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WO2001086349A2 - Rear projection screen for video display system - Google Patents

Rear projection screen for video display system Download PDF

Info

Publication number
WO2001086349A2
WO2001086349A2 PCT/US2001/014479 US0114479W WO0186349A2 WO 2001086349 A2 WO2001086349 A2 WO 2001086349A2 US 0114479 W US0114479 W US 0114479W WO 0186349 A2 WO0186349 A2 WO 0186349A2
Authority
WO
WIPO (PCT)
Prior art keywords
screen
lens
screen assembly
sided adhesive
assembly
Prior art date
Application number
PCT/US2001/014479
Other languages
French (fr)
Other versions
WO2001086349A3 (en
Inventor
James Mccoy
George Mihalakis
Edmund Sandberg
Arthur L. Berman
Steven Peart
Original Assignee
Digital Reflection, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Digital Reflection, Inc. filed Critical Digital Reflection, Inc.
Priority to AU2001259491A priority Critical patent/AU2001259491A1/en
Publication of WO2001086349A2 publication Critical patent/WO2001086349A2/en
Publication of WO2001086349A3 publication Critical patent/WO2001086349A3/en

Links

Classifications

    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03BAPPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00Projectors or projection-type viewers; Accessories therefor
    • G03B21/54Accessories
    • G03B21/56Projection screens
    • G03B21/60Projection screens characterised by the nature of the surface
    • G03B21/62Translucent screens
    • G03B21/625Lenticular translucent screens

