Abstract:
A lifting arrangement for overhead traveling cranes. The lifting arrangement includes two single reeved drums that are reeved together to provide true vertical lift of a load. The lifting arrangement allows for equalization of full up and full down rope fleet angles through utilization of axially staggered dual drums and/or a bottom block with two separate sheave nests. The lifting arrangement may utilize commercially available components to reduce the overall cost of the crane when compared with other powerhouse crane designs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to overhead traveling cranes, and more particularly, to a lifting arrangement for overhead traveling cranes.  
           [0002]    Powerhouse or class “A” overhead traveling cranes are generally utilized for maintenance of power producing equipment, such as generators and turbines. The number of lifts a powerhouse crane performs over its life span is very small, however, the capacity and lift height of the lifts that are performed are extreme. Because the duty cycle of the crane is very low, the lift speeds tend to be slow, especially when the load is heavy. The work done by the crane requires very good control and spotting ability to ensure proper procedure. True vertical lift is also required for ease of assembly of very large machine parts and assemblies.  
           [0003]    A powerhouse crane typically includes a long, large diameter drum that is selectively rotated by a motor. The drum is coupled to the motor by a large, high ratio gearbox. A rope wound around the drum winds on to and off of the drum in response to rotation of the drum in opposite directions. Typically, the rope is wire rope and the drum has a double helical groove in which the rope is double reeved as the rope winds on to the drum. A bottom block is supported by the rope such that the bottom block moves up and down as the rope winds on to and off of the drum.  
         SUMMARY OF THE INVENTION  
         [0004]    Powerhouse cranes generally include a large amount of rope because of the extreme lift heights and the use of a double reeved rope configuration to provide true vertical lifting. The drum needs to be sized to store this rope. Generally, the length and/or the diameter of the drum can be increased to add rope storing capacity. Both solutions result in separate problems. As the length of the drum is increased, the length of the trolley frame that supports the drum must also be increased. A longer trolley frame experiences greater bending moments, and therefore, the load members of the trolley frame must be increased in size to compensate. As the diameter of the drum is increased, so does the amount of torque which is required to turn the drum. Typically, a larger gearbox is necessary to provide more torque.  
           [0005]    The costs associated with providing enlarged drums, gearboxes and trolley frames add significantly to the overall price of the crane. The components often need to be custom designed for each application, thereby resulting in the manufacturing of only a single crane at a time. Use of mass produced components could significantly reduce the overall cost of these cranes.  
           [0006]    Accordingly, the invention provides a crane that can utilize mass produced drums, trolley frames and gearboxes. The invention includes the use of two lift trains. Each lift train includes a drum that is single reeved together with the drum of the other lift train. In some embodiments, both lift trains include similarly sized drums, gearboxes and motors where. The components of each lift train are generally smaller than those typically used on powerhouse cranes. Because the costs associated with the components increase exponentially with the size and torque requirements, the cost of two smaller lift trains is less expensive than the cost of a single custom built lift train.  
           [0007]    For lifts of a similar height, a lifting arrangement that includes a single reeved drum generally requires half as much rope as a lifting arrangement that includes a double reeved drum. Although the invention utilizes a lifting arrangement that includes a single reeved drum, the overall amount of rope utilized is similar to that of a lifting arrangement that includes a double reeved drum because the invention utilizes two drums that are singly reeved together. However, the use of two drums reduces the amount of rope stored on each drum by half. Accordingly, the length and/or diameter of each drum can be dramatically reduced when compared to the drums typically utilized on powerhouse cranes. When the length of the drum is reduced, the length of the trolley frame is reduced resulting in the ability to use a mass produced trolley frame, such as the trolley frame disclosed in U.S. Pat. No. 5,992,730, which is assigned to the assignee of this application. When the diameter of the drum is reduced, the torque requirements are reduced resulting in the ability to use a smaller mass produced gearbox. A ring gear external to the gearbox may be utilized to increase the torque of a smaller gearbox such that very high ratios (e.g., ratio of 600 to 1) can be achieved with a standard three stage helical gearbox.  
