EP0986042A1 - Reflective display device with liquid crystal cell - Google Patents

Abstract

The liquid crystal signaling mechanism has a back reflecting surface (14) with a forward liquid crystal unit (12) made up of interface sections (20,22) and the liquid crystal itself. The liquid crystal section can be modulated to be opaque or transmit light at rates between 0.2 and 5 Hz providing a blinking output to input light. There is an output filter (30) filtering the light.

Description

Technical field of the invention

• un élément réflecteur destiné à réfléchir des rayons lumineux pour les renvoyer vers une source d'éclairage d'émission,
• une cellule transducteur à cristal liquide placée devant l'élément réflecteur pour constituer une valve optique à mode réflexif, ladite cellule étant composée de deux lames support planes en matériau transparent, ménageant entre elles ladite cavité remplie de cristal liquide, et d'une paire d'électrodes transparentes ou semi-transparentes, recouvrant la face interne des deux lames à l'intérieur de la cavité,
• un circuit électronique délivrant un signal de commande d'activation ou de déactivation à la cellule transducteur à cristal liquide, laquelle est susceptible de se trouver dans un état transparent ou dans un état opaque selon la nature du signal de commande qui engendre des modifications du champ électrique dans la cavité de ladite cellule, le passage d'un état à l'autre provoquant une modulation du flux lumineux réfléchi par l'élément réflecteur.

The invention relates to a light signaling device comprising:

• a reflective element intended to reflect light rays to return them to a source of emission light,
• a liquid crystal transducer cell placed in front of the reflective element to constitute an optical valve in reflective mode, said cell being composed of two flat support blades of transparent material, forming between them said cavity filled with liquid crystal, and a pair of '' transparent or semi-transparent electrodes, covering the internal face of the two blades inside the cavity,
• an electronic circuit delivering an activation or deactivation control signal to the liquid crystal transducer cell, which is likely to be in a transparent state or in an opaque state depending on the nature of the control signal which generates field modifications electric in the cavity of said cell, the transition from one state to another causing a modulation of the light flux reflected by the reflective element.

State of the art

Classic retro-reflectors used in road signs at night return the light in the exact direction from which it is emitted by the headlights cars. The effectiveness of this type of road signage nevertheless remains questionable because of the eye's addiction to the environment and multitude of visual information intended to capture his attention, in particular horizontal signage (indications painted on the roadway), vertical signage (various signs, low beams, etc.), and advertising billboards and illuminated signs.

Display panels and conventional signaling devices are generally lit by a light source, which can be integrated or be placed near the panel or device signage. This light source consists of at least one bulb electric, supplied by the low voltage distribution network, or by a backup battery. The large current consumed involves costs significant operating costs.

Document US-A-4 893 903 describes with reference to FIG. 21 a device with liquid crystals, where the material producing the blackout effect is taken sandwich between two transparent plates covered with a serving deposit activation electrode. The device does not include a polarizing filter the cell entrance, which requires the use of a certain type of transducer to liquid crystal, which consumes relatively large electrical energy.

Subject of the invention

The object of the invention is to provide a light signaling device attractive and visible from afar, and benefiting from a large autonomy for a reduced operating cost.

• des moyens pour ajuster la fréquence du signal de commande dans une fourchette de 0,2Hz à 5Hz dans le cas d'un clignotement, ou pour activer cycliquement des modules synchronisés montés en cascade,
• et un filtre d'entrée polarisant agencé sur la face externe de la lame support antérieure à l'opposé de l'élément réflecteur.

According to the invention, the light signaling device further comprises:

• means for adjusting the frequency of the control signal in a range from 0.2Hz to 5Hz in the case of a flashing, or for cyclically activating synchronized modules connected in cascade,
• and a polarizing input filter arranged on the external face of the anterior support plate opposite the reflective element.

According to a preferred embodiment, each electrode is obtained at by means of an invisible conductive coating. The reflective element can be formed by a reflector attached to the posterior support plate of the cell liquid crystal transducer, or by a reflective film with high luminosity by concentration of light, and having a colored structure as a function of color desired.

According to a characteristic of the invention, the electronic circuit comprises a chopper powered by a direct current source, and controlled by a clock, the output of the chopper being connected to the two electrodes.

The direct current supply source for the chopper can be constituted by a simple battery or accumulator, giving the whole a great autonomy.

Preferably, the electronic circuit includes a time base generator integrated in a logic stage supplied by a first supply voltage, and connected via a capacitive divider to an interface circuit comprising two transistors mounted in Push-Pull, said interface circuit being supplied by a second supply voltage corresponding to the voltage nominal of LCD cells.

• la figure 1 est une vue schématique en coupe du dispositif de signalisation selon l'invention ;
• la figure 2 montre le circuit électronique de commande du dispositif de signalisation à cristaux liquides.

Other advantages and characteristics will emerge more clearly from the description which follows of an embodiment of the invention given by way of nonlimiting example, and represented in the appended drawings, in which:

• Figure 1 is a schematic sectional view of the signaling device according to the invention;
• Figure 2 shows the electronic control circuit of the liquid crystal signaling device.

