JPH0452704Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention uses the reflected light obtained by irradiating a part of the laser beam onto the mirror surface of the gravity detection parallel rod, and the reference light obtained from a part of the laser beam. This invention relates to a gravimeter that detects displacement of gravity by making it incident on a dry plate to generate interference fringes.

(b) Conventional technology Conventional gravimeters have various structures. Typical devices currently in use are so-called spring gravimeters, which suspend a weight from a spring and measure the expansion and contraction of the spring depending on the magnitude of gravity, and normal light (light naturally emitted from a light source). This is a so-called optical lever gravimeter, etc., which illuminates a gravity detection parallel rod, receives the reflected light with a light receiving plate, and measures the displacement of gravity based on the change in the width of the reflected light.

Both gravimeters are instruments that measure the value of gravity using a static method, and are capable of measuring displacement of gravity with a certain degree of accuracy.

(c) Problems to be solved by the invention All of the conventional gravimeters mentioned above have the disadvantage of not being able to accurately measure minute changes in gravity.

For example, in the former spring method, the expansion and contraction of the spring is measured electrically in response to changes in the magnitude of gravity, but since the expansion and contraction of the spring is mechanical, the expansion and contraction are minute. may not be exactly proportional to the change in gravity,
There was a limit to the resolution of minute changes in gravity. Also,
In the case of the latter optical lever method, changes in the magnitude of gravity are detected by the displacement of the width of the reflected light from a normal single light (light naturally emitted from a light source), so the deflection of the gravity detection parallel rod is If the difference is small, there is a possibility that the width of the reflected light will not change. In other words, there was a limit to the accuracy of reading the width of the reflected light, and there was a disadvantage that minute changes in gravity could not be detected accurately.

This idea solves the above problems,
It is an object of the present invention to provide a gravimeter that has high reading accuracy and can accurately measure minute changes in gravity.

(d) Means and action for solving the problem In order to achieve this purpose, the gravimeter of this invention has the following configuration.

The gravimeter consists of a gravity detection parallel rod whose one end is fixed to a fixed plate spring and whose other end has a mirror surface, and a laser that irradiates the mirror surface of the gravity detection parallel rod with a laser beam via a half mirror. , a reference light extraction means for extracting a part of the laser light irradiated by the laser as a reference light through the half mirror, and a reference light extraction means for receiving the laser reflected light reflected by the mirror surface of the gravity detection parallel rod and the reference light. The apparatus includes means for forming interference fringes and means for imaging the interference fringes.

In a gravimeter with such a configuration, a highly coherent laser beam is used to detect gravity changes, and the reflected light reflected on the mirror surface of the gravity detection parallel rod and the reference light (directly irradiated by the laser) are used to detect changes in gravity. The light) forms interference fringes, or holograms, on the surface of the dry plate, and converts these interference fringes into electrical signals.
Gravity is measured from the change in spacing.

When the gravity detection parallel rod is tilted and displaced due to a change in the magnitude of gravity, the difference in the phase of the reflected light appears as a change in the fringe spacing of the interference fringes (bright and dark fringes) on the dry plate. In other words,
The displacement of the gravity detection parallel rod, which is the subject, is detected as a difference in brightness (fringe spacing) among the varying interference fringes. Therefore, this fringe interval (frequency of interference fringes) corresponds equally to the vibration period of the gravity detection parallel rod, and by converting the displacement of the fringe interval into a change in electrical signal using the imaging means, the gravity detection parallel rod This can be read as the displacement of the rod, that is, the change in gravity.

(E) Embodiment FIG. 1 is a diagram explaining the principle of a specific embodiment of the gravimeter according to this invention.

The gravimeter includes a leaf spring 1, a gravity detection parallel rod 2 whose base end is fixed to one end of the leaf spring 1, a laser 3 facing the gravity detection parallel rod 2 and arranged at a certain angle, It consists of a dry plate 4 and a reference light extraction means 7.

