WO2019245361A1

WO2019245361A1 - Method and apparatus for orientating a load suspended on a crane by lifting cables

Info

Publication number: WO2019245361A1
Application number: PCT/NL2019/050333
Authority: WO
Inventors: Cornelis Stinis
Original assignee: Stinis Beheer B.V.
Priority date: 2018-06-18
Filing date: 2019-06-04
Publication date: 2019-12-26
Also published as: NL2021143B1

Abstract

The invention relates to a method for orientating a load suspended from a crane by hoisting cables, comprising the steps of: - detecting a rotation of the load in a horizontal plane [31] by means of a detector (19); - determining a desired correction [33] by means of a control unit (15); and - moving an engagement point of a hoisting cable on the load [34] by means of an actuator (16) in order to achieve the desired correction. The point of engagement can thereby be moved while the load is transferred by the crane from a first to a second location. The invention further relates to a device for performing the method, a crane (1) in which such a device is applied and a hoisting frame provided with the device.

Description

METHOD AND APPARATUS FOR ORIENTATING A LOAD SUSPENDED ON A CRANE BY LIFTING CABLES

The invention relates to a method for orienting a load which is suspended from a crane by hoisting cables, comprising the steps of detecting skew of the load in a horizontal plane by means of at least one detector; and determining a desired correction by means of a control unit. Such a method is known from EP 1 894 881 A2.

Speed is of great importance in the transfer of loads, particularly intermodular loads such as containers. Containers are usually transported worldwide on container ships with a loading capacity of thousands or tens of thousands of TEU (Twenty-foot Equivalent Units), which represent a very high value. The amount of time that such container ships are stationary for loading and/or unloading of containers thus has to be limited as far as possible. Use is therefore made in container ports of increasingly larger and faster cranes for the transfer from Ship To Shore (STS). The hoisting frames (spreaders) which are used for picking up the containers and the main frames (headblocks) with which the spreaders are suspended from the hoisting cables of the crane are also becoming increasingly larger and stronger. Already known are spreaders which can pick up two 20-foot containers or a 40-foot container as desired - marketed by applicant under the brand name Long-Twin® - and main frames which can carry one or two spreaders as desired - marketed by applicant under the brand name Split-Headblock®.

A problem which often impedes a fast transfer is that the spreaders with the containers, these hanging by long and flexible hoisting cables under a displaceable trolley of the crane, can perform undesired movements. The accelerations in horizontal direction as a result of the displacement of the trolley from ship to shore or vice versa thus result in swinging movements of the spreaders and containers. In addition, unevenly loaded containers or simultaneous transport of a plurality of containers of different weights may result in undesired movements of the spreaders with containers. Finally, weather influences, particularly strong winds, can also cause undesired movements.

Because of these undesired movements it takes a relatively greater amount of effort and more time to set containers down accurately at their destination location. On the one hand, this is an issue on the water, where containers often have to be lowered into cells in the hold of a container ship, but this can also be a problem on land, when containers have to be accurately placed on waiting trucks. A movement which causes a lot of delay is a rotating movement of the spreader with container in the horizontal plane, so about a vertical axis. This movement is referred to as skew and has the result that a container comes to hang above a cell or above a truck askew. In order to be able to lower the container into the cell or onto the truck the skew must first be undone so that the container is once again oriented parallel to a longitudinal axis of the cell or the truck. Undoing the skew and orienting the container is currently done manually by a crane operator by manipulating the different hoisting cables with which the load is attached to the crane. In addition, the crane operator works by sight, and must try to align the container with the cell or truck from a height of several tens of metres. This often takes 10-15 seconds, which extends the overall duration of a cycle - picking up a container, trajectory from ship to shore or vice versa, setting down the container and trajectory of empty spreader from shore to ship or vice versa - by up to 10 percent.

