Abstract:
A gripper, has a frame for movably guiding four radially movable gripper jaws in four shafts which extend radially outwards. An arbor is disposed centrally between longitudinal carriers of the frame in parallel relationship thereto, whereby the arbor, at least over a portion of its lengths, is conically tapered downwardly and can be shifted longitudinally by a piston-cylinder unit. The gripper jaws are spring biased radial against the arbor, whereby the contact surfaces of the gripper jaws are configured in conformity with the outer arbor surface. Each gripper jaw includes a plate-shaped central element and at least two parallel plate-shaped lateral elements which are laterally disposed to the central element and include a depression directed towards the outer side of the gripper jaw and having a cross-section, which, as viewed in the direction of the lateral surface of the lateral element, may have the shape of an isosceles triangle.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of prior filed provisional application, Appl. No. 60/229,399, filed Aug. 31, 2000, pursuant to 35 U.S.C. 119(e). 
     
    
     
         [0002]    This application claims the priority of German Patent Application Serial No. DE 100 44 527.6, filed Sep. 4, 2000, the subject matter of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0003]    The invention relates, in general, to a gripper having four gripper jaws which can be moved in radially outward direction, for grabbing loads, in particular from above.  
           [0004]    Grippers with four gripper jaws are known in general, particularly for loads which need to be gripped at the top and which have a cylindrical carrier opening. For this, the gripper jaws are introduced into the carrier opening and they are moved in radially outward direction, so as to secure the load by clamping action. A gripper of this type has a single-piece frame in which the gripper jaws are guided so as to be radially movable and axially fixed. The frame has four parallel longitudinal carriers spaced from one another at uniform radial distance as well as uniform angular distance and having upper and lower ends which are respectively fixedly connected to one another by a plate-shaped face element. The frame prevents shifting of the gripper jaws in the longitudinal direction of the frame, that is, they are guided in such a manner that only a radial movement is permitted. The gripper jaws are in contact with the arbor by means of the force exerted by the reset springs and actuated by the arbor via the piston-cylinder unit. The longitudinal carriers and the face elements form four shafts which extend radially outward, for receiving the gripper jaws, with an arbor disposed centrally between the longitudinal carriers in parallel relationship. The arbor can be guided through an opening in the upper plate element to the exterior, and, at least over a portion of its lengths tapers downwards. The arbor can be shifted in longitudinal direction by means of a piston-cylinder unit which is securely fixed to the upper plate element, whereby the gripper jaws are respectively in contact with the arbor as a consequence of a force applied by a reset spring. The contact surfaces of the gripper jaws are configured in at least the region of contact in conformity to the outer surface area of the arbor, such that a longitudinal shifting movement of the arbor is respectively converted into a radially directed movement of the gripper jaws. In this manner, it is assured that the movement of the arbor in the longitudinal direction is converted into a radial movement of the gripper jaws.  
           [0005]    A disadvantage of known grippers is that the assembly thereof includes a frame and gripper jaws, which are complicated to make and thus incur considerable expenditures.  
           [0006]    It would therefore be desirable and advantageous to provide an improved gripper which obviates prior art shortcomings and which can be economically produced with reduced manufacturing and assembly expenditures and obviating the afore-stated drawbacks.  
         SUMMARY OF THE INVENTION  
         [0007]    According to one aspect of the present invention, a gripper is provided having gripper jaws, wherein each gripper jaw is formed by a plate-shaped central element and at least two lateral elements which extend parallel with respect to one another and which are disposed laterally with respect to the central element, which lateral elements respectively are provided with a depression which is directed to the outer side of the gripper jaw. The depression may have a cross section in the form of an isosceles triangle, with a base side extending parallel to the longitudinal carriers and two shorter roof sides directed inwardly toward the arbor and having same length, whereby the two ends of the base side are provided with pockets for receiving the ends of a leaf spring, with the leaf spring, having an the outer side for central abutment of a tensioning element provided at the associated longitudinal carrier and engaging in the depression. Alternatively, the cross-section of the depression may have a projection which is directed away from the arbor into the depression and which is opposed by a longitudinal side extending parallel to the longitudinal carriers, with the leaf spring in the relaxed condition extending parallel to this longitudinal side. Secured to each of the ends of the leaf spring is a tensioning element which engages in the depression and is arranged at the associated longitudinal carrier, whereby the tensioning element and the projection are configured to respectively effect a corresponding reset force to move the gripper jaw in outward direction. The face elements are made from sheet metal, and the longitudinal carriers are made either of longitudinal profiles or from the legs of at least four U-shaped metal sheets, whereby the metal sheets are arranged in such a way that they provide a central free space of quadratic cross-section and are disposed, respectively by an angle of 90 degrees, in an offset manner about the central axis of the arbor. This sheet metal configuration can be made in a highly cost-efficient manner and can selectively be provided with equally highly economic longitudinal profiles, for example, angle profiles. The latter also is more appealing in appearance.  
