Lifting Device Provided With an Auxiliary Device for Counteracting Tipover of the Boom in Sudden Loss of Load

Provided is a lifting device with a force-absorbing base to which a boom with hoisting cable for lifting a load in substantially vertical direction is tiltably connected. The lifting device is provided with an auxiliary device for counteracting tipover of the boom in the case of sudden loss of load. The auxiliary device is connected to the base of the lifting device, provides a contact surface which is in permanent contact with a contact surface of the boom or comes into contact therewith in the case of tipover, and further comprises a drive and control system which is configured to stop the boom movement when a predetermined force between the contact surfaces is exceeded as a result of the boom tipping over. The described auxiliary device can take an autonomous form and can be arranged on a lifting device.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a lifting device with a force-absorbing base to which a boom with hoisting cable for lifting a load in substantially vertical direction is tiltably connected, wherein the lifting device is further provided with an auxiliary device for counteracting tipover of the boom in the case of sudden loss of load, for instance due to the hoisting cable breaking. The invention likewise relates to an auxiliary device for counteracting tipover of a boom in the case of sudden loss of a load.

The invention can in principle be applied to lift any object, both on land (onshore) and at sea (offshore). The advantages of the invention however become most clearly manifest when lifting an object offshore. A typical application for instance relates to offshore placing of a foundation for a wind turbine.

Description of Related Art

A lifting device for lifting a load generally comprises a force-absorbing base of which a so-called A-frame for instance forms part and to which a boom tiltable around a horizontal axis is connected. The base is configured to transmit the forces acting on the boom to a ground surface, for instance the deck and the hull of a vessel. The pivoting connection between the base and the boom allows the boom to be tilted with a so-called luffing cable in a vertical plane between the most luffed-in position, in which the boom is positioned at a minimal angle to the vertical direction, and the most luffed-out position in which the boom is positioned at a maximum angle to the vertical direction. The operating range of the boom then lies between these two positions. Connected to the boom is a hoisting cable to which a load can be attached for the purpose of lifting the load, wherein the hoisting cable extends in a substantially vertical direction.

When lifting a load it is possible that the boom suddenly falls backward and is forced beyond the most luffed-in position. Such tipover of the boom could for instance occur in the case of sudden loss of load, for instance due to the hoisting cable breaking, or in the event of the load suddenly detaching from the hoisting cable. When the load is lifted, a force opposite to the force of gravity exerted on the load is exerted on the lifting device. This force is particularly exerted on the hoisting cable, boom and luffing cable. Compared to the two cables, the boom is relatively rigid and will not deform a great deal. Elastic energy will however be built up in the hoisting cable and the luffing cable. In the case of such so-called sudden loss of load the boom tends to ‘shoot’ away from the load due to the suddenly released elastic energy built up in the luffing cable. If the lifting device is located on a vessel and the boom protrudes transversely, for instance to starboard (SB), water ballast may be taken on on the opposite port side (PS) in order to restore equilibrium. In that case the equilibrium is disrupted in the case of a sudden loss of load and the ship will begin to roll, away from the load, in this case to PS. This has the result that the boom co-rotates around the base and is as it were luffed in further. This strengthens the tipover effect, and it is then even possible that the boom moves over its vertical equilibrium point and destroys itself. Such a situation is of course highly undesirable.

It is noted that the term ‘tipover’ is not limited to the above described movement of the boom beyond the vertical point of equilibrium. Even if the boom were not to ‘tip over’ in this way and the luffing cable instead becomes slack due to a sudden rearward movement (away from the load) of the boom, the luffing cable may afterwards come under tension again with sudden force. The luffing cable, but also the boom, can be overloaded by such a snatch load. This phenomenon is also grouped under ‘tipover’, and must also be avoided.

An object of the present invention is to provide an auxiliary device for counteracting tipover of the boom in the case of sudden loss of load, and a lifting device provided with the auxiliary device. This avoids the damage associated with tipover, or at least reduces the risk thereof.

SUMMARY OF THE INVENTION

This object is achieved by providing a lifting device with the characteristics herein. The invented lifting device comprises a force-absorbing base to which a boom with hoisting cable for lifting a load in substantially vertical direction is tiltably connected, and is further provided with an auxiliary device for counteracting tipover of the boom in the case of sudden loss of load, for instance due to the hoisting cable breaking, wherein the auxiliary device is connected to the base of the lifting device, provides a contact surface which is in contact with a contact surface of the boom or comes into contact with a contact surface of the boom in the case of tipover, and further comprises a drive and control system which is configured to stop or to block the boom movement when a predetermined force between the contact surfaces is exceeded as a result of the boom tipping over.

