US3489941A - Light valve fluid thickness regulator - Google Patents

Description

Jan. .13, 1970 H. E. TOWLSON LIGHT VALVE FLUID THICKNESS REGULATO R Filed March 28, 1969 2 Sheets-Sheet 1 i 6 R 2 T C E L E N U G INVENTORZ HOWARD E. TOWLSON,

HIS ATTORNEY.

Jan. 13, 1970 H.- EQTOWLSON Y 3,489,941 LIHT VALVE FLUID THICKNESS REGULATOR- Filed March,28, I969 2 Sheets-Sheet 2 INVENTOR HOWARD E. TOWLSON,

BY HIS ATTORN United States Patent 3,489,941 LIGHT VALVE FLUID THICKNESS REGULATOR Howard E. Towlson, Baldwinsville, N.Y., assignor to General Electric Company, a corporation of New York Filed Mar. 28, 1969, Ser. No. 811,431 Int. Cl. H01 29/12 U.S. Cl. 31391 12 Claims ABSTRACT OF THE DISCLOSURE A light modulating fluid layer on the surface of a rotatable disk of a light valve is maintained smooth and of uniform thickness by use of a stationary, substantially flat, shaped plate spaced at a predetermined distance from, and at an angle with, the disk. Fluid in a sump through which the lower portion of the disk rotates rises by capillary action in the space between the disk and the plate to form a meniscus boundary, leaving a uniform thickness of fluid on the disk surface in the regions where the disk has moved past the boundary.

This invention relates to light valves for optical projection of images generated electronically on a fluid layer, and more particularly to a regulator for maintaining the fluid layer smooth and at a uniform thickness.

One form of light valve suitable for optical projection of electronically generated images onto a remote display surface comprises an evacuated envelope containing an electron gun in alignment with a transparent disk. The disk is rotated through a reservoir of light modulating fluid to deposit a continuously replenished layer of fluid on the disk surface. An electron beam, generated by the electron gun, is directed through electrostatic beam deflecting and focusing means and is scanned across a portion of the light modulating fluid layer so as to selectively deform the layer. The fluid deformations thus formed constitute diffraction gratings which. in conjunction with a Schlieren optical system, selectively control passage of light from a light source through the disk and through an output window in the light valve envelope in order to create visible images at a remote display surface on which the light impinges.

Because the modulating information is applied to the deformable fluid medium entirely in the form of surface deformations, it is particularly important, in order to minimize spurious images and to obtain uniform dark fields, that the surface of the deformable fluid medium be extremely smooth, uniform, and free from extraneous deformations as it is carried into the regionin which deformation-producing charges are to be deposited on the medium. This region is known as the raster area. In addition, effective control of the deformable medium thickness as it enters the raster area is particularly important from the standpoint of controlling light modulation efficiency and deformation decay time.

Various types of smoothing means have been employed in the past in order to achieve desired smoothness and uniform thickness of the deformable medium in light valves. Prominent among the earlier smoothing means is the mechanical smoothing bar, which merely comprises a blade maintained at a desired level above the surface supporting the deformable medium. Blades of this type, however, require that the disk surface, as well as the blade edge, be made flat to a high degree of precision, and that both the blade and the disk be positioned with extreme accuracy. Moreover, the blade must be positioned very close to the fluid medium supporting surface, not only giving rise to the likelihood that a small particle might become lodged between the blade and the disk surface 3,489,941 Patented Jan. 13, 1970 and scratch the disk surface as the disk rotates, but also imposing high torque requirements in order to achieve uniform velocity of disk rotation.

To overcome the drawbacks of the mechanical smoothing bar, the so-called electronic dam has been employed. This involves impingement of an electron beam onto the deformable medium immediately prior to entry of the medium into the raster area, in order to smooth the medium, as described and claimed in E. F. Schilling Patent 3,164,- 671, issued I an. 5, 1965, and assigned to the instant assi-gnee. However, any momentary power loss may allow some of the dammed fluid to flow into the raster area, causing interference in the displayed image. Moreover, when the electronic circuitry is turned on, a certain length of time is required after the electronic circuitry has begun functioning before the fluid over the entire raster area has become smooth enough to produce a useable image.

The aforementioned drawbacks of the mechanical smoothing bar are overcome by the present invention. Moreover, the quality of image produced by a light valve employing the present invention is unaffected by momentary power loss and, when the electronic circuitry begins operating, the image is available for display immediately.

Accordingly, one object of the invention is to provide smoothing means for the deformable fluid medium of a light valve which may be fabricated without a high degree of precision and which may be positioned in the light valve without extremely accurate positioning requirements.

Another object is to provide smoothing means for the deformable fluid medium of a light valve which exhibit a very low probability that a foreign particle might scratch the surface of the light valve rotating disk.

