CN1227897C - Projection device for rear projection TV - Google Patents

Abstract

A projection device of back projection TV set is mainly divided into three parts of projector, light returning device and screen, said projector is formed from a double-beam projection lens capable of projecting divided picture and its internal optical component, the light returning device can implement the detour and turn of projected light, and the screen for displaying image is placed in the front of projector. Two reversed image beams are projected from the projector, and then reflected back and forth three times by the reflector in the light returning device to reach the screen, so as to combine to form an enlarged image, thereby achieving the purpose of reducing the space in the television.

Description

Projection device for rear projection TV

technical field

The invention relates to a projection device for a rear projection television.

Background technique

The structure of a general rear projection TV is mainly a three-lens type with a group of red, green and blue primary colors separated, or a single-lens type with three primary colors in one, combined with an internal electronic optical development device, and by means of two mirrors The reflection of the image, and then focus the light beam of the image on the screen. This kind of rear projection TV integrated with the projector and the screen can indeed shorten the projection distance because of the use of reflective lenses, so that the thickness of the TV body can be about Reduced by half to achieve the function of reducing part volume. However, this structure makes the projector must be arranged under the screen in the fuselage, so that the lower half of the TV itself has to be installed as a large-scale cover speaker, resulting in a bulky and uncoordinated overall appearance, which has been popularized. Very restrictive.

Contents of the invention

Therefore, the main purpose of the present invention is to provide a projection device for a rear projection TV that can make the TV body flat and thin and have a simple appearance.

The projection device of the rear projection TV set of the present invention includes a group of projections, two groups of light return devices and a screen, and is characterized in that the projector is arranged at the rear of the center in the cabinet, and includes a light source, a light-collecting lens array, Video board and projection lens. The projection lens includes two groups of lens groups arranged up and down side by side with the same structure. The sum of the positive and negative aberration coefficients of all the lenses in the upper or lower group of the two is equivalent to the effect of a convex lens. The lens group can capture the dynamic image formed by the video board and divide it into two half-cone beams with the upper and lower images reversed. Before the beams are reflected, the central optical axes of the two half-cone beams are parallel to each other. The group light return device is a combination of up and down symmetry. The upper or lower group of the two is composed of three mirrors facing each other. The mirror surface of the primary mirror is roughly 120 degrees from the optical axis of the corresponding projection lens. Angle, while the mirror surface of the secondary reflector is roughly perpendicular to the screen, and has an angle of approximately 60 degrees with the mirror surface of the third reflector; when two image beams from the projector are put into the two groups of return When in the light area, the light has a three-level spatial overlap from the primary reflector to the third reflector, and is imaged on the screen after a 360-degree circle. The screen is set at the two projection ports of the projector and two sets of return light It is directly in front of the light outlet of the mirror, and forms a 90-degree vertical angle with the central axis of the projection light source; it is used as a composite display interface of the double-beam image, and the two split images reflected by the return mirror are finally displayed on the screen. merged into a single complete enlarged image.

The projection device of the rear projection TV of the present invention includes a group of projections, two groups of light returning devices and a screen. The video screen is divided into two inverted image beams, and the light return device realizes the detour of the light to shorten the distance between the projector and the screen. It is divided into upper and lower groups, and each group consists of three It is composed of two mirrors facing each other, and the screen of the terminal is placed directly in front of the projector. In addition to displaying images, the screen also has the effect of increasing the gain and diffusing the viewing angle. Through the conversion of the internal photoelectric system, the main function of the projector is to generate high-brightness images that can be projected, and through the division and capture of two sets of projection lenses, the captured image beams are injected into the return light in different directions In the area, the light reflects back and forth in the two groups of return light areas, and waits for a 360-degree circle before reaching the screen, and the originally divided image beams are merged into a single complete image picture by the screen. The light is projected from the lens to the terminal screen, and there are three layers of reflection overlapping in the area of its path, and the projector is set right behind the screen, so that there is no need for speakers or cabinets outside the perimeter of the screen. Therefore, the projection television of the present invention can indeed achieve the above-mentioned thin and simple functions.

