CN1987527A - Image display device and fresnel lens sheet used therefor - Google Patents
Image display device and fresnel lens sheet used therefor Download PDFInfo
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- CN1987527A CN1987527A CN 200610107775 CN200610107775A CN1987527A CN 1987527 A CN1987527 A CN 1987527A CN 200610107775 CN200610107775 CN 200610107775 CN 200610107775 A CN200610107775 A CN 200610107775A CN 1987527 A CN1987527 A CN 1987527A
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- 230000003287 optical effect Effects 0.000 description 17
- 230000002093 peripheral effect Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 238000002834 transmittance Methods 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 3
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- 230000003014 reinforcing effect Effects 0.000 description 3
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- 239000003795 chemical substances by application Substances 0.000 description 1
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Abstract
The present invention provided a technic of eliminating the brightness uneven of a projection image in a visual display unit of projecting the image light to the rear projection screen and amplifying the projection image. The Fresnel lens sheet is provided with a first prism group in an area of a light entrance plane of the Fresnel lens sheet where the incident angle of light is equal to or more than a predetermined incident angle and a second prism group in an area of a light entrance plane of the Fresnel lens sheet where the incident angle of light is less than the predetermined value. The first prism group contains the first plane of refraction which refractes the light whose incident angle is equal to or more than a predetermined incident angle, and the first complete reflective surface which reflects the light refracted by the first plane of refraction and leads the light to the emergente side of the Fresnel lens. The second prism group contains the second plane of refraction which refractes the light whose incident angle is less than the predetermined value and leads the light to the emergente side of the Fresnel lens, and the second complete reflective surface which reflects a part of light refracted by the second plane of refraction and leads the light to the emergente side of the Fresnel lens.
Description
Technical Field
The present invention relates to a rear projection type or direct view type image display device and a fresnel lens sheet used for the same.
Background
In a rear projection type image display device (hereinafter, referred to as a device in some cases) which projects a small image on a screen in an enlarged manner, it is desired to make the device thin (reduce the depth dimension). If the depth of the device is shortened, the incident angle of light is increased particularly in the peripheral portion of the screen. Therefore, the light utilization efficiency is reduced (that is, reflection loss is increased) in the peripheral portion of the screen, and the image becomes dark. As a prior art for dealing with this, for example, one described in japanese patent laid-open No. 2004-170862 is known. In this disclosure, a prism having a refraction surface and a total reflection surface is provided on a light incident surface (image generation source side) of a fresnel lens sheet which is a component of a screen, and light having a large incident angle is refracted by the refraction surface, is totally reflected by the total reflection surface, and is emitted to the screen.
In addition, in a direct-view type image display device, for example, as described in japanese patent laid-open No. 2004-273396, it is known that a plurality of cold cathode fluorescent lamps are provided on a light incident side of a rear surface as an image generation source (for example, a liquid crystal panel) in order to reduce the thickness of the device.
Disclosure of Invention
As described in the above-described conventional art, in the invention in which the total reflection type prism is provided on the incident surface side, when light having a small incident angle is incident on the fresnel lens sheet, it is impossible to totally reflect all of the incident light by the total reflection type prism. The light that is not totally reflected becomes stray light (light that is totally reflected inside the fresnel lens sheet and reaches a place other than a desired place), and the contrast of the image is reduced. Further, the stray light causes unevenness in brightness of an image on a screen, and is not suitable for a case where uniform brightness is required over the entire screen. Therefore, in the case where the total reflection type prism is provided on the incident surface side, it is important to effectively bend (totally reflect) the incident light to the screen toward the viewing side to widen the range of possible light incident angles. That is, it is important to reduce the lower limit value of the incident angle of the light capable of total reflection to realize high quality of the screen.
As described in the above-mentioned patent document 1, as described in paragraph No. 0034 (table 1), when the incident angle to the screen is 35 degrees, the occurrence rate of stray light becomes 20% or more. That is, in the invention described in patent document 1, since the occurrence rate of stray light is relatively high in the vicinity of the lower limit value, it is necessary to further suppress the occurrence rate of stray light.
On the other hand, in a direct-view type image display device using a liquid crystal panel, for example, a cold cathode fluorescent lamp is used for thinning, and light is diffused to a portion where no lamp is provided by a reflector or a diffuser plate, thereby realizing light uniformity. However, light other than the predetermined light incident angle causes deterioration of the contrast of an image on the liquid crystal panel. Therefore, when light is diffused and made incident on the liquid crystal panel as in the conventional technique, the incident angle of light toward the liquid crystal panel becomes various values and becomes large, and thus the contrast of an image may be deteriorated. In order to improve the contrast, the light may be incident on the liquid crystal panel at a predetermined incident angle, but a factor for selecting predetermined light from stray light becomes necessary again, and the efficiency is also lowered.
In the direct-view image display device using the liquid crystal panel, a plurality of fluorescent lamps are arranged on the back surface of the liquid crystal panel, but the fluorescent lamps become dark as the emission luminance decreases during the lighting time. Since the deterioration of the luminance is different for each lamp, unevenness in luminance occurs in a display image. It is therefore necessary to replace the lamp in the event of significant brightness unevenness or lamp misfiring. However, since the lamp is disposed on the back surface of the liquid crystal panel, a complicated operation is required for replacement.
The invention provides a technique for obtaining a high-quality image while thinning a device.
