Maneuvering system, control method for maneuvering system, and vessel

Abstract

To properly retain bearing in bearing retaining control.SOLUTION: A maneuvering system 17 of a vessel 10 including IMU 13 to 16 estimates configuration of a wave received by the vessel 10 based on behavior of a hull 11 of the vessel 10 measured by the IMU 13 to 16 and takes into consideration influence due to the wave with the estimated configuration when carrying out bearing retaining control.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a ship steering system equipped with a plurality of inertial measurement units, a control method for the ship steering system, and a ship. [Background technology]

[0002] When fishing on a boat, heading control is sometimes performed to keep the boat's heading in a target heading. A boat steering system that performs this heading control typically includes an inertial measurement unit (IMU), which detects the heading in which the boat's bow is actually pointing (hereinafter referred to as the "actual heading") (see, for example, Patent Document 1). Feedback control is then performed to set a target rudder angle based on the difference between the target heading to which the bow should be pointed and the actual heading. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-160045 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when waves are present on the sea surface, a ship undergoing heading-keeping control may ride over the waves. At this time, the waves may cause a yaw rate in the ship's hull. This yaw rate caused by the waves is added to the yaw rate caused by the target rudder angle determined by feedback control, so the amount of change in the ship's heading when steered differs from the amount of change to the target heading, and proper heading maintenance may not be achieved. In other words, there is still room for improvement in ship heading-keeping control.

[0005] An object of the present invention is to perform proper heading maintenance in heading maintenance control. [Means for solving the problem]

[0006] A ship steering system according to one aspect of the present invention is a ship steering system that performs heading maintenance control, and is equipped with a plurality of inertial measurement units.The system estimates the shape of waves that the ship will encounter based on the behavior of the ship's hull measured by the plurality of inertial measurement units, and takes into account the influence of the waves whose shape has been estimated when performing the heading maintenance control.

[0007] With this configuration, when performing heading maintenance control, the influence of waves whose configuration is estimated based on the behavior of the ship's hull measured by multiple inertial measurement units is taken into consideration, so that, for example, when setting a target rudder angle based on the difference between the target heading and the actual heading, the target rudder angle is determined after subtracting a rudder angle corresponding to the yaw rate that occurs in the ship's hull due to the waves whose configuration is estimated. This makes it possible to prevent the amount of change in the heading of the ruddering ship from becoming larger than the amount of change to the target heading, even if the yaw rate caused by the waves is added to the yaw rate that occurs due to the target rudder angle, and enables appropriate heading maintenance. [Effects of the Invention]

[0008] According to the present invention, proper heading can be maintained in heading maintenance control. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view schematically showing a ship according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram for schematically illustrating the configuration of a ship maneuvering system installed on the ship of FIG. 1. [Figure 3] 1 is a graph showing the transition of the hull roll angle measured by the port IMU and the stern IMU when the ship is hit by a head wave from the front starboard side. [Figure 4] 1 is a graph showing the transition of the yaw rate of the ship measured by the port IMU and the stern IMU when the ship is hit by a head wave from the front starboard side. [Figure 5]FIG. 4 is a diagram for explaining a ship maneuvering mode corresponding to heading maintenance control. [Figure 6] FIG. 1 is a block diagram for explaining a conventional heading holding control. [Figure 7] FIG. 10 is a diagram for explaining a yaw rate caused by waves. [Figure 8] FIG. 1 is a diagram for explaining the change in the direction of yaw rate and its influence when a ship overcomes a wave. [Figure 9] FIG. 1 is a block diagram for explaining heading control that takes into account a yaw rate caused by waves. [Figure 10] FIG. 10 is a block diagram for explaining heading maintenance control in which the absolute value of the target steering angle is limited. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a plan view schematically illustrating a boat according to an embodiment of the present invention. In FIG. 1, the boat 10 includes a hull 11 and at least one, for example, two outboard motors 12 as propulsion units attached to the stern of the hull 11 via a bracket (not shown) or the like. Each outboard motor 12 is configured to be able to turn approximately horizontally with respect to the hull 11 of the boat 10, with the bracket as a fulcrum. When each outboard motor 12 turns and the direction of action of the thrust generated by each outboard motor 12 tilts relative to the longitudinal centerline of the hull 11, a yaw moment is generated that turns the hull 11, causing the boat 10 to change course (steer). In this embodiment, the angle between the direction of action of the thrust of each outboard motor 12 and the longitudinal centerline of the hull 11 is referred to as the "rudder angle." The propulsion units included in the boat 10 are not limited to outboard motors 12 and may be, for example, inboard motors or inboard-outboard motors. The power source of the propulsion device may be an internal combustion engine, an electric motor, or a hybrid of an internal combustion engine and an electric motor.

