Abstract:
In a multiple-sheet monitoring device for sheet-processing machines, provision is made to arrange a number of sensing elements spaced apart from one another over the format width of the sheets to be conveyed or the sheet stream to be conveyed, and in this case all the sensing elements interact with the same switching element in order to stop the sheet-processing machine.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a multiple-sheet monitoring device and, more particularly, to such a device for sheet-processing machines, having a rotatable roller disposed underneath a sheet to be conveyed, a sensing element pivotally disposed at a spaced distance above the roller, and a switching element fixed in position, the switching element being actable upon in accordance with the pivoting position of the sensing element. 
     A multiple-sheet monitoring device of this general type has become known heretofore from the published German Patent Document DE 38 23 202 C2. 
     The lever for operating the switch and for supporting or holding the sensing element is disposed on a cyclically operated shaft in the aforementioned German Patent Document DE 38 23 202 C2. A continual reciprocating movement of the lever produces oscillations of the entire device and therefore leads to inaccurate measurement results. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a multiple-sheet monitoring device which operates with greater precision than the heretofore known device of this general type. 
     With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a multiple-sheet monitoring device for a sheet-processing machine, having a plurality of sensing elements pivotally disposed above a sheet and an overlapping sheet stream, respectively, at a spaced distance therefrom, and a switching element disposed in a fixed position and being actable upon in accordance with the pivoting position of the sensing elements, the sensing elements being arranged over the format width of the sheets and the overlapping sheet stream, respectively, to be conveyed, comprising an adjustment device for adjusting all of the sensing elements in common to the thickness of a sheet to be processed. 
     In accordance with another aspect of the invention, there is provided a multiple-sheet monitoring device for sheet-processing machines, having a rotatable roller disposed underneath a sheet to be conveyed, a sensing element pivotally disposed at a spaced distance above the roller, and a switching element fixed in position, the switching element being actable upon in accordance with the pivoting position of the sensing element, comprising a pivotable cross member, and an actuating element for the switching element mounted on the cross member so as to be fixed against rotation relative thereto. 
     In accordance with another feature of the invention, the multiple-sheet monitoring device includes at least one additional sensing element, and all of the sensing elements cooperate with only one switching element. 
     In accordance with a further aspect of the invention, there is provided an assembly including the multiple-sheet monitoring device, wherein the multiple-sheet monitoring device is disposed in vicinity of the beginning of a feed table. 
     In accordance with an added feature of the invention, the sensing element is a roller. 
     In accordance with an additional feature of the invention, the multiple-sheet monitoring device includes a counter-roller spaced from the sensing roller, and an adjusting screw for indirectly adjusting the spaced distance between the sensing roller and the counter-roller via a pivotable support. 
     In accordance with yet another feature of the invention, the switching element is mounted on a holder and is adjustable in common therewith by the adjusting screw. 
     In accordance with yet a further feature of the invention, the spaced distance between the sensing roller and the counter-roller is slightly greater than the thickness of the sheet and an overlapping sheet stream, respectively, to be monitored. 
     In accordance with yet an added feature of the invention, a rotatable roller is mounted underneath the sheet and an overlapping sheet stream, respectively, to be conveyed. 
     In accordance with yet an additional feature of the invention, the roller is disposed opposite to the sensing element. 
     In accordance with still another feature of the invention, all of the sensing elements cooperate with only one switch element. 
     In accordance with still a further feature of the invention, the sensing elements are rollers. 
     In accordance with still an added feature of the invention, the multiple-sheet monitoring device includes a respective counter-roller spaced from each of the sensing rollers, and an adjusting screw for indirectly adjusting the spaced distance between the respective sensing rollers and counter-rollers via a pivotable support. 
     In accordance with still an additional feature of the invention, the spaced distance between the respective sensing rollers and counter-rollers is slightly greater than the thickness of the sheet and an overlapping sheet stream, respectively, to be monitored. 
     In accordance with another feature of the invention, a plurality of rotatable rollers are mounted underneath the sheet and the overlapping sheet stream, respectively, to be conveyed. 
     In accordance with a concomitant aspect of the invention, there is provided an assembly including the multiple-sheet monitoring device, wherein the rotatable rollers, respectively, are disposed opposite the plurality of sensing elements, respectively. 
     Thus, a significant advantage of the invention lies in the arrangement of a number of sensing elements, at least two thereof, side-by-side on the cross member. Due to this feature, the sheet and the overlapping sheet stream, respectively, can be monitored simultaneously at a number of locations. In particular, in an edge region of the sheet and the overlapping sheet stream, respectively, dog-eared corners are reliably detectable. 
     A further advantage of the invention is the arrangement of an actuating element for a switching element that is provided, so that it is fixed against rotation relative to the pivotable cross member of the sensing elements. 
