Tensioner Reflector Sheet With Press Forms

Abstract

A reflector of radiation that is formed in its place of intended use by anchoring a sheet of the reflective material between fixed abutments and thrusting spaced press forms into contact with the sheet with sufficient force to conform the sheet elastically to the contour of the press forms.

Description

This invention relates to reflectors of radiation and particularly to a reflector which is caused to assume a predetermined geometric shape as an incident to its installation into its use position. It is here illustrated and described in connection with a luminaire, but its use may well extend to other projectors and receivers of radiated or broadcast energy.

It is an observed fact that metallic reflectors in luminaires or the like that are subjected to high temperatures in normal usage exhibit some tendency to distort in use, the effect being particularly noticeable in those kinds of reflectors that might be described as straight-line generated in geometric shape. This may be due to the fact that a surface curved with respect to only one reference plane is more subject to buckling than is a surface of multiple-axis curvature, or it may be that distortion from whatever cause is more noticeable on the usual intercept of visible radiation beamed from a luminaire having a reflector of the straight-line generated or linear element type.

In any case, it is the object of this invention to overcome the distortion tendency, and to do so by actually forming the reflector surface in situ, i.e., at the site of the intended use.

In the drawings:

FIGS. 1a and 1b in succession illustrate diagrammatically the forming of the desired optical contour in a reflector surface by its assembly with press forms which, in the assembly of the device, causes the reflector sheet to assume the desired geometric shape;

FIG. 2 is a fragmentary perspective view of a luminaire whose outer casing is partially broken away to show a reflector in accordance with the invention;

FIG. 3 is a side elevation of a complete luminaire embodying the invention in a double or vertically stacked arrangement that is more apparent from FIG. 4; and

FIG. 4 is a front elevation of the luminaire shown in FIG. 3.

The sequence of illustrations of FIGS 1a and 1b indicate diagrammatically how this invention is utilized. In essence, its practice contemplates spaced opposed abutments 10 which are fixed relative to one another. Between the two abutments there is suspended a sheet 12 of flexible material, for example metal, at least one surface of which is highly polished, in the case of a luminaire application, or otherwise rendered reflective with respect to the particular radiation with which this scheme is to be employed. This sheet need have no previous forming insofar as its optical character is concerned, the sheet 12 in the illustrations of FIGS. 1a and 1b, having merely been formed slightly at its opposite edges to form mounting flanges 14 which are punched to facilitate assembly of the reflector sheet with the abutments in any convenient manner, for example, by rivets, screws, bolts, or the like.

The curve, therefore, which is assumed by the sheet 12 in the illustrations of FIG. 1a is not any particular curve, but whatever curve the sheet may take upon having been flexed from a flat condition in being assembled with the abutments 10. It may be equally feasible, however, to preform the sheet, if desired, to give it an initial curvature which may approach as nearly as one might wish to the desired final form, which is imposed upon the sheet, and retained therein, by a pair of opposed curved press forms 16.

The press forms are machined accurately to the desired final shape of the surface of the sheet with which they are engaged, the press forms 16 illustrated in FIGS 1a and 1b having a parabolic contour. The length of that portion of the sheet which extends between the abutments is at least slightly greater than the mating surface of the press form in order that the resistance of the sheet, i.e., its reaction to the force exerted upon the sheet by the press forms, is carried to the anchoring abutments only through the sheet itself, inasmuch as it is desired that the sheet be placed in tension between the abutments in order to assure conformance to the contour of the press form. The forces acting on the system of press form 16, reflector sheet 12, and anchoring abutments 10, are illustrated by the arrows in FIG. 1b.

When the opposed press forms are assembled with the reflector sheet as indicated in FIG. 1b, the mating surface of the reflector sheet 12 assumes the shape of the press form 16, which is inserted with sufficient force to achieve this result. The amount of force employed is such as to stress the sheet material only within its elastic limit, as it is preferred to maintain the sheet in tension between the abutments, i.e., to avoid such stretching as might interfere with conformance of the sheet to the press forms at some later time in the life of the device, e.g., as the material ages, or under such design or operating conditions as might serve either to relieve the tensile stress in the sheet, or conversely, to cause that stress to exceed the elastic limit of the sheet material.

