Liquid crystal display projector

Abstract: The object of the present invention is to make a projection lens retractable inside of a cabinet. A liquid crystal display projector of the present invention comprises a light source, a group of mirrors, liquid crystal display devices, a projection lens, a main body cabin containing the foregoing light source, group of mirrors, liquid crystal display devices and projection lens, and a mechanism whereby the afore-mentioned projection lens is allowed to retract into and protrude from the main body. The foregoing projection lens comprises: an outer cylinder that includes a ring-like shape; a drive motor provided with a gear; a ring-like intermediate cylinder which has a first cam groove, second cam groove and gearwork that is provided on the exterior thereof with the gearwork meshing with the gear of the drive motor and is installed on the inner side of the outer cylinder so as to be made movable by sliding; a first inner cylinder which has a first axis to fit in the first cam groove and fits with the inner surface of the intermediate cylinder in the front part thereof so as to be made movable by sliding according to the movement of the first axis caused by the rotation of the first cam groove; a second inner cylinder which has a second axis to fit in the second cam groove and fits with the inner surface of the intermedate cylinder toward the back thereof so as to be made movable by sliding according to the movement of the second axis caused by the rotation of the second cam groove; and a plurality of lenses installed in the first inner cylinder, second inner cylinder, intermediate cylinder and outer cylinder at positions as specified in a given way. The projection lens thus structured operates in such a manner that driving of the drive motor causes the intermediate cylinder to rotate and the rotation of the intermediate cylinder allows the projection lens to zoom by protruding and retracting the first inner cylinder.

Description: TECHNOLOGICAL FIELD OF THE INVENTION The present invention relates to a liquid crystal display projector according to the preamble of claim 1 and as known from US-A-5 347 324, whereby video images displayed on liquid crystal display panels and the like are projected on a screen. BACKGROUND OF THE INVENTION For many years by now, projectors using a metal halide lamp and the like as the light source, whereby video images displayed on liquid crystal panels are enlarged and projected on a screen, have been available on the market. With such projectors, the light emitted from the light source is gathered on liquid crystal panels by means of mirrors and the like and projected on a screen through a projection lens. There are two kinds of liquid crystal display projectors, one being a 1-panel type that employs one liquid crystal display panel and the other being a 3-panel type wherein three liquid crystal display panels are used and color splitting and color combining are performed by means of dichloic mirrors and the like. Each respective type of the above has a projection lens protruding from the projector's main body cabinet. As shown in Fig. 6, a 1-panel type liquid crystal display projector has, in general, a projection lens 41, a field lens 42, a liquid crystal display panel 43 and polarizers 45 for light incident side and light radiant side. There are two types in the projection lens 41, one having a fixed focus length and the other having a zooming function. A 3-panel type liquid crystal display projector is basically of the same structure except for having half mirrors 44 that,are additionally built in for color splitting and combining. These types of liquid crystal display projectors were proposed in a Japanese patent application published for public examination, Showa 62(1987)-316710, for example. Each respective liquid crystal display projector of 1-panel type and 3-panel type has generally a structure wherein a projection lens protrudes from the main body cabinet of the projector due to limitations in layout. The structure wherein the projection lens protrudes has often caused a problem of damaging the protruding lens and the like when a liquid crystal display projector is carried. In addition, the protruding projection lens has imposed many restrictions on designing liquid crystal display projectors, thereby leading to a reduction in freedom of design. Furthermore, there is a drawback that dust easily settles on a protruding projection lens. US-A-5347324, already mentioned at the beginning, discloses a video projector having a projection lens being displaceable between a protruding and a retracted position relative to the housing of the video projector. When the video projector is not in use, the projection lens is contracted and stored in the housing. US-A-4018520 discloses a transparency projector including a focusing mechanism having an objective lens carried within a lens barrel supported within a sleeve carried by the projector housing for axial reciprocal displacement along the optical axis. The sleeve is provided with a means for engaging a guide rod supported within the projector housing for limiting movement of the sleeve to axial movement. A reversible electric motor within the housing receives slide position error signals from an automatic focusing system. The electric motor operates to drive a disk rotatably carried on the sleeve. The disk is provided with a spiral groove on one face. A pin fixably supported on the projector housing is arranged for engagement with the spiral groove so that upon rotation of the disk, engagement of the pin within the spiral will produce axial movement of the lens barrel supporting sleeve along the guide rod. SUMMARY OF THE INVENTION The object of the invention is to provide a liquid crystal display projector allowing to protrude and retract the objective in a simple and a comfortable way. This object is achieved by the features of claim 1. Advantageous embodiments are set forth in the independent claims. With the structure according to the invention, no lenses are protruding from the main body cabinet of a liquid crystal display projector when the projector is carried, thereby eliminating dangers to damage lenses. Furthermore, the main body cabinet of a liquid crystal display projector can be made simple in design, looking like a rectangular prism that is similar to the configuration of a suit case. In addition, such a novel design as a door provided in front of the projection lens side of a liquid crystal display projector is possible, for example. Thus, production of liquid crystal display projectors having whatever designs as desired is now possible. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a liquid crystal display projector in an exemplary embodiment of the present invention when electric power is turned on. including a diagram for explaining the optical system used in the projector. Fig. 1(a) is a plan view and Fig. 1(b) is a front view of the liquid crystal display projector. Fig. 2 is a diagram for explaining the optical system of the liquid crystal display projector of Fig. 1 when electric power is turned off. Fig. 2(a) is a plan view and Fig. 2(b) is a front view of the liquid crystal display projector. Fig. 3 shows the structure of a projection lens zoomed for wide-angle projection as used in a liquid crystal display projector in an exemplary embodiment of the present invention. Fig. 3(a) is a plan view and Fig. 3(b) is a cross-sectional view of the projection lens. Fig. 4 shows the structure of a projection lens zoomed for close-up projection as used in a liquid crystal display projector in an exemplary embodiment of the present invention. Fig. 4(a) is a plan view and Fig. 4(b) is a cross-sectional view of the projection lens. Fig. 5 shows the structure of a projection lens as used in a liquid crystal display projector in an exemplary embodiment of the present invention when electric power is turned off. Fig. 5(a) is a plan view and Fig. 5(b) is a cross-sectional view of the projection lens. Fig. 6 is a plan view of a prior art liquid crystal display projector for explaining the optical system thereof. Key to Reference Numerals and Symbols 1 Light Source 2 Mirror 3 Liquid Crystal Panel 4 Prism 5 Projection Lens 6 Main Body Cabinet 8 Intermediate Cylinder 8a First Cam Groove 8b Second Cam Groove 8c Gearwork 10 Outer Cylinder 10a First Elongated Hole 11 First Inner Cylinder 11a Second Elongated Cylinder 12 Second Inner Cylinder 13 Group of Lenses 13(L1) First Lens 13(L2) Second Lens 13(L3) Third Lens 13(L4) Fourth Lens 14 First Axis 15 Second Axis DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Next, a few exemplary embodiments of the present invention will be explained with reference to Fig. 1 through Fig. 5. Exemplary Embodiment 1 Fig. 1 shows the main body of a 3-panel type liquid crystal display projector in an exemplary embodiment of the present invention when electric power is turned on and a diagram of the whole optical system used in the projector. Fig. 1(a) is a plan view and Fig. 1(b) is a front view of the liquid crystal display projector. Fig. 2 shows how the projector's main body looks like when electric power is turned off Fig. 2(a) is a plan view and Fig. 2(b) is a front view of the projector. Fig. 3 to Fig. 5 show the structure only of a projection lens as used in the liquid crystal display projector in the present exemplary embodiment. Fig. 3 shows a state wherein the projection lens is zoomed for wide-angle projection, Fig. 4 shows a state wherein the projection lens is zoomed for close-up projection and Fig. 5 shows a state of the projection lens when electric power is turned off. Fig. 3(a) to Fig. 5(a) are plan views of the projection lens in each respective state thereof as mentioned in the above. Fig. 3(b), Fig. 4(b) and Fig. 5(b) are partially sectional views of the projection lens looked in the directions as indicated by arrows S1, S2 and S3, respectively. As illustrated in Fig. 1, the light emitted from a lamp 1 serving as a light source is split into red, green and blue colors by a plurality of mirrors 2. Each respective color light thus produced is incident on a corresponding liquid crystal panel 3 serving as a liquid crystal display device. Then, all the lights of the images displayed in each respective color on the liquid crystal panels 3 are combined to form image lights in natural color by means of a prism 4 and the like. The composite image lights of natural color are projected on a screen to form enlarged images by a projection lens 5. All the components as mentioned above are contained inside of a main body cabinet 6. Each respective liquid crystal panel 3 is capable of forming images of light by means of a plurality of liquid crystal pixels, each of which is acting as a light valve to pass or block light. The projection lens 5 comprises: an intermediate cylinder 8 with a ring-like cross-section; a drive motor 9 serving as a driving means to move the intermediate cylinder 8: an outer cylinder 10 fitted with the outer surface of the intermediate cylinder 8; a first inner cylinder 11 fitted with and yet capable of sliding on the inner surface of the intermediate cylinder 8; a second inner cylinder 12 installed in the back inside of the first cylinder 11 to slide on the inner surface thereof; and a plurality of lenses 13 mounted on the first inner cylinder 11, second inner cylinder 12, intermediate cylinder 8 and outer cylinder 10 at specified positions thereof. The intermediate cylinder 8 has a first cam groove 8a and second cam groove 8b formed on the outer surface thereof and also has gearwork 8c provided on the exterior thereof. The outer cylinder 10 is completely contained in the main body cabinet 6 and the end thereof is not sticking out of the main body cabinet 6. The shape of the first cam groove 8a and second cam groove 8b is curving so that the first inner cylinder 11 and second inner cylinder 12 are allowed to move by sliding, respectively. With the present exemplary embodiment, the first cam groove 8a and second cam groove 8b are curving in a direction slanting from the perimeter of the circular outer surface of the intermediate cylinder 8, respectively. The drive motor 9 is mounted on the outer cylinder 10. The drive motor 9 has a gear which meshes with