Accommodation ladder control system and method

Abstract

The invention relates to a control system and a corresponding method suitable for controlling a gangway ladder structure gangway ladder, a crane or a similar structure suitable for transferring persons or goods to or from a floating structure, such as a marine vessel, relative to a fixed landing point or a moving landing point. The system comprises: global position measuring means for measuring the position of the floating structure and the position of the landing point and thus a first relative position between the floating structure and the landing point; and a control unit configured to move the gangway ladder relative to the landing point. The system also includes a local position measurement unit positioned at the distal end of the gangway ladder or positioned relative to the distal end of the gangway ladder, and a local position measurement unit configured to measure a second relative position between the landing point and the distal end of the gangway ladder, the local position measurement unit connected to the control system unit to communicate the second relative position to the control system unit. The system is configured to adjust the first relative position based on the second relative position to generate a corrected reference signal, and the control unit is configured to adjust the position of the gangway ladder to position the distal end of the gangway ladder to a desired position relative to the landing point.

Description

Technical Field

[0001] The present technical teachings relate to a gangway, crane or the like suitable for transferring persons or cargo to or from a floating structure, such as a marine vessel. Background Art

[0002] Gangway operations are frequently used to transfer personnel and cargo between floating vessels and other fixed or floating structures. In the wind energy industry, gangway transfer is one of the most common ways to transfer personnel, equipment or cargo between service vessels and wind turbines to perform maintenance tasks. It is also a common way to transfer personnel between offshore accommodation vessels (floatels) and other fixed or floating structures.

[0003] In offshore gangway operation, the gangway is usually moved to a certain distance from the connection point before landing. The landing process itself is well known, for example, according to EP3699078, a contact sensor at the distal end of the gangway is used to measure the relative position between the distal end or tip of the gangway and the landing point, according to EP3305650A1 (KM) and US2020 / 0262521 (KM), a camera or similar device is used to measure the relative position between the distal end or tip of the gangway and the landing point, wherein the gangway is stabilized in a so-called "hover mode" before and possibly after landing. WO2015 / 009163 (ICD) discloses a method for stabilizing a gangway to help the operator control the landing process.

[0004] US2020 / 0262521 describes a landing process in which the vessel moves towards a landing site and at some stage a camera is used to detect the position of the landing site relative to the distal end or tip of the gangway. The system uses a combination of a motion reference unit ("MRU") and a global positioning system ("GPS") to stabilize the distal end of the gangway in a desired hovering position, which is typically provided by a park database for a particular area. This introduces a global positioning function for controlling the distal end of the gangway. In addition, a camera can be used to determine the relative position and movement between the landing site and the distal end of the gangway. As discussed in US2020 / 0262521 and EP3305650A1, movement may be performed in five degrees of freedom, which complicates adjustment.

[0005] It is desirable to include the use of a local reference system mounted at the distal end of the gangway to correct for insufficient position accuracy in the GPS sensor device, for example due to inaccurate park data configuration or due to atmospheric interference, thereby improving the local positioning capability for controlling the distal end of the gangway. If the use of a local reference system is not included, position inaccuracies resulting from using only the GPS sensor device may cause the gangway to crash into the landing field. However, US2020 / 0262521 does not address the subject of how to combine these different types of position sensors to ultimately obtain a position sensor device having both global positioning capability and local positioning capability.

[0006] The straightforward solution of how to combine these global and local sensor systems is usually to use a GPS position measurement device when the distal end of the gangway is far from the landing field, and then switch to a local position sensor measurement device when the distal end of the gangway is close to the landing field. However, the problem of switching to a local position measurement device as described in this article is not trivial for stability characteristics, because the local measurement device is positioned close to the distal end of the gangway. The gangway structure is usually a flexible arrangement, so it ends up with a non-minimum phase control system. This is caused by the physical characteristics of the gangway structure (loop dynamics from the base of the gangway to the tip) introducing time transients in the camera measurement. For example, in the case of a step change in the rotation of the gangway base, the tip will not immediately move in the same direction. The rotation of the tip will be a function of time and eventually align with the gangway base. Initially, the camera will measure the movement in the opposite direction of the base movement due to the non-minimum phase effect. Over time, the tip will start to move in the direction of the base rotation and eventually align with the base. In the feedback control loop, this can cause a highly oscillatory system, so there is a potential risk of damage to both personnel and expensive structures.

