Imagina 90
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The Imagina 90 is the world's first large-format video projector with a liquid crystal screen (LCD) to be mass-produced and which is also suitable for continuous operation.
history
Video projectors (also known colloquially as projectors ) were offered early on by traditional manufacturers of overhead projectors (e.g. Kindermann and Liesegang ) as a support on overhead projectors in pizza box format.
The imagina 90 pursued a different concept from the beginning: A small, handy device in which a small LC display was inserted like a small-image slide and projected in large format. The imagina 90 was able to realize this because it had a unique, special cooling technology that allowed it to guarantee a cool LC display and thus flawless projection despite the high light output of the projection lamp.
The device was developed over a period from 1985 to 1990 by the Bonn-based engineering office for optoelectronics CrystalVision. Today's successor is imago GmbH, Bornheim. The development was financed exclusively with own funds.
In 1987 it was the declared aim of the Federal Ministry of Education and Research to develop a large-screen projector as part of the HDTV program that was able to generate a color HDTV image using opto-electronic means. An estimated 70 million DM were invested in technically interesting projects. z. B. the further development of the Schlieren projector from General Electric, or electrically deformable elastomers in incident light. In the end, the only positive feature that could be recorded was that the state-funded laboratories were well equipped at the beginning of the 1990s, the expected results for a large-screen projector suitable for the market or even a manufacturable flat screen technology did not materialize. Even additional funds from the Eureka pots did nothing to change the fact that the entire production of TV end devices migrated to Asia (Japan, South Korea, Taiwan, China).
The technique of the imagina
It had been known since the early 1970s that LC displays could be projected and could be used as screen projectors . When the Japanese company Oki presented an approximately 8-inch LCD with 640 × 200 pixels at the Hanover Fair in 1987 , it made sense to try to use an overhead projector to project such displays, which were intended for portable computers. The following problem arose: After a short time, the LC display changed color over the heat radiation of the projection lamp and the display ran in blue to yellow colors, or it gave up completely because the clearing point of the liquid crystal layer was exceeded. However, this is a reversible process.
In general, the technicians were of the opinion that neither the polarizers of the LCDs nor the LC liquid itself ( liquid crystals : phenylcyclohexane, azoxybenzenes , 4- ( trans -pentyl-cyclohexyl) -benzonitrile) were stable and, especially under the UV light component, chemically decompose would. This opinion was also confirmed by the fact that Japanese data sheets of LC displays always warned against exposing the display to sunlight or operating outside the specifications of the permissible temperatures.
This effect could be mitigated or delayed by infrared filters and ventilation measures, but continuous operation, especially on a bright daylight projector, was a tricky undertaking. Suggestions to cool the LCD ranged from the installation of very strong and therefore very noisy ventilation in the most varied of designs to slowly flowing transparent cooling liquids that crossed the LC display above or below the display level and were supposed to dissipate the heat. Because of the cooling problem, the idea remained in the drawer or it stayed with prototypes that were shown backstage at trade fairs.
The experiment
The engineers at the Bonn office solved the cooling problem by carefully observing how the various layers of the LCD, namely polarization filter and LC display (with crystalline liquid), individually and proportionally absorbed the heat radiation from the projection lamp.
Here is a schematic drawing of the structure and an explanation:
The polarization filters alone mainly absorbed the radiation from the projection lamp; the liquid crystal cell itself only made up 5% of the absorption. It was just astonishing in the absence of knowledge of the properties of LCDs and was thus not expected. This is because an ideal linear polarizer physically absorbs half of the incident, non-polarized light. In an idealized arrangement of an LCD according to the scheme shown, the polarizer absorbs the first half of the light when light falls and the analyzer after the LC layer absorbs the remaining light when the display is dark.
The logical consequence was that the filters had to be separated from the LC cell in principle. The structure has been optimized by preventing heat transfer between the polarization filter and the liquid crystal cell with continuous ventilation.
Since the polarization filter is no longer applied directly to the display, but mostly on a separate glass carrier, there is also the additional advantage that this optical element can easily be replaced. Since the polarization filter is connected to a necessary glass substrate with a structural adhesive, aging of the adhesive with possible associated clouding of the filter can also be calculated.
This solved a major problem in LCD projection technology in one fell swoop. The remote polarizing filter ( english separated polarizer ) Although no basic invention, but it guarantees such as the radiator in the engine that the device is not destroyed. Only smoothly and reliably running motors and projectors convince investors and buyers. Evidence of unproblematic continuous operation is viewed by all investors as a kind of necessary insurance. In particular, projectors are in close proximity to viewers, sometimes in the immediate vicinity and at head height. For this reason alone, increased security requirements must be demanded and observed here.
Analogous to the polarization filters, it was also recognized that color filters should be separated from the LCD. In addition, since the polarization elements were mounted separately from the LCD, there was now the option of replacing them during the guarantee period if they were damaged by continuous operation of the projector. Since these are inexpensive and the handling was manageable, the large Japanese companies such as Epson, Sharp and Toshiba first got into this technology, whereby the remote polarization filter also provides an ever higher light output on an ever smaller display area (less than 1 inch) due to its effectiveness. allowed. The invention has been registered for a patent worldwide and has also been granted in the most important industrial countries.
As an exemplary embodiment, the so-called lighthouse or light engine of a commercially available LCD projector is shown here, in which three LCDs are grouped as image generators around a so-called prism cube. The three necessary polarizers are located in a shaft approx. 10 mm wide on transparent carrier plates with holding frames, which are air-cooled on both sides as in the drawing above and are thus kept thermally insulated from the LCD. One of the three polarizers has been pulled up out of the shaft with its frame for better visibility and covered with a piece of white paper.