In an embodiment in which the contact surface of the auxiliary device is in contact with the contact surface of the boom, the boom will during normal movement of the boom exert a force on the auxiliary device which is lower than the predetermined maximum force. The contact surface of the auxiliary device is then freely co-displaceable with the movement of the boom. In the case of tipover, the force exerted on the auxiliary device will exceed the predetermined maximum force. The drive and control system will then ensure that the movement of the contact surfaces is stopped, inhibited or blocked, for instance by blocking means suitable for this purpose. This prevents the boom from tipping over.

In an embodiment in which the contact surface of the auxiliary device comes into contact with the contact surface of the boom in the case of tipover, the boom will exert substantially no force on the auxiliary device during normal movement of the boom. Because the predetermined force—which can otherwise have a different value in this embodiment than in the above described embodiment, even zero—is not exceeded, the contact surface of the auxiliary device will be freely co-displaceable with the movement of the boom, and follow the movement of the boom. In the case of tipover the boom will come into contact with the contact surface of the auxiliary device. The force exerted on the auxiliary device then exceeds the predetermined force, whereby the drive and control system will ensure that the movement of the contact surfaces is stopped, inhibited or blocked, for instance by the blocking means. This prevents the boom from tipping over.

In an embodiment of the lifting device the contact surface of the auxiliary device is in contact with the contact surface of the boom by connecting the auxiliary device, and more particularly a moving part thereof, to the boom, preferably at an outer end of this moving part.

In another embodiment of the lifting device the drive and control system is configured to hold the contact surface of the auxiliary device and the contact surface of the boom at a small mutual distance so that the boom is only capable of limited acceleration during tipover.

The invented auxiliary device is able to stop the boom immediately (or in a relatively short amount of time) following a sudden loss of load. This prevents the boom from being able to accelerate or build up kinetic energy. The auxiliary device is connected to the base in order to be able to transmit the forces caused by the rebounding of the boom to a ground surface connected to the base, such as for instance the hull of a vessel.

The lifting device can be used onshore, and further on any type of vessel, wherein the advantages of the invention become particularly manifest in use on a monohull crane vessel. The auxiliary device is further configured to stop the (accelerating) boom in positions lying between the most luffed-in and the most luffed-out position. According to the invention, it is not necessary to stop the (accelerating) boom in all positions lying between the most luffed-in and the most luffed-out position. It may suffice to provide only a part of this range, for instance from the most luffed-in position to a position halfway to the most luffed-out position.

According to an embodiment of the invention, the contact surface of the auxiliary device is held at a small mutual distance from a contact surface of the boom by a drive and control system so that the boom is only able to accelerate to limited extent during tipover. The auxiliary device is therefore not connected to the boom in this embodiment. This has the advantage that any movements—for instance torsion or bending—of the boom during normal use will not be transmitted to the auxiliary device. The auxiliary device can hereby take a relatively light form.

The small mutual distance can be selected within limits. A practical embodiment relates to a lifting device wherein the mutual distance between the two contact surfaces is kept between a minimum and a maximum distance.

In a suitable embodiment a lifting device is provided wherein the minimum distance amounts to between 1 and 10 mm and the maximum distance to between 5 and 30 mm. In normal use of the boom (so in a situation wherein no tipover is occurring) the contact surface of the auxiliary device is then held at a distance which can lie between 1 and 30 mm.

It is further advantageous to characterize the lifting device in that the mutual distance between the two contact surfaces is kept constant by the drive and control system. It is for instance possible here to control on the basis of vector distance. A further improved embodiment of the lifting device comprises a driving and control system which is configured to control the mutual distance in a horizontal direction, preferably keep it within limits, and still more preferably keep it constant.

A suitable embodiment of the invention provides a lifting device wherein the boom has two legs and the auxiliary device provides two contact surfaces which, in the case of tipover, come into contact with two corresponding contact surfaces of the boom.

In an embodiment of the invention it is further possible to characterize the lifting device in that the boom is tiltable around a tilting point and the contact surface of the boom lies at least at ⅖ of and more preferably at least halfway along the length of the boom from the tilting point. This makes it possible to limit the forces acting on the auxiliary device in the case of tipover.

In another embodiment the base of the lifting device comprises an A-frame and the auxiliary device is connected to the A-frame of the lifting device, preferably to an upper side of the A-frame.

