Patent Publication Number: US-9403367-B2

Title: Printing machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase, under 35 U.S.C. 371, of PCT/EP2014/059616, filed May 12, 2014; published as WO 2014/184126A1 on Nov. 20, 2014 and claiming priority to DE 10 2013 208 751.9, filed May 13, 2013, the disclosures of which are expressly incorporated herein by reference in their entireties. 
     FIELD OF THE INVENTION 
     The present invention is directed to a printing press which has at least one printing unit. The at least one printing unit has at least one printing material guiding element which is capable of rotating about a rotational axis that defines an axial direction (A) and at least four print heads. At least four positioning devices are provided in the printing unit with each one of the positioning devices being usable to selectively place at least one of the printing heads at least either in a respective printing position assigned to that print head or in a respective idle position assigned to that print head. At least one first print head of the at least four print heads can selectively be placed at least either in a first printing position assigned to that print head or in a first idle position assigned to that first print head. At least a second print head of the at least four print heads can selectively be placed at least either in a second printing position assigned to that print head or in a second idle position assigned to that second print head. 
     A variety of different printing processes for use in printing presses are known. One such printing process is inkjet printing or ink-jet printing. In this process, individual droplets of printing ink are ejected through nozzles of print heads and are transferred to a printing material so as to produce a printed image on the printing material. By actuating a plurality of nozzles individually, different printed images can be produced. Since no fixed printing forme is involved, each printed product can be produced individually. This allows personalized printed products to be produced, and/or, since printing formes are dispensed with, allows small print runs of printed products to be produced at low cost. 
     The precise alignment of printed images on the front and back sides of a printing material that is imprinted on both sides is referred to as register (DIN 16500-2). In multicolor printing, the merging and precise correlation of individual printed images of different colors to form a single image is referred to as color-to-color registration (DIN 16500-2). Suitable measures are necessary in inkjet printing in order to maintain color-to-color registration and/or register. 
     EP 2 202 081 A1 and JP 2003-063707 A each disclose a printing press which has a first printing unit and a dryer, the first printing unit comprising a central cylinder with a separate drive motor assigned to the first central cylinder and at least one inkjet print head. 
     U.S. Pat. No. 5,566,616 A discloses a printing press comprising a rotatable central cylinder, inkjet print heads, a cooling unit and a dryer, which operates using either temperature and air flow or radiation-induced curing. 
     U.S. Pat. No. 6,053,107 A discloses a printing press which has a driven central cylinder and a dryer with a cooling unit. 
     DE 10 2011 076 899 A1 discloses a printing press which has at least one printing unit and at least one print head embodied as an inkjet print head. 
     DE 10 2010 001 146 A1 and DE 43 18 299 A1 each disclose a threading means for threading web-type printing material into a printing press. EP 1 197 329 A1 discloses a threading tip that can interact with a threading belt or a threading chain. US 2011/0043554 A1 discloses a printing press in which at least one printing material guiding element is moved away from at least one print head in order to thread in a material web. 
     DE 10 2004 017 801 A1, US 2005/0024421 A1, DE 10 201 0 037 829 A1, JP 2004 268 511 A, US 2006/0119646 A1, U.S. Pat. Nos. 5,206,666 A, 5,757,399 A and 7,455,401 B2 each disclose a printing press comprising print heads and a maintenance device that can be moved along an actuating path. US 2011/0149004 A1 discloses a printing press having print heads that can be moved along an actuating path. U.S. Pat. No. 8,262,198 B2 discloses a printing press with adjustable print heads. DE 23 49 453 A1 discloses movable nozzles of a liquid jet recorder. 
     US 2009/0284566 A1 discloses a printing press in which four positioning devices can be used to move print heads in different linear directions to ensure positioning accuracy, and said print heads can be transported to a stationary maintenance device by moving parallel to a rotational axis of a printing material guiding element. 
     DE 10 2005 060 786 A1, EP 2 127 885 A1 and US 2008/0273063 A1 each disclose a printing press which has at least one system for supplying coating medium and at least two inkjet print heads, each of which is connected via a fluid line to a main reservoir, the main reservoir being connected via a supply line and a drain line to an intermediate reservoir. 
     U.S. Pat. No. 6,764,160 B1 discloses a sheet-fed printing press, the print heads of which can be moved radially away from a transfer cylinder, and which has wiper blades for cleaning residue of a meltable ink off of the print heads. 
     JP 2008 055756 A discloses a printing press in which four print heads can be moved away from a central cylinder in different radial directions, and a maintenance device can pivot around a rotational axis of the central cylinder. 
     JP H10 323987 A discloses a sheet-fed inkjet printing press in which all the print heads can be moved together vertically away from a central cylinder, and in which a maintenance device is arranged so as to be movable horizontally and orthogonally to a rotational axis of the central cylinder. 
     US 2011/149 003 A1 discloses a printing press which has print heads that can be moved away together linearly and a pivotable maintenance device. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a printing press. 
     This object is attained according to the invention by the provision of the respective idle position as a respective maintenance position, in which at least one maintenance device, which is embodied as a cleaning device, is or can be assigned to at least one nozzle of the respective print head. The at least one maintenance device is arranged as being movable along a staging path at least partially orthogonally to the axial direction (A). 
     A printing press preferably has at least one printing unit, wherein the at least one printing unit preferably has at least one print head, particularly embodied as an inkjet print head, and preferably has at least one printing material guiding element that is rotatable around a rotational axis, and wherein the at least one print head can preferably be positioned in at least one idle position, preferably embodied as a maintenance position, in which preferably at least one maintenance device is and/or can be assigned to at least one nozzle of the at least one print head. The at least one print head can preferably be placed in at least one printing position. The ejecting direction of at least one nozzle of the at least one print head, at least in a printing position, is preferably aligned toward a circumferential surface of the at least one printing material guiding element. The at least one maintenance device is preferably embodied as at least one protective cover and/or as at least one cleaning device. 
     The at least one printing unit preferably has the at least one printing material guiding element, which is capable of rotating around a rotational axis that defines an axial direction. The at least one printing unit preferably has at least four print heads, particularly embodied as inkjet print heads. In the at least one printing unit, at least four positioning devices are preferably provided, by means of each of which at least one print head can selectively be placed at least either in a respective printing position assigned to said print head or in a respective idle position, in particular a maintenance position and/or assembly position, assigned to said print head. In particular, at least a first print head of the at least four print heads can selectively be placed, in particular by means of at least one first positioning device, at least either in a first printing position assigned to said first print head or in a first idle position, in particular a first maintenance position and/or a first assembly position, assigned to said first print head. In particular, at least one second print head of the at least four print heads can selectively be placed, in particular by means of at least one second positioning device, at least either in a second printing position assigned to said second print head or in a second idle position, in particular a second maintenance position and/or a second assembly position, assigned to said second print head. The respective idle position is preferably embodied as a respective maintenance position, in which at least one maintenance device, embodied as a cleaning device, preferably is and/or can be assigned to at least one nozzle of the respective print head. One advantage is that, since the maintenance device and the print heads must be moved only short distances relative to one another, a particularly compact printing unit is possible. 
     In particular, the first idle position is preferably embodied as a first maintenance position, in which at least one first maintenance device, embodied as a first cleaning device, is and/or can be assigned to at least one nozzle of the first print head. In particular, the second idle position is preferably embodied as a second maintenance position, in which at least one second maintenance device, embodied as a second cleaning device, is and/or can be assigned to at least one nozzle of the second print head. In particular, at least one third idle position of a third print head is preferably embodied as a third maintenance position, in which at least one third maintenance device embodied as a third cleaning device is and/or can be assigned to at least one nozzle of the third print head. In particular, at least one fourth idle position of a fourth print head is preferably embodied as a fourth maintenance position, in which at least one fourth maintenance device embodied as a fourth cleaning device is and/or can be assigned to at least one nozzle of the fourth print head. 
     The at least one maintenance device is preferably arranged as movable along a staging path, at least partially orthogonally to the axial direction. In particular, the at least one first maintenance device is preferably arranged as movable along a first staging path, at least orthogonally to the axial direction. In particular, the at least one second maintenance device is preferably arranged as movable along a second staging path, at least orthogonally to the axial direction. 
     A minimum distance, preferably referred to as the idle distance, in particular the maintenance distance and/or assembly distance, between at least one first nozzle of the at least one first print head in its first idle position and at least one second nozzle of the at least one second print head in its second idle position is preferably at least 2 cm, more preferably at least 5 cm, even more preferably at least 10 cm and more preferably still at least 20 cm greater than a minimum distance, preferably referred to as the operating distance, between at least the at least one first nozzle of the at least one first print head in its first printing position and the at least one second nozzle of the at least one second print head in its second printing position. This results particularly in the advantage that the at least four print heads are more accessible for maintenance and/or assembly purposes, but are nevertheless situated close to one another during printing operation, allowing high print quality to be achieved due to fewer negative influences between applications of printing ink of different colors. 
     Printing ink in the above and in the following is understood generally as a coating medium, particularly also a varnish. In particular, no differentiation is made between printing ink and ink; printing ink and coating medium are also understood to include particularly inks. 
     Print heads are embodied, for example, such that each individual print head does not extend across an entire working width of the printing press, defined by a maximum printing material width that can be processed in the printing press. A plurality of print heads are thus preferably assigned to the same printing ink, and/or at least one nozzle bar is preferably provided, which further preferably contains a plurality of print heads that can be moved together by means of the same positioning device. At least four positioning devices are particularly preferably provided in the printing unit, by means of each of which at least one nozzle bar and/or respectively a plurality of print heads assigned to the same printing ink are embodied as movable together, and in particular are and/or can be selectively placed at least either in a respective printing position assigned to said nozzle bar and/or said print heads or in a respective idle position assigned to said nozzle bar and/or said print heads. The positioning devices are preferably positioning devices of the printing unit and are particularly components of the printing unit. In particular, the at least one print head is preferably arranged such that it can be moved away from a transport path provided for at least one printing material web, by means of at least one positioning device. The at least one printing unit preferably has at least two, particularly at least four nozzle bars, each of which has at least two, particularly at least four print heads, and the at least two, in particular at least four nozzle bars are arranged so as to be movable along a respective linear actuating path by means of a respective positioning device. The printing press is preferably characterized in that each nozzle bar, individually and independently of other nozzle bars, can be moved along its actuating path and/or can be placed in its printing position and/or its idle position by means of the positioning device assigned to said nozzle bar. 
     The at least one printing unit preferably has at least one positioning device per double row of print heads arranged in the printing unit, and/or at least one positioning device per nozzle bar arranged in the printing unit and/or at least one positioning device per coating medium arranged in the printing unit. 
     The printing press is preferably characterized in that the at least one maintenance device is arranged such that it can be moved by means of at least one transport device along at least one staging path between at least one parked position and at least one operating position. The at least one maintenance device is preferably arranged such that it can be moved at least orthogonally to the axial direction A. The printing press is preferably characterized in that the respective maintenance device in its respective operating position is assigned to the respective at least one nozzle of the respective print head in its maintenance position. When any print head is arranged in its printing position, at least one nozzle of said respective print head is preferably situated below the staging path of the respective at least one maintenance device, and when any print head is arranged in its idle position, said respective at least one nozzle is preferably situated above said respective staging path. 
     The respective staging path of the particularly four maintenance devices preferably extends linearly and in a respective or common direction that deviates a maximum of 45°, preferably a maximum of 30°, more preferably a maximum of 20° and even more preferably a maximum of 10° from a horizontal direction. The respective or common staging direction is preferably horizontal. 
     The printing press is preferably characterized in that a location of at least one reference nozzle of a respective print head in its printing position differs from a location of said at least one reference nozzle of said respective print head in its maintenance position, with respect to an axial direction defined by the rotational axis of the at least one printing material guiding element, by a maximum of 50% of the width, measured in the axial direction, of an operating region of a nozzle bar that contains the respective print head, and/or by a maximum of 50% of a working width of the printing press, defined by a maximum printing material width that can be processed in the printing press. This allows a particularly space-saving printing press to be realized, which is nevertheless easy to maintain and the print heads of which are preferably easy to install and remove. In particular, the printing press is preferably characterized in that a location of the at least one first nozzle in the at least one printing position differs from a location of said at least one first nozzle in the at least one maintenance position, with respect to an axial direction defined by the rotational axis of the at least one printing material guiding element, by a maximum of 50% of the width, measured in the axial direction, of the operating region of the nozzle bar that contains the at least one print head, and/or by a maximum of 50% of the working width of the printing press, defined by the maximum printing material width that can be processed in the printing press. 
     In the at least one maintenance position of the respective print head, at least one maintenance device preferably is and/or can be assigned to at least one nozzle of the at least one print head, and more preferably, the at least one maintenance device is and/or can be arranged at least partially opposite at least one nozzle of the at least one print head with respect to a respective ejecting direction of the at least one nozzle. 
     The printing press is preferably characterized in that at least a first of at least two print heads, particularly of a first printing unit, can selectively be placed, preferably by means of a respective first positioning device assigned to said print head, at least either in the first printing position assigned to said print head or in a first idle position, particularly a maintenance position and/or an assembly position, assigned to said print head, wherein in the at least one first idle position, an idle location of at least one first nozzle of the at least one first of the at least two print heads is spaced by a first idle distance, in particular a maintenance distance and/or an assembly distance, from a first operating location of the same at least one first nozzle of the same at least one first of the at least two print heads in its first printing position. Preferably, at least a second of the at least two print heads, particularly of said first printing unit, can selectively be placed, preferably by means of a respective second positioning device assigned to said print head, at least either in a second printing position assigned to said print head or in a second idle position, in particular a maintenance position and/or assembly position, assigned to said print head, wherein in the at least one second idle position, an idle location of at least one second nozzle of the at least one second of the at least two print heads is spaced by a second idle distance, in particular a maintenance distance and/or an assembly distance, from a second operating location of the same at least one second nozzle of the same at least one second of the at least two print heads in its second printing position. 
     The first idle distance, in particular maintenance distance and/or assembly distance, preferably differs from the second idle distance, in particular maintenance distance and/or assembly distance, by at least 2 cm, more preferably at least 5 cm, even more preferably at least 10 cm and more preferably still at least 20 cm. An idle distance is particularly a distance between a location of a nozzle when the print head containing said nozzle is arranged in its idle position and a location of the same nozzle when the same print head is arranged in its printing position. This results particularly in the advantage, for example, of allowing a rectilinear and therefore simple and cost-effective transport device to be provided, by means of which one maintenance device can be used for different print heads. As a further advantage, sufficient space is then available for all maintenance devices in their respective operating positions. At least two print heads, arranged on different positioning devices, of the total of at least four print heads preferably arranged on different positioning devices preferably have the same idle distances in pairs. This is achieved, for example, by a symmetrical arrangement of the positioning devices, in which, for example, one plane of symmetry contains the entire rotational axis of the at least one printing material guiding element. 
     The printing press is preferably characterized in that, when a third print head is arranged in its idle position, an idle location of at least a third nozzle of the at least one third print head is spaced by a third idle distance from an operating location of the same at least one third nozzle of the same at least one third print head in its third printing position, and in that, when the fourth print head is arranged in its idle position, an idle location of the at least one fourth nozzle of the at least one fourth print head is spaced by a fourth idle distance from an operating location of the same at least one fourth nozzle of the same at least one fourth print head in its fourth printing position, and in that the third idle distance is equal to the second idle distance and/or in that the fourth idle distance is equal to the first idle distance. 
     The printing press is preferably characterized in that, when particularly the first print head is arranged in the particularly first maintenance position, at least one particularly first maintenance device can be and/or is arranged between the at least one particularly first nozzle of the at least one particularly first print head and a region of the transport path provided for the printing material, which region is closest to said at least one particularly first nozzle, and/or in that when particularly the first print head is arranged in the at least one particularly first maintenance position, at least one particularly first maintenance device can be and/or is arranged between the at least one particularly first nozzle of the at least one particularly first print head and a region of a transfer element, which region is closest to said at least one particularly first nozzle. 
     The printing press, which preferably has at least one printing unit, preferably having at least two and more preferably at least four print heads and at least one printing material guiding element that is rotatable around a rotational axis that defines an axial direction, is preferably characterized in that each of the at least two print heads is arranged so as to be movable along a respective linear actuating path by means of a respective positioning device, assigned at least to said print head, wherein the linear actuating paths point in respective actuating directions that differ in pairs by at least 10° and by at most 150°. Further preferably, each of the at least two print heads can selectively be placed, by means of the respective positioning device, at least either in a printing position assigned to said print head or in at least one maintenance position assigned to said print head. Further preferably, when a first print head of the at least two print heads is in the at least one maintenance position, at least one maintenance device is and/or can be assigned to at least one first nozzle of said at least one first print head. Further preferably, the at least one maintenance device is arranged so as to be movable along at least one staging path between at least one parked position and at least one operating position, at least partially orthogonally to the axial direction, by means of at least one transport device. This results particularly in the advantage that the printing unit can be highly compact in configuration. Arranging the linear actuating paths at corresponding angles, for example around a central cylinder, requires less installation space than if all the print heads were to be arranged so as to be movable in the axial direction or in opposite directions. The at least partially orthogonal mobility of the maintenance device likewise favors a compact configuration of the printing unit, especially since the maintenance device can be the same width as the operating region of the nozzle bars and the printing unit, but need not be twice as wide. As compared with print heads that are movable parallel to one another, an enlarged space for maintenance devices in their operating positions is produced, while the printing positions of the print heads are arranged very close to one another. 
