Abstract:
A device for laterally aligning sheets in sheet-processing machines includes a pulling device having a drivable transport roller and a dabber roller mounted on a pivotable lever. A spring system cooperates with the lever for adjusting a pressing force between the rollers. The spring system has a progressive spring characteristic.

Description:
BACKGROUND OF THE INVENTION 
   FIELD OF THE INVENTION 
   The invention relates to a device for laterally aligning sheets in sheet-processing machines, especially printing presses. 
   Lateral alignment of an infed sheet is usually performed by a pulling or pushing lay, which pulls or pushes the sheet against a stop. In this regard, a force is exerted on the sheet, which moves the sheet into a friction lock against the stop. The pull force or traction has to be adjusted in accordance with the speed, grammage and other settings, such as, vacuum or suction air applied to the suction belt. For printing materials with a low grammage, for example, a low pulling force is needed, and for printing materials with a high grammage, a high pulling force is needed. In addition, regions of lower grammages require a more precise setting of the pulling force than regions of high grammages. 
   A device of the type referred to at the introduction hereto has been disclosed in German Published, Non-Prosecuted Patent Application DE 30 11 626 A1. In that case, the pulling or pushing force is effected by two rollers which are set against one another and by which, in principle, cost-effective, exact lateral alignment of the sheet is made possible. In particular, in this regard, the sheet is pressed against a rotating roller by a freely rotatable roller, a so-called dabber roller. The required pressing force is applied by a tension or compression spring. 
   In the heretofore known reel-to-reel system according to the aforementioned German Published, Non-Prosecuted Patent Application DE 30 11 626 A1, the pulling force is adjusted via a spring and an adjusting screw. The spring is of the type having a linear characteristic. The adjustment is thereby equally precise over the entire range of the pulling force. If one would wish to increase the maximum possible pulling force within the existing installation space, this increase would be achieved at a cost of the adjustment accuracy. 
   Attempts have been made to vary the precision of the adjustment (note hereinabove), depending upon the respective requirements, by providing different compression springs, which the printer has to install in the pulling lay, depending upon the grammage. A disadvantage of such a solution for the problem is the great effort that must be made for installation or assembly purposes when the printing material has to be changed, and that material parts tend to lie around in the open in the vicinity of the feeder. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a device for laterally aligning sheets in sheet-processing machines, especially printing presses, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which it is possible to adjust a pulling force in a relatively simple manner without additional installation or assembly work over the greatest possible region of printing material, so that adjustment accuracy should be high in regions that require only a comparatively low pulling force. 
   With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for laterally aligning sheets in sheet-processing machines, comprising a pulling device having a drivable transport roller and a dabber roller mounted on a pivotable lever. A spring system cooperates with the lever for adjusting a pressing force between the rollers. The spring system has a progressive spring characteristic. 
   In accordance with another feature of the invention, the lever has a bearing axis and has a point at which the spring system is applied to the lever. At least one of the bearing axis and the spring application point is adjustable in location along the lever. 
   In accordance with a further feature of the invention, the spring system serves for applying a force to the lever in a direction defined by an angle which is adjustable. 
   In accordance with an added feature of the invention, the spring system has a spring characteristic composed of a plurality of linear sections of varying slope. 
   In accordance with an additional feature of the invention, the spring system has a continuously progressive characteristic. 
   In accordance with yet another feature of the invention, the spring system further comprises at least two helical compression springs disposed coaxially with respect to one another and connected in tandem. 
   In accordance with yet a further feature of the invention, the at least two helical compression springs are of different hardness and, together with a guide pin extending therethrough, are disposed behind one another in a blind borehole provided in a sleeve part formed as an adjusting screw. A first one of the helical compression springs has a harder spring characteristic and serves for acting directly on the lever of the pulling device. A second one of the helical compression springs has a softer spring characteristic and adjoins the first helical compression spring at a rear end thereof. 
   In accordance with yet an added feature of the invention, the guide pin has a collar spatially separating the first and the second helical compression springs. The sheet-aligning device further includes a ledge formed in the adjusting screw in an upper part of the blind borehole. The ledge serves as a stop in cooperation with the collar. 
