A LIFTING DEVICE AND METHODS OF OPERATING A LIFTING DEVICE

Abstract

A lifting element, such as for a vessel or vehicle, comprising a lifting element, such as an oblong element, rotated by a number of electrical motors via a rotatable, such as an eccentric, element. The eccentric element ensures that the lifting element can only be tilted within a predetermined angle area increasing the safety thereof. Multiple electric motors are used where one motor counteracts the other within an angle interval to ensure that the tilting element does not tilt undesirably.

Claims

1. A lifting device for a vessel or vehicle, the device comprising: a lifting element tiltable around a predetermined first axis, a drive arrangement for tilting the lifting element, the drive arrangement comprising: a drive rod connected to the lifting element, a rotatable element rotated by one or more electrical motors around a second axis, the drive rod being connected to the rotatable element so as to rotate around a third axis not identical to the second axis, the rotatable element being rotatable around the second axis between a first position where the distance between the second axis and the fourth axis is a minimum distance and a second position where the distance between the second axis and the fourth axis is a maximum distance, the motor(s) being configured to rotate more than 360° to bring the rotatable element from the first position to the second position.

2. The lifting device according to claim 1, wherein the first, second and third axes are at least substantially parallel.

3. The lifting device according to claim 1, wherein the drive rod is connected rotatably to the lifting element around a fourth axis not identical to any of the other axes.

4. The lifting device according to claim 1, wherein the drive rod is connected to the lifting element at a predetermined distance from the first axis.

5. A method of operating the lifting device according to claim 1, wherein the electrical motor(s) rotate(s) the rotatable element driving the drive rod, the drive rod rotating the lifting element around the first axis.

6. The method according to claim 5, wherein, during a 360 degree rotation of the rotatable element around the second axis, the distance between the second axis and the fourth axis varies between a minimum distance and a maximum distance.

7. The method according to claim 5, wherein, at a first rotational angle of the rotatable element, the lifting element is at a first extreme angle and, at a second rotational angle of the rotatable element, the lifting element is in a second, opposite, extreme angle and, for rotational angles between the first and second rotational angles of the rotatable element, the lifting element is at an angle between the first and second extreme angles.

8. The method according to claim 5, wherein the rotatable element is rotatable around the second axis between a first position where the distance between the second axis and the fourth axis is a minimum distance and a second position where the distance between the second axis and the fourth axis is a maximum distance, the motor(s) rotating more than 360° to bring the rotatable element from the first position to the second position.

9. A method of operating a lifting device, the device comprising a lifting element tiltable around a predetermined first axis and a plurality of motors for tilting the lifting element, the method comprising: determining a parameter of the lifting device and controlling the motors so that: if the parameter is within a predetermined interval, operating at least one motor to provide a torque to the lifting element in a direction opposite to a direction in which torque is applied by one or more of the other motors, if the parameter is outside of the interval, operating all motors to provide torque to the lifting element in the same direction.

10. The method according to claim 9, wherein the parameter is an angle between vertical and a longitudinal axis of the lifting element.

11. The method according to claim 9, wherein the parameter is a torque with which the motors affect the lifting element.

12. A lifting device comprising a lifting element, a plurality of motors configured to tilt the lifting element as well as a controller for controlling the motors according to the method of claim 8.

13. The lifting device according to claim 12, wherein the motors are electrical motors.

14. The lifting device according to claim 12, further comprising a sensor for outputting information relating to an angle between a longitudinal direction of the lifting element and vertical, the processor being configured to receive the information.

15. The lifting device according to claim 12, wherein the controller is configured to receive a signal representing a torque applied by the motors on the lifting element.

Description

[0063] In the following, preferred embodiments are described with reference to the drawings, wherein:

[0064] FIG. 1 illustrates a first embodiment of a lifting device for a vessel,

[0065] FIG. 2 illustrates an embodiment where multiple motors drive a lifting element,

[0066] FIG. 3 illustrates a parameter of a lifting element,

[0067] In FIG. 1, a vessel 10 comprises a lifting device 12 comprising a crane, boom or rod 14 rotatable around an axis 16. In many applications, the boom 14 actually is an A frame, such as a Launch And Recovery System (LARS) having two uprights rotatable around the same axis 16 and usually both driven by a separate hydraulic drives.

[0068] In the present embodiment, the lifting element 14 is driven by a drive rod 18 driven by a motor (not illustrated) via an eccentric or rotatable element 20. The motor drives the eccentric element 20 around an axis 22, and the eccentric 20 is rotatably connected to the drive rod 18 around an axis 24.

[0069] The drive rod 18 is rotatably connected to the lifting element at an axis 26.

[0070] In operation, the eccentric is rotated around the axis 22. Clearly, the drive rod 18, due to this movement, will pull or push the lifting element, so that the lifting element rotates around the axis 16.

[0071] The lifting element 14 may then be rotated to e.g. be able to receive instruments or the like 50 from outside of the vessel and to on board the vessel—or vice versa. Naturally, a wire, chain or the like 54 may be anchored or supported by the upper end of the lifting element for that purpose.

[0072] The operation of the eccentric is, apart from transferring movement and torque to the drive rod 18, to ensure that the lifting element 14 cannot move outside of an angle interval defined by a first, maximum angle α-max and a second, minimum angle α-min. These angles may be defined relative to e.g. horizontal. The maximum angle is seen when the axes 22, 24 and 26 are aligned (eccentric indicated at 20-max and the lifting element at 14-1) and the axis 22 is as close as possible to the axis 26 as possible. The minimum angle is seen (eccentric indicated as 20-min and lifting element at 14-2) when the axes 22, 24 and 26 are aligned and the axis 22 is as far away as possible from the axis 26.