           [0008]    Exchange of the grippers can be easily implemented, when the piston-cylinder unit is connectable to the upper face element by means of a connector in the form of a bayonet coupling. Suitably, the arbor may include an upper and a lower arbor element which can be releasably connected to one another, whereby the upper arbor element is disposed in the piston-cylinder unit and the lower one is disposed in the frame. In a simple manner, the connector may includes pin-shaped closing elements which are arranged at the piston-cylinder unit and extend in the longitudinal direction of the cylinder beyond the outer contour, and which have thickened ends for passage through complementary openings of the face element which openings are tapered in circumferential direction. The closing elements are introduced into the tapered portion by turning the entire piston-cylinder unit.  
           [0009]    To prevent an inadvertent release of this connection between the piston-cylinder unit and the frame, for locking at the piston-cylinder unit, there is provided a locking element which latches in a depression or through-opening in the face element.  
           [0010]    In order to move the gripper jaws in outward direction only when the gripper is fully positioned on the load, it may be suitable to provide an annular control element which emits a control signal when the gripper has been fully positioned on the load.  
           [0011]    According to another feature of the present invention, the plate-shaped elements of the gripper jaws and the U-shaped metal sheets can be cut to size by laser from sheet metal. In this way, manufacture of the gripper is highly cost-efficient. Manufacture may be simplified and cost-efficiency enhanced, when the arbor is designed in a rotation symmetric manner and the carrier opening is cylindrical. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0013]    [0013]FIG. 1 a  is a front view of one embodiment of a gripper with angle profiles as longitudinal carriers;  
         [0014]    [0014]FIG. 1 b  is a plan view of the gripper;  
         [0015]    [0015]FIG. 2 is an illustration of another embodiment of a gripper with a releasable piston-cylinder unit and with U-shaped metal sheets as longitudinal carriers;  
         [0016]    [0016]FIG. 3 is a detailed illustration of the releasable piston-cylinder unit;  
         [0017]    [0017]FIG. 4 a  is a front view of the gripper of FIG. 2, without piston-cylinder unit;  
         [0018]    [0018]FIG. 4 b  is a sectional view of the gripper of FIG. 2, without piston-cylinder unit;  
         [0019]    [0019]FIG. 4 c  is a plan view of the gripper of FIG. 2, without piston-cylinder unit;  
         [0020]    [0020]FIGS. 5 a, b  show the U-shaped metal sheets of the longitudinal carrier in accordance with FIG. 2; and  
         [0021]    [0021]FIG. 6 shows a modified embodiment of a depression with leaf spring for provision in the grippers of FIGS. 1 and 2. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals.  
         [0023]    [0023]FIGS. 1 a ,  1   b  illustrate a front view and a plan view of a gripper which includes an upper piston-cylinder unit, generally designated by reference numeral  1  and a lower gripper unit, generally designated by reference numeral  2 . The piston-cylinder unit  1  has an upper flange plate  3  for attachment of a pneumatic cylinder  4  which extends in downward direction and has a lower end which is firmly connected with an upper face plate  5  of the gripper unit  2 . As best seen in FIG. 1 a , a control unit  6  is disposed on the right hand side of the piston-cylinder unit  1  in opposition to the pneumatic cylinder  4 . By means of the pneumatic cylinder  4 , the face plate  5  and the flange plate  3  can be moved in opposite direction with respect to one another.  
         [0024]    The gripper unit  2  includes a frame  7 , which is made from four rectangular longitudinal profiles (angle profiles) as longitudinal carriers  8  and the face plate  5  (above), as well as the face sheet metal  9  (below), as plate-shaped face elements  10 , whereby the face elements  10  and the longitudinal carriers  8  are firmly secured to one another, for example, by welding. As shown in FIG. 1 b , the longitudinal carriers  8  are arranged at a same radial distance from the center line  11 , as well as at a same angular distance (90 degrees) with respect to one another. Arranged between the outer sides of two neighboring longitudinal carriers  8  is a shaft  12 . The shafts  12  are confined at the top and at the bottom by the face elements  10 . The gripper unit  2  further includes four gripper jaws  13  which are guided in the shafts  12  for radial displacement and secured in axial direction.  
