JP2005084575A - Rear projection display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the drawback that the height of a projector is unavoidably and considerably higher than the display screen height on the screen. <P>SOLUTION: In a display device having three image display panels and a projection system which includes a lightning system for lighting the three image display panels, a refractive optical element, two free curved surface mirrors, and a plane mirror and which obliquely projects the lights from the three image display panels to the screen, among the optical paths in which the light rays of the central luminous fluxes emitted from the centers of the three image display panels to the center of the screen, the optical path in the projection system and from the projection system to the screen is not included within one plane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rear projection display device in which the device is made ultra thin by oblique projection.

Conventionally, for example, WO97 / 01787 has been disclosed as this type of apparatus. An example of the configuration of the projection optical system is shown in FIG. In this case, the image on the image display panel 11 is tilted with respect to the screen 16 without trapezoidal distortion by three coaxial aspherical reflecting mirrors (12, 13, 14 in the figure) and one vertically arranged flat mirror (5 in the figure). It was something to project.
International Patent Publication No. WO97 / 01787

  However, in the conventional example, as a result of the examination of the trace, the total height of the optical system is about 120 cm (H in FIG. 5) in the diagonal 60 ″ (1524 mm) projection, and the total height when the device is used is also displayed on the screen surface. It has been found that it has the disadvantage of becoming considerably higher than the height.

  The trace examination results are shown in the lens data of Table 1 and the ray tracing diagram of FIG. Further, in this trace examination, the maximum distortion of the projected image was 2.1% (trapezoidal distortion) and the projected image average MTF (at 1 Lp / mm) was 30% at the aperture NA = 0.08. In this case, the display size of the image display panel is 34 mm diagonal, the aspect 16: 9, and the enlarged display size on the screen is 60 ″ (1524 mm) diagonal.

  In the data of Table 1, the surface distance d is reversed every time the light beam from the image display panel is reflected by the curved reflecting mirror and its propagation direction is reversed. Further, the radius of curvature r indicates that + is a concave surface and − is a convex surface.

In order to solve the above-described problems, the display device of the present invention includes:
At least one image display panel, an illumination system that illuminates the at least one image display panel, at least one refractive optical element, two or more free-form surface mirrors, and one or more plane mirrors, A display device having a projection system that obliquely projects light from one image display panel onto a screen, and a light beam at the center of a light beam that exits from the center of the at least one image display panel and reaches the center of the screen passes through the display device. Among the optical paths, an optical path in the projection system and from the projection system to the screen does not fit in one plane. Here, “the optical path through which the light beam at the center of the light beam that is emitted from the center of the at least one image display panel and reaches the center of the screen” is the center of the at least one image display panel and the center of the stop of the projection system. Or a light beam passing through the aperture of the projection system and the center of the screen.

  And a plurality of illumination systems that illuminate the at least one image display panel, at least one refractive optical element, two or more free-form curved mirrors, and one or more plane mirrors. A display device having an optical element and having a projection system that obliquely projects light from the at least one image display panel onto a screen, and is emitted from the center of the at least one image display panel and is centered on the screen When the optical path of the light beam at the center of the reaching light beam is divided into a plurality of optical paths by the plurality of optical elements, at least one of the plurality of optical paths has a twisted relationship with respect to the other optical paths. Yes.

  Also, at least an image display panel, an illumination system for the panel, at least one lens (refractive optical system), two or more free-form surface mirrors, and one or more located in the optical path between the panel and the screen A projection system having a plane mirror, and when the light emitted from the image display panel reaches the screen by repeatedly refracting and transmitting the lens and reflecting between the mirrors, the optical image of the image panel is projected onto the screen. In the display device characterized in that the image is enlarged and projected, the optical path from the image display panel to the screen, which is mainly formed by the reflection action of the plane mirror and the curved mirror, is three-dimensional, and within one plane It is characterized by a configuration that does not fit.

  Here, it is preferable to form an intermediate image of the image display panel in the optical path from the lens constituting the projection system to the screen. The intermediate image may be formed on a position other than the vicinity of each mirror surface.

  Further, it is preferable that an entrance aperture pupil is provided in or near the lens constituting the projection system, and that the pupil image position of the entrance aperture is in the optical path from the lens constituting the projection system to the screen. . Here, the pupil image may be formed on each mirror surface or at a position other than the vicinity thereof.

  Further, when the focal length of the lens (refractive optical system) constituting the projection system is f_a, it is more preferable that the following conditional expression is satisfied with respect to the focal length f of the entire projection optical system.

