Abstract:
A lifting device for lifting manhole tops and manhole covers. The lifting device includes a scissor arrangement consisting of two crossed arms. Each arm includes a gripping assembly for grasping a manhole top and a set of hooks for lifting a manhole cover. One of the arms is offset to provide greater gripping ability for the lifting device and to provide a more compact lifting device. Chains are connected to ends of each arm to allow raising of the lifting device. Raising the lifting device by the chains causes the gripping assemblies to come together horizontally and grip the perimeter of the manhole top or, in the case of the manhole cover, the arms come together to set the hooks into slots on the manhole cover. The weight of the object lifted creates a horizontal gripping force to urge the gripping assemblies into lifting contact with the object.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    This invention relates in general to a lifting device and, more particularly, to a lifting device for use in lifting manhole tops and manhole covers.  
           [0005]    2. Description of Related Art  
           [0006]    In residential and commercial construction, the installation and repair of storm sewer lines and sanitary sewers lines is a common occurrence. The design of all types of sewer line mandates the placement of a manhole at every point where there is a change in direction of the sewer line. Thus, at the apex point of every angle made within a sewer line, a manhole can be found.  
           [0007]    Each of these manholes normally consists of a circular tower-like construction of concrete, bricks, and mortar topped off by a heavy metal manhole top. To allow access into the manhole tower and the sewer line below, the manhole top has a manhole cover. Because the manhole cover is usually located at ground or street level, the manhole cover is generally made from very heavy metal to prevent the displacement or breakage of the manhole cover which would otherwise allow an unsuspecting person walking upon the cover to fall into the manhole and sustain serious injury.  
           [0008]    Due to these design consideration, the manhole top and the manhole cover are very heavy. Additionally, the manhole top and the manhole cover are virtually always circular in shape. The combination of the heavy weight and the awkward shape of the manhole tops and manhole covers make it very difficult to move and place these items onto the manhole towers during installation and off of the manhole towers during repair.  
           [0009]    This is particularly true because the bottom of the manhole cover and the manhole top must be kept clear of lifting hooks and other such items during installation. Because the manhole top must lay flat upon the top of the manhole tower, any lifting hook which holds the manhole top from underside would interfere with the placement of the manhole top. Due to the circular shape and design of the manhole top, there are no other points where other types of lifting devices can be attached to the manhole top for lifting and moving the top.  
           [0010]    A similar situation arises with the manhole cover. Although most manhole covers have two slots located about 180 degrees part on the upper surface of the manhole cover, these slots are more readily used for insertion of a pry bar into the tops to disengage the manhole cover from the manhole top than for lifting and placing the manhole cover onto the manhole top. Because the perimeter of the manhole cover has very little clearance when installed within the circular opening of the manhole top, it can be very problematic to place the manhole cover into the manhole top without snagging the lifting device being used between the manhole cover and the manhole top.  
           [0011]    Previous attempts to create a lifting device to lift manhole covers have suffered from various disadvantages. In U.S. Pat. No. 6,276,732 issued to Hauss, a lifting device is disclosed which may be used to lift and place manhole covers. The lifting device disclosed is primarily for hand use wherein two person manually lift a scissor-like arrangement of lengthy arms. Plate members at the end of the two arms contact the upper ring of a manhole when the two people lift upward on the device. While this device may lift manholes tops, there is no provision to lift manhole covers. Additionally, the straight line arrangement of the arms makes the lifting device large and cumbersome as well as acting to reduce the amount of horizontal grip the plate members have on the manhole top. While there are eyehole members on the device for allowing a lifting cable to be used to connect the device to a manhole top for relocation, the relatively central location of these eyehole members acts to further reduce the leverage of the handles and this results in even lower horizontal forces at the plate members gripping the manhole top. Altogether, the oversize style of the device and the lower horizontal grip from the device act to reduce the capability of the device.  
           [0012]    U.S. Pat. No. 4,572,566 issued to Terrington also discloses a lifting device having scissor-like action. However, the overall design is almost identical to the Hauss device above. The arms of the scissors are straight and long. Additionally, the device is made for lifting slabs and would be unable to lift a manhole top or manhole cover. Even more importantly, the straight line scissor arms fail to provide the greatest horizontal grip available. While the device also has a central washer hole which would allow a cable to be attached to the device for lifting the device and an object, as in the Hauss device, the central location of the central washer hole acts to reduce the amount of horizontal gripping force at the gripping areas at the ends of the scissor arms.  
           [0013]    In U.S. Pat. No. 6,286,881 issued to Yakushinji, a load clamping and lifting device is disclosed. While the device generally incorporates a scissor action, this device has folded back the scissor arms in a manner which allows the top ends of the arms to meet at the center for connection to a lifting cable. While this device may be capable of lifting objects, a great deal of mechanical leverage is lost when there is a large vertical dimension between the gripping points and the lifting point.  
