Abstract:
A lift frame adapted to be pivotally mounted on a hoist include a tubular sleeve guide that guides a lift slide. The lift slide carries a lift frame for supporting a load such as a beam or truss to be lifted, and is spring loaded in an upward direction by a spring extending between a slider tube and the lift frame. The spring keeps the bracket seated on the load for a limited distance along the lift path. The lift slide has a stop that limits the amount of downward movement of the lift slide relative to the guide as the load is lifted. Specifically, a pair of frames are mounted at opposite ends of a spreader bar for lifting an elongated beam. A bracket on each lift slide engages one end of the beam and supports it under spring load for a selected amount of vertical travel, and thereafter the beam or load is directly lifted mechanically by having the stop on the lift slide engaging the sleeve guide.

Description:
This application is based upon and claims priority from U.S. Provisional Application Ser. No. 60/437,840, filed Jan. 3, 2003, the contents of which is incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a lifting frame assembly used with a hoist or crane for holding elongated beams, trusses and the like, which has a pair of spaced apart lifting frames mounted onto a spreader bar. The lifting frames have lift slides that support the beam and provide a spring load on the beam to be lifted for a selected amount of vertical travel of the spreader bar. The load lift slides also remain engaged with the beam being lifted under the spring load for a selected amount of lowering movement of the lift frame assemblies after the beam is supported on an object. 
     A problem arises in the construction industry when placing long trusses or beams (called beams for convenience in this specification), into position, in particular, in that the rigging is generally controlled by a crane operator in a cab some distance away from the actual placement. It is possible for a lifted load to unexpectedly hang-up on the surrounding structure before it is secured in its final position. This condition is difficult for the hoist operator to sense. If the crane continues to lower the frame, the lifting hardware will likely prematurely dis-engage from the load. If the now unsecured load dislodges from the surrounding structure, the load falls out of control. This can result in damage to the structure being built, and hazards to workers. 
     In the prior art there have been springloaded lifts of various designs, but generally the holders and rigging are fairly complex and do not provide for a direct, limited amount of spring load needed for ensuring proper operation. 
     SUMMARY OF THE INVENTION 
     The present invention relates a lifting or hoisting frame that is attached to a hoist for raising a load. As shown, the frame is lifted by a crane or similar hoist, and which as shown in one form, a spreader bar has lift frames pivotally mounted at opposite ends. The lift frames are formed as multiple parts, including a yoke that attaches to the spreader bar or hoist about a generally horizontal pivot. 
     The lift frame carried by a yoke includes an outer guide, formed as a tube or pipe in which an internal lift slide, as shown a sliding lift pipe is mounted. The lift slide has a beam holder or load support at a lower end and is mounted in a guide for limited vertical movement. The lift slide or sliding pipe is supported on a spring relative to the lift frame and guide for limited sliding from a retracted position to a stopped, extended position. When the lift slide is under load sufficient to overcome the spring force, it can slide from its retracted position relative to the yoke and lift frame guide downwardly a limited amount. The downward movement of the lift slide is limited by a stop acting between the lift slide and the guide. 
     The lower end of the lift supports a load holder, as shown a beam holder support frame that has a support base configured to mate with the shape of the beam or load to be lifted so the load center is along the central axis of the guide for the lift slide. 
     The beam holder frames are “C” shaped, that is, they have a horizontal top leg and a lower or base leg and a side bar joining the top and base legs. The side bar spaces the legs sufficiently so they can be moved over the top and bottom of the beam or load to be lifted and then when the frame is raised, the bottom leg engages the beam. The lifting force from the center axis of the spring and lift slide guide on the lift frame is along the center plane of the beams being lifted. 
     The spring supports for the lift slides will maintain a load on the beam holder frame against the lift surfaces of the load or beam as the lift slide moves from the time the load or beam holder frame is in a retracted position and first engages a beam, to the extended stopped position as the lift slide is loaded. As the spreader bar or other hoist is lifted by a crane, the spring load against the beam to be lifted increases until the lift slide or pipe reaches the stop, at which time the lift slide will no longer extend. The hoisting continues under a mechanical connection between the lift slide and the slide guide. 
