Abstract:
A printer has a printing drum with recesses on the surface thereof into which ink is provided for printing. After printing, any remaining ink is removed at a cleaning station including immersion in a fluid, air jets, or an air suction. The cleaning station and the inking station operate simultaneously.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed to a method for printing a carrier material, whereby a printing drum with a plurality of depressions arranged on the surface of the printing drum for the acceptance of printing fluid turns around its longitudinal axis during a printing event. With the assistance of an inking station, printing fluid is introduced during the printing event into all depressions that move past the inking station. At a transfer printing location, the printing fluid contained in some of the depressions moving past the transfer printing location is employed for printing the carrier material. The printing fluid in the other depressions moving past the transfer printing location remains in the depressions. 
   2. Description of the Related Art 
   European Letters Patent EP 0 756 544 B1 discloses a thermoelectric printing unit for the transfer of an ink onto a recording medium. An inking station, a transfer printing station and a cleaning station are arranged around a printing drum having a plurality of depressions for the acceptance of ink. Only the inking station and the transfer printing station are in operation during the printing event. The depressions proceed to the inking station after they have passed by the transfer printing station. Printing fluid is re-introduced into the emptied depressions at the inking station. The cleaning station is actuated only after the end of the printing event. German Patent Document DE 295 07 416 U1, discloses a rotogravure unit wherein a rotogravure printing cylinder has ink-accepting depressions at image locations and no such depressions at non-imaging locations. The depressions are filled with ink at an inking station. This ink is transferred onto a rubber cylinder for later transfer onto paper. Subsequently, the ink residues are washed from the depressions of the image locations on the rotogravure printing cylinder with the assistance of a water jet and are thus removed. 
   German Patent Document DE 195 44 099 A1 discloses a thermographic printer device wherein a glass cylinder has a cup structure on its generated surface, the cups thereof being filled with ink. The ink in the cups is solidified with the assistance of a cooling device. In a printing zone, the ink in selected cups is melted with the assistance of laser light dependent on the image structure to be printed and is transferred onto paper. A doctor blade strips the residues of the ink from the surface of the inking cylinder, the cups thereof being subsequently re-filled with ink. 
   German Patent Document DE 195 03 951 A1 discloses a rotogravure method, whereby a rotogravure printing cylinder is filled with ink in depressions at imaging locations, said ink being directly printed onto a carrier material. After the printing event, the specific depressions are cleaned of ink residues and re-filled with ink for a further printing event. 
   German Patent Document DE 16 11 272 C2, further, discloses an offset rotary printing press that has a printing cylinder on whose generated surface a planographic form is chucked. This planographic form accepts ink in depressions that correspond to image locations to be inked, the ink being supplied via an ink application roller. The ink that is not picked up by the printing cylinder is removed from the ink application roller and is supplied to the ink circulation. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide a method for printing a carrier material that is simple and enables a printing with high printing quality. Moreover, a printer device suitable for the implementation of the method should be recited. 
   The object relating to the method is achieved with the method steps for printing a carrier material, whereby a printing drum having a plurality of depressions for the acceptance of printing fluid arranged on the surface of the printing drum rotates around its longitudinal axis during a printing event, printing fluid is introduced by an inking station into depressions moving past the inking station, printing fluid from some of the depressions moving past a transfer printing location is employed at the transfer printing station for printing the carrier material, and printing fluid remains in the rest of the depressions, printing fluid is removed by a cleaning station from depressions moving past the cleaning station, and whereby the cleaning station and the inking station are simultaneously in operation during the printing event. 
   In the preferred method, the cleaning station contains a cleaning drum that lies parallel to the printing drum and whose surface touches the surface of the printing drum in a cleaning region during cleaning; and the surface of the cleaning drum is manufactured of an elastic or absorbent material. The cleaning drum may carry a potential that differs from a potential on the surface of the printing drum. Specifically, the cleaning station contains a stripper drum that lies parallel to the cleaning drum and whose surface exerts pressure onto the surface of the cleaning drum in a stripping region; and the surface of the stripper drum is fabricated of a hard material. In one embodiment, the emptied depressions are cleaned with a cleaning fluid after the removal of the printing fluid from depressions moving past the cleaning station and before the introduction of printing fluid into depressions moving past the inking station. The cleaning station can contain a cleaning container with a cleaning fluid that is preferably arranged under the printing drum; and depressions moving past the cleaning container are immerse into the cleaning fluid. As a further development of the invention, the printing fluid is employed as the cleaning fluid. The cleaning fluid may be moved by additional measures, preferably by introduction of ultrasound. 