           [0014]    In addition to the lifting problems in each of the above devices, none of these devices is capable of lifting both manhole tops and manhole covers.  
           [0015]    Thus, despite the existence of these various types of lifting devices, there is no lifting device which provides a compact scissor-like design which gives a high level of horizontal force for gripping manhole tops and manhole covers.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention overcomes these and other problems by providing a lifting device having the ability to lift manhole tops and manhole covers, and which provides enhanced horizontal gripping abilities. Specifically, the present invention resides in a lifting device which incorporates a compact scissor mechanism having an offset scissor arm which reduces the overall size of the lifting device while at the same time enhancing the gripping ability of invention. Additionally, the present invention provides a single device which can be used to grip both manhole tops and manhole covers without the need for adding or removing auxiliary attachments.  
           [0017]    The present invention also resides in the various embodiments of the above invention. Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a front view of the lifting device in relation to a standard manhole cover and manhole top.  
         [0019]    [0019]FIG. 2 is a side view of the lifting device showing the operation of the lifting device when used to lift a manhole cover.  
         [0020]    [0020]FIG. 3 is a side view of the lifting device showing the operation of the lifting device when used to lift a manhole top.  
         [0021]    [0021]FIG. 4 is a side view of the gripping assemblies.  
         [0022]    [0022]FIG. 5 is a cross section of the gripping assemblies.  
         [0023]    [0023]FIG. 6 is a side view of the manhole cover hooks. 
     
    
       [0024]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Referring now to the drawings, FIG. 1 shows one embodiment of the present invention. A lifting device A is used to lift either a manhole cover  1  or a manhole top  2 , or a manhole top  2  in combination with the manhole cover  1  wherein the manhole cover  1  is placed within and upon the manhole top  2 . The lifting device A consists of a first scissor arm  3  and a second scissor arm  4  which are attached at a pivot point  6 . Two lifting chains  5  are attached to one end of the scissor arm  3  and the scissor arm  4 .  
         [0026]    The first scissor arm  3  includes a first arm segment  7 , a second arm segment  8 , two connector plates  9 , a return segment  10 , a gripper assembly  11 , and a manhole cover hook  21 . The first arm segment  7  has a distal end  12  and a proximal end  13 . The second arm segment  8  has a distal end  14  and a proximal end  15 . In the embodiment shown in FIG. 1, the first arm segment  7  and the second arm segment  8  are made from a high strength square metal tubing. In other embodiments, any other structural material may be used so long as the material is strong enough to support the loads the lifting device is anticipated to carry.  
         [0027]    The first arm segment  7  and the second arm segment  8  are connected together by the two connector plates  9  such that there is a gap  16  between the proximal end  13  of the first arm segment  7  and the distal end  14  of the second arm segment  8 . In the embodiment shown, the connector plates  9  are substantially diamond-shaped.  
         [0028]    The two connector plates  9  hold the first segment  7  and the second segment  8  in alignment and are attached to the first and second segments by welding the two connector plates to the segments. While in the preferred embodiment the two connector plates  9  are welded to the first segment  7  and the second segment  8 , other means may be used, such as fasteners or other similar devices, provided the means selected must be capable of firmly attaching the two connector plates  9  to the segments  7  and  8  and be able to withstand the forces exerted on the scissor arm  3  without deformation of any scissor arm components or other structural failure. Each connector plate  9  has a round opening  16  and the round opening of one connector plate  9  is in axial alignment with the round opening of the other connector plate  9  after the two connector plates have been connected to the first arm segment  7  and the second arm segment  8 .  
         [0029]    The return segment  10  is substantially perpendicular to the second arm segment  8 . In the embodiment shown, the return segment  10  is a separate piece of square tubing which has been mitered and welded to the proximal end  15  of the second arm segment  8 . In other embodiments, the return segment can be formed as an integral portion of the second arm segment  8  by bending one end portion of the segment  8  until the end portion is perpendicular to the main body of the second arm segment  8 .  
         [0030]    A chain connector plate  17  is attached to the distal end  12  of the first arm segment  7 . The chain connector plate  17  is shaped to match the generally square form of the distal end  12  of the first arm segment  7 . The chain connector plate  17  also has a bent end  18  which has a mounting hole  19 . The end of one chain  5  is connected to the chain connector plate  17  by installing a fastener  20  through the mounting hole  19  and through the opening in the end link of the chain  5 . In the preferred embodiment, the fastener  20  includes a high strength bolt, a high strength nut, a washer directly under the head of the high strength bolt, and another washer between the high strength nut and the chain  5 .  
