Liquid crystal display device and its in situ diagnostic method.

Abstract

A liquid crystal display device comprising a light-emitting surface (LES) capable of emitting a light beam (LUB), a liquid crystal layer (LCL) disposed opposite the light-emitting surface, a light-transparent output screen (EPR2) disposed opposite the liquid crystal layer itself disposed between the light-emitting surface and the output screen, and an electronic control module (ECM) capable of controlling the liquid crystal layer, and further comprising optical detection means (SDI, PDI) capable of capturing a fraction of the light beam propagating inside the output screen and signal processing means (SPM) for the output signal delivered by the optical detection means, capable of comparing the output signal to a reference value to deduce the integrity level of the liquid crystal layer. (Figure 4)

Description

Description Title of the invention: Liquid crystal display device and its in situ diagnostic process.

[0001] — The technical field generally concerns crystal display devices liquids usually referred to by LCD display (LCD being the English acronym for LCD) Saxon for "Liquid Crystal Display") and relates more specifically to such af- files used to perform photometric functions, particularly in dis- Positive rear signaling devices for motor vehicles. Conventional rear signaling devices use different methods to illuminating surfaces also called "screens", in a homogeneous, pixelated or mixed (reflectors, light guides, combined with diffusers, lenses, refractors, etc.). The required light distributions are specified by the regulations. (functions: light, stop, direction indicator, etc.). As part of the rear signaling of motor vehicles, it is also known in particular from document FR3026689A 1, a rear signaling device DSA of a motor vehicle VHL including an AFF display type screen LCD, capable of performing classic photometric functions and also displaying other Extended graphical information such as pictograms, text, animations, etc. as schematically illustrated in figure 1.

[0002] — Figure 2 illustrates a state-of-the-art LCD display, AFF, from a view in perspective.

[0003] — Figure 3 illustrates the same AFF display in an exploded view allowing distinguish the different elements of the AFF display.