In order to further illustrate the purpose, structural features and effects of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings.

Description of drawings

Shown in Fig. 1 is the structural representation of the present invention.

Figure 2 is a perspective view of the combination of the present invention.

FIG. 3 is a schematic diagram of a conventional rear projection TV.

FIG. 4 is a schematic diagram of the light path of a conventional rear projection TV.

FIG. 5 is a schematic diagram of the light path of the present invention.

FIG. 6 is a schematic diagram of the minimum internal space of a conventional rear projection TV under ideal conditions.

FIG. 7 is a schematic diagram of the minimum internal space of the present invention under ideal conditions.

FIG. 8 is a schematic diagram of the principle of dual-beam projection of the present invention.

FIG. 9 is a schematic diagram of the relationship between the double-beam projection image and the light barrier of the present invention.

FIG. 10 is a schematic diagram showing the relationship between the vertical viewing angle and the diagonal viewing angle of the TV frame.

FIG. 11 is a schematic diagram showing the comparison between the double-beam projection of the present invention and the reflection via the retroreflector.

FIG. 12 is a schematic diagram of the structure of the first reflecting mirror placed in the lens barrel of the projection lens.

FIG. 13 is a schematic diagram of image synthesis with idealized uniform brightness.

FIG. 14 is a schematic diagram of image synthesis projected through an optical lens.

FIG. 15 is a schematic diagram of the relationship between the projected light and the screen of a traditional rear projection TV.

Fig. 16 is a perspective view of the present invention from the side, and a schematic diagram of the relationship between projected light and the trumpet-shaped screen.

Fig. 17 is a perspective view of the present invention from above, and a schematic diagram of the relationship between the projected light and the trumpet-shaped screen.

Figure 18 shows a flat screen with a trumpet shape, and a schematic structural view of its longitudinal section.

Detailed ways

As shown in Figures 1 and 2, the structure of the present invention can be divided into three parts, one is a projector, the other is a light return device, and the third is a screen. About its structure, imaging principle and generated characteristics, it is explained respectively in back:

1. Projector: mainly consists of a light bulb light source 1, a set of Condenser Lens, including lenses 11, 11', 12, 12' and 13, a video display board (Video Display) 2, a Diaphram 3 and two sets of projection lens groups 4 and 4' juxtaposed up and down.

2. Light return device: mainly consists of upper and lower groups, each group is composed of three mirrors facing each other, and the primary mirror 5 mirrors of the upper group have an included angle of 120 degrees with the central axis of the projection lens 4 , the secondary reflector 6 is approximately 90 degrees perpendicular to the screen, and has an angle of approximately 60 degrees with the tertiary reflector 7. The primary reflector 5' mirror surface of the lower group is approximately in the same direction as the central axis of the projection lens 4' With an included angle of 120 degrees, the secondary reflector 6' is approximately 90 degrees perpendicular to the screen, and has an included angle of approximately 60 degrees with the tertiary reflector 7'.

3. Screen 8: It is set at the exit ports of the two projection mirrors 4 and 4', and directly in front of the reflection ports of the two sets of return mirrors. The screens can have various forms and structures, but the main function is in real imaging. , increase the gain and widen the viewing angle.

