Abstract:
A gripping assembly, comprising gripper elements ( 2, 3 ) adapted to be opened and closed for gripping and clamping a load, is adapted to be secured to the boom of traveling equipment. A control mechanism ( 40 ) is provided for controlling the opening and closing movements of gripper elements ( 2, 3 ) between an opened and a closed condition. The control mechanism ( 40 ) senses the relative movements between two parts of the gripping assembly, with a locking element of the control mechanism ( 40 ) being movable between a released position in which gripper elements ( 2, 3 ) perform a closing movement and a locked position in which the gripper elements ( 2, 3 ) are held in their opened position. When the opened gripping assembly is suspended from the boom and undergoes swinging movements, means, incorporated in control mechanism ( 40 ) and adapted to slow down movements of the locking element, prevent the locking element from reaching the released position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a gripping assembly, especially a scissor-type clamp, having gripper members for gripping and clamping a load, which incorporates a control mechanism for controlling the opening and closing movements of the gripper elements. 
         [0002]    The German Patent No. DE 27 27 919 discloses a control mechanism for a scissor-type clamp, the mechanism comprising a control plate having therein a control groove engaging a control stud secured to the bottom end of a control rod. When the scissor-type clamp is raised with its grippers opened after a load—such as stack of a building material—has been laid down, the control stud engages a recess in an entrainment member. One problem of scissor-type clamps of this type equipped with a control mechanism is that, when the clamp attached to a long boom of a lift vehicle is improperly handled in the condition described, serious difficulties may arise. For example, if the lift vehicle travels over uneven ground on a relatively large building site and under substantial time pressure in order to pick up a load, with the aforesaid control stud engaging the recess in the entrainment member, the boom and thus the clamp itself may swing up and down, the amplitude of such swinging being the greater the longer the boom. As a consequence, a forced upward movement may result in the clamp being accelerated upwards with a very high force so that, as the swinging movement reverses to downwards to lower the boom, the clamp may “hover” for a short period of time, resulting in the aforesaid control stud being removed from the recess in the entrainment member. As gravity starts to act again, the unlocked gripper portion of the clamp drops and continues to do so until the grippers of the clamp meet or until a catch mechanism—comprising chains, for example—limits the closing movement to some predetermined extent. As a consequence of these dynamics, and especially if the drop of the clamp is to be limited, the load surges give rise to enormous forces acting upon the limiting element. As the dynamics are ill-defined, the magnitude of these forces cannot be computed; in the long term, they cause substantial damage to the steel structures of the scissor-type clamp. 
         [0003]    In order to avoid such damage, attempts have been made to equip the aforesaid limiting elements with some kind of a damping or spring-action mechanism which avoids impact-like stopping movements and instead slows the drop down over some distance, thereby “softening” it. Surge-limiting damper elements of this kind are very expensive, however; different kinds of scissor clamps require different designs, different hinges and articulations, different dimensions and, particularly, different maintenance schemes. 
         [0004]    In the aforesaid scissor clamps, one solution of the problem was obtained by designing the recess for the control stud to be very deep, whereby the swinging movements of the boom would require the control stud to oscillate with a greater amplitude to be undesirably released from the recess. In turn, this would require the over-all design height of the clamp to be increased, so that its use would be limited. A similar scissor-type clamp is disclosed in the German Patent Application No. 91 03 520.1 also. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore a principal object of the present invention to provide a gripping assembly that is simplified in construction and designed to prevent the high-amplitude swinging of the clamp attached to a boom of a lift vehicle from inadvertently unlocking the gripping assembly and causing it to drop. 
         [0006]    This object, as well as other objects which will become apparent from the discussion that follows, are achieved, according to the present invention, in the environment of a gripping assembly, having a control mechanism for controlling the opening and closing movements of gripper elements between an opened and a closed condition, by providing a control mechanism which senses the relative movements between two parts of the gripping assembly, with a locking element of the control mechanism being movable between a released position in which gripper elements perform a closing movement and a locked position in which the gripper elements are held in their opened position. When the opened gripping assembly is suspended from the boom and undergoes swinging movements, means, incorporated in control mechanism and adapted to slow down movements of the locking element, prevent the locking element from reaching the released position. 
