KR100863837B1 - Prism and Prism fixing structure of an optical engine - Google Patents

Abstract

The present invention relates to a prism fixing structure of an optical engine. Specifically, when the prism of the optical engine is coupled to the case, a prism having a predetermined shape and a separate fixing member for fixing the prism are provided, whereby the prism and the case are provided. The prism fixing structure of the optical engine which prevents the air gap (gap) which arises in between.

Prism of the optical engine according to the present invention for achieving the object as described above, the first prism; And a second prism formed to have a width different from that of the first prism, and coupled to the first prism, and a engaging end is formed at a coupling portion of the first prism and the second prism.

On the other hand, the prism fixing structure of the optical engine according to the present invention, the case; A prism seated on one end surface of the case and having two widths having different widths so that protrusions are formed on a joining surface of the two parts; And a prism holder formed to be in contact with the protrusion to prevent the prism from being removed from the case.

By such a configuration, there is an effect that no air layer is generated between the prism and the prism attachment surface attached to the reflectometer case.

Optical engine, prism, air layer

Description

Prism and Prism fixing structure of an optical engine

1 is a cross-sectional view schematically showing a projection system according to the spirit of the present invention.

2 is an external perspective view of an optical engine according to the spirit of the present invention;

3 is a partially exploded perspective view of the optical engine;

4 is an exploded perspective view showing a state in which the optical engine according to the spirit of the present invention is coupled to the base.

5 is an exploded perspective view of the optical engine.

6 is an exploded perspective view showing a coupling state of the reflectometer constituting the optical engine according to the spirit of the present invention.

7 is an exploded perspective view of a prism fixing structure of the optical engine according to the present invention.

8 is a perspective view showing the structure of a prism of an optical engine according to the present invention;

9 is a perspective view showing the structure of a prism holder of the optical engine according to the present invention;

10 is a combined perspective view of a prism fixing structure of the optical engine according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110: prism 113: hanging end 120: prism holder

121: prism engaging portion 130: prism placement portion 131: prism seating surface

The present invention relates to a prism and a prism fixing structure of an optical engine, and more particularly, when a TIR (Total Internal Reflection) prism installed in a DLP (Digital Lighting Processing) optical engine is bonded to a reflectometer case, The present invention relates to a prism and prism fixing structure of an optical engine capable of preventing an air gap generated between a prism and a case by providing a prism having a shape and a separate fixing member for fixing the prism.

In general, a projection television is a device for projecting an image generated by an image generator to a screen at a predetermined magnification with a lens system and a reflection mirror in order to obtain an image screen of 40 inches or more. An apparatus for projecting an image from a projection television is called an optical engine. Such a projection television includes a CRT projection, an LCD projection, and a DLP projection method according to the type of the image generating unit.

Among them, the DLP projection method is a new display method compared to LCD (LCD) liquid crystal display (LCD) projection system, and realizes high definition image quality by using a light reflecting element. More specifically, this is a technology that expresses high brightness and high resolution images by selectively reflecting light using a device in which hundreds of thousands of reflective elements are integrated on a single chip, such as a projector, a cathode ray tube (CRT), and a liquid crystal display (LCD). Although it is an extension of the projection type display technology that has been developed over time, it has a characteristic of being reflective than the already commercially available LCD projection system.

DLP-type projection television uses a digital device that determines the blocking and opening of light through a circuit board and reflects the light reflected on the surface of a number of fine digital micromirror devices (DMDs). Adjust the degree to implement the image. Therefore, there is no noise or image quality deterioration when converting a digital signal to an analog signal, and different characteristics are not corrected for each device, so that the original picture can be perfectly reproduced.

In addition, the response speed of the device is faster than that of LCD and Plasma Display Pannel (PDP) methods, so that video can be reproduced more smoothly and flexibly than LCD and PDP without interrupting moving images, and the wide viewing angle can accommodate many viewers. It is easy to adjust as it is not affected by geomagnetism and is suitable for both front and rear projection.

On the other hand, the total reflection prism among the components of the DLP type projection television is an important component that directly affects the illumination system such as the screen size and focus in the optical engine. Among the factors affecting the optical system, the total reflection prism is treated with very precise installation with an installation error of ± 0.05 mm or less.

