CA2642805A1 - Propulsion system for an autonomous underwater vehicle - Google Patents
Propulsion system for an autonomous underwater vehicle Download PDFInfo
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- CA2642805A1 CA2642805A1 CA 2642805 CA2642805A CA2642805A1 CA 2642805 A1 CA2642805 A1 CA 2642805A1 CA 2642805 CA2642805 CA 2642805 CA 2642805 A CA2642805 A CA 2642805A CA 2642805 A1 CA2642805 A1 CA 2642805A1
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- rudder
- underwater vehicle
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- axis
- pitch
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- 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
- B63G8/14—Control of attitude or depth
- B63G8/16—Control of attitude or depth by direct use of propellers or jets
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- 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
- B63G8/14—Control of attitude or depth
- B63G8/18—Control of attitude or depth by hydrofoils
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63H—MARINE PROPULSION OR STEERING
- B63H25/00—Steering; Slowing-down otherwise than by use of propulsive elements; Dynamic anchoring, i.e. positioning vessels by means of main or auxiliary propulsive elements
- B63H25/42—Steering or dynamic anchoring by propulsive elements; Steering or dynamic anchoring by propellers used therefor only; Steering or dynamic anchoring by rudders carrying propellers
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Aviation & Aerospace Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Ocean & Marine Engineering (AREA)
- Earth Drilling (AREA)
Abstract
An underwater vehicle is provided to move in various orientations and directions, including pitch, yaw, roll, heave, surge and sway. The underwater vehicle comprises an upper body and a lower body, wherein both bodies are separated by two rudders. One rudder is positioned towards the fore of the underwater vehicle, while the other is positioned towards the aft. Each rudder forms the basis of a propulsion system, such that the underwater vehicle has at least two independently controlled propulsion systems. Each propulsion system further comprises an elevator extending horizontally from the sides of each rudder and a thrust generator attached to the elevator. The elevator and thrust generator are able to pitch about an axis extending horizontally through the sides of the rudder, and the rudder is able to yaw about an axis extending vertically through the top and bottom of said rudder.
Description
PROPULSION SYSTEM FOR AN AUTONOMOUS UNDERWATER VEHICLE
TECHNICAL FIELD:
[0001] The following relates generally to propulsions systems for marine vehicles, and has particular utility when applied to underwater vehicles.
DESCRIPTION OF THE RELATED ART
100021 In the field of marine vehicles, a vehicle may be propelled using one or more fixed rear thrusters and the vehicle's orientation and positioning may be controlled using various control surfaces mounted to the hull of the vehicle. The flow of water across the control surfaces generates a force depending on the orientation of the control surface, and thus a force on the vehicle itself. Such an arrangement may be suitable when the vehicle is moving at sufficiently high speeds, wherein a greater force is generated as more water flows over the control surfaces.
[0003] At slower speeds, generally less water flows over the control surfaces, thereby reducing the force directed to control the vehicle. The reduced force generated by the control surfaces affects the performance of underwater vehicles when carrying out hovering manoeuvres.
During a hovering manoeuvre, an underwater vehicle may maintain a generally fixed position and orientation of the vehicle's hull for some time period, while compensating for the effects of cross-currents. This manoeuvrability may be used in various underwater operations, including without limitation, inspections that may involve high-detail imaging equipment and robotic manipulations that may involve precise movements.
[0004] Differential thrust systems may be used to produce a hover in low-speed underwater conditions. Generally, a differential thrust system may comprise several thrusters that are mounted at strategic locations around a vehicle and these thrusters are aimed in certain directions, allowing the vehicle to have some percentage of its total available thrust act in any direction. By varying the magnitude of thrust from each of the thrusters, a vehicle may be able to manoeuvre in various dimensions. Many remotely operated underwater vehicles (ROVs) may make use of differential thrust systems.
21824162.1 [0005] The differential thrust system for propulsion allows for hovering for inspection and intervention in low speed applications and environments. The differential thrusters also suitably compensate for cross-current conditions while maintaining an absolute heading.
[0006] There are many configurations that strive to optimize the positioning of differential thrusters for increased control, such as positioning each of the differential thrusters away from vehicle's hull. However, many of such configurations may also reduce the hydrodynamic streamlining of the underwater vehicle, thereby leading to a loss in energy efficiency.
100071 In many cases, the reduced operational and travel efficiency is compensated by tethering the underwater vehicle, wherein the tether provides some form of energy to the vehicle.
As a result, an underwater vehicle's travel distance and path is limited to the length of the tether.
Moreover, the above design considerations can add additional cost and complexity to an underwater vehicle.
100081 It is an object of the following to provide a propulsion system that is configured to address the above issues.
SUMMARY OF THE INVENTION
100091 In one aspect, there is provided an underwater propulsion system comprising at least one assembly comprising a rudder configured to be rotatably connected to the hull of an underwater vehicle to permit complete rotation of the rudder with respect to the hull, an elevator pivotally attached to the rudder to pitch about an axis perpendicular to the axis of rotation of the rudder, and a thrust generator extending from and attached to the elevator such that the thrust generator pitches with the elevator.
100101 In another aspect, there is provided an underwater vehicle comprising:
an upper and lower body positioned vertically above one another and separated by at least one propulsion assembly; and the at least one propulsion assembly, each propulsion assembly comprising: a vertically oriented rudder configured to be rotatably connected between the upper and lower bodies and is fully rotatable about an axis of rotation; an elevator pivotally attached to the rudder to pitch about an axis perpendicular to the axis of rotation of the rudder;
and a thrust generator 21824162.1 extending from and attached to the elevator such that the thrust generator pitches with the elevator.
BRIEF DESCRIPTION OF THE DRAWINGS
100111 Embodiments will now be described by way of example only with reference to the appended drawings wherein:
100121 Figure 1 a is a perspective view of an exemplary underwater vehicle.
[0013] Figure 1 b is a top planar view of the underwater vehicle shown in Figure Ia.
100141 Figure 2 is a perspective view in isolation of the exemplary propulsion system shown in Figure 1 a.
[0015] Figure 3 is a block diagram of an exemplary embodiment of an underwater vehicle and propulsion system.
[0016] Figure 4 is a perspective view of the propulsion system similar to Figure 2 and showing various internal components shown schematically in Figure 3.
100171 Figure 5a is a top planar view of top and bottom cross sections of the rudder, shown in Figure 2.
[0018] Figure 5b is a top planar view of a middle cross section of the rudder, shown in Figure 2.
[0019] Figure 6 is a top planar view in isolation of the propulsion system shown in Figure 2.
[0020] Figure 7 is a perspective view of another embodiment of an exemplary underwater vehicle deployed in an underwater environment.
100211 Figure 8 is a perspective view of the underwater vehicle shown in Figure 7 while heaving, surging and pitching.
21824162.1 100221 Figure 9a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
100231 Figure 9b is a profile view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
[0024] Figure 9c is a planar view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
[0025] Figure 10 is a perspective view of the underwater vehicle shown in Figure 7 while heaving.
100261 Figure 11 a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
[0027] Figure l lb is a profile view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
100281 Figure 11 c is a planar view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
[0029] Figure 12 is a perspective view of the underwater vehicle shown in Figure 7 while yawing.
[0030] Figure 13a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
[0031] Figure 13b is a profile view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
[0032] Figure 13c is a planar view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
21824162.1 DETAILED DESCRIPTION
100331 It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein.
[0034] Generally, underwater vehicles comprise a body or hull to transport various loads while protecting the loads from a submersed marine environment. Various loads may include without limitation, scientific equipment, people and components required to operate the underwater vehicle. The body or hull of a vehicle may protect the loads from the effects of the water, including wetting, and hydrostatic and hydrodynamic pressure. Typically a propulsion unit attached to the body is used to move the body in certain directions.
100351 Figure 1 a shows an underwater vehicle comprising two bodies or hulls, an upper body 2 and a lower body 4. It is noted that the terms `body' and `hull' refer to the same structure, as described in more detail below. Both bodies 2, 4 comprise an oblong-shaped geometry for streamlining. In the particular embodiment shown in the Figure 1 a, both the upper and lower bodies 2, 4 comprise a cylindrical hull having the end portions rounded to reduce hydrodynamic resistance. It is noted that the front end, or nose, of each body 2, 4 may be comprise a more hemispherical geometry, while the rear end, or tail, may comprise a more conical geometry.
This profiled geometry allows for reduced water drag. The purpose of each body or hull 2, 4 is to house various loads while streamlining the flow of water over the surface of each body or hull 2, 4 and that any means of doing so are encompassed within the various possible configurations for the underwater vehicle.
100361 Turning to Figure 1 b, a top planar view of the underwater vehicle is shown in context with directional terminology. The front of the underwater vehicle is referred to as the fore and 21824162.1 the rear is referred to as the aft. From the perspective of a person on the underwater vehicle facing towards the fore, the left-hand side is referred to as the portside, while the right-hand side is referred to as the starboard.
