Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B59/00—Hull protection specially adapted for vessels; Cleaning devices specially adapted for vessels
  • B63B59/06—Cleaning devices for hulls
  • B63B59/08—Cleaning devices for hulls of underwater surfaces while afloat
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B59/00—Hull protection specially adapted for vessels; Cleaning devices specially adapted for vessels
  • B63B59/06—Cleaning devices for hulls
  • B63B59/10—Cleaning devices for hulls using trolleys or the like driven along the surface
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
  • B63G8/00—Underwater vessels, e.g. submarines; Equipment specially adapted therefor
  • B63G8/001—Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations
  • B63G2008/002—Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations unmanned

Definitions

• the present invention relates to an underwater vehicle for operating on a submerged surface of a submerged body, such as a ship's hull below the water line, or a subsea installation, as recited in the preamble of the accompanying patent claims.
• ROVs remote controlled vehicles
• the object of the invention is to provide a versatile underwater vehicle with a design that takes in to consideration environment, different operational requirements and efficient component lay-out, the influence of locomotion transition on design and control, attitude control strategy on curved surfaces to optimize attitude according to surface and water and to set up feed-forward loops to improve controller integration, and attitude measurement involving fusion of sensors, such as e.g. inertial measurement sensors and ultrasonic sensors.
• an object of the design of the underwater vehicle of the present invention is to provide a universal platform to perform inspection and maintenance on complex curvatures on ship hulls.
• the principle axes of motion are surge, sway, heave, pitch, yaw, and roll.
• a further object of the underwater vehicle of the present invention is to provide an underwater vehicle that does not demand a full selection of these motions, but with advanced maneuverability that is simpler in design with respect to the usually employed separate or coupled actuators to control all these movements.
• adaptation to the topology at ship stern and bow are considered, and optimization of the location of thrusters, and of the allocation of buoyancy and ballast, while taking into account stability which may interfere balancing on the surface to be worked on.
• the design takes into account that the center of rotation is CG in water or contact point on surface, depending on the actual mode, and the switching of maneuver mode by e.g attachment recognition.
• Attitude Control Strategy considers which ⁇ shall be kept, as the angle ⁇ could be derived from inertial measurement sensors and compass, however, magnetic field distortion could be caused by a ship's hull, electric motors and magnetic wheels, or the angle ⁇ ' can be derived from ultrasonic sensors or auxiliary wheels.
• Sensor Fusion and Filter considerations could involve utilization of e.g. an inertial measurement unit, or IMU, for measuring and reporting the craft's velocity, orientation, and gravitational forces, using a combination of accelerometers and gyroscopes, sometimes also magnetometers.
• the present invention provides an underwater vehicle operable in a first mode of free swimming and a second mode of climbing on a submerged surface of an object, the features of which are recited in the accompanying independent patent claim 1.
• the underwater vehicle 1 of the present invention comprises a multi mode platform including a mechatronic system, which inherits strong dynamic characteristics and demands competent control schemes.
• the operation in the "swimming mode" is in some aspects akin to the movement of a conventional ROV, whereas the dynamic
• a single thruster could represent a plurality of thrusters in an actual underwater vehicle 1 that embodies the features of the present invention.
• the underwater vehicle 1 of the present invention is designed as a universal platform to perform inspection and maintenance on complex curvatures on ship hulls 2.
• Its primary locomotion mode hereinafter referred to as "cart mode" is to attach to a surface of a ship's hull or similar surface of a submerged body 2, with two magnetic wheels 200a, 200b, accompanied with one vectored thruster 300, or a pair of vectored thrusters 300a, 300b, to propel and balance the body.
• the vehicle stays in various attitudes according to the surface.
• the restoring moment resulted by the couple of the buoyancy and gravity is compensated for by the thrusters, in order to keep the vehicle in the expected attitude.
• the "free-swimming" mode is the secondary locomotion mode of the underwater vehicle 1 of the present invention, employed typically when the robotic underwater vehicle 1 of the invention is firstly deployed in a location away from the surface of the ship's hull 2, when it comes into difficult situation, so that the robot can maneuver in open water by harnessing its thrusters.
• the vehicle 1 places its XT plane in the horizontal plane.
• the center of gravity is ballasted in separation from the center of buoyancy, as illustrated in figures 15a, b and c.