   In accordance with yet an additional feature of the invention, a first one of the helical compression springs is directly active on the lever and has a harder characteristic than a second one of the helical compression springs. The first spring carries a pot-like sleeve at a rear end of the first spring. The pot-like sleeve is formed with a radially outwardly directed rim by which the sleeve engages over the rear end of the first spring. The second spring is received in the pot-like sleeve and is braced against a rear end of an adjusting screw which is surrounded by the first and second helical compression springs in such a manner that the first and second helical compression springs are disposed concentrically with respect to one another. 
   In accordance with still another feature of the invention, the spring system further comprises at least two helical compression springs disposed coaxially with respect to one another and connected in parallel. 
   In accordance with still a further feature of the invention, the two springs, respectively, are a first helical compression spring with a harder characteristic, and a second helical compression spring with a softer characteristic disposed concentrically within the first helical compression spring. The two springs are directly actable on the lever. The first helical compression spring is braced against a rear surface of a stop fixed to a housing, and the second helical compression spring is braced against a rear surface of an adjusting screw surrounded by both the first and the second helical compression springs. 
   In accordance with still an added feature of the invention, the spring system is a conical helical compression spring having a diameter which increases towards the lever. 
   With the objects of the invention in view, there is also provided a sheet-fed printing machine, comprising a device for laterally aligning sheets, including a pulling device having a drivable transport roller and a dabber roller mounted on a pivotable lever. A spring system cooperates with the lever for adjusting a pressing force between the rollers. The spring system has a progressive spring characteristic. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a device for laterally aligning sheets in sheet-processing machines, especially printing presses, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic, partly-sectional, side-elevational view of an embodiment of a pulling device according to the invention, with two compression springs connected in series or tandem; 
       FIG. 2  is an enlarged, fragmentary, partly-sectional view of a portion of  FIG. 1 , showing the embodiment of the pulling device in a different operating phase thereof wherein the compression springs have only a weakly loaded setting; 
       FIG. 3  is a further view similar to  FIG. 2  showing the embodiment of the pulling device in yet a different operating phase thereof wherein the compression springs are in a heavily loaded end setting thereof; 
       FIG. 4  is a greatly diagrammatic, longitudinal-sectional view of a different embodiment of the pulling device of  FIG. 1 , having compression springs connected in series or in tandem, i.e., behind one another; 
       FIG. 5  is a view similar to  FIG. 4 , of yet a different embodiment of the pulling device in a different operating phase thereof, having yet a different construction of the springs; 
       FIG. 6  is a view similar to those of  FIGS. 4 and 5 , of a helical compression spring for the pulling device, which is conical; 
       FIG. 7  is a plot diagram depicting spring force with respect to spring travel of a plurality of different characteristic curves of a spring system for a pulling device; 
       FIG. 8  is a greatly diagrammatic side-elevational view of an embodiment of a pulling device; 
       FIG. 9  is a top-plan view of  FIG. 8 ; 
       FIG. 10  is a view similar to  FIG. 8 , but for the bearing axis of the lever being longitudinally displaced; 
       FIG. 11  is a top-plan view  FIG. 10 ; 
       FIG. 12  is a view similar to that of  FIG. 8  showing the pulling device according to  FIG. 8 , however, with a force application point of the spring system thereof displaced in longitudinal direction from the force application point shown in  FIG. 8 ; and 
       FIG. 13  is a view similar to that of  FIG. 8  showing the pulling device according to  FIG. 8 , however, with the direction of force application of the spring system thereof being swivelled away from that of FIG.  8 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a pulling device according to the invention including a driven transport roller  10  for non-illustrated sheets to be printed, and a freely rotatable dabber roller  11 . The dabber roller  11  is mounted at  12  on a lever  13 , which is pivotably attached at  14  to a supporting frame generally identified by reference numeral  15 . 
   The lever  13  is acted upon from above by a force applied by a spring system  16 . As can also be seen in particular from the enlarged fragmentary and somewhat simplified view of  FIG. 2 , the spring system  16  is formed of two helical compression springs  17  and  18  which are disposed in tandem coaxially with respect to one another and are disposed in a blind borehole  19  formed in an adjusting screw  20  constructed as a sleeve part. The adjusting screw  20  has a (lower) threaded shank  21 , by which it is screwed into a corresponding threaded bore  22  formed in a housing part  23 . A lock nut  24  is screwed onto the upper end of the threaded shank  21 . Also disposed in the blind borehole  19 , surrounded by the two compression springs  17  and  18 , is a guide pin  25  formed with a collar  26 . Braced against the collar  26  on one side, from below, is the compression spring  17  and, on the other side, from above, is the compression spring  18 . The (upper) compression spring  18  has a lower spring constant and therefore a flatter characteristic than the (lower) compression spring  17  (in this regard, note also FIG.  7  and the associated explanations provided further hereinbelow). The collar  26  on the guide pin  25  thus forms a stop which limits the spring travel of the upper (softer) compression spring  18 . In this regard, the guide pin  25  is moved upwardly by the harder (lower) compression spring  17  braced against the collar  26 , thereby compressing the softer (upper) compression spring  18 , until it comes to rest on a ledge  27  in the blind borehole  19  (note the corresponding position in FIGS.  1  and  3 ). From this instant on, the spring force acting on the lever  13  and, therefore, the pulling force of the pulling device, is determined by the characteristic of the harder compression spring  17 . 
