Abstract:
A folding gear is comprised of a cylinder that is mounted to a frame for rotation. At least one clamp is arranged on the outer surface of the cylinder. The at least one clamp can be positioned by an actuator which includes a flexible toothed shell that is shaped by a non-circular section of a shaft. A hollow gear engages this flexible shell and cooperates with it to form a harmonic drive gear.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a folding apparatus having a cylinder whose circumference is adjustable. The cylinder is rotatably supported on the frame and has at least one hoop or ring supported on its shell surface. 
   BACKGROUND OF THE INVENTION 
   A prior folding apparatus is known from DE 38 21 442 C2, for example. A folding apparatus with a folding cylinder is described in this document as the prior art of this technology. A shell surface of the cylinder of this prior device is constructed of segments which are fixedly mounted on a frame of the cylinder, as well as of movable hoops, which bridge gaps between the segments. These hoops have two ends in the circumferential direction of the cylinder, one of which is fixedly mounted on one of the segments, while the other is adjustable with the aid of a strip which can be displaced parallel with the axis of the cylinder. A conversion of the axis-parallel adjustment movement of the strip, to a displacement of the end of the hoop, takes place with the aid of a pin, which pin is fixedly mounted on a sliding plate of the strip connected with the displaceable end of the hoop and which engages an elongated hole, that is oriented obliquely, in respect to the extension of the strip. By displacing the movable end of the hoop in the direction of the fixed end of the hoop, with the aid of this mechanism, arching of the hoop and therefore an increase of the circumference of the cylinder is achieved. 
   In connection with a folding apparatus described as the invention in DE 38 21 442 C2, the adjustment movement of the strip itself is driven with the aid of a planetary gear which, with the folding cylinder rotating, allows the rotation of two sun wheels which are coaxial with the folding cylinder. One of the sun wheels meshes with a plurality of intermediate wheels, which in turn mesh with pinion gears. The pinion gears are connected, fixed against relative rotation, with a helical spindle which engages a screw thread of the strip. The rotation of the spindles drives a translation of the strips. 
   With this construction, the hoops are compressed in the longitudinal direction if the circumference is to be increased. Since the hoops or bows must have a degree of stiffness, which is not negligible, in order not be deformed during contact with the material to be processed during the operation of the folding apparatus, a considerable force is required to accomplish this compression. In most cases, an adjustment movement requires a multitude of revolutions of the spindle. 
   DE 197 55 428 A1 describes a device for displacing two cylinder bodies of a folding cylinder by the use of a harmonic drive mechanism. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is directed to providing a folding apparatus including a cylinder whose circumference can be adjusted. 
   In accordance with the present invention, this object is attained by providing the cylinder, which is rotatably supported in a frame, with at least one hoop on its shell surface. The at least one hoop can be displaced by the operation of an adjusting gear assembly. That adjusting gear assembly is in the form of a flexible toothed sleeve, which is deformed by an out of round section of a shaft, and at least one internally geared wheel which meshes with the sleeve. The result is a harmonic drive gear. 
   The advantages which can be obtained by the present invention consist, in particular, in that the employment of a “harmonic drive” mechanism permits a very compact structure, along with a large load-bearing capacity. 
   By connecting the out-of-round section of the shaft of the “harmonic drive” mechanism with the drive mechanism for driving the displacement of the hoops, it is possible to achieve very low gear ratios for the transmission of the revolution of the drive mechanism to the hoops, and therefore to obtain and to accomplish a very sensitive regulation with a small outlay of force at the drive mechanism. 
   The “harmonic drive” mechanism is preferably designed with two stages. The internally geared wheel of one stage is coupled to the rotation of the cylinder, and the one of the other stage provides coupling to the movement of the hoops by way of a gear wheel which is rotatable around the axis of the cylinder relative to the latter. 
   In accordance with a first preferred embodiment of the present invention, a gear wheel, by the use of which the internally geared wheel coupled to the rotation of the cylinder is driven, can be rigidly connected with the cylinder. In other words, a drive train for the internally geared wheel can extend via the cylinder, or a common drive train for the internally geared wheel and the cylinder extends via this gear wheel. Alternatively, there is the option of providing an independent drive train for this internally geared wheel which is parallel with the one for the cylinder. Both drive trains can, in particular, originate from a common second driven cylinder. 
