Abstract:
A method for controlling register settings of a printing press, includes rotating imaging cylinders of a first print unit and a second print unit, located downstream of the first print unit in a movement direction of a print medium, at a rotational speed to print an image on the print medium. The method includes of changing a length of the print image to a pre-determined length. The method further includes changing a register setting of the imaging cylinder of the second print unit based on the predetermined change in length of the print image to avoid misalignment of the print image printed by the first and the second print units on the print medium. Changing the register setting is dependent on a length of a section of the print medium between the first and the second print units. A device for controlling register settings of a printing press is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of the Swiss Patent Application No. 00875/10, filed on Jun. 2, 2010, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method and device for controlling register settings of a printing press, as well as to a printing press provided with such a device. 
     For multi-color printing, at least two color components are printed over each other in a printing press with the aid of a plurality of imaging cylinders. If a printing press is in register or, differently expressed, is in an overlapping fit, the images printed by the different print units, which respectively print on a single color component, are placed to fit precisely one above the other. 
     In web-fed presses, a print medium or substrate, for example, paper or film, frequently travels long distances between two print units. Devices are integrated into these web-fed presses which make it possible to precisely adjust the register settings and to continuously re-adjust the register settings during the course of the printing operation. Such devices are also used in sheet-fed printing presses. 
     Markings such as the so-called registration marks or registration crosses are auxiliary means used for known register settings. These markings are also printed on outside of the picture area by each printing press. With the aid of image-processing systems, the positions of the respectively relevant registration marks, relative to each other, are recorded as well as evaluated and the printing press is readjusted accordingly. 
     To evaluate the register or the register accuracy, a distinction is made between the lineal register (in the movement direction of the web of print medium), the side or lateral register (transverse to the movement direction) and the diagonal register. The problem defined for the invention essentially relates to the lineal register. 
     For example, deviations detected in the lineal register can be compensated for by displacing individual guide rollers, meaning the register rollers, which shorten or lengthen the distance between two print units. Alternatively, the lineal register can also be adjusted by rotating the imaging cylinders relative to each other. 
     A deviation in the register is normally caused by the use of a different type of print medium which exhibits a different expansion behavior as compared to the previously used print medium. The speed of the printing press can also require a readjustment of the register because the print medium web behaves differently, depending on the speed of the printing press. 
     Controls for register settings of this type are disclosed, for example, in the German patent documents DE 102006060212 A1 or DE 10254836 A1. 
     Known register settings take into account, insufficiently or not, that the length of the print medium web section between the print units that take part in the printing operation can vary noticeably as a result of changes in the configuration of the printing press. The deviations in the register can consequently exceed those normally occurring in the detection range for standard register settings, thus making it impossible for the register to be adapted automatically. Also not addressed as a subject is the influencing of the register as a result of a change specified by the machine operator in the length of the intended print image. With known printing presses, this is realized by specifying a heterodyne speed for the individual drives of the imaging cylinders belonging to adjacent print units, which participate in the image-printing process. 
     The length of the print image can be shortened by approximately up to 1 mm, relative to the original format of the print image, wherein this can be achieved through accelerating the drive of the imaging cylinder. Owing to the higher but constant rotational speed, as compared to the theoretically correct speed for the print medium, the print image is correspondingly shortened. 
     In contrast, the print image is lengthened by approximately up to 3 mm, relative to the original format for the print image, if the speed of the respective imaging cylinder drive is slowed as compared to the speed of the print medium web. Thus, the print image can be pulled over a longer section of the web than is provided based on a corresponding negative on the imaging cylinder. 
     Register deviations caused by changes in the length of the print image as a rule do not fall within the detection range of the above-discussed register settings. For example, if five print images and/or formats, which must respectively be lengthened, are located between two adjacent print units, the change in the length of each print image on the whole results in a register deviation in the downstream arranged print unit, as seen in production direction, in the order of magnitude of five times the change in length for the print image. 
     With printing presses that are especially flexible for use, the length of the print medium section between two adjacent print units frequently varies considerably as a result of production changes, so that it is not automatically certain just how many print images are located between two adjacent print units. 