   In other embodiments of the invention, the cleaning station contains a blower unit that, with the assistance of air, displaces printing fluid out of the depressions moving past the cleaning station. In the present method, the cleaning station contains a suction unit with whose assistance air is sucked in, the air entraining printing fluid from the depressions moving past the cleaning station. The printing fluid removed with the assistance of the cleaning station is collected; and the collected printing fluid is conducted to the inking station. 
   Further advantages of the invention are realized in an embodiment wherein the printing fluid is cleaned and/or rejuvenated. 
   A printer device for printing a carrier material is also provided wherein a printing drum rotating around its longitudinal axis during the printing event and on whose surface a plurality of depressions for the acceptance of printing fluid are arranged, 
   an inking station for introducing printing fluid into depressions that move past the inking station, a transfer printing station at which printing fluid from some of the depressions moving past the transfer printing location is employed for printing the carrier material, and at which the printing fluid remains in the rest of the depressions moving past the transfer printing station, a cleaning station for removing printing fluid from depressions that move past the cleaning station, and a control unit for the actuation of the cleaning station and of the inking station, the control unit simultaneously places the cleaning station and the inking station into operation during the printing event. 
   In the printer device, a cleansing station for cleansing the depressions emptied in the cleaning station with a cleaning fluid may be provided. The cleaning station may contain a cleaning drum that lies parallel to the printing drum and whose surface touches the surface of the printing drum in a cleaning region; and the surface of the cleaning drum preferably carries a different potential than the surface of the printing drum. Preferably, the cleaning station contains a stripper drum that lies parallel to the cleaning drum and whose surface presses onto the surface of the cleaning drum in a stripping region. The cleaning device may contain a blower unit with whose assistance air is blown into the depressions moving past the cleaning station; and/or the cleaning station contains a suction unit with whose assistance air is sucked out of the depressions moving past the cleaning station. 
   The invention proceeds on the basis of the perception that a printing having high printing quality can only be achieved when all depressions are completely emptied before the depressions are transported past the inking station and are filled anew with printing fluid by the inking station. This is particularly significant in printing methods wherein the volume of a respective depression prescribes the volume of printing fluid to be applied onto a picture element. Even given depressions whose printing fluid is used during printing, it is not assured that all of the printing fluid can be applied onto the carrier material. This is especially true when, due to adhesive forces between the printing fluid and the carrier material, the printing fluid is drawn toward the carrier material. In this case, forcing the printing fluid out of the depression is foregone, this, for example, being implemented with the assistance of a gas bubble. 
   The inventive method therefore employs a cleaning station that removes the printing fluid from the depressions moving past the cleaning station. The cleaning station and the inking station operate simultaneously during the printing event. In the inventive method, thus, the printing fluid is removed from all of the depressions before the depressions are employed in a new printing event. Due to the removal of the printing fluid at the cleaning station, the printing fluid is also prevented from drying on the sidewalls of the depressions during the printing event. The volume capacity of the depressions remains unchanged during the entire printing event. The printing fluid is also prevented from remaining in a depression over a plurality of revolutions of the printing drum and physically or chemically changing during this time, for example in terms of viscosity or composition when highly volatile tensides are contained in the printing fluid. 
   What the utilization of the inventive method achieves is that a prescribed quantity of printing fluid having a prescribed composition and prescribed physical parameters can be employed for each picture element even given a continuous printing mode. The result is a print image having a high quality. 
   In a development of the inventive method, the cleaning station contains a cleaning drum that lies parallel to the printing drum and whose surface touches the surface of the printing drum in a cleaning region during cleaning. The surface of the cleaning drum is manufactured of an elastic or of an absorbent material that can be pressed into the depressions. The employment of a cleaning drum is a simple possibility for removing the printing fluid that remains in the depressions. Given an elastic surface of the cleaning drum, this can be pressed against the printing drum in an enlarged cleaning region. The printing fluid remaining in the depressions thus has comparatively more time to attach to the surface of the cleaning drum. Cleaning drums at whose surface bristles are arranged are also employed. The cleaning device must be pressed tightly against the printing drum in order to avoid contamination of the printing unit due to printing fluid that spatters during brushing. 