The above stated document EP 1 894 881 A2 describes a system for orienting a container hanging under a crane by four hoisting cables. Use is made here of a downward facing CCD camera, mounted in the crane, for detecting skew of the container. The outer ends of the four hoisting cables in the crane are each connected to an actuator, whereby the relevant hoisting cable is as it were lengthened or shortened so that an engagement point of the relevant hoisting cable on the load is moved upward or downward. The skew can hereby be undone. This known system has the drawback that the corrections are performed at the ends of the hoisting cables, whereby the effects thereof at the position of the container are influenced by the properties of the hoisting cables, such as their elasticity or resilience. The performed corrections hereby do not fully achieve the desired result, or do not do so quickly enough.

The invention has for its object to provide a method whereby the stated problems are obviated or at least reduced. According to the invention, this is achieved in a method of the above described type by the step of displacing at least one engagement point of a hoisting cable on the load by means of at least one actuator in order to bring about the desired correction.

By performing the correction at the position of the engagement point of the hoisting cable on the load instead of at the top of the crane the undesired skew is undone quickly and effectively.

The at least one engagement point is preferably displaced while the load is being transferred from a first to a second location by the crane. The load is thus already hanging in the correct position when it arrives at the destination location, and can be set down immediately.

In order to be able to orient the load quickly it is preferred for at least two engagement points of hoisting cables on the load to be displaced substantially in opposite directions. When the load is suspended from the crane by four hoisting cables engaging on said load close to corner points, two engagement points of hoisting cables on the load lying diagonally relative to each other are advantageously displaced in opposite directions.

Because the displacement is performed under load, the at least one engagement point is preferably displaced substantially in horizontal direction. In contrast to the vertical displacement described in EP 1 894 881 A2, it is hereby not necessary to locally hoist the load up further, whereby the correction requires considerably less power. By displacing the engagement point in horizontal direction the angle at which the hoisting cable runs from the crane to the load changes, and with this the horizontal component of the tensioning force in the hoisting cable. The resulting horizontal force on the load can be used to correct the undesired skew.

In order to be able to ascertain when the desired correction has been achieved a displacement of the at least one engagement point by at least one sensor can be detected and passed on to the control unit.

The load can comprise at least one hoisting frame. The hoisting frame can be a spreader which is suspended directly from the hoisting cables or a headblock to which the spreader is attached. Undesired skew can also occur, and it may also be important to correct it, when the hoisting frame is displaced without container, for instance in order to retrieve a subsequent container. In addition, the load can comprise at least one container attached to the at least one hoisting frame.

The invention also relates to a device for orienting a load which is suspended from a crane by hoisting cables, comprising at least one detector for detecting skew of the load in a horizontal plane, and a control unit, connected to the at least one detector, for determining a desired correction. Such a device is also known from EP 1 894 881 A2. The invention has for its purpose to provide an improved device of this type. This is achieved according to the invention by providing the device with at least one actuator, connected to the control unit, for displacing at least one engagement point of a hoisting cable on the load.

The at least one engagement point of the hoisting cable on the load can here comprise a rotatable cable sheave which is mounted slidably. Such a slidable cable sheave can be displaced in relatively quick and simple manner.

The load can more particularly comprise a frame on which a number of cable sheaves are slidably mounted. Giving a plurality of cable sheaves a slidable form creates different correction options. The frame can be a spreader or a headblock to which a spreader is attached. The headblock can particularly be a two-part headblock, such as Split-Headblock® of applicant.

When at least the control unit and the at least one actuator are arranged on the frame, the device can react quickly to detected instances of skew. When the at least one detector is in addition also arranged on the frame, no modifications need to be made to the crane, and the device as a whole can be accommodated on the frame.

In order to be able to perform a correction relatively quickly and effectively, the control unit and the at least one actuator can be configured to displace at least two cable sheaves substantially in opposite directions. The frame can here comprise four cable sheaves placed close to the corners thereof, and the control unit and the at least one actuator can be configured to displace two cable sheaves placed diagonally relative to each other substantially in opposite directions. All cable sheaves are preferably displaceable under the influence of the control unit. When the at least one cable sheave is mounted slidably in horizontal direction, the corrections can take place without the load having to be displaced in vertical direction, whereby the device will consume relatively little energy. The at least one cable sheave can here be slidable in longitudinal direction or in transverse direction of the load, or in both directions. When the at least one cable sheave is displaceable in transverse direction, it is possible to suffice with relatively small displacements for correcting skew.

