Patent Publication Number: US-6901854-B2

Title: Drive mechanism of a printing unit

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a drive mechanism for a printing unit. The printing unit has at least two cylinders, at least one of which may be axially movable. The two are driven by a common drive motor. 
   BACKGROUND OF THE INVENTION 
   A printing group with forme and transfer cylinders driven in pairs is known from DE 44 30 693 A1. The forme cylinder is driven and its output is transmitted to the transfer cylinder via spur wheels. A journal of the forme cylinder, embodied as a rotor, is axially displaceable in the stator for adjusting the lateral register on the forme cylinder. 
   EP 0 644 048 B1 discloses cylinders which are driven while coupled in pairs. The possibility of coupling an associated inking system with the driving connection of the pair is mentioned. In a schematic representation, the transfer cylinder is driven by the drive motor, and power is transferred from the transfer cylinder to the forme cylinder, and from the forme cylinder to the inking system. 
   In DE 196 03 663 A1, the forme cylinder, and the transfer cylinder that is acting together with it, are driven in parallel by a motor. The forme cylinder can be axially displaced by a gear, and can be displaced in the circumferential direction in relation to the transfer cylinder by the use a helical gear. An inking system, which is assigned to the forme cylinder, can be driven by a spur wheel arranged on the journal of the forme cylinder. 
   DE 20 14 070 A1 discloses a drive mechanism for a rotary printing press. Driving of a pair of cylinders consisting of forme and transfer cylinder takes place on the forme cylinder. In order to produce a definite driving connection in the frictional drive of two transfer cylinders acting together, the two transfer cylinders are non-positively, but releasably connected with each other. 
   DE 34 09 194 A1 discloses the drive mechanism of a cylinder pair by the use of a spur-toothed gear. Driving takes place from the drive motor via the gear to the transfer cylinder. 
   Driving of a four-cylinder printing unit with a drive mechanism acting on the respective forme cylinder is known from DE 20 14 753 A1. At least one of the transfer cylinders, driven by a respective forme cylinder, can be charged with a braking moment for preventing changing of tooth faces. 
   SUMMARY OF THE INVENTION 
   It is the object of the present invention to provide a drive mechanism for a printing unit. 
   In accordance with the present invention, this object is attained by the provision of the printing unit, having a forme cylinder that is axially shiftable and a transfer cylinder, with a common drive motor for both of the cylinders. The two cylinders are driven by the common drive motor via an at least partially spur-toothed gear. Power is transferred from the drive motor, via the at least partially spur-toothed gear, to the forme cylinder, and from the forme cylinder to the driving connection and to the transfer cylinder. Alternatively, the forme cylinder, and the transfer cylinder, which is in positive driving connection with the forme cylinder, are driven via a gear by a common drive motor. A counter-pressure cylinder that is assigned to this cylinder pair is driven by a separate drive motor. A gear is arranged between the separate drive motor and the counter-pressure cylinder. 
   The advantages to be realized by the present invention consist, in particular, in that by the forme cylinder being driven, no movement of the drive motor needs to be performed in the print-on and print-off position of the transfer cylinder, such as would be the case with some direct drives of the transfer cylinder. A compromise, which is typically based on such a pivot movement of the transfer cylinder in connection with the position of the drive motor and the engagement of the gear wheels when arranging the drive motor at the transfer cylinder can be omitted when the forme cylinder is being driven. In the prior case, the gear wheel engagement can lead to tooth breakage, or to a reduction of the printing quality because of the play in the drive mechanism. 
   The drive mechanism of the printing unit of the present invention is independent of the drive mechanism of a further cylinder of an additional or printing unit which may be constituting a printing position with the printing unit, and the drive mechanism preferably does not have a mechanical, and in particular a positively connected drive connection with the further cylinder or additional printing unit. 
   If only an inking system and the transfer cylinder are embodied for being brought into, or out of contact, a rigid coupling of the drive motor with a lateral frame can take place. 
   A spur-toothed pinion of the drive motor can transfer power directly to a spur-toothed spur wheel on the journal of the forme cylinder. The teeth and the axial movement are configured in such a way that the stability values, for example degrees of contact and breaking strength, are assured. 
