US2237566A - Variable density window - Google Patents

Description

April 8, 1941. E. H. LAND VARIABLE DENSITY WINDOW Filed Nov. 1 0'.. 1958 'llllllllllllllll Illll//Illlllllllllll Patented Aprk 8, 1941 VARIABLE DENSITY WINDOW Edwin H. Land, Boston, Mass., assignor to Polaroid Corporation, Dover, Del., a corporation o! Dela- Application November 10, 1938, Serial No. 239,796

Claims.

This invention relates to variable density windows.

An object of the invention is to provide a variable density window comprising a plurality of overlying light-polarizing elements and means associated therewith for controlling at will the amount of light transmitted thereby.

A further object of the invention is to provide a variable density window of the character described wherein one of the light-polarizing elements is fixedly positioned and the other element movable with respect thereto.

A still further object of the invention is to provide such a window wherein the movable element is movable linearly with respect to the fixed element and wherein the motion of the movable element imparts a predetermined stress or strain to material showing photoelastio effects and positioned between the polarizing elements.

A still further object is to provide such a window wherein the light-polarizing elements are xedly positioned with respect to each other and the density of the window as a whole is altered by altering the tension on a sheet of material showing photoelastic eiiects and positioned between the polarizing elements.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises an article of manufacture possessing the features, properties, and the relation of elements which will be exemplified in the article hereinafter described and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects' of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which- Fig. 1 is a view in section of one form of the invention;

Fig. 2 is a view in front elevation of the device shown in Fig. 1;

Fig. 3y is a view in section of a still further modication of the invention; and

Fig. 4 is a view, partially in elevation and partially in section, of the device shown in Fig. 3 taken along the line l-l.

Heretofore, when it has been necessary or desirable to reduce the intensity of light transmitted by a window in a dwelling, vehicle, or the like, the desired result has been accomplished by drawing across the window a supplemental translucent or opaque substance, such as a shade or curtain or blind. Speaking generally this has resulted in an impairment or complete destruction of the clarity of the image visible through the window, or at least through those portions of the window over which the shade or blind has been drawn. As a result it has been found that frequently a considerable portion of the window area performs no useful function, except on rare occa sions. This is particularly true in railroad vehicles, where the upper portion of the window almost invariably remains covered by an opaque curtain or screen, only the lower portion being usefully employed. So also in dwellings it is frequently customary to leave a shade or curtain drawn over a considerable portion of the window area or to hang drapes or curtains or similar light-obstruction elements so as to block appreciable portions of the window areas.

The control of light intensity at the windows has thus been accomplished frequently by a restriction of the window aperture usefully employed. In other cases it has been accomplished by drawing across the window a curtain, screen or the like which completely destroys the transparency of the window unit and makes it impossible for a person positioned Within the vehicle, dwelling or the like to see through the window.

It is an object of the present invention to provide a variable density window of a character such that the intensity of the light transmitted Vthereby may be controlled accurately from a predetermined maximum to complete cut-oi, if desired, without obstructing the clarity of the image transmitted by the window, at least until the point of substantially complete cut-off is reached. This may be accomplished by providing a pair of overlying light-polarizing elementseach preferably substantially the size of the full window aperture and by the provision of means for moving a transparent element, for example one of the polarizing elements with respect to the other of the elements, so that the intensity of the light transmitted by the combination of elements may be controlled.

In one form of the invention the movable element may be slidably mounted with respect to the xedly positioned polarizing element, and the two elements may have their polarizing axes positioned at right angles to each other or parallel to each other, and preferably in a direction or directions substantially at 45 to the direction of motion of the movable element with respect to the xed element. For example, if the movable element is to be moved vertically, the polarizing axis of the iixed element. may be inclined at an angle of 45 to the vertical in the plane of the element, and the polarizing axis of the movable element may be similarly inclined and may be either parallel to or at right angles to the axis of the fixed element.

With such a structure an intermediate transparent layer, showing photoelastic effects when extended, may be employed between the two polarizing elements, and this layer may preferably be of such a character that when it is subjected to an extension of predetermined amount it becomes a half-wave plate or shows half-wave retardation, and hence causes a rotationin the plane of polarization of light transmitted by the polarizing element nearest the light source such that the direction of vibration of that light is rotated through an angle of 90. Under these circumstances, if the two polarizing elements were positioned to block light initially-the stress or strain in the intermediate layer will result in a combination of elements such that the window transmits incident light, whereas if the elements were positioned initially to transmit a maximum of light, the strain in the intermediate layer would result in a condition such that the incident light is blocked by the two polarizing elements.