   The overall characteristic of the spring system  17 ,  18  which results is illustrated in  FIG. 7  by the (kinked) curve  28 . In this regard, a flatly rising curve branch  29  identifies the characteristic of both compression springs  17 ,  18 , while a more steeply rising curve branch  30  represents the characteristic of the (harder) compression spring  17 . A kink or point of inflection  31  formed between the two curve branches  29  and  30  marks the instant at which the collar  26  of the guide pin  25  comes to rest against the ledge  27  of the blind borehole  19  (FIGS.  1  and  3 ). 
   With the aforedescribed in tandem-connected spring configuration, an overall characteristic is therefore realized in a simple way which permits more precise adjustment in the range of low pulling force and, at the same time, permits a high pulling force with a limited adjustment travel of the setting screw  20 . 
   A different embodiment of an in tandem-connection of two compression springs, which is modified somewhat in comparison with the spring configuration according to  FIGS. 1  to  3  and by which an overall characteristic similar to the curve  28  in  FIG. 7  can also be realized, is shown in FIG.  4 . In a manner similar to that in the embodiment according to  FIGS. 1  to  3 , a harder first compression spring  17   a  acts directly on the lever  13 . At the upper end of the compression spring  17   a , however, it is supported on a rim  32  of a pot-like sleeve  33  which accommodates therein a second, softer compression spring  18   a . At the upper end of the softer compression spring  18   a , it is acted upon by an adjusting element  20   a , shown diagrammatically as a plate part, which may be, for example, an adjusting screw similar to the sleeve part  20  shown in  FIGS. 1  to  3 . In the embodiment of  FIG. 4 , quite similar in result to the embodiment according to  FIGS. 1  to  3 , in the position of the adjusting element  20   a  shown in  FIG. 4 , the characteristic curve of the softer compression spring  18   a  initially comes into effect (note the curve branch  29  in FIG.  7 ). The significance of this setting, preferably in the case of thin sheets to be processed, is therefore that a precisely adjustable force acts on the lever (note the lever  13  in FIG.  1 ). On the other hand, the harder compression spring  17   a , and only this spring, comes into use at a setting wherein the components  20   a  and  32  are in contact. At this setting, the result is a correspondingly steeper characteristic for the adjustment of the force acting on the lever  13  (compare with the curve branch  30  in FIG.  7 ). 
     FIG. 5  shows a further different embodiment wherein two compression springs  17   b  and  18   b  with different spring characteristics are connected in parallel rather than in series or tandem. The two compression springs  17   b  and  18   b  are again disposed, concentrically with respect to one another, in an adjusting element  20   b  (for example a setscrew or adjusting screw like the sleeve part  20  in  FIGS. 1  to  3 ), but both act directly on the lever  13 . In the setting shown in  FIG. 5 , when the adjusting element  20   b  is adjusted, the softer characteristic of the spring  18   b  initially comes into effect, which permits precise adjustment of the force acting on the lever  13  (compare with the curve branch  29  in FIG.  7 ). The harder compression spring  17   b  braced against a stop  34 , on the other hand, does not come into effect here at all. This changes only when, upon further adjustment of the adjusting element  20   b , the latter comes into contact with the stop  34 . From this setting, the two spring characteristics add. The total characteristic of the spring system  17   b ,  18   b  is also similar here to the course of the (kinked) curve  28  in FIG.  7 . 
