Patent Application
20130258485
The present disclosure relates to autostereoscopic displays and, more particularly, glass lenticulars for autostereoscopic displays.
A lenticular array is used in an autostereoscopic display to create an impression of three-dimension (3-D) to the viewer. The lenticular array is made up of a plurality of cylindrical lenses that create views of the image that are different for each eye of the viewer when the lenticular array is placed in front of a pixelated image source. The lenticular array needs to be manufactured with micron-scale accuracy in order to properly locate the cylindrical lenses about the pixels of the image source.
One manner of forming the lenticular array, i.e., bonding cylindrical lenticules to a support where the lenticules and the support are made of different materials, can suffer from lack of accuracy because attachment of numerous lenticules to the plate can result in more defects. Thus, there is a need for alternative means of manufacturing the lenticular array.
Numerous methods and materials may be used to fabricate complex, precision optical elements. Because a great majority of conventional machining processes for the manufacture of optical components are unsuited for producing very small features, components having surface features or dimensions as small as 500 μm or smaller typically can be fabricated only through a few methods of limited applicability. Fabrication of microstructured surfaces using polymers have leveraged off of processes developed by the semiconductor industry for making integrated circuits. Using photolithography and ion etching techniques, some have created submillimeter surface features. These methods, however, are not conducive to large scale manufacturing. The process time needed to etch a microstructure in proportionately dependent on the required total depth of the microstructure. Moreover, the methods are typically expensive and etching processes can create rough surfaces. A smooth concave or convex profile, or true prismatic profiles, cannot be readily achieved using either of the two aforementioned techniques.
Molding or hot embossing of plastic or glass materials, on the other hand, can form submillimeter-sized features. Plastics can conform to molds and reproduce faithfully intricate designs or fine microstructures. Unfortunately, plastic materials are not ideal since they suffer from several shortcomings. Plastic materials are often not sufficiently robust to withstand environmental degradation over time. First, they exhibit large coefficients of thermal expansion and limited mechanical properties. Plastic devices often cannot withstand humidity or high temperatures for long periods of time. Both the volume and refractive indices of plastics vary substantially with changes in temperature, thereby limiting the temperature range over which they may be useful. Since plastics for optical applications are available in a limited range of dispersion and refractive index, plastics provide only a restricted transmission range. Hence, their usefulness even within a restricted transmission bandwidth is limited by the tendency to accumulate internal stresses, a condition that results in distortion of transmitted light during use. In addition, many plastics can scratch easily and are prone to yellowing or develop haze and birefringence. Application of abrasion-resistant and anti-reflective coatings, unfortunately, still has not fully solved these flaws. Finally, many chemical and environmental agents degrade plastics, which makes them difficult to clean effectively.
In comparison, glass possesses properties that make it a better class of optical material over plastics. Glass normally does not suffer from the material shortcomings of plastics, and it can better withstand detrimental environmental or operational conditions.
Precision optical elements of glass are customarily produced by one of two complex, multi-step processes. In the first, a glass batch is melted at high temperatures and the melt is formed into a glass body or gob having a controlled and homogeneous refractive index. Thereafter, the glass body may be reformed using pressing techniques to yield a shape approximating the desired final article. The surface quality and finish of the body at this stage of production, however, are not adequate for image forming optics. The rough article is annealed to develop the proper refractive index and the surface features improved by conventional grinding and polishing methods. In the second method, the glass melt is formed into a bulk body that is immediately annealed, cut and ground into articles of the desired configuration. Both of these methods have their limitations. On one hand, grinding and polishing are restricted to producing relatively simple shapes, such as flats, spheres and parabolas. Other shapes and general aspheric surfaces are difficult to grind and complicated to polish. On the other hand, conventional techniques for hot pressing of glass do not provide the exacting surface features and qualities required for clear image formation. The presence of chill wrinkles in the surface and surface figure deviations constitute chronic afflictions.
The molding of glass traditionally has presented a number of other problems. Generally, to mold glass one must use high temperatures to make the glass conform or flow into a requisite profile defined by the mold. First, at such relatively high temperatures that produce molten glass, the glass becomes highly chemically reactive. Due to this reactivity of molten glass, highly refractory molds with inert contact surfaces are required. Some materials used to fabricate molds include silicon carbide, silicon nitride or other ceramic materials, or intermetallic materials such as iron aluminides, or hard materials such as tungsten. In many cases such materials do not present sufficient surface smoothness or optical quality for making satisfactory optical surface finishes. The potential for air or gas bubbles to be entrapped in the molded article is another drawback of high temperature molding. If captured within the glass, gas bubbles tend to degrade the optical properties of the article. The bubbles distort images and generally disrupt optical transmission. Even at high temperatures, hot-glass molding cannot create efficiently high-frequency submillimeter microstructures on the surface of the glass.
