Aquatic Robots Research Articles

Inspired by Sharks: A Biomimetic Skeleton for the Flapping, Propulsive Tail of an Aquatic Robot

AbstractThe vertebral column is the primary stiffening element of the body of fish. This serially jointed axial support system offers mechanical control of body bending through kinematic constraint and viscoelastic behavior. Because of the functional importance of the vertebral column in the body undulations that power swimming, we targeted the vertebral column of cartilaginous fishes—sharks, skates, and rays—for biomimetic replication. We examined the anatomy and mechanical properties of shark vertebral columns. Based on the vertebral anatomy, we built two classes of biomimetic vertebral column (BVC): (1) one in which the shape of the vertebrae varied and all else was held constant and (2) one in which the axial length of the invertebral joint varied and all else was held constant. Viscoelastic properties of the BVCs were compared to those of sharks at physiological bending frequencies. The BVCs with variable joint lengths were then used to build a propulsive tail, consisting of the BVC, a vertical septum, and a rigid caudal fin. The tail, in turn, was used as the propeller in a surface-swimming robot that was itself modeled after a biological system. As the BVC becomes stiffer, swimming speed of the robot increases, all else being equal. In addition, stiffer BVCs give the robot a longer stride length, the distance traveled in one cycle of the flapping tail.

Nature’s Design of Hierarchical Superhydrophobic Surfaces of a Water Strider for Low Adhesion and Low-Energy Dissipation

The mechanics of wet adhesion between a water strider's legs and a water surface was studied. First, we showed that the nanoscale to microscale hierarchical surface structure on striders' legs is crucial to the stable water-repellent properties of the legs. The smallest structure is made for the sake of a stable Cassie state even under harsh environment conditions, which sets an upper limit for the dimension of the smallest structure. The maximum stress and the maximum deformation of the surface structures at the contact line are size-dependent because of the asymmetric surface tension, which sets a lower limit for the dimension of the smallest structure. The surface hierarchy can largely reduce the adhesion between the water and the legs by stabilizing the Cassie state, increasing the apparent contact angle, and reducing the contact area and the length of the contact line. Second, the processes of the legs pressing on and detaching from the water surface were analyzed with a 2D model. We found that the superhydrophobicity of the legs' surface is critically important to reducing the detaching force and detaching energy. Finally, the dynamic process of the legs striking the water surface, mimicking the maneuvering of water striders, was analyzed. We found that the large length of the legs not only reduces the energy dissipation in the quasi-static pressing and pulling processes but also enhances the efficiency of energy transfer from bioenergy to kinetic energy in the dynamic process during the maneuvering of the water striders. The mechanical principles found in this study may provide useful guidelines for the design of superior water-repellent surfaces and novel aquatic robots.

USC CINAPS Builds Bridges

More than 70% of our earth is covered by water, yet we have explored less than 5% of the aquatic environment. Aquatic robots, such as autonomous underwater vehicles (AUVs), and their supporting infrastructure play a major role in the collection of oceanographic data. To make new discoveries and improve our overall understanding of the ocean, scientists must make use of these platforms by implementing effective monitoring and sampling techniques to study ocean upwelling, tidal mixing, and other ocean processes. Effective observation and continual monitoring of a dynamic system as complex as the ocean cannot be done with one instrument in a fixed location. A more practical approach is to deploy a collection of static and mobile sensors, where the information gleaned from the acquired data is distributed across the network. Additionally, orchestrating a multisensor, long-term deployment with a high volume of distributed data involves a robust, rapid, and cost-effective communication network. Connecting all of these components, which form an aquatic robotic system, in synchronous operation can greatly assist the scientists in improving our overall understanding of the complex ocean environment.

1P1-C30 水中倒立振子の試作と性能評価

An aquatic pendulum is reported in order to educate the aquatic robot. Much work of pendulum in the air has studied and offered teaching machine which is excellent in learning the control system. The aquatic pendulum has many advantages to educate the control theory in the field of mechatronics because of being easy to its parameter identification, being easy to stable and unstable states and being effective to a buoyancy. The prototype aquatic pendulum is represented with characteristics and performance of one dimensional dynamic model. It is useful to enlightenment for the aquatic robot field.