The leaf spring 1 has its base end fixed to a proper position in the instrument housing 5 and is held horizontally. Further, the gravity detection parallel rod 2 is held horizontally with its base end fixed to the tip of the leaf spring 1 and the other end left as a free end. This gravity detection parallel rod 2 is equipped with a certain gravitational mass (weight), and a reflecting mirror (mirror surface) 21 is provided at the tip.

A half mirror 6 is provided with a predetermined distance between the mirror surface 21 of the gravity detection parallel rod 2 and the laser 3.
and an optical lens 8 are provided so that a portion of the laser light emitted from the laser 3 passes through the half mirror 6, is reflected by the mirror surface 21, and this reflected light is set to enter the dry plate 4. Further, on the opposite side of the dry plate 4, a reference light extraction means 7 is provided. This reference light extraction means 7 includes a mirror 71 and an optical attenuator 72 on the opposite side of the half mirror 6.
and reference mirrors 73 are arranged at regular intervals, a part of the laser beam (direct light) refracted by the half mirror 6 is received by the mirror 71 via the optical lens 74, and this direct light is transmitted to the optical attenuator 72 and the reference mirror 73. The reference light is set to be incident on the dry plate 4 via the reference mirror 73.

As the dry plate 4, a photographic plate with particularly good resolution is used that can record extremely dense patterns of interference fringes.
Further, the dry plate 4 is connected with an image sensor 41 that images the recorded interference fringes (hologram).

In a gravimeter having such a configuration, the gravity detection parallel rod 2 is normally held horizontally, and a part of the laser beam irradiated by the laser 3 passes through the half mirror 6 and reaches the gravity detection parallel rod. 2
The light is reflected by the mirror surface 21 and enters the dry plate 4 as reflected light. On the other hand, the other part of the laser beam is
It is refracted by the half mirror 6, and this refracted light (direct light) enters the dry plate 4 via the mirror 71 and the reference mirror 73 as a reference light. Then, on the upper surface of the dry plate 4, interference fringes (bright and dark fringes of light) in which the reflected light and the reference light interfere, that is, a hologram is recorded.

Now, if a change in the magnitude of gravity occurs, the gravity detection parallel rod 2 will tilt slightly in the vertical direction (up and down direction). At this time, the phase of the laser reflected light that is irradiated onto the mirror surface 21 and reflected changes. This causes a change in the distance between interference fringes created by the reflected light and the reference light. The interval between the interference fringes, that is, the change in the interference fringes, corresponds equally to the vibration of the gravity detection parallel rod that is displaced due to changes in gravity. Therefore, dry plate 4
By forming a large number of interference fringes with various fringe intervals over a constant in-plane width, changes in the magnitude of gravity can be detected with extremely high resolution. Changes in the magnitude of gravity are determined by reading the interval between these interference fringes as light intensity using the image sensor 41.
converted into an electrical signal. Gravity is then measured from this electrical signal.

(f) Effects of the device As described above, in this device, a part of the laser beam emitted from the laser is irradiated onto the gravity detection parallel rod, this reflected light is made incident on the dry plate, and the other part of the laser beam is is incident on the dry plate as a reference light,
We decided to form interference fringes on the dry plate using the reflected light and the reference light, and convert these into electrical signals using the imaging means, so that when the gravity detection parallel rod is tilted and displaced due to fluctuations in gravity, the spacing of the interference fringes can be adjusted. The width changes. By reading the displacement of the interval between these interference fringes,
It has excellent effects that achieve the purpose of its invention, such as being able to detect minute changes in gravity extremely accurately.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of the example gravimeter. 1...Plate spring, 2...Gravity detection parallel rod, 3...
Laser, 4...Dry plate, 6...Half mirror, 7...
...Reference light extraction means.

Claims (1)

[Scope of utility model registration request] A gravity detection parallel rod whose one end is fixed to a fixed plate spring and whose other end has a mirror surface, a laser that irradiates the mirror surface of the gravity detection parallel rod with a laser beam via a half mirror, and a reference light extracting means for extracting a part of the irradiated laser light as a reference light through the half mirror; and receiving the laser reflected light reflected by the mirror surface of the gravity detection parallel rod and the reference light to form interference fringes. A gravimeter comprising: a means for imaging the interference fringes; and a means for imaging the interference fringes.