Abstract:
A turning bar is used to turn a web of material. The turning bar includes an outer jacket that is provided with holes on at least one section of its circumference. An inner chamber of the turning bar is provided with compressed air. A piston is arranged in the inner chamber and is movable to block selected ones of the holes. A motor is used to move the piston via a control signal provided by a control circuit. The turning bar can be pivoted by 90° on a frame around a pivot axis that is perpendicular to a longitudinal axis of the turning bar. A transmission couples a rotational movement of the piston around the longitudinal axis to a pivoting motion of the turning bar.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a turning bar for deflecting a web of material. The turning bar has a jacket with a plurality of holes and an interior compressed air compartment with a movable blocking element. 
     BACKGROUND OF THE INVENTION 
     Turning bars are used, in particular, at the output side of a rotary printing press if it is necessary to reroute several partial webs into which a paper web imprinted in the rotary printing press has been cut and which partial webs leave the press, lying next to each other, to a cutting device, in such a way that the partial webs can be placed on top of each other, folded, if necessary, and further processed. 
     DE 34 36 870 C1 discloses a turning bar. Displaceable pistons have a shape of their free ends which is matched to the course of travel of the web. These pistons can be rotated over 180°. 
     Turning bars, which are configured with an interior which can be supplied with compressed air, are known from U.S. Pat. No. 5,464,143 A. The jacket of the turning bar is provided with holes over at least a part of its circumference. Air can escape through these holes from the interior of the turning bar in order to form an air cushion between the turning bar and the web of material. 
     Pistons can be axially displaced in the interior of these turning bars which pistons, depending on their position inside the turning bar, will block a greater or fewer number of holes. This is done in order to match the width of the air cushion generated on the turning bar to the width of the web of material to be rerouted. 
     Such a matching of width is necessary, because compressed air escaping through the holes in the turning bar shell that is not covered by the web of material leads to an undesirable weakening of the air cushion which is generated by the holes covered by the web of material. As a result, the effect of the air cushion can be insufficient in the case of a narrow web of material. Moreover, the air currents exiting through the uncovered holes can interfere with the running of adjacent webs of material. 
     By using the turning bar disclosed in the above mentioned document, it is not possible to achieve an optimum matching of the shape of the air cushion to the course of the web of material. The reason for this is that the piston interiors are planar, while the edge of a web of material on the shell of the turning bar, which web of material typically is to be deflected by 90°, follows a helical line. If the piston is set in such a way that all of the holes which are not covered by the web of material are blocked, triangular zones are created in the edge areas of the web of material, in which zones the material web is not completely supported by an air cushion. If the pistons are set in such a way that the entire web is supported by an air cushion, holes which are supplied with compressed air necessarily remain uncovered. 
     To avoid this problem, pistons are used whose side facing the interior of the turning bar is not planar, but instead has edges whose courses respectively correspond on one half of the circumference to a right-turning helical line, and on the other half to a left-turning helical line. The pistons can be rotated around their axes within the turning bar so that, depending on the direction in which the web of material is rerouted, one or the other of the two helically-shaped edges can be turned toward the perforated portion of the circumference of the outside of the turning bar around which the web of material to be rerouted is looped. 
     By use of a piston shaped in this way it is possible to optimally use the compressed air available. The web of material is homogeneously supported by an air cushion over its entire width, and the escape of air which flows from uncovered holes is prevented. 
     In order to make use of the advantages of the piston described in the above mentioned U.S. patent, as well as those of the piston described here, every time the turning bar is used for rerouting a web of material of a different width, it is necessary to match the position of the pistons exactly to this material web width. Even if, instead of the width of material being changed, only the direction of rerouting the web of material is changed, this change can require a repositioning of the pistons. This process is very labor-intensive and arduous, because the pistons are not visible inside the shell of the turning bar. Although an operator can possibly look through the holes in the turning bar, as long as no web is conducted over the turning bar, in order to determine whether or not a hole is blocked by a piston, as soon as the web is being conducted over the turning bar, there is no longer an opportunity to check whether all holes covered by the web are indeed free, so that the air cushion is, in fact, generated over the required width. 
     DE 93 20 281 U1 discloses a pivotable turning bar which is coupled with an axially displaceable piston. The axial movement of the piston is coupled to the pivot movement of the turning bar. In another embodiment, a stationary motor, which displaces the piston via a flexible shaft, is provided for the axial movement of the piston. 
