EP0000594B1 - Electro-optical display device and method for operating same - Google Patents

Electro-optical display device and method for operating same Download PDF

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Publication number
EP0000594B1
EP0000594B1 EP78200048A EP78200048A EP0000594B1 EP 0000594 B1 EP0000594 B1 EP 0000594B1 EP 78200048 A EP78200048 A EP 78200048A EP 78200048 A EP78200048 A EP 78200048A EP 0000594 B1 EP0000594 B1 EP 0000594B1
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EP
European Patent Office
Prior art keywords
electrode
electrodes
signals
display elements
display device
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EP78200048A
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German (de)
French (fr)
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EP0000594A1 (en
Inventor
Allan R. Dr.-Ing. Kmetz
Klaus Dr.-Phys. Müller
Terry J. Dr.-Phys. Scheffer
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BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0102—Constructional details, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G02F1/134327—Segmented, e.g. alpha numeric display

Definitions

  • the present invention relates to an electro-optical display device for displaying symbols consisting of separately controllable display elements according to the preamble of claim 1 and to a method for controlling such a device.
  • a display device of the aforementioned type in which partial electrodes are provided on the front panel, one of which, in the absence of a supply line, cannot be acted upon by electrical signals.
  • the result of this is that no electrical field can form in the electro-optically activatable medium located between this partial electrode and the opposite rear electrodes and can influence the medium.
  • Such display devices are designed for the principle of the twisted nematic liquid crystal and must therefore be provided with polarizers and surface treated.
  • an electro-optically activatable medium which absorbs light when it is in the field-free state and transmits light when signals are present at the front and rear electrodes, the differential voltage of which is greater than a transition voltage at which the medium is light lets through, bright symbols appear on the display surface on a dark background.
  • a display device is known in which each partial electrode surface of the front electrode is congruent with the surface of the display element.
  • the liquid-crystalline medium located between the partial electrodes of the front and back electrodes of a symbol is optically activated by electrical activation of the corresponding electrodes and scatters the incident ambient light, so that a viewer can read the activated symbol.
  • Such display devices are designed to take advantage of the dynamic scattering effect of liquid crystals and have a high energy consumption because they are driven with relatively high voltages.
  • This display device is also not always to be used advantageously for electro-optical media, the activation of which is based on a different physical effect, since these devices also display bright symbols on a dark background, for example when using a cholesterol guest-host substance. This is not always advantageous, since the symbol shown is optimally readable if it is present like the letters of a newspaper as a dark marking against a light background. The invention seeks to remedy this.
  • the invention achieves the object of providing a display device of the aforementioned type in which dark symbols are displayed on a light background by actuation with low voltages and without the use of polarizers, and in which the control is also carried out by a simple, low-energy method.
  • the display device even with illumination with unpolarized light and with control with comparatively low voltages, extremely high-contrast representations of the displayed symbols on a light background can be achieved. It is particularly advantageous here that the device can be controlled using the same integrated circuits that are used in the very common rotary crystal display device.
  • FIG. 1 shows on the left side the top view of the electrode pattern of the front electrode applied on a transparent front plate and on the right side the electrode pattern of the rear electrode applied on a back plate of a possible embodiment of the display device according to the invention.
  • a, b, ..., g, h are the partial electrodes of the front and i, j the partial electrodes of the rear plate.
  • Leads extend from the electrodes to the connection lugs a ", b", ..., i “, j" located on the edge of the front panel.
  • the lines between the electrodes denote recesses A, A ', B, B', through which the partial electrodes covering the front and rear plates almost completely are electrically insulated from one another.
  • the thick black lines A 'and B ' indicate the delimitation of partial electrodes caused by the recesses in the area of a display element belonging to a symbol to be displayed.
  • each of these display elements is completely covered by a corresponding partial electrode of the front panel on the one hand and completely by the area of the counter electrode j of the rear panel on the other.
  • the limitation of each display element is given by the overlap area of the corresponding partial electrode of the front panel and the partial electrode j of the rear panel.
  • the front plate has a further partial electrode h, the surface of which does not coincide with any of the display elements.
  • the connecting lugs i ", j" of the two partial electrodes i, j of the rear plate are attached to the front plate.
  • This front plate can, for example, be plugged into a standardized connection piece, so that each electrode of the display device can be easily controlled.
  • the contact from the leads of the electrodes i and j of the rear plate to the connection lugs i "and j" can be carried out in a simple manner, since the leads of the electrodes i and j are also guided to the edge of the backplate and are directly opposite the associated connection lugs.
  • the electrode h of the front plate completely covers the supply line of the partial electrode j of the rear plate and the electrode i of the rear plate completely covers the supply lines of the partial electrodes a, b, ..., g of the front plate, whereby the part of the partial electrode that is to be understood as the supply line does not coincide with the area of the display elements. This prevents the feed lines from becoming visible when the device is in operation.
