Using Reinforcement Learning to Develop a Novel Gait for a Bio-Robotic California Sea Lion.

While researchers have made notable progress in bio-inspired swimming robot development, a persistent challenge lies in creating propulsive gaits tailored to these robotic systems. The California sea lion achieves its robust swimming abilities through a careful coordination of foreflippers and body segments. In this paper, reinforcement learning (RL) was used to develop a novel sea lion foreflipper gait for a bio-robotic swimmer using a numerically modelled computational representation of the robot.

Fish robotics: multi-fin propulsion and the coupling of fin phase, spacing, and compliance.

Fish coordinate the motion of their fins and body to create the time-varying forces required for swimming and agile maneuvers. To effectively adapt this biological strategy for underwater robots, it is necessary to understand how the location and coordination of interacting fish-like fins affect the production of propulsive forces. In this study, the impact that phase difference, horizontal and vertical spacing, and compliance of paired fins had on net thrust and lateral forces was investigated using two fish-like robotic swimmers and a series of computational fluid dynamic simulations.

The effect of sensory feedback topology on the entrainment of a neural oscillator with a compliant foil for swimming systems.

The sensorimotor system of fish endows them with remarkable swimming performance that is unmatched by current underwater robotic vehicles. To close the gap between the capabilities of fish and the capabilities of underwater vehicles engineers are investigating how fish swim. In particular, engineers are exploring the sensorimotor systems of fish that control the motion of fins.

Passing the Wake: Using Multiple Fins to Shape Forces for Swimming.

Fish use coordinated motions of multiple fins and their body to swim and maneuver underwater with more agility than contemporary unmanned underwater vehicles (UUVs). The location, utilization and kinematics of fins vary for different locomotory tasks and fish species. The relative position and timing (phase) of fins affects how the downstream fins interact with the wake shed by the upstream fins and body, and change the magnitude and temporal profile of the net force vector.

Development of a vortex generator to perturb fish locomotion.

Knowledge about the stiffness of fish fins, and whether stiffness is modulated during swimming, is important for understanding the mechanics of a fin's force production. However, the mechanical properties of fins have not been studied during natural swimming, in part because of a lack of instrumentation. To remedy this, a vortex generator was developed that produces traveling vortices of adjustable strength which can be used to perturb the fins of swimming fish.

The Effects of Fluidic Loading on Underwater Contact Sensing with Robotic Fins and Beams.

As robots become more involved in underwater operations, understanding underwater contact sensing with compliant systems is fundamental to engineering useful haptic interfaces and vehicles. Despite knowledge of contact sensation in air, little is known about contact sensing underwater and the impact of fluid on both the robotic probe and the target object. The objective of this work is to understand the effects of fluidic loading, fin webbing, and target object geometry on strain sensation within compliant robotic fins and beams during obstacle contact.

The envelope of motion of the cervical spine and its influence on the maximum torque generating capability of the neck muscles.

The posture of the head and neck is critical for predicting and assessing the risk of injury during high accelerations, such as those arising during motor accidents or in collision sports. Current knowledge suggests that the head's range-of-motion (ROM) and the torque-generating capability of neck muscles are both dependent and affected by head posture. A deeper understanding of the relationship between head posture, ROM and maximum torque-generating capability of neck muscles may help assess the risk of injury and develop means to reduce such risks.

Predicting propulsive forces using distributed sensors in a compliant, high DOF, robotic fin.

Engineered robotic fins have adapted principles of propulsion from bony-finned fish, using spatially-varying compliance and complex kinematics to produce and control the fin's propulsive force through time. While methods of force production are well understood, few models exist to predict the propulsive forces of a compliant, high degree of freedom, robotic fin as it moves through fluid. Inspired by evidence that the bluegill sunfish (Lepomis macrochirus) has bending sensation in its pectoral fins, the objective of this study is to understand how sensors distributed within a compliant robotic fin can be used to estimate and predict the fin's propulsive force.

A robotic fish caudal fin: effects of stiffness and motor program on locomotor performance.

We designed a robotic fish caudal fin with six individually moveable fin rays based on the tail of the bluegill sunfish, Lepomis macrochirus. Previous fish robotic tail designs have loosely resembled the caudal fin of fishes, but have not incorporated key biomechanical components such as fin rays that can be controlled to generate complex tail conformations and motion programs similar to those seen in the locomotor repertoire of live fishes. We used this robotic caudal fin to test for the effects of fin ray stiffness, frequency and motion program on the generation of thrust and lift forces.

Use of biorobotic models of highly deformable fins for studying the mechanics and control of fin forces in fishes.