     U.S. Pat. No. 4,453,465 A discloses a pivotable turning bar, whose piston, which can be pivoted in the circumferential direction, is displaced by use of a gear. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a turning bar. 
     In accordance with the present invention, this object is attained by providing a turning bar, which is usable to guide a web of material, with a jacket that has a plurality of holes over at least a portion of its circumference. An interior chamber of the turning bar is supplied with compressed air. At least one blocking element is arranged in the interior chamber for the selective blockage of the holes. The turning bar is pivotable on a frame about an axis of rotation extending transversely to its longitudinal axis. Movement of the blocking element is coupled to the pivot movement of the turning bar. 
     The advantages to be obtained by the present invention consist, in particular, in that a matching of the position of the piston or pistons to the width, or to the position of a web of material on the turning bar can take place rapidly and definitely. Even the matching of the position of the piston or pistons, with a displacement of the web while the web is running, is easily possible. 
     To obtain these results and advantages, a motor for use in displacing the piston, and a control circuit are provided. The control circuit operates the motor in such a way that the piston takes up a desired position, which is determined by a control signal supplied by the control circuit. 
     Two types of signals in particular are considered for use as the control signal for the control circuit. One is a quantitative signal, i.e. a signal which can be assigned a numerical value and which makes it possible for the control circuit to operate the motor long enough until the piston has achieved a position corresponding to the numerical value. The other is a signal with at least two discrete states, one of which can be called a “prohibited” state, and the other of which can be called a “permitted” state, in which case the control can consist in operating the motor until the signal changes to the “permitted” state. 
     The first type of control signal is particularly suited for being picked up or generated at a device which is located upstream of the guide roller and which processes the web of material, such as a cutting tool. The control signal is formed either indirectly by measuring the position of an installation which determines the position of a web edge, or directly by derivation from a control signal which determines the position of such an installation. 
     A control signal of the second type can preferably be generated with the aid of a movable detector, which is coupled to the respective position of the piston for detecting the position of the web edge. In this case, the coupling can contain a mechanical connection between the piston and the detector. However, a coupling by mechanical control can be considered, in particular if the detector is distantly arranged along the path of the web of material. 
     A rapid and controlled adaptability of the piston position is particularly important in connection with a pivotable guide roller which is usable for permitting the selective deflection of the web of material in two different directions. The process of positioning the piston can be completely automated in this way, which further simplifies the adaptation of the guide roller in accordance with the present invention to various web widths, and possibly deflection directions. 
     A further advantage of the present invention resides in that following the pivoting of the turning bar, a separate work step of turning the piston for adapting the course of its edge to the course of the web edges can be omitted. 
     To prevent the escape of air through the slit, a sealing tape, which is being pressed against the edges of the slit by the air pressure, can advantageously be provided. In order to prevent an interference with the movement of the support by the sealing tape, the latter is preferably coupled to the piston and can be displaced in front of the slit. 
     Alternatively, the detector can also be applied inside the piston for use in detecting the presence or the absence of the web of material in front of one of the holes. 
     If the turning bar can be pivoted by 90° around an axis which is perpendicular with respect to the longitudinal axis of the guide roller, in order to selectively deflect the web of material in opposite directions, the edges of the web of material will describe a left-turning helical line or a right-turning helical line on the surface of the turning bar, depending on the direction of the deflection. By use of an axial rotation of the piston or pistons, it is always possible to bring the area of the piston edge, whose direction of rotation corresponds to that of the web edge, into contact with the perforated area of the surface of the guide roller in order to achieve, in this way, a course of the edge of the piston which is congruent with the course of the web edge. 
     To rapidly match the rotational position of the piston or pistons to the respective deflection direction, the axial rotation of the piston or pistons is preferably coupled to the pivot movement of the guide roller by the use of a gear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention are represented in the drawings and will be described in greater detail in what follows. 