The conventional method of fixing the total reflection prism to the reflectometer case is to bond the prism to the case by injecting a bond between the prism seating surface of the reflectometer case and the prism.

However, the bond injected between the prism seating surface and the prism forms an air gap between the prism seating surface and the prism while the bond is hardened. Such an air layer has a problem of causing a fatal error in the back focal length (BFL) of the optical engine to be precise.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a prism and prism fixing structure of an optical engine such that no air layer is generated between the prism and the prism mounting surface attached to the reflectometer case.

In addition, unlike the prior art by providing a prism and prism fixing structure that can be fixed without a separate adhesive, such as bond, there is no air layer, prevent the phenomenon that the prism is removed from the reflectometer case when the bond strength of the bond is reduced, the bond hardening It is an object of the present invention to provide a prism and prism fixing structure of an optical engine, in which time is no longer needed, thereby reducing working time and improving workability.

Prism of the optical engine according to the present invention for achieving the object as described above, the first prism; And a second prism formed to have a width different from that of the first prism, and coupled to the first prism, and a engaging end is formed at a coupling portion of the first prism and the second prism.
On the other hand, the prism fixing structure of the optical engine according to the present invention, a case; a prism seated on one end surface of the case, consisting of two parts having different widths, the engaging end is formed on the joint surface of the two parts; And a prism holder formed to be in contact with the locking end to prevent the prism from being detached from the case, wherein the prism holder is formed with one or more prism locking parts to which the locking end is caught.

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By such a configuration, there is an effect that no air layer is generated between the prism and the prism attachment surface attached to the reflectometer case.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the spirit of the present invention is not limited to the embodiments presented, and other embodiments included within the scope of other inventive inventions or the scope of the present invention can be easily added by adding, changing, or deleting other elements. I can suggest.

1 is a cross-sectional view schematically showing a projection system according to the spirit of the present invention.

Referring to FIG. 1, a projection system 1 according to the present invention includes a cabinet 2 forming an appearance, a screen 4 mounted on the front surface of the cabinet 2, and an optical seat mounted on a lower end of the cabinet 2. An engine unit 10 and a rearview mirror 3 mounted to the inner circumferential surface of the cabinet 2 to reflect the image emitted from the optical engine unit 10 onto the screen 4 are included.

In detail, the image screen formed and projected by the optical engine unit 10 is reflected by the rearview mirror 3. The reflected image is extended and projected onto the screen 4 so that the image screen is recognized by the user.

Hereinafter, the structure and function of each part of the optical engine unit 10 will be described in more detail with reference to the accompanying drawings.

2 is an external perspective view of an optical engine according to the inventive concept, and FIG. 3 is a partially exploded perspective view of the optical engine.

2 and 3, the optical engine unit 10 according to the present invention includes a base 11, an optical engine 20 mounted on the base 11, and an outer portion of the optical engine 20. Various parts to be mounted are included.

In detail, a power supply unit 15 for supplying an appropriate amount of power to various electrical components constituting the optical engine unit 10 may be provided to various components mounted on the outside of the optical engine 20, and the power supply unit 15. A power supply supporter 16 for supporting the lamp, a lamp cooling fan assembly 14 for cooling a lamp (to be described later) constituting the optical engine 20, and a ballast 13 mounted to one side of the base 11. ), A projection lens cap 17 surrounding the projection lens (to be described later) constituting the optical engine 20, and a DMD fan 12 for cooling the DMD (to be described later) constituting the optical engine 20. ) Is included.

In more detail, the power supply unit 15 is a switching mode power supply (SMPS), and is a modular power supply unit that converts electricity supplied from the outside to match the electric device. In addition, the power supply unit 15 controls the intermittent control at a high frequency of a commercial frequency or higher and mitigates the impact by using semiconductor switching characteristics.

In addition, the ballast 13 functions to apply a high voltage when the lamp constituting the optical engine 20 is turned on and to appropriately adjust the current so that an overcurrent does not flow after the lamp is turned on.

As shown in FIG. 3, in the case of the optical engine unit 10 according to the present invention, each part except for the optical engine 20 may be independently separated from the base 11. Thus, the optical engine 20 is mounted to the base 11, and then each of the components mentioned above are coupled to the base 11.

4 is an exploded perspective view illustrating a state in which an optical engine according to the spirit of the present invention is coupled to a base, and FIG. 5 is an exploded perspective view of the optical engine.