     The printing press preferably has at least one printing unit, which preferably has at least one print head embodied as an inkjet print head. The at least one printing unit preferably has at least one printing material guiding element, which is rotatable around a respective rotational axis. The at least one print head is preferably embodied as movable along an actuating path in at least one actuating direction, the actuating direction preferably having at least one component oriented orthogonally to the axial direction which is defined by the rotational axis of the at least one printing material guiding element. The printing press is preferably characterized in that at least one and preferably precisely one threading means for threading in a web of printing material, which threading means can be moved along at least one threading path and is preferably continuous, is and/or can be arranged, at least intermittently, at least within a printing unit, and in that at least parts of the at least one threading path are spaced a distance of at least 2 cm with respect to the axial direction from every target region of every nozzle of every print head of said printing unit. At least parts of the at least one threading path and preferably the entire threading path are/is preferably spaced a distance of at least 2 cm, more preferably at least 4 cm, even more preferably at least 6 cm and more preferably still at least 8 cm, with respect to the axial direction, from every target region of every nozzle of every print head of said printing unit. Preferably at least parts of the threading means and more preferably the entire threading means are/is spaced a distance of at least 2 cm, more preferably at least 4 cm, even more preferably at least 6 cm and more preferably still at least 8 cm, with respect to the axial direction, from every target region of every nozzle of every print head of said printing unit. This results particularly in the advantage that a printing material web can be threaded particularly easily and quickly and precisely into the printing press, with no risk of damage to and/or soiling of the nozzles of print heads occurring during the process. 
     The printing press is preferably characterized in that at least one printing material web is and/or can be connected via at least one connecting element to the at least one threading means, wherein the at least one connecting element is more preferably embodied as at least one threading tip. The printing press is preferably characterized in that the at least one threading means is embodied as at least one continuous threading belt and/or in that at least one threading guide element is provided, by means of which the at least one threading path of the at least one threading means can be and/or is defined, wherein the at least one threading guide element is more preferably embodied as at least one turning roller or as at least one chain guide, and/or the at least one threading guide element is embodied as at least one rotatable threading guide element. 
     The at least one threading means for threading in a printing material web along the provided transport path of the printing material web is preferably arranged, particularly permanently, along its at least one threading path within the printing press. The at least one threading means preferably has at least two and more preferably at least five designated connecting points at which at least one printing material web can be connected, directly and/or via at least one connecting element, to the at least one threading means. The printing press is preferably characterized in that the at least two connecting points are spaced in the axial direction by a maximum of 10 cm, more preferably a maximum of 5 cm, even more preferably a maximum of 2 cm and more preferably still by no distance at all, and/or the at least two connecting points are spaced from one another along the at least one threading path. A threading path of the at least one threading means preferably wraps around the at least one rotatable printing material guiding element over an angular range of at least 180°, as viewed from the rotational axis of the at least one printing material guiding element, and at least one rotatable threading guide element is preferably provided, by which at least one threading path of the at least one threading means can be and/or is defined, and which is arranged so as to rotate around the same rotational axis as at least one printing material guiding element of a printing unit of the printing press. More preferably, the threading path of the at least one threading means, at least along said angular range, has a radius of curvature that differs a maximum of 5 cm from a radius of curvature of said at least one printing material guiding element. 
     The printing press is preferably characterized in that an axial projection plane is defined by a surface normal that lies parallel to the axial direction or deviates from said axial direction by a maximum of 2°, and in that a projection, in the axial projection plane, of the transport path provided for printing material in the axial direction and a projection, in the axial projection plane, of the threading path provided for the at least one threading means in the axial direction overlap at least over more than 25% of the length of the projection of the threading path provided for the threading means, and/or in that only at least one threading means is provided, which is arranged on only one side of the provided transport path for printing material, with respect to the axial direction, and/or the threading path of said threading means extends on only one side of the provided transport path for printing material. 
     In particular, a method for threading at least one printing material web into at least one printing unit of a printing press can preferably be carried out using the printing press, wherein the axial direction extends parallel to the rotational axis of the at least one printing material guiding element of the at least one printing unit, and wherein in a throw-off process, at least one print head, embodied as an inkjet print head, of the at least one printing unit, is moved in at least one actuating direction away from a provided transport path of the at least one printing material web, and wherein in a subsequent threading process, at least one threading means is moved along a threading path through the at least one printing unit, and thereby draws the at least one printing material web along the transport path provided for the at least one printing material web, and wherein the threading path and the transport path are spaced from one another, as viewed in the axial direction. This at least one actuating direction is preferably oriented at least partially orthogonally to the axial direction. 
     The method is preferably characterized in that the at least one threading means is connected to the at least one printing material web in a connecting process by means of at least one connecting element. The at least one connecting element preferably passes a printing position of the at least one print head while said head is moved away from the provided transport path and/or is arranged in at least one idle position, and/or the at least one connecting element passes through at least one target region of at least one nozzle of the at least one print head during the threading process, and/or no component of the at least one threading means passes through a target region of a nozzle of the at least one print head during the threading process. The method is preferably characterized in that in a subsequent throw-on process, the at least one print head is moved opposite the at least one actuating direction and/or along an actuating path toward the provided transport path of the at least one printing material web, and/or said print head is placed in its printing position. 
     The method is preferably characterized in that, during the throw-off process, at least two print heads of the at least one printing unit are moved in a respective actuating direction away from a provided transport path of the at least one printing material web, the respective actuating directions differing in pairs by at least 10° and by at most 150°. 
     The method is preferably characterized in that, in at least one operating mode, the at least one threading means is connected by means of the at least one connecting element to the printing material, and the at least one print head is moved away from the provided transport path and/or is placed in at least one idle position, and at least one nozzle is aligned with its ejecting direction facing toward the at least one connecting element and/or in that in said at least one operating mode, the at least one connecting element is in contact with the at least one printing material guiding element or with at least one transfer element, and/or in that in said operating mode, the at least one threading means is spaced a distance of at least 2 cm in the axial direction from every target region of every nozzle of every print head of said printing unit. 
     Preferably, only at least one threading means is used, said threading means being arranged on only one side of the provided transport path for printing material, with respect to the axial direction, and/or the threading path of said threading means extending on only one side of the provided transport path for printing material. 
     The at least one first printing unit preferably comprises the at least two print heads, particularly embodied as inkjet print heads and preferably arranged on at least one first movable nozzle bar. The printing press is preferably characterized in that the printing press has at least one system for supplying coating medium and in that the at least one supply system has at least one main reservoir and in that each of the at least two print heads is arranged such that it is and/or can be connected via at least one first fluid line to the at least one main reservoir. For example, each of the at least two print heads is arranged such that it is and/or can be connected via at least one first fluid line to the at least one main reservoir. The at least one supply system preferably has at least one return flow reservoir and at least one intermediate reservoir. The at least one main reservoir preferably has at least one overflow drain, which more preferably is and/or can be connected via the at least one return flow reservoir and at least one drain line to the at least one intermediate reservoir, and/or which is preferably embodied as at least one passive overflow drain. The at least one main reservoir and the at least one return flow reservoir are preferably arranged so as to be movable together with the at least one nozzle bar. Preferably, the at least one nozzle bar can selectively be placed by means of at least one of the positioning devices, particularly by means of at least one of the positioning devices of the at least one printing unit, at least either in a printing position assigned to said nozzle bar or in at least one maintenance position assigned to said nozzle bar. 
     A section of the at least one drain line, within which at least one valve, in particular at least one second valve, is arranged, is preferably located between the at least one overflow drain and the at least one return flow reservoir. At least a first valve is preferably arranged within at least one supply line, and the at least one intermediate reservoir is preferably arranged such that it is and/or can be connected via at least one supply line to the at least one main reservoir. At least one first liquid pump is preferably arranged in the at least one supply line. 
     It is a particular advantage that the at least one main reservoir can be separated from the at least one return flow reservoir by means of the at least one valve arranged in the drain line between the at least one overflow drain and the at least one return flow reservoir. This allows a pressure within the main reservoir to be increased, for example, so that a nozzle cleaning of the print heads can be performed, and at the same time and independently thereof, coating medium can be removed from the at least one return flow reservoir. 
     In particular, the ability to move the at least one return flow reservoir together with the at least two print heads ensures that coating medium can always drain from the overflow drain under constant conditions and therefore in an optimized manner, for example solely by virtue of gravitational force, even when the positioning device is in the maintenance position. This advantage results particularly when the at least one return flow reservoir is located along the at least one drain line, downstream of the at least one overflow drain and upstream of any pump. At least one return flow pump is preferably arranged along the at least one drain line, downstream of the at least one return flow reservoir. This allows coating medium to be pumped out of the at least one return flow reservoir regardless of the location of the positioning device and regardless of any other adjusted pressure within the at least one main reservoir. 
     The stated advantages result particularly when, as is preferred, an actuating direction of an actuating path of the at least one nozzle bar, which path can be implemented particularly by means of the at least one positioning device, has at least one component in the vertical direction that preferably measures at least 10 cm, more preferably at least 20 cm and even more preferably at least 30 cm, because without the appropriate measures, hydrostatic pressure changes resulting from the differences in height could result in different conditions. The at least one nozzle bar is further preferably arranged so as to be movable relative to a frame of the printing unit by means of the at least one positioning device, while the at least one intermediate reservoir is arranged stationary relative to the frame of the printing unit. This allows a relatively large intermediate reservoir to be provided, since it does not need to be moved by means of the positioning device. 
     In addition, the at least one main reservoir is preferably at least indirectly connected to at least one intermediate reservoir via at least one supply line and at least one drain line, and the at least one main reservoir and/or the at least one drain line preferably has at least one overflow drain, the drain side of which is arranged such that it is and/or can be connected at least indirectly to the at least one intermediate reservoir. At least one volume provided as a first gas-filled space is preferably arranged in the at least one main reservoir, and is and/or can be connected via at least a first gas line to at least a first gas pump. This results particularly in the advantage that constant pressure conditions prevail particularly at the print heads, thereby improving printing quality and facilitating handling, for example by decreasing the number of manual adjustments and/or cleaning measures that must be carried out. At least one volume, provided as particularly a third gas-filled space, is preferably arranged in the at least one return flow reservoir, and is and/or can be connected via at least a first equalizing line to at least a first gas pump. For example, a gas volume is provided in the at least one main reservoir, which volume is at a normal pressure which is lower than the ambient pressure present at an ejection side of at least one nozzle of the at least one print head. Further preferably, the at least one first gas line and the at least one equalizing line are and/or can be separably connected to one another via at least one pressure regulator. Thus either the same pressure can be ensured in all relevant gas-filled spaces, or alternatively, for example when the first and second valves are closed, a pressure and the at least one main reservoir supply can be increased, while in the third gas-filled space pressure equalization is enabled, for example during a pumping process. 
     At least two main reservoirs are preferably arranged so as to be movable together with the same at least one nozzle bar, and each of these at least two main reservoirs is preferably arranged such that it is and/or can be connected via at least one first fluid line to at least one of the at least two print heads. This allows uniform hydrostatic pressure to be achieved in all print heads, even if said heads are arranged at different heights. More preferably, the at least two print heads are arranged at different heights relative to one another on the at least one nozzle bar, and the vertical distances of each of the at least two print heads from the respective main reservoir connected to each via a first fluid line are equal, up to a maximum tolerance limit of 1 cm, more preferably 0.5 cm. 
     The printing press is preferably characterized in that the printing press has at least one first printing unit and at least one system for supplying coating medium, and in that the at least one supply system has at least one main reservoir, and in that each of the at least two print heads is arranged such that it is and/or can be connected via at least a first fluid line to the at least one main reservoir, and in that the at least one main reservoir is connected via at least one supply line and at least one drain line to at least one intermediate reservoir, and in that the at least one main reservoir and/or the at least one drain line has at least one overflow drain, the drain side of which is arranged such that it is and/or can be connected to the at least one intermediate reservoir. This results particularly in the advantage that constant operating conditions for the print heads can be ensured, more particularly that a constant pressure is maintained within the coating medium at nozzle openings of the print heads. 
     The printing press is characterized, for example, in that an ejecting direction of at least one first nozzle of the at least one first print head in the first printing position differs from the ejecting direction of said at least one first nozzle of the at least one print head in the first idle position, in particular the maintenance position and/or the assembly position, by an angle of at least 5°, more preferably at least 10°, even more preferably at least 15° and more preferably still at least 20°. This applies similarly to at least every four print heads, for example. 
     Preferably, however, the ejecting direction of each nozzle of the at least two, particularly at least four print heads, is the same in the respective printing position and in the respective idle position, in particular maintenance position, assembly position. 
     Preferably, a location of the at least one nozzle when the print head is arranged in the at least one printing position and a location of the at least one nozzle when the print head is arranged in the at least one idle position, in particular the maintenance position and/or assembly position, with respect to the axial direction defined by the rotational axis of the at least one printing material guiding element, differ by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width, measured in the axial direction, of the operating region of the nozzle bar that contains the at least one print head, and/or by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of the printing press, defined by the maximum printing material width that can be processed in the printing press. This results particularly in the advantage that constant conditions are enabled for all print heads during maintenance processes and/or particularly with a similar or the same maintenance device, while at the same time allowing the geometry during printing operation to be optimized to a specific print operation. A plane in which this angle is measured is preferably defined by a surface normal which extends parallel to the axial direction A or deviates from said axial direction A by a maximum of 2°; more preferably, said plane is the axial projection plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiment examples of the invention are depicted in the set of drawings, and will be described in greater detail in the following. 
       The drawings show: 
         FIG. 1 a    a schematic diagram of a web-fed printing press; 
         FIG. 1 b    a schematic diagram of a web-fed printing press having an alternate web path; 
         FIG. 2  a schematic diagram of a part of a printing unit, which has a double row of print heads; 
         FIG. 3  a schematic diagram of a printing unit having a plurality of nozzle bars, the print heads of which are arranged in printing positions; 
         FIG. 4  a schematic diagram of a printing unit having a plurality of nozzle bars, the print heads of which are arranged in idle positions, in particular maintenance positions, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 5  a schematic diagram of a printing unit having a plurality of nozzle bars, the print heads of which are arranged in idle positions, in particular assembly positions, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 6  a schematic diagram of a printing unit having a plurality of nozzle bars, the print heads of which are arranged some in idle positions, in particular maintenance positions, and some in printing positions, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 7 a    a schematic diagram of a printing unit having a plurality of nozzle bars, the print heads of which are arranged some in maintenance positions and some in assembly positions, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 7 b    a schematic diagram of a printing unit having a plurality of nozzle bars, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 7 c    a schematic diagram of a printing unit having a plurality of nozzle bars, with positioning drives depicted as discontinuous for the sake of clarity; 
         FIG. 8 a    a schematic diagram of a system for supplying coating medium; 
         FIG. 8 b    a schematic diagram of an alternate system for supplying coating medium; 
         FIG. 9 a    a schematic diagram of a printing unit having four positioning devices and four maintenance devices, in which print heads are placed in printing positions by means of the two positioning devices on the right, and print heads are placed in idle positions, embodied as assembly positions, for example, by means of the two positioning devices on the left, the maintenance devices being located in parked positions, and in which only some main reservoirs and return flow reservoirs are shown, by way of example; 
         FIG. 9 b    a schematic diagram of a printing unit according to  FIG. 9 a   , in which print heads are placed in printing positions by means of the two positioning devices on the right, and print heads are placed in maintenance positions by means of the two positioning devices on the left, and the two maintenance devices on the left are located in operating positions. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A printing press  01  comprises at least one printing material source  100 , at least one first printing unit  200 , preferably at least one first dryer  301 , preferably at least one second printing unit  400  and preferably at least one second dryer  331 , and preferably at least one post-processing unit  500 . Printing press  01  is further preferably embodied as an inkjet printing press  01 . Printing press  01  is preferably embodied as a web-fed printing press  01 , and more preferably as a web-fed inkjet printing press  01 . Printing press  01  is embodied, for example, as a rotary printing press  01 , for example as a web-fed rotary printing press  01 , in particular a web-fed rotary inkjet printing press  01 . In the case of a web-fed printing press  01 , printing material source  100  is embodied as a roll unwinding device  100 . In the case of a sheet-fed printing press or a sheet-fed rotary printing press, printing material source  100  is embodied as a sheet feeder. In printing material source  100 , at least one printing material  02  is preferably aligned, preferably with respect to at least one edge of said printing material  02 . In the roll unwinding device  100  of a web-fed printing press  01 , at least one web-type printing material  02 , that is, a printing material web  02 , for example, a paper web  02  or a textile web  02  or a film  02 , for example a plastic film  02  or a metal film  02 , is unwound from a roll of printing material  101  and is preferably aligned with respect to its edges in an axial direction A. Axial direction A is preferably a direction A that extends parallel to a rotational axis  111  of a roll of printing material  101  and/or at least one printing material guiding element  201 ;  401 , for example at least one central cylinder  201 ;  401 . A transport path of the at least one printing material  02  and particularly of printing material web  02  downstream of the at least one printing material source  100  preferably extends through the at least one first printing unit  200 , where printing material  02  and particularly printing material web  02  is provided with a printed image, preferably by means of at least one printing ink, at least on one side, and in combination with the at least one second printing unit  400 , preferably on both sides. 
