Patent Publication Number: US-2009225281-A1

Title: Projection display system and prism set and manufacturing method thereof

Description:
The present application claims priority under U.S.C. §119(a) on Patent Application No(s) 97108183. filed in Taiwan, Republic of China on Mar. 7, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a projection display system, a prism set and a manufacturing method thereof and, in particular, to a prism assembly for improving efficiency of light-combining. 
     2. Description of the Related Art 
     Present rear projector and rear projection TV systems include three types of systems, digital light processing (DLP) systems, liquid-crystal display (LCD) systems, and liquid crystal on silicon (LCoS) systems. Due to prism sets are applied to LCD systems and LCoS systems to combine light, the demand of prism sets have increased. 
     Referring to  FIG. 1 , it shows a base structure of a conventional projector. The conventional projector comprises three liquid-crystal light valves  42 ,  44 , and  46 , a prism set  48 , and a projection lens  50 . A red reflective film  48 R intersects a blue reflective film  48 B to form an X shape. Three primary colors, red, blue and green, are combined via the prism set  48  and then adjusted by the liquid-crystal light valves  42 ,  44 , and  46  for illuminating a combined light beam toward the projection lens  50 . The combined light beam is focused on a projection screen  52  via the projection lens  50 . 
     The prism set  48  is formed by four equal-sized prisms adhered to each other However, when adhering four equal-sized prisms for forming the prism set  48 , it is difficult to accurately adhere the prisms and keep the red reflective film  48 R and the blue reflective film  48 B on the same plane, respectively, thereby influencing the reflective and transparent characteristics of the red reflective film  48 R and the blue reflective film  48 B. As such, the prism set  48  is deficient. Additionally, when the deficient prism set is applied to a projector, multiple images, various-sized images or stripes generated by light scattering appear on the projection image. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a projection display system, a prism set and a manufacturing method thereof for improving light-combining efficiency. 
     To achieve the above, the invention provides a method for manufacturing a prism set. The steps include: providing a first prism, a second prism, a third prism and a fourth prism, wherein the length of the first prism is greater than that of the second prism, and the lengths of the third prism and the fourth prism are greater than that of the first prism; and assembling the first prism, the second prism, the third prism and the fourth prism together to form a prism assembly. 
     The first prism and the second prism are assembled via a first tool to form a first assembly, and a plane of the first assembly is completely attached to a plane of the first tool. When the first prism is assembled with the second prism, the lengths of the two protruding sides of the first prism are almost the same. 
     The first assembly formed by the first prism and the second prism is assembled with the third prism via a second tool to form a second assembly and a plane of the second assembly is completely attached to a plane of the second tool. When the first assembly is assembled with the third prism, the lengths of the two protruding sides of the third prism are almost the same. The second tool comprises a hole, the length of the second tool corresponds to the length of the second prism, and the width of the second tool is two times greater than the width of the second prism. Alternatively, the second tool comprises a hole, the hole comprises a first portion and a second portion, the length of the first portion of the hole corresponds to the length of the first prism, the length of the second portion of the hole corresponds to the lengths of the third prism and the fourth prism, and the width of the hole is two times greater than the width of the second prism. 
     The second assembly formed by the first prism, the second prism, and the third prism is assembled with the fourth prism via a third tool to form the prism assembly, and a plane of the prism assembly is completely attached to a plane of the third tool. Two sides of the third prism are aligned to two sides of the fourth prism. The second tool comprises a hole, the length of the third tool corresponds to the length of the first prism, and the width of the third tool is two times greater than the width of the fourth prism. 
     The lengths of the third prism and the fourth prism are similar. 
     A join between the first prism and the second prism, and a join between the third prism and the fourth prism respectively have a first optical film. The two first optical films are disposed on the same surface. A join between the first prism and the third prism, and a join between the second prism and the fourth prism respectively have a second optical film. The two second optical films are disposed on the same plane. The first optical films intersect the second optical films to form an x shape in the prism set, and a central intersection of the first optical films and the second optical films is discontinuous. 
     A connecting surface of the first prism is plated with the first optical film, a connecting surface of the fourth prism is plated with the second optical film, and two connecting surfaces of the third prism is respectively plated with the first optical film and the second optical film. 
     The first optical film comprises a red reflective film and the second optical film comprises a blue or a green reflective film. The first optical film and the second optical film are formed via deposition or sputtering process. The first prism, the second prism, the third prism and the fourth prism are adhered via epoxy, UV adhesive or adhesive. The first prism, the second prism, the third prism and the fourth prism are a pillar-shaped prism with a cross section of an isosceles triangle, a right-angled and equilateral triangle, or a right-angled and non-equilateral triangle. 
     The method for manufacturing the prism set further includes a step of cutting the prism assembly to form one or more prism sets. 