The present invention is characterized in that a 1 st prism group is provided in a region of the light incident surface of the fresnel lens sheet which is equal to or larger than a predetermined light incident angle, and a 2 nd prism group is provided in a region of the light incident surface of the fresnel lens sheet which is smaller than the predetermined light incident angle, wherein the 1 st prism group includes a 1 st refraction surface which refracts light incident at the predetermined light incident angle or larger and a 1 st total reflection surface which reflects light refracted by the 1 st refraction surface and guides the reflected light to the output side of the fresnel lens sheet, and the 2 nd prism group includes a 2 nd refraction surface which refracts light incident at the predetermined light incident angle or smaller and guides the reflected light to the output side of the fresnel lens sheet and a 2 nd total reflection surface which reflects a part of the light refracted by the 2 nd refraction surface and guides the reflected light to the output side of the fresnel lens sheet.
The light reflected by the 1 st total reflection surface of the prism group at the position separated from the 2 nd prism group in the 1 st prism group is emitted in a direction substantially parallel to the normal of the Fresnel lens sheet, and the light reflected by the 1 st total reflection surface of the prism group in the vicinity of the 2 nd prism group in the 1 st prism group is emitted in a direction toward the inside of the normal of the Fresnel lens sheet. In the light emitting surface of the fresnel lens sheet, a region of the 1 st prism group facing the prism group located away from the 2 nd prism group may be flat, a 3 rd prism group may be provided in a region of the 1 st prism group facing the prism group located in the vicinity of the 2 nd prism group, and a 4 th prism group may be provided in a region of the 1 st prism group facing the 2 nd prism group. Further, the 4 th prism group includes: a 3 rd refraction surface for refracting the light refracted by the 2 nd refraction surface of the 2 nd prism group again, and a 4 th refraction surface for refracting the light reflected by the 2 nd total reflection surface, so that the light refracted from the 2 nd prism group is refracted to the direction approximately parallel to the normal direction of the Fresnel lens sheet.
Further, a region of the light incident surface of the Fresnel lens sheet, in which light is incident at a smaller incident angle than a region in which the 2 nd prism group is provided, is formed in a planar shape, and a 5 th prism group for refracting light incident on the planar region is provided in a region of the light exit surface of the Fresnel lens sheet, in which the region faces the planar region.
The fresnel lens sheet having the above-described configuration may be used as one element of a screen used in a rear projection type image display device, or may be used by being disposed on the incident side of an image generation source of a direct-view type image display device. When the fresnel lens sheet is attached to the device, the fresnel lens sheet may be fixed to the frame of the image display device by applying tension to the periphery of the fresnel lens sheet, or the fresnel lens sheet may be fixed to the frame of the image display device by inverting the fresnel lens sheet so that the fresnel lens sheet is recessed toward the light source (lamp) side of the device.
Therefore, according to the present invention, it is possible to obtain an image with high image quality and high brightness while reducing the thickness of the device.
Drawings
Fig. 1 is a diagram showing an example of a configuration of a rear projection type image display device using the present invention;
fig. 2 is a diagram showing one configuration example of a transmission type screen according to the present invention;
FIG. 3 is a vertical sectional view showing the overall configuration of a Fresnel lens sheet according to example 1 of the present invention;
fig. 4 is a partially enlarged view illustrating the optical action of the 1 st prism group 12 a;
FIG. 5 is a partially enlarged view illustrating the optical effects of the 1 st prism group 12a and the 3 rd prism group 15 a;
FIG. 6 is a partially enlarged view illustrating the optical effects of the 2 nd prism group 12b and the 4 th prism group 15 b;
fig. 7 is a diagram showing an example of a configuration of a direct-view image display device using the present invention;
FIG. 8 is a sectional view in the vertical direction showing the overall constitution of a Fresnel lens sheet according to example 2 of the present invention;
fig. 9 is a partially enlarged view illustrating the optical action of the 5 th prism group 15 c;
FIG. 10 is a graph showing the transmittance of the Fresnel lens sheet according to example 2 of the present invention.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the drawings.
Example 1
Fig. 1 is a sectional view of an image display device of a rear projection type according to the present invention. The image generating source 1 is configured by an image modulation element such as a projection cathode ray tube, a reflective or transmissive liquid crystal panel, or a display element having a plurality of micromirrors, and displays a small image. The projection lens 2 enlarges a small image displayed on a display screen of an image generation source and projects the enlarged image on the rear projection screen 3. A mirror 4 is provided in the middle of the optical path from the exit surface of the projection lens 2 to the entrance surface of the screen 3. Thus, the image enlarged by the projection lens 2 is reflected by the mirror 4 and projected onto the rear surface of the screen 3. Thereby, the depth of the device is reduced. These elements are housed in the case 5 and fixed at predetermined positions. Here, in order to make the depth of the case 300mm or less, for example, the incident angle range to the rear projection screen is about 30 to 70 degrees. That is, when the minimum incident angle 7 is about 30 degrees, the maximum incident angle 6 is about 70 degrees or more.
Fig. 2 shows one configuration example of a rear projection type screen 3 used in the image display apparatus according to the present invention. The rear projection screen 3 includes a fresnel lens sheet 8 and a lenticular lens sheet 9 as a diffusion sheet. The fresnel lens sheet 8 has a total reflection prism 12 formed on its light incident surface and a refraction prism 15 formed on its light emitting surface. According to the rear projection screen 3 having the above-described configuration, the enlarged projection image projected in the direction of the arrow "a" in the figure is converted into substantially parallel light (i.e., light having an exit angle of substantially 0 degree with respect to the normal line of the principal plane of the fresnel lens sheet) or light directed substantially inward by the action of the fresnel lens sheet 8, i.e., the action of the refraction prism 15 formed on the fresnel lens sheet. The light enters the lenticular lens sheet 9 and is diffused in the horizontal and vertical directions of the screen.