     It is therefore necessary for only one switch to be provided, because each sensing element is arranged so that it is fixed against rotation relative to the pivotable cross member, and each deflection of a sensing element results in the actuation of the switch. 
     The multiple-sheet monitoring device is preferably installed at the beginning of the conveyor table. Due to this feature, a large time window is afforded for stopping the sheet-processing machine, in particular a printing machine, even at high processing speeds. 
     The sheet and overlapping sheet stream, respectively, are advantageously monitored without contact with the sensing roller, because only when multiple sheets or faulty sheets are present is the sensing roller contacted and a pivoting movement initiated, which causes a stoppage of the sheet conveying system. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a multiple-sheet monitoring device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side elevational view of a sheet-fed rotary printing machine incorporating the multiple-sheet monitoring device according to the invention; 
     FIG. 2 is a much-enlarged fragmentary view of FIG. 1 showing the multiple-sheet monitoring device in greater detail; and 
     FIG. 3 is a slightly enlarged plan view, rotated approximately 45° counterclockwise, of the multiple-sheet monitoring device shown in FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and, first, particularly to FIG. 1 thereof, there is shown therein a rotary printing machine, for example a printing machine  1  for processing sheets  7 , having a feeder  2 , at least one printing unit  3 ,  4  and a delivery  6 . The sheets  7  are taken off a sheet pile  8  and fed separately or in overlapping or imbricated form over a feed table  9  to the printing units  3  and  4 . Each of the printing units  3  and  4  includes, in a conventional manner, a respective plate cylinder  11 ,  12 . Each of the plate cylinders  11  and  12 , respectively, has a device  13 ,  14  for fastening flexible printing plates thereon. In addition, a respective device  16 ,  17  for semiautomatic or fully automatic printing-plate changing is assigned to each plate cylinder  11 ,  12 . 
     Disposed first of all between a feeder  2  and a feed table  9 , as viewed in the sheet conveying direction, is a cyclically operated roller pair  18 ,  19 . The cyclically operated roller  18  is freely rotatably mounted and reciprocatingly movable, due to which a spaced distance between the cyclically operated roller  18  and the driven counter-roller  19  is reduced and increased at the cycle rate of the sheet-processing machine. Disposed downline from the cyclically operated roller pair  18 ,  19  in the sheet-conveying direction is a multiple-sheet monitoring device  21  according to the invention, which is located at the beginning of the feed table  9 . The multiple-sheet monitoring device  21  includes for the most part a freely rotatably mounted counter-roller  22  which, as shown in FIG. 2, is disposed in a recess  23  formed in the feed table  21 , and a sensing element  24  located above the feed table  21 , opposite the counter-roller  22 . 
     The sensing element  24  is preferably constructed as a rotatably mounted roller. other forms, such as a sliding shoe, a stirrup, a sensing pin or the like, are conceivable. 
     As further seen in FIG. 2, the rotatably mounted roller  24  is seated on a lever  27  pivotally mounted on a support or holder  26  that is axially displaceable on a cross member  28 . A locking screw  29  serves to secure the support or holder  26  in a desired position. Supported on the support or holder  26  is a compression spring  31 , which acts at one end thereof on an arm  32  of the lever  27 , so that the latter is pressed against an adjustable stop  33 . 
     The cross member  28  is pivotally mounted in side frames  34  and  36 , as shown in FIG.  3 . In the vicinity of the side frame  34 , as shown in FIG. 3, the cross member  28  is formed with a lever  37 . 
     A holder  39  for a switch  41  for stopping the sheet-conveying system is pivotally seated on a bearing journal  38  of the cross member  28 . 
     In addition, the holder  39  carries a stop  42  that engages with the lever  37 . A compression spring  44  supported on the side frame  34  presses the lever  37  against the stop  42 . An adjusting screw  46  cooperates with the holder  39  and pivots the latter about the bearing journal  38  counter to the force of the compression spring  44 . Due to this measure, the distance between the roller  24  and the counter-roller  22  is adjusted when the thickness of the printing material is changed. 
     In order to detect small pieces or scraps of sheets, a relatively large number of supports or holders  26 , respectively, having an assigned sensing roller  24  are arranged on the cross member  28 . In order to adjust in common all of the sensing rollers  24  arranged on the cross member  28  to the thickness of the sheets to be processed, for example, the thickness of the printing material in the case of printing machines, the common adjusting screw  46  is used. 
     For the purpose of mutually aligning the sensing rollers  24  vertically, the adjustable stop  33  is provided, for example, in the course of the basic adjustment made during assembly. 
     The result of any deflection of a single sensing roller  24  is that the cross member  28  is pivoted counter to the force of the compression spring  44  which engages the lever  37 . Upon the occurrence of a pivoting movement, the lever  37  comes into contact with the switch  41 , which then stops the sheet-conveying system.