Abstract:
A semiconductor radiation source, having at least two light sources which are fixed on a common base body and so light can be emitted gently over a total emission spectrum, the first light source having a short-wave, in particular from 400 to 430 nm emission spectrum, and the second light source having a longer-wave, in particular from approximately 450 to 480 nm emission spectrum. The first light source ( 16 ) is arranged in an optical axis ( 22 ) and the second light source ( 18 ) has at least two chips ( 24, 26, 28, 30 ) which are arranged in particular symmetrically with respect to one another and with respect to the optical axis ( 22 ) and in a manner surrounding the optical axis ( 22 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims foreign priority benefits under 35 U.S.C. §119 from German patent application Ser. No. 10 2006 015 336.7 filed Apr. 3, 2006. 
   TECHNICAL FIELD 
   The present invention relates to a semiconductor radiation source which may be used as a light curing device, and more particularly to such a device which includes at least two light sources which are fixed on a common base body and by means of which light can be emitted gently over differing emission spectrums. 
   BACKGROUND OF THE INVENTION 
   It has been known for a long time to have a radiation source using groups of light sources which emit light having different wavelengths, see for example from U.S. Pat. No. 4,568,558 and also EP 879 582. In the case of the first-mentioned solution, dental material is intended firstly to be partly polymerized with a wavelength of between 400 and 450 nm and subsequently to be completely polymerized with a wavelength of 350 nm. By contrast, LED chips having various wavelengths such as 435, 450 and 470 nm are intended to be used in the case of the second-mentioned solution. 
   The LEDs are arranged in bundled fashion and are uniformly supplied with voltage, with the result that selective driving is not possible. Different photoinitiators having different spectral sensitivities cannot be taken into account with this solution. 
   In the last 10 years numerous investigations have been undertaken in order to improve the effectiveness of the photopolymerization, in order to enable shorter treatment cycles for the dentist or, if appropriate, the dental technician without jeopardizing the reliability of the dental restoration upon full curing. 
   Accordingly, various photopolymerizable materials have been investigated and used, there generally having been the tendency to realize a greatest possible spectral overlap between the emission spectra of the light sources used and the sensitivity spectra of the photoiniators used. This of course necessitates the use of different spectral emission spectra which have been striven for in different photoinitiators. 
   Recently, so-called dual-curing systems have also been proposed, the solution 
   in accordance with U.S. Pat. No. 6,866,506 enabling the curing result to be significantly improved. This solution provides two semiconductor radiation sources having different emission maxima which are spaced apart from one another and are each, in particular, at different points in time. 
   In the case of this solution, however, a multiplicity of chips is used for providing the light power, so that this solution is more likely to be considered for high-quality light curing devices. In order to provide the desired curing, use is made of chips having high light emission which are comparatively expensive, moreover, and which emit an intensive light radiation. This is all the more so since, in the case of this solution, the curing is performed by a respective group of chips successively, so that a subgroup of the chips must also have a power sufficient for the curing. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   Against this background the invention is based on the object of providing a radiation source which can be used universally, is comparatively cost-effective to produce, but nevertheless enables a good radiation efficiency. 
   The invention provides for the light sources to be divided into two light sources, both light sources, which may each comprise a plurality of chips, being arranged in a central region of a common base body. The light sources therefore occupy only a very small portion—for example 10% or 15% or even just 5%—of the surface of the base body. 
   The invention provides for the first light source to be arranged in an optical axis and the second light source to have at least two chips which are arranged in particular symmetrically with respect to one another and with respect to the optical axis and in a manner surrounding the optical axis. 
   This surprisingly leads to a markedly high luminous efficiency in comparison with the previous solutions. By dispensing with a multiplicity of light sources that are rather arranged peripherally, the luminous efficiency can be significantly increased with corresponding converging lenses. This means that a significantly higher optical radiation can be emitted for the same introduced electrical energy. This effect is reinforced by the fact that a base body which is large in relation to the chip area is available when the peripheral chips are dispensed with, said base body accordingly acting as a cold buffer. The heat dissipation is therefore particularly high, precisely also during pulsed operation, so that the chips can basically be operated in the full-load range or even in the overload range without their service life being impaired. 
   The invention provides for all the chips to be arranged near the optical axis. A first light source is arranged in the optical axis, and a second light source is arranged in a manner surrounding the latter and closely adjacent to the latter. 
   The second light source is preferably arranged symmetrically, and it goes without saying that at least two chips are required for this symmetrical arrangement. Preferably, the second light source can be formed from four chips each arranged along an edge of the square central chip, to be precise with a smallest possible gap between the individual chips. 
