Abstract:
In one aspect, the invention is directed to an overhead crane with one or more bridge rails, that incorporates a reinforcement truss into its one or more bridge rails so as to reduce the overall mass of the one or more bridge rails. This facilitates movement of a load carried by the bridge by an operator to a destination point, particularly in embodiments wherein the one or more bridge rails do not have any bridge drive motors thereon. Reducing the mass of the bridge can increase the amount of lifted load that can comfortably be maneuvered by an operator, particularly when the bridge is manually moved along the runway. Additionally, reducing the mass of the bridge reduces the momentum associated with the bridge, which can increase the amount of control that the operator has when it is desired to stop the bridge when the load has been maneuvered to its desired destination point. The second reinforcement members may have first and second ends that are inserted into receiving apertures in the first reinforcement member and in a bracket that mounts to the bridge rail respectively. In embodiments wherein the bridge includes two rails and is capable of supporting a load in such a way as to generate a downward force that is offset from the bridge axis, the second reinforcement members may be connected to the first reinforcement member and to brackets in such a way as to prevent the withdrawal of the second reinforcement members from the receiving apertures.

Description:
FIELD OF THE INVENTION 
     The present invention relates to overhead cranes for use in industrial plants, and more particularly to an overhead crane that is configured to lift a load using motorized means, but wherein an operator manually pulls or pushes the lifted load to its destination. 
     BACKGROUND OF THE INVENTION 
     Overhead cranes typically include a pair of runways, which may be mounted fixedly to the roof joists of an industrial plant, a bridge that includes one or more bridge rails which have rollers at their ends for rolling along the runway rails, and a trolley which has rollers thereon for rolling along the one or more bridge rails. A hoist or some other lifting device is provided on the trolley for lifting a load. 
     For cranes having capacities of more than 4000 lb, I-Beam crane rails are typically used for the one or more bridge rails and for the runways. For cranes having capacities of less 4000 lb, enclosed track crane rails, such as the crane rail shown at  100  in  FIG. 1  are typically used. 
     A particular category of cranes are referred to as ‘light’ cranes, and typically have a capacity of about 2000 lb or less. Light cranes typically do not have tractor drives on the bridge and trolley, which means that the load, once lifted off the plant floor, is moved around manually by the crane operator. 
     For such cranes, the weight of the bridge rails directly impacts the effort that the operator is required to exert when moving the lifted load to its destination. It is thus generally desirable to reduce the weight of the bridge rails. By reducing their weight, the effort required to move a given size of lifted load can be reduced. 
     A typical enclosed bridge rail is shown in  FIG. 1 . One method that has been used to reduce the weight of the bridge rail is to manufacture the bridge rail out of aluminum. 
     It would be desirable to find other ways of reducing the weight of the bridge rail particularly for light cranes that lack tractor drives for moving the bridge on the runways. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention is directed to an overhead crane with one or more bridge rails, that incorporates a reinforcement truss into its one or more bridge rails so as to reduce the overall mass of the one or more bridge rails. This facilitates movement of a load carried by the bridge by an operator to a destination point, particularly in embodiments wherein the one or more bridge rails do not have any bridge drive motors thereon. Reducing the mass of the bridge can increase the amount of lifted load that can comfortably be maneuvered by an operator, particularly when the bridge is manually moved along the runway. Additionally, reducing the mass of the bridge reduces the momentum associated with the bridge, which can increase the amount of control that the operator has when it is desired to stop the bridge when the load has been maneuvered to its desired destination point. The second reinforcement members may have first and second ends that are inserted into receiving apertures in the first reinforcement member and in a bracket that mounts to the bridge rail respectively. In embodiments wherein the bridge includes two rails and is capable of supporting a load in such a way as to generate a downward force that is offset from the bridge axis, the second reinforcement members may be connected to the first reinforcement member and to brackets in such a way as to prevent the withdrawal of the second reinforcement members from the receiving apertures. 
