Liquid crystal cells – elements and systems – Particular structure – Detector of liquid crystal temperature
Reexamination Certificate
1999-07-01
2001-09-04
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Detector of liquid crystal temperature
C349S153000, C345S101000
Reexamination Certificate
active
06285421
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to liquid crystal display (LCD) devices in general and in particular to LCD devices comprising temperature measuring means, and to manufacturing and operating methods for such devices.
RELATED ART
There is a growing market for electronic devices of the type having a LCD display for displaying visual information. In many cases the electronic devices also comprises touch screens covering the LCD, by which the user communicates with the device, or other screens connected to the LCD.
Liquid crystals are characterised by their ability to change their optical properties in response to applied electromagnetic fields. This has made them ideal for displaying altering information, such as in liquid crystal displays (LCD). This ability is affected by the temperature of the liquid crystals, which in its turn is dependent on a number of factors, such as air temperature, radiation from the sun, heat generated by electronic equipment in the vicinity of the display etc. The effects of varying LCD temperature is especially pronounced when the optical state of the liquid crystals is determined by low-voltage multiplexing technique, since this puts high requirements on the flexibility of the crystals.
It is therefore desirable to determine as close as possible the actual temperature of the liquid crystals. To obtain as good an estimation as possible of the temperature of the liquid crystals a temperature sensor should be disposed as near the liquid crystals as possible. Numerous patents are concerned with this task.
For example, the abstract of the Japanese patent JP-A-9-160001 describes a LCD control system wherein the contrast of the LCD is controlled by way of measuring the ambient temperature, and adjusting the contrast after comparing the measured temperature to a stored temperature and a contrast setting associated with the stored temperature. A similar system is also described in the abstract of the Japanese patent JP-A-8-114785. Such a control system has the disadvantage that the contrast adjustment is based on an ambient temperature that may differ considerably from temperature of the liquid crystals. This is the case regardless of whether the temperature is measured outside of the equipment in which the LCD is mounted, or inside the housing of the equipment.
It is also known, for example through JP-A 9-258161, to attach a small thermocouple sensor on a LCD display in order to measure its temperature. However, this has the disadvantage that only a point estimation of the LCD temperature is obtained. Therefore, considerable errors could occur, for example in a case where sunlight falls on only a part of the equipment.
Furthermore, through the Japanese patent publication No. 54-064998 it is known to cover a surface of a LCD display with a tin oxide film, and measuring the resistance of the tin oxide film to determine the temperature of the LCD. The tin oxide film may also act as a heating means, to provide a suitable operation temperature to the liquid crystals. If practised in conjunction with a touch screen, this invention has the disadvantage that even a highly transparent additional temperature sensing layer would undesirably reduce the visual contrast of the LCD. Since the touch screen that covers the LCD causes a certain loss of contrast and brilliance in itself, it is generally not desirable to cover the LCD with yet another transparent sheet.
SUMMARY OF THE INVENTION
Common for most of the temperature measuring and compensating LCD systems according to the state of the art is that they include additional means, thermocouples, tin oxide films, sensors, etc. A disadvantage with such solutions is that the areas in which such additional means are located often are very limited and every additional feature causes problems of short circuits or simple space problems, as well as increased mounting costs.
Another problem with solutions according to the state of the art is that most of the sensors are point sensors, which are not able to sense temperature differences over the LCD area.
It is therefore a general object of the present invention to provide a device for measuring the temperature of a LCD, wherein the measurement is performed very near the liquid crystals without introducing additional means. Another object of the present invention is to provide a device for measuring the temperature of a LCD, which gives an weighted temperature estimation over the LCD area. It is also a general object of the present invention to provide a method of manufacturing and a method of operation of such devices.
This and other objects are achieved by the present invention as defined in the accompanying independent claims.
Thus, in a first aspect of the present invention, there is provided an LCD device with an adhesion material, used for adhering the top and bottom sheet of the LCD, which adhesion material has a temperature dependent electric property. In a second aspect of the present invention, there is provided an LCD device with an adhesion material, used for adhering a covering sheet to one side of the LCD, which adhesion material has a temperature dependent electric property. In a third and fourth aspect of the present invention, there are provided portable electronic devices, comprising LCD devices of the above mentioned type. In a fifth aspect of the present invention, there is provided a manufacturing method comprising the step of adhering the top and bottom sheet of the LCD by an adhesion material which has a temperature dependent electric property. In a sixth aspect of the present invention, there is provided a manufacturing method comprising the step of adhering a covering sheet to one side of the LCD by an adhesion material which has a temperature dependent electric property. In a seventh aspect of the present invention there is provided a temperature measuring method comprising the step of measuring a temperature dependent electrical property of an adhesion material in an LCD device. In an eighth aspect of the present invention there is provided an LCD control method comprising the step of measuring a temperature dependent electrical property of an adhesion material in the LCD device.
In preferred embodiments, the covering sheets are printed circuit boards or touch screens. Furthermore, in preferred embodiments, said electronic property is the electric resistivity, and the temperature dependence is monotonic over a user temperature range. In a most preferred embodiment, the adhesion material encircles an area corresponding the liquid crystal operation area.
By the features of the present invention, a high precision estimation of the liquid crystal temperature is achievable. The temperature measurement is furthermore sensitive to temperature gradients. The present invention also has the potential to be cost efficient, since already present means are used for multiple purposes and few new components are added, and the assembling efforts are small.
REFERENCES:
patent: 5029982 (1991-07-01), Nash
patent: 5406400 (1995-04-01), Matsuda
patent: 0845696 A2 (1998-06-01), None
patent: 59-197020 A (1984-11-01), None
patent: 54-64998 A (1997-05-01), None
patent: 9-258161 A (1997-10-01), None
patent: WO 9811468 A1 (1998-03-01), None
patent: WO 982977A1 (1998-07-01), None
Balzer, W., et al; “Combination of Heating and Temperature Measurement in a Compact Liquid-Crystal Cell,” J. Phys. E. Sci. Instrum. vol. 20, 1987, (UK), pp. 568-571.
Säfsten, K.; International—Type Search Report, May 19, 1999; Search Request No. SE 98/00892; pp. 1-4.
Dudek James A.
Jenkens & Gilchrist P.C.
Schechter Andrew
Telefonaktiebolaget LM Ericsson
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