Abstract:
A gripper for conveying a sheet through a printing machine makes it possible to increase speed. The gripper includes gripper fingers with finger tips disposed at a rotary articulation or joint.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2007 057 459.4, filed Nov. 29, 2007; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a gripper for conveying a sheet through a printing technology machine, including two gripper fingers on a revolving body, finger tips with gripping surfaces at respective ends of the gripper fingers, a device for cyclically pivoting the gripper fingers about an axis, and a device for cyclically opening and closing the gripper fingers. 
         [0004]    Gripper systems each having a series of spaced-apart grippers on gripper bars are used to convey a sheet through a printing machine. The grippers each include a gripper finger, which interacts with a gripper support, or two interacting gripper fingers. 
         [0005]    In the case of turning drums, gripper fingers are used which interact in pairs, receive a sheet at a trailing edge from an upstream storage drum and transfer it to a gripper system of a downstream impression cylinder, as in German Published, Non-Prosecuted Patent Application DE 24 14 998 A1, corresponding to U.S. Pat. No. 4,101,122. When the sheets are conveyed from the storage drum to the impression cylinder, the gripper fingers execute a cyclic pivoting movement during a revolution of the turning drum. The pivot axis of the gripper fingers is located, in the radial direction, approximately on the revolving contour or periphery of the turning drum. When a sheet is received from the storage drum, the gripper fingers pivot in over the trailing sheet edge. As the sheet is being received, the gripper surfaces on the gripper fingers are located in the sheet-running direction, which is not ideal, and that results in undesired deformation of the sheet edge. A convex configuration of the gripping surfaces is intended to compensate for the non-ideal orientation of the gripping surfaces in the transfer positions. Following transfer, the gripper fingers are pivoted, at a short time interval, through an angle of more than 180°, and high accelerating forces occur. The accelerating forces are supplied through the use of a gripper-control mechanism, with it being necessary for the mechanism members and the gripper fingers to be configured with a high level of rigidity. The installation-space conditions with respect to the drums, and the movement geometries of the gripper fingers, limit the level of rigidity which can be achieved. 
       SUMMARY OF THE INVENTION 
       [0006]    It is accordingly an object of the invention to provide a gripper for conveying a sheet through a printing technology machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which makes it possible to increase speed. 
         [0007]    With the foregoing and other objects in view there is provided, in accordance with the invention, a gripper for conveying a sheet through a printing technology machine. The gripper comprises two gripper fingers disposed on a revolving body, finger tips each being disposed at an end of a respective one of the gripper fingers and each having a respective gripping surface, a device for cyclically pivoting the gripper fingers about an axis, a device for cyclically opening and closing the gripper fingers, and rotary joints. The finger tips on the gripper fingers are each disposed at a respective one of the rotary joints. 
         [0008]    Therefore, according to the invention, the finger tips of gripper fingers have an articulated construction, in which gripping surfaces on the finger tips can be moved about a joint axis which is not a pivot axis of the gripper fingers. This makes it possible to orient the gripping surfaces in such a way that undesirable deformation of the sheet edge does not occur. The gripping surfaces are located approximately in the sheet-running direction. 
         [0009]    In accordance with another feature of the invention, the finger tips can be pivoted in such a way that their pivoting movement precedes the pivoting movement of the gripper fingers. In one embodiment, the finger tips are retained at a rotary articulation or joint, with a pivoting movement of the gripping surfaces being initiated through two connecting rods. 
         [0010]    In accordance with a further feature of the invention, a pivot axis of gripping surfaces may be provided on a revolving crank, with the crank being located in such a way that it can be pivoted about a pivot axis of the gripper fingers. In the case of this variant, a spring may be provided in order to open the gripper fingers. 
         [0011]    In accordance with an added feature of the invention, it is possible for gripper fingers to be displaceable relative to one another perpendicularly to their pivot axis in such a way that the gripping surfaces are oriented in the sheet-running direction. In the case of this embodiment, one of two gripper fingers, which interact in pairs, may be disposed in such a way that it can be pivoted about an axis which is spaced apart at a distance from, and parallel to, a joint pivot axis of the gripper fingers. 
