Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal eyewear
Patent
1995-11-08
1998-08-11
Sikes, William L.
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal eyewear
G02F 11335
Patent
active
057934495
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a protective device comprising a body and a filtering unit supported by the body and acting as a visor, said filtering unit being electrically shiftable between at least two light transmitting conditions and comprising, for this purpose, one or more liquid crystal cells, in the following called LC cells.
The invention is specifically developed for welding helmets with automatic darkening and will therefore be described below with reference to this application, but it will be appreciated that also other applications are possible within the scope of the invention, such as helmet visors for pilots, motor cyclists etc.
Protective devices of the type mentioned by way of introduction are described in U.S. Pat. No. 3,873,804 (filed in 1973, inventor M. Gordon) which discloses an eye piece of a welding helmet, comprising a liquid-crystal-based electro-optical cell (EO cell) in combination with a light-controlled electric circuit. In response to welding light, the EO cell is caused to change from a light transmitting condition to a light blocking condition. The EO cell is composed of two parallel glass plates, and the space between these plates is filled with a nematic liquid crystal material with a dielectric anisotropism, called TN type liquid crystal. On the interior surfaces of the glass plates are transparent electrodes to be applied to an electric field across the nematic liquid crystal for shifting the degree of light rotation of the liquid crystal. Outside of the glass plates are polarisers which in combination with the light rotation condition of the nematic liquid crystal permits or counteracts light transmission through the eye piece. As illustrated in FIG. 1 of U.S. Pat. No. 3,873,804, the eye piece is arranged as a rectangular window in the front side of the welding helmet in front of the welder's eyes.
A development of the welding helmet in U.S. Pat. No. 3,873,804 is disclosed in U.S. Pat. No. 4,039,254 (filed in 1976, inventor M. Gordon), using two or more EO cells and at least three polarisers arranged in tandem, thereby achieving a higher degree of darkening in the light blocking condition. Also in this patent, use is made of a nematic liquid crystal material between glass plates. The eye piece shape and position on the welding helmet are essentially the same as in U.S. Pat. No. 3,873,804.
A further prior art darkening device for a welding helmet of essentially the same construction as the device of U.S. Pat. No. 4,039,254 is disclosed in SE 425,048 (filed in 1978, inventor A. G. Hornell). This device comprises, in turn, a first polariser, a first EO cell, a second polariser, a second EO cell, and a third polariser. Like in the above-mentioned U.S. patents, each EO cell consists of two flat, parallel glass plates, the space between the plates enclosing a liquid crystal consisting of a nematic material with a dielectric anisotropism. FIG. 4 of SE 425,048 illustrates how the light-controlled eye piece, like in the above-mentioned patents, is arranged as a rectangular window in the front side of the welding helmet.
EP-A1-0,157,744 (filed in 1985, inventor P. Toth) discloses a darkening device for welding helmets, comprising two EO cells of which at least one is of the nematic type with an admixture of dichroic colouring agents with anisotropic light absorption (so-called guest-host design). A filter disc in the ray path eliminates residual light from the "colour cell" in the light blocking condition thereof. Like in the above-mentioned patents, the EO cells of EP-A1-0,157,744 are composed of parallel glass plates and in the space between the glass plates, nematic liquid crystals. Like in the above-mentioned variants, the eye piece is designed as a rectangular window in the front side of the welding helmet, as shown in FIG. 1 of EP-A1-0,157,744.
The above welding helmets with automatic darkening have successively been developed towards improved contrast and improved rapidity. There remains however a serious drawback of these prior art devices, viz. that they afford the
REFERENCES:
patent: 3873804 (1975-03-01), Gordon
patent: 4071912 (1978-02-01), Budmiger
patent: 4155122 (1979-05-01), Budmiger
patent: 4728173 (1988-03-01), Toth
patent: 4904065 (1990-02-01), Yuasa et al.
Patent Abstracts of Japan, Vol. 14, No. 360, P-1088, abstract of JP, A, 2-132417 (Baiotoron K.K.), May 21, 1990.
Dudek James A.
Optrel AG
Sikes William L.
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