JPH06258336A - Acceleration sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an acceleration sensor that is small, lightweight, and capable of detecting acceleration with high accuracy. According to an acceleration sensor of the present invention, a transparent hollow sphere having a fine diameter, a liquid metal sphere having a finer diameter arranged freely inside the sphere, and a center of the sphere. It is characterized in that it is provided with a point light source and a multi-element photodetection element which are arranged outside the sphere which are symmetrical with respect to each other.

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 suitable for detecting gravitational acceleration.

[0002]

2. Description of the Related Art In recent years, it has become increasingly necessary to directly input human behavior data such as robotics and virtual reality into a computer for processing, but in order to realize this, the movement of each part of the human body is required. There is a need for sensors that detect without limitation.

Generally, in motion, acceleration is detected and velocity is calculated by integration of the acceleration, and position is calculated by double integration. Acceleration detection is highly accurate in order to reduce calculation error.
It is necessary to accurately detect the gravitational acceleration that always exists on the earth as a correction factor for the error.

In order to know the direction of gravity, there is widely known a spirit level in which a glass container containing a liquid is calibrated and the position of the liquid surface is visually inspected.

In order to take out an electrical signal based on this principle, a detection method is conceivable in which mercury is used as the working liquid and a large number of electrical contacts are provided in the container to detect the position of mercury.

However, in this method, since the number of contacts is large in order to detect the direction with high accuracy, the signal processing is complicated, and a quick response cannot be obtained due to the vibration of the liquid surface. It is only used as a fall switch for safety monitoring.

Further, conventionally, a small and lightweight sensor has been required for use in automobile collision detection and the like, for detecting displacement due to acceleration of an object supported by a spring as a change in electrostatic capacity, and a piezoelectric element. The one that detects the stress strain applied to the piezo-voltage is used.

Since all of them detect uniaxial acceleration, it is necessary to detect the absolute acceleration in the three-dimensional direction in order to detect the gravitational acceleration regardless of the arrangement of the sensors. It was necessary to use it in combination with three axes.

In the capacitance type accelerometer which detects the minute displacement due to acceleration as a capacitance change, the sensor part of the sensor part Since the impedance is capacitive and high, it is weak against external noise, and there are drawbacks that the connection distance to the detection circuit is limited and there are many restrictions.

[0010]

As described above, there has been no acceleration sensor capable of detecting acceleration with high precision and small size in the past, and it is an urgent task to realize it.

Therefore, the present invention has been made in view of the above points, and an object thereof is to provide an acceleration sensor which is small in size and light in weight and capable of detecting acceleration with high accuracy.

[0012]

According to the present invention, a transparent hollow sphere having a fine diameter, a liquid metal sphere having a finer diameter disposed inside the sphere so as to be freely floated, There is provided an acceleration sensor comprising a point light source and a multi-element photodetection element arranged at a position outside the sphere that is symmetrical with respect to the center of the sphere.

Further, according to the present invention, there is provided an acceleration sensor characterized by further comprising a conductive transparent film attached to the transparent hollow spherical inner surface.

[0014]

As described in the above means for solving the problems, the present invention can realize a small, lightweight and highly accurate acceleration sensor by utilizing fine processing.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

1 (a) and 2 are views showing the basic structure of the present invention, in which 1 is a liquid metal sphere arranged inside a hollow sphere 2, 2 is a transparent hollow sphere having a fine diameter, Three
a and 3b are lenses, 4a and 4b are point light sources such as LEDs, and 5
Reference numerals a and 5b denote multi-element photodetectors, which are circular photodetection elements divided into quadrants in this embodiment.

Reference numeral 6 is a case structure for connecting the above-mentioned respective basic elements 1-5.

As shown in the sectional view of FIG. 2, two sets of point light sources 4a and 4b and multi-element photodetectors 5a and 5b symmetrically opposed to the center of the transparent hollow sphere 2 are arranged orthogonally. The light from the point light sources 4a and 4b shielded by the liquid metal sphere 1 appears as shadows on the surfaces of the two multi-element photodetection elements 5a and 5b.

Light from the point light sources 4a and 4b is reflected by the lenses 3a and 3b.
At b, the light becomes almost parallel and passes through the hollow sphere 2.

It is well known that if the shell of the hollow sphere 2 has a uniform thickness, the light remains parallel inside the sphere 2, and there is a liquid metal sphere 1 as a light shield inside. Therefore, the shadow is projected on the opposing multi-element photodetectors 5a and 5b.

In this embodiment, the diameter of the hollow sphere 2 is 100 μm.
m or less.

When the liquid metal introduced therein has a small leak property with the material of the housing, it tends to become a shape having the smallest surface area as compared with the volume, that is, a sphere due to its own surface tension.

In this case, the liquid metal is not actually a perfect sphere but is deformed into a flat shape as shown in FIG. 3 by acceleration, and the hollow sphere 2 has the lowest potential. That is, it is located in the acceleration direction when viewed from the center of the sphere 2.

As described above, the liquid metal sphere 1 is deformed by the acceleration, but the acceleration is always applied in the direction of the center of mass of the sphere. Therefore, the liquid metal is compressed from the sphere only in the radial direction of the spherical housing, and is flatly rotated. It transforms into an ellipsoid and becomes a larger circle on the plane.

