Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1999-07-06
2001-10-30
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C349S012000, C374S141000
Reexamination Certificate
active
06309100
ABSTRACT:
BACKGROUND
The invention concerns a device for measuring the temperature near the liquid crystals of a liquid crystal display (LCD), and more specifically a device for measuring the temperature near the liquid crystals of a liquid crystal display (LCD) covered with a touch screen.
There is a growing market for electronic devices of the type having a LCD display for displaying visual information and a touch screen covering the LCD by which the user communicates with the device.
Liquid crystals are characterized 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 practiced 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
It is a general object of the invention to provide a device for measuring the temperature of a LCD provided with a touch screen, wherein the measurement is performed within the touch screen very near the liquid crystals and gives an integral temperature estimation substantially over the entire LCD area.
This and other objects are achieved by the invention as defined in the accompanying claims.
Thus, in a first aspect of the present invention there is provided a device for measuring the temperature of a LCD provided with a touch screen.
According to this aspect of the invention, one of the sheets constituting the touch screen, namely the bottom sheet being disposed adjacent to the LCD surface, is provided with a transparent conductive layer having a known relationship between temperature and its electrical resistance. At selected intervals the resistance of the transparent layer is measured and interpreted as the temperature of the touch screen bottom sheet.
As the touch screen bottom sheet is in thermal contact with the LCD surface, and as the LCD glass sheet that parts the liquid crystals from the touch screen bottom sheet has excellent heat conductivity, the temperature of the touch screen bottom represents a good estimation of the temperature of the liquid crystals of the LCD.
Furthermore, as the touch screen bottom sheet covers substantially the entire LCD area the measured electrical resistance of the touch screen bottom sheet represents an overall estimation which, in cases of uneven temperature distribution, is an integral measure of both warmer and cooler areas on the LCD.
In general, the components necessary to carry out the invention are already present in a LCD/touch screen assembly. Any additional components are of low cost and are easy to assemble, thereby providing for cost effective production.
Apart from being cost effective, the invention makes it unnecessary to provide an additional temperature sensing transparent sheet in addition to the touch screen, thereby avoiding an undesired reduction in the visual contrast of the LCD.
Thus, the present invention shows a number of advantages, such as:
high precision estimation of the liquid crystal temperature as the temperature measurement is made very near the liquid crystals,
temperature measurement that is sensitive to temperature gradients across the LCD display, since the measurement is made across the entire LCD surface,
cost efficiency due to few new components, said components being cheap and easy to assemble, and
combination of the temperature sensor with the already present touch screen avoids further contrast losses.
In a second aspect of the present invention is provided a method for manufacturing a device according to the invention there.
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W. Balzer, et al, “Combination of heating and temperature measurement in a compact liquid-crystal cell,” pp. 568-571.
Burns Doane Swecker & Mathis L.L.P.
Gutierrez Diego
Telefonaktiebolaget LM Ericsson (publ)
Verbitsky Gail
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