Crane rail

An overhead crane has first and second runway rails that extend parallel to a generally horizontal runway axis and a bridge that extends along a bridge axis that is generally horizontal and perpendicular to the runway axis and that is movable on the runway rails along the runway axis. The bridge includes a first bridge reinforcement member pre-loaded under tension to provide an upward deflection of the bridge rail. The first bridge reinforcement member may have at least two upwardly extending struts and a common upper end where the at least two struts meet, the at least two struts having lower ends mechanically connected to the bridge rail at positions longitudinally spaced apart with respect to the bridge axis. The lower ends of the at least two struts are longitudinally translatable along the bridge rail to adjust the tension on the first bridge reinforcement member to thereby adjust the extent of upward deflection of the bridge rail. The bridge further includes a pair of second bridge reinforcement members extending between the upper end of the first bridge reinforcement member and mechanically connected to the bridge rail proximate the first and second outer ends, the second bridge reinforcement members loaded in compression. The runway rails may be constructed in a similar manner as the bridge rail.

FIELD

This application 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

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 pounds, 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 pounds, enclosed track crane rails, such as the crane rail shown at100inFIG. 1are typically used.

A particular category of cranes is referred to as ‘light’ cranes, and typically have a capacity of about 2000 pounds 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 inFIG. 1. One method that has been used to reduce the weight of the bridge rail is to manufacture the bridge rail out of aluminum.

Another way has been disclosed in U.S. Pat. No. 8,960,459 issued on Feb. 25, 2015 to Givens.

It would be desirable to find other ways of reducing the weight of the bridge rail while reducing the possibility that the bridge rail may twist when loaded, particularly for light cranes that lack tractor drives for moving the bridge on the runways.

SUMMARY

In a first aspect, the invention is directed to an overhead crane, comprising: first and second runway rails that extend parallel to a generally horizontal runway axis; a bridge that extends along a bridge axis that is generally horizontal and perpendicular to the runway axis and that is movable on the runway rails along the runway axis, wherein the bridge includes a bridge rail having first and second ends and rolling structures at the first and second ends which are rollably supported on the first and second runway rails; a trolley having a plurality of trolley wheels thereon permitting movement of the trolley along the bridge rail; and a lifting device for holding a load, wherein the lifting device is supported by the trolley, wherein the bridge further includes a first bridge reinforcement member pre-loaded under tension to provide an upward deflection of the bridge rail, the first bridge reinforcement member comprising at least two upwardly extending struts and a common upper end where the at least two struts meet, the at least two struts having lower ends mechanically connected to the bridge rail at positions longitudinally spaced apart with respect to the bridge axis, the lower ends of the at least two struts longitudinally translatable along the bridge rail to adjust the tension on the first bridge reinforcement member to thereby adjust the extent of upward deflection of the bridge rail, a single pair of second bridge reinforcement members extending between the upper end of the first bridge reinforcement member and mechanically connected to the bridge rail proximate the first and second outer ends, the second bridge reinforcement members loaded in compression, and the bridge reinforcement members providing the greatest increase in bending strength at the longitudinal center of the bridge rail.

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.

In another aspect, there is provided a bridge or runway for an overhead crane, the bridge or runway comprising: a rail; a first reinforcement member pre-loaded under tension to provide an upward deflection of the rail, the first reinforcement member comprising at least two upwardly extending struts and a common upper end where the at least two struts meet, the at least two struts having lower ends mechanically connected to the rail at positions longitudinally spaced apart with respect to a longitudinal axis of the rail, the lower ends of the at least two struts longitudinally translatable along the rail to adjust the tension on the first reinforcement member to thereby adjust the extent of upward deflection of the rail; and, a single pair of second reinforcement members extending between the upper end of the first reinforcement member and mechanically connected to the rail proximate the first and second outer ends, the second reinforcement members loaded in compression.

Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art.