• the position of center of buoyancy is determined generally by the overall submerged geometry of die vehicle, however, a means for buoyancy control is also contemplated.
• a restoring moment resulted by the offset buoyancy and gravity, is formed when the vehicle is not lying in the horizontal plane.
• the balancing movement is generally accomplished by an on-board controller of the vehicle 1 of the invention.
• the vehicle 1 of the invention is advantageously maneuvered by human above water through a tether.
• the human maneuver input includes, but is not limited to, the switch of control mode, locomotion and steering commands, and device configurations.
• the vehicle also transmits data and video to the human through the tether.
• the control scheme contemplated comprises a controller, such as e.g. in the system illustrated in figure 12a or figure 12b.
• the controller handles the human operator's command and manoeuvre input and governs the motion of each actuator according to the control scheme of each working mode.
• the vehicle is propelled by its thrusters, which are governed by the controller under the human command.
• the controller is adapted to the curved surface it works on, provided with a control scheme for manecute and navigation on complex surfaces.
• the controller can switch between the two locomotion modes which have specific control schemes in free water and on the surface.
• the balancing movement is accomplished by the servo control of the orientation of thrust provided by one or more thrusters 300.
• One possible solution is to have a thruster with fixed orientation, while controlling the attitude of robot by adjusting the propeller speed.
• the reaction of the change of propeller speed typically appears to be not as fast as the change of the orientation of the thruster. Therefore, an initial design of the underwater vehicle 1 of the present invention has in an advantageous embodiment adopted only one vectored thruster, as illustrated in the accompanying figure- 2.
• a dual vectored thruster scheme is proposed, as illustrated in figures la - Id-.
• An advantage of symmetric vectored thrusters is the more efficient maneuvering in yaw movement.
• the differential thrust orientation will result in the rolling moment, and the differential thrust intensity results in the yawing moment.
• the pitch, roll and yaw movements are defined as the rotational movements about X, Y and Z axis, respectively, shown in Figure 15a.
• Figure la is a perspective view drawing illustrating a first embodiment of an underwater vehicle according to the present invention submerged and operating on a surface of a submerged structure;
• Figure lb is a perspective view detailed drawing the first embodiment of an underwater vehicle illustrated in figure la, with semi transparent body elements;
• Figure lc is a perspective view detailed drawing the first embodiment of an underwater vehicle illustrated in figures la and lb, with an attitude sensing element;
• figure Id is a side view of an underwater vehicle according to the present invention submerged and operating on a surface of a submerged structure, with indications of buoyancy and gravity centres;
• Figure 2 is a perspective view drawing illustrating a second embodiment of an underwater vehicle according to the present invention submerged and operating on a surface of a submerged structure;
• Figures 3 and 4 are perspective view drawings illustrating by way of the second embodiment reference systems and forces acting for consideration in motion and attitude control;
• Figures 5 a and Sb are side view drawings illustrating by way of variants of the second embodiment further reference systems and forces acting from gravity and buoyancy in different configurations for consideration in motion and attitude control;
• Figures 6a and 6b are schematic bond graph drawings, illustrating a basis of the control system of the underwater vehicle by a general framework featuring I-fields useful for model representation and simulation with modulated transformer elements MTF, and the framework specific to parameters and control dynamics of an underwater vehicle according to the present invention, respectively;
• Figures 7a and 7b are perspective view drawings illustrating by way of the second embodiment forces acting on a single wheel of the wheel set, and the forces acting on the single wheel translated into forces and moment applied on the body of the vehicle, respectively;
• Figure 8 is a schematic bond graph drawing illustrating a basis of the control system of the underwater vehicle by model representation control dynamics and parameters related to the single wheel illustrated in figures 7a and 7b;
• Figures 9a and 9b are perspective view drawings illustrating by way of the second embodiment forces acting by input from a vectored thruster, and the forces acting by input from the vectored thruster translated into forces and moment applied on the body of the vehicle, respectively;
• Figure 10 is a schematic bond graph drawing illustrating a basis of the control system of the underwater vehicle by model representation control dynamics and parameters related to the thruster illustrated in figures 9a and 9b;
