Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
  • G09G3/3611—Control of matrices with row and column drivers
  • G09G3/3696—Generation of voltages supplied to electrode drivers
• • 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
  • G02F1/13306—Circuit arrangements or driving methods for the control of single liquid crystal cells
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0252—Improving the response speed

Definitions

• This invention relates to the activation of liquid crystal devices by the application of electric potential thereto to alter the state of some or all of the liquid crystal material thereof.
• Nematic liquid crystal display devices are well known. These devices generally include transparent plates between which is positioned a thin layer of a nematic liquid crystal material. Light polarisers are positioned one to either side of the plates. Electrodes 10 in; the form of transparent conductive coatings, usually arranged in a desired pattern forming configuration, applied to the inner surfaces of- the- plates are provided and, when an electric potential greater than a critical voltage is applied across the electrodes, the liquid . crystal material directly interposed between the electrodes is affected in such a way as to cause a change in the optical density of that part of the device coinciding with the electrodes.
• the liquid crystal material and light polarisers may be 20. arranged so that before application of electric potential to the device light can freely pass through the device, but that on application of electric potential to the electrodes the optical density of the device coinciding therewith is greatly increased.
• U.S. Patent 4,071,912. This discloses a welder's mask: in which the lens includes a liquid crystal layer- the state of which is changed to opacify the lens by means of an UV-sensitive photocell responsive to exposure to a welding flame or arc.
• U...S. Patent 4,241,286 This also relates to we-dler's masks but in which the opacifying is dependant on the welder blowing on, or making a sound to affect, a transducer within the mask.
• ⁇ '.K. Patent 2,029,343. This discloses modification of the reflectivity of a mirror by alteration of the on/off duty cycle of a high frequency controlling voltage of a liquid crystal device associated with the mirror.
• German Patent 2,442,98 The opacity of a lens is controlled by feed back from a photo-sensor controlling variation of the voltage applied to 10. a liquid crystal component of the lens to maintain a constant transmissability.
• the present invention is applicable in all of the applications instanced in the abovementioned prior art and is also particularly, but not exclusively concerned with affecting a high speed change of state required in respect of welder's helmets or masks.
• the response time that is to say the time taken to achieve the change in state after application
• che present invention contemplates the application a high electric potential to the liquid crystal device, but only for a short period, when effecting change of state of the device by application of electric potential. It has been found that application of a short high voltage pulse of the order of, say, five milliseconds duration will effect very rapid change of state as compared with conventional methods, without causing significant lessening of life of the device.
• a method of altering the state of a liquid crystal device, to vary the optical density of the device comprising applying to the device a short pulse of high electric potential.
• the pulse may be followed by a maintained lower level of potential sufficient to maintain the change of state.
• the invention also provides means for applying electric potential to a liquid crystal device for altering the state of the device, to vary the optical z ⁇ density of the device, arranged whereby on said applying of electric potential, the electric potential applied is generated as a relatively high magnitude pulse of short duration.
• the electric potential applied may be changed to a lower level after occurrence of said pulse.
• the pulse may be of magnitude 2 to 5 times the critical voltage for the device and the subsequent potential applied may be of magnitude substantially the same as but higher - a -
• the means for applying electric potential may comprise two voltage generators, one operable to apply a steady state voltage sufficient to maintain the liquid crystal display device in its
• the said pulse and any electrical potential applied to maintain the change of state of the device may be direct current voltages, possibly of pulsating form, or may be alternating current voltages.
• the pulse may be generated as a series of relatively high frequency signals such as 20KHz, whilst the subsequent maintenance electrical potential may be generated as an alternating voltage of relatively low frequency, such as 50 Hz.
• Figure 1 is a cross sectional diagram of a conventional liquid crystal display device
• FIGS. 2 to 4 are graphs explaining the operation of the invention.
• FIG. 5 is a circuit diagram of a representative supply device constructed in accordance with the invention.
• a liquid crystal display device 10 is shown as comprising two glass plates 12, 14 arranged in closely spaced parallel relationship and sealed around the edges by a seal 16 therebetween so as to maintain the inner surfaces of the plates spaced apart a small distance.
• the cavity within the device between the glass plates 12, 14 and seal 16 is filled with a nematic liquid crystalline material 20.
• Crossed polarisers 22, 24 are provided against the outer faces of the glass plates 12, 14 whilst the inner surfaces of the glass plates in contact with the material 20 are coated with a suitable transparent conductive material.