     In another aspect, the invention is directed to a retrofit kit that permits the reinforcing structure described above to be easily retrofitted to existing bridge rails without the need for welding and without the need to install an inordinate quantity of fasteners. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described by way of example only with reference to the attached drawings, in which: 
         FIG. 1  is an end view of a bridge rail used in a crane in accordance with the prior art; 
         FIG. 2  is a perspective view of an overhead crane including a bridge in accordance with an embodiment of the present invention; 
         FIG. 3  is a magnified end view of a bridge rail that is part of the bridge shown in  FIG. 2 ; 
         FIG. 4  is a magnified end view of an alternative bridge rail that could alternatively be part of the bridge shown in  FIG. 2 ; 
         FIG. 5  is a magnified end view of another alternative bridge rail that could alternatively be part of the bridge rail shown in  FIG. 2 ; 
         FIG. 6  is a magnified end view of another alternative bridge rail that could alternatively be part of the bridge rail shown in  FIG. 2 ; 
         FIG. 7  is a magnified end view of another alternative bridge rail that could alternatively be part of the bridge rail shown in  FIG. 2 ; 
         FIG. 8  is a magnified perspective view of the mounting of a first reinforcement member to the bridge rail shown in  FIG. 2 ; 
         FIG. 9  is a magnified perspective view of the mounting of a second reinforcement member to the bridge rail shown in  FIG. 2 ; 
         FIG. 9   a  is a magnified sectional view of a bracket shown receiving the second reinforcement member in  FIG. 9 ; 
         FIG. 10  is a magnified perspective view of an end of the bridge rail shown in  FIG. 2  and an end of a runway rail shown in  FIG. 2 ; 
         FIG. 11  is a perspective view of a double rail bridge that may be used with the overhead crane system shown in  FIG. 2 ; 
         FIG. 12  is a magnified end view of the double rail bridge shown in  FIG. 11  supporting a trolley and a manipulator; 
         FIG. 13  is a magnified perspective view of a portion of one of the bridge rails shown in  FIG. 11 ; 
         FIG. 14  is a magnified perspective view showing the mounting of one of the second reinforcement members shown in  FIG. 11  to one of the bridge rails shown in  FIG. 11 ; 
         FIG. 14   a  is a magnified perspective view further showing the mounting of the second reinforcement member shown in  FIG. 14  to a bracket, which is mounted to the bridge rail shown in  FIG. 14 ; and 
         FIG. 15  is a magnified perspective view of the double rail bridge showing the connection between the first and second bridge rails. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to  FIG. 2 , which shows an overhead crane  10  in accordance with an embodiment of the present invention. The overhead crane  10  includes a pair of runway rails  20 , a bridge  14 , a trolley  16  and a lifting device  18 , such as a hoist. The runway rails  20  extend parallel to a generally horizontal runway axis. The bridge  14  is made up of a single bridge rail  24  that extends parallel along a generally horizontal bridge axis that is perpendicular to the runway axis. The bridge rail  24  is rollably supported on the runway rails  20  at each end by bridge wheels  28 . The bridge  14  may be manually rollable along the runway rails  20  through the bridge wheels  28 . Alternatively a bridge drive motor may be provided (not shown) to drive the bridge  14  on the runway rails  20 . The trolley  16  is rollably supported on the bridge rail  24  by means of trolley wheels  30 . The trolley  16  may be manually rollable along the bridge rail  24 . Alternatively a trolley drive motor (not shown) may be provided to drive the trolley  16  along the bridge rail  24 . 
     The bridge  14  shown in  FIG. 2  has a single bridge rail  24 . It will be noted that, in an alternative embodiment the bridge  14  could be provided with two or more bridge rails  24  (as shown in  FIG. 11 ), and with a trolley that has wheels that roll along each bridge rail. 
     The bridge rail  24  in  FIG. 2  has a pair of track flanges  32  (shown individually at  32   a  and  32   b ), which define a track  34  on which the trolley wheels  30  travel. The flanges  32  may be oriented towards each other so that the track  34  is an enclosed track as shown in  FIG. 3 . Alternatively, the flanges  32  may be oriented away from each other in which case the track  34  is an open track, as shown in  FIG. 4 . Other suitable shapes for the bridge rail  24  are shown in  FIGS. 5 ,  6  and  7 . 
     The bridge rail  24  may be made from any suitable material, such as aluminum. It will be understood that, throughout this disclosure, the term aluminum is intended to encompass both pure aluminum and aluminum alloys. By manufacturing the bridge rail  24  out of aluminum the bridge rail  24  is lighter than if it were manufactured from a material such as steel. 
     Referring to  FIG. 2 , the bridge  14  further includes a first bridge reinforcement member  36 , and two second bridge reinforcement members  38  (shown individually at  38   a  and  38   b ). The first and second bridge reinforcement members  36  and  38  may be made from any suitable material, such as aluminum tubing. The tubing may be round, which provides increased resistance to buckling (which is advantageous for the members that are in compression—in this case, the second members  38 ). 
