HEAVE COMPENSATOR ENABLING ACTIVE HEAVE COUNTERACTION

Abstract

A heave compensator includes a main hydraulic cylinder including a first connection device located at an upper end of the main hydraulic cylinder and a first piston having a piston rod. The interior of the main hydraulic cylinder is divided by the first piston into an upper first chamber and a lower second chamber filled with hydraulic liquid. The piston rod has a second connection device located at a lower end of the piston rod. The heave compensator includes a lifting accumulator comprising a second piston dividing the interior of the lifting accumulator into a third chamber filled with gas and a fourth chamber filled with hydraulic liquid. The fourth chamber is fluidly connected to the second chamber by a first liquid conduit having a first actuator controlled valve regulating the flow of hydraulic liquid in the first liquid conduit. The heave compensator includes a lowering accumulator comprising a third piston dividing the interior of the lowering accumulator into a fifth chamber filled with gas and a sixth chamber filled with hydraulic liquid. The sixth chamber is fluidly connected to the second chamber by a second liquid conduit having a second actuator controlled valve regulating the flow of hydraulic liquid in the second conduit. The sixth chamber is fluidly connected to the fourth chamber by a third hydraulic liquid conduit comprising an actuator controlled pump unidirectionally regulating the flow of hydraulic liquid from the sixth chamber to the fourth chamber. The heave compensator further includes a sensor kit including a motion sensing unit registering the vertical movements of the main hydraulic cylinder, a logical controller unit including a processor loaded with a Valve Regulation Module containing logic commands which when executed controls and regulates the actuator of the first actuator controlled valve, the actuator of the second actuator controlled valve, and the actuator of the actuator controlled pump, and signal transferring lines electronically connecting the logic controller unit to the motion sensing unit of the sensor kit, the actuators of the first and the second actuator controlled valves, and the actuator of the actuator controlled pump.

Claims

1. A heave compensator, comprising: a main hydraulic cylinder comprising a first connection device located at an upper end of the main hydraulic cylinder and a first piston having a piston rod, where the interior of the main hydraulic cylinder is divided by the first piston into an upper first chamber and a lower second chamber filled with hydraulic liquid, and where the piston rod has a second connection device located at a lower end of the piston rod, a lifting accumulator comprising a second piston dividing the interior of the lifting accumulator into a third chamber filled with gas and a fourth chamber filled with hydraulic liquid, wherein the fourth chamber is fluidly connected to the second chamber by a first liquid conduit having a first actuator controlled valve regulating the flow of hydraulic liquid in the first liquid conduit, a lowering accumulator comprising a third piston dividing the interior of the lowering accumulator into a fifth chamber filled with gas and a sixth chamber filled with hydraulic liquid, wherein the sixth chamber is fluidly connected to the second chamber by a second liquid conduit having a second actuator controlled valve regulating the flow of hydraulic liquid in the second conduit, wherein the sixth chamber is fluidly connected to the fourth chamber by a third hydraulic liquid conduit comprising an actuator controlled pump unidirectionally regulating the flow of hydraulic liquid from the sixth chamber to the fourth chamber, and the heave compensator further comprises: a sensor kit comprising a motion sensing unit registering the vertical movements of the main hydraulic cylinder, a logical controller unit comprising a processor loaded with a Valve Regulation Module containing logic commands which when executed controls and regulates the actuator of the first actuator controlled valve, the actuator of the second actuator controlled valve, and the actuator of the actuator controlled pump, and signal transferring lines electronically connecting the logic controller unit to the motion sensing unit of the sensor kit, the actuators of the first and the second actuator controlled valves, and the actuator of the actuator controlled pump.

2. The heave compensator according to claim 1, wherein the first and the second actuator controlled valves are either throttle valves, dampening valves, or proportional valves, preferably electrically driven proportional valves which may continuously regulate the cross-section of the first or the second liquid conduit, respectively, from zero to 100% opening, and wherein the actuator of the hydraulic pump is an electric motor.

3. The heave compensator according to claim 1, wherein the logic control unit is either a PID-controller, a feed-forward controller, a fuzzy logical controller, a process-model based controller, or a combination thereof, and the motion reference unit is an inertial measurement unit with single- or multi-axis MEMS gyroscope based motion sensors.