   In another development, the cleaning drum carries an electrical potential that differs from the potential of the surface of the printing drum. This measure facilitates the release of the printing fluid from the depressions because the electrostatic forces attract the printing fluid out of the depression, it acts in addition to the adhesion forces between printing fluid and surface of the cleaning drum. Potentials having different operational signs are also employed. 
   In a next development, the cleaning station, in addition to containing the cleaning drum, contains a stripper drum lying parallel to the cleaning drum whose surface exerts pressure onto the surface of the cleaning drum in a stripping region. The surface of the stripper drum is made of a hard material, for example of metal. Whereas absorbent material can be damaged when being squeezed by a doctor blade, stripping the printing fluid from the stripper drum can be carried out without damage. The stripper drum has a smooth surface on which the doctor blade lies well. 
   In one development of the inventive method, the emptied depressions are cleaned with a cleaning fluid after the emptying of the printing fluid from the depressions by moving the depressions past the cleaning station before the introduction of the printing fluid into the depressions moving past the inking station. The cleaning step leads to a more thorough emptying and cleaning of the depression and assures that the printing fluid is always filled into the depressions in the inking station under constant conditions. During cleaning, dirt particles are also removed from the edges of the depressions, the dirt particles being produced, for example, due to abrasion of the carrier material or by abrasion at the edges of the depressions. 
   In a next development, the cleaning fluid is contained in a cleaning container arranged under the printing drum. The depressions move past the cleaning container immersed into the cleaning fluid. The immersion assures that the cleaning fluid is forced into the depressions with a specific pressure. Moreover, the cleaning fluid is agitated due to the immersion. The increased pressure and the movement of the cleaning fluid lead to a better removal of the dirt particles seated at the sidewalls of the depressions. In a next development, the printing fluid is employed as a cleaning fluid, so that additional cleaning fluids can be foregone. When, however, a very thorough cleaning is important, then solvents are employed as the cleaning fluid. 
   In a next development, the cleaning fluid is moved by additional measures that proceed beyond the movement of the cleaning fluid due to the immersion of the printing drum. The employment of ultrasound assures that dirt particles that adhere very firmly to the sidewalls can also be released. Moreover, larger dirt particles are comminuted by the ultrasound. 
   In one development of the inventive method, the cleaning station contains a blower with whose assistance air is blown into the depressions moving past the cleaning station. When the air is blown into the depressions, the printing fluid is blown out at the same time. Blowing the air in is implemented instead of or in combination with the cleaning by the cleaning drum. 
   In a next development, a suction pump is employed in the cleaning station, to suction air out of the depressions moving past the cleaning station. Any printing fluid remaining in the depressions is also removed simultaneously with the air. No spattering of printing fluid occurs in the suctioning process, so that measures to prevent spattering printing fluid need not be undertaken. 
   When, in a next development, the printing fluid that has been removed in the cleaning station is collected and conducted to the inking station, then a circulation derives for the printing fluid that assures that the printing fluid can be completely printed. 
   In a next development, the printing fluid is cleaned and/or rejuvenated as it is carried in the printing fluid circulation. Filtering makes it possible to remove foreign bodies and ink particles that have already dried from the printing fluid. A rejuvenation of the printing fluid may involve in, for example, introducing additives such as water or solvent into the printing fluid. 
   The invention also applies to a printer device that is employed for the implementation of the inventive method. The technical effects indicated above thus also apply to the inventive printer device and developments thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained below on the basis of the attached drawings. 
       FIG. 1  is an enlarged cross section of a portion of a printing drum. 
       FIG. 2  is a schematic diagram of a printing unit of a printer. 
       FIG. 3  is a schematic diagram of a cleaning station with a cleaning drum and an ultrasound bath. 
       FIG. 4  is a magnified illustration of a cleaning region. 
       FIG. 5  is a cleaning station with a potential-carrying cleaning drum. 
       FIG. 6  is a cleaning station with a blower. 
       FIG. 7  is a cleaning station with a suction unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a longitudinal section along the surface  8  of a printing drum  10 . A plurality of depressions arranged matrix-like are located in the surface  8  of the printing drum  10 , two depressions  12  and  14  thereof being shown in  FIG. 1 . The depressions are arranged next to one another in a row direction, see arrow  16 . Neighboring depressions  12  and  14  have a spacing A from one another that determines the resolution of the printer. A plurality of rows of depressions are arranged following one another in column direction  18 , whereby neighboring depressions with a column also have a spacing from one another that corresponds to the spacing A. The depressions are all identically constructed, so that the structure of only the depression  12  is explained below. 
