JP7709898B2 - Automatic Steering System for Ships - Google Patents

Description

The present invention relates to technology for automatically steering a ship.

In recent years, there has been active development of autonomous vehicles that move on land, sea, air, and even underwater. The uses of autonomous vehicles are diverse, including transportation, investigation, exploration, and rescue. A familiar example of an autonomous vehicle is a robot vacuum cleaner that moves autonomously around a room to clean. A commander gives such an autonomous vehicle a purpose and destination, and the vehicle's trajectory planning and execution, as well as the control of its attitude, speed, position, and other aspects are managed and controlled by a computer.

Autonomous ships, which are ships that have been made autonomous, are also controlled in the same way as the mobile bodies described above. Technologies related to autonomous ships can be broadly categorized into motion control for docking and undocking, tracking, and avoidance. Known control technologies for autonomous ships include technologies that control the ship to be controlled to move from a stopped state at the departure point, turn along the way, and stop at the destination. It is also important that such technologies are versatile enough to be applicable to many ships.

As is well known, ships have larger inertia and weaker braking forces than other navigational bodies, and are characterized by extremely small resistance from fluids at low speeds. For this reason, ship positioning control (SPC) is one of the core elements of autonomous ships. SPC plans a reference trajectory that achieves a given planned route, sailing speed, and turning conditions, and tracks the ship's position against this, and is an extension of the dynamic positioning system (DPS).

It is difficult to stop a ship so that a desired heading and hull position are maintained without using a DPS. The technology described in Non-Patent Document 1 achieves stopping control using a DPS. However, with the technology described in Non-Patent Document 2, which uses an SPC, the ship speed follows the deceleration of the reference speed with a delay, which causes the ship to overshoot its destination.

Hitoshi Tamaru, Hideki Hagiwara, Hideki Yoshida, Tetsuo Tazaki, Hiroaki Miyabe, "Development of an automatic docking system for the Kaisho Maru and its performance evaluation", Journal of the Japan Institute of Navigation, 2005, 113: 157-164 Fuyuki Hane, "Design of Berthing and Unberthing Technology Using Ship Positioning Control", Proceedings of the Japan Society of Naval Architects and Ocean Engineers Conference, March 2021, (32): 1-9 Fuyuki Hane, "Design of a ship positioning system based on non-interference and route sequence", Proceedings of the Japan Society of Naval Architects and Ocean Engineers Conference, May 2020, (30): 33-41 Fuyuki Hane, “Design of Reference Signal Considering Heading Initial Condition and Steering Gear Constraints: Application to Course Maneuvering of a Ship”, Transactions of the Society of Instrument and Control Engineers, 2008, 44(4): 333-342 Fuyuki Hane, "Design of Course-Keeping System by Analytical Method Based on Course-Keeping Control", Journal of the Japan Society of Naval Architects and Ocean Engineers, June 2016, 23: 33-44

The problem that this invention aims to solve is to provide technology that allows a ship to stop closer to its destination.

The automatic steering device for a ship of the embodiment is an automatic steering device for a ship that controls a ship equipped with a propulsion drive unit capable of controlling the speed in the surge direction and the sway direction and the angular velocity around the yaw, and a sensor that detects the bow heading and the ship's position, and includes a reference trajectory generation unit that generates a reference trajectory including a trajectory from a starting point to a destination point based on a planned route, a reference distance that is a time function of the surge direction distance from the starting point to the destination point, and a reference heading that is a time function of the heading, a distance control that causes the position of the ship to follow the reference distance, and a distance control unit that causes the position of the ship to follow the trajectory and the heading of the ship to follow the reference distance. The system is equipped with a movement control unit that controls the ship by using a route control to make the ship follow a reference heading, a holding control unit that controls the ship to maintain its position, and a switching unit that switches from control by the movement control unit to control by the holding control unit when the intersection of the orthogonal line that passes through the ship's position and is perpendicular to the trajectory and the trajectory reaches the destination point, and the distance control is characterized by performing feedforward control that makes the ship distance, which is the distance from the starting position to the intersection, follow the reference distance, and feedback control that makes the distance error between the reference distance and the ship distance converge to zero.