[0073] Thus, even if the drive of the eccentric 20 breaks down, the lifting element 14 cannot move outside of the above angle interval, which makes the lifting device safe.

[0074] In FIG. 2, a drive is illustrated using multiple motors 30-1, 30-2 and 30-3, each having a toothed wheel 32-1, 32-2, and 32-3, respectively, engaging a central toothed wheel 34, which may be connected to the lifting element 14, such as at the axis 16, or to the eccentric 20, such as at the axis 22.

[0075] The use of multiple motors naturally may be preferred in order to achieve a sufficient torque and/or for providing redundancy so that if one motor becomes inoperable, the other motors may still provide the desired drive.

[0076] However, another advantage may be obtained if the motors are driven according to an embodiment of the invention.

[0077] In this embodiment, the torque required to rotate the lifting element will depend on the angle to vertical. Naturally, the torque required to rotate the lifting element will also depend on e.g. a pulling force exerted to a load via the lifting element if the winch is not provided on the lifting element. Thus, an angle will exist where the rotation of the lifting element will require zero torque. This could be called the “top point” even though this point may not be a vertical position. When the lifting element is in the top point, however, manufacturing imperfections in the device 12 may allow the lifting element to rotate slightly around the axis 16, even when the motors are stationary, where wind, waves or the swinging of the load exerts even a small force on the lifting element bringing it over the top point. This is not desired and in particular not when a heavy load 50 is hanging from the lifting element.

[0078] A solution to this is to have one motor, 30-1, provide a torque in the opposite direction, at least when the lifting element is sufficiently close to vertical (top point). In that situation, the lifting element is not allowed to rotate around the axis 16 unless allowed to do so by the motors. Clearly, the motor 30-1 will, in order for the lifting element 14 to still rotate, provide a lower torque than the combined torque of the motors 30-2 and 30-3. This mode of operation may be altered, when the lifting element passes vertical (top point), such as by a predetermined margin. Now, the motor 30-1 actually provides a force in a direction preventing the lifting element from rotating with the gravity. Then, also the motor 30-2 may be co-operating with the motor 30-1 to counteract the weight of the lifting element, where the motor 30-3 now provides a counter-acting torque preventing the lifting element from moving toward or beyond vertical again.

[0079] When the lifting element has a sufficiently large angle to vertical (from the top point), all motors may again move in synchronism in a direction preventing the lifting element from moving with gravity. Alternatively, one or more motors may always exert a torque counter-acting the rotation of the lifting element.

[0080] Clearly, two motors may also perform this operation, as may even more motors if desired.

[0081] In this situation, what controls the change-over between the situation where all motors co-operate and the situation where one or more motors work against the other(s) may be the angle of the lifting element vis-à-vis vertical (top point).

[0082] As mentioned, often, other elements provide a torque on the lifting element, such as when the load 50 is supported by the lifting element and is pulled upwardly by a winch 52 not supported by the lifting element but present on e.g. a vessel or vehicle supporting the lifting element. In this situation, the size of the load and the angles (of the cable 54) between the lifting element and, on one side, the load and, on the other side, the winch, will also affect the overall torque on the lifting element. In this situation, the problematic angle or position (top point) of the lifting element may be far away from vertical.

[0083] In addition, when the lifting device is used on a vessel (or a vehicle positioned on a non-horizontal surface), the angle between the vessel and the lifting element may not be an optimal parameter for the controlling, when the vessel/vehicle is not horizontal, such as due to waves.

[0084] In one situation, the torque applied by the motors may be used. In another situation, the torque on the drive rod or the axes/bearings may be used if desired.

[0085] Often, the torque provided by a motor may be read-out and used (together with the direction of the torque around the axis). In this connection, the change-over may take place when the combined torque of all motors (driving in the same direction) falls below a predetermined limit.

[0086] The torque applied by a motor may be sensed using a sensor or may be estimated from the power consumption of the motor.

[0087] Clearly, the counter-action of one (or more) motor(s) should be taken into account, as the resulting torque from the motors on the lifting element is the difference between the torque provided in one direction subtracted the torque provided in the other direction.

[0088] In FIG. 3, a further embodiment is illustrated. When lifting a load on a lifting element which is rotatable, the rotation of the lifting element clearly will shift the centre of gravity of the load 50. In the drawing, a picking-up position is seen at 14-1. This will cause the load 50 to swing which is not desired, especially if the load is to be set down on a surface.

[0089] This is aggravated, if additional movement is experienced, such as if the assembly is provided on a vessel or if wind is present.

[0090] A swinging of the load 50 is illustrated by the vertical arrows extending from the load.

[0091] This swinging may be halted by rotating the lifting element (vertical arrows extending from the lifting element), so that the point of engagement 14-3 of the load, which is often a wire or chain block, may be positioned directly over the load 50, such as when at standstill in relation to the lifting element, the point 14-3, the first axis or the like, such as at an extreme of a swinging movement. Alternatively, the movement of the load may be tracked or predicted and the lifting element moved in accordance to remain above the load or to break the movement of the load.

[0092] It is noted that this movement of the lifting element is possible over the full angle range of the lifting element but is easiest when the lifting element is around vertical and/or where rotation of a predetermined angle requires the least torque. When rotation requires the least torque, the movement may be made swifter, so that any swinging may swiftly be stopped.

[0093] It is noted, as indicated above, that the lifting element preferably is an A frame, such as a LARS, which has two lifting elements rotated around the same axis. Both lifting elements may be rotated by a single drive or two drives. The top beam may have one or more wire or chain blocks and the like for directing wires and chains for moving loads.