The octopus uses the arm-swimming behavior primarily for escape, defense, or foraging. This mode of locomotion is comprised of two strokes, with the arms opening slowly and closing rapidly, and generally results in considerable propulsive acceleration. In light of the recent development by our group of an octopus-like eight-arm underwater robot, we are interested to analyze the details of the biological arm swimming motion, in order to understand its kinematics. In this paper, we address methodological aspects of the 3D reconstruction process of octopus arm trajectories, based on computer vision, and present the resulting arm swimming movement of a benthic common octopus. The 3D trajectories of all eight octopus arms were tracked and analyzed, providing information about speed, acceleration and arm elongation. The animal's performance is then used for a direct comparison with our 8-arm robotic swimmer. The data obtained provide new kinematic information about this, relatively unknown, propulsive mode, which can be exploited for multi-functional underwater robots.

The present paper considers the modeling, control, development and experimental validation of bio-inspired multiarm underwater robotic swimmers actuated by compliant actuating elements, in the context of the soft robotics paradigm. Each one of the swimmer's compliant arms is actuated at its base by a pair of antagonistic compliant shape memory alloy (SMA) springs. The base joint of each such arm displays hysteretic behavior and asymmetries, which are compensated via the modified Prandtl-Ishlinskii (MPI) model of the joint's response, in conjunction with angular position feedback from a potentiometer. This closed-loop control scheme achieves fast and efficient tracking of a sculling joint motion profile. Experimental results based on a pair of such submerged arms, integrated in a catamaran hull, indicate the feasibility of this actuation and control scheme, providing propulsive speeds up to approximately 0.5 arm lengths per second (~50 mm/sec) and propulsive forces up to 30 mN. The experimental studies presented, regarding the effect of the arm kinematic parameters on propulsive speed and force, are in qualitative agreement with previous results of our group for rigid-actuator multi-arm underwater swimmers.

This paper presents an 8-arm compliant robot, able to propel itself underwater by movements of its arms, either alone or interconnected via a passively-compliant web. The robot is inspired by the morphology and outstanding locomotor capabilities of the octopus, and is fabricated primarily from compliant materials. This robotic swimmer is first investigated computationally via dynamical models capturing the arm and web compliance, and indicating the effect of various kinematic parameters of the system on its motion. The performance of the robotic prototype is, then, tested experimentally, to demonstrate this novel mode of underwater propulsion by combining various patterns of sculling movements of the arms and web. Speeds of 0.5 body lengths per second and propulsive forces of up to 10.5 N were achieved, with a cost of transport as low as 0.62.

The locomotion of miniature medical robots in the interior of the human body, possibly in contact with the tissue of organs and vessels, is a challenging problem in robotics, which, if properly addressed, might favorably impact several significant applications. This paper investigates the potential of employing relatively low-frequency vibrations, generated by an on-board eccentric motor, to reduce friction for such robots, moving by some other primary mechanism over and in contact with liver tissue. This study focuses on the computational modeling and the experimental assessment of the interaction between vibratory-actuated miniature robots and compliant tissue. The computational model developed to analyze the effect of such vibrations, for a robot moving over a substrate with normal-wise viscoelasticity, is employing a modified Dahl model with viscous damping for the tangential friction. Experiments with a vibratory-actuated platform pulled over ex-vivo bovine liver tissue indicate that the friction reduces as the frequency of vibrations increases, in a manner consistent with the model's predictions, reaching a reduction of up to 40%.

Inspired by the octopus arm morphology and exploiting recordings of swimming octopus, we investigate the propulsive capabilities of an 8-arm robotic system under various swimming gaits, including arm sculling and arm undulations, for the generation of forward propulsion. A dynamical model of the robotic system, that considers fluid drag contributions accurately evaluated by CFD methods, was used to study the effects of various kinematic parameters on propulsion. Experiments inside a water tank with an 8-arm robotic prototype successfully demonstrated the sculling-only gaits, attaining a maximum speed of approximately 0.2 body lengths per second. Similar trends were observed, as in the simulation studies, with respect to the effect of the kinematic parameters on propulsion.

We consider robotic analogues of the arms of the octopus, a cephalopod exhibiting a wide variety of dexterous movements and complex shapes, moving in an aquatic environment. Although an invertebrate, the octopus can vary the stiffness of its long arms and generate large forces, while also performing rapid motions within its aquatic environment. Previous studies of elongated robotic systems, moving in fluid environments, have mostly oversimplified the effects of flow and the generated hydrodynamic forces, in their dynamical models. The present paper uses computational fluid dynamic (CFD) analysis to perform high-fidelity numerical simulations of robotic prototypes emulating the morphology of octopus arms. The direction of the flow stream and the arm geometry (e.g., the presence of suckers), were among the parameters that were shown to affect significantly the flow field structure and the resulting hydrodynamic forces, which have a non-uniform distribution along the arm. The CFD results are supported by vortex visualization experiments in a water tank. The results of this investigation are being exploited for the design of soft-bodied robotic systems and the development of related motion control strategies.

