A classification of stability margins for walking robots

Throughout the history of walking robots several static and dynamic stability criteria have been defined. Nevertheless, different applications may require different stability criteria and, up to the authors’ best knowledge, there is no qualitative classification of such stability measurements. Controlling a robot gait by means of using the wrong stability criterion may prevent the task from succeeding. By the other hand, if the optimum criterion is found the robot gait can also be optimized. In this work, the stability criteria that have been applied to walking robots with at least four legs are examined attending to the stability margin on different static and dynamic situations. As a result, a qualitative classification of stability criteria for walking machines is proposed so that the proper criterion can be chosen for every desired application.Peer reviewe

Hexapod robot stability research

El trabajo consiste en una primera parte en la que se estudia analíticamente la composición del robot hexápodo, descomponiéndolo en sus diferentes componentes físicos así como una introducción a la estabilidad del robot, tipos de estabilidad y métodos para su análisis.Grado en Ingeniería en Electrónica Industrial y Automátic

Analytical Workspace, Kinematics, and Foot Force Based Stability of Hexapod Walking Robots

Many environments are inaccessible or hazardous for humans. Remaining debris after earthquake and fire, ship hulls, bridge installations, and oil rigs are some examples. For these environments, major effort is being placed into replacing humans with robots for manipulation purposes such as search and rescue, inspection, repair, and maintenance. Mobility, manipulability, and stability are the basic needs for a robot to traverse, maneuver, and manipulate in such irregular and highly obstructed terrain. Hexapod walking robots are as a salient solution because of their extra degrees of mobility, compared to mobile wheeled robots. However, it is essential for any multi-legged walking robot to maintain its stability over the terrain or under external stimuli. For manipulation purposes, the robot must also have a sufficient workspace to satisfy the required manipulability. Therefore, analysis of both workspace and stability becomes very important. An accurate and concise inverse kinematic solution for multi-legged robots is developed and validated. The closed-form solution of lateral and spatial reachable workspace of axially symmetric hexapod walking robots are derived and validated through simulation which aid in the design and optimization of the robot parameters and workspace. To control the stability of the robot, a novel stability margin based on the normal contact forces of the robot is developed and then modified to account for the geometrical and physical attributes of the robot. The margin and its modified version are validated by comparison with a widely known stability criterion through simulated and physical experiments. A control scheme is developed to integrate the workspace and stability of multi-legged walking robots resulting in a bio-inspired reactive control strategy which is validated experimentally

Bacterial motion and spread in porous environments

Micro-swimmers are ubiquitous in nature from soil and water to mammalian bodies and even many technological processes. Common known examples are microbes such as bacteria, micro-algae and micro-plankton, cells such as spermatozoa and organisms such as nematodes. These swimmers live and have evolved in multiplex environments and complex flows in the presence of other swimmers and types, inert particles and fibers, interfaces and non-trivial confinements and more. Understanding the locomotion and interactions of these individual micro-swimmers in such impure viscous fluids is crucial to understanding the emergent dynamics of such complex systems, and to further enabling us to control and direct this dynamics. The focus is on studying through mathematical modeling, analysis and computer simulations, the collective dynamics and chemotactic aggregation of a suspension of micro-swimmers immersed in a fluid that also contains inert impurities or stationary obstacles. Such an environment can be regarded as a wet porous medium. A continuum model for micro-swimmers in such a wet porous medium that accounts for the presence of the impurities or obstacles through the Brinkman approximation, which encompasses their effect using a resistance or friction parameter in the fluid flow equations is presented. This resistance introduces supplementary friction in the individual locomotion and alters the way each swimmer disturbs the surrounding fluid and the hydrodynamic interaction with its neighbors. The analysis of the linearized system reveals that the resistance affects and hinders the hydrodynamic interactions and collective swimming. Asymptotic analysis and the numerical solution of the dispersion relations help compose a parameter phase space for four predicted and distinct types of dynamics: hydrodynamic collective swimming, chemotactic aggregation, dynamic aggregation, and uniform motion. Simulations of the full nonlinear system show that resistance impacts the collective dynamics for each of these dynamics states. Firstly, resistance inhibits the collective motion of the swimmers. In an environment where resistance is strong, the swimmers find it challenging to synchronize their movements and form cohesive groups. The presence of obstacles and the associated resistance disrupt the fluid flow patterns collectively generated by the swimmers, leading to a less organized or coherent collective behavior. Secondly and surprisingly, resistance hampers the chemotactic behavior of swimmers. Chemotaxis is the process by which micro-swimmers respond to chemical gradients and move towards regions of higher concentration; if the chemical is produced by the swimmers themselves as in quorum sensing scenarios, this leads to aggregation. However resistance hinders the ability of pusher swimmers to aggregate and form dense clusters because it impedes their ability to efficiently navigate towards chemotactic cues and assemble into concentrated populations. Simulations also reveal unexpected dynamics far from the parameter regimes predicted by the linear analysis, ultimately showcasing the nonlinear couplings in this complex system. Lastly, resistance restricts the spreading of an already accumulated swimmer suspension, for example a bacterial cluster. When swimmers are already clustered or perhaps introduced into a specific region, resistance impedes their ability to disperse to other areas of the medium, effectively detaining them to localized regions and reducing their ability to spread out and cover larger distances. These findings show that complex emergent dynamics also depends on the initial state of the system, and ultimately help towards better understanding of recent experimental observations