Definitions

  • the present invention relates to video image systems. More particularly, the present invention relates to method and system for providing rear projection video system and screen assembly for rear projection based video display systems.
  • video images produced by a video projector is observed on a screen.
  • video images projected from the back of the projection system with a transmissive screen is viewed from the front of the screen projection.
  • FIG. 1 illustrates a typical rear screen projection system.
  • rear screen projection system 100 includes a video projector 101 which is configured to project video images through a fresnel lens 102 onto a screen 103.
  • the fresnel lens 102 may be configured to approximately coUimate the light incident on the rear of the screen 103.
  • the video projector 101 is configured to project video images onto the rear side of the screen 103 such that the viewing direction is substantially opposite to the direction of the video image projection from the video projector 101.
  • the gain generally refers to the ratio of the amount of light that is reflected from a Lambertian reflector compared to the amount of light transmitted on axis through a transmissive screen.
  • field of view refers to the off normal angle required for the transmitted light intensity to fall to one half of the normal value. In most video applications, typical viewing conditions are such that it is desirable to have the horizontal field of view (FOV) be larger than the vertical field of view (FOV).
  • speckle in the video systems referred to above is a power intensity pattern produced by mutual interference of partially coherent light beams that are subject to minute temporal and spatial fluctuations. More specifically, speckle is superimposed on the projected video image and is especially apparent in the light areas of static images. The magnitude of the speckle can be more severe in a "small" aperture light source such as a microdisplay based video projector system. In most cases, it is desirable to maintain the speckle to a minimum.
  • the screen 103 is configured to transmit the projected video images (light) received from the video projector 101.
  • the screen should transmit as large a fraction of the received light as possible.
  • both large scale and small scale transmission should be as uniform as possible to reduce the possibility of hot spots.
  • the amount of room light reflected from the front of the screen and back into the eyes of the viewer is generally referred to as the front screen reflection.
  • the front screen reflection may include both specular and diffuse reflectance, and should be maintained as low as possible to achieve a high contrast ratio.
  • Resolution often measured with a "resolution target" and expressed in line pairs/mm refers to the ability of the screen to reproduce as separate entities the points, lines and surfaces of the input image. To minimize input image quality degradation, it is desirable to maintain the resolution sufficiently high.
  • the screen properties should be independent of polarization, while if the input light is linearly polarized, the screen could be linearly polarized as well.
  • the characteristics desired in a screen for rear projection video system may depend upon the specific application for which it is intended. For example, in the case of a computer monitor, the gain should preferably be low, while narrower field of view (FOV) is acceptable.
  • a fresnel lens With the use of a fresnel lens, it is possible to obtain the light incident on the rear of the screen to be approximately coUimated. Some types of display screens may require that the rear of the screen be approximately coUimated for optimal performance.
  • the properties for a screen in a rear projection video system may depend upon the particular application intended for the projection system, and some of these criteria are discussed below.
  • Lenticular array is a two dimensional array of lenslets that can be configured to provide a range of gain by varying the shape of the lenslets.
  • manufacturing tools for manufacturing lenticular arrays are expensive, and large screens are difficult to manufacture.
  • lenticular arrays have the same vertical and horizontal gains.
  • Ribbed screens are typically provided with vertically oriented, transmissive, cylindrical lenses which determine the horizontal gain, and can obtain high transmission rates.
  • speckle for ribbed screens can be high, and these types of screens are difficult to manufacture.
  • front screen reflections may be problematic, and if diffusion is used for vertical gain, the resolution and transmission may be reduced.
  • beaded screens comprise a single layer of clear, spherical (glass) balls, which has the advantage of providing a range of gain by varying the diameter of the spherical balls.
  • speckle can be high and are difficult to manufacture.
  • beaded screens it may be difficult to obtain uniform transmission over a large screen area, and the transmission may also be low.
  • resolution for beaded screens may be limited by the diameter of the spherical balls, and the vertical and horizontal gain for this type of screens is the same.
  • a screen for use in a video projection system in accordance with one embodiment includes a vertical rib array, and a horizontal rib array positioned substantially in series with the vertical rib array, the horizontal and vertical rib arrays provided in an optical path forming a cross ribbed screen.
  • a screen for use in a video projection system in accordance with another embodiment includes a single ribbed screen including a plurality of vertical and horizontal ribs, each cross section of the vertical and horizontal ribs being dithered.
  • a screen for use in a video projection system in accordance with still another embodiment includes a screen having a ribbed side and a viewing side, the viewing side including a photoimagable coating layer illuminated with a coUimated light to form a striped pattern thereon.
  • a light path introduced from the ribbed side may be substantially aligned between a gap portion of the striped pattern on the viewing side.
  • a screen for use in a video projection system in accordance with yet still another embodiment includes a two dimensional array of overlapping substantially round lenslets provided in a first surface of a screen, the lenslets provided in a horizontal direction on the first surface with a predetermined stepping distance, and further, the lenslets provided in a vertical direction on the first surface with a predetermined stepping distance.
  • the predetermined stepping distance in the horizontal direction and the predetermined stepping distance in the vertical direction may be substantially the same. Furthermore, each cross section of the lenslets may be substantially spherical or aspheric.
  • a screen assembly for use in a video projection system in accordance with yet a further embodiment includes a lens provided in an optical path of a signal source, a diffusion layer positioned substantially between the lens and the optical path, a screen provided substantially on the opposite side of the lens to the diffusion layer.
  • the lens may include a fresnel lens.
  • the diffusion layer may be integrated with the lens as a single lens body.
  • the signal source may include a video projector.
  • an air gap may be defined between the lens and the screen.
  • a screen assembly for use in a video projection system in accordance yet further still a further embodiment includes a lens provided in an optical path of a signal source, the lens including a first surface and a second surface, and an anti-reflecting layer provided on the first surface of the lens, said anti-reflecting layer configured to substantially minimize the reflection of the lens.
  • the lens may include a fresnel lens.
  • the optical path may be introduced into the first surface of the lens and substantially exit the lens at the second surface.
  • the anti-reflecting layer may include one of a single layer index matching material and a stack of thin film coatings.
  • the screen assembly may further include a screen positioned substantially adjacent to the second surface of the lens.
  • an air gap may be defined between the lens and the screen.
  • a screen assembly for use in a video projection system in accordance with yet still another embodiment includes a lens provided in an optical path of a signal source, the lens including a first surface and a second surface, a screen positioned substantially adjacent to the second surface of the lens, the screen including a first surface and a second surface, and a cover plate provided on the second surface of the screen.
  • the lens may include a fresnel lens, and the optical path may be introduced into the first surface of the lens and configured to exit the lens at the second surface of the lens.
  • the cover plate may be laminated onto the second surface of the screen.
  • the cover plate may include one of a glass plate and a scratch resistant plastic plate.
  • the second surface of the screen may be coated with an anti-scratching coating, and may substantially face the first surface of the screen.
  • the screen assembly may further include an anti-reflection layer provided on the second surface of the screen between the second surface of the screen and the cover plate.
  • the anti-reflection layer may be laminated onto the second surface of the screen.
  • the second surface of the screen may be coated with a mat finish.
  • the cover plate may include a first surface and a second surface, the optical path configured to enter the first surface of the cover plate and to exit the cover plate at the second surface, the second surface of the cover plate coated with a mat finish.
  • cover plate second surface may be overcoated with a thin film anti- reflection coating over the mat finish.
  • the screen assembly may further include a linear polarizer provided between the screen and the cover plate, and the linear polarizer may be laminated on the second surface of the screen.
  • an air gap may be defined between the second surface of the lens and the first surface of the screen.
  • a screen assembly for use in a video projection system of another embodiment includes a holographic lens positioned in an optical path from a signal source, and a screen positioned in the optical path on an opposite side of the lens to the signal source.
  • a screen assembly mounted in a video projection system of a further embodiment includes a housing, a lens positioned in an optical path within the housing, the lens including a first surface and a second surface, and a screen positioned in the optical path within the housing, the screen including a first surface and a second surface, the second surface of the lens and the first surface of the screen defining an air gap, the screen further mounted to the housing.
