Image generation method with a fluorescence projection screen and a uv radiation source

The invention relates to a projection system comprising a radiation source for generating electromagnetic radiation outside the visible wavelength range, an imaging unit which can be irradiated by the radiation source and a projection screen, having a radiation-sensitive surface which, when excited by said invisible radiation, can emit fluorescent light in the visible wavelength range.

The invention further relates to a method for the imaging representation of information on a projection screen irradiated from a radiation source via an imaging unit with electromagnetic radiation outside the visible wavelength range, with a radiation-sensitive surface which, upon excitation with said invisible radiation, can emit fluorescent light in the visible wavelength range.

From the <patcit id="pcit0001" dnum="JP11041548A"><text>JP 110 41 548 A</text></patcit> A projection system and a method of the aforementioned type are known, wherein ultraviolet (UV) radiation is emitted from a radiation source. A two-dimensional mirror field with a plurality of micro-mirrors which can be controlled in their angular orientation on a silicon substrate which is irradiated by the UV source is modulated onto the UV radiation with a two-dimensional image signal which is reflected onto a fluorescence projection screen, each micro-mirror Corresponds to a pixel (pixel). In a radiation-sensitive layer of the fluorescence projection screen, three spatially different subpixels, each of which are made of different materials, are arranged in the region of each pixel. These different materials are excited by irradiation with UV radiation of the same wavelength range for the emission of visible fluorescent light in material-specifically different wavelength regions.

One disadvantage of this known projection system and method is, on the one hand, the complicated production of the projection screen, in which different materials have to be arranged with great spatial precision. This leads to high reject rates and thus to high production costs, in particular in the case of larger-area displays. In addition, the maximum achievable resolution is greatly reduced. On the other hand, such a system and method are highly sensitive with respect to the relative alignment of the individual components with respect to one another. Even small deflections from the ideal position result in a general color shift of the display because, instead of the correct subpixel, an adjacent subpixel is irradiated, but emits light of a different color. The known devices or the known method are therefore only suitable for small displays with components which are rigidly connected to one another and are as low as possible vibrating.

From the <patcit id="pcit0002" dnum="US5684621A"><text>US 5,684,621 A</text></patcit> is further e known in projection system for displaying three-dimensional images. A cuboid consisting of a rare earth-doped, crystalline or glassy, ​​transparent material in the visible and infrared (IR) wavelength range serves as a projection volume. The projection volume is scanned by two IR-emitting lasers, which are controlled so that their beams intersect at specific points. In these points, the energy density of the radiation is so high that there is a considerable degree of so-called two-photon excitation, ie, simultaneous absorption of two IR photons by a rare earth ion. The ion relaxes to its basic state by emitting a fluorescence photon in the visible wavelength range, as a result of which the respective intersection of the laser beams appears as a light point. Control of the color of the luminous point is possible by changing the wavelength of at least one of the two lasers. The rare earth ions firmly embedded in the crystal or glass structure of the base material have different, relatively sharp energy levels which can be excited by different excitation energies and relax to the basic state by emitting different, ie, differently colored photons.

A disadvantage of this known projection system, however, is the large space requirement of the projection volume, as well as the complicated control of the lasers, which is highly sensitive with respect to the relative orientation of their components.

Dieselben cons also apply to the from the <patcit id="pcit0003" dnum="US5684621A"><text>US 5,684,621</text></patcit> the <patcit id="pcit0004" dnum="US5764403A"><text>US 5,764,403 A</text></patcit>, Which is substantially functionally the same. The projection volume or the screen is here, however, flat, but also three-dimensional as a radiation-sensitive cuboid, into which radiation is irradiated in a plane and which is viewed perpendicularly thereto. The height of the cuboid therefore plays an essential role and can not be reduced as desired. Other imaging procedures are out<patcit id="pcit0005" dnum="US2002063946A"><text>US 2002 063946</text></patcit> and <patcit id="pcit0006" dnum="EP0455449A"><text>EP 0 455 449</text></patcit> known.

It is therefore an object of the present invention to provide a method for imaging in motor vehicles which is favorably suited for manufacturing and robust in application and therefore for use in a motor vehicle.

This object is achieved according to the invention by the features of claim 1. The radiation-sensitive surface of the projection screen consists of a material that emits fluorescence light of different wavelengths independently of the wavelength of the excitation radiation and that the radiation source can emit excitation radiation of different wavelengths.

By the design of the projection screen, for example by using one of the projection screens shown in FIG <patcit id="pcit0007" dnum="US5684621A"><text>US 5,684,621</text></patcit> The problem of controlling different colors in the display can be shifted from the spatial orientation of all components to the substantially simpler handling of different excitation wavelengths. Thus, on the one hand, a considerably greater flexibility with regard to the possible applications, but on the other hand a much more robust design is possible than with the prior art. In particular, vibrations of the system only lead to a corresponding spatial displacement of the projection image, but not to a color shift, so that an insert is made possible, for example, in motor vehicles.