     SUMMARY 
     It is an object of the present invention to provide a method and a device which make use of a control unit to correct register deviations located outside of the normal detection range of known register settings. For this, essential influencing factors must be determined and these must be supplied to the printing press in the form of control variables. 
     The above and other objects are accomplished according to one aspect of the invention wherein there is provided a method for controlling register settings of a printing press, which, in one embodiment, includes rotating imaging cylinders of a first print unit and a second print unit, located downstream of the first print unit in a movement direction of a print medium, at a rotational speed to print an image on the print medium; changing a length of the print image to a predetermined length; changing a register setting of the imaging cylinder of the second print unit based on the predetermined change in length of the print image to avoid misalignment of the print image printed by the first and the second print units on the print medium, where the changing of the register setting is dependent on a length of a section of the print medium between the first and the second print units. 
     The application furthermore relates to a device for controlling register settings of a printing press, which, according to one embodiment includes a first print unit and a second print unit, located downstream of the first print unit in a movement direction of the print medium, which each respectively include an imaging cylinder rotating with a rotational speed for printing images on the print medium, where the imaging cylinder of the second print unit includes register settings that are changeable to avoid misalignment of the images printed on the print medium by the first and second print units; a control unit adapted to determine a length of a section of the print medium between the first and second print units; a sensor coupled to each of the first and second print units, where each sensor is adapted to detect a marking on the print medium, generate a corresponding signal, and transmit the signal to the control unit; and a drive system that is adapted to change the register settings of the imaging cylinder of the second print unit based on the length of the section of the print medium. 
     According to one embodiment, the method for the register control may be used in a printing press provided with a first print unit and at least one additional print unit. The print units may be respectively provided with at least one imaging cylinder operating with a rotational speed. To avoid a running of the images printed on by a plurality print units, the register settings of the at least one imaging cylinder of the additional print units may be changed, to correspond to a specified change in the length of a print image. 
     According to one embodiment, the register settings may be changed in dependence on at least the length of a print medium section between the print units. 
     As a result of this method, it may be possible to save waste paper and set-up time because the register control may automatically carry out a correction. An intervention by the machine operator may therefore not be required, meaning that the process is more secure. 
     According to one embodiment of the method, the register settings may be changed while the printing press is operational. A predetermined change in the length of a print image may be realized by changing the rotational speed of the at least one imaging cylinder of the additional print units, relative to the speed of the print medium web. The theoretically correct rotational speed of the at least one imaging cylinder thus may be relative to the rotational speed assigned to the changed length of the print image, wherein this ratio may generally exit between the rotational speed of a rubber-blanket cylinder and the speed of a counter-pressure cylinder. 
     The change in the register settings of the at least one imaging cylinder of the additional print units may be corrected according to a different embodiment by correcting the length of the print medium section between the print units, relative to a reference position in the printing press. According to one embodiment, this reference position may be defined by the first print unit which participates in the printing process, as seen in web movement direction. 
     According to another embodiment, the correction value may be formed by multiplying the change in length of the print image with the number of print images located between the respectively adjacent print units. The number of print images may be determined by dividing the length of the print medium section between the respectively adjacent print units by the length of one print image, as seen in movement direction of the print medium. 
     The length of the print medium section between the respectively adjacent print units may be determined by evaluating at least one signal from at least two sensors. The sensors of favorable embodiments may emit a signal once they have identified a marking on the print medium. 
     The marking may be affixed to the print medium with the aid of a marking device, either upstream of the first print unit or in the print unit, in particular through stamping, punching, applying color or gluing it on. 
     Light barriers may be used for the sensors. 
     The length of the print medium section between the respectively adjacent print units may be determined with the aid of expedient methods and an accuracy of less than 0.2 mm. 
     Pulse transmitters provided in print unit drive systems, in particular in servo-drive systems, may be used to additionally evaluate the angular position of the print units. A signal may be generated on the basis of the determined angular position for the print units and may then be evaluated together with the signals relating to the length of the print medium section between respectively adjacent print units, wherein the register settings of the at least one imaging cylinder of the additional print units may be changed in accordance with the evaluation that is carried out. 