The light source of the projector is produced by the light bulb 1 of the active component. The light first passes through the single convex mirrors 11 and 11' to form parallel beams, and the upper and lower edges of the beams pass through two vertical concave mirrors 12 and 12 ', the circular light beam will be split into two enlarged semicircular light cones, and then the light cones will meet at the convex mirror 13, and 13 will converge the two semicircular light cones, and the separated light beams will pass through the sides of the video board 2 respectively. The upper and lower parts are finally focused in the lens barrels of the projection mirrors 4 and 4', so the first Conjugate relationship is formed between the focal points in 4 and 4' and the light bulb. On the other hand, the video board 2 forms a penetrable dynamic video image on the surface through photoelectric conversion, and the projection mirrors 4 and 4' capture and divide the dynamic image of 2 into two upside-down images. The semi-cone beam, the two divided image beams, are then directed to the opposite mirrors 5 and 5', respectively reflecting the light into the upper and lower groups of return light areas, and the mirrors 5, 6, 7 constitute The light return area of the upper group, as seen in the order of light path walking, first the light enters the secondary reflector 6 from the primary reflector 5, then enters the tertiary reflector 7 from 6, and finally reaches the upper half of the screen 8, along the With the expansion of the light cone, the reflective areas of the three mirrors increase in a trapezoidal shape, such as 7 is greater than 6, 6 is greater than 5, and so on. Reflectors 5', 6', and 7' constitute the return light area of the lower group, and their optical paths The order of walking also enters the secondary reflector 6' by the primary reflector 5', and then enters the third reflector 7' by the primary reflector 5', and finally reaches the lower half of the screen 8, and the order of its specular reflection area is 7' greater than 6', 6' is greater than 5'. The focal point formed on the screen 8 forms a second conjugate relationship with the video board 2 in the course of light recirculation. In general, regardless of the light return area of the upper group or the lower group, the course of its light just goes around 360 degrees from the beginning to the end, if from the upper edge of the screen 8 to the junction point of the reflector 6 and 7, or The distance from the lower edge of 8 to the intersection point of 6' and 7' is the depth of the fuselage. It is not difficult to see from Figure 1 that because the light has three-stage back and forth reflections, the depth of the fuselage in the present invention can be shortened to the original throw distance. At the same time, the projector is also placed in the center of the fuselage rather than below, and all of its photoelectric components can be changed in configuration and direction according to actual needs, so that they can be accommodated in the space behind the reflector , so that there is no need for redundant objects outside the perimeter framed by the screen and the mirror, which is quite in line with the requirements of body engineering balance and symmetry.

The final component of the projection TV is the screen, and the screen must match the vision of the human eye, the brightness of the projector, and the orientation point of the projection to determine the form. The projection TV of the present invention has its equivalent projection point just behind the upper and lower edges of the screen. Therefore, the structure of the screen, in addition to the traditional ones that can be used together, if further optimized display effects are to be obtained, the screen must have a structural change different from the previous ones, and the relevant details are left for illustration in FIG. 12 . In addition, in the above description, the arrangement position of the projector components is not fixed. For example, the arrangement of all the up and down positions in Fig. The position is reversed, but its structure and function remain unchanged.

In Figures 1 and 2, the two groups of projection lenses 4 and 4' have a light barrier 3 between them and the video board 2, in addition to preventing the image beams of the projection lenses 4 and 4' from generating each other inside and outside the lens barrel. In addition to the interference of ghost images, the vertical projection angles of the projection mirrors 4 and 4' can also be changed, which will be explained in FIG. 9 .

The projector of the present invention, such as the video board 2 listed in Figure 1, is a transmissive LCD with three primary colors in one display, which is only a representative of many display methods, other such as separation of three primary colors, The X-Cube three-color three-in-one three-LCD imaging method, and the reflective DLP (Digital Light Process) imaging method using color wheel rotation are common projection processing methods, but no matter what imaging method is used The main purpose is to produce an original image that emits a powerful beam of light to provide a light source for the projection lens to capture the image. As for the technology to improve the performance of the projector, such as the heat dissipation method, the utilization efficiency of light energy and the uniformity of luminosity Diffusion, etc., are all traditional general-purpose technologies, and will not be described in this article.

In addition, as can be seen from FIG. 1, the inside of the projection lens group 4 and 4' used in the present invention is a general term including a polygonal lens. No matter how many kinds of convex mirrors and concave mirrors the projection lens is combined, The sum of the negative aberration coefficients is still equal to the function of a convex lens. Since an oversimplified single projection lens will produce shortcomings such as field curvature, dispersion or spherical aberration, in practice In the application, glass with different refractive index and color dispersion coefficient will be used, combined with multiple convex-concave lenses, to produce positive and negative aberration cancellation, so as to form a low-distortion image. As for the combination of lenses in the lens barrel, there are two pieces to more than two dozen pieces, which vary with the manufacturer's preferences and uses, and each has its advantages and disadvantages. Basically, the projection lens group used in the present invention is in the form of two sets of upper and lower lenses arranged side by side, which is a necessary structural arrangement for optical image segmentation.

