Abstract:
The invention relates to an optoelectronic sensor comprising an integrated arrangement of a plurality of light emitting diodes arranged in the region of an optical receiving system for the illumination of a sensing region, with beam-shaping optical elements being associated with the light emitting diodes. The beam-shaping optical elements have optical properties which differ from one another and are dependent on their relative position to the optical receiving system. Furthermore, the beam-shaping optical elements have a wedge shape, with in each case precisely one wedge element or regions of up to four adjacent wedge elements being associated with the light emitting diodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of German Patent Application No. 10 2005 004 419.0, filed on Jan. 31, 2005. The disclosure of the above application is incorporated herein by reference.  
       FIELD AND BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to an optoelectronic sensor comprising an integrated arrangement of a plurality of light emitting diodes arranged in the region of an optical receiving system for the illumination of a sensing region, with beam-shaping optical elements being associated with the light emitting diodes.  
         [0003]     Optoelectronic sensors are known from the prior art and are used, for example, both for object sensing and in particular for the sensing of codes. In this process, simple sensors work without beam-shaping optical elements, which has the consequence that a comparatively large proportion of the light transmitted by the light emitting diodes does not reach the sensing region so that the illumination of the sensing region ultimately does not take place in a very efficient manner.  
         [0004]     Sensors for demanding applications improved with respect to sensors of this type are, as already mentioned above, fitted with beam-shaping optical elements in front of the light emitting diodes. These beam-shaping optical elements ensure that the light radiated from the light emitting diodes reaches the sensing region as completely as possible so that increased efficiency can be achieved here with the illumination.  
         [0005]     However, despite the provision of beam-shaping elements, it is not yet possible with known optoelectronic sensors to generate respectively desired illumination profiles in the sensing region which are required for specific applications. It is, for example, desirable in many applications to ensure an illumination of the sensing region which is as homogeneous as possible. In other applications, however, a more intensive illumination of the sensing region at its edges can also be desired (peripheral increase). Furthermore, it is often desirable, for example with optoelectronic sensors having light emitting diodes arranged over a rectangular area to direct the light radiated from these light emitting diodes as completely as possible to a square sensing region.  
         [0006]     Illumination profiles of this type with their respective characteristics cannot be generated or can only be generated in inadequate quality by optoelectronic sensors of the initially named kind.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the invention consists of designing an optoelectronic sensor of the initially named kind such that respectively desired illumination profiles can be generated in the sensing region, with a maximum efficiency simultaneously being achieved in that as much as possible of the whole light quantity radiated by the light emitting diodes is directed to the sensing region.  
         [0008]     This object is satisfied in accordance with the invention and in particular in that the beam-shaping optical elements have: 
    optical properties which differ from one another and which are dependent on their relative position to the optical receiving system; and furthermore     have a wedge shape, with precisely one wedge element or regions of up to four adjacent wedge elements being respectively associated with the light emitting diodes.    
 
         [0011]     In accordance with the invention, respective individual beam-shaping elements are associated with the light emitting diodes, in particular with all the light emitting diodes of the optoelectronic sensor, and are suitable to radiate the light transmitted by the respective light emitting diode in the desired direction with respect to the respective light emitting diode. Light in the sense of the invention is generally also to be understood as radiation in the non-visible range, that is e.g. IR or UV radiation. In accordance with the invention, the individual beam-shaping optical elements can therefore be made in their design and/or position relative to the optical receiving system of the optoelectronic sensor such that the respective desired illumination profile is adopted in the sensing region by overlap of the light radiated by all light emitting diodes. The light transmitted from each light emitting diode can therefore be directed as completely and precisely as possible to that position of the sensing region at which it is required so that, for example, illumination profiles with a homogeneous illumination or illumination profiles with peripheral increase can be generated without problem. It is equally possible without difficulty in accordance with the invention to direct light radiated from a rectangular field of light emitting diodes completely onto a square sensing region. Any other desired characteristics of illumination profiles can likewise be generated in accordance with the invention.  
         [0012]     Due to the wedge-shaped design of the beam-shaping optical elements in accordance with the invention, the latter can be manufactured comparatively cost-favorably and simply in comparison with spherical lenses or Fresnel lenses so that the total costs of the optoelectronic sensor are not substantially increased by the beam-shaping optical elements designed in accordance with the invention.  
