Abstract:
A rotating stitcher  4  for driving U-shaped wire stitches  43  into printed products  3  being conveyed along a linear path, wherein a stapling closing device  5  cooperates with the stitcher  4 , for closing the wire stitches  43 . The rotating stitcher  4  has stitching heads  7  which are hinged around a rotating support  6 . A control device guarantees that the stitching heads  7  are swung into a position where the direction of displacement E of the stitch plunger  10  is at right angles to the direction of transport A of the products  3  to be stitched. This takes place before or during entry of the stitching head  7  into the stitching area. While the wire stitches are driven in and stitched, the stitching heads  7  are held in this position and thus move linearly in the stitching area. The heads  32  of the stapling closing device  5  are guided in the same way, so that they move linearly during stapling, just like the allocated staple head  7.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for the longitudinal stitching of multipiece printed products. 
     U.S. Pat. No. 4,204,626 discloses a wire-stitching device of this type in which a rotationally driven rotary stitcher is assigned to a stitching-hook closing arrangement, which is formed by a likewise rotationally driven stitching-hook closing cylinder. The axes of rotation of the stitcher and the stitching-hook closing cylinder are parallel to one another and run at right angles to the conveying direction of the products to be stitched. The rotary stitcher has a cylindrical carrier, in which a guide bush for a displaceable stitching-hook drive-in plunger is arranged, the guide bush running in the radial direction. The guide bush, which is rotatable about its radial longitudinal axis, is held in a fixed position in the radial direction in the carrier. 
     When the rotating stitching head meets the product advanced along an essentially rectilinear path, the U-shaped stitching hook transported by the stitching head is driven into the product in such a way that first one stitching-hook leg and then the other stitching hook leg penetrates the product and passes through the latter. During the driving-in operation, the position of the stitching-hook legs changes relative to the product. The stitching-hook legs are then bent. To this end, the stitching-hook closing cylinder has two bending elements, of which one is attached to the stitching-hook closing cylinder in a fixed position and the other is attached to the stitching-hook closing cylinder in a rotational manner. The two bending elements, as viewed in the direction of rotation of the stitching-hook closing cylinder, are arranged one behind the other in such a way that the leading bending element comes into effect on the leading leg of the stitching hook and the trailing bending element comes into effect on the trailing leg of the stitching hook. 
     The object of the present invention, then, is to provide a longitudinal-stitching device of the type mentioned at the beginning which enables the legs of the stitching hooks to be driven at high speed into the products simultaneously and essentially in an approximately right-angled direction relative to the products. 
     SUMMARY OF THE INVENTION 
     The above and other objects and advantages of the present invention are achieved by the provision of a rotating stitcher which is provided with at least one stitching head for setting wire stitching hooks in the products. Each stitching head includes a pivotally mounted guide which extends essentially radially to the axis of rotation of the stitcher, and a displaceable stitching-hook drive-in plunger is mounted in each guide. A control arrangement is provided for pivoting each pivotally mounted guide during rotation of the stitcher, and each guide together with the guide together with the stitching-hook drive-in plunger, in the stitching region, is held over a certain section in a position in which the displacing direction of the stitching-hook drive-in plunger is approximately at right angles to the conveying direction of the products, which enables the wire stitching hooks to be satisfactorily driven in with both stitching-hook legs simultaneously without the direction of the stitching-hook legs changing relative to the product during the driving-in operation. The closing of the set stitching hooks, i.e. the bending of the two stitching-hook legs, may be effected in a simple manner, since the stitching hooks perform a linear movement during the closing operation. 
     Two or more stitching heads per stitcher of the type defined above are preferably provided, and these stitching heads in each case interact in the stitching region with linearly moving bending members of the stitching-hook closing arrangement. 
