Abstract:
A drum for a creasing device, a resilient creasing ring and method are provided. The drum includes first and second drum parts that cooperate with one another to define a circumferential channel of the drum a base and two side wall for receiving a resilient creasing ring. At least one of the side walls includes recess for receiving a portion of the resilient creasing ring such that the resilient creasing ring cannot be removed radially from the channel. The creasing ring may be continuous or a split ring. A method of mounting the creasing ring includes mounting the resilient creasing ring on a first drum part and axially sliding a second drum part into cooperation with the first drum part to mount the creasing ring within a channel formed therebetween.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This patent application is a continuation of U.S. patent application Ser. No. 11/805,653 filed May 24, 2007 now U.S. Pat. No. 7,686,754, issued on Mar. 30, 2010, which is a continuation of PCT/GB2006/003057 filed Aug. 16, 2006, designating the United States, which claims the benefit of United Kingdom Application No. 0517115.2 filed Aug. 20, 2005, the teachings and disclosures, of all references, are hereby incorporated in their entireties by reference thereto. 

   FIELD OF THE INVENTION 
   This invention relates to the drum that mounts a resilient creasing ring in a device for creasing stock such as paper, card, film, foil or other sheet material to enable it to be easily folded. The device is especially well suited for fitting to the output of a printing machine or the input of a folding machine but it can also be used in a stand-alone creasing machine or in other contexts. 
   BACKGROUND OF THE INVENTION 
   A high percentage of printed stock such as book covers or greetings cards needs to be creased before the next operation of folding can be carried out. 
   A known device for creasing stock is described in international patent application WO 00/55080. The device consists of a first drum mounted on a first rotary shaft, the first drum having at least one groove for holding a resilient ring that protrudes from the groove. A second drum is mounted on a second, parallel rotary shaft and has at least one corresponding groove. When the resilient ring protruding from the first drum is aligned with the groove of the second drum, a sheet of the stock fed between the two rotating drums will be creased by the pressure of the resilient ring deforming the paper into the groove of the second drum. 
   The first and second parallel shafts may conveniently be the top and bottom shafts of a conventional folding machine. The first drum is clamped on the first shaft so that the drum and the resilient ring rotate with the shaft. The second drum may be clamped on the second shaft with the corresponding grooves in alignment. Alternatively, as described in international patent application WO 2004/073966, the second drum may be mounted on bearings so that it can rotate independently of the second shaft and in a preferred arrangement can also slide axially along the second shaft. 
   A first problem with the aforementioned prior art is that the resilient ring must be stretched beyond its working diameter in order to pass over the outer surface of the drum and reach the groove. Despite the resilience of the ring, this stretching—particularly if done repeatedly during the lifetime of the ring—may cause the ring to lengthen so that it does not retract fully into the groove and does not have sufficient tension to grip the groove tightly. As a result, creasing may become less reliable and—because a loosely held ring is continuously deformed as the drum turns—the lifetime of the ring may be shortened. 
   A second problem with the aforementioned prior art is that a new ring can only be added to the creasing device by removing the shaft from the machine in which it is mounted. Although the device may provide space for storage of spare rings, their lifetime is limited and the rings will eventually need to be replaced. The difficulty of removing the shaft varies between machines but is always a time-consuming operation, during which the entire machine cannot be used for any of its functions. 
   BRIEF SUMMARY OF THE INVENTION 
   One embodiment of the invention provides a drum for a creasing device, comprising a first drum part having a cylindrical outer surface and a bore for mounting the first drum part about a shaft; and a second drum part having a cylindrical outer surface and a bore for mounting the second drum part about the shaft; wherein the first and second drum parts are shaped such that the two drum parts may abut one another to define between them the base and two side walls of a channel for receiving a resilient creasing ring; and wherein at least one side wall of the channel is recessed so that a resilient creasing ring located in the channel and projecting laterally into the recess cannot be withdrawn radially from the channel. 