  • FIG. 3 A simplified representation of the display device according to FIG. 1, the partial electrodes being connected as a two-part matrix, is shown in FIG. 3.
  • the two partial electrodes i and j of the rear plate are represented by two horizontal lines and the partial electrodes a, b ..., h of the front plate by eight vertical lines. The intersections of these lines correspond to those areas of the display device where the corresponding front and rear electrodes overlap and a local electric field can be applied.
  • the display elements a ', b' and c ' are activated in such a way that they remain dark, ie that the liquid crystal layer in question is field-free, while the remaining liquid crystal layer forming the background is in a sufficiently strong electric field so that a light background is present.
  • the electrode j is operated with a pulsed DC voltage signal Ug of the amplitude 2V and in a 50% cycle, while a continuous DC voltage signal U 9i of the potential V is applied to the second partial electrode i of the backplate.
  • the front plate-side electrodes a, b, c of the display elements a ', b', c ' are operated with the same pulsed DC voltage signal U S1 , which is applied to the rear plate-side electrode j. All other electrodes on the front plate side d, e, f, g and h are operated with a pulsed direct current signal Us which is 180 ° out of phase with the signal at the electrodes a, b, c and j and has the same amplitude as this.
  • the voltage level V is selected so that it lies above a critical voltage U e at which the cholesteric phase of the liquid crystal completely changes into the nematic phase. This voltage is hereinafter referred to as the “transition voltage”. No further reorientation of the liquid crystal can take place above the transition voltage and the feature characterizing the electro-optical property reaches a saturation value.
  • the method for driving the display device described above has the advantage that the same integrated circuits that are usually used when driving nematic rotary cells can be used.
  • the only additional elements are a simple logic inverter and a voltage divider.
  • FIG. 6 shows the means for driving a known nematic rotary crystal display.
  • a DC voltage U is applied to an integrated circuit IC, from which 50% pulsed signals U a , ..., Ug reach the front electrodes a, ..., g and a signal U B p to the rear electrode BP of a liquid crystal cell D.
  • FIG. 7 shows the means for controlling the display device according to the invention according to FIG. 1. These means include the same integrated circuit IC, but this time the DC voltage 2U is present. However, part of the signal U SP is now phase-shifted to the front electrode h and another part in an inverter I (for example one of the type RGA CD 4041 A) by 180 ° and then applied to the back electrode j.
  • an inverter I for example one of the type RGA CD 4041 A
  • the other back electrode i is supplied with a continuous DC voltage V, which can be generated, for example, in a simple voltage divider R ', R " .
  • a further method for controlling the display device according to the invention is specified below.
  • a simplified addressing scheme of this method is shown in FIG All signals are unipolar pulse trains with a 50% pulse-pause ratio and an amplitude U.
  • the display signals a ', b' and c ' have the same signals on both the front and rear electrodes, so that
  • the display elements d ', e', f 'and g' are given phase-shifted pulses on the front and on the back electrode, so that the potential difference is a bipolar square wave voltage of the amplitude U and is without a DC component.
  • U is greater than the transition voltage U c , these indicators are present elements in the nematic state, absorbing little light.
  • the partial electrode i of the rear plate which covers the leads of the front electrodes, is operated at a higher frequency, preferably a harmonic to the frequency of the signals applied to the electrodes of the front plate.
  • the potential difference between the overlapping areas of the front electrodes and the rear electrode i then has the shape shown in FIG. 8.
  • U the pulse-pause ratio
  • U the pulse height
  • the front electrode h is operated like the partial electrodes a to g. Therefore, the liquid crystal layer of the entire background is in the nematic state, while only the display elements a ' , b', c 'are in the light-absorbing cholesterol state.
  • this method Since the higher-frequency signal is tapped, for example, in clocks from the frequency chain of the means used to control conventional rotary crystal displays, a particular advantage of this method is that no two voltage sources, the levels of which have to be carefully coordinated with one another to avoid harmful DC components, are now necessary. In addition, this method can also be used for liquid crystals with transition voltages greater than 7.5 V in commercially available integrated circuits operated at 15 V voltage.
  • FIG. 10 shows the minimum voltage difference U necessary for setting and maintaining the nematic phase of a cholesteric liquid crystal in a display device (controlled as described above) as a function of the frequency f of the higher-frequency signal applied to the partial electrode i.
  • a liquid crystal with a transition voltage of 7.5 [V] is provided. Below 20 [Hz] the flickering of the display cannot be eliminated even when the voltage is raised.
  • the energy consumed is greatest at the locations of the display where the high-frequency voltages are present, because of the capacitive losses, it is advisable to reduce the areas of these locations. This can be done, for example, by changing the electrodes according to FIG. 9.
  • the leads of the electrodes a, ..., g of the front panel and corresponding to the electrode i of the rear panel are kept as small as possible. It is also possible to lead the leads of the electrodes a, ..., g to opposite edges of the front panel.
  • the display device according to the invention is not only limited to cells with liquid-crystalline guest-host substances, it can also be used, for example, for the use of electro-phoretic suspensions as an electro-optically activatable medium, and above all because such substances cover the entire display area an electrical potential must be present in order to maintain or set a fully defined optical state. It is particularly advantageous here that, for example, the 7-segment display of a number can be switched without the feed lines to these segments becoming visible.

