JPS61159613A - Reflecting curved mirror - Google Patents

Abstract

PURPOSE:To obtain a lightweight, small-sized reflecting curved mirror which is variable in focal length by spreading a flexible film which reflects an electromagnetic wave in a circular opening formed in liquid-tight container, and adjusting the pressure in the container. CONSTITUTION:The circular opening 2 is formed at the upper end of the container 1 formed by coupling, for example, a short cylindrical side wall 1a and a bottom plate 1b airtightly with each other, and the flexible discoid film 3 is fixed to the container 1 so that the opening 2 is sealed hermetically. This film 3 has a reflecting surface 3a which reflects an electromagnetic wave. Then, the pressure in the airtight space 4 formed of the container 1 and flexible film 3 in the container is adjusted by a pressure adjusting means 5.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a reflective curved mirror such as a concave mirror or a convex mirror for converging or diverging electromagnetic waves such as light and radio waves, particularly in outer space. This invention relates to a reflective curved mirror suitable for use in.

(Prior art) Reflecting curved mirrors such as concave mirrors and convex mirrors are used in many fields in various sizes, from optical devices such as cameras and W4 microscopes to solar heat collectors and radio telescope antennas. has been done. Such reflective curved mirrors are usually made by polishing a block of glass or metal or by injection molding plastic to form a required curved surface such as a paraboloid of revolution.
It is manufactured by coating its surface with a thin layer of metal or dielectric material that reflects electromagnetic waves such as light and radio waves.

By the way, with the development of artificial satellites in recent years, exploration and observation from outer space have become widespread. For such exploration and observation, it is essential to install reflective curved mirrors, especially concave mirrors, on artificial satellites. Conventionally, concave mirrors manufactured by the method described above have been used for this purpose.

(Problems to be Solved by the Invention) However, the reflective curved mirror manufactured by the method described above has a problem in that it inevitably becomes heavy due to its large wall thickness. the result,
Due to the limitations of the launch vehicle's loading capacity, it is not possible to mount large-diameter reflective curved mirrors on artificial satellites.9 For example, a laser beam is emitted from an artificial satellite toward the earth, and the reflected light is It is thought that the degree of pollution in the atmosphere can be investigated by observing the radio waves, but for this purpose, it is necessary to carry a large-diameter concave mirror on the satellite, so such observation is currently not possible. has become almost impossible.

Furthermore, it is desired that curved reflecting mirrors used on the ground be as light as possible from the viewpoint of transportation and assembly.

Furthermore, in the conventional method of polishing a block of glass, metal, etc. to form a necessary curved surface, there is a problem that the process is complicated and requires skill.

In addition, even if plastic is injection molded, there are similar problems in manufacturing the mold, and the cost ends up being high.The cost increases geometrically as the diameter of the reflective curved mirror increases. do. In the curved reflecting mirror manufactured in this way, it was completely impossible to adjust the focal length.

The present invention has been made in view of these circumstances, and its purpose is to provide a reflective curved mirror that is lightweight, inexpensive, and whose focal length can be changed.

(Means for solving the problem) In order to achieve this object, the present invention provides a flexible membrane stretched over a circular opening provided in a fluid-tight container to reduce the pressure inside the container. I'm trying to make adjustments. The film is said to be able to reflect electromagnetic waves.

(Function) With this configuration, for example, when the pressure inside the container is lower than the outside pressure, the flexible membrane bends inward and curves. Therefore, if electromagnetic waves are reflected by the outer surface of the film, a concave mirror can be obtained. Furthermore, when the pressure inside the container is made greater than the pressure outside, the flexible membrane bends outward and curves, so that the outer surface of the membrane forms a convex mirror.

Here, we will theoretically consider the deflection of the membrane.

As shown in Figure 4, the radius a with a fixed peripheral part
Consider a situation in which a uniformly distributed load p acts on an isotropic thin disk. Then, the deflection W of this disk is expressed by the distance r from the center of the disk as follows.

Here, D is the bending rigidity of the thin plate.

As is clear from this equation, the deflection W of the disk becomes a quartic curved surface with respect to r. In a region where r is smaller than a, that is, near the center of the disk, the fourth-order term is sufficiently smaller than other terms and can be ignored.