4. The heave compensator according to claim 1, wherein the third chamber of the lifting accumulator is preloaded with an amount of gas giving a set point gas pressure, sp.sub.2, which ensures that the gas pressure inside the third chamber is larger than p.sub.1 for any position of the second piston, and the fifth chamber of the lowering accumulator is preloaded with an amount of gas giving a set point gas pressure, sp.sub.3, which ensures that the gas pressure inside the fifth chamber is smaller than p.sub.1 for any position of the third piston, where p.sub.1 is the load induced hydrostatic pressure of the hydraulic liquid in the second chamber when a load intended to be lifted is suspended from the second connection device.

5. The heave compensator according to claim 1, wherein the sensor kit further comprises a first pressure and temperature sensor located in and registering the gas pressure, p.sub.2, inside the third chamber of the lifting accumulator, and a second pressure and temperature sensor located in and registering the gas pressure, p.sub.3, inside the fifth chamber of the lowering accumulator.

6. The heave compensator according to claim 3, wherein the sensor kit further comprises a first position sensor registering the position of the first piston of the main hydraulic cylinder.

7. The heave compensator according to claim 6, wherein the Valve Regulation Module of the control unit further comprises a Heave Compensation Module containing logic commands, which when executed, utilises sensor data from the motion sensing unit to determine a vertical velocity component, v.sub.heave, of a heave movement affecting the main hydraulic cylinder, and further utilises sensor data from the first position sensor to determine the velocity, v.sub.pist1, of the piston of the main hydraulic cylinder, and then engages the actuator of the first actuator controlled valve and the actuator of the second actuator controlled valve to regulate the movement of the first piston of the main hydraulic cylinder such as to satisfy the relation: |v.sub.heave+v.sub.pist1|=0.

8. The heave compensator according to claim 7, wherein the regulation of the movement of the first piston of the main hydraulic cylinder is obtained by adjusting the opening of the respective actuator controlled valve of the respective liquid conduit of the lowering or lifting accumulator being engaged to move the first piston.

9. The heave compensator according to claim 7, wherein the program module of the control unit further comprises a Pump Activation Module containing logic commands, which when executed, applies sensor data from the second pressure and temperature sensor to engage the pump whenever the measured gas pressure, p.sub.3, in the fifth chamber becomes higher than 1.2.Math.sp.sub.3, preferably higher than 1.15.Math.sp.sub.3, more preferably higher than 1.1.Math.sp.sub.3, and most preferably higher than 1.05.Math.sp.sub.3, and to disengage the pump whenever the measured gas pressure in the fifth chamber becomes lower than 0.8.Math.sp.sub.3, preferably lower than 0.85.Math.sp.sub.3, more preferably lower than 0.9.Math.sp.sub.3, and most preferably lower than 0.95.Math.sp.sub.3, where sp.sub.3 is the set point pressure of the gas being preloaded into the fifth chamber prior to a lifting operation.

10. The heave compensator according to claim 7, wherein the program module of the control unit further comprises a Pump Activation Module containing logic commands, which when executed, applies sensor data from the first pressure and temperature sensor and the second pressure and temperature sensor to regulate the revolutions per minute of the pump to minimise an error function e=max(ep.sub.2, ep.sub.3, 0), where ep.sub.2=sp.sub.2-p.sub.2, ep.sub.3=p.sub.3-sp.sub.3, sp.sub.2 is the set point gas pressure, i.e. the set point pressure, in the third chamber of the lifting accumulator, sp.sub.3 is the set point gas pressure in the fifth chamber of the lowering accumulator, p.sub.2 is the measured gas pressure by the first pressure and temperature sensor in the third chamber of the lifting accumulator, p.sub.3 is the measured gas pressure by the second pressure and temperature sensor in the fifth chamber of the lowering accumulator, and which stops the pump if the error function returns the value 0 when both ep.sub.2 and ep.sub.3 are negative.

11. The heave compensator according to claim 7, wherein the program module of the control unit further comprises a Quick Lift Module containing logic commands, which when executed, causes the Valve Regulation Module to initially closing the first valve and opening the second valve, and then when the quick lift is to be executed, closes the second valve and fully opens valve.