Further, on the light incident surface of the lenticular lens sheet 9, as shown in fig. 2, a plurality of lenticular lenses 20 whose longitudinal direction is the vertical direction of the screen are arranged in the horizontal direction of the screen. This serves to diffuse the image light from the lenticular lens sheet 8 in the horizontal direction of the screen. Further, on the exit surface of the lenticular lens sheet 9, a plurality of plastic stripes 10 extending in the vertical direction of the screen are arranged in the horizontal direction of the screen. Thereby, the external light incident from the screen exit side is absorbed. The lenticular lens sheet 9 is made of a transparent resin material into which the light diffusion material 11 is mixed. The mixed light diffusion material 11 plays a role of diffusing the image light in horizontal and vertical directions of the screen. A transparent reinforcing sheet (not shown) may be disposed on the front surface of the lenticular lens sheet 9. Further, by integrating the reinforcing sheet bonded to the lenticular lens sheet 9, the mechanical strength of the lenticular lens sheet 9 can be improved. The lenticular lens sheet 9 may contain no light diffusing agent 11, and a reinforcing sheet disposed in front of the lenticular lens sheet 9. In the present embodiment, there are two types of the reflective prisms 12 of the lenticular lens sheet 8 shown in fig. 2. The first prism group 1 is provided in a region of a predetermined light incident angle or more (for example, 40 degrees or 50 degrees or more) on the light incident surface of the fresnel lens sheet 8. The second is a 2 nd prism group provided in a region less than the predetermined light incident angle. The 1 st prism group includes a 1 st refraction surface for refracting light incident at a predetermined light incidence angle or more, and a 1 st total reflection surface for reflecting the light refracted by the 1 st refraction surface and guiding the light to the exit side of the Fresnel lens sheet. The 2 nd prism group includes a 2 nd refracting surface which refracts light incident at an angle less than the predetermined incident angle and guides the light to the exit side of the Fresnel lens sheet 8, and a 2 nd total reflecting surface which reflects a part of the light refracted by the 2 nd refracting surface and guides the light to the exit side of the Fresnel lens sheet 8. Further, a 3 rd prism group and a 4 th prism group are provided as refraction type prisms on the output surface of the Fresnel lens sheet 8. The 3 rd prism group is disposed in a region facing the 1 st prism group located in the vicinity of the 2 nd prism group on the incident surface. The 3 rd prism group comprises a 5 th refraction surface for refracting the light refracted by the 1 st refraction surface of the 1 st prism group and reflected by the 1 st total reflection surface again. The 4 th prism set opposite to the 2 nd prism set comprises a 3 rd refraction surface for refracting the light refracted by the 2 nd refraction surface of the 2 nd prism set again and a 4 th refraction surface for refracting the light reflected by the 2 nd total reflection surface of the 2 nd prism set. Further, a 1 st plane region 17 having a plane shape in which no prism is formed is provided in a region other than the vicinity of the 2 nd prism group at a position facing the 1 st prism group on the output surface of the Fresnel lens sheet 8.
The Fresnel lens sheet 8 is constructed as shown in FIG. 3. FIG. 3 is a sectional view showing the vertical direction of the Fresnel lens sheet 8 according to the present embodiment. As shown in fig. 3, in the present embodiment, the fresnel lens sheet 8 is divided into two regions according to the incident angle of light along the vertical direction. The region a is a region where light enters at an incident angle of, for example, 45 degrees to 70 degrees (maximum incident angle). The region B is a region where light is incident at an incident angle of, for example, 30 degrees (minimum incident angle) to 44 degrees.
The 1 st prism group 12a having the 1 st refraction surface SK1 and the 1 st total reflection surface SH1 is provided IN the area a of the light incident surface IN of the fresnel lens sheet 8, and the 2 nd prism group 12B having the 2 nd refraction surface SK2 and the 2 nd total reflection surface SH2 is provided IN the area B. On the other hand, the 1 st plane area 17 and the 3 rd prism group 15a are provided in the area a of the light output surface OUT of the fresnel lens sheet 8. The 3 rd prism group 15a has the 5 th refractive surface SK5, and is disposed at a position facing the 1 st prism group 12a within a predetermined range from the boundary between the region a and the region B. The 1 st plane area 17 faces the 1 st prism group 12a other than the predetermined area. Further, on the region B of the light exit surface OUT, the 4 th prism group 15B having the 3 rd refractive surface SK3 and the 4 th refractive surface SK4 is provided. In this way, the 3 rd prism group 15a is disposed in a region facing the 1 st prism group 12a, and the 4 th prism group 15b is disposed in a region facing the 2 nd prism group 12 b.
In the present embodiment, the 1 st to 4 th prism groups are formed in a linear shape having a longitudinal direction in a horizontal direction of the screen, but may be formed in a concentric circle shape having a certain point as a center. Further, the 1 st and 2 nd prism groups on the incident side may be formed in the linear shape, and the 3 rd and 4 th prism groups on the output side may be formed in concentric circles.
