Abstract:
Disclosed is a top part of a screen printing machine, wherein the bearing elements ( 4,4   a ) for the screen printing stencil ( 2 ) are respectively and directly guided and held on lateral longitudinal guide elements ( 10,11 ) by means of carriages ( 9 ), enabling said bearing elements ( 4, 4   a ) to be adjusted in relation to each other and to be fixed. Said configuration makes it possible for the screen printing stencil ( 2 ) to be held in a stable and exact manner, irrespective of the size thereof. According to the invention, one of the bearing elements ( 4   a ) can also be raised in order to lift the screen printing stencil ( 2 ) when pressed against the other bearing element ( 4 ). The bearing elements ( 4, 4   a ) are thus respectively held on the carriers thereof ( 7,8 ) by means of pivoting hinges ( 5, 6 ).

Description:
FIELD OF THE INVENTION 
   The invention relates to a top part for a screen printing machine, having a fixture for a screen stencil. The fixture can be lifted and lowered with respect to a printing table as a function of the movement of a squeegee carrier disposed in lateral guide bars and is provided with bearing elements for the screen stencil. 
   BACKGROUND OF THE INVENTION 
   It is known to accommodate the screen stencil in a master frame for a reception in the top part. The master frame is, in particular, constructed of rectangular cubes. The screen stencil is clamped to the bearing elements, which are clamped to the longitudinal sides of the master frame and can be slid in the longitudinal direction of these longitudinal sides to fit with the screen stencil. For adjusting the position of the screen stencil, the master frame includes adjusting devices which are applied in the area of its corners. Clamping cylinders are also provided, fixing the master frame after the adjustment. During printing operation the master frame is lifted up on one side in order to detach the screen stencil from the material subjected to the printing. After each printing operation, the master frame is lifted parallel to the printing table in a known manner to remove and insert material subjected to the printing. If the screen stencil is smaller than the master frame and one of the bearing elements must therefore be held in a center area of the master frame, far away from the clamping points at the corner of the master frame, the adjustment of the master frame and the screen stencil relative to the printing table is relatively inexact and affects printing quality. 
   The goal of the present invention is to provide a top part that ensures a simple and precise fixing for a screen stencil independent of the size of the screen stencil. 
   SUMMARY OF THE INVENTION 
   To achieve this goal, bearing elements of a top part of a screen printing machine are connected to cross members, and both ends of each cross member are connected to carriages, which are longitudinally slidably guided on lateral carrying rails of guide bars to adjust the bearing elements to the screen stencil. Further, on the carriages can be clamped to the lateral guide bars. 
   As a result of this further development, a master frame can be eliminated. Independently of its size, each screen stencil is held by way of the cross members directly on the lateral carrying rails and is therefore clamped in a stable manner. In order to permit the required one-sided lift off movement in the case of such an embodiment, it is provided as a further development of the invention that the bearing elements are fastened by swiveling hinges to the cross members. During a one-side lifting of one of the bearing elements, a swiveling movement of the screen stencil clamped to the bearing elements centered to an axis extending in parallel to the bearing elements. In order to avoid the necessity of lifting off of one of the cross members during this one-sided lifting operation, a further development of the invention includes a lifting device and hinges assigned to one of the bearing elements. The lifting device and the hinges allow a swiveling movement as well as a lifting movement of the bearing elements with respect to the cross members. In particular this can be achieved in that a portion of the hinge connected to the bearing element is vertically displaceably arranged on a guide pin, which is fixedly screwed to the cross member. In this embodiment of the invention the swiveling hinges, or at least a portion thereof, are fixedly screwed to the cross members so that a very stable arrangement is also achieved. 
   The lift-off movement of the entire screen stencil can take place in a conventional manner. The one-sided lift-off movement can be achieved in that an electric motor is provided which carries out the screen stencil lifting function synchronized with the squeegee movement. The electric motor also lifts up one of the bearing elements by way of swiveling levers in the above described manner during the printing. In such an embodiment of the invention, mechanical elements for the lifting connected with driving elements for a squeegee movement are superfluous. 