   The tooth numbers of the first and second tooth arrangement at the internally geared wheels of the “harmonic drive” mechanism, of the drive wheels which are coaxial to the cylinder, and of the flexible sleeves, are preferably selected in such a way that, with a stopped drive mechanism, the gear wheels rotate at the same number of revolutions. However, in this case, the tooth numbers of the first and second tooth arrangements, of the drive wheels which are coaxial to the cylinder, and of the flexible sleeves, must not all be identical in pairs. 
   Preferably, the tooth numbers of the flexible sleeves are selected to be identical, but those of the internally geared wheels are selected to be different. If then, the tooth numbers of the second tooth arrangements are identical, the tooth numbers of the coaxial gear wheels and of the second tooth arrangements should be in the same ratio. 
   In accordance with a first preferred embodiment of the present invention, the other gear wheel, which is coupled to the hoops, has an external tooth arrangement. In accordance with a further preferred development, however, this other gear wheel is embodied as a crown gear. This makes possible the placement of the “harmonic drive” gear near the shaft of the cylinder, and therefore results in a particularly compact construction of the folding apparatus. 
   One option of driving the displacement of the hoops is the use of an eccentric that is driven by the other gear wheel. A second option is the use of a displaceable strip with cam faces, which cam faces are engaged by the respective loops of the cylinder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are represented in the drawings and will be described in greater detail in what follows. 
     Shown are in: 
       FIG. 1 , a partial section through a cylinder in accordance with a first preferred embodiment of the present invention and taken transversely to its longitudinal axis, in 
       FIG. 2 , a partial section through the cylinder and taken parallel to the longitudinal axis of the cylinder, and showing the eccentric shaft, in 
       FIG. 3 , a simplified partial section, analogous to that shown in  FIG. 1  through the cylinder, and taken in a first phase of the adjustment movement of the eccentric shaft, in 
       FIG. 4 , a partial section analogous to that in  FIG. 3  taken in a second phase of the adjustment movement, in 
       FIG. 5 , a partial section through a first modification of the cylinder of the first preferred embodiment shown in  FIG. 1 , in 
       FIG. 6 , a partial section through a second modification of the cylinder of the first preferred embodiment shown in  FIG. 1 , in 
       FIG. 7 , a cross-section through an adjustment gear for rotating the eccentric shafts, in 
       FIG. 8 , a perspective plan view of a folding cylinder and of a blade cylinder of a folding apparatus in accordance with a second preferred embodiment of the present invention, in 
       FIG. 9 , a schematic representation of the gear of the folding apparatus in  FIG. 8 , in 
       FIG. 10 , a first modification of the gear shown in  FIG. 9 , in 
       FIG. 11 , a second modification of the gear shown in  FIG. 9 , in 
       FIG. 12 , a third preferred embodiment of the present invention, in the form of a cross-section through the head area of a folding cylinder, in 
       FIG. 13 , a section through the folding cylinder in  FIG. 12  at the level of the toothed belt, and in 
       FIG. 14 , a modification of the embodiment in  FIG. 12 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A schematic partial cross-sectional view through a cylinder  01 , for example a folding cylinder  01 , and in particular through a folding blade cylinder, in a plane perpendicularly to its longitudinal axis, is shown in  FIG. 1 . A shell surface of the folding cylinder  01  is substantially composed of three segments  02 , two of which segments  02  are represented in  FIG. 1 , and all three of which segments  02  are mounted fixedly on a frame of the folding cylinder  01  with cover disks, which are not specifically represented. The segments  02  are separated from each other by a cylinder gap  03 . The number of the segments  02  and of the gaps  03  of the folding cylinder  01  can, of course, also be other than three. 
   A folding blade is pivotably housed in each cylinder gap  03 . Since the folding blade in each cylinder gap  03  is not a part of the present invention, it is not represented in  FIG. 1  and will not be further described here. 