As shown in Figure 3, the traditional single-beam projector 10 that is placed at the bottom in the figure and contains a light source, a collector mirror, a video plate and a projection lens, the light projected by it enters the secondary reflection through the primary reflector 20 The mirror 30 is reflected by the mirror 30 and thrown into the screen 40 to form an image. As can be seen from Figure 3, the traditional rear projection TV has a relatively simple structure, but it has a huge body. The design of this large space is different from the The size of the projector or other electronic equipment is irrelevant, only because most of the space of the fuselage is in the area where the light is re-reflected, so that all electronic and optical equipment in the TV must be placed on the screen below.

In addition, as can be seen from FIG. 4 , in the reflection course of the light, 31 is the incident light, 32 is the primary reflected light, and 33 is the secondary reflected light. When the light is traveling, the incident light 31 and the outgoing light 33 have exactly the same 31 and 32 have a small part of overlap, and 32 and 33 have most of the overlap. Since only two levels of overlap are used, the internal space can only be reduced by half at most. This is the limit of the efficiency of traditional projection TVs. .

As shown in Figure 5, during the reflection of the light, 71 and 21 are the incident light on the upper and lower sides, 72 and 22 are the primary reflected light, 73 and 23 are the secondary reflected light, and 74 and 24 are the tertiary reflected light , when the light is traveling, 71 and 72 on the upper half have a small overlap, while 72 and 73, 73 and 74, and 74 and 72 have most of the three-degree overlap, and the outgoing light 74 and the incident light 71 , has the completely opposite relationship between up and down and left and right. Similarly, 21 and 22 in the lower half have a small overlap, while 22 and 23, 23 and 24, and 24 and 22 also have three levels of spatial overlap, and the outgoing light 24 and the incident light 21 also have completely opposite phases up and down and left and right. Therefore, it can be seen from the comparison of Fig. 4 and Fig. 5 that in terms of space utilization efficiency, the present invention has one more level of space overlap than the traditional one, so the volume can also be smaller than the traditional one.

As for how to use exact data to prove that the present invention can reduce more space than the traditional rear projection TV set, then as shown in Figures 6 and 7, the dotted line marked in Figure 6 is the equivalent direct projection without the reflector. The projection line, point E is equivalent to the equivalent projection point of point B. In theory, the most ideal projection viewing angle of a mirror-type rear projection TV is an equilateral triangle with 60 degrees intersecting sides. If the equivalent light When the acute angle of the projection point is greater than 60 degrees, it cannot form a double-fold reflection projection. Practically, the acute angles are all less than 60 degrees, but if the more acute angles are less than 60 degrees, the walking distance will be longer, and the more space will be wasted. The first and second sides in the figure are screens, and the first and third sides are reflectors. The vertical distance between point C and first and second sides of the screen is I, and the distance between point five and first and second sides of the screen is II. If analyzed with geometric figures, the three points A, B, and E in Figure 6 form an equilateral triangle, and the three points A, B, and C form a right triangle including 60 degrees and 30 degrees, and its area is A, B, and E. B and E are half of the triangle. Therefore, the calculation method of the ratio of the depth I of the fuselage to the screen height A and B is as follows:

According to the theorem of trigonometric functions

cosθ=adjacent side/hypotenuse= A C / A B

Suppose ∠B, A, C=θ θ=30°

but

And II= first and third I=II/2= first and third /2

therefore

From the calculation of the above formula, it is known that the length I is 0.43 times that of sides A and B, which means that no matter how small the depth of the body of any conventional rear projection TV is, it is impossible to be less than 0.43 times the height of the screen.

