Abstract:
A clamping element for attaching a gripper onto a clamping tongue as well as a gripper with this kind of clamping element is provided. The clamping element has a longitudinal carrier the width of which substantially corresponds to the width of the clamping tongue and at least two mutually distanced clamping regions. At least one fastening element for the detachable fastening of the clamping elements to the clamping tongue ( 42, 44 ) is provided. The clamping element provides an improved force division as well as a secure support on the clamping tongue.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is in the field of conveying technology. It pertains to a clamping element for fitting onto a clamping tongue of a gripper as well as a gripper with this kind of clamping element. 
     2. Description of Related Art 
     The publication WO 2007/115421 describes a gripper comprising two clamping tongues as well as a means for generating a clamping force. The clamping tongues are pivotable in relation to one another on a pivot axis between two extreme positions, which corresponds to an open or closed configuration of the gripper respectively. At least one of the clamping tongues comprises, on its outer edge, two laterally protruding springing arms, i.e. protruding in parallel to the pivot axis. On these arms per clamping tongue two clamping elements are attached, in order to divide the clamping force between the two points or regions respectively and to make it uniform within these clamping regions. 
     Clamping elements, which, as described in WO 2007/115421, are attached only by attaching them on the clamping tongues, have the disadvantage that they may come off the clamping tongues during operation, in particular in that the small displacements occurring during operation add up, such that the clamping element falls off the arm laterally. 
     A rubber coating fixed permanently to the clamping tongue is already known from DE-A 310 22 42. The rubber coating is on the one hand to protect the product from being damaged and on the other hand to increase the adhesion between the clamping tongues and the product. The clamping tongue is, however, compared to the objects to be gripped, relatively narrow. On the other hand the clamping force is exerted over an extended region. With objects with variations in thickness, e.g. due to inserted products this may lead to the clamping force being concentrated to one single point, namely the location of the greatest thickness, and the held objects may twist around this point. 
     The invention, thus, has the object to provide a clamping element for grippers, which in case of wear may be easily exchanged, in mounted condition, however, is reliably fixed to the clamping tongue of the gripper and is, thus, suitable for continuous duty. Apart from this it is a further object of the invention to guarantee a reliable clamping effect and a stable product position. 
     The clamping element according to the invention is adapted to grippers on which at least one clamping tongue is formed in a T-shape, i.e. comprises two arms laterally protruding from a central clamping tongue part. For removable fastening of the clamping element to the clamping tongue at least one fastening element, preferably two fastening elements are provided. With the fastening element(s), the clamping element may be fitted to the clamping tongue in a planar manner or in several fastening locations respectively. According to the invention, the clamping element has a lengthy carrier, the width of which substantially corresponds to the width of the clamping tongue in the region of the arms, which thus can cover the arms over their complete width. For secure holding of an object, at least two distanced clamping regions are provided, which are arranged on the carrier such that they are located in the region of the arms in the case of use. The clamping regions may be designed in one piece with the carrier or they may be elements connected to the carrier, which define the clamping regions. 
     The invention thus suggests using, instead of several clamping elements fitted to the clamping tongue unilaterally, an extended carrier, on which at least two clamping regions are realised and which may be fastened to the arms of the clamping tongue in a suitable manner. 
     The term clamping region means the region of the clamping elements in which in the case of application the clamping forces are mainly transmitted to the held object. By means of the two or more independent clamping regions, a clamping effect concentrated to different regions is realised. A dislocation of the product is thus impeded even if it comprises variations in thickness in the held regions. This can be supported by fitting the arms on the central clamping tongue part in a springing manner, which thus may additionally compensate thickness variations. The clamping regions differ from the rest of the regions of the carrier, e.g. by having an enlarged cross section (e.g. cushion-type swelling in the carrier) and/or by means of the elasticity module, in particular lower compliance in clamping direction. In the clamping region, preferably a certain elasticity/flexibility is provided in order to make the clamped force constant over the clamped area by means of adaptation to the form of the counter element or to the product and in particular to achieve a frontal area running in parallel to the product or the counter element respectively. 