   Each of the cylinder gaps  03  is bridged by a plurality of hoops  04  or hoop-like bands which are longitudinally extending in a circumferential direction of the folding cylinder  01 . In the axial direction the of the folding cylinder  01 , hoops  04  are separated from each other by spaces, through which spaces respective teeth of the folding blade can be extended out of the cylinder gap  03 . Each of two spaced linear ends  06 ,  07  of each of the hoops  04  have an eye  08 , which eye  08  protrudes, or extends into an interior region of the folding cylinder  01  and each which eye  08  has a circular bore, in which an eccentric  09  is rotatably seated. As shown in  FIG. 2 , the eccentric  09  is embodied as one part of a shaft  11 . On each of its ends, the shaft  11  is supported by a bearing  12 , for example by a roller bearing  12 , in a cover disk  13 ,  14 , which cover disk  13 ,  14  is a part of the frame of the folding cylinder  01 . A first gear wheel  16  is mounted at an end of the shaft  11 , which shaft end  11  extends past the adjacent cover disk  13 . 
   In the first preferred embodiment of the present invention, as shown in  FIG. 1 , a shaft  11  is arranged on each of the two sides of each gap  03 . Since the folding cylinder  01  has a total of three gaps  03 , there is a total of six shafts  11 . The first gear wheels  16  of all of these six shafts  11  all mesh in the same way with a second gear wheel  17 , depicted here in the form of a crown gear  17  and provided with an external tooth arrangement, which crown gear  17  is arranged, concentrically rotatable around an axis of rotation A of the folding cylinder  01 , on the cover disk  13 , and whose pitch circle is indicated in the form of a dash-dotted line in  FIG. 1 . Thus, by the effecting of a rotation of the second gear wheels  17 , all eccentrics  09  are rotated to the same extent, and the hoops  04  are moved. The way the second gear wheel  17  is rotationally driven will be discussed in more detail subsequently. 
     FIGS. 3 and 4  show two distinct phases of the movement of the hoops  04  which are caused by the rotation of the gear wheels  17 ,  16 .  FIG. 3  corresponds, in a simplified form, to the plan view of  FIG. 1 . With respect to the centers M 11  of the shafts  11 , in  FIG. 3  the centers M 09  of the eccentrics  09  are each offset radially in the direction toward the center M 01  of the folding cylinder  01 , i.e. an eccentricity vector E, extending respectively from the center M 11  of the shaft  11  to the center M 09  of the eccentric  09 , is oriented radially inward. The hoop  04  rests against the surfaces of the segments  02  at the spaced sides of the cylinder gap  03 . 
   The eccentricity vectors E of each of the two shafts  11  for each hoop  04  intersect at an angle corresponding to the angular distance of the shafts  11  in relation to the center M 01  of the folding cylinder  01 . This does not change, even with a rotation of the second gear wheel  17  with respect to the folding cylinder  01 . 
   In  FIG. 4 , the shafts  11  are each rotated by 180° from their positions in  FIG. 3 , and the centers M 09  of the eccentrics  09  are now displaced radially outward with respect to the centers M 11  of the shafts  11 , i.e. the eccentricity vector E is now directed radially oriented toward the outside. The hoop  04  is now spaced at a distance from the surface of the segments  02  corresponding to twice the eccentricity of each eccentric  09  with respect to its position shown in  FIG. 3 . 
   During the transition of the hoops  04  from the inner position shown in  FIG. 3  to the outer position shown in  FIG. 4 , the two eyes  08  of the hoop  04  not only move away from the center M 01  of the folding cylinder  01 . They also move apart from each other. To make such a movement possible, the hoop  04  can be extended in the circumferential direction with the aid of a rail mechanism which is not specifically shown. For example, one of the hoop&#39;s eyes  08 , the one on the left in  FIG. 4 , is connected, displaceable in the circumferential direction, with the associated linear end  07  of the hoop  04  by the use of a guide rail. 
     FIG. 5  shows a modified preferred embodiment of the folding cylinder  01 . In this second embodiment, the eccentricity vectors E of the two eccentrics  09  are always exactly parallel. This means that in the position of the eccentrics  09  represented in  FIG. 5 , their centers M 09  are displaced in the vertical direction of  FIG. 5  in respect to the centers M 11  of the shafts  11 . The parallel orientation of the eccentricities is maintained, even if the shafts  11  are rotated with the aid of the second gear wheel  17 , which is not specifically represented in  FIG. 5 . During a complete revolution of each of the shafts  11 , each point on the hoop  04  travels in a circular track of a radius corresponding to the amount of eccentricity of the eccentrics  09 . No deformation of the hoop  04  occurs. The connection of the hoop  04  with the eyes  08  can also be rigid in this embodiment, since, in the course of a revolution of shafts  11 , the distance between the two eyes  08  does not change. With this embodiment, it is not possible that, in a “retracted” position of hoop  04 , corresponding to a minimal circumference of the folding cylinder  01  analogous to the position depicted in  FIG. 3 , the hoop  04  simultaneously touches both segments  02 , which are partially covered by it. Instead, in the “retracted” position represented in  FIG. 5 , and corresponding to a minimal circumference of the folding cylinder  01 , the hoop  04  is separated from both adjacent segments  02  by a respective gap  18 . 