The multi-arm morphology of octopus-inspired robotic systems may allow their aquatic propulsion, in addition to providing manipulation functionalities, and enable the development of flexible robotic tools for underwater applications. In the present paper, we consider the multi-arm swimming behavior of the octopus, which is different than their, more usual, jetting behavior, and is often used to achieve higher propulsive speeds, e.g., for chasing prey. A dynamic model of a robot with a pair of articulated arms is employed to study the generation of this mode of propulsion. The model includes fluid drag contributions, which we support by detailed Computational Fluid Dynamic analysis. To capture the basic characteristics of octopus multi-arm swimming a sculling mode is proposed, involving arm oscillations with an asymmetric speed profile. Parametric simulations were used to identify the arm oscillation characteristics that optimize propulsion for sculling, as well as for undulatory arm motions. Tests with a robotic prototype in a water tank provide preliminary validation of our analysis.

The octopus arm is a unique tool that combines strength and flexibility. It can shorten, elongate and bend at any point along its length. To model this behavior, a hyper-redundant manipulator composed of multiple segments is proposed. Each segment is a parallel robotic mechanism with redundant actuation. The kinematics and dynamics of this manipulator are analyzed and simulated utilizing a modular computational modeling method. Simulation results for some primitive movements are presented, and the effect of hydrodynamic forces is included.

This paper addresses the problem of vision-based closed-loop control for undulatory robots. We present an image-based visual servoing scheme, which drives the robot to a desired location specified by a target image, without explicitly estimating its pose. Instead, the control relies on the computation of the epipolar geometry between the current and target images. We analyze controllability and stability of the proposed control scheme, which is validated by simulation studies using the SIMUUN computational tools. Preliminary experiments, involving the Nereisbot undulatory robotic prototype, are also presented.

The present paper explores the effect of the mechanism-substrate frictional interface on the locomotion characteristics of robotic mechanisms employing traveling waves for propulsion. For these investigations, an extended class of undulatory robotic locomotors is considered, termed pedundulatory, which augment lateral body undulations by coordinated dorso-ventral oscillations of multiple pairs of lateral paddle-shaped appendages (parapodia). We examine how, the same robotic prototype, allows the implementation of four distinct bio-inspired undulatory and pedundulatory modes of locomotion, by modifying the motion control strategy depending on the mechanism-substrate frictional interface. These modes employ retrograde or direct body waves, either standalone (giving rise to eel-like and ochromonas-like undulatory locomotion modes, respectively), or combined with appropriately coordinated substrate contact by the parapodial appendages (giving rise to centipede-like and polychaete-like pedundulatory modes, respectively). These four modes are investigated and comparatively assessed, both in simulation and via extensive experiments on granular substrates with the Nereisbot prototype. Our results validate the identified locomotion principles and also highlight the enhanced performance and gait repertoire of pedundulatory systems, compared to purely undulatory ones.

In this paper, two visual cues are proposed, to be exploited for the navigation of active endoscopic capsules within the gastrointestinal (GI) tract. These cues consist of the detection and tracking of the lumen and of an illumination highlight in capsule endoscopy (CE) images. The proposed approach aims at developing vision algorithms which are robust with respect to the challenging imaging conditions encountered in the GI tract and the great variability of the acquired images. Cases where no or more than one lumens exists, are also detected. The proposed approach extends the state-of-the-art in lumen detection, and is demonstrated for in-vivo video sequences acquired from endoscopic capsules.

The polychaete annelid marine worms propel themselves in a variety of challenging locomotion environments by a unique form of tail-to-head body undulations, combined with the synchronized action of numerous parapodial lateral appendages. This combined parapodial and undulatory mode of locomotion is termed pedundulatory in the present work. Robotic analogues of this type of locomotion are being studied, both in simulation, and via experiments with biomimetic robotic prototypes, which combine undulatory movements of their multi-link body with appropriately coordinated parapodial link oscillations. Extensive experimental studies of locomotion on sand demonstrate the potential of the pedundulatory robotic prototypes, especially their rich gait repertoire and their enhanced performance compared to robotic prototypes relying only on body undulations

A biological paradigm of versatile locomotion and effective motion control is provided by the polychaete annelid worms, whose motion adapts to a large variety of unstructured environmental conditions (sand, mud, sediment, water, etc.), and could thus be of interest to replicate by robotic analogs. Their locomotion is characterized by the combination of a unique form of tail-to-head body undulations (opposite to snakes and eels), with the rowing-like action of numerous lateral appendages distributed along their long segmented body. Focusing on the former aspect of polychaete locomotion, computational models of crawling and swimming by such tail-to-head body undulations have been developed in this paper. These are based on the Lagrangian dynamics of the system and on resistive models of its interaction with the environment, and are used for simulation studies demonstrating the generation of undulatory gaits. Several biomimetic robotic prototypes have been developed, whose undulatory actuation achieves propulsion on sand and other granular unstructured environments. Extensive experimental studies demonstrate the feasibility of robot propulsion by tail-to-head body undulations in such environments, as well as the agreement of its qualitative and quantitative characteristics to the predictions of the corresponding computational models.

Polychaete annelid worms provide a biological paradigm of versatile locomotion and effective motion control, adaptable to a large variety of unstructured environmental conditions (water, sand, mud, sediment, etc.). The undulatory locomotion of their segmented body is characterized by the combination of a unique form of tail-to-head body undulations, with the rowing-like action of numerous lateral appendages distributed along their body. Computational models of polychaete-like crawling and swimming have been developed, based on the Lagrangian dynamics of the system and on resistive models of its interaction with the environment, and used for simulation studies demonstrating the generation of undulatory gaits. Several lightweight robotic prototypes have been developed, whose undulatory actuation achieves propulsion on sand. Extensive experiments demonstrate that the propulsion of these robots is characterized by essential features of polychaete locomotion, in agreement with the corresponding simulations.