DETAILED DESCRIPTION

Reference is made toFIG. 2, which shows an overhead crane10in accordance with an embodiment of the present invention. The overhead crane10includes a pair of runway rails20, a bridge14, a trolley16and a lifting device18, such as a hoist. The runway rails20extend parallel to a generally horizontal runway axis. The bridge14is made up of a single bridge rail24that extends parallel along a generally horizontal bridge axis that is perpendicular to the runway axis. The bridge rail24is rollably supported on the runway rails20at each end by end trucks28. The bridge14may be manually rollable along the runway rails20through the end trucks28. Alternatively, a bridge drive motor may be provided (not shown) to drive the bridge14on the runway rails20. The trolley16is rollably supported on the bridge rail24by means of trolley wheels30. The trolley16may be manually rollable along the bridge rail24. Alternatively, a trolley drive motor (not shown) may be provided to drive the trolley16along the bridge rail24.

The bridge14shown inFIG. 2has a single bridge rail24. It will be noted that, in an alternative embodiment the bridge14could be provided with two or more bridge rails24(as shown inFIG. 11), and with a trolley that has wheels that roll along each bridge rail.

The bridge rail24inFIG. 2has a pair of track flanges32(shown individually at32aand32b), which define a track34on which the trolley wheels30travel. The flanges32may be oriented towards each other so that the track34is an enclosed track as shown inFIG. 3. Alternatively, the flanges32may be oriented away from each other in which case the track34is an open track, as shown inFIG. 4. Other suitable shapes for the bridge rail24are shown inFIG. 5,FIG. 6andFIG. 7.

The bridge rail24may 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 rail24out of aluminum the bridge rail24is lighter than if it were manufactured from a material such as steel.

Referring toFIG. 2, the bridge14further includes a first bridge reinforcement member36, and two second bridge reinforcement members38(shown individually at38aand38b). The first and second bridge reinforcement members36and38may 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 members38).

The first bridge reinforcement member36may comprise two struts36aand36bconnected together at a common upper end50of the reinforcement member36. In some embodiments, more than two struts may be used. Lower ends of the struts36aand36bmay be mounted to the bridge rail24at longitudinally spaced apart positions on the bridge rail24. The struts36aand36bform an inverted V-shape between the upper end50of the first bridge reinforcement member36and the bridge rail24. The struts36aand36bmeet and form an angle A at the common upper end50, as shown by dashed lines inFIG. 8.

The first bridge reinforcement member36may be mounted to the bridge rail24in any suitable way, such as by a mechanical connection. For example, as shown inFIG. 8, the first bridge reinforcement member36may be provided with support flanges42at lower ends of the struts36aand36bshown at44. The struts36aand36bmay be mounted on respective support flanges42with pins45, for example threaded fasteners such as bolt and nut fasteners, that pass through the lower ends44of the struts36aand36band through respective mounting blocks43fixedly attached to the support flanges42. Mechanical fasteners46(e.g. bolt and nut fasteners) may be provided that pass through the support flanges42, through a slot51between a pair of flanges49on the bridge rail24, and into first member clamping plates47. When the fasteners46are tightened the two elements42and47together clamp the flanges49on the bridge rail24thereby fixing the first bridge reinforcement member36in position on the bridge rail24. The second flanges49may be referred to as reinforcement support flanges as they support reinforcement structure35.

Each second bridge reinforcement member38has a first end48that may be mechanically connected to the upper end (shown at50) of the first bridge reinforcement member36. For example, as shown inFIG. 8, the first ends48of the second reinforcement members38may pass through apertures55in the upper end50of the first member36, Each aperture55may be referred to as a first member receiving aperture. The first ends48of the second reinforcement members38may be secured in the first member receiving apertures55by pins, for example threaded fasteners such as bolt and nut fasteners, that pass through the first member receiving apertures55and the first ends48of the second reinforcement members38. Upper ends of the struts36aand36bmay be secured to the common upper end50of the reinforcement member36by the pins41.

Each second bridge reinforcement member38has a second end52(FIG. 9andFIG. 9A) that may be inserted into a receiving aperture53in a bracket54on the upper portion of the bridge rail24. The brackets54may be joined to the bridge rail24in any suitable way. For example, each bracket54may have one or more bracket mechanical fasteners57that pass through the bracket54, through the slot51between the reinforcement support flanges49and into a bracket clamping plate59. Tightening of the bracket mechanical fasteners57causes the bracket54and the bracket clamping plate59to clamp the flanges49on the bridge rail24to hold the bracket54in place during use. InFIG. 9A, only one of the upper flanges49is shown for simplicity.

The receiving aperture53may be a blind aperture with an end wall to support the second end52of the second bridge reinforcement member38. The receiving aperture53may be referred to as a bracket receiving aperture53.