100371 Returning to Figure 1 a, the upper body 2 is positioned directly above the lower body 4 and extending vertically between the two bodies 2,4 are a pair of rudders 6.
In the embodiment shown in Figure 1 a, a fore rudder 6a is positioned towards the front of the underwater vehicle and an aft rudder 6b is positioned towards the back of the underwater vehicle.
For continued clarity of the description, suffix `a' herein refers to the fore portion of the underwater vehicle and suffix `b' refers to the aft portion. Both the fore rudder 6a and aft rudder 6b comprise rigid structures that position the upper body 2 at a fixed distance from the lower body 4. It is appreciated that a rudder 6 is a control surface that affects the yaw of the underwater vehicle.
Both rudders 6a, 6b are able to yaw independently of each other, as indicated by the movement arrows 16a and 16b. The fore and aft positioning of the rudders 6a, 6b and the independent direction of yaw forces generated from the fore rudder 6a and aft rudder 6b allow for manoeuvres of various complexities as discussed further below.
100381 In this example, the purpose of each rudder 6 is to act as a control surface affecting the yaw, and any configuration capable of doing so is encompassed by the embodiments described herein.
100391 The two rudders 6a, 6b form a structural base for the underwater vehicle's propulsion system, which further comprises respective elevators 12 and thrusters 14. An elevator 12 protrudes from both sides of a rudder 6 and comprises a rigid control surface or plane that is generally perpendicular to the rudder 6. The flow of fluid over the elevator 12 generates forces that affect the pitch or inclination of the underwater vehicle. Each elevator 12 is able to rotate or pitch, as indicated by the movement arrows 18a and 18b. In the embodiment shown in Figure 1 a, both the fore elevator 12a and aft elevator 12b have a swept wing geometry to reduce drag. It is understood that elevators 12 comprising other geometries to control the pitch while reducing drag are equally applicable.
21824162.1 100401 Similar to the rudders 6a, 6b, both the fore elevator 12a and aft elevator 12b are able to move independently from one another. In one example, the fore elevator 12a may pitch downwards, while the aft elevator 12b may pitch upwards to create a coupled moment, thereby pitching the underwater vehicle downwards. The fore and aft positioning of the elevators 12a, 12b and the independent direction of pitch forces generated from the fore elevator 12a and aft elevator 12b allow for manoeuvres of various complexities as discussed further below.
[0041] It is noted that all control planes (i.e. rudder 6 and elevator 12) advantageously use NACA OOxx airfoil profiles, an industry standard in naval architecture. The NACA OOxx airfoil profiles provide hydrodynamic efficiency and geometrical convenience. It will be appreciated that other airfoil profiles that allow for the same are equally applicable.
100421 Fixed to each elevator 12 is a thrust generator 14, such that the thrust generator 14 is oriented with the same pitch as the elevator moves. Since each elevator 12 is fixed to a rudder 6, the elevator 12 and, therefore the thrust generator 14, will also be oriented to have the same yaw as the rudder 6. The thrust generator 14 is located behind the trailing edge of the rudder 6 so as to allow for a larger range of pitch rotation, while avoiding interference between the thrust generator 14 and rudder 6. Other configurations between the thrust generator 14, elevator 12, and rudder 6 that allow the thrust generator to move across a sufficient range for pitch and yaw are equally applicable.
[0043] The thrust generator 14 shown in Figure 1 a, comprises a single propeller driven by a motor. Other embodiments of a thrust generator 14 may include one more motors driving one or more propellers. Alternatively, a thrust generator 14 may comprise the release of a pressurized gas or liquid. It is appreciated that any mechanisms for generating thrust are equally applicable.
[0044] The direction of the force generated by the thrust generator 14 is indicated by the direction arrows 20a and 20b. The coupling of a thrust generator 14 to the elevator 12 and rudder 6, allows the thrust generator 14 to direct the thrust at various pitch and yaw angles. The independent movement of the fore and aft thrust generators 14a, 14b, and the positioning of the tbrust generators 14a, 14b in relation to the upper and lower bodies 2, 4 allow the underwater vehicle to carry out complex manoeuvres, discussed in further detail below.
21824162.1 [0045] Turning to Figure 2, a perspective view of an isolated propulsion system is shown in greater detail. The thrust generator 14, in one embodiment shown in Figure 2, comprises a propeller 24 driven by a motor assembly 22. The motor 22 may be located external to the rudder 6 and elevator 12 to allow the thrust generator 14 to rotate or pitch relative to the rudder 6. In addition to increased range of rotation, placing the motor 22 external to the rudder 6 and elevator 12 reduces the complexity of transferring the motor's energy to the propeller 24. The motor assembly 22 is fixed to a U-shaped bracket 26, and more particularly to the portion that bridges the two armatures of the bracket 26. Each armature on the bracket 26 is situated between the elevator 12 and rudder 6. The bracket 26 is fixed to the elevator 12, wherein the pitch movement of the elevator 12 and, therefore, the thrust generator 14 may be identical.
The bracket 26 also positions the propeller 24 further away from the trailing edge of the rudder 6, thereby allowing the thrust generator 14, in this case the propeller 14, to achieve a larger range of pitch rotation.
It is appreciated that alternate configurations of the propeller 14, motor 22 and bracket 26 that allow for a sufficient range of rotation are equally applicable.
100461 Also shown in Figure 2 is an XYZ reference frame that in this example is fixed relative to the underwater vehicle body for the purpose of describing the various configurations below. The XYZ reference frame is oriented such that the X axis is oriented along the length of the vehicle and is directed toward the rear or aft of the vehicle. The Z axis is oriented vertically between the upper body 2 and lower body 4, such that the Z axis is aligned with the vertical length of the rudder 6, and is directed upwards toward the upper body 2. The Y
axis is oriented perpendicular to both X and Z axes and, in accordance with chirality, is directed towards the starboard side of the underwater vehicle in this example. This reference may be used to describe the axes of rotation for the above components.
[0047] The propeller 24 rotates about the axis A. The axis A, in this case, extends along the length of the bracket 25 and motor assembly 22. The axis A and the elevator 12 both rotate, or pitch, about axis B. It is appreciated that the A axis rotates with the elevator 12 about axis B
since the bracket 25 and motor assembly 22 are fixed to the elevator 12. It is further understood that rotational axes A and B remain perpendicular to one another. Axes A and B, and the rudder 6 rotate, or yaw, about axis C.
21824162.1 -g-[0048] The three rotational axes, A, B, and C, introduced above, may be described relative to the underwater vehicle's XYZ reference frame. In a neutral orientation, the underwater vehicle's control surfaces are oriented such that the underwater vehicle is directed in a straight heading, with no yawing or pitching movements. In this neutral orientation, the rotational axis A is parallel with the X axis. The A axis is oriented towards the back or aft of the underwater vehicle in the same direction with the X axis, which is also oriented towards the back or aft of the vehicle. In a neutral orientation, the rotational axis B is oriented parallel to the Y axis.
However, according to the convention shown here, the positive B axis is oriented towards the portside of the underwater vehicle and the positive Y axis is oriented towards the starboard side of the underwater vehicle. The rotational axis C always remains oriented parallel and in the same direction as the vertical Z axis when using this reference frame.
[0049] It is noted that the A axis may pitch about the B axis by some angle +/-alpha (a). It is also understood that the thrust from the thrust generator 14 is directed along the A axis. For example, when the A axis inclines above the X axis by + alpha, the elevator 12 and direction of thrust is pitched in a downward direction. Similarly in another example, when the A declines below the X axis by - alpha, the elevator 12 and the direction of thrust is pitched in an upward direction. It is further appreciated that when the thrust is directed in along the X axis, then the thrust is directed towards the aft of the underwater vehicle, thereby propelling or pushing the underwater vehicle forward.
[0050] With regard to the yaw movement, both A and B axes, as well as the rudder 6, may pivot about axis C by some angle +/- beta ((3). For example, when the propulsion assembly yaws by +beta, the rudder 6 and the A axis rotate from the X axis in a counter clockwise direction.
Similarly, the B axis rotates from the -Y axis in a counter clockwise direction by +beta. In yet another example, when the propulsion assembly yaws by beta, the trailing edge of the rudder 6 and the A axis rotate from the X axis in a clockwise direction, and the B axis rotates from the -Y
axis in a clockwise direction. It can be appreciated that the propulsion system may yaw about the C axis by 360 degrees in either a clockwise or counter clockwise direction. As will be exemplified below, such freedom of rotation about the C axis enables complex and controlled movements that provides greater handli.ng and control of an underwater vehicle.
21824162.1 [0051] The combined movements of the pitch and yaw allows the axis A, and therefore thrust vector, to be oriented in various directions. The combination of the two or more in-line propulsion systems with the described underwater vehicle allow for various manoeuvres with five degrees of freedom, including pitch, yaw, heave (i.e. moving up and down), surge (i.e.
moving forward and backward) and sway (i.e. moving left and right).
