Patent Publication Number: US-6659456-B2

Title: Sheet transport drum

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention relates to a sheet transport drum in a sheet printing machine, the transport drum including a first comb segment and a second comb segment, of which the latter is mounted so as to be rotatable relative to the first comb segment for adjusting to a format length corresponding with a printing-material sheet. 
     Heretofore known sheet transport drums of the foregoing general type are subject to the following problem: depending upon how far the second comb segment is rotated relative to the first comb segment, interspaces of greater or lesser size gape open between prongs of the comb segments, and air flows outwardly through the interspaces from the interior of the sheet transport drum under the action of centrifugal force. The air flowing out of the sheet transport drum in an undesired manner causes the printing-material sheet overlapping the interspaces to be lifted off in an uncontrolled manner as the sheet is transferred from the sheet transport drum to a further sheet transport drum. Until the present, this unavoidable disruption of the sheet transport resulting from the construction of the heretofore known sheet transport drums has stood as an obstacle to a further increase in the rotational speed of the sheet transport drum, i.e., the speed of the sheet-fed printing machine. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a sheet transport drum with comb segments which prevent the printing-material sheet from being lifted off the drum in an uncontrolled manner even at very high machine speeds. 
     With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, in a sheet-fed printing machine, a sheet transport drum, comprising a first comb segment and a second comb segment, the second comb segment being mounted so as to be rotatable relative to the first comb segment for providing an adjustment to a format length corresponding with that of a printing-material sheet, the comb segments being formed of prongs having interspaces therebetween, and at least one covering provided for covering the interspaces between the prongs. 
     In accordance with another feature of the invention, the at least one covering engages, at the inside thereof, at least one of the comb segments. 
     In accordance with a further feature of the invention, the at least one covering is constructed so as to be actuatable pneumatically. 
     In accordance with an added feature of the invention, the at least one covering is inflatable. 
     In accordance with an additional feature of the invention, the at least one covering is selected from the group consisting of a flexible tube, a bellows and a balloon. 
     In accordance with yet another feature of the invention, the at least one covering engages at the outside thereof with at least one of the comb segments. 
     In accordance with yet a further feature of the invention, the at least one covering is a foil. 
     In accordance with yet an added feature of the invention, the at least one covering is partially wound up. 
     In accordance with another aspect of the invention, there is provided a sheet-fed printing machine including at least one sheet transport drum, comprising a first comb segment and a second comb segment, the second comb segment being mounted so as to be rotatable relative to the first comb segment for providing an adjustment to a format length corresponding to that of a printing-material sheet, the comb segments being formed of prongs having interspaces therebetween, and at least one covering provided for covering the interspaces between the prongs. 
     In accordance with a further feature of the invention, the sheet-fed printing machine includes a reversing device of which the sheet transport drum is a constituent part. 
     In accordance with a concomitant feature of the invention, the sheet transport drum is constructed as a storage drum, and the reversing device includes a further sheet transport drum constructed as a reversing drum. 
     Thus, the invention calls for interspaces between prongs of the comb segments to be covered by at least one covering. 
     Of course, this covering is not identical with the printing-material sheet. 
     The printing-material sheet is guided on the sheet transport drum according to the invention just as reliably as on a sheet transport drum having a continuous circumferential surface or as on an impression cylinder, even at very high machine speeds of, for example, 15,000 or more printed sheets per hour. 
     It is possible, for example, to provide a first covering for covering interspaces between the prongs of the first comb segment, and a second covering for covering interspaces between the prongs of the second comb segment. The at least one covering may be constructed so that it can be pneumatically actuated and/or wound up and unwound. It is also possible for the covering, at the outside or the inside thereof, to engage with at least one of the comb segments. 
     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 sheet transport drum, 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 having a reversing or turning device; 
     FIG. 2 is a fragmentary diagrammatic plan view of a sheet transport drum of the reversing or turning device constructed in accordance with the invention; and 
     FIGS. 3 to  5  are diagrammatic end elevational views, partly in section, of FIG. 2, showing different exemplary embodiments of the sheet transport drum. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, and first particularly to FIG. 1 thereof, there is shown therein a sheet-fed rotary printing machine constructed as a unit with a sheet feeder  1 , printing units  2  and  3  for printing on printing-material sheets by the offset printing method, a reversing or turning device  4  disposed between the printing units  2  and  3 , and a sheet delivery  5 . 