     According to the invention, a device for controlling the register of a printing press may be designated for use in a printing press. The printing press may comprise a first print unit and at least one additional print unit. Each print unit may be provided with at least one imaging cylinder that may move with a rotational speed. The register settings of the additional print units which follow the first print unit may be changed to avoid a running of images which may be printed one over the other by a plurality of print units. 
     The device for the register control may include a control unit and respectively at least one drive system and at least one sensor for the print units, wherein the drive system in particular is a servo-drive system. The at least one sensor may detect a marking on the print medium, may generate a corresponding signal, and may transmit this signal to the control unit. The length of a print medium section between the print units may be determined with the aid of the signals received from the at least one sensor. Depending on the length that is determined, the register settings for the additional print units may be changed with the drive systems. 
     According to one embodiment of the device, the at least one sensor may be respectively arranged either on the print units or behind the print units, as seen in movement direction of the print medium. 
     The device according to a different embodiment may be provided with a marking device which may be arranged in the movement direction of the print medium either upstream of or in a first print unit. With the aid of the marking device, a marking may advantageously be affixed to the print medium, either upstream of or in the first print unit, or may be incorporated therein, in particular through stamping, punching, applying color or gluing. 
     According to a different embodiment, the device may be provided with at least one pulse transmitter, in particular arranged on the drive system, for detecting the angular position of at least one of the print units and to transmit this position to the control unit as well as to the drive system. 
     It may be particularly expedient if a printing press is equipped with one of these devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view from above of two parallel-arranged print medium webs, showing their respective division into print images, according to an embodiment of the present invention; 
         FIG. 2  is a schematic representation of a radial section through a printing press equipped with five print units comprising separately driven imaging cylinders, wherein a print medium web is guided through the printing press, according to an embodiment of the present invention; 
         FIG. 3  is a first block diagram, designed to illustrate the process sequence for determining the geometric lengths between the print units according to an embodiment of the present invention; and 
         FIG. 4  is a second block diagram, designed to illustrate the process steps for realizing the register correction, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  schematically illustrates a printing press  6  with five print units  1 ,  2 ,  3 ,  4 ,  5 , namely a first print unit  1  and four additional print units  2 ,  3 ,  4 ,  5 . A print medium  9  web is guided in the movement direction  12  through the printing press  6  and, in the process, passes the print units  1 ,  2 ,  3 ,  4 ,  5  one after another. Two webs  13 ,  13 ′ of print medium  9  are shown in  FIG. 1  in a view from above, to clearly illustrate the division of these webs into sections representing the print images  11 ,  11 ′. Each of the print units  1 ,  2 ,  3 ,  4 ,  5  with imaging cylinders  26 ,  27 , which are also called format cylinders, is used to print one color component of the multi-color print image  11 ,  11 ′ onto the print medium  9 . The complete multi-color print image  11 ,  11 ′ is generated at the downstream end of the printing press  6  through printing of the individual color components, one over the other, with the print units  1 ,  2 ,  3 ,  4 ,  5 . 
     According to  FIG. 2 , the print units  1 ,  2 ,  3 ,  4 ,  5  are provided with respectively two imaging cylinders  26 ,  27 , arranged vertically one above the other, namely a plate cylinder  26   a  on the top and a rubber-blanket cylinder  27   a  on the bottom, below which in turn a counter-pressure cylinder  28  is positioned. The print medium  9  is transported in movement direction  12  between the rubber-blanket cylinder  27   a  and the counter-pressure cylinder  28 . The print image  11 ,  11 ′ is initially created above the print medium  9  in that the plate cylinder  26   a  rolls off the rubber-blanket cylinder  27   a . These imaging cylinders  26 ,  27  rotate with the same rotational speed and are operated synchronized with the speed of the print medium  9 , or are operated at a faster and/or slower speed than the sprint medium speed, depending on the desired length of the print image  11 ,  11 ′. Finally, the rubber-blanket cylinder  27   a  rolls off the print medium  9 , thereby transferring the print image  11 ,  11 ′ to the latter. If the plate cylinder  26   a  and the rubber-blanket cylinder  27   a  rotate with a constant, but slightly lower speed than that of the web  13 ,  13 ′ of print medium  9 , then a slightly longer print image is created. The speed of the counter-pressure cylinder on the other side of the web  13 ,  13 ′ of print medium  9  remains unchanged in that case. 