   In another embodiment of the drive mechanism in accordance with the present invention, the drive motor can be arranged directly axially in relation with the forme cylinder. In order to make possible an axial movement of the forme cylinder for a change of the lateral register, a spur-toothed gear or a coupling, which is flexible in the axial direction, can again be arranged between the forme cylinder journal and the drive motor. The embodiment of the drive motor with a planetary gear arranged between the rotor and the journal of the cylinder is advantageous in respect to advantageous rpm ranges, in particular in the start-up phase. 
   In cases wherein stability requires helical gears for the force transmission, an arrangement is of advantage wherein the pinion of the drive motor does not transfer power directly to the spur wheel of the forme cylinder. If no additional precautions were to be taken, with an axial movement of the forme cylinder, a simultaneous displacement of the circumferential register would take place. Precautions could be, for example, a simultaneous correction by use of a control device, which correction requires technical control outlay, or a permissible movement of the pinion with respect to the spur wheel of the forme cylinder. This, however, requires guide devices, which cannot be produced, or which can be produced only with a large outlay, without play in the circumferential direction. In an advantageous manner, a coupling, which is flexible in the axial direction, can again be employed for the axial mobility of the forme cylinder. 
   Driving of the forme cylinder, namely via a spur-toothed gear, is advantageous, because the pivot movement of the transfer cylinder must be compensated for, and only the forme cylinder must have a lateral register displacement device at the same time. 
   It is advantageous in connection with the discussed embodiments of the drive mechanism for the forme cylinder, if an inking system which is assigned to the forme cylinder and, if provided, also a dampening system assigned to the forme cylinder, are driven by the same drive motor. This saves expense and, assuming the correct gear ratio conditions, assures synchronization. 
   For the exact and accurate rotation of the cylinders and rollers during production, a common flow direction of the moments or the torque from the drive motor to the various units to be driven is particularly advantageous. In an advantageous embodiment, this is achieved because driving takes place from the forme cylinder to the transfer cylinder, and from the transfer cylinder to the inking system, i.e. serially. In this connection, an embodiment is particularly economical wherein the driving takes place from the transfer cylinder to the inking system via a gear wheel that is rotatably arranged on the journal of the forme cylinder. 
   If the inking system and the transfer cylinder are driven in parallel, the use of auxiliary runners, in case of gear wheel trains, or the use of belt drives, which are as free of play as possible, is required at least for one of the two drive trains. 
   A coupling, which is flexible in the axial direction, and which is located between the drive motor and the forme cylinder, is preferably embodied as a torsionally rigid shaft coupling which, however, is flexible or resilient in the axial direction, and is configured for example, as an expansion coupling or as a compensation coupling. The employment of a non-switchable, positively-connected multi-disk coupling is particularly advantageous which coupling, in contrast to other positively-connected couplings, is almost entirely free of play in the circumferential direction, does not require an extensive production outlay and simultaneously makes an axial position change of the coupling itself, and thus an axial movement of the forme cylinder, possible. The coupling is embodied to be positively-connected in the axial direction, but to be flexible or resilient in its length, for example by elastic or reversible deformation. 
   The definite direction of the moment or torque flow is used for minimizing the play in the drive mechanism, and therefore for improving the printing quality. 
   The mechanical outlay for driving the cylinder pair can be considerably reduced by the use of a spur-toothed gear for driving the forme cylinder, while taking an out-of-contact movement, as well as a lateral register adjustment, into account. 

   
     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 schematic depiction of a first preferred embodiment of the drive mechanism of a printing unit in accordance with the present invention, in 
       FIG. 2 , a second preferred embodiment of the drive mechanism of a printing unit, in 
       FIG. 3 , a third preferred embodiment of the drive mechanism of a printing unit, in 
       FIG. 4 , a fourth preferred embodiment of the drive mechanism of a printing unit, in 
       FIG. 5 , a fifth preferred embodiment of the drive mechanism of a printing unit, in 
       FIG. 6 , a sixth preferred embodiment of the drive mechanism of a printing unit, and in 
       FIG. 7 , a seventh preferred embodiment of the drive mechanism of a printing unit in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring initially to  FIG. 1 , there may be seen a first preferred embodiment of a drive mechanism of a printing unit in accordance with the present invention. A printing unit of a printing press has a first cylinder  01 , for example a forme cylinder  01 , and a second cylinder  02 , for example a transfer cylinder  02 . The two cylinders  01 ,  02  can be driven together by the use of a first drive motor  03 , which is in operative connection with the forme cylinder  01 . The forme cylinder  01 , in turn, drives the transfer cylinder  02  via a drive connection. During printing, the transfer cylinder  02  works together with, and forms a printing position with a third cylinder  05  which is only shown schematically in FIG.  1 . For example the third cylinder  05  may be a second transfer cylinder  05  of a cooperating printing unit, or a counter-pressure cylinder  05  which does not transfer ink, for example a satellite cylinder  05 . The drive mechanism of the third cylinder  05 , or that of the cooperating second printing unit, is not in a positively connected driving connection with the printing unit which is driven by the first drive motor  03 . 
