Abstract:
In a gripper mechanism for devices for handling sheet-like or plate-like articles, particularly for mail-processing machines, simple and reliable setting for the handling of light, thin and also heavy, thick articles can be effected by the use of pivotable gripper claws on the gripper hand provided at the end of a pivotable gripper arm, by virtue of the fact that a plane which is oriented approximately perpendicular to the gripper arm longitudinal axis, and in which the contact area between articles to be handled and a pivotable gripper claw also lies, is at such a distance in the direction of the longitudinal axis of the gripper arm from the pivot axis of this pivotable gripper claw that an additional pivoting moment acts on the latter in the closure direction, generated under the effect of tensile forces which seek to remove the articles to be handled from the gripper claws when these are closed, as a result of which articles of widely varying weight and varying thickness are at all times gripped securely.

Description:
TECHNICAL FIELD 
     The invention relates to a gripper mechanism for devices for handling objects in the form of sheets or plates, in particular for post processing machines. 
     BACKGROUND ART 
     Generally known gripper mechanisms of this type, which have been in use for a long time, contain a gripper arm which can pivot about a gripper arm pivoting shaft and can be moved transversely with respect to the movement direction of a transfer chain, which is driven intermittently for example, by means of an appropriate drive, for example a crank drive, to carry out reciprocating pivoting movements. At its free end, the gripper arm is fitted with a gripper hand which has a pair of interacting gripper claws of which, in general, one is designed to be fixed relative to the gripper arm and the other is fitted such that it can pivot relative to the gripper arm. The pivoting gripper claw is moved by means of a claw operating drive against the force of spring means, which hold the gripper claws in the closed position, in specific pivoting positions of the gripper arm in the open position in order to grip either a specific object in the form of a sheet or plate, or a corresponding stack of such objects, and once the gripper claws have closed, to transport them to the transfer chain or else, when this handling process has been completed, to release the relevant object or stack of objects once again so that the compartment on the transfer chain which has now been filled can continue to move with said chain. One known embodiment of a gripper claw operating drive provides an operating lever arrangement which is mounted on the gripper arm such that it can pivot, can be pivoted by means of a claw operating drive apparatus during the pivoting movements of the relevant gripper arm, and is connected via a coupling linkage to the gripper claw which can pivot with play or a clearance which allows a specific opening of the gripper claws against the force of the spring prestressing means regardless of the respective position of the operating lever arrangement. In general, the operating lever arrangements for a plurality of gripper arms which are operated at the same time and are forced to move synchronously in a reciprocating manner are seated on a common operating shaft which is mounted on each of the simultaneously moved gripper arms, and is rotated in a reciprocating manner in specific gripper arm pivoting positions via a slotted guide link, a slotted guide link feeler and a feeler roll lever, which is firmly attached to the operating shaft, in order to operate the respective pivoting gripper claws on the individual gripper arms simultaneously, so that the operating lever arrangements which are seated on the operating shaft move the moving gripper claws to the open position via the individual coupling linkage. 
     For certain post processing tasks, it is necessary to make up a despatch from enclosures which consist of a sheet or a small number of sheets, and possibly folded sheets, and enclosures which consist of a stack of bound or stapled sheets. In this case, difficulties arise in setting gripper mechanisms of the same type and at processing stations arranged successively along a transfer chain to enclosures of different thickness such that, on the one hand, thin enclosures can be gripped reliably when being handled and a monitoring device provided on the respective gripper mechanism responds correctly in order to record multiple outputs or empty outputs and, on the other hand, when handling thick enclosures, to ensure that the clamping forces during handling are sufficient for the relevant gripper mechanism to apply the required forces when drawing the enclosure from the stack and to introduce the necessary acceleration forces to the enclosure, without losing it. The setting effort required to do this is in some cases high with known gripper mechanisms. 
     DISCLOSURE OF THE INVENTION 
     The invention is thus intended to achieve the object of refining a gripper mechanism having the features of the precharacterizing clause of claim  1  such that it can be set easily and reliably to handle both light, thin objects and thick, heavy objects. 