     By realising two or more clamping areas on the same carrier, these being allocated to the two arms arranged in symmetry to one another, forces can additionally be made constant, which act on the clamping element during operation and e.g. in the case of a carrier and clamping region allocated to only one arm, may lead to a detachment of the carrier. 
     The manner of the fastening on the clamping tongue is preferably adapted to the form of the clamping tongue, in particular the fastening elements act together with the clamping tongue by means of form or force engagement, e.g. by enclosing these or the two arms respectively between them. The fastening elements preferably limit the region in which the clamping element may be displaced in relation to the clamping tongue, such that no unintended detachment of the clamping element can occur. The fastening element is e.g. extended in a planar manner and reaches over the whole width of the clamping tongue. Alternatively, at least two mutually distanced fastening elements may be provided. 
     The fastening elements may e.g. be brackets with which the carrier is fitted to the clamping tongue and which reach over the complete width of the carrier or which may be arranged on the faces of the carrier. Fastening elements such as bolts or the like or a latching connection are also possible. In a preferred embodiment, the carrier itself is flexible at least in regions and may be deformed such that it can be applied onto the clamping tongue under the effect of force and in unstressed condition is held on it, in particular by form or force engagement. 
     The gripper according to the invention has, as known per se, a first and a second clamping tongue as well as a means for generating a clamping force, e.g. a spring. The clamping tongues each comprise on their distal ends clamping elements and are pivotable on a pivot axis in relation to each other such that the gripper may be brought into an open configuration or a closed configuration respectively, wherein the clamping elements of both clamping tongues lie upon each other or on the flat object in the closed configuration and are pressed against each other by the clamping force. At least one of the clamping tongues comprises two lateral arms, such that a T-shape is formed. At least one of the clamping elements is, as described above, designed with a lengthy carrier, at least two clamping regions and at least one fastening element and detachably fastened to the T-shaped clamping tongue. 
     Preferably, the clamping element substantially extends over the complete width of the clamping tongue including the arms and is preferably detachably fastened on both arms. 
     The invention has the advantage that the clamping elements, by means of the division of force onto two clamping regions enable a reliable holding of the objects by the gripper. They are easily exchangeable when worn or contaminated, however, are not displaced during operation or only to a low degree in relation to the clamping tongue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of the invention are shown diagrammatically in the drawings and described in the following. Hereby 
         FIGS. 1   a  and  b  show a gripper with a clamping element in different views; 
         FIGS. 2   a  and  b  show a clamping element in different views; 
         FIGS. 3 and 4  show a clamping tongue with clamping element; and 
         FIGS. 5-8  show different examples for the design of the clamping regions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1   a  and  b  show a gripper  40  with two clamping tongues  42 ,  44 , which are pivotable on a pivot axis S in relation to one another, in a view in the direction of the pivot axis ( FIG. 1   a ) or in top view in perpendicular to it ( FIG. 1   b ) respectively. With a means for creating a clamping force  46 , e.g. a spring, the distal ends of the clamping tongues  42 ,  44  in closed condition of the gripper are pressed against each other or against the gripped product respectively. As shown in  FIG. 1   b , one of the clamping tongues  42  is designed in a T-shape and comprises laterally protruding arms  43 ,  43 ′. This kind of gripper is e.g. known from the publications DE-A310 2242 and WO 2007/115421 named at the outset and from EP-A 0 600 183, which is referenced here regarding the further construction and the mode of operation. 
     In order not to damage the product, to increase the extraction force in closed condition and to concentrate the clamping force to two regions, clamping elements  1 ,  1 ′ are arranged on the distal edges of the clamping tongues  42 ,  44 . The clamping element  1  fitted to the T-shaped clamping tongue  42  is designed according to the invention; the further clamping element  1 ′ may be implemented in a conventional manner. The clamping element  1  according to the invention comprises a lengthy carrier  10 , which extends over the complete width (viewed in direction of the pivot axis S) of the clamping tongue  42  in the distal region, i.e. including arms  43 ,  43 ′. The carrier  10  (partly drawn in broken lines) is on the other side of the clamping tongue  42  in viewing direction. On the outer ends of the carrier  10 , two fastening elements  30 ,  30 ′ are located with which the carrier  10  is held on the clamping tongue  42  or on the arms  43 ,  43 ′ respectively, in particular fitted onto the arms  43 ,  43 ′. On the outer edges two clamping regions  20 ,  20 ′ are furthermore provided, in which the clamping effect of the clamping element  1  is the largest. Due to the fact that the arms  43  and  43 ′ are e.g. attached to the clamping tongue  42  in a springing manner and the clamping effect is concentrated by the form and elastic characteristics of the clamping element  1  on the clamping regions  20 ,  20 ′, non-homogeneous product thicknesses may be compensated and the products held in a stable manner. 