As shown in Figure 7, the light is projected from the dot to the upper and lower directions. Since the light paths in the upper and lower directions and the geometric figures formed by them are exactly the same, only the lower figure can be discussed representatively. First, the light is projected downward from point D, and then reaches the edge D through the reflection of the edge Geng-Xin, and then the light is reflected to the edge D-Geng of the screen. The dotted line marked in the figure is the equivalent projection line without reflection. Ren is equivalent to the equivalent projection point of Ding Ding. If analyzed in terms of geometric figures, Ding Gengxin forms a right triangle with 30 degrees and 60 degrees, and Ding Gengren also forms a right triangle with 30 degrees and 60 degrees. Therefore, the depth III of the fuselage and the height of the screen are equal to each other. The ratio calculation method is as follows:

According to the theorem of trigonometric functions

tanθ=opposite side/adjacent side= Geng Xin / Ding Geng

Let ∠G Ding Xin = θ θ = 30°

but

And Hexygen =2 Ding Geng III= Geng Xin

therefore

Know that III is 0.29 times of hexagen by the calculation of above formula, is the minimum limit, is equal to projection television of the present invention, and the depth of its fuselage minimum can only be 0.29 times of screen height. In addition, it is known from the inductive comparison of Figure 6 and Figure 7 that:

If A and B = He and G then $\mathrm{III}/I=(\sqrt{3}/6)/(\sqrt{3}/4)=2/3$

Thus it can be proved that the projection TV set of the present invention has a body thickness of 2/3 times that of the conventional one.

The dual-beam projection system of the present invention adopts a method different from the traditional one. As shown in FIG. 8, 50 is the original object image, and the projection mirrors 4 and 4' stand upright together, which realize the upper half of the object image 50 respectively. Image segmentation and projection with the lower half, the lens 4 forms an inverted image 500 after projection, the projected light beam is a semi-cone with the hypotenuse facing up and the side facing down, and the right-angled side 600 is equivalent to the light of the lens 4 Axis, lens 4' forms an inverted image of 700 after projection, and the projected light beam is a semi-cone with the hypotenuse facing down and the stock side facing upward, and the right-angled stock side 800 is equivalent to the optical axis of lens 4', and the two lenses The central optical axes are parallel to each other before refraction or reflection processing, and the images 500 and 700 formed after the light beams are divided and projected by the lenses 4 and 4' are not only inverted, but also the head and feet are opposed to the middle, because the 4 It has a wide field of view with 4', and the projection angle α1 and projection angle α2 will also expand accordingly, so the images 500 and 700 partially overlap. However, in practice, projection angles exceeding 30 degrees will not be able to be displayed in the retroreflector Shuttle back and forth.

Fig. 9 adds a piece of Diaphram 3 parallel to the optical axis between the lenses of 4 and 4' and 50, which is slightly different from the Diaphram used to block halation in the general optical lens barrel. 3 is mainly to limit the vertical viewing angles of 4 and 4', so that the projection angles β1 and β2 are each less than and close to 30 degrees, and the images 300 and 400 only have a very small part of the overlap, and the back and forth reflection in the return mirror, Can avoid unnecessary waste of space.

For the square TV frame shown in Figure 10, no matter 4 to 3 or 16 to 9, its diagonal must be larger than the vertical line A and B. Generally, the projection TV set can accommodate the diagonal of the TV frame. As the projection angle, the range within the circle in the figure is the projection angle of point E. For example, when the angle corresponding to the diagonal line Ziwu exceeds 80 degrees, and the angle AB corresponding to the vertical line AB, Because of the blocking of the light barrier, its projection angle is limited to within 60 degrees, while the oblique angle can not be affected if it exceeds 80 degrees as before.

Generally speaking, if the present invention only focuses on the projection method of two beams, then no practical value can be seen, but the focus of the present invention is that the image is transformed through the refraction of the light return device in FIG. 11 . In the figure, the two image beams projected by the upper and lower lenses are reflected back and forth three times by the upper and lower groups of return light areas, and when they reach the screen, the combined image 200 will have an enlarged image with the same phase as the original object image 50. The conversion relationship of the image phase has already been explained in Fig. 5 above, and will not be repeated here.

