NL2021758B1

NL2021758B1 - An outdoor digital screen comprising electrowetting optical panels

Info

Publication number: NL2021758B1
Application number: NL2021758A
Authority: NL
Inventors: Feil Hermanus
Original assignee: Miortech Holding B V
Priority date: 2018-10-04
Filing date: 2018-10-04
Publication date: 2020-05-11

Abstract

The present invention relates to outdoor digital screens which comprise a plurality of electrowetting optical panels. In accordance with a first aspect of the invention the above-mentioned object is achieved with an electrowetting optical outdoor digital screen, comprising: an active display comprised of: one or more electrowetting optical panels comprising a reflective layer for reflecting incident light back through the panel, as well as; a cabinet for housing the one or more electrowetting optical panels. The electrowetting optical outdoor digital screen further comprises: one or more internal or external light sources, disposed at a distance from, and directed towards the active display for illuminating the electrowetting optical outdoor digital screen; a sensor for detecting presence of an object in a field of view of the electrowetting optical outdoor digital screen; a light intensity sensor for detecting an environmental light intensity level near the active display; a driver module for driving the one or more light sources, wherein the driver module is arranged to control a light intensity level of the one or more light sources in accordance with the detected presence of the object and the detected environmental light intensity level.

Description

Title: An outdoor digital screen comprising electrowetting optical panels

Field of the invention

The present invention relates to outdoor digital screens which comprise a plurality of electrowetting optical panels.

Background of the invention

Electrowetting technology is based on modification of an energy balance between on one hand surface tension forces of liquids and wetting properties of a solid surface, and on the other hand electrostatic forces induced by an applied voltage over a capacitor arrangement comprising said boundary layer.

An electrowetting optical element, further referred to as electrowetting element, according to the state of the art may from bottom to top be comprised of respectively an electrode layer stack comprising a substrate and an electrode layer, an electrically insulating hydrophobic layer or an insulating layer having a hydrophobic surface on a side opposite to the other electrode layer, for interfacing to a polar liquid and a non-polar liquid immiscible with each other. From a viewing path, this stack, at the bottom ofthe element can be denoted as the second stack, comprising the second electrode layer.

The element may further comprise another electrode layer stack, which is opposite to the above described electrode stack and comprising an electrode layer which is electrically in contact with the polar liquid and a superstrate for supporting the electrode layer. This electrode layer may have a hydrophobicity that is lower than the hydrophobic interface surface of the second electrode layer stack. This stack, at the top of the element, can be denoted as the first stack, comprising the first electrode layer.

Cell walls attached to the electrode layer stack and extending from one electrode layer stack towards the other electrode layer stack, form a containment space between both electrode stacks and the cell walls. The cell walls thus form a barrier for the polar liquid between the electrowetting cell and adjacent electrowetting cells to keep the polar liquid from moving towards other cells. An electrowetting element can form a picture element or pixel. A plurality of electrically controlled electrowetting elements can together form a display or part thereof comprising pixels, which can be used for displaying arbitrary images by appropriately controlling the electrowetting elements forming the display. Electrowetting elements can have arbitrary shapes determined by the shape of the electrodes, such that displays can be manufactured for specific purposes.

An electrowetting element is mainly transparent, except for the nonpolar liquid in each of the cells formed by the cell walls. The non-polar liquid is often non- transparent or has a low optical transmission coefficient. The transmission coefficient of the non-polar liquid typically depends on the application of the electrowetting element. In a colour display, an electrowetting element comprising coloured non-polar liquids may be used.

The principles of operation of an electrowetting element are as follows. In an unpowered state, i.e. when no voltage is applied over the first and second electrode, the lowest energetic state of the system is where the non-polar liquid forms a boundary layer between the polar liquid and the hydrophobic surface of the insulating layer. This is because the polar liquid is repelled by the hydrophobic layer. The poor transmissibility of the non-polar liquid then forms an obstruction to light that penetrates the system.