     The first bridge reinforcement member  36  may be mounted to the bridge rail  24  in any suitable way, such as by a mechanical connection. For example, as shown in  FIG. 8 , the first bridge reinforcement member  36  may be provided with a support flange  42  at its lower end shown at  44 . Mechanical fasteners  46  (eg. bolts) may be provided that pass through the support flange  42 , through a slot  51  between a pair of flanges  49  on the bridge rail  24 , and into a first member clamping plate  47 . When the fasteners  46  are tightened the two elements  42  and  47  together clamp the flanges  49  on the bridge rail  24  thereby fixing the first bridge reinforcement member  36  in position on the bridge rail  24 . The second flanges  49  may be referred to as reinforcement support flanges as they support the reinforcement structure  35 . 
     Each second bridge reinforcement member  38  has a first end  48  that may be mechanically connected to the top end (shown at  50 ) of the first bridge reinforcement member  36 . For example, as shown in  FIG. 8 , the first ends  48  of the second reinforcement members  36  may pass through apertures  55  in the top end  50  of the first member  36 , and may abut each other so that the first end  48  of each member  36  braces the first end  48  of the other member  36 . Each aperture  55  may be referred to as a first member receiving aperture. It is alternatively possible instead to make each aperture  55  as a blind aperture that has an end wall that acts to brace the first end  48  of each second member  38 . 
     Each second bridge reinforcement member  38  has a second end  52  ( FIGS. 9 and 9   a ) that may be inserted into a receiving aperture  53  in a bracket  54  on the upper portion of the bridge rail  24 . The brackets  54  may be joined to the bridge rail  24  in any suitable way. For example, each bracket  54  may have one or more bracket mechanical fasteners  57  that pass through the bracket  54 , through the slot  51  between the reinforcement support flanges  49  and into a bracket clamping plate  59 . Tightening of the bracket mechanical fasteners  57  causes the bracket  54  and the bracket clamping plate  59  to clamp the flanges  49  on the bridge rail  24  to hold the bracket  54  in place during use. In  FIG. 9   a , only one of the upper flanges  49  is shown for simplicity. 
     The receiving aperture  53  may be a blind aperture with an end wall to support the second end  52  of the second bridge reinforcement member  38 . The receiving aperture  53  may be referred to as a bracket receiving aperture  53 . 
     During use with a chain type hoist on the trolley  16 , the first member  36  is in tension and the second members  38  are in compression. 
     It will be noted that, because the second members  38  are in compression when in use, they do not require further fastening to the brackets  54  and to the first member  36 . Accordingly, they can be relatively simple to mount to the first member  36  and to the bridge rail  24 . 
     Referring to  FIG. 2 , the position of the first bridge reinforcement member  36  may be generally centered along the length of the bridge rail  24 . The positions of the second ends  52  of the second bridge reinforcement members  38  may be proximate the ends of the bridge rail  24  while ensuring that the brackets  54  and the reinforcement members  38  do not interfere with the rolling of the bridge  14  along the runway rails  20 . 
     The reinforcement members  36  and  38  together form a truss that is relatively simple and inexpensive to manufacture and that is relatively simple and quick to mount to the bridge rail  24  and is particularly advantageous in embodiments wherein the bridge rail  24  is made from aluminum. While mechanical joints are preferred for connecting the reinforcement members  36  and  38  to each other and to the bridge rail  24 , particularly when all of these components are made from aluminum, it is nonetheless contemplated that these components could alternatively be welded together. 
     In general, welding to an aluminum bridge rail can be difficult to achieve without weakening the parent material that makes up the bridge rail. Use of mechanical fasteners instead to join reinforcement members to a bridge rail can be relatively time consuming however. Some proposed prior art reinforcement structures do not lend themselves to be joined to an aluminum bridge rail, since they entail joining to the bridge rail at many points, which would involve either many welds, which would weaken the bridge rail, or many mechanical fasteners, which would make the bridge rail prohibitively time consuming to manufacture. 
     The reinforcement structure  35  provides the greatest increase in bending strength to the bridge rail  24  at the longitudinal center of the bridge rail  24 , shown at  64 , which is also where the lifting device  18  exerts the greatest bending moments on the bridge rail  24 . The amount of bending strength the reinforcement structure  35  provided to the bridge rail  24  decreases from the longitudinal center  64  toward the outer ends (which are shown at  65   a  and  65   b ). It will be noted that the increased resistance to bending provided by the reinforcement members  36  and  38  generally matches the bending moment profile of bending moments exerted by the lifting device  18  on the bridge rail  24  at different points along the bridge rail  24  while holding a load. As a result, the reinforcement members  36  and  38  are efficient in the sense that they provide the most strengthening to the portion of the bridge rail  24  that incurs the highest bending moments (ie. the middle of the bridge rail  24 ). 