The auxiliary device can take any suitable form, as long as it provides a contact surface for the boom and can stop the boom in case of a sudden rearward movement away from the load.

A practical embodiment relates to a lifting device wherein the auxiliary device comprises a frame to which is attached a support beam which is displaceable in horizontal direction between end positions using the drive system, wherein an end surface of the support beam forms the contact surface.

In an embodiment a particularly suitable drive system comprises a rack and pinion system comprising a gear rack driven by a pinion. An outer end of the gear rack provides the contact surface with the boom. The rack and pinion system takes a form such that it is able to absorb the forces acting on the auxiliary device by the accelerating boom in the case of tipover, so that the movement of the boom is counteracted.

In a suitable embodiment the lifting device has the feature that the pinion stops the boom movement through the action of blocking means, for instance a brake acting on the pinion, when a predetermined maximum torque as a result of tipover of the boom is exceeded. The pinion can for instance be driven by an electric drive, for instance an electric motor. If the drive torque exceeds a predetermined torque (which is derived from the predetermined force) in the case of tipover, a brake on the electric drive is activated so that this drive is stopped and blocked. A suitable brake can for instance comprise a number of plates which are held apart with an electromagnet. Activation of the brake turns off the electromagnet, whereby springs ‘slam’ the plates against each other. It will be apparent that there are multiple options and that the invention is not limited to this specific embodiment.

A rack and pinion system is per se known and is for instance used in jack-up platforms, particularly for moving the legs of such a jack-up platform up and downward. A rack and pinion system is able to transmit relatively great forces.

In order to be able to adjust the mutual distance between the contact surfaces automatically the lifting device is provided in an embodiment with a control system comprising measuring means for measuring the mutual distance between the two contact surfaces. Any measuring means suitable for this purpose can in principle be applied. The measuring means preferably comprise optical measuring means.

In an embodiment the measuring means are provided at the position of the contact surface of the auxiliary device.

The auxiliary device as provided on a lifting device can be integrated with the lifting device. According to another aspect of the invention however, an auxiliary device is provided which is autonomous and can be placed on a lifting device. Such an auxiliary device for counteracting tipover of a boom in the case of sudden loss of a load can be connected to the base of the lifting device, provides a contact surface which comes into contact with a contact surface of the boom in the case of tipover, and further comprises a drive and control system which is configured to hold the contact surface of the auxiliary device and the contact surface of the boom at a small mutual distance so that the boom is only capable of limited acceleration during tipover.

Possible embodiments of the auxiliary device have already been described at length above, and a reference to this description will suffice hereinbelow.

In the case the auxiliary device is applied in combination with a lifting device for lifting a load at sea, such as for instance components of a wind turbine, work preferably takes place from a (floating) vessel, or from a jack-up platform, which provides more stability.

DESCRIPTION OF THE INVENTION

The same or similar components are designated in the figures with the same reference numerals.

FIG.1shows a lifting device1according to the invention. This embodiment consists of, among other things, a force-absorbing base, itself consisting of a bottom frame11, and an A-frame12. A boom10is arranged tiltably on the force-absorbing base. A luffing cable13is further arranged from roughly the height of bottom frame11, over an upper outer end of A-frame12and at least to an upper outer end14of boom10for the purpose of lifting a load in substantially vertical direction. Luffing cable13may also be tensioned along other paths. Lifting device1is optionally also rotatable in that bottom frame11is a rotatable bottom frame or because bottom frame11is arranged on another rotatable element.

Such a lifting device is susceptible to tipover, which occurs in the case of sudden loss of load. This can for instance occur when the hoisting cable breaks, when a hook or other connecting means connecting the hoisting cable to a load breaks, or when the load itself partially or wholly collapses.

Tipover includes any undesired movement of boom10as a result of the release of tension built up in boom10. In the case of severe tipover there is a risk that boom10ends up in a fully upright position and that remaining momentum tilts the whole or a part of boom10beyond this point, after which the part of boom10tilted beyond this upright point will fall backward. This is also referred to as complete tipover. In the case of less severe but nevertheless serious tipover there is a risk that boom10becomes only partially more upright and that luffing cable13thereby becomes slack. When boom10then falls back forward, tension will return to luffing cable13with sudden force. This is also referred to as a snatch load. Just as complete tipover, snatch load has disastrous consequences.

