Optical: systems and elements – Mirror – Including specified control or retention of the shape of a...
Patent
1997-10-09
2000-04-18
Shafer, Ricky D.
Optical: systems and elements
Mirror
Including specified control or retention of the shape of a...
359871, 359900, G02B 508, G02B 7182
Patent
active
06050692&
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of constructing a thin film mirror.
The use of thin film mirrors as part of image projection display systems for use in large field-of-view presentation is well known. The large field-of-view presentation may be, for example, simulation, leisure, computer aided design or visualization presentation. Typically, thin film mirrors are used in simulation apparatus such for example as flight simulation apparatus where the thin film mirrors are used in off-axis optical systems to produce a wide angle collimated or near collimated display to be viewed by a pilot or trainee.
The thin film mirrors are usually constructed by a method which involves attaching a thin plastics film to form the mirror on a chamber which has one open side. A suction pump is used to partially evacuate the chamber so that the thin plastics film is sucked into the required shape for forming the thin film mirror. The shape of the thin film mirror is determined by characteristics of thin plastics film used, and by the shape of the edges of the chamber which provide the support for the mirror surface,
The geometric accuracy of the mirror is often one of the major factors in the quality and usefulness of the image projection display systems. The accuracy of the edges of the chamber and the way in which the plastics film is applied to the edges is crucial to the geometry of the thin film mirror. The thin film mirror is normally required to be spherical, toroidal, or spheroidal. The edges of the chamber are shaped such that they lie on the mirror surface. Thus the top and bottom edges of the mirror are usually parts of minor circles, and the ends of the mirror are usually lines of longitude. Minor circles are those described by the circumference of a circular plane section that is produced when a sphere is cut in a plane that does not pass through the sphere centre. An example of a minor circle is a line of latitude, upon which the top and bottom edges of a mirror cell typically lie.
The mirror film is initially a sheet which is part of a frustum of a cone laid flat. With known designs of suction chambers, the thin plastics film can be lightly tensioned to form a cord between the top and bottom chamber edges, to which the thin plastics film can then readily be attached. Attachment to the side edges of the chamber is more difficult because the thin plastics film must be stretched uniformally in order to transition from a chord to an arc which corresponds to the curvature of the end of the suction chamber. This stretching must be performed in a radial direction from the centre of curvature, in order to minimise distortion in the finished thin film mirror. The problem of securing the film at the ends to accommodate both directions of curvature and to reduce distortion to an insignificant extent is well known.
There are two principal methods currently used to construct thin film mirrors. The first method is to use temporary chamber extensions which are removed after the thin plastics film has been stretched to the required shape. The second method is to use a mechanical stretching device to force the mirror film edge to take up the required shape. Both of these known methods result in an abrupt discontinuity of the film edge at each corner of the final thin film mirror assembly. The film is initially in sheet form and it is converted into its final form by plastic and elastic deformation. In the corners of the suction chamber, the film is constrained along two edges by the use of an edge fixing arrangement and hence is considerably more resistant to stretching than a section of film located at an edge well away from the corner, where it is restrained only along one edge. In the case of the mechanical stretching device, friction between the mirror film and the stretching device can result in non-uniform stretching of the film which results in local geometrical errors in the produced thin film mirror.
It is an aim of the present invention to obviate or reduce the above mentioned problems.
Accordingly, the present inven
REFERENCES:
patent: 2952189 (1960-09-01), Pajes
patent: 3031928 (1962-05-01), Kopito
patent: 3337660 (1967-08-01), Bagby
patent: 3877139 (1975-04-01), Martinez
patent: 3973834 (1976-08-01), Penn et al.
patent: 4046462 (1977-09-01), Fletcher et al.
patent: 4097126 (1978-06-01), Mahleen et al.
patent: 4128310 (1978-12-01), Miller
patent: 5247395 (1993-09-01), Martinez
SEOS Displays Limited
Shafer Ricky D.
LandOfFree
Method of constructing a thin film mirror does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of constructing a thin film mirror, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of constructing a thin film mirror will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2331471