     Further preferred developments of the longitudinal-stitching device according to the invention are outlined in the following detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the subject matter of the invention are explained in more detail below with reference to the drawings, in which, in a purely schematic manner: 
     FIG. 1 in side view, and 
     FIG. 2 in front view in the direction of arrow II in FIG. 1, show a first embodiment of a longitudinal-stitching device according to the invention, 
     FIGS. 3-8 show various phases of the stitching-hook closing and setting operation in the device according to FIGS. 1 and 2, 
     FIGS. 9-15 show various arrangements and possible uses of a stitching device or a plurality of stitching devices of the type according to the invention, 
     FIGS. 16-19 show a stitching arrangement with three longitudinal-stitching devices according to the invention in various working phases, 
     FIGS. 20-22 show a stitching arrangement with two longitudinal-stitching devices according to the invention in various working phases, 
     FIG. 23 shows in side view a stitching arrangement having a second embodiment of longitudinal-stitching devices according to the invention, 
     FIG. 24 shows part of the stitching-hook closing arrangement on an enlarged scale compared with FIG. 23, and 
     FIG. 25 in a representation corresponding to FIG. 2, shows a longitudinal-stitching device of the type shown in FIG. 23 in front view and partly in section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Shown in FIGS. 1 and 2 is a collecting section  1 , which has a saddle  2  in a manner known per se. The printed product  3  to be stitched, which consists of a plurality of superimposed folded sheets, rests on the saddle  2  in a straddling manner and is continuously fed forward in the direction of arrow A. The folding edge  3   a  of the printed product  3  therefore runs in the conveying direction A. Available for the stitching of the printed product  3  is a longitudinal-stitching device, which in the exemplary embodiment shown in FIGS. 1 and 2 has a rotating stitcher  4  as well as a stitching-hook closing arrangement  5 , which is opposite the rotating stitcher  4  relative to the saddle  2 . 
     The rotating stitcher  4  has a disk-shaped carrier  6 , which is rotationally driven about the axis  6   a  in the direction of arrow B. In this case, the axis of rotation  6   a  of the carrier  6  runs at right angles to the conveying direction A of the printed product  3 . Two stitching heads  7 , whose longitudinal axes are designated by  7   a , are attached diametrically opposite one another to the carrier  6 . Each stitching head  7  has a housing  8 , in which a stitching-hook guide  9  is arranged, and this stitching-hook guide  9  extends in the stitching-head longitudinal axis  7   a  and is mounted in the housing  8  in such a way that it can be pushed back against the force of springs (not shown) The stitching-hook guide  9  serves as a guide for a stitching-hook drive-in plunger  10 , which carries a control roller  11  on its one free end. For the more detailed construction of the stitching heads  7 , i.e. of the arrangement of the stitching-hook guide  9  and the stitching-hook drive-in plunger  10  in the interior of the housing  8 , reference is made to U.S. Pat. No. 5,464,199. 
     The housing  8  carries a journal  12 , which is rotatably mounted in the carrier  6  by means of ball bearings  13  FIG.  2 . The longitudinal axis of the journal  12  forms the pivot axis  12   a  for the housing  8  and thus for the stitching head  7 . Firmly connected to the journal  12  is a control lever  14 , which at its other end carries a spindle  15 , on which two control rollers  16  and  17  are rotatably mounted. Serving to control the pivoting movement of the housing  8  is a fixed disk cam  18  (FIG.  2 ), which has a running surface  19  for the control rollers  16  and a control groove  20  for the control rollers  17 . The path of the control groove  20  and accordingly of the running surface  19  is indicated by a dash-dotted line in FIG.  1  and is likewise designated by  20 . As FIG. 2 also shows, the carrier  6  sits on a driven drive shaft  22 , which passes through the disk cam  18 . 
     The pivot axes  12   a  of the housings  8 , during the rotation of the carrier  6 , move along a circular path, which is designated in FIG. 1 by D. The control groove  20  has such a path that the stitching heads  7  or their housings  8  extend approximately in the radial direction during the rotation of the carrier  6  and, before or during entry into the stitching region C, are pivoted into a position in which the longitudinal axis  7   a  of the stitching heads  7  runs essentially at right angles to the conveying direction A and thus to the folding edges  3   a  of the printed products  3 . Furthermore, due to the special design of the cam path  20 , a situation is achieved in which the stitching heads  7  in the stitching region C, i.e. when passing through a section designated by  23  in FIG. 1, maintain this position, as shown in FIG. 1 by the stitching-head positions depicted by dash-dotted lines. After leaving the stitching region C, the housings  8  and thus the stitching heads  7  are swung back into the radial position again. 