In the <patcit id="pcit0008" dnum="US5684621A"><text>US 5,684,621</text></patcit> As materials which are appropriately disclosed for the production of projection volumes, can be readily integrated into projection screens of different shapes, either essentially planar carriers themselves being doped with suitable ions or coated with doped material, for example by coating or evaporation.

According to a preferred embodiment, the radiation source comprises a laser with a controllable output wavelength. As a result, the control of the system is particularly uncomplicated, since the advantageous intensity and focussing properties of the laser can be utilized and, at the same time, only the control of a beam can be achieved.

However, according to another embodiment, it is also possible that the radiation source comprises a plurality of lasers of different output wavelengths. As a result, the control is less complicated, but the image formation can take place faster, which allows for larger, higher-resolution and 1-fader or low-light projections.

In the embodiment according to the invention, the radiation source emits electromagnetic radiation in the ultraviolet wavelength range. This is based on the realization that fluorescent materials generally have a negative Stokes shift, ie, a higher-energy, ie, shorter-wave excitation, is required for the emission of visible light. This also applies to the products described in the<patcit id="pcit0009" dnum="US5684621A"><text>US 5,684,621</text></patcit> As materials which are appropriately disclosed for the production of projection volumes. However, due to the spatial representation desired there, no UV excitation radiation could be used since this fluorescence would generate over the entire absorption path of the UV beam and not only at the desired image point. However, in the present case of a substantially planar projection screen, directly higher-energy excitation radiation can also be used.

In another exemplary embodiment, however, it is also possible for the radiation source to emit electromagnetic radiation in the infrared wavelength range. However, the intensity of the beam must be so high that two-photon absorption is sufficient in the radiation-sensitive layer of the projection screen. This can be done, for example, by using a plurality of beams intersecting in the radiation-sensitive layer or by using a single, sufficiently intense beam.

In a particularly advantageous embodiment, a plurality of projection screens are provided which are irradiated by a radiation source via an imaging unit. This has the advantage that several viewers have an optimal view of the displayed information at different locations, or that different information can be displayed to a viewer at different points in a clear manner, whereby only one opto-electronic unit is required at a time. Thus, by far the most expensive and expensive part of the system has to be provided only once.

Preferably, the projection system or the projection screen is arranged in or on a motor vehicle. This results in flexible possibilities for information and / or entertainment in the motor vehicle, which corresponds to the steadily increasing number of monitoring and control parameters in modern motor vehicles, in particular cars, and the related problems of the clear and clear presentation of the information.

Particularly preferred is an embodiment in which at least one projection screen is arranged in the region of the dashboard of a motor vehicle. The customary arrangement of displays in the motor vehicle can thus be maintained, but a fixed installation of specific display devices, such as tachometers, speed indicators, etc., is avoided. Rather, it is possible to create user-specific and / or situation-specific displays by appropriate programming of the imaging unit.

In a further advantageous embodiment it is provided that at least one projection screen is arranged in the region of a side window or the windshield of a motor vehicle. This offers the advantage that the driver can read the displays without having to look completely away from traffic.

Furthermore, it can be provided that at least one projection screen is arranged in the region of the rear side of the driver's and / or passenger's seat of a motor vehicle. This makes it possible to present on the seats during the ride entertainment in the form of video, TV or computer games. The control of the imaging unit must, of course, be suitably designed for this purpose.

The imaging unit may be embodied in various manners known to those skilled in the art. Suitable for this purpose are microelectromechanical systems (MEM). These include DMD microdisplays (DMD), biaxially deflectable micro mirrors and GLV (Grating light Valve). Also suitable are designs such as an LCOS microdisplay (liquid crystal on silicon), a scanning system comprising two galvanometer mirrors, a combination of galvanometer mirror and MRS (mechanical resonant scanner) or two MRSs.

Such elements as well as the associated controls in hardware and software are commercially available and can thus be integrated cost-effectively. They can be operated together with laser or other light sources. The imaging unit can be controlled by a programmable computer.

In an advantageous embodiment, provision may be made for arranging the radiation source and the imaging unit behind the projection screen from the viewer. This prevents the viewer from shading the projection screen against the imaging unit, in particular in narrow driver's cabins of a motor vehicle. Rather, concealed installation in the vehicle is possible.

On the other hand, it is also possible for the radiation source and the imaging unit to be arranged in front of the projection screen from the viewer. This also makes it possible to project onto screens which are not built-back, such as window panes of a motor vehicle.

It is particularly advantageous if the projection screen is provided with a coating which is impermeable or absorbing for the excitation radiation used. This must, of course, be applied to the side of the screen facing away from the imaging unit. This prevents the viewer from being exposed to the excitation radiation - in transmission or in reflection - which is an important safety aspect in particular in the case of intense laser radiation.