         [0025]    Provided centrally between the longitudinal carriers  8  is an arbor  14 , which has, preferably, a rotation-symmetric configuration, and aligned in parallel relationship to the longitudinal carriers  8 . The arbor  14  is guided upwardly through an opening  5  in the face element  10  (face plate  5 ) out of the frame  7  into the piston-cylinder unit  1  for securement to the flange plate  3 . In this manner, a movement that is effected by the pneumatic cylinder  4  on the flange plate  3  relative to the face element  10  (face plate  5 ), is converted into a longitudinal shift of the arbor  14  within the frame  7 .  
         [0026]    Within the frame  7 , the arbor  14  has two conical tapers  16 ,  17  which are illustrated by dash lines in FIG. 1 a (see also FIG. 2). At their side confronting the arbor, the gripper jaws  13  are acted upon by a spring force for abutment upon the outer surface area of the arbor  14 . The contact surfaces of the gripper jaws  13  are configured in conformity with the outer surface area of the arbor  14 , at least in the contact area, i.e., at least along the line of contact.  
         [0027]    The two tapers  16 ,  17  and the complementary contact surfaces of the gripper jaws  13  convert a longitudinal shifting of the arbor  14  into a radial movement of the gripper jaws  13 .  
         [0028]    As is illustrated in FIG  1   a , each gripper jaw  13  includes a central metal sheet which defines a plate-shaped central element  18 . On both sides of the central element  18  are lateral metal sheets defining plate-shaped lateral element  19 . Thus, each gripper jaw  13  is comprised of three sheets which are secured to one another. It is preferred that only the central element  18  is in contact with the arbor  14 . As shown in FIG. 1 a , in particular the central element  18  is provided with gripper teeth  20  which point in outward direction.  
         [0029]    Each lateral element  19  is made of sheet metal and has a depression  21 , which can be particularly viewed in FIG  1   a  in the shown breakaway portion. The depression  21  is suitably produced by cutting the lateral elements  19  to form a through-opening with respective cross-sectional configuration. After securing the lateral elements  19  to the central element  18 , for example, by welding, a depression  21  is formed which is directed to the outer side of the gripper jaw  13  and which is open on this side. The depression  21  is covered by the longitudinal carrier  8  which is in immediate opposite relationship.  
         [0030]    [0030]FIG. 1 a  illustrates that the cross-sectional configuration of the depression  21  cut lengthwise substantially resembles an isosceles triangle, with a base side  22  which extends parallel to the longitudinal carriers  8 , and with two shorter roof sides  23 , approximately of same length, which are directed inwardly towards the arbor  14 , so that also the tip of the triangle points inwardly. A leaf spring  24  is positioned in the depression  21  and has angled ends which engage in pockets  25  provided at the ends of the base side  22 . Bearing upon the outer side of the leaf spring  24  is a pin which serves as tensioning element  26  and is secured to the longitudinal carriers  8  at locations  27  (compare FIG. 1 b ). Of course, the tensioning element  26  can extend fully through the entire gripper jaw  13 . To ensure the mobility in radial direction of the gripper jaws  13 , they are provided with a slot  28  through which the tensioning element  26  is guided. A movement of the gripper jaws  13  in outward direction (due to a lengthwise shifting of the arbor  14 ), results in a tensioning of the leaf spring  24 , which, as a consequence, applies a reset force in conformity with the displacement. A alternate configuration of the depression  21  is shown in FIG. 6.  
         [0031]    [0031]FIG. 2 illustrates a gripper in accordance with FIG. 1, in which the piston-cylinder unit  1  can be connected, in the manner of a bayonet coupling, with the upper face element  10  (face plate  5 ), so that the gripper unit  2  can be quickly replaced by another one.  