     While the stitching heads  7  are passing through the stitching region C, a fixed control link  24  comes into effect on the control rollers  11  of the stitching-hook drive-in plunger  10 , which results in a displacement of the stitching-hook drive-in plunger  10  in its longitudinal direction, which coincides with the longitudinal axis  7   a  of the stitching heads  7 , i.e. in the direction of arrow E. The control link  24  has a section which is designated by  24   a  and runs parallel to the conveying direction A of the printed product  3 . 
     Opposite the stitching region C, a stitching-wire feed  25  is arranged adjacent to the carrier  6 . The stitching wire  26  is fed forward in the direction of arrow F by feed means (not shown) and fed to a wire cutter  27 . The latter cuts off wire sections  28  from the stitching wire  26 , and these wire sections  28  are received at a wire-transfer point  29  by the stitching heads  7  running past, i.e. by the stitching-hook guides  9 . Arranged downstream of the stitching-wire feed  25  as viewed in the direction of rotation B of the carrier  6  is a fixed wire-bending link  30 , which serves to bend the straight wire section  28  received into U-shaped stitching hooks, which are held in the stitching-hook guides  9  of the stitching heads  7 . 
     As can be seen in particular from FIG. 2, the stitching wire  26  in the exemplary embodiment shown is fed in a direction F, which is at right angles to the feeding direction A of the printed products  3  and thus at right angles to the folding edge  3   a  of the printed products  3 . This means that the stitching-hook guide  9 , during its movement from the wire-transfer point  29  to the stitching region C, must be rotated by 90° about its longitudinal axis, i.e. about the longitudinal axis  7   a  of the stitching heads  7 , so that the stitching hooks can be driven in the direction of the folding edge  3   a  into the printed product  3 . The rotary mechanism for such a rotation of the stitching-hook guides  9  is not shown in FIGS. 1 and 2. In this connection, however, reference is made to FIG. 25, in which a possible design of such a rotary mechanism is shown. 
     However, it is also possible to feed the wire sections  28  to the stitching heads  7  in a direction which runs parallel to the conveying direction A of the printed products  3 . In addition, instead of straight wire sections  28 , which then have to be bent into a U-shape, finished stitching hooks which are already U-shaped may be delivered to the stitching heads  7 . 
     The stitching-hook closing arrangement  5  has two stitching-hook closing heads  32 , which are likewise diametrically opposite one another and whose longitudinal axes  32   a , just as with the stitching heads  7 , normally run in the radial direction. Each stitching head has two bending elements  33 , which are mounted in an articulated manner and are pivoted from the rest position into the operative position by means of an actuating plunger  34 . The actuating plungers  34  carry a control roller  35  at one end and are guided in a housing  36  so as to be displaceable in the longitudinal direction  32   a  of the stitching-hook closing heads  32 , i.e. in the direction of the arrow I. The housing  36  is fastened to a carrier  37  so as to be pivotable about an axis designated by  36   a , the carrier  37  being rotationally driven about the axis  37   a  in the direction of arrow G. Attached to each housing  36  is a control lever  38 , which carries a pin  39  at its free end, and this pin  39  engages in a groove  40  (only indicated by a dash-dotted line in FIG. 1) by means of a control roller (not shown). This groove  40  is formed on a fixed disk cam  41  (FIG.  2 ). 
     While the pivot axes  36   a  of the stitching-hook closing heads  36  are moved along a circular path of movement H, the control rollers of the pins  39  move along a path which is established by the control groove  40  and has such a shape that the stitching-hook closing heads  32 , before or when running into the stitching region C, are pivoted into a position in which the longitudinal axis  32   a  of the stitching-hook closing heads  32  and thus the displacing direction I of the actuating plungers  34  are at right angles to the conveying direction A of the printed products  3  and thus at right angles to the folding edge  3   a  of the printed products  3 . The stitching-hook closing heads  32  are held in this position in the stitching region C while passing through the section  23  already mentioned. This means that the stitching-hook closing heads  32 , in the same way as the stitching heads  7 , perform a linear movement, which runs parallel to the conveying direction A of the printed products  3 , along the section  23 . 