616 SMAアクチュエータを用いた水中推進ロボット(アクチュエータ,OS-12 スマート構造システム,総合テーマ「伝統を,未来へ!」)

Fish-like aquatic robot driven by shape memory alloy (SMA) is developed. The robot has a drive tail-fin made of a flexible polypropylene plate. Two fiber-like SMAs are pasted on the both surface of the plate. The SMA used here can contract by applying electricity. When the SMA is contracted, the fin bends to the one side. By switching the electricity, active SMA changes alternately, and the robot can move the fin. Characteristics of the fin are investigated, and it is shown that the robot represents the fish-like locomotion. Also a possibility to realize a smart fin is discussed.

Frequency-weighted feedforward control for dynamic compensation in ionic polymer–metalcomposite actuators

Ionic polymer–metal composites (IPMCs) are innovative materials that offer combinedsensing and actuating ability in lightweight and flexible package. IPMCs have beenexploited in robotics and a wide variety of biomedical devices, for example, as sensorsfor teleoperation, as actuators for positioning in active endoscopy, as fins forpropelling aquatic robots, and as an injector for drug delivery. In the actuationmode, one of the main challenges is precise position control. In particular, IPMCactuators exhibit relaxation behavior and nonlinearities; and at relatively highoperating frequencies dynamic effects limit accuracy and positioning bandwidth. Afrequency-weighted feedforward controller is designed to account for the IPMC’sstructural dynamics to enable fast positioning. The control method is applied to acustom-made Nafion-based IPMC actuator. The controller takes into account themagnitude of the control input to avoid generating excessively large voltages which candamage the IPMC actuator. To account for unmodeled effects not captured by thedynamics model, a feedback controller is integrated with the feedforward controller.Experimental results show a significant improvement in the tracking performance whenfeedforward control is used. For instance, the feedforward controller shows over75% reduction in the tracking error compared to the case without feedforward compensation. Finally,the integrated feedforward and feedback control system reduces the tracking error to less than10% for tracking an 18-Hz triangle-like trajectory. Some of the advantages of feedforward controlas well as its limitations are also discussed.

Four flippers or two? Tetrapodal swimming with an aquatic robot

To understand how to modulate the behavior of underwater swimmers propelled by multiple appendages, we conducted surge maneuver experiments on our biologically-inspired robot, Madeleine. Robot Madeleine is a self-contained, self-propelled underwater vehicle with onboard processor, sensors and power supply. Madeleine's four flippers, oscillating in pitch, can be independently controlled, allowing us to test the impact of flipper phase on performance. We tested eight gaits, four four-flippered and four two-flippered. Gaits were selected to vary the phase, at either 0 or π rad, between flippers on one side, producing a fore–aft interaction, or flippers on opposite sides, producing a port–starboard interaction. During rapid starting, top-speed cruising, and powered stopping, the power draw, linear acceleration and position of Madeleine were measured. Four-flippered gaits produced higher peak start accelerations than two, but did so with added power draw. During cruising, peak speeds did not vary by flipper number, but power consumption was double in four flippers compared to that of two flippers. Cost of transport (J N−1 m−1) was lower for two-flippered gaits and compares favorably with that of aquatic tetrapods. Two four-flippered gaits produce the highest surge scope, a measure of the difference in peak forward and reverse acceleration. Thus four flippers produce superior surge behavior but do so at high cost; two flippers serve well for lost-cost cruising.

Limits of Nature and Advances of Technology: What Does Biomimetics Have to Offer to Aquatic Robots?

In recent years, the biomimetic approach has been utilized as a mechanism for technological advancement in the field of robotics. However, there has not been a full appreciation of the success and limitations of biomimetics. Similarities between natural and engineered systems are exhibited by convergences, which define environmental factors, which impinge upon design, and direct copying that produces innovation through integration of natural and artificial technologies. Limitations of this integration depend on the structural and mechanical differences of the two technologies and on the process by which each technology arises. The diversity of organisms that arose through evolutionary descent does not necessarily provide all possible solutions of optimal functions. However, in instances where organisms exhibit superior performance to engineered systems, features of the organism can be targeted for technology transfer. In this regard, cooperation between biologists and engineers is paramount.

