1988-04-28
1989-04-18
Henry, Jon W.
G02B 718, G02B 510, G02B 508
Patent
active
048221554
DESCRIPTION:
BRIEF SUMMARY
This invention relates to mirror assemblies.
Mirrors are well known optical components having a large variety of uses and variable focal length mirrors have previously been proposed utilising a thin flexible carrier having a reflective surface, the carrier with its reflective surface being displaced from planar by suction. Particular forms of such mirror assemblies and which are characterised by good image forming characteristics are disclosed in European Patent Publication No. 0152268.
It is an object of the present invention to provide an improved form of mirror assembly.
According to the present invention there is provided a mirror assembly comprising a rigid circular structure defining a hollow chamber having a circular aperture, a flexible membrane disposed across said circular aperture and in contact with the periphery of the circular aperture, said flexible membrane having a reflective coating adherent to the membrane face which is distal to said circular aperture, circularly-extending secural means peripherally engaging said membrane radially outwardly of said circular aperture and capable of rendering flat that portion of the membrane covering said circular aperture, pneumatic means connected to said chamber for varying the differential pneumatic pressure across the membrane to thereby apply a pneumatic membrane deformation force to the membrane, said reflective coating being rendered variable in focal length according to the magnitude of the applied deformation force, said secural means providing peripherally continuous clamping of the membrane between opposed circularly-extending clamp surfaces at least one of which is mounted for movement axially of said circular structure in order to effect rendering said membrane portion flat in the absence of and deformation force applied by said pneumatic means, said secural means including peripherally-discontinuous adjustment means for adjusting the tension in individual peripheral regions of said membrane portion, and stress control means located at the interface between the circular structure and the reflective coating for controlling the stress distribution in the membrane around the periphery of the circular aperture when deformation force is applied by said pneumatic means.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 is a sectional view of the embodiment; and
FIG. 2 is a plan view of a portion of the FIG. 1 embodiment.
In the drawings, mirror assembly 10 is formed by a reflective coating 11 on one surface of a flexible substrate 12 which overlies a circular aperture 13 at the open end of a hollow chamber 14 formed by a circular structure 15. The structure 15 comprises a radially thick ring wall 18 which is secured by a plurality of bolts 16 to a rigid base plate 17 and provision is made at the interface for a plastic O-ring to effect a pneumatic seal. Base plate 17 is of greater diameter than the ring wall 18 and the annular skirt thereby provided, supports a circularly-extending secural means 20 for peripherally engaging the membrane 12 radially outwardly of the circular aperture 13.
Secural means 20 comprises a lower ring element 21 which is resiliently secured to base plate 17 by three equi-angularly spaced bolts 22 to provide a three-point mounting, each bolt being surrounded by a spring 23. With this arrangement adjustment of the plane of element 21 is easily effected without introducing distortion of the ring element into a non-planar condition. A second ring element 24 is secured to the first ring element 21 by means of a plurality of bolts 25. Bolts 25 may be twenty-four in number and the abutting surfaces of ring elements 21, 24, are substantially planar and provide peripherally continuous clamping of the membrane 12 between opposed circularly-extending clamp surfaces. Because of bolts 22 and springs 23 both of these surfaces are capable of movement axially with respect to the circular structure 15 for the purpose of rendering the central portion
REFERENCES:
patent: 1060447 (1913-04-01), Geisler
Henry Jon W.
University of Strathclyde
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