     By providing the reinforcement members  36  and  38 , the bridge rail  24  can be made lighter than would otherwise be required if it consisted only of the bridge rail  24 , for holding a selected size of load. This reduces the overall amount of weight that an operator must push or pull in embodiments wherein bridge drive motors are not provided. This is also advantageous in embodiments that do include drive motors for the bridge since the bridge drive motor (or motors) have less work to do to move the lighter bridge along the runway rails. 
     Another advantage to this configuration is that the bridge  14  has less momentum associated with it, and so the operator has a greater degree of control over stopping the bridge  14  after rolling the bridge  14  to a selected point along the runway rails  20 . This is particularly relevant for bridges  14  that have relatively long spans, which are necessarily heavier and which have larger bending moments associated therewith resulting from the greater distances between their points of support on the runway rails and the load. 
     Referring to  FIG. 10 , the bridge  14  further includes a rolling structure  60  mounted at each end of the bridge rail  24  by clamping the upper flanges  49 , in similar fashion to the clamping of the flanges  49  by the first member  36  and by the brackets  54 . The rolling structure  60  rolls along flanges shown at  62  on the runway rails  20 . 
     The trolley  16  may be made substantially from aluminum. Other materials may also be used in addition to or instead of aluminum. 
     The lifting device  18  may be a hoist or may be some other suitable type of lifting device. 
     Other configurations of the reinforcement structure  35  are possible, which provide increased bending strength to the bridge rail  24 , while keeping the number of mounting points between the reinforcement structure  35  and the bridge rail  24  relatively low, and while generally matching the bending moment profile exerted on the bridge rail  24  by the load being held by the lifting device  18  at different positions along the length of the bridge rail  24 . In one exemplary alternative configuration, two first reinforcement members  36  may be provided, each of which is connected to a second member  38 . The two members  36  may optionally share a common support flange, or may optionally have separate support flanges. The two first members  36  can be positioned proximate each other at the longitudinal center  64  of the bridge rail  24  such that the increase in bending resistance to the bridge rail  24  has roughly the same shape as it did with one centrally positioned first member  36 . Alternatively, the two first members  36  can be spaced from each other, and optionally a third reinforcement member can extend between them (eg. generally horizontally between their upper ends). In another alternative, a single centrally positioned first member  36  may be provided, and smaller third members may be provided partway along the length of each second member  38  extending vertically between the second member and the bridge rail  24  to increase the buckling resistance of the second member  38 . 
     Referring to  FIG. 2 , the runway rails  20  may be made similarly to the bridge rail  24  in that they each include flanges  62  that define a track  63 . Each runway rail  20  may further be strengthened by a reinforcement structure  72  which increases the bending resistance of the runway rail  20  so as to resist bending forces from the bridge  14 . In the exemplary embodiment shown in  FIG. 2 , the reinforcement structure  72  comprises a first runway reinforcement member  78  which extends upwardly from the longitudinal center of the runway rail  20 , and two second reinforcement members  80  which extend between the upper end of the first member  78  and the runway rail  20  proximate the ends  76   a  and  76   b . By strengthening the bending resistance of the runway rail  20  in this way, the runway rail  20  itself may be made smaller than it would need to be if the reinforcement structure  72  were omitted. As a result, the overall weight and cost of the runway rail  20  may be reduced relative to a runway rail that did not have a reinforcement structure thereon. It will be noted, however, that reducing the weight of the runway rail, while advantageous, does not facilitate the movement of a lifted load to a destination point, since the runway rails  20  remain fixed in place throughout any operation with the overhead crane. The runway rails  20  may be made from any suitable material, such as steel, or aluminum. 
     Reference is made to  FIG. 11 , which shows a double rail bridge  200  which can be used as part of the overhead crane  10  instead of the single rail bridge  14  ( FIG. 1 ). The double rail bridge  200  has first and second bridge rails  202  (shown individually at  202   a  and  202   b ), which together support a trolley  203  that may hold a lifting device such as a manipulator  204 . During use of the manipulator  204  forces may be applied to the bridge  200  that are laterally offset from the longitudinal centerline of the bridge  200  (which is shown at  206  as a point in  FIG. 12 ). An exemplary offset force is shown at F. The force F generate reaction forces F 1  and F 2  on the bridge  200 . As shown the force F generates an upwardly directed force F 1  on the bridge rail  202   a  and a downwardly directed force F 2  on the bridge rail  202   b . Each bridge rail  202  has a reinforcement structure  208  thereon that includes a first bridge reinforcement member  210  and two second reinforcement members  212 . Brackets  214  may be provided to connect the second ends of the second reinforcement members  212  to the bridge rail  202 . 