       Shown are in: 
         FIG. 1 , a schematic view from above of a turning bar in accordance with the present invention, in 
         FIG. 2 , a side elevation view of the turning bar in  FIG. 1 , taken in the direction of the arrow II, in 
         FIG. 3 , a partial cross-section through the area of the turning bar identified by III in  FIG. 1 , in 
         FIG. 4 , a cross-section through the turning bar along the line IV—IV in  FIG. 1 , in 
         FIG. 5 , a sectional view through the end area of the turning bar in  FIG. 1 , in 
         FIG. 6 , an axial section through the center areas of the turning bar, in 
         FIG. 7 , a sectional view analogous to the one in  FIG. 5  through the end area of a turning bar in accordance with a second preferred embodiment of the present invention, in 
         FIG. 8 , a cross-section through a turning bar in accordance with a third preferred embodiment, and in 
         FIG. 9 , a schematic representation of turning bars and their control in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning initially to  FIG. 1 , there may be seen, generally at  01 , a first preferred embodiment of a turning bar in accordance with the present invention. The turning bar  01 , and which is shown in a view from above in  FIG. 1 , is a cylindrical hollow body, which is connected with a frame that is not specifically represented, by the use of a support arm  03  which is acting approximately on the center of a jacket  02  of the turning bar  01 . The support arm  03  has a joint  04 , which permits a pivotal movement of the turning bar  01  through an angle of 90° around an axis which extends perpendicularly to the plane of  FIG. 1 . The turning bar  01  is connected with the joint  04  by a connecting piece  06  which connecting piece  06 , in the end positions of the pivot movement of the turning bar  01 , comes into contact with one of two stops  07  situated on the support arm  03 . The length of each of the stops  07  is adjustable in order to be able to adjust the freedom of movement of the turning bar to exactly 90°. 
     A compressed air feed line, which is not specifically represented, extends through the support arm  03 , the joint  04  and the connecting piece  06 , and through which compressed air feed line an interior chamber of the turning bar  01  is supplied with compressed air. This interior chamber is bordered by the turning bar jacket  02  and by two blocking elements, for example pistons  17 , as seen in  FIG. 3 , which pistons  17  are axially displaceable inside the jacket  02  and whose structure will be discussed in greater detail in connection with  FIG. 3 . The turning bar jacket  02  is provided, on the half of its periphery that is facing away from the connecting piece  06 , with a regular arrangement of holes  08 , through which compressed air can escape from the interior chamber in order to form an air cushion for a web of material  09  that is deflected on the turning bar  01 . In  FIG. 1  this web of material  09  is shown as being transparent, its edges  11  are represented as dashed lines. 
     On the back of the turning bar jacket  02 , which is facing away from the holes  08 , two slits  12 , each of a length I, are provided and extend in the longitudinal direction of the turning bar  01 , on both sides of the connecting piece, one of which slits  12  can be seen in a side elevation view in  FIG. 2 .  FIG. 2  represents a side elevation view of the turning bar  01  taken in the direction of the arrow II in  FIG. 1 . A rod  13 , which connects a detector holder  14  or  15  with one of the two previously disclosed pistons  17  in the interior of the turning bar  01 , extends through each of the two slits  12 . In the preferred embodiment, the detector holder  14  is in the shape of a frame with an elongated hole, in which a detector unit of two photoelectric cells  16 , as seen in  FIG. 2 , is held adjustably parallel with the longitudinal axis of the turning bar  01 . As can be seen in  FIG. 2 , one of the two photoelectric cells  16  is oriented toward the top, or facing up, the other toward the bottom, or facing down. In the position of the turning bar  01  represented in  FIG. 1 , the downward oriented or facing photoelectric cell  16  of the detector holder  15  detects an edge  11  of the outgoing web of material  09 . The upward oriented or facing photoelectric cell  16  in the detector holder  14  detects an edge  11  of the incoming web of material  09 . 
     When the turning bar  01  is pivoted out of its first end position shown in solid lines in  FIG. 1  by 90° into its second or other end position, shown by dashed lines in  FIG. 1 , the upward oriented or facing photoelectric cell  16  of the detector holder  15  detects an incoming edge  11 , and the downward oriented or facing photoelectric cell  16  of the detector holder  15  detects an outgoing edge  11 . 
       FIG. 3  is a partial cross-sectional view through the turning bar  01  shown in  FIG. 1  and taken in the encircled area identified by III in  FIG. 1 . This partial cross-section shows a portion of the inner structure of the turning bar  01 , and in particular one of the two pistons  17 , which can be displaced in it. The level of the cross-sectional view is shown by the dash-dotted line identified by III in  FIG. 1 . The holes  08  and the slit  12  in the surface area of the turning bar  01  can be clearly seen in the cross-sectional view depicted in  FIG. 3 . 