The at least one detector can comprise a camera or a gyroscope. A camera, which could be mounted on the crane and could be aimed at an identifying mark on the upper side of the load, has the advantage that the detection is direct. There is no possible drift, such as with a gyroscope. A gyroscope conversely has the advantage that it can be mounted directly on the load, so that no modification of the crane is necessary. The possible drift could be compensated by setting the rotation angle of the gyroscope to zero each time a container is picked up or set down.

The at least one actuator can comprise a hydraulic piston/cylinder combination. Such a hydraulic actuator can be compact and exert a great force.

The device can further comprise at least one sensor, connected to the control unit, for detecting a displacement of the at least one engagement point. The performed correction can thus be measured and fed back.

The control unit can be configured to run a control program, for instance on the basis of a PID algorithm. Other manners of control can also be envisaged, for instance on the basis of state feedback control or on the basis of fuzzy logic.

The at least one sensor can comprise a laser distance measurer or an inductive sensor. A laser distance measurer can accurately determine the displacement up to a relatively great distance, but is more fragile and expensive relative to an inductive sensor. An inductive sensor has a relatively small measurement range but could be combined with a rack, the number of teeth of which can then be counted in order to measure the displacement. A second sensor can be used to measure an intermediate position and to set a new zero position after each measurement.

When the control unit and the at least one actuator are configured to displace the at least one engagement point while the load is being transferred by the crane from a first to a second location, a significant time saving can be made during the transfer.

The invention also relates to a crane which comprises a number of hoisting cables and a frame suspended therefrom and which is further provided with a device as described above.

And finally, the invention relates to a frame which comprises at least two rotatable cable sheaves for suspending from hoisting cables of a crane and which is further provided with a device of the above described type.

The invention is now elucidated on the basis of an example, wherein reference is made to the accompanying drawings, in which: Fig. 1 shows a crane with a load suspended therefrom,

Fig. 2 shows schematically the possible movements of a load hanging under a crane,

Fig. 3 shows a front view of a load, suspended from hoisting cables, which comprises a headblock, a spreader and a container,

Fig. 4 shows a side view of a cable sheave and the forces acting thereon,

Fig. 5 is a schematic top view of a frame with four cable sheaves, which indicates how an undesired rotation in the horizontal plane (skew) can be corrected by displacement of the cable sheaves,

Fig. 6 is a perspective view of a two-part headblock which is provided with the device according to the invention, in which schematic displacements of cable sheaves are indicated,

Fig. 7 shows schematically the most important steps of the method according to the invention, and

Fig. 8 shows a number of graphs which show how an undesired angular displacement is corrected in the case of different loads.

A crane 1 (Fig. 1) comprises on the land side a gantry 2, which can travel over a quay K, and a girder 3 suspended therein, an outer end 8 of which protrudes on the water side above the water W by the quay. A trolley 4, from which a load 5 is suspended by means of hoisting cables 6, can travel along the girder. Load 5 can be moved upward or downward by hauling in or paying out hoisting cables 6. Also mounted on trolley 4 is a cab 7 from which an operator can control crane 1.

The load 5 suspended from hoisting cables 6 has six degrees of freedom (Fig. 2). Load 5 can perform translating movements along the X-axis (from the water to the quay), along the Y-axis (parallel to the quay) and along the Z-axis (hoisting and lowering of the load). In addition, load 5 can rotate round the X-axis (referred to as list, angle Q), round the Y-axis (referred to as trim, angle f) and round the Z-axis (referred to as skew, angle y). The desired movements of load 5 are brought about by moving trolley 4 and hauling in or paying out hoisting cables 6. In addition, load 5 undergoes undesired movements because hoisting cables 6 are not rigid. These undesired movements are for instance the result of the acceleration and deceleration of trolley 4, of uneven loading and of weather influences. Load 5 will thus not always hang directly under trolley 4, but load 5 may lag when trolley 4 begins to move, or conversely overshoot when trolley 4 comes to a standstill. This is referred to as sway (angle g).

