The invention is related to an offshore lifting system for offshore hoisting and lifting operations. The system comprises at least a first and a second lifting element, and wherein the second lifting element is moveable relative to the first lifting element by means of at least one pivot system. The pivot system comprises at least one gear section and at least one pinion. In particular, the invention relates to a lifting system that includes a compact and reliable pivot system.

The present invention relates to offshore lifting systems such as offshore cranes. In particular the invention relates to cranes for offshore hoisting and lifting operations. Offshore lifting cranes are often constructed large in scale and heavy in weight in order to satisfy the need to lift heavy weights. Larger and heavier cranes require larger and heavier hydraulic cylinders to operate the booms, and larger and more powerful cylinders at connection points. Furthermore, big and heavy cranes require more space and demanding high energy consumption during transit and in operation.

Heavy cranes put limitations to the maximum allowable payload, and also reduces the stability of the offshore structure, such as a vessel or a platform, on which the crane is placed. Standards for cranes mounted on ships or offshore platforms are somewhat stricter than traditional land-based cranes, because of the dynamic load on the crane due to vessel motion. Additionally, the stability of the vessel or platform must be considered.

There are three major considerations in the design of cranes. First, the crane must be able to lift the weight of the load; second, the crane must not topple; third, the crane must not rupture.

Fixed cranes are exchanging mobility for the ability to carry greater loads and reach greater heights due to increased stability, these types of cranes are characterized by the fact that their main structure does not move during the period of use. However, many fixed cranes can still be assembled and disassembled. The structures basically are fixed in one place allowing less range covered during use.

Knuckle-boom cranes are known to be particularly useful in offshore environments, both because they occupy little deck space and because their low center of gravity compared to other known offshore cranes. On a knuckle-boom crane, the main boom is hinged at the middle, this creating a knuckle -boom. The luffing motion of both the main boom and the knuckle-boom is usually controlled by hydraulic cylinders. In this manner, movements of the loads can be limited as the boom tip can be kept at a limited height above the deck. Deck cranes are located on the ships and boats, these are used for cargo operations or boat unloading and retrieval where no shore unloading facilities are available. Most are diesel -hydraulic or electric -hydraulic.

A gantry crane has a hoist in a fixed machinery house or on a trolley that runs horizontally along rails, usually fitted on a single beam (mono -girder) or two beams (twin-girder). The crane frame is supported on a gantry system with equalized beams and wheels that run on the gantry rail, usually perpendicular to the trolley travel direction. These cranes come in all sizes, and some can move very heavy loads, particularly the extremely large examples used in shipyards or industrial installations. A special version is the container crane, designed for loading and unloading ship-borne containers at a port. Some gantry cranes are provided with knuckle booms and crane arms that are moveable relative to the gantry crane.

A common feature of offshore cranes or lifting systems are that they comprise a first lifting arm or boom pivotally connected to a second arm/boom or a base. The first lifting arm/boom are moveable relative to the second arm/boom or base by means of a pivot system. The pivot system can be a set of hydraulically or pneumatically operated cylinders.

A major disadvantage of the prior art cranes is the risk of spilling oil from hydraulic cylinders. Furthermore, the prior art cranes can be large in scale and has relatively complicated and costly installation processes. The large weight of the cranes requires larger vessel and limits the possibility to move the cranes from a structure to another. A further upscaling of cranes is often limited by the obtainable capacity of the hydraulic cylinders.

Publication WO 2017/082739 discloses a knuckle-boom crane comprising a main boom rotatably connected to a crane housing. A main boom luffing means in form of cylinders enables a luffing motion of the main boom relative to the crane housing. The cylinders may be of hydraulic or electric type. Furthermore, a knuckle boom is connected to the main boom and operable by tension wire ropes running through sheaves and connected to a winch. The system is complicated, and the wire ropes are exposed to wear and reduces the reliability of the crane.

The publication US 3,666,120 discloses a crane comprising a boom assembly pivotally supported on a rotatable base. A pair of axially spaced gear segments are arranged for driving the boom assembly. The gear segments are fixed to the boom assembly and driven by a drive train connected to a worm situated on the base. The worm is activated through an electrically driven motor, such that it drives the drive train for rotating the gear segments. The crane of US 3,666,120 comprises a complicated gear system. For lifting heavy items, the crane has to be constructed quite heavy in weight and the connection between the gear segment and the drive train need to take on heavy loads. The crane further has many complicated mechanical systems, thereby increasing the possibility of wear and corrosion.