     After passing through the at least one first printing unit  200 , the transport path of printing material  02  and particularly of printing material web  02  preferably passes through the at least one first dryer  301 , where the applied printing ink is dried. Printing ink in the above and in the following is generally understood as a coating medium, including particularly varnish. More particularly, no differentiation is made between printing ink and ink; printing ink and coating medium are also understood to include particularly ink. The at least one first dryer  301  is preferably a component of a dryer unit  300 . After passing through the at least one first dryer  301  and preferably the at least one second printing unit  400  and/or the at least one second dryer  331 , printing material  02  and particularly printing material web  02  is preferably fed to the at least one post-processing unit  500 , where it is further processed. The at least one post-processing unit  500  is embodied, for example, as at least one folding apparatus  500  and/or as a winding apparatus  500  and/or as at least one planar delivery unit  500 . In the at least one folding apparatus  500 , printing material  02 , preferably imprinted on both sides, is preferably further processed to produce individual printed products. 
     Preferably, along the transport path of printing material  02  and particularly of printing material web  02  through printing press  01 , at least the first dryer  301  is preferably arranged downstream of the at least one first printing unit  200 , and/or at least the second printing unit  400  is preferably arranged downstream of the at least one first dryer  301 , and/or the at least one second dryer  331  is preferably arranged downstream of the at least one second printing unit  400 , and/or the at least one post-processing unit  500  is preferably arranged downstream of the at least one second dryer  331 . This serves to ensure capability for high quality double-sided imprinting of printing material  02  and particularly of printing material web  02 . 
     In the following, a web-fed printing press  01  will be described in greater detail. Corresponding specifics can be applied likewise to other printing presses  01 , for example to sheet-fed printing presses, where such specifics are not incompatible. Rolls of printing material  101 , which are preferably used in roll unwinding device  100 , preferably each have a core onto which web-type printing material  02  for use in web-fed printing press  01  is wound. Printing material web  02  preferably has a width of 700 mm to 2000 mm, but can also have any smaller or preferably greater width. At least one roll of printing material  101  is rotatably arranged in roll unwinding device  100 . In a preferred embodiment, roll unwinding device  100  is configured suitably for receiving one roll of printing material  101 , and thus has only one storage position for a roll of printing material  101 . In another embodiment, roll unwinding device  100  is embodied as roll changer  100  and has storage positions for at least two rolls of printing material  101 . Roll changer  100  is preferably embodied to enable a flying roll change, that is, a splicing of a first printing material web  02  of a roll of printing material  101  currently being processed to a second printing material web  02  of a roll of printing material  101  to be subsequently processed while both the roll of printing material  101  currently being processed and the roll of printing material  101  to be subsequently processed are in rotation. 
     A working width of printing press  01  is a dimension that preferably extends orthogonally to the provided transport path of printing material  02  through the at least one first printing unit  200 , more preferably in axial direction A. The working width of printing press  01  preferably corresponds to a maximum allowable width of a printing material for processing in printing press  01 , that is, a maximum printing material width that can be processed in printing press  01 . 
     Roll unwinding device  100  preferably has at least one roll holding device  103 , embodied as a chucking device  103  and/or as a clamping device  103 , for example, for each storage position. The at least one roll holding device  103  preferably represents at least one first motor-driven rotational body  103 . The at least one roll holding device  103  rotatably secures at least one roll of printing material  101 . The at least one roll holding device  103  preferably has at least one drive motor  104 . 
     Along the transport path of printing material web  02  downstream of roll holding device  103 , roll unwinding device  100  preferably has a dancer roller  113 , preferably arranged to swivel outward on a dancer lever  121 , and/or a first web edge aligner  114 , and/or an infeed unit  139 , which has an infeed nip  119  formed by a traction roller  118  and a traction pressure roller  117 , and has a first measurement device  141 , embodied as a first measuring roller  141 , particularly as a nip measuring roller  141 . Said traction roller  118  preferably has its own drive motor  146 , embodied as a tractive drive motor  146 , which is preferably connected to a machine controller. Traction roller  118  preferably represents at least one second motor-driven rotational body  118 . A web tension can be adjusted and held within limits by means of the dancer roller  113 , and/or the web tension is preferably held within limits. Roll unwinding device  100  optionally has a splicing and cutting device, by means of which a roll change can be carried out on a flying basis, i.e. without stopping the printing material web  02 . 
     Infeed unit  139  is preferably arranged downstream of the first web edge aligner  114 . The at least one traction roller  118  is preferably provided as a component of infeed unit  139 , and preferably cooperates with traction pressure roller  117  to form infeed nip  119 . Infeed nip  119  serves to control a web tension and/or to transport printing material  02 . 
     The web tension can preferably be measured by means of the at least one first measuring device  141 , embodied as first measuring roller  141 . The at least one first measuring device  141 , embodied as first measuring roller  141 , is preferably arranged upstream of infeed nip  119  in the direction of transport of printing material web  02 . 
     A first printing unit  200  is arranged downstream of roll unwinding device  100  along the transport path of printing material  02 . First printing unit  200  has at least one printing material guiding element  201 . The at least one printing material guiding element  201  is preferably embodied as at least one first central printing cylinder  201 , or central cylinder  201 . In the following, when a central cylinder  201  is mentioned, a central printing cylinder  201  is always meant. The at least one first central cylinder  201  preferably represents at least one third motor-driven rotational body  201 . During printing operation, printing material web  02  wraps at least partially around first central cylinder  201 . The wrap angle in this case is preferably at least 180° and more preferably at least 270°. The wrap angle is the angle, measured in the circumferential direction, of the circumferential cylinder surface of first central cylinder  201  along which printing material  02 , and particularly printing material web  02 , is in contact with first central cylinder  201 . Therefore, during printing operation, as viewed in the circumferential direction, preferably at least 50% and more preferably at least 75% of the circumferential cylinder surface of first central cylinder  201  is in contact with printing material web  02 . This means that a partial surface area of a circumferential cylinder surface of the at least one first central cylinder  201 , provided as the contact surface between the at least one first central cylinder  201  and printing material  02 , preferably embodied as printing material web  02 , has the wrap angle around the at least one first central cylinder  201  that preferably measures at least 180° and more preferably at least 270°. 
     Along the transport path of printing material web  02 , upstream of first central cylinder  201  of first printing unit  200 , at least one second measuring device  216 , preferably embodied as a second measuring roller  216 , is provided for measuring web tension. Along the transport path of printing material web  02 , upstream of first central cylinder  201  of first printing unit  200 , at least a first printing material preparation device  202  or web preparation device  202  is preferably arranged so as to act on printing material web  02  and/or as aligned toward the provided transport path of printing material web  02 . The first printing material preparation device  202  is assigned at least to a first side and preferably to both sides of printing material web  02 , and is particularly aligned to act or be capable of acting at least on this first side of printing material web  02  and preferably on both sides of printing material web  02 . Infeed nip  119  formed by traction roller  118  and traction pressure roller  117  is preferably arranged between first web edge aligner  114  and the at least one first central cylinder  201  along the transport path of printing material web  02 . 
     In a preferred embodiment, the at least one first printing material preparation device  202  is arranged downstream of infeed nip  119  and upstream of first central cylinder  201  along the transport path of printing material web  02 , acting on printing material web  02  and/or aligned toward the transport path of printing material web  02 . The at least one first printing material preparation device  202  is preferably embodied as at least one printing material cleaning device  202  or web cleaning device  202 . Alternatively or additionally, the at least one printing material preparation device  202  is embodied as at least one coating device  202 , particularly for water-based coating medium. A coating of this type is used, for example, as a base coat (primer). Alternatively or additionally, the at least one printing material preparation device  202  is embodied as at least one corona device  202  and/or discharge device  202  for corona treatment of printing material  02 . 
     A roller  203 , embodied as a first turning roller  203  of first printing unit  200 , is preferably arranged with its rotational axis parallel to the first central cylinder  201 . This first turning roller  203  is preferably arranged spaced from first central cylinder  201 . In particular, a first gap  204 , which is greater than the thickness of printing material web  02 , is preferably provided between first turning roller  203  and first central cylinder  201 . The thickness of printing material web  02  in this context is understood as the smallest dimension of printing material web  02 . Printing material web  02  preferably wraps around part of the first turning roller  203  and is turned by said roller such that the transport path of printing material web  02  in first gap  204  extends both tangentially to first turning roller  203  and tangentially to first central cylinder  201 . The circumferential surface of turning roller  203  in this case is preferably made of a relatively inelastic material, more preferably of a metal, even more preferably of steel or aluminum. 
     At least one first cylinder  206 , embodied as first impression cylinder  206 , is preferably provided in first printing unit  200 . First impression cylinder  206  preferably has a circumferential surface made of an elastic material, for example an elastomer. First impression cylinder  206  is preferably arranged such that it can be thrown on and/or thrown off of first central cylinder  201  by means of an actuating drive. In a state in which it is thrown onto first central cylinder  201 , first impression cylinder  206 , together with first central cylinder  201 , preferably forms a first impression nip  209 . During printing operation, printing material web  02  preferably passes through first impression nip  209 . By means of first turning roller  203  and/or preferably by means of first impression cylinder  206 , printing material web  02  is preferably placed in planar contact, and more preferably in a specific and known position, against first central cylinder  201 . Preferably, apart from first impression cylinder  206  and/or optionally additional impression cylinders, no additional rotational elements, in particular no additional roller and no additional cylinder, is in contact with the at least one first central cylinder  201 . 
     The rotational axis of first impression cylinder  206  is preferably arranged below rotational axis  207  of first central cylinder  201 . 
     First central cylinder  201  preferably has its own first drive motor  208 , assigned to first central cylinder  201 , which drive motor is preferably embodied as an electric motor  208  and is more preferably embodied as a direct drive  208  and/or an independent drive  208  of first central cylinder  201 . A direct drive  208  in this case is understood as a drive motor  208  which is connected to the at least one first central cylinder  201  so as to transmit torque or be capable of transmitting torque, without interconnection of additional rotational elements that are in contact with printing material  02 . An independent drive  208  in this context is understood as a drive motor  208  which is embodied as the drive motor  208  exclusively of the at least one first central cylinder  201 . First drive motor  208  of first central cylinder  201  preferably has at least one permanent magnet, which further preferably is part of a rotor of first drive motor  208  of first central cylinder  201 . 
     On first drive motor  208  of first central cylinder  201  and/or on first central cylinder  201  itself, a first rotational angle sensor is preferably provided, which is embodied to measure and/or be capable of measuring an angular position of first drive motor  208  and/or of first central cylinder  201  itself, and to transmit and/or be capable of transmitting said measurement to a higher level machine controller. The first rotational angle sensor is embodied, for example, as a rotation encoder or absolute value encoder. A rotational angle sensor of this type can be used to determine in absolute terms the angular position of first drive motor  208  and/or preferably the angular position of first central cylinder  201 , preferably by means of the higher level machine controller. Additionally or alternatively, first drive motor  208  of first central cylinder  201  is connected in terms of circuitry to the machine controller such that the machine controller is informed at all times regarding the angular position of first drive motor  208  and therefore at the same time regarding the angular position of first central cylinder  201 , on the basis of target data relating to the angular position of first drive motor  208 , predefined by the machine controller to first drive motor  208  of first central cylinder  201 . In particular, a region of the machine controller that specifies the rotational angle position or angular position of first central cylinder  201  and/or of first drive motor  201  is preferably connected directly, in particular without an interconnected sensor, to a region of the machine controller that controls at least one print head  212  of first printing unit  200 . 
     At least one first printing element  211  is arranged inside first printing unit  200 . The at least one first printing element  211  is preferably arranged downstream of first impression cylinder  206  in the direction of rotation of first central cylinder  201  and therefore along the transport path of printing material web  02 , preferably so as to act and/or be capable of acting on, and/or as aligned and/or capable of being aligned toward the at least one first central cylinder  201 . The at least one first printing element  211  is embodied as a first inkjet printing element  211 , and is also referred to as first inkjet printing element  211 . First printing element  211  preferably has at least one nozzle bar  213  and preferably a plurality of nozzle bars  213 , in particular four. The at least one first printing element  211 , and therefore the at least one first printing unit  200 , preferably comprises the at least one first print head  212 , which is embodied as inkjet print head  212 . Each at least one nozzle bar  213  has at least one print head  212  and preferably a plurality of print heads  212 . Each print head  212  preferably has a plurality of nozzles, from which droplets of printing ink are and/or can be ejected. A nozzle bar  213  in this case is a component that preferably extends across at least 80% and more preferably at least 100% of the working width of printing press  01  and serves as a support for the at least one print head  212 . The axial length of the body of the at least one first central cylinder  201  is preferably at least as great as the working width of printing press  01 . A single nozzle bar or a plurality of nozzle bars  213  is/are provided per printing element  211 . Each nozzle is preferably assigned a clearly defined target region with respect to direction A of the width of printing material web  02  and preferably with respect to direction A particularly of rotational axis  207  of the at least one first central cylinder  201 . Each target region of a nozzle, particularly with respect to the circumferential direction of the at least one first central cylinder  201 , is preferably clearly defined, at least during printing operation. A target region of a nozzle is particularly the spatial region, particularly substantially rectilinear, that extends outward from said nozzle in an ejecting direction of said nozzle. 
     The at least one first nozzle bar  213  preferably extends orthogonally to the transport path of printing material  02  across the working width of printing press  01 . The at least one nozzle bar  213  preferably has at least one row of nozzles. The at least one row of nozzles, as viewed in axial direction A, preferably has nozzle openings spaced evenly across the entire working width of printing press  01  and/or across the entire width of the body of the at least one first central cylinder  201 . In one embodiment, a single continuous print head  212  is provided for this purpose, which extends in axial direction A across the entire working width of printing press  01  and/or across the entire width of the body of the at least one first central cylinder  201 . In this case, the at least one row of nozzles is preferably embodied as at least one linear row of individual nozzles, extending across the entire width of printing material web  02  in axial direction A. In another preferred embodiment, a plurality of print heads  212  are arranged side by side in axial direction A on the at least one nozzle bar  213 . Since such individual print heads  212  are usually not equipped with nozzles up to the edges of their housing, preferably at least two and more preferably precisely two rows of print heads  212 , extending in axial direction A, are preferably arranged offset from one another in the circumferential direction of first central cylinder  201 , preferably such that successive print heads  212  in axial direction A are preferably assigned alternatingly to one of the at least two rows of print heads  212 , preferably alternating constantly between a first and a second of two rows of print heads  212 . Two such rows of print heads  212  form a double row of print heads  212 . The at least one row of nozzles is preferably not embodied as a single linear row of nozzles, and instead results as the sum of a plurality of individual rows of nozzles, more preferably two, arranged offset from one another in the circumferential direction. 
     If a print head  212  has a plurality of nozzles, all the target regions of the nozzles of said print head  212  together form an operating region of said print head  212 . Operating regions of print heads  212  of a nozzle bar  213  and particularly of a double row of print heads  212  border one another as viewed in axial direction A and/or overlap as viewed in axial direction A. This serves to ensure that target regions of nozzles of the at least one nozzle bar  213  and/or particularly of each double row of print heads  212  are spaced at regular and preferably periodic distances, as viewed in axial direction A, even if print head  212  is not continuous in axial direction A. In any case, an entire operating region of the at least one nozzle bar  213  preferably extends across at least 90% and more preferably across 100% of the working width of printing press  01  and/or across the entire width of the body of the at least one first central cylinder  201  in axial direction A. On one or on both sides with respect to axial direction A, a narrow region of printing material web  02  and/or of the body of first central cylinder  201  may be provided which is not assigned to the operating region of nozzle bar  213 . An entire operating region of the at least one nozzle bar  213  is preferably composed of all the operating regions of the print heads  212  of said at least one nozzle bar  213  and is preferably composed of all the target regions of nozzles of said print heads  212  of said at least one nozzle bar  213 . An entire operating region of a double row of print heads  212 , as viewed in axial direction A, preferably corresponds to the operating region of the at least one nozzle bar  213 . 
     The at least one nozzle bar  213  preferably has a plurality of rows of nozzles in the circumferential direction with respect to the at least one first central cylinder  201 . Preferably, each print head  212  has a plurality of nozzles, which are further preferably arranged in a matrix of a plurality of lines in axial direction A and/or a plurality of columns, preferably in the circumferential direction of the at least one first central cylinder  201 , with columns of this type more preferably being arranged extending at an angle relative to the circumferential direction, for example in order to increase the resolution of a printed image. In a direction orthogonally to axial direction A, particularly in the transport direction along the transport path of printing material  02  and/or in the circumferential direction with respect to the at least one central cylinder  201 , preferably a plurality of rows of print heads  212 , more preferably four double rows, and even more preferably eight double rows of print heads  212  are arranged in succession. Further preferably, at least during printing operation, a plurality of rows of print heads  212 , more preferably four double rows, and even more preferably eight double rows of print heads  212  are arranged in succession in the circumferential direction with respect to the at least one first central cylinder  201 , aligned toward the at least one first central cylinder  201 . 
