GB2266159A - Projection apparatus with rear projection screen of variable height - Google Patents

Abstract

Projection apparatus comprises a rear projection screen 9, a video image or computer data projection unit 2 and an optical image projection unit 4. The optical paths from the units result in screen images of substantially the same area. The height of the screen area may be varied from a lower, transport, position to a higher, viewing, position allowing the apparatus to pass through doors. In its transport position the height of the top of the apparatus may be less than two metres and in its viewing position the top of the apparatus may be at least 2.3 metres high. The lower unit is adapted to be easily propelled while the upper, vertically moveable, portion carries the screen 9 and, preferably a main mirror for reflecting the projected images to the screen. One image source has a primary mirror 18 which reflects the image from the source to the main mirror 15 so that both images are simultaneously in focus on the screen. The upper portion is slideably mounted externally of the lower portion for preference and moved vertically form its lower position to its upper position by means of an electrically operated raising mechanism. The main mirror may be hingeably mounted to rear of the upper portion. <IMAGE>

Description

PROJECTION APPARATUS This invention relates to projection apparatus and particularly to mobile apparatus for viewing projected images in confined spaces.

When a number of people need to view an image simultaneously it is customary to provide a large image by front or rear projection on to a screen. The image may be formed by projecting light through a transparency a liquid crystal display (LCD) or from one or more high intensity cathode ray tubes. In order that the screen image is of an appropriate size and is free from distortion it is necessary to use lenses having a compar- atively long focal length and hence a long optical path is required between the projection lens and the screen. The optical path may be direct from the lens to the screen but this is seldom convenient in small rooms so it is customary to fold the optical path using one or more mirrors.

If direct projection on to a screen is used the image is seen by reflection. A reflective screen also reflects ambient illumination so that a screen image with acceptable contrast is only obtained if the illumination in the room is severely reduced. An alternative arrangement involves the use of rear projection screens which can be designed to have a low reflectance but high transmission so that acceptable projected images can be viewed without reduction in the ambient illumination. This enables viewers to write notes while images are being viewed.

Portable projection apparatus is known in which images are directed to a rear projection viewing screen via a folded optical path involving one or more mirrors.

In known projection apparatus of this type the optical path from the image source. an optical projector an LCD projector or a set of high intensity cathode ray tubes. is fixed. The overall dimensions of the apparatus are frequently constrained by the need for portability and in particular for the need to be capable of passage through standard door frames having a width of about 750 mm. A further constraint is the height of a standard door frame which is normally less than 2 metres.

Apparatus which can be carried or wheeled through standard door frames is available however the screen height is necessarily too low for comfortable viewing by an audience set out in rows. Attempts have been made to increase the height of the screen by raising the apparatus on to a platform or stand which is seldom convenient and frequently hazardous.

The present invention provides projection apparatus whose screen height is not constrained by door sizes. The apparatus may be viewed in most ambient light conditions and the viewed images may originate from optical transpar encies or electronic image sources such as video signals or computer images.

According to the present invention there is provided a projection apparatus comprising a rear projection screen. a video image or computer data projection unit and an optical image projection unit. characterised in that the optical paths from the said units result in screen images of substantially the same area and in that the height of the screen area may be varied from a lower. transport. position to a higher. viewing. position. The movement of the screen between the two positions may be adjusted manually or by pneumatically. hydraulically or electrically operated means.

In a preferred form of the invention the apparatus is mounted on wheels enabling it to be propelled easily on flat surfaces. In its transport position the height of the top of the apparatus is less than two metres. On reaching its operating position the screen is elevated to its viewing position so that the top of the apparatus is higher than two metres. preferably at least 2.3 metres high. The upper limit of the apparatus height is constrained by the ceiling height of the viewing room.

In a preferred form of the apparatus a lower unit. adapted to be easily propelled. carries the two projection units while an upper. vertically moveable. portion carries the screen. The rear of the upper. screen. portion preferably carries a mirror for reflecting the projected images from the units to the screen. The upper. screen. portion preferably moved vertically from its lower. transport.

position to its upper. viewing. position by means of an electrically operated raising mechanism. In a most preferred embodiment the upper portion is slideably mounted externally of the lower portion.