Additionally, the system does not have proper redundancy in case of a failure in the gear system.

It is therefore an object of the present invention to provide a lifting system with reduced overall weight, fuel consumption and maintenance cost without reducing the operability strength of the lifting system.

It is another object of the present invention to provide a lifting system which reduces the harmful spill of oil to the environment. It is yet another object of the present invention to provide a lifting system that increases flexibility, i.e. is easy to move between different locations.

It is yet another object of the present invention to provide a lifting system has different operation modes and with reduced power consumption during operation.

It is yet another object of the present invention to provide a lifting system with increased reliability and maintains increased availability.

The invention is related to an offshore lifting system comprising a first lifting element connected to a second lifting element at a pivot connection. The second lifting element is moveable relative to the first lifting element by means of a pivot system. The pivot system comprises:

a gear section comprising an outer curvature, and

a first pinion interacting with the gear section.

The first pinion is operated by a first motor for movement of the first pinion along the outer curvature of the gear section. The gear section further comprises an inner curvature situated between the outer curvature and the pivot connection (hence, closer to the pivot connection than the outer curvature). A second pinion is operated by a second motor for movement of the second pinion along the inner curvature of the gear section.

At least a section of the outer curvature and at least a section of the inner curvature may be arranged in parallel.

The term parallel is referred to a curve extending in the same direction, equidistant at all points. According to the present invention, the first lifting element is connected to the second lifting element at a pivot connection, at which connection point, the second lifting element is pivotable relative to the first lifting element. A pivot system, comprising a gear section and a first and second pinion, is arranged for controlling the movement of the second lifting element relative to the first lifting element.

According to an embodiment of the present invention, the inner and outer curvature of the gear section comprises a plurality of teeth for interaction with corresponding plurality of teeth provided on the first and the second pinion. The pinions may be a drive gear, driven by the first and/or the second motor.

The first and the second motor may constitute one motor for driving the first and second pinions.

In a preferred embodiment of the present invention, the teeth of the respective outer and inner curvature may be arranged opposite facing, such that they are facing away from each other.

The gear section and pinion system according to the present invention may comprise a gear section (or cogwheel section) provided with cut teeth (or cogs) along the outer and inner curvature. The teeth of the gear section mesh with another toothed part provided on the pinions, such that a torque is transmitted from the pinions to the gear section when the pinions are rotated. The teeth of the two meshing gears/pinion may have the same shape and size. At least one pinion may mesh with a curved toothed part on the gear section. Preferably, the curvature has a shape of a section of a circle.

An advantage of the gear and pinion system of the present invention, is that the teeth prevent slippage, allowing the system to take up more power and provide additional safety and reliability. According to an embodiment of the invention, the meshing teeth of the gear section and the at least one pinion may have different shapes, appropriate teeth shapes can be found in prior art gear systems, such as in; spur gears, helical gears, bevel gears, hypoid gears, crown gears, worm gears, and even non-circular gears. Such gears and their advantages and disadvantages are already known in prior art and will not be discussed further in this application.

The pivot system of the present invention comprises a gear section and a first and a second pinion. Wherein the gear section is connected to any one of; the first lifting element or the second lifting element, and wherein the first and the second pinion are connected to the corresponding first lifting element or second lifting element. Hence, the gear section and the pinions are situated on their respective first or second lifting element for relative movement between the gear section and the pinions.

In one embodiment, the gear section may be fixedly mounted to the first lifting element and the first and the second pinions are mounted to the second lifting element. The first pinion and the second pinion are moveable along their respective outer and inner curvature provided on the gear section such that the second lifting element is moved relative to the first lifting element.

In another embodiment, the first pinion and the second pinion may be mounted to the first lifting element and the gear section fixedly mounted to the second lifting element. The gear section rotates when the pinions are operated along their respective outer and inner curvature, and thereby allowing the second lifting element to rotate relative to the first lifting element.

Thus, the gear section of the pivot system may be mounted to any one of the first or the second lifting element.

In an embodiment of the present invention, the gear section may be incorporated into the first or second lifting element such hat the lifting element and the gear section is provided in one piece.

Preferably, the first lifting element may be at least one of: a crane arm, a base, a pedestal, a machine housing, an offshore structure, a deck surface.

