Papers by Dimitris Tsakiris
IFAC Proceedings Volumes, Sep 1, 1994
The nonholonomic motion planning problem is considered for a novel class of modular mobile manipu... more The nonholonomic motion planning problem is considered for a novel class of modular mobile manipulators, where each module is implemented as a planar parallel manipulator with idler wheels. This assembly is actuated by s h a p e c hanges of its modules, which, under the in uence of the nonholonomic constraints on the wheels, induce a global snake{like motion of the assembly. The kinematics for a 2{ module assembly of this type are formulated and the corresponding motion planning problem is studied.
IEEE Transactions on Robotics, Dec 1, 2007
A biological paradigm of versatile locomotion and effective motion control is provided by the pol... more 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 rowinglike 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.
International Journal of Modelling and Simulation, 2006
This paper presents SIMUUN, a block-based simulation environment, which has been developed on top... more This paper presents SIMUUN, a block-based simulation environment, which has been developed on top of Matlab/Simulink TM , in order to facilitate research into various aspects of undulatory locomotion in biology and robotics. Simulations of snake-like mechanisms are set up in this environment by connecting customizable SIMUUN body segment modules via appropriate joint blocks, which are activated either by explicit or by neuromuscular joint control modules, to propagate a travelling wave along the mechanism. Several force models are included in SIMUUN to characterize the interaction with the locomotion environment, and emulate crawling, walking and swimming. The simulation tools developed were used to study anguilliform swimming in robotics and in biology, and assess the effect of different body configurations on gait generation. Related simulation results are presented to illustrate the versatility of these tools and the potential of their use in a variety of domains.
Polychaete annelid worms provide a biological paradigm of versatile locomotion and effective moti... more 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.
IFAC-PapersOnLine, 2017
Increasing the functionality and efficiency of small underwater marine robotic systems has been a... more Increasing the functionality and efficiency of small underwater marine robotic systems has been a significant challenge, particularly regarding their use in tasks requiring enhanced maneuverability, long-distance travel and delicate underwater manipulation of objects. In this paper, we explore the impact of bio-inspired arm morphology on underwater propulsion, through examination of the generated hydrodynamic forces and the corresponding complex vortical patterns in the wake of a novel two-arm underwater robotic swimmer, inspired by the octopus arm-swimming behavior. We demonstrate for the first time, via detailed modelling and CFD studies, the use of a variety of slender arm morphologies as thrust actuators in a system that can achieve forward propulsion, by the slow opening and rapid closing of these arms ("arm sculling"), while minimizing the lateral excursion of the system. Robotic prototypes, based on such principles, have already been used by our group to observe marine ecosystems, without disturbing them as much as current ROVs. Further applications of such robotic systems could be envisioned in future medical rehabilitation studies.
Computers & Fluids, 2018
The propulsive efficiencies of multi-functional appendage configurations in a small dragbased swi... more The propulsive efficiencies of multi-functional appendage configurations in a small dragbased swimmer are investigated computationally. Due to the lack of actual actuators to measure input power, efficiency is evaluated indirectly and may be instinctively associated to higher production of forward thrust. However, the relation is not intuitively self-evident, since the shape of the propulsive system is known to influence the generation of hydrodynamic forces, along with the particular kinematics used, which in turn affect the power consumption. The current article investigates this topic in the case of a reduced-size appendage-based swimmer producing small values of thrust, and discusses the role of design in the relation between propulsive efficiency and thrust production under a "sculling" kinematic motion profile. The study implements seven different shapes of appendages, inspired by both the biology and engineering, which perform a dragbased swimming pattern while being attached, in pairs, at the dorsal side of a common body. The work utilises an immersed boundary approach to solve numerically the fluid equations and capture the flow patterns around the swimmer. The results contribute to our understanding of drag-based propulsive systems and may influence the development of novel underwater robotic systems and limb prosthetic devices for underwater rehabilitation.
2016 24th Mediterranean Conference on Control and Automation (MED), 2016
The present paper investigates the effect of compliance on the locomotion of a biologically-inspi... more The present paper investigates the effect of compliance on the locomotion of a biologically-inspired soft-body pedundulatory robotic system, employing lateral undulations of its elongated body, which are augmented by the oscillation of sets of lateral appendages (parapodia), to propel itself on unstructured granular substrates. We explore control strategy alternatives for the robot to generate two different locomotor gaits by employing direct or retrograde lateral body waves, combined with appropriately coordinated parapodial motion (pedundulatory modes). Computational models of this class of robots have been devised, which demonstrate the effects of joint compliance on gait generation and on the characteristics of robot propulsion. A new three-segment soft-body robotic prototype has been developed, whose body was fabricated by molding polyurethane elastomers, and was tested extensively on an experimental sandbox, on various formations of the granular substrate, to compare the performance of stiff and compliant joints. Body and joint compliance were found to enhance the adaptability of the robot to environmental irregularities, however they may deteriorate the proper formation of the undulatory body wave, degrading somewhat system performance in terms of the attained velocities.
2015 IEEE International Conference on Robotics and Automation (ICRA), 2015
The octopus uses the arm-swimming behavior primarily for escape, defense, or foraging. This mode ... more 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.
2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2015
The present paper considers the modeling, control, development and experimental validation of bio... more 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.
The present work considers corridor-following maneuvers for nonholonomic mobile robots, guided by... more The present work considers corridor-following maneuvers for nonholonomic mobile robots, guided by sensory data acquired by panoramic cameras. The panoramic vision system provides information from an environment with textured walls to the motion control system, which drives the robot along a corridor. Panoramic cameras have a 360 visual field, a capability that the proposed control methods exploit. In our sensor-based control scheme, optical flow information from several distinct viewing directions in the entire field of view of the panoramic camera is used directly in the control loop, without the need for state reconstruction. The interest of this lies in the fact that the optical flow information is not sufficient to reconstruct the state of the system, it is however sufficient for the proposed control law to accomplish the desired task. Driving the robot along a corridor amounts to the asymptotic stabilization of a subsystem of the robot's kinematics and the proposed control schemes are shown to achieve this goal.