     Thus at least during printing operation, print heads  212  are preferably aligned such that the nozzles of each print head  212  point substantially in the radial direction toward the circumferential cylinder surface of the at least one first central cylinder  201 . Deviations of radial directions within a tolerance range of preferably 10° at most and more preferably 5° at most are considered substantially radial directions. This means that the at least one print head  212 , aligned toward the circumferential surface of the at least one first central cylinder  201 , is aligned with respect to rotational axis  207  of the at least one first central cylinder  201  in a radial direction toward the circumferential surface of the at least one first central cylinder  201 . Said radial direction is a radial direction with respect to rotational axis  207  of the at least one first central cylinder  201 . A printing ink of a specific color, for example one each of the colors black, cyan, yellow and magenta, or a varnish, for example a clear varnish, preferably is and/or can be assigned to each double row of print heads  212 . The corresponding inkjet printing element  211  is preferably embodied as a four-color printing element  211 , and enables single-sided, four-color imprinting of printing material web  02 . It is also possible to use one printing element  211  to print with fewer or more different ink colors, for example additional special ink colors. In that case, correspondingly more or fewer print heads  212  and/or double rows of print heads  212  are preferably arranged within said corresponding printing element  211 . In one embodiment, at least during printing operation, a plurality of rows of print heads  212 , more preferably four double rows and even more preferably eight double rows of print heads  212  are arranged in succession, aligned toward at least one surface of at least one transfer element, for example at least one transfer cylinder and/or at least one transfer belt. 
     The at least one print head  212  acts to generate droplets of printing ink, preferably using the drop-on-demand method, in which droplets of printing ink are produced selectively as needed. At least one piezoelectric element is preferably used per nozzle, which is capable of reducing a volume filled with printing ink by a certain percentage at high speed when a voltage is applied. This causes printing ink to be displaced and ejected through a nozzle connected to the volume that is filled with printing ink, forming at least one droplet of printing ink. By applying different voltages to the piezoelectric element, the actuating path of the piezoelectric element and as a result the reduction in the volume and thus the size of the printing ink droplets can be influenced. This allows color gradations to be achieved in the resulting printed image, without altering the number of droplets used to produce the printed image (amplitude modulation). It is also possible to use at least one heating element per nozzle, which generates a gas bubble at high speed in a volume filled with printing ink by vaporizing printing ink. The additional volume of the gas bubble displaces printing ink, which is in turn ejected through the corresponding nozzle, forming at least one droplet of printing ink. 
     In the drop-on-demand method, droplet deflection once a droplet has been ejected from the corresponding nozzle is not necessary, because the target position of the respective printing ink droplet on the moving printing material web  02  can be defined in relation to the circumferential direction of the at least one first central cylinder  201  based solely on an ejection time of the respective printing ink droplet and a rotational speed of first central cylinder  201  and/or based on the rotational position of first central cylinder  201 . Actuating each nozzle individually allows printing ink droplets to be transferred only at selected times and at selected locations from the at least one print head  212  onto the printing material web  02 . This is carried out as a function of the rotational speed and/or the rotational angle position of the at least one first central cylinder  201 , the distance between the respective nozzle and printing material web  02  and the position of the target region of the respective nozzle in relation to the circumferential angle. This results in a desirable printed image, produced as a function of the actuation of all nozzles. Ink droplets are preferably ejected from the at least one nozzle of the at least one print head  212  based on the angular position of first drive motor  208 , as predefined by the machine controller. The target data relating to the angular position of first drive motor  208 , as specified by the machine controller to first drive motor  208 , are preferably incorporated in real time into a calculation of data for actuating the nozzles of the at least one print head  212 . A comparison with actual data regarding the angular position of first drive motor  208  is preferably not necessary, and preferably is not carried out. Thus a precise and constant positioning of printing material web  02  relative to the at least one first central cylinder  201  is critical for producing a printed image that is true to registration and/or register. 
     The nozzles of the at least one print head  212  are arranged in such a way that the distance between the nozzles and printing material web  02  arranged on the circumferential cylinder surface of the at least one first central cylinder  201 , at least when print head  212  is arranged in a printing position, is preferably between 0.5 mm and 5 mm and more preferably between 1 mm and 1.5 mm. The high angular resolution and/or high scanning frequency of the rotational angle sensor and/or the high precision of the target data relating to the angular position of first drive motor  208  of first central cylinder  201 , as predefined by the machine controller and processed by first drive motor  208  of first central cylinder  201 , enable a highly precise position determination and/or knowledge of the location of printing material web  02  in relation to the nozzles and the target regions thereof. The droplet flight time between the nozzles and printing material web  02  is known, for example, from a learning process and/or from the known distance between the nozzles and printing material web  02  combined with a known droplet speed. The rotational angle position of the at least one first central cylinder  201  and/or of the first drive  208  of the at least one first central cylinder  201 , the rotational speed of the at least one first central cylinder  201  and the droplet flight time are used to determine the ideal time for ejection of a respective droplet so that printing material web  02  will be imprinted in a manner that is true to registration and/or true to register. 
     At least one sensor embodied as a first printed image sensor is preferably provided, more preferably at a point along the transport path of printing material web  02  downstream of first printing element  211 . The at least one first printed image sensor is embodied, for example, as a first line camera or as a first surface camera. The at least one first printed image sensor is embodied, for example, as at least one CCD sensor and/or as at least one CMOS sensor. The actuation of all the print heads  212  and/or double rows of print heads  212  of first printing element  211 , arranged and/or acting in succession in the circumferential direction of the at least one first central cylinder  201 , is preferably monitored and controlled by means of this at least one first printed image sensor and a corresponding analysis unit, for example the higher level machine controller. In a first embodiment of the at least one printed image sensor, only a first printed image sensor is provided, the sensor field of which encompasses the entire width of the transport path of printing material web  02 . In a second embodiment of the at least one printed image sensor, only a first printed image sensor is provided, however it is embodied as movable in direction A, orthogonally to the direction of the transport path of printing material web  02 . In a third embodiment of the at least one printed image sensor, a plurality of printed image sensors are provided, the respective sensor fields of which each encompass different regions of the transport path of printing material web  02 . These regions are preferably arranged offset from one another in direction A, orthogonally to the direction of the transport path of printing material web  02 . The total of the sensor fields of the plurality of printed image sensors preferably makes up one entire width of the transport path of printing material web  02 . 
     The positioning of pixels formed by printing ink droplets, each of which emerges from a respective first print head  212 , is preferably compared with the positioning of pixels formed by printing ink droplets, each of which emerges from a respective second print head  212  situated downstream of the respective first print head  212  in the circumferential direction of the at least one first central cylinder  201 . This is preferably carried out regardless of whether said respective first and second print heads  212 , which are arranged and/or act in succession in the circumferential direction of the at least one first central cylinder  201 , are processing the same or a different printing ink. The correlation of the positions of the printed images coming from different print heads  212  is monitored. If the same printing inks are being used, the true-to-register joining of partial images is monitored. If different printing inks are being used, the registration or color registration is monitored. Quality control of the printed image is also preferably carried out based on the measured values of the at least one printed image sensor. 
     During regular printing operation, all print heads  212  are arranged as stationary. This serves to ensure a consistently true-to-registration and/or true-to-register alignment of all nozzles. Various situations are conceivable in which a movement of the print heads  212  might be necessary. A first such situation is a flying reel change or generally a reel change involving a splicing process. In such a process, one printing material web  02  is connected by means of an adhesive strip to another printing material web  02 . This results in a spliced region, which must pass through the entire transport path of the printing material web  02 . The thickness, that is, the smallest dimension of said spliced region is greater than the thickness of the printing material web  02 . The spliced region has essentially the same thickness as two printing material webs  02  plus the adhesive strip. This can cause difficulties when the spliced region passes through the gap between the nozzles of print heads  212  and the circumferential cylinder surface of the at least one first central cylinder  201 . Thus the at least one nozzle bar  213  can be moved in at least one actuating direction and/or along at least one actuating path relative to rotational axis  207  of the at least one first central cylinder  201 . This allows the spacing to be increased sufficiently; however, it must be decreased again accordingly afterward. A second such situation arises, for example, during maintenance and/or cleaning of at least one of print heads  212 . Print heads  212  are preferably secured individually to the at least one nozzle bar  213  and can be individually removed from the at least one nozzle bar  213 . This allows individual print heads  212  to be maintained and/or cleaned and/or replaced. 
     When a plurality of nozzle bars  213  that can be moved relative to one another is provided, minimal misalignments of the nozzle bars  213  relative to one another can occur during the return of at least one nozzle bar  213  to its printing position. Thus it can be necessary to perform an alignment, specifically of all the print heads  212  of one nozzle bar  213  in relation to the print heads  212  of other nozzle bars  213 . When a new print head  212  and/or a print head to be replaced is installed on the at least one nozzle bar  213  on which at least one other print head  212  is already installed, this will not necessarily produce a precisely matched alignment of this new print head  212  and/or print head to be replaced with the at least one print head  212  that is already installed, specifically in the circumferential direction and/or in axial direction A with respect to the at least one first central cylinder  201 ; at best, such an alignment will occur accidentally. Thus it may also be necessary to perform an alignment in this case, specifically of an individual print head  212  in relation to other print heads  212  of the same nozzle bar  213  and/or other nozzle bars  213 . 
     At least one sensor preferably detects the location of the target region of at least one new and/or replaced print head  212  relative to the location of the target region of at least one previously mounted print head  212 . The installed position of the at least one new and/or replaced print head  212  can be adjusted in the circumferential direction with respect to the at least one first central cylinder  201  by actuating the nozzles of said print head  212 , preferably in a manner similar to the adjustment of print heads  212  of different double rows of print heads  212  already described. The installed position of the at least one new and/or replaced print head  212  is adjusted in axial direction A with respect to the at least one first central cylinder  201  by means of at least one adjustment mechanism. Preferably, each of a plurality of print heads  212  has its own adjustment mechanism, and more preferably, each print head  212  has its own adjustment mechanism. 
     Printing press  01  has at least one system  251  for supplying coating medium, in particular at least one printing ink supply system  251 . Preferably, a plurality of print heads  212 , for example a plurality of print heads  212  of a common nozzle bar  213 , in particular a plurality of print heads  212  or more preferably all the print heads in each double row of print heads  212 , have a common system  251  for supplying coating medium. The at least one supply system  251  and particularly the entire system  251  for supplying coating medium preferably has at least one main reservoir  252 , in particular at least one main reservoir  252  for coating medium. At least one fluid line  253 , preferably embodied as an ink line  253 , per print head  212  is preferably connected to the at least one main reservoir  252 . In particular, each of at least two print heads  212  preferably is and/or can be connected, via at least one first fluid line  253  each, preferably directly to the at least one main reservoir  252 . The respective first fluid line  253  can be a flexible line, for example, in particular at least one hose. The at least one main reservoir  252  preferably is and/or can be connected via at least one supply line  254  and at least one drain line  256 , directly or via interconnected components  263 ;  280 ;  285 ;  295 , for example at least one second flow check valve  263  and/or at least one return flow reservoir  295  and/or at least one return flow pump  285  and/or at least one return flow valve  280 , to at least one and preferably at least the same intermediate reservoir  257 , in particular intermediate reservoir  257  for the at least one coating medium. The dimension of the interior of the at least one main reservoir  252  in axial direction A is at least as great as 50% of the width, measured in axial direction A, of the operating region of the nozzle bar  213  that contains the at least two print heads  212 , and/or at least 50% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . 
     The at least one printing unit  200 ;  400  preferably has a plurality of main reservoirs  252 , more preferably at least one main reservoir  252  for each printing ink to be printed, for example four main reservoirs  252 . This is particularly preferably the case when print heads  212  which are assigned to different printing inks are aligned at different angles from vertical, as in that case, different liquid column heights result for relevant hydrostatic pressures. This is particularly preferably the case when print heads  212 ;  412  are arranged so as to be movable relative to one another, for example to different positions such as printing positions and/or idle positions, for example by means of corresponding positioning devices  217 ;  218 ;  219 ;  221 . More preferably, therefore, two main reservoirs  252  are provided per double row of print heads  212 ;  412 , thus particularly four main reservoirs  252  for each coating medium. Printing unit  200 ;  400  preferably has one return flow reservoir  295  for each nozzle bar  213  and/or for each positioning device  217 ;  218 ;  219 ;  221 , with said return flow reservoir being connected at least indirectly to each of four main reservoirs  252 . 
     The fill level of main reservoir  252 , at least during a printing operation and more preferably perpetually, is preferably constant with only slight deviations within a narrow tolerance range. This constant fill level can be achieved, for example, by providing an influx of printing ink and an overflow drain  258 . An overflow drain  258  is understood as a drain which establishes the maximum height of a fill level, particularly of the main reservoir  252 . A controlled overflow drain  258  may be provided, which has at least one fill level sensor and at least one valve, for example. Preferably, however, at least one passive overflow drain  258  is provided. A passive overflow drain  258  is preferably an overflow drain  258  consisting substantially of an opening, the lower edge of which is arranged at a specific height, and which thereby establishes a maximum fill level. The at least one main reservoir  252  and/or the at least one drain line  256  preferably have at least one preferably passive overflow drain  258 , the drain side of which is preferably arranged such that it is and/or can be connected directly or via interconnected components  263 ,  280 ;  285 ;  295  to the at least one intermediate reservoir  257 , more preferably to the same at least one intermediate reservoir  257  to which the at least one main reservoir  252  is and/or can be connected via the at least one supply line  254 . At least one filtering device  259  and/or at least one venting device  261  and/or at least one damping device  299  for damping pulsations is preferably arranged along the at least one supply line  254 . At least one valve  262 , preferably embodied as a first flow check valve  262 , is preferably arranged within the at least one supply line  254 , and/or at least one valve  263 , preferably embodied as a second flow check valve  263 , is preferably arranged within the at least one drain line  256 . 
     At least one first liquid pump  264  is preferably arranged in the at least one supply line  254 . Coating medium, in particular printing ink, is preferably pumped constantly into main reservoir  252 , with excess coating medium being discharged through the at least one overflow drain  258 , and with a level of the coating medium in main reservoir  252  being defined by the height at which an opening of overflow drain  258  is located. A controlled and/or regulated normal pressure preferably prevails in main reservoir  252 , and is more preferably controlled and/or regulated relative to an ambient pressure, in particular atmospheric pressure. The constant level and the controlled and/or regulated normal pressure ensure that the pressure within the coating medium at the nozzle openings of print heads  212  is held constant. Constant operating conditions for print heads  212  are thereby ensured. In at least one first gas-filled space  266  of the at least one main reservoir  252 , at least one gas volume is preferably provided, in which a normal pressure prevails which is lower than an ambient pressure present at an ejection side of at least one nozzle of the at least one print head  212 . Thus the normal pressure in main reservoir  252  is preferably a negative pressure in relation to the ambient pressure. This negative pressure is preferably between 4 kPa (four kilopascal), or 40 mbar (forty millibar), and 6 kPa (six kilopascal), or 60 mbar (sixty millibar), more preferably between 4.5 kPa (four-and-a-half kilopascal), or 45 mbar (forty-five millibar), and 5.5 kPa (five-and-a-half kilopascal), or 55 mbar (fifty-five millibar). The installed position of print head  212  is preferably factored into any pressure adjustment, because the inclination of said print head will result in a different level and therefore in a different hydrostatic pressure, which can be compensated for by means of said pressure. The at least one main reservoir  252  preferably extends across at least 50%, more preferably at least 75%, and even more preferably at least 90% of the width of the operating region of the at least one nozzle bar  213  in axial direction A and/or the working width of printing press  01 . 
     At least one return flow reservoir  295  is preferably arranged in the at least one drain line  256 , more preferably at a lower height than the at least one main reservoir  252 . At least one return flow pump  285 , for example for pumping coating medium back into intermediate reservoir  257 , which is preferably situated at a higher level, is preferably arranged along the at least one drain line  256 , in particular downstream of the at least one return flow reservoir  295 . The at least one intermediate reservoir  257  is preferably, but not necessarily, situated at a higher level than the at least one main reservoir  252 . At least one reflux valve  280  is preferably arranged along the at least one drain line  256 , upstream or preferably downstream of the at least one return flow pump  285 . This ensures that a circular flow of coating medium is provided, within which coating medium can be conveyed by means of pumps and gravity. 
     Coating medium, for example printing ink, is preferably pumped by the at least one first liquid pump  264  from intermediate reservoir  257  into main reservoir  252 . At least one and preferably precisely one volume provided as a first gas-filled space  266  is preferably arranged in the at least one main reservoir  252 . The at least one first gas-filled space  266  is preferably arranged such that it is and/or can be connected via at least one first gas line  267  to at least one vacuum source  268 ;  276 ;  277 . The at least one vacuum source  268 ;  276 ,  277  is embodied, for example, as at least one gas pump and/or at least one vacuum buffer  276  and/or at least one vacuum regulator  277 . At least one liquid trap  293 , in particular a coating medium trap  293 , is preferably arranged in the at least one first gas line  267 . The same normal pressure as in the at least one first gas-filled space  266  of the at least one main reservoir  252  is preferably present in a second gas-filled space  269  of intermediate reservoir  257 . This is achieved, for example, by connecting the second gas-filled space  269  by means of at least one second gas line  271  to at least one second gas pump and/or to the at least one first gas-filled space  266  and/or to the at least one first gas pump  268  and/or to the at least one vacuum buffer  276  and/or more preferably to the at least one vacuum regulator  277 . The at least one second gas line  271  preferably has at least one vacuum sensor  294 . 