     In  FIG. 3 , the piston  17  is shown in a view from above to the left of the longitudinal axis X—X of the turning bar  01 , and in section to the right of the longitudinal axis. Piston  17  has the approximate shape of a cup with a bottom  18  and with a lateral wall  19 , whose edge facing an interior chamber  21  of the turning bar  01  is formed by two helically shaped sections  22 ,  23 , each with an opposite hand or direction of turning. In the position of the piston  17  represented in  FIG. 3 , the section  22  facing the holes  08  has a right-handed direction of turning, and the section  23  facing the slit  12  has a left-handed direction of turning. 
     In this orientation of the piston  17 , as seen in  FIG. 3 , the right handed edge area  22  extends exactly parallel in respect to a web edge  11 , which web edge is shown looped around the turning bar  01  in its position shown in solid lines in  FIG. 1 . 
     To be able to bring the course of the right handed edge section  22  of the piston  17  into exact congruence with the web edge  11 , an axial displaceability of the piston  17  in the interior of the turning bar  01  is required. A first threaded spindle  24  is used for this purpose, which first threaded spindle  24  is in engagement with a screw thread in the bottom  18  of the piston  17  and which first threaded spindle  24  is rotatingly driven by an actuator, for example a motor  36 , shown in greater detail in  FIG. 5 . A second threaded spindle  26 , which can be rotatingly driven by the same motor  36 , passes through an opening in the bottom  18  of piston  17  without engaging the screw thread. It is in engagement with a screw thread in the bottom  18  of a second piston  17 , which second piston  17  is configured analogously to the depicted piston  17 , and which second piston  17  is housed diametrically opposite the first, depicted piston  17  in the turning bar  01 . 
     A rod  27 , which, as seen in  FIG. 5 , has a square cross section, extends along the axis X—X of the turning bar  01  and passes, with little play, through an opening in the bottoms  18  of both pistons  17 . It is fixedly connected with a gear  44 ,  46 ,  27 , represented in  FIG. 6 , and is used for rotating the pistons  17  around the axis X—X in response to the pivoting of the turning bar  01  between its two stop positions. 
     An annular groove  28 , in which a ring  29  can be rotated, is formed in the vicinity of the piston bottom  18  in the piston lateral wall  19 . The ring  29  is fixedly connected with the previously described rod  13  on which the detector holder  14  is arranged. It is possible, by use of the ring  29 , to rotate the piston  17  about the axis X—X without the detector holder  14  having to follow this rotating movement. Furthermore, a sealing strip  31 , which extends over the entire length of the slit  12 , and which slit  12  is open toward the interior chamber  21 , has been attached to the rod  13 , as seen in  FIG. 4 . 
       FIG. 4  shows this above described arrangement in a cross-sectional view at the height of the line IV—IV in  FIG. 1 . Over its entire length, the sealing strip  31  is inserted into recesses  32  on both sides of the slit  12 , so that it does not hinder the rotatability of the pistons  17 . A bracket  33  can be attached to the end of the slit  12  facing the connecting piece  06 , as seen in  FIGS. 3 and 4 , which maintains the sealing strip  31  pressed against the jacket  02  even when the interior chamber  21  is not charged with pressure and assures, in this way, that sealing strip  31  performs its sealing function as soon as compressed air is introduced into the interior chamber  21 . 
       FIG. 5  shows a section along the longitudinal axis X—X of the turning bar  01  through its end area  34 , which end area  34  of turning bar  01  is identified in  FIG. 1 . The previously mentioned motor  36  is housed in this end area  34  in a chamber, which is delimited in the direction toward the pistons  17 , which is an upward direction, as seen in  FIG. 5 , by a plate  37 . The plate  37  is maintained rotatably in the jacket  02  with the aid of a rolling bearing  38 . The square cross-section rod  27  is engaged, fixed against relative rotation, with the plate  37 . The threaded spindles  24 ,  26  are rotatably extended through the plate  37 , and each one has a driven wheel  39 ,  41  on its end in the interior of the chamber. A drive wheel  42 , which is complementary to the driven wheels  39 ,  41 , has been mounted on the driveshaft  43  of the motor  36 . The driveshaft  43  can be displaced in the direction of the longitudinal axis X—X between the position shown in  FIG. 5 , in which the drive wheel  42  is in engagement with the driven wheel  39 , and an engagement position with the driven wheel  41 . Thus, by the selective displacement of the driveshaft  43 , the motor  36  can be selectively used for displacing either piston  17 . The wheels  39 ,  41 ,  42  can be friction wheels or gear wheels, to make the engagement of the wheels with each other easier, the driven wheels  39 ,  41  can be frustoconical, and the drive wheel  42  can be double-frustoconical. 