   The depression  12  is fashioned as a conoidal frustum-shaped recess (see contour  20 ) and thus has circular crossections. The axis of the conoidal frustum lies in the direction of the normal of the surface  8 . The conoidal frustum-shaped contour  20  tapers with increasing distance from the surface  8  of the printing drum  10 . A bottom surface  24  of the depression  12  has a smaller diameter than the opening  26  of the depression  12  lying on the surface of the printing drum  10 . The circumference of the opening  26  lies on a circle and prescribes the shape of the picture elements to be printed. 
   An all-around sidewall  28  of the depression  12  is arranged obliquely relative to the surface  8  of the printing drum  10 . The filling of a chromatic ink  30  is facilitated by the conoidal frustum-shaped fashioning of the depression  12 . The ink  30  is held within the depression  12  by capillary forces. The capillary forces are greater than the force of gravity the earth exerts on the ink  30 , so that the ink also remains within the depression  12  when the opening  26  is directed down, i.e. toward the center of the earth. After the filling of the ink  30  and the squeegeeing of the printing drum  10  with a doctor blade, the surface  32  of the ink  30  has a surface tension at which a convex curvature occurs, i.e. the surface  32  of the ink  30  is arced inward. The surface  32  is in a condition I wherein a wetting angle RI has a value of approximately 45°. The wetting angle RI is described by a vector VI of the surface tension on the surface  30  and by the side wall  28 . The vector VI begins at the edge of the depression  12 , i.e. at a location at which the fluid  30  adjoins the sidewall  28  or, respectively, surface  8 . The volume capacity of the depression  12  is selected such that exactly that quantity of ink  30  that is required for printing a single picture element is accepted. 
   How a condition II of the surface  36  of the ink  34  affects the printing event shall be explained below on the basis of a printing fluid  34  within the depression  14 . After being filled into the depression  14 , the ink  34  also has an inwardly arced, i.e. concave, surface. The surface tension of the ink  34  was increased due to the evaporation of tensides with the assistance of an exposure device (shown at the bottom in  FIG. 2 ), as a result whereof the surface  36  has arced outward. A wetting angle RII between a surface tension vector VII and the sidewall of the depression  14  has a value of somewhat above 90°. The vector VII begins at the sidewall of the depression  14  and proceeds in the direction of the surface tension of the surface  36 . The starting point of the surface tension vector VII lies at the boundary between printing fluid  34  and the sidewall of the depression  14 . A middle region  38  of the surface  36  projects beyond the surface  8  of the printing drum  10  by a distance B. When the depression  14  is conducted past paper to be printed upon at a distance that is less than the distance B, then a wetting of the paper occurs. The adhesion forces between the paper and the printing fluid  34  are higher than the capillary forces between printing fluid  34  and depression  14 . All of the printing fluid  34  is therefore drawn out of the depression  14  and inks a region on the paper that is provided for a picture element. 
     FIG. 2  shows a printing unit  50  of a printer that has a resolution of 600 dpi (dots per inch). A printing drum  10   a  turns in counter-clockwise direction, see arrow  52 . The devices enumerated below are successively arranged along the circumferential direction of the printing drum  10   a.    
   At the beginning of a revolution of the printing drum  10   a , the depressions for printing a row that extend in a longitudinal direction of the printing drum  10   a  are free of the printing fluid, see position P 1 . Ink  56  is filled into the depressions of a row at an inking station  54 . The inking station  54  contains a scoop drum  58  whose axis proceeds parallel to the axis of the printing drum  10   a . At the position P 2 , the surface of the scoop drum  58  touches the surface of the printing drum  10   a . The scoop drum  58  turns in a direction opposite that of the printing drum  10   a , see arrow  60 . The lower part of the scoop drum  58  immerses into the ink  56  held by a reservoir  62 , so that the surface of the scoop drum  58  is moistened with ink when the surface reaches the position P 2 . Due to the capillary forces, the ink  56  is drawn from the surface of the scoop drum  58  into the depressions  12 ,  14  of the printing drum  10   a , which is located at position P 2 . 
   A doctor blade  64  is situated at a position P 3 , the doctor blade  64  sweeping over the surface of the printing drum  10   a  such that no ink remains on the surface of the printing drum  10   a  outside the depressions. After being swept with the doctor blade  64 , the ink in all depressions respectively has an inwardly arced surface. 