By transforming the shape into a shape that can be described by two parameters of the radius and thickness of this circle, the magnitude and direction of the acceleration can be determined from the two images projected on the multi-element photodetectors 5a and 5b which are orthogonal to each other. It can be measured at the same time.

When the liquid metal sphere 1 in the hollow sphere 2 is forcibly moved from a stable position, it acts as a kind of rolling pendulum, so that its free vibration period T has a radius of the liquid metal sphere 1 R , T = 2π (meL / mg) ^0.5 where R ′ is the radius of the hollow sphere 2, gravitational acceleration is g, and the mass of the liquid metal sphere 1 is m, where L = R′−R, me: equivalent mass = 7 m / Since it is expressed as 5 (homogeneous sphere), a free vibration frequency of about 40 Hz can be obtained at L <50 μm.

Since there are various resistances in practice, even when the position of the liquid metal sphere 1 is changed by changing the angle of the sensor, for example, as shown in FIG. The sphere 1 moves to perform damping vibration around the next stable position II, and finally settles at a predetermined stable position.

Usually, the human action frequency is as short as several Hz or less, and it can be said that this sensor has a sufficient band.

It is well known that detection can be performed in a band close to the above free vibration frequency by giving appropriate damping, and the mass of the liquid metal sphere 1 can be reduced to effectively increase the air resistance or the hollow sphere 2. It can be adjusted by forming an oil film on the inner surface of the.

FIG. 4 exemplifies the relationship between the shape of the shadow detected on the multi-element photodetectors 5a and 5b and the position of the liquid metal sphere 1 or the acceleration acting on the liquid metal. If the downward direction of the figure is the direction of the gravity field, it is normally
The arrangement is as shown in (a).

At this time, the shadow on the multi-element photo-detecting element 5a is in a centrally symmetric position, and the shadow on the multi-element photo-detecting element 5b is unidirectionally displaced.

When the sensor is tilted, or when acceleration is applied to the liquid metal sphere 1 and the direction of the acceleration vector applied to the liquid metal sphere is changed, the shadow moves in the moving direction of the liquid metal sphere 1.

FIG. 4 (b) shows a case where the liquid metal sphere 1 is located right next to the hollow sphere 2.

By thus comparing the amounts of light detected by the multi-element photodetectors 5a and 5b, the position of the liquid metal sphere 1 and the acceleration direction acting on the liquid metal sphere can be easily detected.

FIG. 4 (c) shows the case where the liquid metal sphere 1 is directly above the hollow sphere 2 having the opposite positional relationship to that of FIG. 4 (a).

Although it is possible to widen the detection band by making the whole system small in size, on the other hand, since the hollow sphere 2 uses glass or plastic having high insulation in order to make the hollow sphere transparent, The fine liquid metal spheres 1 may stick to the sphere wall due to static electricity, and the above operation may not be performed reliably.

Therefore, in the present invention, in order to solve this,
An ITO (transparent oxide conductive) film is formed inside the hollow sphere 2 to prevent charging.

In order to form the cross-sectional structure shown in FIG. 2, a hemisphere that divides the hollow sphere 2 into two halves may be assembled into a cylindrical assembly guide (not shown) and then bonded.

At this time, IT is applied to the inner surface and the bisector of the hemisphere.
For depositing the O film, a widely used technique such as ECR sputtering and vacuum deposition can be used as it is.

Since the inside of the hollow sphere can be electrically conducted to the outside by attaching the ITO film and then inserting the liquid metal sphere and adhering the liquid sphere, it is possible to easily prevent the static electricity inside, and Even in the case of the present invention using liquid metal balls, there is no possibility of malfunction due to static electricity.

There are various methods for forming a hemisphere, but the simplest method is to obtain a thin plate of glass, plastic, etc. by press molding with an anvil having a curvature of several tens of μm.

[0042]

As described above, according to the present invention, therefore, there is an advantage that a highly accurate acceleration sensor can be constructed in a small size, a light weight and a low cost.

[Brief description of drawings]

FIG. 1 is a perspective view and an output waveform diagram of a main part showing an embodiment of the present invention.

FIG. 2 is a sectional view showing an embodiment of the present invention.

FIG. 3 is a diagram showing a deformed state of a liquid metal sphere used in one embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the embodiment of the present invention.

[Explanation of symbols]

 1 ... Liquid metal sphere, 2 ... Hollow sphere, 3a, 3b ... Lens, 4a, 4b ... Point light source, 5a, 5b ... Multi-element photodetector, 6 ... Case structure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyo Itao Nihonhon Telegraph and Telephone Corporation, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo

Claims (2)

[Claims] 1. A transparent hollow sphere having a fine diameter, a liquid metal sphere having a finer diameter, which is rotatably disposed inside the sphere, and symmetrical with respect to the center of the sphere. An acceleration sensor comprising a point light source and a multi-element light detection element arranged at a position outside the sphere. 2. A conductive transparent film attached to the inner surface of the transparent hollow sphere.
The acceleration sensor according to.