The present invention allows the ship to be stopped closer to the destination.

1 is a block diagram showing an overall configuration of a system including a marine automatic steering device. FIG. 2 is a diagram showing the configuration of a planned route. FIG. 1 is a diagram showing classification of control systems in ship positioning control. FIG. 2 is a diagram showing a control object including a hull model and a driving machine model. FIG. 13 is a diagram showing ship speed characteristics of a hull parameter T _r . FIG. 2 is a diagram illustrating a configuration of a control unit. FIG. 13 is a diagram showing errors in a moving mode. FIG. 13 illustrates an error in the hold mode. FIG. 2 is a diagram showing a configuration of a control system using a distance control unit. FIG. 13 shows the time series of the reference distance _dR and the feedforward rotation _λFF . FIG. 13 is a diagram showing ship position estimation when turning a course. FIG. 13 is a diagram showing the calculation results of the reference position and the route position. FIG. 13 is a diagram showing the planned route and ship position track when the tidal current is zero. FIG. 13 is a diagram showing the planned route and ship position track when there is a tidal current. FIG. 13 is a diagram showing the response of the ship motion. FIG. 13 illustrates an error response. FIG. 13 is a diagram showing a response to a command. FIG. 11 is a diagram showing the response of the drive motor output.

The following describes an embodiment of the present invention with reference to the drawings.

(1) Hull positioning control
(1.1 Configuration of marine automatic steering device)
A system including a marine automatic steering device according to this embodiment will now be described. Fig. 1 is a block diagram showing the overall configuration of a system including a marine automatic steering device.

As shown in FIG. 1, the automatic ship steering device 1 in this embodiment controls a ship having a hull 2 equipped with a propulsion drive unit 3 and sensors 4. In this embodiment, the propulsion drive unit 3 is a drive unit that can control the speed in the surge direction and sway direction, and the angular velocity around the yaw, and in this embodiment, is configured as an azimuth thruster provided at the bow and stern of the hull 2.

The sensors 4 include a gyrocompass that detects the bow direction of the hull 2, a speedometer that detects the speed of the hull 2 through the water, and a GNSS sensor that detects the hull position from a global navigation satellite system (GNSS) such as GPS. The sensors 4 may include any sensor that can detect the bow direction and the hull position.

The automatic ship steering device 1 includes a reference trajectory generating unit 11 and a control unit 12. The reference trajectory generating unit 11 generates a reference trajectory based on the planned route output by the trajectory planning unit 5. The control unit 12 outputs commands to the propulsion drive unit 3 based on the bow heading and hull position detected by the sensors 4 to control the hull speed and angular velocity so that the hull 2 follows the reference trajectory generated by the reference trajectory generating unit 11.

(1.2 Planned Route)
The planned route will now be described. Fig. 2 is a diagram showing the configuration of the planned route.

As shown in Figure 2, the planned route includes a starting point, a destination point, forward speed, and turning conditions, and is composed of a combination of straight lines and circular arcs. In Figure 2, O-XY is the Earth fixed coordinate system, ψ _plan is the planned heading, point A is the starting point, and point B is the destination point. Also, points C, S, and F are the center point, start point, and end point of turning, respectively, ρ _set is the turning radius, and ψ _set is the turning angle.

(1.3 Ship positioning control)
Now, the ship positioning control will be described with reference to Fig. 3, which shows classification of control systems in the ship positioning control.

The hull positioning control by the control unit 12 of the marine automatic steering device 1 controls the vessel to accelerate its forward speed from point A on the planned route shown in Figure 2, turn while moving at a constant speed, and then decelerate to reach the destination point B and maintain its position.

As shown in FIG. 3, the hull positioning control has two control modes: a moving mode and a hovering mode. The control unit 12 executes distance control DC and route control TC in the moving mode, and executes hull position holding control DP, which includes static control and route sequence control (see Non-Patent Document 3), in the hovering mode.