FIG.1therefore further shows that lifting device1is provided with an auxiliary device3which in this embodiment is arranged at an upper outer end of A-frame12. It is also possible to mount auxiliary device3lower on A-frame12or on a different part of the force-absorbing base. Auxiliary device3consists particularly of, among other things, frame31, on which a rack and pinion system32and an orienting device34are arranged. In this embodiment rack and pinion system32and orienting device34form the drive and control system, and in other embodiments the drive and control system can also consist of different components. A support beam30is arranged in each rack and pinion system32. The outer end of support beam30which is directed toward boom10provides a contact surface33. Support beam30can be displaced substantially in horizontal direction between end positions by the drive and control system, in this embodiment by rack and pinion system32.

A corresponding number of contact surfaces33′ can be designated on boom10, this at positions where contact surface33comes into contact with boom10in the case of sudden loss of load.

In order to prevent boom10from gaining momentum during tipover, i.e. to prevent boom10from accelerating too much, the distance between contact surfaces33,33′ is kept small. In this embodiment in that the drive system is able to displace contact surface33.

As soon as contact surfaces33,33′ come into contact with each other, part of the momentum of boom10is absorbed by auxiliary device3. This part is proportionate to the portion of boom10which is situated below contact surface33′. A remaining part of the momentum of boom10which is not absorbed by contact surface33strains the integrity of boom10. If the remaining momentum turns out to be too much for the integrity of boom10despite auxiliary device3, boom10may still tip over. It is therefore preferred that contact surface33′ is situated as high up as possible on boom10. In specific embodiments these contact surfaces on boom10are thus located at at least ⅖ of boom10, and preferably at least halfway along the height of boom10.

Orienting device34controls the angle of orientation of support beam30relative to boom10from frame31. Orienting support beam30in this way enables contact surface33′ to be made independent of the angle of tilt of boom10, which has the advantage that, if it is desired to reinforce the contact surface on boom10, only a small part of boom10need be reinforced. A further advantage of orienting contact surface33relative to boom10in this way is that, when contact surfaces33,33′ come into contact with each other, this surface is immediately as large as possible—or, in other words, that contact surfaces33,33′ come into contact with each other in the most frontal way possible. This is desirable since, if support beam30were to come into contact with boom10at an angle, it could absorb less of the momentum of boom10and/or do undesirable damage to boom10.

The shown embodiment of auxiliary device3comprises two contact surfaces33. It is also possible to provide only one, or three or more contact surfaces. The number of desired contact surfaces is for instance determined on the basis of the number of legs of boom10. In the shown embodiment boom10has two, although it is also possible for boom10to consist of only one leg.

In the shown embodiment the base is provided with A-frame12. The figure shows two slightly inclining posts and a number of beams connecting the posts. The A-frame is further optionally provided with two rear legs extending further rearward, down from the top part of A-frame12. Further frame forms which fulfil this function can also be provided.

FIG.2shows a detail of lifting device1, once again showing boom10, A-frame12and luffing cable13. This figure further shows the construction of frame31, on which two support beams30rest in this case. For each support beam frame31is provided with a horizontal leg31A and a diagonal leg31B, wherein these legs are attached to each other at a protruding outer end31D and, at an outer end31C,31E lying opposite, are both connected to A-frame12.

FIGS.1and2together show that this embodiment of lifting device1is suitable for lifting a load on a first side thereof. In this embodiment boom10is arranged on the base so as to be tiltable toward this first side of lifting device1. As seen from boom10, the side toward which it can tilt is also a first side for which boom10is configured to lift. When no auxiliary device3is provided, boom10will accelerate in a direction opposite to the direction in which boom10can tilt when a load is released suddenly.

In this embodiment auxiliary device3is therefore preferably arranged on a second side of boom10, lying opposite the first side, and auxiliary device3, particularly contact surface33, thereby lies in a path which would be travelled by boom10in the case of sudden loss of load.

FIG.3shows a schematic top view of a vessel2on which lifting device1according to the invention is provided. In this embodiment lifting device1can also be rotated. In this embodiment boom10is therefore configured to lift a load in the area extending from an inner radius40—wherein boom10is positioned as upright as possible—and an outer radius41—wherein boom10is tilted forward as far as possible. Auxiliary device3makes it possible to avoid tipover of boom10in sudden loss of load during lifting of this load within a low-risk area42. As indicated above, it is possible for boom10to be configured to tilt beyond the point where auxiliary device3can prevent tipover, this leaving an area43where the risk is as usual.

