Browse Prior Art Database

Overhead Projection Display

IP.com Disclosure Number: IPCOM000051679D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Kirkman, DH: AUTHOR [+2]

Abstract

An overhead projection display unit, shown schematically in plan (Fig. 1) and side elevation (Fig. 2), comprises a display light valve 1 which may be of the liquid crystal or electrochromic type. The light valve is located in the head 2 of the unit and is illuminated from a source 3 by means of a long light guide 4 in the neck 5 of the unit. The light guide terminates in a wedge portion 6 which totally internally reflects the light in the guide obliquely onto light valve 1.

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Overhead Projection Display

An overhead projection display unit, shown schematically in plan (Fig. 1) and side elevation (Fig. 2), comprises a display light valve 1 which may be of the liquid crystal or electrochromic type. The light valve is located in the head 2 of the unit and is illuminated from a source 3 by means of a long light guide 4 in the neck 5 of the unit. The light guide terminates in a wedge portion 6 which totally internally reflects the light in the guide obliquely onto light valve 1.

Scattered light from the image formed on light valve 1 is reflected through the outer face of the wedge to projection lens system 7. The projected light beam from lens system 7 then passes through a fixed beam-splitting mirror 8 to a totally reflecting mirror 9 in a swivel head 10. The mirror 9 reflects the projected image upon a wall or screen. By rotating the head 10 through 180 degrees, the image can be thrown to either side of the unit.

Beam splitting mirror 8 diverts a small amount, e.g., 2%, of the light from lens system 7 downwardly through a diverging lens 11 onto a small screen 12 supported by a tablet portion 13 of the unit.

The image on this screen 12 may be viewed conveniently by an operator without causing shadowing of the main image.

In order for the screen images to be correctly oriented, the light valve 1 must be written with an inverted image.

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