     At least one third gas-filled space  290  is preferably provided in the at least one return flow reservoir  295 . The same normal pressure as in the at least one first gas-filled space  266  of the at least one main reservoir  252  is preferably present in the third gas-filled space  290  of return flow reservoir  295 , at least as long as the at least one first valve  262  and the at least one second valve  263  are closed. This is achieved, for example, by connecting the third gas-filled space  290  by means of at least one equalizing line  286  to the at least one second gas pump and/or to the at least one first gas-filled space  266  and/or to the at least one first gas pump  268  and/or to the at least one vacuum buffer  276  and/or more preferably to the at least one vacuum regulator  277 . The at least one equalizing line  286  preferably has at least one liquid trap  293 , in particular a coating medium trap  293 . 
     The at least one liquid trap  293 , for example coating medium trap  293 , is embodied, for example, as at least one hollow chamber having an inlet and an outlet. The inlet is preferably located at a distance above a lowest point in the hollow chamber. The outlet is preferably located at the level of the inlet or higher. The cross-section of the hollow chamber is preferably greater than the cross-section of a line connected to the inlet. Vacuum pressure is preferably applied to the outlet, thereby suctioning gas in via the inlet and through the hollow chamber. If liquid is suctioned in at the same time, it will preferably settle at the lowest point in the hollow chamber under the force of gravity, and will not be conveyed into the vacuum line connected to the outlet. A check can be made by means of a sensor and/or manually, for example visually, to determine whether liquid is present at the lowest point in the hollow chamber and needs to be removed. Removal can be carried out manually or automatically by means of an outlet, for example at the lowest point in the hollow chamber, which can be sealed and/or connected to a pump. 
     At least one vacuum pump  268  is preferably provided, to which the at least one vacuum buffer  276  is connected via at least one vacuum supply line  278 . The at least one vacuum buffer  276  preferably is and/or can be connected via at least one venting line  279  to the at least one venting device  261 . The at least one vacuum buffer  276  is preferably arranged such that it is and/or can be connected via at least one vacuum line  281  to at least one vacuum regulator  277 , which preferably is and/or can be connected via at least one fresh air filter  292  to the surrounding environment. At least one normal pressure line  282  preferably connects the at least one vacuum regulator  277  to at least one pressure regulator  283 . Vacuum regulator  277  preferably serves to adjust the pressure in the at least one normal pressure line  282  to normal pressure, in particular by admixing ambient air, for example at atmospheric pressure, into the air coming from vacuum buffer  276 . The at least one pressure regulator  283  is preferably arranged connected to at least one compressed air source  284 , for example at least one air pump  284 , or to a connection to the surrounding environment  284 . The at least one pressure regulator  283  is preferably arranged such that it is and/or can be connected via the at least one first gas line  267  to the at least one first gas-filled space  266  of the at least one main reservoir  252 . In this manner, the normal pressure or an overpressure can optionally be generated in first gas line  267  and therefore in first gas-filled space  266  of main reservoir  252  by means of pressure regulator  283 . Any resulting gas volumes that become enclosed as the system is being filled with coating medium can preferably be pumped out by means of respective equalizing lines  286 , and/or can at least be acted on by the respective normal pressure. Such gas volumes can occur, for example, in an area of the at least one flow check valve  263  and/or particularly in the area of the at least one return flow reservoir  295 . 
     The at least one intermediate reservoir  257  is preferably connected to at least one buffer reservoir  272 , more preferably via at least one supply line  273 . In a first embodiment of supply line  273 , by way of example, the at least one intermediate reservoir  257  is connected via at least one supply line  273  embodied as a suction line  273  to the at least one buffer reservoir  272 . In that case, no liquid pump, or no pump at all, is provided along the at least one suction line  273  between the at least one buffer reservoir  272  and the at least one intermediate reservoir  257 , for example, and/or buffer reservoir  272  is at ambient pressure and/or no pump is arranged between buffer reservoir  272  and intermediate reservoir  257 , and instead, printing ink is conveyed out of buffer reservoir  272  into intermediate reservoir  257  by virtue of the relative negative pressure. This allows constant conditions to be ensured particularly in intermediate reservoir  257  and in main reservoir  252 , in particular with respect to normal pressure. In a preferred second embodiment of supply line  273 , by way of example, supply line  273  has at least one supply pump  296  and/or preferably at least one flow meter  297  and/or preferably at least one supply valve  298  and/or local supply valve  298 . A supply line  273  can be subdivided downstream of a supply valve  298  into a plurality of partial lines, for example, which are connected to different printing units  200 ;  400  and which are embodied as sealable, independently of one another, by means of local supply valves  298 . (In  FIG. 8 b   , this option is indicated by a dashed line.) 
     Buffer reservoir  272  is and/or can be connected, for example, to a replaceable storage tank  274 , which can also serve to supply other print heads  212  and/or other nozzle bars  213  and/or other printing units  200 ;  400  and/or other printing presses  01 . The at least one buffer reservoir  272  preferably is and/or can be connected via at least one second supply line  273 , for example suction line  273 , to at least one additional intermediate reservoir  257 , which is assigned to at least one additional, for example second printing unit  200 ;  400  of printing press  01 . For example, at least one reserve supply pump  289  and at least one reserve supply valve  291  are arranged along at least one reserve supply line  288  between the at least one reserve storage tank  274  and the at least one buffer reservoir  272 . The at least one buffer reservoir  272  has at least one overflow device  287 , for example, via which excess coating medium can be discharged as needed, for example if the at least one reserve supply pump  289  and/or the at least one reserve supply valve  291  should malfunction. This serves to prevent any negative impact on the normal pressure. In one embodiment, by way of example, the at least one buffer reservoir  272  is eliminated, and instead, reserve storage tank  274  is provided directly at the location of buffer reservoir  272 ; in that case, reserve supply pump  289  is also eliminated, for example, and coating medium is fed in by means of reserve supply pump  296 . 
     At least one and more preferably precisely one intermediate reservoir  257  is preferably provided for each printing unit  200 ;  400  and each coating medium. At least one main reservoir  252  and more preferably precisely four main reservoirs  252  are preferably provided for each printing unit and each coating medium. At least one and more preferably precisely one return flow reservoir  295  is preferably provided for each printing unit and each coating medium. For example, in the case of a four-color press that has two printing units  200 ;  400 , eight intermediate reservoirs  257  and thirty-two main reservoirs  252  and eight return flow reservoirs  295  are provided. Precisely one vacuum source  268  is preferably provided for each printing unit  200 ;  400  and more preferably for each printing press  01 . Precisely one reserve storage tank  274  and/or precisely one buffer reservoir  272  is preferably provided for each coating medium, in particular for printing ink for the entire printing press  01 . 
     The at least one intermediate reservoir  257  is preferably stationary relative to a frame  231  of the respective printing unit  200 ;  400 . The at least one main reservoir  252 , together with the at least one print head  212 ;  412  and/or the at least one nozzle bar  213 ;  413 , is preferably arranged so as to be movable by means of a corresponding positioning device  217 ;  218 ;  219 ;  221 , and/or the at least one return flow reservoir  295 , together with the at least one print head  212 ;  412  and/or the at least one main reservoir  252  and/or the at least one nozzle bar  213 ;  413 , is preferably arranged so as to be movable by means of a corresponding positioning device  217 ;  218 ;  219 ;  221 . As a result, constant hydrostatic pressure conditions are particularly ensured, for example within the at least one main reservoir  257  and/or within the at least one print head  212 ;  412 . 
     Printing press  01  preferably permits a process for cleaning at least one nozzle of each of at least two print heads  212 , embodied as inkjet print heads  212 , of printing press  01 , wherein printing press  01  comprises the at least one supply system  251 , which comprises the at least one main reservoir  252 , preferably for the at least one coating medium, and the at least one intermediate reservoir  257 , preferably for the at least one coating medium, and wherein each of the at least two print heads  212 ;  412  is arranged such that it is and/or can be connected via at least a first fluid line  253  preferably directly to the at least one main reservoir  252 , and wherein the at least one main reservoir  252  is connected via the at least one supply line  254  and the at least one drain line  256  to preferably the same at least one intermediate reservoir  257 , and wherein first, each of the at least one supply lines  254  is preferably closed by means of the at least one first flow check valve  262  and each of the at least one drain lines  256  is preferably closed by means of the at least one second flow check valve  263 , and wherein subsequently, a pressure within the gas volume located within the at least one main reservoir  252  is preferably increased by means of at least the at least one first gas pump  268  and/or by means of at least the at least one compressed air source  284 , and as a result, coating medium and particularly printing ink is conveyed through the at least one nozzle of the at least two print heads  212  and preferably ejected. 
     A plurality of print heads  212 , for example a plurality of print heads  212  of a common nozzle bar  213 , in particular a plurality of print heads  212  or more preferably all the print heads of a double row of print heads  212 , preferably have a common voltage supply system. At least one common power supply line for the voltage supply preferably extends within the respective at least one nozzle bar over at least 50%, more preferably at least 75% and even more preferably at least 90% of the width of the operating region of the respective at least one nozzle bar  213  in axial direction A and/or of the working width of printing press  01 . Each print head  212  of said respective at least one nozzle bar  213  preferably has at least one dedicated power line, which is connected to said common power supply line for the voltage supply. Each print head  212  of said respective at least one nozzle bar  213  preferably has at least one dedicated data line, which is connected to a computer unit which is arranged outside the operating region of the respective at least one nozzle bar  213  with respect to axial direction A, and/or outside of each transport path provided for printing material  02  in printing press  01  with respect to axial direction A. Thus at least one data line per print head  212  of said at least one nozzle bar  213  extend parallel to one another, at least along a section of nozzle bar  213  that extends in axial direction A. 
     Printing press  01  preferably has at least one printing unit  200 ;  400 , wherein the at least one printing unit  200 ;  400  has at least one print head  212 ;  412 , preferably embodied as an inkjet print head  212 ;  412  and having an ejecting direction, and preferably has a plurality of print heads  212 ;  412 , preferably each being embodied as an inkjet print head  212 ;  412  and having an ejecting direction, and also preferably has at least one printing material guiding element  201 ;  401  which is rotatable around a respective rotational axis  207 ;  407 , by means of which preferably at least one transport path provided for preferably a web-type printing material  02  is and/or can be at least partially defined. The at least one nozzle, and more preferably each nozzle, preferably has an ejecting direction which is clearly defined relative to the nozzle and relative to the print head  212  that contains the nozzle. Ejecting directions of nozzles of a common print head  212  are preferably aligned parallel to one another. The ejecting direction of at least one nozzle of the at least one print head  212  is preferably aligned toward a circumferential surface of the at least one printing material guiding element  201 ;  401 , at least when print head  212  is in a printing position. 
     The at least one printing material guiding element  201 ;  401  is preferably arranged within the at least one printing unit  200 ;  400 , and/or the at least one printing material guiding element  201 ;  401  is preferably embodied as at least one web guiding roller and/or one turning roller  203 ;  214 ;  312 ;  403 ;  414  and/or as at least one central printing cylinder  201 ;  401  and/or as at least one transfer element. 
     The at least one print head  212 ;  412  preferably is and/or can be connected to at least one positioning device  217 ;  218 ;  219 ;  221 . More preferably, the at least one print head  212  is permanently connected to the at least one positioning device  217 ;  218 ;  219 ;  221  and can be removed from the at least one positioning device  217 ;  218 ;  219 ;  221  only for purposes of assembly and/or disassembly and/or for replacing the at least one print head  212 . The at least one printing unit  200 ;  400  preferably has at least two and more preferably at least four nozzle bars  213 ;  413 , each of which has at least two print heads  212 ;  412 . Each nozzle bar  213 ;  413  preferably is and/or can be connected to at least one positioning device  217 ;  218 ;  219 ;  221 , and in this way, each corresponding print head  212 ;  412  is and/or can be connected simultaneously to at least one positioning device  217 ;  218 ;  219 ;  221 . The at least two, particularly at least four nozzle bars  213 ;  413  are preferably arranged so as to be movable by means of a respective positioning device  217 ;  218 ;  219 ;  221  along a respective, for example linear actuating path. Preferably, at least one of at least two print heads  212  can selectively be placed at least either in a printing position assigned to said print head or in at least one idle position assigned to said print head, further preferably by means of a positioning device  217  assigned to said print head. Further preferably, each of at least four print heads  212 ;  412  can selectively be placed at least either in a printing position assigned to said print head or in at least one idle position assigned to said print head, further preferably by means of a positioning device  217 ;  218  assigned to said print head. 
     The at least one print head  212  can preferably be placed in at least one printing position, in particular by means of at least one positioning device  217 ;  218 ;  219 ;  221 . A print head  212  arranged in its printing position is preferably characterized in that at least one nozzle of the at least one print head  212  is spaced from a provided transport path for printing material  02  and/or from printing material  02  and/or from a transfer element and/or from printing material guiding element  201 ;  401  by a distance of at most 5 mm and more preferably at most 1.5 mm and/or by a distance of at least 0.5 mm and more preferably at least 1 mm. 
     A print head  212  arranged in its printing position is preferably characterized in that the ejecting direction of each of a majority of all the nozzles of the at least one print head  212  deviates a maximum of 10° and more preferably a maximum of 6° and even more preferably a maximum of 3° from a surface normal of a surface element of the provided transport path for printing material  02  that is closest to the respective nozzle, and/or from a surface normal of a surface element of the printing material  02  that is closest to the respective nozzle and/or from a surface normal of a surface element of a transfer element that is closest to the respective nozzle and/or from a surface normal of a surface element of a printing material guiding element  201 ;  401  that is closest to the respective nozzle. 
     A print head  212  arranged in its printing position is preferably characterized in that the ejecting direction of each of a majority of all the nozzles of the at least one print head  212  deviates from a vertical direction by a maximum of 30°. At least when print head  212  is arranged in the printing position, an ejecting direction of at least one and preferably of each nozzle of at least said print head  212  is preferably aligned toward at least one printing material guiding element  201 ;  401  and/or at least one transfer element. At least when print head  212  is arranged in the printing position, at least one nozzle of said print head  212  is preferably arranged in a position designated for a printing operation of said at least one nozzle. 
     The at least one print head  212  can preferably be placed in at least one idle position and more preferably in at least two different idle positions, in particular by means of the at least one positioning device  217 ;  218 ;  219 ;  221 . The at least one idle position is embodied, for example, as at least one maintenance position and/or as at least one assembly position. A maintenance position in this context is preferably a position in which maintenance can be performed on the at least one print head  212 , for example it can be cleaned and/or aligned and/or held in a state in which it is protected particularly against soiling and/or drying out, in particular without removing the at least one print head  212  from printing press  01  and/or from the at least one printing unit  200 ;  400 . An assembly position in this case is preferably a position in which the at least one print head  212  can be removed from printing press  01  and/or from the at least one printing unit  200 ;  400  and/or from the at least one nozzle bar  213 , and/or can be installed in printing press  01  and/or in the at least one printing unit  200 ;  400  and/or in the at least one nozzle bar  213 . In particular, the assembly position preferably provides additional space to an operator for accessing the at least one print head  212 , whereas the maintenance position preferably provides only enough space to allow internal, particularly automatically running processes to be performed within printing press  01 . 
     Respective idle positions of the print heads  212 , regardless of whether said positions are embodied as maintenance positions and/or as assembly positions, are preferably characterized in that different print heads  212  in their respective idle positions are spaced at least partially different distances from the provided transport path for printing material  02  and/or from a printing material  02  and/or from a transfer element and/or from the printing material guiding element  201 ;  401 , in particular central cylinder  201 ;  401 . Each nozzle of the at least one print head  212 ;  412  arranged in its maintenance position is preferably spaced a distance of at least 10 cm and more preferably at least 25 cm from a surface element of the provided transport path for printing material  02  that is closest to the respective nozzle, and/or from a surface element of printing material  02  that is closest to the respective nozzle, and/or from a surface element of a transfer element that is closest to the respective nozzle and/or from a printing material guiding element  201 ;  401 , in particular a central cylinder  201 ;  401 . 
     Respective maintenance positions of print heads  212  are preferably characterized in that the spacing between different print heads  212  arranged in their respective maintenance positions is different from the spacing between said print heads in their respective printing positions and/or in their respective assembly positions. 
     Respective assembly positions of print heads  212  are preferably characterized in that the spacing between different print heads  212  arranged in their respective assembly positions is different from the spacing between said print heads in their respective printing positions and/or in their respective maintenance positions. Each nozzle of the at least one print head  212 ;  412  arranged in its assembly position is preferably spaced a distance of at least 20 cm and more preferably at least 35 cm from a surface element of the provided transport path for printing material  02  that is closest to the respective nozzle, and/or from a surface element of printing material  02  that is closest to the respective nozzle, and/or from a surface element of a transfer element that is closest to the respective nozzle and/or from a printing material guiding element  201 ;  401 , in particular a central cylinder  201 ;  401 . Said distances are preferably measured in the axial projection plane. 