[0004] — The AFF display includes a BOI housing defining a first part forming a flat EMB base supporting a CCI printed circuit board, known also known by the Anglo-Saxon acronym "PCB" for Printed Circuit Board, and whose The face opposite the EMB base supports a MAL matrix of light sources. type light-emitting diodes or LEDs (Light Emitting Diodes), defining the The light-emitting surface (SEL) of the AFF display. The BOI housing also includes a second part forming a CADI frame which is attached to the EMB base in sandwiching the peripheral edges of the ICC card, not including LEDs are positioned between the peripheral edges of the CADI frame and the EMB base. The opening The opening of the CADI frame reveals the LED matrix, MAL, and therefore the surface SEL light-emitting. The CCI card has a protrusion / extension in the diagram of the CCI card protruding from the BOI housing to define a connection pin electrical connection between the AFF display and an MCE electronic control module the display, located away from the display and connected to the CCI card by a wired electrical connection (WIRE). A liquid crystal layer CCL, also called an LCD layer, is arranged on one face of the CADI frame, called the outer face of the CADI frame, opposite the LED matrix, MAL, which is arranged on the inner face of the CAD1 frame. The liquid crystal layer CCL is protected by an inner protective screen EPRI and an outer protective screen EPR2, arranged respectively on the inner face of the CCL layer and on the outer face of the CCL layer. The light produced by the LED matrix, MAL, propagates from the inside of the BOI housing of the AFF display to the outside of the BOT housing; the terms "inner(s)" and "outer(s)" will be used in relation to the direction of propagation of the light. The external protective screen EPR2 is also called the output screen because it is through this screen that the light produced by the LED matrix, MAL, finally exits. A FIP polarizing filter is interposed between the inner protective screen EPR1 and the outer face of the CADI frame. The assembly formed by the CCL layer, the EPRI, EPR2 protective screens and the FIP polarizing filter, is fixed to the outer face of the CADI1 frame by a CAD2 cover in the shape of a frame having PAT tabs distributed around the CAD2 cover and which fix the CAD2 cover to the outer walls of the CADI frame by clipping. The light produced by the LED matrix, MAL (emitting surface SEL), passes through the assembly described above and exits the AFF display through the EPR2 output screen, which is made of glass or a transparent plastic material that allows light to pass through while protecting the LCD layer, CCL, which is inherently fragile. The light from the LED matrix (MAL) passes through the polarizing filter (FIP) to reach the LCD layer (CCL), which allows or blocks light depending on the orientation of its molecules. The orientation of the molecules is controlled by electric fields sent by the electronic control module (MCE) using known but unrepresented methods. The resulting "encoded" light information is then output by the EPR2 display. There is currently no diagnostic procedure that allows for "in situ" diagnosis of a failure of the LCD layer, CCL, of an LCD display, AFF. An in-situ diagnostic method for an LCD display is a method that allows continuous monitoring of the condition of the LCD layer, which is the essential element of the LCD display. Such a failure can result, for example, in a loss of display brightness. This then poses a problem in terms of quality (degraded rendering), adjustment... mentation (non-compliance with the photometric grid) and safety (poor vehicle visibility) for an example of a light signaling application of a motor vehicle, in particular a rear signaling. One aim of the present invention is to overcome this drawback by introducing on the LCD display means capable of participating in the diagnosis of the liquid crystal layer. To this end, the invention has as its first object a liquid crystal display device, comprising a light-emitting surface capable of emitting a light beam, a liquid crystal layer, disposed opposite the light-emitting surface, a light-transparent output screen disposed opposite the liquid crystal layer itself disposed between the light-emitting surface and the output screen, and an electronic control module capable of controlling the liquid crystal layer, characterized in that it further comprises optical detection means capable of capturing a fraction of the light beam which propagates inside the output screen and means for processing the output signal delivered by the optical detection means, capable of comparing the output signal to a reference value in order to deduce the level of integrity of the liquid crystal layer. According to one characteristic, the optical detection means comprise at least one optoelectronic transducer disposed opposite the output screen and a diffusive surface arranged on the output screen so as to deflect the fraction of the light beam propagating inside the output screen towards the optoelectronic transducer. According to another characteristic, the diffusive surface is obtained by a surface treatment of the output screen or by depositing a reflective layer on the surface of the output screen. According to another characteristic, the optical detection means comprise a plurality of optoelectronic transducers arranged according to a distribution determined with respect to the periphery of the output screen. According to another characteristic, the output screen is made of glass or a light-transparent plastic material. According to another characteristic, the light-emitting surface consists of an LED matrix. The invention has as its second object, a method of in situ diagnosis of a device as described above, characterized in that it consists of detecting a fraction of the luminous flux propagating inside the output screen, comparing this fraction of the luminous flux to a reference value obtained after a prior calibration step of the luminous flux exiting the output screen of the display device in order to deduce the level of integrity of the liquid crystal layer. According to one characteristic, the process consists of controlling the luminous flux exiting the display device at a determined pulse frequency, not perceptible to an observer, and in that it only processes signals from optical detection means that are synchronous with this frequency. The invention has as its third object a rear signal light for a motor vehicle, characterized in that it comprises at least one display device as described above. Finally, the invention has as its fourth and final object, a motor vehicle comprising at least one display device as described above. The advantages of the device according to the invention are that it allows for in-situ diagnosis of the LCD display's condition by identifying faults in this type of display. Having the ability to diagnose faults in this type of display is essential for continuously monitoring its reliability. Other advantages and features will become clearer from the following description, given solely as a non-limiting example and with reference to the drawings in which: [fig.1] as already described, represents a vehicle rear signaling device with an LCD display known from the state of the art: [fig.2] already described, represents a perspective view of a state-of-the-art LCD display; [fig.3] already described, represents the LCD display of figure 2 in an exploded view; [fig.4] represents a cross-sectional view of an LCD display according to the invention in the vicinity of the output screen of the LCD display according to the invention; and [fig.5] represents an example of photodiode arrangement on the output screen of the LCD display according to the invention. In these figures, the same references are used to designate the same elements. To be able to detect temporary or permanent failures of the LCD layer, CCL, due to thermal or other effects which cause the CCL layer not to follow or no longer follow the instructions of the electronic control module MCE, one or more PDI photodiodes are arranged opposite the inner face of one of the edges of the output screen EPR2; inner face which is opposite the CCL layer. Figure 4 schematically illustrates, along a cross-section of the LCD, a portion of the display revealing the LED matrix, MAL, the layer LCD, CCL, and EPR2 output screen. An optoelectronic transducer such as a PDI photodiode is arranged opposite an edge of the inner face of the EPR2 output screen. In order for the PDI photodiode to capture a fraction of the outgoing light beam from the LCD layer and which propagates naturally due to the air / PR2 output screen / air interfaces, between the inner and outer faces of the EPR2 output screen (inside / within the thickness of the EPR2 output screen), an SDI diffusive surface is arranged on the same edge of the EPR2 output screen but on the outer face of the EPR2 output screen extending opposite the PDI photodiode. This SDI diffusive surface can be produced from a surface treatment of the outer face of the EPR2 output screen, for example by graining or by local machining of the outer face, for example striations, or by deposition of a reflective layer, etc. The set defined by the SDI diffusive surface and the PDI optoelectronic transducer constitutes optical detection means. The OCL openings left in white in the LCD layer, CCL, represent passages for light created by the orientation of molecules in the LCD layer, CCL. A luminous flux FLU, symbolically represented by an arrow, starts from the LED matrix, MAL, then passes through the LCD layer, CCL, via the OCL passages left free by the molecules of the LCD layer, CCL. Most of the FLU light flux having passed through the LCD layer, then passes through the EPR2 output screen, being deflected at the EPR2 output screen / air interface due to the differences in refractive index between the material constituting the EPR2 output screen and the air. Another part of the FLU luminous flux, symbolically represented by a sawtooth line, not meeting the conditions of the angles of refraction allowing the FLU flux to pass through the EPR2 exit screen, propagates under conditions of total reflection inside the EPR2 exit screen, until it interacts with the SDI diffusive surface. A beam of light resulting from this interaction with the SDI diffusive element is then captured by the PDI photodiode arranged opposite the SDI diffusive element. Although not shown, the PDI photodiode is, for example, supported by a printed circuit board ensuring the transfer of electrical signals from the detection of a light signal received by the PDI photodiode, to the electronic control module MCE. The PDI photodiode, like any other optoelectronic transducer, transforms the optical signal (light beam) into an electrical signal which is then amplified by the PDI transducer itself or by the MCE electronic control module. The electronic control module (MCE) includes signal processing means (MTR) which, based on a suitable calibration of the amplified signals (allowing the definition of a reference value such as a threshold or setpoint), determine whether the fraction of luminous flux (FLU) emerging from the LCD layer (CCL) and actually exiting the output screen (EPR2) is being analyzed by comparing this fraction to the reference value. This comparison allows for the diagnosis of non-failure of the LCD layer (CC) if, for example, this fraction exceeds a threshold or setpoint. Conversely, if a decrease in the expected flux or an insufficient fraction of the FLU flux is below the threshold, the setpoint, … then a failure, total or partial, of the LCD layer, CCL, is diagnosed. Thus, through an adapted calibration process, the MTR signal processing means are able to detect situations of failure of the LCD layer, CCL. The number and distribution of PDI photodiodes relative to the periphery of the EPR2 output screen are optimized according to the geometry of the EPR2 output screen, the desired accuracy and the electronic characteristics of the display components. Figure 5 schematically illustrates an example of the distribution of PDI photodiodes (six PDI photodiodes are represented by circles) on the periphery of the EPR2 output screen. The LCD layer, CCL, is delimited by a rectangular outline inscribed within the EPR2 output screen. To prevent external light from entering the display and interfering with the detection of the PDI photodiodes, the electronic control module (MCE) controls the luminous flux (FLU) generated by the LED matrix (MAL) at a specific pulse frequency (imperceptible to an observer) and only processes signals from the PDI photodiodes that are synchronized with this frequency. This optimizes the signal-to-noise ratio and therefore the diagnostic efficiency. The object of the present invention is of course not limited to the application mentioned in the preamble of this description but can be applied to any LCD display requiring optimal quality control.