Description of a preferred embodiment

In FIG. 1, a signaling device 10 comprises a cell liquid crystal transducer 12, associated with a rear reflector 14 for constitute a reflective mode optical valve.

The reflector 14 is advantageously formed by a reflector 15 or by any other high brightness optical device, reflecting light rays to the emission source. The reflector 15 may have a surface prismatic reflective, or microbead structure. he is also possible to use a high brightness reflective film by concentration of light, and having a colored structure as a function of color desired.

The signaling device 10 allows direct vision with observation an image or a message on the liquid crystal transducer cell 12. The light emission source is located at the front of the transducer cell, and at opposite of reflector 14.

The light emission source can be a lighting lamp 16, in particular the headlights of a vehicle, or a spot delivering an incident light towards the liquid crystal transducer cell 12. The incident light can also be constituted by ambient lighting if the brightness is sufficient.

Direct vision on the liquid crystal transducer cell 12 is optimum when the observer's eye 18 is located in the light field reflected, and when the viewing angle relative to the vertical direction or horizontal to normal of the cell is less than 50 °.

The liquid crystal transducer cell 12 is composed of two support blades 20, 22 planes of glass or other transparent material, leaving between them a cavity 24 of small thickness, filled with liquid crystal. A pair of electrodes 26, 28 transparent or semi-transparent, is deposited on the internal face of the two blades 20, 22, inside the cavity 24. Each electrode 26, 28 is obtained by way of example by coating with a conductive paint invisible.

The liquid crystal transducer cell 12 operating as an optical valve is thus transparent in all of its constituents. The modification local light transmission occurs by means of a signal electrical control applied to the two electrodes 26, 28. The presence of this electrical control signal generates an electric field in the cavity 24, which activates the volume of liquid crystal by causing an electro-optical effect orientation of molecules to modulate light transmission by the transducer cell 12.

A polarizing input filter 30 is deposited on the external face of the support blade 22 to polarize the light and make the modulation effect visible. he it is thus possible to use liquid crystal occulters operating according to the principle of rotation of the polarization of light. These liquid crystals require the presence at the input of the polarizing filter to transform the effect rotary of the light components in effect of concealment. The cost of wagering use of this type of crop is relatively small.

The electrical control signal of the liquid crystal transducer cell 12 is supplied by an electronic circuit 32, which is supplied by a source 34 direct current, and controlled by a clock 36. Means of the circuit electronic 32 act on the output signal to adjust the frequency of flashing in a range between 0.2Hz and 5Hz in the case of a flashing device, or to adjust the scrolling speed in the case of a running lights central control unit. For modules constituting a set of running lights, it is possible to connect each cell to a common central unit, or to equip each module with an electronic circuit command with synchronization on the previous module. The circuit electronics 32 includes for example a chopper or any other converter delivering the control signal, for example a square signal having a fixed frequency, the value of which falls within the above-mentioned range. The circuit electronics 32 can advantageously be produced using integrated circuits to limit the electrical energy supplied by the source 34 feed. The latter can be obtained by means of a simple stack or of an accumulator of a few Volts allowing to obtain a large autonomy for the operation of the electronic circuit 32.

For example, a 2 Hz control signal causes a flashing of the liquid crystal transducer cell 12 which takes place at a frequency of two flashes per second. Almost all of the energy is light energy produced by the external lamp 16, and the light flux reflected by the reflector is modulated, by periodically changing the transmission of light through the liquid crystal transducer cell 12 constituting a mask.

The liquid crystal transducer cell 12 is respectively in a state opaque after application to the electrodes 26, 28 of a non-zero voltage, or of a square signal at 30Hz depending on the type of liquid crystal cell, and in a transparent state in the absence of voltage or by applying a fixed voltage or zero for LCD cells with refresh. The latter type of LCD cells to refresh must indeed be ordered alternately by two sequences, comprising on the one hand a square signal at 30Hz to activate the effect of mask, and on the other hand a constant voltage signal (positive, negative or null) to deactivate it.

For the flashing devices, the respective durations of these sequences will be adjusted to obtain an effective blinking of the LCD cell going from 0.2Hz to 5Hz.

The resulting changes in the electric field in the cavity 24 cause rapid passage from one state to another, causing a flashing effect of the mask, which is perfectly visible thanks to the very low frequency of the control signal. Each state remains stable until the next change of the control signal.

Modulation of light transmission by the crystal transducer cell liquid 12 associated with the reflector effect of the reflector 15 attracts the eye of the observer. This therefore results in various applications.

Referring to Figure 2, the electronic control circuit 32 includes a EL logic stage supplied with 3 volts, and including a basic generator time 40, responsible for producing regularly sequenced signals, for the flashing or running lights control, followed by a shaping stage (and possibly production of the different phases necessary for a running light system). Finally, to order the LCD liquid crystals, a IN interface circuit is adapted to the supply voltage of the liquid crystal LCD which is commonly around 12 Volts.

The time base generator 40 is formed by a resistor R9 and a capacitor C1. The resistive divider with resistors R5 and R6 associated with MOS components Q4 and Q5, is intended to reduce the current consumed by the EL logic stage.