     According to the invention, this object is achieved by the characterizing features of claim  1 . Advantageous refinements and developments are the subject matter of the claims but are dependent on claim  1 , whose content hereby expressly forms part of the description without having to repeat the wording in detail here. 
     One particular embodiment of the gripper mechanism of the type specified here can be dismantled with a few actions for servicing and repair. The settings made are maintained on the gripper mechanism under the influence of reaction forces in operation even if adjustable parts on the gripper mechanism are fixed with comparatively low clamping forces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment will be described in more detail in the following text with reference to the drawings, in which: 
     FIG. 1 is a side view of a gripper arm of a gripper mechanism in accordance with an embodiment of the present invention; 
     FIG. 2 is an enlarged view of a gripper hand of the gripper arm illustrated in FIG. 1; 
     FIG.  3  and FIG. 4 are perspective views of the gripper hand illustrated in FIG. 2, on the side of the gripper claw opening, seen obliquely from above and obliquely from underneath, respectively; 
     FIG. 5 is a perspective view of the gripper hand housing; 
     FIG. 6 is a perspective view of the gripper claw which is fixed relative to the gripper hand; 
     FIG. 7 is a cross-sectional view along a vertical center plane of the gripper claw illustrated in FIG. 6; and 
     FIG. 8 is a perspective view of a gripper claw part of the gripper claw which can pivot relative to the gripper hand. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, major parts of a gripper mechanism of the type specified here are shown in a side view, and partially in section. The gripper mechanism includes a gripper arm  1  whose upper end is coupled to a gripper arm pivoting shaft  2  such that they rotate together. In the illustrated embodiment, the gripper arm  1  is clamped onto the gripper arm pivoting shaft  2  by means of a clamping mechanism  3 . The gripper arm pivoting shaft can be driven to carry out oscillating rotary movements by means of a pivoting drive, which is not shown in FIG. 1, so that the gripper arm  1  carries out reciprocating pivoting movements about the gripper arm pivoting axis of the pivoting shaft  2 , as is known for gripper mechanisms of the general type under discussion here. 
     At the lower end of the gripper arm  1  there is a gripper hand  4 , which is provided with an upper gripper claw  5  fixed firmly to the gripper hand  4 , and with a lower gripper claw  6  fitted to the gripper hand  4  such that it can pivot. The claw  6 , which can pivot relative to the gripper hand  4 , is connected to the lower end of a coupling linkage  7 , whose upper end is attached to a shaft  8 . The ends of the shaft  8 , which project beyond the connecting point of the coupling linkage  7  at the sides, are each inserted into bearing recesses  9 , which are approximately U-shaped or in the form of circle sectors, of operating levers  10  of an operating lever arrangement which are located on both sides of the gripper arm, and are also used as tension spring anchor points for helical tension springs  11  which are stretched to further spring anchor points on both sides of the gripper arm  1 . The further spring anchor points are indicated at  12  in FIG.  1  and are located on the gripper hand  4 . 
     The operating levers  10  are mounted on a gripper claw pivoting shaft  13 , for which purpose each of the operating levers  10  is provided with a clamping apparatus, which is indicated schematically at  14  in FIG.  1 . The gripper claw pivoting shaft  13  is mounted in the gripper arm  1  such that it can rotate. If there are a number of gripper mechanisms of the type specified here alongside one another in workstations arranged successively along a transfer chain in a post processing machine, then the gripper claw pivoting shaft  13  for a plurality of gripper mechanisms is provided jointly and is in each case mounted in the gripper arms  1  such that it can rotate. 