An animatronic system including lifelike robotic fish

This paper provides an outline of a new animatronic system, based on the technology of the flexible oscillating fin. The oscillating fin propulsion system was designed and constructed to be combined with a ship model. The system's feasibility has been confirmed by tank tests using the ship model. As a result, several advantages of the oscillating fin system have been found. A neural network was successfully applied for an identification of the ship model dynamics with the oscillating fin and its effectiveness was confirmed. The animatronic system is a computer-controlled biomechanically engineered model, rapidly gaining popularity throughout the world. We have developed aquatic robots with oscillating fins for the animatronics system to build a virtual aquarium. We have proposed an exhibition system for enhancing event spaces that includes an animatronic system for modern-day fish, coelacanths, and Cambrian-world creatures, able to swim under their own electric power.

Tissue engineering of fish skin: behavior of fish cells on poly(ethylene glycol terephthalate)/poly(butylene terephthalate) copolymers in relation to the composition of the polymer substrate as an initial step in constructing a robotic/living tissue hybrid.

This study presents the development of a biosynthetic fish skin to be used on aquatic robots that can emulate fish. Smoothness of the external surface is desired in improving high propulsive efficiency and maneuvering agility of autonomous underwater vehicles such as the RoboTuna (Triantafyllou, M., and Triantafyllou, G. Sci. Am. 272, 64, 1995). An initial step was to determine the seeding density and select a polymer for the scaffolds. The attachment and proliferation of chinook salmon embryo (CHSE-214) and brown bullhead (BB) cells were studied on different compositions of a poly(ethylene glycol terephthalate) (PEGT) and poly(butylene terephthalate) (PBT) copolymer (Polyactive). Polymer films were used, cast of three different compositions of PEGT/PBT (weight ratios of 55/45, 60/40, and 70/30) and two different molecular masses of PEGT (300 and 1000 Da). When a 55 wt% and a 300-Da molecular mass form of PEGT was used, maximum attachment and proliferation of CHSE-214 and BB cells were achieved. Histological studies and immunostaining indicate the presence of collagen and cytokeratins in the extracellular matrix formed after 14 days of culture. Porous scaffolds of PEGT/PBT copolymers were also used for three-dimensional tissue engineering of fish skin, using BB cells. Overall, our results indicate that fish cells can attach, proliferate, and express fish skin components on dense and porous Polyactive scaffolds.

Propulsion Performance of an Aquatic Mobile Robot Using Traveling-Wave Motion of a Flexible Fin. Relationship between Propulsion Efficiency and Flow Pattern.

This paper discusses an experimental study of the propulsion performance of an aquatic mobile robot using waving motion of a flexible plate modeled on the flexible caudal fin of fish. In the experiment, the propulsion force and side force generated by the waving motion of the flexible plate are examined in stationary water in a channel. And the propulsion speed and efficiency are examined with varing the length and flexiblility of the plate. As a result, it is found that the propulsion performance of the robot becomes high when the traveling-wave motion occurs in the flexible plate. And high propulsion performance of efficiency of 62% is obtained by using the traveling-wave motion of the flexible plate.

Limits of Nature and Advances of Technology: What Does Biomimetics Have to Offer to Aquatic Robots?

In recent years, the biomimetic approach has been utilized as a mechanism for technological advancement in the field of robotics. However, there has not been a full appreciation of the success and limitations of biomimetics. Similarities between natural and engineered systems are exhibited by convergences, which define environmental factors, which impinge upon design, and direct copying that produces innovation through integration of natural and artificial technologies. Limitations of this integration depend on the structural and mechanical differences of the two technologies and on the process by which each technology arises. The diversity of organisms that arose through evolutionary descent does not necessarily provide all possible solutions of optimal functions. However, in instances where organisms exhibit superior performance to engineered systems, features of the organism can be targeted for technology transfer. In this regard, cooperation between biologists and engineers is paramount.