   A further different embodiment according to  FIG. 6  differs from the embodiments according to  FIGS. 1  to  5  described hereinbefore in that only a single compression spring, namely the spring  16   c  in  FIG. 6 , is provided. The special feature of this compression spring  16   c  is in the conical shape thereof, the spring  16   c , starting from the lever  13  upon which it acts, tapering continuously upwardly as far as the adjusting element  20   c . Due to the conical shape of the compression spring  16   c , there is produced a progressive course of the spring characteristic, which is represented in  FIG. 7  by the curve  35 . In addition, the embodiment according to  FIG. 6  permits precise adjustment of the adjusting element  20   c  at the beginning of the adjustment travel thereof and, during further progressive adjustment, coarser adjustment of the spring force acting on the lever  13  and, therefore, of the pulling force of the pulling device. 
     FIG. 7  also shows a further curve  36 , which overall has a highly progressive course. It is composed of three linear sections  37 ,  38  and  39 , which form two points of inflection or kinks  40  and  41 . A curve of this type may be achieved by connecting three individual springs, respectively, in series or in parallel, analogously to the spring configurations shown in  FIGS. 1  to  5 . 
   For the purpose of comparison with the spring characteristics  28 ,  35  and  36  having a progressive course overall, a further linear spring characteristic  42 , corresponding to the prior state of the art for pulling devices, is represented in the plot diagram of FIG.  7 . The aforedescribed advantages of the spring system according to the invention become particularly clear therefrom. 
   As is believed to be apparent from  FIGS. 8  to  11 , a progressive characteristic of the spring force exerted on the lever  13 , at the free end of which the dabber roller  11  is mounted, can also be realized by axial displaceability of the lever support or bearing. In this regard, the displaceable bearing axis of the lever  13  is at  43 , and the point of application of the spring system is at  44 . An arrow  45  marks the direction of the force. 
   In the position of the lever bearing axis  43  according to  FIGS. 8 and 9 , the spring system represented by the arrow  45  acts on the dabber roller  11  via a comparatively large lever arm  46  (force arm). The so-called load arm  47  located on the right-hand side of the lever bearing axis  43 , as viewed in  FIG. 8 , has approximately the same length as the force arm  46 . Accordingly, this configuration corresponds to a coarse setting of the pulling force (compare the steep curve branch  30  in FIG.  7 ). 
   In the configuration according to  FIGS. 10 and 11 , the lever bearing axis  43  has been shifted to the lefthand side a distance a from the location thereof in  FIGS. 8 and 9 . As a result, the force arm, identified by the reference character  46 ′ in  FIGS. 10 and 11 , is shortened accordingly, and the load arm, identified by the reference character  47 ′ in  FIGS. 10 and 11 , has experienced a corresponding lengthening. In order to exert the same force on the dabber roller  11  as in the case of the setting according to  FIGS. 8 and 9 , a greater force or a greater spring travel is therefore required at the location  44 ,  45 . The setting according to  FIGS. 10 and 11  therefore permits precise adjustment of the pulling force on the dabber roller  11 . 
   The measures described hereinabove and revealed by  FIGS. 8  to  11  in principle do not require any spring system with a progressive overall characteristic. On the contrary, they can also be realized with a conventional spring system having a linear characteristic. There should be an advantageous effect, however, in practice, if the spring measures according to  FIGS. 1  to  6  are combined with the lever measures according to  FIGS. 8  to  11 . 
   Additionally or alternatively, the measures apparent from FIGS.  12  and/or  13  can also be taken. In the alternative embodiment according to  FIG. 12 , wherein the lever bearing axis  43  remains at the same location as for the embodiment of  FIG. 8 , longitudinal adjustability of the force action point  44  of the spring system  45  is provided. Thus, the spring system  45  has been displaced to the righthand side a distance b, which results in a correspondingly shortened force arm  46 ″ of the lever  13 , with a new force application point  44 ′. With regard to the effects of this shortening of the force arm on the lever  13 , that which is stated hereinbefore in relation to  FIGS. 10 and 11  applies accordingly. 
     FIG. 13  shows another different embodiment of the invention, wherein, although the spring force application point  44  on the lever  13  remains the same as for the embodiment of  FIG. 8 , swivelling of the direction of the force  45  and  45 ′, respectively, of the spring system is provided. If the swivelling occurs over an angle α, as is apparent from  FIG. 13 , the illustrated spring-force direction  45 ′ results. Consequently, there is, indirectly, a reduction of the spring forces acting on the lever arm  46  when the spring travel is in the same direction as the direction of the force  45 , because only the force component X then comes into effect at the point  44 .