The present invention relates to the field of underwater vehicles, including, more particularly, to underwater robots.
To access complex underwater structures robots must be tetherless, compact, highly maneuverable, and have a smooth body shape with minimal appendages. These requirements are challenging because few propulsive systems can be designed to fit into a smooth, streamlined body. A moment referred to as the “Munk moment” is destabilizing for elongated bodies. For example, the moment tends to rotate them broadside to the flow.
Thus, there is a need to provide improved robotic systems and techniques.
A new 5 degree of freedom (DOF) underwater robot is provided. This robot is propelled using a novel pump-valve system and is therefore able to achieve a smooth, symmetric outside shape. The yaw direction of the robot is stabilized using feedback control. The pitch direction is designed to be passively stable by placing the center of mass below the geometric center. The vehicle therefore does not need external stabilizers and can have a smooth outer shape. Due to its symmetry and unique design, the robot is capable of unique motions and maneuvers such as turning in place, sideways translation, and forward-stop-reverse motions. In addition, due to the propulsion system being completely internal, this robot is very quiet and creates relatively small disruptions to the surrounding fluid.
In a specific embodiment, an underwater robot includes a body including a first end, and a second end, opposite the first end, and first and second actuation units positioned inside the body, each actuation unit a pump and two valves coupled to the pump. The first and second actuation units generate jets of fluid that are discharged through the first and second ends to propel the underwater robot, and the first and second ends are smooth.
In another specific embodiment, an underwater robot includes a body having a shape of a spheroid and including a first end, and a second end, opposite the first end, a first actuation unit to propel the underwater robot, the first actuation unit being positioned inside the body and including a first pump having a first outlet, and a second outlet, a first valve coupled to the first outlet of the first pump, and a second valve coupled to the second outlet of the first pump; and, a second actuation unit to propel the underwater robot, the second actuation unit being positioned inside the body and including a second pump having a third outlet, and a fourth outlet, a third valve coupled to the third outlet of the second pump, and a fourth valve coupled to the fourth outlet of the second pump. An angle between the first and second outlets of the first pump is 90 degrees, and an angle between the third and fourth outlets of the second pump is 90 degrees.
In a specific implementation, a method includes placing a robot in water, where the robot includes first and second actuation units to propel the robot through the water, each actuation unit including a pump having two outlets 90 degrees apart, and a valve coupled to each of the two outlets of the pump, maneuvering the robot via at least one of the first or second actuation units in a surge motion, maneuvering the robot via at least one of the first or second actuation units in a sway motion, maneuvering the robot via at least one of the first or second actuation units in a heave motion, maneuvering the robot via at least one of the first or second actuation units in a pitch motion, and maneuvering the robot via at least one of the first or second actuation units in a yaw motion.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
An underwater vehicle propulsion system is provided that allows a smooth, symmetric underwater robot to move with 5 degrees of freedom (DOF). Maneuvering forces and moments are provided by using internal pumps and valves to eject fluid jets through various exit ports. The degrees of freedom include surge, sway, heave, pitch, and yaw. In a specific embodiment, the vehicle is entirely symmetric and has no external appendages such as propellers or fins. The use of an internal propulsion system allows the robot to operate very quietly and create few disruptions to the surrounding fluid. These robots can be used for a variety of applications ranging from the inspection of water-filled piping structures, to exploration of underwater infrastructure and wildlife, just to name a few examples. In a specific embodiment, the robot is completely or substantially smooth yet capable of stable motions in 5 translations or rotations.
In a specific embodiment, a smooth spheroidal robot is capable of 5 degrees of freedom and has no external appendages such as propellers or fins. In this specific embodiment, the smooth outer shape and 5 degrees of freedom are achieved through the use of a pump-valve architecture based on retrofitted centrifugal pumps and fluidic valves. Angled jets are provided which enable translations in surge, sway, and allows the system to be stabilized through feedback control.
Developing these types of smooth, spheroidal vehicles is a challenging task due to the fundamental fluid mechanics. Smooth, streamlined robots are subjected to directional instability caused by the Munk Moment. For this reason, streamlined underwater vehicles often use fins at their rear to move their aerodynamic center backwards and therefore make them passively stable. However, the fins can add extra size making the robot less compact. Second, at large angles of attack, fins can add substantial induced drag that can inhibit the turning robot of the vehicle. Finally, while fins in the rear of the vehicle will stabilize the vehicle in one direction they will further destabilize the vehicle when the direction is reversed. Therefore a robot with fins will be required to turn around 180 degrees rather than simply being able to move in reverse. This limits the maneuverability and omni-directional properties of the robot. This phenomenon is illustrated with a diagram in
The current development presented here introduces a combination of a novel design and closed loop control that overcomes the issue of instability and addresses the shortcomings of previous systems. In a specific embodiment, a jet arrangement is provided that enables the planar robot dynamics to be fully controllable. Linear control system design techniques are used to develop a closed loop controller capable of stabilizing the robot.