In this form of the invention the intermediate layer may be extended independently of any motion of the polarizing elements, or it may be so aixed to the polarizing elements as to be responsive to relative linear motion of one of said elements with respect to the other. It willI be apparent that a preferred structure contemplates the provision of surfaces of relatively large area.. as the intensity of light transmitted through the entire window should preferably vary simultaneously over all portions of the window area. This implies the use of lightpolarizing material of large surface area. Such a material is available under the trade name polaroid, one form of which, for example, comprises asuspension of polarizing particles in a light-transmitting medium, the particles being oriented with their polarizing axes parallel and so distributed throughout the medium as to impart substantially uniform polarization to a transmitted beam. A preferred form of this material for use in the present invention is a high concentration of polarizing crystals, such as crystals of iodosulfate of quinine or iodosulfate of cinchonidine in a very thin film or layer of a light-transmitting plastic, preferably the material sold under the trade name Vinylite XYSG. Films of this material of less thickness than .0003 inch have been found to be excellent polarizers. Such films are now available in areas at least as great as any desired for use in the present invention.

It may be desirable to employ films or sheets of the above type laminated to or between sheets of glass or other rigid light-transmitting supporting media,l and the use of such polarizing means is preferred. It is to be understood, however, that any other light-polarizing elements of `large area, or adapted to be assembled to form large areas, may be employed in the present invention. It will be apparent that for satisfactory results the sheets or lms of -polarizing material employed should be relatively thin and highly efficient, and if it is necessary to piece out the area by lamination or by overlapping smaller areas oi"4 polarizers the materials employed should be of a character such that large areas may be# produced without the appearance' of unsightly overlaps.

Where a photoelastic bonding material is to be.

' 50, 5 2, each providing a polarizing surface, preferably in the form of a thin adherent illm 54, 56. These films are preferably on the inner faces of their supporting plates. Each of the plates and its associated lmmay be mounted, as shown in Fig. 1, xedly in the frame of the vehicle or dwelling in which the window is employed.

Between the elements 50 and 52 there is provided a layer of a material 58 showing photoelastic effects when subjected to extension. This material may comprise, for example, a polymerized incomplete polyvinyl acetal resin, such as the material sold as Vinal, an acrylic acid ester or the like. It is preferably present in such thickness as to show substantially a half-wave retardation when subjected to a predetermined stress or strain.

Such a stress may be imparted to the sheet 58 by means of the apparatus shown in Fig. 1. The upper edge of the sheet may be rmly held as at 60 between the frames of the window elements. The lower edge of the sheet may be aixed by any suitable means 62 to a roller element 84 in the base of the inner window element. The roller 64 may be provided with a gear 66 adapted to mesh with a worm 68 which in turn may be driven by rotation of the handle 10.

The polarizing films 54, 56 are preferably so positioned that their polarizing axes, indicated generally by the arrows 12, 14, are at right angles to each other and at angles of 45 to the direction of extension of the element 58. Under these circumstances the strain set up in the material 58, which is a directional strain corresponding to the direction of extension of the element, will be at an angle of 45 to each of the polarizing axes, and if the material 58 acts as a half-wave retardation plate, it will cause a rotation in the direction of vibration of polarized light transmitted -by either of the elements 54, 56. Thus, if the axes 12, 14 are atright angles, the window as a whole will be most nearly opaque when no strain is on the material 58, and the window as a whole will transmit the most light when the strain on the material 58 is such that it acts as a half-wave plate.

'I'he material 58 is preferably selected of such thickness that a relatively slight extension, for example less than one inch, will impart to it the desiredv stress. It is preferably also resilient or rubber-elastic, i. e., it tends to return to its initial unstrained state when the tension is released. If desired, stops may be provided in connection with the roller 64 to prevent too great a stress being applied to the element 58. Under certainl circumstances, and where it is desired to impartcolor to the light traversing the win dow. elements, the sheet 58 may be stretched a considerably greater amount, for example so that I it no longer acts as a. half-wave device.

A still further modication of the invention is SRCH RO' shown in Figs. 3 and 4. In this form two window elements 500 and 520 are provided, each coated on its inner face with a polarizing layer 540, 5". Intermediate the window elements there is provided a resilient, extensible element 580, adapted when stretched a predetermined amount to function as a half-wave plate. This sheet 580 is aflxed along one of its edges to the window element 500, as at 582, and along its opposite edge to the window element 52B, as at 584.

One of the window elements, for example the element 500, is mounted for vertical motion, linear and parallel to the flxedly mounted element 52. This motion may be accomplished in any suitable manner, for example by supporting the element 500 on one or more cam members 600. which in turn rest upon a sliding bar or rack 602 provided, as shown in Fig. 4, with similar and cooperating cam surfaces.