The behavioural significance of animal play

Play is frequently reported to be difficult to define but nevertheless easy to recognise. Other workers' attempts at definition are reviewed. These commonly involve initial subjective recognition of play followed by description in terms of characteristics which are frequently shared with the play of other species. Play appears to have certain associated costs and is therefore assumed to benefit the animal in some way in order to justify its existence in evolutionary terms, but the nature of this benefit is unknown. Theories regarding the functions of play are discussed in the light of its properties and potential costs. Chapter 2 describes an experiment to test the common assumption that observers agree on what constitutes play. Comparison of the judgements of the ten naive observers on the behaviour of young rats indicated that the majority agreed, and the activities which they called play formed the basis of the working definition of rat play which is used in the studies described below. A longitudinal study of aspects of the play and other behaviour of littermate groups of rats is described in Chapter 3. The quantitative findings are used to test the validity of certain characteristics for rat play. The experiments described in Chapters 4 and 5 examined aspects of the rat's motivation to play. The nature of recent social experience was found to influence the rat's tendency to play, and a series of choice experiments showed that play was highly reinforcing by comparison with other forms of social experience. The extent to which existing definitions of play can be applied to that of rats is examined in the light of the observational and experimental evidence described in Chapters 2-5 concerning its characteristics. The cost of play for rats is estimated using indirect evidence and tentative suggestions are made as to its functions