         [0007]    The essential advantage of the gripping assembly, and particularly of the scissor-type clamp according to the invention, is that, when the opened scissor-type clamp, suspended from a long boom, is moved and the boom swings, an undesirable dropping of the clamp&#39;s gripper area is safely avoided by the unlocking movement—which occurs as a locking pawl of the control mechanism is released—being slowed down by the specialized damping device. 
         [0008]    For this reason, and advantageously, damage to the steel structure of the scissor-type clamp can be reliably avoided, as can injury to operating personnel. 
         [0009]    Another essential advantage of the present invention resides in the relatively simple design of the damping device used to slow down the locking pawl. Advantageously, and regardless of the type of the mechanical gripping means, a damping device of this kind is suitable for incorporation in the control mechanism in the same manner throughout. For different weights and configurations of gripping assemblies, it is possible to use a damping device of variously higher or lower strengths. 
         [0010]    The present invention thus relates to a gripping assembly, and especially to a scissor-type clamp having a pair of opposing gripper arms and a control mechanism. The clamp is adapted to be secured by fastening means to the boom of a mobile working device, with the control mechanism controlling the opening and the closing of the gripper arms. The control mechanism comprises an entrainment member or locking pawl arranged to be blocked or released by an abutment device in dependence on the scissor clamp movements. In accordance with the invention, means are provided to slow down the movement of the locking pawl from the area of the abutment device in a manner such that undesirable premature release of the locking pawl is avoided when and if the scissor clamp is handled improperly. 
         [0011]    Preferably the locking pawls are located in a gripper-side area of the scissor clamp and the abutment device is located in a suspension-side area of the scissor clamp. 
         [0012]    In a further development of the invention, the locking pawl and a positioning pawl are provided in a housing portion for movement between a first position, in which they extend from the housing portion, and a second position in which they are retracted into the housing portion. The pawls are moved to cause the following operation to proceed as the scissor clamp is actuated: 
         [0013]    (a) As the scissor clamp is lifted, the abutment device reaches under the locking pawl protruding from the housing portion, with the gripper arms being open. 
         [0014]    (b) As the scissor clamp is subsequently placed on a load to be clamped, such as a stack of building material, the abutment device releases the locking pawl so that it moves from the area of the abutment device and returns into the housing portion. 
         [0015]    (c) The subsequent lifting of the building material stack and the clamping thereof by its own weight between the grippers and by the intrinsic weight of the scissor clamp cause a positioning pawl to be actuated and the locking pawl to by moved from the housing portion. 
         [0016]    (d) After the scissor clamp is transported to a prescribed location, and as it is set down and the gripper arms are opened so as to release the load, the abutment device is moved past the locking pawl, with the locking pawl being moved into the housing portion and then re-emerging therefrom. 
         [0017]    (e) As the scissor clamp is then lifted, the abutment device reaches under the locking pawl. Initially, the locking pawl moves a short distance upwardly, causing the positioning pawl to be unlocked and to tilt forwardly from the housing portion. In the process, the locking pawl is blocked so that the opened scissor clamp can be lifted. Thus the condition described in (a) is restored. 
         [0018]    In another embodiment of the present scissor-type clamp, the positioning pawl actuating the locking pawl is mounted to pivot in the housing portion, with the abutment device having two abutment members placed one above the other, with one of them actuating the positioning pawl above the locking pawl and the other actuating the locking pawl. This embodiment is particularly advantageous when used in a short-stroke gripping assembly. 
         [0019]    The damping device preferably comprises a rotation damper including an arm member rotatable about an axis, the arm member having therein a slot engaging an axle connected with the locking pawl so that pivoting movements of the locking pawl are transmitted to the rotation damper and slowed down in the direction of the locking pawl away from the abutment means. The pivoting movement is not slowed down in the opposite direction. 