During use with a chain type hoist on the trolley16, the first member36is in tension and the second members38are in compression.

Referring toFIG. 2, the position of the first bridge reinforcement member36may be generally centered along the length of the bridge rail24. The positions of the second ends52of the second bridge reinforcement members38may be proximate the ends of the bridge rail24while ensuring that the brackets54and the reinforcement members38do not interfere with the rolling of the bridge14along the runway rails20.

The reinforcement members36and38together form a truss that is relatively simple and inexpensive to manufacture and that is relatively simple and quick to mount to the bridge rail24and is particularly advantageous in embodiments wherein the bridge rail24is made from aluminum. While mechanical joints are preferred for connecting the reinforcement members36and38to each other and to the bridge rail24, 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 structure35inFIG. 2provides the greatest increase in bending strength to the bridge rail24at the longitudinal center of the bridge rail24, shown at64, which is also where the lifting device18exerts the greatest bending moments on the bridge rail24. The amount of bending strength the reinforcement structure35provided to the bridge rail24decreases from the longitudinal center64toward the outer ends (which are shown at65aand65b). It will be noted that the increased resistance to bending provided by the reinforcement members36and38generally matches the bending moment profile of bending moments exerted by the lifting device18on the bridge rail24at different points along the bridge rail24while holding a load. As a result, the reinforcement members36and38are efficient in the sense that they provide the most strengthening to the portion of the bridge rail24that incurs the highest bending moments (i.e. the middle of the bridge rail24).

By providing the reinforcement members36and38, the bridge rail24can be made lighter than would otherwise be required if it consisted only of the bridge rail24, 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 bridge14has less momentum associated with it, and so the operator has a greater degree of control over stopping the bridge14after rolling the bridge14to a selected point along the runway rails20. This is particularly relevant for bridges14that 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.

In another advantage, the first bridge reinforcement member36provides for less deflection of the bridge rail24under load, especially near the center of the bridge rail24compared to prior art crane rails. The first reinforcement member may be pre-tensioned thereby pre-loading the crane rail upward before any load is applied to the crane rail. Pre-loading the crane rail results in an upward deflection of the crane rail before any load is applied. As a load is applied, the crane rail will first flatten out and then deflect downward. When a load is applied to the crane rail, the maximum load of the crane rail is not reached by attaining a maximum stress, but rather by coming to a maximum allowable deflection of the crane rail. Beyond maximum deflection, the load will tend to roll downhill and there will be a perceptible effort in order to pull the load uphill. In the present invention, the first bridge reinforcement member36spreads out support over more of the midsection of the bridge rail24, which provides for less deflection of the bridge rail24under load, especially near the center of the rail, which permits applying larger loads compared to prior art crane rails before the maximum allowable deflection is reached.

In another advantage, adjustment of the first bridge reinforcement member36rather than adjustment of the two second bridge reinforcement members38may be utilized to adjust the amount of pre-loading and therefore the extent of upward deflection of the bridge rail24. In prior art crane rails, adjusting the amount of pre-loading required adjusting the positions of the brackets that secured far ends of the second bridge reinforcement members to the crane rail. In the prior art, adjusting the brackets requires two operators, one at each end of the crane rail, each operator independently moving respective brackets in a relatively uncoordinated manner. As a result, the brackets are prone to being moved by differing distances, which would result in movement and off-centering of the upper end of the first bridge reinforcement member, compromising the ability of the crane to handle loads and providing uneven stresses on the reinforcement members during use of the crane.