For example, in a particular application using a linear light source 18 such as is indicated in FIGS. 2 and 4, which is of the type referred to commonly as the "quartz-iodine" type, the temperature of the lamp bases under standard ambient conditions rises to 350.degree. C. This heat source induces high temperatures in the surroundings, not only by virtue of conduction from the lamp itself and its appurtenances, but also by direct radiation from the source, which as a substantial element of radiation of a frequency lower than the visible spectrum. If the design of the luminaire is such as to promote substantial differences of temperature between the press form and the sheet which constitutes the reflector, or if the materials employed have substantially different rates of thermal expansion, the initial stress may be quite important. For example, if the reflector sheet were to expand more than the press form, the tensile force at high temperature might be insufficient to maintain the conformance of the reflector sheet to the press forms. Conversely, if the press forms were to expand linearly more than the sheet, they could induce tensile stress of magnitude sufficient to give the sheet a permanent set, and thus to interfere with its conformance to the press form at lower temperatures.

It is accordingly desired to maintain the stressed conformance in the sheet at all times and under all conditions of operation within the elastic limit of the sheet material, a condition which is obviously most easily achieved under most circumstances by employing as reflector sheet and press form materials substances having the same thermal coefficient of expansion. In the illustrated application, I have found it quite satisfactory indeed to employ aluminum alloys of substantially identical thermal coefficients of expansion.

A practical physical structure for achieving the aforementioned conditions is illustrated by the luminaire 18 shown in FIGS. 2, 3 and 4. As illustrated, the luminaire comprises a rectangular box which encloses two substantially identical reflector systems of the kind just described in principle. They are stacked one above the other in vertical array, and project the luminous radiation from two pencil-like light sources 20 of the quartz-halogen type outwardly through a flat "lens" 22 which may be optically null or optically directional. The lens is secured in a peripheral frame 24, which is formed of T-shaped cross section, hinged along one of its long edges at 26 to the rectangular box, and held tight to the box along its opposite long edge by means of toggle clamps 28 of the general type common in luggage.

The box serves as structure as well as outer casing, and is formed of aluminum sheet which is bent to shape and flanged at its front edges (FIG. 2) to form a seat 30 for the lens frame. For convenience of manufacture, the box of the illustrated luminaire is made in three pieces, a body sheet 32 which forms the back wall and sidewalls, a top sheet 34 and a bottom sheet 36 which are assembled to the body sheet by means of rivets through lapped seams. To aid in shedding rain, the downturned flanges of the top sheet are on the outside of the body sheet, whereas the upturned flanges of the bottom sheet are on the inside of the body sheet.

Also shown in FIGS. 3 and 4 are the flanged enclosing cups 38 which are secured to the sidewalls of the luminaire to cover holes therein aligned with the axis of the tubular light source, thereby to provide additional clearance for the tube sockets. The cups 38 are secured to the casing by means of rivets, and the flanges of the cups are gasketed to keep out the elements.

Extending rearwardly from the back wall of the luminaire casing is a junction box 40 to which the leads of the lamp sockets are brought for connection to a supply conductor 42 from a suitable power source.

The entire luminaire is adjustably supported in a yoke 44 in which it is pivoted by means of sidewardly extending trunnions 46 upon which the luminaire may swivel. Any desired position of adjustment is maintained by tightening the nuts on the threaded terminal portions of the trunnion. A protractor 48 is provided at the swivel for convenient restoration of any preset alignment that may necessarily be disturbed in the course of maintenance. A mounting bracket 50 on the base or cross leg of the yoke is likewise provided with a main pivot hole 52 as well as an arcuate slot 54 thereabout for pivotally mounting the yoke upon a suitable mating support, and for maintaining any desired angular adjustment.

In the case of directive illumination of this sort, the necessary alignment can be achieved by predetermined angulation from established reference planes. It is also useful, however, to align luminaires of this kind by visual sighting, and for that reason, a bracket 56 is mounted on the outer casing for receiving a telescopic sight of the kind used in riflery.

The earlier-described reflector arrangement of FIG. 1 is mounted upon interior peripheral framing 58 which is secured to the inside faces of the side and top and bottom walls of the outer casing by means of rivets. The framing is of angle-shaped cross section to provide an attaching flange 60 to secure the frame in place and to add to the beam strength of the framing, the other angular flange 62 providing seats for the mounting of the press forms 16, as well as anchoring abutments 10 for the secured ends of the reflector sheet.

