Abstract:
A lens for illumination purposes is disclosed, in particular a lens for a headlamp for projecting the light emitted by a light source and reflected by a reflector in order to produce a pre-defined illumination pattern. Each lens is provided with an individualized code. For the purpose of coding, a laser is used, by means of which extremely small micro cracks are produced on the surface of the lens and can be read by means of a suitable reading device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a lens for illumination purposes, in particular a lens for a headlamp for projecting the light emitted by a light source and possibly reflected by a reflector in order to produce a predefined illumination pattern.  
         [0002]     The invention relates further to a method of producing a lens, in which the lens is produced in a production method which operates intermittently or cyclically.  
         [0003]     The invention further relates to a method of marking a lens with a code.  
         [0004]     Since the mid-80s, for cars in the upper and upper-middle-class, what is known as a “poly-ellipsoid headlamp” (PES) has been offered which, instead of the diffuser disc, has a plane-asphere as a lens, which is matched with a threefold ellipsoid reflector or, in recent times, also with free-form surface reflectors.  
         [0005]     The basic structure of such headlamps is known and can be gathered from DE 198 14 480 A, for example. Such a PES head-lamp comprises a reflector which consists of a section of an ellipse and has a single light source, which is arranged in the region of the first focus of the reflector. In this headlamp, a plane-convex lens is provided at a distance from the reflector, its focus lying in a region of the second focus of the reflector. Inserted in between the reflector and the plane-convex lens is a mask, which is positioned in a region of the second focus of the reflector. It has an appropriately adapted shape in order that the bundle of light emerging from the head-lamp satisfies the prescribed light-dark limit.  
         [0006]     Because of the stipulations relating to quality control in the car industry, which are increasing more and more in recent times, the quality requirements which are placed on such lenses increase continuously.  
       SUMMARY OF THE INVENTION  
       [0007]     It is a first object of the invention to provide a method of producing a lens which allows for a simple and reliable demonstration of compliance with a quality standard.  
         [0008]     It is a second object of the invention to disclose a method of marking a lens with a code that is highly reliable and allows for a read out of the code even after years of use.  
         [0009]     These and other objects are solved according to the invention, by a lens having an individualized code and by a method of producing such a lens.  
         [0010]     The lenses may be made of glass or plastic.  
         [0011]     The object is, moreover, achieved by an apparatus for producing lenses for illumination purposes, having a shaping device for shaping lenses, in particular a pressing device for hot-pressing lenses, having a coding device for identifying the lenses with a code, and having a counting device which has a counter whose value can be increased by an increment with each lens supplied to the coding device, the coding device having a laser for producing a write beam and a laser control device for controlling the write beam, the counting device being coupled to the laser control device for controlling the write beam in such a way that individualization of the code as a function of the value of the counter is ensured.  
         [0012]     The object of the invention is, moreover, achieved by a method for producing lenses comprising the following steps: 
    shaping a series of lenses, preferably in a production method that operates intermittently;     producing a characteristic value for each lens, and     producing a code on the lens, in particular on a surface of the lens, which is individualized as a function of the characteristic value for each lens.    
 
         [0016]     In this way, the object of the invention is achieved completely.  
         [0017]     Since each lens is specifically provided with an individualized code in a continuous production process, compliance with the predefined tolerance limits can be documented continuously and, in particular, each lens produced can be traced back completely at any time, even after relatively long use in a headlamp, with respect to the location and time of its production and, in particular, including the assignment to a production run whose quality was regularly checked and documented.  
         [0018]     In an apparatus according to the invention, a counting device is provided having a counter whose value is increased by an increment with the supply of each lens. The write beam of the laser used for coding is controlled by its control device in such a way that a code individualized for each lens is produced on the lens.  
         [0019]     The term “counter” is to be understood quite generally in this connection. In addition to a counter in the conventional sense, this is also to be understood to mean any electronic counter, that is to say for example also a timer which is used to produce a date or a time of day.  
         [0020]     The individualized product data preferably have at least one characteristic value which is produced from a production process by a continuously running counter.  
         [0021]     According to a further advantageous refinement of the invention, the code is applied to an optically inactive region of the lens.  
         [0022]     In this case, the code can be provided, for example, on a circumferential fixing edge of the lens, which is designed to hold the lens.  
         [0023]     These measures have the advantage that the optical functioning of the lens is in no way affected by the code and in that the code cannot be detected when the lens is installed.  
         [0024]     In this case, the code can also be provided on the circumferential surface of the fixing edge.  