• Figure 11 is a schematic simplified bond graph drawing illustrating a basis of the control system of the underwater vehicle by model representation control dynamics and parameters related to a fluid current disturbance on the vehicle based on current force FDst acting on the body of the vehicle and translated into force and moment applied to the body of the vehicle;
• Figures 12a and 12b are block schematic drawings of a general control scheme of an underwater vehicle according to the present invention, without and with a feed forward arrangement, respectively;
• Figure 13 is a first graph plot drawing illustrating a simulation of attitude angle control by only thruster of an underwater vehicle according to the present invention operating in the locomotion mode under conditions of a fluctuating fluid current disturbance
• Figure 14 is a second graph plot drawing illustrating a simulation of attitude angle control by both thruster and wheels of an underwater vehicle according to the present invention operating in the locomotion mode under the conditions of the fluctuating fluid current disturbance.
• the inertial reference frame is defined with X, Y, Z axis and origin 0.
• the vehicle is considered as a rigid body with a total mass and a body fixed coordinate frame with X b , Y b , Z axis and the origin 0 b .
• the origin o is defined at the center point between the two wheels, as shown in Figure 3.
• the body fixed coordinate is derived from inertial reference frame with the transitional displacement of D x , D y , D z and Euler angles ⁇ , ⁇ and ⁇ about X, Y and Z axis respectively, as illustrated in figures 3, 4, and 5.
• the sequence of the rotation is in the order of the axis Z, Y and then X.
• the trajectory coordinate is introduced with X t , Y t , Z t axis and origin O t which coincides with the origin in body fixed coordinate.
• the trajectory coordinate inherit the same Euler angle ⁇ , whose rotation is firstly made in the derivation of body fixed coordinate, while keeping axis Z t perpendicular to the XY plane, as shown in figures 3 and 4.
• the trajectory coordinate can be seen as an intermediate coordinate between the inertial reference frame and body fixed coordinate.
• the chassis or body 100 which constitutes the main body of the underwater vehicle 1 of the present invention, is generally an elongated, rigid body, which contributes the major inertia of the vehicle.
• the vehicle's body frame 110 is advantageously built with plastic pipes and sheet metal. Compartments 140, 240, 340, actuators and sensors 500 are advantageously mounted on the sheet frame 110 with clamps and fasteners.
• a water tight case 140 located in the middle of the vehicle is designed to contain the electric and electronic devices, and battery.
• the case 140 is in communication with other compartments 240, 340 with hose or pipes, which have the signal and power cables inside.
• An ultrasonic sensor 500 is mounted on a adjustable platform, which aligns line of sight 550 of the sensor 500 to have an angle advantageously of between 15° and 45° to a direction of a longitudinal axis 150 of the body, enabling the ultrasonic sensor to detect the distance to a surface of a submerged body 2. Therefore the vehicle's attitude to the surface is derived.
• the total weight of the vehicle is typically ballasted equal to the buoyancy of the vehicle 1 when fully submerged.
• the vehicle when the vehicle is not placed with its longitudinal axis 150 oriented away from the vertical direction, i.e. away from the direction of the force of gravity, providing the distance rgb between the center of buoyancy Cb and the center of gravity Cg results in a restoring moment, caused by buoyancy B and gravity G, as shown in Figure 5.
• the chassis body assembles all the external force inputs through its 1 -junction. These forces are superimposed and then apply to the I-field.
• a resistor element R represents the fluid and mechanical friction applied on the vehicle.
• the general modeling structure of the body of the vehicle of the invention is represented by marine vehicle bond graph model, as shown in Figure 3.
• the inertia matrix M is defined with vehicle weight m, the skew-symmetric matrix about the position of center of gravity rg and the inertia tensor ⁇ I ⁇ , where I is the identity matrix.
• the motion of the vehicle is generated in form of flow in the body fixed coordinate system.
• the flow of velocity is then integrated into position and translated into inertial reference frame for transformation between body fixed coordinate and trajectory coordinate.
• the two wheels 200a, 200b on respective sides of the vehicle 1 are advantageously driven by separate servo DC motor systems 241a, 241b housed in a wheel motor compartment 240.
• the steering is accomplished with a differential movement on the wheels.
• a rubber tire on the rim of each of the wheels enhances grip between the vehicle 1 and the ferromagnetic surface of the ship's hull or submerged body 2.
• Figure 7a shows the forces and torque applied to the wheel.
• Fxt and Fzt is the tractive force and the normal force, respectively.
• the lateral force Fyt provides the vehicle centripetal force when the vehicle turns.