[0052] It may be noted that roll movements may also be achieved if the elevators 12 are controlled to pitch in opposite directions. For example, if the starboard elevators were to pitch upwards and the portside elevators were to pitch downwards, then the underwater vehicle may tend to roll towards the portside.
[0053] Turning to Figure 3, the various components in the propulsion system are shown schematically. The rudder 6 subassembly, elevator 12 subassembly and thrust generator 14 subassembly each comprise a motor 30, 36, 42 motor controller 28, 34, 40 and gearbox 32, 38, 44. In general, each motor controller 28, 34, 40 receives signals from a vehicle control unit 48 through a network communication system 46. The motor controller 28, 34, 40 then actuates its corresponding motor 30, 36, 42, which may be coupled to a gearbox 32, 38, 44, to modify the speed and power output of the motor 30, 36, 42.
[0054] The vehicle control unit 48 is preferably a computer, housed in the upper body 2 of the underwater vehicle, which contains the vehicle's control system software (not shown but can be appreciated as any computer instructions, data structures, memory and other software components stored on and/or accessible from a computer readable medium). Based on navigational sensor input (e.g. GPS, DVL, Altimeter, Attitude Sensor) and using pre-programmed mission criteria, the control system software may calculate the desired vehicle speed, pitch, roll, and heading. Then, based on the current speed, pitch, roll, and heading, the control system sends control information via a network communication system 46, such as a controller-area network (i.e. CAN) bus (as shown in Figure 3), to the respective motor controllers 28, 34, 40 for each rudder 6, elevator 12 and thrust generator 14 to achieve the desired orientation.
21824162.1 [0055] The sub-assemblies in Figure 3 are indicated by the dashed lines, while the outer solid lines indicate the pressure housings. The rudder subassembly, comprising the rudder's motor controller 28, motor 30 and gearbox 32, is completely contained within its own pressure housing, located in the upper body 2 of the underwater vehicle. Components from the elevator and thrust generator subsystem share a pressure housing located in the rudder 6. The elevator's motor controller 34, motor 36 and gearbox 38, as well as the thrust generator's motor controller 40 are located within the pressurized portion of the rudder 6. The thrust generator's motor 42 and gearbox 44 are located external to the rudder 6 and elevator 12 in a separate pressure housing 22 fixed to the end of the bracket 26. The purpose of placing the above components in various pressure housings is to protect the above components from the effects of the water while reducing mechanical complexity.
100561 Figure 4 shows various ones of the above components when housed in the physical structures. In this embodiment, the rudder 6 is divided into three logical and physical sections;
the top 52, middle 54, and bottom 56 sections. The top 52 and bottom 56 sections are free-flooding to allow for water to enter and exit freely through designated drainage holes. The drainage holes are positioned in certain areas along the airfoil of the rudder 6 to maintain hydrodynamic efficiency. In one embodiment, the drainage holes may be placed along the top and bottom surfaces of the rudder 6, wherein the top surface is adjacent to the underside of the upper body 2 and the bottom surface is adjacent to the topside of the lower body 4. The middle section 54 of the rudder 6 is pressurized to house the elevator's motor controller 34, motor 36 and gearbox 38, as well as the thrust generator's motor controller 40. It can be appreciated that the top 52 and bottom 56 sections of the rudder 6 are free-flooding to reduce the effects of dynamic shifting buoyancy forces on the underwater vehicle.
[0057] Cabling from the upper body 2 to the lower body 4 may also be routed through the hollow shaft 50 around which the rudder 6 rotates. Cabling from the upper body 2 to the respective elevators 12 and thrust generators 14 on the rudder 6 is also routed through this hollow shaft 50 to the components in the pressure housings, which require access to power and the communication network 46.
21824162.1 100581 In this embodiment, the rudder's top 52 and bottom 56 sections are almost identical or mirror images of each other except for one difference pertaining to the joints. The joint from the top section 52 to the upper body 6 contains the motor 30 for rotating the rudder 6, whereas the joint from the bottom section 56 to the lower body 4 contains a bearing to allow for smooth yaw movement.
[0059] The geometry and functionality of the rudder's middle section 54 differ from the top 52 and bottom 56 sections, although it is mechanically attached to the other two sections. The profile of a top 52 or bottom 56 section, shown in Figure 5a, comprises a rounded leading edge and a pointed trailing edge. The front face of the middle section 54 is curved to match the nose radius of the airfoil-like profile of the rudder's top 52 and bottom 56 sections. However, as shown in Figure 5b, the trailing edge portion of the rudder's middle section 54 has a different rectangular profile instead of a pointed edge.
100601 Returni.ng to Figure 4, the rectangular profile towards the trailing edge increases the volume within the middle section 54 of the rudder 6 and, therefore, allows room for components, such as motor controllers 34, 40, to be stored within the pressure housing. At least one shaft 58 extends horizontally through the middle section, via two waterproof shaft seals, connecting the elevator motor 36 and gearbox 38 to the elevator planes 12. The rotation of the horizontal shaft 58 may cause the elevator planes 12 to pitch. It may be noted that the horizontal shaft 58 corresponds to the rotational axis B. The elevator 12 may be composed of two identical planes, attached on either side of the rudder's middle section 54 via the horizontal shaft 58, as well as the attached bracket 26 used for mounting the motor assembly 22 and propeller 24 aft of the two planes.
[0061] Figure 4 also illustrates where the elevator planes may be connected and aligned together, such that one motor 36 is required to actuate both planes of the elevator 12. A single motor configuration reduces power consumption, reduces complexity and reduces the amount of space required. Alternatively, in another embodiment, the starboard plane and portside plane may each be coupled to their own separate motor for independent control.
Therefore, the two separate motors may facilitate rolling movement.
21824162.1 [0062] It may be noted that both planes in the elevator 12 do not contain pressure housings, and are free-flooding. Similar to the rudder 6, drainage holes are provided to allow water to enter and exit the elevator 12, and the holes are placed along the elevator 12 to maintain hydrodynamic efficiency. In one embodiment, the drainage holes are placed on the face of the elevator plane 12 attached to the bracket 26 and further, coincident with an identical hole in the bracket 26 itself. This embodiment allows water to enter and/or exit through the drainage holes in the elevator 12, through the coincident holes in the attached bracket 26.
The elevator 12 is free-flooding to reduce the effects of shifting buoyancy forces on the underwater vehicle. As the elevator 12 extends away from the centerline of the underwater vehicle, and pitches and yaws in various directions, the effects of positioning a pressurised housing, or buoyancy generator, may be avoided by flooding the elevator 12 structure. It is noted that the effects of positioning a pressurised housing in the elevator 12 may comprise changes in resulting moments and force vectors acting on the underwater vehicle during various manoeuvres.
[0063] Figure 4 further shows the thrust generator 14, which, in one embodiment, comprises a motor 42 and planetary gearbox 44 mounted inside a hydrodynamic pressure housing for the motor assembly 22, with a sealed bearing connecting the output shaft to a large diameter propeller 24. A cable from the motor assembly housing 22 to the pressurised rudder housing, or middle section 54, connects the motor 42 to the motor controller 40. It can be appreciated that the motor controller 40 is housed in the rudder's pressurised middle section 54 in this example.
[0064] The motor assembly 22 and propeller 24 are mounted to the bracket 26, which is mechanically attached to the elevator planes and placed slightly aft of the trailing edge of the rudder 6. The angle of rotation of the elevator 12 is limited to prevent the bracket 26 and propeller 24 from impacting the trailing edge of the rudder 6. Both hard stops, implemented mechanically, and soft stops, implemented in the vehicle control unit 48, may be added to prevent impacts.
[0065] Figure 6 shows the propulsion assembly from a top planar view. Seen more clearly, the axis A pitches about axis B and yaws about axis C. It is also noted in this embodiment, the pitch axis B may be offset from the yaw axis C. This offset is also reflected in the 21824162.1 implementation, wherein the rudder 6 pivots about the vertical hollow shaft 50, which is located towards the leading edge of the rudder 6. The elevator 12 is attachable to the rudder 6 by the horizontal shaft 58, which is located further back from the leading edge of the rudder 6.
[0066] In Figure 6, the profile of the rudder's middle section 54, which comprises a rectangular-shaped trailing edge, is also shown relative to the profile of the rudder's top section 52. In addition, the bracket 26 is shown attached to an inner portion of the elevator 12.
100671 Turning to Figure 7, one embodiment of the underwater vehicle in an underwater enviromnent is shown relative to a seabed 64. In this embodiment, various sensors 60, for example sonar and imaging equipment, are located in the lower body 4 and may be used to collect data about the seabed 64. Some sensors 60 may be positioned in the lower body 4 to allow for better line-of-sight with the area below the underwater vehicle.
Other sensors 60 may also be located in the upper body 2. The upper body 2, for example, may house a wireless communications receiver and transceiver 62 to communicate with other marine vessels or a base station. The communications system 62 may relay various information including for example, control commands and sensor data. The communications system 62 may relay command signals to the vehicle control unit 48 to carry out various manoeuvres by orienting the propulsion system in particular configurations.
