Vectored Buoyancy Engine System

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 63/708,150 filed 16 Oct. 2024. The entire contents of the above-mentioned application are incorporated herein by reference.

STATEMENT REGARDING GOVERNMENT LICENSE RIGHTS

The invention described herein was made with U.S. government support under Grant No. 2133029 awarded by the National Science Foundation. The U.S. Government has certain rights in the invention.

FIELD OF THE INVENTION

This invention relates to autonomous underwater vehicles maneuverable by manipulating at least one of buoyancy and/or mass in at least two engines.

BACKGROUND OF THE INVENTION

There is a growing need for underwater robotic platforms to provide monitoring and exploration capabilities in complex and dynamic environments, such as coral reefs or kelp forests. Of interest are autonomous robotic platforms that can provide high-fidelity observations in a body of water using sensors such as hydrophones and cameras, while minimizing noise generated from the vehicle and maximizing observation time. These vehicles need to be low energy, minimally disturbing to the environment, and highly maneuverable.

Underwater gliders, wavegliders, and sailing drones are in active use for these purposes but are often used for large-scale oceanography and to resolve environmental features on the order of tens of meters to kilometers. Thruster-actuated robots have also been used for passive acoustic monitoring of coral reefs to observe acoustic bioactivity. To deal with thruster noise, these robots interleave their trajectory with periods of drifting during which they have no control. However, that approach has problems because acoustic samples can be collected over only very short time periods when the thrusters are off. Furthermore, due to continuous thruster use for most of its operating time, such robots have a very short operating time (2-3 hours) and are not suitable for long-term monitoring tasks.

As opposed to thrusters, gliders almost exclusively rely on buoyancy and barycentric control for actuation. Vehicles such as University of Washington Seagliders, Spray gliders, or Slocum gliders are commonly used to provide long-term monitoring of large-scale ocean regions. They are especially effective for these tasks because they are low energy, so their mission lengths can be up to several months. Additionally, in most cases, gliders only need to occasionally move a mass weight, or modify buoyancy via a bladder or linear actuator, making them relatively silent, allowing their use for acoustic measurements.

Underwater gliders typically use wings (either passive or active) and a moveable mass to control orientation, but this results in large turning radii, such as the 7 m radius of the Slocum or larger for others. In turn, this makes them mostly appropriate for large-scale data collection, often on the order of kilometers. Some gliders, and most highly maneuverable vehicles are designed to include thrusters and additional wing surfaces for added maneuverability, but thrusters nullify many of the silent and energy-efficient benefits of the buoyancy-driven vehicle. One vehicle utilizes an additional roll mechanism for the mass, which was used on a smaller glider to reduce its turning radius to 3-meters while maintaining the other desired characteristics.

Most autonomous underwater vehicles (AUVs) use a set of thrusters, and optionally control surfaces, to control their depth and pose. AUVs utilizing thrusters can be highly maneuverable, making them well-suited to operate in complex environments such as near coral reefs. However, they are inherently power-inefficient and produce significant noise and disturbance. Underwater gliders, on the other hand, use changes in buoyancy and center of mass, in combination with a control surface to move around. They are extremely power efficient but not very maneuverable. Gliders are designed for long-range missions that do not require precision maneuvering.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a new class of autonomous underwater vehicles (AUVs) that are energy efficient, highly maneuverable, inobtrusive, and minimize noise.

This invention features a buoyancy engine system, and method of using same, for a vehicle configured to move through a water column in a body of water, the vehicle having a center of mass, a center of buoyancy, and at least one passive component exposable to the water to create drag and/or lift The engine system has a first buoyancy engine configured to alter the center of buoyancy and total net buoyancy of the vehicle at a first location on the vehicle, and at least a second engine configured to move a mass and/or to alter buoyancy at a second location on the vehicle. A controller commands the first buoyancy engine and the second engine to shift at least one of the center of mass and/or the center of buoyancy to control orientation, horizontal motion and/or vertical motion of the vehicle.

In a number of embodiments, the controller is configured to provide successive commands to the first buoyancy engine and the second engine to propel the vehicle in a selected direction or to hold a selected position in a body of water. In certain embodiments, the engine system has at least two buoyancy engines including the first buoyancy engine, with at least two of the buoyancy engines spaced apart from each other and, in other embodiments, has at least three buoyancy engines, with at least two of the buoyancy engines spaced apart from the other buoyancy engine. In one embodiment, the first buoyancy engine is a first pair of buoyancy engines and the second engine is a second pair of buoyancy engines. The engines may be aligned radially, along a longitudinal axis and/or along a lateral axis of the vehicle.