   A third, preferred embodiment of the folding cylinder  01  of the present invention is represented, in a simplified manner, in  FIG. 6 . Here, an eye  08  has been arranged on only one linear end  06  of the hoop  04 . The other linear end  07  of hoop  04  is fastened on a cylinder segment  02 , for example with the aid of a screw  19  which passes through an elongated hole  20  situated at the linear end of the hoop  04  not provided with eye  08 . If, with this embodiment, the shaft  11  is rotated, the linear end  06 , with the eye  08 , is lifted and lowered in the radial direction. At the same time, the linear end  07  without the eye  08 , is displaced in the circumferential direction of cylinder  01  in relation to the screw  19 . A deformation of the hoop  04  is practically not required for such a displacement of hoop  04 . Therefore the displacement of hoop  04  requires only a small outlay of force. 
   Such a construction of the end  07  of hoop  04 , without the eye  08 , can also constitute the rail mechanism mentioned above in relation to  FIG. 4 . 
   There is also a possibility of fastening the linear end  07  immovably on the segment  02 . In this case, a rotation of the shaft  11  and a change of the circumference of the folding cylinder is also possible, but it is necessary, in order to accomplish this, that the hoop  04  have a greater elasticity than in the previously discussed preferred embodiments, since the change is connected with a compression of the hoop  04 . 
   Changing the circumference of the cylinder  01  means that an at least partial change of the radius of cylinder  01  also takes place. 
     FIG. 7  shows a mechanism which, in use with a rotating folding cylinder  01 , permits a turning of the second gear wheel, or crown gear,  17 , shown in  FIG. 2 , relative to the folding cylinder  01 , and therefore accomplishes a change of the circumference of folding cylinder  01 .  FIG. 7  is a partial section through a frame of a folding apparatus in a plane which is parallel to the longitudinal axis of the folding cylinder  01 . A hollow shaft  21  formed on one of the cover disks  13  is rotatably seated in a lateral plate  22  of the frame. A drive gear wheel  23 , which transfers the torque of a non-represented motor to the folding cylinder  01 , is wedged on an end of the hollow shaft  21  facing away from the cover disk  13 . 
   An adjusting gear assembly  26 , for example a “harmonic drive” gear  26 , is fixedly mounted on the frame of the folding apparatus. It comprises a shaft  27 , for example an adjusting shaft  27 , which is connected with a drive mechanism, which is not specifically represented in  FIG. 7 , for example a motor or an arrestable crank. The adjusting shaft  27  has an out-of-round section  28 , or more exactly an elliptical cross section, also called rotor  28 , on which, separated by bearings  30 , for example ball bearings  30  of elliptical cross section corresponding to the shape of the rotor  28 , two flexible sleeves  29 ,  31  have been pushed, each of which has exterior tooth arrangements. The two sleeves  29 ,  31  are connected with each other, fixed against relative rotation, and mesh with respective tooth arrangements  32  or  33 , for example interior tooth arrangements  32  or  33 , of a internally geared wheel  41  or  42  of circular cross section surrounding them. The internally geared wheels  41 ,  42  are connected with further gear wheels  45 ,  50 . These gear wheels  45 ,  50  are seated, rotatable around the adjusting shaft  27 , with the aid of bearings  34 , for example ball bearings  34 . Each of these further gear wheels  45 ,  50  has a tooth arrangement  36 ,  37 , for example an exterior tooth arrangement  36 ,  37 , of which the one exterior tooth arrangement  36  meshes with a gear wheel  24 , which is arranged next to the drive gear wheel  23  and is wedged, the same as the latter, on the hollow shaft  21 . The other exterior tooth arrangement  37  meshes with a gear wheel  38 , which is rotatable around the axis A of the folding cylinder  01  and is connected with a rigid sleeve  39  extending through the interior of the hollow shaft  21  into the interior of the folding cylinder  01  and there supports the already mentioned second gear wheel  17 , which drives the displacement movement of the hoops  04  via the first gear wheels  16 . 
   If the folding cylinder  01  is driven at a circumferential speed n 01 , this results in the internally geared wheel  41  of the “harmonic drive” gear  26  also rotating at a speed of 
           n41   =     n01   ⁢     z24   z36             
wherein the respective tooth numbers z 24 , z 36  are those of the gear wheel  24  or of the external tooth arrangement  36 . If the adjusting shaft  27  is at rest, this results in a rotation of the sleeves  29 ,  31  at a rotational speed of
 
