Abstract:
Tension of a web in a rotary printing press is regulated. The web passes through at least two printing groups in the printing press. A change in the extension of the web during the print run is determined based on a phase shift between a first phase position of a printing group and a second phase positioned measured after a last printing group. The change in phase position is compensated for by a change in the web tension prior to the first printing group.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a method for regulating a web elongation in a rotary printing press. The web passes through at least one print unit in the printing press. 
   BACKGROUND OF THE INVENTION 
   A register-maintaining drive mechanism for a rotary printing press is disclosed in EP 0 951 993 A1. A longitudinal elongation of the web to be imprinted is determined from web tension and from operating values of the drive mechanisms. Elongation is compensated for by adjusting the circumferential register at the cylinders, or the register rollers. A change in transverse elongation detected by use of a sensor for detecting the web width is fed back via a correcting value to the reference variable of the traction roller, which is regulated to web tension constancy. 
   A method for regulating the drive mechanisms of a printing press, directed toward producing a constant web elongation, is disclosed in U.S. Pat. No. 3,025,791. Here, the measurement of the web elongation takes place close to the first print unit by comparing the angular position of the print unit, and thereafter the position of a marker on the material to be imprinted. A change in the relative position causes a change in the tension of the web of material to be imprinted to be effected in the draw-in unit. 
   DE 92 16 978 U1 discloses a first regulating circuit, where a tension between a print unit and a traction roller is regulated by a first circuit to be constant. In a second regulating circuit, the angular position of the cutting cylinder is regulated via the drive mechanism of the cutting cylinder on the basis of a rotary position of the print unit and the cutting cylinder, as well as on the basis of an optical signal which processes the position of a marker. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is directed to providing methods for regulating a web elongation in a rotary printing press. 
   In accordance with the present invention, this object is attained by passing a web through at least one print unit. A first phase position of the at least one print unit is measured. A second phase position is measured downstream of the at least one print unit. These phase position measurements are used to control the elongation in the web. 
   The advantages which can be achieved by the present invention reside, in particular, in that fluctuations or changes in the elongation of a web during a production run, i.e. of a web during continuous printing, can be measured in a simple way, and that this measurement is used for regulating the web draw-in unit which is located upstream of the first print unit. 
   Measurement downstream of the last print unit, in particular, provides the most information regarding the operational state of the web prior to running the printing web into a subsequently provided superstructure of the printing press, in particular into a hopper inlet. 
   The tension/elongation behavior of the web, when the web passes through the imprinting position, changes with the addition of water and/or ink to the web and causes, for example, an increase in the web elongation after the last print unit. So that during multiple web operations, a problem-free insertion of the multiple webs into the hopper is assured, the suitable web tension level of each of the webs with respect to each other for achieving the necessary gradation in the web tension after water and ink have been added is matched, if possible, only by adjusting the web draw-in unit. 
   The paper web expands under the effects of the damping agent and/or the ink applied to it, both in the longitudinal and in the transverse directions in relation to the web conveying direction. This expansion has the effect of elongating the web, in particular in connection with multi-color printing, with a resulting creation of empty spaces between neighboring imprinting locations. As long as this effect remains almost chronologically constant at each imprinting location, this web elongation can be compensated for, at least partially, for example by changing the register at the cylinders, by changing the position of register rollers, or by changing other devices. 
   However, the elongation behavior of the paper web is subject to many influences such as, but not limited to, the tension/elongation characteristics of the respective paper, and thus to the prevailing tension, the instantaneous moisture, the sensitivity of the web to moisture, the penetrating behavior of the moisture into the web, the position of the roll as it is produced in the reel spool which, for example, has the effect of changing winding tightness, or a positionally-dependent fluctuation of the module of elasticity of the web. 
   Therefore, the web elongation, both the longitudinal and the transverse web elongation, is not uniform because of the varying paper properties of the unwinding paper web itself, and because of changing, and fluctuating operating parameters of the printing press. A fluctuating web tension, changing printing speeds, fluctuations in dampening, or a change of the web roll also can affect the elongation of the paper web, so that the web elongation is not constant or uniform over time. 
   With the aid of the method of the present invention, it is possible, in an advantageous manner, to compensate for changes or fluctuations in the web elongation, and in particular to compensate for changes in the longitudinal elongation in the web conveying direction. 
   The determination of the change in web elongation at the end of a printing tower or following the last print unit in the conveying direction is also beneficial. It provides good information regarding the entire web change for the subsequent processing steps, and allows the initiation of counter-measures, if desired in the interest of maintaining a constant tension or, as preferred here, a constant elongation of the web, for the subsequent travel of the web or the processing steps. In this sense, it is also advantageous that the regulation takes place not in the area of measurement, but at the start of the web, by which regulation, a level of the web tension, or a resulting initial web elongation, is fixed and is regulated thereafter without causing substantial changes of the web tension and/or elongation in the superstructure, in particular upstream of the hopper draw-in roller. 