Furthermore, the at least one second lifting element may be at least one of: a crane arm, a boom, a jib, a davit arm, an A-frame, a gantry crane. The at least one second element may be defined a lifting element that can move or rotate relative to a first lifting element.

The first and second pinions, according to the present invention, is transmitting rotational motion to the gear section. The size of the pinions, which may be smaller than the gear section, will rotate faster than the gear section. Since the larger gear section is rotating less quickly, its torque is proportionally greater.

According to the present invention, the first pinion and the second pinion may have different size (different diameters). Accordingly, the teeth of the inner and outer curvature may have corresponding different sizes, such that the pinions can be driven along their respective inner and outer curvature at different speed. The speed of the pinions can also be controlled individually by means of the first and/or second motor. According to another embodiment of the present invention, the first pinion and the second pinion may be coupled to/from their respective outer and inner curvature independent of each other. This embodiment has several advantages:

The first pinion and the second pinion can be driven simultaneously to increase the strength of the lifting system.

The inner or outer curvature can be driven at different speed, independently of each other.

If failure should occur at inner or outer curvature, at least one remaining curvature can still operate, providing the lifting system with redundancy.

This appropriate solution has the advantage that in case of a failure in a pinion or in a curvature of the gear section, the other pinions and curvature can still operate. Furthermore, the appropriate simultaneous operation of the pinions on the first and second curvature, provides increased strength and thereby allowing increased lifting weight.

The inner curvature may be arranged in an opening in the gear section. The inner curvature may be situated opposite and in parallel to the outer curvature.

The first pinion and the second pinion are operated by a first and second motor and arranged to move along to their respective outer and inner curvature provided on the gear section. The driving of the first pinion and the second pinion, may be controlled by one or several motors. Which at least one motor, drives at least one pinion along a curvature of the gear section. Hence, the at least one motor may comprise a first and a second motor, and wherein the first motor is arranged for moving the first pinion along the outer curvature, and the second motor is arranged for moving the second pinion along the inner curvature. Hence, first pinion and the second pinion may be operated by respective first and second electric motors. The electric motors may be driven independently of each other, such that the first pinion and the second pinion may cooperate or operate independently.

According to the present invention, the first and second motor may be at least any one of; an electric motor, a hydraulic motor or a pneumatic motor. In a preferred embodiment according to the present invention, the first and the second motor is an electric motor.

In another preferred embodiment of the present invention, the first and the second lifting element may be made from composite material.

In yet, another preferred embodiment, the at least one pivot system is made from composite material. The present invention is related to an offshore lifting system such as a crane, but not limited to, intended for deploying loads in offshore conditions from a vessel to another vessel and/or retrieving load from another vessel back to own vessel and/or deploying a load from a vessel to the seabed and/or retrieving a load from the seabed back to the vessel.

In a preferred embodiment as described above, the main load carrying structural members may be manufactured in composite material such as, but not limited to, epoxy reinforced fiberglass or carbon fiber in order to reduce weight, power consumption and maintenance cost and of the construction without reducing strength operability of the lifting system.

The use of composite material to construct the load carrying members of a lifting system will reduce the installed weight on an ocean-going vessel, leading to less fuel consumption in transit.

The use of a gear section and pinions to move the crane elements relative to each other will remove the need for hydraulic ram cylinders and reduce the possibility of harmful spill to the environment from an ocean-going vessel.

The use of electrical motors and drive systems will reduce the power consumption in operation of the lifting system, leading to reduces fuel consumption for the ocean-going vessel.

The description above, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the preferred embodiment which should be read in

conjunction with the accompanying drawings in which:

Fig. 1 shows a crane with a main boom and a knuckle boom, the pivot

system of the present invention is situated between the base and the main boom, and between the main boom and the knuckle boom.

Fig. 2 shows the pivot system where the gear section is mounted on a deck surface and the first and second pinions are provided on the second element.

Fig. 3 shows an A-frame where each pivot system comprises of two gear sections provided at each pivot connection of the A-frame. Figure 1 shows an offshore lifting system 100 of the present invention in form of an offshore crane 100. The crane 100 comprises a base 101, a main boom 102, 111 and a knuckle boom 112. The crane 100 has two pivot connections 109, 119 arranged between respective:

the base 101 and the main boom 102, in the first pivot connection 109. the main boom 111 and the knuckle boom 112, in the second pivot connection 119.