   Overall, this produces a cross comprising the first light source as central chip and the four chips of the second light source, which surround the chip of the first light source in a manner adjoining it. 
   This surprisingly enables the luminous efficiency to be significantly increased, and it goes without saying that any suitable means can be used, that is to say for example a covering lens that covers the chips and concentrates emerging light, and also, if appropriate, a converging lens, which enables further focusing of the emitted light radiation. 
   On account of the small dimensions of the chips overall it is also possible, however, to act directly upon the introduction end of an optical waveguide. 
   It is particularly expedient according to the invention that as a result of dividing the light emission between two light sources, it is possible to excite photoinitiators in light-curing compositions in any suitable manner. By way of example, the first light source may be designed for the excitation of Lucerin in the wavelength range of 400 to 430 nm and the second light source may be designed for the excitation of camphorquinone for the wavelength range of between 450 and 480 nm. 
   When using dental compositions with both photoinitiators, it is then possible for both light sources to be switched on jointly, while it is also possible for each light source to be switched on separately depending on the material used. 
   In a particularly expedient refinement, the radiation source according to the invention can be used multifunctionally, that it to say not only as a light curing device, but also as an illumination device, in particular also for inspecting whether or not there are tooth gaps given the presence of plastic fillings in the patient&#39;s mouth. 
   A handheld device shaped in the manner of a handheld light curing device is particularly well suited to this because, by virtue of the usually fixed optical waveguide and the slender form, the light source can be directly introduced into the patient&#39;s mouth in a targeted manner and the illumination can be performed there without glare. 
   Preferably, for inspecting the edge gap situation, only one of the light sources, for example the first, weaker light source, is switched on in order that no glare effect arises. In this context, it goes without saying that the inspection wavelength can also be adapted to the requirements within wide ranges; it is preferably the shorter wavelength emitted by the first light source, which lies in the optical axis. 
   A further advantageous refinement provides for the second light source to have four chips which are arranged in the manner of a cross around the first light source, and for the first light source to have one chip. 
   A further advantageous refinement provides for the light sources to closely adjoin one another, the width of the gap that remains between them amounting to less than one fifth, in particular approximately one tenth, of the diameter of each chip. The gap width is preferably 0.5 to 2 mm, and in particular approximately 1 mm. 
   A further advantageous refinement provides for the first and second light sources to be arranged in a central region of the base body. 
   A further advantageous refinement provides for at least the first light source, in particular all the light sources, to be arranged in a central projection, in particular having a height of between 0.1 and 1 mm, of the base body. 
   A further advantageous refinement provides for the form of the projection to follow that of the light sources, and in particular essentially to have the form of a cross. 
   A further advantageous refinement provides for the light sources to be fixed on the base body or the projection by means of an adhesive bonding connection or by means of a soldering connection. 
   A further advantageous refinement provides for the base body and/or the projection to have a thermal conductivity which is better than 0.5 C/W. 
   A further advantageous refinement provides for the base body and/or the projection to be electrically conductive. 
   A further advantageous refinement provides for the base body to at least partly comprise copper. 
   A further advantageous refinement provides for the base body to be at least partly coated with gold or nickel-gold. 
   A further advantageous refinement provides for a printed circuit board to be arranged in a manner surrounding a central region, in particular the projection, of the base body, said printed circuit board carrying electrical connection contacts. 
   A further advantageous refinement provides for electrical connection contacts for the light sources to be arranged as zones on the outer periphery of the base body, in particular on a printed circuit board, and for bonding wires to extend from the chips to the electrical connection contacts. 
   A further advantageous refinement provides for the light sources to be covered by a convex covering lens, which is formed in plane fashion in particular on the side facing the light sources. 
   A further advantageous refinement provides for a spacer supported on the printed circuit board, in particular, to surround the light sources, and for the spacer together with the covering lens, in particular, to form a closed space in front of the light sources. 
   A further advantageous refinement provides for the closed space to have a liquid or viscous substance, in particular silicone gel, or a potting composition. 
   A further advantageous refinement provides for an optical element extending in front of the light sources, in particular the covering lens or a composition extending in front of the light sources, to have phosphorus particles. 
   A further advantageous refinement provides for a converging lens to be arranged in front of the light sources, at a distance of a multiple of the diameter thereof, in particular in front of the covering lens. 
   A further advantageous refinement provides for the covering lens to have a significantly larger diameter than the light sources and for a converging lens to have a significantly larger diameter than the covering lens, the diameter ratios in each case lying between 1.2:1 and 10:1, in particular. 