Accordingly, embodiments described herein address some of these shortcomings of conventional glass forming techniques. In one example aspect, a method of making a glass lenticular array is provided. The method comprises the steps of: heating a sheet of glass to a deformable state; and contacting the heated sheet of glass with a forming body, the forming body comprising a plurality of elongate projections protruding therefrom, the plurality of elongate projections arranged substantially parallel to one another and at substantially equal distances apart, each of the elongate projections comprising a distal end and a root end. The step of contacting forms a plurality of cylindrical lenses in the heated sheet of glass arranged in substantially parallel rows with a depressed region between two adjacent rows. During the step of contacting, the heated sheet of glass contacts the distal ends of the elongate projections but does not contact the root ends.
In another example aspect, a forming body for forming a lenticular array on a sheet of glass is provided. The forming body comprises a plurality of elongate projections protruding therefrom. The plurality of projections is arranged substantially parallel to one another and at substantially equal distances apart. Each of the elongate projections comprises a distal end and a root end. The root ends are configured not to contact the sheet of glass where at least one of the forming body and the sheet of glass are brought into contact such that the distal ends deform the sheet of glass so as to form cylindrical lenses arranged in substantially parallel rows with a depressed region between two adjacent rows.
In yet another example aspect, a method of making a glass lenticular array is provided. The method comprises: heating a sheet of glass, the sheet of glass comprising contact regions located thereupon in substantially parallel linear rows; and deforming the heated sheet of glass by applying force on the contact regions so as to form a plurality of cylindrical lenses in the heated sheet of glass, the plurality of cylindrical lenses arranged in substantially parallel rows with a depression region between two adjacent cylindrical lenses. The depressed regions are formed at the contact regions while at least apex regions of the cylindrical lenses are kept untouched during the step of deforming.
In yet another example aspect, a glass lenticular array comprises a base portion and rows of cylindrical lenses protruding from the base portion. The cylindrical lenses and the base portion are formed as a single-piece. The lenses are spaced apart from one another by a depressed region between two adjacent cylindrical lenses. Each of the depressed regions is covered with dark material.
These and other aspects are better understood when the following detailed description is read with reference to the accompanying drawings, in which:
Examples will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, aspects may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
Referring now to
The lenticular array 10 may be formed from a sheet of glass 18 produced by a variety of methods. For example, the glass sheet may be produced by a fusion down draw process, a float process, a slot draw process, or any other known or future method of making a glass sheet. Glass sheet 18 may be any suitable thickness, but for television or hand-held device applications, a thickness of the glass sheet is preferably equal to or less than 1100 μm, equal to or less than 700 μm, equal to or less than 500 μm, equal to or less than 300 μm and in some embodiments equal to or less than about 100 μm. The glass sheet may be formed from a glass of any suitable composition capable of being molded.
As shown by
As shown in FIGS. 3 and 5-6, the lenticular array 10 may be formed by contacting the sheet of glass 18 with the distal ends 22a of the elongate projections 22 and thereby deforming the sheet of glass 18 with force applied through the distal ends 22a. In some examples, the force may be applied passively by gravity, or actively as described further below. Deformation of the sheet of glass 18 is made possible by heat applied thereto. Heating of the sheet of glass 18 may be conducted before or while the sheet 18 makes contact with the distal ends 22a.
It should be noted that the forming body 20 may be isothermally heated so that the forming body is at a uniform temperature. Preferably, the temperature of the forming body is substantially equal to the temperature of the heated sheet of glass. Accordingly, in some embodiments, the sheet of glass and the forming body are heated together in the furnace and the contacting occurs within the furnace.
It should also be noted that a variety of arrangements for contacting the sheet of glass 18 with the forming body 20 is possible. In the example embodiments of
It may also be possible to make a lenticular array 10 having cylindrical lenses 14 on both sides. In order to make such a lenticular array 10, a sheet of glass 18 may be positioned between two forming bodies 20 that are oriented such that the distal ends 22a of one forming body 20 point at the distal ends 22a of another forming body.