         [0031]    It will be appreciated that there a number of ways in which the chains  5  can be attached to the first scissor arm  3  or second scissor arm  4 . For example, in lieu of a chain connector plate  17 , the chains could be directly connected to the end of the scissor arm  3  or  4  with fasteners such as eye bolts, chain repair links, or other general fasteners. Any type of chain connection method may be used as long as the scissor arms  3  and  4  are allowed to produce the scissor action described herein and the fastening method used is strong enough to sustain the forces placed on the chain connection point during use of the lifting device A.  
         [0032]    The second scissor arm  4  has a first arm segment  25 , an offset arm segment  26 , a second arm segment  27 , a return segment  28 , a gripper assembly  11 , and a manhole cover hook  21 . Similar to the first scissor arm  3 , the scissor arm  4  is constructed of a metal tube. In other embodiments, other materials such as solid round bars and solid square bars may also be used.  
         [0033]    The shape of the second scissor arm  4  is different than the first scissor arm  3 . Rather than having all of the arms segments be aligned, the arm segments of the second scissor arm  4  are offset near the longitudinal center of the scissor arm  4  where the first scissor arm  3  pivots with the second scissor arm  4 . More specifically, the offset segment  26  is mitered at each of its ends at an angle that allows the offset segment  26  to be connected with matching miters on the ends of the first arm segment  27  and the second arm segment  25 . The miter angles are such that when the first arm segment  25 , the offset segment  26 , and the second arm segment  27  are assembled, the fist arm segment  25  and the second arm segment  27  are generally parallel.  
         [0034]    As with the return segment  10  of the first scissor arm  3 , the return segment  28  of the second scissor arm  4  is substantially perpendicular to the second arm segment  27 . In the embodiment shown, the return segment  28  is a separate piece of square tubing which has been mitered and welded to the one end of the second arm segment  27 . In other embodiments, the return segment can be formed as an integral portion of the second arm segment  27  which has been bent until the end portion is perpendicular to the main body of the second arm segment  27 .  
         [0035]    A ring  22  connects together the other ends of the two chains  5  to from a lifting point where a hook  23  can be used to grab the ring  22  for raising the lifting device A. The hook  23  is normally connected to a lifting chain  24 . It will be appreciated that the same fastener  20  which is used to connect one end of each chain to the chain connector plate  17  at the end of the first arm segment  7  and the arm segment  25  is also used to connect the two chains  5  to the ring  22 .  
         [0036]    Referring now to FIG. 4, a gripper assembly  11  is attached to one end of each of the scissor arms  3  and  4 . The gripper assembly  11  includes two hinge plates  29  attached to plate  30 , the two hinge plates  29  being spaced apart to allow the return segment  28  of the scissor arm  3  or  4  to slide between the two hinge plates  29 . The two hinge plates  29  are located symmetrically on the back surface of the plate  30 . The plate  30  is curved to match the radius of the outside perimeter found on a standard manhole top.  
         [0037]    Each hinge plate  29  (FIG. 5) has a round opening  31  which is located on the horizontal centerline of the hinge plates  29  and which is located to be on the longitudinal centerline of the return segment  28 . The return segment  28  has two second round opening  32  which are sized to match the two round openings  31  and are located to allow for the axial alignment of both round openings  31  with both round openings  32 . In the embodiment shown, a gripping pad  38  made from a resilient material such as rubber is attached to the surface of the plate  30  with a plurality of rivets, although any method of attaching the gripping pad  38  to the plate  30  is suitable as long as the gripping pad is not displaced during use of the lifting device and the method of attachment is generally water resistant. It will be appreciated that other types of gripping pads such as smooth pads, pads with a rough surface, pads with horizontal grooves, pads with numerous pointed shapes, or any other similar pad that is made from any type of material, can be used as long as the design of the gripping pad and the material used provides sufficient friction coefficient between the manhole top  2  and the gripping pads  38  to allow the manhole top  2  to be lifted by the lifting device A without slippage of the manhole  2  top from the gripping pads  38 .  
         [0038]    The two hinge plates  29  are connected to the return segment  28  by axially aligning the round openings  31  and  32 , and then installing a bolt  33 , two washers  34 , and a nut  35 . During installation of the bolt  33 , the hinge tubing  36  is aligned with the openings  31  and  32  and the bolt  33  is inserted through the hinge tubing  36 . Upon proper installation of these components, the hinge tubing  36  will be able to rotate around the outer surface of the bolt  33  with the bolt  33  acting as a hinge pin.  
         [0039]    The manhole cover hook  21  (FIG. 6) comprises a hook  37  which is connected to the outer surface of the hinge tube  36 . After the manhole cover hook is installed within the return segment  28  (FIG. 5) with the bolt  33 , the manhole cover hook can be rotated to allow the manhole cover hook  21  to engage with the lifting slots  39  (FIG. 1) normally found on the manhole cover  1 .  
         [0040]    While the above description describes the gripper assembly  11  and manhole cover hook  21  on the second scissor arm  4 , the gripper assembly  11  and the manhole cover hook  21  of the first scissor arm  3  is the same.  
         [0041]    Returning now to FIG. 1, the lifting device A is used to move manhole tops  2  by attaching the lifting device A to a lifting line  24  by attaching the hook  23  onto the chain bridge  22 . The lifting device A is raised by the lifting line  24  and moved until the lifting device is positioned over the manhole top  2  to be relocated. The lifting device A (FIG. 3) is lowered over the manhole top  2  until the lifting device A rests upon the manhole top  2  with the gripping assemblies  11  positioned adjacent to the vertical sides of the outside perimeter of the manhole top  2 . The two gripping assemblies  11  are swiveled on the return segments  28  and  10  until the surface of the gripping pads  38  is generally parallel with the vertical surface of the outside perimeter of the manhole top  2 .  
         [0042]    To lift the manhole top  2 , the lifting line  24  (FIG. 1) raises the lifting device A. As the lifting device A is raised, the first scissor arm  3  and the second scissor arm  4  pivot at the pivot point  16 . As the scissor arms  3  and  4  pivot, the two gripper assemblies  11  move horizontally and in an opposing direction until the gripping pads  38  come into contact with the vertical surface of the outside perimeter of the manhole cover  2 . By continuing to raise the lifting device A with the lifting line  24 , pressure is increasingly applied to the pads  38  of the gripper assemblies  11  thus allowing the gripping pads  38  to grip the manhole top  2 . It should be noted that the gripping force on the gripping pads  38  will be proportionate to the weight of the manhole top  2  being lifted. Additionally, the offset design of the second scissor arm  4  acts to enhance the amount of gripping force to make the lifting device A more efficient than other lifting device designs.  
         [0043]    At some point, the raising action of the lifting line  24  will overcome the weight of the manhole top  2  and the gripping force of the gripping assemblies will grip the manhole top  2  to allow the manhole top  2  to be lifted from its resting position. The lifting line  24  is subsequently moved to another position where the lifting line  24  is then lowered to allow the lifting device A and the manhole top  2  to be lowered to its new position As the manhole top  2  comes to rest in its new position, the scissor action of the scissor arms  3  and  4  allows the scissor arms to pivot around pivot point  16 , thereby reducing the amount of horizontal gripping force transferred to the gripping pads  38 . As the lifting line  24  continues to be lowered, the gripping force on the gripping pads  38  will continue to be reduced until the gripping pads  38  and gripping assemblies  11  can no longer hold the manhole top  2 . When this point is reached, the lifting device A will release the manhole top  2  and the relocation of the manhole top  2  is completed.  
         [0044]    The process of lifting the manhole cover  1  is similar to the lifting of the manhole top  2  as just described. The lifting device A is moved into position over the manhole cover  1  and then lowered to a point just above the manhole cover. Then, rather than using the gripping assemblies  11  to lift and move the manhole cover  1 , the manhole cover hooks  21  are used. Thus, the lifting device A is not lowered completely onto the manhole cover  1 , but is instead positioned over the manhole cover  1  until the hooks  37  of the manhole cover hooks  21  are located near the lifting slots  39  in the manhole covers  1 . The ends of the hooks  37  are inserted fully into the lifting slots  39  to engage the hooks  37  into the lifting slots  39 . Because the manhole cover hooks  21  can be rotated, the lifting hooks  37  are rotated to engage or disengage the hooks  37  with the lifting slots  39  (FIG. 1). The lifting line  24  is then raised to lift the lifting device A with the manhole cover  1  connected to the hooks  37 . It is noted that the scissor action of the two scissor arms  3  and  4  enhances the lifting capability of the lifting device A by exerting opposing horizontal pressure on the hooks  37  which tends to encourage the engagement of the hooks  37  with the lifting slots  39 .  
         [0045]    Using the lifting line  24 , the lifting device A and the manhole cover  1  are moved to a new location where the lifting line  24  lowers the lifting device A and the manhole cover  1  into a new position, usually onto the top of a manhole top  2 . As the lifting line  24  is further lowered, the pressure on the lifting hooks is reduced to a point where the hooks  37  can be disengaged from the lifting slots  39  of the manhole cover  1 .  
         [0046]    While the above description describes various embodiments of the present invention, it will be clear that the present invention may be otherwise easily adapted to fit any configuration where a lifting device may be utilized.  
         [0047]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.