Description

Die vorliegende Erfindung bezieht sich auf eine elektro-optische Anzeigevorrichtung zur Darstellung von aus getrennt ansteuerbaren Anzeigeelementen bestehenden Symbolen gemäss dem Oberbegriff des Patentanspruchs 1 und auf ein Verfahren zum Ansteuern einer solchen Vorrichtung.The present invention relates to an electro-optical display device for displaying symbols consisting of separately controllable display elements according to the preamble of claim 1 and to a method for controlling such a device.

Aus der DE-A 2459058 ist eine Anzeigevorrichtung der vorgenannten Art bekannt, bei der auf der Frontplatte Teilelektroden vorgesehen sind, von denen eine in Ermangelung einer Zuleitung nicht mit elektrischen Signalen beaufschlagbar ist. Dies hat zur Folge, dass sich in dem zwischen dieser Teilelektrode und den gegenüberliegenden Rückelektroden befindlichen elektro-optisch aktivierbaren Medium kein elektrisches Feld ausbilden und das Medium beeinflussen kann. Derartige Anzeigevorrichtungen sind für das Prinzip des verdrillten nematischen Flüssigkristalls konzipiert und müssen demnach mit Polarisatoren versehen und oberflächenbehandelt werden. Wird in einer derartigen Anzeigevorrichtung ein elektro-optisch aktivierbares Medium verwendet, welches Licht absorbiert, wenn es sich im feldfreien Zustand befindet, und Licht durchlässt, wenn an Front- und Rückelektroden Signale anliegen, deren Differenzspannung grösser als eine Übergangsspannung, bei der das Medium Licht durchlässt, ist, so erscheinen auf der Anzeigefläche helle Symbole auf dunklem Untergrund. Aus der DE-OS 2450698 ist eine Anzeigevorrichtung bekannt, bei der jede Teilelektrodenfläche der Frontelektrode deckungsgleich mit der Fläche des Anzeigeelements ist. Das zwischen den Teilelektroden der Front- und Rückelektrode eines Symbols befindliche flüssigkristalline Medium wird durch elektrisches Ansteuern der entsprechenden Elektroden optisch aktiviert und streut das einfallende Umgebungslicht, so dass ein Betrachter das angesteuerte Symbol ablesen kann. Solche Anzeigevorrichtungen sind zur Ausnutzung des dynamischen Streueffekts von Flüssigkristallen konzipiert und weisen einen hohen Energieverbrauch auf, da sie mit relativ hohen Spannungen angesteuert werden. Auch diese Anzeigevorrichtung ist für elektro-optische Medien, deren Aktivierung auf einem anderen physikalischen Effekt beruht nicht immer mit Vorteil einzusetzen, da diese Vorrichtungen etwa bei Verwendung einer cholesterinischen Gast-Wirt-Substanz ebenfalls helle Symbole auf dunklem Untergrund darstellen. Dies ist nicht immer vorteilhaft, da die optimale Ablesbarkeit eines dargestellten Symbols dann gegeben ist, wenn es wie die Lettern einer Zeitung als dunkle Markierung gegen einen hellen Untergrund vorliegt. Hier will die Erfindung Abhilfe schaffen. Die Erfindung, wie sie in den Ansprüchen gekennzeichnet ist, löst die Aufgabe, eine Anzeigevorrichtung der vorgenannten Art zu schaffen, bei der eine Darstellung von dunklen Symbolen auf hellem Untergrund durch Ansteuerung mit geringen Spannungen und ohne die Verwendung von Polarisatoren erzielt wird, und bei der die Ansteuerung zudem durch ein einfaches, einen geringen Energieverbrauch aufweisendes Verfahren erfolgt.From DE-A 2459058 a display device of the aforementioned type is known, in which partial electrodes are provided on the front panel, one of which, in the absence of a supply line, cannot be acted upon by electrical signals. The result of this is that no electrical field can form in the electro-optically activatable medium located between this partial electrode and the opposite rear electrodes and can influence the medium. Such display devices are designed for the principle of the twisted nematic liquid crystal and must therefore be provided with polarizers and surface treated. In such a display device, an electro-optically activatable medium is used, which absorbs light when it is in the field-free state and transmits light when signals are present at the front and rear electrodes, the differential voltage of which is greater than a transition voltage at which the medium is light lets through, bright symbols appear on the display surface on a dark background. From DE-OS 2450698 a display device is known in which each partial electrode surface of the front electrode is congruent with the surface of the display element. The liquid-crystalline medium located between the partial electrodes of the front and back electrodes of a symbol is optically activated by electrical activation of the corresponding electrodes and scatters the incident ambient light, so that a viewer can read the activated symbol. Such display devices are designed to take advantage of the dynamic scattering effect of liquid crystals and have a high energy consumption because they are driven with relatively high voltages. This display device is also not always to be used advantageously for electro-optical media, the activation of which is based on a different physical effect, since these devices also display bright symbols on a dark background, for example when using a cholesterol guest-host substance. This is not always advantageous, since the symbol shown is optimally readable if it is present like the letters of a newspaper as a dark marking against a light background. The invention seeks to remedy this. The invention, as characterized in the claims, achieves the object of providing a display device of the aforementioned type in which dark symbols are displayed on a light background by actuation with low voltages and without the use of polarizers, and in which the control is also carried out by a simple, low-energy method.

Mit der erfindungsgemässen Anzeigevorrichtung lassen sich selbst bei Beleuchtung mit unpolarisiertem Licht und bei Ansteuerung mit vergleichsweise niedrigen Spannungen noch äusserst kontraststarke Darstellungen der angezeigten Symbole auf hellem Untergrund erzielen. Hierbei ist es besonders vorteilhaft, dass die Ansteuerung der Vorrichtung mit denselben integrierten Schaltkreisen, die bei der sehr gebräuchlichen Drehkristall-Anzeigevorrichtung eingesetzt sind, erfolgen kann.With the display device according to the invention, even with illumination with unpolarized light and with control with comparatively low voltages, extremely high-contrast representations of the displayed symbols on a light background can be achieved. It is particularly advantageous here that the device can be controlled using the same integrated circuits that are used in the very common rotary crystal display device.

In der Zeichnung sind nachfolgend Ausführungsbeispiele des Erfindungsgegenstandes vereinfacht wiedergegeben.In the drawing, exemplary embodiments of the subject matter of the invention are shown in simplified form below.

Es zeigt:

  • Fig. 1 eine Aufsicht auf die Elektrodenmuster der Front- und der Rückelektrode einer Anzeigevorrichtung nach der Erfindung,
  • Fig.2 eine Aufsicht auf die Anzeigeelemente der Anzeigevorrichtung nach Fig. 1,
  • Fig.3 eine schematische Darstellung der Anzeigevorrichtung nach Fig. 1, wobei die Teilelektroden als zweizeilige Matrix geschaltet und drei Anzeigeelemente optisch angesteuert sind,
  • Fig.4 eine schematische Darstellung der an die Elektroden der Anzeigevorrichtung nach Fig. 3 angelegten Ansteuersignale,
  • Fig. 5 die funktionale Abhängigkeit der Helligkeit des Untergrundes der Anzeigevorrichtung nach Fig. 1 von der an die Elektroden angelegten wirksamen Spannungsdifferenz U [Volt],
  • Fig. eine schematische Darstellung der Mittel zum Ansteuern einer bekannten Drehkristall-Anzeigevorrichtung,
  • Fig. 7 eine schematische Darstellung der Mittel zum Ansteuern der Anzeigevorrichtung nach Fig.1,
  • Fig. 8 ein Adressierschema zum Ansteuern der Anzeigevorrichtung nach Fig. 1,
  • Fig. eine Aufsicht auf die Elektrodenmuster der Front- und Rückelektrode einer weiteren Anzeigevorrichtung nach der Erfindung, und
  • Fig. 10 die zur Einstellung und Aufrechterhaltung der nematischen Phase eines cholesterinischen Flüssigkristalls in einer gemäs Fig. 8 angesteuerten Anzeigevorrichtung notwendige minimale Spannungsdifferenz in Abhängigkeit von der Frequenz des an die Teilelektrode i gelegten höherfrequenten Signals.
It shows:
  • 1 is a plan view of the electrode patterns of the front and rear electrodes of a display device according to the invention,
  • 2 shows a plan view of the display elements of the display device according to FIG. 1,
  • 3 shows a schematic illustration of the display device according to FIG. 1, the partial electrodes being switched as a two-line matrix and three display elements being optically controlled,
  • 4 shows a schematic illustration of the control signals applied to the electrodes of the display device according to FIG. 3,
  • 5 shows the functional dependence of the brightness of the background of the display device according to FIG. 1 on the effective voltage difference U [volt] applied to the electrodes,
  • 1 shows a schematic representation of the means for driving a known rotary crystal display device,
  • 7 shows a schematic representation of the means for controlling the display device according to FIG. 1,
  • 8 is an addressing scheme for driving the display device of FIG. 1,
  • Fig. Is a plan view of the electrode patterns of the front and rear electrodes of a further display device according to the invention, and
  • 10 shows the minimum voltage difference necessary for setting and maintaining the nematic phase of a cholesteric liquid crystal in a display device controlled according to FIG. 8 as a function of the frequency of the higher-frequency signal applied to the partial electrode i.