In the example embodiments of
Particular glass compositions may adhere to the material of the forming body. To reduce adherence of the distal ends 22a to the sheet of glass 18, the forming body 20 as a whole, the elongate projections 22 or the distal ends 22a thereof can be coated with a coating or film 30 (
In FIGS. 3 and 5-9, the distal ends 22a of the elongate projections 22 act as contacting elements configured to touch contact regions on the sheet of glass 18. Contrastingly, the root ends 22b of the projections 22 are configured not to contact the sheet of glass 18 when at least the sheet of glass 18 or the forming body 20 are brought into contact with one another. That is, the depressed regions 16 are formed at the contact regions of the sheet of glass 18 through the application of force by the distal ends 22a (
Once the cylindrical lenses 14 are shaped, a material configured to reduce scattering of light that may be caused by any imprints left by the distal ends 22a, and improve contrast, can be applied to the depressed regions 16. The applied material may be dark (e.g., black, opaque or the like). For example, black pigment particles suspended in a dilute solvent may be coated on the lenticular such that the particles settle by gravity in the depressed regions 16. Alternatively, a polymer selected to match the refractive index of the glass forming the cylindrical material may be used instead of the dark material, wherein the refractive index-matched polymer material is applied to the front surface of the lenticular array in the depressed regions 16 formed by contact with projections 22.
One way to keep the curved surface of the cylindrical lenses 14 from contacting the forming body 20 is to dimension the height of the elongate projections 22 to be sufficiently greater than the desired height of the cylindrical lenses 14. As shown in
Although the peak-to-peak (apex-to-apex) pitch of the lenticular array may be formed to a value suitable for a specific application, for certain display applications the average peak-to-peak pitch between adjacent cylindrical lenses is preferably equal to or less than 1000 μm, more preferably equal to or less than 600 μm. However, for other applications where pixel sizes of the display are very large, the pitch may be as large as 10 mm. In contrast, a minimum pitch may in some instances be as small as 150 μm. Thus, the pitch may range from about 150 μm to about 10 mm. Preferably, the variation in pitch does not exceed about ±10 μm.
The forming body 20 is preferably made of a material that can withstand the temperatures in which the glass is processed without significant dimensional changes occurring as the forming body 20 varies between the processing temperature and room temperature. For example, the viscosity of the sheet of glass during processing is preferably at least equal to or greater than the annealing viscosity of approximately 1013 poise, so the forming body should be capable of withstanding a temperature that equates to the annealing viscosity for the particular glass sheet being processed. In one example, the coefficient of thermal expansion of the forming body 20 may be different from that of glass. For example, the coefficient of thermal expansion of the forming body 20 may be larger or smaller than the coefficient of thermal expansion of the sheet of glass 18, for example, by at least 10×10−7 m/m ° C. In some examples, the difference in coefficients of thermal expansion between the forming body and the glass sheet may be useful in ensuring the forming body separates from the lenticular array. Furthermore, the forming body 20 can be constructed from a material capable of withstanding temperatures greater than an annealing point of the sheet of glass. Materials satisfying one or more of these criteria may be graphite, glassy carbon, a nickel-chromium alloy, various types of steel, or the like. In preferred embodiments, the forming body may be formed from a plate of austenitic nickel chromium-based alloy such as Inconel. Inconel is particularly capable of withstanding the high temperatures involved in processing the sheet of glass without corrosion or significant wear or damage from use.
The trenches 24 between the elongate projections 22 may be formed on the forming body 20 by a variety of methods such as plunge electric discharge machining, as shown in
The curvature of the lenses 14 may depend on the type of application for which the lenticular array 10 is used since some applications involve close up viewing of the display while others require far away viewing. A variety of factors can affect the formation or shape of the cylindrical lenses 14. These factors may be the area of the contact regions, the viscosity of the glass sheet at the process temperature, the coefficient of thermal expansion of the glass sheet, the thermal conductivity of the glass sheet, the chemical composition of the glass sheet, the surface roughness of the glass sheet prior to processing, the surface tension of the glass sheet, the process temperature, the force applied to the forming body and/or the glass sheet, the process time, the ramp rate of the temperature, etc. For a given glass composition, a specific curvature of the lenses 14 can be obtained by primarily controlling four factors, i.e., the distance between adjacent elongate projections 22 (the wall or elongate projection pitch), the process temperature (i.e., the temperature of the atmosphere in which the glass 18 is processed), the process pressure (i.e., the force applied by the elongate projections 22 on the glass 18) and process time (i.e., the length of time that the elongate projections 22 are kept in contact with the glass 18). For a given glass composition, it is more difficult to form lenses 14 having large radius of curvature as the process temperature increases. While the process temperature may need to be lowered to form lenses 14 with large radius of curvature, it may instead be necessary to increase the force or to lengthen the process time. Contrastingly, for the same glass composition, at higher process temperatures, lenses 14 with smaller radius of curvature can be formed with smaller process pressure or shorter process time. The combination of process parameters will be dictated by the requirements of the lenticular array, and many combinations to achieve the desired results are possible.