     Apart from the operating levers  10 , a slotted-link feeler lever with a slotted link feeler roll is mounted on the gripper claw pivoting shaft  13 . The slotted link feeler roll interacts with a slotted guide link during the pivoting movements of the gripper arm  1 , this slotted guide link being fixed to the framework. These details, however, are not shown in FIG.  1 . Pivoting movements of the slotted link feeler lever  15  anticlockwise about the axis of the gripper claw pivoting shaft  13  likewise result in the operating levers  10  being pivoted anticlockwise and the shaft  8  and the coupling linkage  7  being raised in the process, so that the pivoting gripper claw  6  is opened against the prestressing force of the helical tension springs  11  in order to release objects to be handled which are clamped in between the gripper claws of the gripper hand  4 , or to receive such objects, which are then clamped in by means of the gripper claws. 
     The slotted bearing recesses  9  in the operating levers  10  result in the operating levers  10  being connected with play and via the coupling linkage  7  to the pivoting gripper claw, and this play allows the gripper claws to open to a certain extent against the force of the prestressing means irrespective of the position of the operating levers  10  and irrespective of the instantaneous operating position of the gripper arm, in order that objects of different thickness can be clamped in between the gripper claws  5  and  6 . 
     As can be seen particularly clearly in FIG. 5, the gripper hand  4  contains a bearing housing  15 , which is connected to the gripper arm  1 , is open at the top before being assembled, is essentially in the form of a box and has side walls  16  and  17  which are connected to one another by a front wall  48  and a rear wall  49 . The bearing housing  15  is manufactured from a tough, high-strength plastic and is designed as a casting. In an upper region, projecting beyond the front wall  48  and the rear wall  49 , the side walls  16  and  17  are provided with coaxial holes  18  and  19 , and  20  and  21 , although the hole  21  can be seen only in the illustration in FIG.  4 . The holes  18  and  19 , and  20  and  21  are used to attach the gripper hand  4  to the lower end of the gripper arm  1 , which is provided with appropriate transverse holes for this purpose. While a fastening screw is pushed through the holes  18  and  19  and the associated transverse hole in the gripper arm  1  and is secured by a nut, a pin  22  which is provided with annular grooves at its outer ends is pushed through the holes  20  and  21  and the corresponding transverse hole in the gripper arm  1 , and its outer ends project at the sides out of the gripper hand  4  and form the further spring anchor points  12  mentioned above, which will be described in more detail in the following text. 
     Sleeves  23 ,  24  which surround the holes  20  and  21 , respectively and are coaxial with respect to them project at the sides from the side walls  16  and  17 , and are integrally formed on the respective associated side wall  16  or  17 . The sleeves  23  and  24  each have attachments  25  and  26 , respectively, which are in the form of circular cylindrical sectors and whose axial length is dimensioned such that the annular grooves provided on the pin  22  just remain freely accessible when the pin  22  is pushed through the holes  20  and  21  and through the transverse hole in the gripper arm. When the helical tension springs  11  are stretched from corresponding annular grooves in the shaft  8  to the spring anchor points  12 , that is to say to the end annular grooves at the ends of the pin  22 , then the spring eyes of the helical tension springs  11  at the same time act as stops interacting with the attachments  25  and  26  to fix the pin  22  in a symmetrical position in the gripper hand  4 . Thus, all that is necessary for removing the gripper hand  4 , is to detach the helical tension springs  11  from the further spring anchor points  12 , to push the pin  22  through the sleeves  23  and  24  out of the holes  20  and  21  and out of the transverse hole in the gripper arm  1 , and, furthermore, to detach the screw connection which passes through the holes  18  and  19  and the corresponding transverse hole in the gripper arm  1 , so that the gripper hand  4  can be removed from the gripper arm  1 . 
     It should also be mentioned that the pin  22  is passed through a fitting transverse hole in the region of the gripper arm  1 , which is generally in the form of an aluminum part, and forces exerted on the further spring anchor points  12  by the helical tension springs are thus not supported on the plastic material of the sleeves  23  and  24 , but are absorbed by the metallic gripper arm  1 . 
     The strength of the bearing housing  15  of the gripper hand  4  is also increased by means of angled webs  27  and  28  which are fitted integrally on the side walls  16  and  17  and on the sleeves  23  and  24 . 