[0068] It has also been found that various ones of these components can be housed in the lower body 4 in order to lower the center of gravity, which assists in the various movements of the vehicle. By way of background, when a marine vessel is tilted the center of buoyancy of the vessel moves laterally. The point at which a vertical line through the tilted center of buoyancy crosses the line through the original, non-tilted center of buoyancy is the metacenter. Lowering of the center of gravity increases the metacentric height, that is the distance between the metacentre and center of buoyancy. A larger metacentric height increases the natural stability of the vehicle in pitch and roll.
[0069] It is appreciated that various manoeuvres, many of which utilize the natural stability of the underwater, may be achieved with the described propulsion system as described below.
21824162.1 [0070] Figure 8 shows the underwater vehicle ascending with the length of the bodies 2, 4 being generally parallel with the flat seabed 64, and having a slight pitch.
This manoeuvre involves the fore elevator 12a and thrust generator 14a pitching upwards, which causes the nose or front end of the underwater vehicle to move in an upwardly direction.
Simultaneously, the aft elevator 12b and thrust generator 14b pitch upwards as well, which also causes the tail or back end of the underwater vehicle to move in an upwardly direction as well. This combined movement of both the fore and aft propulsion systems allows the underwater vehicle to move both forward and upward simultaneously. Alternatively, this manoeuvre may be characterised by pitch, heave and surge.
100711 Figures 9a to 9c show the perspective view, profile view and planar view of the rotational axes A, B, and C relative to the underwater vehicle's XYZ reference frame during an upward and forward ascending manoeuvre, according to Figure 8. From Figure 9a, the fore rotational axis Al rotates below the X axis by some angle -al degrees, thereby directing the thrust downwards. The aft rotational axis A2 also rotates below the X axis by some angle -a2 degrees, such a2 is slightly less than al. Therefore, more thrust is generally directed downwards towards the fore of the underwater vehicle compared to the aft, which may cause the overall underwater vehicle to pitch slightly upwards. The profile view in Figure 9b also shows that the A axis has a horizontal component direct along the X axis and, thus, the some of the force or thrust from the thrust generators 14a, 14b is acting along the X axis to propel the underwater vehicle forward.
100721 Figure 9c also shows that no yawing action is involved in this manoeuvre, since the planar view shows that A1 and A2 are still aligned with X axis, and Bl and B2 are still aligned with the -Y axis. Therefore, rotational angles (31 and (32 both equal0 .
10073] Turning now to Figure 10, the underwater vehicle is shown carrying out another manoeuvre, such that the underwater vehicle is vertically translating upwards, or heaving, only.
There are no yaw, pitch, roll, surge and sway movements. This heave manoeuvre may be useful in various situations. For example, when the underwater vehicle wants to inspect or navigate with respect to the vertical face of an underwater cliff, the underwater vehicle may move 21824162.1 upwards and downwards along the height of the cliff while maintaining a fixed horizontal distance from the cliff face.
[0074] Figures 11 a to 11 c show different views of the orientations of the rotational axes relative to the XYZ reference frame for the heave-only manoeuvre. First, the fore propulsion system yaws 180 about the C axis, such that the leading edge of the fore rudder 6a is directly facing the leading edge of the aft rudder 6b. This yaw rotation is represented by the angle (31, which equals 180 . As shown in Figures 11 a and 11 c, after the rotation of (31, the rotational axis Bl is aligned and pointed in the same direction as the +Y axis. It is noted that the aft propulsion system does not yaw and, thus, (32 equals 00.
100751 After the first Bl rotation, Figures 11a and 11 b show that the elevator 12 and thrust generator both pitch upwards. Therefore, the A1 axis rotates below the -X axis in a counter clockwise direction by some angle +al, and the A2 axis rotates below by the X
axis in a clockwise direction by some angle -a2. Assuming the magnitude of thrust is the same from both thrust generators 14a and 14b, the pitch angles a1 and a2 are equal in order to cancel out the horizontal forces along the X axis. The horizontal forces cancel each other out since the thrust generators 14a and 14b are directed in opposite directions along the X axis, resulting in only vertical forces. This allows the underwater vehicle to translate vertically upwards.
100761 Turning to Figure 12, the underwater vehicle is shown in the middle of a turn manoeuvre towards the left or starboard side. The two separate propulsion systems located at the fore and aft of the underwater vehicle create a coupled moment about the center of the underwater vehicle, which allow for a smaller turning radius. In effect, the underwater vehicle could yaw about a central point with little forward or lateral movement. For example, if the fore rudder 6a directs its leading edge to the face the portside and the aft rudder 6b directs its leading edge to face the starboard side, then the underwater vehicle may rotate or yaw in a counter clockwise direction about a point. This manoeuvrability may be used, for example, to face a forward mounted sensor on the vehicle in an opposite direction while in an environment with constrained space.
21824162.1 100771 Figures 13a to 13c show the different views of the rotational axes A, B
and C relative to the underwater vehicle's XYZ reference frame for a the starboard turn, according to Figure 12.
It is appreciated that this manoeuvre does not require any pitching motion and, thus, both fore and aft elevators 12a, 12b do not rotate about the B axis. As a result al and a2 are equal to 0 , as shown most clearly in Figure 13b.
100781 Figures 13a and 13c show the fore propulsion system yawing by some angle -(31 in counter clockwise direction about the Cl axis. The rotational axis Al rotates away from the X
axis by -(31, and the rotational axis Bl rotates away from the -Y axis by -(31. It is noted that in this embodiment, the rotational axes A and B remain perpendicular to one another. With this clockwise rotation, the leading edge of the fore rudder 6a is directed towards the starboard side and the thrust is directed towards the portside. This causes the nose of the vehicle to turn towards the right or starboard.
100791 Similarly, the aft propulsion system yaws by some angle (32 in a clockwise direction about the C2 axis. The rotational axis A2 rotates away from the X axis by (32, and the rotational axis B2 rotates away from the -Y axis by (32. It is noted that in this embodiment, the rotational axes A and B remain perpendicular to one another. With this counter clockwise rotation, the leading edge of the aft rudder 6b is directed towards the portside and the thrust is directed towards the starboard. This causes the tail end of the vehicle to turn towards the left or portside.
In this example manoeuvre, the angle (32 is less than the angle (31 and, thus, the nose of the underwater vehicle turns more quickly to the starboard than the tail end turns to the portside.
100801 There may be various combinations of pitch and yaw that allow for different movements. For example, if both rudders 6a, 6b direct their leading edges to the left or portside, then the entire underwater vehicle will sway, or laterally translate, towards the portside. This sway movement does not require any yawing rotations. Other movements may include, for example, pitching and yawing simultaneously, or heaving and yawing simultaneously, or moving backwards and pitching simultaneously. In a more specific example, the underwater vehicle may maintain a constant downwards pitch, while moving backwards and side-to-side.
Various combinations of pitch, yaw, heave, surge and sway may be accomplished with the propulsion 21824162.1 system described herein. Furthermore, with independent starboard and portside elevators, roll may also be achieved. Therefore, the underwater vehicle may move in all six degrees of freedom.
[0081] Another advantage in movement is the underwater vehicle's ability to hover, or stay in a fixed position, while maintaining an absolute heading. The propulsion system also allows the underwater vehicle to hover in the presence of currents in any direction and of reasonable speed.
[00821 Different manoeuvres may also be achieved by varying the force produced by the thrust generators 14. In one manoeuvre, for example, the fore thrust generator 14 may produce more force during a turn than the aft thrust generator 14b, thereby causing the nose of the underwater vehicle to move at a faster speed. This variable thrust may be generated by increasing or decreasing the speed at which the propeller 24 rotates about the axis A. In addition, the thrust may be varied by controlling the pitch, or angle of attack, or the propeller's blades.
[0083] Having two or more of the propulsion systems positioned towards the fore and aft of the underwater vehicle also allows for high manoeuvrability. This configuration encompasses the advantages of both thrust vectoring and differential thrusters.
Furthermore, by positioning the two propulsion systems in-line with one another and situated between the upper body 2 and lower body 4, the drag is reduced and hydrodynamic efficiency is maintained.
100841 The configuration of the upper body 2 and lower body 4 also provides the advantage of increased stability with respect to pitch and roll. Separating and placing the lower body 4 below the upper body 2, lowers the center of gravity and provides a higher center of buoyancy.
100851 Although the above has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.
21824162.1
TECHNICAL FIELD:
[0001] The following relates generally to propulsions systems for marine vehicles, and has particular utility when applied to underwater vehicles.
DESCRIPTION OF THE RELATED ART
100021 In the field of marine vehicles, a vehicle may be propelled using one or more fixed rear thrusters and the vehicle's orientation and positioning may be controlled using various control surfaces mounted to the hull of the vehicle. The flow of water across the control surfaces generates a force depending on the orientation of the control surface, and thus a force on the vehicle itself. Such an arrangement may be suitable when the vehicle is moving at sufficiently high speeds, wherein a greater force is generated as more water flows over the control surfaces.
