Deformable Aquatic Vehicle

This patent application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent App. No. 63/634,212, filed Apr. 15, 2024, entitled “DEFORMABLE IMPELLER POWERED AQUATIC VEHICLE,” incorporated herein by reference in entirety.

This Invention was made with Government support under contract Nos. CMMI-1752195 and DGE-1922761, awarded by the National Science Foundation (NSF). The Government has certain rights in the Invention.

Robotics are continually becoming more integrated into manual tasks previously performed by human actions such as grasping and holding objects. Robotic elements are typically constructed of rigid materials to provide sufficient strength and structural integrity. Robotic actuation often involves rigid movable, driven members and corresponding axial, pivoting or articulated joints having sufficient mass to withstand the actuated forces.

A submersible, aquatic robot employs a deformable, tubular tail operable as a wave spring for directing movement through impelled fluid and controlled vectors based on directional orientation of the deformable tail. A central impeller in a toroidal housing forms a continuous fluid channel through the housing and tubular tail, while a series of tethers draws on opposed sides of the deformable tail for directing movement to one side or the other. The directed, tubular tail channels water for propulsion based on a vector defined by the directional tail. Wireless control of a fleet of aquatic robots can achieve widespread sensory deployment for related tasks.

Configurations herein are based, in part, on the observation that robotic actuation is beneficial for performing tasks that are repetitive, voluminous and dangerous or unhabitable by human actors. Unfortunately, conventional approaches to robotics suffer from the shortcoming that they entail mechanized joints and actuators that are often rigid and dense, requiring substantial power for actuation. Waterborne tasks therefore encounter problems with buoyancy, and an associated need for water propulsion. Further, most electronic and mechanical fixtures are not amendable to water exposures, and salt water in particular, which can short circuit electronics and induce oxidation and corrosion.

Accordingly, configurations herein substantially overcome the shortcomings of conventional waterborne robotic approaches by providing a low-cost, deformable impeller powered robot with a small mass and minimal propulsion needs for mitigating energy drain. A small size and deformable tubular wave-spring tail is actuated by tensioning on one side of the tubular tail to unevenly compress the tubular shape and direct impelled water for forming a transport vector for propulsion. Actuated control of multiple tethers attached to the distal circumference of the tubular tail allows vector propulsion based on wireless control. A plurality of deformable aquatic robots deployed over an area facilitates sensory gathering or other tasks at various waterborne depths.

In further detail, an aquatic robotic device includes a housing configured for submersion, and a void through the housing, such that the void defines a channel through the housing for fluid flow. A deformable tail is perimetrically attached to a distal end of the housing and forming a continuous fluid volume with the channel, and a pair of tethers attached to the tail are configured for deforming the tail via actuated tensioning for directing the water flow for robotic propulsion.

Depicted below are example configurations of aquatic robot vehicle having a deformable tail defined by a wave spring structure under controlled deformation without hinged or articulated joints. The wave spring has a spring or helical appearance, formed from flexible, deformable materials printable via any suitable form of extrusion or deposition, often referred to as 3-dimensional printing or additive manufacturing.

One beneficial implementation of the disclosed device is research and investigation of environmental conditions related to climate change across the vastness of the world's oceans. These oceanographic conditions create microclimates, a small scale marine climate unaffected by greater overlying climate conditions. These microclimates can vary based on geographical position or even location in the water column. It is imperative to understand how climate change is affecting marine animal populations on this scale in order for climate scientists to better understand and protect them. Widely used methods of data collection, such as static sensors on buoys or weights, lack the resolution required for a nuanced understanding of the impacts of temperature variation on marine species. Current climate associations are analyzed at a temperature resolution of kilometers or more, while most organisms experience climate at scales of millimeters to meters.

The aquatic robot device is an effective tool to solve this challenge. They are mobile, capable of moving throughout the entire water column, and can host a variety of sensors to collect data and observe the surrounding environment. There has already been a shift in physical oceanography towards robotic and remote sensing due to the labor intensive and limited data of ship-based sensing.

The robotic device is operated by an impeller that pulls water through the center of the robot and the deformable wave spring tail. The wave spring can bend, directing the outflow of water, and thereby turning the robot. The robot includes three main parts: an impeller, servo motor and electronics housing, and the wave spring defining the flexible, deformable tail (tail).

Soft robotic implementations, such as the deformable tail, in particular offer a unique opportunity to closely interact with waterborne environments. The compliant body can adapt to changes in the environment and deform and absorb energy during a collision. This protects sensitive biological features the robot could come into contact with coral or other fish. While this approach is much more biologically accurate and safe, it can be difficult to manufacture and challenging to control and model. It presents challenges, as discussed below, to operate these devices remotely over long periods of time or distance.

is a side schematic view of an aquatic robot as disclosed herein. Referring to, the aquatic robotic deviceas defined herein includes a housingconfigured for submersion in a fluid, such as water. A voidin the housing defines a channelthrough the housing for fluid flow. The channelcontinues through the deformable tail, such that the tailis perimetrically attached to a distal endof the housing and forms a continuous fluid volumewith the channel. A pair of tethers-. . .-(generally) attach to the tail and are configured for deforming the tailvia actuated tensioning. The generally cylindrical or tubular shape of the tailforms an openingat a distal end of the tail, the housing and the attached tail forming a continuous, enclosed fluid pathwaythrough the housing and tail.