  • the lens may be taped to the screen using either a two-sided adhesive tape or a double sided adhesive with a closed or open cell foam interlayer.
  • the two sided adhesive tape or the double sided adhesive with the closed or open cell foam interlayer may be applied continuously around the outer periphery of the screen, or alternatively, may be applied at a predetermined interval around the outer periphery of the screen.
  • the two-sided adhesive tape taping the lens to the screen may have a thickness range of approximately 0.001 inch and 0.05 inch.
  • the screen is taped to the housing using either a two-sided adhesive tape or a double- sided adhesive with a closed or open cell foam interlayer.
  • the two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer may be applied continuously around the outer periphery of the screen, or may be applied at a predetermined interval around the outer periphery of the screen.
  • the two-sided adhesive tape taping the screen to the housing has a thickness range of approximately 0.1 mm to 5 mm. Additionally, the second surface of the screen may be coated with a striped pattern.
  • rear projection screen systems are provided with improved optical properties that are less expensive and easier to manufacture than typical rear projection systems available.
  • Figure 1 illustrates an overall rear projection video system
  • Figure 2 illustrates a cross ribbed screen with variable vertical and horizontal gain in accordance with one embodiment
  • Figure 3 illustrates a dithered ribbed screen with variable vertical and horizontal field of view (FOV) in accordance with one embodiment
  • Figure 4 illustrates one embodiment of minimizing reflection from the front of a screen for ribbed type screens
  • Figure 5 illustrates another embodiment of the screen with variable vertical and horizontal gain using overlapping lenslets
  • Figures 6A-6B illustrate a manufacturing procedure for a screen with overlapping lenslets in accordance with one embodiment
  • Figure 7 illustrates a screen in a rear projection video system with suppressed speckle in accordance with one embodiment
  • Figure 8 illustrates a rear projection video system screen with suppressed reflection and light loss in accordance with one embodiment
  • Figure 9 illustrates a rear projection video system with screen surface protection in accordance with one embodiment
  • Figure 10 illustrates a rear projection video system with suppressed front screen reflections in accordance with one embodiment
  • Figure 11 illustrates a rear projection video system with improved screen contrast in accordance with one embodiment
  • Figure 12 illustrates a rear projection video system with an improved fresnel lens in accordance with one embodiment
  • Figure 13 illustrates a screen assembly mounting technique in a rear projection video system in accordance with one embodiment
  • FIGS 14A-14C illustrate screen assembly mounting techniques in the rear projection video system of Figure 13.
  • Figure 2 illustrates a cross ribbed screen with variable vertical and horizontal gain in accordance with one embodiment.
  • a vertical rib array 210 and a horizontal rib array 220 is shown.
  • the vertical rib array 210 is arranged in the optical path in series with the horizontal rib array 220 as shown in Figure 2.
  • a screen for a rear projection type video system is provided with a cross rib configuration such that differing vertical and horizontal gain as well as different vertical and horizontal field of view (FOV) may be obtained.
  • FOV vertical and horizontal field of view
  • the shape of the vertical and the horizontal ribs determines the desired corresponding horizontal and vertical gain as well as the vertical and horizontal FOVs.
  • Figure 3 illustrates a dithered ribbed screen with variable vertical and horizontal field of view (FOV) in accordance with one embodiment.
  • FOV field of view
  • this pattern of shaping a section of the rib to produce the desired FOV in the vertical direction and shaping the next section of the same rib to produce the desired FOV in the horizontal direction is periodically repeated along the entire length of each rib of the ribbed screen.
  • differing vertical and horizontal FOVs in the ribbed screen may be obtained, requiring only one screen layer as compared to the approach shown in conjunction with Figure 2 which includes a vertical rib array 210 and a horizontal rib array 220.
  • Figure 4 illustrates one embodiment of minimizing reflection from the front of a screen for ribbed type screens.
  • a screen 410 is shown with a ribbed side 410A and a relatively flat side 410B.
  • a photoimagable black material 420 is coated onto the opposite side 410B of the ribbed section 410A of the screen 410.
  • the ribs are configured to focus the light onto and expose the coated photoimagable black material 420.
  • the intensity of the coUimated light in one embodiment is configured sufficiently to form a striped pattern 430 on the photoimagable black material 420.
  • the self-aligning process of the light path through the ribbed section 410A of the screen 410 ensures relatively perfect alignment between the striped portion 430 of the photoimagable black material 420 and the ribs provided on the ribbed section 410A of the screen.
  • the ribs on the ribbed section 410A of the screen 410 focus the light rays such that the light rays pass through the gap section 431 of the striped portion 430 of the photoimagable black material 420. In this manner, very little light is absorbed during transmission.
  • Figure 5 illustrates another embodiment of the screen with variable vertical and horizontal gain using overlapping lenslets.
  • a screen 510 for use in a rear projection video system in provided with a two dimensional array of overlapping substantially round lenslets 520.
  • the degree of overlap may be different along the vertical direction 530 as compared to the horizontal direction 540.
  • the extent to which there is overlap in the vertical direction 530 and in the horizontal direction 540 which can be seen from the corresponding vertical stepping distance 511 and the horizontal stepping distance 512, may determine the FOVs in the vertical and horizontal directions.
  • the cross section of the lenslets 520, whether spherical or aspheric, provided on the screen 510 may impact the FOVs in the vertical and horizontal directions.
  • the screen 510 for a rear projection video system may be configured such that differing vertical and horizontal gain profiles may be obtained without the use of resolution degrading diffusers.
  • Figures 6A-6B illustrate a manufacturing procedure for a screen with overlapping lenslets shown in Figure 5 in accordance with one embodiment.
  • a diagonal facet in a conical diamond 610 is formed by cutting for example, along the plane of cut 611 shown in the Figure.
  • the leading edge of the cut facet on the conical diamond 610 is substantially in the shape of the desired half cross-section of the lenslet.
  • the conical diamond 610 is polished to form the diamond spin bit 620.
  • the prepared diamond spin bit 620 is then used to machine a negative of the lenslet into the surface of a copper drum 640 by, for example, rotating the diamond spin bit 620 in the direction 630 as shown in the Figure.
  • the surface 641 of the copper drum 640 is coated with, for example, a metal such as nickel to prevent oxidation.
  • the diamond pin bit 620 is stepped across the width of copper drum 640.
  • the horizontal stepping distance 650 may be chosen such that the desired amount of horizontal overlap is produced.
  • the copper drum 640B is slightly rotated and the subsequent rows 651, 652, 653 of negative of the lenslets 670 may be machined using the diamond spin bit 620.
  • the vertical stepping distance 660 may be selected such that a desired amount of vertical overlap is produced. This process is repeated until the entire circumference of the coated copper drum 640 is covered with the negative of the lenslets 670.
  • the coated copper drum 640A is shown with the first row of overlapping negative of the lenslets 670 formed thereon with the predetermined vertical stepping distance 660, and the coated copper drum 640B is shown with subsequent columns of overlapping negative of the lenslets 670 with the predetermined horizontal stepping distance 650.
  • a master drum 640 is created that has arrays of negative lens features.
  • the screen based on overlapping lenslets is produced.
  • the copper drum 640 is rolled over in the direction 685 as shown in the Figure across the uncured UV material 681 to emboss the surface with positive lens features.
  • the UV material 681 is then cured by exposure to UV light rays from UV light source 690. In this manner, screens for rear projection video system with overlapping lenslets may be manufactured relatively easily and inexpensively.
  • Figure 7 illustrates a screen in a rear projection video system with suppressed speckle in accordance with one embodiment.
  • a video projector 710 is provided for projecting video signals from the rear of the video projection system onto a diffusion layer 720 behind a fresnel lens 725.
  • a screen 730 which is used for viewing the projected video images in the viewing direction 740.
  • the diffusion layer 720 may be integrated into the fresnel lens 725.
  • diffusion may introduced in the optical path of the video projection onto the screen 730.
  • speckle may be minimized and thus producing a higher quality image projection.
  • the diffusion introduced in the optical path as discussed above should not be greater than necessary since the greater the diffusion, the lower the speckle but the higher the degradation of resolution and the lower the transmission.
  • FIG 8 illustrates a rear projection video system screen with suppressed reflection and light loss in accordance with one embodiment.
  • a similar rear projection video system as that shown in Figure 7 is illustrated including a video projector 810 configured to project video images through a fresnel lens 820 onto a screen, where the viewing direction 840 is opposite the direction of the video image projection from the video projector 810.
  • ah anti-reflecting coating 850 provided on the back surface of the fresnel lens 820.
  • the anti-reflection coating 850 may in one embodiment include a single layer index matching material deposited from a liquid or a stack of thin film coatings. Alternatively, a microscopic "Moth's eye" may be used to texture the back surface of the fresnel lens 820 to provide the anti-reflection coating 850