   Forming the drum in two parts, with the channel defined at the junction of the two parts, allows the drum to be assembled round the resilient creasing ring, rather than stretching the ring to pass around the drum. In particular, the ring may be slid into place against the first drum part by a predominantly axial movement, so that the ring is not stretched beyond its working diameter, before the second drum part is brought into abutment to complete the channel. Preferably, the first drum part is shaped to define the base and one side wall of the channel; while the second drum part is shaped to define the other side wall of the channel. This allows the ring to be seated securely against the base of the channel before the second drum part is brought into abutment. 
   Once the two drum parts are locked in their abutting relationship to define the channel between them, the interlocking geometry of the recessed channel walls and the ring holds the ring in place in the channel. It is no longer required that the ring be under tension to hold it in place so a split ring can be used and can be added to the device without removing the shaft from the machine in which it is mounted. 
   To achieve the purpose of the recess—that a resilient creasing ring located in the channel and projecting laterally into the recess cannot be withdrawn radially from the channel—it is sufficient that, when the channel is viewed looking radially inwards, some part of the channel is hidden from view. This includes but is not limited to the case where the mouth of the channel is the narrowest part. “Recess” and cognate words are used in this specification in that sense. 
   In some embodiments, the cross section of the channel has a generally flat base and two side walls converging from their junction with the base towards the mouth of the channel. Such a channel can accommodate a resilient ring of “dovetail” cross-section and it allows the flat base to be the widest part of the channel, whereby the ring is securely located and retained within the channel. 
   In a preferred embodiment of a drum according to the invention, the first drum part has an outwardly facing guide surface of smaller radius than the outer cylindrical surface; and the second drum part has an inwardly facing surface that slides on the guide surface of the first drum part to bring the two drum parts into axial abutment. The guide surface of the first drum part may ramp up to the base of the channel to assist in expanding a continuous resilient ring to its working diameter; or the guide surface may be a cylindrical surface that also forms the base of the channel to assist in locating a split ring. 
   The second drum part may be in the form of a collar that slides solely on the guide surface of the first drum part, the inwardly facing surface of the second drum part being constituted by the bore of the second drum part. 
   In one embodiment, the invention also provides a resilient creasing ring for a creasing device, the ring comprising a radially projecting creasing rib and at least one lateral rib for location in a recessed side wall of a channel in a drum of the creasing device. As previously described, the ring may be split to form two abutting ends to make it possible to add the ring to the device without dismounting the shaft. 
   Finally, in one embodiment, the invention provides a method of mounting a resilient creasing ring in the drum of a creasing device, comprising the steps of locating the resilient creasing ring against a base and one side wall of a channel defined by a first drum part; and axially sliding a second drum part into abutment with the first drum part, whereby the resilient creasing ring is also located against a second side wall of the channel defined by the second drum part. 
   In one embodiment of the invention, the creasing ring includes a creasing rib that projects radially outwardly from the creasing ring; and on each side of the creasing rib is an outwardly facing resilient surface. The resilient surface stands very slightly proud of the cylindrical outer surface of the drum so that it can provide traction to stock that is fed through the creasing device and assist or replace dedicated traction bands known in the prior art. 
   In one embodiment of the invention, the creasing device provides both female and male creasing drums. 
   Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  illustrates a first embodiment of drum according to the invention, the upper half being shown in longitudinal section; 
       FIG. 2  illustrates a second embodiment of drum according to the invention, the upper half being shown in longitudinal section; 
       FIGS. 3   a - 3   f  illustrate alternative channel cross sections for use in a creasing device according to the invention; 
       FIG. 4  illustrates a third embodiment of a drum according to the invention, the upper half being shown in longitudinal section; and 
       FIG. 5  is a pair of the drums of  FIG. 1  arranged in an operational orientation. 
   

   While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a drum  2  mounted on a rotary shaft  4  which forms part of a creasing device. The drum  2  defines a channel  6  in which is received a resilient creasing ring  8  such that a creasing rib  10  of the ring  8  projects above a cylindrical outer surface  12  of the drum  2 . In use, the illustrated drum  2  is placed adjacent to another, female drum (not shown) mounted on a second, parallel shaft (not shown), as is well known from the prior art The female drum may be fixedly mounted for rotation with the second shaft but preferably it is free to rotate independently of the second shaft and to slide axially along the second shaft. The female drum has at least one circumferential groove around its cylindrical outer surface, which receives the creasing rib  10 . As the male drum  2  of this invention rotates and the female drum counter-rotates, a sheet of paper, card or other stock fed between the creasing rib  10  of the male drum and the circumferential groove of the female drum them is deformed and creased. 