Next, the operation of each prism group, that is, the optical operation will be described with reference to fig. 4, 5, and 6. Fig. 4 shows an enlarged cross section of a portion of the 1 st prism group 12a and the 1 st plane area 17 disposed in the area a of fig. 3. That is, fig. 4 shows a portion of the area a, particularly where the incident angle is the largest, and here, the 3 rd prism group 15a is not provided on the exit surface side. In the area a, in a portion where light enters at a large incident angle, as shown in fig. 4, the 1 st prism portion 12a is provided on the light entrance side of the fresnel lens sheet 8, and the 1 st plane area 17 is provided on the light exit surface side. Light 32 from the image generation source is incident on the 1 st refractive surface SK1 of the 1 st prism group, and is refracted by the 1 st refractive surface SK 1. Then, the light is reflected by the 1 st total reflection surface SH1 and is emitted from the 1 st plane region 17 on the emission side of the fresnel lens sheet 8 to the observation side. The light outgoing direction at this time is parallel to the normal line of the principal plane of the fresnel lens sheet 8.
Next, the optical action of the portion in the vicinity of the region B in the region a will be described. Fig. 5 shows an enlarged view of the 1 st prism group 12a located in the vicinity of the region B and a part of the 3 rd prism group 15a opposed thereto. As shown in fig. 5, the 1 st prism group 12a is provided on the light incident side of the fresnel lens sheet 8, and the 3 rd prism group 15a is provided on the light emitting side. Light 34 from the image generation source is incident on the 1 st refractive surface SK1 of the 1 st prism group, and is refracted by the 1 st refractive surface SK 1. The refracted light is totally reflected by the 1 st total reflection surface SH1 and enters the 5 th refraction surface SK5 of the 3 rd prism group. The light incident on the 5 th refraction surface SK5 is refracted by the 5 th refraction surface SK5 to be substantially parallel to the normal line of the principal plane of the Fresnel lens sheet 8. That is, the 5 th refraction surface SK5 of the 3 rd prism group 15a is used to refract the light directed inward by the 1 st total reflection surface SH1 of the 1 st prism group 12a in the normal direction.
In the area B where light enters at a smaller incident angle than the area a, as shown in fig. 6, the 2 nd prism group 12B is provided on the light-entering side of the fresnel lens sheet 8. Further, a 4 th prism group 15b is provided on the light emitting side of the Fresnel lens sheet 8. The light ray 34 from the image generation source side is incident on the 2 nd refractive surface SK2 of the 2 nd prism group, and is refracted by the 2 nd refractive surface SK 2. The refracted light is totally reflected by the 2 nd total reflection surface SH2 and enters the 4 th refraction surface SK4 of the 4 th prism group 15 b. The light incident on the 4 th refraction surface SK4 is refracted by the 4 th refraction surface SK4 to be substantially parallel to the normal line of the principal plane of the fresnel lens sheet 8. That is, the 4 th refraction surface SK4 of the 4 th prism group 15b is used to refract light deflected inward by the 2 nd total reflection surface SH2 of the 2 nd prism group 12b in the normal direction. On the other hand, the light ray 33 enters the 2 nd refracting surface SK2 of the 2 nd prism group, is refracted by the 2 nd refracting surface SK2, and then enters the 2 nd refracting surface SK3 of the 4 th prism group 15 b. The light is refracted by the 3 rd refraction surface SK3 to be substantially parallel to the normal line of the principal plane of the fresnel lens sheet 8. That is, the 3 rd refracting surface SK3 of the 3 rd prism group 15b refracts light that is not totally reflected by the 2 nd total reflecting surface SH2 of the 2 nd prism group 12b in the normal direction.
As described above, the 2 nd total reflection surface SH2 of the 2 nd prism group 12b is directed to a part of the light that is incident on the 2 nd refraction surface SK2 and refracted. That is, the light incident on the 2 nd refraction surface SK2 of the 2 nd prism group 12b is mainly emitted from the fresnel lens sheet 8 through the 2 nd total reflection surface SH2 and two optical paths of the optical path passing through the 4 th refraction surface SK4 and the optical path passing through the 3 rd refraction surface SK 3.
Here, the angle formed by the light rays refracted by the 2 nd refraction surface SK2 of the 2 nd prism group 12b and the principal plane of the fresnel lens sheet 8 is set smaller than the tilt angle of the 4 th refraction surface SK4 of the 4 th prism group 15 b. In addition, the angle between the light reflected by the 2 nd total reflection surface SH2 of the 2 nd prism group 12b and the main plane of the fresnel lens sheet 8 is set to be smaller than the inclination angle of the 3 rd refraction surface SK3 of the 4 th prism group 15 b. When the above arrangement is adopted, the light refracted by the 2 nd refraction surface SK2 is incident only on the 3 rd refraction surface SK3, instead of the 4 th refraction surface SK 4. The light beam reflected by the 2 nd total reflection surface SH2 is incident only on the 4 th refraction surface SK4, instead of the 3 rd refraction surface SK 3. Therefore, almost all of the light incident on the fresnel lens sheet 8 can be emitted from the fresnel lens sheet 8. Thus, according to the fresnel lens sheet of the present embodiment, even if light is incident at a wide range of incident angles, the occurrence of unnecessary light can be significantly reduced.
Next, table 1 shows an example of the specifications of optical components (prisms) in the case where the fresnel lens sheet 8 described above is applied to an image display device. This specification shows an example of specific numerical values of the tilt angles and prism apex angles of the refraction surfaces SK1 and SK2 of the 1 st and 2 nd prism groups 12 disposed on the light incident side, and the tilt angles and prism apex angles of the refraction surfaces SK4 and SK5 of the 3 rd and 4 th prism groups 15 disposed on the light emitting side. Also, in this example, the refractive index of the material constituting the fresnel lens sheet was taken to be 1.53. In table 1, the incident angles of 31 to 44 degrees are the regions B, and the incident angles of 45 to 70 degrees are the regions a. Further, the range of 45 degrees to 64 degrees in the region a is a range in which the 3 rd prism group 15a is provided on the light output surface thereof. The angle of inclination of the refractive surfaces of the prism assembly decreases with increasing angle of incidence and connects to the 1 st planar area 17 at an angle of incidence of 65 degrees. That is, in the range of 65 degrees to 70 degrees of the region a, the 1 st plane region 17 is formed on the light exit surface side.
