Abstract:
According to one aspect, a supporting truck for a crane comprises a load bearing member and a frame rigidly coupled to the load bearing member. A plurality of substantially equally spaced and substantially equally sized wheels is rigidly journaled in the frame at substantially equal heights such that the wheels have a single degree of freedom comprising rotational movement with respect to the frame and the load bearing member. The load bearing member and the frame have a moment of inertia of at least a particular value to cause the wheels to experience substantially equal loading by forces applied to the load bearing member.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable 
       REFERENCE REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable 
       SEQUENTIAL LISTING 
       [0003]    Not applicable 
       FIELD OF DISCLOSURE 
       [0004]    This invention pertains to gantry cranes, overhead cranes, portal cranes, and the like, and, more particularly, to a crane having a multi-wheel end truck. 
       BACKGROUND 
       [0005]    Cranes of the above type are known in the art and are used to support heavy loads, as such loads are transported, for example, in a rail yard, a shipyard, a factory, etc. Such a crane may include a trolley supported on trolley girders. Ends of the trolley girders may be supported by end trucks that are movable on spaced bridge girders. In some cranes, the bridge girders are supported at each end thereof. In other cranes, the bridge girders may extend beyond support columns or other structural support members such that the girders terminate at cantilevered ends. In either case, the loading applied to the bridge girders determines the required strength thereof, and thus, the amount of material that is required to construct the girders. More material results in increased weight and material costs, which, in turn, results in increased initial and operating costs. 
         [0006]    In the case of a crane having cantilevered bridge girders, for example, the distance that the cantilevered end of the girder extends from its closest support is critical as any load or weight positioned on the cantilevered portion of the girder creates a moment with respect to the nearest support (e.g., column, frame, etc.). This moment (i.e., force applied over a distance) is determined by multiplying the weight of the load by the distance between the load and the nearest support member. If the moment created by the load exceeds the capacity of the girder, the girder may deflect, bend, or even fail, possibly causing grave injury to personnel in the area and damage to goods and equipment being transferred. 
         [0007]    In order to allow for the movement of heavy loads such as those found in a container rail yard or shipyard, the bridge girders may comprise heavy weight box beams to support the loads. Depending on the length of the cantilever (if present) and the weight of the loads, such girders may become cost prohibitive because of the weight of the girder required to satisfy loading requirements. In order to overcome this problem, either the length of the cantilever must be shortened or eliminated altogether and/or the weight of the load decreased. However, even if the cantilevered sections are eliminated, the remaining sections of the bridge girders must, of course, still be sized to support the expected loading thereon. 
         [0008]    Conventional trolley end trucks utilize a plurality of wheels that are mounted at relatively widely spaced locations. In a known end truck design, the wheels are supported by equalizing and/or compensating devices that are pivotable or otherwise movable. The pivoting or other moving action allows the wheels to share the applied loads equally. However, the wide spacing of the wheels results in application of relatively widely spaced point loads where the wheels contact the bridge girder. Also, in the case of cantilevered bridge girders, the overall center of gravity of the end truck is displaced relatively far from the support column closest to the cantilevered girder section. The bridge girder must be designed with these factors in mind so that the bridge girders can safely support all expected loading conditions. 
       SUMMARY 
       [0009]    According to one aspect, a supporting truck for a crane comprises a load bearing member and a frame rigidly coupled to the load bearing member. A plurality of substantially equally spaced and substantially equally sized wheels is rigidly journaled in the frame at substantially equal heights such that the wheels have a single degree of freedom comprising rotational movement with respect to the frame and the load bearing member. The load bearing member and the frame have a moment of inertia of at least a particular value to cause the wheels to experience substantially equal loading by forces applied to the load bearing member. 