   A further advantageous refinement provides for an optical waveguide to be arranged in the optical axis of the semiconductor radiation source, in particular downstream of the converging lens in the radiation direction. 
   A further advantageous refinement provides for the first and second light source to be able to be switched on jointly. 
   A further advantageous refinement provides for the first and second light sources to be able to be switched on or switched off at different points in time. 
   A further advantageous refinement provides for illumination and optical detection of edge gaps in the case of plastic fillings in or on teeth, in particular by means of the switching on of the first light source. 
   A further advantageous refinement provides for an essentially annular spacer to support the covering lens at least partly on the printed circuit board and/or the base body and to surround the LED chips. 
   A further advantageous refinement provides for the spacer to have a conical or parabolic section on its side facing the LED chips. 
   A further advantageous refinement provides for a reflector to be arranged downstream of the covering lens in the beam path. 
   A further advantageous refinement provides for a reflector to support a converging lens arranged downstream of the covering lens in the beam path. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Further advantages, details and features of the invention emerge from the following description of a plurality of exemplary embodiments of the invention with reference to the drawing, in which: 
       FIG. 1  shows a first schematic embodiment of a radiation source according to the invention in plan view; 
       FIG. 2  shows a second embodiment of a radiation source according to the invention likewise in plan view; 
       FIG. 3  shows a further embodiment of a radiation source according to the invention in plan view; 
       FIG. 4  shows the embodiment in accordance with  FIG. 3  in side view; 
       FIG. 5  shows a further embodiment of a radiation source according to the invention in plan view; 
       FIG. 6  shows the embodiment in accordance with  FIG. 5  in side view; 
       FIG. 7  shows the embodiment in accordance with  FIGS. 5 and 6  in an enlarged illustration; 
       FIG. 8  shows a further embodiment of the radiation source according to the invention in plan view; per se. 
       FIG. 9  shows the embodiment in accordance with  FIG. 8  in side section; 
       FIG. 10  shows a further embodiment of a radiation source according to the invention in plan view; 
       FIG. 11  shows the embodiment in accordance with  FIG. 10  in lateral section; 
       FIG. 12  shows a further embodiment of a radiation source according to the invention in lateral section; 
       FIG. 13  shows a further embodiment of a radiation source according to the invention in lateral section; 
       FIG. 14  shows a further embodiment of a radiation source according to the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a semiconductor radiation source  10  in schematic plan view. A base body  12  is provided, which carries two chips in a central region  14 . In this case, a first light source  16  is provided, which is arranged in an optical axis. In this exemplary embodiment, both light sources  16  and  18  are arranged directly in the central region of the base body  12  on which they are mounted, and which simultaneously serves for dissipating the heat generated by the chips. In this exemplary embodiment, the two chips are in each case arranged in a manner directly adjoining the optical axis  22 . They have a gap  20  between them, which is kept as small as is technically and electrically possible in order to avoid short circuits, in which case the distance may be a few micrometers. 
   Each chip is formed in square fashion in a manner known per se. 
   A further embodiment of the semiconductor radiation source  10  according to the invention can be seen from  FIG. 2 . Here and also in the further FIGS., identical reference symbols denote identical or corresponding elements. In the exemplary embodiment in accordance with  FIG. 2 , the first light source  16  is provided directly in the optical axis  22 . The second light source  16  comprises four chips  24 ,  26 ,  28  and  30  arranged in cruciform fashion around the chip of the first light source  18 . All the chips have the same dimensions, so that the edge lengths correspond to one another. Markedly narrow gaps  20  are again provided, which enable electrical isolation but do not influence the spatial proximity of all the chips in the central region  14 . 
   In this case, too, the first and second light sources  16  and  18  can be switched independently of one another and occupy the central region  14  of the base body  12 , a significantly larger region remaining free. 
   A further embodiment of a radiation source  10  according to the invention can be seen from  FIG. 3 . In the case of this embodiment, which is illustrated in side view in  FIG. 4 , a projection  31  is provided, which carries the first and second light sources  16  and  18 . The form of the projection  31  follows the cross formed by the first and second light sources  16  and  18 , the junctions of the limbs at  32  each having radii and in this respect being somewhat rounded and enlarged. This enables simplified mounting of the chips onto the base body  12  and good heat dissipation from the chips to said base body. 
   The base body  12  preferably essentially comprises copper and is coated with a nickel-gold layer in particular on its front side, that is to say adjacent to the light sources. In modified refinement, the base body is completely coated with said layer on the outside. 
   It can be seen from  FIG. 3  that the base body  12  has a bevel  34  at one corner. The bevel  34  serves to facilitate mounting in order to ensure that the contact areas discussed with reference to the subsequent FIGS. are connected correctly. 
