Patent Publication Number: US-2022219928-A1

Title: Rotary Frame Construction for Web Transport Control Devices

Description:
The invention relates to a rotary frame construction for web transport control devices, the rotary frame construction comprising a carrier frame and a rotary frame which extends in parallel with the carrier frame and carries an input roller and an output roller for a web to be controlled and is pivotably mounted on the carrier frame by means of a bearing, the bearing having a virtual rotation center that is defined by control surfaces of one of the carrier frame and the rotary frame, the control surfaces being scanned by cam followers on the other of the frames, the frames being held in parallel alignment by means of support rollers on one of the frames and associated run surfaces on the other frame, the frames being connected with one another so as to be pivotable by means of a drive system. 
     When running material webs are processed, for example in a rotary printing press, it is generally necessary to steer or feedback-control the movement of the web, in order to prevent the web from migrating in the direction transverse to the running direction. To that end, the web is threaded through the rotary frame construction such that it is respectively deflected, by 90° for example, at the input roller and at the output roller. If the running direction deviates from the desired direction, the rotary frame which carries the input roller and the output roller is rotated relative to the carrier frame such that the input and output rollers take another posture and steer the web back into the desired direction. 
     In most conventional rotary frame constructions, the input roller and the output roller are mounted, with their axes in parallel, on a plane that is parallel with the rotary frame but is offset from the plane of the rotary frame such that the rollers can rotate freely. The rotary frame and the carrier frame are approximately congruent and are also arranged in planes that are offset from one another, so that they can be pivoted relative to one another. Thus, as a whole, the rotary frame construction has a three-layer design. 
     The rotation center about which the rotary frame is pivoted relative to the carrier frame should ideally be positioned in the center of the incoming web, so that the pivotal axis is orthogonal to the plane of the rotary frame and extends tangentially with respect to the outer vertex of the input roller. In this way, it can be achieved that, when the rotary frame is pivoted, the incoming web remains practically stationary whereas the outgoing web is displaced in the desired direction. 
     A bearing with a virtual rotation center has the advantage that the ideal position for the pivotal axis can be realized without any mechanical axis or bearing elements that could collide with the incoming web being present in this position. 
     A rotary frame construction of the type described above has been disclosed in DE 20 2017 100 819 U1. The control surfaces that define the virtual rotation center are formed by cylindrically curved walls that are centered on the virtual rotation center. The corresponding cam followers are formed by sets of follower rolls which run on both, the concavely curved side and the convexly curved side of the walls, so that the degrees of freedom of motion in the plane parallel with the frame are reduced to one degree of freedom of rotation. The run surfaces for the support rollers are formed by support sheets that extend in parallel with the frame, and the support rollers are respectively arranged on both sides of the support sheet and run on both surfaces of the support sheet, so that the frames are held in a fixed position in the direction normal to the planes of the frames and cannot be tilted about an axis extending in parallel with the plane of the frame, neither. 
     It is an object of the invention to provide a rotary frame construction that has a simplified design. 
     According to the invention, in order to achieve this object, the control surfaces are constituted by three control curves that are formed at the outer edges of a cam plate that is rigidly held on one of the frames, two of the control curves being located on one side of the cam plate and the third on the opposite side of the cam plate, and the other of the frames has three cam followers that are respectively associated with one of the control curves. 
     In the construction according to the invention, the control surfaces can simply be formed by a single plate which can be machined, for example by laser cutting, such that the edges of the plate form the control curves with the desired curvature. Since the cam followers, e.g. follower rolls, engage the control curves from opposite sides, the restriction of the degrees of freedom of motion in the direction parallel to the planes of the frames is achieved with only three cam followers. In this way, it is possible to achieve a low-resistance pivotal movement of the rotary frame, which movement can therefore be controlled precisely. 
     At the same time, a low constructional height of the frame construction (when installed horizontally) is achieved because at least parts of the carrier frame and the rotary frame, namely the cam plate and the cam followers, must be arranged in a common plane, and therefore additional design freedom is obtained for installing the rotary frame construction in a machine. 
     Useful embodiments of the invention are indicated in the dependent claims. 