Therefore, due to the uniformly distributed load p, the disk is bent so that the vicinity of the center portion approximately forms a paraboloid of revolution.

The thickness of the deflection W, that is, the focal length of the paraboloid of rotation, changes depending on the magnitude of the load P.

When the membrane is bent due to the pressure difference between the inside and outside of the container, the direction in which the force acts is the normal direction of the membrane, and the elongation of the membrane must also be taken into consideration, so strictly speaking, the above theoretical formula is It will be different. However, when the deflection is small, the theoretical formula provides a sufficient approximation.

Thus, it can be seen that by creating a pressure difference between the inside and outside of the container, the membrane is deflected to almost form a paraboloid of revolution. Therefore, by reflecting electromagnetic waves using the film, it is possible to obtain a concave mirror that focuses the electromagnetic waves to a single point or a convex mirror that diverges the electromagnetic waves. The focal length can be adjusted by adjusting the pressure inside the container.

(Example) Hereinafter, the present invention will be described in detail based on the drawings.

1.2 shows an embodiment of a reflecting curved mirror according to the present invention, FIG. 1 is a perspective view thereof, and FIG. 2 is a longitudinal sectional view thereof.

As is clear from these figures, the container 1 has a short cylindrical side wall 1a and a bottom plate 1b that are airtightly connected, and a circular opening 2 is formed at the upper end. The opening 2 is hermetically sealed by a flexible disc-shaped membrane 3 whose periphery is fixed to the container l. This l! i3 is Teflon membrane, vinyl membrane, polyethylene I! By coating the outer surface of a flexible thin film such as i with aluminum foil or depositing aluminum, the reflective surface 3
a, and is fixed to the container 1 so that its reflective surface 3a becomes the -E surface.

In this way, an airtight space 4 is formed inside the container 1 by the container 1 and the flexible membrane 3.
The pressure inside is adjusted by pressure adjustment means 5. This pressure adjustment means 5 is connected to the side wall 1a of the container l.
It consists of a valve 7 that can open and close the air passage 6 provided in the space 4, and a pump 8 that can exhaust the air in the space 4. By closing the valve 7, the pressure in the space 4 is maintained constant. It looks like this.

In the reflecting curved mirror configured in this way, when the valve 7 is opened and the pump 8 is operated, the air in the space 4 is exhausted and the pressure inside the container 1 is lowered than the outside pressure. As a result, a pressure difference is generated between the front and back sides of the lug 3, and the membrane 3 is bent inward, and the reflective surface 3a on the outer surface thereof almost forms a paraboloid of revolution. Therefore, when electromagnetic waves such as light are incident on this curved mirror from above, the electromagnetic waves are reflected by the reflecting surface 3a and converge to a single point. That is, it can be used as a concave mirror. Note that the outer periphery of the membrane 3 does not form a precise paraboloid of rotation, so the electromagnetic waves incident thereon are not necessarily focused on one point, but this is a particular problem if it is a condenser or the like that does not need to form an image. In addition, if the outer peripheral portion of 1113 is prevented from becoming the reflective surface 3a, image disturbance can be reduced.

When the focal point of the reflective surface 3a reaches a required position, the valve 7 is closed. This prevents air from flowing inside and outside the container 1, and keeps the shape of the membrane 3 constant.

FIG. 5 is a graph showing the results of an experiment on how much parallel light rays are focused by the concave mirror thus obtained. A concave mirror with a diameter of 14 cs was used in this experiment, and the pressure inside the container was adjusted so that the focal length was about 23 cs. Then, a sensor was placed at a distance g123 cm from the mirror surface, and it was measured how much the position where the spot light parallel to the mirror axis was reflected and projected deviated from the center.

As is clear from this experimental result, 3 points from the center of the concave mirror
．． The rays reflected within a range of up to 5 cm, ie half of the total diameter, are focused into a spot of approximately 0.31 diameter. According to a NASA report, it is said that it is practical to measure atmospheric conditions from space as long as it can collect light within a convergence angle of approximately 1 m radian. This means that it can be used effectively within half the range. The weight of the thus obtained concave mirror can be reduced to about 1/100 of that of conventional mirrors, so sufficient effects can be obtained even if the effective area is half.