       FIGS. 2   a  and  b  show an example for a clamping element  1  with a lengthy carrier  10 , which here is formed by a hollow profile  12  with several chambers  13  continuous in longitudinal direction. The carrier  10  comprises a basic layer  14  as well as a covering layer  15  arching over it. Between the basic layer and covering layer  14 ,  15  separating walls  16  run obliquely to the basic layer  14 , which walls separate the chambers  13  from each other and under strain keep the covering layer at a (variable) distance from the basic layer  14 . The basic layer  14  lies on the clamping tongue  42  in the case of operation, and the covering layer  15  is directed towards the object to be held or the other clamping tongue  44  respectively. 
     On the outermost edges of the carriers  10  two clamping regions  20 ,  20 ′ are provided, by means of a distance between the covering layer  15  and the basic layer  14  being larger in the end regions than in the middle region. This is shown in an exaggeratedly strong manner in  FIG. 2   b . The clamping effect is thus mainly exerted in the end regions. The same effect could e.g. also be achieved with a homogenous thickness of the profile  12  by means of differing compliance in the end regions and in the intermediate middle region, e.g. by only providing the profile  12  with separating walls  16  inside in the end regions. 
     The oblique separating walls  16  have, among other things, the function of realising differing elasticity modules in the clamping regions  20 ,  20 ′, in particular in order to impede a drawing out against the orientation of the separating walls  16  (here downwards) of the objects held between two clamping elements  1  and a flattening and thus to facilitate homogenising the force within the clamping region on force impact in the other direction. The cushion-like structure, thus, leads to a flattening of the clamping region and a homogenising of the clamping force, even if the clamping tongues as in the case of  FIG. 1   a  meet at an angle. In order to secure the appropriate assembly, in the present case an orientation aid  19  is applied to the carrier  10 . 
     In the end regions, two fastening elements  30 ,  30 ′ are arranged on the side averted to the covering layer  15  of the carrier  10 . These, here each comprise a hollow body  32 ,  32 ′, which is formed in one piece with the carrier  10  and encloses a respective hollow space  34 ,  34 ′. The shape of the hollow space  34 ,  34 ′ and the distance of the fastening elements  30 ,  30 ′ is adapted to the form of the clamping tongue, here to arms protruding from it laterally. The hollow spaces  34 ,  34 ′ have facing openings  36 ,  36 ′ into which the arms may be stuck in the case of application, such that the clamping tongue is taken up between the fastening elements  30 ,  30 ′. 
     The clamping element  1  is made in one piece of an elastic material and, e.g. a thermoplastic material. As shown in  FIG. 2   b , the carrier  10  may be bent in perpendicular to its longitudinal direction in order to be able to put the clamping element onto the arms of the clamping tongue. In order to prevent material fatigue release slots  17  may be provided in the basic layer  14 . 
     The clamping element  1  may be manufactured very cost-efficiently by means of mass production, e.g. by means of die-casting. Due to reasons in connection with die release the faces of the clamping element  1  in the shown example are open; they can also be closed if a different method of manufacture is used. 
       FIGS. 3 and 4  show different examples for clamping elements  1 , which are attached to a clamping tongue  42 ,  44  or to arms  43 ,  43 ′ protruding laterally from it. They are shown in views as directed towards the side of the clamping tongues  42 ,  44  facing the respective other clamping tongue, i.e. towards the clamping regions  43 ,  43 ′. In both examples, two respective clamping regions  20 ,  20 ′ are provided, which are at a distance from one another and the position of which approximately corresponds to that of the arms  43 ,  43 ′. The clamping regions  20 ,  20 ′ are connected to one another by the lengthy carrier  10  or are part of the carrier  10 . The carrier  10 , outside the clamping regions  20 ,  20 ′, may simply be a material bridge. 