   As represented in  FIG. 1 , a forme cylinder gear wheel  06  is arranged, fixed against relative rotation, on a journal  04  of the forme cylinder  01 . A transfer cylinder gear wheel  08  is arranged, fixed against relative rotation, on a journal  07  of the transfer cylinder  02 . Gear wheels  06  and  08  constitute the driving connection between the forme cylinder  01  and the transfer cylinder  02 . In an advantageous embodiment, the driving connection has at least two members  06 ,  08 , in this case the gear wheels  06 ,  08 , which are both embodied as spur-toothed gear wheels and are movable in relation to each other in the axial direction. In this way, an axial movement between cylinders  01 ,  02  becomes possible without changing the relative position in the circumferential direction between cylinders  01  and  02 . 
   In a first preferred embodiment of the present invention, as shown in  FIG. 1 , the drive of the forme cylinder  01  is provided via a first gearing arrangement  10  in that a motor gear wheel  11 , for example a pinion  11 , arranged on a shaft  09  of the drive motor  03 , directly drives the gear wheel  06  arranged on the journal  04  of the forme cylinder  01 . The gearing  10  from the drive motor  03  to the journal  04 , or to the gear wheel  06 , can also be provided by the use of a differently designed gear, for example via further gear wheels, via toothed belts, via bevel wheels, or in other ways. 
   For assuring the axial displaceability of the forme cylinder  01 , which axial displaceability is indicated by a two-headed arrow in  FIG. 1 , the pinion  11 , as well as the gear wheels  06 ,  08 , are embodied to be spur-toothed. The position and width of the pinion  11  and of the gear wheels  06 ,  08  has been selected such that, with an axial displacement of the forme cylinder  01  by an amount ΔL, a sufficient contact of the teeth is assured. The minimum contact is of such a size that the maximum load of the teeth, with respect to wear and breaking resistance, is not exceeded in any of the relative positions of the gear wheels  06 ,  11 , or of a gear structured in another way, during operations. 
   The same applies to the driving connection constituted by the gear wheels  06 ,  08 . If, for example, the forme cylinder gear wheel  06  is configured having a greater width and, in a zero position of the forme cylinder  01  acts together with the pinion  11  and the gear wheel  08  approximately in the center, only one of the gear wheels  06 ,  08 ,  11  of the drive train need to be provided with a greater width. 
   A reduction gear  15 , for example a planetary gear  15  and/or an attached reducing gear  15 , which is shown in dashed lines, can be arranged between the drive motor  03  and the gearing  10 . This may be seen in FIG.  1 . 
   A further transfer cylinder gear wheel  12  which is represented in dashed lines in  FIG. 1 , is arranged, fixed against relative rotation, on the journal  07  of the transfer cylinder  02 . An inking system  13  assigned to the forme cylinder  01  and, if provided, a dampening system  14 , are driven by this further transfer cylinder gear wheel  12 . The the inking system  13  and the dampening system  14  are shown only as reference numerals in the drawing figures. 
   In the first preferred embodiment, the further transfer cylinder gear wheel  12  drives a further forme cylinder gear wheel  16 , which is represented in dashed lines in  FIG. 1 , which is rotatably seated on the journal  04  of the forme cylinder  01  and which, in turn, meshes with a gear wheel  17 , also represented in dashed lines of a drive mechanism, not further represented, of the inking system  13  and, if provided, of the dampening system  14 . 