This invention also features an underwater vehicle configured to move through a water column in a body of water, and having a vehicle body having a center of mass, a center of buoyancy, and at least one passive component exposable to the water to create drag and/or lift. The vehicle further includes a first buoyancy engine configured to alter the center of buoyancy and total net buoyancy of the vehicle body at a first location on the vehicle body, and at least a second engine configured to move a mass and/or to alter buoyancy at a second location on the vehicle body. A controller commands actuation of the first buoyancy engine and the second engine to shift at least one of the center of mass and/or the center of buoyancy to control orientation, horizontal motion and/or vertical motion of the vehicle.

In some embodiments, the controller is configured to provide successive commands to the first buoyancy engine and the second engine to propel the vehicle in a selected direction or to hold a selected position in the body of water. In certain embodiments, at least one pressure sensor determines depth and at least one inertial measurement unit determines changes in at least two of roll, pitch, and yaw as orientation signals, and the controller is configured to process the pressure and orientation signals. In some embodiments, a transceiver communicates remotely to receive target pressure, roll and/or pitch command signals to be processed by the controller.

This invention further features a method of propelling an underwater vehicle having a center of mass, a center of buoyancy and at least one passive component exposable to the water to create drag and/or lift, the method including selecting at least a first buoyancy engine configured to alter the center of buoyancy and total net buoyancy of the vehicle at a first location on the vehicle, and selecting at least a second engine configured to move a mass and/or to alter buoyancy at a second location on the vehicle. The method further includes deploying the vehicle in a body of water having a water column and altering the center of buoyancy and total net buoyancy of the vehicle at the first location on the vehicle while moving the mass and/or altering buoyancy at the second location on the vehicle to propel the vehicle in a selected direction or to hold a selected position in the body of water.

In a number of embodiments, successive commands are provided to the first buoyancy engine and the second engine to propel the vehicle in the selected direction or to hold the selected position in the body of water. In one embodiment, the orientation of the underwater vehicle is changed by providing successive commands to the first buoyancy engine and the second engine to alter roll and pitch by changing the center of mass and/or center of buoyancy on the vehicle while holding total buoyancy constant. In some embodiments, the method utilizes only changes in buoyancy to propel and maneuver the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

To enable a better understanding of the present invention, and to show how the same may be carried into effect, certain embodiments of the invention are explained in more detail with reference to the drawings, by way of example only, in which:

FIG. 1A is an upper perspective view of a four-engine system according to one embodiment of the present invention, referred to herein as the ReefGlider™ system, mounted on a rectangular base plate;

FIG. 1B is a transparent housing view of FIG. 1A;

FIG. 1C is a schematic diagram of buoyancy forces generated by the system of FIGS. 1A-1B;

FIG. 1D is a partial cross-sectional side view of one novel double-piston buoyancy engine of FIGS. 1A-1C having two linear actuators;

FIG. 2 is a schematic block diagram depicting feedback control for VBC (vectored buoyancy control) according to one embodiment of the present invention wherein a mixer of a microcontroller sums the sensed pressure, roll, pitch, and Open Loop (OL) control signals and sends the corresponding actuation to each of the linear actuators;

FIG. 3 is a schematic diagram of signal processing and weighting within the microcontroller of FIG. 2;

FIG. 4A is a schematic top view of vectored COM (center of mass) and buoyancy control engines according to another embodiment of the present invention;

FIG. 4B is a schematic top view of another vectored COM and buoyancy control engines according to yet another embodiment of the present invention;

FIG. 5A has six charts depicting a depth-hold experiment showing ground-truth pose data from AprilTag tracking by a GoPro camera submerged in test tank by distance or angle over time;

FIG. 5B has three charts depicts a depth-hold experiment: roll, pitch, and depth readings with their corresponding set points plotted for changing depth set points;

FIG. 6A has three charts depicting a pitch-oriented sawtooth transect experiment with roll, pitch, and depth readings given with their corresponding set points plotted and with indicators corresponding to the positions in FIGS. 6B and 6C;

FIG. 6B is a side view of successive images of the ReefGlider™ as it moves from left to right in the test tank TT merged into a single trajectory image;

FIG. 6C is a view similar to FIG. 6B showing the trajectory of the ReefGlider™ as it moves from right to left and returns to the starting position;

FIG. 7A has three charts depicting a roll-oriented sawtooth transect experiment with roll, pitch and depth readings (in blue) and their corresponding set points plotted with indicia corresponding to the positions shown in FIGS. 7B and 7C;

FIG. 7B is a side view of successive images of the ReefGlider™ as it moves from left to right in the test tank merged into one trajectory image;