[0003] At slower speeds, generally less water flows over the control surfaces, thereby reducing the force directed to control the vehicle. The reduced force generated by the control surfaces affects the performance of underwater vehicles when carrying out hovering manoeuvres.
During a hovering manoeuvre, an underwater vehicle may maintain a generally fixed position and orientation of the vehicle's hull for some time period, while compensating for the effects of cross-currents. This manoeuvrability may be used in various underwater operations, including without limitation, inspections that may involve high-detail imaging equipment and robotic manipulations that may involve precise movements.
[0004] Differential thrust systems may be used to produce a hover in low-speed underwater conditions. Generally, a differential thrust system may comprise several thrusters that are mounted at strategic locations around a vehicle and these thrusters are aimed in certain directions, allowing the vehicle to have some percentage of its total available thrust act in any direction. By varying the magnitude of thrust from each of the thrusters, a vehicle may be able to manoeuvre in various dimensions. Many remotely operated underwater vehicles (ROVs) may make use of differential thrust systems.
21824162.1 [0005] The differential thrust system for propulsion allows for hovering for inspection and intervention in low speed applications and environments. The differential thrusters also suitably compensate for cross-current conditions while maintaining an absolute heading.
[0006] There are many configurations that strive to optimize the positioning of differential thrusters for increased control, such as positioning each of the differential thrusters away from vehicle's hull. However, many of such configurations may also reduce the hydrodynamic streamlining of the underwater vehicle, thereby leading to a loss in energy efficiency.
100071 In many cases, the reduced operational and travel efficiency is compensated by tethering the underwater vehicle, wherein the tether provides some form of energy to the vehicle.
As a result, an underwater vehicle's travel distance and path is limited to the length of the tether.
Moreover, the above design considerations can add additional cost and complexity to an underwater vehicle.
100081 It is an object of the following to provide a propulsion system that is configured to address the above issues.
SUMMARY OF THE INVENTION
100091 In one aspect, there is provided an underwater propulsion system comprising at least one assembly comprising a rudder configured to be rotatably connected to the hull of an underwater vehicle to permit complete rotation of the rudder with respect to the hull, an elevator pivotally attached to the rudder to pitch about an axis perpendicular to the axis of rotation of the rudder, and a thrust generator extending from and attached to the elevator such that the thrust generator pitches with the elevator.
100101 In another aspect, there is provided an underwater vehicle comprising:
an upper and lower body positioned vertically above one another and separated by at least one propulsion assembly; and the at least one propulsion assembly, each propulsion assembly comprising: a vertically oriented rudder configured to be rotatably connected between the upper and lower bodies and is fully rotatable about an axis of rotation; an elevator pivotally attached to the rudder to pitch about an axis perpendicular to the axis of rotation of the rudder;
and a thrust generator 21824162.1 extending from and attached to the elevator such that the thrust generator pitches with the elevator.
BRIEF DESCRIPTION OF THE DRAWINGS
100111 Embodiments will now be described by way of example only with reference to the appended drawings wherein:
100121 Figure 1 a is a perspective view of an exemplary underwater vehicle.
[0013] Figure 1 b is a top planar view of the underwater vehicle shown in Figure Ia.
100141 Figure 2 is a perspective view in isolation of the exemplary propulsion system shown in Figure 1 a.
[0015] Figure 3 is a block diagram of an exemplary embodiment of an underwater vehicle and propulsion system.
[0016] Figure 4 is a perspective view of the propulsion system similar to Figure 2 and showing various internal components shown schematically in Figure 3.
100171 Figure 5a is a top planar view of top and bottom cross sections of the rudder, shown in Figure 2.
[0018] Figure 5b is a top planar view of a middle cross section of the rudder, shown in Figure 2.
[0019] Figure 6 is a top planar view in isolation of the propulsion system shown in Figure 2.
[0020] Figure 7 is a perspective view of another embodiment of an exemplary underwater vehicle deployed in an underwater environment.
100211 Figure 8 is a perspective view of the underwater vehicle shown in Figure 7 while heaving, surging and pitching.
21824162.1 100221 Figure 9a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
100231 Figure 9b is a profile view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
[0024] Figure 9c is a planar view of the rotational axes of the underwater vehicle shown in Figure 8, relative to the underwater vehicle's reference frame axes.
[0025] Figure 10 is a perspective view of the underwater vehicle shown in Figure 7 while heaving.
100261 Figure 11 a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
[0027] Figure l lb is a profile view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
100281 Figure 11 c is a planar view of the rotational axes of the underwater vehicle shown in Figure 10, relative to the underwater vehicle's reference frame axes.
[0029] Figure 12 is a perspective view of the underwater vehicle shown in Figure 7 while yawing.
[0030] Figure 13a is a perspective view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
[0031] Figure 13b is a profile view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
[0032] Figure 13c is a planar view of the rotational axes of the underwater vehicle shown in Figure 12, relative to the underwater vehicle's reference frame axes.
21824162.1 DETAILED DESCRIPTION
100331 It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein.
[0034] Generally, underwater vehicles comprise a body or hull to transport various loads while protecting the loads from a submersed marine environment. Various loads may include without limitation, scientific equipment, people and components required to operate the underwater vehicle. The body or hull of a vehicle may protect the loads from the effects of the water, including wetting, and hydrostatic and hydrodynamic pressure. Typically a propulsion unit attached to the body is used to move the body in certain directions.
100351 Figure 1 a shows an underwater vehicle comprising two bodies or hulls, an upper body 2 and a lower body 4. It is noted that the terms `body' and `hull' refer to the same structure, as described in more detail below. Both bodies 2, 4 comprise an oblong-shaped geometry for streamlining. In the particular embodiment shown in the Figure 1 a, both the upper and lower bodies 2, 4 comprise a cylindrical hull having the end portions rounded to reduce hydrodynamic resistance. It is noted that the front end, or nose, of each body 2, 4 may be comprise a more hemispherical geometry, while the rear end, or tail, may comprise a more conical geometry.
This profiled geometry allows for reduced water drag. The purpose of each body or hull 2, 4 is to house various loads while streamlining the flow of water over the surface of each body or hull 2, 4 and that any means of doing so are encompassed within the various possible configurations for the underwater vehicle.
100361 Turning to Figure 1 b, a top planar view of the underwater vehicle is shown in context with directional terminology. The front of the underwater vehicle is referred to as the fore and 21824162.1 the rear is referred to as the aft. From the perspective of a person on the underwater vehicle facing towards the fore, the left-hand side is referred to as the portside, while the right-hand side is referred to as the starboard.
100371 Returning to Figure 1 a, the upper body 2 is positioned directly above the lower body 4 and extending vertically between the two bodies 2,4 are a pair of rudders 6.
In the embodiment shown in Figure 1 a, a fore rudder 6a is positioned towards the front of the underwater vehicle and an aft rudder 6b is positioned towards the back of the underwater vehicle.
For continued clarity of the description, suffix `a' herein refers to the fore portion of the underwater vehicle and suffix `b' refers to the aft portion. Both the fore rudder 6a and aft rudder 6b comprise rigid structures that position the upper body 2 at a fixed distance from the lower body 4. It is appreciated that a rudder 6 is a control surface that affects the yaw of the underwater vehicle.
Both rudders 6a, 6b are able to yaw independently of each other, as indicated by the movement arrows 16a and 16b. The fore and aft positioning of the rudders 6a, 6b and the independent direction of yaw forces generated from the fore rudder 6a and aft rudder 6b allow for manoeuvres of various complexities as discussed further below.
100381 In this example, the purpose of each rudder 6 is to act as a control surface affecting the yaw, and any configuration capable of doing so is encompassed by the embodiments described herein.
100391 The two rudders 6a, 6b form a structural base for the underwater vehicle's propulsion system, which further comprises respective elevators 12 and thrusters 14. An elevator 12 protrudes from both sides of a rudder 6 and comprises a rigid control surface or plane that is generally perpendicular to the rudder 6. The flow of fluid over the elevator 12 generates forces that affect the pitch or inclination of the underwater vehicle. Each elevator 12 is able to rotate or pitch, as indicated by the movement arrows 18a and 18b. In the embodiment shown in Figure 1 a, both the fore elevator 12a and aft elevator 12b have a swept wing geometry to reduce drag. It is understood that elevators 12 comprising other geometries to control the pitch while reducing drag are equally applicable.
21824162.1 100401 Similar to the rudders 6a, 6b, both the fore elevator 12a and aft elevator 12b are able to move independently from one another. In one example, the fore elevator 12a may pitch downwards, while the aft elevator 12b may pitch upwards to create a coupled moment, thereby pitching the underwater vehicle downwards. The fore and aft positioning of the elevators 12a, 12b and the independent direction of pitch forces generated from the fore elevator 12a and aft elevator 12b allow for manoeuvres of various complexities as discussed further below.