When a voltage is applied over the electrodes, the lowest energetic state of the system becomes the situation wherein the (poorly conductive or insulating) non- polar liquid is pushed aside by the (conductive) polar liquid, and the polar liquid thereby being in direct contact with the insulating hydrophobic layer. Note that the voltage must be large enough for the electrostatic forces to overcome the repellent and surface tension forces that separate the polar liquid from the hydrophobic surface. In this situation, light that penetrates the system has rather unobstructed access to the insulating hydrophobic layer because of the well transmissibility of the polar liquid and the non-polar liquid being pushed aside. In the powered-up state, when voltage is applied over the electrodes, the electrowetting element is thus transmissive.

Electrowetting technology is suitable for a wide range of applications. An important application for which electrowetting technology is particularly suitable is for outdoor digital screens which may be used as digital traffic signs, message centers, billboards, etc. Such digital screens are currently mostly equipped with Light Emitting Diodes, LEDs, panels. Although LED panels have rapidly emerged due to the significant lower power requirements as compared to the conventional illumination sources like halogen light sources, the use of LED technology still has some drawbacks.

The outdoor digital screens are, as the name already explains, placed outside. As a result thereof, the light conditions in which these digital outdoor screens are placed may vary enormously. For example, an outdoor digital screen placed in one country may perform better than in the other country due to a large difference in sun intensity which may improve or decrease readability of such LED backlighted screen. Not only sun intensity has a large influence on the performance of such an LED screen, also location (permanently out ofthe sun/in the shade), other light sources in the neighborhood, impinging light of headlights or time of day may strongly influence the readability of the screen. To cope with such different light conditions most currently known LED screens are provided with high intensity LED light sources to provide sufficient light which guaranties that the images and/or text that is displayed on the screen can be read under all possible light conditions. The drawback of such a high intensity LED screens is that these not only emit light at such intensity levels that it may cause light pollution but also that is may be considered unsafe for road user as it may blind then or cause distraction.

As compared to outdoor digital screens that are equipped with LED panels, the electrowetting panels are reflective and thus do not require a LED backlight. Although electrowetting panels have superior contrast ratio’s and scientifically lower the power consumption levels, such screens do not benefit from the possibility to increase the light intensity if the environmental light conditions requires it.

Accordingly, there is a need for an improved outdoor digital screen which is suitable for the above-mentioned applications but which on the one hand does not cause light pollution or distraction to drivers, and on the other hand has efficient power consumption and readably under all light conditions.

Summary of the invention

It is an object of the present invention to provide an improved outdoor digital screen which is suitable for the above-mentioned applications but which on the one hand does not cause light pollution or distraction to drivers, and on the other hand has efficient power consumption and readably under all light conditions.

In accordance with a first aspect of the invention the abovementioned object is achieved with an electrowetting optical outdoor digital screen, comprising:

an active display comprised of:

one or more electrowetting optical panels comprising a reflective layer for reflecting incident light back through the panel, as well as;

a cabinet for housing the one or more electrowetting optical panels.

The electrowetting optical outdoor digital screen further comprises:

one or more internal or external light sources, disposed at a distance from, and directed towards the active display for illuminating the electrowetting optical outdoor digital screen;

a sensor for detecting presence of an object in a field of view of the electrowetting optical outdoor digital screen;

a light intensity sensor for detecting an environmental light intensity level near the active display;

a driver module for driving the one or more light sources, wherein the driver module is arranged to control a light intensity level of the one or more light sources in accordance with the detected presence of the object and the detected environmental light intensity level.

As indicated, outdoor digital screens are known that are based on Light Emitting Diode, LED, technology. Some applications may require large screens, e.g. digital billboards or road signs and the like with require a huge amount of LED modules which results in a significant power consumption. Although LEDs are known for having low energy requirements, the setup of these displays due to size and use in environments with already high ambient light levels require LEDs which emit intense light, higher than for example in standard displays which are mostly used inside buildings. Only with these high intensities or high-power LEDs the daylight can be compensated. This requirement, in combination with the large dimensions of the billboard, makes billboards even with energy efficient LED technology still high power consuming applications. The amount of power required can even equal the amount of 30 standard households.