By making it possible to supply air from the outside to the space 4 inside the container 1 using the pump 8, the pressure inside the container 1 can be made higher than that outside. Thereby, the membrane 3 can be deflected outward so that its reflective surface 3a forms a convex mirror. Therefore, a single reflecting curved mirror can be used as either a concave mirror or a convex mirror by simply increasing or decreasing the air pressure inside the container l, and its focal length can also be adjusted arbitrarily. .

In outer space, no pressure acts on the outer surface of the membrane 3, so a curved mirror like the one in the above embodiment cannot form a concave mirror in outer space.
Fig. 3 shows an embodiment in which a concave mirror can be obtained even in outer space.
Components similar to those of the embodiment shown in the figures are designated by the same reference numerals, and their explanations will be omitted.

As is clear from FIG. 3, in this embodiment, the container l has a cylindrical shape with openings 2 and 9 at both upper and lower ends. The second opening 9 is hermetically sealed by a transparent film 10 that allows electromagnetic waves to pass through. Further, the film 3 that seals the opening 2 at the upper end has a reflective surface 3b formed on its inner surface. Gas is supplied to the space 4 in the container 1 from a reservoir 11.
and valve 7 constitute pressure regulating means 5.

In the reflective curved mirror configured in this way, the reservoir 1
When gas is supplied from 1 into the container 1, the pressure causes the membrane 3 to curve outward.

Therefore, the reflective surface 3b formed on the inner surface of the film 3
becomes a concave paraboloid of revolution toward the bottom. Therefore, electromagnetic waves such as light that are incident on this curved mirror from below are transmitted through the transparent film 10 and reflected by the reflective surface 3b, so that they are focused on approximately one point. That is, a concave mirror can be obtained.

The focal length can be adjusted by supplying gas from the reservoir 11 through the valve 7 into the space 4 of the container l, or by opening the valve 7 and discharging the gas in the space 4 into space. When the valve 7 is closed, the membrane 3 is held in its current deflected state.

At this time, the transparent membrane 10 bends outward due to the pressure of the gas in the container 1, but this does not pose any practical problem.If there is no need to consider the zero weight problem, this transparent membrane 10 is bent outwards by the pressure of the gas in the container 1. It can also be replaced by a plate or the like.

In each of the above embodiments, the fluid supplied to and discharged from the space 4 in the container 1 is gas, but it may also be a liquid. In that case, the overall weight will be large, but the weight can be reduced by draining the liquid from the container l during transportation and assembly.

(Effects of the Invention) As is clear from the above description, according to the present invention, a reflecting curved mirror is formed by the container and the flexible film, so it can be extremely lightweight. Not only that, but the production of 7 can be done easily and inexpensively. Therefore, even large-diameter devices can be mounted on artificial satellites, etc., and space utilization can be further promoted. Furthermore, it is also suitable for cases where a large number of heat collectors, light collectors, etc. are used, such as in devices that utilize solar energy.

Since the pressure inside the container is adjusted by the pressure adjustment means, it is not only possible to adjust the focal length arbitrarily by changing the curvature of the reflecting surface, but also to convert a single curved mirror into a concave mirror. It is also possible to use it for both a convex mirror and a convex mirror.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the reflective curved mirror according to the present invention as a concave mirror, FIG. 2 is a vertical sectional view of the concave mirror, and FIG. 3 is another embodiment of the concave mirror according to the present invention. FIG. 4 is a longitudinal sectional view showing an example; FIG. 4 is an explanatory diagram for explaining the present invention in detail; FIG. 5 is a graph showing the results of an experiment conducted using the concave mirror shown in FIGS. 1... Container 2... Opening 3--・f@
3 a, 3 b--Reflecting surface 4...
・Space 5...Pressure adjustment means 7...Valve 8...Pump 9...Second opening 1
o...Transparent H (transparent plate) 11...Reservoir

Claims (2)

[Claims] (1) A fluid-tight container 1 having a circular opening 2; a flexible membrane 3 capable of reflecting electromagnetic waves, which is fixed to the container 1 so as to seal the opening 2; A reflecting curved mirror comprising pressure adjusting means 5 for maintaining internal pressure at a level different from external pressure. (2) The container 1 has a second opening 9 on the surface facing the opening 2, and the second opening 9 is sealed by a transparent plate 10 through which electromagnetic waves can pass. The reflective curved mirror according to claim 1.