Abstract:
A reflector apparatus with a reflector, in particular a parabolic mirror, with a plastic layer, on which a plastic sheet with a metal structure is provided, and with a casing consisting of two hollow cylinders which can be arranged inside one another and between which the reflector is held is provided, wherein the reflector comprises a further plastic layer which forms a substantially hollow cylindrical collar on the edge of the reflector and wherein this collar is held between the hollow cylinders of the casing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates to a reflector apparatus, in particular a parabolic mirror, with a plastic layer on which a plastic sheet with a metal structure is provided and with a casing consisting of two hollow cylinders which can be arranged inside one another and between which the reflector is held. 
     2. Description of the Prior Art 
     Reflectors or transreflectors are used for many applications, in particular for the orientation of radar waves. It is already known to produce reflectors for radar applications where a plastic sheet is coated with a metal, in particular aluminum, the plastic sheet is fixed in an injection moulding die and is then overfed with a plastic layer having the necessary shape, for example a parabolic shape. A parabolic mirror is thus formed which is arranged relative to a radar source by a casing. In many cases, this casing consists of a metal, for example of aluminum. A casing of this type can be produced as a cast casing. 
     It is also known to fix the parabolic mirror in the cast casing between an outer cylinder and an inner cylinder with a seal inserted in-between. In an outer hollow aluminum cylinder having a peripheral, inwardly orientated flange, a seal is placed against this flange, the reflector is subsequently introduced that is followed by an inner cylinder which presses the reflector and the seal against the flange of the outer cylinder. 
     It has been found that pronounced deformation of the components may occur owing to the different coefficients of thermal expansion of the casing and the reflector. Owing to this deformation, a precise orientation in the radial direction of the reflector relative to the radar transmitter is no longer ensured. As the centrality of the reflector relative to the transmitter is very important for applications where safety is paramount, it is necessary not only to accommodate production tolerances with a reflector apparatus consisting of reflector and casing but also to accommodate for the differing thermal expansion of the various components. 
     SUMMARY OF THE INVENTION 
     Starting from this state of the art, it is an object of the present invention to provide a reflector arrangement which ensures a defined position of the parabolic mirror over a predetermined temperature range. A further object of the invention is to provide a process for producing a reflector arrangement of this type. 
     The reflector arrangement according to the invention comprises a reflector with a first plastic layer on which a plastic sheet with a metal structure is provided and a further plastic layer which forms a substantially hollow cylindrical collar at the edge of the reflector as well as a casing which consists of two hollow cylinders adapted to be arranged inside one another, the collar of the second plastic layer being held between the hollow cylinders of the casing. As the collar of the reflector is fixed at the end remote from the reflector and the edge of the reflector is not fixed directly between the hollow cylinders, stresses between collar and hollow cylinders owing to differing thermal expansion have only a slight effect on the reflector itself. 
     The hollow cylinders and the plastic layers of the reflector are produced from different materials. These different materials also have different coefficients of thermal expansion, which results in differing expansion of casing and reflector. As the hollow cylindrical collar is accommodated between the hollow cylinders of the casing, the differing expansion of these components has to be absorbed. It is particularly advantageous to provide the collar with substantially axially extending slots which are distributed along the periphery, for example by milling material from the collar in these slots. If the collar and the hollow cylinders expand to different extents, this variation can be absorbed by the slots so that excessive stresses are avoided. 
     A further particular advantage is that catch fingers are arranged on the collar between the hollow cylinders for defined fastening of the collar. These catch fingers each comprise a catch projection and are also distributed along the periphery of the collar. They are separated from the collar by axially extending slots. 
     A further particular advantage is that one of the hollow cylinders includes a shoulder behind which the catch projection engages and that the second hollow cylinder comprises a stop for the edge of the collar. The position of the collar relative to the hollow cylinders is therefore defined in the axial direction. 
     It is also particularly advantageous to provide a resilient element which is part of the collar and is fixed between the shoulder and the stop of the hollow cylinders. This resilient element serves to compensate for production tolerances between the two hollow cylinders and the reflector. 
     It is also particularly advantageous to provide ribs on the collar which are deformed as the collar is inserted between the hollow cylinders of the casing. These ribs also serve to compensate for production tolerances. 
     It is also further advantageous to provide these ribs on the catch fingers, as this ensures that the catch fingers are fixed securely between the two hollow cylinders whereas the region between the catch fingers, which are separated from the catch fingers by slots, can shift between the two hollow cylinders of the casing if necessary due to different thermal expansion. 
     A further particular advantage is that a radially extending peripheral flange is provided outside the collar at the edge of the reflector. This flange serves as a seal seat for a seal that is arranged between the outer hollow cylinder and the collar and flange of the reflector. This is advantageously a low-pressure seal which does not exert a great force on the collar of the reflector and is able to absorb differing thermal expansions. A part of the seal is also located between the flange and the outer hollow cylinder. A rib, which serves to fasten the reflector on the outer hollow cylinder so it is sealed against contaminants such as spray water, is provided on the outer hollow cylinder in this region. 