         [0013]     In accordance with a variant in accordance with the invention, precisely one wedge element can be respectively associated with one light emitting diode, said wedge element providing the desired beam shaping and beam direction with respect to the respective light emitting diode. Alternatively, however, it is also possible to associate regions of precisely two adjacent wedge elements, or also of up to four adjacent wedge elements with a light emitting diode, which will be explained in more detail in the following by way of example with reference to precisely two adjacent wedge elements.  
         [0014]     At least some of the beam-shaping elements in accordance with the invention can be designed such that they deflect the light radiated from the respective light emitting diodes somewhat in the direction of the optical axis of the optical receiving system. This is advantageous since no light emitting diodes can be provided in the region of the optical receiving system so that there is no sufficient illumination in the sensing region disposed directly beneath the optical receiving system or in that region of the sensing region which surrounds the point of intersection between the optical axis of the optical receiving system and the plane of the sensing region. When light is directed directly into the region in accordance with the invention, it can be ensured that this region is also illuminated sufficiently strongly.  
         [0015]     For the case that precisely one wedge element is associated with a light emitting diode, the former can be made as a wedge plate with a sloping surface which is provided at the side facing the light emitting diode and/or at the side of the wedge plate remote from the light emitting diode. In order to achieve the respectively required illumination profile, the inclination of the sloping surface of each wedge plate can be matched individually to the relative position between the respectively associated light emitting diode and the optical receiving system in two directions perpendicular to one another. The light transmitted by each light emitting diode can be directed very precisely to the respectively desired position of the sensing region by an individual inclination of the sloping surface of this type.  
         [0016]     The inclination of the sloping surface of each wedge plate in two directions perpendicular to one another can also then be set individually in the respectively necessary manner when e.g. regions of two or four mutually adjacent wedge plates are associated with a light emitting diode. With, for example, four mutually adjacent wedge plates, the light emitting diode can then be arranged such that it is located opposite that point at which all four wedge plates adjoin one another.  
         [0017]     It is preferred in an economic respect for the wedge element associated with a light emitting diode not to be made as an individual wedge plate, but rather as a section of precisely one wedge strip or wedge ring with a sloping surface which is provided at the side facing the light emitting diode and/or at the side of the wedge strip or wedge ring remote from the light emitting diode. It is of advantage in an embodiment of this type that it is not necessary to produce a number of individual wedge plates, but that one wedge strip or one wedge ring can be arranged such that it is associated with a plurality of light emitting diodes which are arranged along the wedge strip or wedge ring so that ultimately only a section of the wedge strip or wedge ring is associated with each light emitting diode. The optical properties of the wedge strip or wedge ring are constant over its longitudinal extent. The optical properties of a plurality of provided wedge strips or wedge rings among one another, in contrast, differ from one another and are dependent on their relative position to the optical receiving system.  
         [0018]     The wedge plate, wedge strip or wedge ring can be aligned with the respectively associated light emitting diode such that the light transmitted by this light emitting diode passes as completely as possible through the sloping surface of the respective wedge plate or of the respective wedge strip or wedge ring. In this manner, the light quantity incident onto the sensing region is maximized.  
         [0019]     The wedge element associated with a light emitting diode can also be made as a section of up to four, preferably of precisely two, mutually adjoining wedge strips or wedge rings. It in turn also applies here that the optical properties of the wedge strips or wedge rings are constant over their longitudinal extent, but differ from one another from wedge strip to wedge strip or from wedge ring to wedge ring.  
         [0020]     The wedge strips or wedge rings can in this case be aligned with the respectively associated light emitting diode such that approximately half the light transmitted by this light emitting diode passes through the sloping surface of a wedge strip or of a wedge ring and the other half passes through the sloping surface of a further wedge strip or wedge ring. It is thus achieved that the light transmitted by one light emitting diode is divided into two light quantity regions which can undergo different beam shaping. The fact is particularly advantageous with this arrangement that increased efficiency results since the light losses occurring in the wedge stripes or wedge rings are minimized. This will be explained in more detail in connection with the description of the Figures.  
         [0021]     It is particularly preferred with the last described embodiment for the sloping surface of each wedge strip or wedge ring to be formed by two sections which extend in parallel to one another and have inclinations differing from one another, with in particular each of the two sections forming approximately half the sloping surface. It is advantageous in this process for the two sections to merge steplessly into one another. This embodiment will also be explained within the framework of the description of the Figures.  