The devicefurther includes an actuatorand a pulleyconnected to the tethers, such that the actuatoris configured for alternately tensioning the tethersfor drawing at least a portion of the tail towards the housing. An impellerin the housingprojects the fluid flow along the pathwaythrough the channeland through the continuous fluid volumefor exiting at the distal endof the tail. The housingforms a toroidal body around the impeller, such that the toroidal body is engaged with the impellerthrough a motoror other source for controlling propulsion. Based on the direction of the opening, discussed further below, the water passing through the fluid flow and deformable taildefine a propulsion vector for disposing the devicearound the aquatic environment. A plurality of tethersapplied with different tension unevenly tension the tailand cause it to point in the direction of greatest tension, such that the tensioning directs the distal end of the tail for forming the propulsion vector.

is a side elevation of a partial view of the aquatic robot in. Referring to, in the example configuration, the taildefines a tubular shape, generally circular or oval, attached to a circumferenceof the housing at a proximal endof the tail, and forming the openingat a distal end, wherein the plurality of tethersform a pair of tethers-. . .-to opposed circumferential attachments-. . .-, respectively, on the tail (generally).

On the housing, a plurality of elongated, curved directional members-. . .-(generally) extend from the housingopposed from the tail, defining the foremost (front) region in the direction of forward travel. The elongated curved directional membersmeet at a forward junction, such that the forward junction is configured to engage an impacted surface or object prior to a front housing facefor deflection thereof. A generally flat or blunt leading surface such as the housing could become engaged or “stuck” by approaching a flat surface at a normal angle, whereby the directional membersand junctiontend to deflect the devicefrom impacted surfaces.

is a completed view of the aquatic robot of. Referring to, the deformable tailincludes a plurality of shaped ribssupporting a flexible planar materialwrapped around the ribsto form an enclosure, such that the shaped ribsform a circumference defining the continuous fluid volume. The flexible planar materialextends around an outer surface of the shaped ribsand forms the rearward openingat the distal endof the tail.

In the example configuration, the tailis a single cylindrical flexible wave spring fabricated by fused deposition modeling (FDM) using Ultimaker Thermoplastic Polyurethane (TPU) with a shore hardness of 95 A. The tailstructure is a mesh of diamond-shaped cells formed by two mirrored helices formed from the ribs. The wave spring can bend, stretch, compress, and is completely hollow. Water can pass through the center of the cylinder shape as well as the diamond-shaped cells. The wave spring is a versatile tool in underwater locomotion.

Since the wave spring is directing the outflow of water that is impelled through the robot, the hollow cells needed to be covered so water only exits the wave spring at the distal opening. This was accomplished by the addition of a latex skin forming the flexible planar materialthat was wrapped around the outside of the wave spring. The latex seals the wave spring while not impairing an ability to bend.

are top views of wave spring tail actuation in the aquatic robot of. Referring to, the devicemaneuvers from water propelled or impelled through the housing void, and passing through the tail, where the tensioned tethers contract to bend or compress the tail towards the shortest tether distance to “steer” the flow of water according to a direction vector (vector). The tetherspull one side of the tailat the attachment, which responds by deforming and curving in the direction of the shortening tether.

The actuatormay further comprise a servoattached to the housingfor alternately tensioning the tethersfor individually tensioning a respective tether, which directs the tailin a direction defined by the tension. The servoactuates a semicircular pulleyhaving opposed sides-. . .-(generally), where the tethersattach to each respective opposed side, and the semicircular pullyis configured for semicircular rotation for tensioning one of the respective tethers.

In the example configuration, the proximal endof the wave spring tailis fixed to the housingof the robot and the other end is connected internally by polyethylene non-elastic braided cables to a 20 kg-cm, 0.080 s per 60°-rated servo motor. The tethersare wound around a 4 mm diameter pulleythat is affixed to the servo motor. As the motor rotates from 90° to 0°, the wave spring bends left, and as the motor rotates from 90° to 180°, the wave spring bends right.

shows calculation of the bending angle of the wave spring tail, where curvature along the curveis constant, x and y are the coordinates at the tip of the wave spring tail, r is the radius of curvature of the curve, a is the angle between the x-axis and the hypotenuse of the right triangle generated by x and y, and q is the bending angle. Assuming constant curvature and the measured positions of the bent body, we calculated the bending angle of the wave spring tail:

where x and y are the coordinates of the center of the wave spring tip and a is the angle between the x-axis and the virtual line generated from the tip of the wave spring to the origin. a is shared by both triangles in, so using the law of cosines, we calculated the bending angle q (Eq. 1 and 2).