TABLE 1
| Angle of incidence | Incident side prism refracting surface inclination angle | Incident side prism apex angle | Inclination angle of refraction surface of exit side prism | Prism apex angle of emergent side prism |
| 31 degree | 28 degree | 64 degree | 60.7 degree | 52.4 degree |
| 44 degree | 53 degree | 45.4 degree | 67.4 degree | 24.7 degree |
| 45 degree | 54 degrees | 44 |
70 degree | 21.8 degree |
| 64 degree | 54 degrees | 66 degree | 1.5 degree | 90.4 degree |
| 65 degree | 52.2 degree | 68.1 degree | - | - |
| 70 degree | 44.3 degree | 71.6 degree | - | - |
In patent document 1, the incidence angle of 35 degrees is 20% or more, and in contrast, according to the present embodiment, the incidence rate of stray light can be suppressed to approximately 0% even at an incidence angle of 31 degrees to the screen. This makes the entire incident light effective, and therefore the width of the screen incident angle of the image light becomes wider, and the passing efficiency also becomes good. Thus, if the present embodiment is employed, it is known that unnecessary light on the screen can be reduced.
Further, if the fresnel lens sheet 8 according to the present embodiment is applied to a rear projection type image display device, a bright image can be displayed in the peripheral portion of the screen even if the depth of the device is reduced. Thus, if this embodiment is applied, in an image display device having a screen diagonal of 50 inches (a vertical/horizontal ratio of 9: 16), the thickness of the device can be set to 300mm, for example. This makes it possible to further reduce the thickness of the device. However, in the present embodiment, the numerical values of the dimensions and the characteristics of the above-described components are not particularly limited to those shown in the above-described embodiments. Those skilled in the art will appreciate that these values can be appropriately changed in accordance with specifications such as an oblique projection angle and a projection distance, together with the presence or absence of a mirror (not limited to a plane). .
In order to further reduce the thickness, a curved mirror having a free-form surface may be used as the mirror 4. In this case, the prism surface (refractive surface) of the fresnel lens constituting the fresnel lens sheet may be formed into an aspherical (generally spherical) shape that eliminates the amount of displacement from the spherical system due to the curved surface mirror. The aspherical surface coefficient (coefficient when the degree of aspherical surface is expressed by a polynomial) at this time may be set so that an image reflected and incident by the curved surface mirror is projected on substantially the entire surface of the rear projection screen and emitted from the emission surface of the fresnel lens sheet 8 at an emission angle of substantially 0 degrees.
As described above, according to the present embodiment, the width of the screen incident angle of the image light can be made wide, the passing efficiency can be improved, and the occurrence of stray light can be reduced. Therefore, a bright image can be displayed, the contrast is good, and a thinner and more compact rear projection type image display device can be realized.
Example 2
Next, embodiment 2 of the present invention will be described with reference to fig. 7 to 9. Fig. 6 shows an example of a configuration of a direct-view image display device used in the present invention, fig. 7(a) is a sectional view of the device as viewed from above, and fig. 7(b) is a sectional view of the device as viewed from the side.
The light source 27 includes a high-pressure mercury lamp of a substantially point light source, and a reflector that reflects light emitted from the lamp and emits it. The luminance of the light emitted from the light source 27 is uniformized by the rod lens 26. Although the method of uniformizing the luminance can further utilize a multi-lens array, any element may be used in the present embodiment. The light emitted from the rod lens 26 is reflected by a mirror 25, which is one component of the projection unit, and is projected on the image generation source 21 in an enlarged manner through the fresnel lens sheet 22. Here, the image generation source 21 is constituted by, for example, a transmissive liquid crystal panel, and modulates light transmitted through the fresnel lens sheet 22 for each pixel to form an image on the display surface. In the present embodiment, light is made incident on the liquid crystal panel via the fresnel lens sheet 22, and the fresnel lens sheet 22 is configured to make the incident light into parallel light (light parallel to the normal line of the principal plane of the fresnel lens sheet 22) and emit the light to the liquid crystal panel. Therefore, the incident light to the liquid crystal panel becomes substantially parallel to the normal line of the display surface of the liquid crystal panel due to the optical action of the fresnel lens sheet 22.
Here, as an element for magnifying the light from the rod lens 26 to the size of the image generation source 21, for example, a known magnifying lens, a curved mirror, or the like can be used. Such elements may also be located on the path from the light source 27 to the reflector 25. The reflecting mirror 25 may have a curved surface. The reflector 25, the rod lens 26, the light source 27, the image generation source 21, and the fresnel lens sheet 22 are attached to or housed in the housing 5.
In the image display device having the above configuration, the thickness of the image display device can be reduced as the angle at which the enlarged light beam is incident on the peripheral edge of the fresnel lens sheet 22 is increased. For example, in an image display device having a display surface diagonal of 50 inches (a vertical/horizontal ratio of 9: 16), if the maximum incident angle on the peripheral edge of the fresnel lens sheet 22 is 80 degrees, the depth of the device can be reduced to approximately 150 mm. Thus, the range of the incident angle to the Fresnel lens sheet 22 is about 0 to 80 degrees in order to form the depth of the device to 150mm or less. The fresnel lens sheet 22 according to the present embodiment makes the incident light having the above-described angle range into parallel light and exits to the liquid crystal panel.