         [0010]    According to another aspect, a crane includes first and second spaced bridge members wherein each bridge member extends between an associated pair of supports and the bridge members are parallel to one another. The crane further includes first and second spaced trolley girders and a movable trolley is disposed on the trolley girders. First and second end trucks support first and second ends, respectively, of the first and second trolley girders and the trolley girders extend transversely with respect to the bridge members. Each of the first and second end trucks includes a load bearing member, a frame rigidly attached to the load bearing member, and a plurality of substantially equally spaced and substantially equally sized wheels rigidly journaled in the frame at substantially equal heights. The wheels have a single degree of freedom comprising rotational movement with respect to the frame and the load bearing member, and the load bearing member and the frame have a moment of inertia I at least equal to Mc/f, where M is a load moment on a particular cross section of the load bearing member, c is a distance from a neutral axis of the particular cross section to an extreme fiber of the particular cross section, and f is a given stress magnitude, to cause the wheels to experience substantially equal loading by forces applied to the load bearing member. 
         [0011]    Other aspects and advantages will become apparent upon consideration of the following detailed description and the attached drawings wherein like numerals designate like structures throughout the specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view showing an embodiment of a crane comprising a cantilever gantry crane; 
           [0013]      FIG. 1A  is a further perspective view of the embodiment of  FIG. 1 ; 
           [0014]      FIG. 2  is a fragmentary enlarged perspective view showing one of the end trucks used in the cantilever gantry crane of  FIG. 1 ; 
           [0015]      FIG. 3  is a side elevational diagrammatic view of an end truck used in the embodiment of  FIG. 1 ; 
           [0016]      FIG. 4  is a perspective view of a further embodiment of a crane that does not have cantilevered sections or portions and which may include the trolley of  FIGS. 1-3 ; and 
           [0017]      FIG. 5  is a cross sectional view of a truck comprising a box girder that supports a load. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIGS. 1 and 1A  show a crane, more particularly, a cantilever gantry crane  10  comprising first  12  and second bridge girders  14  each of which extends between first and second supports  16   a ,  18   a  and  16   b ,  18   b , respectively. In the illustrated embodiment each of the first and second bridge girders  12 ,  14  terminates in a cantilevered section or portion  20 ,  22 , respectively, that extends outboard of the first supports  16   a ,  16   b , respectively. As noted hereinafter and as seen in  FIG. 4 , the bridge girders need not have the cantilevered sections or portions  20 ,  22 . In any event, first and second trolley girders  25   a ,  25   b  extend transversely between the bridge girders  12 ,  14  and are supported in spaced relation by supporting trolley end trucks  26   a ,  26   b . Each of the end trucks  26   a ,  26   b  is movable along the respective bridge girders  12 ,  14  on a plurality of wheels  28 , respectively (only the wheels  28  of the end truck  26   a  are visible in the FIGS). A trolley  29  is movable on the trolley girders  25   a ,  25   b  between the first and the second bridge girders  12 ,  14 , transverse to the movement of the end trucks  26   a ,  26   b  on the bridge girders  12 ,  14 . 
         [0019]    In an embodiment, the trolley  29  is movable on the first and second trolley girders  25   a ,  25   b  in a direction perpendicular to the longitudinal extent of the first and second bridge girders  12 ,  14 . In such an embodiment, each of the first and second trolley girders  25   a ,  25   b  supports one half the weight of a load being transferred by the gantry crane  10 . 
         [0020]    The end trucks  26   a ,  26   b  are substantially if not completely identical to one another except that the end truck  26   a  is a mirror image of the end truck  26   b ; accordingly, only the end truck  26   a  will be described in detail herein together with the associated portions of the crane  10 . Referring also to  FIGS. 2 and 3 , the end truck  26   a  has a length T L , and a frame  30  in which the plurality of wheels  28  is journaled. The wheels  28  are identical or substantially identical to one another in size, shape, and material, and are journaled at equal or substantially equal heights above an upper surface  12   a  of the bridge girder  12 . The wheels  28  are not isolated from one another or from a load bearing surface  32  (seen in  FIG. 3 ) of the end truck  26   a  by springs, pivoting members, other relatively movable members, or the like. Rather, each wheel  28  is rigidly mounted with respect to the frame  30 , and the frame  30  is rigidly mounted to the load bearing surface  32  such that the wheels  28  have only one degree of freedom of movement, i.e., the wheels are only able to rotate relative to the frame  30  and the load bearing surface  32  and are not otherwise movable relative to such structures. Further, the frame  30  is not able to move at all (or is at least substantially immovable) relative to the load bearing surface  32 . In addition, the moment of inertia and the stiffness of the load bearing member  32  and the frame  30  are increased, the number of wheels is increased, and the spacing of the wheels is decreased, as noted in greater detail hereinafter. Such an arrangement results in a load supported by the trolley  24  being evenly distributed among each of the plurality of wheels  28  on the end truck  26  and that such loading is applied to the bridge girder  12  over a wheelbase distance. This even distribution of weight on the closely spaced wheels  28  results in a relatively uniform loading of the bridge girder  12  thereby allowing the bridge girder  12  to be designed to have less mass while still adequately supporting the applied loads, leading to reduced initial and operational costs. 