     Each of the printing units  2  and  3  includes a printing-form cylinder, a blanket cylinder and an impression cylinder  6 ,  7 . The reversing or turning device  4  has three sheet transport drums  8 ,  9  and  10 , which are arranged between the impression cylinders  6  and  7 . The sheet transport drum  9  functions as a so-called storage drum and, by a gripper system thereof, firmly holds the printing-material sheet at the leading edge thereof. The sheet transport drum  10  functions as a so-called reversing or turning drum and, by the gripper system thereof, grips a trailing edge of the printing-material sheet in order to reverse or turn the latter and draw it off the sheet transport drum  9 . 
     FIG. 2 is a fragmentary plan view of the sheet transport drum  9 , this plan view showing that the sheet transport drum  9  comprises at least a first comb segment  11  and a second comb segment  12 , which is mounted so that it can be rotated and/or pivoted about a pivot axis  13 , which corresponds to the center axis of the sheet transport drum  9 , relative to the first comb segment  11  for the purpose of adapting the sheet transport drum  9  to different format lengths of printing-material sheets which are to be transported. Each of the comb segments  11 ,  12  has prongs  14 , which engage in interspaces  15  between the prongs of the respectively other comb segment. 
     An adjustment of the second comb segment  12  to the first comb segment  11 , for the purpose of adapting it to a smaller sheet format, causes the prongs  14  to be pushed farther into the interspaces  15 , the interspaces  15  being thereby narrowed, and an adjustment of the second comb segment  12  away from the first comb segment  11 , for the purpose of adapting it to a larger sheet format, results in a widening of the interspaces  15 . 
     The gripper system of the sheet transport drum  9  includes gripper supports  16 , which are arranged on the front edge of the first comb segment  11 , and grippers  17  (note FIG.  3 ), which are assigned to the gripper supports, in order to clamp the printing-material sheet in. Nozzle-like suckers  18  for applying suction to the printing-material sheet at the trailing edge thereof for holding the sheet are arranged in a row on the second comb segment  12  and are connected to a suction-air source. 
     For the purpose of adjusting the necessary distance, depending upon the format length, between the gripper system and the suckers  18 , the latter, together with the second comb segment  12 , are pivoted about the pivot axis  13  relative to the gripper system into a position wherein the suckers  18  are located in the vicinity of the trailing edge of the printing-material sheet held in the gripper system and beneath the printing-material sheet. 
     FIG. 3 is an end sectional view of a first exemplary embodiment of the sheet transport drum  9 , according to which at least one covering  19  is disposed in the hollow interior of the sheet transport drum  9 , beneath the comb segments  11  and  12 . The covering  19  which, on the inside, abuts the comb segments  11  and  12 , covers the interspaces  15  as a sealing element and prevents air flows out of the sheet transport drum  9  through the interspaces  15 . The wall formed by the covering  19 , which is constructed as a variable-volume expansion chamber or, more precisely, as a balloon, is formed of an expandable, flexible material, preferably an elastomer. 
     In contrast with the exemplary embodiment shown in FIG. 3, it is also possible for the variability of the volume to be provided by forming the covering  19  as an accordion-like bellows, the zigzag-shaped wall of which has inflection locations serving as bending joints. 
     Via a line  20 , e.g., a tube, the illustrated covering  19  can be pumped up and/or inflated with air, and the air can later be evacuated again from the covering  19 , e.g., by the air being forced or sucked out. Instead of air, it is also possible to use some other pressure fluid or gas for filling the covering  19 . 
     The covering  19  functions as follows: as a result of each format conversion of the sheet transport drum  9  from a small format length to a large format length, i.e., due to each adjustment of the second comb segment  12  away from the first comb segment  11 , a cavity which is bounded by the comb segments  11  and  12  and a core of the sheet transport drum  9 , and which the covering  19  is able to fill, suitably widens. 
     Without an appropriate countermeasure, the widening of the cavity would cause the contact pressure of the covering  19  against the comb segments  11  and  12 , which slackens as a result of the widening, to be lost somewhat, so that air-tight closure of the interspaces  15  by the covering  19  would no longer be ensured in an absolutely reliable manner. Moreover, due to this adjustment of the second comb segment  12 , some of the interspaces  15  of the latter no longer overlap the covering  19 . 