A glass lenticular array 10 may provide the following advantages over a conventional lenticular array with a glass support portion and plastic cylindrical lenses. Glass can reduce the number of processing steps because there would be no step needed to bond the lenticules to the support portion. The glass lenticular array 10 can improve the pitch accuracy of the lenticules relative to the positions of the pixels in the image source because glass compositions can be produced that expand or contract less than typical plastics for a given change in temperature and because for a glass lenticular array the degree of expansion of the glass as a whole and the lenticules will be the same. Glass can also provide good dimensional stability during handling and in use. On the other hand plastic lenticules are more susceptible to stretching and can deform more easily. Glass is often used in products requiring high quality optics and may match well with optical coatings. Glass may provide superior damage resistance due to its hardness and resistance to chemicals and solvents. Properties such as scratch resistance provided by glass may be desired for use in hand-held applications. Glass can also be strengthened through surface chemical hardening, thermal tempering, ion exchange or the like. Glass may also provide better reliability and life because the damage resistance of glass is not diminished with time and glass is less susceptible to degradation due to ultraviolet light, moisture or exposure to low heat. Glass may also provide greater stiffness for a predetermined thickness that enables the position of the optics to be held in a stable position thereby reducing the need of additional structures that might otherwise be needed with plastic. Annealing of glass can deliver stress-free lenses with no retardance or other optical defect likely to disturb polarized light LCD transmission. Molded polymer lens arrays generally suffer from the rapid cooling required for registration and overall geometrical control.
In some aspects, the glass lenticular array 10 according to embodiments described herein can be adhered to a display panel, such as an LCD or organic light emitting diode (OLED) display panel. For example, the glass lenticular array can be adhered to the display panel with a refractive index-matching adhesive such as a suitable epoxy adhesive. The refractive index matching adhesive can be effective to reduce light scattering by the distal surface of the lenticular array. Additionally, it is preferable that the refractive index of the glass lenticular array be substantially the same as the refractive index of the display panel surface to which the lenticular array is adhered to. It is also preferred that if the glass lenticular array is adhered to the glass display panel that the coefficient of thermal expansion of the glass lenticular array be substantially the same as the glass of the display panel to which it is adhered. In other embodiments, the glass lenticular array may be removably attached to the display panel, or to the device comprising the display panel so that the glass lenticular array can be readily removed when not needed.
In one example fifteen glass lenticular arrays were formed from samples of an aluminoborosilicate glass (Corning Incorporated® Eagle™ XG glass) having a softening temperature of 965° C. and a CTE of approximately 32×10−7 m/m ° C. over the range from about 0° C. to about 300° C. The sheets of glass had thicknesses of 500 μm and 600 μm, and external (length by width) dimensions of 50 mm×50 mm. A graphite forming body as described supra was placed in a box furnace with the elongate projections facing upward, a sample glass sheet was placed on the forming body in contact with the elongate projections and a weight block was then placed on the glass sheet distal surface. The furnace temperature was raised to a hold temperature, and maintained at the hold temperature for a predetermined hold time as indicated in the Table below. As indicated, the hold temperatures were less than the softening temperature of the sheets of glass, ranging from about 800° C. to about 950° C. The furnace was filed with a nitrogen atmosphere to prevent oxidation of the graphite forming body. At the conclusion of the hold time the furnace temperature was reduced and the forming body, glass sheet sample and weight block were removed. Lenticular lens heights ranged from 32 μm to 396 μm.
The data from the Table show that varying lens heights can be obtained by varying the hold (process) temperature, the length of time the forming body is in contact with the sheet of glass and the force applied to the sheet of glass (or alternatively the forming body). It should be apparent that other glass compositions having different thermal characteristics can be accommodated by making suitable adjustments to the process temperature, hold time and force.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the claimed invention.