[0041] It is noted that all control planes (i.e. rudder 6 and elevator 12) advantageously use NACA OOxx airfoil profiles, an industry standard in naval architecture. The NACA OOxx airfoil profiles provide hydrodynamic efficiency and geometrical convenience. It will be appreciated that other airfoil profiles that allow for the same are equally applicable.
100421 Fixed to each elevator 12 is a thrust generator 14, such that the thrust generator 14 is oriented with the same pitch as the elevator moves. Since each elevator 12 is fixed to a rudder 6, the elevator 12 and, therefore the thrust generator 14, will also be oriented to have the same yaw as the rudder 6. The thrust generator 14 is located behind the trailing edge of the rudder 6 so as to allow for a larger range of pitch rotation, while avoiding interference between the thrust generator 14 and rudder 6. Other configurations between the thrust generator 14, elevator 12, and rudder 6 that allow the thrust generator to move across a sufficient range for pitch and yaw are equally applicable.
[0043] The thrust generator 14 shown in Figure 1 a, comprises a single propeller driven by a motor. Other embodiments of a thrust generator 14 may include one more motors driving one or more propellers. Alternatively, a thrust generator 14 may comprise the release of a pressurized gas or liquid. It is appreciated that any mechanisms for generating thrust are equally applicable.
[0044] The direction of the force generated by the thrust generator 14 is indicated by the direction arrows 20a and 20b. The coupling of a thrust generator 14 to the elevator 12 and rudder 6, allows the thrust generator 14 to direct the thrust at various pitch and yaw angles. The independent movement of the fore and aft thrust generators 14a, 14b, and the positioning of the tbrust generators 14a, 14b in relation to the upper and lower bodies 2, 4 allow the underwater vehicle to carry out complex manoeuvres, discussed in further detail below.
21824162.1 [0045] Turning to Figure 2, a perspective view of an isolated propulsion system is shown in greater detail. The thrust generator 14, in one embodiment shown in Figure 2, comprises a propeller 24 driven by a motor assembly 22. The motor 22 may be located external to the rudder 6 and elevator 12 to allow the thrust generator 14 to rotate or pitch relative to the rudder 6. In addition to increased range of rotation, placing the motor 22 external to the rudder 6 and elevator 12 reduces the complexity of transferring the motor's energy to the propeller 24. The motor assembly 22 is fixed to a U-shaped bracket 26, and more particularly to the portion that bridges the two armatures of the bracket 26. Each armature on the bracket 26 is situated between the elevator 12 and rudder 6. The bracket 26 is fixed to the elevator 12, wherein the pitch movement of the elevator 12 and, therefore, the thrust generator 14 may be identical.
The bracket 26 also positions the propeller 24 further away from the trailing edge of the rudder 6, thereby allowing the thrust generator 14, in this case the propeller 14, to achieve a larger range of pitch rotation.
It is appreciated that alternate configurations of the propeller 14, motor 22 and bracket 26 that allow for a sufficient range of rotation are equally applicable.
100461 Also shown in Figure 2 is an XYZ reference frame that in this example is fixed relative to the underwater vehicle body for the purpose of describing the various configurations below. The XYZ reference frame is oriented such that the X axis is oriented along the length of the vehicle and is directed toward the rear or aft of the vehicle. The Z axis is oriented vertically between the upper body 2 and lower body 4, such that the Z axis is aligned with the vertical length of the rudder 6, and is directed upwards toward the upper body 2. The Y
axis is oriented perpendicular to both X and Z axes and, in accordance with chirality, is directed towards the starboard side of the underwater vehicle in this example. This reference may be used to describe the axes of rotation for the above components.
[0047] The propeller 24 rotates about the axis A. The axis A, in this case, extends along the length of the bracket 25 and motor assembly 22. The axis A and the elevator 12 both rotate, or pitch, about axis B. It is appreciated that the A axis rotates with the elevator 12 about axis B
since the bracket 25 and motor assembly 22 are fixed to the elevator 12. It is further understood that rotational axes A and B remain perpendicular to one another. Axes A and B, and the rudder 6 rotate, or yaw, about axis C.
21824162.1 -g-[0048] The three rotational axes, A, B, and C, introduced above, may be described relative to the underwater vehicle's XYZ reference frame. In a neutral orientation, the underwater vehicle's control surfaces are oriented such that the underwater vehicle is directed in a straight heading, with no yawing or pitching movements. In this neutral orientation, the rotational axis A is parallel with the X axis. The A axis is oriented towards the back or aft of the underwater vehicle in the same direction with the X axis, which is also oriented towards the back or aft of the vehicle. In a neutral orientation, the rotational axis B is oriented parallel to the Y axis.
However, according to the convention shown here, the positive B axis is oriented towards the portside of the underwater vehicle and the positive Y axis is oriented towards the starboard side of the underwater vehicle. The rotational axis C always remains oriented parallel and in the same direction as the vertical Z axis when using this reference frame.
[0049] It is noted that the A axis may pitch about the B axis by some angle +/-alpha (a). It is also understood that the thrust from the thrust generator 14 is directed along the A axis. For example, when the A axis inclines above the X axis by + alpha, the elevator 12 and direction of thrust is pitched in a downward direction. Similarly in another example, when the A declines below the X axis by - alpha, the elevator 12 and the direction of thrust is pitched in an upward direction. It is further appreciated that when the thrust is directed in along the X axis, then the thrust is directed towards the aft of the underwater vehicle, thereby propelling or pushing the underwater vehicle forward.
[0050] With regard to the yaw movement, both A and B axes, as well as the rudder 6, may pivot about axis C by some angle +/- beta ((3). For example, when the propulsion assembly yaws by +beta, the rudder 6 and the A axis rotate from the X axis in a counter clockwise direction.
Similarly, the B axis rotates from the -Y axis in a counter clockwise direction by +beta. In yet another example, when the propulsion assembly yaws by beta, the trailing edge of the rudder 6 and the A axis rotate from the X axis in a clockwise direction, and the B axis rotates from the -Y
axis in a clockwise direction. It can be appreciated that the propulsion system may yaw about the C axis by 360 degrees in either a clockwise or counter clockwise direction. As will be exemplified below, such freedom of rotation about the C axis enables complex and controlled movements that provides greater handli.ng and control of an underwater vehicle.
21824162.1 [0051] The combined movements of the pitch and yaw allows the axis A, and therefore thrust vector, to be oriented in various directions. The combination of the two or more in-line propulsion systems with the described underwater vehicle allow for various manoeuvres with five degrees of freedom, including pitch, yaw, heave (i.e. moving up and down), surge (i.e.
moving forward and backward) and sway (i.e. moving left and right).
[0052] It may be noted that roll movements may also be achieved if the elevators 12 are controlled to pitch in opposite directions. For example, if the starboard elevators were to pitch upwards and the portside elevators were to pitch downwards, then the underwater vehicle may tend to roll towards the portside.
[0053] Turning to Figure 3, the various components in the propulsion system are shown schematically. The rudder 6 subassembly, elevator 12 subassembly and thrust generator 14 subassembly each comprise a motor 30, 36, 42 motor controller 28, 34, 40 and gearbox 32, 38, 44. In general, each motor controller 28, 34, 40 receives signals from a vehicle control unit 48 through a network communication system 46. The motor controller 28, 34, 40 then actuates its corresponding motor 30, 36, 42, which may be coupled to a gearbox 32, 38, 44, to modify the speed and power output of the motor 30, 36, 42.
[0054] The vehicle control unit 48 is preferably a computer, housed in the upper body 2 of the underwater vehicle, which contains the vehicle's control system software (not shown but can be appreciated as any computer instructions, data structures, memory and other software components stored on and/or accessible from a computer readable medium). Based on navigational sensor input (e.g. GPS, DVL, Altimeter, Attitude Sensor) and using pre-programmed mission criteria, the control system software may calculate the desired vehicle speed, pitch, roll, and heading. Then, based on the current speed, pitch, roll, and heading, the control system sends control information via a network communication system 46, such as a controller-area network (i.e. CAN) bus (as shown in Figure 3), to the respective motor controllers 28, 34, 40 for each rudder 6, elevator 12 and thrust generator 14 to achieve the desired orientation.
21824162.1 [0055] The sub-assemblies in Figure 3 are indicated by the dashed lines, while the outer solid lines indicate the pressure housings. The rudder subassembly, comprising the rudder's motor controller 28, motor 30 and gearbox 32, is completely contained within its own pressure housing, located in the upper body 2 of the underwater vehicle. Components from the elevator and thrust generator subsystem share a pressure housing located in the rudder 6. The elevator's motor controller 34, motor 36 and gearbox 38, as well as the thrust generator's motor controller 40 are located within the pressurized portion of the rudder 6. The thrust generator's motor 42 and gearbox 44 are located external to the rudder 6 and elevator 12 in a separate pressure housing 22 fixed to the end of the bracket 26. The purpose of placing the above components in various pressure housings is to protect the above components from the effects of the water while reducing mechanical complexity.
