Device to position a copy master in a copying apparatus
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for positioning a copy master in the focal plane of a copying apparatus. 
     In automatic continuous copying installations, e.g., photographic printers, the copy master is usually held in the copying position on the master stage by means of a hold-down plate, with the plate in most cases being equipped with lead-in bevels to prevent catching parts of the master that protrude from the transport path on the plate. Such hold-down plates operate satisfactorily if relatively long, continuous film strips are involved. In the case of noncontinuous copy masters, if for example individual images or short film strips are lined up at spaced intervals on a carrier strip, as is usually done with reorders, these hold-down plates have a disadvantage. More particularly, the copy master, at least at its leading edge which in the copying position is located exactly in the area of the lead-in bevel, is not held down and therefore the normally present curvatures and warps of the master are not eliminated, which in turn leads to defective copies. 
     OBJECT AND BRIEF SUMMARY OF THE INVENTION 
     It is the object of the present invention to improve a positioning device of this type so that it no longer has these shortcomings and, particularly in the case of noncontinuous copy masters, a satisfactory flat position of the copy masters is assured. 
     In accordance with the present invention, two pairs of pivotable flap clamps are arranged on a copy master stage in the area of its exposure window, each pair having flaps respectively disposed above and below the master plane. The pairs of flaps are driven by means of an electromagnet and can be symmetrically opened and closed relative to the master plane. In their closed state, the flaps hold the copy master on two opposing sides with their front edges. Additionally, spring elastic hold-down strips are provided to hold the copy master on its lateral sides. By means of the bilateral clamping of the copy masters by the two pairs of flap clamps an absolutely flat position of the copy master is obtained. The positioning device is particularly suitable for processing copy masters in which short strips of film or individual images are spaced apart on a carrier strip. 
     Further appreciation of the features and advantages of the invention can be gained from the following detailed description of a preferred embodiment thereof illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view through the positioning device along the section line I--I of FIG. 3, with the flap clamps open; 
     FIG. 2 is a similar cross-sectional view along the line II--II of FIG. 3 with the flap clamps closed; 
     FIG. 3 is a top view of the positioning device; 
     FIG. 4 is an enlarged detail view of a portion of FIG. 2; and 
     FIG. 5 is a view of a detail taken along the line V--V in FIG. 4. 
    
    
     DETAILED DESCRIPTION 
     In the drawing only the essential parts of the positioning device that are necessary for an understanding of the invention are shown. These components comprise a master stage 1 for supporting the device, with the upper, flat surface of the master stage defining the master (focal) plane 11 or coinciding with it, two pairs 3 and 4 of flap clamps for guiding and holding copy masters 5, two lateral hold-down strips 6 and 7 and various drive means for actuating the pairs of flap clamps and the hold-down strips. 
     The two pairs of flap clamps 3 and 4 are arranged in the area of an exposure window 12 disposed in the master stage 1. Each pair comprises two flaps 31, 32 and 41, 42, with one of each pair being located above the master plane 11 and the under underneath it. The two flaps of each pair pivot around axles 33 and 43, which are parallel to the focal plane and perpendicular to the direction of transport (arrow P) of the copy masters. Thus, the flaps can be opened and closed in the manner of a beak, essentially symmetrically with respect to the plane 11 of the stage, as shown in FIGS. 1 and 2. 
     The flaps 31, 32, 41 and 42 are pivoted by means of an electromagnet 8, which acts on the two upper flaps 31 and 41 through a connecting rod 81 coupling lateral flat tangs 34 and 44. Referring specifically to FIGS. 4 and 5, to couple the two flaps within each pair 3 and 4 of flaps, the upper flaps 31 and 41 are each equipped with a pin 35 and 45, which engages a spring action strap 36 and 46 fastened to a lateral flat tang 37 and 47 of the lower flaps 32 and 42. To limit their movement, the lower flaps 32 and 42 are further provided at their flat tangs 37 and 47 with adjusting screws 38, cooperating with the master stage 1. 
     The hold-down strips 6 and 7 serve to laterally secure the copy masters on the surface 11 of the master stage 1. They are elastically biased against the master stage and are equipped with entrance and exit bevels. 
     The mode of operation of the illustrated positioning device is as follows: 
     The copy masters are introduced with the flap clamp pairs 3 and 4 open (FIG. 1) in the direction of the arrow P. When the image field to be copied is in its correct copying position, the pairs of flaps are electromagnetically closed (FIG. 2), whereupon the front edges 39 and 49 of the flaps 31, 32, and 41, 42 (that extend transversely to the direction of transport of the copy masters) clamp and secure the copy master between them. Lateral clamping is effected by the hold-down strips 6 and 7. Simultaneously, the pairs of flaps 3 and 4, with their front edges 39 and 40, and the hold-down strips 6 and 7 define the format of the image. Following the completion of the copying process, the pairs 3 and 4 of flap clamps are opened and the next image field is brought into copying position. 
     In the case of the pair 3 of flaps, the front edges 39 are bevelled with an overhang, to assure that the flaps can be opened even if the masters are cut excessively short. 
     Compared to conventional positioning devices the apparatus embodying the invention has the advantage that the master is always held at both of its front and rear edges, whereby an absolutely flat positon of the master is achieved. In particular, the device according to the invention is suitable for copy masters in which individual images or short strips of films are mounted spaced apart on a carrier strip. 
     It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiment is therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.