         [0012]    In accordance with a concomitant feature of the invention, the movement of the gripping surface may be coupled to the movement of the gripper fingers. A tong gripper may, in particular, be used for this purpose. 
         [0013]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0014]    Although the invention is illustrated and described herein as embodied in a gripper for conveying a sheet through a printing technology machine, 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. 
         [0015]    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 SEVERAL VIEWS OF THE DRAWING 
         [0016]      FIG. 1  is a fragmentary, diagrammatic, side-elevational view of a gripper in an angled position with gripper-finger tips which can be pivoted by a linkage mechanism; 
           [0017]      FIG. 2  is a fragmentary, side-elevational view of the gripper in a straightened-out position with pivotable gripper tips; 
           [0018]      FIG. 3  is a mechanism diagram for controlling the grippers according to  FIGS. 1 and 2 ; 
           [0019]      FIG. 4  is a fragmentary, side-elevational view of the gripper in an angled position with gripper-finger tips which can be pivoted by a crank drive; 
           [0020]      FIG. 5  is a fragmentary, side-elevational view of the gripper in a straightened-out position with gripper-finger tips which can be pivoted by a crank drive; and 
           [0021]      FIGS. 6-8  are fragmentary, side-elevational views of the gripper in three different pivoting positions with pivotable gripper-finger tips and a separately mounted gripper finger. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a body, member or element  1  of a turning drum of a sheet-fed printing machine having a tong-gripper system  2 . The turning drum is located between an upstream storage drum and a downstream impression cylinder. The turning drum is driven, in the direction of an arrow  3 , synchronously with the storage drum and the impression cylinder. The tong-gripper system  2  includes a series of gripper fingers  4 ,  5  which interact in pairs and are spaced apart along a gripper shaft  6 . The gripper fingers  4  are fixed to the gripper shaft  6 . The gripper fingers  5  are coupled in each case individually or in groups to a pinion  7 , which is mounted in a rotatable manner on the gripper shaft  6 . The gripper shaft  6  and the pinions  7  can be pivoted about an axis  8  located parallel to the axis of rotation of the drum body  1 . The axis  8  is located on a radial line R 1  on the drum body  1 , in which case the shaft  6  and the pinion  7  are located within a revolving contour or periphery  9  of the turning drum. 
         [0023]    The gripper fingers  4 ,  5  can be opened and closed by rotating the gripper shaft  6  and the pinion  7  relative to one another. When a sheet  10  is conveyed from the storage drum to the downstream impression cylinder, the closed gripper fingers  4 ,  5  jointly execute a pivoting movement about the axis  8 . In order to initiate this pivoting movement, the pinion  7  engages with a pinion  11 , which is disposed in a rotationally fixed manner on a drive shaft  12  disposed parallel to the gripper shaft  6 . There is a 1:1 transmission ratio between the pinions  7 ,  11 . 
         [0024]    The sheet  10  is retained at the edge in finger tips  13 ,  14  which have planar gripping surfaces. Guide components  15 ,  16  retain the finger tips  13 ,  14  at the ends of the gripper fingers  4 ,  5  when the grippers are open. In the closed state of the gripper fingers  4 ,  5 , the finger tips  13 ,  14  are located symmetrically relative to a joint pivot axis S (see  FIG. 3 ), which runs parallel to the axis  8 . Cylindrical half-shells  17 ,  18  at the ends of the gripper fingers  4 ,  5  form a rotary articulation or joint for the finger tips  13 ,  14  about the axis S. Connecting rods  21 ,  22  are retained on the finger tips  13 ,  14  at rotary articulations or joints  19 ,  20 . The other respective ends of the connecting rods  21 ,  22  are retained on a pinion  25  at rotary articulations or joints  23 ,  24  and this pinion  25  is mounted in a rotatable manner on the gripper shaft  6 . The axes of rotation of the articulations  19 ,  20 ,  23 ,  24  are located parallel to the axis  8 . The axes of rotation of the articulations  23 ,  24  are spaced apart in each case by a distance a from the axis  8 . The pinion  25  engages with a further pinion  26 , which is seated in a rotationally fixed manner on the drive shaft  12 . The pinions  26  and  25  form a transmission, in which case the rotary articulations or joints  23 ,  24  are pivoted further than the gripper fingers  4 ,  5  about the axis  8 , for example in order for a sheet  10  to be received from the storage drum. 
