Abstract:
A machine tool having a protective cabinet and an illumination system comprising at least one discharge lamp installed in the interior space of the protective cabinet. The discharge lamp is formed as a flat lamp radiating over a large area with a uniform luminous intensity and disposed on a cabinet wall in order to obtain an enhanced illumination of the entire workspace of the machine as well as of the interior space of the protective cabinet.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to a machine tool comprising a protective cabinet and an illumination system comprising at least one discharge lamp installed in the interior space of the protective cabinet. 
     DISCUSSION OF PRIOR ART 
     Modern machine tools and machining centers regularly comprise a protective cabinet surrounding the workspace and, where required, also surrounding the secondary devices during operation. To enable access to the workspace sliding doors are provided which are movable rectilinearly or on round guides. The side walls as well as the sliding doors comprise viewing windows in respectively suitable arrangements and sizes in order to enable an observation of the operation and the progress of the work. For work within the workspace with the sliding doors opened as well as for monitoring the operating cycles, one or, in most cases, a plurality of lamps are provided at suitable positions of the inner wall of the protective cabinet, these lamps having a sufficient lighting efficiency to securely monitor and trace machining operations even when the atmosphere of the workspace is contaminated by droplet fog caused by the lubrication and cooling fluids or by the finest chips. 
     Illumination systems designed for the protective cabinets of machine tools generally comprise one or more built-in lamps as described, for example, in EP 1 389 711. Such built-in lamps are individually, or in a plurality, mounted in the interior space of the protective cabinet on one cabinet wall and comprise elongated gas discharge lamps formed as so-called fluorescent lamps and mounted in plurality adjacent to each other in a housing containing the required electrical circuits. These fluorescent lamps radiate over a wide area and with a uniform luminous density, at least in their longitudinal extension. Depending on the type the height of the built-in lamps is approximately 100 mm so that they protrude into the interior space of the cabinet in the installation height when they are installed on the inner side of a cabinet wall. Due to the dimensions of the built-in lamps the selection of their positioning is limited since only certain positions in the respective workspace within the protective cabinet are suitable for placing and mounting such elongated lighting elements. The lamps are usually integrated in the upper or lateral corner sections of the protective cabinet, and reductions with respect to optimum illumination of the workspace caused by the use of fluorescent lamps have to be tolerated. 
     From patent publication US 2002/0163311 A1, a discharge lamp designed for dielectrically impeded discharges is known which may, for example, be used for a flat panel display or a display designed in LCD technology. This discharge lamp comprises a bottom plate, a transparent top plate and a discharge space filled with a discharge medium disposed between the two plates. A set of electrodes is provided for generating dielectrically impeded discharges in the discharge medium. Support elements are formed as integrated components of the cover plate and have a tapered contour in the direction toward the bottom plate. The support elements are a large number of support protrusions uniformly distributed over the entire active surface of the lamp and consist of glass or another transparent material. 
     In DE 100 16 714 C2 a flat lamp is described in which a plurality of uniformly distributed light emitting diodes are disposed in a closed, flat glass housing and positively fastened between the front and rear sides. 
     SUMMARY OF THE INVENTION 
     It is a purpose of embodiments of the invention to provide an illumination system for a machine tool enabling an enhanced illumination of the workspace as well as of the remaining interior space of a protective cabinet. 
     In connection with a machine tool comprising a protective cabinet and an illumination system comprising at least one discharge lamp which is installed in the interior space of the protective cabinet on one cabinet wall and formed as a flat lamp radiating over a large area, the purpose is, according to the invention, met by the flat lamp comprising a flat luminous element radiating with a uniform luminous intensity over its entire surface and is encapsulated in a flat, gas-tight housing including a transparent plate on one side. 
     In the illumination system according to the invention flat lamps may be used which function according to the principle already described in the cited US 2002/0163311 A1 or in DE 100 48 187 A. For the results and effects aspired according to the invention it is important that the flat lamps used have sufficiently large dimensions in one plane and radiate uniformly with a high luminance over their entire active area. The small overall thickness of these flat lamps, which should not exceed 30 mm, gives rise to the possibility to position the respective flat lamp in a predetermined area of an inner wall of the protective cabinet via suitable fixing means. Since the flat lamp only protrudes into the internal space of the cabinet by an amount corresponding to its thickness, the internal space of the protective cabinet and thus the workspace is only insignificantly reduced. This creates the option to position one or a plurality of flat lamps in the areas of the respective cabinet walls or the cabinet ceiling which guarantee an optimum illumination of the entire workspace as well as, where appropriate, secondary spaces within the protective cabinet. 
     Depending on the type of machine and the size or contour of the protective Cabinet the number and position of the respectively-used flat lamps may be selected in view of an all around and shadowless illumination of the workspace. The shape of the respectively-used flat lamps may be polygonal, circular, oval, or arcuate. Aside from that, so-called light ribbons are feasible in which the lamps are individually, or in a plurality mounted behind each other on the cabinet walls or the cabinet ceiling as a narrow, continuous, or discontinuous luminescent strip. 
     To avoid a reduction of the interior space of the protective cabinet the flat lamps according to the invention may also be installed in indentations in one or more cabinet walls or in the cabinet ceiling, a permanent sealing being required in that case. 