Electrowetting optical outdoor digital screens or further also referred to as electrowetting screens, provide a far better alternative in such applications as the power consumption is significantly lower. Moreover, the readability of an electrowetting screen as compared to LED based screens if much better. Amongst other reasons this is the result of higher contrast ratio’s and absence of active light sources.

Electrowetting screens do not use LED technology but use the known electrowetting phenomenon which is the modification of the wetting properties of a surface (which is typically hydrophobic) by applying an electric field. With the applied electric field, the wetting properties of a hydrophobic surface can be modified and the surface becomes increasingly hydrophilic. This way two immiscible liquids,

i.e. a polar liquid such as a water-based liquid, and a non-polar liquid, such as an oily liquid, can rearrange. The amount of power needed to drive the element is very low, in particular when compared to active displays such as LEDs. Amongst other reasons this reason makes electrowetting screens part curly suitable as an improved alternative for LED based digital billboard.

When activated, i.e. when an electric field is applied to the electrodes, the non-polar liquid, e.g. the oil within the cell of the element is displaced and the light that penetrates the system has rather unobstructed access and either move unobstructed through the element or is reflected by the second stack. By activating electrodes of the matrix corresponding to particular pixels, the display can show static or dynamic content such as text, an image or a video.

In comparison with LED based screens that apply high power LEDs, the active display of the electrowetting screen may be provided with a highly reflective surface in order to assure high visibility or readability. When environmental conditions are normal the visibility of the electrowetting screen is indeed extremely high. Under difficult environmental conditions such as in low light conditions during twilight or during night, the visibility may decrease. However, in the application of electrowetting screens as road signs billboards near roads, the light coming from headlights of the passing cars may illuminate the screen and provide sufficient light levels to maintain high visibility of the screen.

Sometimes however, the screen may have a certain position or application in which the direct illumination by headlights of passing cars may be absent or not reach the electrowetting screen. For such conditions, the visibility may not be guaranteed.

Active illumination may be beneficial for such situations. An electrowetting screen could thus be equipped with an active backlight corresponding to a LED LCD display. However, by use of such an active backlight, the reflective properties of the electrowetting display are lost and some of the advantages of choosing electrowetting screens over LED screens become superfluous.

The invention is based on the insight that the presence of a light source may be required but only in these situations if visibility of the electrowetting screen may not be guaranteed due to absence of sufficient environmental light and/or light coming from external light sources such as car headlights that illuminate the screen. As such, the electrowetting optical outdoor digital screen according to a first aspect of the invention is provided with one or more internal or external light sources, which are disposed at a distance from, and directed towards the active display. The light sources may be placed at a distance from the active display or may be attached to the bezel as well. Or these light sources can be integrated in the display or integrated in the panels. These light sources can illuminate the electrowetting optical outdoor digital screen when natural light is too low or when car headlights are absent or not directed to the screen.

By adding a presence sensor, the screen can detect whether or not an object such as a person is in or is approaching the field of view of the electrowetting screen. Only upon detecting presence of the object, e.g. a person, a driver module of the light sources is controlled to enable the light sources to emit light and illuminate the active display.

Since the light sources could cause too high levels of light intensity the screen is further equipped with a light intensity sensor for detecting an environmental light intensity level near the active display. The light intensity sensor may detect not only if twilight or night conditions may apply, but also if non-natural light sources may already provide a sufficient level of illumination on the active display. As such, the driver module for driving the one or more light sources, is arranged to control or drive the light sources based on the input received from both the light intensity sensor as well as the presence sensor.