I n its continuous attempt to build intelligent artificial creatures, robotics has often been ins... more I n its continuous attempt to build intelligent artificial creatures, robotics has often been inspired by nature. Particularly interesting is the remarkable variety of lightsensing structures and information processing strategies occurring in animal visual systems. The physiology of these systems appears to have been influenced, through evolution, by the ecological niche and lifestyle of each animal species. Insects such as bees, ants, and flies have become a particularly appealing source of inspiration because of the remarkable navigational capabilities they display, despite their relatively restricted neural system. This, apparently, forced them to develop solutions to navigation tasks, which are ingenious in their simplicity and robust in their implementation, both of which are invaluable characteristics for robotic systems. The navigation task examined in this work is the centering behavior, which consists of moving in the middle of a corridor-like environment. Bees are able to accomplish similar tasks by exploiting three features of their visuo-motor system: the wide field of view of their eyes, their ability to estimate retinal motion, and a control mechanism that reorients their flight so that retinal motion in the two eyes remains balanced [1]. Inspired by this biological solution, we attempt to create a reactive, vision-based centering behavior for a nonholonomic mobile robot equipped with a panoramic camera, providing a 360 • visual field and a sensor-based control law, where optical flow information from several distinct directions in the entire field of view of the panoramic camera is used directly in the control loop. No reconstruction of the robot's state is attempted; the information extracted from the sensory data is not sufficient for this. It is, however, sufficient for the proposed control law to accomplish the desired task. The use of a panoramic camera, as opposed to that of a multicamera setup or of a mechanism that reorients the gaze of a typical perspective camera, simplifies the processing of the sensory information and reduces the complexity of the required hardware. A detailed theoretical analysis, followed by extensive experimentation, demonstrates the effectiveness of this biologically motivated approach. From Insects to Robots Fundamental analogies exist between the behaviors that biological organisms and robots exhibit: mobile robots should be able to perceive the static and dynamic aspects of their environment and modify their behavior accordingly, very much like their biological counterparts. In insects, the centering behavior facilitates safe navigation by maximizing the animal's distance from surrounding obstacles. For the same reason, this type of behavior is important for robots, particularly those operating in man-made, indoor environments with many corridors and narrow passages through which the robot must safely navigate.
We consider robotic analogues of the arms of the octopus, a cephalopod exhibiting a wide variety ... more 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.
Biomimetic and Biohybrid Systems, 2018
This paper considers aquatic swimming of a pedundulatory bio-robotic system, inspired by the outs... more This paper considers aquatic swimming of a pedundulatory bio-robotic system, inspired by the outstanding aquatic and terrestrial locomotion capabilities of the polychaete annelid marine worms. The robot employs lateral undulations of its elongated body, augmented by the oscillation of active lateral appendages (parapodia), to propel itself. The efficient propulsion and terrain adaptability of such robots on unstructured terrestrial substrates have been demonstrated in previous work. Here, we explore gait generation for underwater propulsion by direct (tail-to-head) lateral body waves, either alone (undulatory modes) or combined with appropriately coordinated parapodial motion (pedundulatory modes). A three-segment compliant-body robotic prototype is used, whose body was fabricated by molding polyurethane elastomers. This robot was tested in a laboratory water tank, to demonstrate the advantage gained from the exploitation of both tail-to-head body undulations and parapodia for underwater swimming. The forward speed may more than double and the propulsive force may increase ten-fold, compared to the case where only undulations are used.
The Young Scholars Program at the Institute for Systems Research of the University of Maryland at... more The Young Scholars Program at the Institute for Systems Research of the University of Maryland at College Park is an innovative summer research experience for high school students from Maryland, Virginia, and Washington D.C. Its goal is to steer talented high school seniors toward higher education and careers in science and engineering. One particularly popular component of this program is a two-week mini-course in robotics. This course utilizes the resources of the Intelligent Servosystems Laboratory of the university to introduce and demonstrate theoretical and practical aspects of robotics. This paper reports on the characteristics that make this a unique e#ort in robotics-related education for both the Young Scholars Program participants and the small group of University of Maryland graduate students who have been responsible for the development and instruction of this course. 1 Introduction The Young Scholars Program (YSP) is an innovative summer research experience for ...
Bioinspiration & Biomimetics, 2015
Computers & Fluids, 2015
The complexity in structure and locomotion of cephalopods, such as the octopus, poses difficultie... more The complexity in structure and locomotion of cephalopods, such as the octopus, poses difficulties in modeling and simulation. Their slender arms, being highly agile and dexterous, often involve intense deformations, which are hard to simulate accurately, while simultaneously ensuring numerical stability and low diffusion of the transient motion results. Within the Immersed-Boundary framework, this paper focuses on an arm geometry performing prescribed motions that reflect octopus locomotion. The method is compared with a Finite-Volume numerical approach to determine the mesh requirements that must be employed for sufficiently capturing, not only the near wall viscous flow, but also the off-body vortical flow field in intense forced motions. The objective is to demonstrate and exploit the generality of the immersed boundary approach to complex numerical simulations of deforming geometries. Incorporation of arm deformation was found to increase the output thrust of a single-arm system. It was further found that sculling motion combined with arm undulations provides an effective propulsive scheme for an octopus-like arm.
Procedia Engineering, 2011
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Papers by Dimitris Tsakiris