• the forces Fxt, Fyt and Fzt are transformed into the forces with the same magnitude and orientation at the origin O, together with induced moments Mfxt, Mfyt and Mfzt, where Wis the width of the vehicle, rwh is the radius of the wheel. Therefore, the forces and torques in Figure 7b shows the force input to the chassis body 100 from one wheel 200a, 200b.
• the wheel axis 250 is regarded as the pivot corresponding to a pivot angle ⁇ of the body 100 of the vehicle 1 with respect to a surface of the ship's hull or submerged body 2 .
• the wheel 200 applies the force Fwh and the induced moment Mwh to the chassis body
• the wheel is driven by a modulated effort source with a torque input, as provided according to figure 6.
• the terrain is described as a modulated flow source, determining the lateral movement of the vehicle 1.
• the force Fxt induced by moment Mwh is introduced with a zero-junction and a transformer which represents the wheel radius.
• the tire is simplified in the model as a classic spring-damper system between terrain input and the chassis body.
• the lateral friction between the tire and surface is manipulated as coulomb friction model. Therefore, no skid occurs before the lateral force exceed to the threshold, which is determined by the force in Z direction.
• the tire thickness is advantageously about 0.6mm.
• the output of the wheels model of figure 8 is a multi-bond with 3 forces and 3 moments after being translated by a transformer regarding to the origin in trajectory coordinate.
• the wheels 200a, 200b are located at what is here referred to as the upper end of the elongated chassis body 100, while the vectored thruster 300, or thrusters 300a, 300b, is preferably located on the opposite, lower end of the chassis body 100.
• the orientation or vectoring of the thrust of the thruster 300, 300a, 300b is determined by a servo motor adapted to rotate the thruster 300 about an axis of rotation 350, 350a, 350b to an effective thruster angle a which typically will correspond to the thrust orientation to the Zb axis in the body fixed coordinate, while the thrust value could be set to a fixed value which can provide sufficient thrust to manipulate the attitude and also propel the underwater vehicle against fluid drag induce by sea current, as illustrated in Figure 9a.
• the thruster is set at a constant speed while the thruster angle a is assigned as the control parameter.
• an induced thrust force Fth is transferred to the wheel axis, in addition to a moment Mth.
• the balancing moment is then provided by the moment Mth, where L is the length along the vehicle body from thruster to pivot axis, and a is the thrust orientation to the Zb axis in the body fixed coordinate.
• a proportional-integral-derivative controller (PID controller) is employed to govern the attitude angle or body tilt angle ⁇ between chassis and surface, by actively adjusting the thruster orientation.
• the modulated effort source represented by MSe in Figure 10
• MSe is modified with an addition signal input of body tilt angle ⁇ and the thrust setpoint.
• the output of nonzero generalized forces which are the resulting forces and moments applied to the vehicle, are as follows:
• the orientation of the vectored thruster is controlled by an actuator, such as e.g. a position servo motor 341a, 341a housed in a respective compartment 340, which has limited rotational speed. Therefore, the output orientation from controller is processed by a rate limiter.
• an actuator such as e.g. a position servo motor 341a, 341a housed in a respective compartment 340, which has limited rotational speed. Therefore, the output orientation from controller is processed by a rate limiter.
• the damping model is simplified as a 6 by 6 R- field, connected to the 1 -junction in body fixed coordinate, as shown in Figure 6.
• the sea current disturbance is defined as a time-varying force , which is applied on the chassis body 100 at a distance Ldst from the wheel axis 250, which for the model is then transformed into a force at the origin with the induced moment Fdts * Ldst.
• the magnitude of the disturbance force and moment is assumed as a superposition of a low- frequency sinusoidal wave and Gaussian Noise, representing the sea wave and random sea water current, respectively, as illustrated in figure 11.
• the control of attitude angle is advantageously accomplished by a PID controller and a inverse sine operator.
• the PID controller calculates the appropriate output moment according to the error between the set point angle and the measured angle .
• the inverse sine operator firstly limit the calculated moment within the range that the vectored thruster can provide, then transform of the moment into the corresponding orientation angle a of the thruster is made.
• the control of wheels is made by the differential operator which distributes an offset rate on each wheel when the steering motion is applied. The two separate PID controllers then govern the rotational rate of the wheel.
• the induced forces Twh and Fth are expected to be counteracted by the moment Mth and the force Fwh.
• the wheels and thruster should be governed to eliminate the unwanted movement brought by the each other.
• the movement of the vehicle is represented by the attitude angle ⁇ , the speed Vxt and rotational rate cotz
• the focus of stabilization is to maintain the pivot angle ⁇ of the chassis body 100 as the predefined value, also when a disturbance force is applied on vehicle.