  • reflection and light loss from the fresnel lens 820 during projection of video images may be minimized.
  • the video images are projected into the back surface of the fresnel lens 820, some portion of the projected images is reflected back. This reduced the light available to the viewer, and further, the reflected light may reflect around the cabinet of the video projector 810 and eventually project out onto the screen 830 resulting in a decrease in the contrast ratio.
  • the anti-reflection coating 850 as discussed above, it is possible to minimize the decrease in the contrast ratio by minimizing the reflection of the projected video images from the back surface of the fresnel lens 820 and the screen 830.
  • FIG 9 illustrates a rear projection video system with screen surface protection in accordance with one embodiment.
  • video projector 910 is provided for projecting video images through a fresnel lens 920 onto the rear surface of a screen 830 opposite to the viewing direction 940.
  • a cover plate 950 is laminated onto the front surface of the screen 930.
  • the laminated cover plate 950 may be glass or a scratch resistance plastic.
  • the screen 930 may be coated with an anti-scratching coating (such as, for example, those used to protect the front of the polarizer in a laptop computer). Additionally, the cover plate 950 may also provide added rigidity to the screen 930.
  • the surface of the screen 930 may be protected from exposure to the environment as well as to the viewers.
  • the screen 930 is the outermost surface of the rear projection video system, its exposure to potential damaging sources is particularly acute.
  • the screen 930 may be better protected from potential physical damages.
  • Figure 10 illustrates a rear projection video system with suppressed front screen reflections in accordance with one embodiment.
  • a video projector 1010 is provided along with a fresnel lens 1020 and a screen 1030 with a cover plate 1040.
  • the video projector 1010 is configured to project video images through the fresnel lens 1020 onto the screen 1030 in the opposite direction to the viewing direction 1060.
  • an anti- reflection layer 1050 is provided onto the viewing direction surface of the screen 1030.
  • the anti-reflection layer 1050 over the cover plate 1040 laminated onto the screen 1030 may be provided by coating the surface with a mat finish, thus effectively "spoiling" any specular reflection and minimizing reflectivity from the front of the screen 1030.
  • the viewing direction side of the screen 1030 with the cover plate 1040 may be coated with a thin film anti-reflection coating as the anti-reflection layer 1050. This approach has the added advantage over using the mat finish without a loss of resolution.
  • the viewing direction side of the screen 1030 with the cover plate 1040 may be coated with the mat finish and then overcoated with the thin film anti-reflection coating. This has a further front screen reflection suppression result as compared to using just one of the two approaches discussed above.
  • Figure 11 illustrates a rear projection video system with improved screen contrast in accordance with one embodiment.
  • a linear polarizer 1140 is laminated over the viewing direction 1160 side of the screen 1130 opposite the fresnel lens 1120.
  • an optical cover glass 1150 for the protection of the screen 1130 and the polarizer 1140 is provided.
  • the orientation of the transmission axis of the linear polarizer 1140 is substantially parallel to the polarization axis of the projected light from the video projector 1110. Since the projected light from the video projector 1110 is rarely perfectly tinearly polarized, but rather, is generally slightly elliptically polarized, the linear polarizer 1140 is configured to remove any unwanted component. Furthermore, any stray light, such as reflected light from the back surface of the fresnel lens 1120 as discussed above, that reaches the screen 1130 tends to be depolarized, and thus the stray light will be partially suppressed by the linear polarizer 1150. In this manner, by providing the output of all channels to be linearly polarized and have the same orientation through the implementation of the linear polarizer 1140, the contrast ratio of the rear projection video system may be maximized.
  • Figure 12 illustrates a rear projection video system with an improved fresnel lens in accordance with one embodiment.
  • a holographic fresnel lens 1220 is provided to improve input light collimation.
  • the fresnel lens is generally provided to provide coUimated light.
  • the fresnel lens may introduce artifacts to the image, such artifacts including chromatic separation of the projected light and the establishment of a Moire pattern between the periodicity of the lines in the fresnel lens and the repetitive features in the screen.
  • a hologram 1220 as a substitute for the fresnel lens, in accordance with the present invention, input light may be coUimated without the potential for introducing artifacts to the projected images.
  • an air gap 1250 between the hologram fresnel lens 1220 and the screen 1230 is also shown in the Figure.
  • visually observable artifacts such ⁇ s Newton rings may occur between the fresnel lens and the screen.
  • the visually observable artifacts in turn, have degrading impact on the quality of the projected video images.
  • By providing the air gap 1250 between the hologram fresnel lens 1220 and the screen 1230 it may be possible to suppress the Newton rings and thus minimize the degradation of the projected video images.
  • Figure 13 illustrates a screen assembly mounting technique in a rear projection video system in accordance with one embodiment.
  • a side view of the interior 13 A of a rear projection video system and a front view of the exterior 13B of the video system is shown.
  • an enclosure 1310 is provided which houses a large mirror 1320, a screen assembly 1330, a small mirror 1340 and a light engine 1350.
  • the screen assembly 1330 is mounted within the enclosure 1310 on the viewing side of the video projection system, and includes a fresnel lens and a screen.
  • the large mirror 1320 Substantially on the opposite side from the screen assembly 1330 within the enclosure 1310 is mounted the large mirror 1320, and substantially at the lower end with in the enclosure 1310 is provided the light engine 1350 and the small mirror 1340.
  • the tracings of the marginal rays from the light engine 1350 can be seen from the figure along the path 1360 as shown within the enclosure 1310 for projection onto the screen assemblyl330.
  • the screen assembly 1330 is attached to the enclosure 1310 of the display system, and the enclosure 1310 acts as a "picture frame" around the screen assembly 1330.
  • the front view of the exterior 13B substantially illustrates the enclosure 1310 as a picture frame around the screen assembly 1330.
  • Figures 14A-14C illustrate screen assembly mounting techniques in the rear projection video system of Figure 13.
  • Figures 14A-14B illustrate a side view and a close up side view of the screen assembly mounting technique in accordance with one embodiment of the present invention.
  • screen assembly 1330 is provided with a fresnel lens 1410 and a screen 1430 with an air gap 1420 therebetween.
  • the screen 1430 is provided with a plurality of lenslets 1460 on the surface facing the fresnel lens 1410, and the black striped surface 1440 facing the viewing direction.
  • screen assembly 1330 is mounted to the enclosure 1310 by a two-sided adhesive tape 1450, while the fresnel lens 1410 and the screen 1430 is taped to each other using the two-sided adhesive tape 1450.
  • the two-sided adhesive tape 1450 is applied around the entire perimeter of the screen assembly 1330 that is located between the fresnel lens 1410 and the screen 1430.
  • a double sided adhesive with a closed or open cell foam interlayer may be used instead of the two-sided adhesive tape 1450.
  • the two-sided adhesive tape 1450 or the double sided adhesive with a closed or open cell foam interlayer may be applied at a predetermined spaced interval rather than continuously covering the entire perimeter as discussed above.
  • the thickness of the two-sided adhesive tape 1450 may be approximately within the range of 0.001 inch to 0.05 inch.
  • bonding the two layers (fresnel lens 1410 and the screen 1430) together forms a rigid, less flexible screen assembly 1330 which provides for a mechanically more desirable condition for a substrate that is to be mounted to the enclosure 1310. Additionally, in this manner, no compression mounting technique can be provided for screen assembly 1330 in rear projection based video display system.
  • the thickness of the two-sided adhesive tape 1450 introduces an air gap 1420 between the fresnel lens 1410 and the screen 1430, which advantageously prevents the introduction of Newton rings as discussed above. Additionally, the two-sided adhesive tape 1450 is applied around the perimeter of the screen assembly 1330 on the black stripe surface 1440 of the screen 1430 with tape thickness of approximately 0.1 mm to 5 mm. The tape 1450 is used to attach the screen assembly 1330 to the wall off the enclosure 1310.
  • FIG. 14C a side view of the screen assembly mounting technique in accordance with another embodiment of the present invention is shown in Figure 14C.
  • the screen assembly 1330 is mounted to the outer surface of the enclosure 1310. More specifically, the light receiving side of the fresnel lens 1410 of the screen assembly 1330 is mounted to the outside surface of the enclosure 1310 (for example, on the opposite surface of the enclosure as compared to the embodiment shown in Figures 14A-14B) using the two-sided adhesive tape 1450 by applying the adhesive tape 1450 around the outer perimeter of the screen assembly 1330. Mounting the screen assembly 1330 as shown in Figure 14C may permit easier screen replacement in the event of such need.
  • the screen assembly mounting technique for the rear projection video system in accordance with one embodiment provides for mounting the screen assembly to the enclosure such that it substantially eliminates Newton rings and visible, stress- induced phenomena.
  • any stress associated with either of the attachments may be evenly distributed within the screen assembly 1330.
  • the elimination of stress points in this manner minimizes the occurrence of stress induced birefringence, and thus, undesirable visible phenomena.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Projection Apparatus (AREA)
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  • Transforming Electric Information Into Light Information (AREA)

Abstract

Rear projection video system screen assembly including a cross ribbed screen with variable vertical and horizontal gain, a dithered ribbed screen (410) with variable vertical and horizontal field of view, a screen with overlapping lenslets, a screen assembly to reduce speckle and to suppress reflection and minimize light loss as well as provide screen surface protection while providing improved screen contrast, and a technique for mounting the screen assembly (410) in the rear projection video system is provided.

Description

SPECIFICATION
ADVANCED SCREEN TECHNOLOGIES FOR REAR PROJECTION APPLICATIONS AND SCREEN ASSEMBLY MOUNTING IN A REAR PROJECTION BASED VIDEO
DISPLAY SYSTEM
RELATED APPLICATION The present application claims priority under 35 USC §119 to provisional application no. 60/208,603, filed on May 5, 2000, and to provisional application no. 60/273,482, filed on March 2, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to video image systems. More particularly, the present invention relates to method and system for providing rear projection video system and screen assembly for rear projection based video display systems.
2. Description of the Related Art
In general, video images produced by a video projector is observed on a screen. In particular, in rear screen projection video systems, typically, video images projected from the back of the projection system with a transmissive screen is viewed from the front of the screen projection.
Figure 1 illustrates a typical rear screen projection system. Referring to Figure 1, rear screen projection system 100 includes a video projector 101 which is configured to project video images through a fresnel lens 102 onto a screen 103. The fresnel lens 102 may be configured to approximately coUimate the light incident on the rear of the screen 103. As can be seen from the Figure, the video projector 101 is configured to project video images onto the rear side of the screen 103 such that the viewing direction is substantially opposite to the direction of the video image projection from the video projector 101.
In such video systems, the gain generally refers to the ratio of the amount of light that is reflected from a Lambertian reflector compared to the amount of light transmitted on axis through a transmissive screen. Moreover, field of view (FOV) refers to the off normal angle required for the transmitted light intensity to fall to one half of the normal value. In most video applications, typical viewing conditions are such that it is desirable to have the horizontal field of view (FOV) be larger than the vertical field of view (FOV).
Additionally, speckle in the video systems referred to above is a power intensity pattern produced by mutual interference of partially coherent light beams that are subject to minute temporal and spatial fluctuations. More specifically, speckle is superimposed on the projected video image and is especially apparent in the light areas of static images. The magnitude of the speckle can be more severe in a "small" aperture light source such as a microdisplay based video projector system. In most cases, it is desirable to maintain the speckle to a minimum.
Referring back to Figure 1, the screen 103 is configured to transmit the projected video images (light) received from the video projector 101. Generally, to achieve optimum performance, the screen should transmit as large a fraction of the received light as possible. In addition, both large scale and small scale transmission should be as uniform as possible to reduce the possibility of hot spots.
Referring back to the screen 103 shown in Figure 1, the amount of room light reflected from the front of the screen and back into the eyes of the viewer is generally referred to as the front screen reflection. The front screen reflection may include both specular and diffuse reflectance, and should be maintained as low as possible to achieve a high contrast ratio. Resolution often measured with a "resolution target" and expressed in line pairs/mm, refers to the ability of the screen to reproduce as separate entities the points, lines and surfaces of the input image. To minimize input image quality degradation, it is desirable to maintain the resolution sufficiently high. Moreover, it is desirable to have the video screen properties be substantially the same in all portions of the spectrum - referred to as achromatic. In the context of rear projection screens, if the input light is unpolarized, then the screen properties should be independent of polarization, while if the input light is linearly polarized, the screen could be linearly polarized as well. Indeed, the characteristics desired in a screen for rear projection video system may depend upon the specific application for which it is intended. For example, in the case of a computer monitor, the gain should preferably be low, while narrower field of view (FOV) is acceptable.
With the use of a fresnel lens, it is possible to obtain the light incident on the rear of the screen to be approximately coUimated. Some types of display screens may require that the rear of the screen be approximately coUimated for optimal performance. The properties for a screen in a rear projection video system may depend upon the particular application intended for the projection system, and some of these criteria are discussed below.
For example, in the case of a computer monitor, typically, low gain is desired, while narrower field of view is acceptable. Moreover, very low speckle is required for optimal display performance while lower transmission is acceptable. Computer monitors generally require very little front surface reflection, but high resolution is typically required to insure the necessary high quality level for peak performance. By contrast, in the case of large diagonal high definition television (HDTV) screens, comparatively, higher gain is necessary with wide field of view, while some level of speckle may be acceptable. Indeed, in such HDTV screens, compared to computer monitors, higher transmission is necessary while some level of front surface reflection and lower resolution are acceptable.
Currently available screen technologies for rear projection applications include, diffuser, lenticular array, ribbed or beaded screens. Diffusers generally use a mat surface which diffuses transmitted light, and while speckle is typically low for diffusers which are easy to and relatively inexpensive manufacture, vertical and horizontal gains are the same, and resolution and transmission can be degraded. Lenticular array is a two dimensional array of lenslets that can be configured to provide a range of gain by varying the shape of the lenslets. However, manufacturing tools for manufacturing lenticular arrays are expensive, and large screens are difficult to manufacture. Furthermore, as with the diffusers, lenticular arrays have the same vertical and horizontal gains.
Ribbed screens are typically provided with vertically oriented, transmissive, cylindrical lenses which determine the horizontal gain, and can obtain high transmission rates. However, speckle for ribbed screens can be high, and these types of screens are difficult to manufacture. Moreover, front screen reflections may be problematic, and if diffusion is used for vertical gain, the resolution and transmission may be reduced.
By comparison, beaded screens comprise a single layer of clear, spherical (glass) balls, which has the advantage of providing a range of gain by varying the diameter of the spherical balls. However, as with the ribbed screens, speckle can be high and are difficult to manufacture. Furthermore, with beaded screens, it may be difficult to obtain uniform transmission over a large screen area, and the transmission may also be low. Moreover, resolution for beaded screens may be limited by the diameter of the spherical balls, and the vertical and horizontal gain for this type of screens is the same.
SUMMARY OF THE INVENTION
In view of the foregoing, a screen for use in a video projection system in accordance with one embodiment includes a vertical rib array, and a horizontal rib array positioned substantially in series with the vertical rib array, the horizontal and vertical rib arrays provided in an optical path forming a cross ribbed screen.
A screen for use in a video projection system in accordance with another embodiment includes a single ribbed screen including a plurality of vertical and horizontal ribs, each cross section of the vertical and horizontal ribs being dithered.
A screen for use in a video projection system in accordance with still another embodiment includes a screen having a ribbed side and a viewing side, the viewing side including a photoimagable coating layer illuminated with a coUimated light to form a striped pattern thereon. In the screen of above, a light path introduced from the ribbed side may be substantially aligned between a gap portion of the striped pattern on the viewing side.
A screen for use in a video projection system in accordance with yet still another embodiment includes a two dimensional array of overlapping substantially round lenslets provided in a first surface of a screen, the lenslets provided in a horizontal direction on the first surface with a predetermined stepping distance, and further, the lenslets provided in a vertical direction on the first surface with a predetermined stepping distance.
The predetermined stepping distance in the horizontal direction and the predetermined stepping distance in the vertical direction may be substantially the same. Furthermore, each cross section of the lenslets may be substantially spherical or aspheric.
A screen assembly for use in a video projection system in accordance with yet a further embodiment includes a lens provided in an optical path of a signal source, a diffusion layer positioned substantially between the lens and the optical path, a screen provided substantially on the opposite side of the lens to the diffusion layer.
The lens may include a fresnel lens.
The diffusion layer may be integrated with the lens as a single lens body.
The signal source may include a video projector.
Moreover, an air gap may be defined between the lens and the screen.
A screen assembly for use in a video projection system in accordance yet further still a further embodiment includes a lens provided in an optical path of a signal source, the lens including a first surface and a second surface, and an anti-reflecting layer provided on the first surface of the lens, said anti-reflecting layer configured to substantially minimize the reflection of the lens.
In one aspect, the lens may include a fresnel lens.
The optical path may be introduced into the first surface of the lens and substantially exit the lens at the second surface.
The anti-reflecting layer may include one of a single layer index matching material and a stack of thin film coatings.
The screen assembly may further include a screen positioned substantially adjacent to the second surface of the lens.
Furthermore, an air gap may be defined between the lens and the screen.
A screen assembly for use in a video projection system in accordance with yet still another embodiment includes a lens provided in an optical path of a signal source, the lens including a first surface and a second surface, a screen positioned substantially adjacent to the second surface of the lens, the screen including a first surface and a second surface, and a cover plate provided on the second surface of the screen.
The lens may include a fresnel lens, and the optical path may be introduced into the first surface of the lens and configured to exit the lens at the second surface of the lens.
The cover plate may be laminated onto the second surface of the screen.
Also, the cover plate may include one of a glass plate and a scratch resistant plastic plate.
The second surface of the screen may be coated with an anti-scratching coating, and may substantially face the first surface of the screen.
The screen assembly may further include an anti-reflection layer provided on the second surface of the screen between the second surface of the screen and the cover plate.
The anti-reflection layer may be laminated onto the second surface of the screen.
The second surface of the screen may be coated with a mat finish.
The cover plate may include a first surface and a second surface, the optical path configured to enter the first surface of the cover plate and to exit the cover plate at the second surface, the second surface of the cover plate coated with a mat finish.
Additionally, the cover plate second surface may be overcoated with a thin film anti- reflection coating over the mat finish.
The screen assembly may further include a linear polarizer provided between the screen and the cover plate, and the linear polarizer may be laminated on the second surface of the screen.
Moreover, an air gap may be defined between the second surface of the lens and the first surface of the screen.
A screen assembly for use in a video projection system of another embodiment includes a holographic lens positioned in an optical path from a signal source, and a screen positioned in the optical path on an opposite side of the lens to the signal source.
A screen assembly mounted in a video projection system of a further embodiment includes a housing, a lens positioned in an optical path within the housing, the lens including a first surface and a second surface, and a screen positioned in the optical path within the housing, the screen including a first surface and a second surface, the second surface of the lens and the first surface of the screen defining an air gap, the screen further mounted to the housing.