           n29   =     n41   ⁢     z29   z32             
wherein the respective tooth numbers z 29 , z 32  are those of the sleeve  29  or the interior tooth arrangement  32  of the internally geared wheel  41 . From this results a number of revolutions
 
           n42   =     n29   ⁢     z31   z33             
of the internally geared wheel  42  in turn, wherein the respective tooth numbers z 31 , z 33  are those of the sleeve  31  or of the interior tooth arrangement  33  of the internally geared wheel  42 . From this results a number of revolutions
 
           n38   =     n41   ⁢     z37   z38             
of the gear wheel  38 , wherein the respective tooth numbers z 37 , z 38  are those of the exterior tooth arrangement  37  or of the gear wheel  38 .
 
   So that, with the adjusting shaft  27  stopped, the second gear wheel  17  will rotate at exactly the speed of the folding cylinder  01 , it is necessary that the requirement 
                     z37   ⁢           ⁢   z31   ⁢           ⁢   z32   ⁢           ⁢   z24       z38   ⁢           ⁢   z33   ⁢           ⁢   z29   ⁢           ⁢   z36       =   1           (   1   )               
be met.
 
   In order to cause a rotation of the second gear wheel  17 , in relation to the folding cylinder  01 , by the rotation of the adjusting shaft  27 , it is furthermore necessary that either the tooth numbers z 29 , z 31 , z 32 , z 33  of the two sleeves  29 ,  31 , or of the crown gears  32 ,  33 , or both, differ. If this were not the case, a rotation of the adjusting shaft  27  would not result in a rotation of the internally geared wheels  41 ,  42  in relation to each other. 
   This means that the mechanism in  FIG. 7  must fulfill the conditions of equation 1 and, at the same time
 
z29≠z31V z32≠z33  (2)
 
must apply.
 
   The two conditions can be met in general, because the gear wheels  24 ,  38  have a considerably greater diameter than the internally geared wheels  41 ,  42  and can have a large number of teeth z 24 , z 38 , which are only slightly different from each other. 
   Thus, it is possible, for example, to select the tooth numbers of the interior and of the exterior tooth arrangements of the internally geared wheels  41 ,  42  to be identical in pairs, and to accept a slight difference between the tooth numbers z 29 , z 31  of the flexible sleeves  29 ,  31 . In this case the equation 1 is reduced to 
                     z31   ⁢           ⁢   z24       z38   ⁢           ⁢   z29       =   1           (   3   )               
i.e. the synchronous running of the gear wheel  17  with the folding cylinder  01 , while the adjusting shaft  27  is stopped, is assured if the tooth numbers z 29 , z 31  of the flexible sleeves  29 ,  31  are at the same ratio to each other as those of the gear wheels  24 ,  38 :
 
   
     
       
         
           
             z29 
             z31 
           
           = 
           
             z38 
             z24 
           
         
       
     
   
   It is therefore sufficient to select the tooth numbers z 24 , z 38  of the gear wheels  24 ,  38  and of the flexible sleeves  29 ,  31  to be identical in pairs. 
   The smaller the difference of the tooth numbers z 9 , z 31  of the flexible sleeves  29 ,  31 , the more sensitively can the turning of the gear wheels  24 ,  38  toward each other be performed by rotating the adjusting shaft  27 . Approximately n 31 /(n 31 −n 29 ) revolutions of the adjusting shaft  27  are required for rotating the gear wheels  24 ,  38  by 360° in relation to each other. 
   Alternatively, it is possible, for example, to select the tooth numbers z 29 , z 31 , z 36 , z 37  of the flexible sleeves  29 ,  31  and of the exterior tooth arrangements  36 ,  37 , respectively identical in pairs, and to accept a slight difference between the tooth numbers z 32 , z 33  of the interior tooth arrangements  32 ,  33 . In this case, Equation 1 is reduced to 
                     z32   ⁢           ⁢   z24       z38   ⁢           ⁢   z33       =   1           (   4   )               
i.e. the synchronous running of the gear wheel  17  with the folding cylinder  01 , while the adjusting shaft  27  is stopped, is assured, if the tooth numbers z 29 , z 31  of the flexible sleeves  29 ,  31  are at the same ratio to each other as are those of the gear wheels  24 ,  38 :
 