[0007] The traditional method used to mitigate this problem is to reduce the gain in the feedback loop, thereby reducing the system's ability and performance to compensate for disturbances, but increasing the robustness to unwanted oscillations of the structure. For such a gangway structure, a reduction in the gain of the feedback loop may result in the system being unable to compensate for environmental disturbances acting on the vessel, thereby failing to complete the overall control task of landing the distal end of the gangway on the landing structure. Summary of the invention

[0008] The object of the present invention is to provide a solution for precise positioning and maintaining stability of the tip of the structure in the final sequence before connection with the landing pad, further applying certain principles to include a camera system without reducing performance. This object is achieved as described in the appended claims.

[0009] In other words, the present invention relates to how to use sensors with given physical positions on a gangway and how to process the signals to avoid non-minimum phase problems or instability problems in the gangway control system.

[0010] The first part of the solution consists of introducing a second sensor with a non-optimal placement from a stability perspective. The resulting secondary measurement is used to improve the accuracy of the relative position between the distal tip and a known structure. This is a practical approach to improving accuracy over current state-of-the-art global position sensors.

[0011] The second part of the solution consists in processing a second measurement signal that separates the non-minimum phase frequency content of the measurement, using only the offset value to make a correction to the global position. The placement of the second sensor in the flexible structure control system is problematic and inherently prone to instability issues due to the non-minimum phase, but the proposed control system does not use the secondary measurement directly. It uses a filtered value from the secondary measurement to bias the global position measurement of the floating structure, thus ignoring the issues of the non-minimum phase system configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be discussed below with reference to the accompanying drawings and will be explained by way of examples.

[0013] Figure 1a to Figure 1c Shows the prior art

[0014] Figure 2 A flow chart according to the present invention is shown.

[0015] Figure 3 A signal processing unit according to the invention is shown. DETAILED DESCRIPTION

[0016] Figure 1a to Figure 1c The prior art is shown, namely when the distal end 2a of the gangway is located near the landing site 1, wherein, for illustrative purposes, the gangway is shown as a flexible rod-shaped member 4, wherein a camera 2 or a similar device is located on or near the distal end 2a of the gangway. The camera is aimed at the landing point 1, and the camera is configured to detect the position and movement of the landing point 1 relative to the tip 2a of the gangway, as mentioned in US2020 / 0262521 and EP3305650A1, taking into account several degrees of freedom, wherein the measured relative position is corrected using the joints and actuators of the gangway structure. The camera or similar device can use the system for assisting the docking of a ship discussed in WO2020 / 070114. The landing point can be an automatically detected feature on the device, or it can also be selected by the operator through user input entered into the system.

[0017] Reference Figure 1c In order to stabilize the position of the tip 2a at the desired position relative to the landing point 1, an actuator base 3 is provided on the vessel, which is configured to move the gangway 4, where only one degree of freedom is shown for simplicity. As shown, this is achieved by providing feedback from a camera 2 or similar device that detects the relative position of the landing target 1 relative to the camera 2 to a servo 6 in the actuator base 3 through a controller 5, which in turn moves the gangway 4 to stabilize the relative position between the landing point 1 and the distal end 2a of the gangway. However, as shown by curve 10, this stabilization process may cause oscillations, which may escalate to the point where landing cannot be made or the gangway and / or the landing point is damaged. A typical solution to address instabilities is to reduce the controller gain. This is suitable for a fixed (or slowly changing) actuator base. However, this is not the case for ships sailing in rough seas.