     The countermeasure that is taken thus involves further inflating the covering  19 , preferably by compressed air, as a result of which the covering  19  expands, on the one hand, in the circumferential direction of the sheet transport drum  9 , i.e., in the adjustment direction of the second comb segment  12 , and, on the other hand, in the radial direction of the sheet transport drum  9 . Due to the circumferential expansion of the covering  19 , the interspaces  15  of the second comb segment  12  are completely closed again by the covering  19 . The radial expansion of the covering  19  causes the covering  19  to fit more closely against the comb segment  12 , so that the hermetic sealing of the interspaces  15  is ensured again. The air volume enclosed in the covering  19  is increased during or after each format adjustment from the small format length to the large format length. 
     Before or during each format adjustment in the opposite direction, from the large format length to the small format length, i.e., each adjustment of the second comb segment  12  to the first comb segment  11 , the air volume enclosed in the covering  19  is reduced again by letting a given quantity of air out of the covering  19 . 
     FIG. 4 illustrates a second exemplary embodiment, the parts  11  to  18  and  20  thereof corresponding to similarly identified parts of the first exemplary embodiment to which reference can be made for an explanation thereof, thereby avoiding unnecessary repetition herein. 
     Although the covering  19  of the second exemplary embodiment can indeed be expanded depending upon the format length, just like the covering of the first exemplary embodiment, by varying the internal pressure and/or the enclosed air volume thereof, it is constructed not as a balloon but as an inflatable flexible tube, a number of which are provided, i.e., one for each interspace  15 . 
     The tubular covering  19  is guided by a prong-shaped guide  23  which extends beneath the corresponding interspace  15  equidistantly from the prongs  14  which bound the interspace  15 . As to the inflation thereof, and the deflation thereof, depending upon the adjustment of the second comb segment  12 , the tubular covering  19  is virtually the same, in functional terms, as the balloon-shaped covering of the first exemplary embodiment. 
     During or before inflation of the tubular covering  19 , the latter can be unwound partially from a reel  21  fastened on the second comb segment  12 , and as the air is let out therefrom, or just thereafter, the covering can be wound up partially onto the reel  21  again. A front end of the tubular covering  19  is fastened on the first comb segment  11 , and a rear end of the covering  19  is fastened on the reel  21 , with the result that, during each adjustment of the second comb segment  12  away from the first comb segment  11 , the covering  19  is automatically unwound from the reel  21 . The covering  19  and the reel  21  may form a type of roller blind, of which the spring is stressed or tightened by unwinding the covering  19 , and subsequently drives the wind-up operation of the covering  19 , wherein the spring is again relieved of stress. 
     FIG. 5 illustrates a third exemplary embodiment, of which those parts which are also common to the other exemplary embodiments and which have already been described herein in conjunction with the latter, namely the parts  11  to  18 ,  20  and  21 , will not be described again in order to avoid unnecessary repetition. 
     The covering  19  provided in the third exemplary embodiment is formed as a foil or sheeting covering all of the prongs  14  and the interspaces  15  of the comb segments  11  and  12 , and made of polyester or a similar material, which provides the covering  19  with a given dimensional stability which is greater than the dimensional stability of the inflatable coverings shown in FIGS. 3 and 4. 
     The foil or sheeting-like covering  19  is tautened as cylinder dressing over the sheet transport drum  9 , so that the covering  19  rests tautly on outer circumferential surfaces of the comb segments  11  and  12  and closes the interspaces  15  in an air-tight manner in order to prevent the follow-on flow or afterflow of the air through the interspaces  15 , which adversely affects the transport of the sheets. A front end of the sheeting-like covering  19 , which abuts the comb segments  11  and  12  on the outside, is fastened onto, for example, adhesively bonded to, the first comb segment  11  and a rear end is fastened onto the reel  21  integrated in the sheet transport drum  9 , for example, is clamped therein. In the third exemplary embodiment, the reel  21 , in the same manner as for the second exemplary embodiment, is rotatably fastened onto the second comb segment  12 . The sheeting-like covering  19  is guided through a slit  22  extending parallel to the pivot axis  13 , the slit  22  being formed in the second comb segment  12 , located upline from the suckers  18 , beneath the circumferential contour of the sheet transport drum  9  as far as the reel  21 , which is seated in the interior of the drum and onto which the sheeting-like covering  19  is partially wound. 
     The winding-up and unwinding operations of the sheeting-like covering  19 , these operations occurring automatically during the format conversions of the second comb segment  12 , take place in a manner which is comparable to the herein aforedescribed operations of winding up and unwinding the tubular covering of the second exemplary embodiment.