Patent Publication Number: US-6209938-B1

Title: Lifting tool for safe 90 degree rotation

Description:
RELATED APPLICATIONS 
     The subject matter disclosed herein is related to the subject matter disclosed in copending application Ser. No. 09/473,880, filed on even date herewith, titled “Lifting Tool For Safe 105 Degree Rotation,” the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to lifting tools. More particularly, the present invention relates to a lifting tool for safe, 90 degree, off-center rotation of large, heavy objects. 
     BACKGROUND OF THE INVENTION 
     It is often necessary to lift large, heavy objects during a manufacturing process, such as, for example, during the process of painting steel enclosures (known as “tanks”) for pad mounted transformers. These large, usually rectangular tanks can be painted in an automatic paint facility using the following process, for example. 
     The tanks are placed one at a time onto a carrier rack that can hold up to four tanks. The carrier rack can be adapted to be carried via a conveyor system to a paint vat, into which the carrier rack is dipped along with the tanks. Preferably, the tanks are oriented on the carrier rack to allow good coverage as they pass through the painting operation. For example, the tanks can be oriented horizontally (i.e., with one of the four side faces facing downward) by placing them on horizontal arms of the carrier rack. 
     Typically, the tanks are delivered to the conveyor system on a towed cart. To minimize the size of the cart needed, the tanks are positioned on the cart vertically (i.e., with the top or bottom face facing downward). Thus, not only must each tank be lifted off of the cart and onto the carrier, but each tank must also be rotated by about 90 degrees at the same time. Similarly, the painted tanks must be taken from the carrier, rotated by about 90 degrees, and moved back onto the cart. 
     As a tank typically weighs more than 50 pounds (and frequently up to as much as 100 pounds or more), a tank is too heavy and too large for an ordinary person to move from the cart to the carrier, or vice versa, without the aid of a lifting tool. Thus, there is a need in the art for a lifting tool that can aid a person in lifting and moving large, heavy objects, while rotating the objects up to 90 degrees. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies these needs in the art by providing lifting tools for safe, 90 degree off-center rotation of large, heavy objects. The lifting tool uses the weight of the object itself to create an opposing rotational force nearly equal to the rotational force acting at the center of gravity. This stabilizes the object, and thus enables a person to rotate the object safely, as if the object were nearly balanced at the point of rotation. 
     A lifting tool of the invention includes a bar that can be positioned generally parallel to a centerline of the object, and first and second clamps that are coupled to first and second ends of the bar, respectively. The clamps can be rotatably coupled to the bar, or slidably coupled thereto. The clamps are adapted to secure the tool to edges of the object. 
     The tool also includes a pivot arm that is rotatably coupled to the bar, which allows the object to be lifted, rotated up to 90 degrees, moved, and then set down. The pivot arm includes a pair of idler pulleys disposed along a length thereof. A first end of the pivot arm can be coupled to a hoist hook, for example, via a cable that wraps partially around the pulleys and is coupled to the bar at a point between the clamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, it being understood, however, that the invention is not limited to the specific apparatus and methods disclosed. 
     FIGS. 1A and 1B depict a preferred embodiment of a lifting tool according to the present invention for safe, 90 degree off-center rotation. 
     FIG. 2 depicts another preferred embodiment of a lifting tool according to the present invention for safe, 90 degree off-center rotation. 
     FIG. 3 depicts a preferred embodiment of pivot bar according to the present invention. 
     FIG. 4 depicts a preferred embodiment of a cable attachment device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A lifting tool according to the present invention is a device that can be hung from a bridge crane hoist hook, for example, and used to safely lift and rotate a large object, such as a rectangular enclosure. The lifting tool uses the weight of the object to provide counter torque to help a person to safely rotate the object up to 90 degrees. In a preferred embodiment, the invention can be used to lift such an enclosure from a transport cart, and to rotate the enclosure up to 90 degrees so that it can be placed on horizontal arms of a process rack. Similarly, the invention can be used to unload an enclosure from the rack, rotate it up to 90 degrees, and place it back onto the cart. 
     The lifting tool requires no air or electric power assist to clamp the enclosure off-center from its center of gravity, and easily and safely rotate it up to 90 degrees. The tool also does not require the use of a counterweight to offset the weight of the object to be lifted and rotated. Such counterweights typically add undesirable additional weight to the system. A lifting tool of the present invention is a relatively small, lightweight tool that uses the weight of the object and a unique design of cables and pulleys to accomplish its intended purpose with a relatively small cost. Moreover, it provides an additional advantage in that it can operated safely by one person. 
     FIGS. 1A and 1B depict a preferred embodiment of a lifting tool  100  according to the present invention. Basically, lifting tool  100  includes a bar  102  positioned generally parallel to a centerline  90  of an object  10 . Tool  100  also includes a pair of clamps  104  to hold object  10  at top and bottom edges  10 A,  10 B thereof. Lifting tool  100  includes a pivot arm  106  that allows the object to be lifted, rotated up to 90 degrees, moved, and then set down. A first end of pivot arm  106  is coupled to a hoist hook (not shown) via a cable  112 , while a second end of pivot arm  106  is attached to bar  102  at point  110 . A first end of cable  112  is attached to bar  102  at point  118 . Cable  112  wraps part way around idler pulleys  114  and  116 . The other end of the cable  112  is attached to the bridge crane hoist hook. Although point  110  can be located anywhere along bar  102 , it is preferred that point  110  be somewhat off-centered to avoid interference between the tool and cable  112 , as well as with anything that may be overhead (such as the above-described conveyor). 
     Consider an exemplary object  10 , such as a rectangular transformer tank, that weighs 100 pounds and is 20 inches deep front to back. Initially, the tanks sits in a vertical position on a delivery cart, and an operator wishes to lift the tank, rotate it 90 degrees, and then set it in a horizontal position on a paint conveyor. An operator can then simply clamp the lifting tool to one side of the tank, and use the tool to lift the tank off of the cart. In contrast to a “squeezing” tool (i.e., a tool that lifts objects by squeezing them at their sides), the tool of the present invention can be clamped to the top and bottom of the backside of the tank so that a plurality of tanks can be spaced closely together on the cart and/or rack. 
     Once tank  10  is lifted off the cart, it would try to rotate naturally (i.e., due to gravity) from the vertical position to the horizontal position. The force on the object&#39;s center of gravity would create a moment of 10 inches times 100 pounds or 1000 inch-pounds (i.e., 83 foot-pounds). Likewise, it would require 83 foot-pounds to rotate the tank from horizontal to vertical. The average person cannot handle this safely. 
     Lifting tool  100  is designed to use the weight of the object itself to create an opposing rotational force nearly equal to the rotational force acting at the center of gravity. This stabilizes the object, and thus enables a person to rotate the object safely, as if the object were nearly balanced at the point of rotation. 
     As shown in FIG. 1A, object  10  has a center of gravity at point  120 . If the distance from pivot point  110  (i.e., the point at which pivot arm  106  attaches to bar  102 ) to center of gravity  120  is about equal to the distance from pivot point  110  to cable attachment point  118 , then object  10  will be approximately balanced as it moves from vertical to horizontal. This is because, at this point, the full weight of object  10  hangs on cable  112 . The tension on cable  112  curves around pulley  116  and creates a rotational force at cable attachment point  118  about pivot point  110 . The rotational force at point  118  is in the opposite direction, and approximately equal, to the rotational force of the object&#39;s weight acting at center of gravity  120 . As object  10  moves toward horizontal, the rotational force due to gravity is reduced as the distance from pivot point  110  to center of gravity  120  is reduced. This force is approximately balanced at cable attachment point  118  because the angle  122  formed by points  116 ,  118 , and  110  is reduced, thereby reducing the component force at attachment point  118  perpendicular to a line through pivot point  110 . 
     FIG. 2 depicts another preferred embodiment of a lifting tool  200  according to the present invention. In the embodiment shown, lifting tool  200  includes a bar  202 , such as, for example, a 36 inch long, ½-inch diameter, Sch. 80 pipe. Tool  200  also includes a pair of sliding clamps  204  to hold the object at its top and bottom edges, and a pair of collars  205  corresponding to each clamp that govern the extent to which each clamp can slide along bar  202 . Lifting tool  200  includes a pivot arm  206  that allows the object to be lifted, rotated up to 90 degrees, moved, and then set down. A first end of pivot arm  206  is coupled to a hoist hook (not shown) via a cable  212 , while a second end of pivot arm  206  is attached to bar  202  at point  210  via an attachment device  224 . FIG. 3 provides another perspective of a pivot arm  206  and attachment device  224 . 
     A first end of cable  212  is attached to bar  202  at point  218  via a cable attachment device  226  (which is shown in detail in FIG.  4 ). Cable  212  wraps part way around idler pulleys  214  and  216 . The other end of the cable  212  is attached to the bridge crane hoist hook. Preferably, cable attachment device  226  slides along bar  202  so that the balance can be optimized. Initially, cable attachment device  226  is positioned such that the distance from pivot point  210  to the object&#39;s center of gravity is about equal to the distance from pivot point  210  to cable attachment point  218 . The position of cable attachment device  226  is then adjusted until the balance is optimized. The ability to adjust the position of cable attachment device  226  allows the user to account for the effects of the weight of tool  200 . 
     Thus there have been described preferred embodiments of a lifting tool for safe, 90 degree, off-center rotation. Although the present invention has been described with reference to large, rectangular enclosures, such as tanks for pad mounted transformers, it should be understood that a lifting tool according to the present invention can be used generally to balance a load using gravity where it has to be supported at a distance from its center of gravity. Those skilled in the art will appreciate that numerous changes and modifications may be made to the preferred embodiment of the invention, and that such changes and modifications may be made without departing from the spirit of the invention. It is therefore intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the invention.