100561 Figure 4 shows various ones of the above components when housed in the physical structures. In this embodiment, the rudder 6 is divided into three logical and physical sections;
the top 52, middle 54, and bottom 56 sections. The top 52 and bottom 56 sections are free-flooding to allow for water to enter and exit freely through designated drainage holes. The drainage holes are positioned in certain areas along the airfoil of the rudder 6 to maintain hydrodynamic efficiency. In one embodiment, the drainage holes may be placed along the top and bottom surfaces of the rudder 6, wherein the top surface is adjacent to the underside of the upper body 2 and the bottom surface is adjacent to the topside of the lower body 4. The middle section 54 of the rudder 6 is pressurized to house the elevator's motor controller 34, motor 36 and gearbox 38, as well as the thrust generator's motor controller 40. It can be appreciated that the top 52 and bottom 56 sections of the rudder 6 are free-flooding to reduce the effects of dynamic shifting buoyancy forces on the underwater vehicle.
[0057] Cabling from the upper body 2 to the lower body 4 may also be routed through the hollow shaft 50 around which the rudder 6 rotates. Cabling from the upper body 2 to the respective elevators 12 and thrust generators 14 on the rudder 6 is also routed through this hollow shaft 50 to the components in the pressure housings, which require access to power and the communication network 46.
21824162.1 100581 In this embodiment, the rudder's top 52 and bottom 56 sections are almost identical or mirror images of each other except for one difference pertaining to the joints. The joint from the top section 52 to the upper body 6 contains the motor 30 for rotating the rudder 6, whereas the joint from the bottom section 56 to the lower body 4 contains a bearing to allow for smooth yaw movement.
[0059] The geometry and functionality of the rudder's middle section 54 differ from the top 52 and bottom 56 sections, although it is mechanically attached to the other two sections. The profile of a top 52 or bottom 56 section, shown in Figure 5a, comprises a rounded leading edge and a pointed trailing edge. The front face of the middle section 54 is curved to match the nose radius of the airfoil-like profile of the rudder's top 52 and bottom 56 sections. However, as shown in Figure 5b, the trailing edge portion of the rudder's middle section 54 has a different rectangular profile instead of a pointed edge.
100601 Returni.ng to Figure 4, the rectangular profile towards the trailing edge increases the volume within the middle section 54 of the rudder 6 and, therefore, allows room for components, such as motor controllers 34, 40, to be stored within the pressure housing. At least one shaft 58 extends horizontally through the middle section, via two waterproof shaft seals, connecting the elevator motor 36 and gearbox 38 to the elevator planes 12. The rotation of the horizontal shaft 58 may cause the elevator planes 12 to pitch. It may be noted that the horizontal shaft 58 corresponds to the rotational axis B. The elevator 12 may be composed of two identical planes, attached on either side of the rudder's middle section 54 via the horizontal shaft 58, as well as the attached bracket 26 used for mounting the motor assembly 22 and propeller 24 aft of the two planes.
[0061] Figure 4 also illustrates where the elevator planes may be connected and aligned together, such that one motor 36 is required to actuate both planes of the elevator 12. A single motor configuration reduces power consumption, reduces complexity and reduces the amount of space required. Alternatively, in another embodiment, the starboard plane and portside plane may each be coupled to their own separate motor for independent control.
Therefore, the two separate motors may facilitate rolling movement.
21824162.1 [0062] It may be noted that both planes in the elevator 12 do not contain pressure housings, and are free-flooding. Similar to the rudder 6, drainage holes are provided to allow water to enter and exit the elevator 12, and the holes are placed along the elevator 12 to maintain hydrodynamic efficiency. In one embodiment, the drainage holes are placed on the face of the elevator plane 12 attached to the bracket 26 and further, coincident with an identical hole in the bracket 26 itself. This embodiment allows water to enter and/or exit through the drainage holes in the elevator 12, through the coincident holes in the attached bracket 26.
The elevator 12 is free-flooding to reduce the effects of shifting buoyancy forces on the underwater vehicle. As the elevator 12 extends away from the centerline of the underwater vehicle, and pitches and yaws in various directions, the effects of positioning a pressurised housing, or buoyancy generator, may be avoided by flooding the elevator 12 structure. It is noted that the effects of positioning a pressurised housing in the elevator 12 may comprise changes in resulting moments and force vectors acting on the underwater vehicle during various manoeuvres.
[0063] Figure 4 further shows the thrust generator 14, which, in one embodiment, comprises a motor 42 and planetary gearbox 44 mounted inside a hydrodynamic pressure housing for the motor assembly 22, with a sealed bearing connecting the output shaft to a large diameter propeller 24. A cable from the motor assembly housing 22 to the pressurised rudder housing, or middle section 54, connects the motor 42 to the motor controller 40. It can be appreciated that the motor controller 40 is housed in the rudder's pressurised middle section 54 in this example.
[0064] The motor assembly 22 and propeller 24 are mounted to the bracket 26, which is mechanically attached to the elevator planes and placed slightly aft of the trailing edge of the rudder 6. The angle of rotation of the elevator 12 is limited to prevent the bracket 26 and propeller 24 from impacting the trailing edge of the rudder 6. Both hard stops, implemented mechanically, and soft stops, implemented in the vehicle control unit 48, may be added to prevent impacts.
[0065] Figure 6 shows the propulsion assembly from a top planar view. Seen more clearly, the axis A pitches about axis B and yaws about axis C. It is also noted in this embodiment, the pitch axis B may be offset from the yaw axis C. This offset is also reflected in the 21824162.1 implementation, wherein the rudder 6 pivots about the vertical hollow shaft 50, which is located towards the leading edge of the rudder 6. The elevator 12 is attachable to the rudder 6 by the horizontal shaft 58, which is located further back from the leading edge of the rudder 6.
[0066] In Figure 6, the profile of the rudder's middle section 54, which comprises a rectangular-shaped trailing edge, is also shown relative to the profile of the rudder's top section 52. In addition, the bracket 26 is shown attached to an inner portion of the elevator 12.
100671 Turning to Figure 7, one embodiment of the underwater vehicle in an underwater enviromnent is shown relative to a seabed 64. In this embodiment, various sensors 60, for example sonar and imaging equipment, are located in the lower body 4 and may be used to collect data about the seabed 64. Some sensors 60 may be positioned in the lower body 4 to allow for better line-of-sight with the area below the underwater vehicle.
Other sensors 60 may also be located in the upper body 2. The upper body 2, for example, may house a wireless communications receiver and transceiver 62 to communicate with other marine vessels or a base station. The communications system 62 may relay various information including for example, control commands and sensor data. The communications system 62 may relay command signals to the vehicle control unit 48 to carry out various manoeuvres by orienting the propulsion system in particular configurations.
[0068] It has also been found that various ones of these components can be housed in the lower body 4 in order to lower the center of gravity, which assists in the various movements of the vehicle. By way of background, when a marine vessel is tilted the center of buoyancy of the vessel moves laterally. The point at which a vertical line through the tilted center of buoyancy crosses the line through the original, non-tilted center of buoyancy is the metacenter. Lowering of the center of gravity increases the metacentric height, that is the distance between the metacentre and center of buoyancy. A larger metacentric height increases the natural stability of the vehicle in pitch and roll.
[0069] It is appreciated that various manoeuvres, many of which utilize the natural stability of the underwater, may be achieved with the described propulsion system as described below.
21824162.1 [0070] Figure 8 shows the underwater vehicle ascending with the length of the bodies 2, 4 being generally parallel with the flat seabed 64, and having a slight pitch.
This manoeuvre involves the fore elevator 12a and thrust generator 14a pitching upwards, which causes the nose or front end of the underwater vehicle to move in an upwardly direction.
Simultaneously, the aft elevator 12b and thrust generator 14b pitch upwards as well, which also causes the tail or back end of the underwater vehicle to move in an upwardly direction as well. This combined movement of both the fore and aft propulsion systems allows the underwater vehicle to move both forward and upward simultaneously. Alternatively, this manoeuvre may be characterised by pitch, heave and surge.
100711 Figures 9a to 9c show the perspective view, profile view and planar view of the rotational axes A, B, and C relative to the underwater vehicle's XYZ reference frame during an upward and forward ascending manoeuvre, according to Figure 8. From Figure 9a, the fore rotational axis Al rotates below the X axis by some angle -al degrees, thereby directing the thrust downwards. The aft rotational axis A2 also rotates below the X axis by some angle -a2 degrees, such a2 is slightly less than al. Therefore, more thrust is generally directed downwards towards the fore of the underwater vehicle compared to the aft, which may cause the overall underwater vehicle to pitch slightly upwards. The profile view in Figure 9b also shows that the A axis has a horizontal component direct along the X axis and, thus, the some of the force or thrust from the thrust generators 14a, 14b is acting along the X axis to propel the underwater vehicle forward.