[0018] Likewise Figure 1a As shown, before the landing process, the system is usually controlled by an inverse kinetic unit 7, which uses the measured global position 8 of the gangway tip 2a and the global position reference 9 of the landing point to calculate the global relative position of the gangway tip relative to the landing point, thereby turning the gangway to the landing point. The relative position in the global coordinates needs to be mapped into local coordinates 25 and then fed into the inverse kinematic unit 7, which is the case when the switch 23 is in the position shown. Typically, when the ship reaches the desired position and heading, the stabilization function of the gangway is enabled. The actuated gangway then moves the position of the distal end or tip 2a so that it eventually hovers in a position near the desired hovering point. Therefore, when the distal end is close to the landing point, the gangway control system uses switch 23 to switch from using a global position sensor to using a local position sensor (e.g., a camera-based sensor).

[0019] As discussed above, the present invention is directed to avoiding the oscillations 10 inherent in the movement of the gangway, which has a bandwidth that can cope with the environmental dynamics. Figure 2 , the relative position error measured by the camera is initially represented in the remote end frame. This error is then mapped to a representation in the earth fixed frame. The error measured by the camera (represented in the earth fixed frame) is used to adjust the desired remote end hovering x, y, and z point. The gangway system is designed to adjust the remote end to the desired hovering x, y, and z point.

[0020] More specifically, refer to Figure 2, a difference from the prior art is that the local controller 5 for directly controlling the gangway 4 shown in Figure 1 is omitted. Instead, the camera 2 is configured to measure the deviation or error of the position of the distal end 2a of the gangway relative to the target 1. The data from the camera 2 is transmitted to the hybrid controller unit 20. The hybrid controller unit 20 is connected to a global positioning measurement system 11 and a global attitude measurement system 12, such as GPS and MRU. Preferably, the hybrid controller unit 20 is connected to the global positioning measurement system 11 and the global attitude measurement system 12 through a filter, thereby receiving the position and attitude data 8 of the distal end 2a of the gangway 4 that is the same as the global position control device using the inverse dynamics unit 7. In this way, the gangway is steered relative to the global reference and the corrected or biased position of the landing point. The correction for the position of the landing point therefore corresponds to the error or deviation measured by the camera.

[0021] Although the measurement of the second relative position discussed here is based on a camera 2 or other imaging device, other types of measurement units capable of detecting the relative position between the gangway tip 2a and the landing point 1 can be used to measure the second relative position, thereby enabling the system to move the tip to the desired position. In addition, the information from the local position measurement unit 2 can be filtered to eliminate vibrations, wave motions and movements with higher frequencies, thereby stabilizing the position data when turning the gangway tip to the predetermined position. The system can handle these faster changes at the stage when the gangway tip is actually connected to the landing point. The filter can be preset or dynamically adjusted according to the measured movement of the gangway tip.

[0022] The hybrid controller unit 20 thus combines the global position of the base 3 with the local relative position detected by the camera 2, thereby adding a correction 17 to the control signal from the operator 18 and / or the predetermined landing position 19. This earth-fixed corrected reference signal 9' is then combined with the estimated global position 8 of the gangway tip 2a, thereby calculating 21 the difference between the global estimated tip value 8 and the earth-fixed corrected reference value 9' based on the data from the camera and the positions of the targets stored in the database. The estimated tip value 8 is calculated by the forward kinematics base to tip positioning unit 22. The control signal 21 is then used to calculate, first using the global to local coordinate mapping unit 25 and then using the inverse dynamics unit 7, the joint position and velocity, which are used as a reference for controlling the position of the distal end of the gangway 4. Once the system is stabilized in the desired position relative to the landing point, the landing operation can be performed automatically or manually using the local servo 6 controlling the gangway 4 and the camera 2.

[0023] According to the present invention, the hybrid controller unit 20 may include a forward dynamics base to the camera unit 13, which feeds the received global position and global attitude to the mapping unit 14. The mapping unit 14 also receives local position data from the camera 2 and provides a combined data set representing the position error measured by the camera in the global coordinates. The output from 14 is combined with the expected hovering distance 18 corresponding to the expected distance of the gangway tip 2a relative to the landing point (for example, pre-stored or selected by the operator) and the measured error between the expected position and the actual position. The resulting error is used to construct a correction or bias data signal. The correction is calculated using a signal processing unit 16 (for example, a filter, but not limited to a filter).