In an example, the driver may be controlled based on a first control level and a second control level, wherein the first control level may be defined as a state in which the one or more light sources are disabled, and the second control level as a state in which the brightness or light intensity level of the one or more light sources is equal to or approximately equal to the maximum design level of the light sources. However, the second control level may also be controlled by the light intensity sensor and set in accordance with the detected environmental light conditions. This way, the light sources may be enabled only when someone is nearby, by detecting presence of that person, and provide just sufficient levels of light to guaranty visibility of the screen, but prevent the glare caused by the reflection of the electrowetting panels of the screen.

In an example, the driver module is arranged for a control of the light intensity level of the one or more light sources in accordance with the detected presence of the object and the detected environmental light intensity level within a predetermined time period.

To prevent over illumination of the screen and to prevent the screen to be illuminated in situations when no one is present, the driver may be arranged to apply a timer variable upon initiation of the light sources. Once presence of a person is detected, the light sources are enabled only for the pre-determined time period and then disabled again. However, as an alternative, the time period could also be initiated not upon detecting presence, but upon a lack of detecting presence, hence, upon determining that the person is out of the viewing area of the screen.

In an example, the driver module is arranged to drive the one or more light sources by control of at least one of the group of light control variables consisting of: light intensity, light temperature, light color, light source distance, number of light sources, level of refraction caused by a lens on the light source.

The light sources may be driven or controlled not only on light intensity level but also on color, color temperature, level of refraction, etc. As such, the driver may be arranged to increase the level of brightness from a first to a second value (e.g. from zero to maximum) upon detecting presence of a person. The driver may however also increase the color temperature in order to increase visibility and to prevent glare.

In an example, the control of the light control variables is performed in least a first, second and third subsequent light control periods, and wherein the light control periods differ from each other.

The invention is also based on the insight that during the period that a person is in the field of view or is approaching or leaving the field of view of the screen different measures may be required. Upon approaching the screen and thus the field of view, it may be important to prevent glare or distraction from discrete enabling of the light sources or too high levels of brightness. However, the person is within reach, hence within the field of view and the attention is directed towards the screen, then is may be required to prefer visibility over preventing glare, and thus during this period of control the intensity may be high and the light may be very bright. Accordingly, in an example, different control periods may be introduced which match with the specific requirements that are needed during that moment in time. Preferably, the light sources may be controlled by an initial, first glare and distracting preventing period which may be followed by a high light intensity or high brightness period in which the attention is drawn to the screen and in which visibility prevails. Even more preferably, the control is performed gradually at an intermediate period.

In an example, at least one of the light control variables varies during each of the subsequent light control periods.

In an example, the driver module is arranged for control of the one or more light sources by varying the light control variable in accordance with a sigmoid function.

In an example, the driver module is arranged for control of the one or more light sources by varying the light control variable in accordance with a Gaussian function.

In an example, the varying is initiated upon detecting presence, and in particular upon detection presence of the object in the field of view of the electrowetting optical outdoor digital screen.

In an example, the one or more external light sources comprise Light Emitting Diode, LED modules.

In an example, the electrowetting optical outdoor digital screen further comprises a battery unit for powering said active display and for powering said one or more external light sources.

In an example, the electrowetting optical outdoor digital screen further comprises a photovoltaic solar panel for converting sunlight into electricity for recharging said battery unit.

Brief description of the drawings

The invention will further be described with reference to the enclosed drawings wherein embodiments of the invention are illustrated, and wherein:

Figure 1 illustrates an outdoor digital screen with electrowetting optical panels in accordance with the invention.

Detailed description of the drawings

Figure 1 shows a visual presentation assembly or an electrowetting optical outdoor digital screen 1. The screen 1 is housed in a frame 4 or a housing 4. The housing of this example shown in Figure 1 is constructed as an outdoor digital display which can for example be used as a road sign. The invention is however not limited solely to such an example but can also be implemented in digital traffic signs, message centers, billboards, wall scrapings, or other indoor or outdoor (active) displays. The housing 4 of Figure 1 comprises, in an illustrative manner, two posts 6 for connecting the housing on or in a foundation or base.