     To achieve the above, the invention provides a prism set. The prism set includes a first prism, a second prism, a third prism and a fourth prism. The first prism, the second prism, the third prism and the fourth prism are assembled to each other. A join between the first prism and the second prism, and a join between the third prism and the fourth prism respectively have a first optical film. The two first optical films are disposed on the same plane. A join between the first prism and the third prism, and a join between the second prism and the fourth prism respectively have a second optical film. The two second optical films are disposed on the same plane. The first optical films intersect the second optical films to form an x shape in the prism set, and a central intersection of the first optical films and the second optical films is discontinuous. 
     To achieve the above, the invention provides a projection display system. The projection display system includes a light source, a color-separating apparatus separating light from the light source for color separation, a light adjuster adjusting the separated light according to an image signal to form an adjusted light, and a prism set combining the adjusted light to form a combined light beam. The prism set includes a first prism, a second prism, a third prism and a fourth prism. The first prism, the second prism, the third prism and the fourth prism are assembled to each other. A join between the first prism and the second prism, and a join between the third prism and the fourth prism respectively have a first optical film. The two first optical films are disposed on the same plane. A join between the first prism and the third prism, and a join between the second prism and the fourth prism respectively have a second optical film. The two second optical films are disposed on the same plane. The first optical films intersect the second optical films to form an x shape in the prism set, and a central intersection of the first optical Films and the second optical films is discontinuous. 
     The projection display system further comprises a projection lens to focus the combined light beam on a projection screen. 
     The projection display system further comprises a UV-IR filter to filter ultraviolet and infrared light from the light source. 
     The color-separating apparatus includes a polarization conversion system, a plurality of dichroic filters, and a plurality of reflector. The light adjuster comprises a liquid-crystal light valve, a polarizer, or a control panel. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will become more fully understood from the subsequent detailed description and accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic view of a base structure of a conventional projector; 
         FIGS. 2A to 2K  are schematic views of a method for manufacturing a prism set according to the present invention; 
         FIG. 3  is a schematic view of a tool applied to a method for manufacturing another prism set according to the present invention; and 
         FIG. 4  is a schematic view of an embodiment of an LCD projection display system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the related drawings, a projection display system and a prism set and manufacturing method thereof is described according to the preferred embodiments of the invention. The same elements are labeled with the same symbols. 
     Referring to  FIGS. 2A to 2K , they show a method for manufacturing a prism set according to the present invention. As shown in  FIGS. 2A to 2C , the method includes the steps of: providing a first prism (or named a long prism)  11  and a second prism (or named a short prism)  12 . The length L 1  of the long prism  11  is greater than the length L 2  of the short prism  12 . A connecting surface P 1  of the long prism  11  is plated with the first optical film (in this embodiment, the first optical film is, for example, a red reflective film formed via deposition or sputtering process) and connected to a connecting surface P 2  of the short prism  12  via an assembling tool  21 . The connection material includes epoxy, UV adhesive or adhesive. A plane S 1  of an assembly  10  formed by the long prism  11  and the short prism  12  is completely attached to a plane W 1  of the assembling tool  21  for minimizing deviation between the long prism  11  and the short prism  12  to increase the coplanarity of the plane S 1 . When assembling, it is necessary to ensure that the lengths D 1  and D 2  of two protruding sides of the long prism  11  are almost the same for a smooth manufacturing process. 
     Referring to  FIGS. 2D to 2G , the method includes the steps of: providing a third prism (or named a extra-long prism)  13 . The length L 3  of the extra-long prism  13  is greater than the length L 1  of the long prism  11  and the length L 2  of the short prism  12 . A connecting surface P 4  of the extra-long prism  13  is plated with the second optical film (in this embodiment, the second optical film is, for example, a blue reflective film) and a connecting surface P 5  of the extra-long prism  13  is plated with the first optical film (in this embodiment, the first optical film is, for example, a red reflective film). The blue reflective film is formed via deposition or sputtering process. A connecting surface P 3  of the assembly  10  is connected to the connecting surface P 4  of the extra-long prism  13  to form an assembly  10 ′ via a tool  22 . A plane S 2  of the assembly  10 ′ is completely attached to a plane W 2  of the tool  22  for minimizing deviation between the long prism  11  and the extra-long prism  13  to increase the coplanarity of the plane S 2 . When assembling, it is necessary to ensure that the lengths D 3  and D 4  of two protruding sides of the extra-long prism  13  are almost the same for a smooth manufacturing process. The tool  22  comprises a hole  220 , the length L of the hole  220  of the tool  22  corresponds to or is slightly greater than the length L 2  of the short prism  12  to provide a maximum support surface on the plane S 2  to support the plane W 2 . The width W of the hole  220  is two times greater than the width a of the short prism  12  to prevent the tool  22  from interference of the the short prism  12 . 