[0011] Furthermore, four IMUs 13 to 16 are disposed on the hull 11. Specifically, IMU 13 is disposed at the bow, IMU 14 at the stern, IMU 15 at the starboard side, and IMU 16 at the port side. However, it is not necessary to dispose IMUs at all of the bow, stern, starboard, and port sides; it is sufficient to dispose IMUs in at least two locations among the bow, stern, starboard, and port sides.

[0012] Fig. 2 is a block diagram for explaining the schematic configuration of a maneuvering system mounted on the boat 10 of Fig. 1. In Fig. 2, the maneuvering system 17 includes an outboard motor 12, IMUs 13 to 16, a BCU (Boat Control Unit) 18, an MFD (Multi-Function Display) 19, a GPS 20, a compass 21, a remote control unit 22, a joystick 23, a steering mechanism 24, a maneuvering panel 25, a remote control ECU 26, a key switch unit 27, and an SCU (Steering Control Unit) 28. The components of the maneuvering system 17 are connected to each other so that they can communicate with each other.

[0013] The GPS 20 detects the current position and speed of the ship 10 and transmits the current position and speed of the ship 10 to the BCU 18. Each of the IMUs 13 to 16 measures the behavior of the ship 10, such as the pitch, yaw, and roll of the hull 11 at the location where it is installed, and transmits the measurement results to the BCU 18. The compass 21 detects the actual heading of the ship 10 and transmits the actual heading of the ship 10 to the BCU 18.

[0014] The remote control unit 22 has levers 22a corresponding to each outboard motor 12, and the boat operator operates each lever 22a to switch the direction of action of the propulsive force generated by the corresponding outboard motor 12 between forward and backward, and to adjust the output of the corresponding outboard motor 12 to adjust the boat speed. At this time, the remote control unit 22 transmits signals to the BCU 18 and the remote control ECU 26 to control the outboard motors 12 in response to the operation of the levers 22a. The joystick 23 is a control stick for steering the boat 10, and transmits signals to the BCU 18 and the remote control ECU 26 to move the boat 10 in a tilting direction. The steering mechanism 24 is a device used by the boat operator to determine the course of the boat 10. When the boat operator rotates the steering wheel 24a of the steering mechanism 24 left and right, each outboard motor 12 turns, generating a yaw moment and changing the course of the boat 10.

[0015] The key switch unit 27 has a main switch 27a and an engine shutoff switch 27b. The main switch 27a is an operator for collectively starting and stopping the engines 29, which are the power sources of the outboard motors 12, and the engine shutoff switch 27b is a switch for emergency shutdown of the engines of each outboard motor 12. The MFD 19 is, for example, a color LCD display that functions as a display for displaying various information and also as a touch panel for receiving inputs from the operator. The operation panel 25 has switches (not shown) corresponding to various operation modes, and the operator switches the boat 10 to the desired operation mode by operating the corresponding switch. An SCU 28 is provided for each outboard motor 12 and controls a steering unit (not shown) that turns the corresponding outboard motor 12 approximately horizontally, thereby changing the direction of thrust of each outboard motor 12.

[0016] The BCU 18 detects the state of the boat 10 based on signals transmitted from each component of the steering system 17, determines the magnitude of thrust that each outboard motor 12 should generate and the direction of thrust that should be taken, and transmits these to each remote control ECU 26. One remote control ECU 26 is provided for each outboard motor 12, and transmits signals to the engine ECU 30 and SCU 28 of each outboard motor 12 to control the engine 29 and steering unit of each outboard motor 12 in response to signals transmitted from the BCU 18, steering mechanism 24, remote control unit 22, joystick 23, etc., thereby adjusting the magnitude and direction of thrust of the outboard motor 12.