12. The heave compensator according to claim 7, wherein the program module of the control unit further comprises a Quick Lift Module containing logic commands, which when executed, causes the Valve Regulation Module to automatically preparing the heave compensator for a quick-lift by, in successive order: closing, if open, the first valve and opening the second valve, applying the registered temperature and pressure data from the first pressure and temperature sensor and/or position data from the second position sensor to determine a measured volume, V.sub.meas, of hydraulic liquid present in the lifting accumulator, and if V.sub.meas<V.sub.int, where V.sub.int is a desired initial volume of hydraulic fluid in the lifting accumulator (10): engaging pump to transfer hydraulic fluid from the sixth chamber of the lowering accumulator to the fourth chamber of the lifting accumulator, and applying the registered position data from the second position sensor to disengage the pump when V.sub.meas≥V.sub.int, or else: closing the second valve, and then, when the quick-lift is to be executed: fully opening the first valve.

13. The heave compensator according to claim 12, wherein Quick Lift Module further comprises a Prepare for Heave Compensation Module to be engaged after the quick-lift is commenced, and which contains logic commands which, when executed, performs in successive order: closes the first valve, applies position data from the first position sensor to continuously determining the position of the first piston, opens the second valve to enable the weight of the suspended load to controllably extend the first piston until it reaches a position at the middle length of the main hydraulic cylinder and then closes the second valve, engages the Pump Activation Module to transfer hydraulic liquid from the lowering accumulator to the lifting accumulator, and then engages the Heave Compensation Module.

14. The heave compensator according to claim 1, wherein the amount of hydraulic liquid in the heave compensator is adapted such that when hydraulic fluid is distributed equally between the second, fourth, and the sixth chamber, that the first, second, and the third piston, are positioned in the middle of the main hydraulic cylinder, the lifting accumulator, and the lowering accumulator, respectively.

15. The heave compensator according to claim 5, wherein the heave compensator further comprises an electric battery for supplying electric energy to the actuators of the first and the second valves, the pump, the logic control unit, the motion sensing unit, and the sensor kit.

Description

LIST OF FIGURES

[0073] FIG. 1 is a cut-view drawing as seen from the side schematically illustrating an example embodiment of a heave compensator according to the invention being prepared for a quick-lift.

[0074] FIG. 2 is a cut-view drawing as seen from the side schematically illustrating the same example embodiment as in FIG. 1 during commencement of a quick-lift.

[0075] FIGS. 3 a) and 3 b) are cut-view drawings as seen from the side schematically illustrating the same example embodiment as in FIG. 1 during restoration of the balance of hydraulic liquid after execution of a quick-lift.

[0076] FIGS. 4 a) to 4 c) are cut-view drawings as seen from the side schematically illustrating the same example embodiment as in FIG. 1 during different stages of normal heave compensation.

[0077] FIG. 5 displays diagrams showing calculated performance of the heave compensator according to the invention during a lift of 75 tons heavy object under heave movements of amplitude of 0.5 metres.

DETAILED DESCRIPTION OF THE INVENTION

[0078] The working principle of the heave compensator according to the invention is described illustrated by reference to FIGS. 1 to 5 which illustrates an example embodiment of the heave compensator according to the invention executing a quick-lift and then goes over to a normal heave compensation mode.

[0079] This example embodiment applies a main hydraulic cylinder 1 having a first piston 2 with a piston rod 6. The main hydraulic cylinder 1 has two inner chambers separated by the piston 2, an upper first chamber 3 filled with a relatively low pressurised gas, or preferably a vacuum, and a lower second chamber 4 filled with hydraulic liquid. The piston rod 6 extends a varying distance down from the main hydraulic cylinder and thus regulates the total length of the main hydraulic cylinder. The main hydraulic cylinder 1 will in operation be attached to a lifting wire by the first connection device 5, and a load to be lifted will be attached to the lower end of the piston rod 6 by the second connection device 7. The lifting wire and load are omitted in the figures since they are no part of the claimed invention.

[0080] The example embodiment comprises further a lifting accumulator 10 having a second piston 11 separating a gas-filled third chamber 12 and a hydraulic liquid filled fourth chamber 13, and a lowering accumulator 20 having a third piston 21 separating a gas-filled fifth chamber 22 and a hydraulic liquid filled sixth chamber 23. The hydraulic liquid filled second 4 and fourth chamber 13 are fluidly interconnected by a first hydraulic liquid conduit 30 having a first actuator-controlled valve 31 which regulates the flow of hydraulic liquid in the first liquid conduit 30. Likewise, the second 4 and the sixth chamber 23 are fluidly interconnected by a second hydraulic liquid conduit 32 having a second actuator-controlled valve 33 which regulates the flow of hydraulic liquid in the second liquid conduit 32. A third liquid conduit 40 with an actuator controlled pump 41 enables transferring hydraulic liquid from the lowering 20 to the lifting 10 accumulator. The example embodiment comprises further a motion sensing unit 51. The logical controller unit 50 of this example embodiment contains a Valve Regulation Program Module, a Heave Compensation Module, a Pump Activation Module, a Quick Lift Module, and a Prepare for Heave Compensation Module as described above, and the sensor kit comprises a first position sensor 53 registering the position of the first piston 2, a first pressure and temperature sensor 54 registering the gas pressure in the third chamber 12, a second pressure and temperature sensor 55 registering the gas pressure in the fifth chamber 22, a third pressure sensor 56 registering the ambient gas/hydrostatic pressure, a fourth pressure sensor 57 registering the hydrostatic pressure in the second chamber 4, and a second position sensor 58 registering the position of the second piston 11.

[0081] FIG. 1 illustrates a typical preparation situation before a quick-lift is commenced. The heave compensator is here suspended between the lifting wire of a crane (not shown) and the load to be lifted (not shown) and the first piston 2 of the main hydraulic cylinder 1 is moved downward by the crane lifting and stretching the main hydraulic cylinder. The hydraulic liquid exiting the second chamber 4 of the main hydraulic cylinder is passed into the lowering accumulator since the second valve 33 is open. This causes the third piston 21 to move upwards in the lowering accumulator 20 and to relatively gently tensioning the lifting wire and the slings (but without sufficient force to lift the load off its ground/basement). The movements of the first 2 and third 21 piston are indicated by the stapled arrows. Furthermore, as shown on the figure, the lifting accumulator 10 is made ready for creating a long return stroke by being loaded with a relatively huge volume of high-pressurised hydraulic liquid making it necessary to have the first valve 31 closed to contain the hydraulic fluid in the lifting accumulator 10.

[0082] In this embodiment, the heave compensator is pre-loaded with nitrogen gas such that obtains a pre-set gas pressure, sp.sub.3, ensuring a gas pressure, p.sub.3<p.sub.1, in the fifth chamber 22 at any possible position of the third piston 21 and a pre-set gas pressure, sp.sub.2, ensuring a gas pressure, p.sub.2>p.sub.1, in the third chamber 12 at any possible position of the second piston 11. Furthermore, the amount of hydraulic liquid in the heave compensator is adapted such that when hydraulic fluid is distributed equally between the second 4, fourth 13, and the sixth 23 chamber, that the first 2, second 11, and the third 21 piston are respectively positioned in the middle of the main hydraulic cylinder 1, the lifting accumulator 10, and the lowering accumulator 20.

[0083] FIG. 2 illustrates the example embodiment shown in FIG. 1 during execution of the Quick Lift Module. In this phase, the first valve 31 is opened to allow the relatively high pressurised gas in the third chamber to press down the second piston 11 and the second valve 33 is closed to disengage the lowering accumulator 20 and force the hydraulic liquid being pressed out of the lifting accumulator 10 to enter the second chamber 4 of the main hydraulic cylinder 1 and create a return stroke. This makes the second piston 11 to move downwards and the first piston 2 to move upwards as indicated by the stapled arrows.

[0084] FIG. 3 a) illustrates the same example embodiment early in the execution of the Prepare for Heave Compensation Module, i.e. when the first piston 2 is lowered to a position in the middle of the main hydraulic cylinder 1 by utilising the weight of the suspended load. In this phase, the first valve 31 is closed and the second valve 33 is opened to allow the hydraulic fluid exiting the main hydraulic cylinder to enter the lowering accumulator 20. FIG. 3 b) illustrates the next step phase in the execution of the Prepare for Heave Compensation Module when the second valve 33 is closed to prevent the main piston 2 to be lowered below the middle of the main hydraulic cylinder and the pump 41 is engaged to transfer hydraulic liquid from the lowering accumulator 20 to the lifting accumulator 10 until the hydraulic liquid is distributed equal between them and the heave compensator obtains a neutral state and puts the heave compensator in a mode ready for heave compensation functionality.

[0085] FIGS. 4 a) to 4 c) illustrate the same example embodiment after ending the execution of the Quick-lift Module and the Prepare for Heave Compensation Module and after initiating the Valve Regulation Program Module, the Heave Compensation Module, and the Pump Activation Module which puts the heave compensator into normal heave compensation mode.