         [0020]    In a particularly preferred embodiment, the rotation damper comprises a conventional hydraulic damper and especially an oil damper. In addition to the aforesaid scissor-type clamp, bell crank lever clamps, single-lever clamps or the like are contemplated for use with gripping assemblies. 
         [0021]    For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows a scissor-type clamp with an inventive control mechanism in the open condition. 
           [0023]      FIG. 2  shows a side view of the scissor-type clamp of  FIG. 1  in a partly open condition. 
           [0024]      FIG. 3  shows a three-dimensional detailed representation of a control mechanism to be used in accordance with the invention. 
           [0025]      FIG. 4  shows a side view of the present control mechanism of  FIG. 3 , with the scissor-type clamp in a raised position, the clamp&#39;s grippers opened. 
           [0026]      FIG. 5  shows the control mechanism in a condition in which the scissor-type clamp is placed on top of a load to be clamped, with the grippers opened. 
           [0027]      FIG. 6  shows the condition in which the scissor-type clamp is lifted by the boom of a lifting vehicle being swung upwards, with the clamp grippers clamped shut. 
           [0028]      FIG. 7  shows the control mechanism in the condition in which the scissor-type clamp and the load therein are set down and the grippers opened. 
           [0029]      FIG. 8  is a detailed side view of a curbstone clamping device according to a further preferred embodiment of the invention. 
           [0030]      FIG. 9  is a perspective view of the scissor-type clamp according to still another preferred embodiment of the invention. 
           [0031]      FIGS. 10   a  and  10   b  are representational diagrams illustrating the operation of the scissor-type clamp according to the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-10  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
         [0033]      FIG. 1  schematically shows a scissor-type clamp  1  of the type known in the art, which consists essentially of a first gripper element  2  and a second gripper element  3 . First gripper element  2  comprises pair of transversely spaced gripper arms  5 ,  6  interconnected by a first cross member  4 . Essentially, gripper arms  5 ,  6  each have a first portion  7  or  8 , respectively, and a second portion  9  and  10 , respectively, which preferably are disposed at a substantially right angle. At the bottom free end of portions  9 ,  10  is disposed a gripper jaw or bar  11  extending in the transverse direction to interconnect portions  9 ,  10 . 
         [0034]    Gripper element  3  is constructed correspondingly to comprise transversely spaced gripper arms  12 ,  13 , cross member  14  and gripper bar  15 . Gripper arm  12  preferably comprises portions  16 ,  17  extending at a substantially right angle and gripper arm  13  comprises portions  18 ,  19  also extending at a substantially right angle, with gripper bar  15  extending in a transverse direction between the lower ends of portions  17 ,  19 . Portions  7 ,  8  of gripper arms  5 ,  6  and portions  16 ,  18  of gripper arms  12 ,  13  are interconnected for pivoting movement about a transverse axis  20 , said axis  20  located about midway between portions  7 ,  8 ,  16  and  18  and allowing gripper arms  5 ,  6  to be pivoted against each other. 
         [0035]    At the free ends of portions  7 ,  8 , connector rods  23 ,  24  are provided to pivot about pivots  21 ,  22 ; these rods have their free ends connected with a cross-member  25  to rotate about pivots  26 ,  27 . Correspondingly, the free ends of portions  16 ,  18  of gripper arms  12 ,  13  are connected to pivot about pivots  28 ,  29  with connector rods  30 ,  31 ; these rods have their ends connected to cross-member  25  to pivot about pivots  26 ,  27 . Cross-member  25  has centrally connected thereto mounting means  32  allowing scissor clamp  1  to be fastened to a lifting or traveling vehicle (not shown in detail). Gripper arms  5 ,  6  and  12 ,  3  are caused to be moved to the closed position by the intrinsic load of scissor clamp  1  suspended from the boom. 