In Fig. 1 ist auf der linken Seite die Aufsicht auf das Elektrodenmuster der auf einer transparenten Frontplatte aufgebrachten Front- und auf der rechten Seite das Elektrodenmuster der auf einer Rückplatte aufgebrachten Rückelektrode einer möglichen Ausführungsform der erfindungsgemässen Anzeigevorrichtung dargestellt. Mit a, b, ..., g, h sind die Teilelektroden der Front- und mit i, j die Teilelektroden der Rückplatte bezeichnet. Von den Elektroden erstrecken sich Zuleitungen zu den am Rand der Frontplatte gelegenen Anschlussfahnen a", b", ..., i", j". Die Linien zwischen den Elektroden bezeichnen Ausnehmungen A, A', B, B', durch welche die die Front- bzw. Rückplatte nahezu vollständig bedeckenden Teilelektroden voneinander elektrisch isoliert sind. Die dick ausgezogenen schwarzen Linien A' bzw. B' kennzeichnen hierbei die durch die Ausnehmungen bewirkte Begrenzung von Teilelektroden im Bereich eines zu einem darzustellenden Symbol gehörenden Anzeigeelementes.1 shows on the left side the top view of the electrode pattern of the front electrode applied on a transparent front plate and on the right side the electrode pattern of the rear electrode applied on a back plate of a possible embodiment of the display device according to the invention. With a, b, ..., g, h are the partial electrodes of the front and i, j the partial electrodes of the rear plate. Leads extend from the electrodes to the connection lugs a ", b", ..., i ", j" located on the edge of the front panel. The lines between the electrodes denote recesses A, A ', B, B', through which the partial electrodes covering the front and rear plates almost completely are electrically insulated from one another. The thick black lines A 'and B ' indicate the delimitation of partial electrodes caused by the recesses in the area of a display element belonging to a symbol to be displayed.

In Fig. 2 sind die durch Ansteuerung sichtbar werdenden Anzeigeelemente a', b',.... g' dieser Anzeigevorrichtung dargestellt. Die Fläche jedes dieser Anzeigeelemente wird vollkommen von einer entsprechenden Teilelektrode der Frontplatte einerseits und vollkommen von der Fläche der Gegenelektrode j der Rückplatte andererseits überdeckt. Die Begrenzung jedes Anzeigeelementes ist durch den Überlappungsbereich der entsprechenden Teilelektrode der Frontplatte und der Teilelektrode j der Rückplatte gegeben. Neben den zur Darstellung der Anzeigeelemente a', ..., g' notwendigen Teilelektroden a,2 shows the display elements a ', b', ... g 'of this display device that become visible through activation. The area of each of these display elements is completely covered by a corresponding partial electrode of the front panel on the one hand and completely by the area of the counter electrode j of the rear panel on the other. The limitation of each display element is given by the overlap area of the corresponding partial electrode of the front panel and the partial electrode j of the rear panel. In addition to the sub-electrodes a, ..., g 'required to display the display elements a,

..., g weist die Frontplatte noch eine weitere Teilelektrode h auf, deren Fläche mit keinem der Anzeigeelemente koinzidiert. Auf der Frontplatte sind neben den Anschlussfahnen der auf der Frontplatte befindlichen Teilelektroden auch die Anschlussfahnen i", j" der beiden Teilelektroden i, j der Rückplatte angebracht. Diese Frontplatte kann beispielsweise in ein standardisiertes Verbindungsstück gesteckt werden, so dass jede Elektrode der Anzeigevorrichtung leicht anzusteuern ist. Der Kontakt von den Zuleitungen der Elektroden i und j der Rückplatte zu den Anschlussfahnen i" und j" kann in einfacher Weise durchgeführt werden, da die Zuleitungen der Elektroden i und j ebenfalls an den Rand der Rückplatte geführt werden und den zugehörigen Anschlussfahnen unmittelbar gegenüberliegen. Die Elektrode h der Frontplatte überdeckt vollständig die Zuleitung der Teilelektrode j der Rückplatte und die Elektrode i der Rückplatte überdeckt vollkommen die Zuleitungen der Teilelektroden a, b, ..., g der Frontplatte, wobei unter Zuleitung derjenige Teil der Teilelektrode zu verstehen ist, der nicht mit der Fläche der Anzeigeelemente koinzidiert. Hierdurch wird vermieden, dass bei Betrieb der Vorrichtung die Zuleitungen sichtbar werden...., g, the front plate has a further partial electrode h, the surface of which does not coincide with any of the display elements. In addition to the connecting lugs of the partial electrodes located on the front plate, the connecting lugs i ", j" of the two partial electrodes i, j of the rear plate are attached to the front plate. This front plate can, for example, be plugged into a standardized connection piece, so that each electrode of the display device can be easily controlled. The contact from the leads of the electrodes i and j of the rear plate to the connection lugs i "and j" can be carried out in a simple manner, since the leads of the electrodes i and j are also guided to the edge of the backplate and are directly opposite the associated connection lugs. The electrode h of the front plate completely covers the supply line of the partial electrode j of the rear plate and the electrode i of the rear plate completely covers the supply lines of the partial electrodes a, b, ..., g of the front plate, whereby the part of the partial electrode that is to be understood as the supply line does not coincide with the area of the display elements. This prevents the feed lines from becoming visible when the device is in operation.