     For the displacement of the actuating plunger  34  in the stitching region C, there is a control link  42 , which comes into effect on the control roller  35  of the actuating plunger  34 . 
     The stitching operation, in so far as it does not already follow from the preceding description, is explained in more detail with reference to FIGS. 3-8 and to FIGS. 1 and 2. 
     As already mentioned, each stitching head  7  and the associated stitching-hook closing head  32 , before or when running into the stitching region C, are pivoted into a position in which the longitudinal axis  7   a  or  32   a  of the stitching head  7  or the stitching-hook closing head  32  respectively runs approximately at right angles to the conveying direction A and thus to the folding edge  3   a  of the printed product  3  to be stitched. Since the flight path of the stitching-hook guides  9  of the stitching heads  7  intersects the rectilinear path of movement of the folding edge  3   a  of the printed product  3 , i.e. the top edge of the saddle  2 , the stitching-hook guides  9  guiding the U-shaped stitching hooks  43  are pushed back against a resilient restoring force relative to the stitching-hook drive-in plungers  10 , as explained in more detail in U.S. Pat. No. 5,464,199 already mentioned. The stitching hook  43  guided in the stitching-hook guide  9  extends in the direction of the folding edge  3   a  of the printed product  3  (FIG.  3 ). As soon as the control roller  11  of the stitching-hook drive-in plunger  10  starts to run onto the control link  24 , the stitching-hook drive-in plunger  10  is displaced downward in the direction of arrow E, the result of which is that the stitching hook  43  is simultaneously driven with both legs into the printed product  3  in the region of the folding edge  3   a  (FIG.  4 ). In FIG. 5, the stitching-hook drive-in plunger  10  is shown in its bottom end position, in which it has pushed the stitching hooks  43  completely into the printed product  3 . During the rectilinear drive-in section, designated by  24   a  in FIGS. 1,  5  and  6 , of the control link  24 , the stitching-hook drive-in plunger  10  remains in this bottom end position. The actuating plunger  34  of the stitching-hook closing head  32  is at the same time moved upward in the direction of arrow I. The result of this is that the bending elements  33  are pivoted into the operative position and are brought into effect on the stitching-hook legs (FIGS.  5  and  6 ). During the simultaneous bending of the stitching-hook legs, the stitching-hook drive-in plunger  10  remains in the abovementioned bottom end position. After completion of the stitching-hook setting and closing operation, the control rollers  11  and  35  of the stitching-hook drive-in plunger  10  and the actuating plunger  34  respectively run off the associated control links  24  and  42  respectively. The stitching-hook drive-in plunger  10  and the actuating plunger  34  are moved back (FIG.  7 ). The stitching head  7  and the associated stitching-hook closing head  23  are then swung back into the radial position again. Part of the printed product  3  with the finished stitching hook  43  is shown in FIG.  8 . 
     The stitching hooks  43  are set and closed in the stitching region C during a linear movement of the stitching hooks  43  along the section  23 . As mentioned, both the stitching head  7  and the stitching-hook closing head  32  interacting with it are controlled in such a way that their movement along the abovementioned section  23  is likewise linear. 
     Various conveying systems for the printed products  3  to be stitched are shown in FIGS. 9-11, there being in each case a longitudinal-stitching device of the type as has been explained with reference to FIGS. 1 and 2. 
     In the embodiment according to FIG. 9, the printed products  3 ,  3 ′ as explained with reference to FIGS. 1-8, are conveyed along a collecting section  1 . At a collecting section  1 , the multipiece, folded printed products  3 ,  3 ′, are produced by placing the folded individual sheets one on top of the other. The end products are therefore put together from inside to outside. 