     In a first possible embodiment, the at least one positioning device  217 ;  218 ,  219 ;  221  has at least one positioning guide  224  embodied as a lever arm  224 , for example a plurality of positioning guides  224 , particularly four, preferably embodied as lever arms  224 , and for example in each case one positioning guide  224 , preferably embodied as a lever arm  224 , per movable nozzle bar  213  and/or per movable print head  212 . For example, and particularly if the at least one positioning guide  224  is embodied as at least one lever arm  224 , the actuating path of the at least one print head  212 ;  412  is embodied as at least one arc. A pivot axis  227  of the at least one lever arm  224  is arranged parallel to axial direction A, for example. This serves to ensure that movements of the at least one lever arm  224  and of the at least one print head  212  and/or nozzle bar  213  arranged thereon, for example, will occur only within a plane defined by a surface normal which is arranged parallel to axial direction A, in particular within the axial projection plane. At least two positioning devices  217 ;  218  have different pivot axes  227  from one another, for example. Additionally or alternatively, at least two positioning devices have a common pivot axis  227 , for example. 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , respective maintenance positions of the print heads  212  are characterized, for example, in that when print head  212  is arranged in its respective maintenance position, the ejecting directions of all the nozzles of said print head  212  point in a vertical direction, in particular a vertically downward pointing direction, to within a maximum tolerance range of 20° and more preferably 12° and even more preferably 8°. In particular, a direction which is defined as the arithmetic mean of all the ejecting directions of all the nozzles of the nozzle bar  213  containing the at least one print head  212 ;  412  arranged in its maintenance position preferably deviates from the vertical direction by a maximum of 12°, more preferably a maximum of 8° and even more preferably a maximum of 4°. 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , respective maintenance positions of the print heads  212  are characterized, for example, in that the ejecting directions of each of the nozzles of different print heads  212  arranged in their respective maintenance positions are oriented at different angles in relation to the next closest surface element of the provided transport path for printing material  02  and/or of the web guiding element  201 ;  401  and/or of the transfer element and/or of printing material  02 , with said difference between the angles more preferably amounting to at least 2°, preferably at least 6°, and more preferably at least 10°. A plane in which this angle is measured is preferably defined by a surface normal which extends parallel to axial direction A or deviates from said axial direction A by a maximum of 2°. This plane is preferably referred to as the axial projection plane. 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , respective assembly positions of print heads  212  are characterized, for example, in that the ejecting directions of each of the nozzles of different print heads  212  arranged in their respective assembly positions are oriented at different angles in relation to the next closest surface element of the provided transport path for printing material  02  and/or of web guiding element  201 ;  401  and/or of the transfer element and/or of printing material  02 , said difference between the angles more preferably amounting to at least 2°, preferably at least 6° and more preferably at least 10°. A plane in which this angle is measured is preferably defined by a surface normal which extends parallel to axial direction A or deviates from said axial direction A by a maximum of 2°. Said plane is more preferably the axial projection plane. 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , respective assembly positions of print heads  212  are characterized, for example, in that, when print head  212  is arranged in its respective assembly position, the ejecting directions of each of the nozzles of said print head  212  differ by preferably at least 4° and more preferably at least 6° and even more preferably at least 8° from a vertical direction, in particular a downward pointing vertical direction. In particular, a direction which is defined as the arithmetic mean of all the ejecting directions of all the nozzles of the nozzle bar  213  that contains the at least one print head  212 ;  412  arranged in its assembly position deviates from a vertical direction by at least 4°, more preferably at least 6° and even more preferably at least 8°. 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , respective assembly positions of print heads  212  are characterized, for example, in that, when print head  212  is arranged in its respective assembly position, a direction that is defined as the arithmetic mean of all the ejecting directions of all the nozzles of the nozzle bar  213  that contains the at least one print head  212 ;  412  arranged in its assembly position deviates at least 20° and more preferably at least 30° from a surface normal of a surface element of the provided transport path for printing material  02  that is closest to the respective nozzle and/or from a surface normal of a surface element of printing material  02  that is closest to the respective nozzle and/or from a surface normal of a surface element of a transfer element that is closest to the respective nozzle and/or from a printing material guiding element  201 ;  401 . 
     With respect to the first possible embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , at least one assembly position of at least one print head  212  and preferably of all print heads  212  is characterized, for example, in that, in the axial projection plane and/or in a plane that is defined by a surface normal that extends parallel to axial direction A or that deviates from said axial direction A by a maximum of 2°, the ejecting directions of all the nozzles of print head  212  arranged in its printing position have a horizontal component which is precisely opposite a horizontal component of the ejecting directions of all the nozzles of said print head  212  in its assembly position. As a result, in particular, respective print heads  212  can preferably be transferred by at least one pivoting movement from their printing position through their maintenance position to their assembly position. 
     In a second and preferred embodiment of the at least one positioning device  217 ;  218 ,  219 ;  221 , the at least one positioning device  217 ;  218 ,  219 ;  221  has at least one linear positioning guide  224 , preferably embodied as a track  224 , and more preferably has a plurality of positioning guides  224 , in particular four, preferably embodied as tracks  224 , and even more preferably has at least one positioning guide  224 , preferably embodied as a track  224 , for each movable nozzle bar  213  and/or for each movable print head  212 . More preferably, two positioning guides  224 , embodied as tracks  224 , are provided for each nozzle bar  213 , in particular one track  224  for each axial end of the at least one printing material guiding element  201 ;  401 , or a total of at least eight tracks  224  per printing unit  200 ;  400 . Preferably, and particularly if the at least one positioning guide  224  is embodied as at least one track  224 , the actuating path of the at least one print head  212 ;  412  is embodied as linear. 
     Preferred therefore is a printing press  01  which has at least one printing unit  200 ;  400  having at least two, more preferably at least three and even more preferably at least four print heads  412 ,  212  and at least one printing material guiding element  201 ;  401  that is rotatable around a rotational axis  207 ;  407 , wherein each of the at least two, preferably at least three and more preferably at least four print heads  212 ;  412  is arranged so as to be movable along a respective linear actuating path by means of a respective positioning device  217 ;  218 ;  219 ;  221  assigned to at least said print head  212 ;  412 . More preferably, the linear actuating paths have respective actuating directions that differ in pairs by at least 10° and more preferably by at least 15°, and regardless of the lower limit, differ by at most 150°, more preferably by at most 120°, even more preferably by at most 90° and more preferably still by at most 60°. All the actuating directions of positioning devices  217 ;  218 ;  219 ;  221  of the same printing unit  200 ;  400  in all possible pairwise arrangements preferably differ by at least 10° and more preferably by at least 15°, and regardless of the lower limit, differ by at most 150°, more preferably by at most 120°, even more preferably by at most 90° and more preferably still by at most 60°. Actuating directions of print heads  212 ;  412  to which adjacent positioning devices  217 ;  218 ,  219 ;  221  are assigned preferably differ from one another by at least 10° and more preferably by at least 15°, and regardless of the lower limit, differ by at most 60°, more preferably by at most 45°, even more preferably by at most 30° and more preferably still by at most 20°. Preferably, it is ensured that movements of the at least one print head  212  and/or nozzle bar  213  occur only within a plane that is defined by a surface normal which is parallel to axial direction A, in particular within the axial projection plane. 
     Each of the at least two, preferably at least three and more preferably at least four print heads  212 ;  412  preferably can selectively be placed, by means of the respective positioning device  217 ;  218 ;  219 ;  221 , at least either in a printing position assigned to said print head and in at least one maintenance position assigned to said print head, wherein when a first print head  212 ;  412  of the at least two, preferably at least three and more preferably at least four print heads  212 ;  412  is in the at least one maintenance position, at least one maintenance device  222  is and/or can be assigned to at least one first nozzle of the at least one first print head  212 ;  412 . The description above and in the following in reference to the at least one maintenance device  222  preferably applies to each maintenance device  222 , particularly also when two, three or four maintenance devices are provided per printing unit  200 ;  400 . The at least one maintenance device  222  is preferably arranged so as to be movable along at least one staging path between at least one parked position and at least one operating position, in particular by means of at least one transport device  223 . If a plurality of maintenance devices  222  is provided, a separate staging path, a separate parked position and a separate operating position are preferably assigned to each maintenance device  222 . An optionally provided component of the respective staging path of the at least one maintenance device  222  in an axial direction A defined by rotational axis  207 ;  407  of the at least one rotatable printing material guiding element  201 ;  401  preferably amounts to a maximum of 50% of the width, measured in axial direction A, of an operating region of a nozzle bar  213  containing the at least one print head  212 , and/or a maximum of 50% of a working width of printing press  01 , defined by a maximum printing material width that can be processed in printing press  01 . 
     The actuating directions of the linear actuating paths are preferably each aligned orthogonally and particularly radially in relation to rotational axis  207 ;  407  of the at least one rotatable printing material guiding element  201 ;  401 . All the print heads  212 ;  412  in their printing positions and their idle positions, in particular maintenance positions and/or assembly positions, are preferably arranged such that their respective nozzles are always in the respectively same alignment in terms of their ejecting direction. Print heads  212 ;  412  preferably have linear actuating paths. 
     The at least one positioning device  217 ;  218 ,  219 ;  221  preferably has at least one positioning drive  226  and more preferably a plurality of positioning drives  226  and even more preferably one positioning drive  226  per movable nozzle bar  213 . For example, one positioning drive  226  is assigned to each positioning guide  224 . The at least one positioning drive  226  is embodied, for example, as at least one hydraulic cylinder  226  and/or as at least one pneumatic cylinder  226  and/or preferably as at least one electric motor  226 . The at least one positioning drive  226  is preferably arranged such that it can move the at least one print head  212  either to its printing position, or to its maintenance position or to its assembly position, and can more preferably hold it there. The at least one positioning drive  226  is preferably embodied as at least one electric motor  226 , for example as at least one stepped motor  226 , and/or is connected to at least one threaded spindle. The at least one threaded spindle is preferably engaged with at least one spindle nut, which is connected to the respective nozzle bar  213 . 
     At least four positioning devices  217 ;  218 ;  219 ;  221  are preferably provided, by means of each of which at least one nozzle bar  213  and/or particularly a plurality of print heads  212  assigned to the same printing ink can be moved together. This enables particularly configurations in which the print heads  212  of at least one nozzle bar  213  and/or at least one printing ink are arranged in their printing position while the print heads  212  of at least one other nozzle bar  213  and/or one other printing ink are arranged in an idle position, for example a maintenance position. In this manner, for example, all the print heads  212  of one printing ink, for example black, can be activated, while all the print heads  212  of other printing inks are held in a maintenance position, where they are protected against drying out and/or are cleaned, for example by suitable means. 
     At least one first locking element is preferably provided, for example, at least one printing stop. The at least one first locking element can preferably secure the at least one print head  212  in its printing position, for example by the at least one positioning drive  226 , in particular pneumatic cylinder  226  and/or electric motor  226 , pulling and/or pushing the at least one print head  212  and/or the nozzle bar  213  that contains the at least one print head  212  against the at least one printing stop. This serves to ensure that the printing position is reproducibly and precisely defined. 
     At least one second locking element is preferably provided, for example at least one assembly stop. The at least one second locking element can preferably secure the at least one print head  212  in its assembly position, for example by the at least one positioning drive  226 , in particular pneumatic cylinder  226  and/or electric motor  226 , pulling and/or pushing the at least one print head  212  and/or the nozzle bar  213  that contains the at least one print head  212  against the at least one assembly stop. This serves to ensure that the assembly position is reproducibly and precisely defined. 
     At least one third locking element is preferably provided, for example at least one maintenance stop. The at least one third locking element can preferably secure the at least one print head  212  in its maintenance position, for example by the at least one positioning drive  226 , in particular pneumatic cylinder  226  and/or electric motor  226 , pulling and/or pushing the at least one print head  212  and/or the nozzle bar  213  that contains the at least one print head  212  against the at least one maintenance stop. This serves to ensure that the maintenance position is reproducibly and precisely defined. 
     At least one locking element, preferably the at least one third locking element and/or at least one locking element arranged between two locking elements and/or at least one maintenance stop is preferably embodied as movable, to enable movement between extreme positions of an actuating path of the at least one print head  212  and/or of the at least one nozzle bar  213 , in particular between printing position and assembly position. For example, at least one maintenance device  222  is embodied as at least one movable stop, in particular as a maintenance stop. 
     In the at least one maintenance position, at least one maintenance device  222  preferably is and/or can be assigned to at least one nozzle of the at least one print head  212 ;  412 , and more preferably, the at least one maintenance device  222  is and/or can be arranged at least partially opposite at least one nozzle of the at least one print head  212 ;  412  in terms of a respective ejecting direction of said at least one nozzle. 
     A location of said respective at least one nozzle when print head  212  is arranged in the at least one printing position and a location of said respective at least one nozzle when print head  212  is arranged in the at least one maintenance position and/or assembly position, with respect to axial direction A, which is defined by the rotational axis  207 ;  407  of the at least one printing material guiding element  201 ;  401 , preferably embodied as central cylinder  201 , preferably differ by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of a width, measured in axial direction A, of an operating region of a nozzle bar  213  that contains the at least one print head  212 ;  412 , and/or by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by a maximum printing material width that can be processed in said printing press  01 . 
     When print head  212  is arranged in the at least one maintenance position, at least one maintenance device  222  preferably can be and/or is arranged between at least one nozzle of the at least one print head  212 ;  412  and a region of the transport path, provided for printing material  02 , that is closest to said at least one nozzle, and/or, when print head  212  is arranged in the at least one maintenance position, at least one maintenance device  222  can be and/or is arranged between at least one nozzle of the at least one print head  212  and a region of a transfer element that is closest to said at least one nozzle. 
     The dimensions of the at least one maintenance device  222  in each spatial direction are preferably greater than 3 mm, more preferably greater than 10 mm. The dimension of the at least one maintenance device  222  in axial direction A is preferably at least as great as the operating region of the at least one nozzle bar  213  in axal direction A. The dimension of the at least one maintenance device  222  in a transport direction of printing material  02  is preferably at least as great as the operating region of the at least one nozzle bar  213  in the transport direction of printing material  02 . In this manner, all the nozzles of all the print heads  212  of the at least one nozzle bar  213  can preferably be maintained simultaneously. Marginal areas and/or the housing will result in even greater dimensions in some directions. 
     The at least one nozzle bar  213  can preferably be moved fully independently of components of printing press  01  that are arranged touching printing material web  02  and/or tangential to the provided transport path of printing material  02 . Thus cleaning and/or maintenance can be performed without affecting the printing material web  02  and particularly without having to remove printing material web  02  from printing press  01 . 
     The at least one maintenance device  222  is preferably movable at least orthogonally to axial direction A. A staging path of the at least one maintenance device  222  is preferably defined by at least one transport device  223 . 
     The at least one transport device  223  is preferably embodied as at least one guiding system  223 . The at least one maintenance device  222  is preferably arranged so as to be movable along the at least one staging path between at least one parked position and at least one operating position. The staging path of the at least one maintenance device  222 , which path is further preferably defined by the at least one transport device  223 , preferably has no component in axial direction A that is greater than a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width of the operating region, measured in axial direction A, of the nozzle bar  213  that contains the at least one print head  212 , and/or a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . This means that an optionally existing component of the staging path of the at least one maintenance device  222  in axial direction A is preferably a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width, measured in axial direction A, of the operating region of the nozzle bar  213  that contains the at least one print head  212 , and/or a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . 
     Thus an optionally provided portion of an axial movement of the at least one maintenance device  222 , assuming such movement is present, preferably amounts to a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width, measured in axial direction A, of the operating region of the nozzle bar  213  that contains the at least one print head  212 ;  412 , and/or a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . Further preferably, the at least one maintenance device  222  is movable exclusively orthogonally to axial direction A. The portion of a movement is particularly a length of a path traveled during said movement, and in this case is particularly only the length of a component of the path that is or will be traveled in axial direction A, assuming such a component is present. 
     A location of the at least one maintenance device  222  in its parked position, provided in relation to axial direction A, preferably differs from a location of the at least one maintenance device  222  in its operating position, provided in relation to axial direction A, by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of a width, measured in axial direction A, of an operating region of a nozzle bar  213  that contains the at least one print head  212 , and/or by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of a working width of printing press  01 , defined by a maximum printing material width that can be processed in printing press  01 . 
     Each maintenance device  222  preferably has at least one dedicated transport device  223 . The at least one transport device  223  preferably has at least one transport drive  229  and at least one pulling means  228  and/or pushing means  228 . In one embodiment, the at least one transport drive  229  is arranged stationary on a frame  231  of the at least one printing unit  200 ;  400 , and the at least one pulling means  228  and/or pushing means  228  is connected to the at least one maintenance device  222  and is embodied as movable relative to the frame  231  of the at least one printing unit  200 ;  400 , for example as a chain  228 . In an alternative embodiment, the at least one transport drive  229  is arranged so as to be movable, particularly together with the at least one maintenance device  222 , and the at least one pulling means  228  and/or pushing means  228  is arranged as stationary, and is embodied, for example, as at least one track  228  and/or toothed rack  228 . The at least one transport device  223  preferably has at least one rotatable threaded spindle, which is engaged with at least one spindle nut mounted on the respective maintenance device  222  and is arranged so as to rotate, for example by means of at least one transport drive  229  preferably embodied as a stepped motor  229 . 