     A particularly compact design can be achieved by arranging the carrier frame and the rotary frame approximately in a common plane, with the one frame (e.g. the rotary frame), surrounding the other frame (the carrier frame) with a certain spacing. 
     The cam plate can optionally be part of the rotary frame or part of the carrier frame. For simplicity, only the case that the cam plate forms part of the rotary frame shall be discussed in the description below. Then, the rotary frame, which surrounds the carrier frame with its outer legs, has a horizontal cross-bar on which the cam plate is arranged such that it is also surrounded by parts of the carrier frame on which the cam followers have been formed. 
     In a useful embodiment, the support rollers which assure the parallel alignment of the frames and are arranged for example on the carrier frame, are respectively accommodated with little play in a slot that is formed in the other frame (the rotary frame), with the parallel edges of the slot forming the run surfaces for the support rollers. In this way, a relative movement in the direction normal to the planes of the frames can be prevented already with a single support roller because this support roller can only move in the slot in the direction parallel with the plane of the frame. A little play between the support roller and the edges of the slot enables the support roller to roll with low friction on either the one or the other of the edges of the slot, depending upon which of the two edges of the slot the support roller is urged against. The play can be kept so low that it is smaller than the admissible tolerance for a relative movement of the frames in the direction normal to the planes of the frames. 
     This mechanism for parallel alignment of the frames can also be taken advantage of independently of the features of claim  1  as discussed above. Thus, the present disclosure encompasses also a rotary frame construction according to the preamble of claim  1 , which is characterized in that each of the support rollers is accommodated with little play in a slot formed in the other frame and having parallel edges that constitute the run surfaces. 
     If the cam plate is held in a cross-bar that extends in parallel with the plane of the rotary frame, then the slots for the support rollers can be formed in connector parts that connect the cam plate to the cross-bar. In this way, a particularly simple design of the rotary frame construction can be achieved. The follower rolls that roll along the edges of the cam plate can be rotatably supported on a plate of the carrier frame so as to be rotatable about vertical axes (if the planes of the frames extend horizontally). This plate may also mount brackets which have vertical legs in which the support rollers that engage in the slots of the connector part are rotatably supported with horizontal axes of rotation. 
     Due to inevitable manufacturing tolerances, the bearing that defines the virtual rotation center has a certain bearing play that may compromise the accuracy of the web transport control. Also, the drive system that moves the rotary frame relative to the carrier frame in the one direction at one time and into the other direction at another time has generally a certain play. In a useful embodiment, the drive system is self-arresting at least in one direction. Then, both, the bearing play and the play in the drive system can easily be eliminated by elastically biasing the frames against one another and against the self-arresting force of the drive system. This feature can also be taken advantage of independently of the features of claim  1 . The present disclosure therefore encompasses also a rotary frame construction according to the preamble of claim  1  which is characterized in that the drive system is self-arresting at least in one direction and the frames are elastically biased against one another in the rotary direction in which the drive system is self-arresting. 
     For example, the drive system may be a linear drive that acts between two levers that are formed on the two frames. The elastic bias may for example be achieved by means of a simple tension spring that draws the two levers together. 
    
    
     
       An embodiment example will now be described in conjunction with the drawings, wherein: 
         FIG. 1  is a schematic top plan view of a rotary frame construction; 
         FIG. 2  shows the rotary frame construction with a slightly pivoted rotary frame; 
         FIG. 3  is a view of the rotary frame construction as seen in the direction of arrows III-III in  FIG. 1 ; 
         FIG. 4  is an enlarged side view of the rotary frame construction as seen in the direction of arrows IV-IV in  FIG. 1 ; 
         FIG. 5  is a plan view of a base plate of a carrier frame; 
         FIG. 6  is a top plan view of a support plate of the carrier frame; 
         FIG. 7  is the front view of the carrier frame; 
         FIGS. 8 and 9  are front views of two fastening members for fastening a cam plate to the rotary frame; and 
         FIG. 10  is a plan view of the cam plate. 
     
    
    
       FIG. 1  shows a top plan view of a rotary frame construction comprising a carrier frame  10  and a rotary frame  12  that are pivotable relative to one another about a virtual rotation center P.  FIG. 2  shows the rotary frame construction with the rotary frame slightly pivoted. For ease of distinction, all parts that belong to the (stationary) carrier frame  10  have been shown in bolder lines than the parts that are movable with the rotary frame  12 . 