         [0036]      FIGS. 1 and 2  show the scissor clamp in the totally, and in the partly, opened conditions, respectively. 
         [0037]    Connector rods  30 ,  31  are connected about midway by a cross-member  34  while connector rods  23 ,  24  are connected about midway by a cross-member  35 . Further, portions  7  and  8  are interconnected by a cross-member  36 ; portions  16 ,  18  are also interconnected by a cross-member (not shown). 
         [0038]    Between cross-member  36 , which interconnects gripper arm  5 ,  6 , and cross-member  35 , which interconnects connector rods  23 ,  24 , there is located a control mechanism  40  referred to schematically as  40  in the  FIG. 1  and explained in greater detail in connection with  FIG. 3 . It is pointed out, however, that control mechanism  40  can be located differently between places which move relatively to each other as gripper arms  5 ,  6  open and close. 
         [0039]    Essentially, and in the manner already explained at the outset, control mechanism  40  comprises an abutment device  41  disposed on cross-member  34  of the scissor clamp  1  and having a bottom abutment member  43 . Preferably, the abutment device  41  is U-shaped, with abutment member  43  forming the bottom transverse bar of the U-shape and the legs of the U-shape being secured on or welded to cross-member  35 . 
         [0040]    A cross-member  36  has a housing portion  45  fastened—preferably welded—thereto having a side along which abutment member  43  slides when scissor clamp  1  reaches the area of its opened position. In the manner initially explained, the housing portion  45  has mounted thereon a positioning pawl  52  and locking pawl  51 , of which the functions are explained in greater detail below under reference to the schematic representations in  FIGS. 4 to 8 . Details in  FIGS. 4 to 8  which were explained under reference to  FIG. 3  are referenced correspondingly. 
         [0041]      FIG. 4  shows the condition in which scissor clamp  1  is lifted by the boom and gripper arms  9 ,  10  and  17 ,  19  are open ( FIG. 1 ). In the manner shown, the locking pawl  51  protrudes from housing  45  to lock abutment device  41  in place, causing a lock to act between cross-member  36  of gripper arms  5 ,  6  and cross-member  35  between connector rods  23 ,  24 . 
         [0042]    As scissor clamp  1  is placed down onto a load to be clamped, with gripper arms  9 ,  10  and  17 ,  19  opened, abutment device  41  moves downwards, causing locking pawl  51  to be released and retracted into housing  45 . 
         [0043]    As the boom and scissor clamp  1  are lifted, the abutment device  41  moves upwardly (see  FIG. 6 ) and actuates position pawl  52  so that the latter actuates locking pawl  51  to re-emerge from the housing portion  45 . In the process, abutment member  43  moves the positioning pawl  52  into the housing portion  45 . At that point, the load has been securely clamped and can be transported to its destination. 
         [0044]    To release the load, and as shown in  FIG. 7 , scissor clamp  1  and the load clamped therein are then placed down on some ground, causing abutment element  43  to move downwardly and to urge locking pawl  51  back into housing  45 . After abutment  43  has moved downwardly past locking pawl  51 , the latter pivots from the housing  54 . During the subsequent lift, abutment member  43  contacts locking pawl  51  from below and moves it slightly upwards, whereby the positioning pawl  52  re-emerges forwardly from housing portion  45 . The condition shown in  FIG. 4  has again been attained. In this condition, gripper arms  9 ,  10  and  12 ,  13  of scissor clamp  1  are open. If scissor clamp  1  is lifted again, the cycle starts anew. 