     In FIG. 10, the printed products  3 ,  3 ′ to be stitched are moved along an insertion section  45 . This insertion section  45  has a V-shaped passage, which is open at the top and into which the folded individual sheets are placed one inside the other with their folding edge  3   a  underneath. During the insertion, the end product  3 ,  3 ′ is put together from outside to inside. In the case of the insertion section  45  shown in FIG. 10, in contrast to the embodiment according to FIG. 9, the rotating stitcher  4  is located below the insertion section  45 . 
     In the embodiment according to FIG. 11, the printed products  3 ,  3 ′ to be stitched are conveyed resting on a belt conveyor  46 . The end products  3 ,  3 ′ may consist of folded or unfolded individual leaves or sheets placed one on top of the other. However, it is also conceivable to convey multipiece printed products  3 ,  3 ′ consisting of folded sheets lying one inside the other on the belt conveyor  46 . In any case, the products  3 ,  3 ′ to be stitched are transported in such a way that that side edge  3   b  of the printed products  3 ,  3 ′ along which the stitching hooks  43  are to be set run parallel to the conveying direction A. 
     In all three FIGS. 9-11, the distance between the two stitching hooks  43  of each printed product  3 ,  3 ′ is designated by a. This distance a corresponds to the distance between the ends of the stitching heads  7  as measured in the circumferential direction of the carrier  6 . In this case, it is assumed that the circumferential velocity of the stitching-head ends and the conveying speed of the printed products  3 ,  3 ′ are the same. The distance b between the rear stitching hook  43  of the leading product  3  and the front stitching hook  43  of the following printed product  3 ′ is designated by b and corresponds to the stitching hook distance a. However, the distance b may also be an integral multiple of the distance a. The distance between successive products  3  and  3 ′ is designated by T. 
     Shown in FIGS. 12 and 13 are two collecting sections  1  and  1 ′ (FIG. 12) and respectively two insertion sections  45 ,  45 ′ (FIG. 13) which run parallel to one another. Assigned to each collecting section  1 ,  1 ′ or insertion section  45 ,  45 ′ respectively is a longitudinal stitcher, of which only the rotating stitcher  4 ,  4 ′ is shown. The products  3  are stitched simultaneously on both transport sections  1 ,  1 ′ and  45 ,  45 ′ respectively. 
     Shown in FIGS. 14 and 15 are a collecting section  1  (FIG. 14) and an insertion section  45  (FIG. 15) respectively. There are two longitudinal-stitching devices, working in synchronism with one another, of the type shown in FIGS. 1 and 2 at each conveying section  1 ,  45 . The two stitchings for each printed product  3  are effected simultaneously. The distance between the two longitudinal-stitching devices may be set in order to change the distance between the two stitching hooks of each product  3  and in order to permit a changeover to other product formats. 
     Shown in FIG. 16 is an embodiment in which not only one longitudinal-stitching device but three longitudinal stitchers  48 ,  49 ,  50  working in synchronism with one another are arranged along an insertion section  45  as has already been explained with reference to FIG.  10 . Each stitcher  48 ,  49 ,  50  is constructed as explained with reference to FIGS. 1 and 2, although the positions of the rotating stitchers  4  and of the associated stitching-hook closing arrangements  5  are reversed compared with the representation in FIGS. 1 and 2. 
     Three stitching hooks  43 ,  43 ′ and  43 ″ are set at each product, specifically in a consecutive sequence, by means of the three longitudinal stitchers  48 ,  49  and  50 . The longitudinal stitcher  48  sets the frontmost stitching hook  43  as viewed in the conveying direction A of the printed products  3 ,  3 ′,  3 ″. The centre stitching hook  43 ′ is then set by the stitcher  49 . During the passage through the longitudinal stitcher  50 , the third, rearmost stitching hook  43 ″ is set. As mentioned, the setting and closing of the three stitching hooks  43 ,  43 ′ and  43 ″ are effected simultaneously, but in each case at a different product  3 ,  3 ′ and  3 ″ respectively. 
     A variant of the stitching arrangement according to FIG. 16 is shown in various working phases in FIGS. 17-19. 