   By detecting the web elongation change downstream of the last print unit, and by effecting a corresponding regulation of the web inlet elongation, it is possible to assure that the number and the exact phases of the print images between the last print unit, or between the last imprinting location, and a folding apparatus, for example, is constant. This is something which is cumbersome or difficult to do by merely adjusting individual registers. Therefore, the method in accordance with the present invention makes the constant readjustment of the cutting register of a web by the use of all of the drive mechanisms of the print units, or by the use of register rollers, during the production run, at least partially unnecessary. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention is represented in the drawings and will be described in greater detail in what follows. 
     Shown are in: 
       FIG. 1 , a schematic representation of the guidance of a web from the draw-in unit over four print units and past a second traction roller up to the hopper inlet roller, and in 
       FIG. 2 , a schematic representation of the web tension level during the production run. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The course of travel of a web B, for example a web B to be imprinted, or a paper web B, through a printing press, and in particular through a web-fed rotary printing press, is represented in  FIG. 1 . The web B runs in the web conveying direction T from the roll changer  01  through a draw-in unit  02  with a first traction roller  03  through the, for example, four print units  06  to  09  and to a second traction roller  11 . Turning bars, cutting blades, further traction or guide rollers, which are not specifically represented, and finally a hopper inlet roller  12  follow downstream of the second traction roller  11 . In an advantageous embodiment, the first and second traction rollers  03 ,  11 , respectively are each equipped with their own drive mechanisms  13 ,  14 , and each is also provided with a drive regulating device  16 ,  17 . In a preferred embodiment, tensions S 1 , S 2 , S 3  and S 4  of the web B are measured upstream of the draw-in unit  02 , between the draw-in unit  02  and the first print unit  06 , between the last print unit  09  and the second traction roller  11 , and on the free path between the second traction roller  11  and the hopper inlet roller  12 , respectively, all as seen in  FIG. 1 . Each tension measurement can take place, for example, via measuring rollers, or via a measurement of the power consumption of the drive motors of the traction members. 
   The absolute and the relative tensions S 4  of the individual webs B, with respect to each other at the hopper inlet roller  12 , are the starting point for setting the tension in a web B, in particular when, during multi-web operations, several webs B are combined at the hopper inlet by use of the hopper inlet roller  12 . Therefore, the setting of the tensions in the web B is made starting with the desired level of the tension S 4  of each web B at the hopper inlet roller  12 . The level of the entire tension in the web B is preferably set by an adjustment made at the draw-in unit  02 . In a customary way, a change of the tension in the web B also occurs, in an advantageous manner during the production run, by a change of the tension S 2  at the draw-in unit  02 . As schematically represented in  FIG. 2 , for example, the basic setting of the web tension during the production run is set, via use of the traction roller  03 , which is regulated in accordance with web tension, in accordance with web speed or position, by the also regulated hopper draw-in roller  12  and/or by other compensating rollers, not represented. 
   Because of the tension imparted to the web and, in particular, during the production run, because of the moisture applied to the web, the web B is subjected to longitudinal elongations, during its travel from the draw-in unit  02  to the second traction roller  11  downstream of the last print unit  09 , with there being an initial elongation ε 1  of the web B and with a subsequent elongation ε of the web B downstream of the last print unit  09 . With the web B passing through the four print units  06  to  09 , ε 2  represents an elongation between the first print unit  06  and the second print unit  07 , ε 3  represents an elongation between the second print unit  07  and the third print unit  08 , and ε 4  represents an elongation between the third print unit  08  and fourth print unit  09 . 
   This condition of the web B, wherein, as a rules the web tension is regulated during the production run, i.e. at the printing speed and by adding water and/or ink, and where the first traction roller  03  trails and the second traction roller  11  leads with respect to the speed of the press, already takes into consideration an elongation of the web B which is a result of the printing process and the effects of the moisture imparted to the web. 
   The determination of the speed of the press and/or the phase position of the press at the print units  06 ,  07 ,  08 ,  09  can take place in different ways. In case each one of the print units  06 ,  07 ,  08 ,  09  is individually driven, it is possible to use the output data, the angle of rotation positions, or other characteristic values of all, or of individual ones of the print units  06 ,  07 ,  08 ,  09 . 