     An input roller  14  and an output roller  16  are rotatably supported in the rotary frame  12 , and a material web which has not been shown and the movement of which shall be steered by means of the rotary frame construction is threaded over the input and output rollers. For example, the material web may, in inverted U-thread, run upwards (in the direction towards the viewer in  FIG. 1 ) to the input roller  14  where it is deflected in the horizontal direction so as to be passed-on to the output roller  16  where it is deflected again so that it will then move downwards. 
     The carrier frame  10  has a horizontal base plate  18  the greatest part of which is hidden by the rotary frame  12  in  FIG. 1 , so that only the left edge of the base plate  18  is visible. On the right side in  FIG. 1 , the base plate  18  forms a lever  20  that projects beyond the lateral edge of the rotary frame  12  and is connected to a bracket or a lever  24  of the rotary frame via an articulated linear drive  22 . When the linear drive  22  draws the levers  20  and  24  together, the rotary frame  20  pivots about the vertical pivotal axis that passes through the rotation center P, as has been shown in  FIG. 2 . This pivotal axis forms a tangent to the input roller  14 , so that the input roller and, therewith, the incoming material web does not make any lateral movement when the rotary frame  12  is rotated, whereas the output roller  16  and the outgoing material web are displaced in lateral direction. 
     The rotary frame  12  forms a gutter-shaped downwardly open casing  26  the top wall of which forms a cross-bar  28  for holding a cam plate  30  that is accommodated in the interior of the casing  26  and is connected to the cross-bar  28  by a wall member  32  that is trapezoidal in plan view. The edge of the cam plate  30  forms, on the bottom side in  FIG. 1 , two control curves  34  shaped as circular arcs and, on the top side, another control curve  36  shaped as a circular arc. The control curves  34  and  36  are centered on the virtual rotation center P. In order to illustrate the curvature of the control curves  34 ,  36  more clearly,  FIG. 1  shows extended circular arc segments (continuous lines). Associated with each of the control curves  34 ,  36  is a follower roll  38  that is supported on the carrier frame  10  so as to be rotatable about a vertical axis. The three follower rolls  38  engage the edge of the cam plate  30  practically without play, so that this cam plate and, therewith, the entire rotary frame  12  can only perform a circular movement relative to the carrier frame about the virtual rotation center P. 
     Four brackets  40  that project vertically from the base plate and each support a support roller  42  have been welded onto the carrier frame  10 . Two of these support rollers  42  are accommodated in slots  44  ( FIG. 8 ) that extend horizontally in the legs of the trapezoidal wall member  32 . These legs of the wall member  32  are angled such that they extend tangentially to an arc of a circle around the virtual rotation center P. If a downwardly directed force (weight) acts upon the rotary frame  12 , then the top edges of the slots  44  are urged against the support rollers  42  so that the wall member  32  and, therewith, the entire rotary frame  12  are supported on the support rollers  42 . When the rotary frame is pivoted, there is a relative movement between the support roller and the slot, and the support roller rolls along the top edge of the slot. 
     In the case that the rotary frame  20  is subject to an upwardly directed force, the lower edges of the slots  44  are urged against the support rollers  42 , and in case of a pivotal movement, the support rollers will roll along these lower edges of the slots. The play of the support rollers  42  in the slots  44  is on the one hand so large that the support rollers can move with low friction and is on the other hand so small that the vertical movement of the wall member  32  relative to the support frame, as admitted by the play, remains within the admissible tolerances. 
     The casing  26  of the rotary frame  12  accommodates another wall member  46  that is trapezoidal in plan view and is fixed on the bottom side of the cross-bar  28 , and slots  48  are formed in the angled legs of this wall member ( FIG. 9 ). Two of the four support rollers  42  are accommodated in these slots of the wall member  46 . The legs of this wall member are also angled such that they extend tangentially to an arc of a circle around the virtual rotation center P. The wall member  46  is therefore guided and supported with low play by the support rollers  42  in the same manner as the wall member  32 . All in all, the engagement of the support rollers  42  in the slots  44 ,  48  prevents a vertical movement of the rotary frame relative to the carrier frame, and the rotary frame and the carrier frame are held in exact parallel alignment. 