Eine vereinfachte Darstellung der Anzeigevorrichtung nach Fig. 1, wobei die Teilelektroden als zweiteilige Matrix geschaltet sind, ist in Fig. 3 wiedergegeben. Die beiden Teilelektroden i und j der Rückplatte sind durch zwei horizontale und die Teilelektroden a, b ..., h der Frontplatte durch acht vertikale Linien dargestellt. Die Schnittpunkte dieser Linien entsprechen denjenigen Bereichen der Anzeigevorrichtung, wo sich die entsprechenden Front- und Rückelektroden überlappen und ein lokales elektrisches Feld angelegt werden kann.A simplified representation of the display device according to FIG. 1, the partial electrodes being connected as a two-part matrix, is shown in FIG. 3. The two partial electrodes i and j of the rear plate are represented by two horizontal lines and the partial electrodes a, b ..., h of the front plate by eight vertical lines. The intersections of these lines correspond to those areas of the display device where the corresponding front and rear electrodes overlap and a local electric field can be applied.

Soll etwa die Ziffer «7» angezeigt werden, so bedeutet dies, dass gemäss den Fig. 1 und 2 die Anzeigeelemente a', b' und c' so angesteuert werden, dass sie dunkel bleiben, d.h., dass die betreffende Flüssigkristallschicht feldfrei ist, während sich die verbleibende, den Untergrund bildende Flüssigkristallschicht in einem ausreichend starken elektrischen Feld befindet, so dass ein heller Untergrund vorliegt.If, for example, the number “7” is to be displayed, this means that, according to FIGS. 1 and 2, the display elements a ', b' and c 'are activated in such a way that they remain dark, ie that the liquid crystal layer in question is field-free, while the remaining liquid crystal layer forming the background is in a sufficiently strong electric field so that a light background is present.

Dies kann z.B. durch Ansteuerung der Teilelektroden a, b, ..., j mit den in Fig. 4 angegebenen Signalen erfolgen.This can e.g. by controlling the partial electrodes a, b, ..., j with the signals indicated in FIG. 4.

Hiernach wird die Elektrode j mit einem gepulsten Gleichspannungssignal Ug der Amplitude 2V und in einem 50%igen Zyklus betrieben, während an der zweiten Teilelektrode i der Rückplatte ein kontinuierliches Gleichspannungssignal U9i des Potentials V anliegt. Die frontplattenseitigen Elektroden a, b, c der Anzeigeelemente a', b', c' werden mit dem gleichen gepulsten Gleichspannungssignal US1 betrieben, welches an der rückplattenseitigen Elektrode j anliegt. Alle anderen frontplattenseitigen Elektroden d, e, f, g und h werden mit einem gepulsten Gleichstromsignal Us betrieben, welches um 180° zu dem an den Elektroden a, b, c und j liegenden Signal phasenverschoben ist und die gleiche Amplitude wie dieses aufweist. An den Anzeigeelementen a', b' und c' liegt daher eine verschwindende Potentialdifferenz, während an den optisch nicht angewählten Elementen d', e', f' und g' und dem Überlappungsbereich zwischen den Elektroden h und j eine Potentialdifferenz von 2V und an allen anderen Bereichen eine Potentialdifferenz von V liegt. Kein Bereich der Anzeigefläche erhält dabei eine konstante Gleichspannung, so dass eine elektrochemische Zersetzung des Flüssigkristalls weitgehend vermieden wird.Thereafter, the electrode j is operated with a pulsed DC voltage signal Ug of the amplitude 2V and in a 50% cycle, while a continuous DC voltage signal U 9i of the potential V is applied to the second partial electrode i of the backplate. The front plate-side electrodes a, b, c of the display elements a ', b', c 'are operated with the same pulsed DC voltage signal U S1 , which is applied to the rear plate-side electrode j. All other electrodes on the front plate side d, e, f, g and h are operated with a pulsed direct current signal Us which is 180 ° out of phase with the signal at the electrodes a, b, c and j and has the same amplitude as this. There is therefore a vanishing potential difference at the display elements a ', b' and c ', while at the optically not selected elements d', e ', f' and g 'and the overlap area between the electrodes h and j there is a potential difference of 2V and in all other areas there is a potential difference of V. No area of the display area receives a constant DC voltage, so that electrochemical decomposition of the liquid crystal is largely avoided.

Der Spannungspegel V wird so gewählt, dass er oberhalb einer kritischen Spannung Ue, bei der die cholesterinische Phase des Flüssigkristalls vollständig in die nematische Phase übergeht, liegt. Diese Spannung wird in der Folge «Übergangsspannung» genannt. Oberhalb der Übergangsspannung kann keine weitere Umorientierung des Flüssigkristalls mehr stattfinden und das die elektro-optische Eigenschaft charakterisierende Merkmal erreicht einen Sättigungswert.The voltage level V is selected so that it lies above a critical voltage U e at which the cholesteric phase of the liquid crystal completely changes into the nematic phase. This voltage is hereinafter referred to as the “transition voltage”. No further reorientation of the liquid crystal can take place above the transition voltage and the feature characterizing the electro-optical property reaches a saturation value.