FIGS.4A-4Cshow side views of lifting device1as described above with reference toFIGS.1and2. In particular,FIGS.4A-Conce again show boom10, A-frame12and auxiliary device3, wherein this embodiment of auxiliary device3once again consists of frame31, drive and control system32,34and support beam30comprising contact surface33.FIGS.5A-Cshow details of these side views, wherein the figures with the same letter designation correspond to each other.

Of the shown side views, boom10has the greatest outreach inFIG.4A. In this case auxiliary device3can no longer keep the distance between the contact surfaces small when boom10tilt beyond this first angle of tilt. The effectiveness with which auxiliary device3can counteract tipover of boom10will therefore decrease proportionally to how far boom10tilts beyond this angle. A second angle of tilt can therefore be designated, for which it is the case that when boom tilts beyond it, auxiliary device3can no longer prevent boom10from tipping over in the case that the boom experiences sudden loss of load.

FIG.5Ashows in more detail that, in order to keep the distance between contact surface33and the opposite contact surface of boom10small, support beam30is extended to an extreme position. In this case orienting system34has oriented support beam30downward at the greatest possible angle.

InFIG.4Bboom10has a smaller outreach than inFIG.4A. In a preferred embodiment the mutual distance between the two contact surfaces is kept constant at all times while boom10is being adjusted. For instance when boom10is being adjusted from the angle of tilt as shown inFIG.4Ato a smaller angle of tilt as shown inFIG.3B.

In order to realize this, lifting device1can be provided with measuring means for measuring the mutual distance between the two contact surfaces. Such measuring means can for instance comprise optical measuring means, which can particularly be arranged on frame31or on support beams30. From frame31, an absolute angle of tilt of boom10can be measured, and it is possible to estimate how far support beam30must protrude in order to keep the mutual distance between the contact surfaces small. From support beam30, a relative distance between boom10and the measuring means can be measured. If these measuring means are arranged on support beam30in fixed manner then the distance between contact surface33and boom10can also be derived, and thus be kept constant by having the drive and control systems32controlled by the measuring means displace support beams30.

FIG.5Bshows in more detail that support beam30has been co-displaced with boom10in order to keep the distance between contact surface33and the opposite contact surface of boom10small. The angle of orientation of support beam30relative to boom10has been reduced by orienting system34.

Of the shown side views, boom10has the smallest outreach inFIG.4C. In each of these embodiments the mutual distance between the two contact surfaces is kept between a minimum and maximum distance. The minimum distance for instance amounts to between 1 and 5 mm and the maximum distance for instance amounts to between 5 and 10 mm. This mutual distance relates mainly to the mutual distance in horizontal direction.

FIG.5Cshows in more detail that support beam30has once again been co-displaced with boom10by drive and control system32,34in order to keep the distance between contact surface33and the opposite contact surface of boom10small. The angle of orientation of support beam30relative to boom10has also been reduced, and support beam30is substantially horizontal in this position.

FIG.6shows a cross-section of an embodiment of auxiliary device3according to the invention. Once again, lifting device1comprises boom10and, as part of the force-absorbing base, A-frame12, and auxiliary device3. In this embodiment rack and pinion system32consists of a pinion37and a gear rack36arranged on support beam30. When pinion37rotates, support beam30is displaced in a desired direction via gear rack36. As stated above, this is done in order to keep the distance between contact surfaces33,33′ small.

In the case of tipover it is however desirable for support beam30not to move, or hardly so, relative to frame31connected to the force-absorbing base. In a preferred embodiment rack and pinion system32is therefore provided with blocking means which counteract any movement of support beam30relative to horizontal leg31A in the case of tipover. It should also be appreciated that in this embodiment horizontal leg31A takes a heavier form than diagonal leg31B, so that the risk of horizontal leg31A collapsing when contact surfaces33,33′ come into contact is minimized.

The blocking means can for instance block movement of support beam30as soon as support beam30is no longer being moved, i.e. when boom10has a constant angle of tilt. In this case support beam30is preventatively blocked, and will indeed be blocked more frequently in the case of tipover. The angle of tilt of boom10is however often not constant; also for reasons other than boom10being tilted by lifting device1. In the case that boom10tilts or twists slightly, for instance due to wind forces, it is still desirable to keep the distance between contact surfaces33,33′ small. It may therefore occur that support beams30are adjusted frequently, in which case support beams30would therefore find themselves not blocked with the same frequency. In a preferred embodiment rack and pinion system32is therefore provided with force detection means configured to detect whether an external force is being exerted on support beam30, for instance in the direction from boom10, and to control the blocking device to block support beam30.