         [0045]    The core of the present invention resides in that, preferably and for the reasons initially detailed, the pivoting-in movement or the return speed of locking pawl  51  from the area of abutment member  43  is damped or slowed down or delayed by a rotation damper  60  ( FIG. 3 ) so that powerful upward and downward swinging boom and clamp movements; e.g., because of rapid travel of the lifting vehicle over uneven ground—cannot result in the clamping area of scissor clamp  1  dropping rapidly because locking pawl  51  inadvertently contacts abutment member  43 . In other words, if an upward swing of the boom reverses rapidly to a downward movement of locking pawl  51 , which is not loaded from below by member  43  of the abutment device  41  any longer, the rotation damper  60  returns the locking pawl  51  into housing portion in a damped or slowed down manner, preventing the grip range of scissor clamp  1  from being unlocked already and falling downwards as gravity starts to act again. Thus, the rotation damper  60  acts to damp or slow down the return movement of locking pawl  51  into housing portion  45 , and it does so in a manner ensuring in any event that, as gravity re-commences to act, locking pawl  51  has not yet left the area of the abutment member  43  and a reliable lock continues to act between cross-member  35  of connector rods  23 ,  24  and cross-member  36  of gripper arms  5 ,  6 . As the load is lifted thereafter, the abutment member  43  contacts locking pawl  51  from below. Locking pawl  51  moves slightly upwards, causing positioning pawl  52  to re-emerge forwardly from housing portion  45 . The condition shown in  FIG. 4  has again been attained now. 
         [0046]    In accordance with  FIG. 3 , rotation damper  60 , which is fastened to a side wall  61  of housing  45 , comprises an arm portion  62  mounted to pivot about an axis  63  of rotation damper  60 , such pivoting being slowed down or inhibited by rotation damper  60  as locking pawl  51  returns into housing portion  45 . Arm portion  62  has therein a slot  64  engaging an axle  65  connected to the locking pawl  51 . As a result, the locking pawl  51  can move into the housing portion  45  only against the damping force that the arm portion  62  of rotation damper  60  exerts, with the aforesaid movement being slowed down to the extent required. 
         [0047]    The rotation damper  60  preferably comprises a commercial damper acting to damp pivotings in one direction of rotation (return of the locking pawl into the housing) and allowing a comparably undamped or not slowed movement in the opposite direction (pivoting of the locking pawl outwards from the housing). 
         [0048]    Stated in general terms, it is possible also to use other devices such as brakes, gas pressure dampers or the like which are suited to prevent the locking pawl  51  from pivoting out of the area of abutment member  43  under the conditions described above. 
         [0049]      FIG. 8  shows an exemplary curbstone laying clamp  40  suited for use in connection with the present invention. Clamp  40  comprises two gripper elements  48 ,  44  adapted to be pivoted against each other about a pivot  42 , with one gripper element  44  adapted to be affixed to a boom of a lifting or transport vehicle (not shown in detail) by a chain link  43 . A control mechanism, not shown in detail, may be disposed between gripper elements  48 ,  44 . In  FIG. 8 , solid lines are used to show the curbstone laying clamp  40  in the closed position, while clamp  40  is shown in the open condition in phantom. 
         [0050]      FIG. 9  shows a finished-parts clamp  50  having gripper elements  51  and  52 . Clamp  50  may be affixed by means  54  to the boom of a lifting or transport vehicle. Gripper elements  51 ,  52  are adapted to be opened and closed in a manner known per se by the chain mechanism  53  shown. In this finished-parts clamp too, a control mechanism may be used for sensing the relative movement of gripper elements  51 ,  52  and for controlling the opening and closing movements thereof. 
         [0051]    Contemplated also is the use of the present invention in connection with the transport clamps  60  shown in  FIGS. 10   a,    10   b,  as disclosed in the above-mentioned German Patent No. DE 27 27 919, for example, having means to prevent, under the conditions explained above that, in the case of upward and downward swings of transport clamp  60  secured to attaching means  63 , the control stud  61  on the shift rod  62  leaves the area of control recess  64  on entrainment member  65 . In the process, the aforesaid means slows down the movement of control stud  61  from the area of control recess  64 . In  FIG. 10   b,  the gripper elements of transport clamp  60  and the control mechanism are referred to as  66 ,  67  and  68 , respectively. 
         [0052]    There has thus been shown and described a novel gripping assembly, especially a scissor-type clamp, having a control mechanism, which fulfills all the objects and advantages sought therefore. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.