     After the beam or load is carried to its intended location, and the spreader bar is lowered, and the holder frame that is supporting the beam will maintain contact in its supporting position on the beam after the beam is supported on an object until the lift slide moves under spring load to its retracted position as the spreader bar is lowered. The amount of lowering of the hoist or spreader bar after the beam is supported and before the holder frame no longer exerts a load against the beam so it can be released (which is after the slide reaches its retracted position) is sufficient so that an operator of a hoist or crane will notice if the beam has hung up prematurely and so the holder frame is retracting before the beam or load is properly seated. The spring-loaded lifting system serves to prevent release of the beam before it is properly seated because the hoist operator or a flagman can easily see the spring and lift slide retracting, which indicates to them that the load is supported by something other than the hoist line. There is ample warning to stop lowering, and then raise the hoist line until the load is once again supported totally by the hoist line. 
     This visual clue provided by the lift slide that the beam or load is no longer lowering, but that the spreader bar or hoist is lowering, insures that the beam or load can be safely dislodged from any snag or unwanted support. 
     When the beam or load being lifted is in its correct position, the spreader bar is lowered and the lift slides and beam holder frames will retract to their retracted position under spring load. Further downward movement of the spreader bar permits the beam holder frame to disengage from the beam so the beam holder frames can be removed. 
     The spring-loaded lifting system insures positive engagement of the lifted load until the deliberate release by the hoist operator. It also allows the hoist operator to automatically release the load at the desired time without the need for other personnel to gain access onto the lifted load to disconnect the lifting hardware. This greatly increases the safety and productivity of the erection process and lessens the likelihood of a load slipping from a snag if it is hung up. 
     The term “beam” as used herein is to be broadly interpreted and covers various beams, trusses, frames and other support structures that are hoisted into position for use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side elevational view of a typical rigging utilizing lift frames made according to the present invention; 
         FIG. 2  is an end elevational view of  FIG. 1 ; 
         FIG. 3  is an enlarged front elevational view of a left hand end beam holder frame and supported lift slide, slide guide and yoke for connecting the frame to a spreader bar and rigging, with the lift slide in a retracted position; 
         FIG. 4  is a side elevational view of the holder frame and yoke of  FIG. 3 ; 
         FIG. 5  is a side view of the lifting frame showing the beam holder frame retracted and positioned about to engage a beam; 
         FIG. 6  is a side elevational view of the beam holder frame of  FIG. 5  shown in the position engaging the beam and with the lift slide partially extended under spring load; 
         FIG. 7  is a side elevational view of the beam holder frame in its extended position such that the load is totally supported on a stop on the lift slide engaging the top of the slide guide; 
         FIG. 8  is an enlarged view showing a lift slide supporting the beam on the lift slide guide with the lift slide guide in cross section; 
         FIG. 9  is a sectional view taken as on line  9 — 9  in  FIG. 8 ; 
         FIG. 10  is a side view showing the beam holder frame supporting a different size beam; 
         FIG. 11  is a sectional view taken on line  11 — 11  in  FIG. 10 . 
         FIG. 12  is a side view of the beam holder frame showing the beam holder frame converted with adapters to hold a truss; 
         FIG. 13  is a sectional view taken on line  13 — 13  in  FIG. 12 ; 
         FIG. 14  is a side view of the beam holder frame of  FIG. 12  with adapters in place to hold a truss; and 
         FIG. 15  is a sectional view taken on line  15 — 15  in  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a lift rigging indicated generally at  10  comprises a pair of lift frame assemblies  12 , which are pivotally mounted at opposite ends of a spreader bar  16 , and which are used for lifting a beam  14 . The spreader bar  16  is conventional, and the frame assemblies  12  are pivotally mounted about transverse pivots indicated at  22  to the opposite ends of the spreader bar. The spreader bar  16  is supported through suitable rigging such as cables  18  and connecting links  19 . The links  19  are pivotally mounted on pivot  22  at the opposite ends of the spreader bar to form a sling that is in turn supported from a block  21  that is controlled for raising and lowering from a crane or hoist  20 . The crane or hoist  20  has a controllable cable  23 , which can be payed out or retracted with a drum on a hoist or winch  24 . 
     Alternatively, the crane  20  can comprise a boom that would raise and lower directly for placing the spreader bar  16  in the desired location to properly position the beam or truss  14  on its desired supports on the building or other construction being assembled. 
     The support rigging can be conventional, and spreader bars are also conventional. The present invention relates to improvements in the pivoting end lift frame assemblies  12 , which are used for supporting beam or load holders for holding the beam or load to be lifted in position. 