  2 <| f_a / f |

  As described above, in the present invention, the oblique projection system using a coaxial lens and several free-form surface mirrors and three-dimensionally arranging the optical paths formed by them is applied to the rear projection display device, thereby achieving high performance. It has become possible to provide a large-screen rear projection display device that has not only high image quality and thinness, but also extremely low device height.

(Example 1)
FIG. 1 is a perspective view (framework ray tracing diagram) of a thin rear projection display device according to a first embodiment of the present invention, FIG. 2 is a horizontal sectional configuration diagram (ray tracing diagram), and FIG. Ray tracing diagram). In the figure, 1 is a reflection type display panel such as DLP (DMD), 2 is a coaxial lens, 4 and 5 are Ag deposition free-form surface mirrors 3 and 6 are plane mirrors, and 7 is a screen for oblique incidence.

  Although the parts other than the above are not particularly shown in the figure, the display panel 1 is illuminated from an oblique upper side of the display panel 1 by an illumination system (not shown), and the image light reflected from the display panel 1 is coaxial. Head to lens 2. Then, the light beam that has been subjected to a predetermined refraction action by this coaxial lens is directed to the plane mirror 3, and the path of the light beam so far is taken in the lateral direction of the apparatus (the direction parallel to the projected image display screen surface). Next, the light beam is bent by about 90 ° toward the front of the apparatus (depth direction) by the reflection by the plane mirror 3 and heads toward the free-form surface mirror 4. Thereafter, the light advances while being reflected by the free-form curved mirrors 4 and 5 as shown in the ray diagram in the figure. The light beam emitted from the free-form surface mirror 5 is reflected by the plane mirror 6 located at the back of the screen, that is, the rear side of the apparatus as shown in the figure, and then illuminates the screen 7 from the obliquely downward direction to the obliquely upward direction. That is, the image light is obliquely projected onto the screen 7 from below. Here, the plane mirror 6 is arranged so as to be parallel to the screen 7 and vertical (the coordinate definition in this example is independent of the vertical direction).

  The projection system has a light reflection angle modulation action of the free-form mirrors 4 & 5 and an image forming action by combining the coaxial lens 2. This image forming action causes the rectangular image surface of the display panel 1 to move along the optical axis. Are projected in an enlarged rectangular shape on the screen 7 which is arranged obliquely (optical axis incident angle 41 °). With this layout, the depth of the rear projection can be greatly reduced when the rear projection is configured. Incidentally, according to this example, it is expected that a depth of 25 cm is possible on a display screen having an aspect ratio of 4: 3 diagonal 43 ”. Further, in this example, only two free-form curved mirrors are used, Folding of the optical path formed by the arrangement of the mirror 15 and the plane mirrors 13 and 16 is three-dimensionally packed in the lower part of the apparatus without waste. Especially, the overall height of the apparatus is greatly increased by the effect of bending the optical path in the lateral direction by the plane mirror 13 The total height is expected to be 85 cm or less even in the above screen size. The total height of 120 cm introduced in the previous example was a value for 60 ″ projection (aspect 16: 9). Is 105 cm even if converted to the same projection size and aspect as in this example.

  The overall configuration and mechanism have been described so far. Next, a projection system including the coaxial lens 2 and the free-form surface mirrors 4 and 5 will be described. FIG. 4 shows a partially enlarged sectional view of the projection system. As shown here, the coaxial lens 2 comprises an aperture 21, two bonded lenses 22 & 23, and two single lenses 24 & 25. Table 4 below shows lens data of the projection system (each surface curvature radius, each surface spacing, each surface eccentricity, each surface definition, etc.). The display panel display area size in this example is a diagonal 12 mm aspect ratio 4: 3, and the on-screen enlarged display size is a diagonal 43 ″ (1093 mm) aspect ratio 4: 3.