The reference trajectory is generated by the reference trajectory generation unit 11 based on the planned route, and is composed of a direction, position, and time that satisfy the trajectory plan. Specifically, the reference trajectory includes a trajectory from the starting point to the destination point, a reference distance that is a time function of the surge direction distance from the starting point to the destination point, and a reference direction that is a time function of the direction. The control unit 12 determines the hull position along the reference trajectory using point H, which is the intersection of the reference trajectory and a line that passes through the hull position and is perpendicular to the reference trajectory, as the basis for the reference trajectory.

The control unit 12, in the movement mode, makes the bow heading and hull position follow the heading and position associated with the time set in the reference trajectory, and when point H reaches point B, switches the control mode from the movement mode to the holding mode. Furthermore, in the holding mode, the control unit 12 corrects the error between the terminal point B' in the movement mode control, which is located near point B, and the hull position by static determination control, and when the terminal point B' and the destination point B are different, moves the hull position from the terminal point B' to the destination point B by path sequence control. Note that the movement from the terminal point B' to the destination point B may be controlled by a control law other than the path sequence control. According to Non-Patent Document 3, the magnitude of the transient phenomenon of the holding response is proportional to the distance between the terminal point B' and point B. In order to reduce this phenomenon, the destination point is replaced with the terminal point B' instead of point B in the static determination control.

(2) Control Object
The controlled object will be described. Fig. 4 is a diagram showing the controlled object including a hull model and a driving machine model. As shown in Fig. 4, the controlled object is a double-ended ship composed of a hull model and a driving machine model.

(2.1 Hull model)
The ship model will be described. In the ship model, the surge direction is represented by the subscript _u , the sway direction by the subscript _v , and the yaw direction by the subscript _r .

Here, s is the Laplace operator, P(s) is the transfer function, U(s) is the surge speed, V(s) is the sway speed, and R(s) is the yaw angular velocity. Also, Λu(s), Θv(s), and Θr(s) are the control inputs (command amounts), which are the propeller speed and the two thrust angles, respectively. The transfer function of the ship model is

Here, T and K are both hull parameters, and are the time constant and gain, respectively.

Figure 5 shows the ship speed (speed through water) characteristics of the hull parameters. Of the hull parameters, only T _r is shown in Figure 5, but the other variables {K _r , K _u , T _u , K _v , T _v } are also related to the ship speed. The low speed range characteristics in _{T r} are based on the assumption that the inertia term is dominant, ignoring propulsive resistance. From Figure 5, the hull parameters have the following ship speed characteristics:

1. The holding mode region is constant at |u|≦2kn.
2. The transfer mode range is u>2 kn and is proportional to the ship speed.

(2.2 Driving Machine Model)
The driver model will now be explained. The driver azimuth thruster model (hereafter referred to as ATM) controls the thrust vector by the propeller rotation speed (which does not reverse) and its direction. There are limitations to the rotation speed and thrust angle. In Figure 4, the rotation speed λ and thrust against water F of the two ATMs are

Here, the subscripts _f and _a represent the ATMs at the bow (fore) and stern (aft), respectively, and λ ₀ is a constant rotation speed.

The relationship between the command amount and thrust angle is

Here, θ _f and θ _a are the angles of the thrust direction of the ATM relative to the ship's baseline. At this time, the equivalent amount of force generated is

become.

Therefore, the output of the ATM is calculated by multiplying the above formula by the scale factor,

Here, c _θ ^v is a coefficient for converting the unit from speed to thrust angle.

(3) Control System
(3.1 Configuration of the control unit)
The configuration of the control unit will be described with reference to Fig. 6, which is a diagram showing the configuration of the control unit.