The lens may be taped to the screen using either a two-sided adhesive tape or a double sided adhesive with a closed or open cell foam interlayer.
The two sided adhesive tape or the double sided adhesive with the closed or open cell foam interlayer may be applied continuously around the outer periphery of the screen, or alternatively, may be applied at a predetermined interval around the outer periphery of the screen.
The two-sided adhesive tape taping the lens to the screen may have a thickness range of approximately 0.001 inch and 0.05 inch.
The screen is taped to the housing using either a two-sided adhesive tape or a double- sided adhesive with a closed or open cell foam interlayer.
The two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer may be applied continuously around the outer periphery of the screen, or may be applied at a predetermined interval around the outer periphery of the screen.
The two-sided adhesive tape taping the screen to the housing has a thickness range of approximately 0.1 mm to 5 mm. Additionally, the second surface of the screen may be coated with a striped pattern.
J-n the manner described, in accordance with the embodiments of the present invention, rear projection screen systems are provided with improved optical properties that are less expensive and easier to manufacture than typical rear projection systems available.
These and other features and advantages of the various aspects and embodiments of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates an overall rear projection video system;
Figure 2 illustrates a cross ribbed screen with variable vertical and horizontal gain in accordance with one embodiment;
Figure 3 illustrates a dithered ribbed screen with variable vertical and horizontal field of view (FOV) in accordance with one embodiment;
Figure 4 illustrates one embodiment of minimizing reflection from the front of a screen for ribbed type screens;
Figure 5 illustrates another embodiment of the screen with variable vertical and horizontal gain using overlapping lenslets;
Figures 6A-6B illustrate a manufacturing procedure for a screen with overlapping lenslets in accordance with one embodiment;
Figure 7 illustrates a screen in a rear projection video system with suppressed speckle in accordance with one embodiment;
Figure 8 illustrates a rear projection video system screen with suppressed reflection and light loss in accordance with one embodiment;
Figure 9 illustrates a rear projection video system with screen surface protection in accordance with one embodiment;
Figure 10 illustrates a rear projection video system with suppressed front screen reflections in accordance with one embodiment;
Figure 11 illustrates a rear projection video system with improved screen contrast in accordance with one embodiment;
Figure 12 illustrates a rear projection video system with an improved fresnel lens in accordance with one embodiment;
Figure 13 illustrates a screen assembly mounting technique in a rear projection video system in accordance with one embodiment; and
Figures 14A-14C illustrate screen assembly mounting techniques in the rear projection video system of Figure 13.
INCORPORATION BY REFERENCE
What follows is a cite list of references each of which is, in addition to those references that may be cited above and below herein, including that which is described as background, and the above invention summary, are hereby incorporated by reference into the detailed description of the preferred embodiment below, as disclosing alternative embodiments of elements or features of the preferred embodiments not otherwise set forth in detail below. A single one or a combination of two or more of these references may be consulted to obtain a variation of the preferred embodiments described in the detailed description below. Further patent, patent application and non-patent references may be cited in the written description and are also incorporated by reference into the detailed description of the preferred embodiment with the same effect as just described with respect to the following references:
United States patent applications no. 60/192,258, 60/192,732, 60/194,735, 60/198,436, 60/200,094, 60/202,265, 60/208,603, 60/210,784, 60/210,285, 60/213,334, 60/214,574, 60/215,932, 60/217,758, 60/220,979, 60/224,617, 60/224,961, 60/224,257, 60/224,503, 60/224,291, 60/224,290, 60/224,060, 60/224,059, 60/224,061, 60/224,289, 60/227,229, 60/229,666, 60/230,330, 60/230,326, 60/232,281, 60/234,415, 60/245,807 and 60/249,815, each of which is assigned to the same assignee as the present application. DETAILED DESCRIPTION OF THE INVENTION
Figure 2 illustrates a cross ribbed screen with variable vertical and horizontal gain in accordance with one embodiment. Referring to Figure 2, a vertical rib array 210 and a horizontal rib array 220 is shown. In one embodiment, the vertical rib array 210 is arranged in the optical path in series with the horizontal rib array 220 as shown in Figure 2. In this manner, a screen for a rear projection type video system is provided with a cross rib configuration such that differing vertical and horizontal gain as well as different vertical and horizontal field of view (FOV) may be obtained. In particular, the shape of the vertical and the horizontal ribs determines the desired corresponding horizontal and vertical gain as well as the vertical and horizontal FOVs.
Figure 3 illustrates a dithered ribbed screen with variable vertical and horizontal field of view (FOV) in accordance with one embodiment. Referring to Figure 3, using a ribbed lenticular screen, the cross sections of the ribs are dithered. In other words, the cross section of the vertical rib is periodically modulated. Further, a section of the ribbed screen is shaped so as to produce the desired FOV in the vertical direction, and the next section of the same ribbed screen is shaped so as to produce the desired FOV in the horizontal direction.
Indeed, this pattern of shaping a section of the rib to produce the desired FOV in the vertical direction and shaping the next section of the same rib to produce the desired FOV in the horizontal direction is periodically repeated along the entire length of each rib of the ribbed screen. In this manner, differing vertical and horizontal FOVs in the ribbed screen may be obtained, requiring only one screen layer as compared to the approach shown in conjunction with Figure 2 which includes a vertical rib array 210 and a horizontal rib array 220.
Figure 4 illustrates one embodiment of minimizing reflection from the front of a screen for ribbed type screens. Referring to Figure 4, a screen 410 is shown with a ribbed side 410A and a relatively flat side 410B. In one embodiment, a photoimagable black material 420 is coated onto the opposite side 410B of the ribbed section 410A of the screen 410. Thus, when the ribbed section 410A of the screen 410 is illuminated with coUimated light, the ribs are configured to focus the light onto and expose the coated photoimagable black material 420. In particular, the intensity of the coUimated light in one embodiment is configured sufficiently to form a striped pattern 430 on the photoimagable black material 420.
Moreover, the self-aligning process of the light path through the ribbed section 410A of the screen 410 ensures relatively perfect alignment between the striped portion 430 of the photoimagable black material 420 and the ribs provided on the ribbed section 410A of the screen. In this manner, the ribs on the ribbed section 410A of the screen 410 focus the light rays such that the light rays pass through the gap section 431 of the striped portion 430 of the photoimagable black material 420. In this manner, very little light is absorbed during transmission.
As discussed above, in one embodiment, by forming and employing black stripes 430 implemented in a ribbed type screen 410, reflections from the front of the screen 410 in the rear projection video system can be minimized without decreasing transmission through the video screen. It should be noted that in this approach, from the perspective of the viewing direction as shown in Figure 4, a large fraction of the screen 410 may appear black. This effectively reduced reflection. Furthermore, this approach provides a simple and inexpensive approach to manufacturing screens for rear projection video systems with lninimized reflections.
Figure 5 illustrates another embodiment of the screen with variable vertical and horizontal gain using overlapping lenslets. Referring to Figure 5, a screen 510 for use in a rear projection video system in provided with a two dimensional array of overlapping substantially round lenslets 520. In one aspect, the degree of overlap may be different along the vertical direction 530 as compared to the horizontal direction 540. The extent to which there is overlap in the vertical direction 530 and in the horizontal direction 540 which can be seen from the corresponding vertical stepping distance 511 and the horizontal stepping distance 512, may determine the FOVs in the vertical and horizontal directions. Moreover, the cross section of the lenslets 520, whether spherical or aspheric, provided on the screen 510 may impact the FOVs in the vertical and horizontal directions.
In the manner described above, by providing a two dimensional array of overlapping substantially round lenslets 520 in accordance with one embodiment, the screen 510 for a rear projection video system may be configured such that differing vertical and horizontal gain profiles may be obtained without the use of resolution degrading diffusers.
Figures 6A-6B illustrate a manufacturing procedure for a screen with overlapping lenslets shown in Figure 5 in accordance with one embodiment. Referring to Figure 6A, a diagonal facet in a conical diamond 610 is formed by cutting for example, along the plane of cut 611 shown in the Figure. The leading edge of the cut facet on the conical diamond 610 is substantially in the shape of the desired half cross-section of the lenslet. Thereafter the conical diamond 610 is polished to form the diamond spin bit 620. The prepared diamond spin bit 620 is then used to machine a negative of the lenslet into the surface of a copper drum 640 by, for example, rotating the diamond spin bit 620 in the direction 630 as shown in the Figure. After machining the negative of the lenslet onto the surface 641 of the copper drum 640, the surface 641 of the copper drum 640 is coated with, for example, a metal such as nickel to prevent oxidation.
As can be further seen from Figure 6A, the diamond pin bit 620 is stepped across the width of copper drum 640. In particular, the horizontal stepping distance 650 may be chosen such that the desired amount of horizontal overlap is produced. Thereafter, as shown, the copper drum 640B is slightly rotated and the subsequent rows 651, 652, 653 of negative of the lenslets 670 may be machined using the diamond spin bit 620. In one embodiment, the vertical stepping distance 660 may be selected such that a desired amount of vertical overlap is produced. This process is repeated until the entire circumference of the coated copper drum 640 is covered with the negative of the lenslets 670. Referring again to Figure 6A, the coated copper drum 640A is shown with the first row of overlapping negative of the lenslets 670 formed thereon with the predetermined vertical stepping distance 660, and the coated copper drum 640B is shown with subsequent columns of overlapping negative of the lenslets 670 with the predetermined horizontal stepping distance 650. In this manner, a master drum 640 is created that has arrays of negative lens features.
With the master dram 640, as shown in Figure 6B, the screen based on overlapping lenslets is produced. In particular, starting with a rigid, transparent substrate 680 that has been coated with UV curable material 681, the copper drum 640 is rolled over in the direction 685 as shown in the Figure across the uncured UV material 681 to emboss the surface with positive lens features. The UV material 681 is then cured by exposure to UV light rays from UV light source 690. In this manner, screens for rear projection video system with overlapping lenslets may be manufactured relatively easily and inexpensively.
It should be noted that the rolling process described above in conjunction with Figure 6B may also be used to manufacture the ribbed screen shown in Figure 2 as well as the dithered ribbed screen shown in Figure 3.
Figure 7 illustrates a screen in a rear projection video system with suppressed speckle in accordance with one embodiment. Referring to Figure 7, a video projector 710 is provided for projecting video signals from the rear of the video projection system onto a diffusion layer 720 behind a fresnel lens 725. On the opposite side of the fresnel lens 725 is provided a screen 730 which is used for viewing the projected video images in the viewing direction 740. In an alternate embodiment, the diffusion layer 720 may be integrated into the fresnel lens 725.
In the manner described above, in one embodiment, diffusion may introduced in the optical path of the video projection onto the screen 730. By doing so, speckle may be minimized and thus producing a higher quality image projection. However, it should be noted that the diffusion introduced in the optical path as discussed above should not be greater than necessary since the greater the diffusion, the lower the speckle but the higher the degradation of resolution and the lower the transmission.