   It can be seen from  FIG. 4  that the thickness of the chips is significantly smaller than the thickness of the base body, for example by a factor of 10. 
   Moreover, the thickness of the chips for the light sources  16  and  18  is also somewhat smaller than the height of the projection  31 . 
     FIG. 5  shows that the central region  14  may be surrounded by a ring area  40 , which is preferably formed by a printed circuit board  41  bearing on the base body  12 . An annulus fitted into the essentially square form of the base body  12  is preferably formed. 
   It is particularly expedient that four contact zones  42 ,  44 ,  46  and  48  spaced apart from one another are formed on the other side of the ring area  40 . The contact zones  42  to  48  serve for making contact with connection wires or bonding wires for the chips of the light sources  16 ,  18 . Accordingly, the bonding wires (also cf.  FIG. 7 ) extend across the ring area  40 . This also benefits the concentration of the light emission on the actually important central region  14 . 
   It can be seen from  FIG. 6  that the printed circuit board  41  can extend essentially at the same height as the projection  31 . It goes without saying that a height adaptation can be performed in an arbitrary manner, so that the printed circuit board or the projection may also be thicker. 
   In this embodiment, series resistors are additionally provided for the LED chips, and a series resistor  49  can be seen from  FIG. 6 . With these series resistors, their calibration can be performed when LED chips are connected in parallel, so that it is also possible to use unsorted LED chips, which are cost-effective. 
   The way in which the bonding wires  50  extend for making contact with the individual chips can be seen from  FIG. 7 . The corresponding contact-making ensures separate driving of the chips  24  to  30  on the one hand, and of the light source  16 , on the other hand. 
   It goes without saying that the electrical insulation of the chips  24  to  30  and of the chip of the light source  16  can be realized in a manner known per se, for example by means of a corresponding oxidation layer of the semiconductor material used. This is not in conflict with the fact that the chips can be securely fixed on the projection  31  or the base body  12 . 
   It can be seen from  FIG. 7  that a spacer  40  can surround the central region  14 . The spacer  40  may be formed from plastid or light metal, for example, and protect the light sources  16  and  18 . In the exemplary embodiment illustrated, it is annular and provided for receiving the covering lens  52  that can be seen from  FIGS. 10 and 11 . 
   Whereas in the embodiment in accordance with  FIGS. 8 and 9 , a space  54  remains above the light sources  16  and  18 , this space  54  is closed and filled with a particular substance in the embodiment in accordance with  FIGS. 10 and 11 . In the exemplary embodiment illustrated, silicone gel  56  provided with yellow phosphorus particles is provided for this purpose. This ensures that the emitted light acquires a higher proportion of white without the light power being appreciably impaired. 
   In a particularly preferred refinement which can be seen from  FIG. 12  and in modified form from  FIG. 13 , the radiation source according to the invention is incorporated into a partially illustrated combined illumination and light curing device. For this purpose, a converging lens  60  is provided, which is mounted by means of an optical holder  62  in such a way that it extends above the covering lens  52 , to be precise in a manner overlapping and covering the latter. In the embodiment in accordance with  FIG. 13 , an optical waveguide  64  extends in the radiation direction adjacent to the converging lens  60 . The light curing device, as indicated schematically in  FIG. 13  has a housing  70  and is formed as a hand held device. 
   As can be seen from  FIGS. 12 and 13 , the light sources  16 ,  18  and also the covering lens  52 , but also the converging lens  60  and the optical waveguide  64  are arranged along the optical axis  22 . This enables a particularly good yield and easy focusing on the desired focal point. 
     FIG. 14  shows a further embodiment of a radiation source according to the invention. In this embodiment, the LED chips  16 ,  18  are surrounded by a spacer  72 , which simultaneously serves for supporting the covering lens  52 . Adjacent to the spacer  72  there is a reflector  74 , which expands parabolically and simultaneously forms a support for the converging lens  60  at a shoulder  76 . Adjacent to the converging lens, the reflector  74  further extends parabolically or conically obliquely outward in order thus to ensure optimum concentration of the emitted light. 
   While a preferred form of this invention has been described above and shown in the accompanying drawings, it should be understood that applicant does not intend to be limited to the particular details described above and illustrated in the accompanying drawings, but intends to be limited only to the scope of the invention as defined by the following claims. In this regard, the term “means for” as used in the claims is intended to include not only the designs illustrated in the drawings of this application and the equivalent designs discussed in the text, but it is also intended to cover other equivalents now known to those skilled in the art, or those equivalents which may become known to those skilled in the art in the future.