In the present structure, the mechanical fasteners46, the pins45and the pins41may be loosened without removal to permit the support flanges42together with the clamping plates47to translate longitudinally within the slot51, and to permit the struts36aand36bto pivot around the pins41and45. With the mechanical fasteners46and the pins41and45loosened but in place, the lower ends44of the struts36aand36bmay be separated farther apart or brought closer together, followed by retightening of the mechanical fasteners46and the pins41and45. As seen inFIG. 8AandFIG. 8Bin an exaggerated manner to illustrate principles, separating the lower ends44of the struts36aand36bpulls the bridge rail24upward thereby increasing pre-loading tension on the first bridge reinforcement member36thereby increasing upward deflection of the bridge rail24, permitting the bridge rail24to support greater loads (seeFIG. 8A). Bringing the lower ends44of the struts36aand36bcloser together decreases pre-loading tension on the first bridge reinforcement member36thereby decreasing upward deflection of the bridge rail24(seeFIG. 8B). The ability to finely move the lower ends42of the struts36aand36blongitudinally along the bridge rail24with respect to each other and with respect to the common upper end50of the first bridge reinforcement member36advantageously permits fine adjustment of the amount of pre-loading and upward deflection on the bridge rail24. Because the struts36aand36bare relatively closer together and more easily moved than the brackets54holding the two second bridge reinforcement members38to the bridge rail24, a single operator may adjust the struts36aand36bindividually or simultaneously in a coordinated manner to ensure that the lower ends44of the struts36aand36bare moved the same distance to provide symmetry in position with respect to the position of the common upper end50of the first bridge reinforcement member36without causing the common upper end50to move.

In yet another advantage, transverse horizontal deflection on opposite sides of the first bridge reinforcement member36when the bridge rail24is placed under load is unexpectedly reduced in comparison to prior art crane rails. In prior art crane rails, loading the bridge rail produces twisting at the joint between the second bridge reinforcement members, and twisting of the first reinforcement member. The limit of the capacity of such crane rails is reached when the second bridge reinforcement members begin to buckle. Typically, one second reinforcement member will buckle out in one direction and the other will buckle out in the opposite direction. Viewed from above, the second reinforcement members begin to form an S-shape, with the first reinforcement member significantly twisted. In the present invention, such buckling and twisting is minimized or prevented, allowing higher loads to be supported before the onset of buckling, allowing a reduction in size (and weight) of the second reinforcement members, and allowing for longer crane spans to be used.

The angle A (seeFIG. 8) between the struts36aand36bmay have a significant impact on the ability to resist deflections under load. As the angle A approaches 0° or approaches 180°, deflections become more of a problem. For best results, the angle A is preferably in a range of about 40° to about 90°.

Referring toFIG. 10, the bridge14further includes a rolling structure60mounted at each end of the bridge rail24by clamping the upper flanges49, in similar fashion to the clamping of the flanges49by the first member36and by the brackets54. The rolling structure60rolls along flanges shown at62on the runway rails20.

The trolley16may be made substantially from aluminum. Other materials may also be used in addition to or instead of aluminum.

The lifting device18may be a hoist or may be some other suitable type of lifting device.

Referring toFIG. 2, the runway rails20may be made similarly to the bridge rail24in that they each include flanges62that define a track63. Each runway rail20may further be strengthened by a reinforcement structure72which increases the bending resistance of the runway rail20so as to resist bending forces from the bridge14. In the exemplary embodiment shown inFIG. 2, the reinforcement structure72comprises a first runway reinforcement member78which extends upwardly from the runway rail20, and two second reinforcement members80which extend between a common upper end of the first member78and the runway rail20proximate ends76aand76bof the runway rail20.

The first runway reinforcement member78comprises two struts78aand78bconnected together at a common upper end of the runway reinforcement member78. Lower ends of the struts78aand78bmay be mounted to the runway rail20at longitudinally spaced apart positions on the runway rail20. The struts78aand78bform an inverted V-shape between the upper end of the first runway reinforcement member78and the runway rail20. The first runway reinforcement member78may be designed in a similar manner as the first bridge reinforcement member36.

By strengthening the bending resistance of the runway rail20in this way, the runway rail20itself may be made smaller than it would need to be if the reinforcement structure72were omitted. As a result, the overall weight and cost of the runway rail20may 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 rails20remain fixed in place throughout any operation with the overhead crane. The runway rails20may be made from any suitable material, such as steel, or aluminum.

Reference is made toFIG. 11, which shows a double rail bridge200which can be used as part of the overhead crane10instead of the single rail bridge14(FIG. 2). The double rail bridge200has first and second bridge rails202(shown individually at202aand202b), which together support a trolley203that may hold a lifting device such as a manipulator204. During use of the manipulator204forces may be applied to the bridge200that are laterally offset from the longitudinal centerline of the bridge200(which is shown at206as a point x inFIG. 12). An exemplary offset force is shown at F. The force F generates reaction forces F1and F2on the bridge200. As shown, the force F generates an upwardly directed force F1on the bridge rail202aand a downwardly directed force F2on the bridge rail202b. Each bridge rail202has a reinforcement structure208thereon that includes a first bridge reinforcement member210and two second reinforcement members212. The first bridge reinforcement member210may comprise two struts210aand210bconnected at a common upper end and mounted on the bridge rail202at longitudinally spaced apart positions. Brackets214may be provided to connect the second ends of the second reinforcement members212to the bridge rail202. The first and second bridge reinforcement members210and212are the same as previously described for the embodiment shown inFIG. 2.

It will be noted that, for the bridge rail202a, the first reinforcement member210is under compression and the two second reinforcement members212are under tension. Conversely, the first reinforcement member210on the second bridge rail202bis under tension and the second reinforcement members212on the second bridge rail202bare under compression, in similar manner to the single rail bridge14shown inFIG. 2. It will be understood that in situations during use of the crane200, the manipulator204may be positioned on the other side of the centerline206and so the tension and compression in the members of the reinforcement structures208on the two bridge rails202aand202bwill be reversed.

Referring toFIG. 13, the first reinforcement member210may be mounted to the bridge rail202in any suitable way, such as by use of one or more threaded fasteners220that pass through support flanges222at bottom ends224aand224bof the struts210aand210b, respectively, of the first reinforcement member210. The threaded fasteners220pass through a slot226between first and second reinforcement support flanges228on the bridge rail202, and pass into a threaded aperture in clamping plates230so that the support flanges222and the clamping plates230together clamp the flanges228on the bridge rail202.

Referring toFIG. 13still, an upper block234of the first reinforcement member210comprises mounting posts218thereon for receiving and retaining first ends216of the second reinforcement members212. The first ends216of the second reinforcement members212may comprise apertures within which the mounting posts218are seated.

The upper block234may be connected to the main bodies shown at236aand236bof struts210aand210b, respectively, of the first reinforcement member210by retaining pins215, for example threaded fasteners such as bolt and nut fasteners. The struts210aand210bmay be mounted on respective support flanges222with pins217, for example threaded fasteners such as bolt and nut fasteners, that pass through lower ends of the struts210aand210band through respective mounting blocks219fixedly attached to the support flanges222. In a similar manner as described previously, the threaded fasteners220, retaining pins215and pins217may be loosened to permit movement of the lower ends of the struts210aand210balong the bridge rail202.

Referring toFIG. 14, each second reinforcement member212has a second end238that extends into a bracket receiving aperture240in one of the brackets214. A laterally extending second end retaining pin242extends laterally through the bracket214and through the second end238of the second reinforcement member212. The pin242may be any suitable type of pin, such as a spring pin.

Referring toFIG. 14A, each bracket214may connect to the bridge rail202by means of mechanical fasteners which pass vertically through the bracket214, through the slot226between the upper flanges228on the bridge rail202, and into a threaded aperture in a clamping plate244so as to clamp the flanges228.

As can be seen inFIG. 14A, the bridge rails202may each have a similar profile to the bridge rail24. The bridge rails202may have any suitable profile, such as any of the profiles shown inFIG. 3andFIG. 7. The bridge rails202may thus have track flanges245, which are similar to the track flanges32and which together define a track.

Referring toFIG. 11andFIG. 15, one or more X-bracing structures246may be provided between the first and second bridge rails202aand202bso as to structural connect them. Each X-bracing structure246may be made up of first and second cross members247, shown individually at247aand247b. Each cross member246may be connected at its ends to the bridge rails202by means of threaded fasteners and clamping plates at shown at248and250inFIG. 15. The cross members247aand247bare also connected to each other at their respective middles by pin connection251.

Referring toFIG. 11, each of the bridge rails202has a rolling structure252at each end that may be similar to the rolling structure60(FIG. 10).

It will be noted that the reinforcement structures35and208can easily be retrofitted to existing bridge rails24,202in an existing overhead crane10,200, 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 structure35,208without the need for welding elements to the rails24,202, without drilling through the rails24,202and without requiring an inordinate number of fasteners.

It is optionally possible to provide the retaining pins215and242on a single rail bridge, such as the bridge14, for use in situations where the single rail bridge14will be subjected to upward forces from the lifting member.

The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.