• This voltage corresponds to an RMS voltage close to but somewhat above the - - critical voltage V , for customarily used liquid j . c crystal materials.
• FIG 4 illustrates a cycle of operation of device 10, in accordance with this invention.
• a voltage represented by graph 37 is applied. Over the bulk of the time period, represented by part 37b of graph 37, the voltage is maintained at the same level as in Figure 2, being sufficient to maintain turn on but not being so high as to be likely to cause damage to the device 10.
• the applied voltage is generated as a high magnitude pulse shown at 37a in Figure 4.
• the magnitude of the applied voltage represented by this pulse would be sufficient to cause damage to the device 10 were it applied for any significant length of time.
• this high peak voltage has the effect of considerably reducing the turn on time, such as to the order of 2 milliseconds as shown by the transmissivity curve 36, whilst leaving the turn off time substantially the same as in the example of Figure 2.
• Figure 5 shows an embodiment of a supply device 50 for providing the voltage waveform represented by graph 37 in Figure 4.
• the voltage applied is an alternating voltage consisting a high frequency voltage of high potential to form the pulse 37a together with a lower frequency voltage component to form the - 9 - subsequent maintenance voltage as represented at 37b in
• the supply device 50 is operated from a twelve vol ' t- direct current supply (not shown) .
• the supply device 50 includes a first oscillator 52 comprised of a
• Schmit inverter device 60 which has one input connected to a supply line 54 and its other input coupled to ground via a capacitor 113 and to its output terminal via a resistor 58.
• Line 54 is connected via a switch 56 coupled to the aforementioned twelve volt supply.
• fr ⁇ r oscillator 52 is connected, on the one hand, to one off the conductive layers (26) of the device 10 and on the other hand to the two inputs of -a second Schmit inverter device 61, the output terminal of which is connected via a. diode 62 to the other conductive layer 28 of the device 10.
• a second oscillator 64 is formed from a Schmit inverter device 66 having both inputs connected together and. coupled to ground via a capacitor 68. The inputs of device 66 are also connected to the output terminal of that inverter via a resistor 70. Output from oscillator
• 20 64 is taken via a capacitor 74 to a conventional voltage multiplier 80 comprised of three series connected capacitors 82, 84, 86 with capacitor 82 being bridged by two series connected diodes 88, 90 and capacitor 86 being bridged by two series connected diodes 92, 94.
• Diode 88 has a capacitor 96 connected in parallel thereacross whilst a further capacitor 98 is connected between the junction of diode 88 with diode 90 and the junction of diode 92 with diode 94.
• Output from the - - voltage multiplier appears across a capacitor 100 connected between earth and the junction of diode 94 with capacitor 86.
• Supply from line 55 is provided to the voltage multiplier via a diode 106.
• Oscillator 52 is a relatively low frequency oscillator of, for example 50Hz and is arranged to provide an alternating current supply voltage, via Schmit inverter device 60 and diode 62, of RMS voltage close to but somewhat above the critical voltage V for the device 10.
• the output from voltage multiplier 80 comprises a relatively high voltage alternating potential of, say, 40 volts and this output is connected via a line 102, a transistor 110 and a diode 112 to the device 10, particularly to the layer 28 thereof.
• Line 102 connects to the emitter of transistor 110 whilst diode 112 -connects to the collector thereof.
• the base of the transistor 110 is connected via a capacitor 115 to the output of an inverter 122 having its input connected to line 55.
• the initial voltage conditions on the transistor 110 are effective to permit the oscillatory voltage on line 102 to pass through the transistor through diode 112 whereby the high voltage high frequency signal from oscillator 64 and multiplier 80 is applied across the device 10.
• capacitor 115 charges and after a time period determined, inter alia by the value of the capacitor 115 eventually reaches a state at which the terminal conditions of the transistor 110 are such as
• each time switch 56 is actuated to effect a new cycle of turn on of the device 10 the oscillator 64 operates to apply voltage to the device 10 for a time period determined by the value of the capacitor 115. As mentioned, this time period may be selected to be of the
• oscillator 52 may be arranged to provide alternating current voltages of frequency between 25 and 100Hz, in accordance with conventional practice as determined principally by the particular liquid crystal material used.
• the voltage generated by oscillator 52 may be of the order of 3 to 15 volts RMS depending on the liquid crystal material.
• oscillator 64 and multiplier 80 may be of voltage between 20 and 60 volts, applied for a time duration between 1 and 10 milliseconds.
• the frequency of operation of oscillator 64 is not critical, but frequencies of the order of 20 Khz, such as between 5 and 40 Khz, have been found satisfactory, it is prefereed that the frequency be higher than that of oscillator 52.
• the frequency of the oscillator 52 may, conveniently, be in the range 25 to 120 Khz.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Computer Hardware Design (AREA)
• Theoretical Computer Science (AREA)
• Mathematical Physics (AREA)
• Optics & Photonics (AREA)
• Liquid Crystal Display Device Control (AREA)

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• 1986
  • 1986-09-05 EP EP19860905171 patent/EP0236361A1/de active Pending
  • 1986-09-05 WO PCT/AU1986/000264 patent/WO1987001468A1/en unknown

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