To prove operability, a prototype of a robot was fully built, tested, and verified to operate as intended.
There are a set of openings 221 on the body. The openings allow for the intake of a fluid, such as water, and the output of the fluid as jets which propel the robot through the fluid. More particularly, as shown in
This example of the robot includes eight ejection openings and one intake opening. The number of openings, however, can vary depending on the factors such as the application of the robot, number of pumps, number of valves, desired movements (e.g., degrees of freedom), and so forth. For example, there can be fewer or more than eight ejection openings. There can be more than one intake opening. In a specific implementation, there are at least eight ejection openings.
Actuation units can be positioned inside the body that suck in the fluid and eject the fluid as jets through the openings. For example, depending on the type of motion desired fluid may be outputted through the first end, second end, or both. Further discussion of the actuation units is provided below.
The body can further house other components of the robot such as one or more cameras (e.g., two cameras), controller, RF transmitter, RF receiver, antenna (e.g., for wireless operation), power source (e.g., battery), motor, switch, storage device (e.g., hard drive or flash memory for recording images), sensors (e.g., temperature sensor, or depth sensor), lights (e.g., light emitting diodes (LEDs)), measuring instruments, collection instruments, and the like. The body can be designed to be watertight and may include seals, o-rings, gaskets, and the like.
In a specific embodiment, the body is made of plastic. Portions or sections of the body may include a transparent material so that a camera inside the body can capture images. For example, in a specific embodiment, the intermediate section includes a transparent material (e.g., transparent piece of plastic) for capturing images via the camera. Some examples of materials that the body may be fabricated or made from include polymers, nylon, rubber, carbon fiber, metal (e.g., steel, stainless steel, or titanium), glass, or combinations of these.
In a specific embodiment, the length of the robot is about 146 millimeters and a width of the robot is about 108 millimeters. The small size of the robot allows the robot to navigate through tight spaces. The dimensions of the robot, however, can vary greatly depending upon its application. For example, the length of the robot may be greater or less than 146 millimeters. The width of the robot may be greater or less than 108 millimeters.
As shown in
The symmetry of the robot shape facilitates movement of the robot through the various directions or degrees of freedom. For example, having the shape of the first end being the same as the shape of the second end facilitates the robot's movement in a first direction (e.g., forward direction) and a second direction (e.g., reverse direction), opposite the first direction.
In this specific embodiment, the robot does not include an external propeller, fins, foils, stabilizing attachments, or other appendages that may break off or snag on obstacles. For example, an exterior surface of the robot may be smooth or substantially smooth, continuous, or uninterrupted by an appendage.
The smooth, spheroidal robot shown in
In other words, the surge motion may be unaccompanied or substantially unaccompanied by the sway, heave, pitch, and yaw motions. The sway motion may be unaccompanied or substantially unaccompanied by the surge, heave, pitch, and yaw motions. The heave motion may be unaccompanied or substantially unaccompanied by the surge, sway, pitch, and yaw motions. The pitch motion may be unaccompanied or substantially unaccompanied by the surge, sway, heave, and yaw motions. The yaw motion may be unaccompanied or substantially unaccompanied by the surge, sway, heave, and pitch motions.
In a specific embodiment, an actuation unit includes a centrifugal pump for the propulsive component. Centrifugal pumps are advantageous because of their mechanical simplicity, availability at centimeter (cm) size scales, and the ease of use with electronic circuitry. However, one common issue with some centrifugal pumps is that they are not reversible. This means that the pump can only provide force in one direction and will need to be combined with a second one in order to achieve bi-directional forces. Ideally, the pump could be designed to provide forces in 2 directions 180 degrees apart. This would save substantial space and weight. An example of this geometry is provided in
Applicants have discovered that by orienting the two exit ports adjacent to each other but 90 degrees apart, problems with backflow can be eliminated or reduced. This outlet design may be referred to a “90 degree retrofit.”
In this specific embodiment, an angle 530 between the first exit and the second exit is about 90 degrees. That is, the angle is a right angle. In the example shown in
Computational Fluid Dynamic (CFD) illustrations of the 90 degree retrofit are provided in
More particularly, in a specific embodiment, the unique capabilities of the robot are enabled by three components: retrofitted centrifugal pumps, use of fluidic valves to achieve bidirectional in-line forces, and the use of angled jets to achieve multi axis forces. Each of these three components will be discussed in greater detail below.