         [0022]     An end surface of the wedge plate, of the wedge strip or of the wedge ring having no sloping surfaces can extend perpendicular to the main radiation direction of the light emitting diode. The named end surfaces of all wedge plates, wedge strips or wedge rings can in this case be arranged inside a single plane. If end surfaces of this type are arranged at the side remote from the light emitting diode, the composite of all wedge plates, wedge strips or wedge rings can form a planar front device plate of the sensor in accordance with the invention.  
         [0023]     It is particularly preferred for all beam-shaping optical elements to be firmly connected to one another since a complex adjustment of the optical elements relative to one another is omitted in this case. It is particularly advantageous for all beam-shaping optical elements to be formed in a uniform step plate having a plurality of wedge-shaped steps. A step plate of this type, which can be made as a post-processed injected molded part, for example, can be manufactured particularly cost favorably, with all beam-shaping optical elements of an optoelectronic sensor here being able to be manufactured together by means of one single injection procedure.  
         [0024]     A plurality of concentric wedge rings can be provided in the step plate, which in particular directly adjoin one another. An arrangement of this type is sensible when the optoelectronic sensor has light emitting diodes arranged in ring form around the optical receiving system. A wedge ring or, alternatively, sections of two adjacent wedge rings, can then be associated with each ring of light emitting diodes. If the light emergence window of the optoelectronic sensor has a rectangular shape and if the light emitting diodes are also arranged in the region of a rectangular surface, it is advantageous for the step plate also to have a rectangular shape, with at least some of the concentric wedge rings only being present incompletely on the step plate in this case. An embodiment of this type will likewise be explained in more detail in the following within the framework of the description of the Figures.  
         [0025]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0027]      FIG. 1  illustrates a section through wedge elements in accordance with the invention with light emitting diodes arranged in front of them;  
         [0028]      FIG. 2  illustrates a section through a step plate made in accordance with the invention with a light emitting diode arranged in front of a wedge element of the step plate;  
         [0029]      FIG. 3  illustrates a section through a further embodiment of a step plate in accordance with the invention with a light emitting diode arranged in the region of two wedge elements;  
         [0030]      FIG. 4  illustrates a three-dimensional representation of a step plate in accordance with the invention with light emitting diodes arranged in front of it; and  
         [0031]      FIG. 5  illustrates a plan view of a step plate in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0033]      FIG. 1  shows a section through a portion of a step plate  2  in accordance with the invention with light emitting diodes  4  arranged in front of the step plate  2 . The portion of the step plate  2  shown has a total of three wedge elements in accordance with the invention made as wedge plates  6 , with the sloping surfaces  8  of the wedge plates  6  facing the light emitting diodes  4 .  
         [0034]     The end surfaces  10  of the wedge plates  6  remote from the light emitting diodes  4  and from the sloping surfaces  8  extend perpendicular to the main radiation direction A of the light emitting diodes  4  in a common plane. Accordingly, the step plate  2  can be manufactured from a uniform plate which is only worked on the side facing the light emitting diodes  4  such that the sloping surfaces  8  are formed. The step plate  2  in this case forms an outside planar front device plate of a sensor in accordance with the invention.  
         [0035]     The light rays transmitted by the light emitting diodes  4  are refracted a first time on entering into the step plate  2  in the region of the sloping surfaces  8  and a second time on exiting from the step plate  2  in the region of the end surfaces  10  and are thus deflected in a respectively desired direction with respect to the main radiation direction A of the light emitting diodes  4 . In this process, the respectively desired deflection can be set by the magnitude of the angle of inclination of the sloping surfaces  8 . The inclination of the sloping surfaces  8  can be set both by around axis of inclination extending perpendicular to the plane of the drawing and—where required—around an axis of inclination which extends from top to bottom in the plane of the drawing. A setting of the sloping surface by the last-named axis of inclination is, however, not possible when wedge strips or wedge rings such as have already been explained above are used instead of individual wedge plates.  
         [0036]     A setting of the inclination of the sloping surfaces  8  in all directions advantageously makes it possible, on the one hand, to direct the light radiated by the light emitting diodes precisely in the respectively desired direction; on the other hand, such an individual matching of the sloping surfaces  8  to each individual light emitting diode  4  is, however, associated with a high effort. This effort can be reduced by the use of wedge strips or wedge rings, which still always allows a direct deflection of the light radiated from the light emitting diodes  4  sufficient for most applications.  