Load 5 can be formed by one or more hoisting frames 9, 10 and one or more containers 11 attached thereto (Fig. 3). In the shown example load 5 comprises a headblock 10 on which four cable sheaves 12 are arranged (only two shown), over which hoisting cables 6 are carried. Two spreaders 9 A, 9B are attached to the headblock 10, which in this example is a splittable headblock (for instance Split-Headblock® of applicant) with two parts 10A, 10B. The parts 10A, 10B are connected movably to each other by arms 13 with a hinge 14 therein in order to be able to pick up containers 11 A, 11B which are not positioned directly adjacently of each other. It is particularly in the case of this type of load, with two containers 11 A, 11B hanging adjacently of each other from hoisting cables 6, that undesired rotation about the vertical axis can occur as a result of differences in the weight of the two containers 11 A, 11B.

The invention relates to the correcting of such an undesired rotation about the Z-axis (skew). Use can be made for this purpose of a horizontally oriented component Fcab,hor of the tensioning force Fcab in a hoisting cable 6 when this hoisting cable 6 encloses an angle with the vertical axis (Fig. 4). This horizontal component Fcab,hor can be increased or reduced by displacing the engagement point of hoisting cable 6 on load 5. By displacing the engagement point relative to the (fixed) centre of gravity CG of load 5 the distribution of the load over hoisting cables 6 is changed. The relevant hoisting cable is hereby loaded more heavily or conversely partially relieved, whereby the tensioning force Fcab increases or decreases, and thereby also the horizontal component Fcab,hor of this force. In addition, the displacement of the engagement point also changes the angle of hoisting cable 6 to the vertical axis, which likewise results in a change in the horizontal component Fcab,hor.

The effect of the displacement of an engagement point on the moment of torque round the vertical axis depends on the ratio between the mutual distance of the engagement points on load 5 on the one hand and the mutual distance of hoisting cables 6 at the position of trolley 4 on the other. When trolley 4 is wider than load 5 (as seen in the direction of the short side of a container 11), hoisting cables 6 will converge from trolley 4 to load 5, but when load 5 is wider than trolley 4, hoisting cables 6 will diverge from trolley 4 to load 5. This latter situation may occur in the headblock 10 of Fig. 3, which consists of two parts, when the parts 10A, 10B have been moved apart and headblock 10 carries two spreaders 9A, 9B (referred to as tandem lift). When block 10 is however closed and carries a single spreader 9 (single lift, not shown here), the first situation occurs. In order to be able to calculate the effect a displacement of an engagement point will have it is important to know the ratio of the width of load 5 to the width of trolley 4. For this purpose a control unit 15 to be discussed below must receive information about the properties of load 5 and, in the case of a headblock 10 consisting of two parts, control unit 15 must receive information about the position of headblock 10 at all times.

The engagement points, so in general the points where cable sheaves 12 are attached to load 5, can in principle be displaced both in longitudinal direction of the load (this being the Y- direction in the coordinate system of the crane) and in transverse direction of the load (the X- direction). As shown in Fig. 5, displacements in the X-direction are very effective, since cable sheaves 12 are removed relatively further from the centre of gravity CG in the Y-direction, and the moment arm A of the horizontal force is then thus relatively great. It is effective here for two cable sheaves 12 to be displaced in opposite directions on opposite sides of load 5, as shown in Fig. 6. The maximal moment arm is achieved when two cable sheaves 12 lying diagonally opposite each other are displaced in opposite directions.

The cable sheaves can be displaced by means of actuators 16 in the form of hydraulic piston/cylinder combinations, which can be actuated by a pump 17 which is driven by an electric motor 18. Electricity is always available on a hoisting frame such as a spreader 9 or headblock 10. The hydraulic actuators are controlled by a control unit 15, which in turn receives error signals from one or more detectors 19. The detector(s) can comprise a downward facing camera, mounted on the crane, which detects one or more marks on the load. In the shown example detector 19 is a gyroscope which is mounted on the hoisting frame.