Bony fish swim with a level of agility that is unmatched in human-developed systems. This is due, in part, to the ability of the fish to carefully control hydrodynamic forces through the active modulation of the fins' kinematics and mechanical properties. To better understand how fish produce and control forces, biorobotic models of the bluegill sunfish's (Lepomis macrochirus) caudal fin and pectoral fins were developed.

The effect of fin ray flexural rigidity on the propulsive forces generated by a biorobotic fish pectoral fin.

A biorobotic pectoral fin was developed and used to study how the flexural rigidities of fin rays within a highly deformable fish fin affect the fin's propulsive forces. The design of the biorobotic fin was based on a detailed analysis of the pectoral fin of the bluegill sunfish (Lepomis macrochirus). The biorobotic fin was made to execute the kinematics used by the biological fin during steady swimming, and to have structural properties that modeled those of the biological fin.

A biorobotic model of the sunfish pectoral fin for investigations of fin sensorimotor control.

A comprehensive understanding of the control of flexible fins is fundamental to engineering underwater vehicles that perform like fish, since it is the fins that produce forces which control the fish's motion. However, little is known about the fin's sensory system or about how fish use sensory information to modulate the fin and to control propulsive forces. As part of a research program that involves neuromechanical and behavioral studies of the sunfish pectoral fin, a biorobotic model of the pectoral fin and of the fin's sensorimotor system was developed and used to investigate relationships between sensory information, fin ray motions and propulsive forces.

Artificial muscle actuators in biorobotic fish fins.

Artificial muscle technologies offer the possibility of designing robotic systems that take full advantage of biological architectures. Of current artificial muscle technologies, nickel titanium (Ni-Ti) shape memory alloys are among a few that are readily usable by engineering labs without specialized skills in material science and/or chemistry. Ni-Ti actuators are now being used to replace servomotors in biorobotic fins.

A biorobotic pectoral fin for autonomous undersea vehicles.

A biorobotic fin for autonomous undersea vehicles (AUVs) was developed based on studies of the anatomy, kinematics, and hydrodynamics of the bluegill sunfish pectoral fin. The biorobotic fin was able to produce many of the complex fin motions used by the sunfish during steady swimming and was used to investigate mechanisms of thrust production and control. This biorobotic fin is an excellent experimental tool and is an important first step towards developing propulsive devices that give AUVs maneuvering characteristics that match and exceed those of highly maneuverable fish.

Fish biorobotics: kinematics and hydrodynamics of self-propulsion.

As a result of years of research on the comparative biomechanics and physiology of moving through water, biologists and engineers have made considerable progress in understanding how animals moving underwater use their muscles to power movement, in describing body and appendage motion during propulsion, and in conducting experimental and computational analyses of fluid movement and attendant forces. But it is clear that substantial future progress in understanding aquatic propulsion will require new lines of attack. Recent years have seen the advent of one such new avenue that promises to greatly broaden the scope of intellectual opportunity available to researchers: the use of biorobotic models.

The application of conducting polymers to a biorobotic fin propulsor.

Conducting polymer actuators based on polypyrrole are being developed for use in biorobotic fins that are designed to create and control forces like the pectoral fin of the bluegill sunfish (Lepomis macrochirus). It is envisioned that trilayer bending actuators will be used within, and as, the fin's webbing to create a highly controllable, shape morphing, flexible fin surface, and that linear conducting polymer actuators will be used to actuate the bases of the fin's fin-rays, like an agonist-antagonist muscle pair, and control the fin's stiffness. For this application, trilayer bending actuators were used successfully to reproduce the cupping motion of the sunfish pectoral fin by controlling the curvature of the fin's surface and the motion of its dorsal and ventral edges.

System identification of the human vestibulo-ocular reflex during head-free tracking.

A method was developed to identify the linear, system level dynamics of the horizontal, angular vestibulo-ocular reflex (VOR) as it stabilized vision during head-free tracking of a visual target. Small amplitude, broad spectrum, stochastic torque perturbations were applied to the head while the subject tracked an unpredictable, moving target with active head and eye motions. Stochastic system identification techniques were used to design the torque and target inputs and to conduct the analysis such that the linear dynamics of the VOR, independently of the visual system's influence on eye motions, were determined.

Dynamics of the human head-neck system in the horizontal plane: joint properties with respect to a static torque.

The vestibular system has often been studied by perturbing the position of the head. This study was conducted to identify the dynamic properties of the head-neck system in response to horizontal plane perturbations. A quasilinear approach was used to quantify the dynamics of the head-neck system at different levels of static torque.