A pivot system 103,113 is arranged at respective first connection 109 and second connection 119. According to the invention, the main boom 102 of the first pivot connection 109 is defined as the second lifting element 102. Wherein in the second pivot connection 119, the main boom 111 is defined as the first lifting element 101.

The second lifting element 102,112 is moveable relative to the first lifting element 101, 111 by means of the pivot system 103,113 arranged at the connection between the first 101,111 and the second lifting element 102,112.

At the first pivot connection 109, the pivot system 103 of figure 1 comprises a gear section 104 fixedly mounted to the main boom 102. Three first pinions 105 are fixedly arranged on the base 101 and adapted for interacting with an outer curvature

106 provided on the gear section 104. Furthermore, three second pinions 108 are fixedly arranged on the base 101 and adapted for interacting with an inner curvature

107 provided on the gear section 104. The inner curvature 107 is located inside (closer to the pivot connection 109) and in parallel with the outer curvature 106. In other words, the inner curvature is arranged on the gear section 104 between the outer curvature 106 and the pivot connection 109. Figure 1 shows the first and second pinions 105,108 mounted to an upper part of the base 101. The upper part of the base 101 in figure 1 are made transparent to easier show the cooperation between the curves 106,107 and the pinions 105,108.

The first and second pinions 105, 108 may be driven by one common electric motor (not shown) or they may be driven independently by separate electric motors (not shown).

According to the invention the outer and inner curvature 106,107 of the gear section 104 may comprise a plurality of teeth 113 (not shown) meshing with a plurality of teeth 112 (not shown) provided on the outer surface of the three first pinions 105 and the three second pinions 108.

The outer 106 and inner curvature 107 of the gear section 103 may comprise teeth that meshes with another toothed part provided on the pinions 105,108 such that a torque is transmitted from the pinions 105,108 to the gear section 104 when the pinions are rotated. When the electric motor (not shown) drives the pinions 105,108 the torque acting on the outer and the inner curvature 106,107 will turn the gear section 104 such that the main boom 102 is rotated.

The same applies to the second pivot connection 119, the torque transmitted from the first and second pinions 115,118 situated on the main boom 11 1, to the gear section 114 situated on the knuckle boom 112, will cause the knuckle boom 112 to rotate relative to the main boom 11 1. At the second pivot connection 113, the first pinion 115 comprises two pinions and the second pinion 118 comprises two pinions.

Figure 2 shows another embodiment of the present invention where the first and second pinions 105,108 may be fixedly mounted to a second lifting element 102.

The first lifting element 101 being a base, a deck floor, a structure, etc. (not shown). The gear section 104 is fixedly mounted to the first lifting element 101, such that the second lifting element 102 is moveable relative to the first lifting element 101. The first and second pinions 105,108 comprises teeth provided at their outer circumference and arranged such that they mesh with teeth provided along the outer and inner curvature 106,107 of the gear section 104. An enlarged section drawing of the cooperation between the first and second pinions 105,108 and their respective outer and inner curvature 106,107, as shown in figure 2. The enlarged drawing shows the opposite side (inner side/ back side) of the gear section 104. Furthermore, the figure 2 shows the plurality of teeth 120,121 provided on the respective outer and inner curvature, and the first and second pinions 105,108. According to figure 2, the inner and outer curvature 106,107 of the gear section 104 may comprise a plurality of teeth 121 for interaction with corresponding plurality of teeth 120 provided on the first and the second pinion 105,108. The pinions 105,108 are a drive gear, driven by the at least one motor (not shown), and made smaller than the gear section 104. In a preferred embodiment of the present invention, the teeth 121 of the respective outer and inner curvature may be arranged opposite facing, such that they are facing away from each other.

Furthermore, the plurality of first and second pinions 105,108 are driven by the electric motor (not shown) such that they can move along their respective outer and inner curvature 106,107. Since the pinions 105,106 are fixedly connected to the crane arm (second lifting element), the crane arm will pivot relative to the gear section 104.

Figure 3 show the embodiment of figure 2 arranged on an A-frame. The A frame comprises a pivot connection 109 provided at each end of a boom or a beam. Each pivot connection 109 is arranged with a pivot system 103 comprising two gear sections 104 provided at each pivot end. Each gear section 104 is fixedly mounted to the deck of a vessel (not shown), and wherein the first and second pinons 105,108 are arranged on the A-frame ends and thereby allowing the A-frame to pivot along the outer and inner curvature 106,107 of the gear section 104.