   The drum  2  shown in  FIG. 1  itself has a circumferential groove  13  in the outer surface  12 . This allows an identical drum  2  to be used, inverted, as the female drum on the second shaft to form a crease (as illustrated in  FIG. 5 ). Moreover, if the identical drum also carries a creasing ring  8 , then the creasing rib  10  of each drum can engage the groove  13  of the other drum so as to form a closely spaced pair of creases (e.g. 6 mm apart), one up and one down, which is useful for applications such as the covers of catalogues and directories. 
   The drum  2  comprises a first drum part  14  and a second drum part  15 . Each drum part  14 ,  15  is annular in shape with a central bore that fits closely around the shaft  4 . Grub screws  16 ,  17  can be tightened to clamp the respective drum parts  14 ,  15  to the shaft  4  or loosened to allow the drum parts  14 ,  15  to slide along the shaft  4 . 
   The channel  6  for retaining the creasing ring  8  (shown also in  FIG. 3   a ) is located in the outer surface  12  of the drum  2  at the junction between the two drum parts  14 ,  15 . The first drum part  14  defines the base  18  and a first side wall  20  of the channel  6 , while the second drum part defines a second side wall  21  of the channel  6 . The base  18  of the channel is formed by part of an outwardly facing, cylindrical guide surface  22  of the first drum part  14 , which has a smaller radius than the cylindrical outer surface  12 . The second drum part  15  has a corresponding, inwardly facing, cylindrical guide surface  24 , which slides along the guide surface  22  of the first part until facing end surfaces of the respective parts  14 ,  15  come into abutment. 
   The channel  6  has a generally rectangular cross section but each side wall  20 ,  21  has an undercut  26 , whereby the channel  6  is wider at its base  18  than at its mouth. The resilient creasing ring  8  has a corresponding cross section, with a broad base tapering to a narrower body. Alternatively, this can be viewed as a body of generally rectangular cross section with lateral ribs  27  extending into the undercut recesses  26  of the side walls  20 ,  21  of the channels  6 . The creasing rib  10  projects radially outwardly from the creasing ring  8 ; and on each side of the creasing rib  10  is an outwardly facing resilient surface  28 . The resilient surface stands very slightly proud of the cylindrical outer surface  12  of the drum  2  so that it can provide traction to stock that is fed through the creasing device and assist or replace dedicated traction bands known in the prior art. 
   Because the creasing ring  8  will be held in place by the interlocking geometry of the recessed side walls  20 ,  21  of the channel  6  and the lateral ribs  27  of the ring  8 , the creasing ring  8  does not need to be under tension around the drum  2 . Therefore the creasing ring  8  may be split at a point  30  around its circumference. The split may be formed either by moulding the ring originally with the split in place or by moulding a continuous ring which is subsequently cut. Alternatively, if the thickness of the ring and the curvature of the channel are not too great, then the ring  8  may be moulded or extruded as a straight strip and subsequently wrapped around the drum  2  to form a ring in situ. 
   The drum  2  is assembled in the following manner. The two drum parts  14 ,  15  are mounted on the shaft  4  and the grub screw  16  is tightened to lock the first drum part  14  in the correct axial position for a creasing ring  8  located in the channel  6  to form a crease at the desired point. Next a creasing ring  8  is located on the first drum part  14 . The ends of the ring  8  may be separated at the split  30  and the resilient ring  8  deformed to pass the gap between the ends over the shaft. The base of the ring  8  is then wrapped around the guide surface  22  of the first part  14  and slid axially so that the ring  8  engages the side wall  20  of the channel  6  with a lateral rib  27  located in the undercut recess  26 . The two ends of the split ring  8  should meet perfectly so that there is no gap in the creasing rib  10 . Next, the second drum part  15  is slid axially along the shaft  4  and along the guide surface  22  of the first drum part  14  until the facing end surfaces of the respective parts  14 ,  15  abut one another, at which point the second lateral rib  27  of the creasing ring  8  is located in the undercut  26  of the second side wall  21  of the channel  6 . The grub screw  17  is tightened to lock the second drum part  15  in position. The sequence may be reversed to remove or exchange a creasing ring  8 . 