the gearwork 8c. With the present exemplary embodiment, the plurality of lenses 13 include a first lens 13 (L1) and second lens 13 (L2) installed inside the first inner cylinder 11, a third lens 13 (L3) installed inside the second inner cylinder 12 and a fourth lens 13 (L4) installed inside the outer cylinder 10. According to the foregoing structure, the rotation of the drive motor 9 causes the intermediate cylinder 8 to rotate and the rotation of the intermediate cylinder 8 causes the first inner cylinder 11 to move by sliding out of and sliding into the outer cylinder 10. Next, a more detailed explanation will be made on the present exemplary embodiment. The first inner cylinder 11 is provided with a first axis 14 which is insertable in the first cam groove 8a and the second inner cylinder 12 is provided with a second axis 15 which is insertable in the second cam groove 8b. The outer cylinder 10 is provided with a first elongated hole 10a, the length of which extends in the same direction as the first inner cylinder 11 slides. The first inner cylinder 11 is provided with a second elongated hole 11a at a position opposite to the first elongated hole 10a and the second axis 15 is inserted in the first elongated hole 10a running through the foregoing second elongated hole 11a. When the drive motor 9 runs, the intermediate cylinder 8 is rotated over a specified angle. At this time, the first axis 14 is moved in the direction indicated by an arrow "X" as shown in Fig. 3 (a) along the the first elongated hole 10a according to the rotational positions of the first cam groove 8a. As a result, the first inner cylinder 11 with the first lens 13 (L1) and second lens 13 (L2) installed therein is moved in the direction as indicated by the arrow "X". In the same way as above, the second inner cylinder 12 is also moved a little bit in the direction of the arrow "X" along the first elongated hole 10a of the outer cylinder 10 according to the rotational positions of the second cam groove 8b. An explanation on the fourth lens 13 (L4) installed inside the outer cylinder 10 is omitted since it has nothing to do with the operation of the present invention's projector. Interlocking with the rotation of the intermediate cylinder 8 made over a specified angle when the drive motor runs. the first inner cylinder 11 slides along the curving first cam groove 8a to get to a specified position and the second inner cylinder 12 slides along the curving second cam groove 8b to get to a specified position. At this time, the projection lens 5 is allowed to change positions thereof for zooming from wide-angle projection to close-up projection while the projection lens 5 rotating over an angle corresponding to a travel of the first axis 14 from a position "C" to position "D" along the first cam groove 8a. The first inner cylinder 11 retracts inside the outer cylinder 10 while the projection lens 5 rotating over an angle corresponding to a travel of the first axis 14 from a position "D" to position "E" along the first cam groove 8a. In other words, Fig. 3 shows the state of wide-angle projection, wherein the first inner cylinder 11 is protruding the most from the outer cylinder 10 of the projector's main body cabin 6. Fig. 4 shows the state of close-up projection, wherein the first inner cylinder is protruding a little bit from the outer cylinder 10 of the projector's main body cabin 6. In Fig. 5, the first inner cylinder 11 is retracting inside the outer cylinder 10 of the projector's main body cabin 6 and the second inner cylinder 12 is retracting in the further back inside the outer cylinder 10. The control of stopping angle for the drive motor 9 is made by means of a timing switch, which is not shown in the drawing. According to the structure as described in the above, when electric power is turned off the entire projection lens 5 is housed inside the projector's main body cabin 6 as shown in Fig. 5. When electric power is turned on, the first inner cylinder 11 protrudes from the main body cabin 6. The control of zooming drive for wide-angle projection and close-up projection is conducted by means of a specified mechanism, which is not shown in the drawings. In the present exemplary embodiment, it is particularly preferred to have the outer cylinder 10 fixed to the main body cabin 6. However, the foregoing is not necessarily needed as far as the first inner cylinder 11 is allowed to protrude from the main body cabin 6. In the foregoing, it is also Possible to employ a structure wherein the second inner cylinder 12, second cam groove 8b and second axis 15 are not in place. In this case, the first inner cylinder 11 protrudes from and retracts into the outer cylinder 10 and intermediate cylinder 8 by sliding. In other words, the projection lens 5 Protrudes from and retracts into the main body 6. In the foregoing structure, it is also possible to have the second inner cylinder 12 placed inside of the intermediate cylinder 8 in the far back thereof. In this case, it is not necessary to form the elongated hole 11a on the surface of the first inner cylinder 11 and the second axis 15 is moved while being engaged in the first elongated hole 10a and second cam groove 8b. According the structure disclosed by the present invention, the following effects can be achieved: When electric power is turned off, a projection lens does not protrude from a projector's main body cabin and is housed inside the main body cabin, thereby preventing lenses from becoming damaged when a liquid crystal display projector is carried. Furthermore, dust is prevented from settling on lenses. Since dust is prevented from entering into the area where liquid crystal panels are installed, designing of a dust proof structure can be made simple. In addition, a simple design of a rectangular prism like configuration that appears like a suit case becomes possible. Moreover, it becomes possible to design a liquid crystal display projector with a desired appearance, resulting in enhanced freedom of designing. A simpler structure needed for an operation of protruding and retracting a projection lens contributes to a reduction in production cost.