         [0025]     This has the advantage that the code is also easily accessible for the purpose of reading when the lens is installed.  
         [0026]     As already mentioned above, the code is preferably produced by means of a laser. This can be, for example, a CO 2  laser.  
         [0027]     This has the advantage that the code can be applied in a particularly time-saving manner without mechanical detriment arising in this case. Furthermore, the code produced by a laser is very resistant and can still be read by means of a suitable reading device even after years of use.  
         [0028]     According to a further embodiments of the invention, micro cracks or crystallization regions, which can be evaluated as a code, are produced by means of the laser beam.  
         [0029]     In this way, a detrimental influence on the functioning and durability of the lens is avoided.  
         [0030]     In addition, color changes can be used for the code. This is advantageous in particular for plastic lenses.  
         [0031]     The code can comprise alphanumeric characters, for example.  
         [0032]     According to a further particularly preferred embodiment of the invention, the code comprises a machine-readable code, in particular a data matrix code (DMC) according to the ECC 200 Standard.  
         [0033]     The advantage of such a code is that a relatively large amount of information (15-character string) can be stored in a very small space (of, for example, 2.4×2.4 mm). This permits the code to be applied to the relatively small fixing edge of the lens, so that it is not visible when installed.  
         [0034]     In order to make the individual bits (dots) of a machine-readable code highly legible and in order to ensure a very permanent code, micro shape changes in the form of break-outs or recesses are produced by a laser beam. These break-outs can be produced by the stresses induced by means of the laser beam. For this purpose, for example, the laser beam can move around an approximately self-contained curved path, for example in the form of a partial circle. In this case, if appropriate the intensity of the laser beam can additionally be changed in order, for example to induce the break-out of the glass at the end by means of a short increase in intensity. Alternatively, a plurality of point irradiations can be carried out in a predetermined pattern in order to induce the break-out.  
         [0035]     The surface of such break-outs produced by stresses is relatively rough, so that high legibility results from the scattering action of the light.  
         [0036]     It goes without saying that the features of the invention mentioned above and those still to be explained below can be used not only in the respective specified combination but also in other combinations or on their own without departing from the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]     Further features and advantages of the invention emerge from the following description of preferred exemplary embodiments with reference to the drawing, in which:  
         [0038]      FIG. 1  shows the basic structure of a PES headlamp having a lens according to the invention in an exploded illustration;  
         [0039]      FIG. 2  shows a side view of a lens according to the invention;  
         [0040]      FIG. 3  shows a view of the lens according to  FIG. 2  from the front;  
         [0041]      FIG. 4  shows a basic illustration of an apparatus according to the invention for producing lenses;  
         [0042]      FIG. 5  shows a partial cross section through a lens according to the invention in the region of a data bit in the form of a micro break-out, in an enlarged illustration;  
         [0043]      FIG. 6  shows a partial view of a lens according to the invention with the indicated travel path of a laser beam for producing a micro break-out for a data bit; and  
         [0044]      FIG. 7  shows a partial view of a lens according to the invention in the region of a data bit in the form of a micro break-out having a plurality of laser point irradiations indicated. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]     A poly-ellipsoid (PES) headlamp having a lens according to the invention is illustrated in  FIG. 1  and designated overall by the number  10 . The PES headlamp  10  comprises a poly-ellipsoid reflector  12 , a light source  14 , for example in the form of a halogen lamp, a mask  16  and a lens  20 . The mask  16  is arranged in the beam path between the light source  14  and the lens  20 . By means of the mask  16 , the lower half of the beam is cut off, so that, after emerging after the lens  20 , the headlamp light is directed substantially downwards. The graduation of the upper edge of the mask  16  achieves the situation in which the light beam is in particular deflected downwards to the right, in order to dazzle the opposing traffic as little as possible.  
         [0046]     A lens  20  according to  FIG. 1  is illustrated in the side view in  FIG. 2 . This is a plane-convex lens having an optically active region  22  and an optically inactive region  24 , which is formed as a circumferential, plane-parallel edge region which projects outwards by a few millimetres from the plane-convex region.  
         [0047]     As can be seen from the front view of the lens  20  according to  FIG. 3 , a code  26  having an area of about 2.4×2.4 mm is applied to the optically inactive edge region  24 .  
         [0048]     This code, which in principle could also have alphanumeric characters, preferably comprises a data matrix code (DMC) according to the ECC 200 Standard. This code is produced with the aid of a CO 2  laser and a suitable control device. By means of the laser beam, local micro cracks or depressions are produced on the glass surface and can be read as pixels by means of a suitable reading device.  