     At least two maintenance devices  222 , which are and/or can be assigned, particularly by means of their respective transport devices  223 , to different print heads  212 ;  412  of the at least two, in particular at least four print heads, are preferably arranged with one at least partially above the other, at least in their respective parked positions. More preferably, these at least two maintenance devices  222 , which are and/or can be assigned, particularly by means of their respective transport devices  223 , to different print heads  212 ;  412  of the at least two, in particular at least four print heads, are arranged offset and/or spaced from one another in a direction orthogonal to axial direction A, at least in their operating positions. In a preferred embodiment, four nozzle bars  213 ;  413  are provided, each of which is arranged so as to be movable out of its printing position in a respective linear actuating direction by means of a respective positioning device  217 ;  218 ;  219 ;  221 . More preferably, four maintenance devices  222  embodied as cleaning devices  222  are provided and can be moved individually between parked position and operating position by means of respective transport devices  223 . Each of the respective transport devices  223  preferably has two tracks  228  arranged on opposite sides of the frame  231 . Each of the respective transport devices  223  preferably has at least one transport drive  229  or two transport drives  229  arranged on opposite sides of the frame  231 . The maintenance devices  222  are preferably arranged symmetrically around a plane of symmetry that contains the entire rotational axis  207 ;  407  of the at least one printing material guiding element  201 ;  401 . The four staging paths preferably extend horizontally and at a total of two different heights. The maintenance devices  222  are arranged at a higher level than the tracks  228  assigned to them, for example. 
     The respective assembly positions of two and more preferably of all nozzle bars  213 ;  413  are preferably arranged at the same height and therefore at different distances from the corresponding printing positions. The respective maintenance positions of two nozzle bars  213 ;  413  are preferably arranged at a first common height, which differs from a second common height at which the respective maintenance positions of the other two nozzle bars  213 ;  413  are arranged. These heights differ by at least five centimeters, for example. Sufficient space is thereby provided for all the maintenance devices  222  in their respective operating positions because the heights of these operating positions are different and therefore the volumes required by the different maintenance devices  222  do not collide. 
     A unique maintenance position is preferably assigned to the at least one print head  212  and more preferably to each print head  212 . When the at least one maintenance device  222  is located in its operating position, it serves, for example, as the third locking element, for example in the form of at least one maintenance stop. When a print head  212  is located in its maintenance position, the nozzle bar  213  that contains the corresponding print head  212  is preferably pulled and/or pushed against the maintenance device by a force exerted by means of the at least one positioning drive  226  and/or by the force of gravity, in particular when positioning drive  226  is switched off. The maintenance position is thereby clearly defined. Alternatively and preferably, each positioning drive  226  has at least one stepped motor, by means of which the respective maintenance device  222  can be moved into unique positions. As a result, a positioning drive  226  and a transport drive  229  are sufficient for reproducibly and precisely positioning the print heads  212  in their printing positions, maintenance positions and assembly positions. 
     A unique operating position of at least one and preferably of precisely one maintenance device  222  is preferably assigned to each maintenance position of at least one print head  212 . For example, the at least one maintenance device  222  is embodied as at least one protective cover  222 , which can more preferably be used to delimit an isolated volume together with the at least one print head  212 ;  412 . The at least one maintenance device  222  is preferably additionally or alternatively embodied as at least one cleaning device  222 . The at least one maintenance device  222  is preferably embodied as at least one inspection device  222 . 
     In a first embodiment, by way of example, at least two or at least three operating positions and/or at least one parked position in which the respective maintenance device  222 , and more preferably optionally different maintenance devices  222  are and/or can be arranged can be assigned to the at least one maintenance device  222 . For a total of four nozzle bars  213  of a printing unit  200 ;  400 , for example, a total of two maintenance devices  222  are provided, each of which is equipped with at least two regions that serve and/or can be used as a protective cover, and each of which or at least one of which is equipped with a region that serves as a cleaning region. The at least one cleaning region can then be assigned in succession to the nozzle bars  213  to be cleaned, whereupon the nozzles of the respective nozzle bar  213  are cleaned. Once all the necessary cleaning steps have been completed, the at least one maintenance device  222  can be positioned such that each of its two regions that serve as a protective cover is assigned to one nozzle bar  213 , and said nozzle bars are then lowered onto the common maintenance device  222 , preferably following deactivation of the respective positioning drives  226 . Each region that serves as a protective cover can selectively be assigned to different nozzle bars  213 , for example, enabling some nozzle bars  213  to be arranged in the printing position while at the same time other nozzle bars are covered, to protect them against drying out, for example. 
     Preferably, however, each nozzle bar  213  is and/or can be assigned its own maintenance device  222 , and/or precisely one operating position and precisely one parked position in which the respective maintenance device  222  is and/or can be arranged are assigned to each maintenance device  222 . For a total of four nozzle bars  213  of a printing unit  200 ;  400 , a total of four maintenance devices  222  are preferably provided, each being equipped with a region that serves and/or can be used as a protective cover  222 , and each being embodied as a cleaning device  222 . Once all the necessary cleaning steps have been completed, the at least one maintenance device  222  can be positioned such that each of its regions that serve as a protective cover  222  is assigned to a nozzle bar  213 , and said nozzle bars are then lowered onto the common maintenance device  222 , for example during deactivation of the respective positioning drives  226 , or are held in their maintenance position by shutting off the respective positioning drives  226 . A cleaning is preferably carried out, for example, during which the respective maintenance device  222  serves as a protective cover  222 , and/or during which a cleaning region and a region that serves as a protective cover  222  are identical. Each maintenance device  222  that serves as a protective cover  222  can be assigned, selectively and independently of other maintenance devices  222 , to said respective nozzle bar  213 , for example, enabling some nozzle bars  213  to be arranged in the printing position while other nozzle bars  213  are covered and protected against drying out, for example. 
     The at least one maintenance device  222  is preferably embodied as at least one cleaning device  222 . The at least one cleaning device  222  preferably has at least one cleaning module, in particular at least one cleaning module that can be moved in and/or counter to axial direction A relative to the at least one print head  212 ;  412 , by means of at least one cleaning drive. The at least one cleaning module preferably has at least one contact element, which can be placed in contact by means of at least one actuating drive with at least one nozzle surface of the at least one print head  212 ;  412 , at least when cleaning device  222  is located in its operating position and the corresponding print head is located in its maintenance position. The at least one cleaning module preferably has at least one first device for dispensing cleaning agent, for example at least one spray nozzle, which is and/or can be directed toward the at least one print head  212 ;  412  and/or toward the at least one contact element. The at least one contact element is preferably embodied as at least one wiper. 
     When at least one print head  212  is arranged in the printing position, at least one nozzle of said at least one print head  212  is preferably located below the staging path along which the at least one maintenance device  222  is preferably arranged so as to move, preferably between the at least one parked position and the at least one operating position, preferably by means of the at least one transport device  223 . When the at least one print head  212  is arranged in the idle position, said at least one nozzle is preferably located above said staging path. 
     An actuating path of at least one print head  212  is preferably a preferably predetermined path along which the at least one print head  212  can be moved, in particular to move the at least one print head  212  between its printing position and its idle position, for example maintenance position and/or assembly position. The actuating path of the at least one print head  212  preferably has no component in axial direction A that is greater than a maximum of 50%, more preferably a maximum of 20%, even more preferably 10% and more preferably still a maximum of 2% of the width of the operating region, measured in axial direction A, of the nozzle bar  213  that contains the at least one print head  212 , and/or a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . This means that an optionally provided component of the at least one print head  212  in axial direction A is preferably a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width, measured in axial direction A, of the operating region of the nozzle bar  213  that contains the at least one print head  212 , and/or a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . 
     Preferably, at least a first of the at least two print heads  212 , in particular of first printing unit  200 , can selectively be placed, preferably by means of a first positioning device  217  assigned to said print head, at least either in the first printing position assigned to said print head or in a first idle position, in particular maintenance position and/or assembly position, assigned to said print head, wherein in the at least one first idle position, an idle location of at least one first nozzle of the at least one first of the at least two print heads  212  is spaced by a first idle distance, in particular a maintenance distance and/or an assembly distance, from a first operating location of the same at least one first nozzle of the same at least one first of the at least two print heads  212  in its first printing position. Preferably, at least a second of the at least two print heads  212 , in particular of said first printing unit  200 , can selectively be placed, preferably by means of a respective second positioning device  218  assigned to said print head, at least either in a second printing position assigned to said print head or in a second idle position, in particular maintenance position and/or assembly position, assigned to said print head, wherein in the at least one second idle position, an idle location of at least one second nozzle of the at least one second of the at least two print heads  212  is spaced by a second idle distance, in particular maintenance distance and/or assembly distance, from a second operating location of the same at least one second nozzle of the same at least one second of the at least two print heads  212  in its second printing position. The first idle distance, in particular maintenance distance and/or assembly distance, preferably differs from the second idle distance, in particular maintenance distance and/or assembly distance, by at least 2 cm, more preferably at least 5 cm, even more preferably at least 10 cm and more preferably still at least 20 cm. An idle distance is particularly a distance between a location of a nozzle when the print head  212  that contains said nozzle is arranged in its idle position and a location of the same nozzle when the same print head  212  is arranged in its printing position. 
     In particular, the at least one first print head  212  can preferably be selectively placed, by means of at least one first positioning device  217  assigned to said print head, at least either in a first printing position assigned to said print head or in a first idle position, in particular a first maintenance position and/or a first assembly position, assigned to said print head. In particular, the at least one second print head  212  can preferably be selectively placed, by means of at least one second positioning device  218  assigned to said print head, at least either in a second printing position assigned to said print head or in a second idle position, in particular a second maintenance position and/or a second assembly position, assigned to said print head. 
     Thus printing press  01  and more preferably each printing unit  200 ;  400  preferably has at least two positioning devices  217 ;  218 ;  219 ;  221 , to each of which at least one of the at least two print heads  212 ;  412  is assigned, and by means of which each of the at least two print heads  212 ;  412  can be moved and can be selectively placed at least either in a respective printing position and/or in at least one respective idle position, for example a maintenance position and/or an assembly position. More preferably, each printing unit  200 ;  400  has at least four such positioning devices  217 ;  218 ;  219 ;  221 . 
     Preferably, a minimum distance between the at least one first nozzle of the at least one first print head  212 ;  412  in its first idle position, in particular a maintenance position and/or an assembly position, and the at least one second nozzle of the at least one second print head  212 ;  412  in its second idle position, in particular a maintenance position and/or an assembly position, preferably referred to as the idle distance, in particular maintenance distance and/or assembly distance, is at least 2 cm, more preferably at least 5 cm, even more preferably at least 10 cm and more preferably still at least 20 cm greater than a minimum distance between at least the at least one first nozzle of the at least one first print head  212 ;  412  in its first printing position and the at least one second nozzle of the at least one second print head  212 ;  412  in its second printing position, preferably referred to as the operating distance. 
     An ejecting direction of at least one first nozzle of the at least one first print head  212 ;  412  in the first printing position differs from an ejecting direction of said at least one first nozzle of the at least one print head  212 ;  412  in the first idle position, in particular maintenance position and/or assembly position, by an angle of at least 5°, more preferably at least 10°, even more preferably at least 15° and more preferably still at least 20°, for example. A location of the at least one nozzle when print head  212  is arranged in the at least one printing position and a location of the at least one nozzle when print head  212  is arranged in the at least one idle position, in particular the maintenance position and/or the assembly position, with respect to axial direction A, defined by rotational axis  207  of the at least one printing material guiding element  201 , preferably differ by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the width, measured in axial direction A, of the operating region of the nozzle bar  213  that contains the at least one print head  212 , and/or by a maximum of 50%, more preferably a maximum of 20%, even more preferably a maximum of 10% and more preferably still a maximum of 2% of the working width of printing press  01 , defined by the maximum printing material width that can be processed in printing press  01 . A plane in which this distance and/or this angle is measured is preferably defined by a surface normal which extends parallel to the axial direction A or deviates from said axial direction A by a maximum of 2°; more preferably, said plane is the axial projection plane. 
     Said printing press preferably enables a process for positioning at least one print head  212 , embodied as an inkjet print head  212 , of at least one printing unit  200 ;  400  of printing press  01 , wherein in a throw-off process, at least one print head  212  of the at least one printing unit  200 ;  400  is moved in at least one actuating direction and/or along an actuating path away from a printing position into at least one idle position, in particular a maintenance position and/or an assembly position, and/or is moved away from a provided transport path of the at least one printing material web  02  and/or is moved away from a printing material guiding element  201  and/or is moved away from a transfer element, and wherein said at least one actuating direction is preferably oriented at least partially and more preferably fully orthogonally to an axial direction A, defined by rotational axis  207  of the at least one printing material guiding element  201 . 
     At least one threading means which is movable along at least one threading path for threading in a printing material web  02  and/or at least one threading means which is movable along at least one provided transport path of printing material web  02  for threading in a printing material web  02  preferably is and/or can be arranged, at least intermittently, at least within one printing unit  200 ;  400  of printing press  01 . Preferably, particularly as described, the at least one print head  212 ;  412  is embodied as movable along an actuating path in an actuating direction, the actuating direction preferably having at least one component which is oriented orthogonally to an axial direction A defined by the rotational axis  207 ;  407  of the at least one printing material guiding element  201 ;  401 . At least parts of the at least one threading path, and more preferably the entire threading path, preferably are/is spaced, with respect to axial direction A, from every target region of every nozzle of every print head  212 ;  412  of said printing unit  200 ;  400  by a distance of at least 2 cm, more preferably at least 4 cm, even more preferably at least 6 cm and more preferably still at least 8 cm. At least parts of the threading means and more preferably the entire threading means preferably are/is spaced, with respect to axial direction A, from every target region of every nozzle of every print head  212 ;  412  of said printing unit  200 ;  400  by a distance of at least 2 cm, more preferably at least 4 cm, even more preferably at least 6 cm and more preferably still at least 8 cm. 
     In particular, the at least one threading path and/or the at least one threading means is preferably arranged outside the operating region of a nozzle bar  213  that contains the at least one print head  212 , and/or outside a working width of printing press  01 , with respect to axial direction A. The actuating direction of the at least one print head  212  preferably has at least one component in a direction of a normal vector of a surface element, closest to the at least one print head  212 ;  412 , of the provided transport path of printing material web  02 . This means that the at least one print head  212  is arranged such that it can be moved away from and/or thrown off of the provided transport path, in particular for threading a printing material web  02  into printing press  01  and/or in particular by means of at least one positioning device  217 ;  218 ;  219 ;  221 . Preferably, printing press  01  at least intermittently and more preferably permanently has at least one and more preferably precisely one threading means for threading in a printing material web  02  along a provided transport path of printing material web  02 . 
     At least one printing material web  02  preferably is and/or can be connected via at least one connecting element, more preferably embodied as at least one threading tip, to the at least one threading means, in particular regardless of whether the at least one threading means is embodied as a threading belt and/or a threading chain and/or as a continuous threading means and/or a finite threading means. A threading tip is preferably a flat means, the smallest dimension of which preferably measures less than 5 mm, and which is preferably substantially triangular in shape, and along one edge of which a bonding agent and/or adhesive agent is preferably provided, and which preferably has at least one fastening means at a tip that is opposite said edge. The bonding agent and/or adhesive agent preferably serves to connect the threading tip to a printing material  02 . The at least one fastening means preferably serves to detachably secure the threading tip to the at least one threading means. 
     The at least one threading means is preferably embodied as at least one continuous threading means, for example as at least one continuous threading belt. Alternatively, the at least one threading means is embodied as at least one finite threading means, for example as a finite threading belt and/or as a finite threading chain. Once a threading process is completed, a finite threading belt is preferably wound back up, that is, it is moved in the opposite direction along the threading path. At least one threading drive is preferably provided, which can be used for moving the at least one threading means along the at least one threading path. In the case of a continuous threading means, it is sufficient for precisely one such threading drive to be provided, for example. Alternatively, the at least one threading means is embodied as finite. In that case, at least one threading storage device is preferably provided, in which the at least one threading means can be at least intermittently arranged, particularly as long as it is not being used for threading a printing material web  02 . In an alternative embodiment, the at least one threading means is embodied as at least one finite threading chain. In the preferred case of the at least one finite threading means, the at least one threading means for threading in a printing material web  02  along the provided transport path of printing material web  02  is preferably arranged, particularly permanently, along its at least one threading path within printing press  01 . More preferably, the at least one threading means for threading in a printing material web  02  along the provided transport path of printing material web  02  is particularly arranged permanently along its at least one threading path within the at least one printing unit  200 ;  400  of printing press  01 . 
     At least one threading guide element is preferably provided, by means of which at least one threading path of the at least one threading means can be and/or is defined. The at least one threading guide element is embodied, for example, as at least one turning roller. Alternatively, the at least one threading guide element is embodied as at least one chain guide. Preferably, the at least one threading guide element is embodied as at least one rotatable threading guide element, for example as at least one turning roller. The at least one rotatable threading guide element and particularly the at least one turning roller is preferably arranged so as to rotate around the same rotational axis  207 ;  407  as at least one printing material guiding element  201 ;  401  of a printing unit  200 ;  400  of printing press  01 , for example the same rotational axis as the at least one central cylinder  201 ;  401 . A chain guide, in particular, can also have switching points for producing different threading paths. 