[0017] For example, when the ship 10 is hit by a head wave from diagonally ahead, the waves (especially the wave crests) reach different parts of the hull 11 at different times, and therefore, the effects of the waves on different parts of the hull 11 at the same time are different. Furthermore, the hull 11 is not a completely rigid body. Therefore, when the ship 10 is hit by a head wave from diagonally ahead, different parts of the hull 11 may behave differently at the same time. In this embodiment, the four IMUs 13-16 are arranged at different parts of the hull 11, and therefore, the pitch, yaw, and roll of the hull 11 measured by each of the IMUs 13-16 at the same time may differ.

[0018] Figure 3 is a graph showing the change in the roll angle of the hull 11 measured by the port IMU 16 and the stern IMU 14 when the ship 10 receives a head wave from the front starboard side, and Figure 4 is a graph showing the change in the yaw rate of the hull 11 measured by the port IMU 16 and the stern IMU 14 when the ship 10 receives a head wave from the front starboard side.

[0019] In the case shown in Figure 3, there is little phase difference between the roll angle of the port side and the roll angle of the stern, but there is a misalignment between the roll angle of the stern and the roll angle of the port side. When a certain point on the hull 11 runs over a wave crest, that point is thought to creak, generating a relatively large roll angle. In other words, it is thought that the wave crest reaches that point at the time when a relatively large roll angle occurs. Therefore, the difference in time when the wave crest reaches the stern and port side can be determined from the difference in time when a relatively large roll angle occurs. By considering this difference in time when the wave crest reaches the stern and port side and the positional relationship between the port IMU 16 and the stern IMU 14, the wave traveling direction and wave speed can be estimated.

[0020] 4, there is a difference in yaw rate between the stern and port side, and the yaw rate occurs earlier on the port side than on the stern, but when a yaw rate occurs at a certain point on the hull 11, it is considered to correspond to a wave reaching that point. Therefore, in the case shown in Fig. 4, it is considered that the wave reaches the port side first, and then the wave reaches the stern, and therefore the wave traveling direction and wave speed can be estimated from the difference between the time the wave reaches the port side and the time the wave reaches the stern, and the relative positions of the port IMU 16 and the stern IMU 14.

[0021] The wave height can also be estimated from the amount of change in pitch measured by the port IMU 16 and the stern IMU 14. For example, the amount of change in the height direction of the vessel 10, i.e., the wave height, can be estimated from the integral value of the amount of change in pitch or the vessel speed, but the relationship between the wave height and the amount of change in pitch on the vessel 10 can be obtained in advance, and the wave height can be estimated from the measured amount of change in pitch based on this relationship. Furthermore, the wave wavelength can also be estimated from the pitch period measured by the port IMU 16 and the stern IMU 14.

[0022] That is, the measurement results of the port IMU 16 and the stern IMU 14 can be used to estimate the wave form, such as the wave traveling direction, wave speed, wave height, and wavelength, of the waves that the ship 10 receives. The present invention is based on these findings, and in the embodiment of the present invention, the form of the waves that the ship 10 receives is estimated based on the measurement results of each of the IMUs 13 to 16.

[0023] In the above example, the measurement results of the port IMU 16 and the stern IMU 14 were used. However, to improve the accuracy of estimating the wave shape received by the vessel 10, it is preferable to have a larger difference in the roll angle, yaw rate, and pitch, and the difference in the measured roll angle, yaw rate, and pitch increases the further apart the two IMUs are. Therefore, to improve the accuracy of estimating the wave shape received by the vessel 10, it is preferable to use the measurement results of the bow IMU 13 and the stern IMU 14.

[0024] Furthermore, when the crew is fishing, the maneuvering system 17 of the boat 10 performs heading maintenance control. In a maneuvering mode corresponding to heading maintenance control, the heading (direction of the bow) of the boat 10 is maintained in a specific direction. Fig. 5 is a diagram illustrating the maneuvering mode corresponding to heading maintenance control.