   The moment or torque flow in the drive system from the drive motor  03  via the forme cylinder  01  to the transfer cylinder  02 , and from there to the inking system  13  and, if provided, to the dampening system  14  is definite, because it is serial. A tooth face change during load changes such as may occur during, for example, putting the cylinders  01 ,  02 , the inking system  13 , the dampening system  14 , in or out of contact, or as a result of changes in the conditions, is avoided to a large extent. This leads to reduced wear and, in particular, to improved printing results. 
   In a second preferred embodiment of the present invention, as seen in  FIG. 2 , the shaft  09  of the drive motor  03  is arranged coaxially with respect to an axis of rotation of the forme cylinder  01 , and is connected, in a torsionally rigid manner, with the journal  04  of the forme cylinder  01 . In one embodiment, a coupling  18 , whose length L can be changed in the axial direction by an amount ±ΔL is arranged between the drive motor  03  and the journal  04 . This coupling  18  can be, in particular, an expansion coupling  18 , a coupling  18  which is elastic in the axial direction, or a non-switchable shaft coupling  18  which, however is positively connected in the axial direction, but is resilient. An end of the coupling  18 , which is facing away from the forme cylinder  01 , is arranged to be fixed in place in respect to an axial direction. By the provision of the coupling  18 , and with an axial displacement of the forme cylinder  01 , the associated drive motor  03  for the forme cylinder  01  can be arranged fixed in place, or fixed on the frame. The amount ΔL of an axial displacement of the forme cylinder  01  preferably lies between 0 and ±4 mm, and in particular lies between 0 and ±2.5 mm. This axial displacement ΔL, and is absorbed by the change of the length L of the coupling  06  by this amount ±ΔL. 
   A particularly suitable coupling  18  is a flexurally elastic, all-metal coupling, also called a diaphragm or ring coupling. 
   A third preferred embodiment of the present invention, as seen in  FIG. 3 , differs from the second preferred embodiment shown in  FIG. 2  in that the drive motor  03  is not arranged coaxially in respect to the forme cylinder  01 . Power is transferred from a pinion  11  connected with the motor shaft  09  of the drive motor  03  to a gear wheel  19 , which is connected, fixed against relative rotation, via a shaft  21  or a journal  21 , with the side of the coupling  18  which is facing away from the forme cylinder  01 . This embodiment is particularly advantageous if, because of high loads, the demands made on the stability values, for example the degrees of contact and breaking strength, require helical gears on the pinion  11  and on the gear wheel  19 . The two cooperating gear wheels  06 ,  08  on the journals  04 ,  07  of the cylinder  01 ,  02  are spur-toothed, for example, since, in this way, a relative movement in respect to each other is made possible without a compensation in the circumferential register being required. The inking system  13  and, if provided the dampening system  14  can also be driven, in a manner similar to the one disclosed in the second preferred embodiment, from the transfer cylinder  02 . 
   For the purpose of easier disassembly, or maintenance, a claw coupling  22 , for example, or a coupling  22  corresponding to the coupling  18 , can be arranged between the drive motor  03  and the pinion  11 . This coupling  22  is shown in FIG.  3 . 
   In a fourth preferred embodiment of the present invention, as seen in  FIG. 4 , the power transfer from the forme cylinder  01  to the transfer cylinder  02  does not take place on a side of the coupling  18  facing the forme cylinder  01 , but instead takes place on the side of the coupling  18  which is not movable in the axial direction. For this purpose, the driving connection between the forme cylinder  01  and the transfer cylinder  02  is not arranged between the coupling  18 , whose length L can be changed in the axial direction, and the forme cylinder  01 , but on the side of the coupling  18  which is facing away from the forme cylinder  01  and which side of coupling  18  is stationary. 
   For the purpose of saving space, it is possible to connect a ring gear wheel  23 , which is arranged, for example, on a bushing  24  that is enclosing the coupling  18 , and which bushing  24  is connected with the side of the coupling  18  that is facing away from the forme cylinder  01 . On one side, this ring gear wheel  23  meshes with a transfer cylinder gear wheel  26 , which is connected, fixed against relative rotation, with the journal  07  of the transfer cylinder  02 , and on the other side ring gear  23  meshes with the pinion  11 . In comparison with the third preferred embodiment of the invention, as depicted in  FIG. 3 , one drive level can be saved with this fourth embodiment. Driving of the two cylinders  01 ,  31  can take place from the drive motor  03  via a helical gear. The driving connection formed by the helically toothed gear wheels  23  and  26  is not located on the side of the coupling  18  facing the cylinder  01 , which is to be moved axially, but on the side of the coupling  18  which is stationary in respect to an axial movement. 