The housing 4 has an active and a passive part. The non-active of passive part 5 forms a cabinet in which one or several of the electrowetting optical panels 3 can be contained. The active part contains the electrowetting optical panels

3. Each housing 4 contains at least one of these panels 3. This can be particularly useful in for example digital traffic signs or in message centers. In the example shown in Figure 1, the housing 4 consists of four optical panels 3. The contours of the individual panels may or may not be visible.

Each of the optical panels contain several electrowetting optical tiles 2a, 2b, 2c. These tiles are preferably rectangular but can also be constructed in other shapes. Each tile 2a, 2b, 2c consists of several pixels and may have more or less pixels depending on the particular application. The dimensions of the individual tiles, and hence also those of the panel 3, can be adapted for particular applications. In a preferred embodiment, the tiles are however 12x8 cm. Preferably, each tile is arranged to display one single character which may include letters, numerical digits, common punctuation marks and whitespaces.

The electrowetting tiles 2a, 2b, 2c of the active area or active display are preferably provided with (not shown) a reflective surface in order to assure high visibility or readability, even under difficult environmental conditions such as in low light conditions. If the environmental conditions are normal, then the visibility of the electrowetting screen is extremely high. However, due to the fact that electrowetting tiles do not have or need a backlight, the visibility of the screen may be less under low light conditions. Although some application of electrowetting screens 1 as road signs, or billboards near roads may provide sufficient light by the headlights of the passing cars, in some applications these headlights are simple not present or the light might not shine sufficiently perpendicular on the screen to guaranty the visibility.

The digital screen 1 according to the invention therefor comprises one or more external light sources 10a, 10b. These light sources may be disposed at a distance from the screen 1, for example through a bar which is attached to the housing 4 of the screen 1. This however may also be a stand-alone light which is not mechanically connected to the screen 1. These light sources 10a, 10b, which preferably comprise one or more LED modules, are arranged to illuminate at least the active part of the screen and are thus directed towards the screen. Preferably the screen 1 is comprised of several of these light sources 10a, 10b to ensure that the full active area can be lit. These light sources 10a, 10b are at least connected with a control unit or driver to power and control these lights. This way the control or driver unit may enable the light sources to be powered on and off at a certain moment in time and for a certain time duration. Preferably, the control unit is capable of controlling several properties of the light source such as the light intensity, the light color, number of light sources that are simultaneously power-on, a level of refraction caused by a lens on the light source, etc.

Thereby the control unit may not only be arranged to control the light sources 10a, 10b to switch between two distinct operational modes, i.e. “on” or “off”, but could also operate the light sources to gradually transition between the “on” and “off” modes, for example by step wise or gradually increasing the intensity or illumination level, color temperature, etc. The control unit may also be arranged to have different transitional profiles between changing from “on” to “off” as compared to the change vise versa. This way the transition profile can be matched to certain applications or desirable behavior of the persons for which the screen is to display information. For example, it could be desirable to have a screen which, upon detecting presence of a person which is in or near the field of view of the screen (i.e. the location at which the person can read the information that is displayed on the screen), rapidly increased the light intensity. This may attract the attention of the person without causing abrupt distraction which may cause dangerous traffic situations. Once the attention has been drawn, the screen may be controlled to display the information. This information may already be present on the screen, i.e. in which the tiles are already controlled to activate certain pixels to display a certain character, or the tiles could be “off” and only activated to control display of the character once the lights are activated.

In order to detect whether a person is preset and is in particular in, near or approaching the field of view of the screen 1, the screen can be equipped with a presence sensor 8. The sensor, which can be a proximity sensor, an occupancy sensor, a passive infrared (PIR), microwave, ultrasonic, tomographic motion, video camera, gesture detector, or laser based sensor system. The sensor is electronically connected to the control unit of the screen 1 to pass information towards the control unit such that the control unit can activate a device or action upon detecting presence by the sensor 8. In the present invention, the sensor is arranged to trigger the activation of the lights, e.g. to switch to an “on” state, an “off” state, or a rapid, slow, gradual or stepwise transition between these states. As such, the screen 1 is capable of detecting when to switch between a passive mode and an active or wake make, wherein in the passive mode the screen consumes little power and draws less attention or gives little (light) disturbance to the environment. But, when the screen 1 detects a person in, near or approaching the field of view, the screen 1 can switch to the active mode in which (a bit) more power is consumed due to the activation of the light units 10a, 10b and in which the attention is drawn towards the screen 1 or at least the active area of the screen.