         [0025]      FIG. 1  shows the gripper fingers  4 ,  5  and the finger tips  13 ,  14  shortly after the trailing edge of a sheet  10  has been received from the storage drum. Starting from the straightened-out position ( FIG. 2 ), the gripper fingers  4 ,  5  have been pivoted through an angle a about the axis  8 , whereas the articulations  23 ,  24  of the connecting rods  21 ,  22 , which control the finger tips  13 ,  14 , have been pivoted through an angle β, where β is greater than α. In accordance with the geometry of the connecting rods  21 ,  22  and of the finger tips  13 ,  14 , the planar gripping surfaces of the finger tips  13 ,  14  are located approximately tangentially in relation to the revolving contour  9 . 
         [0026]      FIG. 2  shows the gripper fingers  4 ,  5  and the finger tips  13 ,  14  in a straightened-out or elongated position. The planar gripping surfaces of the finger tips  13 ,  14  are located in a radial direction  27  of the drum body  1 . 
         [0027]    Where the following description makes use of designations which have already been introduced, these denote elements or symbols with an equivalent effect or equivalent meaning. 
         [0028]      FIG. 3  shows a mechanism diagram for controlling the pivoting movement of the finger tips  13 ,  14  relative to the gripper fingers  4 ,  5 . While the gripper fingers  4 ,  5  are closed and the sheet  10  is retained between the finger tips  13 ,  14 , the gripper fingers  4 ,  5  jointly execute a cyclic pivoting movement  28  about the axis  8 , and the axes of rotation  23 ,  24  of the connecting rods  21 ,  22 , which drive the finger tips  13 ,  14 , execute a further cyclic pivoting movement  29  about the axis  8 . The finger tips  13 ,  14  in this case execute a pivoting movement  29   a  about the axis S. The pinion  25 , the connecting rods  21 ,  22  and the finger tips  13 ,  14 , which are pressed together by way of the gripper fingers  4 ,  5 , are mechanism members of a 4-bar linkage mechanism having the articulations  19 ,  20 ,  23 ,  24 . The different transmission ratios between the pinions  7 ,  11  and  25 ,  26  give rise to different characteristics of the pivoting movements  28 ,  29 . In addition, the pivoting movement  29   a  is dependent on the transmission behavior of the 4-bar linkage mechanism. 
         [0029]      FIG. 4  shows a further variant for pivoting finger tips  13 ,  14  which are retained between the ends of gripper fingers  4 ,  5 . As has been described in relation to  FIGS. 1-3 , the gripper fingers  4 ,  5  are fastened on the gripper shaft  6  and can be pivoted about a joint axis  8  through the use of the pinions  25 ,  26 . The finger tips  13 ,  14  are mounted at a rotary articulation or joint  31  at one end of a crank  30 . The axis of rotation of the rotary articulation or joint  31  is located parallel to the axis  8  of the gripper shaft  6 . The crank  30  is connected to a pinion  32  which is disposed in a rotatable manner on the gripper shaft  6 . The pinion  32  engages with a pinion  33  which, like the pinion  26 , is fastened in a rotationally fixed manner on the drive shaft  12 . The gripper fingers  4 ,  5  open in order to receive and transfer sheets. The finger tips  13 ,  14  in this case are retained at the ends of the gripper fingers  4 ,  5  by a spring  34  and are thus pivoted in relation to one another about the rotary articulation or joint  31 . The transmission ratios between the pinions  25 ,  26  and  32 ,  33  are selected in such a way that, once the sheet  10  has been received from an upstream storage drum, the pivoting movement of the crank  30  follows the pivoting movement of the gripper fingers  4 ,  5 . 