         [0032]    The piston-cylinder unit  1 , removed from the gripper unit  2 , is illustrated in FIG. 3 and includes a plurality of pin-shaped closing elements  29  which extend, when viewed in the longitudinal direction of the cylinder of the pneumatic cylinder  4 , through the face element  10  (face plate  5 ) (compare FIG. 2) downwardly in the frame  7 , that is, they extend beyond the actual outer contour of the piston-cylinder unit  1 . The free lower ends of the closing elements  29  have annular thickened portions  30 . The thickened portion  30  is produced in such a way that a bolt, secured to the flange plate  3 , is provided at its lower end with an annular groove. In addition, the bolt is secured on a support plate  31  on the side which is opposite to the flange plate  3 .  
         [0033]    [0033]FIGS. 4 a - 4   c  illustrate various views of the associated gripper unit  2 . Particularly the plan view in FIG. 4 c  illustrates through-openings  32  in the face element  10  (face plate  5 ), which are formed as oblong holes and tapered in circumferential direction—in reference to FIG. 4—in counterclockwise manner. The through-openings  32  are configured in conformity to the closing elements  29  which can be introduced with their thickened portions  30  through those portions of the through-openings  32  which are not tapered. Turning of the entire piston-cylinder unit  1  about the center line  11  or, respectively, about the arbor  14 , effects a turning of the closing elements  29  into the portion that is reduced in size, such that these engage in the grooves of the closing elements  29  and secure the piston-cylinder unit  1  in axial direction. In the final position, a spring-biased cylinder  33  (compare FIG. 3) is engaged in a through-bore  34  which is provided at the face element  10  (face plate  5 ), and provides a radial securement of the piston-cylinder unit  1 .  
         [0034]    As is illustrated in FIGS.  2  to  4 , the arbor  14  is made of two components. The arbor  14  includes an upper arbor element  14   a  and a lower arbor element  14   b , which are releasably connected to one another. The connection is achieved by means of a spherical head  35  disposed at the lower end of the upper arbor element  14   a  and configured for insertion in latching engagement into a complementary depression of the lower arbor element  14   b . The latch element is provided by a spring element  36  which has the only function to transfer vertically directed forces from the upper arbor element  14   a  to the lower  14   b  during extraction of the arbor  14  from the frame  7 . The upper arbor element  14   a , in accordance with FIG. 2, is arranged in the piston-cylinder unit  1  and the lower  14   b  is arranged in the frame  7 .  
         [0035]    As further illustrated in FIGS. 1 a ,  1   b  and  2 , below the face element  10  (face plate  5 ), there is provided a control ring  37  which is movable in the longitudinal direction of the arbor  14  and is pressed away by means of springs  38  from the face element  10 . As can be best seen from FIG. 2, the control ring  37  actuates a control element  38  of the control unit  6 . The control ring  37  can not be turned radially, i.e. it is secured against turning, and triggers a control signal when a gripper is completely positioned on the load. Furthermore, the thickened portions  30  pass hereby into through-openings in the control element  37 , so as to realize an additional safety locking of the piston-cylinder unit.  
         [0036]    While FIGS. 1 a  and  1   b  illustrate a frame which is made from angle profiles as longitudinal carriers  8 , FIGS. 2 and 4 illustrate a frame  7  which is made from U-shaped metal sheets  39 ,  40 , as shown in detail in FIGS. 5 a ,  5   b . Each metal sheet  39 ,  40  has two legs  41 ,  42 . The distance between two confronting inner sides  43 ,  44  of the legs  41 ,  42  is so selected that respectively two pairs of metal sheets  39 ,  40  can be plugged together in offset relationship at an angle of 90 degrees, whereby same sheets  39  or  40  are arranged in pairs in opposite relationship. Four metal sheets  39 ,  40 , plugged together in corresponding manner, have a central free space in their interior for insertion of at least the lower portion of the arbor  14   b . In this embodiment, the legs  41 ,  42  define the longitudinal carriers  8 . The contour of the metal sheets  39 ,  40  is cut by laser in a cost-efficient manner from a sheet metal.  
         [0037]    The gripper unit  2  is introduced into a carrier opening, for example, of cylindrical configuration. The gripper which is suspended from a rope preferably serves to grab loads from above. Of course, other applications are within the scope of the invention.  
         [0038]    [0038]FIG. 6 illustrates a modified embodiment of the depression, comprising a depression of like formation  21  for receiving therein a leaf spring  24  which can be biased by a tensioning element  26  that is guided at respective ends of the leaf spring  24  in slots  28 .  
         [0039]    While the invention has been illustrated and described as embodied in a gripper with four gripper jaws which can be moved in radially outward direction, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0040]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: