Patent Publication Number: US-2010117389-A1

Title: Lifting apparatus for lifting hollow frames such as manhole or catchment basin frames

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to lifting apparatus for lifting hollow frames, such as the frames used for manholes frames or catchment basin frames. However, the invention is applicable to many kinds of hollow frames which can be engaged by lifting members contacting an interior of the frame. 
     Manhole cover frames, and similar frames used for catchment basins, are usually large metal castings. While some of these can be lifted manually by two or more men, they are heavy and strains and injuries can result from manual lifting. 
     2. Prior Art 
     The prior art contains some suggestions for allowing these frames to be lifted by hoist means such as back-hoes or small cranes. One kind of device is shown in U.S. Pat. Nos. 5,306,062 and 5,476,300 to Dodge, issued respectively Apr. 26, 1994 and Dec. 19, 1995, in which a central, upwardly extending lifting bar connected to the hoist means has its lower end fixed to a horizontal plate. The plate carries laterally extending means for engaging the interior of the frame, these engagement means being in the form of four mutually perpendicular lifting lugs which can be slid outwardly to engage an undersurface of the frame when the device has been positioned within the frame. Use of this device would require some time-consuming manipulation of the lifting lugs. 
     Another patent relating to lifting manhole cover frames is U.S. Pat. No. 6,276,732, issued Aug. 21, 2001 to Haus. Here the device grips the outside of the frame, by frictional gripping pads attached to the lower ends of two scissor-like bars; accordingly this would not appear to provide secure holding of a heavy frame. 
     SUMMARY OF THE INVENTION 
     The present invention provides apparatus which holds a hollow frame securely by using engaging means which engage inner and underside surfaces of the frame, as in the Dodge patents, but the expansion of the engagement means in this case is automatic and does not require time-consuming manipulation. Rather than using a scissor-like mechanism as in Haus, the apparatus uses, in its preferred embodiment, lifting members which are connected by pivots so that inwards movement of upper ends of the lifting members causes outwards movement of members which engage the inside of a frame. 
     According to the broad aspect of the present invention, lifting apparatus for lifting a hollow frame when the apparatus is attached to hoist me ns comprises, a pair of lifting members, each having a normally upright arm and a normally lateral arm, said lateral arms of the lifting members extending outwardly from each other, outer ends of said lateral arms having engaging means for engaging the interior of a frame to be lifted, pivot means connecting said lifting members, said pivot means being connected to said upright arms at positions which are above the lateral arms and such that rotation of each of said lifting members in a first sense about said pivot means causes outwards movement of the lateral arm of that lifting member, flexible suspension means adapted to connect outer end portions of the upright arms of the lifting members to hoisting means positioned above said pivot means, said suspension means being arranged such that tension in said suspension means occurs along a line of force which causes rotation of said lifting members in said first sense, the arrangement being such that when said hoist means applies tension to lift the suspension means, tension in said suspension means rotates the lifting members in said first sense thus causing the lateral arms to extend into contact with the inside of a said hollow frame surrounding the apparatus. 
     Preferably, the suspension means includes flexible members which connect a central hoist means to upper ends of said upright arms, said flexible members diverging outwardly and downwardly from said central hoist means so as to pull the upper ends of the lifting members together when tension is applied thereto, thus rotating the lifting members in said first sense. The flexible members may be chains. 
     The lifting members may be in the form of oppositely facing, back-to-back bell cranks, with the pivot means connecting brackets which extend from the inner sides of the upright arms. 
     The engaging means on said lateral arms may each have an upright flange for contacting the inside of a frame, and a lower flange for contacting the underside of the frame. 
     Preferably, the lateral arms are in the form of hollow sockets, and each said engaging means has a shaft fitting into a said socket. The apparatus may include two interchangeable engaging means for each lifting member, each with a shaft for selective positioning in each lateral arm, and each engaging means carries said upright and lower flanges. The engaging means may be selectively suitable for rectangular or circular or square frames. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which; 
         FIG. 1  is a perspective view of the apparatus as adapted for lifting a rectangular frame, the apparatus shown resting on the ground; 
         FIG. 2  is a view similar to  FIG. 1 , but with the apparatus engaged within a rectangular frame, and with a lifting force being provided by hoist means not shown; 
         FIG. 3  is a side view of a lower portion of a lifting member with engagement means suitable for the rectangular frame; 
         FIG. 4  is a perspective view of a lower portion of a lifting member with engagement means suitable for a circular frame, and 
         FIG. 5  is a perspective view of the apparatus in partly disassembled form, showing the different engagement means for rectangular or circular or square frames. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIGS. 1 ,  2 ,  3  and  5 , the apparatus comprises two lifting members  10 , each with a normally upright arm  12 , shown as vertical in  FIG. 1 , and each with a lateral arm  14  projecting outwards at right angles to the arm  12 ; gussets  15  and welded joints connect the two arms of each member. The two lifting members have brackets  16  extending inwardly from the arms  12 , at about ¼ or ⅓ the height of the upright arms above the level of the lateral arms, and pivot means such as a bolt  18  connects inner ends of the brackets. Thus, the two members take the form of two back-to-back bell cranks, joined by brackets  16  and pivot  18 . 
     The lateral arms  14  are of square sectioned steel tubing with open outer ends. These provide sockets for the shafts  20  of frame engaging means  22  shown in  FIGS. 1 ,  2 ,  3  and  5 ; the shafts  20  can be locked in position by bolts  23  held by cotter pins or nuts  23   a  (seen in  FIG. 3 ), the shafts  20  preferably having multiple holes therein (as illustrated in  FIG. 5 ) which can be used to adjust the engaging means to the width of a frame to be lifted. The engaging means  22  are designed to engage the opposite sides of a rectangular or square frame F as shown in  FIG. 2 . Each of these engaging means, in the form shown in  FIGS. 1 ,  2 ,  3 , and  5 , has an upright flange  24  for engaging the inside of the frame F shown in  FIG. 2 , a horizontal lower flange  26  for engaging the underside of the frame, and an upper horizontal flange  28  for engaging the upper surface of the frame. 
     As seen in  FIGS. 1 and 2 , the arms  12  are also in the form of square tubes, and at their upper ends these arms are provided with cross bolts  30  which each hold the ends of two short chains  32  which provide suspension means by which the lifting members can be lifted by shackle  33  connected to a main chain  34 , which can be lifted by various powered hoist means such as a small crane or a backhoe. Since the short chains  32  slope inwardly from the bolts  30  to shackle  33  they can exert forces along lines of force which are outside the pivot means  18 , and when these chains  32  are tensioned by lifting forces on chain  34  they pull the upper ends of arms  12  inwardly, and so rotate the lifting members in a sense which causes those parts of the lifting members below pivot  18  to move outwardly. This rotation brings the flanges  24 ,  26  and  28  of engaging means  22  into firm contact with the sides of frame F. 
       FIGS. 4 and 5  show another form of engaging means  22 ′ having square shaft  20 ′ which can be selectively fitted into the socket in arm  14 , and which has a short upright flange  24 ′ and a short horizontal flange  26 ′, but has no upper flange. These engaging means  22 ′ are suitable for engaging opposite sides of a circular frame. They are also held in place by a bolt or set screw  23 . The shafts  20 ′ preferably have multiple holes therein (as illustrated in  FIG. 5 ) which can be used to adjust the engaging means to the width or diameter of a frame to be lifted. 
     It will be seen that operation of this apparatus is quite simple, and does not require the manipulation needed in use of the Dodge patents. With the hoist chains slack, the apparatus can rest on the ground, as in  FIG. 1 , within a frame to be lifted, with the upright arms  12  substantially vertical. When lifting tension is applied to the chains, the lifting members  10  are rotated to cause the lateral arms  14  to extend outwards bringing the engaging means  22  or  22 ′ into engagement with the frame, as shown in  FIG. 2 . Further tension on the chains lifts the frame. 
     The present invention has been described herein with regard to preferred embodiments. However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.