In Fig. 5 ist bei einer den Gast-Wirt-Effekt zeigenden Substanz der folgenden Zusammensetzung:

Figure imgb0001
+ 94% einer nematischen Flüssigkristallmischung auf Biphenylbasis, welche in einer 8 µ dicken Anzeigezelle untergebracht ist, die Abhängigkeit der Helligkeit H des von der Zellrückwand reflektierten Umgebungslichtes in Abhängigkeit von der an die Zelle gelegten Spannung U [Volt] aufgetragen. Wegen des steilen Anstiegs und des raschen Erreichens eines Sättigungswertes ist bei dieser Substanz das optische Ansprechvermögen einer oberhalb der Übergangsspannung Uc liegenden Spannung V ebenso gross wie das einer Spannung 2V. Daher weisen alle hellen, als Untergrund wirkenden Bereiche der Anzeigevorrichtung, also gemäss Fig. 3 alle Anzeigeelemente, an denen die Differenzspannung V oder 2V anliegt, das gleiche optische Erscheinungsbild auf. Von grosser Bedeutung ist hierbei natürlich der Energieverbrauch, da fast die gesamte Fläche der Anzeigezelle unter Spannung steht. Es ist daher ratsam, die Anzeige mit einer möglichst geringen Frequenz, etwa 2 Hz, zu betreiben, um die kapazitiven Verluste des Zellenstromes zu minimalisieren.5 shows the following composition for a substance showing the guest-host effect:
Figure imgb0001
 + 94% of a nematic liquid crystal mixture based on biphenyl, which is accommodated in an 8 μ thick display cell, shows the dependence of the brightness H of the ambient light reflected from the cell rear wall as a function of the voltage U [volt] applied to the cell. Because of the steep rise and the rapid reaching of a saturation level, is at of this substance, the optical response of a voltage V above the transition voltage U c is as great as that of a voltage 2V. Therefore, all bright areas of the display device acting as a background, that is, according to FIG. 3, all display elements to which the differential voltage V or 2V is present, have the same visual appearance. Of course, the energy consumption is of great importance, since almost the entire area of the display cell is under voltage. It is therefore advisable to operate the display with the lowest possible frequency, around 2 Hz, in order to minimize the capacitive losses of the cell current.

Das vorstehend beschriebene Verfahren zum Ansteuern der Anzeigevorrichtung hat den Vorteil, dass die gleichen integrierten Schaltkreise, die üblicherweise beim Ansteuern nematischer Drehzellen Verwendung finden, eingesetzt werden können. Die einzigen zusätzlichen Elemente sind ein einfacher logischer Inverter und ein Spannungsteiler.The method for driving the display device described above has the advantage that the same integrated circuits that are usually used when driving nematic rotary cells can be used. The only additional elements are a simple logic inverter and a voltage divider.

In Fig. 6 sind die Mittel zum Ansteuern einer bekannten nematischen Drehkristallanzeige dargestellt. Hierbei liegt eine Gleichspannung U an einem integrierten Schaltkreis IC, von dem 50%ig gepulste Signale Ua, ..., Ug an die Frontelektroden a, ..., g sowie ein Signal UBp an die Rückelektrode BP einer Flüssigkristallzelle D gelangen. In Fig. 7 sind die Mittel zum Ansteuern der erfindungsgemässen Anzeigevorrichtung nach Fig. 1 dargestellt. Diese Mittel umfassen denselben integrierten Schaltkreis IC, an dem diesmal jedoch die Gleichspannung 2U liegt. Ein Teil des Signals USP wird nun aber an die Frontelektrode h und ein weiterer Teil in einem Inverter I (etwa einen des Typs RGA CD 4041 A) um 180° phasenverschoben und danach an die Rückelektrode j gelegt. Die andere Rückelektrode i wird mit einer kontinuierlichen Gleichspannung V versorgt, welche beispielsweise in einem einfachen Spannungsteiler R', R" erzeugt werden kann. Nachfolgend wird ein weiteres Verfahren zum Ansteuern der erfindungsgemässen Anzeigevorrichtung angegeben. Ein vereinfachtes Adressierschema dieses Verfahrens ist der Fig. 8 zu entnehmen. Alle Signale sind unipolare Pulszüge mit einem 50%igen Puls-Pause-Verhältnis und einer Amplitude U. Bei den Anzeigeelementen a', b' und c' liegen sowohl an der Front- als auch an der Rückelektrode die gleichen Signale, so dass keine Potentialdifferenz besteht und sie im cholesterinischen lichtabsorbierenden Zustand bleiben. Die Anzeigeelemente d', e', f' und g' erhalten an der Front- und an der Rückelektrode um je 180° phasenverschobene Pulse, so dass die Potentialdifferenz eine bipolare Rechteckspannung der Amplitude U und ohne Gleichstromkomponente ist. Solange U grösser als die Übergangsspannung Uc ist, befinden sich diese Anzeigeelemente im nematischen, nur wenig Licht absorbierenden Zustand.6 shows the means for driving a known nematic rotary crystal display. In this case, a DC voltage U is applied to an integrated circuit IC, from which 50% pulsed signals U a , ..., Ug reach the front electrodes a, ..., g and a signal U B p to the rear electrode BP of a liquid crystal cell D. . FIG. 7 shows the means for controlling the display device according to the invention according to FIG. 1. These means include the same integrated circuit IC, but this time the DC voltage 2U is present. However, part of the signal U SP is now phase-shifted to the front electrode h and another part in an inverter I (for example one of the type RGA CD 4041 A) by 180 ° and then applied to the back electrode j. The other back electrode i is supplied with a continuous DC voltage V, which can be generated, for example, in a simple voltage divider R ', R " . A further method for controlling the display device according to the invention is specified below. A simplified addressing scheme of this method is shown in FIG All signals are unipolar pulse trains with a 50% pulse-pause ratio and an amplitude U. The display signals a ', b' and c 'have the same signals on both the front and rear electrodes, so that The display elements d ', e', f 'and g' are given phase-shifted pulses on the front and on the back electrode, so that the potential difference is a bipolar square wave voltage of the amplitude U and is without a DC component. As long as U is greater than the transition voltage U c , these indicators are present elements in the nematic state, absorbing little light.