   A fifth preferred embodiment of the present invention is depicted in FIG.  5  and shows a drive for a printing unit, wherein the forme cylinder  01  is driven by the drive motor  03 , and power is transferred parallel from the forme cylinder  01  to the drive motor  03  and also to the inking system  13  and, if provided also to the dampening system  14 . In spite of an undefined direction of the moment or torque flow, a tooth face change is prevented in the case of changing loads. The gear wheel  06 , for example, arranged on the journal  04  of the forme cylinder  01 , is that is arranged together with a further gear wheel  27 , specifically an auxiliary gear wheel  27 . Power can be transferred to the gear wheel  17  which is leading to the drive mechanism of the inking system  13  and, if provided the dampening system  14  via a gear wheel  28 , which is also arranged, fixed against relative rotation, on the journal  04  of the form cylinder  01 . For the purpose of axially displacing the forme cylinder  01 , the gear wheels  06 ,  08 ,  27 , and/or  17 ,  28 , are spur-toothed. 
   As represented in  FIG. 5 , driving of the gear wheel  06 , which is arranged, fixed against relative rotation, on the forme cylinder  01 , can take place via the coupling  18  in one of the ways depicted and discussed above either coaxially in relation to the forme cylinder  01 , in accordance with the second preferred embodiment,  FIG. 2 , or via a pinion  11 , which is not specifically represented in  FIG. 5 , in accordance with the third preferred embodiment. 
   In the sixth preferred embodiment of the present invention, as seen in  FIG. 6 , the driving of the gear wheel  06 , configured in accordance with the fifth preferred embodiment, and which is arranged fixed against relative rotation on the forme cylinder  01 , takes place by the pinion  11  directly meshing with this gear wheel  06 . In a manner the same as that discussed in connection with  FIG. 5 , power is transmitted parallel from the gear wheel  06  to the transfer cylinder  02  and to the inking system  13  and, if provided to the dampening system  14 . In an advantageous embodiment, the gear wheels  06 ,  08 ,  27 , and/or  17 ,  28 , are embodied to be spur-toothed for the purpose of axially displacing the forme cylinder  01 . 
   In a seventh preferred embodiment of the present invention, as seen in  FIG. 7 , the shaft  09  of the drive motor  03  is arranged coaxially with respect to an axis of rotation of the forme cylinder  01 , and is connected in a torsionally rigid manner with the journal  04  of the forme cylinder  01 . In an advantageous embodiment, a gear  29 , for example a spur-toothed planetary gear  29 , is arranged between the drive motor  03  and the journal  04 , which gear  29  permits an axial displacement of the forme cylinder  01  by an amount ΔL. The amount ΔL for an axial displacement of the forme cylinder  01  preferably lies between 0 and ±4 mm, and in particular lies between 0 and ±2.5 mm. This axial displacement is absorbed by the spur-teeth of the gearing, which mesh and which are displaceable with respect to each other. 
   For all of the preferred embodiments, and in particular for the second, fourth and fifth embodiments, shown in  FIGS. 2 ,  4  and  5 , with a drive motor  03  arranged coaxially with respect to the forme cylinder  01 , a planetary gear, that is not specifically represented, can also be arranged in an advantageous further development on the drive motor  03 , or between the drive motor  03  and the driving connection between the forme cylinder  01  and the transfer cylinder  02 . 
   The driving connection  06 ,  08 ,  23 ,  26  between the two cylinders  01 ,  02 , and/or the driving connection  12 ,  16 ,  17  between one of the cylinders  01 ,  02  and the inking system  13  and, if required the dampening system  14 , can also be provided, instead of the embodiment as wheel trains  06 ,  08 ,  23 ,  26 , or  12 ,  16 ,  17 , alternatively as toothed belts, taking into consideration a reversal of the direction of rotation, or as other positively-connected drive connections. 
