gradient is given to the magnetic field orientation density of the magnetic fluid. A magnetic fluid to which a magnetic field is applied has a property of causing a birefringent action on the light depending on the strength of the magnetic field when the light having a plane of polarization perpendicular to the magnetic field is transmitted. When light whose angle of polarization deviates from the direction of the magnetic field is transmitted, the transmitted light becomes elliptically polarized light due to the magneto-optical effect (birefringence). The ellipticity of this elliptically polarized light changes according to the strength of the magnetic field. Therefore, when acceleration is applied, the magnetic fluid moves, the strength of the magnetic field applied to the magnetic fluid changes corresponding to the magnetic gradient of the external magnetic field, and the elliptically polarized state of the transmitted light changes. The acceleration can be measured by transmitting the elliptically polarized transmitted light through a polarizing plate arranged at a specific angle and detecting the light intensity thereof.

An embodiment of the acceleration sensor of the present invention will be described below. FIG. 1 is a schematic configuration diagram of the acceleration sensor of this embodiment as viewed from the side. A magnetic fluid 1 in which fine particles of a ferromagnetic material (particle diameter of 100 Å or less made of magnetite or the like) is uniformly dispersed in a solvent is enclosed in a hollow structure 2. Ferromagnetic magnets 3 and 4 for applying an external magnetic field having a magnetic field gradient are arranged in the vertical position of the hollow structure 2. In this example, the ferromagnetic magnets 3 and 4 have a symmetrical structure with the tip as a boundary, and an intensity gradient is generated with the center as a boundary. Then, the magnetic fluid is positioned at this central portion. Further, the magnetic field generated by the ferromagnetic magnets 3 and 4 has such a magnitude that the magnetic fluid 1 does not deviate from the magnetic field even at the maximum acceleration measured by the acceleration sensor.

On the other hand, at one end of the hollow structure 2, the light emitting element 5 is provided.
(Semiconductor laser, LDE), collimating lens 6,
A polarizing plate 7 for converting the light into linearly polarized light is provided. At the other end, a polarizing plate 8 for taking out the degree of modulation of the elliptically polarized light of the light transmitted through the magnetic fluid 1, a collimating lens 9,
A photodetector 10 (photodiode or the like) is provided. The light emitting element 5 is provided with light generating means 11, and the photodetector 10 is provided with a signal amplifier 12. Although not shown, the output value of the signal amplifier 12 is AD-converted and converted into an acceleration value from the relationship between the light intensity and the acceleration shown in FIG. 3 below.

An example of the operation of the acceleration sensor of the above embodiment will be described below with reference to the schematic view of the plane of polarization of light at each part of the acceleration sensor shown in FIG. In FIG. 2, the upper and lower sides are magnetic field directions, and the front and rear sides of the drawing are acceleration directions. For example, as shown in FIG. 2A, when light linearly polarized in the direction of 45 ° from the direction of the bias magnetic field of the magnet by the polarizing plate 7 is incident on the magnetic fluid 1, when acceleration is not applied, The light passes through the magnetic fluid 1 and is emitted as elliptically polarized light as shown in FIG. From this light, a component of the polarization plane perpendicular to the incident light as shown in FIG. 2C is provided by the polarization plate 8 (in this example, the polarization plane of the polarization plate 7 is shifted by 90 °). Only the light is taken out, is incident on the photodetector 12, and is output as the light intensity.

When acceleration is applied to the acceleration sensor in the left-right direction in FIG. 1, the magnetic fluid 1 moves to a point where the applied acceleration and the attractive force of the bias magnetic field are in equilibrium. This movement changes the strength of the magnetic field applied to the magnetic fluid 1 and changes the magnetized state. The linearly polarized wave (see (a) of FIG. 2) by the polarizing plate 7 that passes through the magnetic fluid 1 is
The degree of elliptically polarized light depending on the magnetized state is, for example, as shown in FIG.
2 (d), the intensity of light emitted from the polarizing plate 8 is uniquely determined according to the amount of movement of the magnetic fluid 1 due to acceleration as shown in FIG. 2 (e).

FIG. 3 shows the relationship between the light intensity detected in this embodiment and the magnitude of acceleration. This is preferably measured in advance and stored in a table (map) or the like.
Furthermore, it is more preferable if it is updated (learning function) in consideration of changes over time. In this embodiment, linearly polarized light that is inclined by 45 ° with respect to the magnetic field direction is incident, but it does not have to coincide with the magnetic field direction in practice. Further, on the detection side, polarization perpendicular to the incident is performed, but this is because the accuracy can be improved because the change in the perpendicular direction is large, and this is not limited.

As described above, since the acceleration is measured by the elliptically polarized light in the magnetic field of the deflecting surface of the light, like the conventional acceleration sensor which detects the acceleration by the moving amount of the magnetic fluid,
It can be used even under a bad electromagnetic environment such as in a car without being affected by an external magnetic field or an external electromagnetic wave. Further, since the detection is based on the change of the deflection surface of the light,
Highly accurate detection is possible.

[0016]

According to the present invention, a small and lightweight acceleration sensor with high reliability and high environmental resistance is provided by using the interaction between magnetism and light in the detection part and the dynamic quantity sensitivity of magnetic fluid. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an acceleration sensor according to a present embodiment as viewed from a side surface.

FIG. 2 is a diagram schematically showing polarization planes of light at respective points of the acceleration sensor of this embodiment.

FIG. 3 is a diagram showing the relationship between the light intensity and the magnitude of acceleration in the acceleration sensor of this embodiment.

[Explanation of symbols]

1 ... Magnetic fluid, 2 ... Hollow structure, 3, 4 ... Ferromagnetic magnet,
5 ... Light emitting element, 6 ... Collimating lens, 7 ... Polarizing plate for making light linearly polarized light, 8 ... Polarizing plate for taking out degree of modulation of elliptically polarized light, 9 ... Collimating lens, 10 ...
Photodetector, 11 ... Light generating means, 12 ... Signal amplifier

Claims (4)

[Claims] 1. A magnetic fluid movably arranged in an acceleration direction, and a magnetic field orientation density gradient in the acceleration direction,
Magnetic field applying means for applying an external magnetic field to the magnetic fluid, light incident means for making light linearly polarized in a direction substantially perpendicular to the magnetic field of the magnetic fluid enter the magnetic fluid, and outgoing light after passing through the magnetic fluid. An acceleration sensor, comprising: a light detection unit that detects the acceleration and an acceleration calculation unit that calculates the acceleration from the detected change in the emitted light. 2. The separation means for separating the light having a polarization plane different from the polarization plane of the incident light from the emitted light,
The acceleration sensor according to claim 1, further comprising: a light intensity detection unit that detects the intensity of the separated light on the polarization plane. 3. A magnetic fluid movably housed in a case, a magnet arranged to sandwich the magnetic fluid, and a magnetic field gradient in a movable direction of the magnetic fluid, and a magnet for injecting light. A light source, a first polarizing plate disposed between the light source and the magnetic fluid, an analyzer for detecting light intensity, and a polarization of the first polarizing plate disposed between the magnetic fluid and the analyzer. An acceleration sensor comprising: a second polarizing plate having a polarization plane that is substantially orthogonal to the plane; and an acceleration calculation unit that calculates acceleration from the output of the analyzer. 4. The acceleration sensor according to claim 3, wherein the acceleration calculation means includes a table that stores the relationship between the light intensity detected by the analyzer and the acceleration.