Die Teilelektrode i der Rückplatte, welche die Zuleitungen der Frontelektroden überdeckt, wird mit einer höheren Frequenz, vorzugsweise einer harmonischen zur Frequenz der an die Elektroden der Frontplatte gelegten Signale, betrieben. Die Potentialdifferenz zwischen den Überlappungsbereichen der Frontelektroden und der Rückelektrode i weist dann die in Fig. 8 dargestellte Form auf. Bei einem 50%igen Puls-Pause-Verhältnis und einer Impulshöhe U des höherfrequenten Signals, ändert sich die Polarität dieser Spannungsdifferenzen mit der Periode der niederfrequenten Signale. Solange U ausreichend hoch über der Übergangsspannung liegt und die Puls-frequenz ausreichend hoch ist, bleibt die von der Fläche der Rückelektrode i begrenzte Flüssigkristallschicht im nematischen und wenig Licht absorbierenden Flüssigkristallzustand, und zwar unabhängig von den Phasen der an Frontelektroden liegenden Signalen.The partial electrode i of the rear plate, which covers the leads of the front electrodes, is operated at a higher frequency, preferably a harmonic to the frequency of the signals applied to the electrodes of the front plate. The potential difference between the overlapping areas of the front electrodes and the rear electrode i then has the shape shown in FIG. 8. With a 50% pulse-pause ratio and a pulse height U of the higher-frequency signal, the polarity of these voltage differences changes with the period of the low-frequency signals. As long as U is sufficiently high above the transition voltage and the pulse frequency is sufficiently high, the liquid crystal layer delimited by the area of the back electrode i remains in the nematic and little light-absorbing liquid crystal state, regardless of the phases of the signals on the front electrodes.

Die Frontelektrode h wird so wie die Teilelektroden a bis g betrieben. Daher befindet sich die Flüssigkristallschicht des gesamten Untergrundes im nematischen Zustand, während sich lediglich die Anzeigeelemente a', b', c' im lichtabsorbierenden cholesterinischen Zustand befinden.The front electrode h is operated like the partial electrodes a to g. Therefore, the liquid crystal layer of the entire background is in the nematic state, while only the display elements a ' , b', c 'are in the light-absorbing cholesterol state.

Da das höherfrequente Signal beispielsweise bei Uhren von der Frequenzkette der zur Ansteuerung üblicher Drehkristallanzeigen verwendeten Mittel abgegriffen wird, besteht ein besonderer Vorteil dieses Verfahrens darin, dass nun keine zwei Spannungsquellen, deren Pegel zur Vermeidung schädlicher Gleichstromkomponenten sorgfältig aufeinander abgestimmt sein müssen, notwendig sind. Darüber hinaus ist dieses Verfahren auch bei Flüssigkristallen mit Übergangsspannungen grösser 7,5 V in handelsüblichen, mit 15 V Spannung betriebenen integrierten Schaltkreisen verwendbar.Since the higher-frequency signal is tapped, for example, in clocks from the frequency chain of the means used to control conventional rotary crystal displays, a particular advantage of this method is that no two voltage sources, the levels of which have to be carefully coordinated with one another to avoid harmful DC components, are now necessary. In addition, this method can also be used for liquid crystals with transition voltages greater than 7.5 V in commercially available integrated circuits operated at 15 V voltage.

In Fig. 10 ist die zur Einstellung und Aufrechterhaltung der nematischen Phase eines cholesterinischen Flüssigkristalls in einer (wie vorgenannt beschrieben angesteuerten) Anzeigevorrichtung notwendige minimale Spannungsdifferenz U in Abhängigkeit von der Frequenz f des an die Teilelektrode i gelegten höherfrequenten Signals dargestellt. Hierbei ist ein Flüssigkristall mit einer Übergangsspannung von 7,5 [V] vorgesehen. Unterhalb 20 [Hz] kann das Flimmern der Anzeige auch bei Anheben der Spannung nicht eliminiert werden. Eine geeignete, fast flimmerfreie Anzeige ergibt sich bei U = 10 [V] und f = 30 [Hz].FIG. 10 shows the minimum voltage difference U necessary for setting and maintaining the nematic phase of a cholesteric liquid crystal in a display device (controlled as described above) as a function of the frequency f of the higher-frequency signal applied to the partial electrode i. Here, a liquid crystal with a transition voltage of 7.5 [V] is provided. Below 20 [Hz] the flickering of the display cannot be eliminated even when the voltage is raised. A suitable, almost flicker-free display results at U = 10 [V] and f = 30 [Hz].

Da wegen der kapazitiven Verluste an den Stellen der Anzeige, wo die hochfrequenten Spannungen anliegen, die verbrauchte Energie am grössten ist, empfiehlt es sich, die Flächen dieser Stellen zu verringern. Dies kann etwa durch eine Änderung der Elektroden gemäss Fig. 9 geschehen. Bei dieser Anordnung sind die Zuleitungen der Elektroden a, ..., g der Frontplatte sowie entsprechend der Elektrode i der Rückplatte so klein wie möglich gehalten. Es ist auch möglich, die Zuleitungen der Elektroden a, ..., g auf einander gegenüberliegende Ränder der Frontplatte zu führen. Durch diese und die vorgenannte Massnahme kann der Energieverlust der erfindungsgemässen Anzeigevorrichtungen etwa um den Faktor 2 herabgemindert werden.Since the energy consumed is greatest at the locations of the display where the high-frequency voltages are present, because of the capacitive losses, it is advisable to reduce the areas of these locations. This can be done, for example, by changing the electrodes according to FIG. 9. In this arrangement, the leads of the electrodes a, ..., g of the front panel and corresponding to the electrode i of the rear panel are kept as small as possible. It is also possible to lead the leads of the electrodes a, ..., g to opposite edges of the front panel. Through this and the aforementioned measure, the energy loss of the display devices according to the invention can be increased by a factor of approximately gate 2 can be reduced.

Die erfindungsgemässe Anzeigevorrichtung ist nicht nur auf Zellen mit flüssigkristallinen Gast-Wirt-Substanzen beschränkt, sie ist beispielsweise auch für den Einsatz von elektro-phoretischen Suspensionen als elektro-optisch aktivierbarem Medium verwendbar und dies vor allem deswegen, da bei derartigen Substanzen an der gesamten Anzeigefläche ein elektrisches Potential anliegen muss, um einen voll definierten optischen Zustand beizubehalten oder einzustellen. Hierbei ist es von besonderem Vorteil, dass etwa die 7-Segment-Anzeige einer Zahl geschaltet werden kann, ohne dass die Zuleitungen zu diesen Segmenten sichtbar werden.The display device according to the invention is not only limited to cells with liquid-crystalline guest-host substances, it can also be used, for example, for the use of electro-phoretic suspensions as an electro-optically activatable medium, and above all because such substances cover the entire display area an electrical potential must be present in order to maintain or set a fully defined optical state. It is particularly advantageous here that, for example, the 7-segment display of a number can be switched without the feed lines to these segments becoming visible.

