Michael Sfakiotakis

Polychaete-like Pedundulatory Robotic Locomotion

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

Robotic underwater propulsion inspired by the octopus multi-arm swimming

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.

Neuromuscular control of reactive behaviors for undulatory robots

Undulatory locomotion is studied as a biological paradigm of versatile body morphology and effective motion control, adaptable to a large variety of unstructured and tortuous environmental conditions. Computational models of undulatory locomotion have been developed, and validated on a series of robotic prototypes propelling themselves on sand. The present paper explores in simulation neuromuscular motion control for these undulatory robot models, based on biomimetic central pattern generators and on information from distributed distance sensors. This leads to reactive control schemes, which achieve (i) traversal of corridor-like environments, and (ii) formation control for swarms of undulatory robots.

Octopus-inspired eight-arm robotic swimming by sculling movements

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.

Polychaete-Like Undulatory Robotic Locomotion in Unstructured Substrates

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.

Effects of vibratory actuation on endoscopic capsule vision

Current research in capsule endoscopy aims at endowing the capsules with some means of actively propelling themselves inside the gastrointestinal (GO tract, as opposed Advantages of these active capsules are the sipificant potential in the duration of the associated diagnostic procedures. as well as the oossihilitv to direct the line-of-sieht of the oh-hoard cameras towards interesting features of the GI tissue. One such means of active propulsion is by vibratory actuation, employing eccentric-mass micromotors, which is shown to reduce the friction of the capsule with the GI tract. The effect of vibrations on the quality of the acquired images is explored in the present study, which demonstrates that such vibrations do not affect adversely the diagnostic effectiveness of the endoscopic capsules. The parameters of vibratory actuation are evaluated as to the loss bf high-frequency information in the acquired images, due to the induced motion blur, and appropriate design guidelines for the vibratory actuation system are established. The validity of this study has been evaluated by ex-vivo and in-vivo experiments.

Biomimetic Centering for Undulatory Robots

Substantial work exists in the undulatory robotics literature on the mechanical design, modeling, gait generation and implementation of robotic prototypes. However, there appears to have been relatively limited work on the use of exteroceptive sensors in control schemes leading to more complex reactive undulatory behaviors. This paper considers a biologically-inspired sensor-based centering behavior for undulatory robots, originally developed for nonholonomic mobile robots. Adaptation to the significantly more complex dynamics of undulatory locomotors highlights a number of issues related to the use of sensors (possibly distributed over the elongated body of the mechanism) for the generation of reactive behaviors, to biomimetic neuromuscular control and to formation control of multi-undulatory swarms. These issues are explored via computational tools specifically geared towards undulatory locomotion in robotics and biology

Undulatory and pedundulatory robotic locomotion via direct and retrograde body waves

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.

Turning maneuvers of an octopus-inspired multi-arm robotic swimmer

Inspired by the agile underwater maneuvering of the octopus, an eight-arm robotic swimmer was developed. Associated dynamical models are used here to design turning maneuvers, an important ability for underwater navigation. The performance of several turning gaits, based on sculling arm movements, of this robotic system was investigated in simulation, with respect to their various kinematic parameters. Experiments with a prototype robotic swimmer confirmed the computational results and verified the multi-arm maneuverability of such systems.

Pedundulatory robotic locomotion: Centipede and polychaete modes in unstructured substrates

The present paper considers a novel class of robotic systems, termed pedundulatory locomotors, which can be thought of as undulatory robots augmented by multiple pairs of lateral paddle-like appendages (“parapodia”). Bio-inspired strategies for synchronizing the movement of the parapodia with the body undulations, emulating organisms like the centipedes and the polychaete worms, are presented, giving rise to distinct pedundulatory modes. These modes are investigated and comparatively assessed, both in simulation and via experiments with the Nereisbot prototype locomoting on sand and on several other unstructured substrates. Our studies demonstrate the rich gait repertoire and enhanced performance of pedundulatory systems, compared to purely undulatory ones.