Another object is to provide smoothing means for the deformable fluid medium of a light valve which do not impose high torque requirements on the light valve rotating disk.

Another object is to provide smoothing means for the deformable fluid medium of a light valve which permit production of an image immediately when the electronic circuitry begins operating and which obviate any detrimental effects upon the image when power has been restored after a momentary power loss.

Briefly, in accordance with a preferred embodiment of the invention, a light valve containing a rotatable disk, a layer of light modulating fluid coated on the disk, a raster area in which the layer of light modulating fluid is bombarded with electrons, and a sump for containing light modulating fluid are provided, with a portion of the disk being submerged in the sump. Apparatus for maintaining the light modulating fluid layer smooth and of uniform thickness comprises a stationary plate of predetermined configuration having a flat surface spaced apart from the disk at a distance everywhere considerably greater than the thickness of the light modulating fluid layer and at a predetermined angle with the disk. The plate is situated, with respect to motion of the disk, at a location ahead of the raster area. A lower edge of the plate is submerged beneath the surface of the light modulating fluid in the sump. Additional light modulating fluid, drawn from the sump by capillary action, partially fills the space between the plate and the disk above the surface of the light modulating fluid in the sump and, as the disk rotates at a substantially constant speed, this fluid emerges from the space in the form of the light modulating fluid layer at a substantially constant thickness on the disk.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a partially cutaway side view of a portion of a light valve showing the fluid thickness regulator means of the instant invention;

FIGURE 2 is a sectional view taken along line 22 in FIGURE 1; and

FIGURE 3 is a sectional view taken along line 33 in FIGURE 2, showing positions of the rotatable disk and the fluid thickness regulator means of FIGURES 1 and 2 relative to each other.

DESCRIPTION OF TYPICAL EMBODIMENTS FIGURE 1 illustrates a light valve containing the fluid thickness regulator means of the instant invention. The light valve comprises an envelope 10, typically comprised of glass, containing a light output window portion 11 and a sump region 12 holding a reservoir of light modulating fluid 13. The interior of envelope 10 is evacuated to a low gas pressure.

The light modulating fluid is typically of the polybenzyltoluene type having a fluid viscosity of 1,000 centistokes at 60 C., with a vapor pressure in the range of 1O l torr. The fluid contained in sump region 12 is that which has drained off of an optically transparent disk 14 which is continuously rotated on bearings 15 about a shaft 16, typically at a speed of 3 revolutions per hour. A spring 20 is maintained in compression by having its cap 21 affixed to a rigid support member 22 which, in turn, is aflixed to envelope of the light valve by any suitable means (not shown). The opposite end of spring 20 bears against the body of a shaft 16. Consequently, a shoulder 23 on shaft 16 urges bearings to force disk 14 against protuberances 17, which may advantageously be formed of fritted glass droplets. These protuberances are iaflixed to output window 11.

Disk 14 is spaced apart from light output window 11 by a distance of about 3 mils so as to permit fluid 18 from sump 12 to rise by capillary action and fill the region between the disk and the output window. The 3 mil spacing is maintained by protuberances 17, as described in greater detail in H. E. Towlson Patent 3,3 85,991, issued May 28, 1968, and assigned to the instant assignee. As pointed out in the aforementioned Towlson patent, adverse effects produced by either a non-uniform fluid coating on the output surface of the rotatable disk, or by fluid condensate or droplets on the output window, are thereby eliminated.

A thin film of light modulating fluid 27 is coated on ductive coating such as indium oxide, is carried on rotating disk 14. Coating 24 may be maintained at any desired potential since a conductive path is formed through bearing 15, shaft 16, spring 20, cap 21 and member 22, permitting a continuous electrical connection to coating 24 through a stationary connection (not shown) which may be made to member 22. An aperture 19 in member 22 permits passage of an electron beam 25, originating at an electron gun 26, to be directed toward conductive coating 24 on disk 14. Disk 14 itself is non-conductive, and is preferably comprised of glass.

A thin film of light modulating fluid 27 is coated on thin film 24 and thus is situated within the direct path of electrons in electron beam 25. Beam 25 is focused and deflected by electron optical means (not shown) within light valve 10 and hence is swept, in raster fashion, over the surface of light modulating fluid layer 27. The pattern of charges on layer 27 produced by electron beam 25 causes corresponding deformations in the thickness of layer 27, resulting in formation of diffraction gratings 30. These gratings correspond to the image to be projected onto a remote display surface. Light from a light source (not shown) positioned behind electron gun 26 impinges upon a lenticular lens system 28 formed on the rear wall of envelope 10 and is directed by the lenticular lens system through aperture 19 onto diffraction gratings 30.