[0025] 5(A), for example, the heading (direction of the bow) of the boat 10 is maintained in a specific direction (upward in the figure) when a forward thrust (indicated by the white arrow in the figure) is acting on the hull 11. When this boat maneuvering mode is performed, the BCU 18 controls the thrust and the direction of thrust action of each outboard motor 12 so as to maintain the direction of the bow even if wind or water current (indicated by the black arrow in the figure) acts on the boat 10 and the boat 10 is carried downstream by the wind or water current. In other words, this boat maneuvering mode is a boat maneuvering mode in which the boat 10 continues to sail while maintaining the direction of the bow in a specific direction, even when wind or water current acts on the boat 10.

[0026] In the maneuvering mode shown in FIG. 5(B), when no forward or reverse thrust is acting on the hull 11, the bow is maintained in a specific direction (upward in the figure). Even when this maneuvering mode is performed, the BCU 18 controls the thrust and thrust acting direction of each outboard motor 12 so that the bow is maintained in a specific direction even if wind or water current (black arrows in the figure) acts on the boat 10 and the boat 10 is carried downstream by the wind or water current. In other words, this maneuvering mode is a maneuvering mode in which the boat 10 is carried downstream by the wind or water current while maintaining the bow in a specific direction. Note that in this maneuvering mode, the thrust generated by each outboard motor 12 is the minimum thrust required to generate a yaw moment acting on the hull 11, and is not a thrust required to actively move the boat 10 to a certain point.

[0027] When the ship steering system 17 performs heading maintenance control, the BCU 18 sets a rudder angle (hereinafter referred to as a "target rudder angle") that generates a yaw moment for maintaining the heading of the bow in a specific direction.

[0028] Figure 6 is a block diagram for explaining conventional heading maintenance control. In Figure 6, first, a target yaw rate is set by feedback control to reduce the heading deviation, which is the difference between the target heading and the actual heading, to zero, based on the target heading, which is the direction of the bow to be maintained and set by the helmsman on the MFD 19 or the like, and the actual heading detected by the compass 21. Then, by feedback control and feedforward control, a target rudder angle to achieve the target yaw rate is set based on the target yaw rate, the actual yaw rate of the hull 11 measured by the IMU 13 or the like ("actual yaw rate" in the figure), and the ship speed detected by the GPS 20.

[0029] When the ship 10 encounters waves, the waves may cause a yaw rate. Figure 7 is a diagram for explaining the yaw rate caused by waves. Normally, waves cause a rotational movement of water in the vertical direction, and at the crest of the wave, the water moves in the direction of the wave's progression (propagation) (indicated by the thick black arrow in the figure), and at the trough of the wave, the water moves in the opposite direction to the direction of the wave's progression.

[0030] Therefore, when the ship 10 is subjected to following waves from diagonally rearward on the starboard side, as shown in Figure 7(A), if the area near the bow is at the wave bottom and the area near the stern is at the wave crest, the bow will be subjected to a force pushing back against the hull 11 due to the water current from diagonally forward left (indicated by the outline arrow in the figure), and the stern will be subjected to a force pushing against the hull 11 due to the water current from diagonally rearward right (indicated by the outline arrow in the figure). As a result, a clockwise moment (indicated by the hatched arrow in the figure) acts on the hull 11 in a plan view, and a yaw rate that turns the ship 10 to the starboard side will be generated.

[0031] Furthermore, when the ship 10 is subjected to following waves from diagonally rearward on the starboard side, as shown in Figure 7(B), when the vicinity of the bow is at the wave crest and the vicinity of the stern is at the wave trough, the bow receives the water current from diagonally rearward to the right and receives a force pushing against the hull 11 (indicated by the outline arrow in the figure), and the stern receives the water current from diagonally forward to the left and receives a force pushing back against the hull 11 (indicated by the outline arrow in the figure). As a result, a counterclockwise moment (indicated by the hatched arrow in the figure) acts on the hull 11 in a plan view, and a yaw rate that turns the ship 10 to the port side is generated.

[0032] Furthermore, when the vessel 10 encounters a head wave, the stern of the vessel 10 is subjected to the water current flowing into the water surface cut by the bow, but if the vessel 10 moves diagonally against the head wave, the bow and stern will be subjected to the water currents from opposite directions, which will also generate a yaw rate that turns the vessel 10.

[0033] The yaw rate caused by such waves is added to the yaw rate generated by the target rudder angle set in the heading maintenance control of Figure 6, so the direction of the bow of the ship 10, which is steering according to the target rudder angle, may exceed the target heading or may not reach the target heading.

