Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-05-21
2001-11-13
Zimmerman, Mark (Department: 2671)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S038000, C345S002100, C345S002200, C345S005000, C345S101000
Reexamination Certificate
active
06317110
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a method for representing variable information on a display device, in particular in a motor vehicle, having a first, dot matrix display having a liquid crystal cell, and having a second display having a liquid crystal cell, said second display being arranged optically in series with the first display, and the liquid crystal cell of the first display being driven using a multiplex method.
Methods of this type which serve to represent information on liquid crystal displays are known. In this case, two identical liquid crystal displays arranged optically in series are used in order to obtain a high image resolution and a high information density of the display by virtue of the superposition of representations of the two displays.
With the multiplex rate which is necessary for the driving in a multiplex method and rises with the number of image rows and columns present, not only does the necessary drive voltage change but also the switching time of the respective display, said switching time resulting from the sum of switch-on time and switch-off time. In this case, the switch-on time encompasses the period of time which elapses from the first drive pulse of a driven display segment until maximum contrast is reached between the driven character and its surroundings; the switch-off time, on the other hand, encompasses the period of time which passes from the cessation of the drive pulse until minimum contrast is reached between the character and its surroundings. The switching time of the display may be dependent on the liquid crystal substance used, the drive voltage and the driving method. Furthermore, there is a great dependence on the ambient temperature such that with falling ambient temperatures, the switching time of the display becomes very long. Therefore, it is not possible to reliably represent information on a display having a large number of dots at low ambient temperatures. This proves to be unacceptable particularly when safety-relevant information is represented by the display.
In order to remedy this deficient state of affairs, it is known, therefore, to provide a light box, serving to illuminate a liquid crystal cell in a liquid crystal display, with a heating wire. By means of the heating wire, the liquid crystal cell is heated and kept at a temperature level which enables the liquid crystal display to be operated with the requisite short switching times even at low ambient temperatures. On account of the relatively large distance between the heating wire and the liquid crystal cell, a high power supply and great heating of the heating wire are necessary in order to be able to generate the necessary heating of the liquid crystal cell. Furthermore, the heating wire heats the entire display unit, in an undesirable manner, on account of its arrangement in the light box and its required high radiation of heat.
SUMMARY OF THE INVENTION
The invention is based on the object of proposing a method for representing variable information of the type mentioned in the introduction by means of which a liquid crystal display device can not only represent a large volume of information during normal operation but can also represent a smaller partial volume of the information reliably and in a manner that still allows good reading in the event of operation at low ambient. temperatures. At the same time, the intention is to avoid undesirable heating of the display device.
This object is first achieved according to the invention by virtue of the fact that a partial volume of the information is represented on the first display. with the liquid crystal cell driven using the multiplex method at an ambient temperature above a limit temperature and is represented on the second display arranged optically in series with the first display below the limit temperature, and that the switching time, formed by the sum of switch-on time and switch-off time, of the liquid crystal cell of the second display is shorter than the switching time of the liquid crystal cell of the first display.
The abovementioned object is also achieved according to the invention by virtue of the fact that a partial volume of the information is represented on the first display with the liquid crystal cell driven using the multiplex method and simultaneously on the second display arranged optically in series with the first display at an ambient temperature above a limit temperature, that the partial volume of the information is represented exclusively on the second. display at an ambient temperature below the limit temperature, and that the switching time, formed by the sum of switch-on time and switch-off time, of the liquid crystal cell of the second display is shorter than the switching time of the liquid crystal cell of the first display.
With the aid of these two methods, it is not necessary to provide separate heating devices in the display device. Consequently, undesirable heating of parts of the display device which are not intended to be heated is precluded and additional provision of electrical power for the heating is not necessary. In addition to the presentation of a partial volume of the information, which is preferably safety-relevant information such as, for example, the display of a traveling speed in a motor vehicle, a large number of further items of information can be displayed at a sufficiently high ambient temperature, that is to say an ambient temperature which is above the limit temperature. This further information may include, in a motor vehicle, for example, service interval displays, function messages of electrical devices and generally informal information. At low temperatures below the limit temperature, the methods according to the invention ensure at least that basic information is represented. In this case, the limit temperature is chosen for instance such that, at temperatures which lie below it, easy and good readability of the first display with the longer switching time would no longer be ensured.
In accordance with the first-mentioned method, the partial volume of the information is in this case represented on the display with a longer switching time, but larger information density, above the limit temperature, whereas the representation is effected on the other display, having a shorter switching time, at a temperature below the limit temperature, it being accepted that in this case the total volume of information that can be represented is smaller.
By contrast, in accordance with the second-mentioned method, the partial volume of the information is represented on both displays at an ambient temperature above the limit temperature, the display with the longer switching times and the greater volume of information that can be represented being switched off when the limit temperature is exceeded in the direction of falling temperatures. A particularly uniform representation of the information on the two displays is achieved in this way.
In accordance with an advantageous development of the invention, the limit temperature comprises a temperature range having a lower limit and having an upper limit, as a result of which, in a manner that increases the readability of the display device, continual switching between the two displays in the case of an ambient temperature which fluctuates around the limit temperature is prevented. When customary liquid crystal substances are used and, in particular, when the display device is used in a motor vehicle, it proves to be favorable here if the lower limit of the temperature range is approximately minus 10° C. and the upper limit of the temperature range is approximately 0° C.
Particularly good readability of the display device can be achieved if at an ambient temperature above the lower limit of the temperature range and below the upper limit of the temperature range, the partial volume of the information is represented simultaneously on the first and on the second display.
The representation on the second display arranged optically in series with the first display can advantageously
Farber Martin A.
Mannesmann VDO AG
Monestime Mackly
Zimmerman Mark
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