         [0037]     The inclinations of the sloping surfaces  8  can be selected to be different from one another so that a superimposition of the light radiated by all light emitting diodes  4  ultimately results in the respectively desired illumination profile in the sensing region of the optoelectronic sensor.  
         [0038]      FIG. 2  shows a representation which substantially corresponds to the representation in accordance with  FIG. 1 , with here, however, only one individual light emitting diode  4  being shown by way of example together with the totality of the light rays transmitted by it for reasons of clarity. The step plate  2 ′ in accordance with  FIG. 2  has a total of four sloping surfaces  8 ′ which have all different inclinations with respect to the main radiation direction A of the light emitting diode  4 . A respective light emitting diode  4  is arranged opposite each sloping surface  8 ′ and, as already mentioned, only one of them is shown in  FIG. 2 . An optical receiving system  14  is provided adjacent to that region  12  of the step plate  2 ′ which has no sloping surfaces  8 ′.  
         [0039]     The inclination of the sloping surfaces  8 ′ with respect to the end face  10 ′ increases in the embodiment shown from wedge element to wedge element as the distance from the optical receiving system  14  increases so that the light rays transmitted by the light emitting diodes  4  are refracted more strongly as the distance from the optical receiving system  14  increases. Generally, the sloping surfaces  8 ′ can, however, have any desired inclination, in particular also independently of the distance from the optical receiving system  14 , in order thus to generate respectively desired illumination profiles.  
         [0040]     It is advantageous for the radiation characteristic of the light emitting diodes  4 , the magnitude and orientation of the sloping surfaces  8 ′ and the distance between the light emitting diodes  4  and the sloping surfaces  8 ′ to be selected such that the light radiated from a light emitting diode  4  is incident as completely as possible onto the sloping surface  8 ′ associated with it. This criterion applies to the light rays marked with B including a double arrow in  FIG. 2 . All these light rays emerge from the end face  10 ′ after they have entered into the step plate  2 ′ through the sloping surface  8 ′ associated with the light emitting diode  4 .  
         [0041]     Some of the radiation transmitted by the light emitting diode  4  is incident in the two regions marked by 16 onto steps which are formed between two adjacent sloping surfaces  8 ′. The radiation incident onto these two step regions  16  is ultimately lost and cannot be used to irradiate the sensing region. Specifically, a lightguide effect occurs within the step plate  2 ′ with respect to the radiation incident onto the upper step region  16  such that this radiation ultimately emerges from the side of the step plate  2 ′ in an undesired manner. The light portion incident onto the lower step region  16  is reflected through the end surface  10 ′ by the step such that it is ultimately guided past the sensing region to be illuminated. The named radiation portions influenced by the step regions  16  are, however, so small that an optoelectronic sensor with a step plate  2 ′ in accordance with  FIG. 2  can nevertheless work in the desired manner in accordance with the invention.  
         [0042]     Further radiation portions of the light emitting diode  4  are incident on adjacent sloping surfaces  8 ′ which are not associated with the light emitting diode  4  drawn in  FIG. 2 . These radiation portions are then refracted by the adjacent sloping surfaces  8 ′ and are directed to a large part in the desired manner to the sensing region. The corresponding light ray regions are marked in  FIG. 2  by C including a double arrow.  
         [0043]     It can be seen from the course of the totality of the light rays drawn in  FIG. 2  that they are substantially refracted somewhat in the direction of the optical receiving system  14 , which is sensible since no illumination of the sensing region can take place starting from the region of the optical receiving system  14 . Accordingly, in accordance with the invention, the light emitting diodes surrounding the optical receiving system  14  also provide an illumination of the sensing region directly with respect to the optical receiving system  14  due to the sloping surfaces  8 ′ provided in accordance with the invention.  
         [0044]     If the step plate  2 ′ in accordance with  FIG. 2  is made as a rotationally symmetrical step plate, concentric rings of light emitting diodes  4  can be formed around the optical receiving system  14  and then provide an optimum illumination of the sensing region.  
         [0045]      FIG. 3  shows an embodiment improved with respect to  FIG. 2 , wherein the light emitting diode  4  again only shown by way of example is arranged directly opposite a step region  18  such that approximately half of the light radiated by the light emitting diode  4  is in each case incident on adjacent sloping surfaces  8 ″ of the step plate  2 ″.  