The overall structure of the Fresnel lens sheet 22 suitable for the thin type device is shown in FIG. 8. FIG. 8 is a sectional view showing the vertical direction of the Fresnel lens sheet 22 according to the present embodiment. Although the Fresnel lens sheet 8 is divided into two zones according to the incident angle of light in the vertical direction in FIG. 3, the Fresnel lens sheet 22 is divided into three zones according to the incident angle of light in the vertical direction in this embodiment. The region a is a region where light enters at an incident angle of 45 to 80 degrees (maximum incident angle). The region B is a region where light enters at an incident angle of 31 to 44 degrees. The region C is a region where light is incident at an incident angle of 0 degree (minimum incident angle) to 30 degrees.
A1 st prism group 12a having a 1 st refraction surface SK1 and a 1 st total reflection surface SH1 is provided IN a region A of a light incident surface IN of the Fresnel lens sheet 22, and a 2 nd prism group 12B having a 2 nd refraction surface SK2 and a 2 nd total reflection surface SH2 is provided IN a region B. IN addition, the 2 nd plane area 16 having a plane shape IN which no prism is formed is provided IN the area C of the light incident surface IN. On the other hand, the 1 st plane region 17 of the flat shape in which no prism is formed is provided in a part of the region a of the light output surface OUT of the fresnel lens sheet 22, and the 3 rd prism group 15a having the 5 th refraction surface SK5 is provided in the vicinity of the region B of the region a of the light output surface OUT. In the region B of the light exit surface OUT, a 4 th prism group 15B having a 3 rd refractive surface SK3 and a 4 th refractive surface SK4 is provided, and in the region C, a 5 th prism group 15C having a 6 th refractive surface SK6 is provided.
In the present embodiment, the 1 st to 5 th prisms are formed in a straight line shape having the horizontal direction of the screen as the longitudinal direction, but may be formed in a concentric circle shape with a certain point as the center. The 1 st and 2 nd prisms on the incident side may be formed in a straight line shape having the horizontal direction of the screen as the longitudinal direction, and the 3 rd to 5 th prisms on the exit side may be formed in a concentric circle shape.
Next, the operation of each prism, that is, the optical operation, will be described with reference to fig. 9. The optical functions of the 1 st prism group 12a and the 3 rd prism group 15a disposed in the area a, and the 2 nd prism group 12B and the 4 th prism group 15B disposed in the area B are substantially the same as those of fig. 4 to 6. Therefore, in the following description, the optical actions of the 1 st, 2 nd, 3 rd, and 4 th prism groups 12a, 12b, 15a, and 15b and the setting of the angle are not described, and only the optical action of the 5 th prism group 15C disposed in the area C will be described.
As shown IN FIG. 9, the 2 nd plane area 16 is provided on the area C on the light incident side IN of the Fresnel lens sheet 22. In the region C on the light output side OUT, a 5 th prism group 15C is provided so as to face the 2 nd plane region 16. The light 35 (light having an incident angle of, for example, 0 to 30 degrees) from the light source 27 is incident on the 2 nd plane area 16 and refracted by the incident surface of the 2 nd plane area 16. The light refracted by the 2 nd plane area 16 is incident on the 6 th refraction surface SK6 of the 5 th prism group 15 c. The light is refracted by the 6 th refraction surface SK6 of the 5 th prism group 15c to exit substantially parallel to the normal to the principal plane of the fresnel lens sheet 22. The light refracted by the 6 th refraction surface SK6 is incident on the image generation source 21 formed of, for example, a liquid crystal panel.
Next, table 2 shows examples of optical component (prism) specifications in the case where the fresnel lens sheet 22 described above is applied to an image display device. This specification shows an example of specific numerical values of the tilt angles and the prism apex angles of the refraction surfaces SK1 and SK2 of the 1 st and 2 nd prism groups 12 provided on the light incident side, and the tilt angles and the prism apex angles of the refraction surfaces SK4, SK5 and SK6 of the 3 rd, 4 th and 5 th prism groups 15 provided on the light emitting side. In this example, the refractive index of the material constituting the fresnel lens sheet was 1.53.
TABLE 2
| Angle of incidence | Incident side prism refracting surface inclination angle | Incident side prism apex angle | Inclination angle of refraction surface of exit side prism | Prism apex angle of |
| 0 degree | - | - | - | - |
| 30 degree | - | - | 60 degree | 72.7 degree |
| 31 degree | 28 degree | 64 degree | 60.7 degree | 52.4 degree |
| 44 degree | 53 degree | 45.4 degree | 67.4 degree | 24.7 degree |
| 45 degree | 54 degrees | 44 |
70 degree | 21.8 degree |
| 64 degree | 54 degrees | 66 degree | 1.5 degree | 90.4 degree |
| 65 degree | 52.2 degree | 68.1 degree | - | - |
| 80 degree | 28.8 degree | 90.9 degree | - | - |
In table 2, the incident angles 0 to 30 degrees are the regions C, the incident angles 31 to 44 degrees are the regions B, and the incident angles 45 to 80 degrees are the regions a. Further, the range of 45 degrees to 64 degrees in the region a is a range in which the 3 rd prism group 15a is provided on the light output surface thereof. The inclination angle of the prism refraction surface of the prism is reduced along with the increase of the incident angle of light, and is connected with the 1 st plane area 17 at the incident angle of 65 degrees. That is, the light exit surface of the light guide plate in the range of the incident angle of 65 degrees to 80 degrees forms the 1 st plane region 17. The angles described herein are not limited to the values in table 2, and the angles may not be boundaries between different prisms. For example, the prisms may be arranged in a mixed manner within a predetermined range centered on the angle. According to the above configuration, it is possible to reduce the disadvantage such as unevenness in luminance due to a change in the prism region. This is also the same in the 1 st embodiment described above.