Referring to FIG. 4, the optical engine 20 for making an image screen in the optical engine unit 10 according to the present invention may be integrally separated from the base 11.

In detail, the optical engine 20 assembly is completely separated by removing only eight fastening members that allow the optical engine 20 assembly to be fixed to the base 11. Therefore, there is an advantage that the service is easily made and the disassembly and assembly process is very simple.

In addition, in order for the optical engine 20 assembly to be secured to the base 11, it is not necessary to first have the components of the optical engine 20 assembled to the base 11. That is, the optical engine 20 is assembled separately, and then integrally mounted on the base 11.

Referring to FIG. 5, the optical engine 20 according to the present invention includes a lamp assembly 21 in which white light is generated by a high voltage supplied by the ballast 13, and unpolarized light emitted from the lamp assembly 21. A color wheel assembly 22 for separating the red, green, and blue, a light tunnel assembly 24 for uniformly making red, green, and blue separated light while passing through the color wheel assembly 22; A condensing lens 25 through which the uniform light is collected while passing through the light tunnel assembly 24, a folding mirror 29 reflecting light passing through the condensing lens 25, and A total reflection prism 110 for reflecting light reflected by the folding mirror 29 again, a prism holder 120 for fixing the position of the total reflection prism 110, and light reflected by the total reflection prism 110; Gather visual information A DMD assembly 26 to be formed, an actuator 27 for doubling and irradiating the number of pixels of light reflected from the DMD assembly 26, and a projection lens for enlarging the light passing through the actuator 27. (31) is included. Here, the assembly of the lamp assembly 21, the color wheel assembly 22, the light tunnel assembly 24 and the condensing lens 25 is called an illumination system. The aggregate of the folding mirror 29 and the total reflection prism 130 is called a reflectometer, and the aggregate of the reflectometer and the DMD assembly 26 is called a synthetic system.

In more detail, the lamp assembly 21 includes a lamp 212 that emits white light and a lamp case 211 that protects the lamp 212. In addition, the reflector of the lamp 212 serves to change the light emitted from the burner of the lamp is reflected to focus at a certain distance, that is, the focal length.

In addition, the color wheel assembly 22 may be divided into red, green, and blue color wheels (also referred to as 221: RGB color filters) and rotate at high speed. A motor 223 driving the wheel 221 and a heat dissipation fin 222 for cooling the motor 223.

In detail, light emitted from the lamp 212 by the reflector of the lamp 212 is focused on the surface of the color wheel 221. In addition, the light collected by the color wheel 221 passes through the color wheel 221 and turns any color of red, blue, and green. Here, the color wheel 221 has a disk shape having a predetermined diameter, the disk is divided into red, green, blue. Accordingly, the unpolarized light reflected by the reflector has one of red, blue, and green colors due to the color of the color wheel located at the moment of condensing.

In addition, the color wheel assembly 22 and the light tunnel assembly 24 are housed inside the light tunnel housing 23.

In addition, the light tunnel assembly 24 is also called a rod lens, and serves to uniformly make colored light passing through the color wheel 221.

In detail, the light tunnel assembly 24 is formed by joining four small, long rectangular bar mirrors facing each other. The light passing through the color wheel assembly 22 is diffusely reflected while passing through the light tunnel, and the brightness distribution is uniform.

In addition, the condensing lens 25 performs a function of collecting red, green, and blue light uniformed while passing through the light tunnel assembly 24 to the DMD elements constituting the DMD assembly 26. do.

In addition, the total reflection prism 110 is also called a TIR (Total Internal Reflection) prism, and a prism having a large refractive index and a prism having a relatively small refractive index are formed by bonding. And, due to the difference in refractive index is totally reflected or transmitted according to the incident angle of the light irradiated from the condensing lens 25.

In detail, each object has its own refractive index, and the difference in refractive index determines the critical angle at which light is totally reflected or transmitted.

Therefore, light incident at an angle greater than or equal to a critical angle is totally reflected by the total reflection prism 110, and light incident at an angle smaller than or equal to a critical angle passes through the total reflection prism 110. The total reflection prism 110 will be described in detail with reference to the accompanying drawings.

In addition, the DMD assembly (Digital Micro-mirror Device Assembly) 26 is composed of a DMD panel 33 and a driver board in which the DMD panel 33 is accommodated. In detail, the driver board is a device for controlling the driving of the ballast and the color wheel or controlling the image.

