No assignee for this patent application has been made.
Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to a display device having a liquid crystal display, for example a head-up display, and to a method for protecting the liquid crystal display of a corresponding display device against incident solar radiation.
"Display devices having liquid crystal displays should not be exposed to direct and intense optical radiation, such as solar radiation, for a prolonged period of time. Owing to the radiation that is incident on the liquid crystal display, the temperature of the liquid crystal display increases and the display may lose its physical properties if the temperature increases too much. In this case, the display clears, and any displayed image information is lost. Even though such a process is generally reversible, irreversible damage may occur if the liquid crystal display is exposed for a prolonged period of time or relatively frequently.
"In motor vehicles having a head-up display (HUD) as a display device, solar rays can pass through a windscreen of the vehicle and, in the case of an unfavorable position of the Sun, impinge directly on the display. The head-up display or front-view display projects an image through a beam path onto the windscreen of the vehicle, which serves as the projection surface, which image can be perceived by the occupants of the vehicle as a virtual image. However, as long as the optical radiation is incident at a particular angle, not only the image is projected, but also the radiation that is incident on the vehicle is guided directly onto the display and concentrated on the display surface owing to a mirror optical system present in the beam path of the head-up display. If the liquid crystal display is irreversibly damaged, for example when stopping in the sunshine for a long period of time, what is referred to as a 'bonanza effect' can occur in a virtual image displayed by the head-up display, in which artifacts caused by the irreversible damage remain visible in the virtual image.
"In order to avoid such irreversible damage to a liquid crystal display, in the case of the head-up displays known from the prior art, for example a polarization filter is mounted in front of the display, which lets only a portion of the incident radiation having a particular polarization direction through, with this polarization direction corresponding to a polarization direction of the display. By way of example, only s-polarized light may pass through the polarization filter. As a result, heating of the liquid crystal display is reduced and the point of time at which the bonanza effect first occurs is delayed. The disadvantage here is that the polarization filter decreases the performance and image sharpness of the liquid crystal monitor and that increased power consumption and associated heat losses are necessary in order to achieve a sufficiently high transmission of the liquid crystal display despite the filters."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "It is therefore an object of the present invention to provide a display device having a liquid crystal display which permits the avoidance of damage to the liquid crystal display on account of very high solar radiation, without thereby negatively affecting a reproduction quality of the display device. It is a further object of the invention to provide a method for protecting a liquid crystal display with which the disadvantage can be avoided, but which permits the reliable avoidance of any irreversible damage to the liquid crystal display on account of solar radiation.
"This object is achieved according to the invention by a display device and a method as described herein.
"According to one aspect of the present invention, the proposed display device comprises a liquid crystal display for reproducing an image, a sensor system for ascertaining the illuminance of incident optical radiation and for determining a current position of the Sun relative to the liquid crystal display, an adjustable shading device for protecting the liquid crystal display against the incident optical radiation, and a control unit. The term 'optical radiation' is not intended to be used solely to be capable of denoting visible light with a wavelength of 400 nm to 780 nm, but also infrared light and/or ultraviolet light. The control unit is adapted to check whether the illuminance ascertained by the sensor system is above a predetermined threshold value and whether the current position of the Sun lies within a predetermined angular range. Furthermore, the control unit is further adapted to actuate, in dependence on a result of this check, the shading device such that it interrupts a beam path of a portion of the optical radiation that is incident on the liquid crystal display and thus protects the liquid crystal display against damage.
"The illuminance and the current position of the Sun are two parameters that are easy to determine and indicate whether the intensity of the optical radiation is at all sufficient to damage the liquid crystal display and whether said radiation is incident on the liquid crystal display. By checking these parameters using the control unit, it is thus possible to reliably determine whether the liquid crystal display can be damaged. The actuation of the shading device for protecting the liquid crystal display in dependence on the result of the check makes it possible for the display device to be operated normally as long as any risk of damage to the liquid crystal display is ruled out and therefore also for protection mechanisms that adversely affect normal operation and are provided from the start to be omitted, while still protecting the liquid crystal display in the case of risk of damage and to interrupt image reproduction if a disturbance of the image reproduction owing to the failing liquid crystal display is expected in any case.
"The predetermined angular range of the position of the Sun can cover those angles in which the optical radiation is incident directly on the liquid crystal display. The predetermined threshold value is preferably defined by the value of the illuminance from which irreversible damage to the liquid crystal display occurs if it is exposed to the incident optical radiation.
"In one aspect, the shading device is preferably adjustable between an activated state, in which it interrupts the beam path, and a non-activated state. The control unit can then be adapted to activate the shading device exactly at that point at which a condition, defined in dependence on the result of the check, is met. A suitable definition of the condition can be used to ensure that the beam path is interrupted only if temporary or irreversible damage to the liquid crystal display is expected in any case and thus image reproduction would be disturbed or interrupted. This condition can be such that only if both the preconditions are present, that is to say if the ascertained illuminance is above the threshold value and the Sun is at a particular angle, the liquid crystal display is protected and reproduction of the image is interrupted, so that premature interruption of the beam path and thus of the image reproduction is prevented. The condition can also require the presence of additional situations, such as a critical temperature being exceeded.
"According to one aspect, provision may accordingly be made for the display device to have a temperature sensor mounted in or on the liquid crystal display or arranged in a surrounding area of the liquid crystal display, which temperature sensor measures a temperature of the liquid crystal display or of an area surrounding the liquid crystal display. The control unit can be adapted in this case such that the shading device is activated only if the temperature measured by the temperature sensor exceeds a predetermined threshold value. The condition is in that case defined as requiring a limit temperature determined by the threshold value to be exceeded. Owing to the threshold value of the temperature that is measured preferably directly on the temperature-sensitive liquid crystal display being predetermined in a suitable manner, the liquid crystal display is interrupted only in the case of imminent damage, such that image reproduction continues up to this point.