   
     
       
         
           
             z32 
             z33 
           
           = 
           
             z38 
             z24 
           
         
       
     
   
   It is therefore sufficient to select the tooth numbers z 24 , z 38 , z 32 , z 33  of the gear wheels  24 ,  38  and of the interior tooth arrangements  32 ,  33  to be identical, in pairs, in order to assure, with the adjusting shaft  27  at a stop, the synchronous running of the gear wheel  38  with the folding cylinder  01  and, in this way, to prevent the unintentional displacement of the hoops  04 . 
     FIG. 8  shows a perspective view of a folding cylinder  01  and of a cooperating cylinder  44 , for example a blade cylinder  44  of a folding apparatus, in accordance with a second preferred embodiment of the present invention. The blade cylinder  44  is directly connected with a drive motor, which is not specifically represented. A drive train of the folding cylinder  01  extends from the motor via the blade cylinder  44  and a gear, also not specifically represented, and which is arranged between the cylinders  01 ,  44 . 
   The blade cylinder  44  supports two blades, each extending over its entire axial width, for use in cutting an endless strand of material into individual products to be folded. These blades, as well as suitable grippers or pointed needles of the folding cylinder  01 , which are used for holding the separated product, are not represented in  FIG. 8 , since they are generally known. Flexible hoops  04  on the surface of the cylinder  01  are maintained fixed on one of their ends and are displaceable in the circumferential direction of the folding cylinder  01  on the other one, as generally disclosed in the publication DE 38 21 442 C2, which was cited at the outset of the specification. Pins, which, starting at their displaceable ends, are oriented into the interior of the folding cylinder  01 , each engage oblique, axially displaceable slits of a strip  61  that is hidden in the interior of the cylinder  01  and which is shown schematically in  FIG. 9 . In this way, the lateral flanks of the slits constitute cam surfaces, by the use of which the strips  61  drive a deformation of the hoops  04 . In the second preferred embodiment represented in  FIGS. 8 and 9  , three groups of hoops  04  are provided, which three groups follow each other in the circumferential direction of the folding cylinder  01 . Three strips  61  are correspondingly provided. Each one of these strips  61  has an internal screw threaded bore on its end face, which internal screw threaded bore is engaged by a threaded shaft. Each threaded shaft, which is maintained rotatably, but axially fixed in the cylinder  01 , has a pinion  46  on one end, which pinion  46  is visible at the end face of the folding cylinder  01 . All three pinions  46  mesh with an exterior tooth arrangement of a crown gear  47 , which is rotatably arranged on the end of the folding cylinder  01  and which encircles a central opening  48 , as seen more clearly in  FIG. 8 . A shaft  49  of a folding blade support or spider extends eccentrically through the opening  48  into the interior of the folding cylinder  01 . The spider supports folding blade shafts on diametrically oppositely located arms  51 , which are essentially hidden in  FIG. 8 , and on each of which, a comb-like folding blade  52  is mounted. The folding blade  52  rotates around its respective folding blade shaft, coupled to the rotation of the spider around the shaft  49 . Tips of the comb-like folding blade  52 , and, extending out of slits between the gaps  04 , are represented in  FIG. 8 . 
   A gear wheel  53  is furthermore arranged in the opening  48  and meshes with an interior tooth arrangement of the crown gear  47 . The gear wheel  53  is rigidly coupled via a shaft  54  with a “harmonic drive” or adjusting gear  26 . The internal structure of the adjusting gear  26 , and its relationship with an adjusting drive mechanism  56  and with the blade cylinder  44  can be best seen in  FIG. 9 , which represents the structure shown in  FIG. 8  in the form of a schematic sectional view. The structure of the “harmonic drive” gear  26  is the same as that described with respect to  FIG. 7  and will not be explained again. In  FIG. 7  and in  FIG. 9  the same reference symbols have been used for identical components of the “harmonic drive” gear  26 . The gear wheel  53 , although separated from the internally geared wheel  42  by the shaft  54 , can be considered to be equivalent with the exterior tooth arrangement  37  represented in  FIG. 7 . 