[0086] FIG. 4 a) illustrates the example embodiment during counteraction of a downwardly directed heave movement (indicated by the white stapled arrow) which lowers the main hydraulic cylinder 1. To compensate for this heave movement, the first valve 31 is opened to allow hydraulic liquid flowing from the lifting accumulator 10 into the main hydraulic cylinder 1 and thus causing the first piston 2 make a return stroke as indicated by the thin stapled arrows.

[0087] FIG. 4 b) illustrates the same example embodiment during an upwardly heave movement hoisting the main hydraulic cylinder 1. Now, the second valve 33 is closed to disengage the lifting accumulator 10 while the first valve 31 is opened to enable hydraulic liquid flowing from the main hydraulic cylinder (1) and into the lowering accumulator 20 to cause the first piston 2 to make an extension stroke as indicated by the thin stapled black arrows.

[0088] FIG. 4 c) illustrates the same example embodiment during execution of the Pump Activation Module to restore a “balanced” distribution of the hydraulic liquid between the lowering 20 and lifting 10 accumulator. The Pump Activation Module may engage the pump 41 at any time except when the first valve 31 is open, since an open first valve 31 would cause hydraulic liquid pumped by pump 41 into the fourth chamber 13 to immediately exit through the conduit 30.

[0089] Verification of the Invention

[0090] The invention will be described further by way of a simulation of the heave compensating functionality of the example embodiment described above and shown in FIGS. 4 a) to 4 c) during a lift of a load having a mass of 75 tons which is subject to a heave movement of 0.5 metres amplitude and a frequency of 1/12 seconds.

[0091] In this embodiment, the maximum stroke length of the main hydraulic cylinder is 0.6 metres, i.e. the length of the inner chamber of the single acting piston cylinder is 1.2 metres. The inner diameter of the main hydraulic cylinder is 28 cm such that when subject to this heave movement, the amount of hydraulic liquid in the main hydraulic cylinder within a 12 second period varies between almost 60 litres to about 5 litres as may be seen from a diagram of FIG. 5.

[0092] The load induced hydrostatic pressure, p.sub.1, in the hydraulic oil resulting of a 75 ton payload is approx. 280 bar, with the current configuration. The lifting accumulator was pre-loaded with an adapted amount of gas to obtain a pre-set gas pressure, sp.sub.2, in the lifting accumulator of 300 bar, while the lowering accumulator was preloaded with an adapted amount of gas to obtain a pre-set gas pressure, sp.sub.3, in the lowering accumulator of 260 bar. Thus, the hydraulic pump had to work against a pressure difference of 40-50 bar, as compared to 280 bar if the pump should work against the full weight of the load.

[0093] The calculated movement of the piston rod 6 and the suspended load with a given cyclic heave movement affecting the crane tip is given in FIG. 5. The figure gives both calculated positions and velocities for the piston rod 6, the load and the crane tip, as well as calculated fluid balance between the main hydraulic cylinder and the lifting and lowering accumulators. They are marked as “Cylinder”, “High” and “Low” on the figure, respectively. As seen on the figure, the piston rod moves in counterphase to the crane tip such that the suspended load is not or only to a small degree affected by the heave movements.

[0094] The figure also gives calculated pressures in the main hydraulic cylinder and the lifting and lowering accumulators. The vertical line marked with A inside a ring indicates a phase where the lift is affected by a downwardly heave movement, while the vertical line marked with B inside a ring indicates a phase where the lift is affected by an upwardly heave movement.

LIST OF REFERENCE SIGNS

[0095] 1 main hydraulic cylinder [0096] 2 first piston [0097] 3 first chamber [0098] 4 second chamber [0099] 5 first connection device [0100] 6 piston rod [0101] 7 second connection device [0102] 10 lifting accumulator [0103] 11 second piston [0104] 12 third chamber [0105] 13 fourth chamber [0106] 20 lowering accumulator [0107] 21 third piston [0108] 22 fifth chamber [0109] 23 sixth chamber [0110] 30 first liquid conduit [0111] 31 first actuator controlled valve [0112] 32 second liquid conduit [0113] 33 second actuator controlled valve [0114] 40 third liquid conduit [0115] 41 actuator controlled pump [0116] 50 logical controller unit [0117] 51 motion sensing unit [0118] 52 signal transferring lines [0119] 53 first position sensor [0120] 54 first pressure and temperature sensor [0121] 55 second pressure and temperature sensor [0122] 56 third pressure sensor [0123] 57 fourth pressure sensor [0124] 58 second position sensor [0125] 59 third position sensor