     FIG. 2  illustrates an embodiment of the invention similar to that shown in  FIG. 1 . Corresponding parts are given the same reference numerals and their description will not be repeated here. The main difference is that in this embodiment the first drum part  14  extends over the whole axial length of the drum  2 ; and the second drum part  15  does not contact the shaft but takes the form of a collar sliding solely on the guide surface  22  of the first drum part. 
   The cross section in  FIG. 2  is taken through the grub screws  16  and  17 . Grub screw  16  is the same as in  FIG. 1  and turns in a threaded bore to bear against the shaft  4  and lock the first drum part  14  in position. Compared with  FIG. 1 , grub screw  17  is shorter and does not bear against the shaft  4  but against the first drum part  14 . It could bear simply on the guide surface  22  but, as shown, it is preferred that it runs in a keyway  32  cut into the guide surface  22 . The keyway  32  could be of any circumferential extent but it is preferred that it should be essentially a linear channel, parallel to the axis, at one circumferential position around the guide surface  22 . The keyway  32  stops short of the end of the drum  2  so that when grub screw  17  is loosened slightly, the second drum part  15  can be slid axially along the guide surface  22  of the first drum part  14  until the grub screw  17  reaches the end of the keyway  32 . That opens the channel  6  enough for a resilient ring  8  to be inserted or removed but prevents the second drum part  15  from becoming detached from the first drum part  2  without unscrewing the grub screw  17  further. 
     FIG. 3  shows various possible cross sections for the channel  6 , though many others can readily be imagined. The junction between the first and second drum parts  14 ,  15  is not shown in these drawings because it may intersect the base  18  of the channel  6  at various points and at various angles. 
     FIG. 3   a  is an enlargement of the channel  6  of  FIGS. 1 and 2 . It has a broad, flat base  18  and the vertical side walls  20 ,  21  are undercut at an angle to intersect the comers of the base  18  and form recesses  26 . 
     FIG. 3   b  shows a variant of the channel  6  in which the side walls  20 ,  21  have no vertical part but are angled from the mouth of the channel to the corners of the base  18  to form recesses  26  over the whole depth of the channel. 
     FIG. 3   c  shows that the narrowest part of the channel  6  need not be at the mouth. 
     FIG. 3   d  shows that recesses  26  can be provided even in a channel  6  of constant width, although this asymmetrical shape is not preferred. 
     FIG. 3   e  shows recesses  26  of semicircular cross section, which do not extend to the base  18  of the channel. 
     FIG. 3   f  shows a channel  6  of circular cross-section, in which there is no clear boundary between the side walls  20 ,  21  and the base  18 . This cross-section still has recesses  26  as previously defined because parts of the channel adjacent to the side walls  20 ,  21  are not visible when viewed from above. 
     FIG. 4  shows an embodiment of the invention that is generally similar to  FIG. 2  and the description of like parts will not be repeated. A third drum part  34  is provided which, like the second drum part  15 , is in the form of a collar sliding on the guide surface  22  of the first drum part  14 . The third drum part  34  may be axially spaced from the second drum part  15  to create a storage channel  36 , which can store spare resilient creasing rings  38  when they are not in use. 
   It will be understood that the embodiments of the invention described here are illustrative only and not limiting. In particular, features shown here in separate embodiments may be used together in various combinations. 
   Although in the illustrated embodiments the second drum part  15  is shown to be sliding on the guide surface  22  of the first drum part  14  and locked in place by a grub screw  17 , it could alternatively be mounted via a screw-threaded connection, provided that care is taken to secure the part  15  against unscrewing as the drum  2  rotates. 
   All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
   The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
   Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.