     As shown in more detail in  FIGS. 2–12 , the frame assemblies  12 ,  12  at opposite ends of the spreader bar  16  are mirror images of each other. The lift frame on the left hand side of  FIG. 1  is illustrated in  FIGS. 3 and 4 .  FIGS. 2 ,  5 – 7  and  10 – 12  show the lift frame assembly  12  on the right hand end of  FIG. 1 . Each of lift frame assemblies  12  comprises a yoke or frame assembly  30  made up of a pair of spaced apart straps  32 ,  32  which straddle the spreader bar  16 , as shown in  FIGS. 3 and 4 , and are held in position with the pivot  22 . The pivot  22  permits pivoting of each yoke  30  about a horizontal axis. The yokes and supported components thus will hang vertically under gravity. 
     The spreader bar  16  has a series of cross holes  34  so that the yoke  30  can be moved to different positions, if different lengths of beams are being lifted. The straps  32 ,  32  are held together with cross members  36  adjacent the upper end of the yoke. The cross members  36  are spaced apart by the width of straps  32 , to leave a space between them, and a pin  38  is supported on the cross members. 
     The lower portion of the yoke or frame assembly  30  supports an outer slide guide tube or sleeve  40  that is supported relative to the straps  32 ,  32  with suitable braces  42 , to center the lift slide guide tube or sleeve  40  in position. As can be seen, the guide  40  extends only partially along the length of the yoke. 
     A beam or load holder frame  44  is made in C-shape with a lower or base beam support leg  46 , a side bar or upright leg  48 , and a top leg  50 . The base leg  46  has an edge shape to mate with a beam  14  being lifted to hold it in place. Adapters on the beam support leg can be used for different beams or trusses. 
     The upper leg  50  is suitably attached, for example with bolts  52 , to an elongated lift slide  54 , as shown a tube or pipe, that is slidably mounted within the lift slide guide  40 , and extends parallel to and between the plates  32 ,  32 . 
     The lift slide  54  is urged upwardly by a spring or biasing member  56  that is on the inside of the tubular lift slide pipe  54 . Spring  56  has one end hooked to the bolt  38 , supported on the cross plates  36  near the upper end of the yoke  30 . The other end of spring  56  is hooked on a cross bolt  52  that is supported at the lower end of the lift slide  54 . The spring  56  is used for providing a spring load for supporting the beam or load holder frame  44 . The biasing member can be an elastomeric member or any type of spring, including a compression spring, if desired. 
     The lift slide  54  has a bearing head or stop ring  58  near its upper end, that is of size to stop against an upper surface  60  of the lift slide guide sleeve  40 , so that the amount of extension of the spring  56  is limited to the travel of the lift slide between the retracted position shown in  FIG. 3  and the extended position shown in  FIGS. 2 and 7 , where the spring  56  is extended and the bearing head or stop ring  58  is engaging the top end of sleeve  40 . If a compression spring is used, it can be compressed fully to form a stop in the extended position. 
     The lower beam support leg  46  of the beam holder frame  44  is formed to center the beam being held, so that the weight center (center of gravity) of the beam is on the axis of the lift slide  54 . There is a direct load on the axis of the lift guide sleeve  40  and lift slide  54 , so that there will not be any binding or cocking of the lift slide relative to the lift slide guide  40  due to the weight of the beam. 
     The spring  56 , as shown, is a tension spring that is easily mounted on its opposite ends and will extend a sufficient amount for permitting the desired travel of the beam holder frame  44  relative to the yoke assembly  30  to accomplish the purposes of retaining the beam in the frame for a selected distance of travel downwardly of the cross bar after the beam is supported in place, whether it is supported in its desired location, or is hanging up on some obstruction. Other types of springs can be used, such as compression springs, electronic members or the like. The spring is a biasing member that provides a resilient force. 
       FIGS. 5 ,  6  and  7  show the beam holder frame  44  in different positions during use, relative to the beam illustrated at  14 .  FIG. 5  shows the beam holder frame and lift slide in a full retracted position held by the spring  56 , and with the beam holder frame moved to underlie the beam supported at its location from which it is to be lifted. The lower or base member  46  is made to slip under the beam, and it can be seen at an upright stop  46 A can be used for preventing the beam from sliding off the outer end of the lower or base member  46 . 