         [0046]     Since the radiation transmitted by the light emitting diode  4  is directed substantially parallel to the extent of the step in the step region  18 , the transmitted radiation is as good as not influenced by the step region  18 , which increases the efficiency of the total arrangement.  
         [0047]     The sloping surfaces  8 ″ of the step plate  2 ″ each have a kink in their central region so that they have different optical properties at each side of the kink. The inclination of the sloping surfaces  8 ″ is accordingly matched by half to that light emitting diode  4  which is located closest to the respective sloping surface region. With respect to the light emitting diode  4  shown only by way of example in  FIG. 3 , the two regions  20  are matched to the light emitting diode shown, whereas the adjacent regions  22  and  24  are matched to the light emitting diodes not shown in  FIG. 3  adjacent to the light emitting diode  4 . The angles of the kinks of adjacent sloping surfaces  8 ″ can differ from one another, as is shown in  FIG. 3 .  
         [0048]     That light portion is in turn marked by B including a double arrow in  FIG. 3  which passes through the regions  20  of the sloping surfaces  8 ″ and is thus directly incident onto the sensing region in the respective desired manner.  
         [0049]     The light portion incident onto the adjacent step regions  16 ′ is minimal in the embodiment in accordance with  FIG. 3  so that practically no light loss occurs here.  
         [0050]     The light portions passing through the regions  22 ,  24  of the sloping surfaces  8 ″ basically not associated with the light emitting diode  4  are marked by C including a double arrow in  FIG. 3  and a larger part thereof reaches the sensing region so that these radiation portions are not lost.  
         [0051]     The step plate  2 ″ in accordance with  FIG. 3  can also be made rotationally symmetrically in the manner such as was already explained in connection with  FIG. 2 .  
         [0052]      FIG. 4  shows a three-dimensional elementary representation of a rotationally symmetrical step plate  26  having concentric wedge rings  28  which surround a central region  30  of the step plate  26 . The central region  30  is made as a piano-parallel plate so that it can be associated with an optical receiving system  14  in accordance with  FIGS. 2 and 3  without influencing the radiation entering into the optical receiving system  14  in a relevant manner. Alternatively, the central region  30  can also be made as a passage hole with the same effect. A design as a receiving lens or as a lens region of an optical receiving system is also possible.  
         [0053]     The wedge rings  28  concentrically surrounding the central region  30  are provided opposite rings of light emitting diodes  32  which are likewise arranged concentrically around the central region  30 , with the light emitting diodes  32  each being located opposite a step formed between two wedge rings  28  in accordance with  FIG. 3 . The light emitting diodes  32  are disposed within a substantially rectangular field such as corresponds to the customary construction of optoelectronic sensors. This means that, when the step plate  26  in accordance with  FIG. 4  is used, it is sectioned along the lines shown as broken lines in  FIG. 4  so that the step plate  26  ultimately also has the shape of a rectangle.  
         [0054]     A step plate of this type is shown in plan view in  FIG. 5 . The central region  30  which is surrounded by concentric rings  28 , of which, however, the outer ones are incomplete due to the rectangular shape of the step plate  26 , can easily be recognized. In  FIG. 5 , the kinks present in the sloping surfaces  8 ″ in accordance with  FIG. 3  are shown by broken lines and, for example, separate the region  20  in accordance with  FIG. 3  from the region  22  in accordance with  FIG. 3 .  
         [0055]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.  
       REFERENCE NUMERAL LIST  
       [0056]      2  step plate  
         [0057]      2 ′ step plate  
         [0058]      2 ″ step plate  
         [0059]      4  light emitting diodes  
         [0060]      6  wedge plates  
         [0061]      8  sloping surfaces  
         [0062]      8 ′ sloping surfaces  
         [0063]      8 ″ sloping surfaces  
         [0064]      10  end faces  
         [0065]      10 ′ end faces  
         [0066]      12  region  
         [0067]      14  optical receiving system  
         [0068]      16  step region  
         [0069]      16 ′ step region  
         [0070]      18  step region  
         [0071]      20  region  
         [0072]      22  region  
         [0073]      24  region  
         [0074]      26  step plate  
         [0075]      28  wedge rings  
         [0076]      30  central region  
         [0077]      32  light emitting diodes