Looking back at the first reflecting mirrors 5 and 5' shown in Figure 11, the smaller the 5 and 5', the more beneficial it is to shorten the projection distance. The best way is to completely hide 5 and 5' into 4 and 5' In the lens barrel of 4', as shown in Figure 12, the right-angled prism 81 on the upper side is placed in the middle of the exit mirror 91 and the incident mirror 92, and its hypotenuse is a reflective surface, and the reflection point 82 is equivalent to the aperture (Stop) in the lens barrel In the original position, the central axes of 91 and 92 form an angle θ1 of about 60 degrees to each other. Because the light has been reversed once in the lens barrel, the image beam projected by the exit mirror can directly reach the secondary reflection mirror, so The projection distance can be shortened, and the lower structure and light traveling method are the same as the upper one, so it is omitted. Although the three-sided mirrors 83 and 84 can be replaced by ordinary flat mirrors, the refraction angle of the three-sided mirrors is constant and accurate, and there are Total reflection with zero light loss is the best choice for reflectors.

Regarding image synthesis processing, it can be divided into electronic type and optical type. As shown in Figure 13, the upper circle 70 is an electronic image with uniform luminosity, assuming that its contrast is 3, and the lower part is the partial overlap of two 70 images. Because of the Enhancing effect at the overlap, there will be an obvious transition light band at the place where the pictures meet, so that it will affect the viewing of the picture.

80 on the top of Fig. 14 is an optical projected image used in the present invention. Since a part of the light beam is blocked by the lens, lens barrel, etc., the light from the center of the picture to the edge will be dimmed (Vignetting), assuming concentric circles The contrast from the center to the periphery of 80 is 4, 3, 2, 1 respectively, and the lower part is the partial overlap of two 80 optical images, and the small adjacent area in the overlap has no obvious contrast difference, so At the point where the screens are handed over, it is not easy to detect the flaws of composite images.

The screen is the final component of the projection TV, and it is also the initial interaction interface with the human visual nerve. The main function of the screen in the projector is not only to display images, but also to increase the gain ratio, expand the viewing angle width, and display good resolution. Highness and uniform brightness are all criteria for considering good and bad screens. For rear projection TVs, the performance and structure of the screen must also be changed with different projection methods. Traditional projection TVs use the center point as the center point. The projection source, combined with the Fresnel flat lens, and the front Lenticular plate that can diffuse the horizontal viewing angle, combine to form a screen with high gain and wide viewing angle. As shown in Figure 15, in order to simplify the concept, the screen is expressed in the form of direct projection of the light source. 61 in the figure is the projection point of the light source and also the focus of the lens screen 40. The light 62 projected by the light source reaches the Fresnel plate lens At 40, all light rays will be refracted into 63 in a parallel state. This surface structure is equivalent to the Fresnel lens of single-sided convex lens 90. Each twill surface faces the periphery of the circle, and the slope of the center is the smallest, and it increases outwards in a curved manner until the slope of the periphery is the largest. If this kind of lenticular screen is properly diffused, its gain ratio can be the highest. Up to 5.5 times, and can eliminate the hot spot effect (Hot spot) of uneven brightness.

Since the projection method of the present invention is different from the previous methods, although the traditional screen can be used to meet the general development requirements, if the display effect of the image is to be brought into play more efficiently, the structure of the screen must be changed. As shown in Figure 16, if viewed only from the side direction, the projection TV of the present invention has two projection points 41 and 43 at the upper and lower edges of the screen, and the screen should be capable of projecting points in different directions. The light beam has the effect of focusing imaging, so no matter from the structure or function, it has the opposite characteristics to the Fresnel lens. The screen 8 is a flat lens with transparent acrylic as the substrate, and concentric circles are formed on its surface. Ribbon-shaped twill processing, the average distance between each stripe is about 0.1mm, and the slopes are all facing the center point, and the slope of the center point is the largest, and decreases outwards in a curved manner until the slope of the outermost periphery is the smallest, etc. The effect structure is the lens 60 in the figure, which is shaped like a trumpet flower mouth (hereinafter referred to as the bell mouth), the center is sunken, and gradually bulges toward the periphery in a curved manner. If viewed from the side, the two focus light sources 41 and 43 When the light is projected to the lens 8, the intersecting light will be refracted into parallel lines of 45°, because the acrylic has proper impurity distribution inside, so the vertical viewing angle will be properly diffused.