     A holder  50  for one end of a tension spring  52  is mounted on the base plate  18  of the carrier frame and on the lever  20  formed by this base plate. The other end of the tension spring is anchored at the lever  24  of the rotary frame  12 , so that a permanent tensioning force is produced that has the tendency to draw the levers  20  and  24  together and to rotate the rotary frame  12  counter-clockwise relative to the carrier frame  10 . However, the linear drive  22  is self-arresting at least in the direction in which its length decreases, so that the torque exerted by the tension spring  52  does not actually cause a rotation of the rotary frame  12 . However, the elastic bias that is caused by the spring  52  has the effect that any play in the bearing formed by the control curves  34 ,  36  and the follower rolls  38  as well as any play in the linear drive  22  and its articulated joints with the levers  20 ,  24  is eliminated. 
     When the machine of which the rotary frame construction described here forms part is operating, the lateral position of the material web is detected by means of a sensor, and the linear drive  22  is controlled by means of a controller such that the position of the material web is adjusted to a target value. In this feedback-control process, the linear drive  22  is alternatingly extended and retracted in order to rotate the rotary frame in the one direction or the other. The tension spring  52  assures that no hysteresis occurs in this control process because the spring will always hold all components of the system in which a certain play may occur at the same limit of the range of movement that is admitted by the play. 
       FIG. 3  shows the rotary frame construction in a front view. Welded on the base plate  18  of the carrier frame  10  is a support plate  54  on which the follower rolls  38  are rotatably supported. The contours of the base plate  18  and the support plate  54  have been shown separately in  FIGS. 5 and 6 .  FIG. 6  also shows bearing holes or bearing axles  56  for the follower rolls  38 . In  FIG. 5 , the positions of these bearings axles have been shown in phantom lines. The base plate  18  has recesses  58 ,  60  which accommodate the ends of the bearing axles. 
     The brackets  40  for the support rollers  42  are also welded to the support plate  54 . In order to assure an exact positioning and safe immobilization of the brackets  40 , these brackets are formed, on the edge facing the support plate  54 , with pegs which have not been shown and which engage in corresponding peg holes of the support plate  54 . 
       FIG. 7  shows the entire carrier frame in a front view. The wall member  32  with trapezoidal contour that forms the slots  44  for the support rollers  42  is visible in  FIG. 3  and has been shown separately in  FIG. 8 . This wall member is also formed with projecting pegs at its top edge, the pegs engaging in corresponding peg holes (not shown) of the cross-bar  28 . 
       FIG. 9  shows a front view of the wall member  46  forming the slots  48  for the two other support rollers  42 . This wall member is also formed with pegs  64  at its top edge, for engagement into peg holes of the cross-bar  28 . 
     In  FIG. 3 , the wall member  46  is largely obscured by the wall member  32  that is disposed in front thereof, so that what is visible are only downwardly projecting studs  66  ( FIG. 9 ). These studs are formed at their bottom ends with pegs  68  for engagement in peg holes  70  of the cam plate  30  a plan view of which has been shown separately in  FIG. 10 . The cam plate  30  is welded to the pegs  68  and is thereby immobilized in its position in the rotary frame  12 . For further stabilization, the cam plate  30  has projections  72  at both ends, these projections being in form-fitting engagement with corresponding recesses in side walls  74  of the casing  28 , as can be seen in  FIG. 3 . 
       FIG. 4  shows the rotary frame construction in a side view. Of the carrier frame, only the base plate  18  is visible here. The side walls  74  of the casing  26  of the rotary frame are prolonged at both ends to form bearing brackets  76  for the input roller  14  and the output roller  16 . These bearing brackets may have different shapes, depending upon the desired type of threading of the material web.  FIG. 4  shows the configuration for inverted U-thread. In this configuration, the entire constructional height of the rotary frame construction is only slightly larger than the diameter of the input and output rollers  14 ,  16 . Moreover,  FIG. 4  shows one of the projections  72  of the cam plate that penetrate the side wall  74 .