The cathode ray tube images may be produced by a projection unit of known type including one or more. preferably three.

cathode ray tubes and associated lens system forming coincident images. To provide a compact apparatus the optical path from the lens system to the screen is reflected by at least one mirror. When a single mirror is used appropriate arrangements must be made to the scanning circuits of the cathode ray tubes to ensure that the screen image is not laterally inverted.

The transparency images may be produced by a slide projector with a magazine or a motion picture projector. In order to conserve space a slide projector with a horizont ally located magazine. such as a 'Carousel' projector is preferred. As with the image projected by the cathode ray tube unit. at least one mirror is used to reflect the projected image from the lens system to the screen. In a preferred embodiment the optical path includes two mirrors; a primary mirror located close to the lens system which reflects the projected image on to a main mirror which is also used to reflect the projected image from the cathode ray tube unit to the screen.In a preferred form of the invention the optical projection unit is mounted on a slideable platform. such as a drawer. so that the slide projector. motion picture projector or other optical projection system may be easily inserted into and removed from the apparatus. When correctly positioned on the slideable platform the lens system of the optical projector will be correctly aligned in the optical path of the apparatus In order that the invention may be clearly understood it will now be described with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of projection apparatus according to the invention Figures 2a and 2b are a cross-sectional view and a front view respectively of the projection apparatus in its lowered position.

Figures 3a and 3b are a cross-sectional view and a front view respectively of the projection apparatus in its raised position.

Figures 4a and 4b are schematic cross-sectional views illustrating the operation of the elevating mechanism. and Figure 5 is a schematic plan view of the elevating mechanism.

A projection apparatus in its operating mode. see Figure 1.

has a base portion 1 containing a cathode ray tube projection unit 2. The base portion 1 is preferably mounted on castors. not shown. to facilitate movement. The base 1 carries slideable support means 3 adapted to carry an optical projector 4. The projection unit 2 has a lens system 5 appropriately positioned to project an image from a cathode ray tube screen 6. The projection unit 2 may comprise a set of cathode ray tubes. e.g.with red. green and blue phosphor screens. to provide colour imayes. The unit 4 has a lens system 7 located to project an image of an illuminated transparency. not shown. within the unit.

A screen portion 8 carries a rear projection screen 9 adapted to be illuminated from its inner surface 11 and having a low reflectance outer surface 12. The portion 8 is arranged for vertical movement with respect to the portion 1. As shown the screen portion 8 is in its upper.

operating. position.

The projection unit 2. by means of the lens system 5 forms an image on the inner surface 11 of the screen 9. The optical path from the lens system 5 to the screen 9. shown by the lines 13 and 14. is reflected by the surface of a main mirror 15. This arrangement reduces the vertical distance from the lens system 5 to the screen 9 and provide es a horizontally facing image from one initially inclined to the vertical.

The optical projector 4. by means of the lens system 7.

forms an image of an illuminated transparency on the inner surface 11 of the screen 9. The optical path from the lens system 7 to the screen 9. shown by the lines 16 and 17. is reflected by the surface of a primary mirror 18 and then by the main mirror 15. This arrangement reduces the horizontal distance from the lens system 7 to the screen 9.

It will be seen that an image may be formed on the inner surface of the screen 11 from a cathode ray tube image and/or an illuminated transparency.

The main mirror 15 is carried by hinges 18 and 19 at its upper and lower edges The upper hinge 18 is attached to the screen portion 3 of the projector. The lower hinge 19 is attached to a folding assembly comprising a back plates 21 and 22 linked by a hinge 23 and a catch 24 to the lower end of the screen portion 3 For purposes of transport the catch 24 may be released and the mirror 15, together with associated hinged back plates 21 and 22. may be folded to form a flat vertical sheet.

When prepared for transport. see Figures 2a and 2b in which like items carry the same reference numerals as shown in respect of Figure 1. the screen portion 8 is in its lower position so that its lower edge almost reaches the base of the portion 1. The side view. see Figure 2a. shows that the mirror 15 is located vertically. together with the back plates 21 and 22. so that the rear surface of the apparatus does not appreciably protrude beyond the rear of the base portion 1. In this form the height of the complete apparatus is low enough to pass below the undersurface of a standard doorway arch and the sideways width permits the apparatus to pass through such doorways.