As shown in Figure 17, if viewed from the up and down direction alone, the projection TV set of the present invention has only one projection point 51 on the screen, and for the cone-shaped light 52 of a single projection point, passing through this is equivalent to a bell mouth For the shape of the screen, the light 53 will converge slightly, but most of it will still diffuse. If combined with the further diffusion of impurities in the acrylic, a wider horizontal viewing angle can be obtained, but if you want to expand a wider horizontal viewing angle, It can also be used with the Lenticular board. As for the gain of the screen and the removal of hot spots, it is similar to the Fresnel screen.

In order to obtain a more specific understanding of the trumpet-like flat screen used in the present invention, as shown in Figure 18, 8 is the twill surface of the screen, and the annular stripe spacing 84 of the concentric circles is all less than 0.1mm, and The twill surface is all towards the center of the circle, and the slope becomes larger as it goes to the center. Such a surface structure is exactly the opposite function of the Fresnel lens.

In summary, the double-beam projection TV set used in the present invention has three-degree overlapping of light rays in the light return area, which can greatly reduce the space inside the TV set. Can make the overall appearance more concise and harmonious.

Of course, those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present invention, rather than as a limitation to the present invention, as long as within the scope of the spirit of the present invention, the implementation of the above Changes and modifications of the examples will fall within the scope of the claims of the present invention.

Claims (4)

1. A projection device for a rear projection television, comprising a group of projections, two groups of light return devices and a screen, characterized in that: The projector is arranged at the central rear of the cabinet, and includes a light source, a light-collecting lens array, a video panel, and a projection lens. In the lower group, the sum of the positive and negative aberration coefficients of all the lenses is equivalent to a convex lens. The two groups of lenses can capture the dynamic image formed by the video board and divide it into two half-cone beams with the upper and lower images reversed. Before being reflected, the central optical axes of the two semi-cone beams are parallel and opposite, and the two groups of light return devices are a symmetrical combination of up and down. The upper or lower group of one of the two is composed of three mirrors facing each other. As a result, the mirror surface of the primary reflector and the optical axis of the corresponding projection lens form an included angle of approximately 120 degrees, while the mirror surface of the secondary reflector is approximately perpendicular to the screen and approximately 60 degrees from the mirror surface of the tertiary reflector. The included angle; when the two image beams from the projector are put into the light return area of the two groups, the light has a three-level spatial overlap from the primary reflector to the three reflectors, and goes back and forth through 360 degrees The image is formed on the screen, which is set directly in front of the two projection ports of the projector and the light exit ports of the two sets of return mirrors, and forms a 90-degree vertical angle with the central axis of the projection light source; it is used as a composite of double-beam images On the imaging interface, the two split images reflected by the retroreflector are finally merged on the screen into a single complete enlarged image. 2. The projection device of the rear projection television as claimed in claim 1, characterized in that: The screen is a transparent acrylic substrate. The surface layer is processed by concentric twill stripes. The distance between each twill is less than 0.1mm. The twill surfaces are all facing the center of the circle, and the slope of the center is the largest. And it decreases outwards in a curved way until the slope of the outermost periphery is the smallest, and its equivalent surface structure is in the shape of a bell flower mouth; the screen can gather the projected light from two different points along the upper and lower sides into parallel rays, and then pass through the acrylic The impurities doped in the force substrate diffuse the light, and then form an image with a wide viewing angle and increased gain. 3. The projection device of the rear projection TV set as claimed in claim 1, characterized in that: There is a light barrier between the two sets of projection lenses and the video board to prevent the two sets of lenses from interfering with each other and to control the vertical projection angle within 30 degrees. 4. The projection device of the rear projection television as claimed in claim 1, characterized in that: The two first reflectors are respectively arranged in the side-by-side projection lens barrel, the reflection surface of which is the hypotenuse of the right-angled prism, and the reflection point is the position of the aperture in the lens barrel. The incident light axis and the exit light axis of the two groups Approximately 60 degrees angle.

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