   In the preferred embodiment, a phase position φ 1  of the first print unit  06  is measured by use of a sensor  18 . This phase position φ 1  can be picked up, for example at a motor shaft of a drive mechanism  19  for the cylinder  21 ; in particular a drive mechanism  19  of a forme cylinder  21  of the print unit  06 , for example by the use of an encoder which is represented in dashed lines in  FIG. 1 . If the forme cylinder  21  of the first print unit  06  is coupled with a cooperating cylinder  22 , and in particular with a transfer cylinder  22 , the phase position φ 1  of the transfer cylinder  22  can also be determined. As represented in  FIG. 1 , it is also possible to use the arrangement of a marker  23  as reference spot  23  on the forme cylinder  21 , or on the transfer cylinder  22 , together with a first sensor  18  for determining a phase position φ 1 . This can be done by use of a scanner or a photoelectric cell, for example. Also, a marker  23  applied by the print unit  06  itself to the web, a portion of the print image itself that is applied to the web, a perforation of the web, or other markings on the web B can also be used as a marker  23  for determining the first phase position φ 1 . 
   A further or subsequent sensor  24  is arranged downstream of the last print unit in the conveying direction T, in this case, the subsequent sensor  24  is arranged downstream of the fourth print unit  09 . A second phase position φ 2 , or a position φ 2  of a second marker  26 , or at least a portion of a print image of an imprinted web B, is measured by this subsequent sensor  24 . The second marker  26  can also be a perforation in the web B, or an equivalently functioning marker on the web B. The phase position φ 2  of the second marker  26  is here understood to be the chronological sequence of the passage of the mark  26  past the detector  24 . If the determination of the phase position φ 1  is performed by use of a marker  23  arranged on the web B, it is possible to employ the marker  23  as the marker  26 , which markers are identical in this case, for the determination of the phase position φ 2 . 
   During the running of the web B, first the phase position φ 1  of the print unit  06  is determined by measuring the passage of the marker  23 . After passing through the print units  06  to  09 , the second phase position φ 2  of the marker  26  printed on the web, or on the portion of the print image, is determined downstream of the last print unit  09 . Assuming a fixed position of the measurement locations with respect to each other, a fixed phase shift Δφ can now be determined, with a chronologically constant elongation ε of the web B, over all partial sections. The method for regulating a web tension in a rotary printing press, in accordance with the present invention, now comes into play since, for the previously discussed reasons, the elongation ε of the web B is not chronologically constant during production. 
   The value of the phase shift Δφ, determined, for example, at the start of the production run and after reaching the desired tensions S 1  to S 4 , is maintained as the reference variable Δφ-Soll in a memory unit, for example. The reference variable Δφ-Soll can be different from one production to another production, since it is a function of the register state of the print units  06  to  09 . However, it should first be fixed during steady state and interference-free operation. Setting the register state, as well as the tensions S 1  to S 4  has already, as has been mentioned above, taken place in their base position, prior to starting production, and is tailored to the paper properties, the web travel and to other, previously mentioned parameters. 
   A deviation Δ of the actual value Δφ from the reference variable Δφ-Soll now provides information regarding changes Δε or fluctuations in the elongation ε occurring in the web in the course of the production run. 
   In order to counteract changes Δε or fluctuations in the web elongation ε, and in particular changes Δε in the web elongation occuring in the printing press section length between the last print unit and prior to further web processing by folding, occurring during the production run for the above mentioned reasons, the phase positions φ 1  and φ 2 , and therefore the phase shift Δφ, are determined and are compared with the reference variable Δφ-Soll. If, in the course of the production run, the deviation Δ in the difference Δφ from the reference variable Δφ-Soll occurs for one of the above mentioned reasons, this is an indication for a change Δε of the elongation ε of the web B. 
   If the phase shift Δφ has been defined as the difference Δφ=φ 2 −φ 1 , for example, an increase in the web elongation ε by Δε causes a deviation Δ of the phase shift Δφ from the reference variable Δφ-Soll, for example. 
   This deviation Δ, and therefore also the change Δε in the elongation ε, is now compensated for with the draw-in unit  02 , which is situated upstream of the first print unit  06 . This compensation is accomplished by effecting a change of the initial elongation ε 1 , until the reference variable Δφ-Soll of the phase shift Δφ has been restored. So that an oscillation, or an erratic web running of the web B is reduced or avoided, the regulation can also allow for certain tolerances in the deviation of the phase shift Δφ from the reference variable Δφ-Soll before the counter-measure of a change in the initial elongation ε 1  is taken. 