On the other hand, the DMD panel 33 is designed so that a minute mirror of the same amount as the resolution of the display is arranged so as to have a one-to-one correspondence with the screen.

In detail, the DMD panel 33 determines whether the red, green, and blue light transmitted through the total reflection prism 110 is to be directed toward the screen or discarded out of the screen. The DMD panel 33 is mounted in a complementary metal oxide semiconductor (CMOS) memory and driven by a signal transmitted from the CMOS memory.

In more detail, the micromirror constituting the DMD panel 33 is manufactured in the form of a fine diamond-shaped pixel of 16 μm in width and length, and tilted by ± 10 degrees according to a signal transmitted from the CMOS, so that the total reflection prism ( Light passing through 110 is reflected to the screen group or is thrown out of the screen.

In addition, the actuator 27 is disposed between the DMD panel 33 and the projection lens 31, and a mirror is mounted at the center portion. In detail, the actuator 27 performs a function of doubling the number of pixels of the image signal by refracting and dividing the image signal emitted from the DMD panel 33 by half a frame. Due to the refraction characteristics of the mirror, the resolution of the screen is increased. In addition, the actuator includes a transmission type and a reflection type.

In addition, the projection lens assembly 31 functions to enlarge the image passing through the actuator 27 toward the rearview mirror 3.

In the optical engine 20 having the above-described configuration, the actuator 27, the total reflection prism 110, and the folding mirror 29 are inserted from different surfaces of the reflector case 130 to provide one reflectometer. Configure. The color wheel assembly 22 and the light tunnel assembly 24 are accommodated in the light tunnel housing 23 to form another assembly. In addition, the lamp assembly 210 forms a separate assembly together with the lamp 212 mounted inside the lamp case 211, and the light tunnel housing 23 is in close contact with the front of the lamp assembly 21. do.

As described above, since a plurality of parts form a single assembly, there is an advantage that parts replacement and service are easily performed.

6 is an exploded perspective view illustrating a coupling state of a reflectometer constituting an optical engine according to the inventive concept.

Referring to FIG. 6, the reflectometer constituting the optical engine unit 10 according to the present invention includes a reflectometer case 130, a folding mirror 29 inserted from a side of the reflectometer case 130, and The actuator 27 inserted from the upper surface of the reflector case 130, the total reflection prism 110 inserted from the front surface of the reflector case 130, and the total reflection prism 130 are the reflectometer case 130. Included is a prism holder 120 to be coupled to.

In detail, a prism seating surface (see 131 of FIG. 7) in which the total reflection prism 110 is mounted is formed in the reflector case 130. A light passage opening 134 is formed on a surface on which the prism seating surface (see 131 of FIG. 7) is formed, that is, a rear surface of the reflector case 130. Accordingly, the light totally reflected by the total reflection prism 110 is projected onto the DMD panel 33 through the light passing opening 134.

In addition, a folding mirror insertion hole 138 for inserting the folding mirror 29 is formed at a side of the reflector case 130. In addition, an actuator insertion hole 137 for inserting the actuator 27 is formed in the upper surface of the reflector case 130. In addition, a prism insertion hole 139 for inserting the total reflection prism 110 is formed on the front surface of the reflectometer case 130.

The assembly process of the reflectometer constituting the above configuration will be described. First, the total reflection prism 110 is inserted through the prism insertion hole 139. The total reflection prism 110 is fixed to the prism seating surface (see 131 of FIG. 7). In addition, the prism holder 120 is coupled to the upper end of the total reflection prism 110 so that the total reflection prism 110 is coupled to the reflectometer case 130.

In addition, the user allows the actuator 27 to be inserted into the reflectometer case 130 through the actuator insertion hole 137. Then, the folding mirror 29 is inserted into the reflectometer case 130 through the folding mirror insertion hole 138. Here, the order of insertion of the folding mirror 29 and the actuator 29 may be performed first.

By the assembly structure as described above, since the folding mirror 29, the actuator 27 and the total reflection prism 110 form one assembly, disassembly and assembly are very easy. In addition, the respective components are inserted from different sides of the reflectometer case 130, so that the assembly and disassembly of the individual components can be easily performed.