         [0021]    Further, in the case of the cantilevered crane of  FIGS. 1-3 , the distance of the moment arm that results from the weight of the load that is supported by the cantilevered portion  20  is shortened such that the center of gravity C G  of the end truck is disposed closer to the first supports  16   a ,  16   b  when the end truck  26   a  is disposed at an end  38  of the cantilevered portion  20 . This limits the moment arm applied to the cantilevered portion  20 , thereby allowing the mass thereof to be reduced, leading to the desirable decrease in costs as noted above. 
         [0022]    In an embodiment, the plurality of wheels on the end truck is mounted adjacent to a support platform  40  to which one or more plates  42 , such as steel, or other stiffening plates or other members are secured, such as by welding, to increase the moment of inertia of the load bearing member  32  and frame  30 . 
         [0023]    Further, as seen in  FIG. 1 , first ends  12   b ,  14   b  of the bridge girders  12 ,  14  are mounted on the supports  18   a ,  18   b  in contact with the ground via wheels, and other sections  12   c ,  14   c , seen in  FIG. 1A , are mounted on the supports  16   a ,  16   b . The cantilevered portions  20 ,  22  are located outboard of the supports  16   a ,  16   b . Other supports may be provided as necessary or desirable. Lower ends  50   a ,  50   b  of the supports  16   a ,  16   b  are carried by supporting gantry trucks  52 ,  54  each having pluralities of wheels  55 ,  56  that rest on a runway beam  58 . The gantry trucks  52 ,  54  are identical or substantially similar to the end trucks  26   a , or  26   b  and are movable along the runway beam  58 . 
         [0024]    In all embodiments motors are operable by a control to move the trolley  29 , the end trucks  26   a ,  26   b  and the gantry trucks  52 ,  54  to transfer loads, such as containers or other items, between locations and/or to move the crane  10 . 
         [0025]    In one embodiment, each of the cantilevered portions  20 ,  22  extends at least 50 feet outboard of the supports  16   a ,  16   b . The first and second bridge girders  12 ,  14  may be of any suitable overall length without departing from the spirit and scope of the invention. For example, in one embodiment, each of the first and the second bridge girders  12 ,  14  may extend at least 150 feet between the first and the second supports  16   a ,  18   a  and  16   b ,  18   b , respectively, and may have a total length of 200 feet. In a particular embodiment, each plurality of wheels  28  of the end trucks  26   a ,  26   b  comprises nine wheels, although a greater or lesser number of wheels may be provided, and the wheels simultaneously roll on rails  70  ( FIG. 2 ) disposed atop the first and second bridge girders  12 ,  14 , respectively. Preferably, although not shown, the wheels are flanged on both sides thereof. In an embodiment, relatively soft mounting pads  74  may be disposed between the bridge girders  12 ,  14  and the rails  70  as shown in  FIG. 2  (only one of the rails  70 , the mounting pads  74 , and the bridge girder  12  are visible in  FIG. 2 ). The wheels  55 ,  56  of the gantry trucks  52 ,  54  may similarly roll on one or more rails (not shown) that are disposed on the runway beam  58 . One or more relatively soft mounting pads (also not shown) similar or identical to the pads  74  may be disposed between the rail(s) and the runway beam  58 . Other similar or identical structures, such as additional trucks and one or more additional runway beams and associated apparatus, may be provided to support and permit movement of the crane  10 . The additional trucks may be identical to the trucks  26   a ,  26   b ,  52 , and  54 . 