     When the turning bar  01  is pivoted, for changing the deflection direction of the web of material  09 , this requires, as already stated above, a rotation of the pistons  17  by 180°. The threaded spindles  24 ,  26  follow this rotation, so that they exchange places in  FIG. 5 . The motor  36  is not rotated during this rotation of the pistons, so that the engagement of the drive wheel  42  with one of the driven wheels  39 ,  41  can be maintained in the course of this rotation and in spite of this rotation. It is, of course, also possible to cause the selective displacement of both pistons  17  with the aid of only one motor  36  with the aid of a different coupling mechanism than the one described above. It is also conceivable to assign each threaded spindle  24 ,  26  its own motor, each of which motor, in this case, could be attached to the respective end of the turning bar  01  which is adjoined by the piston  17  that is driven by the motor. This motor can be arranged fixed in place, or in such a way that it follows the rotating movement of the bar. 
       FIG. 6  shows a drive mechanism that is usable for effective a rotation around 180° of the pistons  17  in response to a pivot movement of the turning bar  01  from one of its work positions into the other. The reference numeral  44  indicates a portion of a drive gear wheel, or a drive gear wheel segment, which is housed in the connecting piece  06 . This drive gear wheel, or drive gear wheel segment,  44  can be arranged fixed in place in the connecting piece  06 , but could also be coupled to the position of the turning bar  01  in such a way that it performs a rotation itself in response to a pivot movement of the turning bar  01 . This drive gear wheel, or drive gear wheel segment,  44  meshes through a helical gearing with a further, or driven gear wheel  46 , which is rotatable around the longitudinal axis X—X of the turning bar  01  and which substantially fills the free cross section of the interior chamber  21  of the turning bar  01 . In  FIG. 6 , this driven gear wheel  46  is shown in section to the left of the longitudinal axis X—X, and in a top plan view to the right of the axis. Driven gear wheels  46  is fixedly connected with the rod  27 . The threaded spindle  26 , which is used for driving the piston  17  at the end of the turning bar  01  facing away from the motor  36 , is passed, freely rotatable, through a bore in the driven gear wheel  46 . The threaded spindle  24 , which is used for driving the piston  17  adjoining the motor  36 , is rotatably seated in the driven gear wheel  46 . The drive gear wheel, or drive gear wheel segment,  44  and the driven gear wheel  46  are laid out in such a way that they convert a pivot movement of the turning bar  01  by 90° around the axis of the joint  04  into a rotation by 180° of the driven gear wheel  46 , and therefore of the pistons  17 . In this way, the gear train  44 ,  46 ,  27  shown in  FIG. 6  assures that the pistons  17  are in a rotation orientation respectively matched to each one of the two working positions of the turning bar  01 . 
     To match the turning bar  01  to the guidance of a fresh web of material  09 , it is possible to proceed as follows. First, the pistons  17  are displaced into their stop positions adjoining the respective ends of the turning bar  01  by operation of the motor  36  and the threaded spindles  24  and  26 . In this position of the pistons, the detectors are not located opposite a web of material  09  guided over the turning bar  01 . A signal level supplied by the detector unit in this state is considered to be a “prohibited” level. 
     Thereafter, each of the pistons  17  is displaced out of its stop position toward the center of the turning bar  01  until the detector unit of each piston  17  registers a web edge  11  and changes its output signal to a “permitted” level. Since, in each of the two working positions of the turning bar  01 , only one of the two photoelectric cells  16  of each detector unit can lie opposite only one web edge  11 , it suffices for evaluating the detector signal to evaluate an OR-linkage of the signals generated by the two photoelectric cells  16  of each detector unit for detecting that the web edge  11  has been detected by the detector unit. To increase the detection assurance, it can also be provided that, depending on the working position of the turning bar  01 , only one of the two photoelectric cells  16  of each detector unit is operated. A control circuit for performing this task is not separately represented in  FIG. 6 . 
     When the position of the detector unit  16  in each of the detector holders  14 ,  15  has been correctly adjusted, at the moment at which the detector unit  16  registers the web edge  11 , the position of the edge section  22  or  23  of the piston  17  facing the outside of the jacket  02  exactly corresponds to the course of the edge  11  of the web of material  09  on the turning bar  01 . Thus, the two pistons  17  cut off or occlude all of those holes  08  on the jacket  02  of the turning bar  01  from the compressed air supply out of the interior chamber  21 , which are not covered by the web of material  09 ; however, it is possible to generate a homogeneous air cushion over the entire surface under the web of material  09 . 
