Supports – Pipe or cable – Extending through plate
Reissue Patent
1995-10-11
2001-02-20
Lee, Michael H. (Department: 2714)
Supports
Pipe or cable
Extending through plate
C345S101000, C349S116000, C349S181000, C349S005000, C349S072000
Reissue Patent
active
RE037056
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a projection display device comprising at least one liquid crystal display device having a layer of liquid crystalline material between two supporting plates provided with electrodes which define at least one pixel, via which electrodes a voltage can be applied across the pixel.
A device of this type is used, for example, in projection television and for other video applications.
The invention also relates to a liquid crystal display device for use in such a device.
When using liquid crystal display devices for color projection display, a display panel having, for example, red, green and blue pixels on one panel can be used. The optical system for this device is simpler than for devices in which a separate display device is used for each color and in which the resultant pictures are projected one across the other on a screen. In the latter type it is possible to design each panel optimally from an optical point of view by optimizing for each of the three colors the optical path length d.&Dgr;n (d: thickness of liquid crystal layer; &Dgr;n: difference in refractive index between ordinary and extraordinary wave) for the central wavelength associated with this color.
At the central wavelength for red, green and blue &lgr;
R
, &lgr;
G
and &lgr;
B
such thicknesses d
R
, d
G
, d
B
and &Dgr;n values &Dgr;n
R
, &Dgr;n
G
and &Dgr;n
B
are chosen that
d
R
·
Δ
n
R
λ
R
=
d
G
·
Δ
n
G
λ
G
=
d
B
·
Δ
n
B
λ
B
=
0.87
(or the value of another Gooch and Tarry extremum).
This can be effected, for example, by varying the cell thickness for a selected material having a given &Dgr;n or by selecting a different liquid crystal material for each colour for a selected fixed thickness. However, this leads to superfluous storage and production control problems.
EP-A 0,311,116 describes a solution to these problems, with the transmission for each one of the three colours red, green and blue being optimized by adjusting the polarizers for each colour differently with respect to each other, which polarizers are present at both sides of the layer of liquid crystalline material. The values of d and &Dgr;n are then chosen to be such that it holds for green &lgr;
G
at the central wavelength that:
d
·
Δ
n
=
3
·
λ
G
2
.
For parallel polarizers the transmission is zero at zero voltage. For the blue and red light paths the same values of d and &Dgr;n are used, but the mutual position of the polarizers is shifted.
A first drawback is that the highest value of the transmission for blue and red is not optimum because the polarizers are no longer parallel.
Moreover, it appears that a shifting of the polarizer positions is necessary due to the temperature dependence, notably of &Dgr;n, at temperature variations (particularly an increase of temperature which may be caused by the high beam intensity in projection display). This is effected in the relevant device by rotating the polarizers with respect to each other so that also for the green beam they are no longer parallel, which has a detrimental effect on the transmission.
The influence of the temperature on the transmission curves can be very different due to the different rotations of the polarizers so that for the three different colors the maximum transmission at the highest operating temperature may vary considerably as a percentage of the maximum transmission at room temperature.
Moreover, the mechanical adjustment of the polarizers relative to one another is slow and cumbersome.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to provide a device of the type described in the opening paragraph in which the above-mentioned problems occur hardly, if at all. It is a further object of the invention to provide a device in which one type of display device is sufficient in the case where three light paths for red, green and blue are used by providing a device which is substantially insensitive to temperature variations.
For this purpose a device according to the invention is characterized in that in at least one of the extreme transmission states in the product d.&Dgr;n of the thickness d the layer of liquid crystalline material and the difference in refractive index &Dgr;n are chosen to be such that d.&Dgr;n at the maximum temperature of use is 0.45-0.50 &mgr;m, the device being also provided with means for correcting the value of an applied voltage in dependence on the temperature.
The electrodes preferably define a matrix of pixels arranged in rows and columns in which the column electrodes are driven by means of corrected or uncorrected data voltages when a row of pixels is being selectively driven.
According to the invention the d.&Dgr;n values at the maximum operating temperature are chosen to be such that in the temperature range to be used the variation of d.&Dgr;n remains limited to a range in the Gooch and Tarry curve where the transmission for (a) given wavelength(s) changes hardly, if at all, while d&Dgr;n may still change considerably. In fact, the above-mentioned conditions are still satisfied for d.&Dgr;n values at 20° C. between 0.50 and 0.65 &mgr;m. The liquid crystal display device is preferably present between mutually perpendicularly crossed polarizers and the extreme state is light-transmissive.
The correction values of the voltages in a device according to the invention are temperature-dependent, but in the range to be used they are almost independent of the voltage (the transmission/voltage curves run substantially parallel for different temperatures). These correction values can then be determined in a simple manner by means of, for example, temperature measurement. On the other hand the correction values can be determined with reference to the transmitted light intensity, for example, in a test element located outside the actual display section, which element is continuously held in its extreme transmission state. Light intensity changes caused by temperature changes then define the correction values.
Such corrections for temperature changes can be simultaneously superimposed on possible corrections for wavelength-dependent behaviour (in a three-channel system); to have optimum results preferably for the cell passing red light at the maximum operating temperature
d
·
Δ
n
λ
=
0.87
is chosen.
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patent: 4031529 (1977-06-01), Borel et al.
patent: 4045791 (1977-08-01), Fukai et al.
patent: 4328493 (1982-05-01), Shanks et al.
patent: 4639722 (1987-01-01), Urabe et al.
patent: 4885599 (1989-12-01), Harwood et al.
patent: 5012274 (1991-04-01), Dolgoff
patent: 5029982 (1991-07-01), Nash
patent: 5088806 (1992-02-01), McCartney et al.
patent: 5414441 (1995-05-01), Memarzadeh et al.
patent: 311116 (1989-04-01), None
patent: 363767 (1990-04-01), None
patent: 390511 (1990-10-01), None
patent: 8901503 (1991-01-01), None
Heynderickx Ingrin E. J. R.
Wierenga Peter E.
Wortel Franciscus J. M.
Lee Michael H.
Spain Norman N.
U.S. Philips Corporation
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