   The depressions of a row filled with ink  56  are subsequently transported by rotation of the printing drum  10   a  to a position P 4  at which an exposure device  70  modifies the surface tension in selected depressions. The exposure device  70  contains a tubular flashbulb  72  whose longitudinal axis is arranged parallel to the longitudinal axis of the printing drum  10   a . A reflector  74  that extends along the flashbulb  72  and has an arcuate crossection is located at that side of the flashbulb  72  facing away from the printing drum  10   a . The flashbulb  72  is located roughly in the focus of the reflector  74 . The exposure device  70  also contains a line composed of ceramic cells  76  arranged next to one another whose transparency can be varied with the assistance of a control voltage. When exposing a row of depressions at the position P 4 , exactly one ceramic cell  76  is located opposite each depression. The ceramic cells  76  are transparent, ferroelectric ceramic laminae. Such ceramic laminae are known in the field of optoelectronics. For example, such ceramic laminae are disclosed as PLZT elements in European Letters Patent EP 0 253 300 B1. However, optoelectronic elements that work according to the Kerr principle are also employed. The exposure device  70  is controlled by a drive device  78  dependent on print data  80  that define the picture elements of the print image to be printed. A clock signal  84  that clocks the flashbulb  72  synchronously with the revolution of the printing drum  10   a  is generated at a first output line  82  of the drive device  78 , so that each row of depressions that is moved past the position P 4  is irradiated exactly once by the flashbulb  72 . 
   Output lines  86  lead from the drive device  78  to the individual ceramic cells  76  of the line of ceramic cells  76 . The drive unit  78  drives the ceramic cells  76  such that a ceramic cell  76  under consideration is light-transmissive when the depression lying opposite the appertaining ceramic cell  76  contains ink that is to be used for printing given the next transport past at a position P 5 . The light coming from the flashbulb  72  can then proceed through the appertaining ceramic cell  76  onto the ink. The light energy evaporates tensides that are situated at the surface of the ink. The result is that the surface tension of the inks rises and the wetting angle becomes larger. When, in contrast, the ink situated in a specific depression is not to be employed for printing a picture element, then the ceramic cell  76  lying there opposite is darkened with the assistance of the control device  78 , so that no light from the flashbulb  72  can be incident onto the depression. The surface tension and the wetting angle of the ink remain unaltered. 
   As explained above on the basis of  FIG. 1 , there are depressions wherein the surface of the printing fluid has the condition I after a row of depressions has been transported past the position P 4 . The surface of the ink has the condition II in other depressions. 
   A transfer printing zone  92  is located at the position P 5  between the printing drum  10   a  and a transport roller  90 . The longitudinal axis of the transport roller  90  lies parallel to the axis of the printing drum  10   a . A transport device (not shown) turns the transport roller  90  in a direction opposite that of the printing drum  10   a , see arrow  94 . Continuous form paper  96  is transported in a transport direction  98  between printing drum  10   a  and transport roller  90 . The continuous form paper  96  lies against the surface of the transport roller  90 . 
   Continuous form paper  96  and the surface of the printing drum  10   a  have the same speed in the region of the transfer printing zone  92 , so that they are at rest relative to one another. That surface of the continuous form paper  96  facing toward the printing drum  10   a  has a spacing from the surface of the printing drum  10   a  that is smaller than the spacing B, see  FIG. 1 . In the region of the transfer printing zone, the continuous form paper  92  is printed at locations that lie opposite depressions whose ink has a high surface tension and, thus, a great curvature at the surface, condition II. 
   After the depressions have been transported past the position P 5 , there are depressions in which ink  56  is still present. The ink  56  was removed from other depressions when printing in the transfer printing zone  72 . A cleaning station  100  is located at a position P 6 . The cleaning station  100  contains a cleaning drum  102  whose longitudinal axis lies parallel to the longitudinal axis of the printing drum  10   a . The cleaning drum  102  turns in a direction opposite that of the printing drum  10   a , see arrow  104 . As noted above in the summary, a control unit for actuation of the cleaning station and the inking station is provided to simultaneously place the cleaning station and the inking station into operation during the printing event. The control unit, marked  103 , in the drawing is connected to both the cleaning station and the inking station to provide the described simultaneous operation. At the position P 6 , the surface of the cleaning drum  102  and the surface of the printing drum  10   a  touch in a cleaning region  105 . The surface of the cleaning drum  102  is fabricated of an absorbent material that draws ink out of the depressions in which ink has remained. Ink that was previously in the depressions on the printing drum  10   a  is squeegeed off from the cleaning drum  102  with the assistance of a doctor blade  106 . The removed ink runs into a collecting basin  108  arranged under the doctor blade  106 . After being transported past the position P 6 , the depressions on the printing drum  10   a  have returned into their original condition as explained above for the position P 1 . 