     Unlike the embodiment shown in FIG. 16, the three longitudinal stitchers  48 ,  49 ,  50  in the variant shown in FIGS. 17-19 do not work in synchronism with one another but with a mutual phase displacement. In the three FIGS. 17,  18  and  19 , in each case the setting and closing of the three stitching hooks  43 ,  43 ′,  43 ″ is shown at a printed product  3 ″. In the representation of FIG. 17, the stitching-hook setting and closing operations at the two leading printed products  3  and  3 ′ have already been completed. FIG. 18 shows that the stitching-hook driving-in operation is starting at the longitudinal stitcher  48 , while the longitudinal stitcher  50  has set the rearmost stitching hook of the product  3 ′. FIG. 19 shows that the longitudinal stitcher  50  is on the point of setting the rearmost stitching hook  43 ″ in the product  3 ″. The longitudinal stitcher  49  is at the start of the stitching-hook setting operation, while a stitching head  7  and the associated stitching-hook closing head  32  of the longitudinal stitcher  48  run toward the stitching region. 
     It can easily be seen from FIGS. 17-19 that the mutual phase position of the stitchers  48 ,  49 ,  50  may be set in order to take into account various parameters, such as, for example, product format, distance between successive products, stitching-hook distance, distance of the frontmost stitching hook from the leading product margin, etc. 
     Two longitudinal stitchers  48  and  49 , which, just as described with reference to FIGS. 17-19, do not work in synchronism but with a mutual phase displacement, are shown in the case of the stitching arrangements shown in FIGS. 20-22. In contrast to the stitching arrangement according to FIGS. 17-19, in the embodiment according to FIGS. 20-22 it is not the frontmost stitching hook but the rear stitching hook  43  which is set first by the first longitudinal stitcher  48  as viewed in the conveying direction A of the printed products  3 . 
     FIGS. 21 and 22 show how the two longitudinal stitchers  48  and  49  can be reset in order to convert the stitching arrangement to a smaller product format. The mutual phase position of the two stitchers  48  and  49  may be set, for example, in such a way that the distance a, a′ between the two stitching hooks  43 ,  43 ′ of a printed product  3  is changed. Furthermore, by changing the phase position of the two longitudinal stitchers  48 ,  49 , a change in the product distance, which is determined by the distance K, K′ of conveying lugs  51 , can be taken into account. 
     Shown in FIGS. 23-25 is another design of a stitching arrangement, which is very similar to the stitching arrangement according to FIG.  16 . In the embodiment according to FIGS. 23-25 too, the printed products  3 ,  3 ′,  3 ″ to be stitched are moved along an insertion section  45  in the direction of arrow A. However, the longitudinal stitchers  53 ,  55  and  55  shown in FIG. 23 (side view) are of a different construction from the stitchers  48 ,  49 ,  50  of the embodiment according to FIG. 16, which of course correspond in design to the stitcher shown in FIGS. 1 and 2. 
     As seen in FIG. 25, which, in a representation comparable with FIG. 2 partly in section, shows a front view of the stitching arrangement according to FIG. 23 in the direction of arrow II in FIG. 23, the insertion section  45  has a V-shaped conveying channel  52  open at the top. The products  3 ,  3 ′,  3 ″ to be stitched lie on the side walls of this conveying channel  52 . In the exemplary embodiment shown, three longitudinal stitchers  53 ,  54 ,  55  working in synchronism with one another are provided (FIG.  23 ), and these longitudinal stitchers, as explained with reference to FIG. 16, set a stitching hook  43 ,  43 ′,  43 ″ one after the other in each printed product  3 ,  3 ′,  3 ″. Each longitudinal stitcher  53 ,  54 ,  55  consists of a rotating stitcher  56 , which is arranged below the conveying channel  52 , and of a stitching-hook closing arrangement  57 , which is arranged opposite the rotating stitcher  56  above the conveying channel  52 . 
     As explained with reference to FIGS. 1 and 2, each rotating stitcher  56  has two diametrically opposite stitching heads  58 , which are fastened to a carrier  59 , which is rotationally driven in the direction of arrow B. The axis of rotation  59   a  of the carriers  59  runs at right angles to the conveying direction A of the printed products  3 . The construction of the rotating stitchers  56  will be described in more detail with reference to FIG.  25 . The carriers  59  of the three rotating stitchers  56  are driven together by a drive source (not shown in any more detail) via a drive chain or a drive belt  60 . 