• the wheels are fixed to the original position.
• the vehicle is considered to be connected to a 1 degree-of- freedom joint.
• the disturbance force affect the pivot angle ⁇ of the chassis body 100 by means of the resulted disturbance moment.
• the thruster orientation shows a manner of actively counteracting the disturbance.
• the measured the pivot angle ⁇ is maintained in the range of [-16°, -28°] after the pivot ⁇ is steadily set at - 23°.
• figure 14 is shown by simulation the contribution of balance moments from both thruster 300 and wheels 200 to counteract the disturbance moment.
• the thruster 300 appear to be responsive to the variation of disturbance moment, while the contribution from the wheels 200 shows less fluctuation.
• the two locomotion modes of the underwater vehicle have separate control schemes, which govern the actuators and sensors under different organizations.
• the transition of the locomotion mode from cart mode to free-swimming mode, or vice versa indicates switching from one control scheme to the other.
• the switch of the control scheme is triggered either by a command sent by the operator, or by a sensor on the vehicle.
• the vectored thrusters are controlled to propel and manoeuvre the vehicle.
• the yaw movement is accomplished by keeping the two thrusters in line to the longitudinal axis of the elongated chassis body 100 while setting different rate on each thruster propeller, resulting in a yawing moment on the vehicle.
• the pitch movement is accomplished by setting the thrusters at an angle relative to the chassis, thereby forming a pitching moment on the vehicle.
• the roll movement is accomplished by setting the thruster to opposite angular directions with respect to the chassis.
• the controller advantageously is adapted to map these three basic movements of axial, roll and pitch movements to three channels at human operator inputs.
• the mapping is defined in the control scheme of the swimming scheme.
• the active attitude control is accomplished advantageously with a PID type controller and an inverse sine operator. It maintains the pivot angle ⁇ of the chassis body 100 relative to a surface of an object on which the vehicle climbs or carts as the set point value, also when a disturbance force is applied on vehicle.
• the controller compares the assigned attitude angle setpoint with the measured attitude angle, also referred to herein as the body tilt or pivot angle, from the sensors.
• the PID controller calculates the appropriate output moment according to the difference between the set point angle and the measured angle.
• the inverse sine operator transform of the moment into the corresponding orientation angle a of the thruster is made.
• the stabilization is inherited in the process of active attitude control.
• the vehicle is considered to be a rigid body connected to a 1 degree-of-freedom joint.
• the disturbance force affects the pivot angle ⁇ of the chassis body 100 by means of the resulted disturbance moment.
• the thruster orientation shows a manner of actively counteracting the disturbance.
• the measured the pivot angle ⁇ is maintained in the range of [-16°, -28°] after the pivot ⁇ is steadily set at -23°.
• figure 14 is shown by simulation the contribution of balance moments from both thruster 300 and wheels 200 to counteract the disturbance moment.
• the thruster 300 appear to be responsive to the variation of disturbance moment, while the contribution from the wheels 200 shows less fluctuation.
• the control of wheels is made by the differential drive which distributes an offset rate on each wheel when the steering motion is applied.
• the two separate PID controllers then govern the rotational rate of the wheel.
• the induced forces Twh and Fth are expected to be counteracted by the moment Mth and the force Fwh with their own PID controllers feed-back loops.
• the wheels and thruster should be governed to eliminate the unwanted movement brought by the each other.
• certain feed-forward loops are added. Therefore, once the one of the actuators applies any moment and force, the counterpart will accordingly anticipate this movement by applying extra effort on its self.
• the parameters kl and k2 of the feed forward arrangement of the control system are set to appropriate values, which are established with technical calculation and final tuning, on basis of the actual, final physical characteristics of the particular underwater vehicle embodiment.
• the movement of the vehicle is represented by the attitude angle ⁇ , the speed Vxt and rotational rate cotz, which are assigned by three parameters from the operator.
• the mapping of the above movements to human operator inputs is also defined in the control scheme.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)
• Cleaning In General (AREA)
• Glass Compositions (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=51898660

Family Applications (1)

Country Status (2)

Cited By (7)

Families Citing this family (1)

Citations (4)

• 2013
  • 2013-05-16 NO NO20130697A patent/NO336097B1/no not_active IP Right Cessation
• 2014
  • 2014-05-16 WO PCT/NO2014/050076 patent/WO2014185791A1/en active Application Filing

Patent Citations (4)

Also Published As

Similar Documents

Legal Events