     In the example of  FIG. 3 , the end regions of the carrier  10  on the backside of the clamping regions  20 ,  20 ′ are designed as fastening elements in the manner of a bush, e.g. as shown in  FIGS. 2   a  and  b  and are applied to the arms  43 ,  43 ′. The elongated carrier  10 , or the material bridge respectively, prevents the entire clamping element  1  from being disconnected from the clamping tongue  42 ,  44 ; a certain clearance, however, in the direction of the axis S is possible. 
       FIG. 4  shows that the arms  43 ,  43 ′ may also be designed as a separate component, which is attached on the actual clamping tongue  42 ,  44 .  FIG. 4  shows an alternative fastening of the clamping element  1  to the arms, namely with hooks or clips attached to the end regions, which encompass the arms S in the direction of axis S and take them up between them. 
       FIGS. 5 through 8  show different examples for the design of the clamping elements  1  in the clamping regions  20 ,  20 ′ in side view. In all figures, the clamping element  1 ′ of the second clamping tongue  44  is a profile with a hollow space, which is formed, as e.g. in  FIG. 4 , on the separately designed arm. The hollow profile additionally comprises a deformable covering layer, which is directed towards the clamping element  1  of the first clamping tongue  42  and thus forms the supporting surface of the clamping element  1 ′. 
     The clamping elements  1 . 1  through  1 . 4  of the first clamping tongue  42  shown in  FIGS. 5 through 8  are also shown separately a in three dimensional view. 
     The clamping element  1 . 1  according to  FIG. 5  is attachable to both arms  43 ,  43 ′ from the free arm end. For this purpose it comprises a tubular restrictedly elastic carrier  10 . In the end regions of the tubular carrier  10 , an inner plate is arranged, which in its middle comprises a spherical recess  52  in its middle. The arms  43 ,  43 ′ in a corresponding location comprise recesses  53  corresponding to the spherical recess  52 , the depth of which is somewhat smaller than the height of the spherical recess  52 . If the clamping element  1 . 1  is attached on the arms  43 ,  43 ′ the spherical recesses  52  are positioned in the recesses  53 , such that the plate  51  is supported over a ball joint on the arm  30 . The inner plate  51  can thus adapt in all directions to the support surface of a counter clamping jaw or to a gripped object. 
     In  FIG. 5 , a recess  55  is additionally shown on the side of the arm  43 ,  43 ′ averted from a gripped object, which, in cooperation with a convexity  56  of the tubular carrier  10  fixes the clamping element to the arm. 
     The clamping element  1 . 2  shown in  FIG. 6  corresponds to the principle of the one shown in  FIGS. 2   a  and  2   b . It is again attachable from both sides to the arms  43 ,  43 ′ and therefore comprises a tubular, restrictedly elastic carrier  10 . On this carrier  10  a laterally open, e.g. multi-chambered hollow profile  12  is arranged, which forms a cushion-shaped supporting surface on preferably oblique supports  13 . 
       FIG. 6  illustrates that the front surface of the clamping element  1  in clamping region  20  is adapted to the held product or to the counter element  1 ′ respectively, although the two clamping tongues  42 ,  44  meet at an angle in the clamping region  20 . The front surface on the clamping region  20  thus, under the influence of an external force effect runs at an angle to the surface of the actual carrier  10 . This is made possible by the flexibility of the clamping element  1  in the clamping region  20 , here, by the profile being subdivided into chambers and by use of an elastic material. The force distribution is, thus, regular and gentle for the product.  FIG. 6  also shows that the chamber walls  13  form a resistance, which impedes the drawing out of the product towards the bottom. 
     The clamping element shown in  FIG. 7  substantially consists of a carrier  10  to which flat cushions  62  closed on all sides and filled with a liquid are attached, which cushions define the clamping regions  20 ,  20 ′. The carrier  10  is fixed by fixing elements  32  on the arms  43 ,  43 ′, which here are designed in the manner of a rail. Instead of a cushion  62  a flat block  63  of an elastically deformable material (e.g. viscoelastically deformable) material could be used ( FIG. 8 ).