   A compensating line  110  via which the ink dripping down from the doctor blade  106  returns into the reservoir  62  is situated between the collecting basin  108  of the cleaning station  100  and the reservoir  62  of the inking station  54 . An ink circulation is thus closed via the compensating line  110 . 
     FIG. 3  shows a cleaning device  100   b  that is employed in a printing unit  50   b . An exposure device employed in the printing unit  50   b  and a transfer printing station past which the carrier material is conducted are not shown in  FIG. 3  since their structure is identical to the structure of the exposure device  70  or, respectively, to the structure of the transfer printing station  90  through  98 . A printing drum  10   b  of the printing unit  50   b  has the same structure as the printing drum  10   a  and turns counter-clockwise in the direction of an arrow  52   b . The cleaning station  100   b  is located at the printing drum  10   b  at approximately the same position as the cleaning station relative to the printing drum  10   a , i.e. obliquely under the shaft of the printing drum  10   b . A cleaning drum  102   b  contained in the cleaning station  100   b  is arranged parallel to the printing drum  10   b . The surface of the cleaning drum  102   b  is formed by an elastic coating  200 . The surface of the coating  200  touches the printing drum  10   b  along a cleaning region  202 . The cleaning drum  102   b  turns in the same sense as the printing drum  10   b , see arrow  204 . 
   A stripper drum  206  lies parallel to the cleaning drum  102   b  at that side of the cleaning drum  102   b  facing away from the cleaning region  202 . The stripper drum  206  turns in a direction opposite that of the cleaning drum  102   b , see arrow  208 . A doctor blade  210 , whose downwardly directed lower edge is arranged above a collecting basin  108   b , is located under the stripper drum  206 . 
   The cleaning drum  102   b  removes ink from the depressions that remained in the depressions of the printing drum  10   b . Due to the rotational movement of the cleaning drum  102   b , the removed ink is transported to the stripper drum  206  and proceeds onto the stripper drum  206  at a stripping region  212 . The ink that is stripped off is then transported to the doctor blade  210  by the stripper drum  206  along the circumferential direction of the stripper drum  206 . The doctor blade  210  squeegees the ink from the stripper drum  206 . The ink drips from the doctor blade  210  into the collecting basin  108 . The collecting basin  108   b  is connected via a compensating line  110   b  to a reservoir  62   b  of an inking station  54   b . The compensating line  110   b  runs through a filter unit  213  than contains a fine-pore filter in which paper fibers and dried ink collect. In another exemplary embodiment, a catalyst substance that decomposes foreign bodies in the ink is employed in the filter unit. 
   An ultrasound bath  214  is arranged under the shaft of the printing drum  10   b  between the cleaning station  100   b  and the inking station  54   b . The ultrasound bath  214  contains a container  216  whose upper edges lie against the printing drum  10   b . The container  216  is completely filled with a solvent-containing cleaning fluid  218 . An ultrasound transmitter  220  in the floor region of the container  216  sends ultrasound waves through the cleaning fluid  218  to the surface of the printing drum  10   b . When depressions of the printing drum  10   b  move past the ultrasound bath  214 , then the depressions immerse into the cleaning fluid  218  and are filled with cleaning fluid  218 . The cleaning fluid  218  forms a transmission medium for the ultrasound, so that the ultrasound proceeds up to the sidewalls of the depressions and strips foreign bodies adhering thereto off. When the depressions leave the ultrasound bath  214 , then the cleaning fluid runs out due to gravity and remains in the container  216 . 