           [0008]    Although the cost of components utilized on a powerhouse crane can be reduced as discussed above, the components must provide a lifting arrangement that meets all safety requirements including fleet angle requirements. In one embodiment, the invention provides a lifting arrangement that meets all fleet angle requirements by staggering the axial position of each drum in relation to the other drum. The fleet angles in the full up and full down positions can be equalized by this positional shift between the two drums to optimize the fleet angles and thus maximize rope life. A bottom block with two separate sheave nests can also be utilized to optimize the rope fleet angles. Use of two separate sheave nests allows for optimum placement of the sheave nests with respect to the corresponding drum. Additionally, the width of the bottom block can be increased such that the sheave nests can be placed at any location with respect to the drums. Generally, the sheave nests are located near the ends of the bottom block. In some embodiments, a combination of drum stagger and custom bottom block length are used to ensure proper fleet angles. Adjustment of the drum stagger and bottom block length can be used to solve the fleet angle limitations of a crane including any combination of variables.  
           [0009]    As is apparent from the above, the invention provides a lifting arrangement for a crane that includes the use of dual drums single reeved together to provide true vertical lift. The invention also provides a lifting arrangement that includes mass produced components. The mass produced components provide a crane having a smaller footprint and height when compared to previous cranes built for similar applications. The invention also provides a lifting arrangement that allows for equalization of full up and full down rope fleet angles through utilization of axially staggered dual drums and/or an extra wide bottom block with two separate sheave nests. The invention also provides a lifting arrangement that includes commercially available components which reduce the overall cost of the crane when compared with current powerhouse crane designs, while still meeting all powerhouse crane requirements. Other objects of the invention will become apparent to those skilled in the art upon review of the following detailed description and drawings in which like numerals are used to designate like features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates a top view of an overhead traveling crane embodying the invention.  
         [0011]    [0011]FIG. 2 illustrates a front view of the crane of FIG. 1.  
         [0012]    [0012]FIG. 3 illustrates a side view of the crane of FIG. 1.  
         [0013]    [0013]FIG. 4 illustrates a perspective view of a representative set of bridge cross-members and trucks of an overhead traveling crane supported for movement on a set of rails.  
         [0014]    [0014]FIG. 5 illustrates a schematic representation of a reeving configuration for the crane of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” and “coupled” are used broadly and encompass both direct and indirect mountings, connections, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
         [0016]    [0016]FIGS. 1, 2 and  3  partially illustrate an overhead traveling crane or hoist apparatus  10  embodying the invention. It should be understood that the lifting arrangement of the present invention is capable of use in other lifting devices (e.g., other types of overhead traveling cranes, hoist apparatus, and the like) and the crane  10  is merely shown and described as one such example. The crane  10  is of the type commonly known as powerhouse cranes.  
         [0017]    The portion of the crane  10  illustrated in FIGS.  1 - 3  includes a trolley  11 . As illustrated in FIG. 4, the crane  10  also includes bridge cross-members  100  and trucks  105  mounted at opposite ends of the bridge cross-members  100 . Drive wheels  110  are rotatably mounted on the trucks  105  in engagement with rails  115  so that the rails  115  support the crane  10 . Additional non-driven or idler wheels  120  are also rotatably mounted on the trucks  105  in engagement with the rails  115  for further support of the crane  10 . The rails  115  are mounted on conventional beams (not shown) or other suitable foundation means. The engagement of the drive and idler wheels  110 ,  120  with the rails  115  permits travel of the crane  10  along the rails  115 . Motors  125  are mounted on the bridge cross-member  100  and drive the wheels  10 .  
         [0018]    The trolley  11  is supported for travel on tracks or rails  130  by wheel assemblies  12 . The rails  130  are mounted on the bridge cross-members  100  of the crane  10 .  
         [0019]    The trolley  11  includes generally parallel first and second trolley sides  13 ,  14 . The trolley sides  13 ,  14  support a first lift train  16  and a second lift train  18 . Each lift train  16  and  18  includes a motor  20 , a gearbox  22  and a drum  24 . As illustrated in FIG. 1, the gearbox  22  and the motor  20  of the first lift train  16  are disposed adjacent the first trolley side  13 , and the gearbox  22  and the motor  20  of the second lift train  18  are disposed adjacent the second trolley side  14 . The drums  24  of the first and second lift train  16  and  18  can be single reeved together using a single rope  26  or a combination of ropes  26 . Rope  26  is wound around the drums  24  such that rotation of the drums  24  causes the rope  26  to wind on to and off of the rotated drum  24 . A bottom block  28  is supported by the rope  26  such that the bottom block  28  moves up and down as the rope  26  wind on to and off of the drums  24 . The bottom block  28  includes two sheave nests  30  and a material handling hook  32  coupled thereto. The sheave nests  30  are generally located at a first and second end of the bottom block  34 . Other sheave nests  34  are mounted on the frame of the trolley  11 . In one embodiment, the rope  26  is dead ended at points  36   a  adjacent respective sheave nests  34 . In another embodiment, an equalizer sheave  36   b  (FIG. 1) is mounted on the frame of the trolley  11  so the rope  26  is reeved through the equalizer sheave  36   b  when transitioning from the first lift train  16  to the second lift train  18 .  
         [0020]    [0020]FIG. 5 illustrates a reeving configuration for the lifting arrangement. A first end of the rope  26  is fixed to a first end of the drum  24  and then wrapped around the drum  24 . The rope  26  may be removably fixed to the drum such that the rope  26  can be adjusted to compensate for differences in the manufactured lengths of rope. Generally, this adjustment is accomplished during reeving of the lifting arrangement.  
         [0021]    Referring to FIG. 5, the rope  26  reeves from the drum  24  down around a first sheave of the sheave nest  30 , back up around a first sheave of the sheave nest  34 , back down around a second sheave of the sheave nest  30 , back up around a second sheave of the sheave nest  34 , back down around a third sheave of the sheave nest  30 , and back up to the dead end  36   a . The other rope  26  is similarly reeved. Such a reeving configuration requires six parts of rope for each lift train  16  and  18 . Other reeving configurations may be utilized that include fewer or more parts of rope.  
         [0022]    When establishing the lifting arrangement for a particular crane, the design is primarily based on lift speed requirements and capacity requirement. Other considerations may include lift height requirements and specifications of generally available components (e.g., the diameters and lengths of drums, the outputs of motors, the ratio of gearboxes, and the cost of each). The lifting arrangement takes into account variables such as the overall length of the rope, the number of parts of rope, the diameter of the rope, the gap between wraps of the rope on the drum, the length of the drum, and the diameter of the drum. The size of the drum is determined by calculating the amount of rope that must be stored on the drum. The overall length of the rope is a function of the lift height and the number of parts of rope. A drum is selected that provides storage for the overall length of the rope. The diameter of the rope and the gap between each wrap of rope are utilized with the length and the diameter of the drum to determine if the overall length of the rope can fit on the drum. In some embodiments, the drum is a mass produced item. The motor is selected to meet the capacity and lift speed requirements. The gearbox is selected to drivingly couple the motor to the drum for rotation so the load is lifted at the required speed. In some embodiment, the motor and the gearbox are preferably mass produced items. A standard gearbox can generally be utilized as a stand alone unit or in combination with a ring gear external to the gearbox. Use of a ring gear external to the gearbox can increase the overall output torque of the gearbox. The two lift trains are coupled to a trolley frame, which is preferably mass produced, and the rope is then reeved accordingly to the selected reeve configuration.  
         [0023]    The final design of a lifting arrangement may be based on various cost considerations. Balancing is performed between the cost of components and the benefits received from use of those particular components. As an example, a lifting arrangement with a wider diameter, shorter, drum may be more cost effective than a lifting arrangement with a smaller diameter, longer, drum. The final determination is generally which design provides the best crane for the best price in accordance with the requirements of the crane purchaser.  
         [0024]    The fleet angles need to be inspected before the crane  10  is operated using the lifting arrangement. If the fleet angles are not within the standard range, the axial position of the drums  24  and/or the placement of the sheave nests  30  on the bottom block  28  must be adjusted. The staggering of the drums  24  can be adjusted such that the fleet angles are equalized in the full up and full down positions. Additionally, the width of the bottom block  28  can be increased to provide such equalization. Adjustment of the drum position can be accomplished while the crane  10  is being assembled. The bottom block  28  can be selected from a number of existing bottom block designs or custom produced if necessary.  
         [0025]    Thus, the invention provides, among other things, a new and useful lifting arrangement for a crane.