Patent US5889614A successfully refreshed from Google Patents.
US5889614A
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US
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Presentation system with overhead projector
Assignee: International Business Machines Corp
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Filing: 1995-12-20
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Granted: 1999-03-30
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Expires: 2015-12-20
Abstract
Abstract A presentation system comprising an image projection screen and an overhead projector is described. The overhead projector comprises an illumination system, a support for supporting an image record carrier and a projection head for projecting the image present in the image record carrier on the image projection screen. The image projection screen is a polarizing screen which transmits radiation having a well-defined direction of transmission polarization, and the overhead projector is adapted to supply light having this direction of polarization. In this way, the quantity of radiation used for forming the image is considerably increased and substantially half the quantity of ambient light incident on the screen is suppressed, so that images having a considerably enhanced contrast and brightness are obtained.
Inventors
- 👤 Louis M. H. Cobben
- 👤 Martinus V. C. Stroomer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 19:05
CPC Classifications
G; G03; G03B; G03B21/00; G03B21/54; G03B21/56; G03B21/60; G03B21/604; G03B21/132
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
125 words
A presentation system comprising an illumination system which provides a polarized projection beam having an intensity and a direction of polarization, said illumination system comprising a cholesteric filter, a light source, and a reflector surrounding said light source at a side away from the cholesteric filter, an image record carrier which modulates the intensity of the polarized projection beam with image information, thereby producing a modulated and polarized beam having said direction of polarization, an optical head for projecting the modulated and polarized beam onto a screen, said illumination system, said image record carrier, and said optical head forming an overhead projector, and a polarizing screen which receives said modulated and polarized beam from said overhead projector and transmits radiation having said direction of polarization.
Claim 2
Dependent Claim
125 words
A presentation system comprising an illumination system which provides a polarized projection beam having an intensity and a direction of polarization, said illumination system comprising a cholesteric filter, a light source, and a reflector surrounding said light source at a side away from the cholesteric filter, an image record carrier which modulates the intensity of the polarized projection beam with image information, thereby producing a modulated and polarized beam having said direction of polarization, an optical head for projecting the modulated and polarized beam onto a screen, said illumination system, said image record carrier, and said optical head forming an overhead projector, and a polarizing screen which receives said modulated and polarized beam from said overhead projector and transmits radiation having said direction of polarization.
Claim 3
Dependent Claim
30 words
A presentation system as in claim 1 wherein said image record carrier is a permanent image record carrier which directly modulates the intensity of the projection beam with image information.
Claim 4
Dependent Claim
30 words
A presentation system as in claim 1 wherein said image record carrier is an electronically controllable image display panel which directly modulates the intensity of the beam with image information.
Claim 5
Dependent Claim
35 words
A presentation system as in claim 3 wherein said electronically controllable image display panel modulates the direction of polarization of the projection beam in order to modulate the intensity of the beam with image information.
Claim 6
Dependent Claim
26 words
A presentation system as in claim 1 further comprising a λ/4 plate arranged at a side of the cholesteric filter facing away from said light source.
Claim 7
Dependent Claim
21 words
A presentation system as in claim 1 where in said cholesteric filter is active throughout essentially the entire visible wavelength range.
Claim 8
Dependent Claim
44 words
A presentation system as in claim 6 wherein said cholesteric filter comprises a plurality of layers of liquid crystal material, each layer having a thickness and being active in respective different wavelength bands, said wavelength bands jointly covering essentially the entire visible wavelength range.
Claim 9
Dependent Claim
57 words
A presentation system as in claim 6 wherein said cholesteric filter consists of a single layer of liquid crystal polymer material having a thickness, said polymer material comprising a molecular helix having a pitch which varies across the thickness between two values which correspond to respective upper and lower limits of essentially the entire visible wavelength range.
Claim 10
Dependent Claim
54 words
A presentation system as in claim 7 wherein said liquid crystal material is a polymer material, said polymer material comprising a molecular helix having a pitch which varies across the thickness of the respective layer between two values which correspond to respective upper and lower limits of the wavelength band of the respective layer.
Claim 11
Dependent Claim
37 words
A presentation system as in claim 1 further comprising a liquid crystal switching cell arranged between the image record carrier and the illumination system, and a pre-analyzer arranged between the switching cell and the image record carrier.
Claim 12
Dependent Claim
23 words
A presentation system as in claim 1 further comprising an adjustable polarization rotator arranged between the overhead projector and the image projection screen.
Claim 13
Dependent Claim
68 words
A presentation system as in claim 11 wherein said adjustable polarization rotator comprises a first λ/4 plate oriented at an angle of 45° to the direction of polarization of the light beam provided by the overhead projector, and a second λ/4 plate which is rotatable to adapt the direction of polarization of the light beam to the direction of polarization of the light transmitted by the projection screen.
References Cited (Backward Citations)
US3126786A
Cited
US4818074A
Cited
EP0295913B1
Cited
US4928123A
Cited
JPH0415634A
Cited
EP0490171A2
Cited
US5631750A
Cited
US5206673A
Cited
US5251065A
Cited
EP0573905A1
Cited
US5333072A
Cited
EP0606940A2
Cited
WO1994022851A1
Cited
US5444570A
Cited
US5486884A
Cited
US5617226A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2002-03-29 | 2002-09-28 | 2003-03-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-03-29 | 2006-09-28 | 2007-03-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-03-29 | 2010-09-28 | 2011-03-30 | $7700.00 | Window Closed / Lapsed |