     This speed variation is valid to the same degree and/or the same speed difference for all print units  1 ,  2 ,  3 ,  4 ,  5 . Each print unit  1 ,  2 ,  3 ,  4 ,  5  can be driven with an individual rotational speed w, either directly with a separate drive system  31 ,  32 ,  33 ,  34 ,  35  or indirectly via drive rollers that are not shown herein. 
     As seen in movement direction  12  of the print medium  9 , a marking device  10  is provided upstream of a first print unit  1 . Alternatively, the marking device  10  can also be arranged inside the first print unit  1 . 
     During the start-up of the printing press  6  or for a change in the configuration, for example a change in the web guidance between the print units  1 ,  2 ,  3 ,  4 ,  5 , the marking device  10  affixes a marking  8  to the print medium  9 . The length of the section of print medium  9  between the print units  1 ,  2 ,  3 ,  4 ,  5 , must therefore be determined only once and need not be repeated until the actual length of the print medium  9  section between the print units  1 ,  2 ,  3 ,  4 ,  5  is changed. 
     As seen in movement direction  12  of the print medium  9 , a separate sensor  21 ,  22 ,  23 ,  24 ,  25  is arranged behind each print units  1 ,  2 ,  3 ,  4 ,  5 , for example a sensor in the form of a light barrier. The sensors  21 ,  22 ,  23 ,  24 ,  25  generate a signal as soon as the marking  8  reaches their position and subsequently transmit this signal to a control unit  29  which is connected to the drive systems  31 ,  32 ,  33 ,  34 ,  35  for the print units  1 ,  2 ,  3 ,  4 ,  5 . A distance s between a print unit  1 ,  2 ,  3 ,  4 ,  5  and the respectively following sensor  21 ,  22 ,  23 ,  24 ,  25  is known. A section of the print medium  9  with a defined length is located within this distance s. 
     Of course, the sensors  21 ,  22 ,  23 ,  24 ,  25  can also be arranged in the respective print unit  1 ,  2 ,  3 ,  4 ,  5  and can furthermore be used to detect tears in the print medium  9  web. The control unit for the printing press can additionally function as the control unit  29 . 
     A section of the web  13 ,  13 ′ of print medium  9  with a first length l 12  is located between the first print unit  1  and the second print unit  2 . A second section with length l 23 , a third section with length l 34  and a fourth section with length l 45  of the web  13 ,  13 ′ of print medium  9  are accordingly assigned to the intermediate spaces following in movement direction  12  between the print units  2 ,  3 ,  4 ,  5 . In particular with production changes, these sections with lengths l 12 , l 23 , l 34 , l 45  of the web  13 ,  13 ′ of print medium  9  can vary. 
     A printing press  6  of this type can detect the respective length l 12 , l 23 , l 34 , l 45  of the web  13 ,  13 ′ sections of print medium  9  between the print units  1 ,  2 ,  3 ,  4 ,  5  with the aid of the sensors  21 ,  22 ,  23 ,  24 ,  25  and the control unit  29 , in particular also during changes in the machine operation. 