It must also be mentioned in this context that the light yield can be increased by using an upstream prepolarizer or otherwise known as a polarization recycler.
Production and equipment
HD Video & Display GmbH was founded in Cologne together with the Cologne businessman Erik Dynowski to produce and sell the device. Production began on January 1, 1989 in the production facility at Gertrudenstrasse 7. The main purpose of the production was to find out whether the system of the detached polarization filter was also suitable for series production for a small, compact video projector with a small LCD and whether it could prove itself to the user.
The only competing product at the time was a 40 kilogram three-tube projector from a Japanese company. In contrast to today's video projectors (beamer), the Imagina 90 was equipped with a VHF / UHF tuner, which made it possible to project television programs directly without additional devices. In addition, there was the possibility of feeding in video signals via an FBAS input.
The possibility of projecting PC image content using the Imagina 90 was not yet available at the time of market launch, as TFT technology was still in its infancy and error-free, high-resolution TFT displays were not available. There were special solutions for daylight projectors with EGA-VGA supports, which, however, initially used STN displays without active addressing and were therefore too sluggish for moving images. The resolution of 100,000 pixels of the Imagina 90, which is quite coarse by today's standards, was a bit annoying at maximum image size and at a small distance from the projection surface. The low resolution could be obscured by targeted defocusing. In the production version, the projector was connected to an external switched-mode power supply with a 220 V connection for the fan of the projection bulb but with a 36 V connection for the bulb itself. The frequency of the switched-mode power supply was chosen so that there should not be any visual vibrations. The projector itself ran flawlessly, complaints only arose with the Mitronic switch-mode power supply that was supplied. However, the company HD Video & Display could not serve a mass market. In addition, there was a lack of professional production facilities and suitable suppliers.
Construction alternatives
Instead, the company Crystalvision turned back to an old idea at the beginning of the 1990s, which it put on paper in 1988 under patent application DE 3720469 A1. Analogous to the cooling of internal combustion engines, it had to be possible to cool an LC display with water or another suitable liquid, behind a mirrored display. This requires a display that is either made from a monocrystalline chip or a normal active matrix display. With both types, the electrodes of the matrix are mirrored and a beam splitter (PBS) is used for polarization . The advantage is obvious:
The switching transistor, which is now located under the mirrored electrode, is no longer in the light path of the lamp, which increases the light yield. In addition, particularly narrow gaps can be made between the electrodes of the matrix, so that the pixel gaps are hardly visible later in the projection. The greatest advantage is now the possibility of using a liquid " backstage " without disturbing the image reproduction, to cool the actual image chip or the display. Either over the entire area or selectively, there are no limits to creativity as in the design of modern PC processors. The Hughes company constructed something similar with US Pat. No. 4,239,346, but without the reference to cooling by a liquid. In any case, the idea appears much later at JVC and is then referred to and advertised as the Direct-Drive ILA.
Most recently, Crystalvision thought about which wafer material would be best suited for the production of a small high-resolution display for projection. The company Crystalvision originally set out to design a new strip drawing process for the production of so-called SOS (silicon on sapphire) wafers. DE 3813519 A1 suggests using this material for the production of an LC display and names the alternative construction options and their applications.
consequences
The ideas and patents went on to Japan, where the separated polarizer system is an integral part of every LCD projector even after 25 years of invention and guarantees the user that the device runs safely and stably.
With the advent of LED technology as a projection lamp, the design of the projectors has also been simplified. Nevertheless, the desire of consumers to want even smaller and more powerful projectors drives manufacturers to neglect the reserves that good cooling must have to such an extent that the projector shows spots or burn-in spots after some operating time.
As far as is known, only three copies of complete Imagina 90 devices with an external switched-mode power supply are available.
Data
- Material: metal
- Resolution: over 100,000 pixels
- Lamp: 36 volts, 400 watts, xenon
- Display: Panasonic
- Lens: Pentacon 1: 2.8 / 150 mm
- Image size: maximum 3 m diagonal
- Cooling: according to EP 0 268 620 B2
- Dimensions: 46.5 × 16 × 14.5 cm
- Weight: 6.9 kg
- Back then: DM 7,985
swell
- TV cinema for everyone . In: Funk- + Fernsehjournal . No. 7 . Werberuf, 1989, ISSN 0723-7480 , p. 8 .
- Brochure of the Imagina 90 from 1989.
- Deutsches Museum: Information on the exhibit Inv.-No. 2005-481, the imagina 90 is exhibited there
- WDR film archive
Individual evidence
- ↑ Patent US4952925 : Projectable passive liquid-crystal flat screen information centers. Registered January 25, 1988 , published August 28, 1990 , inventor: Bernt Haastert. The rights to this patent in 1998 on Seiko Epson Corp., JAPAN transferred.
- ↑ Patent US5566367 : Plate-like polarizing element, a polarizing conversion unit provided with the element, and a projector provided with the unit. Filed December 8, 1993 , published October 15, 1996 , Applicants: Canon KK, Inventors: Hideaki Mitsutake, Noritaka Mochizuki, Shigeru Kawasaki, Kazumi Kimura, Junko Shingaki.
- ↑ Patent DE3720469 : Liquid crystal light valve. Registered on June 20, 1987 , published December 29, 1988 , inventor: Bernd Haastert.
- ↑ Patent DE3813519 : Liquid crystal light valve. Registered on May 22, 1988 , published November 2, 1989 , inventor: Bernd Haastert.