As indicated, the electrowetting display 1 does not require a backlight, at least not in environmental conditions with sufficient natural light, but may require additional light if the light level drops, for example during the evening or at night. If the natural light levels are very low, such as during night, then only very little artificial light is needed. However, during the evening, or when a car passes and shines on the screen with the headlights, then a higher level of artificial light is needed in order to ensure visibility of the screen. To this end, the screen may be equipped with an additional sensor 9 which is able to determine the light intensity on the screen which could be caused by natural light or by artificial light(s) that shine of the screen.

Thus, the light intensity sensor may detect not only if twilight or night conditions may apply, but also if non-natural light sources may already provide a sufficient level of illumination on the active display. As such, the driver module for driving the one or more light sources, is arranged to control or drive the light sources based on the input received from both the light intensity sensor as well as the presence sensor.

As will be appreciated by the person skilled in the art, the present invention may be practiced otherwise than as specifically described herein. Obvious modifications to the embodiments disclosed, and specific design choices, will be apparent to the skilled reader. The scope of the invention is only defined by the appended claims.

Claims

1. Electrowetting optical digital outer screen, comprising:

an active display consisting of:

one or more electrowetting optical panels comprising a reflective layer for reflecting the incident light back through the panel, as well as:

- a housing for housing the one or more electrowetting optical panels:

one or more internal or external light sources recorded at a distance from and directed towards the active display for illuminating the electrowetting optical digital outdoor screen;

a sensor for detecting the presence of an object in a field of view of the electrowetting optical digital outer screen;

a light intensity sensor for detecting an ambient light intensity level near the active display;

a driver module for controlling the one or more light sources, the driver module being arranged for controlling a light intensity level of the one or more light sources according to the detected presence of the objects and the detected ambient light intensity level.

The electrowetting optical digital outer screen of claim 1, wherein the driver module is arranged to control the light intensity level of the one or more light sources according to the detected presence of the objects and the detected ambient light intensity level within a predetermined time period.

The electrowetting optical digital outer screen according to claim 1 or 2, wherein the driver module is arranged for controlling the one or more multiple light vouchers by controlling at least one of the group of a light control variable consisting of light intensity, light temperature, light color, light source distance , number of light sources, level of refraction caused by a lens on the light source.

The electrowetting optical digital outer screen according to claim 3, wherein the control of the light of the light control variables is carried out in at least a first, second and a third consecutive light control periods, and wherein the light control periods differ from each other.

The electrowetting optical digital outer screen of claim 5, wherein at least one of light control variables varies during each of the successive light control periods.

The electrowetting optical digital outer screen according to any one of claims 3-5, wherein the driver module is arranged to control the one or more light sources by varying the light control variables according to a sigmoid function.

The electrowetting optical digital outer screen according to any one of claims 3-5, wherein the control module is arranged for controlling the one or more light sources by varying the light control variables according to a Gaussian function.

The electrowetting optical digital outer screen according to any one of claims 6-7, wherein the varying is initiated by detecting presence, and in particular when detecting presence of the object in the field of view of the electrowetting optical digital outer screen.

An electrowetting optical digital outer screen according to any one of the preceding claims, wherein the one or more external light sources comprise light-emitting diode, LED, modules.

An electrowetting optical digital outer screen according to any of the preceding claims, further comprising:

a battery unit for powering the active display and energizing the one or more external light sources.

The electrowetting optical digital outer screen of claim 10, further comprising:

a photovoltaic solar panel for converting solar light into electricity for charging the battery unit.