7 is an exploded perspective view showing a prism fixing structure of the optical engine according to the present invention. For convenience of understanding, only the configuration of the part of the reflection system case 130 of FIG. 6 to which the total reflection prism 110 is coupled is described in detail.

Referring to FIG. 7, the prism fixing structure of the optical engine according to the present invention includes a total reflection prism 110 composed of two prisms, a reflectometer case 130 on which the total reflection prism 110 is mounted, and the total reflection The prism holder 120 is fixed to the total reflection prism 110 so that the prism 110 is not separated from the reflectometer case 130.

In detail, the total reflection prism 110 is configured in such a manner that the first prism 111 and the second prism 112 are coupled to each other, and the first prism 111 and the second prism 112 have different widths. Thus, a predetermined locking end 113 is formed at the engaging portion of both prisms 111 and 112.

Meanwhile, the light passing through the total reflection prism 110 may be directed to a DMD (see 26 in FIG. 5) below the prism seating surface 131 at an approximately center portion of the reflector case 130. A light passing opening 134 having a predetermined shape that is opened downward is formed. In addition, the prism holder 120 may further include a prism holder coupling protrusion 132 to be coupled to the reflectometer case 130.

In addition, a prism seating surface 131 on which one surface of the total reflection prism 110 is seated is formed around the periphery of the light passing opening 134. The prism seating surface 131 has a substantially constant width around the light passing opening 134 and is formed to surround the light passing opening 134 in a '-' shape. In addition, the prism seating surface 131 is preferably formed on the same plane.

Meanwhile, a prism fixing part 135 formed of a wall having a height higher than the prism seating surface 131 and having a predetermined width is formed at the outermost circumference of the light passage opening 134.

In other words, when the total reflection prism 110 is attached to the prism seating surface 131, the prism fixing part 135 is a component for allowing the total reflection prism 110 to be fixed without being oscillated in the left and right directions. Accordingly, the prism seating surface 131 has a shape surrounded by the prism fixing part 135.

On the other hand, when the total reflection prism 110 is seated on the prism seating surface 131, the inner surface of the prism fixing part 135 is formed to be in contact with the lower surface side of the total reflection prism 110. In other words, the distance between the inner surfaces formed by the prism fixing part 135 is preferably equal to the width of the total reflection prism 110.

The prism holder 120 may include a prism insertion part 123 through which the total reflection prism 110 is inserted and the total reflection prism 110 so that the total reflection prism 110 is not removed from the reflectometer case 130. Supporting prism engaging portion 121, and a coupling hole 122 for coupling the prism holder 120 and the reflectometer case 130 is included.

Here, the prism fixing structure of the optical engine shown in FIG. 7 shows only a portion where the total reflection prism 110 is installed, and the configuration related to the coupling of the prism fixing structure of the optical engine with other components is related to that of the present invention. Since it does not belong to the scope of the idea, a detailed description thereof will be omitted. In the following different drawings, it will be described in more detail with respect to the prism fixing structure according to the present invention.

8 is a perspective view showing the structure of a prism of an optical engine according to the present invention.

Referring to FIG. 8, the total reflection prism 110 according to the present invention includes a first prism 111 having a predetermined shape and a second prism 112 coupled to the first prism 111.

In detail, the second prism 112 is formed to have a width equal to or slightly smaller than the width of the seating surface 131 to be seated on the prism seating surface 131 formed in the reflector case 130.

The first prism 111 is coupled to the upper end of the second prism 112. In this case, the width of the first prism is formed to be slightly smaller than the width of the second prism, so that the engaging end 113 is formed to be stepped on the engaging portion of the first prism 111 and the second prism 112. It is composed.

By the above configuration, since the total reflection prism 110 is coupled to the reflectometer case 130 without using a separate adhesive member, an air layer is not generated between the total reflection prism 110 and the reflectometer case 130. It does not work.

9 is a perspective view showing the structure of a prism holder of the optical engine according to the present invention.

Referring to FIG. 9, the prism holder 120 according to the present invention intervenes in the prism insertion portion 123 through which the total reflection prism 110 is inserted, and the engaging end 113 of the total reflection prism 110. At least one prism catching part 121 supporting the total reflection prism 110 so as not to be removed, and a coupling hole 122 through which the prism holder coupling protrusion 132 of the reflector case 130 is inserted.

