DEFORMABLE AQUATIC VEHICLE

Description

RELATED APPLICATIONS

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.

STATEMENT OF FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

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.

BACKGROUND

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.

SUMMARY

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.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a side schematic view of an aquatic robot as disclosed herein;

FIG. 2 is a side elevation of a partial view of the aquatic robot in FIG. 1;

FIG. 3 is a completed view of the aquatic robot of FIGS. 1 and 2;

FIGS. 4A and 4B are top views of wave spring tail actuation in the aquatic robot of FIGS. 1-3;

FIGS. 4C-4D show alternate wave spring designs for the deformable tail; and

FIG. 5 is a block diagram of a control environment suitable for use with the aquatic robot of FIGS. 1-4B.

DETAILED DESCRIPTION

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.

FIG. 1 is a side schematic view of an aquatic robot as disclosed herein. Referring to FIG. 1, the aquatic robotic device 100 as defined herein includes a housing 110 configured for submersion in a fluid, such as water 102. A void 112 in the housing defines a channel 114 through the housing for fluid flow. The channel 114 continues through the deformable tail 120, such that the tail 120 is perimetrically attached to a distal end 116 of the housing and forms a continuous fluid volume 122 with the channel 114. A pair of tethers 125-1 . . . 125-2 (125 generally) attach to the tail and are configured for deforming the tail 120 via actuated tensioning. The generally cylindrical or tubular shape of the tail 120 forms an opening 124 at a distal end of the tail, the housing and the attached tail forming a continuous, enclosed fluid pathway 115 through the housing and tail 120.

The device 100 further includes an actuator 130 and a pulley 132 connected to the tethers 125, such that the actuator 130 is configured for alternately tensioning the tethers 125 for drawing at least a portion of the tail towards the housing. An impeller 140 in the housing 110 projects the fluid flow along the pathway 115 through the channel 114 and through the continuous fluid volume 122 for exiting at the distal end 128 of the tail 120. The housing 110 forms a toroidal body around the impeller 140, such that the toroidal body is engaged with the impeller 140 through a motor 142 or other source for controlling propulsion. Based on the direction of the opening 124, discussed further below, the water passing through the fluid flow and deformable tail 120 define a propulsion vector for disposing the device 100 around the aquatic environment 102. A plurality of tethers 125 applied with different tension unevenly tension the tail 120 and 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.

FIG. 2 is a side elevation of a partial view of the aquatic robot in FIG. 1. Referring to FIGS. 1 and 2, in the example configuration, the tail 120 defines a tubular shape, generally circular or oval, attached to a circumference 150 of the housing at a proximal end 152 of the tail, and forming the opening 124 at a distal end 154, wherein the plurality of tethers 125 form a pair of tethers 125-1 . . . 125-2 to opposed circumferential attachments 126-1 . . . 126-2, respectively, on the tail (126 generally).

On the housing 110, a plurality of elongated, curved directional members 144-1 . . . 144-4 (144 generally) extend from the housing 120 opposed from the tail 120, defining the foremost (front) region in the direction of forward travel. The elongated curved directional members 144 meet at a forward junction 145, such that the forward junction is configured to engage an impacted surface or object prior to a front housing face 146 for 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 members 144 and junction 145 tend to deflect the device 100 from impacted surfaces.

FIG. 3 is a completed view of the aquatic robot of FIGS. 1 and 2. Referring to FIGS. 1-3, the deformable tail 120 includes a plurality of shaped ribs 121 supporting a flexible planar material 156 wrapped around the ribs 121 to form an enclosure, such that the shaped ribs 121 form a circumference defining the continuous fluid volume 122. The flexible planar material 156 extends around an outer surface of the shaped ribs 121 and forms the rearward opening 124 at the distal end 154 of the tail 120.

In the example configuration, the tail 120 is 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 tail 120 structure is a mesh of diamond-shaped cells formed by two mirrored helices formed from the ribs 121. 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 124. This was accomplished by the addition of a latex skin forming the flexible planar material 156 that was wrapped around the outside of the wave spring. The latex seals the wave spring while not impairing an ability to bend.

FIGS. 4A and 4B are top views of wave spring tail actuation in the aquatic robot of FIGS. 1-3. Referring to FIGS. 1-4B, the device 100 maneuvers from water propelled or impelled through the housing void 112, and passing through the tail 120, 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 tethers 125 pull one side of the tail 120 at the attachment 126, which responds by deforming and curving in the direction of the shortening tether 125.

The actuator 130 may further comprise a servo 430 attached to the housing 110 for alternately tensioning the tethers 125 for individually tensioning a respective tether, which directs the tail 120 in a direction defined by the tension. The servo 430 actuates a semicircular pulley 132 having opposed sides 133-1 . . . 133-2 (133 generally), where the tethers 125 attach to each respective opposed side 133, and the semicircular pully 132 is configured for semicircular rotation for tensioning one of the respective tethers 125.

In the example configuration, the proximal end 152 of the wave spring tail 120 is fixed to the housing 110 of 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 430. The tethers 125 are wound around a 4 mm diameter pulley 132 that is affixed to the servo motor 430. 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.

FIG. 4B shows calculation of the bending angle of the wave spring tail 120, where curvature along the curve 160 is constant, x and y are the coordinates at the tip of the wave spring tail 120, 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 120:

α = cos - 1 ⁢ x x 2 + y 2 , ( 1 ) θ = ( π 2 - α ) ⁢ 360 π , ( 2 )

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 FIG. 3, so using the law of cosines, we calculated the bending angle q (Eq. 1 and 2).

The servo motor 430 that bends the wave spring sits at the center of a toroidal-shaped container forming the housing 110 for 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 void 112 and tail 120.

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.

FIGS. 4C-4D show alternate wave spring designs for the deformable tail 120′ and 120″, 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 tail 120 is 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 FIGS. 4A-4D. 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 tail 120 is 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 tail 120 design is made entirely from soft materials enabling lightweight, inexpensive manufacturing, continuous bending.

FIG. 5 is a block diagram of a control environment suitable for use with the aquatic robot of FIGS. 1-4B. A larger number of the aquatic robot devices 100 may 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 100, projecting fluid (water) through the housing 110, and attaching the deformable tail 120 to the hosing 110 for forming a continuous fluid volume, the deformable tail having an opening 124 distal from the housing 110. By tensioning one or more of a plurality of tethers 125 attached to the deformable tail 120, the deformable tail 120 is responsive to the tensioning for directing the projected fluid through a channel defined by the housing, such that the deformable tail 120 and the opening 124 form a propulsion vector. It should be apparent that the housing 110 is hermetically sealed from intrusion by water or other fluid into which the device 100 is immersed.

Referring to FIG. 5, a communication diagram 500 illustrates the control scheme used to operate the robotic devices 100. Two potentiometers installed in a control hosing 502 are available to the user to change the speed 510 and direction 512 of the robot. Those commands are sent wirelessly via 915 MHz radio signals, and the impeller 140 and flexible tail 120 move accordingly.

An example configuration employs an RFM9x Lora Radio module 514-1. A transponder module is powered by an Arduino® Uno 516 on land that sends signals to a receiver module 514-2 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 110. Once sealed, this container was positively buoyant, so a 160 g counterweight was added to achieve neutral buoyancy.

The servo motor 430 actively 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 pulley 132 rotated 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 device 100 was designed for a small of a profile to enhance mobility in complex environments. The physical profile of the impeller 140, including a 600 kv motor 142 designed 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 housing 110 needed 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 impeller 140 was affixed to the electronics housing 110 to pull water through the void 112 at the center of the robot. The impeller 140 is 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 members 144 was 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.