Connected to each actuator 16 or each cable sheave 12 in this example is a sensor 20, which detects the displacement of the relevant cable sheave 12 and passes it on to control unit 15. Sensor 20 can be an optical sensor, such as for instance a laser distance measurer, or an inductive sensor. In the case of an inductive sensor a transmission is also necessary, since the detection range of such a sensor is much smaller than the required displacement of cable sheave 12. A measuring member which has uniformly distributed points which are detectable by the inductive sensor, such as a rack, and which is connected to the cable sheave 12 or actuator 16 can for instance be chosen as transmission.

In the shown example it has been chosen to embody cable sheaves 12 for displacement in transverse direction of load 5 (the X-direction). Each cable sheave 12 is mounted for rotation about an axis 21 in a housing 22, which in turn is mounted slidably along a slide rod 23 which forms a fixed component of load 5 (Fig. 4, 6). Housing 22 has for this purpose two ears 24 in which are formed openings 25 in which slide rod 23 is received close-fittingly. Hydraulic actuator 16 connects housing 22 to a fixed part of load 5, here the headblock 10.

Although the displacement of the engagement points in horizontal direction has been discussed above, it is also possible to envisage these points being displaced in vertical direction. In this way a local lengthening or shortening of the hoisting cables is achieved, which likewise results in a moment of torque round the vertical axis. This moment of torque can in turn be used to counteract the undesired skew. Although a vertical displacement of the engagement points requires more energy than horizontal displacement, there may be other circumstances due to which a vertical displacement is a better option in a specific situation.

And although the examples up to this point have related mainly to a splittable hoisting frame, it will be apparent that the invention likewise applies to a single, unsplittable hoisting frame.

The method according to the invention starts with picking up and hoisting a load 5, for instance picking up and hoisting out of a cell of a container ship a container 11 which has to be transferred to the chassis of a truck on the quay K (Fig. 7, step 30). Once the load 5, then consisting of headblock 10, spreader 9 and container 11, hangs clear, the position of the load is detected by means of one or more detectors 19 (step 31). After this, a control unit 15 assesses through comparison of the detected position to a desired position whether undesired skew in the horizontal plane (skew) is occurring (step 32). If this is the case, control unit 15 determines a required correction (step 33) and then controls one or more actuators 16 to displace one or more engagement points of the hoisting cables on load 5, such that the undesired skew is cancelled as effectively as possible (step 34). After this, load 5 is transported further (step 35) and lowered and released at the destination location (step 36). As shown with broken lines in Fig. 7, the

displacement of the engagement points in step 34 can take place during the transport (the trajectory) of the container in step 35, so that no delay occurs and the overall cycle time is shortened.

Simulations of a device according to the invention in combination with a splittable headblock and, depending on the load, one or two spreaders, have shown that instances of undesired skew can usually be corrected within 10 seconds using conventional hydraulics and power sources which are ordinarily installed on a hoisting frame (power packs). This can be seen in Fig. 8, which is based on a hoisting frame equipped with two hydraulic pumps with a maximum flow rate of about 110 l/min and an electric power pack with a nominal power of about 20 kW. An undesired angular rotation of 2° is here taken as starting situation. In the case of a 40-foot container such a small angle will already result in a lateral deflection of more than 40 cm, which renders placing of a container on a truck chassis or in a cell impossible.

The simulation shown in Fig. 8 is based on a hoisting height of 30 m and four different loading states. The top graph shows the behaviour in unloaded state, wherein only the splittable headblock and two spreaders (with a collective mass of 40 tons) hang from hoisting cables 6. The second graph shows the situation wherein four empty containers 11 hang from the two spreaders, whereby the total mass of load 5 amounts to 50 tons. In the third and fourth graph the containers are respectively half loaded (total mass 110 tons) and fully loaded (total mass 160 tons). As can be seen, a rotation angle of less than 0.5° is achieved within 10 seconds in all cases. This value is acceptable because the maximum lateral deflection thereby amounts to 10 cm, whereby the container can be placed on a truck chassis or be lowered into a cell. After about 25 seconds the angular displacement has been wholly eliminated. Since the overall cycle of picking up, hoisting, transporting, lowering, releasing and returning for a subsequent container takes 120-150 seconds in practice, the orienting can take place during the trajectory. A time saving in the order of 10 percent is thus achieved compared to the situation in which the orienting is performed“by sight” by the operator as soon as the container is hanging above the destination location.