   In order to achieve the adjusting of the screen stencil in a convenient way, a further development of the invention includes ball bearings on supporting surfaces for the carriages of each cross member. This allows a carriage adjustment and a screen stencil adjustment as well. These adjustments in the longitudinal direction of the carrier rails as well as in the longitudinal direction of the cross members are implemented in particular by way of micrometer screws or the like. Each of the carrier rails includes a tooth rack, which a pinion connected with a carriage engages. The pinion is non-rotatably connected with the pinion of the opposite carriage to synchronize the adjustment of the carriages in the longitudinal direction of the carrier rails. The clamping of the cross members with respect to the carrier rails is realized in particular by means of pneumatic cylinders or the like. Such clamping cylinders are also assigned in particular to the bearing elements for the clamping in of the screen stencil. 
   The invention is illustrated with an embodiment and will be explained as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic top view of the top part of a screen printing machine according to the invention; 
       FIG. 2  is a side view of the top part according to  FIG. 1 ; 
       FIG. 3  is an enlarged, partial sectional view of the arrangement according to  FIG. 1  along the section line III—III; 
       FIG. 4  is an enlarged, also partially sectional top view of the corner area illustrated in  FIG. 3 ; 
       FIG. 5  is a schematic longitudinal sectional view of the area of the screen stencil fixture along the section line V—V in  FIG. 1 ; 
       FIG. 6  is a top view of a corner of the fastening arrangement of the supporting legs for the screen stencil in the direction of the arrow VI; and 
       FIG. 7  is a top view of the opposite corner of the screen stencil fixture viewed in the direction of the arrow VII in FIG.  5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  show guide bars  1  for a squeegee mechanism which is not shown. Below the guide bars  1  a fixture for a screen stencil  2  is included. The shorter sides of the border  3  of the rectangular screen stencil  2  are placed on bearing elements  4  and  4   a  respectively and are clamped on there, as will be explained in detail in  FIGS. 5  to  7 . Each bearing element  4  and  4   a  is connected by hinges  5  and  6  with a cross member  7  and  8 . Cross members  7  and  8  are connected at both of their extreme ends with carriages  9 . The carriages  9  are guided on lateral guides  10  extending parallel to guide bars  1  and are laterally held on guide profiles  11 . The longitudinal guidance of the carriages  9  also includes adjusting devices which permit the adjusting of the carriage position and thus also of the position of the bearing elements  4  and  4   a  respectively. 
   For this purpose the cross member  7 —see FIGS.  1  and  4 —is connected by a clamping device  42  with another cross member  40  which carries a shaft  44 . The shaft  44  is connected on both sides with a pinion  41 , both pinions  41  engaging in tooth racks  43 . The tooth racks  43  extend parallel to the guide bar  1  and to the lateral guide  10  and the guide profile  11  respectively. 
   When the clamping device  42  is activated, the cross members  7  and  40  and analogously the cross members  8  and  40 ′ form a unit which can be rapidly displaced manually in the longitudinal direction of the guide bars by its carriages  9 . A tilting of the cross members is prevented by the pinions  41  arranged on both sides of the cross members and connected with each other, engaging in the tooth racks  43 . After the rough adjustment in the longitudinal direction of the guide bar  1  has been carried out, the fine adjustment of the carriage position and of the bearing elements  4  and  4   a  can take place. To that effect, the clamping devices  42  are released so that the carriages  9  and the cross members  7  and  8  are free from the cross members  40  and  40 ′ respectively. The cross members  7  and  8  are displaceable longitudinally and transversally approximately 10 millimeters with respect to the guide bar  10 . 
   As indicated in  FIGS. 3 and 4 , a displacement in longitudinal and transverse direction can be achieved manually by adjusting devices  12  and  13 , having different designs. The adjusting device  13  allows an adjustment of the assigned carriage  9  in its longitudinal direction, in particular in the direction of the lateral guide  10  and the guide profile  11 . The adjusting device  12  allows the adjustment of the carriage  9  transversely to its longitudinal direction on the lateral guide  10  in order to achieve also a fine adjustment of the screen stencil  2  placed on the bearing elements  4  and  4   a  in this direction. The adjusting device  12  includes a handle  14 , allowing a manual rotation of a spindle  15  engaged in a collet  16 . The collet  16  is placed in opposite to the handle  14  at an application surface of the carriage  9 . Since the housing  17  of the spindle  15  is fixed with respect to the lateral guide  10 , carriage  9  can be displaced along a supporting surface of the lateral guide  10 . Therefore, the carriage  9  is disposed on the lateral guide  10  by ball bearings  18  which allow a transverse displacement. 
