Convection cooled light projector

A convection cooled liquid crystal display panel projector having a low wattage light source. The projector consist of a housing with a plurality of louvered vents preventing light from escaping from the housing while allowing air to circulate there through. A primary lens configuration having a light source, and a liquid crystal display panel, a Fresnel lens and a projector mirror. An overhead lens configuration by said light source and a Fresnel lens and liquid crystal display panel with a mirror in spaced relation thereto.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to convection-cooled projectors and more particularly to employing a low illuminance lamp as a light source used in conjunction with a screen with a high gain rating.

2. Description of Prior Art

Prior art projectors in general use LCD panel projectors comprises a fan cooled box-like housing which supports an illumination lamp, an LCD panel bearing an image to be projected and various configurations of lenses used to magnify the image on the LCD panel. The exhaust fan is incorporated in the housing or exhausting air inside the housing through the air outlet. An 800 Watt to 1000 Watt projection light source is also provided in the housing for illuminating LCD panel. A projection lens is provided for projecting a magnified image on the LCD panel onto a remote viewing surface such as a screen and includes a focusing lens and may include a reflecting mirror for focusing and directing the image from the LCD panel to the screen. The projector of the above-described type recently employs a high illuminance lamp, for example, a halogen lamp, as the light source so that the visibility of the enlarged image projected on the screen can be improved. In this case, however, LCD panel placed would be subjected to high energy heat rays produced by the high illuminance lamp such that the LCD panel goes above 45 degrees Centigrade at which point it ceases to function properly. The use of a low illuminance lamp in conjunction with a high gain screen eliminates the need for a cooling fan. Means need to be provided enhancing convection cooling to stop heat buildup in the projector housing.

In the conventional projectors of the transmissive LCD panel type, air heated by the heat rays from the light source is exhausted by the exhaust fan of the housing. Furthermore, a cold mirror which reflects light energy but few heat rays is employed as a spherical reflecting mirror mounted in the rear of or below the lamp. Moreover, a heat ray-reflecting filter is interposed between the lamp and the Fresnel lens.

Transmissive LCD panels are used with the above described overhead projectors, however, the LCD panels must not heat up to above 45C or they will cease to function. Some LCD projectors have built in fans to provide additional cooling in addition to the cooling fans built into the conventional projectors utilizing high luminance lamps. These LCD panels functionality is easily degraded by heat. Furthermore, dark colored portions of a projected area of the transmissive LCD panels absorb heat rays. Consequently, the above-described conventional means cannot provide sufficient prevention of temperatures above 45C if a secondary fan is not included in the transmissive LCD panel. Use of the low illuminance lamp allows the removal of the need for the secondary fan in the transmissive LCD panel. See for example U.S. Pat. Nos. 3,711,194, 4,880,303, 4,882,599, and 4,904,079.

U.S. Pat. No. 3,711,194 an overhead projection apparatus is disclosed having a housing with a lamp casing therein for projecting a light beam onto a reflective surface that directs a beam upwardly through a film onto a lens assembly for projection of an image onto a screen.

U.S. Pat. No. 4,880,303 is directed towards an overhead projector having a housing with a Fresnel lens, a lamp is positioned within the housing to provide illumination to a liquid crystal display framed in a hinge mounting on the side of the housing which can be positioned down an operative position overlying a Fresnel lens. A projection lens is positioned in spaced relation to the LCD panel and a reflective mirror surface is provided for the output of the projection lens.

U.S. Pat. No. 4,882,599 an overhead projector is illustrated having a housing configuration with an internal light source and lens plus an internal reflective mirror which reflects an image up through a liquid crystal display and then through a projection lens and an angular image mirror thereabove.

U.S. Pat. No. 4,904,709 a liquid crystal display device for overhead projector is illustrated and described in which a liquid crystal lens display is sandwiched between protective plates which are separated from the cell surface to form an air passage provided with a fan so that an airflow can be directed there through which will come in direct contact with the cell cooling same.

Finally, in U.S. Pat. No. 5,683,160 an overhead projector with light illumines lamp as a light source is disclosed in which a housing is illustrated having a light source and mirror within and a pair of air inlets and outlets formed in the respective sidewalls with an exhaust fan incorporated within the housing to provide a cooling flow of air over the projected lens surface.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a projector wherein quieter operation can be obtained by employment of a low illumines projection lamp and transmissive LCD panel can be prevented from achieving temperatures greater than 45 degrees Celsius with simple quiet convection cooling.

To achieve the object, the present invention provides a projector comprising a housing including a transmissive LCD panel bearing an image to be projected and air vents provided in the sidewalls of the projector housing. A low wattage projection light source is provided in the housing for illuminating the transmissive LCD panel such that convection cooling method of the invention is sufficient to keep the temperature of the LCD panel below 45C. Either of two general types of lens configurations are used.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1of the drawings, a graphic illustration shows the basic elements of a convection-cooling projector10of the invention. The projector10has a main support frame11defining a rectangular enclosure with a base12having a projector light source13thereon. A liquid crystal display (LCD) image panel14is positioned within a support frame15in the main frame11in vertical spaced relation to the base12. A projection lens16(of a Fresnel type) is positioned in spaced vertical alignment within the main frame11so as to receive and project the images produced by the (LCD) panel14as will be well known and understood by those skilled in the art.

Referring now toFIG. 2of the drawings, a detailed sectional illustration of an application of the convection cooling projector10is shown in the cross-sectional illustration wherein a projection enclosure17has a base support18with a projector bulb19and concave reflector20in spaced relation thereto supported thereby. Pairs of oppositely disposed upstanding sidewalls21A and21B extend from the base support18defining a multi-wall projection enclosure22. The oppositely disposed sidewall pairs21A have a plurality of spaced parallel venting slots VS therein in vertical spaced relation to one another. A number of thermal bulkheads23,24and25extend between the respective wall pairs21A and21B. Each of the thermal bulkheads23–25has a central optical transparent insert23A,24A and25A therein. The bulkheads23–25define multiple compartments within the enclosure17with the projector bulb19and reflector20in a first compartment C1beginning at the base18. The remaining compartments C2–C4provide thermal isolation between the projector bulb19and an (LCD) panel26.

Each compartment C1–C5has two pairs of light baffles27,28,29and30respectively in spaced adjacent relation to the respective slotted walls21A. The light baffles27–30extend from opposing bulk heads23–26and base18in parallel spaced overlapping orientation to prevent non-direct light indicated by light arrows L from passing directly out through the corresponding vent slots VS in each of the compartments C1and C5as hereinbefore described.

It will be evident by referring toFIGS. 2 and 4of the drawings that the space inbetween the bulkheads23and26is varied with the (LCD) panel26defining a final bulkhead. A projection lens31extends across the top of the enclosure17defined by the largest of the compartments C5therein.

In operation, the low wattage bulb19of reduced heat output can be used within the assembly and heat generated thereby being dissipated by the convection air currents generated through the hereinbefore disclosed thermal isolation compartments C1–C5and the multiple venting slots VS. It is important to dissipate the heat within the enclosure17given that the (LCD) panel26is heat sensitive and by the use of a lower watt low heat output bulb19the convection cooling imparted by the enclosure17of the invention is sufficient for maintaining the proper operation temperature without the use of a conventional fan (not shown). It will be evident that projection enclosure17can be created in reverse direction and still be functional.

Referring now toFIG. 3of the drawings, an alternate form of the invention can be seen wherein a horizontally oriented enclosure32is illustrated having a top33and support bottom34with support feet34A. Oppositely disposed upstanding sidewall pairs35and36and a projection end wall37define the parameters of the enclosure.

The top wall33and bottom34have a plurality of spaced parallel venting slots VS therein which are in communication with a number of thermal isolation compartments38A–38D. The compartments are defined within the enclosure17by thermal dividing walls39A–39C each of which has optically transparent center inserts therein40A–40C.

A projection light and reflector assembly41is positioned within the first compartment38A as will be well understood by those skilled in the art.

Pairs of oppositely disposed light baffles42,43,44and44A are arranged within the respective compartments38A–38D in spaced parallel overlapping relation to the respective venting slots VS in the top and bottom walls33and34respectively.

An LCD panel45is mounted within the compartment38D with a projection lens46in spaced adjacent relation thereto with the ventilation area there between so as to define in combination an effective end wall of the enclosure32.

In operation for both the primary form10and the alternate form of the invention, an image is electronically reproduced on the respective LCD panels26and45as is well known within the art and light from the projector bulbs19and light assembly41respectively pass there through projecting an image through the respective projection lenses31and36which in this example, as noted, are Fresnel lenses.

It will be evident from the above description that during use a cooling convection air current is established through the enclosures17and33bringing in cool air through the respective side and bottom vents VS and exiting hot air through the opposite side and top vents33vents VS as illustrated by the air arrows AA.

In the primary form of the invention10a convection air current is set up and will allow air to be drawn in through the respective vents VS and the sidewalls21A providing cross circulation to the respective thermal compartments as previously described.

Referring now toFIG. 5of the drawings, a second alternate form of the invention46can be seen having a secondary lens47and hinged mirror assembly48positioned in spaced aligned position with a projector P. An enclosure49has the same multiple thermal cooling chambers as the primary form of the invention with oppositely disposed slotted sidewalls50for creating a convection cooling current there through. Secondary lens51will allow a projected image I to be modified and reflected at angular inclination to the projector outlet surface at52.

Referring now toFIGS. 6 and 7of the drawings, a third alternate form of the invention can be seen wherein a hanging projector54can be seen having a light source and platform55supported by a plurality of support linkages56with an LCD panel57held in spaced relation thereto. The support linkage56is comprised of a plurality of cordage or other linkage construction such as metal chains which are secured to a plurality of opposing spaced parallel eyelets59extending from respective corners of the light source platform56and an LCD platform frame61in which the LCD panel57is positioned. An imaging and directional transfer assembly62is held in spaced vertical relation to the LCD frame61by the linkages56the imaging and directional transfer assembly62has a pair of square interengaged pivotal frames62A and62B with an optical quality mirror64secured within the frame62B as best seen inFIG. 6of the drawings. The projection principle is the same as that of the hereinbefore described primary and secondary forms of the invention in which the light source and platform56have a projector bulb65connected to a source of power with the image inducing LCD panel57within the LCD frame61to create an image which is then projected down to the angularly positioned optical quality mirror64and correspondingly projected onto a screen surface for viewing (not shown).

Referring toFIGS. 8,9and10of the drawings, a fourth alternate form of the invention can be seen in which a suspended projector70is illustrated having a pair of conical pleated fabric baffles71and72extending from a central LCD supporting platform frame73. The baffle71has a light source and support frame platform74within at its free end. The baffle72has a pivoted mirror75and a support frame at its free end that will transfer the light image from the LCD panel57as hereinbefore described to a viewing surface (not shown). The respective baffles71and72may have a plurality of elongated slots and flap assemblies76within in both vertical and horizontally spaced relation to one another for cooling of a projection light source77and the LCD panel57as best seen inFIGS. 8 and 10of the drawings. The slot and flap assemblies76have internal slots S each with a light baffle flap F formed there from so as to eliminate ancillary light impingement beyond the confines of the respective baffle and closure71and72as best seen inFIG. 10of the drawings given the suspended projectors70baffled enclosures the slot and flap assemblies will provide for convection cooling thereof.

It will be apparent to those skilled in the art that such an alternate lens and mirror assemblies can also be used with the primary form of the projector10, also a variety of other mirror and lens elements may be used to further process the projected image once it passes through the primary projector lenses.

It will be evident to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.