   The deviation Δ from the reference variable Δφ-Soll can, for example, be superimposed on the reference variable transducer of the drive regulating device  16 , for example as an interference variable Δ. The drive regulating device  16  of the traction roller  03  can be regulated with respect to torque, for example, wherein a feedback of the tension S 2  takes place. A path of the web B over an appropriate measuring roller  27 , for measuring the tension S 2  of the web B, is represented in dashed lines in  FIG. 1 . An interference variable Δ, corresponding to the deviation Δ from the reference variable Δφ-Soll, is superimposed on the reference value transducer of the drive regulating device  16 , for example as a correcting value ΔS2. Such a correcting value ΔS2 can be taken from a stored curve of the dependency of ΔS2 over Δ, for example, or can also be performed iteratively by raising or lowering the tension S2 until the phase shift Δφ again corresponds to the reference variable Δφ-Soll. 
   If it is intended to avoid abrupt changes in the force on the web B, it is also possible to fall back to a drive control device with DROOP behavior for the traction roller  03 . A load-dependent change of the reference variable of a circumferential or of an angular velocity or of the number of revolutions is called DROOP behavior, which behavior takes into consideration a change in the tension of the web B, for example S 4 , as well as a change in the angular velocity. In this case, a correcting value ΔS2 is superimposed on the reference variable S2-Soll for the tension S 2  which, together with the actual value of the tension S 2 , by use of the DROOP function, results in a corresponding trailing of the traction roller  03 , and therefore a different tension S 2  and a resultant different initial web elongation ε 1 , which, in the end, also appears as a change of the elongation ε. 
   Regardless of the type of regulation of the traction roller  03 , or of the draw-in unit  02 , it is essential that an interference variable Δ, derived from difference between the actual phase shift Δφ and the reference variable Δφ-Soll, is superimposed on the reference variable Δφ-Soll for the drive regulating device  16 , for example as the correction value ΔS2 of the desired tension S 2 . If required, it is possible to determine the phase position φ 1  on one of the subsequent print units  07  to  09  instead of at the print unit  06 , which is the first print unit in the conveying direction T. In this case, the phase shift Δφ must be determined between the respective print units  06  to  09  and the position of the marker  23  at the sensor  24 . The deviation Δ of the phase shift Δφ from the reference variable Δφ-Soll is again processed as the interference variable Δ for the drive mechanism of the traction roller  03 . 
   Concurrently with the determination of the phase positions φ 1  and φ 2 , and therefore of the phase shift Δφ from the reference variable Δφ-Soll for establishing the interference variable Δ, it is also possible to use the chronological or time dependant change of the phase shift Δφ or, if the interference variable Δ is determined linearly from the difference in the phase position φ 1  and φ 2 , also to use the change in the difference in the chronological change of the phase positions Δφ=φ 2 −φ 1 . In that case, Δφ≈0 in interference-free operation. 
   The correction value ΔS2, as the tension change ΔS2, can also be changed in other ways at the traction roller  03  by use of the interference variable Δ. The change of the tension S 2 , by use of the interference variable Δ, also includes changes in the force effect from a compensating roller, which is not specifically represented, or from other actuating devices for the tension S 2  arranged upstream of the first print unit  06 . 
   In an advantageous manner, no direct feedback of an elongation change Δε, detected downstream of the last print unit  09 , to the drive regulating device  17  of the traction roller  11  which is also arranged downstream of the last print unit  09 , takes place. Instead, a change of the initial elongation ε 1  takes place by a change of the tension S 2 . 
   With a change Δε of the elongation ε, a deviation Δ of the relative phase position Δφ from the reference variable Δφ-Soll, between a first measurement location by use of the sensor  18 , of the phase position φ 1  of the forme cylinder  21 , and the second measuring location by use of the sensor  24 , the position of the mark  23  on the imprinted web B after passage through the print units  06  to  09 , occurs. This deviation Δ is entered as an absolute value, or as a signed value, as the interference variable Δ for regulating the tension S 2  upstream of the first print unit  06 . By use of this method in accordance with the present invention, it is assured that, for subsequent work steps, such as folding or cutting, for example, there is a constant number of print images between the traction roller  11  and the following processing step, and that the frequency of the passage of the print images at the traction roller  11  is maintained almost constant. 
   A variation in the tension S 2  of the web B upstream of the first print unit  06  is tolerated, if necessary, in favor of a constant section length, or web elongation ε, downstream of the last print unit  09 . In any case, the web tension S 2  moves within a window of the permissible tension and of the resultant tension S 4  in view of the gradation during multi-web operations. 
   While a preferred embodiment of a method for regulation of a web tension in a rotary printing press, in accordance with the present invention, has been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that a number of changes in, for example the specific type of rotary printing press, the number of print units and the like could be made without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the following claims.