FIG. 7C is a view similar to FIG. 7B as the ReefGlider™ moves from right to left and returns to the starting position;

FIG. 8A has six charts depicting a yaw experiment ground-truth: pose data of yaw demonstration gathered by an upward-facing GoPro in the bottom of the test tank recording an AprilTag attached to the bottom of the ReefGlider™

FIG. 8B has four charts for the yaw experiment sensor feedback showing roll, pitch, depth, and yaw sensor data with their corresponding set points plotted;

FIGS. 9A and 9B are schematic top views of radially-positioned buoyancy engines according to the present invention on triangular and elliptical base plates, respectively;

FIGS. 10A and 10B are schematic side partial cross-sectional views of buoyancy engines within different configurations of hydrodynamic hulls or shells; and

FIG. 10C is a schematic bottom view of a hull similar to that of FIG. 10B showing four optional movable vanes.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Described herein is a novel variable buoyancy propulsion system for underwater vehicles, including robots such as AUVs, that uses only buoyancy for control, or buoyancy plus change in center of mass, but is still highly maneuverable due to multiple buoyancy and/or mass control devices. This invention may be accomplished by a system and method that use buoyancy control engines as control actuators rather than thrusters, rudders or other movable hydrodynamic feature. This enables energy and noise savings, while allowing for much higher resolution and sub-meter control, including zero turning radius in some constructions, than conventional gliders. This type of actuation herein is referred to as Vectored Buoyancy Control (VBC).

The ReefGlider™ VBC system shown in FIGS. 1A-1D was designed to be capable of changing roll, pitch, and overall buoyancy without requiring long transects as needed by many underwater gliders. At a high-level, the VBC shifts the center of buoyancy location and buoyancy force magnitude to control orientation and vertical motion. A passive component, such as a planar base piece or wing, creates drag and/or lift which can be used to enable lateral motions.

In one construction as illustrated in FIGS. 1A-1D, the ReefGlider™ system 10 for underwater vehicle 8 achieves this by controlling four individual buoyancy control mechanisms 12, 14, 16 and 18 in buoyancy engine cylinders 11 and 13, which work by changing the amount of water displaced by four linear pistons 112, 114, 116 and 118, respectively. The vehicle pose is controlled by independently moving the pistons to variably compress air or other gas within each cylinder to create a difference between the center of buoyancy (COB) and the center of mass (COM) by changing buoyancy force magnitudes F_FL, F_BL, F_FR and F_BR as shown in FIG. 1C.

The term “engine” is utilized herein in its broadest meaning to include motors which impart motion to an object.

The term “portion” as utilized herein refers to a section or region of a component, without necessarily indicating any physical difference between two or more portions apart from location on the component such as “upper portion” and “lower portion”.

For illustrative purposes, assume that point 140, FIG. 1C, is the COM and the COB in one construction when all four pistons 112, 114, 11 and 118 are halfway retracted within their respective cylinders. More accurate estimations of COM and COB are described below. Point 140 also represents the origin of the body-fixed reference frame with arrows indicating X, Y and Z directions for vehicle movement.

In one construction, the buoyancy engine cylinders 11, 13 and a controller housing 30 are mounted to a passive flat plate 30, FIGS. 1A-1C. Plate 30 is a passive component that can be easily modified to achieve different dynamic goals, as described in more detail below. The buoyancy engine cylinders 11, 13 are mounted in parallel to each other on plate 30 to simplify modelling and each contain two independent pistons 112, 114 and 116, 118, respectively, which are displaced by Actuonix P16-100-256-12-P Linear Actuators (“Actuonix P16-100-256-12-P” n.d.). The middle flange was designed such that two linear actuators could fit side by side as shown in FIGS. 1B-1D. This reduces the static volume of the buoyancy engine (BE_STATIC, FIG. 1C) and the overall footprint of the device.

In this construction, the controller 20 includes a Teensy 4 microcontroller 21 as the main control module responsible for reading data from sensors, represented schematically as features 22 and 23, and actuating the independent linear actuators 113, 115, 117 and 119, respectively. The length of actuation of each linear actuator is commanded by a PWM signal from the Teensy to the external RC control board which is responsible for the position control of the linear actuators. To provide orientation feedback, the ReefGlider relies on an inertial measurement unit (IMU), schematically represented as sensor 23, such as a Bosch BNO055. Similarly, depth or pressure feedback is provided by a BlueRobotics Bar30 pressure sensor 22. Power is supplied by a 3-S LiPo battery 24 at 11.1 V directly to the linear actuators and all other electronics through a Pololu 5V voltage regulator.

