Abstract:
The invention relates to a photoelectric sensor, in particular a light curtain, and its pivotable mounting. The light curtain has an explosion proof housing which is mounted via alignment brackets to a fixed installation in a pivotable manner for alignment. For this, the alignment bracket has two U-shaped members which are connected by a bolt.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a photoelectric sensor, in particular a light curtain, and its pivotable mounting. 
       DESCRIPTION OF RELATED PRIOR ART 
       [0002]    Multi-beam photoelectric sensors disclosed in DE 102006053003 B4, DE 102011050896 A1 and US 2003/0106992 each include units of paired light emitters and photo detectors to span a protective plane, typically called a light curtain, of a desired size by using units of light emitters and photo detectors. Multi-beam photoelectric sensors of this type are widely used for prohibiting intrusion of any part of a worker&#39;s body or any other object into a prohibited Zone like a work area of a dangerous machine tool, press machine or the like. 
         [0003]    These photoelectric sensors usually comprise two opposed housings to hold the paired light emitters and photo detectors. Each light emitter and photo detector must be aligned which means that the directions (optical axes) of each paired emitter and detector much match. To achieve this the light emitters and photodetectors are fixedly mounted in the housing in an aligned manner and the opposed housings are then aligned by special mounts which fix the housing to a fixed installation. These mounts are pivotable to a certain degree along one axes. Different of such mounting constructions are disclosed in DE 102006053003 B4, DE 102011050896 A1 and US 2003/0106992. 
         [0004]    In certain applications photoelectric sensors of the initially named kind are also used in areas where an increased danger of explosion exists. The requirements which must be observed in this regard with respect to explosion protection are, as a rule, relatively high. U.S. Pat. No. 5,998,785 discloses an additional explosion proof housing for such a photoelectric sensor. The problem then is, that the prior art mounting can&#39;t be used for the explosion proof additional housing. The additional housing is much larger and heavier because it is usually designed to be as large as the largest light curtain in order to be able to house all variants of sizes. Further it has no special mounts which have a high mechanical load capacity and are alignable. 
       OBJECT OF THE INVENTION 
       [0005]    It is therefore an object of the invention to provide a photoelectric sensor in an explosion proof housing which can easily be aligned and easily be mounted to an installation while the mounts having enough stability. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    According to the invention there is provided a light grid having
       a first housing which houses light transmitters and/or light receivers and electronic components to drive the light transmitters and/or receivers,   a second housing which is explosion proof and houses the first housing in a fixed manner,   an alignment bracket to mount the second housing to a fixed installation in an aligned manner,   the alignment bracket comprises a first member of a U-shape with a base plate and two side walls orthogonal to the base plate and placed at a distance apart and having a wall thickness, the side walls having aligned openings, and with at least one first base plate fastening element for fixture of the base plate to the fixed installation,   the alignment bracket further comprises a second member of the same structure as the first member wherein the distance of the side walls is reduced or enlarged by twice the wall thickness and with at least one second base plate fastening element for fixture of the second housing to the base plate,   the alignment bracket further comprises a fixable bolt for the feedthrough through the openings of the first and second members in order to connect both members being pivotable relative to each other as long as the bolt is not tightened.       
 
         [0013]    In a preferred embodiement the side walls of the alignment brackets have a symmetrical trapezoidal shape with the longer of the parallel sides being connected with the base plate. This makes larger pivoting angles possible. 
         [0014]    In an embodiement the side walls of the member with the larger distance between the side walls comprises a threaded hole for fixture of the bolt being a headed screw. This measure makes it easy to align since for alignment it is necessary to loosen only one screw, align it and tighten the one screw again. 
         [0015]    In another embodiement the alignment bracket comprises a bushing having a length which is equal to the distance between the side walls of the member with the smaller distance and the bushing is placed in alignment with the openings and receives the bolt. The bushing avoids deformation of the brackets when fixing the bolt by tightening the screw. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a light curtain; 
           [0017]      FIG. 2  an exploded view of an explosion proof housing, alignment brackets and a part of a fixed installation; 
           [0018]      FIG. 3  an alignment bracket; 
           [0019]      FIG. 4  the alignment bracket of  FIG. 2  in an exploded assembly drawing; 
           [0020]      FIG. 5  the two members of the alignment bracket. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]      FIG. 1  shows a light curtain  10 . The light curtain  10  comprises a first transmitter housing  14  and a first receiver housing  24 . The first transmitter housing  14  houses light transmitters  16  and the first receiver housing  24  houses light receivers  22 . Each light emitter  16  is paired with an opposed light receiver  22  so that light beams  20  form a light curtain  12 . Evaluation units  25  evaluate the signals of the light recievers  22  and detect an interruption of a light beam  20 . 
         [0022]    In an explosive environment the first housings must be housed in a second explosion proof housing.  FIG. 2  shows such a second housing  30  which is explosion proof and which houses either one of the first housings  14  or  24 . The first housing  14  or  24  is mounted inside the second housing  30  in a fixed manner, which means that its position inside the second housing  30  is fixed. The second housing  30  comprises a body  32  and front closure  34  transparent openings  36  for the light beams  20 . Handles  38  are provided to handle the heavy second housing  30 . 
         [0023]    The second housing  30  can be mounted to a fixed installation  40  by means of at least one alignment bracket  42 . 
         [0024]    The alignment bracket  42  is shown in detail in  FIGS. 3, 4 and 5  and comprises a first member  44  of a U-shape with a base plate  46  and two side walls  48  and  49  orthogonal to the base plate  46 . The side walls  48  and  49  are placed at a distance D 1  apart and have a wall thickness d 1 . The side walls  48  and  49  have aligned openings of which in the drawings only one (reference numeral  50 ) is visible. The side walls  48  and  49  have a symmetrical trapezoidal shape with the longer of the parallel sides being connected with the base plate  46 . 
         [0025]    The base plate  46  can be fixed to the installation  40  by at least one first base plate fastening element  54 . This fastening element  54  can be a screw with a nut. 
         [0026]    The alignment bracket further comprises a second member  64  of the same structure as the first member  44 . It has a base plate  66  and side walls  68  and  69  of the same shape wherein the distance D 2  of the side walls  68  and  69  is reduced or enlarged (in the figures it is enlarged) by twice the wall thickness d 1  . The side walls  68  and  69  have aligned openings  60  and  61 , preferably of the same size as the openings of the side walls  48  and  49  of the first member  44 . 
         [0027]    There is provided at least one second base plate fastening element  62  for fixture of the second housing  30  to the base plate  66 . 
         [0028]    The alignment bracket  42  further comprises a fixable bolt  70  for the feedthrough through the openings  50 ,  60  and  61  of the side walls  48  and  49  of the first member  44  and side walls  68  and  69  of the second member  64 . The bolt  70  connects both members  44  and  64  together and leaves the members  44  and  64  pivotable relative to each other as long as the bolt  70  is not tightened. The bolt  70  is formed as a headed screw and can be screwed into opening  61  which has a thread realized by a nut  72  which is welded to side wall  69 . 
         [0029]    The alignment bracket further comprises a bushing  74  having a length which is equal to the distance D 1  between the side walls  48  and  49  of the first member  44  with the smaller distance. The bushing  74  is placed in alignment with the openings  50 ,  60  and  61  and receives the bolt  70 . 
         [0030]    The two members  44  and  64  can be pivoted about an axes running through the bolt  70 . In that way the second housing  30  and with it the light transmitters  16  or light receivers  22  within the housing can be aligned (angularly oriented), respectivley which leads to alignment of the light curtain  10 .