Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-01-30
2001-07-03
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000
Reexamination Certificate
active
06256006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) used in a surveying instrument or the like. In particular, the present invention relates to an LCD in which information can be displayed while maintaining the contrast of an LCD plate regardless of the ambient temperature of the LCD plate, and also relates to an LCD in which information can be certainly indicated regardless of the ambient temperature of the LCD plate.
2. Description of the Related Art
Since LCD's can be made light and thin and have low power consumption, they have been used in various information indicating apparatuses. For instance, in surveying instruments, such as a light wave distance-measuring meter or an electronic theodolite, an LCD is used to indicate operation instructions or measurements to an operator.
A plate of the LCD is composed of a glass substrate which includes a liquid crystal enclosed therein. When the polarization state of light passing through the liquid crystal changes, the LCD plate selectively permits light to pass therethrough or interrupts light to indicate information as the contrast of the light which is represented by darkness or brightness of the segments.
Surveying instruments are generally used outdoors where the possibility of a large change in temperature exists thus resulting in the possibility that the characters on the LCD become difficult to read.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display (LCD) in which the contrast of the indication of information can be kept constant regardless of the ambient temperature. Another object of the present invention is to provide a liquid crystal display in which information can be certainly indicated based on indication data, regardless of the ambient temperature of the LCD.
To achieve the objects mentioned above, according to an aspect of the present invention, there is provided a liquid crystal display having a liquid crystal display panel which indicates information represented by a contrast of light when a drive voltage is applied thereto. A temperature measuring device measures the temperature of the LCD panel or the ambient temperature. A drive voltage setting device sets the drive voltage to be applied to the LCD panel so as to keep the contrast constant, in accordance with the temperature value measured by the temperature measuring device.
Preferably, a drive voltage supply is provided for supplying the drive voltage set by the drive voltage setting device to the LCD panel.
The liquid crystal display plate can be of a TN (twisted nematic) type. The drive system of the LCD plate can be either a static type in which the shape of the electrodes corresponds to the shape of the segments which represent information, or a matrix drive type in which the information is indicated by a plurality of dots (segments) corresponding to the electrodes in a matrix arrangement. In the latter type, a TFT (thin-film transistor) type can be used. Also, the LCD plate can be constructed so that the light passes through only the segments to which the drive voltage is applied or only the segments to which no drive voltage is applied.
The temperature measuring device can be brought into direct contact with the LCD plate or can be slightly spaced from the LCD plate. The temperature measuring device can be of a type in which the ambient temperature of the LCD plate is measured or a type in which the conduction heat from the LCD plate is measured. The temperature measuring device can consist of a thermistor or thermocouple, etc.
The relationship between the ambient temperature and the drive voltage to maintain a constant contrast of the indication can be held as a function in the drive voltage setting means. Alternatively, a table which shows the sampled values of the ambient temperature and corresponding drive voltages can be stored in the drive voltage setting device.
An indication data renewal device can vary the interval of renewal of the indication data linearly or stepwise, with respect to the ambient temperature. In the former case, the indication data renewal device can hold an arithmetic function which represents the relationship between the ambient temperature and the renewal interval or can store a table which shows the relationship between sampled values of the ambient temperature and the renewal interval. Preferably, the renewal interval is set to be slightly longer than the indication response time at the corresponding ambient temperature, so that the renewal speed of the indication can be kept relatively high.
According to another aspect of the present invention a liquid crystal display is provided having a liquid crystal display panel which indicates information when a drive voltage is applied thereto. A temperature measuring device measures a temperature of the liquid crystal display panel or an ambient temperature thereof. A drive voltage setting device sets the drive voltage to be applied to the liquid crystal display panel so as to maintain a contrast of the liquid crystal display panel constant, in accordance with a value of the temperature measured by the temperature measuring device.
According to yet another aspect of the present invention, a liquid crystal display is provided having a liquid crystal display panel. An indication control device controls an indication of information on the liquid crystal display panel based on indication data. A temperature measuring device measures a temperature of the liquid crystal display panel or an ambient temperature of the liquid crystal display panel. An indication data renewal device renews the indication data at a time interval corresponding to the ambient temperature measured by the temperature measuring device.
The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 08-16636 (filed on Feb. 1, 1996) and 08-21466 (filed on Feb. 7, 1996) and which are expressly incorporated herein by reference in their entireties.
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Kamasako Shoji
Yamamoto Kiyoshi
Asahi Kogaku Kogyo Kabushiki Kaisha
Bell Paul A.
Greenblum & Bernstein P.L.C.
Saras Steven
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