     It also can be seen that the upright leg  48 , which is made of two spaced plates  48 A and  48 B, as shown in  FIG. 11 , has a pivotally mounted adapter indicated at  91 , that is retracted out of the way in  FIGS. 5 ,  6  and  7 , also, the lower or base member  46  has another adapter or member  93  that can be pivotally mounted to provide for different supporting configurations for a beam. The beam  14 , as shown, is an I beam, and its lower flange is substantially planar. The lower flange rests against the upper edges  46 B of the lower support member  46 . 
       FIG. 6  shows the beam  14  on the base member  46  with the lift slide supported by the spring  56 . The spring  56  is partially extended so that the beam or load holder frame  44  is moved away from its fully retracted position, but the beam is preferably not yet lifted from its support. Part of the lift slide  54  extends out below the guide sleeve  40 . 
       FIG. 7  shows the beam or load holder frame  44  with the lift slide in its fully extended, stopped and working position, with the bearing head or stop ring  58  resting against the upper edge  60  of the slide guide  40 , as can be seen in greater detail in  FIG. 8 . 
     In this position, the beam or load  14  will be held mechanically, or without any spring loads supporting it, so that it will be stable for movement to its working position. 
     The position of the slide and spring shown in  FIG. 6 , can occur if the beam  14  is held up on some supporting structure as the beam is being lowered, and the lift slide  54  starts to retract. The difference in extension of the lift slide  54  from guide  40  can be noticed by a flagman, or by the crane operator, particularly if the lift slide is colored a fluorescent paint color, or has other distinctive indicia on its surface. If the beam  14  is not in its desired, final location, the crane operator will be alerted and know that the beam is hung up, and can stop the lowering operation and lift the beam from this position. The obstruction can be cleared, and the beam is again lowered. 
       FIGS. 12 and 13  show a different type of beam  80  on the beam holder, that is a different size, and which beam will rest upon the lower leg or lower member  46  forming the beam lift member. The beam  80  will be held between a pivotally mounted adapter strap  92  moved to a working position, with adapter strap  93  left in its retracted position, and an adapter  90  pivotally supported on leg  48  and moved to its working position. The beam or load  80  is held centered between the upright side leg  48  and the stop member  46 A at the outer end of lower leg  46 . The two adapters form a slot  96  with inwardly tapered side walls to center the beam  80  as the beam rests on member or leg  46 . 
       FIGS. 14 and 15  show a truss beam  84  that is generally T-shaped and has a depending web  86 . In this position, the adapter strap  91  has been pivoted about is pivot  94 , to rest on the beam support member  46 . The adapter strap  93  pivots upwardly and can rest against the outer flange  46 A and be held in position. The strap adapters  91  and  93  have end surfaces forming an upwardly open, tapered side wall slot  96 , so that the web  86  can slide into a seated position with the web  86  then centered on the axis of the lift slide  54  and guide  40 . 
     The lower beam support leg  46  and the upper leg  50  are spaced vertically sufficiently to insure the beams  14 ,  80  or  84  will fit easily in the recess formed between legs  46  and  50 . 
     If one end of the beam being lifted is hanging up on an obstruction, the travel and force of the spring  56  and the slide  54  insures that the beam will not be released from the beam support leg  46  until the spreader bar  16  has lowered a significant amount (see  FIG. 6 ). If the beam is hanging up, and then slips or becomes loosened, the beam support leg  44  will not have disengaged from the beam, and the beam support leg  44  will remain engaged until the lift slide  54  extends so that the stop collar or bearing head  58  engages the end  60  of the lift slide guide sleeve  40 . If the beam continues to be hung up on something, the extension of lift slide  54  above guide  40 , or the reduction of extension of lift slide  54  below the guide will be noticed by the crane operator or flagman and lowering of the beam will be stopped. 
     The lift slide  54  can be colored with fluorescent, bright paint, so that as it would extend out of the guide sleeve  40 , particularly when it is hung up on an obstruction, the visual information would be enhanced. 
     The loading on the beam holder frames is in line with the center of the spring, and the center of the sliding parts, so that there is no substantial likelihood of binding or excessive wear. The slide guides and lift slide tubes can be lubricated if desired, or coated with low friction material. The holder frame assembly is relatively low cost, yet reliable. 
     The length of the spreader bar  16  can be adjusted as desired, and the amount of extension of the lift slide  54  and spring can also be controlled. Vertical sliding movement in the range of 2 feet can be accommodated. 
     It is apparent that the frame assembly  30 , including the guide tube  40 , lift slide  54  and beam or load holder frame  44  can be used as a simple lift frame assembly, and directly supported on a hoist, through a suitable cable, chain or other connection. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.