       FIG. 7  shows a sectional view through the end area of the turning bar  01  in accordance with a second preferred embodiment of the present invention. The position of the section is the same as in  FIG. 5 . Elements which correspond in their shape or function to elements in the previously described first preferred embodiment have been provided with the same reference symbols. In this second preferred embodiment, the plate  37  is connected, fixed against relative rotation, with the jacket  02 , the rod  27  is rotatably seated on the plate  37 . Through the wheels  42 ,  39 , the motor  36  drives only one spindle  26  of one of the pistons  17 ; a corresponding motor for the other piston is located at the other end of the turning bar  01 . An exterior wheel  48 , acting through a slit  47  in the jacket  02 , is in engagement with the drive wheel  42 . Exterior wheel  48  transmits a rotation of the motor  36  to a threaded spindle  49 , which is maintained outside of the turning bar  01  parallel with the latter. This threaded spindle  49  drives a detector holder, which is not represented in  FIG. 7 , such as the detector holder  14  in  FIG. 1 , to make a movement of the detector holder which is coupled to the movement of the piston  17 . 
       FIG. 8  shows a third preferred embodiment of the turning bar  01  of the present invention in cross section. The essential difference between the previously described first and second preferred embodiments and the third preferred embodiment in accordance with  FIG. 7  is the arrangement of the detectors. The detectors can again be photoelectric cells  16 , for example. In the third embodiment in accordance with  FIG. 8 , these photoelectric cells  16  are arranged in the interior of the turning bar  01 . They are respectively embedded in the lateral wall  19  of the pistons  17 , each in the vicinity of the piston edge section  22 ,  23 , so that they can detect the presence of the web  09  as long as the detectors  16  are located in front of one of the holes  08 . Although with this embodiment the accuracy with which the position of the web edge  11  can be detected is limited by the distance of the holes  08  in the axial direction, this does not interfere with the functionality of the device, since the piston  17  in the interior of the turning bar  01  can be displaced by just this distance without the number of the open or blocked holes being changed by this. 
     With this third embodiment, a flow sensor in particular can be employed, which flow sensor registers the flow of air from the interior chamber  21  to the outside when the flow of air passes a hole  08  which is not covered by the web of material  09 . 
       FIG. 9  shows a schematic representation of turning bars  01  and their control in accordance with the present invention. A plurality of turning bars  01  are arranged, for example, following a cutting device, in which a web of material  09 , in particular an imprinted paper web  09 , is cut into a plurality of partial webs  09 , each of which partial webs  09  is deflected by a turning bar  01 . The position of the individual rotating cutters  51  of the cutting device can be set at a control console  54 . A control signal, indicating the desired position of each cutter  51 , is supplied to actuating units, which are not specifically represented, of the cutters  51 , via a signal line  52 . This control signal, which simultaneously also defines the position of the edges  11  of the partial webs  09  cut by the cutters  51 , is branched off to a control circuit  53  which calculates from this control signal, and taking into consideration the positions of the turning bars  01 , which can be displaced transversely to the web direction, the respective desired positions of the pistons  17  in the interior of the turning bars  01  and actuates their motors  36  in order to cause the pistons  17  take up this desired positions. 
     Alternatively, the control signal could also be obtained with the aid of position detectors, which measure the position of the cutters  51 , or of the web edges  11  created by them, in the cutting direction. 
     In order to set the desired position calculated in this way, the control circuit can maintain the actual position of each individual piston  17  in a memory, can calculate the difference between both positions, and can operate each motor  36  at a known rotational speed until the respective piston  17  should have changed from the actual position into the desired position. The control circuit also has an operating state for displacing the respective piston  17  to an end position. This operating state is independent of the control signal. 
     It is alternatively possible to provide an operating state of the control circuit  53  in which, for matching a changed web width or a changed position of the turning bars, each piston  17  initially moves into a stop position. Once this has been reached, a change into a control state is made, in which the control circuit, starting at this exactly known stop position, arrives at the desired position by operating the motor  36  for a calculated angle of rotation or a calculated time at a known rotational speed. 
     A first actuating element for pivoting the turning bar and a second actuating element for moving the blocking element are alternatively arranged. The two actuator elements are electrically coupled. 
     While preferred embodiments of a turning bar in accordance with the present invention have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that various changes in, for example the printing press with which the turning bar is used, the type of cutters used to cut the web, the widths of the webs 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 appended claims.