Regarding the coordinate system here, first, the center of the display panel 1 was set as the initial origin, and a straight line connecting this and the center of the opening 21 was set as the optical axis and z-axis. The direction in which light is emitted from the origin is the z-axis + direction, the y-axis is the axis perpendicular to the z-axis and the upper direction in FIG. 3 is +, and the x-axis is the depth direction in FIG. 3 perpendicular to the z & y-axis. The axis is defined as + (conforms to Cartesian coordinate definition). As for the lens data of the coaxial lens, each surface interval is set along the z-axis. However, after reflection by the mirror surface, the direction of the optical axis also changes in accordance with the reflection of the optical axis, so that the optical axis after reflection. The light beam is assumed to be a new z-axis, and its direction (sign) is reversed for each reflection. Further, for each free-form curved mirror surface, local coordinates having the local origin as the intersection of the incident optical axis (z axis) and the mirror surface are set for defining the surface shape. With respect to the local xyz axis in the local coordinates, each free-form surface mirror has a tilt angle with the local x axis passing through the local origin as a rotation axis with respect to the incident optical axis (z axis). The axis after tilting by a predetermined angle (symbol) in the predetermined direction (symbol) around the local origin is defined as the local z-axis, and the axis perpendicular to the local z-axis and having the upper direction in FIG. The axis in which the depth direction in FIG. 3 perpendicular to the z & y axis is + is the local x axis (based on Cartesian coordinate definition). The coordinates set on the local xyz axis were used as local coordinates defining the free-form surface. Further, the sign of the tilt angle described above is positive in the direction of tilting so that the + y-axis direction approaches the + z-order axis direction (incident optical axis) with the local x-axis as the rotation axis. Further, the free-form surface shape of each free-form surface is defined by an xy polynomial based on the local coordinates,
_{^{z = C 4 x 2 + C}} 6 y 2 + C 8 x 2 y + C 10 y 3 + C 11 x 4 + C 13 x 2 y 2 + C 15 y 4 + C 17 x 4 y + C 19 x 2 y 3 + C 21 y 5
+ C ₂₂ x ⁶ + C ₂₄ x ⁴ y ² + C ₂₆ x ² y ⁴ + C ₂₈ y ⁶
It was. Each C _n coefficient value in the above equation is shown in Table 3 below as each free-form curved surface shape data. Further, with respect to the surface tilted with the y-axis as the rotation axis (first surface of the flat mirror), the tilting direction is defined as + so that the + x-axis direction approaches the + z-axis direction.

  As for the coordinate system after being reflected by the reflecting surface, the z-axis polarity of the next local coordinate system is reversed with respect to the traveling direction of the light, and otherwise conforms to the coordinate definition described above. Yes. Therefore, in the present case, the definition of the local coordinate system is such that the z-axis (optical axis) polarity is reversed for each reflection, and the sign of the surface interval d and the sign of the tilt angle are reversed for each reflection.

  The projection system having a total of two free-form surface mirror surfaces in accordance with such a surface definition as a constituent element includes a free-form surface mirror formed by molding and Ag deposition on a coaxial lens 2 or the like by an AL frame (not shown). By being held together with the plane mirrors 3 and 6, they are arranged in accordance with the lens data shown in Table 2.

* (Rotation axis is x axis / + y direction is a tilt direction that rotates in the z axis + direction as +)

  According to the present projection system, the light beam and the light beam pass through the coaxial lens 2 and take a three-dimensional zigzag optical path while being reflected by the plane mirror 3 and the free-form surface mirrors 4 and 5 in the same manner as in the previous example. Through the reflection at the plane mirror 6, the screen 7 is obliquely projected from the lower side to the upper side. As a feature of this example, an intermediate image of the image display panel is interposed between the plane mirror 3 and the free-form surface mirror 4. 8 (see FIGS. 2 and 3), and a point where the light beam is narrowed between the free-form surface mirrors 4 and 5, that is, an aperture pupil image 10 (see FIG. 3). With such an optical path configuration, it is possible to reduce the size of the free-form mirrors 4 and 5 in spite of wide-angle projection, and the projection optical system (especially the free-form surface mirror component) is further compact. It became possible to put together. Incidentally, the required size of the free-form surface mirrors 4 and 5 was both 100 × 70 mm. Further, since the intermediate image 8 is located away from the optical member such as a mirror, even if these optical members are contaminated with dust or the like, there is very little adverse effect on the projected image.

  Regarding the optical specifications achieved by this projection system, although the incident angle to the screen is 41 ° and the oblique incidence is quite severe, the distortion is 1.0% or less and the average MTF is 50% (at 0.5 Lp / mm). The object-side numerical aperture was 0.167, and the brightness unevenness was 20% or less. That is, a sufficient luminous flux capturing angle (aperture 0.167) and imaging performance can be obtained, and the level can be applied to image projection corresponding to SVGA (resolution) as well as so-called TV images. For reference, a spot image in this example projection optical system is shown in FIG. Further, the total height H1 of the optical system of this example shown in FIG. 3 is 80 cm, and when the rear projection display device is constituted by this, not only the thinness but also the total height of the device (43 ″ / 4: 3 at 85 cm). It has become possible to suppress this.