     Referring to  FIGS. 2H to 2I , the method includes the step of: providing a fourth prism (or named a extra-long prism)  14 . The length L 4  of the extra-long prism  14  is equal to the length L 3  of the extra-long prism  13 . A connecting surface P 8  of the extra-long prism  14  is plated with the second optical film (in this embodiment, the second optical film is, for example, a blue reflective film). A connecting surface P 5  and a connecting surface P 6  of the assembly  10 ′ are connected to two connecting surfaces P 7  and P 8  of the extra-long prism  14  to form an assembly  10 ″ via a tool  23 . A plane S 3  of the extra-long prism  14  is completely attached to a plane W 3  of the tool  23  for minimizing deviation between the extra-long prism  13  and the extra-long prism  14  to increase the coplanarity of the plane S 3 . When assembling, it is necessary to ensure that two sides of the extra-long prism  14  are aligned to two sides of the extra-long prism  13 . The tool  23  includes a hole  230 , the length L′ of the hole  230  of the tool  23  corresponds to the length L 1  of the long prism  11  to provide a maximum support surface on the plane S 3  to support the plane W 3 . The width W′ of the hole  230  is two times greater than the width a of the extra-long prism  14  to prevent the tool  23  from interference of the long prism  11 . 
     The long prism  1 , the short prism  12 , the extra-long prisms  13  and  14  may be a pillar-shaped prism with a cross section of an isosceles triangle, a right-angled and equilateral triangle or a right-angled and non-equilateral triangle. 
     Referring to  FIG. 2I , the assembly  10 ″ is cut along the dotted line to form the prism set  1 , as shown in  FIG. 2J . The long prism set  1  can be cut into several prism sets. As shown in  FIG. 2K , it shows a sectional view of the prism set  1  according to  FIG. 2J . The red reflective films  1 R intersects the blue reflective films  1 B to form an x shape in the prism set  1 , and a central intersection of the red reflective films  1 R and the blue reflective films  1 B is discontinuous. The positions of the red reflective films  1 R and the blue reflective films  1 B can be exchanged. Further, different colors can be adapted. In this embodiment, the blue reflective film can be replaced with, for example but not limited to, a green reflective film. 
     Referring to  FIG. 3 , it shows a tool applied to a method for manufacturing another prism set according to the present invention. The method for manufacturing the prism set is approximately similar to the above-mentioned embodiment. The difference is that the tools  22  and  23  are integrated as a tool  3 . The tool  3  includes a hole  30 . The hole  30  includes a first portion and a second portion. The length L of the first portion corresponds to the length L 1  of the long prism  11  (the length L of the first portion is less than the length L 1  of the long prism  11  but is greater than the length L 2  of the short prism  12 ). The length L′ of the second portion corresponds to the length L 3  of the extra-long prism  13  (the length L′ of the second portion is less than the length L 3  of the extra-long prism  13  but is greater than the length L 3  of the extra-long prism  13 ). The width of the hole  230  is two times greater than the width of the prism. 
     Referring to  FIG. 4 , it shows an embodiment of an LCD projection display system according to the present invention. The LCD projection display system includes a light source  60 ; a color-separating apparatus separating light from the light source for color separation; three light adjusters adjusting the separated light according to an image signal to form an adjusted light; and a prism set  1  combining the adjusted light to form a combined light beam. The prism set  1  is a finished light-combining product cut via the above-mentioned method. 
     The projection display system further includes a UV-IR filter  61  to filter ultraviolet and infrared light from the light source. The projection display system further includes a projection lens  67  which focuses the combined light beam on a projection screen. The color-separating apparatus includes a polarization conversion system  62 , a plurality of dichroic filters  63  and a plurality of reflectors  64 . The light adjuster includes a liquid-crystal light valve, a polarizer or a control panel. 
     In the operation of the projection display system, the light source  60  emits light to the UV-IR filter  61  to filter UV and IR light. Then, light enters the polarization conversion system  62  and passes through a series of dichroic filters  63  and reflectors  64 . Finally, light enters the prism set  1  via the polarizer  65  and LCD panel  66  to combine red light, blue light, and green light to form white light so as to emit white light to the projection lens  67 . 
     In summary, the method for manufacturing the prism set according to the present invention ensures that the red reflective film and the blue reflective film are accurately positioned on the same plane, thereby substantially improving reflective and transparent characteristics so as to enhance the prism set characteristics. Furthermore, when the prism set of the present invention is applied to a projection display system, the size of the projection display system can be decreased. The surfaces of the four pillar-shaped prisms of the prism set are plated with the reflective film before being assembled. Accordingly, if one of the prisms fails to be plated, the other prisms do not need to be replaced, thereby reducing product cost. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.