     The stitching-hook closing arrangements  57 , of which a region is shown enlarged in FIG. 24, have two opposite stitching-hook closing heads  62 , which are fastened to two chains  63  and  63 ′ driven in a revolving manner (see also FIG.  25 ). The chains  63 ,  63 ′ are each run over a drive wheel  64 ,  64 ′. The drive wheels  64 ,  64 ′ are driven via drive chains or drive belts  65  by the associated rotating stitcher  56  (see FIG.  23 ). The revolving direction of the drive chains  63 ,  63 ′ is designated by L in FIG.  23 . The chains  63 ,  63 ′ continue to run over two deflection wheels  66  ( 66 ′) and  67 , which are arranged next to one another in such a way that the strand  63   a  of the chains  63 ,  63 ′ which runs between the two deflecting wheels  66 ,  67  extends parallel to the conveying direction A of the printed products  3 , as can clearly be seen from FIGS. 23 and 24. 
     As FIG. 24 shows, each stitching-hook closing head  62  has a housing  71 , in which two bending elements  72  are pivotably mounted, and these bending elements  72  interact with an actuating plunger  73 , which is arranged in the housing  71  so as to be displaceable at right angles to the conveying direction A of the printed products  3 , i.e. in the direction of arrow I. At its end opposite the bending elements  72 , the actuating plunger  73  carries a control roller  74 , which interacts with a control link  75  in the stitching region C shown in FIG.  24 . The control link  75  has a linear section  75   a  which runs parallel to the conveying direction A. With regard to the arrangement and mode of operation of the deflecting elements  72  and the actuating plunger  73  with control roller  74 , the stitching-hook closing heads  62  correspond to the stitching-hook closing heads  32  of the embodiment according to FIGS. 1 and 2. The housing  71  of the stitching-hook closing head is connected to a supporting element  76 , which carries rollers  77  and  78  at its ends. These rollers  77 ,  78  run on a rectilinear, fixed guide rail  79 , which runs parallel to the strand  63   a  of the chains  63  ( 63 ′) and thus parallel to the conveying direction A of the printed products  3 . The guide rail  79 , which is only present in the stitching region C, serves as guide and support for the stitching-hook closing heads  62  during the stitching-hook setting and closing operation, which just as explained with reference to FIGS. 1 and 2 runs along a section  23  (FIG.  24 ), along which both the stitching heads  58  and the stitching-hook closing heads  62  perform a linear movement parallel to the conveying direction A of the printed products  3 . 
     The construction and mode of operation of the rotating stitchers  56  and their stitching heads  58  will now be explained in more detail below with reference to FIG.  25 . The rotating stitchers  56  are partly of the same construction as the rotating stitchers  4  of the embodiment according to FIGS. 1 and 2. In FIG. 25, therefore, those components which correspond to the components of the rotating stitcher  4  are provided with the same reference numerals as in FIGS. 1 and 2. The rotating carrier  59 , on which the stitching heads  58  are pivotably mounted, is driven by a drive shaft  22 , which is in operative connection with the drive chain or the drive belt  60 . The mounting of the stitching heads  58  in the carrier  59  and the arrangement for pivoting the stitching heads  58  about the pivot axis  12   a  are effected exactly in the same way as described with reference to FIGS. 1 and 2. Mounted in the interior of the housing  8  of each stitching head  58  is a bush  80 , which is rotatable about the longitudinal axis  58   a  of the associated stitching head  58 . The stitching-hook guide  9  and the stitching-hook drive-in plunger  10  are displaceably mounted in the interior of this rotatable bush  80 , as has already been explained with reference to FIGS. 1 and 2. 