In a specific embodiment, fluidic valves that achieve bidirectional forces are provided. While the centrifugal pumps combined with the 90 degree retrofit provide substantial forces in 2 directions, the 2 directions are 90 degrees apart rather than the desired 180. This fact complicates vehicle design. One approach is to use elbows to redirect the flow. Elbows, however, can cause substantial losses. Thus, in this specific embodiment, custom designed Coanda effect valves are provided. These valves are based on bistable fluidic amplifiers that allow switching the direction of a jet 180 degrees at high speeds.
In a specific embodiment, Applicants have designed these valves for the specific application of water jet propulsion. Computational fluid dynamics (CFD) and experiments have allowed for miniaturizing the design. In this specific embodiment, a special switching mechanism has been designed that uses a small direct current (DC) motor. The small DC motor is used to open and close the control ports, and requires simple commercially available electronics for control.
One of these valves can be attached to each of the two exit ports on the retrofitted pumps. This means that now a single pump can be engineered to provide an output jet in one of two pairs of directions or 4 directions total. This full manifestation may be referred to as a 2DOF actuation unit. These units can serve as the building blocks for robots, as they can be combined and rotated in order to meet the user requirements.
As shown in the example of
A specific embodiment provides for a 5 DOF underwater vehicle design using pump-valve architecture and angled jets. In this specific embodiment, this robot design incorporates two of the actuation units. An illustration of the layout is provided in
For example, Jet 1 is directed through a first channel 930. The ends of the channel are angled 933A and 933B. In a specific implementation, the angle is about 30 degrees from the x-axis. The angle may range from about 15 degrees to about 45 degrees. Similarly, Jet 2 is directed through a second channel 940. The second channel may be similarly angled as the first channel. The angle of the channels allows Jets 1 and 2 to be angled at their outputs as shown by arrows 950A-B. Arrows 950A-B show the direction of the fluid jets from the robot. The angled direction of the fluid jets help to stabilize and control the movement of the robot.
During operation of the robot, the actuation units (e.g., pumps and valves) can be activated and deactivated to achieve the desired movement. In a specific implementation, Pump 1 generates one of Jet 2 or Jet 4. Pump 2 generates one of Jet 1 or Jet 3. The opening and closing of the valve control ports associated with a pump can be rapidly pulsed to achieve the desired movement.
Table A below provides a summary of maneuvering primatives for how each of these DOFs can be achieved.
To achieve translations in the y direction, jets 1 and 2 are angled and then the high speed nature of the Coanda effect valve is used. By switching Jet 1 between positive and negative in a fast but symmetric manner, pure translation in the +y direction can be achieved because the x translations cancel out. This high speed switching is enabled by the use of the Coanda effect valve which has a response time that is much faster than the response time of the vehicle. Slower valves would cause the vehicle to wobble or oscillate. The use of the angled jets is one of the very unique features of this robot design.
Due to the Munk moment effect described in the background above, the yaw and pitch directions of the robot are unstable. Traditionally, these directions are stabilized using fins placed in the rear of the vehicle.
In a specific embodiment, stabilizing yaw is achieved without the use of external fins. In this specific embodiment, the use of external fins is avoided by using a combination of novel design and feedback control. Nonlinear and linearized models for these dynamics are provided in Appendix B. One thing to immediately note from the state space model is the coupling between the sway velocity “v” and the yaw angle “φ.” This unusual coupling is a result of the sideslip angle. Note that if the jets were not angled to produce forces along the “y” direction, the system would be theoretically uncontrollable.
Stabilizing the pitch direction is achieved by placing the center of mass below the geometric center of the robot. Errors in the pitch direction will be eventually balanced by gravitational forces and will therefore not grow unbounded. This solution allows the maintenance of the smooth external shape.
As discussed above, the full design has been realized and tested.
Some advantages of the robot include an outer surface that is entirely or substantially smooth, being capable of 5 degrees of freedom, and a 90 degree pump or a retrofitted pump to achieve large forces in 2 directions using a centrifugal pump. A specific embodiment of the robot is a robot that uses an entirely or substantially smooth shape without external propellers or fins. Other advantages of the robot include water jets manipulated by valves instead of servo motors, a lack of external stabilizes, more than 3 outlet directions for jets that provide the ability to translate in the sway direction, discrete jets for steering rather than vectored thrust, two pumps, angled jets, pumps with 90 degree outlets (which provide an increase in performance over pumps with 180 degree outlets), and others.