[0024] like Figure 3 As shown, an example of a signal processing unit may be to multiply the error signals xe, ye and ze obtained from 14 and 18 by constants Kx, Ky and Kz, respectively, and integrate the resulting signals to obtain deviations xb, yb and zb. A data corruption signal 15 for detecting whether the data from the secondary position measurement is corrupted is fed to a signal processing control unit 24. The signal processing control unit 24 may be used to reset the signal processing unit, turn the signal processing unit on and off, etc. The functions of the signal processing control unit 24 are not limited to the above-mentioned control functions. The signal processing control unit 24 may control each signal or state individually or all signals or states simultaneously.

[0025] In short, the system and method according to the invention controls the gangway based on the measured global position and attitude 8 of the gangway tip and a corrected reference 9' adjusted for the relative position of the landing point and the distal end of the gangway.

[0026] Unlike the case in the prior art, instead of using camera measurements directly in the gangway servo control loop, camera measurements or local measurement devices 2 are used to determine the position of the gangway base 3 required to obtain the desired hovering distance or position. The distal end 2a is then positioned from the base 3 using forward kinematics. In this way, the camera is not used directly in the servo control loop, eliminating the oscillation problem caused by the measurement device being located at the end of the flexible structure (non-minimum phase system). The main function of the camera is to eliminate the position bias that is usually present in the gangway control system by comparing with a database with stored positions and using only measurements from GPS units and MRU units. The camera measurements can be fed into a filter / observer to determine the bias that is present in the global position measurement. This global bias is forwarded to the gangway control system to determine the actual gangway base position relative to the landing point. The new earth-fixed desired hover x, y and z point used by the gangway system now combines the filtered / observed bias to achieve the goal of hovering at the desired distance from the platform. From this point on, the next step is usually to adopt a control method to implement a connection procedure to connect the gangway to the target point.

[0027] In summary, the invention relates to a control system for controlling the movement of a gangway structure on a floating structure to a desired position relative to a fixed or mobile landing point 1, and a method for controlling the movement of an end point 2a of a gangway. The desired position is usually at a distance from the landing point 1, but in some cases it may be at the landing point. It should be noted that, although the term gangway is used throughout the description, the solution according to the invention is also applicable to corresponding systems, such as cranes or similar systems suitable for transferring people or cargo to or from a floating structure, such as a sea vessel.

[0028] The system comprises a global position measurement system 11, such as GPS, for measuring the position of the floating structure 3 and the position of the landing point 1, and therefore, based on the measurement of the position of the floating structure and the landing point, a first relative position between the floating structure and the landing point is calculated. The control unit system according to the present invention is configured to move the gangway relative to the landing point. The system also comprises a local position measurement unit 2, which is located at the distal end 2a of the gangway 4, close to the distal end 2a of the gangway 4 or at least positioned relative to the distal end 2a of the gangway 4, and the local position measurement unit 2 is configured to measure the second relative position between the landing point 1 and the distal end 2a of the gangway. The local position measurement unit is composed of a camera or a similar system, for example as described in WO2020 / 070114, and the local position measurement unit is connected to the control system unit to transmit the second relative position to the control system unit. The control system is configured to calculate an adjustment or bias signal 17 in the control unit 20, and adjust the first relative position based on the second relative position. A corrected reference signal 9 ′ is thereby generated. The control system is configured to adjust the position of the gangway based on the corrected reference signal so that the gangway distal end 2 a moves to a desired position relative to the landing point 1 .

[0029] The corrected reference signal is obtained by combining the measured first relative position and the second relative position, the local relative position between the camera 2 and the target point 1, and the global relative position between the global position of the landing point and the position of the end of the gangway, so that the combination of the first measurement and the second measurement can provide a closed-loop system.

[0030] The bandwidth of the second relative position measurement transmitted may be filtered by a predetermined filter, for example, the bandwidth of the second relative position measurement transmitted may be filtered by a predetermined filter based on a selected bandwidth to eliminate at least a portion of the effect of movement of the gangway and / or the gangway tip. The filter may be predetermined or adjusted in real time based on movement measured by a suitable sensor on the gangway.

[0031] The second relative position is added to the reference position of the landing point to offset or correct the reference position, or the measured global first reference position of the floating structure vessel is added to the reference position of the landing point to offset or correct the global position data of the floating structure.

[0032] Preferably, the second relative position can be measured using an imaging device (e.g., a camera) configured to identify features on the landing site, but other principles that can be used by those skilled in the art can also be considered, such as laser scanning, beacons, etc. The feature can be selected by the operator or automatically identified by the system.

[0033] The method for controlling a gangway on a floating structure is based on measuring the global position of the floating structure using a global positioning system, wherein the distal end of the gangway is configured to be positioned at a predetermined position relative to a landing point, and the landing point has a known global reference position. The method further comprises the steps of:

[0034] - providing a first relative position between the position of the floating structure and the position of the landing point, for example, said first relative position being defined by a difference between a global position of the structure and the landing point, for example, said global position being measured using a global positioning system,

[0035] - measuring a second relative position between the landing point and a predetermined position of the distal end of the gangway relative to the landing point, for example using a camera or other available system for measuring the relative position between two objects, preferably in three dimensions,

[0036] - calculating a corrected or biased first relative position based on the second relative position, for example by adjusting the measured global position data of the landing point or the floating structure, and

[0037] -Based on the offset first relative position, the distal end of the gangway on the floating structure is controlled and moved to a predetermined position, preferably using a floating structure propulsion system and / or a gangway control actuator to control the distal end of the gangway on the floating structure and move the distal end of the gangway on the floating structure to a predetermined position.

Claims

1. A control system for controlling a gangway structure on a floating structure to a desired position relative to a fixed landing point or a mobile landing point, the system comprising: a global position measurement system providing measurements of the global position of the floating structure and the global position of the landing point, and configured to calculate a first relative position between the floating structure and the landing point based on the measurements of the global position of the floating structure and the global position of the landing point; and a control unit configured to move the gangway relative to the landing point, the system further comprising a local position measurement unit positioned at or relative to the distal end of the gangway, the local position measurement unit configured to measure a second relative position between the landing point and the distal end of the gangway, the local position measurement unit being connected to the control system unit to transmit the second relative position to the control system unit, the system being configured to bias the first relative position based on the second relative position to generate a corrected reference signal, the control system being configured to adjust the position of the gangway based on the corrected reference signal to position the distal end of the gangway to a desired position relative to the landing point.

2. The system according to claim 1, wherein: The corrected reference signal is derived from a combination of a first relative position and a second relative position, wherein the combination of the first measurement and the second measurement provides a closed loop system.

3. The system according to claim 1, wherein: The bandwidth conveying the second relative position is filtered such that the filtered bandwidth conveying the second relative position corresponds to a predetermined bandwidth range of the gangway movement.

4. The system according to claim 1, wherein: The second relative position is added to a reference position of the touchdown point, thereby biasing the reference position.

5. The system according to claim 4, wherein: The second relative position is added to the first reference position of the floating structure, thereby adjusting the data of the global position.

6. A system according to any one of the preceding claims, wherein: The second relative position is measured using an imaging device configured to identify features on the landing site.

7. A method for controlling a gangway on a floating structure, the gangway comprising: A global positioning system for measuring the global position of the floating structure, and the distal end of the gangway is configured to be positioned at a predetermined position relative to a landing point, the landing point having a known global reference position, the method comprising the steps of: - providing a first relative position between the position of the floating structure and the position of the landing point, - measuring a second relative position between said landing point and said predetermined position of the distal end of said gangway relative to said landing point, - calculating a biased first relative position based on said second relative position, and - Based on the offset first relative position, controlling the distal end of the gangway on the floating structure so that the distal end of the gangway on the floating structure enters the predetermined position.

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