According to the present embodiment, the occurrence rate of stray light can be made approximately 0% regardless of the incident angle to the screen. Thereby, the width of the screen incident angle of the image light is widened because all of the incident light becomes effective light, and the passing efficiency also becomes good. Fig. 10 shows the transmittance obtained in the example of table 2. Although there is a deterioration of about 20% at the maximum of the transmittance in the range of about 30 to 50 degrees of the incident angle, the fresnel lens sheet as a whole exhibits excellent transmittance corresponding to 0 to 80 degrees.
If the fresnel lens sheet 22 according to the present embodiment is applied to a direct-view image display device, a bright image can be displayed on the peripheral portion of the screen even if the depth of the device is reduced. Thus, if this embodiment is applied, in an image display device having a screen diagonal of 50 inches (a vertical/horizontal ratio of 9: 16), the thickness of the device can be formed to be, for example, about 150 mm. This makes it possible to further reduce the thickness of the device. However, in the present embodiment, the dimensions and the characteristics of the components are not particularly limited to the above values. Those skilled in the art will appreciate that these values can be changed as appropriate, depending on specifications such as an oblique projection angle and a projection distance, and the presence or absence of a mirror (not limited to a plane). In this embodiment, as in embodiment 1, a curved mirror having a free curved surface may be used as the mirror 25, and the prism surface (refractive surface) of the fresnel lens may be set to be aspherical in accordance with the shape of the curved mirror.
As described above, according to the present embodiment, the width of the screen incident angle of the image light can be made wide, the passing efficiency can be improved, and the occurrence of stray light can be reduced. Therefore, a bright image can be displayed, contrast is good, and a thinner and more compact direct-view image display device can be realized.
Although the fresnel lens sheet 22 is described as being applied to the direct-view type image display device in embodiment 2, the fresnel lens sheet may be applied to a rear-projection type image display device in the same manner as in embodiment 1.
In the above-described fresnel lens sheet, if the incident angle of the incident light is increased, there is a problem as described below. For example, if the prism height of the incident surface of the fresnel lens sheet is higher than a predetermined value, the light is blocked or intercepted by the prism, and particularly, the light hardly reaches the vicinity of the screen edge. Thus, the image near the end of the screen becomes dark in this case. For example, at an incident angle of 80 degrees, if the prism height becomes 1mm high, the light ray at the incident angle of 80 degrees is incident on the prism before about 5.6 mm. In this case, a dark portion occurs in a range of 5.6mm in the end direction from the position of the prism. In this case, the fresnel lens sheet may be fixed to the frame in a planar shape by applying tension thereto. Further, the concave surface may be formed by turning the light source side upside down and fixed to the housing.
Claims (15)
1. A Fresnel lens sheet used in an image display device, comprising:
a 1 st prism group provided in a region of the light incident surface of the Fresnel lens sheet, the region being equal to or greater than a predetermined light incident angle; and
a 2 nd prism group provided on a region of the light incident surface of the Fresnel lens sheet which is less than the predetermined light incident angle; wherein
The 1 st prism group comprises: a 1 st refraction surface which refracts light incident at the predetermined light incident angle or higher; and 1 st total reflection surface, used for reflecting the light refracted by 1 st refraction surface, and lead to the emergence side of the stated Fresnel lens sheet;
the 2 nd prism group comprises: a 2 nd refracting surface refracting light incident at a light incident angle less than the predetermined light incident angle and guiding the refracted light to an exit side of the Fresnel lens sheet; and a 2 nd total reflection surface which reflects a part of the light refracted by the 2 nd refraction surface and guides the reflected light to the exit side of the Fresnel lens sheet.
2. The fresnel lens sheet according to claim 1, wherein: the light reflected by the 1 st total reflection surface of the prism group at the position separated from the 2 nd prism group in the 1 st prism group is emitted to the direction approximately parallel to the normal of the Fresnel lens sheet; the light reflected by the 1 st total reflection surface of the prism group in the 1 st prism group, which is in the vicinity of the 2 nd prism group, and the light reflected by the 2 nd total reflection surface of the 2 nd prism group are emitted in a direction toward the inside of the normal line of the Fresnel lens sheet.
3. The fresnel lens sheet according to claim 1, wherein: the area of the light emitting surface of the Fresnel lens sheet, which is opposite to the prism group in the 1 st prism group at the position separated from the 2 nd prism group, is planar; a 3 rd prism group is arranged in an area opposite to the prism group which is positioned near the 2 nd prism group in the 1 st prism group; and a 4 th prism group is arranged in the area opposite to the 2 nd prism group,
the 4 th prism group comprises: a 3 rd refracting surface for refracting again the light refracted by the 2 nd refracting surface of the 2 nd prism group, and a 4 th refracting surface for refracting the light reflected by the 2 nd total reflecting surface of the 2 nd prism group.
4. The Fresnel lens sheet according to claim 3, wherein: and the 4 th prism group refracts the light reflected by the 2 nd total reflection surface of the 2 nd prism group and the light refracted by the 2 nd refraction surface in a direction approximately parallel to the normal of the Fresnel lens sheet.