Control unit 15 can otherwise make use of any desired algorithm for the purpose of determining a required correction and controlling the different actuators 16. The shown example is based on a PID control algorithm, although other algorithms, such as state feedback control or fuzzy logic control, can also be envisaged.

The invention thus makes it possible to considerably increase the transfer speed of containers with relatively simple means.

Although the invention has been described above on the basis of an embodiment, it will be apparent that it is not limited thereto but can be varied in many ways within the scope of the following claims.

Claims

1. Method for orienting a load which is suspended from a crane by hoisting cables, comprising the steps of:

detecting skew of the load in a horizontal plane by means of at least one detector; and

determining a desired correction by means of a control unit; characterized by displacing at least one engagement point of a hoisting cable on the load by means of at least one actuator in order to bring about the desired correction.

2. Method according to claim 1 , wherein the at least one engagement point is displaced while the load is being transferred from a first to a second location by the crane.

3. Method according to claim 1 or 2, wherein at least two engagement points of hoisting cables on the load are displaced substantially in opposite directions.

4. Method according to claim 3, wherein the load is suspended from the crane by four hoisting cables engaging on said load close to corner points, and two engagement points of hoisting cables on the load lying diagonally relative to each other are displaced in opposite directions.

5. Method according to any one of the foregoing claims, wherein the at least one

engagement point is displaced substantially in horizontal direction.

6. Method according to any one of the foregoing claims, wherein a displacement of the at least one engagement point is detected and passed on to the control unit by at least one sensor.

7. Method according to any one of the foregoing claims, wherein the load comprises at least one hoisting frame.

8. Method according to claim 7, wherein the load comprises at least one container

attached to the at least one hoisting frame.

9. Device for orienting a load which is suspended from a crane by hoisting cables,

comprising:

at least one detector for detecting skew of the load in a horizontal plane, and a control unit, connected to the at least one detector, for determining a desired correction;

characterized by

at least one actuator, connected to the control unit, for displacing at least one engagement point of a hoisting cable on the load.

10. Device according to claim 9, wherein the at least one engagement point of the hoisting cable on the load comprises a rotatable cable sheave which is mounted slidably.

11. Device according to claim 10, wherein the load comprises a frame on which a number of cable sheaves are slidably mounted.

12. Device according to claim 11, wherein at least the control unit and the at least one actuator are arranged on the frame.

13. Device according to claim 11 or 12, wherein the at least one detector is arranged on the frame.

14. Device according to any one of the claims 11-13, wherein the control unit and the at least one actuator are configured to displace at least two cable sheaves substantially in opposite directions.

15. Device according to claim 14, wherein the frame comprises four cable sheaves placed close to corners thereof, and the control unit and the at least one actuator are configured to displace two cable sheaves placed diagonally relative to each other substantially in opposite directions.

16. Device according to any one of the claims 10-15, wherein the at least one cable sheave is mounted slidably in horizontal direction.

17. Device according to any one of the claims 9-16, wherein the at least one detector comprises a camera or a gyroscope.

18. Device according to any one of the claims 9-17, wherein the at least one actuator comprises a hydraulic piston/cylinder combination.

19. Device according to any one of the claims 9-18, further comprising at least one sensor, connected to the control unit, for detecting a displacement of the at least one engagement point.

20. Device according to claim 19, wherein the at least one sensor comprises a laser

distance measurer or an inductive sensor.

21. Device according to any one of the claims 9-20, wherein the control unit and the at least one actuator are configured to displace the at least one engagement point while the load is being transferred by the crane from a first to a second location.

22. Crane comprising a number of hoisting cables and a frame suspended therefrom, and further provided with a device according to any one of the claims 9-21.

23. Frame comprising at least two rotatable cable sheaves for suspending from hoisting cables of a crane, and further provided with a device according to any one of the claims 9-21.