     Upon switching on of the printing press, or after it has been reconfigured by changing the length of the web  13 ,  13 ′ section of print medium  9  between two print units  1 ,  2 ,  3 ,  4 ,  5 , a command is first issued to enable the measuring operation, meaning for detecting the new length of the web  13 ,  13 ′ section of print medium  9  between the print units  1 ,  2 ,  3 ,  4 ,  5 . According to the sequence shown in  FIG. 3 , the marking  8  is then applied to the print medium  9 . Of course, the marking  8  can also be incorporated into the print medium  9 . The control unit  29  subsequently evaluates the signals detected by the respective sensor  21 ,  22 ,  23 ,  24 ,  25  as a result of the marking  8  which moves past the respective sensor  21 ,  22 ,  23 ,  24 ,  25 . The control unit knows the distance s between the print unit  1 ,  2 ,  3 ,  4 ,  5  and the respectively following sensor  21 ,  22 ,  23 ,  24 ,  25  but not necessarily also the distance between the first print unit  1  and the marking device  10 . Based on the signals transmitted by the sensors  21 ,  22 ,  23 ,  24 ,  25  and the known distances s, the up-to-date lengths l 12 , l 23 , l 34 , l 45  for the print medium  9  sections between the print units  1 ,  2 ,  3 ,  4 ,  5  are determined by the control unit  29  and are secured, meaning stored. In addition, the control unit  29  generates a signal for changing the register settings in the additional print units  2 ,  3 ,  4 ,  5  and transmits this signal to the respective drive systems  32 ,  33 ,  34 ,  35 . A measuring operation carried out with the first and the second sensor  21 ,  22 , followed by the evaluation of the signals based on the measuring results and transmitted to the control unit  29 , results in at least a corresponding influencing of the register settings of the second print unit  2  and is furthermore used to enable the printing operation. The control unit  29  and the drive systems  31 ,  32 ,  33 ,  34 ,  35  then await the next switching on or the next change in the configuration of the printing press  6 . 
     For a comparison,  FIG. 1  shows two webs  13 ,  13 ′ of print medium  9  which are laid out parallel to each other. The first web  13  has a total length L. Five identical print images  11  with a length l are positioned on this web  13 . The second web  13 ′ of print medium  9  differs from the first web  13  of print medium  9  by a change in the length of the print images  11 ,  11 ′. For the example shown in  FIG. 1 , the resulting total length L′ for the five illustrated print images  11 ′ of the second web  13 ′, which respectively have a length l′, is on the whole noticeably shorter than the length of the first web  13 . 
       FIG. 1  therefore shows a change in the length Δl 1 , specified by the machine operator, for the print images  11 ,  11 ′ as a difference in the length l of the print images  11 , relative to the length l′ of the print images  11 ′. It is clear that after the fifth print image  11 ,  11 ′, a four-fold change in the length Δl 4  of the web  13 ′ is reached on the whole as compared to the web  13 , or vice versa, when this change in length is made for each of the five print images  11 ,  11 ′ positioned in-between respectively two print units  1 ,  2 ,  3 ,  4 ,  5 . 
       FIG. 4  illustrates the sequence of steps to be carried out for making a correction to the register in dependence on the length of the print image. If the respective length l 12 , l 23 , l 34 , l 45  between the print units  1 ,  2 ,  3 ,  4 ,  5  has been determined according to the inventive method and the length of the print images  11 ,  11 ′ is known, the control unit  29  already knows how many print images  11 ,  11 ′ are located between two print units  1 ,  2 ,  3 ,  4 ,  5 . Based on the number of print images  11 ,  11 ′ between two adjacent print units  1 ,  2 ,  3 ,  4 ,  5 , a correction for the register settings is computed with the aid of an operator-specified length change Δl 1  for the print image  11 ,  11 ′. This correction value is then sent from the control unit  29  to the additional print units  2 ,  3 ,  4 ,  5  to be adjusted and/or to the associated drive systems  32 ,  33 ,  34 ,  35 . In this way, the printing press  6 , which is in register prior to the change of the print image length, continues to be in register. 
     According to  FIG. 2 , the print units  1 ,  2 ,  3 ,  4 ,  5  are each provided with a pulse transmitter  30  that is arranged on the drive system  31 ,  32 ,  33 ,  34 ,  35 . The angular position of at least one of the print units  1 ,  2 ,  3 ,  4 ,  5  can thus be detected with the pulse transmitter  30  and can be transmitted to the drive system  31 ,  32 ,  33 ,  34 ,  35  as well as to the control unit  29 . On the basis of the determined angular position, a signal is generated which is evaluated in the control unit  29 , together with the signals relating to the length l 12 , l 23 , l 34 , l 45  of the print medium  9  between the respectively adjacent print units  1 ,  2 ,  3 ,  4 ,  5 , wherein the register settings of the at least one imaging cylinder  26 ,  27  of the additional print units  2 ,  3 ,  4 ,  5  are changed in accordance with the completed evaluation. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.