     A rotary mechanism  81  common to both stitching heads  58  is provided in order to rotate the bearing bushes  80 . The rotary mechanism  81  has a disk  83  mounted in a freely rotatable manner on a fixed bearing arrangement  82 . This disk  83  is inclined relative to the axis of rotation  59   a  of the carrier  59 , i.e. the axis of rotation  83   a  of the disk  83  forms an angle α with this axis of rotation  59   a . Two double-armed levers  84 ,  85  diametrically opposite one another are pivotably mounted on the disk  83 . Acting on one lever arm is a tension spring  86 , which is fastened at the other end to the disk  83 . The other lever arm of the levers  84 ,  85  is connected in an articulated manner to a lever  87 , which is guided in a longitudinal guide  88 , the longitudinal axis of which extends parallel to the axis of rotation  59   a . These longitudinal guides  88  are fastened to a disk  89 , which is connected to the stitching-head housings  8  and thus rotates in synchronism along with the stitching heads  58  and the carrier  59 . Firmly connected to the plungers  87  and projecting away from the latter are actuating elements  91 , which are each connected via a lever  92  to the rotatable bearing bush  80  of each stitching head  58 . These levers  92  act on the bearing bushes  80  outside the axis of rotation  58   a  of the latter. 
     During the rotation of the carrier  59  and thus of the stitching heads  58 , the disk  83  is driven along via the plungers  87  and is rotated about its axis  83   a . Since the latter is inclined by the angle α relative to the axis of rotation  59   a  of the carrier  59 , the plungers  87  and thus also the actuating elements  91  are moved in a reciprocating manner in the direction of arrow M during this rotary movement of the disk  83 . Via the levers  92  acting eccentrically on the bearing bushes  80 , this linear movement of the actuating elements  91  produces a rotation of the bearing bushes  80  by 90° during the movement of the stitching heads  58  from the stitching-wire transfer point to the stitching region. In the process, the feeding of the stitching wire  26 , the preparation and transfer of wire sections, and the bending of the stitching hooks  43  are effected in the manner described with reference to FIGS. 1 and 2. 
     It follows from the above description of the embodiment according to FIGS. 23-25 that, just as described with reference to FIGS. 1-3, the stitching heads  58 , before or when running into the stitching region C, are pivoted into a position in which the longitudinal axis  58   a  of the stitching heads and thus the displacing direction E of the stitching-hook drive-in plungers  10  are at right angles to the conveying direction A of the printed products  3 . The stitching heads  58  are held in this position while passing through the section designated by  23 . Correspondingly, the stitching-hook closing heads  62  are moved in the stitching region along the abovementioned section  23  likewise parallel to the conveying direction A of the printed products  3 , i.e. the displacing direction I of the actuating plunger  73  is likewise at right angles to the abovementioned conveying direction A. 
     Therefore the advantages described with reference to FIGS. 1-3 are also obtained in the embodiment according to FIGS. 23-25. 
     Some of the different possible alternative designs of the longitudinal-stitching device according to the invention are referred to below. 
     Although the rotating stitcher  4 ,  56 , as shown, has two stitching heads  7 ,  58 , which are located diametrically opposite one another, it is also possible for only one stitching head or else for more than two stitching heads  7 ,  58  to be provided per rotating stitcher. If there are a multiplicity of stitching heads, these stitching heads may be arranged so as to be distributed in the circumferential direction of the carrier  6 ,  59  at uniform distances or else even at non-uniform distances. 
     If there are a plurality of stitching heads per rotating stitcher, it is also possible, depending on the range of use, for individual stitching heads not to be loaded with a wire section. 
     The preparation of stitching-wire sections and their feed to the revolving stitching heads may also be of a different design from that shown, e.g. in the manner described in U.S. Pat. No. 5,172,897. 
     The stitching-hook closing arrangement  5 ,  57  may be designed in a different way to that shown. As shown and described, however, a stitching-hook closing head is preferably assigned to each stitching head. However, this stitching-hook closing head may also be only an opposing element without controlled bending elements, and the stitching-hook legs are pressed against said opposing element and are bent in the process. Of course, within the scope of the invention, this opposing element must be moved in the stitching region along with the associated stitching head along a linear path of movement. 
     Instead of a revolving movement of the stitching-head closing heads or stitching-head closing opposing elements, a reciprocating movement of these components may also be provided.