Jib crane

A jib crane which can prevent an unexpected movement of a burden and can sufficiently ensure the safety of a burden handling work is disclosed. The jib crane has hoisting wire ropes for lifting and landing a hook, derricking wire ropes for derricking operation of a jib, and a conversion device for fixing tips of the wire ropes to a revolving frame of a revolving table. The conversion device has a V-shaped link pivotally supported on a bearing bracket via a pivot pin. The tips of the wire ropes are connected to paired link arms of the V-shaped link.

TECHNICAL FIELD

The present invention relates to a jib crane for use in transportation of a heavy burden.

BACKGROUND OF THE INVENTION

Some jib cranes are arranged, for example, in shipbuilding yards for use in transportation of heavy burdens. This kind of jib crane comprises an upper revolving table and a jib protruding from the revolving table (see, for example, Patent Literature 1 showing a climbing crane as jib crane). The jib has a base end pivoted on the revolving table and may be derricked through lead-in or pull-out of derricking wire ropes. A hanger such as a hook is suspended from a tip of the jib via hoisting wire ropes and a work of lifting and landing a burden hooked to the hanger, i.e., a burden handling work is carried out by reeling and unreeling the hoisting wire rope.[Patent Literature 1] JP2001-130870A

SUMMARY OF INVENTION

Technical Problems

During the burden handling work, load of the burden is applied through the hoisting wire ropes to the jib which is then inevitably bent by the load. Thus, lift-off of the burden causes the tip of the jib to tilt forward due to the bending of the jib or other structure. When the jib is held at a predetermined upward derricking angle to the horizontal, such forward tilting causes a position of the hanged burden after the lift-off of the burden to be displaced forward of the jib relative to a plumb line of the burden in its lift-off position.

Contrary, when the burden is landed, the load applied to the jib is released to release the bending of the jib so that the tip of the jib is flipped up to its original position. As a result, the burden on its landed position is dragged toward the base end of the jib through the hoisting wire rope and the hanger as the tip of the jib is flipped up.

The above-mentioned positional displacement of the hanged burden and dragging of the burden greatly and adversely affect on centering of a heavy burden during positioning of the burden mainly in a shipbuilding yard or the like, which may not only bring about deterioration in centering efficiency but also is undesirable from viewpoint of securing the safety in the work.

The invention was made in view of the above and has its object to provide a jib crane which can attain improvement in work efficiency and can sufficiently ensure the safety in the work.

Solution to Problems

In order to attain the above object, in a jib crane comprising a jib pivoted on a revolving table for derricking motion, a hoisting device having a hoisting drum on said revolving table with hoisting wire ropes being wound around the hoisting drum, a hanger being suspended by the hoisting wire ropes unreeled from said hoisting drum via a tip of the jib while tips of the hoisting wire ropes are fixed to the revolving table, the hanger being lifted and lowered by reeling and unreeling the hoisting wire ropes to and from the hoisting drum, and a derricking device having a derricking drum on the revolving table with derricking wire ropes being wound around the derricking drum, said jib being suspended by the derricking wire ropes unreeled from the derricking drum while tips of the derricking wire ropes are fixed to the revolving table, the jib being derricked by lead-in and pull-out of the derricking wire ropes to and from the derricking drum, the invention is directed to the jib crane comprising a conversion device on the revolving table for converting load applied to the hoisting wire ropes into lead-in of the derricking wire ropes during a burden handling work.

Specifically, the conversion device includes a link with a base end of said link being pivotally supported on the revolving table and tip ends of said link being connected to the tips of the hoisting and derricking wire ropes, respectively, said link being pivotable in one direction when load is transmitted by the hoisting wire ropes, and a stopper adjacent to the revolving table for preventing the link to be pivoted in the other direction upon contact with the link.

According to the above-mentioned jib crane, during the burden handling work, load of the burden applied to the hoisting wire ropes causes the conversion device, more specifically the link, to be pivoted in the one direction. This pivotal movement pulls the derricking wire ropes to lift the jib upwardly in a lead-in direction by a certain angle. As a result, the derricking angle of the jib is increased so that, even if forward tilting of a tip of the jib is caused due to bending of the jib and other structure, displacement in suspended position due to such forward tilting is compensated to position the suspended and lift-off positions of the burden on a same plumb line.