[0034] Furthermore, when the vessel 10 rides over waves, the direction of the yaw rate caused by the waves may change. Figure 8 is a diagram for explaining the change in the direction of the yaw rate when the vessel 10 rides over waves and its influence.

[0035] For example, when the ship 10 is hit by a head wave diagonally forward on the starboard side, first, as shown in Figure 8(A), when the bow rides over the wave crest, water is moving at the wave crest in the direction of wave travel (indicated by the thick black arrow in the figure), so the bow is hit by the water current from diagonally forward to the right and receives a force pushing back against the hull 11 (indicated by the open arrow in the figure). At this time, the stern is positioned on the slope of the wave, but because water does not move significantly (fast) on the slope of the wave, the stern is also hit by the water current from diagonally forward to the right, but the force pushing back against the hull 11 from diagonally forward to the right is smaller than the force pushing back against the bow. As a result, a counterclockwise moment (indicated by the hatched arrow in the figure) acts on the hull 11 in a plan view, generating a yaw rate that turns the ship 10 to the port side. In other words, since the direction of the bow will swing to the port side of the target heading, the heading maintenance control of Figure 6 sets a target rudder angle that will generate a clockwise yaw moment in a plan view that will return the direction of the bow to the starboard side.

[0036] Then, as shown in Figure 8(B), as the wave moves in the direction of travel, the wave crest approaches the stern, and the bow is positioned on the slope of the wave, the stern receives a force pushing back against the hull 11 (indicated by the open arrow in the figure) due to the water current from the diagonally forward right. The bow also receives a water current from the diagonally forward right, but as described above, the water does not move significantly on the slope of the wave, so the force pushing back against the hull 11 that the bow receives from the diagonally forward right is smaller than the force pushing back against the stern. Then, a clockwise moment (indicated by the hatched arrow in the figure) acts on the hull 11. At this time, a clockwise moment (indicated by the dashed arrow in the figure) resulting from the target rudder angle set by the heading keeping control in Figure 6 acts on the hull 11. As a result, the yaw rate resulting from the wave is added to the yaw rate resulting from the target rudder angle set by the heading keeping control in Figure 6. This causes the hull 11 to experience a yaw rate higher than the yaw rate required to return the bow to the target heading, causing the bow of the steered vessel 10 to move beyond the target heading (Figure 8(C)).

[0037] That is, as explained using the examples in Figures 7 and 8, if a yaw rate caused by waves occurs when performing the heading maintenance control of Figure 6, this yaw rate will be added to the yaw rate caused by the target rudder angle set in the heading maintenance control of Figure 6, and therefore proper heading maintenance may not be performed. In this embodiment, to address this, the influence of waves is taken into consideration when the ship maneuvering system 17 performs heading maintenance control.

[0038] However, depending on the type of waves the ship 10 receives, the yaw rate caused by the waves may be so small that its effect may be negligible. Therefore, in this embodiment, it is determined whether the ship 10 is receiving waves, and if it is determined that the ship 10 is receiving waves, the content of the heading maintenance control is changed depending on the type of waves the ship 10 receives.

[0039] For example, if the wavelength of the received waves is smaller than one time the hull length of the ship 10, a situation such as that described in Figure 7, where a wave crest occurs near the bow and a wave trough occurs near the stern, or a situation such as that described in Figure 7, where a wave trough occurs near the bow and a wave crest occurs near the stern, will not occur, and instead multiple wave crests and wave troughs will exist along the hull length of the ship 11. In this case, the forces that the ship 11 receives from the water current at each wave crest and each wave trough (forces pushing back against the ship 11 and forces pushing against the ship 11) will cancel each other out, and the yaw rate caused by the waves will be very small. Therefore, if the wavelength of the received waves is smaller than one time the hull length of the ship, the conventional heading control of Figure 6 will be performed without considering the yaw rate caused by the waves.

[0040] Furthermore, even if the wavelength of the received waves is equal to or greater than the hull length of the ship 10, if the wave inclination angle determined by the wavelength and wave height of the waves is less than 2 degrees, the force that the ship 11 receives from the water current at the wave crest and wave trough will be very small, and the yaw rate caused by the waves will also be very small. Therefore, even if the wavelength of the received waves is equal to or greater than the hull length of the ship 10, if the wave inclination angle determined by the wavelength and wave height of the waves is less than 2 degrees, the conventional heading keeping control of Figure 6 is performed without considering the yaw rate caused by the waves.

