Abstract:
A testing stand for printing plates has an upright frame, a printing plate support having opposed lateral ends, and guide members connected to the opposed lateral ends of the printing plate support. The guide members engage the frame and connect the printing plate support to the frame so that the printing plate support is vertically moveable. A magnifying glass carriage is slidably connected to the printing plate support. An illumination device is connected to the frame.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a testing stand for printing plates, comprising a movable printing plate support, a movable magnifying glass carriage including a correlated hand rest, and an illumination unit as well as a frame, with means for holding and guiding the aforementioned components provided on the frame. Such testing stands are used for inspection of printing plates in the graphic design industry. 
     2. Description of the Related Art 
     Testing stands for printing plates are known, i.e., so-called offset printing plate testing stands, for example, disclosed in the brochure “megastahl”, offsetplatten-prüftstand, brochure 9003 of the company Barent &amp; Co. -megastahl, Augsburg, Germany, wherein an almost vertically positioned printing plate support is vertically slidably arranged in guides positioned on both sides and mounted on sidewalls. 
     For providing the slightly rearwardly inclined position of the printing plate support, the forward edges of the aforementioned sidewalls are slanted to the rear and a guide for the vertical sliding action of the printing plate support is stationarily arranged on the forward edge, respectively. The sidewalls and the printing plate support guided therebetween form a so-called common upper part which can be placed onto a base frame. For increasing the stability of the upper part, behind the vertically movable printing plate support, between the aforementioned sidewalls, at least one wall connecting the latter is provided which is generally parallel to the movable printing plate support. Moreover, in front of the movable printing plate support a working frame is arranged which has an upper rail and a lower rail which are secured by means of laterally arranged plate-shaped guide members at a spacing to one another. Each one of the lateral guide members is moveably and lockably arranged in a guide rail, respectively, and the guide rails are arranged stationarily on the guides of the printing plate support. The upper rail of the working frame is moreover provided for securing a magnifying glass that is movable in the horizontal direction as well as for receiving parts of the illumination unit. The lower rail of the working frame serves also as a support rail for the hand of the operator as well as for receiving parts of an illumination unit which illuminates the open area between the lower and the upper rails. In preparation for inspection of the printing plate, the operator moves the working frame to an eye level position and locks it then in the selected position. For inspecting the selected section of the printing plate, the operator moves, usually with his left hand, the printing plate support substantially vertically in the upward or downward direction so that the section of the printing plate to be inspected appears between the upper and lower rails of the working frame. The illumination unit arranged within the working frame illuminates the section of the printing plate between the upper and the lower rails of the working frame for inspection. The areas of the printing plate positioned above and below the working frame are illuminated only by the normal ambient light. The inspected section, on the other hand, is exposed to a very high light intensity which, depending on the type of the printing plate, can result in significant after exposure of the same. 
     For facilitating the movement of the printing plate support, the printing plate support is connected with a counterweight arranged in its upper part. When printing plates of different sizes are inspected successively, the adaptation of the counterweight to the mass of the printing plate to be inspected is relatively complex. 
     In order to be able to inspect the selected section of the printing plate more closely, the operator must first move the printing plate support to such an extent that the corresponding horizontal strip of the printing plate appears in the area of the working frame and subsequently he must move the magnifying glass to such an extent that the corresponding section within the horizontal strip can be viewed enlarged. This means that the operator with his “auxiliary” hand must move sequentially two different components of the testing stand in order to reach the section of the printing plate to be inspected more closely. For moving the aforementioned two components, the operator will usually not use his “working” hand and because the working hand generally holds working tools, for example, a retouching brush for corrective work on the printing plate. 
     As can be further taken from the brochure “megastahl”, catalogue 9801, “Ihr starker Partner in der grafischen Industrie” (Your strong partner in the graphic design industry) of the company Grassinger KG, Bobingen, Germany, nothing has changed over the years with respect to the above described basic principle of the configuration of a testing stand for printing plates used in the graphic design industry. From the last mentioned brochure it can be taken that only minimal changes in the configuration of the aforementioned working frame have resulted. A further disadvantage of these known testing stands is moreover their massive and thus heavy construction. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a testing stand for printing plates which substantially does not exhibit the aforementioned disadvantages of the known testing stands and which can be manufactured with a reduced manufacturing-technological expenditure as much as possible. 
     In accordance with the present invention, this is achieved in that on the printing plate support on both sides a respective guide member is arranged, wherein these guide members are connected to the frame and wherein the respective guide path for these guide members are positioned vertically. 