   The exterior tooth arrangement  36  of the internally geared wheel  41  meshes with a gear wheel  57 , for example a first intermediate gear wheel  57 , which is coupled via a further gear wheel  58 , for example a second intermediate gear wheel  58 , with a gear wheel  59 , which is rigidly fixed on the blade cylinder  44 . Thus, a drive train for the crown gear  47  extends from the blade cylinder  44  via the gear wheels  59 ,  58 ,  57  to the “harmonic drive” gear  26 , and via the shaft  54  on to the gear wheel  53 . The ratio of the numbers of revolutions of the blade cylinder  44  and of the folding cylinder  01  corresponds to the ratio of the groups of parallel hoops  04  on the folding cylinder  01  to the number of blades of the blade cylinder  44 , and in the case here considered is 3:2. The tooth numbers on the drive train of the crown gear  47 , such drive train consisting of the components  59 ,  58 ,  57 ,  26 ,  53 , has been fixed in such a way that the crown gear  47  rotates at the same speed as the cylinder  01  as long as the adjusting shaft is stopped. The strip  61  is not axially displaced, and the shape of the hoops  04  thus remains unchanged. Turning the adjusting shaft  27  causes turning of the crown gear  47  with respect to the folding cylinder  01 , and in this way axial movement of strip  61  is used for deforming the hoops  04 , which deformation of the hoops  04  changes the circumference of the folding cylinder  01 . 
   The schematic sectional view represented in  FIG. 10  differs from that in  FIG. 9  in that the exterior tooth arrangement  36  of the internally geared wheel  41  is not coupled to the blade cylinder  44  but, as in the preferred embodiment in  FIG. 7 , meshes directly with a gear wheel  62 , which is rigidly connected with the folding cylinder  01 . In contrast to the gear wheel  38  in  FIG. 7 , the gear wheel  62  is an internally geared wheel  62 . The tooth number formulas cited in connection with  FIG. 7  can be analogously applied in order to determine tooth numbers which assure a synchronous running of the crown gear  47  with the folding cylinder  01  also for this gear. 
   As previously mentioned above, the folding cylinder  01  has holding devices, such as grippers or pointed needles which, in coordination with the rotation of the cylinder  01 , are movable in order to close over or engage a product conveyed to a fixed receiving point of the cylinder circumference and to hold the product for further conveyance and processing at the cylinder  01 , and to open again at a delivery point, so that the product can be passed over to a further cylinder or the like. The holding devices can be operated in a single or in a collection mode of operation. In the single mode of operation the holding devices open during each passage through the delivery point in order to release the product they are holding. In the collection mode of operation, such a holding device passes the delivery point once without opening, then receives a second product in the course of a second passage through the receiving point and then releases both products together in the course of a second passage through the delivery point. The movement of these holding devices is controlled in a generally known manner with the aid of a cam disk, which is not specifically depicted, and which is coaxial to the folding cylinder  01  and on which the pivot arms of the holding devices roll off. The cam disk has a recess at a location corresponding to the delivery point and into which a passing pivot arm dips, whereupon the corresponding holding device opens and releases the product held. In order to accomplish the holding device only opening during every second passage through the delivery point, during collecting operations, a so-called cover disk is employed. This cover disk is parallel with the cam disk and rotates coaxially with the cylinder  01 , but only at half the number of revolutions of the latter. The cover disk has a section of a large radius, which, in the course of every second passage through the delivery point, covers the recess on the cam disk and prevents the opening of the holding device. The cover disk also has a section of a lesser radius which, when it lies in front of the recess on the cam disk, permits the opening of the holding device. In the embodiment of the present invention represented in  FIG. 11 , such a cover disk, identified by  63 , has been integrated into the drive train of the crown gear  47 . As depicted in the diagram of  FIG. 9 , this drive train runs from the directly driven blade cylinder  44 , via the gear wheel  59 , which is rigidly coupled to the blade cylinder  44  and is aligned with the axis B of the latter, and two intermediate wheels  58 ,  57 . The intermediate wheel  57  does not directly mesh with the exterior tooth arrangement  36  of the internally geared wheel  41 , but instead meshes with an exterior tooth arrangement  64  of the cover disk  63 , wherein the latter again has an interior tooth arrangement  66 , which meshes with the exterior tooth arrangement  36 . The tooth numbers of the gear elements  57 ,  58 ,  59 ,  64  have been selected to be such that half of the number of revolutions of the folding cylinder  01  results for the cover disk  63 , i.e. with a ratio of the number of revolutions n 01  of the folding cylinder  01  to the number of revolutions n 44  of the blade cylinder  44  of n 01 /n 44 =2/3, the following must apply to the number of revolutions n 63  of the cover disk  63 : n 63 =n 44 /3. If the number of revolutions of the internally geared wheels  41 ,  42  of the “harmonic drive” gear  26  are identical when the adjusting shaft  27  is stopped, the result for the tooth numbers n 66 , n 36 , n 53  and n 47  of the interior tooth arrangement  66  of the cover disk  63 , the exterior tooth arrangement  36  of the internally geared wheel  41 , of the gear wheel  53  and the interior tooth arrangement of the crown gear  47  is the requirement 
   