   In the longitudinal direction, the carriage  9  is adjusted by operating the screw spindle  19  fixedly connected to a receiving sleeve  20  with respect to the lateral guide  10  and the guide profile  11 . The screw spindle  19  includes at an end opposite to a handle  14   a  a bevel pinion  21  engaged with another bevel pinion  22 . The bevel pinion  22  is non-rotatably disposed on a screw spindle  23  engaging in a threaded sleeve  24 . The threaded sleeve  24  interacts at its end  24   a  with a surface of the carriage  9 , thereby the carriage  9  can be adjusted in its longitudinal-direction. In the same manner, an adjustment of the carriages  9  connected with the cross member  8  is enabled. Clamping devices including pneumatic cylinders  25  allow fixing of the carriages  9  and of the cross members  7  and  8  in the adjusted position for the printing operation. Since the screen stencil  2  rests on the bearing elements  4  and  4   a  and is clamped on these bearing elements (see FIG.  5  and the pertaining description), the screen stencil  2  is held in a very stable and perfectly aligned position for the printing operation. A master frame is superfluous. The screen stencil  2  represents the connection between the two displaceable bearing elements  4  and  4   a.    
   To achieve the one sided lifting of screen stencil  2  during the printing in a known manner, the bearing element  4   a  is liftably held on its assigned cross member  8 . The lifting operation is caused by known levers  26  being actuated by way of a screen lifting motor  27  synchronously to the squeegee movement. Lever  26  is schematically illustrated also in  FIG. 3 , although such a lifting device is not assigned to bearing element  4 . The levers  26  are assigned to both sides of the bearing element  4   a  approximately in the area of the two hinges  6  and can be synchronously operated by a connecting rod  27  (FIG.  3 ). 
   In order to achieve the one-sided lifting of the bearing element  4   a  with respect to the cross member  8 , the hinges  6  are realized as illustrated in  FIGS. 5 and 7 . Naturally, a different design would also be conceivable. 
   As illustrated in  FIG. 7 , hinge  6  includes a base  29  fixedly screwed to the cross member  8  and a movable part  30  being connected to the base  29  by a swivel pin  28 . The movable part  30  is capable of rotating centered to the axis of the swivel pin  28  with respect to the base  29 . The moving part  30  includes a guide pin  32  projecting perpendicularly upwards, and a guide bush  31  surrounding the guide pin  32  is part of a connection piece  33  to the bearing element  4   a.    
   As illustrated in  FIG. 5 , the bearing element  4   a  is realized as a profiled part including a longitudinal groove  34  into which groove blocks of a pneumatic clamping cylinder  35  are engaged, wherein the pneumatic clamping cylinder  35  can slide relative to the bearing element  4   a . The pneumatic clamping cylinder  35  is thereby connected to the bearing element  4   a , allowing clamping the screen stencil  2  onto the bearing element  4   a.    
   Bearing element  4  realized in the same way and corresponding parts have same reference numbers. Different from the suspension of the bearing element  4   a , the bearing element  4  is only swivelably arranged by way of its hinge  5 . Hinge  5  includes a base part  36  fixedly screwed to the cross member  7  and a movable part  37  swivellably held respectively to the base part  36  by way of a pin  28 . The movable part  37  is fixedly screwed to the bearing element  4 . As illustrated in  FIGS. 5  to  7 , the screen stencil  2  can be lifted off the material subjected to the printing by a respective lifting of the bearing element  4   a . For lifting of the screen stencil  2 , the bearing element  4   a  is swiveled centered to pin  28  of its hinge  6 , resulting in an angeled position of the screen stencil  2 . Bearing element  4  is also being swiveled centered to pin  28  of its hinge  6 . A connection piece  33  of the hinge  6  is lifted upwards in the longitudinal direction of the guide pin  32  during the printing operation. 
   Naturally, it is conceivable that other adjusting possibilities for carriages or other possibilities for the construction of the hinges are provided. It is decisive that the invention suggests a design, which makes a master frame superfluous and allows a stable fixing of the screen stencil irrespective of its size on corresponding bearing elements and their fixture.