         [0049]     Alternatively, the code can also be applied to the circumferential surface of the edge region  24 , in particular of the fixing edge, as indicated at  26 ′ in  FIG. 2 .  
         [0050]     Depending on the composition of the glass used and in coordination with the laser beam, microcrystallization regions or elevations can alternatively be produced. However, the common factor in the microstructures produced is that they can all be read as pixels or pixel patterns by means of a suitable reading device.  
         [0051]     In  FIG. 4 , an apparatus according to the invention for producing such a lens is illustrated and designated overall by the number  30 .  
         [0052]     The apparatus  30  has a shaping device, merely indicated schematically by the number  32 , for shaping the lenses. The shaping device  32  is preferably a hot-pressing device, with which the lenses can be produced in one operation by hot-pressing, using a suitable press mold.  
         [0053]     The shaping device  32  is fed with glass melt from a melting furnace  34 , as indicated schematically by the arrow  36 . In order to control the shaping device  32  and the output of glass from the melting furnace  34 , a process control device  38  is provided, which is merely indicated schematically and which can be, for example, a SPS (stored program system) which, as indicated schematically, is coupled via lines  44  and  42  to the shaping device  32  and to the melting furnace  34 , respectively.  
         [0054]     The shaping device  32  is an apparatus that operates intermittently or cyclically and with which single lenses can be produced one after another or a plurality of lenses can be produced simultaneously. The lenses produced are output from the shaping device  32  and, if appropriate, initially accommodated in a storage container. As a rule, likewise after carrying out quality control at least in the manner of random sampling, the lenses are supplied one after another by a handling device  39  to a subsequent coding device, which is designated overall by the number  48 . The handling device  39  comprises a counter  40 , whose value n is increased by an increment upon the respective output of a lens to the downstream coding device  48 .  
         [0055]     In the downstream coding device  48 , each lens is then provided with an individualized code, which is individualized at least as a function of the respective value of the counter  40  and, furthermore, can contain a series of further data.  
         [0056]     The coding device  48  has a holder  47  for holding a lens  20 , furthermore a laser  46  for coding the lens  20 , an associated laser control device  50  and a scanner  52 . The laser  46  has a write beam  49  which, by means of the control device  50 , can be controlled via a control line  54  in a suitable way in order to produce the desired code  26  on the edge region  24  of the lens  20 .  
         [0057]     In this case, the value n of the counter  40 , which is coupled to the laser control device  50  via the line  56 , is taken into account in order to individualize the code of each individual lens  20 . The scanner  52  can additionally be used in order to be able to adapt each code for each lens individually, it being possible for data relating to the production location, the production date, quality control data and the like also to be incorporated. Data  60  can be read into the scanner  52 , as indicated by the arrow  62 .  
         [0058]     It goes without saying that, instead of an input via a scanner  52 , the laser control device  50  could also be supplied in another way with individualized data for the purpose of coding, for example via a SPS interface with data from the production process, for example from the process control device  38 , or can be supplied directly with data from the quality control.  
         [0059]     By using FIGS.  5  to  7 , it will be explained in the following how individual data bits of the code can be produced in the form of micro break-outs or recesses on a lens consisting of glass by means of a laser beam.  
         [0060]     In this case, the machine-readable coding consists of data bits which are formed by a micro break-out at a predetermined point of the code or by the lack of such a micro break-out (that is to say a smooth surface at this point).  
         [0061]     In  FIG. 5 , a data bit  70  in the form of a micro break-out is shown schematically in an enlarged illustration. The inner surface  72  of the micro break-out is relatively rough and thus, as a result of the scattering action, results in good contrast during reading.  
         [0062]      FIG. 6  shows how such a micro break-out can be produced by a laser beam. For this purpose, the laser beam moves on a virtually self-contained curved path  74  in the form of a part circle, beginning with a specific intensity at  76 , and ending at  78 , where the intensity is increased briefly. As a result of the stresses produced hereby, the micro recess is induced to break out.  
         [0063]     In  FIG. 7 , an alternative production of a micro break-out by means of a plurality of laser point irradiations at the points  80 ,  82 ,  84 ,  86 ,  88  is illustrated. Once again, the part circumscribed by the points  80  to  88  breaks out as a result of the induced stresses, so that the micro break-out having the surface  72  results.  
         [0064]     The code produced is very permanent and can be read by means of a suitable reading device even after the rough operation in a motor vehicle and also after time periods of more than 15 years.