5. The fresnel lens sheet according to claim 1, wherein: forming a region of the light incident surface of the Fresnel lens sheet, in which light is incident at a smaller incident angle than a region in which the 2 nd prism group is provided, into a planar shape; a5 th prism group for refracting light incident on the planar region is provided in a region of the output surface of the Fresnel lens sheet facing the planar region.
6. The Fresnel lens sheet according to claim 5, wherein: the 1 st, 2 nd, 3 rd, 4 th and 5 th prism groups are in concentric circles.
7. The Fresnel lens sheet according to claim 6, wherein: the refractive surface of at least one of the plurality of prisms is formed of an aspherical surface.
8. An image display device is characterized by comprising:
a screen;
an image generation source; and
a projection unit including a mirror for enlarging an image from the image generation source and projecting the image onto the screen;
the screen has a Fresnel lens sheet and a diffusion sheet for diffusing light from the Fresnel lens sheet;
the Fresnel lens sheet comprises: a 1 st prism group provided in a region of the light incident surface of the Fresnel lens sheet, the region being equal to or greater than a predetermined light incident angle; and a 2 nd prism group provided on a region of the light incident surface of the Fresnel lens sheet which is less than the predetermined light incident angle; wherein,
the 1 st prism group comprises: a 1 st refraction surface which refracts light incident at the predetermined light incident angle or higher; and a 1 st total reflection surface for reflecting the light refracted by the 1 st refraction surface and guiding the light to the emergent side of the Fresnel lens sheet;
the 2 nd prism group comprises: a 2 nd refracting surface refracting light incident at a light incident angle less than the predetermined light incident angle and guiding the refracted light to an exit side of the Fresnel lens sheet; and a 2 nd total reflection surface which reflects a part of the light refracted by the 2 nd refraction surface and guides the reflected light to the exit side of the Fresnel lens sheet.
9. An image display device is characterized by comprising:
an image generating source that modulates incident light and displays an image;
a lamp for emitting light;
a projection unit including a mirror for projecting light from the lamp to a display region of the image generation source; and
and a Fresnel lens sheet for emitting the light from the projection unit toward the image generation source in a direction substantially perpendicular to the display surface of the image generation source.
10. The image display device according to claim 9, wherein the fresnel lens sheet has:
a 1 st prism group provided in a region of the light incident surface of the Fresnel lens sheet, the region being equal to or greater than a predetermined light incident angle; and
a 2 nd prism group provided on a region of the light incident surface of the Fresnel lens sheet which is less than the predetermined light incident angle;
the 1 st prism group comprises: a 1 st refraction surface which refracts light incident at the predetermined light incident angle or higher; and a 1 st total reflection surface for reflecting the light refracted by the 1 st refraction surface and guiding the light to the exit side of the Fresnel lens sheet,
the 2 nd prism group comprises: a 2 nd refracting surface refracting light incident at a light incident angle less than the predetermined light incident angle and guiding the refracted light to an exit side of the Fresnel lens sheet; and a 2 nd total reflection surface which reflects a part of the light refracted by the 2 nd refraction surface and guides the reflected light to the exit side of the Fresnel lens sheet.
11. The image display apparatus according to claim 9, wherein: the reflecting mirror includes a curved mirror having a curved reflecting surface, and the prism has an aspherical refracting surface,
the aspheric coefficients of the refractive surfaces of the prisms are set so that the image light reflected by the curved mirror and incident on the Fresnel lens sheet is emitted from the emission surface of the Fresnel lens sheet at an emission angle of substantially 0 degrees over substantially the entire surface of the Fresnel lens sheet.
12. The image display device according to claim 9, further comprising: and a member for applying a tension to the periphery of the Fresnel lens sheet and fixing the Fresnel lens sheet to a housing of the image display device.
13. The image display apparatus according to claim 9, wherein: and enabling the Fresnel lens sheet to be sunken and turn over towards the lamp side and fixing the Fresnel lens sheet on a frame body of the image display device.
14. The image display apparatus according to claim 9, wherein: the image generation source is a liquid crystal panel; the Fresnel lens sheet makes the light incident on the display surface of the liquid crystal panel substantially parallel to the normal line of the display surface of the liquid crystal panel.
15. The image display apparatus according to claim 14, wherein: the liquid crystal panel is a transmissive liquid crystal panel.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2005369013 | 2005-12-22 | ||
| JP2005369013 | 2005-12-22 | ||
| JP2006058851 | 2006-03-06 |
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| Publication Number | Publication Date |
|---|---|
| CN1987527A true CN1987527A (en) | 2007-06-27 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 200610107775 Pending CN1987527A (en) | 2005-12-22 | 2006-07-25 | Image display device and fresnel lens sheet used therefor |
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| Country | Link |
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| CN (1) | CN1987527A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2020238663A1 (en) * | 2019-05-30 | 2020-12-03 | 深圳光峰科技股份有限公司 | Projection screen |
| WO2021098516A1 (en) * | 2019-11-20 | 2021-05-27 | 深圳光峰科技股份有限公司 | Fresnel film and display component |
-
2006
- 2006-07-25 CN CN 200610107775 patent/CN1987527A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2020238663A1 (en) * | 2019-05-30 | 2020-12-03 | 深圳光峰科技股份有限公司 | Projection screen |
| US20220221780A1 (en) * | 2019-05-30 | 2022-07-14 | Appotronics Corporation Limited | Projection screen |
| US11892765B2 (en) | 2019-05-30 | 2024-02-06 | Appotronics Corporation Limited | Projection screen |
| WO2021098516A1 (en) * | 2019-11-20 | 2021-05-27 | 深圳光峰科技股份有限公司 | Fresnel film and display component |
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