Claims: A liquid crystal display projector comprising: a main body cabinet (6) including, a light source (1); a group of mirrors (2) for splitting and combining light from said light source (1); liquid crystal devices (3) to control passage of said light; a projection lens (5) with a function of zooming in or out the images of light formed by said liquid crystal devices (3); said projection lens (5) being displaceable between a protruding and retracted position relative to said main body cabinet (6), characterized by said projection lens (5) comprising: a ring-like intermediate cylinder (8); a driving means (9) in rotational driving engagement with said intermediate cylinder (8); an outer cylinder (10) in which said intermediate cylinder (8) is slidably received; a first inner cylinder (11) slidably received in said intermediate cylinder (8); a plurality of lenses (L1,...,L4) installed in at least one of said first inner cylinder (11), intermediate cylinder (8), and outer cylinder (10); said first inner cylinder (11) being coupled (14,8a) with said intermediate cylinder (8) such that a rotation thereof by said driving means (9) is capable of causing a sliding longitudinal movement of said first inner cylinder (11) between said protruding and said retracted position. The liquid crystal display projector according to claim 1, wherein said projection lens (5) further comprising: said outer cylinder (10) having said drive means (9) mounted thereto and receiving said intermediate cylinder (8) for relative rotational movement; said driving means (9) and said intermediate cylinder (8) being in meshing gear engagement; said intermediate cylinder (8) having a first cam groove (8a) receiving a first pin (14) secured to said inner cylinder (11), whereby a rotational movement of said intermediate cylinder (8) causing a displacement of said inner cylinder (11) between said protruding and said retracted position. The liquid cylinder display projector according to claim 1 or 2, wherein said projection lens (5) further comprising: said intermediate cylinder (11) having a second cam groove (8b); a second inner cylinder (12) slidingly received within said first inner cylinder (11) in a rear portion thereof, and having a second pin (15) extending into said second cam groove (8b), and said second inner cylinder (12) being axially displaceable by rotation of said intermediate cylinder (8) comprising said second cam groove (8b). The liquid crystal display projector according to any one of claims 1 to 3, wherein said outer cylinder (10) having a first elongated hole (10a) extending in a lengthwise direction thereof, and receiving said first pin (14) for sliding movement therein; and a rotation of said intermediate cylinder (8) causing said first pin (14) to be moved along said first elongated hole (10a), and thereby causing said first inner cylinder (11) to be displaced within said intermediate cylinder (8). The liquid crystal display projector according to any one of claims 1 to 4, wherein said first inner cylinder (11) comprises a second elongated hole (11a) extending in the axial direction thereof and being formed at a position opposite to said first elongated hole, rotation of said intermediate cylinder (8) causing said first pin (14) to be moved along said first elongated hole (10a) and said second pin (15) to be moved along both of said second elongated holes (11a) and said first elongated hole (10a). The liquid crystal display projector according to any one of claims 2 to 5, wherein said first cam groove has a first position, a second position, and a third position in this order, a movement of said first pin (14) from said first position to said second position of said first cam groove (8a) causing said projection lens (5) to be zoomed while said projection lens (5) being maintained in said protruding state, and a movement of said first pin (14) from said second position to said third position causing said first inner cylinder (11) to slide into the interior of said outer cylinder (10).

Inventors: AONO SHOZO, HASHIMUKAI MASANARI, HOSHINO MAKOTO, OKADA TAKEHIRO, AONO, SHOZO, HASHIMUKAI, MASANARI, HOSHINO, MAKOTO, OKADA, TAKEHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H04N5
IPC codes: G03B21, H04N5, G02F1