To meet the tight tolerance necessary for o-rings, the middle flange, piston head, and outer tubes were custom machined. The middle flange was machined from aluminum so that a simple cable penetrator could be threaded into it and anodized for corrosion resistance. The piston head and outer tube were machined out of acetal to reduce machining costs while still being corrosion resistant. All o-ring dimensions were determined using the Parker O-ring Handbook (Parker 1992). Four threaded rods and two 3D-printed end caps are used to axially constrain the buoyancy engines. A 3D-printed bracket is fastened to both buoyancy engines and to the passive planar component, and hence to each other. Further details are provided in Table 1 below.

Modeling and Control: a simplified linearized model of the ReefGlider™ system was constructed using cylinders and boxes to estimate the geometry of the vehicle. The controller housing is modeled as a cylinder with its COM and COB in the center of the cylinder. The plate is modeled as box with its own COM and COB. Each buoyancy engine is modeled as three independent cylinders with their own COM and COB: two dynamic cylinders as represented by arrows 152 and 154 and one static cylinder, BE_STATIC as shown in FIGS. 1C-1D. The static cylinder BE_STATIC represents the volume of water always displaced by the buoyancy engine an outer diameter of 63.5 mm. The length of the dynamic cylinders 152, 154 can vary between 0 mm and 100 mm, which corresponds to the actuation length of each linear actuator with an outer diameter of 57.15 mm. These are then summed into the full vehicle dynamics 260, FIG. 2, for vehicle 8, FIGS. 1A-1D. The controller and/or the vehicle can carry various sensors and a transceiver for underwater sensing and communication as described below.

Linearized Open-Loop Control Design: With the defined geometry, an open-loop controller is designed to enable control across pitch, roll, and depth (pressure) such as illustrated in FIG. 2 and described in more detail below. Buoyancy force and gravitational forces are the only two forces considered in this model. Additionally, the COM and COB are assumed to coincide at the centroid of the simple shapes defined in the physical model previously described. These are defined relative to an inertial frame and the modelling is simplified by assuming the vehicles is operating near a hover state (roll=0° and pitch=0°), creating a linearized model. Using these assumptions, a static open loop controller u_OL can be developed:

u OL = B 1 ( τ des - g 0 ) ⁢ where ( 1 ) τ des = [ F x F y F z τ x τ y τ z ] , u OL = [ x FL x BL x BR x FR ] , g 0 = [ 0 0 F buoy - gm total 0 0 0 ] B = [ 0 0 0 0 0 0 0 0 1 1 1 1 y BE y BE - y BE - y BE x BE x BE - x BE - x BE 0 0 0 0 ] * α ( 2 ) α = ρ ⁢ gA piston ( 3 )

with F_i and τ_i as respective forces and torques in the inertial frame described in FIGS. 1C-1D, F_buoy the static buoyancy, x{FL, BL, BR, FR} which are offsets of the corresponding linear actuators, x_BE and y_BE are static offsets of buoyancy for each cylinder from the body-fixed reference frame shown in FIG. 1C, environmental restoring force g₀ which is dependent on the static buoyancy, gravity g, and total mass of the vehicle m_total. In order to further linearize the control calculation, we assume that the change in τ_y is linearly dependent on the linear actuator offsets, though in actuality it is dependent on its square since both the COB and the buoyancy itself are simultaneously changing. Because B is non-invertible, we use the pseudo-inverse to compute the open-loop control in Equation (1). Because these assumptions introduce errors into the true solution, a feedback controller is described below.

Physical details as modelled are provided in Table 1 as provided below.

Feedback Control Design: To achieve precise control, the feedback controllers were designed for each of depth, pitch, and roll orientations in one construction. Separate PID (proportional-integral-derivative) control loops within a microcontroller 21, FIG. 2, were utilized for each parameter, where the feedforward term is calculated using the open-loop control above. Pre-selected or remotely provided target values such as pressure target 212, roll target 214 and pitch target 218 are compared with real-time signals in PIDS, 230, 234 and 236, respectively. The open-loop controller 232 provides a baseline control signal 242 representing neutral buoyancy and zero pitch and roll angles for orientation. Feedback is provided from a pressure sensor 210 for depth regulation and an IMU 216 for roll and pitch orientation, signals 220 and 222, respectively. These four control signals 240, 242, 244 and 246 were combined in the mixer 250 and produce a position command 252 for each linear actuator 113, 115, 117 and 119 to generate vehicle dynamics 260. PID control parameters (three for each parameter for a total of nine) were hand-tuned during experiments described below. A Gazebo Garden and ROS 2 Foxy simulation was created to test control policies and to enable the collection of simulated data to gain an understanding on how the system would react in the real world.