Figure 8 illustrates a rear projection video system screen with suppressed reflection and light loss in accordance with one embodiment. Referring to Figure 8, a similar rear projection video system as that shown in Figure 7 is illustrated including a video projector 810 configured to project video images through a fresnel lens 820 onto a screen, where the viewing direction 840 is opposite the direction of the video image projection from the video projector 810. Also shown in Figure 8 is ah anti-reflecting coating 850 provided on the back surface of the fresnel lens 820. The anti-reflection coating 850 may in one embodiment include a single layer index matching material deposited from a liquid or a stack of thin film coatings. Alternatively, a microscopic "Moth's eye" may be used to texture the back surface of the fresnel lens 820 to provide the anti-reflection coating 850
In this manner, reflection and light loss from the fresnel lens 820 during projection of video images may be minimized. In particular, since the video images are projected into the back surface of the fresnel lens 820, some portion of the projected images is reflected back. This reduced the light available to the viewer, and further, the reflected light may reflect around the cabinet of the video projector 810 and eventually project out onto the screen 830 resulting in a decrease in the contrast ratio. By providing the anti-reflection coating 850 as discussed above, it is possible to minimize the decrease in the contrast ratio by minimizing the reflection of the projected video images from the back surface of the fresnel lens 820 and the screen 830.
Figure 9 illustrates a rear projection video system with screen surface protection in accordance with one embodiment. Referring to Figure 9, similar to the embodiments shown in Figures 7 and 8, video projector 910 is provided for projecting video images through a fresnel lens 920 onto the rear surface of a screen 830 opposite to the viewing direction 940. As shown in Figure 9, a cover plate 950 is laminated onto the front surface of the screen 930. The laminated cover plate 950 may be glass or a scratch resistance plastic. Alternatively, the screen 930 may be coated with an anti-scratching coating (such as, for example, those used to protect the front of the polarizer in a laptop computer). Additionally, the cover plate 950 may also provide added rigidity to the screen 930.
In this manner, the surface of the screen 930 may be protected from exposure to the environment as well as to the viewers. In particular, since the screen 930 is the outermost surface of the rear projection video system, its exposure to potential damaging sources is particularly acute. By providing a cover plate 950 in accordance with one embodiment of the present invention, the screen 930 may be better protected from potential physical damages.
Figure 10 illustrates a rear projection video system with suppressed front screen reflections in accordance with one embodiment. Referring to Figure 10, similar to the embodiment shown in Figure 9, a video projector 1010 is provided along with a fresnel lens 1020 and a screen 1030 with a cover plate 1040. the video projector 1010 is configured to project video images through the fresnel lens 1020 onto the screen 1030 in the opposite direction to the viewing direction 1060. In the embodiment shown in Figure 10, an anti- reflection layer 1050 is provided onto the viewing direction surface of the screen 1030.
In one aspect, the anti-reflection layer 1050 over the cover plate 1040 laminated onto the screen 1030 may be provided by coating the surface with a mat finish, thus effectively "spoiling" any specular reflection and minimizing reflectivity from the front of the screen 1030. Alternatively, the viewing direction side of the screen 1030 with the cover plate 1040 may be coated with a thin film anti-reflection coating as the anti-reflection layer 1050. This approach has the added advantage over using the mat finish without a loss of resolution. As a further alternative, the viewing direction side of the screen 1030 with the cover plate 1040 may be coated with the mat finish and then overcoated with the thin film anti-reflection coating. This has a further front screen reflection suppression result as compared to using just one of the two approaches discussed above.
Figure 11 illustrates a rear projection video system with improved screen contrast in accordance with one embodiment. In Figure 11, a linear polarizer 1140 is laminated over the viewing direction 1160 side of the screen 1130 opposite the fresnel lens 1120. As further shown, an optical cover glass 1150 for the protection of the screen 1130 and the polarizer 1140 is provided.
In one embodiment, the orientation of the transmission axis of the linear polarizer 1140 is substantially parallel to the polarization axis of the projected light from the video projector 1110. Since the projected light from the video projector 1110 is rarely perfectly tinearly polarized, but rather, is generally slightly elliptically polarized, the linear polarizer 1140 is configured to remove any unwanted component. Furthermore, any stray light, such as reflected light from the back surface of the fresnel lens 1120 as discussed above, that reaches the screen 1130 tends to be depolarized, and thus the stray light will be partially suppressed by the linear polarizer 1150. In this manner, by providing the output of all channels to be linearly polarized and have the same orientation through the implementation of the linear polarizer 1140, the contrast ratio of the rear projection video system may be maximized.
Figure 12 illustrates a rear projection video system with an improved fresnel lens in accordance with one embodiment. Referring to Figure 12, a holographic fresnel lens 1220 is provided to improve input light collimation. As discussed above, the performance of certain types of screens in rear projection video systems including ribbed and lenticular screens, are optimized when the input light is coUimated. The fresnel lens is generally provided to provide coUimated light. However, in some instances, the fresnel lens may introduce artifacts to the image, such artifacts including chromatic separation of the projected light and the establishment of a Moire pattern between the periodicity of the lines in the fresnel lens and the repetitive features in the screen. By employing a hologram 1220 as a substitute for the fresnel lens, in accordance with the present invention, input light may be coUimated without the potential for introducing artifacts to the projected images.
Referring back to Figure 12, also shown in the Figure is an air gap 1250 between the hologram fresnel lens 1220 and the screen 1230. In some instances, visually observable artifacts such ύs Newton rings may occur between the fresnel lens and the screen. The visually observable artifacts, in turn, have degrading impact on the quality of the projected video images. By providing the air gap 1250 between the hologram fresnel lens 1220 and the screen 1230, it may be possible to suppress the Newton rings and thus minimize the degradation of the projected video images.
Figure 13 illustrates a screen assembly mounting technique in a rear projection video system in accordance with one embodiment. Referring to the Figure, a side view of the interior 13 A of a rear projection video system and a front view of the exterior 13B of the video system is shown. In particular, an enclosure 1310 is provided which houses a large mirror 1320, a screen assembly 1330, a small mirror 1340 and a light engine 1350. The screen assembly 1330 is mounted within the enclosure 1310 on the viewing side of the video projection system, and includes a fresnel lens and a screen. Substantially on the opposite side from the screen assembly 1330 within the enclosure 1310 is mounted the large mirror 1320, and substantially at the lower end with in the enclosure 1310 is provided the light engine 1350 and the small mirror 1340. In one embodiment, the tracings of the marginal rays from the light engine 1350 can be seen from the figure along the path 1360 as shown within the enclosure 1310 for projection onto the screen assemblyl330.
In this manner, the screen assembly 1330 is attached to the enclosure 1310 of the display system, and the enclosure 1310 acts as a "picture frame" around the screen assembly 1330. In particular, the front view of the exterior 13B substantially illustrates the enclosure 1310 as a picture frame around the screen assembly 1330.
Figures 14A-14C illustrate screen assembly mounting techniques in the rear projection video system of Figure 13. In particular, Figures 14A-14B illustrate a side view and a close up side view of the screen assembly mounting technique in accordance with one embodiment of the present invention. As can be seen, screen assembly 1330 is provided with a fresnel lens 1410 and a screen 1430 with an air gap 1420 therebetween. Furthermore, the screen 1430 is provided with a plurality of lenslets 1460 on the surface facing the fresnel lens 1410, and the black striped surface 1440 facing the viewing direction. As can be further seen, screen assembly 1330 is mounted to the enclosure 1310 by a two-sided adhesive tape 1450, while the fresnel lens 1410 and the screen 1430 is taped to each other using the two-sided adhesive tape 1450.
In particular, the two-sided adhesive tape 1450 is applied around the entire perimeter of the screen assembly 1330 that is located between the fresnel lens 1410 and the screen 1430. Alternatively, a double sided adhesive with a closed or open cell foam interlayer may be used instead of the two-sided adhesive tape 1450. Furthermore, the two-sided adhesive tape 1450 or the double sided adhesive with a closed or open cell foam interlayer may be applied at a predetermined spaced interval rather than continuously covering the entire perimeter as discussed above. The thickness of the two-sided adhesive tape 1450 may be approximately within the range of 0.001 inch to 0.05 inch.
In this manner, bonding the two layers (fresnel lens 1410 and the screen 1430) together forms a rigid, less flexible screen assembly 1330 which provides for a mechanically more desirable condition for a substrate that is to be mounted to the enclosure 1310. Additionally, in this manner, no compression mounting technique can be provided for screen assembly 1330 in rear projection based video display system.
Moreover, the thickness of the two-sided adhesive tape 1450 introduces an air gap 1420 between the fresnel lens 1410 and the screen 1430, which advantageously prevents the introduction of Newton rings as discussed above. Additionally, the two-sided adhesive tape 1450 is applied around the perimeter of the screen assembly 1330 on the black stripe surface 1440 of the screen 1430 with tape thickness of approximately 0.1 mm to 5 mm. The tape 1450 is used to attach the screen assembly 1330 to the wall off the enclosure 1310.
Referring back to the Figures, a side view of the screen assembly mounting technique in accordance with another embodiment of the present invention is shown in Figure 14C. In particular, as shown in the Figure, rather than mounting the screen assembly 1330 to the inside wall of the enclosure 1310 as shown in Figures 14A-14B, in the approach shown in Figure 14C, the screen assembly 1330 is mounted to the outer surface of the enclosure 1310. More specifically, the light receiving side of the fresnel lens 1410 of the screen assembly 1330 is mounted to the outside surface of the enclosure 1310 (for example, on the opposite surface of the enclosure as compared to the embodiment shown in Figures 14A-14B) using the two-sided adhesive tape 1450 by applying the adhesive tape 1450 around the outer perimeter of the screen assembly 1330. Mounting the screen assembly 1330 as shown in Figure 14C may permit easier screen replacement in the event of such need.
Indeed, any contact between the fresnel lens 1410 and the screen 1430 produces visually objectionable Newton rings, and further, any mechanism that clamps the screen assembly 1330 to the enclosure 1310 has the potential to induce stress points which may be highly undesirable because they can be visualized in the projected image. In view of the foregoing, in the manner described above, the screen assembly mounting technique for the rear projection video system in accordance with one embodiment provides for mounting the screen assembly to the enclosure such that it substantially eliminates Newton rings and visible, stress- induced phenomena. In particular, by applying the two-sided tape 1450 around the entire perimeter of the screen assembly 1330, any stress associated with either of the attachments (fresnel lens 1410 and the screen 1430) may be evenly distributed within the screen assembly 1330. Moreover, the elimination of stress points in this manner minimizes the occurrence of stress induced birefringence, and thus, undesirable visible phenomena.
While the specific embodiments described herein may be directed to developing a system optimized for rear screen video projection, in one aspect of the present invention, the approach set forth herein may be applied to display systems optimized for other applications including those intended primarily for the display of text or those using direct view.
Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.