         [0030]      FIG. 4  shows the gripper fingers  4 ,  5  in a pivoting position a and the crank  30  in a pivoting position γ, where γ&lt;α. The gripping surfaces of the finger tips  13 ,  14  are located more or less tangentially in relation to the revolving contour or periphery  9  of the drum body  1 . 
         [0031]    As the drum body  1  is rotated further in the direction of the arrow  3 , the gripper fingers  4 ,  5  and the finger tips  13 ,  14  move into a straightened-out or elongated position, which is illustrated in  FIG. 5 . In the straightened-out position, the gripping surfaces of the finger tips  13 ,  14  and the gripper fingers  4 ,  5  are located symmetrically in relation to a radial line  27  of the turning drum. 
         [0032]      FIGS. 6-8  show a further variant of the gripper system on a turning drum in three different rotary positions of gripper-finger pairs. 
         [0033]    A respective first gripper finger  35  of a gripper-finger pair is fastened on a pinion  36 , which is disposed in a rotatable manner on a gripper shaft  6 . A respective second gripper finger  37  is retained on a pinion  39  at a rotary articulation or joint  38 , and this pinion is likewise disposed in a rotatable manner on the gripper shaft  6 . The axis of rotation of the rotary articulation or joint  38  is spaced apart by a distance b from, and parallel to, the pivot axis  8  of the gripper shaft  6 . The pinions  36 ,  39  engage with pinions  40 ,  41  on a drive shaft  12  mounted on the drum body  1 . The pinions  40 ,  41 , which are seated in a rotationally fixed manner on the drive shaft  12 , can be pivoted about an axis  42  located parallel to the axis  8 . The gearwheel pairings of the pinions  36 ,  40  and  39 ,  41  have different transmission ratios. Finger tips  13 ,  14  are retained at the ends of the gripper fingers  35 ,  37  at rotary articulations or joints  43 ,  44 . The finger tips  13 ,  14  are connected to one another in each case at a rotary articulation or joint  45 . The axes of the rotary articulations or joints  43 ,  44 ,  45  are located parallel to the axis  8 . A radial support  46  is formed on the gripper shaft  6 , a lever arm  47  is formed on the gripper finger  37  and a compression spring  48  is disposed therebetween. When the gripper fingers  35 ,  37  are opened and closed, the gripper finger  37  is pivoted about the rotary articulation or joint  38 , with the compression spring  48  compensating for an offset between the support  46  and the lever  47 . 
         [0034]      FIG. 6  shows the gripper fingers  35 ,  37  and the finger tips  13 ,  14  as the trailing edge of the sheet  10  has been received from an upstream storage drum. When the sheet  10  is conveyed from the storage drum to a downstream impression cylinder, the gripper fingers  35 ,  37  and the finger tips  13 ,  14  reach a straightened-out or elongated position, which is illustrated in  FIG. 7 . In the straightened-out position, the gripper fingers  35 ,  37  and the gripping surfaces of the finger tips  13 ,  14  are located symmetrically in relation to a radial line  27  of the drum body  1 , and the direction in which the compression spring  48  acts is tangential to the circumferential direction of the turning drum. 
         [0035]      FIG. 8  shows the gripper fingers  35 ,  37  and the finger tips  13 ,  14  during transfer to the downstream impression cylinder. Pivoting of the gripper fingers  35 ,  37  is initiated by virtue of the drive shaft  12  being rotated during a revolution of the drum body  1 . The drive shaft  12  can be rotated by a cam gear mechanism. As the gripper fingers  35 ,  37  are pivoted about the axis  8 , the transmission ratios between the pinions  36 ,  40  and  39 , 41  causes the finger tips  13 ,  14  to be pivoted relative to the gripper fingers  35 ,  37 , in which case the gripping surfaces of the finger tips  13 ,  14  are oriented substantially in the sheet-running direction. While the finger tips  13 ,  14  are pivoted relative to the gripper fingers  35 ,  37 , the ends of the gripper fingers  35 ,  37  are displaced relative to one another perpendicularly to the axis  8 .