The operation of microcontroller 21 is shown in more detail in FIG. 3, with the “Depth setpoint” representing signal 240 provided by the “Pressure PID” to the Mixer 250. Similarly, the “Roll setpoint” is a Roll PID signal 244 to the Mixer and the “Pitch setpoint” is a Pitch PID″ signal 246 to the Mixer 250. The signals are weighted by lambda weights λ_d, λ_r, and λ_p for depth, roll and pitch, respectively, and summed as shown by Weighting parameters module 310, as influenced by Open Loop signals 242, and then the linear actuators are commanded to move individually as needed to achieve the target parameters via vehicle dynamics 260, FIG. 2.

In a number of constructions, vehicles according to the present invention include a transceiver to communicate remotely to receive target pressure and orientation commands, such as roll, yaw and/or pitch command signals, to be processed by the controller. Various transceivers suitable for underwater communications are well known, such as disclosed in U.S. Pat. No. 9,231,708 and US Patent Pub. No. 2016/0127042 A1 by Farr et al., for example.

The present invention may also be accomplished by a buoyancy system 410, FIG. 4A, having a combination of vectored COM (center of mass) engines 420, 430 and at least one buoyancy control engine 450 according to another embodiment of the present invention. The buoyancy engine system 410 is mounted on a passive component 412 of an underwater vehicle. The first buoyancy engine 450 is configured to alter the center of buoyancy and total net buoyancy of the vehicle at a first location on the vehicle, and second engine 420 includes a linear actuator 422 which operates a linear screw 424 to move a battery 440 which serves as a movable mass in this construction. Third engine 430 has a linear actuator 432 which operates a linear screw 434 to move the linear actuator 422 in the Y direction of arrow 436 which, in turn, moves battery 440 in the Y direction. A caster or other non-fixed support is provided under battery 440 to enable it to move along screw 424 in the X direction as shown by arrow 426 and along the Y direction of arrow 436. A controller (not shown) commands the first buoyancy engine 450 to alter buoyancy of the vehicle in the Z direction and commands the second and third engines 420, 430 to shift the center of mass COM in the X and Y directions to control orientation, horizontal motion and/or vertical motion of the vehicle.

Yet another buoyancy system 410b, FIG. 4B, is mounted on elliptical passive component 412b and includes a first buoyancy engine 450b, a second buoyancy engine 452b, and a third “mass shifter” engine 420b having a linear actuator 422b which drives a linear screw 424b to move battery 440b in the Y direction as shown by arrow 426b to shift center of mass COM. The first and second buoyancy engines 450b, 452b are utilized to change overall buoyancy and to shift the center of buoyancy COB.

Experimental Results: A system according to the present invention can have fewer DOF (degrees of freedom) control than the six DOF typically utilized to control pitch, roll and yaw to change vehicle orientation and/or to propel the vehicle in three dimensions within a water column. The term “water column” is utilized herein in its broadest sense of a 3D volume of water, rather than as a depth profile at a particular geographic point. The ReefGlider™ system shown in FIGS. 1A-1D can function as an autonomous robot that has four actuators to independently control buoyancy at four locations, and hence it is impossible for it to have instantaneous six degrees-of-freedom (DOF) control. However, it was demonstrated that the robot can be controlled with full six DOF using non-holonomic maneuvers in three dimensons.

Four experiments were conducted to show the maneuverability of the ReefGlider™ robot. The first experiment demonstrates the ability of the robot to stay at depth set points while maintaining a “hover” position (approximately zero pitch and roll). The next two experiments show the linear translation capabilities of the robot first by following a sawtooth profile in the pitch direction and second in the roll direction. As in traditional underwater gliders, the ReefGlider™ is non-holonomic and must combine changing the angle of attack (its orientation) followed by a change a depth to move laterally, hence the sawtooth profiles. The fourth experiment shows the ability to control yaw, by performing pitch, roll, pitch maneuvers in series, which illustrate the high maneuverability of this vehicle. These experiments were run completely autonomously by using pre-programmed (pre-selected) trajectories that were manually generated, consisting of time-dependent set points in depth, roll, and pitch.

All experiments were performed in a small test tank (5×10×5 feet) filled with water and labelled “TT” in FIGS. 6B-6C and 7B-7C. The depth-hold and yaw experiments included the use of an AprilTag mounted on the bottom of the vehicle and measured by an upward-facing camera, in this case a GoPro inside an underwater housing, to get ground-truth measurements.