6, the control unit 12 includes a movement control unit 121 that performs distance control DC and route control TC in the movement mode, a hold control unit 122 that performs hull position hold control DP in the hold mode, and a switching unit 123. When point H based on the hull position reaches point B, the switching unit 123 switches the control subject from the movement control unit 121 to the hold control unit 122, thereby switching the control system from the movement mode to the hold mode.
(3.2 Definition of Error)
3.2.1 Movement Mode
The error in the movement mode is set from the ship position point P, the vertical foot point H, and the reference position point R, as shown in Figure 7. The heading error ψ _e , the course error y _e , and the distance error d _e are expressed as follows:

Here, ψ is the heading, ψ _R is the reference heading, and y _e is the distance between points P and H.
represents the signed distance between two points, P and H are the x and y coordinates of points P and H, respectively, _dR is the reference distance from the starting point to point R, and _dH is the ship distance from the starting point to point H. Please refer to Non-Patent Document 2 for error calculation.

3.2.2 Hold Mode
8 shows the state after switching from the moving mode to the holding mode. As described above, the control mode is switched when the point H reaches the destination point B, and at this time, the destination point is replaced from the point B to the point B'. This replacement is specifically shown in the following equation.

where B', ψ _B' are the final x, y coordinates and orientation in the move mode, respectively.

The heading error ψ _ek in the hold mode ^, indicated by the subscript ^K , and the position errors x _ek and _y ^ek in the ship coordinates are expressed as ^follows :

Here, Ω _B ^E (ψ) is a matrix that transforms from Earth coordinates (subscript ^E ) to ship coordinates (subscript _B ),

It is.

3.3 Distance Control
Distance control DC converges the distance error to zero by trajectory tracking control. The trajectory tracking control is composed of a reference distance and a two-degree-of-freedom control system including feedforward control and feedback control. The feedforward control makes the ship distance follow the reference distance, and the feedback control forms a closed loop system with the controlled object and converges the distance error to zero.

(3.3.1 Reference Distance and Feedforward Control)
The configuration of the distance control DC by the distance control unit is shown in Fig. 9. In Fig. 9, RG is the reference distance generator, s is the Laplace operator, C _d ^FF (s) is the feedforward controller, C _d ^FB (s) is the feedback controller, and P _x (s) = P _u (s) · s ^-1 is the distance hull model.

The reference distance generator outputs a reference distance D _R (s) from the input position condition, and the feedforward controller outputs a feedforward rotation Λ _FF (s) from the reference distance D _R (s). The feedback controller outputs a feedback rotation Λ _FB (s) from the distance error D _e (s), and stabilizes the closed loop of the distance control DC and removes the disturbance D _D (s). The command propeller rotation Λ _u (s) of the control amount is expressed by the following equation.

When trajectory tracking control is used, the transfer characteristic of the distance error D _e (s) is

From the above equation, the closed loop stability and disturbance rejection performance depend on the feedback controller C _d ^FB (s), and the tracking performance depends on the feedforward controller C _d ^FF (s).

The feedforward rotation Λ _FF (s) is:

Here, the feedforward controller corresponds to the inverse characteristic of the distance hull model.

Therefore, the ship distance is,

which matches the reference distance.

The reference distance d _R and the feedforward rotation λ _FF are as shown in FIG. 10, and the distance trajectory condition

Here, the subscript _set represents a set value. The relationship between _{d R} and λ _FF is

Here, a is a coefficient, and _td is a reference distance time. For details of the above formula, see Non-Patent Document 4.

(3.3.2 Feedback Control)
The feedback controller consists of an estimator and state feedback.

For details of C _d ^FB (s), see Non-Patent Document 2.

(3.4 Route Control)
The course control TC converges the course error y _e to zero by the heading control and the course error control. The command thrust angle θ _r of the course control is expressed by the following equation.

Here, the subscripts _h and _t represent heading control and course error control, respectively.

3.4.1 Orientation Control
The heading control HC is for converging the heading error ψe to zero, has the functions of maintaining heading and changing course, and has the same configuration as the distance control DC. Therefore, the heading control HC replaces the distance in the distance control DC with a heading. The command thrust angle Θ _h (s) of the control amount by the heading control HC is expressed as follows:

Here, Θ _FF (s) is the feedforward thrust angle, C _h ^FF (s)=(P _ψ (s)) ⁻¹ is the feedforward controller, C _h ^FB (s) is the feedback controller, and P _ψ (s)= _Pr (s)·s ⁻¹ is the azimuth ship model.