In operation. see Figures 3a and 3b. the screen portion 8 is elevated so that the screen 12 is in a high position allowing viewing by a large audience set in rows.

The elevating mechanism. see Figure 4a and 4b. consists of a pair of electrically operated jacks 31 and 32 mounted on the platform 33 of the base portion of the apparatus. The moveable upper plates of the jacks 31 and 32 are attached by brackets 34 and 35 the sides 36 and 37 of the screen portion of the apparatus. In operation. see Figure 4b.

the upper plates of the jacks 31 and 32 move vertically at the same rate to elevate the screen portion.

The base 33. see Figure 5. has strengthening spars 38 to maintain rigidity during transport and during operational use.

The apparatus has an appreciable amount of internal space not occupied by the units or forming part of the optical paths from the units to the screen. A number of ancilliary and control systems may be incorporated withinthis space. For instance audio amplification apparatus and loudspeakers may be fitted to enable video signals to be displayed together with accompanying sound recordings of speech or music. A video recorder may be included alongside the optical projector or elsewhere with easy access to allow video recordings on cassettes to be displayed. A microprocessor may be similarly located to provide images showing numerical. alphabetical and/or graphic data to be displayed.

A practical embodiment of the apparatus was constructed in which the overall dimensions when the screen portion was lowered for transport were 720 mm depth. 1340 mm width and 1940 height. This compact apparatus could be wheeled with ease through standard doorways. When located in its operating position and connected to an electrical mains supply the screen portion was elevated. In its operational mode the lower edge of the screen was 1300 mm above the floor surface permitting viewing of the screen by a large audience. The screen size in this embodiment was 1300 mm by 970 mm. an approximately 3 to 4 aspect ratio image. the format used by television and many motion picture and computer display images. The overall height of the apparatus in its operating mode was 2295 mm. too high to pass through most doorways. After elevating the screen portion to its operating position it was also necessary to move the main mirror rearwardly so that the images from the units were correctly reflected to the screen. This movement extended the depth of the apparatus to 1108 mm.

Claims (14)

1. A projection apparatus comprising a rear projection screen, a video image or computer data projection unit and an optical image projection unit, characterised in that the optical paths from the said units result in screen images of substantially the same area and in that the height of the screen area may be varied from a lower, transport, position to a higher, viewing, position.

2. A projection apparatus as claimed in claim 1, characterised in that in its transport position the height of the top of the apparatus is less than two metres and in its viewing position the top of the apparatus is higher than two metres.

3. A projection apparatus as claimed in claim 2, characterised in that in its viewing position the top of the apparatus is at least 2.3 metres hgh.

4. A projection apparatus as claimed in any of the preceding claims, characterised in that the apparatus comprises a lower unit, adapted to be easily propelled, carrying at least one projection unit and an upper, vertically moveable, portion carrying a screen.

5. A projection apparatus as claimed in claim 4, characterised in that the rear of the upper portion carries a main mirror for reflecting the projected images from the unit or units to the screen.

6. A projection apparatus as claimed in claim 5, characterised in that the main mirror at the rear of the upper portion accepts projected images from two different projection units.

7. A projection apparatus as claimed in claim 6, characterised in that at least one image source has a primary mirror which reflects the image from the source to the main mirror at the rear of the upper portion so that both images are simultaneously in focus on the screen.

8. A projection apparatus as claimed in any of the claims 5 to 7, characterised in that the optical image projection unit is a slide projector having a horizontally located rotary slide magazine.

9. A projection apparatus as claimed in any of the preceding claims, characterised in that the optical image projection unit is mounted on a slideable platform.

10. A projection apparatus as claimed in any of the preceding claims, characterised in that the upper portion is slideably mounted externally of the lower portion.

11. A projection apparatus as claimed in claim 10, characterised in that the upper portion is moved vertically from its lower position to its upper position by means of an electrically operated raising mechanism.

12. A projection apparatus as claimed in any of the claims 5 to 11, characterised in that the main mirror is hingeably mounted to rear of the upper portion and may be folded to a vertical position for when the apparatus is in the transport position.

13. Projection apparatus as claimed in claim 1 and as herein described.

14. Projection apparatus as herein described and illustrated with reference to the accompanying drawings.