BezeichnungslisteLabel list

Figure imgb0002
Figure imgb0002
Figure imgb0003
Figure imgb0003

Claims (11)

1. An electro-optical display device for representing symbols consisting of separately controllable display elements (a', b', ..., g'), which is provided with a layer, arranged between a transparent front electrode and a rear electrode, of a medium which can be electro-optically activated, the front electrode being attached to a transparent front plate and the rear electrode being attached to a rear plate and both electrodes being provided with part-electrodes (a, b, ..., i, j) which are electrically insulated from one another by means of recesses and which cover the plate surfaces in the region of the medium which can be electro-optically activated, and of which part-electrodes the part-electrodes (a, b, ..., g, j) contained in the display elements are provided with feed lines, and electric control signals being applicable to the feed lines via a drive circuit, characterised in that each of the remaining part-electrodes (h, i) is also provided with a feed line, that an electro-optical medium is provided which absorbs light when the control signals (Ug., Ug, USi, USll) are applied if the potential difference between the front electrode and the rear electrode is less than a medium-related transition voltage (Uc), and transmits light when this potential difference is greater than the said transition voltage (UC), and that, between the part-electrodes (a, b, c) of the front electrode and the part-electrode (j) of the rear electrode of the display elements (a', b', c') of the symbols to be represented, a potential difference exists during the operation of the display device, this potential difference being smaller than the transition voltage (Uc), whereas between the remaining part-electrodes (d, e, f, g, h) of the front electrode and the part-electrodes (i, j) of the rear electrode, during the operation of the display device, a potential difference exists which is at least equal to the transition voltage (Uc).
2. A display device according to Claim 1, characterised in that, as the medium which can be electro-optically activated, a liquid-crystal guest- host substance and particularly a cholesteric liquid crystal which is provided with at least one pleochroic dye, or an electro-phoretic suspension which is provided with an electrica Ily-charged pigment is provided.
3. A display device according to Claim 1 or 2, characterised in that in the front electrode every part-electrode (a, b, ..., f, g) except one (h) at least partly overlaps the display elements (a', b', ..., fl, g'), that this one part-electrode (h) of the front electrode overlaps the feed lines of the part-electrodes (i, j), arranged in the rear electrode, except for one (i), and that this one part-electrode (i) of the rear electrode overlaps the feed lines of every one of the part-electrodes (a, b, ..., f, g), arranged in the front electrode, which at least partly overlap the display elements, but does not overlap the feed line of the one part-electrode (h), which does not overlap any of the display elements, of the front electrode.
4. A display device according to one of Claims 1 to 3, characterised in that at one edge of the front plate, connection tabs (a", ..., j") are provided, to which the feed lines of all the part-electrodes (a, ..., j) are connected.
5. A display device according to one of Claims 1 to 4, characterised in that on the rear electrode a metallic-reflecting and electrically insulating coating is provided in the form of a layer.
6. A method for operating the display device according to Claim 3, characterised in that, during the whole operating time, unipolar rectangular signals (USl, Ugl), having identical amplitudes, pulse frequencies, phases and pulse shapes, are applied to the part-electrodes (a, b, c) of the front electrode and the part-electrode (j) of the rear electrode, which overlap the display elements (a', b', c' ) of the symbols to be represented, that, to the front part-electrodes (d, e, f, g) of the display elements (d', e', f', g') contained in the background, and to the front electrode (h) which does not overlap any of the display elements (a', ..., g'), signals (Usll) are applied which are phase-shifted by half a period with respect to the signals (Us,, Ugl) which are applied to the part-electrodes (a, b, c, j) of the display elements (a', b', cl) of the symbols to be represented, but that these signals have the same amplitude, pulse frequency and pulse shape as the latter signals, and that a signal (Ugi) having a higher pulse frequency than that of the other signals is applied to the part-electrode (i) which does not overlap any of the display elements, of the rear electrode.
7. A method according to Claim 6, characterised in that the signal (Ug.) with the higher frequency is a signal which is harmonically related to the signal (Us,) which is applied to the part-electrodes (a, b, c, j) of the display elements (a', b', c') of the symbols to be represented.
8. A method for operating the display device according to Claim 3, characterised in that, during the whole operating time, unipolar rectangular signals (Us), having identical amplitudes, pulse frequencies, phases and pulse shapes, are applied to the part-electrodes (a, b, c) of the front electrode and the part-electrode (j) of the rear electrode, which overlap the display elements (a', b', c') of the symbols to be represented, the amplitudes (2V) of which signals are at least twice the transition voltage (Uc), that, to the remaining front part-electrodes (d, e, f, g, h), signals (Usll) are applied which are phase-shifted by half a period with respect to these signals (Us,) but have the same amplitude, pulse frequency and pulse shape, and that a direct-voltage signal the potential (V) of which has half the amplitude of the aforementioned signals, is applied to the part-electrode (i), which does not overlap any of the display elements, of the rear electrode.
9. A method according to one of Claims 6 to 8, characterised in that the pulse frequency of the signals (Us) applied to the display elements (a,, b', c' ) of the symbols to be represented is at most 10 [Hz].
10. A method according to Claim 7, characterised in that the pulse frequency of the signal (Ugl) having the higher frequency is between 20 and 50 [Hz].
11. A method according to Claim 10, characterised in that, with a medium which can be electro-optically activated and which has a transition voltage (Uc) of approximately 7.5 V, the amplitude of the signal (Ug.) having the higher frequency is about 10 [V] and the pulse frequency of the signal is about 30 [Hz].
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DE2738679C2 (en) 1987-12-23
CH617281A5 (en) 1980-05-14
US4241344A (en) 1980-12-23
DE2738679A1 (en) 1979-02-08
US4281902A (en) 1981-08-04
EP0000594A1 (en) 1979-02-07
HK76185A (en) 1985-10-18

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