[0041] On the other hand, if the wavelength of the waves received is equal to or greater than the hull length of the ship 10, and the wave inclination angle determined by the wavelength and wave height of the waves is equal to or greater than 2 degrees, the force that the ship 11 receives from the water current at the wave crest and wave trough becomes large, causing the ship 11 to generate a yaw rate that should not be ignored. Therefore, heading control is performed as shown in Figure 9, which will be described later, taking into account the yaw rate generated by the waves.

[0042] The waves that the ship 10 receives are waves whose shapes are estimated based on the measurement results of the IMUs 13 to 16.

[0043] Fig. 9 is a block diagram for explaining heading maintenance control that takes into account the yaw rate caused by waves. In Fig. 9, first, a target yaw rate is set from the target heading and the actual heading by feedback control.

[0044] Next, a yaw rate that occurs in the hull 11 due to waves whose form is estimated based on, for example, the measurement results of the bow IMU 13 and the stern IMU 14 is predicted. Note that the measurement results used to estimate the form of waves that the ship 10 will receive are not limited to the measurement results of the bow IMU 13 and the stern IMU 14, and it is sufficient to use at least two of the measurement results of each of the IMUs 13 to 16.

[0045] Then, using feedback control and feedforward control, a target rudder angle for achieving the target yaw rate is set from the target yaw rate, the predicted value of the yaw rate generated in the hull 11 due to waves ("predicted yaw rate value" in the figure), and the ship speed detected by the GPS 20. At this time, the target rudder angle is set so that the target yaw rate is achieved when the predicted yaw rate value is added to the yaw rate generated by the target rudder angle. Specifically, the target rudder angle is set to be the rudder angle required to achieve the target yaw rate minus the rudder angle corresponding to the predicted yaw rate value.

[0046] According to this embodiment, in heading maintenance control, when determining the target rudder angle based on the difference between the target heading and the actual heading, the target rudder angle is determined after subtracting a rudder angle equivalent to the predicted value of the yaw rate generated in the hull 11 due to waves. This makes it possible to prevent the direction of the bow of the steered vessel 10 from exceeding the target heading, even if the yaw rate caused by waves is added to the yaw rate generated due to the target rudder angle, and allows for appropriate heading maintenance.

[0047] In this embodiment, four IMUs 13 to 16 are disposed on the hull 11 of the ship 10. As a result, even if the measurement results of any of the IMUs contain errors, drift effects, or noise, the errors, drift effects, and noise can be eliminated by averaging the measurement results with the measurement results of the other IMUs. As a result, the shape of waves the ship 10 will experience can be accurately estimated. Furthermore, even if one of the IMUs fails, the shape of waves the ship 10 will experience can be estimated by using the measurement results of the other IMUs, and heading control that takes into account the yaw rate caused by the waves can be continued.

[0048] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0049] For example, if the wavelength of the waves received by the ship 10 is equal to or greater than the hull length of the ship 10, and the wave inclination angle determined by the wavelength and wave height of the waves is equal to or greater than 2 degrees, as shown in the heading maintenance control of Figure 9, the maneuvering system 17 predicts the yaw rate that will occur in the hull 11 due to the waves, and sets the target rudder angle after subtracting the rudder angle corresponding to the predicted yaw rate.

[0050] However, in an actual environment, wave heights change irregularly. Furthermore, the vessel 10 may be subjected to swells and wind waves from different directions. In other words, because wave shapes change irregularly, it is difficult to accurately predict the force the vessel 10 will receive from waves. Furthermore, the yaw rate caused by actual waves whose shapes change irregularly may be greater than the yaw rate caused by the estimated wave shapes. Therefore, an upper limit may be set on the absolute value of the rudder angle in accordance with the estimated wave shapes to reduce the yaw rate caused by the rudder angle, thereby preventing the vessel 10 from turning excessively even if the yaw rate caused by actual waves whose shapes change irregularly is added.

[0051] FIG. 10 is a block diagram for explaining heading maintenance control in which the absolute value of the target steering angle is limited.