     
       
         
           
             
               z53 
               z47 
             
             · 
             
               z66 
               z36 
             
           
           = 
           3 
         
       
     
   
     FIG. 12  shows a third preferred embodiment of the present invention, in the form of a cross-section through the head area of the folding cylinder  01  and of the adjoining portions of the lateral frame of a folding apparatus. Portions of two plates  68 ,  69  of the lateral frame can be seen, one of which,  68 , supports a tapered shaft section  71  protruding from a front end of the folding cylinder  01 . The plate  69  supports a “harmonic drive” gear assembly  26 , whose structure, comprising the components  29 ,  31 ,  32 ,  33 ,  36 ,  37 ,  41  and  42 , has been described previously in connection with  FIG. 7  and will thus not be again explained here. The exterior tooth arrangement  36  meshes with a gear wheel  24  that is rigidly fastened on the shaft section  71 . The exterior tooth arrangement  37  meshes with the exterior tooth arrangement of a crown gear  47  mounted rotatably around the end of the shaft section  71 . The shaft  27  is connected with an adjustment drive mechanism, which is not specifically represented. 
   A bore  72  extends in the longitudinal direction of the tapered shaft section  71 . A shaft  73  is rotatably maintained in the bore  72  and supports a pinion  67  on one end thereof, which pinion  67  is meshing with an interior tooth arrangement of the crown gear  47 . On its other end shaft  73  carries a pulley  74 . A toothed belt  76  is looped around the pulley  74  and around a plurality of pulleys  77 . These pulleys  77  are used, in the same way as the pinions  46  in  FIG. 8 , for displacing the strips  61  which the hoops  04  engage in a displaceable manner and which displacement of the hoops  04  cause the circumferential change of the folding cylinder  01 . 
     FIG. 13  shows schematically a section through the folding cylinder  01  at the level of the pulleys  74 ,  77  and the toothed belt  76 . Between two pulleys  77 , the toothed belt  76  loops around respective rollers  78 , at least one of which is displaceable in the radial direction for tightening the toothed belt  76 . 
   As long as the adjustment drive of the shaft  27  remains stopped, a rotation of the gear wheel  24  is transmitted to the crown gear  47  via the “harmonic drive” gear  26  at the same rotational speed. The shaft  73  does not rotate in its bore  72 , and the strips  71  are not axially displaced. When the adjustment drive is actuated and the shaft  27  rotates, this leads to a displacement of the crown gear  47  with respect to the gear wheel  24 . The result is a displacement of the strips  61  and a change of the circumference of the cylinder  01 . 
   Link chains can also be employed in place of the toothed belt  76 . 
     FIG. 14  shows a modification of the third embodiment of the invention. This modification differs from the embodiment shown in  FIG. 12  by the attachment of the crown gear  47 , which in  FIG. 14  is rotatably seated not on the shaft section  71  of the folding cylinder  01 , but instead coaxially with the folding cylinder  01  on the plate  69  that is located opposite to it. The mode of functioning of this modification does not differ from that of the embodiment in  FIG. 12 . 
   While preferred embodiments of a folding apparatus comprising a cylinder with an adjustable circumference, in accordance with the present invention have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that various changes in, for example the overall configuration of the printing device with which this folding apparatus is utilized, the type of material being folded, and the like could be made without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the appended claims.