Because of the stacked, double arrangement in the illustrated case, the reflector frame 58 is divided longitudinally into two parts by a pair of cross members 64 of angle section that are joined back-to-back by stitch rivets which unite and strengthen the assembly. The flanges of the cross-members 64 and the end members that are parallel to the plane of the frame provide the anchorages 10 for the reflector sheets 12 which are secured to those flanges by means of rivets, of which there are three at each secured edge in the illustrated case.

The press forms 16 in the illustrated case are also formed of aluminum alloy plate of substantially greater thickness than the reflector sheets 12, i.e., about one-eighth inch thick. As earlier indicated, the specific plates shown are parabolic in form, the parabolic contour ending at a chord perpendicular to the focal axis to form a straight front edge 66. At the center of the front edge of the press form, there is an angle flange 68 with a central hole through which there is passed a machine screw 70 threaded in a suitable hole in the facing flange 62 of the reflector frame 58. The tightening of this screw provides a thrust in the direction of the focal axis of the parabolic press form, causing it to tighten its engagement with the reflector sheet as earlier described, and causing the sheet to assume the contour of the press form. The press form engages the reflector sheet a short distance inwardly from the bowed edge of the sheet, (see FIG. 2) and the desired perpendicular array of the press form with respect to the sheet is maintained by means of a small tongue 71 which protrudes from the curved surface of the press form 16 as an extension of the focal axis to be received in a suitable rectangular positioning slot in the reflector sheet. (See FIGS. 1a and 1b).

In the illustrated luminaire, it was found desirable to re-direct light emitted sidewardly from the light source by means of plane side reflectors 72 extending at an angle into the field of the parabolic reflector. These are omitted in FIG. 2 as they would have obscured the press forms, but are shown in FIG. 4. The side reflectors are secured in place by means of a couple of screws received in the two flanking holes 74 on the turned-over flange 68 of the press form, and the side reflectors themselves are provided with rectangular holes 76 through which the pencil-like light sources 20 can be inserted into their sockets 78 which are mounted on the press forms themselves in positioning holes 80. Those portions of the lamp sockets which receive the lamp bases float in spring mountings so that the light source may be removed from the sockets by sequential endwise movements of the tube.

With the foregoing arrangement I have found it possible to generate and to maintain the desired optical form of the reflector with greater accuracy and reliability than has heretofore been achieved by other techniques of forming reflectors of metal.

Claims

What is claimed is:

1. A reflector of radiation comprising a flexible sheet having a reflecting surface, a frame member providing opposed abutments spaced apart a fixed distance less than the distance between opposite edges of said sheet when unflexed, said opposite edges of said sheet being secured to said opposed abutments to arch said sheet between said abutments, a press form having a convex edge engaged with the concave surface of the sheet, and means connecting said frame and said press form and urging said press form against said sheet with force sufficient to place said sheet in tension between said opposed abutments and to conform the sheet to the contour of the press form thereby to determine the contour of the reflective surface of the sheet.

2. The reflector of claim 1, in which the flexible sheet is metal and the tensile stress induced therein by the press form is maintained within the elastic limit of the said metal.

3. The reflector of claim 1, in which the flexible sheet is metal, and in which the press form and the sheet have substantially the same coefficient of thermal expansion.

4. The reflector of claim 1, in which the flexible sheet is a light-colored ductile metal and has on its concave surface a specular finish, said reflector including a second press form of the same contour as the first and spaced from the first but likewise so engaged with the sheet that said two press forms determine the optical character of said reflective sheet between the two press forms, and in which said press forms have substantially the same coefficient of thermal expansion as said sheet.

5. In a luminaire having a reflector for projecting light from an essentially linear light source, a frame providing abutments fixed relative to one another and in flanking relation to the axis of the light source, a sheet of metal arched between and secured to said abutments and having on its concave surface a light-reflective finish, a pair of press-forms engaged with the concave surface of the sheet at opposite ends of the light source, screws connecting said press forms and said frame to urge said forms against said sheet with force sufficient to place said sheet in tension between said abutments and to conform the sheet to the contour of the press forms thereby to determine the optical contour of the light-reflective surface of the sheet.

6. In a luminaire according to claim 5, the frame including a case enclosing the reflector and having a lens through which the light emitted from the source is projected.