Stabilizer architecture for humanoid robots collaborating with humans

Hoy en día, los avances en las tecnologías de información y comunicación permiten el uso de robots como compañeros en las actividades con los seres humanos. Mientras que la mayoría de las investigaciones existentes se dedica a la interacción entre humanos y robots, el marco de esta investigación está centrado en el uso de robots como agentes de colaboración. En particular, este estudio está dedicado a los robots humanoides que puedan ayudar a la gente en varias tareas en entornos de trabajo. Los robots humanoides son sin duda los m as adecuados para este tipo de situaciones: pueden usar las mismas herramientas que los seres humanos y son lo m as probablemente aceptados por ellos. Después de explicar las ventajas de las tareas de colaboración entre los humanos y los robots y las diferencias con respecto a los sistemas de interacción y de teleoperación, este trabajo se centra en el nivel de las tecnologías que es necesario para lograr ese objetivo. El problema más complicado en el control de humanoides es el balance de la estructura. Este estudio se centra en técnicas novedosas para la estimación de la actitud del robot, que se utilizarán para el control. El control del robot se basa en un modelo muy conocido y simplificado: el péndulo invertido. Este modelo permite tener un control en tiempo real sobre la estructura, mientras que esté sometida a fuerzas externas / disturbios. Trayectorias suaves para el control de humanoides se han propuesto y probado en plataformas reales: éstos permiten reducir los impactos del robot con su entorno. Finalmente, el estudio extiende estos resultados a una contribución para la arquitectura de colaboración humano-humanoide. Dos tipos de colaboraciones humano humanoide se analizan: la colaboración física, donde robots y humanos comparten el mismo espacio y tienen un contacto físico (o por medio de un objeto), y una colaboración a distancia, en la que el ser humano está relativamente lejos del robot y los dos agentes colaboran por medio de una interfaz. El paradigma básico de esta colaboración robótica es: lo que es difícil (o peligroso) para el ser humano se hace por medio del robot y lo que es difícil para el robot lo puede mejor hacer el humano. Es importante destacar que el contexto de los experimentos no se basa en una unica plataforma humanoide; por el contrario, tres plataformas han sido objeto de los experimentos: se han empleado los robots HOAP-3, HRP-2 y TEO. ----------------------------------------------------------------------------------------------------------------------------------------------------------Nowadays, the advances in information and communication technologies permit the use of robots as companions in activities with humans. While most of the existing research is dedicated to the interaction between humans and robots, the framework of this research is the use of robots as collaborative agents. In particular, this study is dedicated to humanoid robots which should assist people in several tasks in working environments. Humanoid robots are certainly the most adequate for such situations: they can use the same tools as humans and are most likely accepted by them. After explaining the advantages of collaborative tasks among humans and robots and the differences with respect to interaction and teleoperation systems, this work focuses on the level of technologies which is necessary in order to achieve such a goal. The most complicated problem in humanoid control is the structure balance. This study focuses in novel techniques in the attitude estimation of the robot, to be used for the control. The control of the robot is based on a very well-known and simplified model: the double inverted pendulum. This model permits having a real-time control on the structure while submitted to external forces/disturbances. The control actions are strongly dependent on the three stability regions, which are determined by the position of the ZMP in the support polygon. Smooth trajectories for the humanoid control have been proposed and tested on real platforms: these permit reducing the impacts of the robot with its environment. Finally, the study extends these results to a contribution for human-humanoid collaboration architecture. Two types of human-humanoid collaborations are analyzed: a physical collaboration, where robot and human share the same space and have a physical contact (or by means of an object), and a remote collaboration, in which the human is relatively far away from the robot and the two agents collaborate using an interface. The basic paradigm for this robotic collaboration is: what is difficult (or dangerous) for the human is done by the robot and what is difficult for the robot is better done by the human. Importantly, the testing context is not based on a single humanoid platform; on the contrary, three platforms have been object of the experiments: the Hoap-3, HRP-2 and HRP2 robot have been employed

Reimagining Robotic Walkers For Real-World Outdoor Play Environments With Insights From Legged Robots: A Scoping Review

PURPOSE For children with mobility impairments, without cognitive delays, who want to participate in outdoor activities, existing assistive technology (AT) to support their needs is limited. In this review, we investigate the control and design of a selection of robotic walkers while exploring a selection of legged robots to develop solutions that address this gap in robotic AT. METHOD We performed a comprehensive literature search from four main databases: PubMed, Google Scholar, Scopus, and IEEE Xplore. The keywords used in the search were the following: “walker”, “rollator”, “smart walker”, “robotic walker”, “robotic rollator”. Studies were required to discuss the control or design of robotic walkers to be considered. A total of 159 papers were analyzed. RESULTS From the 159 papers, 127 were excluded since they failed to meet our inclusion criteria. The total number of papers analyzed included publications that utilized the same device, therefore we classified the remaining 32 studies into groups based on the type of robotic walker used. This paper reviewed 15 different types of robotic walkers. CONCLUSIONS The ability of many-legged robots to negotiate and transition between a range of unstructured substrates suggests several avenues of future consideration whose pursuit could benefit robotic AT, particularly regarding the present limitations of wheeled paediatric robotic walkers for children’s daily outside use. For more information: Kod*lab (link to kodlab.seas.upenn.edu