Claims

Demands

1. Liquid crystal display (LCD) device comprising a surface light-emitting (SEL) capable of emitting a light beam (FLU), a layer of liquid crystals (LCL), arranged opposite the surface light-emitting (SEL), a transparent output screen (EPR2) light and positioned opposite the liquid crystal layer (LCL) itself arranged between the light-emitting surface (LES) and the output screen (EPR2), and an electronic control module (MCE) capable of controlling the liquid crystal layer (CCL), ca- characterized in that it also includes optical detection means (SDI, PDI) capable of capturing a fraction of the light beam (FLU) which propagates inside the exit screen (EPR2) and means of processing (MTR) of the output signal delivered by the detection means optical (SDI, PDI), capable of comparing the output signal to a value of reference point for deducing the integrity level of the crystal layer liquids (CCL).

2. Device according to the preceding claim, characterized in that the optical detection methods (SDI, PDI) include at least one optoelectronic transducer (PDI) positioned opposite the screen of output (EPR2) and a diffusive surface (SDI) arranged on the screen of output (EPR2) so as to deflect the fraction of the light beam (FLU) propagating inside the output screen (EPR2) towards the optoelectronic transducer (PDI).

3. Device according to the preceding claim, characterized in that the Diffusive surface area (DSA) is obtained by a surface treatment of the exit screen (EPR2) or by depositing a reflective layer on the surface of the output screen (EPR2).

4. Device according to claim 2 or 3, characterized in that Optical detection methods (SDI, PDI) include a plurality of optoelectronic transducers (PDI) arranged according to a distribution determined with respect to the periphery of the output screen (EPR2).

5. Device according to any one of the preceding claims, characterized in that that the output screen (EPR2) is made of glass or a plastic material transparent to light.

6. Display device according to any one of the preceding claims, ca- characterized in that the light-emitting surface (LES) is made up of of an LED matrix (MAL).

7. Method for in-situ diagnosis of a display device according to one of the claims | to 6, characterized in that it consists of detecting a fraction of luminous flux (LUF) propagating inside the screen output (EPR2), to compare this fraction of the luminous flux (FLU) to a reference value obtained after a prior calibration step luminous flux (FLU) exiting the output screen (EPR2) of the device display (AFF) to deduce the integrity level of the layer liquid crystals (LCC).

8. A method according to the preceding claim, characterized in that it consists of controlling the luminous flux (LUF) emanating from the device display (AFF) at a specific pulse frequency, not per- perceptible to an observer, and in that it only processes signals from optical detection methods (SDI, PDI) that are synchronous with this frequency.

9. Rear signal light for a motor vehicle, characterized in that that it includes at least one display device (AFF) according to one of the claims 1 to 6

10. Motor vehicle comprising at least one display device according to one of claims 1 to 6.

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