By modulation of electron beam 25 through application of suitable potentials to the electrostatic focus and deflection means, diffraction gratings 30 in fluid layer 27 are selectively controlled. Consequently, the light passing through transparent rotatable disk 14 and output window 11 is selectively controlled and, in conjunction with externally located lenses of a Schlieren optical system (not shown), is projected on a remote display surface (not shown) to form an image representative of the intelligence modulating the electron beam.

Fresh filtered fluid is supplied from a pump and filter 45, through a tube 46 which may discharge near the top of disk 14. This discharge, of course, occurs on the portion of the disk which has passed the raster area, in order to avoid interference with diffraction gratings 30. This is illustrated in FIGURE 2, described infra. The pump and filter are contained within a metallic enclosure which is affixed, as by fritting, to envelope 10 of the light valve. The flow of fluid to and from pump and filter means 45 as indicated by the arrows in FIGURE 1.

A smoothing bar 40 is fitted onto shaft 16 and spaced apart from disk 14 by an annular shim 41 which is urged against bearing 15 as a result of the force exerted by cap 21 against bar 40. Bar 40 has a substantially flat surface 42 which faces disk 14 and is separated from disk 14 by a distance small enough to permit fluid 43 to rise from sump 12 by capillary action and partially fill the region between the surface 42 and disk 14. The upper surface of fluid 43 forms a meniscus boundary 52.

FIGURE 2, which is a sectional view taken along line 22 of FIGURE 1, shows the shape of smoothing bar 40 and the relative positions of smoothing bar 40 and tube 46 with respect to disk 14 and raster area 50. Raster area 50 is defined by the area of fluid layer 27 which may be bombarded with electrons from electron beam 25, shown in FIGURE 1. Because the substantially flat surface of smoothing bar 40 is large with respect to thickness of the bar, the configuration of the bar is that of a plate. The disk rotates in a counter-clockwise direction as indicated by the arrow in FIGURE 2. The lower edge of bar 40 dips below the surface of fluid 13 so that most of the region between bar 40 and disk 14 is filled with fluid drawn from sump 12 by capillary action. Bar 40 is kept from being rotated by the drag of fluid between the bar and the disk by supports 44 which extend from rigid support member 22 in a direction substantially perpendicular to the plane of disk 14. Accordingly, plate 40 is held stationary within envelope 10.

Near the periphery of disk 14, bar 40 is urged toward the disk by a pair of compression springs, each of which may be supported within a pair of two-piece expandable containers 47 respectively, one piece of each of which is welded to support plate 22. Bar 40 is kept at a predetermined distance from disk 14 near the periphery thereof by a pair of glass protuberances or feet 48 fritted onto the surface of the bar facing the disk. (For simplicity of illustration, containers 47 aand glass feet 48 are not shown in FIGURE 1.) As shown in FIGURE 2, bar 40 releases fluid from meniscus boundary 52 in a smooth layer 27 of uniform thickness on disk 14 at a location just ahead of raster area 50, while tube 46 discharges fluid onto disk 14 at a location beyond the raster area so as to avoid any interference in the raster area due to uneven thickness of fluid on the disk.

In order to achieve a fluid layer of uniform thickness on disk 14, plate 40 must be located at a slight angle with respect to disk 14. This is evident in FIGURE 3, which is a top view of a portion of the apparatus illustrated in FIGURES 1 and 2. In FIGURE 3, it is apparent that spacer 41 maintains the portion of bar 40 near the center of disk 14 at a greater distance from the disk than the portion of the bar separated from the disk by glass pads 48 near the periphery of the disk. The reason that bar 40 is spaced at a slight angle with respect to disk 14 isv that for any given fluid, operating temperature, and disk speed, the spacing between the barand the disk must vary along the disk radius in order to compensate for the diflerent tangential velocities of the disk at different points along the disk radius. For any given fluid, operating temperature, and disk speed, spacing Z, representing the distance between surface 42 and bar 40 and the surface of conductive coating 24 on disk 14, as measured perpendicular to the plane of the disk, may be expressed as where K is a constant and R is the location at any point along the radius of disk 14 where spacing Z is to be determined, measured from the center of the disk. For a disk having a transparent area of about 4.5 inches in diameter, and using a light modulating fluid. of the type previously described, the spacing may conveniently be 50 mils at the center of the disk and only 24 mils at a location 2.1 inches from the center of the disk.