     Attachment lugs  29  and  30 , which are located at the sides approximately at the level of the front wall  18  and are provided with elongated holes, project from the side walls  16  and  17  of the bearing housing  15 . The thickness of these attachment lugs  29  decreases in the radial direction away from the pivoting axis of the gripper arm pivoting shaft  2 . The attachment lugs  29  and  30  thus taper as the distance from the gripper arm pivoting shaft  2  increases. 
     Finally, the bearing housing  15  of the gripper hand  4  is provided at its lower end with bearing holes to hold and support gripper claw shaft parts. The axis of the bearing holes is oriented parallel to the gripper arm pivoting axis and parallel to the axis of the gripper arm pivoting shaft  13 . The bearing holes are denoted generally by  33 . 
     The attachment lugs  29  and  30  of the bearing housing  15  of the gripper hand  4 , which are provided with an elongated hole, are used for adjustable attachment of the upper gripper claw  5 , which is fixed relative to the gripper hand  4  and whose design can be seen in detail particularly well in FIGS. 6 and 7. The gripper claw  5 , which is fixed relative to the gripper arm, contains two gripper claw parts  36  and  37  which each have retaining flanges  38  and  39  oriented approximately in the direction parallel to the gripper arm longitudinal axis  1 , and guide flanges  40  and  41  which project at the sides from them, rest at the sides against the attachment lugs  29  and  30 , respectively, when the gripper claw  5  is attached to the bearing housing  15  and pass beyond these attachment lugs, as can be seen in particular from the illustrations in FIGS. 3 and 4. 
     As is shown particularly in the vertical section side view in FIG. 7, the gripper claw parts  36  and  37  are integrally connected to one another by means of a lower transverse web  42 , a central transverse web  43  and an upper transverse web  44 . Finally, it can be seen from FIGS. 6 and 7 that the retaining flanges  38  and  39  are provided with holes  45  and  46 , respectively, which are aligned with elongated holes in the attachment lugs  29  and  30 . On the side of the retaining flanges  38  and  39  facing the viewer in FIG. 6, these flanges are provided in the region of the mouths of the holes  45  and  46  with recesses into which nuts can be inserted, secured such that they cannot rotate. Fixing screws  47 , which are passed rearwards through the elongated holes in the attachment lugs  29  and  30  and through holes  45  and  46  in the gripper claw  5 , allow the gripper claw  5 , which is fixed with respect to the gripper hand, to be firmly clamped on said gripper hand  4 . If the fixing screws  47  are undone, then the gripper claw  5  can be moved upwards and downwards in the range dictated by the longitudinal extent of the attachment lugs  29  and  30 , and can be fixed in specific positions by tightening the fixing screws  47 . The clamping means formed by the fixing screws  47  and the associated nuts move together with the gripper claw  5  to be adjusted when adjustment movements are carried out and, if the gripper claw  5  is moved upwards, cause the attachment lugs  29  and  30  to be clamped in in the region of greater thicknesses owing to the wedge-shaped design of the attachment lugs  29  and  30 , described above. This configuration of the attachment lugs and of the clamping means which act on them for the gripper claw which is fixed with respect to the gripper hand  4  means that these clamping means do not require a large amount of force to tighten them in order to fix the gripper claw  5  securely, since a gripper claw  5  which is subject to the operational load when objects to be handled are being clamped in would be moved in the direction in which the clamping-in forces increase, so that there is no need to be concerned about the clamp being released with this design specified here. 
     Contrary to the exemplary embodiment illustrated in the drawing, it is self-evident that, if the fixing screws  47  were passed through single holes in the attachment lugs on the gripper hand  4 , it would be necessary to form elongated holes in the retaining flanges of the gripper claws  5 , and the thickness of these retaining flanges would then in any case taper from top to bottom on the gripper claw  5  so that this would result in the clamping-in process being self-locking with an effect corresponding to the effect described above. 