Depth Hold: The ability for ReefGlider™ to reach desired depth set points while maintaining zero pitch and zero roll is shown in FIG. 5A and FIG. 5B. Roll, pitch and yaw are illustrated each by distance and angle over time in FIG. 5A as pose (orientation) ground truth data. Roll readings 502, 5B, are shown with continuous roll set point 504, pitch readings 512 are shown with continuous pitch set point 514, and successive depth readings 522 are shown with varying depth set points 524. The depth set points are controlled by their calculated corresponding hydrostatic pressures and are varied between 0.17 m (103000 Pa) and 0.58 m (107000 Pa). The robot is given a target depth, then allowed to settle before moving onto the next set point. This is shown in FIG. 5A which shows pose data from the AprilTag measurements, and in FIG. 5B which plots data recorded from the on-board IMU and pressure sensor. Depths were computed in post-processing (though it is possible to do them in real-time), by using the hydrostatic pressure equations, utilizing the density of freshwater for the test tank.

Following 3D Trajectories via Sawtooth Profiles: Like a traditional underwater glider, the ReefGlider™ can achieve lateral motions by changing its angle of attack (due to drag and/or lift of the passive plate or wing) followed by a change in depth. The primary difference with the ReefGlider™ is that it capable not only of going forwards and backwards but can also perform these maneuvers along the pitch (inertial x) and roll (inertial y) directions and in-between as well.

To demonstrate the maneuverability of the robot through the water we performed two separate experiments. First by transiting forward and backward along its inertial x-direction, and then second transiting forward and backward along its inertial y-direction, both using sawtooth profiles. In the first sawtooth experiment, the device is first set to a desired pitch angle, then the overall buoyancy is changed. The induced drag on the robot propels it forward. If this is repeated for different pitch angle and depth targets, a sawtooth pattern can be created as shown in FIGS. 6A-6C. FIG. 6A has three charts depicting a pitch-oriented sawtooth transect experiment. Roll readings 602 are shown with continuous set point 604, pitch readings 612 are shown with various pitch set points 614, and depth readings 622 are shown with various set points 624. The vertical lines 1 through 10 correspond to the numbered vehicle positions 6-1 through 6-10 shown in FIGS. 6B and 6C. Starting position 6-1, FIG. 6B, corresponds in “world” location and orientation to finish position 6-10, FIG. 6C. Arrow 630 indicates a left-to-right direction of motion in FIG. 6B while arrow 640 shows returning right-to-left direction of motion in FIG. 6C.

Similarly, the robot can move laterally in the y-direction as shown in FIGS. 7A-7C depicting a roll-oriented sawtooth transect experiment. Roll readings 702 are shown with continuous set point 704, pitch readings 712 are shown with various pitch set points 714, and depth readings 722 are shown with various set points 724. The vertical lines 1 through 7 correspond to the numbered vehicle positions 7-1 through 7-7 shown in FIGS. 7B and 7C. Arrow 730 indicates a left-to-right direction of motion in FIG. 7B while arrow 740 shows returning right-to-left direction of motion in FIG. 7C. The trajectory of the ReefGlider™ as it moves from left to right in the test tank merged into one image in FIG. 7B. Similarly, the trajectory of the ReefGlider™ as it moves from right to left as it returns to the starting orientation (with a different “world” location in test tank TT) is shown in FIG. 7C. This demonstrates the robot's ability to change directions with zero turning radius. While it is non-holonomic and still requires sawtooth patterns, they can be performed faster, allowing the vehicle to visit and station-keep near more complex benthic features or dynamic regions.

Yaw Experiment: Yaw motion can be achieved by a series of pitch-roll-pitch maneuvers. In theory, the robot can set its yaw to any arbitrary direction in one maneuver. However, this requires pitching by 90 degrees, which can induce singularities in the control. Instead, ReefGlider™ uses a series of smaller yaw maneuvers to get to the target yaw state. The robot can achieve this yaw maneuver with minimal lateral or depth motion. This can be seen from the external AprilTag data in FIG. 8A and from the on-board sensor data in FIG. 8B. FIG. 8A depicts Yaw experiment ground-truth: pose (orientation) data for Roll, Pitch and Yaw of the yaw demonstration gathered by an upward-facing GoPro in the bottom of the test tank recording an AprilTag attached to the bottom of the ReefGlider™. Yaw is plotted in the bottom right by angle (in degrees) over time. FIG. 8B illustrates Yaw experiment sensor feedback: roll sensor date 802, pitch sensor data 812, depth sensor data 822, and yaw sensor data 832 with their corresponding set points 804, 814 and 824 for roll, pitch and depth, respectively. Note that the difference in sign from FIG. 8A is due to the difference in reference frame between the IMU and the AprilTag.