  In this projection optical system, the focal length f of the entire system is −5.57 mm (average value of azimuth 90 ° & 0 °), and as shown in the lens data, only the refractive system composed of six lenses is used. The focal length f_a was 46.97 mm (average value with azimuth 90 ° & 0 °), and the parameter | f_a / f | was 8.43. If this parameter | f_a / f | is too small, the effect of the free-form surface reflection system cannot be used effectively. Therefore, in the optical system as in this example, the value is preferably 2 or more.

  In this example, the screen 7 for oblique incidence is used, and at least two of an eccentric Fresnel plate and a lenticular plate are stacked in order from the incident side.

  The eccentric Fresnel plate is formed by cutting at a position offset by a predetermined distance from the center of a general concentric fresnel.

  As described above, in this example, a sufficient light flux taking-in angle of 0.167 aperture and the excellent imaging performance as described above are obtained. However, even under the severe condition of oblique incidence, the number of sheets used is two. This is because a desired optical performance can be obtained by an excellent distortion correcting action by a free curved surface (reflection type). In order to improve the optical performance at the same aperture value, it is necessary to make the total optical path length from the display panel to the screen sufficiently long. Compatibility of ensuring performance is more easily achieved.

  By the way, the configuration of this example described above is merely one example, and various arrangements can be made. For example, in this example, the optical path has a three-dimensional arrangement, but there is no problem even if a plane mirror is frequently used and arranged in a different arrangement. Further, although a DLP (DMD) panel is used as a display device, it is not limited to this as in the previous example.

The perspective view of the thin rear projection display apparatus of 1st Example of this invention. 1 is a horizontal sectional view of a thin rear projection display device according to a first embodiment of the present invention. 1 is a longitudinal sectional configuration diagram of a thin rear projection display device according to a first embodiment of the present invention. Projection system partial enlarged view of the thin rear projection display device of the first embodiment of the present invention. Conventional vertical optical system configuration for thin rear projection Projected spot image in the first embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reflective display panel 2 Coaxial lens 4, 5 Free-form curved mirror 3, 6 Plane mirror 7 Screen 8 Display panel intermediate image 10 Aperture image 21 Aperture

Claims (8)

At least one image display panel, an illumination system that illuminates the at least one image display panel, at least one refractive optical element, two or more free-form surface mirrors, and one or more plane mirrors, A display device having a projection system that obliquely projects light from one image display panel onto a screen,
Of the optical paths through which the central ray of the light beam that exits from the center of the at least one image display panel and reaches the center of the screen passes, the optical path in the projection system and from the projection system to the screen is within one plane. There is no display device. A plurality of optical elements including at least one image display panel, an illumination system that illuminates the at least one image display panel, at least one refractive optical element, two or more free-form surface mirrors, and one or more plane mirrors And a projection system that obliquely projects light from the at least one image display panel onto a screen,
When the optical path of the light beam at the center of the light beam that is emitted from the center of the at least one image display panel and reaches the center of the screen is divided into a plurality of optical paths by the plurality of optical elements, at least one of the plurality of optical paths. One is a display device characterized by being in a twisted relationship with respect to another optical path.   At least an image display panel, an illumination system for the panel, at least one lens (refractive optical system), two or more free-form surface mirrors and one or more planes located in the optical path between the panel and the screen A projection system having a mirror, and the light image of the image panel is magnified on the screen when the light emitted from the image display panel reaches the screen by repeating the refractive transmission of the lens and the reflection between the mirrors. In the display device characterized by being projected, the optical path from the image display panel to the screen, which is mainly formed by the reflection action by the plane mirror and the curved mirror, is three-dimensional and does not fit in one plane. A display device characterized by having a configuration.   4. The display device according to claim 1, wherein an intermediate image of the image display panel is formed in an optical path from a lens constituting the projection system to a screen.   5. The display device according to claim 4, wherein the intermediate image is formed at a position other than on each mirror surface or in the vicinity thereof.   An entrance aperture pupil is provided in or near the lens constituting the projection system, and the pupil image position of the entrance aperture is arranged in the optical path from the lens constituting the projection system to the screen. The display device according to claim 1.   The display device according to claim 6, wherein the pupil image is formed on each mirror surface or in a position other than the vicinity thereof. The following expression is satisfied for the focal length f of the entire projection optical system, where f_a is a focal length of a lens (refractive optical system) constituting the projection system. The display device described in 1.
2 <| f_a / f |

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