     The gripper claw  6 , which is fitted to the gripper hand  4  such that it can pivot, has two gripper claw parts  6   a  and  6   b . The gripper claw parts are provided with shaft attachments which are aligned with respect to one another and of which the shaft attachment projecting away from the gripper claw part  6   b  is shown in FIG. 8, and is denoted by  52 . A shaft attachment (which is coaxial in the assembled state) of the gripper claw part  6   a  telescopically surrounds regions of the shaft attachment  52 . The gripper claw parts  6   a  and  6   b  are axially fixed to one another by means of a nut which is screwed onto a thread on the shaft attachment  52 , but can be rotated relative to one another. The shaft attachments of the gripper claw parts  6   a  and  6   b  are pushed into the bearing holes  33  in the bearing housing  15  of the gripper hand  4  and the gripper claw parts are fixed to one another in the manner just mentioned with respect to the axial direction. The gripper claw parts  6   a  and  6   b  can thus be pivoted about the geometric axis of the shaft attachment or the bearing holes  33  jointly and within specific limits as well somewhat differently in order to carry out the gripper function. 
     Rearward attachments  53  and  54 , respectively, on the gripper claw parts  6   a  and  6   b , respectively, have bearing points  55  and  56 , respectively, for the connection of the coupling linkage  7  via a universal joint  57 , which surrounds a compensating transverse bar  58 , with the compensating transverse bar  58  connecting the bearing points  55  and  56 . When objects to be handled by the gripper claws  5  and  6  are clamped in and whose thickness is not constant in the direction parallel to the pivoting axis of the gripper claw parts  6   a  and  6   b , then a secure grip for the gripper claws  5  and  6  around the edge of those objects to be handled is achieved by the operating thrust of the coupling linkage  7  in that the operating force is distributed uniformly over the gripper claw parts  6   a  and  6   b  via the compensating transverse bar  58  like a differential linkage, and these parts rest against the object to be gripped, and are pivoted slightly differently. 
     Grooves  61  and  62 , respectively, which run parallel to the pivoting axes and are located to the side of the fixed gripper claw  5  are integrally formed in those claw sections  59  and  60 , respectively, of the gripper claw parts  6   a  and  6   b , respectively, which point away from the attachments  53  and  54 , respectively. Elastic strips  63  and  64 , respectively, are pushed into these grooves, as is shown in FIG. 8 for the strip  64  in conjunction with the groove  62  in the gripper claw part  6   b . The strips  63  and  64  are made from an elastic material which has a high coefficient of friction with the material of the surface of the objects to be handled. The arrangement is designed such that, when an object to be handled is clamped in between the gripper claw  5 , which is fixed relative to the gripper hand  4 , and the pivoting gripper claw parts  6   a  and  6   b , the object to the handled is in approximately linear contact with the elastic strips  63  and  64 . 
     According to one important feature of a gripper mechanism of the type mentioned here, a plane oriented at right angles to the gripper arm longitudinal axis and in which the contact areas or contact regions between the strips  63  and  64  on the one hand and the lower surface of an object to be handled, on the other hand, are located is at a specific distance from the axis about which the gripper arm parts  6   a  and  6   b  can be pivoted. This distance is denoted by S in FIG.  2 . 
     It can be seen that, when a tensile force Z which attempts to pull the object G out from between the gripper claws acts on an object G clamped in between the gripper claws  5  and  6 , this tensile force Z acts as if it were applied to the strips  63  and  64  as long as the claw attachments  53  and  60  press (by means of the thrust of the coupling linkage  7 ) the strips  63  and  64  with a force against the lower surface of the clamped-in object, which force, multiplied by the coefficient of friction between the strip material and the material of the object to be handled, is at least equal to the force Z when static friction is acting. The force Z on the gripper claw parts  6   a  and  6   b  thus acts on a lever arm corresponding to the distance S, mentioned above, relative to the pivoting axis of the gripper claw parts and produces additional pivoting torques in the claw closing direction on the gripper claw parts, in order to reinforce the clamping of the object to be handled with respect to forces which try to remove said object from the clamp.