• isoler les deux étages EL et IN ayant des tensions d'alimentation différentes ;
• générer des signaux impulsionnels sur les grilles des transistors MOS Q10 et Q11. Le condensateur C2 laisse passer des impulsions négatives vers le transistor Q10 sur les fronts descendants du signal issu des transistors Q8 et Q9. Le condensateur C3 laisse passer des impulsions positives vers le transistor Q11 sur les fronts montants de ce même signal.

The interface circuit IN includes two MOS transistors Q10 and Q11 mounted in Push-Pull and controlled by short pulses, obtained by passing the logic signal from stage EL through a capacitive divider with capacitors C2 and C3 of very low capacities, these capacitors then recharging thanks to high-value resistors R7 and R8. The logic signal directly attacks the two capacitors C2 and C3 which have a double function:

• isolate the two stages EL and IN having different supply voltages;
• generate pulse signals on the gates of the MOS transistors Q10 and Q11. Capacitor C2 lets negative pulses pass to transistor Q10 on the falling edges of the signal from transistors Q8 and Q9. The capacitor C3 lets positive pulses pass to the transistor Q11 on the rising edges of this same signal.

The electrodes 26, 28 of the liquid crystal transducer cell 12 are connected to the output S3 and to the ground of the interface circuit IN.

The total consumption of an LCD circuit having a dimension of 30cm on 20cm, is less than 40 micro-amperes, which corresponds to an autonomy of several years with a block of dry batteries whose volume is comparable to approximately three 4.5 Volt flat batteries, such as those commonly used in flashlights. It is thus possible to connect such equipment to a existing isolated equipment with battery or sensor power without the additional consumption apparently detectable.

In the area of automotive signaling, the signaling device according to the invention is particularly suitable for attracting the driver's attention on danger information. STOP signs at dangerous crossroads can be fitted with the red flashing device, which corresponds to the indication IMMEDIATE STOP. Any other danger sign may be reinforced at night by a flashing device of suitable color, for example orange. The signaling device according to the invention is particularly suitable temporary signage, including marking of construction sites and maintenance work (narrowing of the roadway, earthworks, temporary traffic stops, etc.), and informing motorists in the event of an accident or stopping a vehicle on the pavement. It could also be used for route marking of a route temporary or deviation, and in town to indicate the recommended direction towards a predetermined location.

In the area of personal safety, the signaling device according to the invention can be affixed to children's clothing or school bags, as well as on the clothes of people working in places dangerous, in particular motorways, urban expressways or tunnels.

It is also possible to make flashing masks intended for highlight advertising or commercial information. In sufficiently lit atmosphere where the reflective effect does not present of interest due to the absence of an individual light source, information written with fluorescent inks on a black background (color of liquid crystal in the opaque state) could replace the reflector.

It is clear that several masks can be juxtaposed to obtain a signaling device having a desired area.

Claims (7)

Light signaling device comprising: a reflective element (14) intended to reflect light rays to return them to a source of emission lighting, a liquid crystal transducer cell (12) placed in front of the reflective element (14) to constitute an optical valve in reflective mode, said cell being composed of two flat support blades (20, 22) made of transparent material, forming between them said cavity (24) filled with liquid crystal, and a pair of transparent or semi-transparent electrodes (26, 28), covering the internal face of the two blades (20, 22) inside the cavity (24), an electronic circuit (32) delivering an activation or deactivation control signal to the liquid crystal transducer cell (12), which is likely to be in a transparent state or in an opaque state depending on the nature of the control signal which generates modifications of the electric field in the cavity (24) of said cell, the passage from one state to another causing a modulation of the light flux reflected by the reflective element (14), characterized in that it comprises Moreover: means for adjusting the frequency of the control signal in a range from 0.2Hz to 5Hz in the case of a flashing, or for cyclically activating synchronized modules connected in cascade, and a polarizing input filter (30) arranged on the external face of the support plate (22) anterior to the opposite of the reflective element (14). Light signaling device according to claim 1, characterized in that each electrode (26, 28) is obtained by means of a coating invisible conductor. Light signaling device according to claim 1, characterized in that the electronic circuit (32) includes a powered chopper or sequencer by a direct current source, and controlled by a clock (36), the output of the the chopper being connected to at least one pair of electrodes (26, 28). Light signaling device according to claim 1, characterized in that the reflective element (14) is formed by a reflector (15) attached to the back support blade (20) of the liquid crystal transducer cell (12). Light signaling device according to claim 1, characterized in that the reflective element (14) is formed by a high reflective film luminosity by concentration of light, and having a colored structure in depending on the desired color. Light signaling device according to claim 3, characterized in that the DC power source for the chopper is constituted by at least one stack. Light signaling device according to claim 1, characterized in that the electronic circuit (32) includes a time base generator (40) integrated in a logic stage (EL) supplied by a first voltage supply, and connected via a capacitive divider (C2, C3) to an interface circuit (IN) comprising two transistors (Q10, Q11) mounted in Push-Pull, said interface circuit (IN) being supplied by a second voltage corresponding to the nominal voltage of the LCD cells.

Images