     With the arrangement according to the invention, the production tolerances of the different components can be allowed for and it is also ensured that differing thermal expansion is compensated so that the variations in the centrality of the reflector arrangement lie within the permitted tolerances despite this differing thermal expansion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the reflector arrangement with reflector and casing; 
     FIG. 2 is a cross-section through the reflector arrangement along line A—A of FIG. 1; 
     FIG. 3 shows an enlargement of Detail X of the reflector arrangement, as shown in FIG. 2; 
     FIG. 4 shows an enlarged partial cross-section of the reflector arrangement along line B—B of FIG. 3; and 
     FIG. 5 is a perspective view of the reflector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention will now be described with reference to FIGS. 1 through 5. FIG. 1 is a plan view of the reflector arrangement  1 . FIG. 2 is a corresponding section along line A 13  A in FIG.  1 . The reflector arrangement consists of a reflector  2  and a casing  3 . The casing  3  is used for mounting the reflector on a plate which carries, for example, the electronic components and also a transmitter, for example for radar waves. The reflector  2  is to be orientated relative to this transmitter by means of the casing  3 . The reflector  2  can be, for example, a parabolic mirror or a transreflector of the type used, for example, in radar systems. For mounting the casing  3 , the casing  3  has a mounting flange  4  with holes  5  for fastening to a plate. The mounting flange  4  is formed integrally with an outer hollow cylinder  6  which is orientated with its axis perpendicular to the mounting flange  4 . The casing  3  also comprises an inner hollow cylinder  7  which is located inside the outer hollow cylinder  6 . It is particularly advantageous to use a cast casing  3  made of aluminum. 
     The reflector  2  comprises a plastic sheet  8  carrying a aluminum structure and is constructed as follows: 
     The plastic sheet is encapsulated in a first plastic layer  9  which gives the plastic sheet  8  its shape; This first plastic layer  9  is in turn overfed by a second plastic layer  10  where the second plastic layer  10  not only is located in the region of the first plastic layer  9 , in other words of the actual reflector, but also has a hollow cylindrical collar  11  which adjoins the edge of the first plastic layer  9  and therefore of the actual reflector. 
     In addition to the hollow cylindrical collar  11 , the reflector or the second plastic layer  10  also includes a peripheral flange  12  extending radially outside the collar  11 . This flange  12  is connected to the outer plastic layer  10  of the reflector via individual ribs  13  which are arranged perpendicularly to the flange  12  and distributed along the periphery. The ribs  13  serve to stiffen and determine the angle between the flange  12  and the actual reflector. 
     The collar  11  of the reflector  2  includes a plurality of axially extending slots  14 . The function of these slots would also be ensured if the slots were to extend obliquely to the axial direction. The slots  14  are distributed along the periphery of the collar  11  and are important for compensating for the different thermal expansion between the collar  11  and the inner and outer cylinders  6 ,  7  of the casing. 
     The collar  11  of the reflector  2  also comprises a plurality of catch fingers  15  which are distributed along the periphery. The catch fingers  15  are separated from the remainder of the collar  11  by the slots  14 . The catch fingers  15  carry catch projections  16  projecting outwardly from the collar  11 . The catch fingers  15  also comprise elastically resilient elements  18  extending outward from their free end  17 . 
     The outer hollow cylinder  6  has a connected end  19  facing the mounting flange  4  and a free end  20 . The outer cylinder  16  includes a peripheral rib  21  with a shoulder  22  orientated toward the connected end  19 . The inner cylinder  7 , on the other hand, comprises a stop  23  which is orientated toward the reflector when in the mounted state. Each catch arm  17  of the collar  11  comprises axially extending ribs  24  which are orientated inwardly. 
     The assembly and construction of the reflector arrangement is accordingly as follows. A low-pressure seal  25  is initially fastened on the reflector  2  between collar  11  and flange  4 . The reflector is then pushed onto the outer cylinder  6  from above, in other words from the end of the casing  3  remote from the mounting flange. The catch fingers  15  with the catch hooks  16  are deflected over the peripheral rib  21  and catch behind the shoulder  22  of the outer cylinder  6 . A space containing the low-pressure seal as is formed between the upper free end  20  of the outer cylinder  6  and the flange  12  of the reflector as well as the collar  11  of the reflector. This low-pressure seal  25  is preferably already located in a seal seat of the reflector  2  when the reflector  2  is mounted on the outer hollow cylinder  6 . The low-pressure seal  25  prevents the seal from exerting direct pressure on the reflector while still ensuring a contaminant-tight connection between outer hollow cylinder  6  and flange  12 . An additional rib  26 , arranged at the free end  20  of the outer hollow cylinder  6 , further improves the sealing effect. 
     Once the reflector is mounted on the outer hollow cylinder  6 , the inner hollow cylinder  7  is inserted from the mounting side. The two hollow cylinders  6  and  7  are mounted relative to one another in such a way that the lower end face  27  of the inner hollow cylinder coincides with the mounting face  28  of the mounting flange  4 . The catch fingers  15  strike the stop  23  of the inner hollow cylinder with their free end  17 . The free ends  17  of the catch arms  15  with the elastic elements  18  are now fixed between the shoulder  22  of the outer hollow cylinder  6  and the stop  23  of the inner hollow cylinder  7 . The resilient elements  18  serve to take up production tolerances between the two cylinders and the collar of the reflector. Production tolerances in the radial direction between the two cylinders are taken up by the ribs  24  on the catch fingers  15 . These ribs are deformed during insertion of the second hollow cylinder to such an extent that a secure fit is produced between the catch fingers  15  and the hollow cylinders  6 ,  7 . 
     If the radius of the hollow cylinders and of the collar vary to different extents, owing to thermal expansion, this will be compensated for by the slots  14 . Whereas the catch fingers  15  are fixed securely between the hollow cylinders  6 ,  7 , the other parts of the collar  11  are able to shift relative to one another due to the slots. 
     As a result of the particular design of the collar  11  of the reflector, the collar is bound in a defined manner between the inner hollow cylinder  7  and the outer hollow cylinder  6 , production tolerances are allowed for and also differing thermal expansion of the components have been allowed for. The collar thus absorbs this differing thermal expansion without affecting the central position of the actual reflector. 
     The only thermal expansions which may still affect the position of the reflector are the axial thermal expansions by which the position of the reflector is changed in the axial direction. These expansions have been found not to have any significant effect, as the permitted tolerance is substantially greater than the sensitivity with respect to the centrality of the reflector.