     The at least one preferably continuous threading means preferably has, in each case, at least two and more preferably at least five designated connecting points, at which at least one printing material web  02  can be connected directly and/or via at least one connecting element, for example, a threading tip, to the at least one threading means. The at least two and more preferably at least five connecting points are preferably spaced with respect to axial direction A by a maximum distance of 10 cm (ten centimeters), more preferably a maximum of 5 cm (five centimeters), even more preferably a maximum of 2 cm (two centimeters) and more preferably still by no distance at all. Even more preferably, the at least two and more preferably at least five connecting points are arranged in the same position with respect to axial direction A. The at least two and more preferably at least five connecting points are preferably spaced from one another along the at least one and preferably precisely one threading path, more preferably by at least 10 cm (ten centimeters), even more preferably by at least 50 cm (fifty centimeters) and more preferably still by at least 100 cm (one hundred centimeters). The at least one threading means has connecting points embodied as eyes and/or hooks, for example, and/or the at least one connecting element accordingly has at least one hook and/or at least one eye. One such hook and/or one such eye forms the at least one fastening means, for example. 
     The threading path of the at least one threading means preferably wraps around the at least one rotatable printing material guiding element  201 ;  401 , more preferably embodied as at least one central cylinder  201 ;  401 , over an angular range of at least 180° and more preferably of at least 270° as viewed from a rotational axis  207 ;  407  of the at least one printing material guiding element  201 ;  401 , and/or as viewed in the axial projection plane. The threading path of the at least one threading means, at least along this angular range, preferably has a radius of curvature that deviates a maximum of 5 cm, more preferably a maximum of 2 cm and even more preferably a maximum of 1 cm from a radius of curvature of this at least one printing material guiding element  201 ;  401 , in particular this central cylinder  201 ;  401 . 
     A projection, particularly in the axial projection plane, of the transport path provided for printing material  02  in axial direction A and a projection, particularly in the axial projection plane, of the threading path provided for the at least one threading means in axial direction A preferably overlap at least partially, more preferably over more than 25% of the length of the projection of the threading path provided for the threading means, and even more preferably over more than 50% of this length. 
     This printing press preferably enables a method for threading at least one printing material web  02  into at least one printing unit  200 ;  400  of printing press  01 , wherein in a throw off process, at least one print head  212 , embodied as an inkjet print head  212 , of the at least one printing unit  200 ;  400  is moved in at least one actuating direction and/or along one actuating path away from a provided transport path of the at least one printing material web  02 , and wherein this at least one actuating direction is preferably oriented at least partially and more preferably fully orthogonally to an axial direction A defined by rotational axis  207  of the at least one printing material guiding element  201 , and wherein in a subsequent threading in process, at least one threading means is moved along a threading path through the at least one printing unit  200 ;  400 , thereby drawing the at least one printing material web  02  along a provided transport path for the at least one printing material web  02 , and wherein the threading path and the transport path, as viewed in the axial direction A, are spaced from one another, preferably by at least 2 cm, more preferably by at least 4 cm, even more preferably by at least 6 cm and more preferably still by at least 8 cm. For threading in the at least one printing material web  02 , it is not necessary to move the at least one print head  212  all the way to its maintenance position and/or its assembly position in the throw-off process. It is sufficient merely to protect the at least one print head  212  from damage, as long as it is spaced a sufficient distance from printing material  02  and/or from the connecting element. In a subsequent throw-on process, the at least one print head  212  is preferably moved opposite the at least one actuating direction and/or along an actuating path toward the provided transport path of the at least one printing material web  02  and/or is positioned in its printing position. 
     In a connecting process, particularly prior to the threading process, the at least one threading means is preferably connected to the at least one printing material web  02  by means of at least one connecting element. In the connecting process, the at least one threading means is preferably connected by means of the at least one connecting element to the printing material web at precisely one of the at least two, more preferably at least five connecting points provided on the at least one threading means. The at least one connecting element preferably passes through a printing position of the at least one print head  212  while said print head is moved away from the provided transport path and/or is arranged in at least one idle position. During the threading process, the at least one connecting element preferably passes through at least one target region of at least one nozzle of the at least one print head  212 . During the threading process, preferably no component of the at least one threading means passes through any target region of any nozzle of the at least one print head  212 . This means that all of the components of the at least one threading means preferably bypass every target region of every nozzle of the at least one print head  212 . 
     This results in at least one operating mode in which the at least one threading means is connected to printing material  02  by means of the at least one connecting element, and in which the at least one print head  212  is moved away from the provided transport path and/or is arranged in at least one idle position, and in which at least one nozzle is preferably oriented with its ejecting direction toward the at least one connecting element. In said at least one operating mode, the at least one connecting element is preferably in contact with the at least one printing material guiding element  201 , in particular with the at least one central cylinder  201 . 
     Alternatively or additionally, in said at least one operating mode, the at least one connecting element is preferably in contact with at least one transfer element. In this operating mode, the at least one threading means is preferably spaced a distance of at least 2 cm, more preferably at least 4 cm, even more preferably at least 6 cm, and more preferably still at least 8 cm with respect to axial direction A from every target region of every nozzle of every print head  212 ;  412  of said printing unit  200 ;  400 . 
     Preferably, only at least one threading means is provided, said threading means being arranged on only one side of the provided transport path for printing material  02 , with respect to axial direction A, and/or the threading path of said threading means extending on only one side of the provided transport path for printing material  02 . Preferably, only at least one threading means is used, said threading means being arranged on only one side of the provided transport path for printing material  02 , with respect to axial direction A, and/or the threading path of said threading means extending on only one side of the provided transport path for printing material  02 . 
     Once printing material web  02  has passed the at least one first printing unit  200 , printing material web  02  is transported further along its transport path and is preferably fed to the at least one first dryer  301  of the at least one dryer unit  300 . The first side of printing material web  02 , which has been imprinted by the at least one first printing unit  200 , preferably is not in contact with any component of web-fed printing press  01  between a last point of contact of printing material web  02  with the at least one first central cylinder  201  of the at least one first printing unit  200  and an area of action of the at least one first dryer  301 . The second side of printing material web  02 , which particularly has not been imprinted by first printing unit  200  and which is in contact with the at least one first central cylinder  201  of the at least one first printing unit  200 , is preferably in contact with at least one turning roller  214  of the at least one first printing unit  200  and/or with at least one turning roller  312  of the at least one first dryer  301 , between the last point of contact of printing material web  02  with first central cylinder  201  of the at least one first printing unit  200  and the area of action of the at least one first dryer  301 . At least one third measuring device  214 , more preferably embodied as a third measuring roller  214 , is preferably provided. This third measuring device  214  is used to measure web tension. Further preferably, the at least one turning roller  214  of first printing unit  200  is identical to the third measuring device  214  embodied as the third measuring roller  214 . 
     The at least one first dryer  301  is preferably embodied as an infrared radiation dryer  301 . The at least one first dryer  301  preferably has at least one radiation source  302 , preferably embodied as an infrared radiation source  302 . A radiation source  302 , preferably an infrared radiation source  302 , in this case is a device by means of which electrical energy is and/or can be purposely converted to radiation, preferably infrared radiation, and is and/or can be directed toward printing material web  02 . The at least one radiation source  302  preferably has a defined area of action. The area of action of a radiation source  302  is particularly the area that contains every point that can be connected, in a straight line and without interruption, directly or via reflectors to the radiation source  302 . The area of action of the at least one first dryer  301  is composed of the areas of action of all radiation sources  302  of the at least one first dryer  301 . The area of action of the at least one first dryer  301  preferably points from the at least one radiation source  302  to a part of the transport path of printing material web  02  that is closest to the at least one radiation source  302 . Air is introduced into the interior of the at least one first dryer  301  through at least one ventilation opening. Inside first dryer  301 , water and/or solvent from the printing inks to be removed from printing material web  02  is removed by means of the infrared radiation and is absorbed into the introduced air. This air is then removed from the at least one first dryer  301  through at least one venting opening. 
     In a preferred embodiment, the provided transport path for printing material  02  through the at least one first dryer  301  has at least two sub-sections, each extending in directions that have vertical components, more preferably greater vertical components than any optionally provided horizontal components. The provided transport path of the printing material along the one sub-section preferably extends with at least one component in an upward vertical direction. The provided transport path of the printing material along the other sub-section preferably extends with at least one component in a downward vertical direction. The one sub-section and the other sub-section of the provided transport path are preferably connected to one another by means of at least one provided connecting section of the provided transport path. The at least one connecting section preferably extends in a direction having a horizontal component, more preferably having a greater horizontal component than an optionally provided vertical component. As a result, the at least one dryer  301  can preferably be particularly compact in configuration. 
     At least one first cooling unit  303  is preferably arranged downstream of the area of action of the at least one radiation source  302  of the at least one first dryer  301  in the direction of transport of printing material web  02 . The at least one first cooling unit  303  preferably comprises at least one first cooling roller  304  and preferably a first cooling pressure roller  306 , which can be and/or is thrown onto the at least one first cooling roller  304 , and preferably comprises at least one turning roller  307 ;  308  that can be and/or is thrown onto the at least one first cooling roller  304 . A first drive motor  311 , embodied as a first cooling roller drive motor  311  and assigned to the at least one first cooling roller  304 , and the first cooling pressure roller  306  are preferably part of a web tension adjusting unit, that is, they are arranged so as to adjust the web tension and for this purpose are preferably connected at least partially and/or intermittently to the higher level machine controller. The at least one first cooling roller  304  preferably represents at least one fourth motor-driven rotational body  304 . Printing material web  02  wraps around and contacts, preferably along its transport path, the at least one first cooling roller  304  with a wrap angle of preferably at least 180° and more preferably at least 270°. The first cooling pressure roller  306  and the at least one first cooling roller  304  together preferably form a first cooling nip  309 , in which printing material web  02  is preferably arranged and/or through which printing material web  02  preferably passes. Printing material web  02  is thereby pressed by cooling pressure roller  306  against the at least one first cooling roller  304 . The at least one first cooling roller  304  of the at least one first cooling unit  303  is preferably embodied as a cooling roller  304  through which a coolant flows. 
     Along the transport path of printing material web  02 , downstream of the at least one first cooling unit  303 , at least one second printing unit  400  is preferably arranged. Along the transport path of printing material web  02 , preferably immediately upstream of the at least one second printing unit  400  and preferably downstream of the at least one first dryer  301 , and particularly downstream of the at least one first printing unit  200 , at least one second web edge aligner, which can preferably be controlled and/or regulated manually or automatically, is preferably provided. The at least one second printing unit  400  is similar in configuration to first printing unit  200 . In particular, second printing unit  400  has a second central printing cylinder  401 , or a central cylinder  401 , around which printing material  02  wraps during printing operation, likewise with a wrap angle of preferably at least 180° and more preferably at least 270°. Second central cylinder  401  preferably represents a fifth motor-driven rotational body  401 . The rotational direction of second central cylinder  401  of second printing unit  400  is preferably opposite the rotational direction of the at least one first central cylinder  201 . Along the transport path of printing material web  02  upstream of second central cylinder  401  of second printing unit  400 , a second printing material cleaning device  402  or web cleaning device  402  is preferably arranged so as to act on printing material web  02 . 
     The transport path of printing material web  02  through the at least one second printing unit  400  extends similarly to the transport path through the at least one first printing unit  200 . In particular, printing material web  02  preferably wraps around part of a second turning roller  403  and is turned by said roller such that the transport path of printing material web  02  in the second gap  404  extends both tangentially to second turning roller  403  and tangentially to second central cylinder  401 . At least one cylinder  406 , embodied as a second impression cylinder  406 , is preferably arranged in second printing unit  400 . Second impression cylinder  406  is preferably similar in configuration and arrangement to first impression cylinder  206 , particularly in terms of its movability and in terms of a second impression nip  409 . Second central cylinder  401  is preferably similar in arrangement and configuration to first central cylinder  201 , particularly with respect to a second drive motor  408  of second central cylinder  401  and with respect to a corresponding preferably provided second rotational angle sensor, which is embodied to measure and/or be capable of measuring the angular position of second drive motor  408  and/or of second central cylinder  401  itself and to transmit and/or be capable of transmitting this measurement to the higher level machine controller. 
     Within second printing unit  400 , at least one second printing element  411 , embodied as an inkjet printing element  411  or ink-jet printing element  411 , is preferably arranged downstream of second impression cylinder  406  in the direction of rotation of second central cylinder  401 , and therefore along the transport path of printing material web  02 , aligned toward second central cylinder  401 . The at least one second printing element  411  of the at least one second printing unit  400  is preferably identical to the at least one first printing element  211  of the at least one first printing unit  200 , particularly with respect to at least one nozzle bar  413 , at least one print head  412  embodied as an inkjet print head  412  and the arrangement thereof in double rows, the implementation and resolution of the printing process, the arrangement, alignment and actuation of the nozzles and the movability and adjustability of the at least one nozzle bar  413  and the at least one print head  412  by means of at least one adjustment mechanism having a corresponding electric motor. A similar protective cover and/or cleaning device is also preferably provided. The proper alignment of the print heads  412  of the at least one second printing unit  400  is also preferably monitored by at least one sensor which detects a printed image and the machine controller which evaluates said printed image. This at least one sensor is preferably at least one second printed image sensor, which is similar in embodiment to the at least one first printed image sensor. The at least one second printing element  411  is preferably embodied as a four-color printing element  411 . 
     At least one second dryer  331  is arranged downstream of the at least one second printing unit  400  with respect to the transport path of printing material web  02 . Once printing material web  02  has passed through the at least one second printing unit  400 , printing material web  02  is transported further along its transport path and is preferably fed to the at least one second dryer  331  of the at least one dryer unit  300 . The at least one second dryer  331  is preferably similar in configuration to the at least one first dryer  301 . The at least one first dryer  301  and the at least one second dryer  331  are components of the at least one dryer unit  300 . The second side of printing material web  02 , which has been imprinted by the at least one second printing unit  400 , is preferably not in contact with any component of web-fed printing press  01  between a last point of contact of printing material web  02  with second central cylinder  401  of the at least one second printing unit  400  and an area of action of the at least one second dryer  301 . At least one turning roller  414  is preferably provided in second printing unit  400 . Said at least one turning roller  414  is preferably embodied as a fifth measuring device  414 , in particular a fifth measuring roller  414 . 
     The configuration of the at least one second dryer  331  is similar to the configuration of the at least one first dryer  301 , particularly with respect to a transport path provided for printing material and/or with respect to its embodiment as an air flow dryer  331  and/or a radiation dryer  331  and/or a hot air dryer  331  and/or an infrared radiation dryer  331  and/or a UV radiation dryer  331 . In particular, the at least one second dryer  331  preferably has at least one second cooling roller  334 , which preferably represents at least one sixth motor-driven rotational body  334 . The second cooling roller  334  preferably is and/or can be driven by means of a second cooling roller drive  341 . The at least one second dryer  331  is preferably substantially and more preferably fully symmetrical in configuration to the at least one first dryer  301 . The at least one second dryer  331  is preferably part of the same dryer unit  300  as the at least one first dryer  301  and is more preferably arranged in the same housing  329 . In terms of a spatial arrangement, dryer unit  300 , and therefore preferably the at least one first dryer  301  and the at least one second dryer  331 , is preferably arranged between the at least one first printing unit  200  and the at least one second printing unit  400 . 
     Along the transport path of printing material web  02 , downstream of the at least one second dryer  331 , at least one outfeed roller  501  is provided. The at least one outfeed roller  501  preferably has its own drive motor  504 , embodied as outfeed roller drive  504 . The at least one outfeed roller  504  preferably represents at least one seventh motor-driven rotational body  504 . The at least one outfeed roller  501 , preferably together with an outfeed pressure roller  502  that is and/or can be thrown onto the at least one outfeed roller  501 , forms an outfeed nip  503 , in which printing material web  02  is clamped and through which printing material web  02  is transported. Outfeed nip  503  preferably serves to regulate web tension and/or to transport printing material web  02 . 
     With respect to the transport path of printing material web  02  upstream and/or downstream of outfeed roller  501 , but particularly along the transport path of printing material  02  downstream of the at least one first dryer  301 , at least one rewetting unit is preferably provided, which preferably compensates for any excess loss of moisture in printing material web  02  as a result of treatment by dryer unit  300 . 
     Along the transport path of printing material web  02  downstream of outfeed nip  503  and/or downstream of the rewetting unit, at least one post-processing unit  500  is arranged, which is preferably embodied as a folding apparatus  500  and/or has a sheet cutter  500  and/or a planar delivery unit  500 , or is embodied as a winding apparatus  500 . In and/or by means of this post-processing unit  500 , printing material web  02  is preferably folded and/or cut and/or stitched and/or sorted and/or inserted and/or transported and/or wound. 
     In at least one variant of the printing press, printing press  01  is embodied as a web-fed rotary inkjet printing press  01 , and at least one transfer element is arranged so as to form a transfer nip with the at least one first central printing cylinder  201 . In that case, the at least one print head  212  is preferably aligned toward the at least one transfer element. 
     While preferred embodiments of a printing machine 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 could be made in the printing machine without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the appended claims.