https://users.dimi.uniud.it/~antonio.dangelo/Robotica/2012/helper/leggedRobot/Ijspeert08NN.pdf

2008 Special Issue: Central pattern generators for locomotion control in animals and robots: A review

Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats e.g. octopus arms and elephant trunks are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control.

/pdf/soft-robotics-biological-inspiration-state-of-the-art-and-1esuws0p9g.pdf

Soft robotics: Biological inspiration, state of the art, and future research

Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

Research in soft matter engineering has introduced new approaches in robotics and wearable devices that can interface with the human body and adapt to unpredictable environments. However, many promising applications are limited by the dependence of soft systems on electrical or pneumatic tethers. Recent work in soft actuation and electronics has made removing such cords more feasible, heralding a variety of applications from autonomous field robotics to wireless biomedical devices. Here we review the development of functional untethered soft robotics. We focus on recent advances in soft robotic actuation, sensing and integration as they relate to untethered systems, and consider the key challenges the field faces in engineering systems that could have practical use in real-world conditions. This Review Article examines the development of functional untethered soft robotics, evaluating recent advances in soft robotic actuation, sensing, and integration in relation to untethered systems.

Untethered soft robotics

During the 1990s, numerous worldwide research and development activities have occurred in underwater robotics, especially in the area of autonomous underwater vehicles (AUVs). As the ocean attracts great attention on environmental issues and resources as well as scientific and military tasks, the need for and use of underwater robotic systems has become more apparent. Great efforts have been made in developing AUVs to overcome challenging scientific and engineering problems caused by the unstructured and hazardous ocean environment. In the 1990s, about 30 new AUVs have been built worldwide. With the development of new materials, advanced computing and sensory technology, as well as theoretical advancements, R&D activities in the AUV community have increased. However, this is just the beginning for more advanced, yet practical and reliable AUVs. This paper surveys some key areas in current state-of-the-art underwater robotic technologies. It is by no means a complete survey but provides key references for future development. The new millennium will bring advancements in technology that will enable the development of more practical, reliable AUVs.

Design and Control of Autonomous Underwater Robots: A Survey

Several physico-mechanical designs evolved in fish are currently inspiring robotic devices for propulsion and maneuvering purposes in underwater vehicles. Considering the potential benefits involved, this paper presents an overview of the swimming mechanisms employed by fish. The motivation is to provide a relevant and useful introduction to the existing literature for engineers with an interest in the emerging area of aquatic biomechanisms. The fish swimming types are presented, following the well-established classification scheme and nomenclature originally proposed by Breder. Fish swim either by body and/or caudal fin (BCF) movements or using median and/or paired fin (MPF) propulsion. The latter is generally employed at slow speeds, offering greater maneuverability and better propulsive efficiency, while BCF movements can achieve greater thrust and accelerations. For both BCF and MPF locomotion, specific swimming modes are identified, based on the propulsor and the type of movements (oscillatory or undulatory) employed for thrust generation. Along with general descriptions and kinematic data, the analytical approaches developed to study each swimming mode are also introduced. Particular reference is made to lunate tail propulsion, undulating fins, and labriform (oscillatory pectoral fin) swimming mechanisms, identified as having the greatest potential for exploitation in artificial systems.

/pdf/review-of-fish-swimming-modes-for-aquatic-locomotion-12dkkh88vr.pdf

Review of fish swimming modes for aquatic locomotion

The transformation of endoscopic capsules from passive tools to robotic devices is increasingly attracting the interest of the research community. In the past few years, significant progress has been achieved in the areas of microelectronics and electromechanical systems. However, their use in commercial endoscopic capsules is hindered by their increased power demands, which, to present, cannot be adequately met by embedded power sources. A 3D inductive powering module, providing over 300 mW to the capsule, overcomes these limitations, thus enabling the integration of active locomotion systems, as well as advanced diagnostic and therapeutic features. This is demonstrated in the present study by a capsule prototype employing the wireless powering unit to drive an onboard vibratory motor for capsule propulsion. Simplified models are employed to illustrate the main principle of this vibratory locomotion scheme. Experimental results, involving movement of the prototype in various environments, confirm both the effectiveness of the wireless powering system, and the efficacy of the vibratory locomotion scheme.