     In accordance with the present invention, this is achieved for a method for inspecting printing plates in that the printing plate support is positioned in an optimal basic position for the operator and in that, for the section-wise manual visual inspection, alternatingly a magnifying glass carriage, which secures the optical aid as well as a hand rest, is guidedly moved in the horizontal direction and/or the optical aid together with the hand rest is guidedly moved in the vertical direction. 
     The new testing stand for printing plates is characterized particularly in that a basically different configuration in comparison to known testing stand is selected. In particular, and especially, this testing stand for printing plates, which comprises a movable printing plate support, a movable magnifying glass carriage with a correlated hand rest, an illumination unit as well as a frame with means for holding and guiding the aforementioned components, is realized such that the almost vertically positioned movable printing plate support is movable only in the vertical direction, in contrast to the prior art construction principle according to which the printing plate support is moved in a plane that is slanted relative to the vertical direction. With this new and significant construction detail it is ensured that the lower edge of the printing plate support, which projects farthest toward the operator, has always a constant spacing to the body of the operator and, in contrast to the known testing stands, does not come closer and closer to the body of the operator upon movement in the downward vertical direction. 
     Preferably, on both lateral ends or sides of the printing plate support a guide member is arranged, respectively, wherein these guide members are connected to the frame and wherein the respective guide path for these guide members is positioned in the vertical direction. A special configuration provides that the guide members are slide bearings which are slidably secured on a column of the frame, respectively. 
     Moreover, it is preferably provided that the illumination unit of the testing stand is arranged in a head member of the frame which is open in the downward direction. The illumination unit is an asymmetric lamp. 
     A further development provides that the printing plate support is arranged on the guide members so as to be pivotable about a horizontal axis and is lockable in a selected pivot position. 
     Moreover, it is particularly provided that the horizontal guide for a magnifying glass carriage is arranged directly on the body of the printing plate support. Instead of two horizontally positioned, spaced apart guide members of a working frame, extending over the entire width of the printing plate support and securing a magnifying glass and forming a hand rest for the operator, it is now provided according to the invention that the magnifying glass is arranged on a guide rail positioned at a right angle to the horizontal direction and coupled with the aforementioned lower and upper horizontal guides. Underneath the glass carriage glass, a hand rest is arranged on this substantially vertically positioned guide rail wherein the hand rest has only the respective width required for securely resting the hand of the operator. The magnifying glass and the hand rest are preferably slidably arranged. 
     With these constructive measures it is ensured that a surface area as small as possible of the printing plate to be inspected is covered during inspection by components of the testing stand. 
     Moreover, it is particularly provided that the movable printing plate support is connected by means of at least one cable with a spring unit for the purpose of weight compensation, wherein the spring unit is preferably arranged in the rear portion of the head member of the frame. 
     Preferably, it is provided that a tabletop is secured on the frame underneath the printing plate support and provides in direct vicinity of the printing plate support an additional shelf surface. 
     Moreover, the subject-matter of the present invention includes a novel method for inspecting a printing plate, wherein the printing plate, while resting against a printing plate support of a testing stand, is manually inspected by an operator in sections and, if needed, is visually inspected with temporal use of optical aids. This method for inspecting a printing plate is characterized in that the printing plate support is positioned in an optimal basic position for the operator and, for the manual visual inspection, alternatingly a magnifying glass carriage, comprising the optical aid and a hand rest, is guidedly moved in the horizontal direction and/or the optical aid together with the hand rest is guidedly moved in the vertical direction. 
     It is moreover advantageous that the printing plate support, even during movement of the magnifying glass carriage and/or of the optical aid, is guidedly movable in the vertical direction and that the vertically guided printing plate as well as the magnifying glass carriage and/or the optical aid are lockable alternatingly within their movement range, as needed. 
     Preferably, it is provided that the plate support is illuminated with inspecting light from above by means of an asymmetric lamp. 
     The testing stand according to the above described new construction principle is particularly useful for performing the method. 
     The testing stand for printing plates according to the invention and the new method according to the invention are suitable, in particular, for use in the computer-to-plate process (CtP). Prior art offset printing plate testing stands have only a narrow working field that is illuminated, sometimes with two tubes which, in connection with the CtP process, has the disadvantage that with the high light concentration the printing plate that is momentarily being inspected is after-exposed. With the illumination unit according to the invention, the working area on the printing plate support, despite a considerably reduced light concentration on the positioned printing plate, is uniformly illuminated without any disadvantages for the viewer. 