Claims

WHAT IS CLAIMED IS:
1. A screen for use in a video projection system, comprising: a vertical rib array ; and a horizontal rib array positioned substantially in series with said vertical rib array, said horizontal and vertical rib arrays provided in an optical path forming a cross ribbed screen.
2. A screen for use in a video projection system, comprising: a single ribbed screen including a plurality of vertical and horizontal ribs, each cross section of said vertical and horizontal ribs being dithered.
3. A screen for use in a video projection system, comprising: a screen having a ribbed side and a viewing side, said viewing side including a photoimagable coating layer illuminated with a coUimated light to form a striped pattern thereon.
4. The screen of claim 3 wherein a light path introduced from said ribbed side is substantially aligned between a gap portion of said striped pattern on said viewing side.
5. A screen for use in a video projection system, comprising: a two dimensional array of overlapping substantially round lenslets provided in a first surface of a screen, said lenslets provided in a horizontal direction on said first surface with a predetermined stepping distance, and further, said lenslets provided in a vertical direction on said first surface with a predetermined stepping distance.
6. The screen of claim 5 wherein said predetermined stepping distance in said horizontal direction and said predetermined stepping distance in said vertical direction are substantially the same.
7. The screen of claim 5 wherein each cross section of said lenslets is substantially spherical.
8. The screen of claim 5 wherein each cross section of said lenslets is substantially aspheric.
9. A screen assembly for use in a video projection system, comprising: a lens provided in an optical path of a signal source; a diffusion layer positioned substantially between the lens and the optical path; and a screen provided substantially on the opposite side of said lens to said diffusion layer.
10. The screen assembly of claim 9 wherein said lens includes a fresnel lens.
11. The screen assembly of claim 9 wherein said diffusion layer is integrated with said lens as a single lens body.
12. The screen assembly of claim 9 wherein said signal source includes a video projector.
13. The screen assembly of claim 9 wherein an air gap is defined between said lens and said screen.
14. A screen assembly for use in a video projection system, comprising: a lens provided in an optical path of a signal source, said lens including a first surface and a second surface; and an anti-reflecting layer provided on said first surface of said lens, said anti-reflecting layer configured to substantially minimize the reflection of said lens.
15. The screen assembly of claim 14 wherein said lens includes a fresnel lens.
16. The screen assembly of claim 14 wherein said optical path is introduced into said first surface of said lens and substantially exits said lens at said second surface.
17. The screen assembly of claim 16 wherein said anti-reflecting layer includes one of a single layer index matching material and a stack of thin film coatings.
18. The screen assembly of claim 14 wherein said signal source includes a video projector.
19. The screen assembly of claim 14 further including a screen positioned substantially adjacent to said second surface of said lens.
20. The screen assembly of claim 19 wherein an air gap is defined between said lens and said screen.
21. A screen assembly for use in a video projection system, comprising: a lens provided in an optical path of a signal source, said lens including a first surface and a second surface; a screen positioned substantially adjacent to said second surface of said lens, said screen including a first surface and a second surface; and a cover plate provided on said second surface of said screen.
22. The screen assembly of claim 21 wherein said lens includes a fresnel lens, and said optical path is introduced into said first surface of said lens and configured to exit said lens at said second surface of said lens.
23. The screen assembly of claim 21 wherein said cover plate is laminated onto said second surface of said screen.
24. The screen assembly of claim 21 wherein said cover plate includes one of a glass plate and a scratch resistant plastic plate.
25. The screen assembly of claim 21 wherein said second surface of said screen is coated with an anti-scratching coating.
26. The screen assembly of claim 21 wherein said second surface of said lens substantially faces said first surface of said screen.
27. The screen assembly of claim 21 further including an anti-reflection layer provided on said second surface of said screen between said second surface of said screen and said cover plate.
28. The screen assembly of claim 27 wherein said anti-reflection layer is laminated onto said second surface of said screen.
29. The screen assembly of claim 21 wherein said second surface of said screen is coated with a mat finish.
30. The screen assembly of claim 21 wherein said cover plate includes a first surface and a second surface, said optical path configured to enter said first surface of said cover plate and to exit said cover plate at said second surface, said second surface of said cover plate coated with a mat finish.
31.' The screen assembly of claim 30 wherein said cover plate second surface is overcoated with a thin film anti-reflection coating over said mat finish.
32. The screen assembly of claim 21 further including a linear polarizer provided between said screen and said cover plate.
33. The screen assembly of claim 32 wherein said linear polarizer is laminated on said second surface of said screen.
34. The screen assembly of claim 21 wherein an air gap is defined between said second surface of said lens and said first surface of said screen.
35. A screen assembly for use in a video projection system, comprising: a holographic lens positioned in an optical path from a signal source; and a screen positioned in said optical path on an opposite side of said lens to said signal source.
36. The screen assembly of claim 35 wherein said signal source includes a video projector.
37. The screen assembly of claim 35 wherein an air gap is defined between said lens and said screen.
38. A screen assembly mounted in a video projection system, comprising: a housing; a lens positioned in an optical path within said housing, said lens including a first surface and a second surface; and a screen positioned in said optical path within said housing, said screen including a first surface and a second surface, said second surface of said lens and said first surface of said screen defining an air gap, said screen further mounted to said housing.
39. The screen assembly of claim 38 wherein said lens is taped to said screen using one of a two-sided adhesive tape and a double sided adhesive with a closed or open cell foam interlayer.
40. The screen assembly of claim 39 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied continuously around the outer periphery of the screen.
41. The screen assembly of claim 39 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied at a predetermined interval around the outer periphery of the screen.
42. The screen assembly of claim 39 wherein said two-sided adhesive tape taping said lens to said screen has a thickness range of approximately 0.001 inch and 0.05 inch.
43. The screen assembly of claim 38 wherein said screen is taped to said housing using one of a two-sided adhesive tape and a double sided adhesive with a closed or open cell foam interlayer.
44. The screen assembly of claim 43 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied continuously around the outer periphery of the screen.
45. The screen assembly of claim 43 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied at a predetermined interval around the outer periphery of the screen.
46. The screen assembly of claim 43 wherein said two-sided adhesive tape taping said screen to said housing has a thickness range of approximately 0.1 mm to 5 mm.
47. The screen assembly of claim 43 wherein said lens is taped to said screen using one of a two-sided adhesive tape and a double sided adhesive with the closed or open cell foam interlayer.
48. The screen assembly of claim 47 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied continuously around the outer periphery of the screen.
49. The screen assembly of claim 47 wherein said two sided adhesive tape or said double sided adhesive with the closed or open cell foam interlayer is applied at a predetermined interval around the outer periphery of the screen.
50. The screen assembly of claim 47 wherein said two-sided adhesive tape taping said lens to said screen has a thickness range of approximately 0.001 inch and 0.05 inch.
51. The screen assembly of claim 50 wherein said second surface of said screen is coated with a striped pattern.
PCT/US2001/014479 2000-05-05 2001-05-03 Rear projection screen for video display system WO2001086349A2 (en)

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EP1395052A1 (en) * 2002-08-30 2004-03-03 Seiko Epson Corporation Light transmittive screen and rear projector
DE102004042648A1 (en) * 2004-09-03 2006-03-30 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Device and method for displaying a static or moving picture uses screen, which has a structure that defocuses the laser beam
WO2006065524A2 (en) * 2004-12-14 2006-06-22 Coherent, Inc. Laser illuminated projection displays
US7872800B2 (en) 2004-08-04 2011-01-18 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Device and method for the presentation of static or moving images

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EP1395052A1 (en) * 2002-08-30 2004-03-03 Seiko Epson Corporation Light transmittive screen and rear projector
US7872800B2 (en) 2004-08-04 2011-01-18 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Device and method for the presentation of static or moving images
DE102004042648A1 (en) * 2004-09-03 2006-03-30 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Device and method for displaying a static or moving picture uses screen, which has a structure that defocuses the laser beam
WO2006065524A2 (en) * 2004-12-14 2006-06-22 Coherent, Inc. Laser illuminated projection displays
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