In the method according to the invention, fluorescence light of different colors is emitted by varying the wavelength of the invisible electromagnetic radiation by the radiation-sensitive surface of the projection screen, which consists of a material that emits independent fluorescence light of different wavelengths depending on the wavelength of the excitation radiation.

Due to the fact that the fluorescent light of different colors or wavelengths is emitted in dependence on the wavelength of the excitation radiation in a location independent manner and by variation of the wavelength of the invisible electromagnetic radiation, a cost-effective and robust representation of information is possible. As stated above, vibrations of the system do not lead to a color shift so that the method can also be used in motor vehicles.

Further details can be gathered from the following detailed description and the appended drawings in which preferred embodiments are illustrated by way of example.

In the drawings:<dl id="dl0001"><dt>FIG. 1:</dt><dd>A schematic representation of the energy levels of a fluorophore,</dd><dt>FIG. 2:</dt><dd>A schematic representation of a first embodiment of a projection system,</dd><dt>FIG. 3:</dt><dd>A schematic representation of a second embodiment of a projection system,</dd><dt>FIG. 4:</dt><dd>5 shows a schematic representation of a third embodiment of a projection system.</dd></dl>

FIG. 1 shows a schematic representation of the energy levels of a fluorophore, ie a fluorescent molecule, ion, atom or the like, for example a rare earth ion in a glass or crystalline carrier material. Normally, the ion is in its basic state S0, which is shown in FIG. 1 as a thick line. The phononic sub-levels shown as thinner lines are generally not stimulated. By irradiation of an energy hv, for example in the form of electromagnetic radiation, the ion can be raised to a higher energetic state. However, this occurs only if the irradiated energy corresponds to the energy gap between the basic state S0 and a higher state S1 or S2. These excitation energies are denoted by hvex1 and hvex2 in FIG. 1, which correspond to radiation of the wavelengths λex1 = c / vex1 and λex2 = c / vex2, where c is the light velocity, v is the frequency and h is the Planckian quantum of action. The energy gap can also be bridged by multi-photon absorption, ie simultaneous absorption of several low-energy photons. However, this is a physically different phenomenon which occurs with a much lesser probability. Since the incidence can also stimulate higher phononic levels, indicated by the thinner lines above the excited states, the absorption bands are not completely sharp, but have a more or less broad spectrum. After the lifetime of the excited state, which usually moves in the ns region, the ion falls from its excited state to the ground state, a photon of the energy hvem1 or hvem2 being emitted. This radiation is usually longer-wave than the excitation radiation, since the excited ion passes before the emission of the fluorescence photon by internal conversion into the lowest phononic level of the excited state, but on the other hand it can fall back to a higher phononic level of the basic state. This is referred to as a negative Stokes shift. Thus, it is possible to produce fluorescence light in the visible spectral range by excitation in the UV range in the case of suitably selected material. As clearly shown in FIG. 1, the wavelength, ie, the color of the fluorescent light, essentially depends on the excited state from which the ion returns to its ground state. However, as explained above, this is primarily dependent on the wavelength of the excitation radiation. Thus, it is possible to produce different colors of fluorescent light by suitable control of the excitation wavelengths.

FIG. 2 shows a projection system 1, consisting of a projection unit 2 and a projection screen 3. The projection unit 1 comprises a radiation source and an imaging unit, both of which are not shown in the drawing. The radiation source can be, for example, a UV laser with a controllable wavelength or a battery of, for example, three UV lasers of fixed but different wavelengths, each of which is adapted to excite red, green or blue fluorescence. In addition to microelectromechanical systems (MEM), imaging devices are, in particular, computer-controlled scanning systems comprising two galvanometer mirrors, biaxially deflectable micro-mirrors, LCOS microdisplays or DMD microdisplays. In the exemplary embodiment of FIG. 2, the projection screen 3 is implemented in the region of a side window 4 of a motor vehicle door 5. This can be done, for example, by the fact that the glass of the side window 4 is doped with suitable ions in the region of the projection screen 3 or carries a corresponding coating, for example as a lacquer coating or evaporation.

FIG. 3 shows a further embodiment of the projection system 1 '. The projection screen 3 ', which is irradiated by the projection unit 2', is arranged here in the region of the dashboard 6 of a motor vehicle.

4, a third embodiment of the projection system 1 "is shown. The projection screen 3", which is irradiated by the projection unit 2 ", is arranged here in the rear region of the headrest 7 of a driver's or passenger seat 8 of a motor vehicle.

Many further, advantageous variants are conceivable. In particular, further surfaces in the region of interior or exterior mirrors, the center console or the windshield of a vehicle can be used as a projection screen or provided with a projection screen.

The invention is defined in the following claim.