         [0026]    Each truck  26   a ,  26   b ,  52 ,  54  may be any suitable size or shape and may have, for example, a box shaped cross section. The wheels  28 ,  55 , and  56  may be of any appropriate size; however, all of the wheels of each plurality should be of the same size for proper weight distribution, although the wheels of one plurality may be of a different size, shape, and/or material than the wheels of one or more of the other pluralities. For example, in one embodiment, each wheel of the pluralities of wheels  28 ,  55 , and  56  has a diameter of 15 inches, and each wheel of the pluralities of wheels  28 ,  55 , and  56  is spaced from the center of adjacent wheels by about 1.5 feet. In a particular embodiment, the standard deviation of the loads on the wheels of a plurality of wheels is no greater than about 2%. 
         [0027]    In an embodiment, each truck  26   a ,  26   b ,  52 ,  54  has a moment of inertia I for an allowable stress magnitude f of at least: 
         [0000]        I=Mc/f    (1)
 
         [0000]    where M is the load moment on a cross section of the rigidly-connected portions of the truck and c is the distance from the neutral axis of the cross section to a farthest point of the cross section along dimensions x and y from the neutral axis (otherwise referred to as the extreme fiber). Thus, for example, in the case of a truck assumed (at least initially) to comprise a box girder  80  as seen in  FIG. 5  that is to be loaded during operation of the crane, the box girder  80  has a moment of inertia I at the illustrated cross section about axes x-x and y-y using the dimensions in such FIG. equal to: 
         [0000]        I =(2)(1/12)( w )( h   3 )+(2)(1/12)( b )( t   3 )+(2)( b )( t )( d/ 2 −t /2) 2    (2)
 
         [0000]    The load moment M is calculated from the loads to be applied to the truck using any known calculation method. Thereafter, using equation (1) above, the actual stress magnitude f that will be experienced at the cross section of the truck is calculated as: 
         [0000]        f=Mc/I    (3)
 
         [0000]    The actual stress magnitude is then compared to a particular maximum magnitude of allowable stress and, if necessary, the design of the truck is modified (for example, by changing the cross sectional or other shape of the truck and/or by adding one or more plates  42  atop surface  40  as noted previously) and the foregoing calculations are repeated. Again, if necessary, one or more further design modifications and further calculations may be iteratively repeated as noted above until the maximum magnitude of allowable stress exceeds the actual stress by a predetermined amount or amounts over the full dimensions of the truck. This results in a truck design that has a load bearing member (e.g., the box girder of  FIG. 5 ) and one or more additional structures rigidly coupled thereto (e.g., the frame) that have at least a predetermined moment of inertia sufficient to achieve the desirable substantially equal wheel loadings. 
         [0028]    Further, in an embodiment, the combination of the load bearing member and other structures rigidly coupled thereto (e.g., the frame) of each truck  26   a ,  26   b ,  52 ,  54  has a stiffness S (i.e., resistance to bending) for a given stress magnitude f of at least: 
         [0000]        S=M/f    (2)
 
         [0000]      where  S=I/c    (3)
 
         [0029]    As noted previously in connection with  FIG. 4 , the first and second bridge girders  12 ,  14  may be supported over the full lengths thereof such that neither girder  12 ,  14  has a cantilevered portion. Thus, for example, the supports  16   a ,  16   b ,  18   a , and  18   b  may be disposed at ends of the bridge girders  12 ,  14 . The crane may otherwise be identical to the crane  10 . 
       INDUSTRIAL APPLICABILITY 
       [0030]    As noted above, the moment of inertia of each end truck is great enough so as to limit deflection of the trucks  26   a ,  26   b ,  52 , and  54  and create a rigid support that allows each wheel of the pluralities of wheels  28 ,  55 , and  56  to support an equal load. In one embodiment, one or more plate of a given thickness and/or other member is added to the truck so as to increase the mass of the truck, and thereby increase its moment of inertia. This results in the ability to reduce the amount of material in each beam leading to reduced costs. 
         [0031]    All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
         [0032]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0033]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.