Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-01-26
2001-10-23
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000, C349S074000
Reexamination Certificate
active
06307605
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to liquid crystal displays and battery tester circuits, and more particularly to battery tester circuits of the type that may be printed on a battery label.
Battery tester circuits exist that may be printed on a battery label. Such existing battery tester circuits are typically either “thermochromic” testers or “electrochromic” testers. Thermochromic testers include a calibrated resistor that is selectively coupled to the opposite poles of the battery through a switch that may be provided at either or both ends of the calibrated resistor. A thermochromic ink is printed over the resistor that responds to changes in temperature of the calibrated resistor to gradually change between opaque and transparent states and thereby enable indicia printed under the thermochromic layer to be viewed or blocked based upon the temperature of the calibrated resistor. Alternatively, the thermochromic layer may change colors in response to the temperature of the calibrated resistor. The temperature of the calibrated resistor is determined by the power which the battery can deliver, which is a function of both the voltage and internal resistance of the battery. The accuracy of a thermochromic tester is determined by not only the rate of change of the open circuit voltage and internal resistance (rate of change of the battery's ability to produce power), but also the sharpness of the color change in the thermochromic ink (the number of degrees of temperature change required to make the thermochromic ink change color). Thus, the thermochromic ink layer functions both as a display and temperature sensor.
Electrochromic testers differ from thermochromic testers in that the display layer changes color directly in response to the open circuit voltage of the battery. The accuracy of an electrochromic tester is determined by the rate of change of the open circuit voltage of the battery with depth of discharge and the sharpness of the change of intensity of the electrochromic display with voltage. Thus, like the thermochromic tester, the electrochromic tester display functions both as a display and a voltage sensor and the accuracy of the tester may be limited by the voltage response of the display.
Since the accuracy of these thermochromic and electrochromic testers is limited by the response of the display, it has been proposed to improve tester accuracy by including a voltage-responsive electronic component, such as a Zener diode or transistor and to thus limit the function of the display to that of a display. Such an approach is disclosed in U.S. Pat. Nos. 5,610,511, 5,460,902, and 5,389,470. In these patents, a tester circuit is disclosed that utilizes discrete electronic components to discriminate between various discharge levels and to selectively activate different segments of a thermochromic display. Thus, these tester circuits provide discrete displays for the various discharge levels that may be discriminated by the separate sensing circuit thereby limiting the function of the display to that of a display. However, because the testers disclosed in these patents utilize discrete electronic components manufactured using conventional semiconductor technology, the electronic components are not small enough to be included in the label of a battery. Further, because the exterior dimensions of batteries are strictly limited by the ANSI standards, such electronic components cannot be provided on the exterior surface of the battery. If such electronic components were to be provided in the interior of the battery, the space occupied by the electronic components would reduce the space in which the active battery ingredients are provided thereby reducing the service life of the battery. For these reasons, the use of a separate voltage discrimination circuit for an on-label tester has not been commercially implemented.
Another problem associated with thermochromic and electrochromic testers concerns the amount of power consumed by these testers. Because these testers consume relatively significant levels of power, switches are provided to enable selective activation of the testers without requiring a constant drain on the battery. Because of the requirement for such switches, however, the displays do not continuously display the current discharge level of the battery.
Although general purpose electric field-responsive liquid crystal displays are known, they are too expensive to include on a battery label and they require activation voltage levels well in excess of the open circuit voltage of most batteries. Further, these liquid crystal displays tend to irreversibly polarize when driven using a direct current (DC) driving signal. For these reasons, field-responsive liquid crystal displays have been considered to be unsuitable for use in an on-label battery tester.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to solve the above problems and to provide a liquid crystal display that requires significantly lower voltages for driving the display. It is another aspect of the present invention to provide a liquid crystal display that may be incorporated in a battery label at a relatively low cost.
To achieve these and other aspects and advantages, the liquid crystal display of the present invention comprises a first electrode provided on a substrate a first liquid crystal layer provided on and in contact with the first electrode, a second electrode provided on and in contact with the first liquid crystal layer, a second liquid crystal layer provided on and in contact with the second electrode, and a third electrode provided on and in contact with the second liquid crystal layer. The liquid crystal display may further include a third liquid crystal layer provided on and in contact with the third electrode, and a fourth electrode provided on and in contact with the third liquid crystal layer. By providing a plurality of such liquid crystal layers, the voltage required to cause the liquid crystal layers to change visual states is substantially reduced without reducing the overall degree through which the liquid crystal display changes visual states.
Preferably, at least one of the electrodes is made of a transparent processable conductive polymer. Because processable conductive polymers are less expensive than the commonly used tin-doped indium oxide (ITO) materials, the overall cost of the display may be significantly reduced by using processable conductive polymers for the electrodes.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.
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Dudek James A.
Eveready Battery Company Inc.
Toye, Jr. Russell H.
Welsh Robert W.
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