In general, the above experiments demonstrate that the ReefGlider™ is capable of sub-meter scale motions (i.e., less than 100 cm maneuvering) in 3D (three dimensions), in both the positive and negative directions along each x-y-z axis, which is not possible in traditional gliders. These experiments also demonstrate zero-radius turning. However, comparing FIG. 6A and FIG. 7A, we see that the vehicle is still not symmetric in terms of motion performance, as the hydrodynamic drag in the y-direction (or roll direction) of motion is more significant than the x-direction (or pitch), which is also more streamlined due to the orientation of the cylinders.

The settling times of the PID controllers in all experiments could be improved by more accurate modelling of the nonlinear dynamics, further controller tuning, or potentially shifting to cascading or rate-based architectures. These and other improvements and alternatives mentioned herein will be readily apparent to those of ordinary skill in designing propulsion and navigation systems for autonomous underwater vehicles after reviewing the present disclosure.

Additionally, the current robot has an estimated maximum depth of 12 meters based on hydrostatic pressure and the maximum dynamic load of the actuators. In terms of physical components, we could improve the physical layout of the device by selecting a more symmetric (potentially radially) passive component and the orientation of the buoyancy engines such as shown in FIGS. 9A-9B below. Also, improvements may be achieved by finding the optimal initial internal pressure of the buoyancy engines or by considering different linear actuators that can increase the maximum operating depth. Alternatively, use of internal-external oil bladders provides a great increase in operating depth as compared to gas-based buoyancy systems.

Finally, the ReefGlider™ can accommodate a wide range of sensor payloads, such as CTD probes, cameras, and hydrophones. While certain payloads, such as water samplers, may cause large changes in hydrodynamics (that is, fluid dynamic changes due to changes in size, shape or orientation of vehicle surfaces contacting water), buoyancy, and mass, most can be countered by including additional passive flotation or weight, to be neutrally buoyant. However, two considerations are the (1) relative location of the center of mass and buoyancy on the payload (and hence the shift they cause to the ReefGlider™) and (2) impact of geometry of the payload on the overall hydrodynamics (mostly drag) unless covered in a shell such as described below in relation to FIGS. 10A-10B. One would need to verify that the ReefGlider™ has sufficient controllable buoyancy to counteract these modified parameters. Alternatively, the ReefGlider™ VBC system can be used as a payload itself on other AUVs to provide buoyancy control, enhance maneuverability and station-keeping, and enable low-noise and lower-energy operation modes.

Alternative geometries of base plates: FIGS. 9A and 9B are schematic top views of radially- and/or axially-positioned buoyancy engines according to the present invention on triangular and elliptical base plates. Buoyancy engine system 910, FIG. 9A, includes buoyancy engines 912, 914 and 916 that are oriented along radial axes extending from the geometric center 930 of triangular passive component 920 to each of the three outer points of component 920. In some constructions, point 930 will also be the COM and, depending on the actuations of the buoyancy engines, may also be the COB at one set of settings for the engines. Other polygonal shapes can be utilized for base plates and other passive components such as a rhombus or hexagon.

Similarly, buoyancy engine system 910b, FIG. 9B, includes buoyancy engines 912b, 914b, 916b and 918b that are oriented along longitudinal and lateral axes passing through the geometric center 930b of elliptical passive component 920b to the two maximum and two minimum outer points of component 920b. In other words, engines 912b and 916b are aligned along the lateral axis and engines 918b and 914b are aligned along the longitudinal axis of curved passive component 920b. Engines 918b and 914b are perpendicular to engines 912b and 916b in this construction.

Alternative coverings and vanes: FIGS. 10A and 10B are schematic side partial cross-sectional views of buoyancy engines within different configurations of hydrodynamic hulls or shells. Vehicle 1010 includes buoyancy engine 1012 within hull 1014 which has an upper portion 1016 that is symmetrically convex in cross-section with lower portion 1018. By comparison, vehicle 1030 includes buoyancy engine 1032 within hull 1034 which has an upper portion 1036 that is convex in cross-section as compared to substantially flat (planar) lower portion 1018.

A schematic bottom view of a hull 1034c, FIG. 10C, is similar to hull 1034 of FIG. 10B with lower portion 1034c being elliptical as well as planar. Additionally, four optional movable vanes 1060, 1062, 1064 and 1066 are movable as indicated by arrows 1061, 1063, 1065 and 1067, respectively as commanded by a controller. In other constructions, fixed vanes or wings are added to alter hydrodynamic performance of vehicles according to the present invention while obviating the need for thrusters, rudders or other movable hydrodynamic elements that alter the fluid dynamics of the vehicle.