There many commercial applications for a robot as described in this patent application. One application includes the inspection of large water filled piping systems such as those inside nuclear power plants. The robot can be equipped to carry cameras that can take pictures and video of various inaccessible areas. In addition, water transport and sewage systems also require inspection and could make use of this robot or aspects of the robot for some of their larger piping systems. Further, this robot is very quiet and highly maneuverable. Therefore it could be relevant for underwater surveillance or other naval applications.
As discussed above, a prototype of the robot has been fully built and tested. Appendix A includes some photos of a prototype. FIG. A1 shows a top view of the robot. FIG. A2 shows an end view. FIG. A3 shows a top view. FIG. A4 shows a bottom view. FIG. A5 shows a front or first end view. FIG. A6 shows a back or second end view. FIG. A7 shows a perspective view of a valve. This view shows an intake port of the valve. Also shown is a winged flapper piece (shown in black) that pivots back and forth to control the opening and closing of the valve control ports. FIG. A8 shows a top view of the valve. A coin has been included in the photograph to show the relative size of the valve. FIG. A9 shows an example of an actuation unit. The actuation unit includes a pump and two valves attached to the pump. FIG. A10 shows a diagram of the inside of the robot. Various components of the robot are shown in color for clarity. FIGS. A11-A12 show diagrams illustrating the direction of the jets. A coordinate system has been shown for orientation. As discussed above, Jets 1 and 2 are angled at their outputs (FIG. A11).
FIG. A12 shows a photograph of the inside of the robot prototype. FIGS. A14-A15 show the robot having been placed in a body of liquid (e.g., water). A movement trace has been superimposed on the photos to show the movement of the robot through the water. FIGS. A16-A17 shows a photo of forward and backward trajectory and an accompanying time graph. FIGS. A18-A19 shows another photo of movement accompanying time graph. FIGS. A20-A21 shows another photo of movement accompanying time graph. FIGS. A22-A23 shows another photo of movement accompanying time graph.
In a specific implementation, a submersible mini-robot is provided that targets inspection of nuclear reactor internals and other critical components. The robot is designed to function wirelessly and without tethers, and has the ability to move in all directions to access difficult locations. Remote-operated vehicles developed for marine applications have proven successful for the visual inspection of submerged components in nuclear reactor vessels and spent fuel pools, but commercially available technologies have several limitations. The robot, as provided in this patent application represents a step-change improvement in the nuclear power industry's underwater inspection capabilities.
The robot is designed to allow safe, reliable, and non-intrusive operation while providing high-fidelity visual inspection across a broad range of components, configurations, and locations. A prototype robot has been built and tested. This robot features a compact and appendage-free design, a high degree of maneuverability, and wireless operation. In this specific embodiment, its ovoid form measures about 4 inches by 6 inches, allowing it to nestle comfortably in the palm of a hand. Its innovative propulsion and navigation system applies centrifugal pumps, high-speed valves, and maneuvering jets for precisely controlled motion.
The robot's shape and umbilical-free operation allow for successful in-plant applications. Many existing technologies employ propellers, rudders, and other appendages and attachments that limit access to some component locations and preclude certain types of motion. These appendages also may break off during collisions or snag on obstacles, creating the potential for contamination of carefully controlled reactor environments or other operational issues. The robot as provided in this patent application has demonstrated the ability to navigate through intricate and tight geometries and to conduct inspection-type passes over surfaces.
For example, under joystick control, it can dive and rise, turn in place, and move forward, backward, and sideways. The robot is capable of carrying cameras and includes a wireless communications system. In a specific embodiment, the payload includes two cameras. The first camera supports real-time navigation and visual examination by the robot operator, and the second camera captures higher-resolution imaging data for subsequent inspection, nondestructive evaluation, and asset management applications.
Improving wireless communications for submersed usage poses challenges. Water attenuates most frequencies, and systems and components pose complex configurations. Features of the robot combine optical communication capable of high data rates at a distance with radio communication capable of two-way data exchange when line of sight is lost between the mini-robot and its controller.
In the description above and throughout, numerous specific details are set forth in order to provide a thorough understanding of an embodiment of this disclosure. It will be evident, however, to one of ordinary skill in the art, that an embodiment may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to facilitate explanation. The description of the preferred embodiments is not intended to limit the scope of the claims appended hereto. Further, in the methods disclosed herein, various steps are disclosed illustrating some of the functions of an embodiment. These steps are merely examples, and are not meant to be limiting in any way. Other steps and functions may be contemplated without departing from this disclosure or the scope of an embodiment.
This patent application claims priority to U.S. provisional patent applications 61/642,007, filed May 3, 2012, and 61/714,290, filed Oct. 16, 2012, which are all incorporated by reference along with all other references cited in this application.
Number | Date | Country | |
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61642007 | May 2012 | US | |
61714290 | Oct 2012 | US |