"The sensor system can, according to one aspect, comprise a computing unit adapted to calculate the current position of the Sun from a date, a time of day, a location and a compass direction. Owing to the calculation it is possible for a complicated measurement of the position of the Sun to be avoided, especially since the current position of the Sun is calculable reliably and uniquely from these parameters. The location and the compass direction are preferably defined by geographic position data, particularly preferably GPS data. The use of GPS data enables precise and simple determination of the location and the compass direction in which the display device is oriented.
"In an advantageously simple-to-realize configuration, the shading device comprises a screen that is foldable in front of the liquid crystal display and/or into the beam path in order to interrupt the beam path. Alternatively or additionally, the shading device can comprise a pivotable mirror arranged in the beam path of the incident optical radiation and serve to image the images reproduced on the liquid crystal display. By using the mirror, which is arranged in the beam path of the display device in any case, as the shading device or part of the shading device, additional components can be largely dispensed with. The beam path can therefore be interrupted and the liquid crystal display protected against incident optical radiation very simply by tilting the mirror.
"In one aspect, the display device is preferably a head-up display. In a head-up display, the liquid crystal display is generally not capable of being viewed directly by a user, such that radiation that is incident on the liquid crystal display also remains unnoticed. In display devices of this type it is therefore particularly favorable for an automatically activatable protection device to be provided for such display types.
"In addition, provision may be made for the sensor system or a part thereof to be arranged spatially separate from the liquid crystal display. Owing to the spatial separation of sensor system and liquid crystal display, already available sensor systems can be used for the display device, for example a brightness sensor, which may be present already as a day/night sensor for automatically actuating headlamps and rear position lamps. In this way, the described display device can be implemented with a minimum of additional outlay. The sensor system is preferably connected, via a bus system, particularly preferably via a CAN bus system, to the control unit for transmitting the ascertained illuminance. Such bus systems have the advantage of permitting a quick data exchange without major configuration problems. Moreover, already existing sensor systems that provide the data via a bus system can thus be incorporated in the display device in a simple manner. A CAN bus system is a common bus system in the field of motor vehicles.
"A vehicle, preferably a motor vehicle such as a car or a truck, advantageously comprises the display device with the described properties. In vehicles, the risk of damage to the liquid crystal display, owing to prolonged driving or stopping in sunshine, is particularly high, and therefore the display device can be used advantageously in this case.
"In one advantageous aspect, provision may be made for the sensor system or part of the sensor system with which the illuminance is measured to be arranged on a dashboard and/or below a windscreen of the vehicle. The incident radiation can be detected simply in this case since no shadow-casting objects obstruct it. If the display device is a head-up display, the windscreen is used as the projection surface or as a semi-transparent mirror for imaging the reproduced images such that the optical radiation that is incident on the windscreen can reach the liquid crystal display through the beam path of the display device. Mounting the sensor system in this location therefore has the advantage in this case that the illuminance is measured at the place where the radiation that is guided to the liquid crystal display is incident.
"According to another aspect of the present invention, a correspondingly advantageous method for protecting a liquid crystal display of a display device against incident solar radiation comprises the following steps:
"ascertaining an illuminance of a solar radiation that is incident in an area surrounding the display device; determining a current position of the Sun relative to the liquid crystal display; transmitting the ascertained illuminance and the determined current position of the Sun to a control unit and checking, using the control unit, whether the ascertained illuminance is above a predetermined threshold value of the illuminance and whether the current position of the Sun lies within a predetermined angular range; in dependence on a result of the check, automatically interrupting a beam path of a portion of the solar radiation that is incident on the liquid crystal display using a shading device actuated by the control unit.
"The ascertainment of the illuminance makes it possible to check whether the illuminance is sufficiently high to damage the liquid crystal display or put it at risk, while it is possible, by determining the current position of the Sun relative to the liquid crystal display, to ascertain whether the liquid crystal display is exposed to part of the incident solar radiation at all. It is thus possible to protect the liquid crystal display against incident solar radiation only in that case by using the shading device actuated by the control unit, and to thereby ensure image reproduction via the display device for as long as possible.
"In one advantageous aspect, the current position of the Sun is calculated, using a computing unit, from a date, a time of day, a location and a compass direction. On account of this, no complicated direct measurement of the position of the Sun is necessary while it is still possible to reliably determine the position of the Sun. The location and the compass direction are preferably calculated from geographic position data, particularly preferably GPS data. Geographic position data permit simple determination of that parameters.
"In another aspect, the method may further provide for a temperature of the liquid crystal display to be ascertained by a temperature sensor and for the beam path of the incident optical radiation to be automatically interrupted only if a predetermined threshold value of the temperature is exceeded. The threshold value can be defined for example such that the beam path is interrupted only if a limit temperature at which a temporary or irreversible damage to the liquid crystal display occurs or is imminent is exceeded and the image reproduction is consequently maintained for as long as possible.
"The method can advantageously be carried out using the previously described display device.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIGS. 1 to 3 illustrate exemplary embodiments of the invention, which are explained using three figures below, in which:
"FIG. 1 is a schematic illustration of a display device with optical radiation incident on a liquid crystal display;
"FIG. 2 is a flowchart of a method for protecting a liquid crystal display; and
"FIG. 3 is a flowchart of a further embodiment of the method for protecting a liquid crystal display."
For more information, see this patent application: Pawusch, Wolfgang-Peter. Display Device Having a Liquid Crystal Display and Method for Protecting a Liquid Crystal Display. Filed
Keywords for this news article include: Patents.
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