Although specific features of the present invention are shown in some drawings and not in others, this is for convenience only, as each feature may be combined with any or all of the other features in accordance with the invention. While there have been shown, described, and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, it is expressly intended that all combinations of those elements and/or steps that perform substantially the same function, in substantially the same way, to achieve the same results be within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. The terms “steps”, “methods”, “techniques” and “functions” may be used interchangeably herein. It is also to be understood that the drawings are not necessarily drawn to scale, but that they are merely conceptual in nature.

It is to be understood that the foregoing embodiments are provided as illustrative only, and do not limit or define the scope of the invention. Various other embodiments, including but not limited to the following, are also within the scope of the claims. For example, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions. Any of the functions disclosed herein may be implemented using means for performing those functions. Such means include, but are not limited to, any of the components disclosed herein, such as the computer-related components described below.

The techniques described above may be implemented, for example, in hardware, one or more computer programs tangibly stored on one or more computer-readable media, firmware, or any combination thereof. The techniques described above may be implemented in one or more computer programs executing on, or executable by, a programmable computer including any combination of any number of the following: a processor, a storage medium readable and/or writable by the processor (including, for example, volatile and non-volatile memory and/or storage elements), an input device, and an output device. The input device and/or the output device form a user interface, also referred to herein as a human-machine interface, in some embodiments. Program code may be applied to input entered using the input device to perform the functions described and to generate output using the output device.

Embodiments of the present invention include features which are only possible and/or feasible to implement with the use of one or more computers, computer processors, and/or other elements of a computer system. Such features are either impossible or impractical to implement mentally and/or manually. For example, embodiments of the present invention automatically and repeatedly sample depth and orientation data and compare it with target depth and orientation data, automatically update data in an electronic memory representing such amounts of depth and orientation data, and can automatically and wirelessly transmit such data to a server or other computer over a digital electronic network for storage and processing. Such features can only be performed by computers and other machines and cannot be performed manually or mentally by humans.

Any claims herein which affirmatively require a computer, a processor, a controller, a memory, or similar computer-related elements, are intended to require such elements, and should not be interpreted as if such elements are not present in or required by such claims. Such claims are not intended, and should not be interpreted, to cover methods and/or systems which lack the recited computer-related elements. For example, any method claim herein which recites that the claimed method is performed by a computer, a processor, a controller, a memory, and/or similar computer-related element, is intended to, and should only be interpreted to, encompass methods which are performed by the recited computer-related element(s). Such a method claim should not be interpreted, for example, to encompass a method that is performed mentally or by hand (e.g., using pencil and paper). Similarly, any product claim herein which recites that the claimed product includes a computer, a processor, a memory, and/or similar computer-related element, is intended to, and should only be interpreted to, encompass products which include the recited computer-related element(s). Such a product claim should not be interpreted, for example, to encompass a product that does not include the recited computer-related element(s).

Each computer program within the scope of the claims below may be implemented in any programming language, such as assembly language, machine language, a high-level procedural programming language, or an object-oriented programming language. The programming language may, for example, be a compiled or interpreted programming language.

Each such computer program may be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a computer processor. Method steps of the invention may be performed by one or more computer processors executing a program tangibly embodied on a computer-readable medium to perform functions of the invention by operating on input and generating output. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, the processor receives (reads) instructions and data from a memory (such as a read-only memory and/or a random access memory) and writes (stores) instructions and data to the memory. Storage devices suitable for tangibly embodying computer program instructions and data include, for example, all forms of non-volatile memory, such as semiconductor memory devices, including EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROMs. Any of the foregoing may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits) or FPGAs (Field-Programmable Gate Arrays).

A computer can generally also receive (read) programs and data from, and write (store) programs and data to, a non-transitory computer-readable storage medium such as an internal disk (not shown) or a removable disk or flash memory. These elements will also be found in a conventional desktop or workstation computer as well as other computers suitable for executing computer programs implementing the methods described herein, which may be used in conjunction with any digital print engine or marking engine, display monitor, or other raster output device capable of producing color or gray scale pixels on paper, film, display screen, or other output medium or other type of user interface. Any data disclosed herein may be implemented, for example, in one or more data structures tangibly stored on a non-transitory computer-readable medium. Embodiments of the invention may store such data in such data structure(s) and read such data from such data structure(s).

It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. Other embodiments will occur to those skilled in the art after reviewing the present disclosure and are within the following claims.

Every issued patent, pending patent application, publication, journal article, book or any other reference cited herein is each incorporated by reference in their entirety.