In detail, the prism holder 120 is formed to be inclined at the same angle as the top surface of the second prism 112 to be combined with the total reflection prism 110. In addition, a prism insertion part 123 having a shape corresponding to the total reflection prism 110 is formed at the center of the prism holder 120 so that the total reflection prism 110 is inserted therethrough. Here, the prism insertion part 123 is formed to have a wider width than that of the first prism 111 in order for the first prism 111 to pass therethrough.

Meanwhile, at least one prism catching part 121 may be formed at the corner of the prism inserting part 123 to catch the catching end 113 of the total reflection prism 110. The prism catching part 121 may be formed in a rectangular columnar shape, and the lower end of the prism catching part 121 may be in contact with the catching end 113 of the total reflection prism in the same manner as the catching end 113. It may be formed to be inclined at an angle.

The total reflection prism 110 is coupled to the reflectometer case 130 and the prism holder 120 without fixing a separate adhesive by the prism catching part 121 and the catching end 113, and the position is fixed. And it is supported so that it may not rock left and right.

Meanwhile, an upper portion of the prism holder 120 may further include a coupling hole 122 into which the prism holder coupling protrusion 132 of the reflector case 130 is inserted.

By the above structure, the reflectometer case 130 and the prism holder 120 and the total reflection prism 110 inserted therebetween are simply and stably coupled.

10 is a combined perspective view of a prism fixing structure of the optical engine according to the present invention.

Referring to FIG. 10, the prism fixing structure according to the present invention is a structure for fixing the total reflection prism 110 on the light passing opening 134, and the total reflection prism 110 fixed by the prism fixing structure according to the present invention. One surface of) is configured to cover all of the light passage openings 134.

In detail, the total reflection prism 110 is mounted on the prism seating surface 131 of the reflector case 130. The prism holder 120 is coupled to the upper end of the total reflection prism 110.

In other words, the prism holder 120 is coupled downward from the upper side of the reflectometer case 130 and the total reflection prism 110 mounted thereon. Accordingly, the total reflection prism 110 is fitted into the prism insertion portion 123 of the prism holder 120, and the prism holder coupling protrusion of the reflectometer case 130 is inserted into the coupling hole 122 of the prism holder 120. 132 is accommodated. The prism holder 120 and the reflectometer case 130 are fixedly coupled by separate coupling members. Therefore, the lower end of the prism engaging portion 121 of the prism holder 120 and the locking end 113 of the total reflection prism 110 are in contact with each other, so that the total reflection prism 110 is not separated from the reflectometer case 130. No position can be fixed.

According to the present invention, there is an advantage that no air layer is generated between the prism and the prism seating surface attached to the total reflection engine case.

Unlike the related art, by providing a prism and a prism fixing structure that can be fixed without a separate adhesive such as a bond, no air layer is generated, and a phenomenon in which the prism is removed from the total reflection engine case when the bond strength of the bond is reduced, and the hardening time of the bond Since it is unnecessary, work time is reduced and workability is improved.

Claims (9)

A first prism; And The prism of the optical engine is formed to have a width different from the first prism, and includes a second prism coupled to the first prism, the engaging end is formed in the coupling portion of the first prism and the second prism. delete case; A prism seated on one end surface of the case and having two widths having different widths so that a locking end is formed at a joining surface of the two parts; And And a prism holder which is formed to be in contact with the locking end to prevent the prism from being detached from the case. The prism holder is formed with at least one prism engaging portion that is caught by the locking end prism fixing structure of the optical engine. delete The method of claim 3, wherein The prism engaging portion is formed at the same angle as the prism, the prism fixing structure of the optical engine, characterized in that the surface contact with the prism. The method of claim 3, wherein And a prism seating surface in which the prism is recessed so that the prism is seated, and a light passage opening through which the light passing through the prism passes through the prism seating surface. The method of claim 3, wherein The case and the prism holder is provided with a coupling hole and a coupling protrusion, the coupling protrusion is a prism fixing structure of the optical engine, characterized in that the fixing hole is inserted into the coupling hole. The method of claim 3, wherein And a prism insertion portion formed in the prism holder such that at least a portion of the prism is inserted therethrough. The method of claim 3, wherein The prism holder is a prism fixing structure of the optical engine is formed so that the narrow portion of the prism is passed, the wide portion is caught.

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