The reference azimuth ψ _R and the feedforward thrust angle θ _FF are the conditions for turning the azimuth.

The relationship between ψ _R and θ _FF is as follows:

where b is a coefficient and t _ψ is the reference orientation time.

(3.4.2 Course Error Control)
The route error control forms a closed loop system with the sway ship motion, converges the route error to zero, and corrects the error due to the tidal current component. The route error controller _Ct (s) filters the route error _Ye (s) and multiplies it by a control gain, and is given by

Here, T _y is the filter time constant, f _y is the route gain, and f _i is the integral gain. The effect of the disturbance components that move the ship's position is compensated for by the action of the integrator. For the setting of the control gain in the above formula, please refer to Non-Patent Document 5.

(3.5 Reach Estimation)
The reach amount estimation executed by the reference trajectory generating unit 11 determines the position at which turning course begins during a course turn and governs the course error during the turn, and is called WOP (Wheel Over Point). The position of the WOP is the reach amount before point S in FIG. 2. The reach amount is calculated from the reference position and the course position. The reference positions _xR , _yR are

Here, ψ _R is the reference heading and ρ _set is the turning radius.

As shown in Figure 11, the route position is calculated from the trajectory plan, the drive motor, and the ship motion model. When the feedforward command set in the trajectory plan is input to the drive motor,

Here, the feedforward rotation λ _FF is for keeping the ship speed constant (set value u _set ).

The ship's position x, y is calculated using the ship's motion r, u, v.

From.

The results of determining the reference position and the route position are shown in Figure 12. In Figure 12, markers on the line indicate the reference direction ψ _R in units of 10 degrees, and the hull parameters and turning conditions in the movement mode use the values described later in Section 4.1.

The reach amount reach is calculated from the positional relationship between the reference position corresponding to ψ _R = 90 degrees in FIG. 12 and the maximum value of the route position.

However, reach depends on the ship motion model and calculation conditions.

(3.6 Holding Mode Control)
In the hold mode, the control unit 12 performs static determination control and path sequence control by operation management. The static determination control and path sequence control are performed by three controllers, and each of the three controllers ensures closed-loop stability and disturbance rejection with the hull motions of surge, sway, and yaw, and has the same configuration as the feedback controller C _d ^FB (s) of the distance control DC. Therefore, each of the three controllers replaces the distance in the feedback controller C _d ^FB (s) with surge, sway, and yaw. Each of the hull parameters uses extremely low speed correspondence for the hold mode. Each of the three controllers has the following:

Here, the subscript ^k represents the hold mode, and C _x (s), C _y (s), and C _ψ (s) are the surge, sway, and yaw controllers, respectively.

(4) Verification
The effectiveness of the marine automatic steering device according to this embodiment will be verified by simulation.

(4.1 Simulation Conditions)
The simulation conditions will be described.

In the simulation, the calculation time is 30 minutes, the first half (18.3 minutes) of which is controlled in moving mode, and the second half (11.7 minutes) is controlled in holding mode, with the step time being 0.1 seconds. The disturbance component in the simulation is a tidal current component with a northward speed of 1.0 kn and an offset around the heading of 0.3 deg/s.

The hull parameters used in the simulation are shown in the table below.

In this table, _T3 is the hull model

and is equivalent to the steering sensitivity time constant.

In addition, in equations (4) to (6), since T ₃ <<|T|, the coefficient corresponding to T ₃ is omitted. T ₃ is used to generate reference signals D _R (s) and Ψ _R (s).

The settings for the planned route in the simulation are shown below.

Further, a turning angular velocity set value r _set =u _set ÷ρ _set =0.172 rad/s is used.

In the simulation, the constant rotation speed of the drive machine is λ ₀ =110 rpm, and the angle limit is 45 deg.

In the simulation, the main control parameters are common to the moving mode and the holding mode, with the proportional gain being _Kp = 1, the damping coefficient being ζ = 1÷√2, and the damping coefficient of the integral gain being _ζi = 0.9. The coefficient for converting the sway direction command speed into an angle is _cθv ⁼ 45 deg/10 kn. The reach amount is calculated using equation (41).