Motion of the bar 602 to the right in Fig. 4,

i. e., in the direction of the arrow 6M, results in a camming action which raises the window element 500, moving it with respect to the element 520 so as to impart the desired stretch to the sheet 580. Motion of the bar 602 in the other die rection permits the window element 500 to fall to its initial position, thus relieving the stress on the element 580. If desired spring means GIB may be provided to insure a prompt return of the element 500 to its lower position.

Knob means BIZ may be provided affixed to the bar 602 to facilitate motion thereof.

It is to be understood that the polarizing axes of the elements 560 and 5&0 are positioned pre!- erably in the same manner as those of the eled ments 56 and 54 in the device shown in Fig. 4 and that the stress applied to the sheet 580 is similar in the results achieved to that applied to the sheet 58.

In any of the devices shown in Figs. l, 2, and 3 and 4, the space between the window elements and surrounding the extensible sheet may be filled, if desired, with a liquid lubricant. Preferably the liquid should have a low vapor pressure and an index of refraction approximately that of the extensible sheet. A very thin llrn of liquid is adequate. It may even be present initially in the extensible sheet and be worked or pressed therefrom in the assembly and operation of the device.

Any of the devices shown and described may be actuated by motor means (not shown) remotely controlled in any suitable way. For example, all the windows of a car or dwelling may be adapted to be simultaneously operated and the intensity of light transmitted accurately controlled from a central control station. All such modications are to be deemed within the scope of the invention.

Although the window elements in Figs. l, 2, 3 and 4 are shown as permanently mounted in the dwelling, vehicle or the like, it is to be understood that they and their associated and related elements, for example the entire assemblage shown in Fig. 1, may be mounted for motion wth respect to the dwelling or vehicle wall. so that the window may be opened and air admitted to the dwelling or vehicle.

Since certain changes may be made in the above article and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all 4the generic and specic features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A variable density window for illumination purposes comprising, in combination, frame means providing a window aperture of substantial area, a plurality of sheet-like, light-polarizing elements at least of substantially the same area as said aperture, means for mounting said elements in substantially parallel relation within said frame, a sheet of light-transmitting, resilient material at least of substantially the same area as said aperture adapted when subjected to a predetermined stress to function as a halfwave retardation device, means for mounting said sheet between and overlying said polarizing elements, and releasable means for subjecting said material to said predetermined stress to vary the amount of light transmitted by* said window.

` 2. A variable density window for illumination purposes comprising, in combination, frame means providing a window aperture of substantial area, a plurality of sheet-like, light-polarizing elements at least oi' substantially the same area as said aperture, means for mounting said elements in substantially parallel relation within said frame, a sheet of light-transmitting, resilient material at least of substantially the same area as said aperture adapted when subjected to a predetermined extension to function as a halfwave retardation device, means for mounting said sheet between and overlying said polarizing elements, and releasable means for subjecting said material to said predetermined extension to vary the amount of light transmitted by said window, said polarizing elements being positioned with their transmission axes at angles of substantially 45 to the direction in which said extending force is applied.

3. A variable density window for illumination purposes comprising, in combination, frame means providing a window aperture of substantial area, a plurality of sheet-like light-polarizingelements at least of substantially the same area as said aperture, means for mounting said elements in substantially parallel relation within said frame, a sheet of light-transmitting, resilient material at least of substantially the same area as said aperture positioned between and overlying said polarizing elements and adapted when subjected to a. predetermined extension to function as a half-wave retardation device, means for mounting one end of said sheet within said frame, and releasable means mounted in said frame for subjecting said material to said predetermined extension to vary the amount of light transmitted by said window.

4. In combination, frame means providing a window aperture, a plurality of sheet-like, lightpolarizing elements at least of substantially the same area as said aperture, means for mounting said elements in substantially parallel relation within said frame With their transmission axes in predetermined relative angular relation, said mounting means permitting linear movement of one of said elements, means for moving said movably mounted element with respect to the other without changing the relative angular relation of the transmission axes thereof, and means comprising a sheet of light-transmitting, resilient material capable of showing photoelastic eiects under stress positioned between said elements, said sheet; being secured at one end within said frame, the opposite end being secured to said movable element.

5. A variable density window comprising, in combination, frame means providing a window aperture of substantial area, means providing a light-polarizing surface at least of substantially the same area as said aperture and positioned within said frame means, means providing a second light-polarizing surface positioned substantially parallel with and overlying said first-mentioned surface, light-transmitting material positioned between said polarizing surfaces and adapted, when subjected to a predetermined strain, to function as a half-wave plate, said material being secured at one end to one of said light-polarizing surfaces and at the opposite end to the other of said light-polarizing surfaces, and means for moving at least one of said lightpolarizing surfaces with respect to the other of said light-polarizing surfaces for subjecting said f material to said predetermined strain.

EDWIN H. LAND.

Images