3D numerical modeling of cell migration and cell-cell interaction

Cell migration has an important role in physiological, biological and pathological processes such as tissue morphogenesis, cell differentiation, cell proliferation, cancer development, wound healing, as well as in tissue engineering applications [1,2]. Although cell behavior during migration is not completely clear for scientists yet, it has conclusively been known that mechanical and biochemical factors strongly affect cell locomotion. Mechanical changes in a substrate, such as topographical features, boundary conditions and stiffness distribution of substrate are all thought to guide and control cell migration. There are many 2D models describing cell behavior on a substrate [3], but there are only few 3D models for this purpose [4]. Majority of them just describe a single cell migration [4], while others study the behavior of high cell populations [5]. One major problem with some of these models is that they fail to properly balance the active locomotive forces acting on the cell or generated by the cell, in some cases the models do not even include them. Some models have an active force that moves the cell, but there is no discussion on where that force is applied. The model described by Borau et al. considers the maximum principal stess for the reorientation of cell and cytoskeleton which is not accurate enough [4]. In this work we will present an improved 3D computational model to investigate the effects of the mechanical properties of the substrate on cell migration. The main objective of this project is to understand the effect of substrate stiffness on cell migration, traction force, velocity and etc. Besides, we will study how deeply the cell feels during surface migration and how the cells interact each other when they are embedded in the same substrate. To validate our model, apart from comparing the obtained results with previous experimental [6] and numerical models [4,5], we will implement experimental part which includes preparation of 3D gel with desired boundary conditions and monitoring of cell behavior during migration. To monitor the cell behavior we are going to use fluorescence microscopy to record the cell movement. This experimental part will be performed by collaboration with laboratory of Aragon Institute of Engineering Research (i3A). Refrences [1] H. Behesti and S. Marino. Cerebellar granule cells: Insights into proliferation, differentiation, and role in medulloblastoma pathogenesis. Journal Applied Physiology, 41:435445, 2009. [2] P. Martin. Wound healing: aiming for perfect skin regeneration. Science, 276:75 81, 1997. [3] P. Moreo, J.M. Garcia-Aznar, and M. Doblaré. Modeling mechanosensing and its e˙ect on the migration and proliferation of adherent cells. Acta Biomaterialia, 4:613621, 2008. [4] C. Borau, R.D. Kamm, and J.M. García-Aznar. Mechano-sensing and cell migration: a 3d model approach. Journal Physical Biology, 8:107888, 2011. [5] E. Palsson. A three-dimensional model of cell movement in multicellular systems. Future Generation Computer System, 17:835852, 2001. [6] E. Hadjipanayi, V. Mudera, and R.A. Brown. Guiding cell migration in 3d: A collagen matrix with graded directional sti˙ness. Cell Motility and the Cytoskeleton, 66:435445, 2009

Planning and Control Strategies for Motion and Interaction of the Humanoid Robot COMAN+

Despite the majority of robotic platforms are still confined in controlled environments such as factories, thanks to the ever-increasing level of autonomy and the progress on human-robot interaction, robots are starting to be employed for different operations, expanding their focus from uniquely industrial to more diversified scenarios. Humanoid research seeks to obtain the versatility and dexterity of robots capable of mimicking human motion in any environment. With the aim of operating side-to-side with humans, they should be able to carry out complex tasks without posing a threat during operations. In this regard, locomotion, physical interaction with the environment and safety are three essential skills to develop for a biped. Concerning the higher behavioural level of a humanoid, this thesis addresses both ad-hoc movements generated for specific physical interaction tasks and cyclic movements for locomotion. While belonging to the same category and sharing some of the theoretical obstacles, these actions require different approaches: a general high-level task is composed of specific movements that depend on the environment and the nature of the task itself, while regular locomotion involves the generation of periodic trajectories of the limbs. Separate planning and control architectures targeting these aspects of biped motion are designed and developed both from a theoretical and a practical standpoint, demonstrating their efficacy on the new humanoid robot COMAN+, built at Istituto Italiano di Tecnologia. The problem of interaction has been tackled by mimicking the intrinsic elasticity of human muscles, integrating active compliant controllers. However, while state-of-the-art robots may be endowed with compliant architectures, not many can withstand potential system failures that could compromise the safety of a human interacting with the robot. This thesis proposes an implementation of such low-level controller that guarantees a fail-safe behaviour, removing the threat that a humanoid robot could pose if a system failure occurred