     A preferred embodiment of the flat lamps used according to the invention comprises a relatively extensive luminous element radiating with a, to the largest extent, uniform luminance over its entire surface and encapsulated in a rigid, flat, gas-tight housing provided with a transparent plate on one side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The advantages, benefits, and features of the invention will become more clear from the following detailed description when read in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a perspective view of a milling and drilling machine in accordance with the invention, comprising a protective cabinet and a lateral flat lamp; 
         FIG. 2  is a cross sectional view of a flat lamp as employed in the  FIG. 1  embodiment; and 
         FIG. 3  is a cross sectional view of another embodiment of a flat lamp for use in the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a program controlled milling and drilling machine which is only to be regarded as an example for an efficient arrangement of a flat lamp. The machine tool comprises machining head  1  which is shiftable on a column along two horizontal coordinate axes by means of a motor, a tool  3  being clamped in vertical work spindle  2  of the machining head. Workpiece table  4  is supported by a panel shiftable along the vertical coordinate axis on the front side of the machine column by means of a motor. The table surface defines the maximum workspace. Rotating spindle  6  for chip discharge is disposed in half-round bottom pan  5  below workpiece table  4 . Toward the front side, bottom pan  5  is limited by a half-round face  7  carrying a guide rail  8  displaced downwardly on its outer side. 
     Protective cabinet  10  consists of two rear side walls  11 ,  12 , covering wall  13  connected between the side walls, and front side wall  14  extending a distance from workpiece table  4  and laterally covering the workspace. Further, protective cabinet  10  shown is provided with a so-called round door  15  comprising cylinder-segment shaped side wall  16  which includes window  17 , and upper, circle-segment shaped cover plate  18 . Lower inclined shoulder  19  has a sliding surface which leads into the bottom pan and shiftably supports round door  15  on lower guide rail  8 . Furthermore, upper cover plate  18  is guided or supported so as to be pivotable about vertical axis  20 . 
     As can be seen in  FIG. 1 , large-area flat lamp  21 , which is shown in a cross Sectional view in  FIG. 2 , is attached to the inner side of side wall  14 . The flat lamp comprises a flat, rigid all around frame  22 , preferably made of metal such as refined steel, with continuous rear wall  23  and large-area glow discharge lamp  24  disposed in frame  22  in a shock proof manner. A shock proof, transparent front cover plate  26 , for example, a laminated glass panel, is fastened within the frame  22  and surrounded by its angled edge  25  on all sides. 
     The free interior space of flat lamp  21  is completely filled with synthetic resin  27 . The entry of dust, liquids, vapours, and gasses is securely prevented in this way and, if required, by other, or additional, sealing means. 
     The flat lamp may be attached to the inner side of side wall  14  as a separate component, and the electric control elements and circuits may be disposed on the outer side of the side wall and connected to glow discharge lamp  24  via pressure-sealed cables  28 . As can be seen in  FIG. 1 , flat lamp  21  is disposed directly adjacent to the workspace above the workpiece table. Since the luminance of the flat lamp is, to the largest extent, uniform over its entire surface an optimum illumination of the workspace is obtained so that the respective operator can accurately observe the machining operations through window  17  of round door  15  when the round door is closed. 
     The alternative embodiment of flat lamp  30 , shown in cross section in  FIG. 3 , substantially corresponds to the embodiment according to  FIG. 2 , and identical components are designated by the same numerals. For this flat lamp also a glow discharge lamp  24 , working in accordance with the functional principle cited as known in the introduction, is used. Glow discharge lamp  24  is mounted in closed housing  31  in a shock-proof manner. On one side housing  31  comprises chamber  32  in which electric or electronic switching elements  33  are accommodated in a protected manner. Supply cable  34  leads into chamber  32 . Corrugated thin sheet  35 , preferably made of a heat-conducting material such as a light metal, is fixed on the bottom plate of housing  31 , which is made of sheet metal or plastics to promote heat dissipation from the interior of the housing. For enhanced heat dissipation the bottom plate or other wall elements, or both, may be profiled, for example, corrugated or fan-folded. The wall elements may conveniently be formed of light metal. Protruding cooling fins may also be used. 
     In the flatter region adjacent to chamber  32 , support  36  is provided by which lamp  30  is adjustably attached to a component of the machine tool. Support  36  comprises support element  37  acting as a spherical shell having lateral bores  38  and central recess  39  formed with a spherical surface. Sphere  40  is disposed in spherical recess  39 . Plate  42  is fixedly connected to the rear wall of housing  31 , the plate having recess  43  and two adjacent bores  44  in its central region. The bores are aligned with bores  38  in support element  37  and are capable of accommodating bolts. Support  36  forms an adjustable spherical surface or spherical shell bearing which can, for example, be fixed by bolts. 
     The arrangement of the flat lamp is, of course, not limited to the position illustrated in the drawings. Rather narrow flat lamps may also be positioned at other suitable positions of the side walls or the rear column wall individually or in combination with large-area flat lamps. It is important that the respective flat lamps do only protrude into the interior space of the protective cabinet by a small amount, preferably no more than about 30 mm, so that the free moving space inside of the protective cabinet is not limited while the illumination of the workspace is, at the same time, optimized.