   The depressions that are emptied at the cleaning station  100   b  and cleaned in the ultrasound bath  214  are transported to the inking station  54   b  due to the rotational motion of the printing drum  10   b . The inking station  54   b  contains a scoop drum  58   b  that is arranged parallel to the printing drum  10   b  and turns in a direction opposite the rotational sense of the printing drum  10   b , see arrow  60   b . The scoop drum  58   b  dips into the ink  56   b  that is present in the reservoir  62   b . Due to the rotational motion of the scoop drum  58   b , ink is transported from the reservoir  62   b  to the printing drum  10   b . The depressions moving past at the inking station  62   b  are filled with ink  56   b  in an inking region  222 . A doctor blade (not shown) subsequently serves the purpose of squeegeeing ink not situated inside depressions from the printing drum  10   b . Moreover, the employment of the doctor blade also causes the printing fluid in the depressions to arc inward. 
     FIG. 4  shows a magnified illustration of the cleaning region  202 . Depressions  230  through  242  in the surface of the printing drum  10   b  are shown disproportionately large in  FIG. 4 . After being transported past the transfer printing location  92  (see  FIG. 2 ), printing fluid  252 ,  256 ,  260  or, respectively,  262  was present in the depressions  232 ,  236 ,  240  or, respectively,  242 . The coating  200  is composed of an elastic material and presses into the depressions in the cleaning region, see depression  236 . Due to the force of adhesion between the printing fluid  256  and the coating  200 , the printing fluid  256  is pulled out of the depression  236 . The printing fluid  260  or, respectively,  262  that was present in the depression  240  or, respectively,  242  was already transferred onto the coating  200  at the cleaning region  202 . 
     FIG. 5  shows a portion of a cleaning station  100   c  that is constructed essentially like the cleaning station  100   b . Instead of the cleaning drum  102   b , a cleaning drum  102   c  that likewise has an elastic coating  200   c  at its surface is employed in the cleaning station  100   c . The cleaning drum  102   c  and a printing drum  10   c , both of which are fabricated of a metallic material, lie opposite one another at a cleaning region  202   c . A potential is generated on the printing drum  10   c  with the assistance of a voltage U1. A voltage U2 generates a potential on the surface of the cleaning drum  102   c  that is lower than the potential on the surface of the printing drum  10   c . The difference in potential leads thereto that printing fluid  252   c ,  256   c ,  260   c  or, respectively,  262   c  easily releases from depressions  232   c ,  2326   c ,  240   c  or, respectively,  242   c  when the printing drum  10   c  and the cleaning drum  102   c  rotate in opposite directions relative to one another, see arrows  52   c  and  204   c . In another exemplary embodiment, one of the voltages U1 or, respectively, U2 is reversed in polarity, so that the potential on the printing drum  10   c  has a different operational sign from the potential on the cleaning drum  102   c.    
     FIG. 6  shows a cleaning station  100   d  that is employed instead of the cleaning station  100 . A printing drum  10   d  turns in a counter-clockwise direction, see arrow  52   d . A blower unit  260  is arranged under the shaft of the printing drum  10   d . A discharge nozzle  262  is directed onto the surface of the printing drum  10   d  along the longitudinal direction of the printing drum  10   d . The blower unit  216  generates a pressure p that is higher than the atmospheric pressure patm. This results in the air being blown through the discharge nozzle  262  into the depressions on the surface of the printing drum  10   d . The air stream forces the printing fluid that has remained in the depressions out into a collecting basin  108   d . The cleaning station  100   d  is surrounded by a housing (not shown) that prevents printing fluid from splattering out of the cleaning device  100   d.    
     FIG. 7  shows a cleaning station  100   e  that is employed instead of the is cleaning station  100 . A printing drum  10   e  rotates in a counter-clockwise direction, see arrow  52   e . The cleaning station  100   e  contains a suction unit  270  that is arranged under the shaft of the printing drum  10   e . An intake nozzle  272  of the suction unit  270  is directed such that an intake opening extends along the longitudinal direction of the printing drum  10   e  and lies at a short distance opposite the depressions moving past the cleaning station  100   e.    
   A pressure p that is lower than the atmospheric pressure patm prevails in the suction unit  270 . Air is thus sucked into the suction unit  270  through the intake nozzle  272 . In common with the air, printing fluid that has remained In the depressions after being transported past the transfer printing location  92  is also suctioned off from the printing drum  10   e . A drain channel  274  of the suction unit  270  discharges into a collecting basin  108   e . The printing fluid that has been suctioned from the surface of the printing drum  10   e  proceeds from the inside of the suction unit  270  through the drain channel  274  and into the collecting basin  108   e . A connection between collecting basin  108   e  and reservoir  62  is not shown in  FIG. 7 . 
   Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.