Although plate 40 is wedge-shaped and substantially flat, neither the wedge shape nor the flatness is extremely critical. Moreover, once viscosity and surface tension of the fluid have been established, and a disk speed has been established, fluid thickness can be regulated to achieve the desired depth. The fluid in sump 12, shown in FIG- URE 1, forms meniscus 52 in the space between conductive coating 24 on rotating disk 14, and surface 42 of bar 40, as illustrated in FIGURE 1. By proper spacing between the bar and the disk, the meniscus radius can be varied along the disk radius in order to compensate for different tangential velocities at diflerent locations along the radius of the disk. Thickness t of the resulting oil film has been found to vary according to the following equation:

where C is a constant, r is the meniscus radius at any particular point along the disk radius, v is the linear or tangential velocity of the disk at the point along the disk radius where the meniscus radius has been determined, and 1; is the viscosity of the fluid. Using the aforementioned parameters, a uniform layer of fluid of about 13 microns thickness may conveniently be formed upon conductive coating 24 on rotating disk 14, although fluid layer thicknesses of from 4 to 24 microns have been produced with variations of only about '-.5 micron variation over the raster area.

Smoothing bar 40 may be made from either glass or metal, and is capable of withstanding a 450 C. bake in air, followed by a 400 C. bake in vacuum, both of which are typically employed in fabrication of the light valve in which the invention is utilized. By spacing bar 40 at distances of between 20 and 50 mils from disk 14, high torque requirements are not imposed on the disk and small particles cannot become lodged in the space between the bar and the disk and scratch the disk. Moreover, because the fluid coated on the disk is drawn by capillary action from below the oil surface, foreign material floating in the oil is not picked up by the disk. The wedge-shaped configuration of the bar and the flatness of the bar are not critical, so that the bar need not be fabricated to a high degree of precision and it need not be positioned with extreme accuracy in the light valve. The smoothing action of the bar is unaffected by momentary power loss, and the bar permits production of an image immediately when the electronic circuitry associated with the light valve begins operating.

While only certain preferred features of the invention have been shown by way of illustration, many modifications and changes will occur to those skilled in the art.

It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

I claim:

1. In a light valve containing a rotatable disk, a layer of light modulating fluid coated on one surface of said disk, a raster area in which said layer of light modulating fluid is bombarded with electrons, and a sump containing light modulating fluid, said disk being partially submerged in said sump, apparatus for maintaining the light modulating fluidlayer smooth and of uniform thickness, said apparatus comprising:

stationary means having a substantially flat surface spaced apart from said one surface of said disk and being situated with respect to motion of said disk at a location ahead of said raster area, said substantially flat surface extending above the surface of the light modulating fluid in said sump; and

additional light modulating fluid contained in the space between said stationary means and said disk, said additional light modulating fluid emerging from said space in the form of said light modulating fluid layer at a substantially constant thickness on said one surface of said disk as said disk rotates at a substantially constant speed.

2. The apparatus of claim 1 wherein said substantially flat surface is situated at a predetermined angle with said disk.

3. The apparatus of claim 1 wherein the separation between said stationary means and said disk is everywhere greater than the thickness of said light modulating fluid layer.

4. The apparatus of claim 2 wherein the separation between said stationary means and said disk is everywhere 1greater than the thickness of said light modulating fluid ayer.

5. In a light valve containing a rotatable disk, a layer of light modulating fluid coated on one surface of said disk, a raster area in which said layer of light modulating fluid is bombarded with electrons, and a sump containing light modulating fluid, said disk being partiall submerged in said sump, apparatus for maintaining the light modulating fluid layer smooth and of uniform thickness, said apparatus comprising:

a stationary plate of predetermined configuration having a substantially flat surface spaced apart from said one surface of said disk, said plate being situated with respect to motion of said disk at a location ahead of said raster area and having a lower edge submerged beneath the surface of the light modulating fluid in said sump; and

additional light modulating fluid drawn from said sump by capillary action partially filling the space between said plate and said disk above the surface of the light modulating fluid in said sump.

6. The apparatus of claim 5 wherein said plate is situated at a predetermined angle with said disk.

7. The apparatus of claim 5 wherein the separation between said disk and said plate is everywhere greater than the thickness of said light modulating fluid layer.

8. The apparatus of claim 6 wherein said plate is spaced further from said disk near the center of said disk than near the periphery of said disk.

9. The apparatus of claim 8 wherein the separation between said plate and said disk is everywhere greater than the thickness of said light modulating fluid layer.

10. The apparatus of claim 5 wherein said plate is of generally wedge-shaped configuration.

11. The apparatus of claim 6 wherein said plate is of generally wedge-shaped configuration.

12. The apparatus of claim 8 wherein said plate is of generally wedge-shaped configuration.

(References on following page) 7 8 References Cited JAMES W. LAWRENCE Primary Examiner UNITED STATES PATENTS v. LAFRANCHI Assistant Examiner 2,776,339 1/1957 Arni 178-7.5 1 3,164,671 1/1965 Schilling 17s 7.s

3,385,991 5/1968 ToWlsOn 313-91 5 1787.5, 7.82; 313232; 350161, 162

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