/pdf/a-multi-coil-inductive-powering-system-for-an-endoscopic-rvu09oyhqw.pdf

A multi-coil inductive powering system for an endoscopic capsule with vibratory actuation

Substantial work exists in the robotics literature on the mechanical design, modeling, gait generation and implementation of undulatory robotic prototypes. However, there appears to have been relatively limited work on closing the control loop for such robotic locomotors using sensory information from on-board exteroceptive sensors, in order to realize more complex undulatory behaviors. In this paper we consider a biologically inspired sensor-based “centering” behavior for undulatory robots traversing corridor-like environments. Such behaviors have been observed and studied in bees, and robotic analogs were originally developed for non-holonomic 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 undulatory behaviors and also related to biomimetic neuromuscular control and to the formation control of multi-undulatory swarms. These issues are explored in simulation by means of computational tools specifically geared towards undulatory locomotion in robotics and biology. Moreover, a series of undulatory robotic prototypes has been developed, which are able to propel themselves on a variety of hard and granular substrates, by means of both head-to-tail (“eel-like”) and tail-to-head (“polychaete-like”) undulatory waves. The undulatory centering behavior is demonstrated experimentally in several layouts of corridor-like environments using these robotic prototypes equipped with infrared distance sensors.

/pdf/biomimetic-centering-for-undulatory-robots-59z6ffbouz.pdf

Biomimetic Centering for Undulatory Robots

To investigate the undulating median fin propulsion and its potential for implementation in man-made underwater vehicles, a "fin actuator" has been developed. The device consists of eight parallel bellows actuators or PBAs (fin rays) arranged in a series and interconnected via a flexible material (fin membrane). The PBAs are pneumatically driven and allow for bending movements in any orientation plane. Position data are provided by flexible electrogoniometers. The forces generated from the fin actuator undulations are measured by a pair of tri-axial force sensors. Initial testing has concentrated on 2D fin ray motions, whereby each PBA moves laterally, with the deflection angle performing a sinusoidal variation. Preliminary measurements, for a range of the propulsive waveform parameters, demonstrate reversible thrust generation and good agreement with the theoretical predictions of a momentum-based model.

An experimental undulating-fin device using the parallel bellows actuator

The outstanding locomotor and manipulation characteristics of the octopus have recently inspired the development, by our group, of multi-functional robotic swimmers, featuring both manipulation and locomotion capabilities, which could be of significant engineering interest in underwater applications. During its little-studied arm-swimming behavior, as opposed to the better known jetting via the siphon, the animal appears to generate considerable propulsive thrust and rapid acceleration, predominantly employing movements of its arms. In this work, we capture the fundamental characteristics of the corresponding complex pattern of arm motion by a sculling profile, involving a fast power stroke and a slow recovery stroke. We investigate the propulsive capabilities of a multi-arm robotic system under various swimming gaits, namely patterns of arm coordination, which achieve the generation of forward, as well as backward, propulsion and turning. A lumped-element model of the robotic swimmer, which considers arm compliance and the interaction with the aquatic environment, was used to study the characteristics of these gaits, the effect of various kinematic parameters on propulsion, and the generation of complex trajectories. This investigation focuses on relatively high-stiffness arms. Experiments employing a compliant-body robotic prototype swimmer with eight compliant arms, all made of polyurethane, inside a water tank, successfully demonstrated this novel mode of underwater propulsion. Speeds of up to 0.26 body lengths per second (approximately 100 mm s(-1)), and propulsive forces of up to 3.5 N were achieved, with a non-dimensional cost of transport of 1.42 with all eight arms and of 0.9 with only two active arms. The experiments confirmed the computational results and verified the multi-arm maneuverability and simultaneous object grasping capability of such systems.

/pdf/octopus-inspired-multi-arm-robotic-swimming-4r9ynuko8r.pdf

Michael Sfakiotakis

Papers

Review of fish swimming modes for aquatic locomotion

A multi-coil inductive powering system for an endoscopic capsule with vibratory actuation

Biomimetic Centering for Undulatory Robots

An experimental undulating-fin device using the parallel bellows actuator

Octopus-inspired multi-arm robotic swimming