Contrary, when the burden is landed, the load applied to the hoisting wire ropes is relieved to eliminated the forward tilting of the jib, the link being pivoted reversely until it abuts on the stopper, which causes the jib to be lowered by said angle. Thus, even if the tip of the jib is flipped up into the original state, the burden is not dragged from its landed position.

Preferably, the derricking wire ropes suspend a longitudinally intermediate portion of the jib, which can suppress the lowering of the tip of the jib due to tilting of the jib.

Advantageous Effects of Invention

According to a an embodiment of the invention, during a burden handling work, even if the tip of the jib is forwardly tilted due to its bending or such forward tilting is relieved, the suspended or landed position of the burden is not undesirably displaced. As a result, even in a case of heavy burden in a shipbuilding work, not only centering of the burden is facilitated to attain substantial improvement in centering efficiency, but also the burden handling work is made favorable from a viewpoint of ensuring safety.

REFERENCE SIGNS LIST

DESCRIPTION OF EMBODIMENT

FIG. 1shows a traveling jib crane having a traveling body2. The traveling body2has a plurality of legs4resting via wheels6on paired rails8. Thus, the traveling body2can travel along the rails8.

Constructed on the traveling body2is a portal frame10on which arranged is a revolving table12revolvable in horizontal plane. The revolving table12has a front portion from which a jib14extends, the jib14having a base end derrickably supported by the table12via a pivot15.

Arranged on the revolving table12are an upper frame or so-called A frame16, a hoisting drum18of a hoisting device and a derricking drum20of a derricking device. Wound around the hoisting drum18are paired hoisting wire ropes22; and wound around the derricking drum20are paired derricking wire ropes24. Base ends of the hoisting and derricking wire ropes22and24are fixed to the corresponding drums18and20, respectively.

Arranged on an upper end of the upper frame16are a row of top sheaves26for the hoisting wire ropes22as well as a row of top sheaves28for the derricking wire ropes24. Arranged on a tip of the jib14are a row of tip sheaves30for the hoisting wire ropes22; and arranged on a longitudinally intermediate portion of the jib14are a row of suspending sheaves32for the derricking wire ropes24.

As is clear fromFIG. 2, the hoisting wire ropes22from the drum18are guided via the top sheave row26to the tip sheave row30, are passed over a row of lifting sheaves36with a hook (hanger)34, are reciprocatingly passed for a plurality of times between the tip and top sheave rows30and26, are returned from the top sheave row26toward the revolving table12and are fixed at their tips via a conversion device38to the revolving table12. Thus, as the hoisting wire ropes22are reeled and unreeled in accordance with the rotation of the hoisting drum18, the hook34is lifted and lowered.

As is clear fromFIG. 3, the derricking wire ropes24from the drum20are guided via the top sheave row28to the suspending sheave row32, are reciprocatingly passed for a plurality of times between the top and suspending sheave rows28and32, are returned from the top sheave row28toward the revolving table12and are fixed at their tips via the conversion device38to the revolving table12. Thus, as the derricking wire ropes24are reeled and unreeled in accordance with the rotation of the derricking drum20, the jib14can be pivoted at its base end about the pivot15, i.e., can be derricked.

FIGS. 4 and 5specifically show vicinities of the tips of the hoisting and derricking wire ropes22and24.

The respective hoisting wire ropes22are connected at their tips to connecting fittings40, respectively, which in turn are connected to a hoisting equalizer42. As is clear fromFIG. 5(a), the hoisting equalizer42is substantially U-shaped and comprises a base44in the form of downwardly directed triangle and paired arms46aand46bextends upward from opposite upper ends of the base44. The respective arms46have base ends pivotally connected to the base44and tip ends connected to the tips of the hoisting wire ropes22through the connecting fittings40.

More specifically, one46aof the paired arms46aand46bis divided longitudinally into parts, the divided parts being connected together via a load cell48which is a load sensor for detection of load applied to the hoisting wire rope22.

The base44has a lower portion from which a connecting fitting50pivotally extends, the connecting fitting50being connected to the above-mentioned conversion device38.

As shown inFIG. 5(b), the paired derricking wire ropes24are connected at their tips to the conversion device38via connecting fittings52, a derricking equalizer54and a connecting fitting55which are similar to the above-mentioned connecting fittings40, hoisting equalizer42and connecting fitting50, respectively.

Next, the conversion device38will be detailed.

As shown inFIG. 4, the conversion device38comprises a bearing bracket56arranged on and fixed to a revolving frame58of the revolving table12. Pivotally supported on the bearing bracket56via a pivot pin60is a base end of a V-shaped link62which has opposite link arms62aand62bwith tip ends to which in turn pivotally connected are the connecting fittings50and55of the hoisting and derricking equalizers42and54, respectively. Thus, the tips of the hoisting and derricking wire ropes22and24are fixed via the V-shaped link62to the revolving table12.

Mounted on the bearing bracket56is a stopper64on which abuts the link arm62aof the link62when the link62is in a condition shown inFIG. 4so as to prevent the pivotal movement of the link62in a clockwise direction inFIG. 4. In other words, tension always applied to the derricking wire ropes24, which suspend the jib14, urges the link62to be pivoted clockwise inFIG. 4so that the link62is held in a condition where the link arm62aadjacent to the hoisting wire rope22abuts on the stopper64.

InFIG. 4, reference numeral66denotes an anti-vibration fitting for the hoisting equalizer42and arranged on the revolving frame58.

Next, an operation of the above-mentioned conversion device38will be explained in conjunction withFIG. 6.

In a burden handling work by the jib crane, the jib14receives load of a burden W through the hoisting wire ropes22so that the jib14is bent due to the load, the tip end of the jib being lowered as shown in chain double-dashed line inFIG. 6. At this time, the jib14has an upwardly inclined derricking angle θ and, if the above-mentioned conversion device38were not provided, the suspended position of the burden W would be displaced into position shown in chain double-dashed line forwardly of the jib14relative to the plumb line of the burden W on its lift-off position shown in solid lines.

However, the load of the burden W contributes to the tension of the hoisting wire ropes22so that, when the tension of the ropes22overcomes the tension applied to the derricking wire ropes24, the link62is pivoted in counterclockwise as shown in chain dashed line inFIG. 6. Such pivotal movement of the link62lengthens path lengths of the derricking wire ropes24between their tips and the top sheave row28so that path lengths of the same between the top and suspending sheave rows28and32are decreased in compensation therefor. As a result, the jib14is raised by the derricking wire ropes24as shown in chain dashed line and the derricking angle θ is increased.

Such increase in derricking angle θ causes the tip of the jib14to be displaced toward the base end of the jib, so that the displacement of the burden W due to the above-mentioned lowering is compensated to maintain the suspended position of the burden W at the plumb line on the lift-off position.

More specifically, in the V-shaped link62, effective length of the link arm62bis decided in view of the above-mentioned bending amount of the jib14, i.e., the lowered amount of its tip end.

On the other hand, when the burden W is landed, the tension applied to the hoisting wire ropes22is reduced so that the V-shaped link62is returned clockwise inFIG. 6due to the tension of the derricking wire ropes24while the lowering at the tip end of the jib14is released and the tip of the jib is flipped up to its original condition. The returning of the V-shaped link62is stopped when the link arm62aabuts on the stopper64.

The returning of the V-shaped link62tilts the jib14and decreases its derricking angle θ so that the lowering and flip-up of the tip of the jib14get balanced out. As a result, no dragging of the burden W due to the above-mentioned flip-up is caused at the landed position of the burden W, so that the burden W can be accurately positioned at the targeted lift-down position.

As a result, when the jib crane is used for transportation and positioning of a heavy burden during a shipbuilding work, centering of the heavy burden is facilitated to attain substantial improvement in centering efficiency. Moreover, in the burden handling work, no unexpected movement of the burden W is caused so that safety in the work can be sufficiently ensured.

Moreover, the derricking wire ropes24suspend not a tip but an intermediate portion of the jib14, so that the lowering of the tip of the jib14can be suppressed to greatly contribute to reduction in size of the above-mentioned conversion device38.

It is to be understood that the invention is not limited to the above-mentioned embodiment and that various changes and modifications may be made.

For example, the invention is applicable not only to a traveling jib crane but also any other type of jib crane such as climbing crane.