The servo motorthat bends the wave spring sits at the center of a toroidal-shaped container forming the housingfor the electronics that drive the robot. The torus shape is beneficial to the design of the robot as it provides a sealed compartment for electronics that cannot be exposed to water, while still allowing the flow of water to pass through the voidand tail.

Alternate configurations may include a pair of servos, each having respective tethers attached to each of the respective opposed sides, the servos rotating in horizontal and vertical planes offset by 90° for directing the deformable tail along two dimensions.

show alternate wave spring designs for the deformable tail′ and″, depicting a resemblance to a biological fish caudal peduncle, the tapered region of the fish where the body attaches to the tail fin, hence the reference to the “tail.” The tailis particularly suited to operate in a reef environment. Reef fish are morphologically diverse, but share a similar body shape. This body shape was emulated in the tail design that evolved to the wave spring as shown in. The wave spring was a tapered oval consisting of two mirrored helixes, which form a mesh of diamond-shaped cells. These diamond-shaped cells can compress easily, allowing the wave spring to extend or bend as desired. To ensure that the tailis only bent laterally, as well as ensure it maintained a fixed length, supports were added on the dorsal and ventral edges of the tail. These supports resist axial torsion, ensuring that the tip of the wave spring remained aligned with the base. This effectively mimics the true movement of a biological fish and reduced drag in the other directions.

In contrast, many conventional designs assemble separate rigid links that are attached on compliant joints. Not only does this increase the manufacturing complexity, but it also takes up unnecessary space and weight. The disclosed taildesign is made entirely from soft materials enabling lightweight, inexpensive manufacturing, continuous bending.

is a block diagram of a control environment suitable for use with the aquatic robot of. A larger number of the aquatic robot devicesmay be deployed over a predetermine area. A system and method for propelling and managing a fleet of waterborne robotic device, may include, for each robotic device, projecting fluid (water) through the housing, and attaching the deformable tailto the hosingfor forming a continuous fluid volume, the deformable tail having an openingdistal from the housing. By tensioning one or more of a plurality of tethersattached to the deformable tail, the deformable tailis responsive to the tensioning for directing the projected fluid through a channel defined by the housing, such that the deformable tailand the openingform a propulsion vector. It should be apparent that the housingis hermetically sealed from intrusion by water or other fluid into which the deviceis immersed.

Referring to, a communication diagramillustrates the control scheme used to operate the robotic devices. Two potentiometers installed in a control hosingare available to the user to change the speedand directionof the robot. Those commands are sent wirelessly via 915 MHz radio signals, and the impellerand flexible tailmove accordingly.

An example configuration employs an RFM9x Lora Radio module-. A transponder module is powered by an Arduino® Unoon land that sends signals to a receiver module-on the robot. All functions on the robot are controlled by an Ardunio Nano 518 on board, selected for its ease of use and small physical profile. The Arduino Nano controls the receiver module, servo motor, 30 A brushless electronic speed controller (ESC), and an INA219 Current Monitor used to collect power consumption data for cost of transport (COT) calculations. Each board, along with a 450 mAh lithium polymer battery, are stored inside the toroidal container housing. Once sealed, this container was positively buoyant, so a 160 g counterweight was added to achieve neutral buoyancy.

The servo motoractively moves the wave spring, placing it outside the electronics container and permanently exposing it to water. 3M 5200 flexible marine sealant was applied to all the seams along the body of the motor and a gasket with silicone grease was used to seal the servo horn. The pulleyrotated by the servo motor must also be centered to evenly bend the wave spring. Therefore, the dimensions of the servo motor and its spool dictated the minimum size of the container, resulting in a height of 0.1 m and a total body length of 0.246 m.

The devicewas designed for a small of a profile to enhance mobility in complex environments. The physical profile of the impeller, including a 600 kv motordesigned for underwater applications, is a cylinder 65 mm in diameter and 70 mm in length. This defined the cylindrical shape of the rest of the robot; both the electronics container and the wave spring were designed to be cylindrical with an inner diameter of 65 mm. The outer diameter of the electronics container in the housingneeded greater width, 100 mm in diameter, to account for the size of the battery and the electronic speed controller (ESC), the largest components that were stored.

One end of the impellerwas affixed to the electronics housingto pull water through the voidat the center of the robot. The impelleris connected to a 30 A Brushless ESC that is in turn connected to the Arduino Nano 518. The other end of the impeller forms the head of the robot. In initial testing, the robot's movement was impeded if the exposed end of the impeller came into contact with a flat surface, effectively adhering the robot to that surface. To mitigate this challenge, a teardrop-shaped nose formed from directional memberswas added to the exposed end of the impeller. This nose was a simple four-spoke design to provide a strong structure while remaining mostly hollow to not block water from entering the impeller.

During testing, it was found that when under power, the robot may tend to dive forward instead of swimming straight, even if the whole system was statically neutrally buoyant, possibly due to small assembly errors affecting the thrust vector. To counteract this effect, closed-cell foam may be added around the end of the impeller to increase buoyancy at the very end of the robot.

While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.