     The guide elements according to the invention in addition to the novel construction principle for the frame provide a significantly more flexible and comfortable manipulation for the operator, wherein at the same time the manufacturing costs as well as the total weight of the testing stand have been lowered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing the only Figure shows in a schematic perspective view the testing stand according to the invention, with the top of the head member partially cut away to show the counterweight arrangement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A testing stand  2  for printing plates according to the present invention is positioned on the floor  1 . The testing stand  2  is used in the graphic design industry. In the special embodiment illustrated, on each base  4 , instead of a single column  5  or  6 , three vertically extending columns  5   a ,  5   b ,  5   c  and  6   a ,  6   b ,  6   c  are arranged. A head member  18  is connected to the upper ends of the front ( 5   a ,  6   a ), rear ( 5   b ,  6   b ), and middle ( 5   c ,  6   c ) columns. This head member  18  is substantially a hollow body whose lower surface is preferably completely open. In the front portion  19  of this head member  18 , an illumination unit (not illustrated) is arranged which is comprised substantially and preferably of an asymmetric lamp. In the rear portion  20  of the head member  18 , a spring unit  21  is arranged which will be explained in more detail in the following. 
     For guiding the printing plate support  11 , onto whose front body surface  11   a  the specimen is placed, the left ( 11   b ) and the right ( 11   c ) body surfaces (lateral ends) are connected each with a guide member  7 ,  8 . Each guide member  7 ,  8  is comprised of two bushing-like slide bearings  7   a  and  7   b ;  8   a  and  8   b . Each pair of slide bearings  7   a ,  7   b ;  8   a ,  8   b  is connected by a connecting stay  7   c  or  8   c . These slide bearings  7   a ,  7   b ;  8   a ,  8   b  are pushed onto the front ( 5   a ,  6   a ) and the middle ( 5   c ,  6   c ) columns and are slidable and lockably on them. The slide bearing  7   a ,  8   a  at the front is provided with a forwardly extending grip  9 , respectively. 
     In a further special embodiment it is provided that a respective drag bearing  10  is arranged on the connecting stays  7   c ,  8   c  so that the printing plate support  11  secured on the guide members  7 ,  8  can be pivoted out of the vertical position to the rear about a virtual horizontal axis which extends through the pivot axis of the drag bearing  10 , wherein the preferred slant angle is 10 to 15°. 
     At the upper and lower body surfaces of the printing plate support  11 , upper and lower horizontal guides  17 ,  17 ′ are arranged. A guide rail  13  of a magnifying glass carriage  12  is positioned at a right angle to the horizontal direction and is horizontally slidably mounted on the lower and upper horizontal guides  17 ,  17 ′. 
     A vertically movable mounting plate  14  is guided on this guide rail  13 . An optical aid, here a magnifying glass  15 , as well as a hand rest  16 , located underneath the magnifying glass  15 , are fastened on the plate  14 . 
     According to a further special embodiment, it is provided that the magnifying glass  15  is secured by means of an alternatingly laterally pivotable leg  14   a  on the mounting plate  14 . If needed, the magnifying glass  15  can thus be laterally pivoted so that it comes to rest on the guide rail  13  and, if needed, provides an even larger freely accessible inspection area for the operator. 
     A further configuration variant of the present invention resides in that for the weight compensation of the printing plate support  11 , instead of the otherwise conventional simple counterweight, the cables  22  engaging on opposite sides the printing plate support  11  or the guide members  7  and  8 , are connected with their other ends to the lateral ends of a spring unit  21 . This spring unit  21  has at least one coil or spiral spring whose initial tension force is selected such that the printing plate support  11  is essentially suspended in a weight-neutral arrangement. When printing plates with greatly varying mass are placed successively onto the printing plate support, with a simple adjustment of an adjusting ring (not illustrated-in-the drawing) of the spring unit  21  the required initial tension force can be quickly and easily adjusted. 
     The new inventive construction principle for the aforementioned type of testing stand, in particular, the novel frame  3  of the testing stand  2 , makes it possible that a tabletop  23 , as illustrated in the drawing, can be arranged below the predetermined vertical movement area of the printing plate support  11  and can be secured on one or several of the columns  5   a  to  6   c  so that the operator has directly an additional shelf area  24  in the vicinity of the printing plate support  11 . This tabletop  23  can be arranged fixedly or can be arranged slidably and lockably. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.