[0052] 10, first, a target yaw rate is set from a target heading and an actual heading by feedback control. Furthermore, for example, the heading of waves whose shape is estimated based on the measurement results of the bow IMU 13 and the stern IMU 14 is detected, and the average value of the yaw rate measured by the bow IMU 13 and the stern IMU 14 is calculated. It is also possible to detect the heading of waves received by the ship 10 and calculate the average value of the yaw rate using not only the measurement results of the bow IMU 13 and the stern IMU 14 but also at least two of the measurement results of the IMUs 13 to 16.

[0053] Then, by using feedback control and feedforward control, a tentative target rudder angle for realizing the target yaw rate is set from the target yaw rate, the average value of the yaw rate, and the boat speed detected by the GPS 20.

[0054] Then, a decision is made as to whether or not to limit the absolute value of the target rudder angle based on the ship speed and the wave height and wavelength of the waves received by the ship 10. Specifically, when the wavelength of the waves received is equal to or greater than 1 time the hull length of the ship 10 and the wave inclination angle determined by the wavelength and wave height of the waves is equal to or greater than 2 degrees, a decision is made as to whether or not the absolute value of the set provisional target rudder angle is, for example, 10 degrees or greater. If the absolute value of the provisional target rudder angle is less than 10 degrees, the provisional target rudder angle is set as is as the target rudder angle. On the other hand, if the absolute value of the provisional target rudder angle is equal to or greater than 10 degrees, the target rudder angle is set so that the absolute value is 10 degrees.

[0055] In addition, if the wavelength of the received waves is less than one time the hull length of the ship 10, or if the wavelength of the received waves is more than one time the hull length of the ship 10 but the wave inclination angle determined by the wavelength and wave height of the waves is less than 2 degrees, the provisional target rudder angle is set as the target rudder angle as is.

[0056] Although the upper limit of the absolute value of the rudder angle is set uniformly to 10 degrees as described above, the upper limit of the absolute value of the rudder angle may be changed depending on the inclination angle of the waves. For example, when the inclination angle is large and the yaw rate caused by the actual waves becomes larger, the upper limit of the absolute value of the rudder angle may be set to a value smaller than 10 degrees. Also, instead of setting the upper limit of the absolute value of the rudder angle to a value smaller than 10 degrees, the target yaw rate may be limited (an upper limit may be set for the target yaw rate).

[0057] Furthermore, the heading maintenance control of Fig. 9 may be combined with the heading maintenance control of Fig. 10. This heading maintenance control is performed when the ship 10 is subjected to waves, the wavelength of the waves is equal to or greater than the hull length of the ship 10, and the wave inclination angle, determined by the wavelength and wave height of the waves, is equal to or greater than 2 degrees.

[0058] In this heading control, first, a target yaw rate is set from the target heading and actual heading using feedback control, the shape of the waves that the ship 10 will encounter is estimated based on the measurement results of the bow IMU 13 and the stern IMU 14, and the yaw rate that will occur in the hull 11 due to this estimated wave shape is predicted.

[0059] Then, using feedback control and feedforward control, a rudder angle for realizing the target yaw rate is set as a provisional target rudder angle from the target yaw rate, the predicted yaw rate value, and the ship speed detected by the GPS 20. This provisional target rudder angle corresponds to the rudder angle required to realize the target yaw rate minus the rudder angle corresponding to the predicted yaw rate value.

[0060] Thereafter, it is determined whether or not to limit the absolute value of the target rudder angle based on the vessel speed and the wavelength and wave height of the vessel 10. Specifically, if the wavelength of the waves received is equal to or greater than the hull length of the vessel 10 and the wave inclination angle determined by the wavelength and wave height of the waves is equal to or greater than 2 degrees, and the absolute value of the set tentative target rudder angle is less than 10 degrees, the tentative target rudder angle is set as the target rudder angle as is. On the other hand, if the absolute value of the tentative target rudder angle is 10 degrees or greater, the target rudder angle is set so that the absolute value is 10 degrees.

[0061] In addition, if the wavelength of the received waves is less than one time the hull length of the ship 10, or if the wavelength of the received waves is more than one time the hull length of the ship 10 but the wave inclination angle determined by the wavelength and wave height of the waves is less than 2 degrees, the provisional target rudder angle is set as the target rudder angle as is.

[0062] In this embodiment, the form of waves received by the ship 10 is estimated based on the measurement results of each of the IMUs 13 to 16, but in addition to the measurement results of each of the IMUs 13 to 16, a camera or LIDAR may be mounted on the ship 10, and images of the sea surface captured by the camera and the form of the sea surface measured by the LIDAR may be used in combination to estimate the form of waves received by the ship 10. This can improve the accuracy of the estimated wave form. [Explanation of symbols]

[0063] 10 Ship, 11 Hull, 13-16 IMU, 17 Steering system, 18 BCU

Claims

1. A ship steering system that performs heading maintenance control, a plurality of inertial measurement units; estimating the type of waves that the vessel will receive based on the behavior of the vessel's hull measured by the plurality of inertial measurement units; A ship maneuvering system that takes into account the influence of the waves whose shape has been estimated when performing the heading maintenance control.

2. The ship steering system according to claim 1 , wherein the inertial measurement units are arranged at least two locations on the bow, stern, starboard side, and port side of the ship.

3. 2. The ship maneuvering system according to claim 1, wherein the type of waves that the ship will experience is estimated based on deviations in yaw rate of the ship's hull measured by the plurality of inertial measurement units.

4. 2. The ship maneuvering system according to claim 1, wherein the type of waves that the ship will experience is estimated based on deviations in roll angle of the ship's hull measured by the plurality of inertial measurement units.

5. 2. The ship maneuvering system according to claim 1, wherein the type of waves that the ship will experience is estimated based on an amount of change in pitch of the ship's hull measured by the plurality of inertial measurement units.

6. 2. The ship maneuvering system according to claim 1, wherein, when it is determined that the ship is receiving waves based on the behavior of the ship's hull measured by the plurality of inertial measurement units, the content of the heading maintenance control is changed depending on the shape of the waves.

7. 7. A ship maneuvering system according to claim 6, wherein the heading holding control with the changed content takes into account a yaw rate occurring in the hull of the ship due to the waves when setting a rudder angle of the ship.

8. 7. The ship maneuvering system according to claim 6, wherein in the heading holding control whose content has been changed, when setting the rudder angle of the ship, an upper limit value is set for the absolute value of the rudder angle of the ship depending on the wave shape.

9. 7. The ship maneuvering system according to claim 6, wherein if the wavelength of the wave whose shape is estimated is equal to or greater than one time the hull length of the ship, the influence of the wave is taken into consideration in the heading keeping control.

10. 10. The ship maneuvering system according to claim 9, wherein even if the wavelength of the wave whose shape is estimated is equal to or greater than one time the hull length of the ship, if the wave inclination angle determined by the wave wavelength and wave height is less than 2 degrees, the influence of the wave is not taken into account in the heading keeping control.

11. A control method for a ship maneuvering system that performs heading maintenance control, comprising: the ship steering system includes a plurality of inertial measurement units; estimating the type of waves that the vessel will receive based on the behavior of the vessel's hull measured by the plurality of inertial measurement units; A control method for a ship maneuvering system, wherein the influence of the waves whose shape has been estimated is taken into consideration when performing the heading maintenance control.

12. 12. The control method for a ship maneuvering system according to claim 11, wherein, when it is determined that the ship is receiving waves based on the behavior of the hull of the ship measured by the plurality of inertial measurement units, content of the heading maintenance control is changed depending on the shape of the waves.

13. A ship equipped with a ship maneuvering system that performs heading maintenance control, The ship steering system is equipped with a plurality of inertial measurement units, estimates the shape of waves that the ship will encounter based on the behavior of the ship's hull measured by the plurality of inertial measurement units, and takes into account the influence of the waves whose shape is estimated when performing the heading maintenance control.

14. 14. The ship according to claim 13, wherein, when the ship maneuvering system determines that the ship is encountering waves based on the behavior of the hull of the ship measured by the plurality of inertial measurement units, it changes content of the heading keeping control depending on the shape of the waves.

15. A ship steering system that performs heading maintenance control, a plurality of inertial measurement units; A ship steering system that measures the behavior of the hull of the ship using the multiple inertial measurement units.

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