     It will be noted that, for the bridge rail  202   a , the first reinforcement member  210  is under compression and the two second reinforcement members  212  are under tension. Conversely, the first reinforcement member  210  on the second bridge rail  202   b  is under tension and the second reinforcement members  212  on the second bridge rail  202   b  are under compression, in similar manner to the single rail bridge  14  shown in  FIG. 2 . It will be understood that in situations during use of the crane  200 , the manipulator  204  may be positioned on the other side of the centerline  206  and so the tension and compression in the members of the reinforcement structures  208  on the two bridge rails  202   a  and  202   b  will be reversed. 
     In order to prevent the second reinforcement members  212  from withdrawing from the first reinforcement member  210 , the second reinforcement members  212  have lateral extending first end retaining pins  215  that pass through their first ends, shown at  216 . The pins  215  engage an inboard face of a wall  218  on the first reinforcement member  210  to prevent the withdrawal of the second reinforcement member  212  therefrom. The pins  215  may be in the form of threaded fasteners (e.g. a bolt and nut). 
     Referring to  FIG. 13 , the first reinforcement member  210  may be mounted to the bridge rail  202  in any suitable way, such as by use of one or more threaded fasteners  220  that pass through a support flange  222  at the bottom end  224  of the first reinforcement member  210 . The threaded fasteners  220  pass through a slot  226  between first and second reinforcement support flanges  228  on the bridge rail  202 , and pass into a threaded aperture in a clamping plate  230  so that the support flange  222  and the clamping plate  230  together clamp the flanges  228  on the bridge rail  202 . 
     Referring to  FIG. 13  still, the walls  218  of the first reinforcement member  210  each have a first member receiving aperture  232  there in for receiving the first ends  216  of the second reinforcement members  212 . The walls  218  may be connected to each other by a bar  234  that is welded (or is otherwise connected) across their respective tops. The walls  218  may each be connected to the main body shown at  236  of the first reinforcement member  210  by welds or by any other suitable type of connection. It can be seen that the space between walls  218  is open in the lateral direction so as to permit easy access for installing the first end retaining pins  215  and for visually ensuring that the first ends  216  are positioned suitably to brace each other. 
     Referring to  FIG. 14 , each second reinforcement member  212  has a second end  238  that extends into a bracket receiving aperture  240  in one of the brackets  214 . A laterally extending second end retaining pin  242  extends laterally through the bracket  214  and through the second end  238  of the second reinforcement member  212 . The pin  242  may be any suitable type of pin, such as a spring pin. 
     Referring to  FIG. 14   a , each bracket  214  may connect to the bridge rail  202  by means of mechanical fasteners  243  which pass through the bracket  14 , through the slot  226  between the upper flanges  228  on the bridge rail  202 , and into a threaded aperture in a clamping plate  244  so as to clamp the flanges  228 . 
     As can be seen in  FIG. 14   a , the bridge rails  202  may each have a similar profile to the bridge rail  24 . The bridge rails  202  may have any suitable profile, such as any of the profiles shown in  FIGS. 3-7 . The bridge rails  202  may thus have track flanges  245 , which are similar to the track flanges  32  and which together define a track. 
     Referring to  FIGS. 11 and 15 , one or more X-bracing structures  246  may be provided between the first and second bridge rails  202   a  and  202   b  so as to structural connect them. Each X-bracing structure  246  may be made up of first and second cross members  247 , shown individually at  247   a  and  247   b . Each cross member  246  may be connected at its ends to the bridge rails  202  by means of threaded fasteners and clamping plates at shown at  248  and  250  in  FIG. 15 . The cross members  247   a  and  247   b  are also connected to each other at their respective middles by pin connection  251 . 
     Referring to  FIG. 11 , each of the bridge rails  202  has a rolling structure  252  at each end that may be similar to the rolling structure  60  ( FIG. 10 ). 
     It will be noted that the reinforcement structures  35  and  208  can easily be retrofitted to existing bridge rails  24 ,  202  in an existing overhead crane  10 ,  200 , particularly where the overhead crane has upper flanges that can be used as reinforcement support flanges. As a result, the bridge rails can be strengthened significantly so as to be capable of supporting increased loads. It will further be noted that the reinforcement can be provided by the structure  35 ,  208  without the need for welding elements to the rails  24 ,  202 , without drilling through the rails  24 ,  202  and without requiring an inordinate number of fasteners. 
     It is optionally possible to provide the retaining pins  215  and  242  on a single rail bridge, such as the bridge  14 , for use in situations where the single rail bridge  14  will be subjected to upward forces from the lifting member. 
     While the above description constitutes a plurality of embodiments of the present invention, it will be appreciated that the present invention is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.