   In an advantageous further development of the preferred embodiments, a third cylinder  05 , as depicted in  FIGS. 1-7 , and which is, for example, embodied as a satellite cylinder  05 , is driven by its own, second drive motor  31  via a gear  32 . In the first preferred embodiment shown in  FIG. 1 , the second drive motor  31  drives a pinion  33  for this purpose, which pinion  33  drives a gear wheel  34  that is arranged on the journal of the satellite cylinder  05 . The gear drive  32  can also be configured in different ways, for example with several gear wheels, with a belt drive, or as a reducing gear drive  32  arranged coaxially in respect to the satellite cylinder  05 , for example a planetary gear  32 , and/or as an attached gear  32  connected with the second drive motor  31 . 
   Driving of the cylinder pair consisting of the forme and transfer cylinders  01 ,  02 , as well as the satellite cylinder  05 , via respectively one gear  11 ,  06 ,  33 ,  34  allows the selection of a suitable reduction gearing, or the employment of smaller, and similarly dimensioned, if possible, drive motors  03 ,  31 . 
   An embodiment of the present invention is advantageous wherein the drive mechanism of the cylinder pair  01 ,  02 , and the drive mechanism of the satellite cylinder  05  are arranged in different, separate lubricant chambers  36 ,  37 , as seen in FIG.  1 . For example, the driving connection  06 ,  08 ,  23 ,  26  between the forme and transfer cylinders  01 ,  02 , possibly together with the driving connection  12 ,  16 ,  17 ,  19  to the inking system  13 , if such is provided, has its own housing  36 , as depicted in dashed lines in  FIG. 1 , in which a thin-bodied lubricant, for example, in particular oil, is contained. If it is not embodied directly as an auxiliary gear  15 ,  29  on the drive motor  03 , the gear  10 ,  15 ,  29  can also be arranged in this lubricant chamber, as is shown, by way of example, in  FIGS. 1 and 7 . 
   The gearing  10  between the drive motor  03  and the drive connection  06 ,  08  can be arranged, individually encapsulated, in its own lubricant chamber, in particular in case where power is coaxially transmitted to the forme cylinder  01 , and/or the gear  10 ,  15 ,  29 , or an additional gear  15 ,  29 , is separate from the driving connection  06 ,  08 . 
   If not arranged as an attached gear  15  directly on the second drive motor  31 , the gear drive  32 , and the gear  15  of the satellite cylinder  05  is arranged in a lubricant chamber inside the housing  37 , which differs from the first mentioned housing  36 . In particular, this housing can be a lubricant chamber that is assigned exclusively to the satellite cylinder  05 , as shown, by way of example in  FIGS. 1 and 7 . 
   The manner of operation of the drive mechanism of a printing unit in accordance with the present invention is as follows: 
   During operation, such as during set-up and during production operations, the cylinder  01  is driven, and, in turn, drives the transfer cylinder  02  from the first drive motor  03 . In a further development, the inking system  13  and, if provided, the dampening system  14  is also driven by this first drive motor  03 . When the transfer cylinder  02  is pivoted in or out, the motor  03  driving the forme cylinder  02  can remain stationary and in a position for the ideal meshing of possibly cooperating pinions  11  and gear wheels  06 . 
   If a correction of the lateral register, i.e. a lateral displacement of the printed image, is required, the cylinder  01  is displaced in the axial direction by an amount ±ΔL by the use of a suitable drive mechanism, which is not specifically represented and which is preferably arranged on the side of the forme cylinder  01  that is located opposite to the drive mechanism, and thus without the drive motor  03  also having to be displaced. 
   In an embodiment with a drive motor  03  which is not coaxially arranged with respect to the forme cylinder  01 , an axial displacement of the forme cylinder  01 , without a simultaneous displacement of the circumferential register, is possible by the use of spur-toothed gearing between the gear wheel  06  and the pinion  11 . 
   In another preferred embodiment, the axial displacement of the forme cylinder  01  is absorbed by the spur-toothed gearing of the gear  29 , which is arranged between the drive motor  03 , that is arranged axially with respect to the forme cylinder  01 , and the forme cylinder  01 . 
   A correction by the use of an electronic shaft between the cylinders  01 ,  02 , as well as a mechanical readjustment of the circumferential register, can be omitted. 
   Wile preferred embodiments of a drive mechanism of a printing unit 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 specific structure of the drive motors, the overall sizes of the cylinders, 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 following claims.