100721 Figure 9c also shows that no yawing action is involved in this manoeuvre, since the planar view shows that A1 and A2 are still aligned with X axis, and Bl and B2 are still aligned with the -Y axis. Therefore, rotational angles (31 and (32 both equal0 .
10073] Turning now to Figure 10, the underwater vehicle is shown carrying out another manoeuvre, such that the underwater vehicle is vertically translating upwards, or heaving, only.
There are no yaw, pitch, roll, surge and sway movements. This heave manoeuvre may be useful in various situations. For example, when the underwater vehicle wants to inspect or navigate with respect to the vertical face of an underwater cliff, the underwater vehicle may move 21824162.1 upwards and downwards along the height of the cliff while maintaining a fixed horizontal distance from the cliff face.
[0074] Figures 11 a to 11 c show different views of the orientations of the rotational axes relative to the XYZ reference frame for the heave-only manoeuvre. First, the fore propulsion system yaws 180 about the C axis, such that the leading edge of the fore rudder 6a is directly facing the leading edge of the aft rudder 6b. This yaw rotation is represented by the angle (31, which equals 180 . As shown in Figures 11 a and 11 c, after the rotation of (31, the rotational axis Bl is aligned and pointed in the same direction as the +Y axis. It is noted that the aft propulsion system does not yaw and, thus, (32 equals 00.
100751 After the first Bl rotation, Figures 11a and 11 b show that the elevator 12 and thrust generator both pitch upwards. Therefore, the A1 axis rotates below the -X axis in a counter clockwise direction by some angle +al, and the A2 axis rotates below by the X
axis in a clockwise direction by some angle -a2. Assuming the magnitude of thrust is the same from both thrust generators 14a and 14b, the pitch angles a1 and a2 are equal in order to cancel out the horizontal forces along the X axis. The horizontal forces cancel each other out since the thrust generators 14a and 14b are directed in opposite directions along the X axis, resulting in only vertical forces. This allows the underwater vehicle to translate vertically upwards.
100761 Turning to Figure 12, the underwater vehicle is shown in the middle of a turn manoeuvre towards the left or starboard side. The two separate propulsion systems located at the fore and aft of the underwater vehicle create a coupled moment about the center of the underwater vehicle, which allow for a smaller turning radius. In effect, the underwater vehicle could yaw about a central point with little forward or lateral movement. For example, if the fore rudder 6a directs its leading edge to the face the portside and the aft rudder 6b directs its leading edge to face the starboard side, then the underwater vehicle may rotate or yaw in a counter clockwise direction about a point. This manoeuvrability may be used, for example, to face a forward mounted sensor on the vehicle in an opposite direction while in an environment with constrained space.
21824162.1 100771 Figures 13a to 13c show the different views of the rotational axes A, B
and C relative to the underwater vehicle's XYZ reference frame for a the starboard turn, according to Figure 12.
It is appreciated that this manoeuvre does not require any pitching motion and, thus, both fore and aft elevators 12a, 12b do not rotate about the B axis. As a result al and a2 are equal to 0 , as shown most clearly in Figure 13b.
100781 Figures 13a and 13c show the fore propulsion system yawing by some angle -(31 in counter clockwise direction about the Cl axis. The rotational axis Al rotates away from the X
axis by -(31, and the rotational axis Bl rotates away from the -Y axis by -(31. It is noted that in this embodiment, the rotational axes A and B remain perpendicular to one another. With this clockwise rotation, the leading edge of the fore rudder 6a is directed towards the starboard side and the thrust is directed towards the portside. This causes the nose of the vehicle to turn towards the right or starboard.
100791 Similarly, the aft propulsion system yaws by some angle (32 in a clockwise direction about the C2 axis. The rotational axis A2 rotates away from the X axis by (32, and the rotational axis B2 rotates away from the -Y axis by (32. It is noted that in this embodiment, the rotational axes A and B remain perpendicular to one another. With this counter clockwise rotation, the leading edge of the aft rudder 6b is directed towards the portside and the thrust is directed towards the starboard. This causes the tail end of the vehicle to turn towards the left or portside.
In this example manoeuvre, the angle (32 is less than the angle (31 and, thus, the nose of the underwater vehicle turns more quickly to the starboard than the tail end turns to the portside.
100801 There may be various combinations of pitch and yaw that allow for different movements. For example, if both rudders 6a, 6b direct their leading edges to the left or portside, then the entire underwater vehicle will sway, or laterally translate, towards the portside. This sway movement does not require any yawing rotations. Other movements may include, for example, pitching and yawing simultaneously, or heaving and yawing simultaneously, or moving backwards and pitching simultaneously. In a more specific example, the underwater vehicle may maintain a constant downwards pitch, while moving backwards and side-to-side.
Various combinations of pitch, yaw, heave, surge and sway may be accomplished with the propulsion 21824162.1 system described herein. Furthermore, with independent starboard and portside elevators, roll may also be achieved. Therefore, the underwater vehicle may move in all six degrees of freedom.
[0081] Another advantage in movement is the underwater vehicle's ability to hover, or stay in a fixed position, while maintaining an absolute heading. The propulsion system also allows the underwater vehicle to hover in the presence of currents in any direction and of reasonable speed.
[00821 Different manoeuvres may also be achieved by varying the force produced by the thrust generators 14. In one manoeuvre, for example, the fore thrust generator 14 may produce more force during a turn than the aft thrust generator 14b, thereby causing the nose of the underwater vehicle to move at a faster speed. This variable thrust may be generated by increasing or decreasing the speed at which the propeller 24 rotates about the axis A. In addition, the thrust may be varied by controlling the pitch, or angle of attack, or the propeller's blades.
[0083] Having two or more of the propulsion systems positioned towards the fore and aft of the underwater vehicle also allows for high manoeuvrability. This configuration encompasses the advantages of both thrust vectoring and differential thrusters.
Furthermore, by positioning the two propulsion systems in-line with one another and situated between the upper body 2 and lower body 4, the drag is reduced and hydrodynamic efficiency is maintained.
100841 The configuration of the upper body 2 and lower body 4 also provides the advantage of increased stability with respect to pitch and roll. Separating and placing the lower body 4 below the upper body 2, lowers the center of gravity and provides a higher center of buoyancy.
100851 Although the above has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.
21824162.1
Claims (3)
1. An underwater propulsion system comprising at least one assembly comprising a rudder configured to be rotatably connected to the hull of an underwater vehicle to permit complete rotation of said rudder with respect to said hull, an elevator pivotally attached to said rudder to pitch about an axis perpendicular to the axis of rotation of said rudder, and a thrust generator extending from and attached to said elevator such that said thrust generator pitches with said elevator.
2. An underwater vehicle comprising:
an upper and lower body positioned vertically above one another and separated by at least one propulsion assembly; and said at least one propulsion assembly, each propulsion assembly comprising:
a vertically oriented rudder configured to be rotatably connected between said upper and lower bodies and is fully rotatable about an axis of rotation;
an elevator pivotally attached to said rudder to pitch about an axis perpendicular to the axis of rotation of said rudder; and a thrust generator extending from and attached to said elevator such that said thrust generator pitches with said elevator.
an upper and lower body positioned vertically above one another and separated by at least one propulsion assembly; and said at least one propulsion assembly, each propulsion assembly comprising:
a vertically oriented rudder configured to be rotatably connected between said upper and lower bodies and is fully rotatable about an axis of rotation;
an elevator pivotally attached to said rudder to pitch about an axis perpendicular to the axis of rotation of said rudder; and a thrust generator extending from and attached to said elevator such that said thrust generator pitches with said elevator.
3. The underwater vehicle according to claim 2, wherein said elevator comprises a starboard plane positioned towards the right of said rudder and a portside plane positioned towards the left of said rudder, and each said starboard and portside planes able to move independently from one another.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2642805 CA2642805A1 (en) | 2008-11-04 | 2008-11-04 | Propulsion system for an autonomous underwater vehicle |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2642805 CA2642805A1 (en) | 2008-11-04 | 2008-11-04 | Propulsion system for an autonomous underwater vehicle |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2642805A1 true CA2642805A1 (en) | 2010-05-04 |
Family
ID=42154753
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2642805 Abandoned CA2642805A1 (en) | 2008-11-04 | 2008-11-04 | Propulsion system for an autonomous underwater vehicle |
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| CA (1) | CA2642805A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112591059A (en) * | 2020-12-01 | 2021-04-02 | 中国科学院深圳先进技术研究院 | Underwater vehicle control method and device |
-
2008
- 2008-11-04 CA CA 2642805 patent/CA2642805A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112591059A (en) * | 2020-12-01 | 2021-04-02 | 中国科学院深圳先进技术研究院 | Underwater vehicle control method and device |
| CN112591059B (en) * | 2020-12-01 | 2022-02-08 | 中国科学院深圳先进技术研究院 | Underwater vehicle control method |
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