(4.2 Simulation Results)
The simulation results will now be described. Figures 13 to 18 all show the simulation results. Figures 13 and 14 are diagrams showing the planned route and ship position track when there is no tidal current and when there is a tidal current, respectively. Figure 15 is a diagram showing the response of ship motion. Figure 16 is a diagram showing the response of errors. Figure 17 is a diagram showing the response of commands. Figure 18 is a diagram showing the response of drive motor output.

As shown in Fig. 13, when there are no disturbance components, point B' falls within a radius of 1 m from point B. As shown in Fig. 14, when there are disturbance components, a route error y _e is generated by the disturbance components, but point B' falls within a radius of 10 m from point B. Also, in the ship position track in the movement mode leading to point B', the distance error d _e is the same as when there are no disturbance components, and the error due to the disturbance has been corrected. On the other hand, the route error y _e is larger than when there are no disturbance components, and it becomes difficult to correct the error as the ship speed decreases.

As shown in Figure 15, the surge velocity u, sway velocity v, and yaw angular velocity r are influenced by disturbance components, resulting in bias.

As shown in Fig. 16, in the moving mode, _xe corresponding to the distance error _de and the course error _ye converge to zero, and the heading error _ψe has a drift angle. The drift angle varies depending on the term due to the tidal current component and the term due to the occurrence of r and v due to the rudder angle offset of the _r0 correction. The following table shows the case where the ship is sufficiently settled.

Figure 17 shows the command response. Figure 18 shows the drive output response, and no saturation occurs.

The above simulation results confirmed that the control by the marine automatic steering device 1 according to this embodiment operates appropriately.

The embodiment of the present invention is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. This embodiment and its variations are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

REFERENCE SIGNS LIST 1 Automatic steering device for vessels 2 Hull 3 Propulsion drive device 4 Sensors 11 Reference trajectory generating unit 12 Control unit 121 Movement control unit 122 Holding control unit 123 Switching unit

Claims (5)

An automatic ship steering device for controlling a ship that includes a propulsion drive device capable of controlling a speed in a surge direction and a sway direction and an angular speed around a yaw, and a sensor for detecting a bow heading and a ship position,
a reference trajectory generating unit that generates a reference trajectory including a trajectory from a starting point to a destination point, a reference distance that is a time function of a surge direction distance from the starting point to the destination point, and a reference direction that is a time function of a direction;
a movement control unit that controls the ship by a distance control that causes the position of the ship to follow the reference distance, and a route control that causes the position of the ship to follow the trajectory and the orientation of the ship to follow the reference orientation;
a holding control unit that controls the vessel to hold a position of the vessel;
a switching unit that switches control from the movement control unit to control by the holding control unit when an intersection of the trajectory and an orthogonal line that passes through the position of the ship and is orthogonal to the trajectory reaches the destination point,
An automatic steering device for a vessel, characterized in that the distance control includes feedforward control for making the hull distance, which is the distance from the starting position to the intersection, follow the reference distance, and feedback control for converging the distance error between the reference distance and the hull distance to zero. The automatic steering device for a vessel according to claim 1, characterized in that the reference trajectory generation unit calculates the reach amount based on a reference position based on the reference heading and turning radius, and a positional relationship between the reference trajectory, a drive model of the propulsion drive unit, and a route position based on a hull model of the vessel. The automatic steering device for a vessel according to claim 2, characterized in that the route position is calculated based on the drive model and the hull model to which a feedforward command by the feedforward control is input. The automatic ship steering device according to any one of claims 1 to 3, characterized in that the controller that performs the route control filters the route error, which is the distance between the trajectory in the orthogonal line direction and the position of the ship, and multiplies it by an integral gain. The controller may be expressed as follows, where _Ct (s) is the controller, _Ty is the filter time constant, _fy is the route gain, and _fi is the integral gain:
5. The marine automatic steering system according to claim 4, wherein the automatic steering system is expressed as follows: