Legged locomotion over irregular terrains: State of the art of human and robot performance

Legged robotic technologies have moved out of the lab to operate in real environments, characterized by a wide variety of unpredictable irregularities and disturbances, all this in close proximity with humans. Demonstrating the ability of current robots to move robustly and reliably in these conditions is becoming essential to prove their safe operation. Here, we report an in-depth literature review aimed at verifying the existence of common or agreed protocols and metrics to test the performance of legged system in realistic environments. We primarily focused on three types of robotic technologies, i.e., hexapods, quadrupeds and bipeds. We also included a comprehensive overview on human locomotion studies, being it often considered the gold standard for performance, and one of the most important sources of bioinspiration for legged machines. We discovered that very few papers have rigorously studied robotic locomotion under irregular terrain conditions. On the contrary, numerous studies have addressed this problem on human gait, being nonetheless of highly heterogeneous nature in terms of experimental design. This lack of agreed methodology makes it challenging for the community to properly assess, compare and predict the performance of existing legged systems in real environments. On the one hand, this work provides a library of methods, metrics and experimental protocols, with a critical analysis on the limitations of the current approaches and future promising directions. On the other hand, it demonstrates the existence of an important lack of benchmarks in the literature, and the possibility of bridging different disciplines, e.g., the human and robotic, towards the definition of standardized procedure that will boost not only the scientific development of better bioinspired solutions, but also their market uptake

Reverse-engineering the locomotion of a stem amniote

Reconstructing the locomotion of extinct vertebrates offers insights into their palaeobiology and helps to conceptualize major transitions in vertebrate evolution. However, estimating the locomotor behaviour of a fossil species remains a challenge because of the limited information preserved and the lack of a direct correspondence between form and function. The evolution of advanced locomotion on land—that is, locomotion that is more erect, balanced and mechanically power-saving than is assumed of anamniote early tetrapods—has previously been linked to the terrestrialization and diversification of amniote lineages. To our knowledge, no reconstructions of the locomotor characteristics of stem amniotes based on multiple quantitative methods have previously been attempted: previous methods have relied on anatomical features alone, ambiguous locomotor information preserved in ichnofossils or unspecific modelling of locomotor dynamics. Here we quantitatively examine plausible gaits of the stem amniote Orobates pabsti, a species that is known from a complete body fossil preserved in association with trackways8. We reconstruct likely gaits that match the footprints, and investigate whether Orobates exhibited locomotor characteristics that have previously been linked to the diversification of crown amniotes. Our integrative methodology uses constraints derived from biomechanically relevant metrics, which also apply to extant tetrapods. The framework uses in vivo assessment of locomotor mechanics in four extant species to guide an anatomically informed kinematic simulation of Orobates, as well as dynamic simulations and robotics to filter the parameter space for plausible gaits. The approach was validated using two extant species that have different morphologies, gaits and footprints. Our metrics indicate that Orobates exhibited more advanced locomotion than has previously been assumed for earlier tetrapods, which suggests that advanced terrestrial locomotion preceded the diversification of crown amniotes. We provide an accompanying website for the exploration of the filters that constrain our simulations, which will allow revision of our approach using new data, assumptions or methods

Ensamblaje e implementación de arquitectura cuadrúpeda modular

This paper describes the assembling process of a quadrupedal architecture using the modular robotic system Mecabot. Several possible topologies are addressed to finally opt for a design that allows the use of an active column. Based on this, the mathematical model of the control is proposed to perform the movements of displacement, open turn and rotation. The locomotion profiles for these first two movement modalities are bio-inspired. For the rotation modality, a characteristic quadrupedal robot transition is used to allow the correct rotation execution without using a great number of degrees of freedom. The robot is tested on structured and unstructured terrains by measuring its speed in function of the movement frequency variation. For the open turn modality, the described circumference radius is measured in function of the offset variation. With the tests, the second Mecabot configuration with legs is finally obtained complementing the research work carried out for apodal configurations (snake, wheel caterpillar) and hexapod.En este documento se describe el proceso de ensamblaje de una arquitectura cuadrúpeda utilizando el sistema robótico modular Mecabot. Varias posibles topologías son abordadas para finalmente optar por un diseño que permita emplear una columna activa. En base a ello es planteado el modelo matemático del control para realizar los movimientos de desplazamiento, giro abierto y giro cerrado. Los perfiles de locomoción que debe ejecutar el robot para estas dos primeras modalidades de movimiento son bioinspirados. Para la modalidad de giro cerrado se emplea una transición característica de los robots cuadrúpedos con el fin de poder seguir ejecutando correctamente la rotación sin necesidad de emplear un número mayor de grados de libertad. El robot es probado en terrenos estructurados y no estructurados midiendo su velocidad en función de la variación de la frecuencia de movimiento, para la modalidad de giro abierto se mide el radio de la circunferencia descrito en función de la variación del offset. Con las pruebas realizadas finalmente se obtiene la segunda configuración con patas implementada en el Mecabot, complementando así los trabajos de investigación previamente realizados para la configuración hexápoda y configuraciones ápodas (serpiente, oruga rueda)

Pattern Generation for Rough Terrain Locomotion with Quadrupedal Robots:Morphed Oscillators & Sensory Feedback

Animals are able to locomote on rough terrain without any apparent difficulty, but this does not mean that the locomotor system is simple. The locomotor system is actually a complex multi-input multi-output closed-loop control system. This thesis is dedicated to the design of controllers for rough terrain locomotion, for animal-like quadrupedal robots. We choose the problem of blind rough terrain locomotion as the target of experiments. Blind rough terrain locomotion requires continuous and momentary corrections of leg movements and body posture, and provides a proper testbed to observe the interaction of different mod- ules involved in locomotion control. As for the specific case of this thesis, we have to design rough terrain locomotion controllers that do not depend on the torque-control capability, have limited sensing, and have to be computationally light, all due to the properties of the robotics platform that we use. We propose that a robust locomotion controller, taking into account the aforementioned constraints, is constructed from at least three modules: 1) pattern generators providing the nominal patterns of locomotion; 2) A posture controller continuously adjusting the attitude of the body and keeping the robot upright; and 3) quick reflexes to react to unwanted momentary events like stumbling or an external force impulse. We introduce the framework of morphed oscillators to systematize the design of pattern gen- erators realized as coupled nonlinear oscillators. Morphed oscillators are nonlinear oscillators that can encode arbitrary limit cycle shapes and simultaneously have infinitely large basins of attraction. More importantly, they provide dynamical systems that can assume the role of feedforward locomotion controllers known as Central Pattern Generators (CPGs), and accept discontinuous sensory feedback without the risk of producing discontinuous output. On top of the CPG module, we add a kinematic model-based posture controller inspired by virtual model control (VMC), to control the body attitude. Virtual model control produces forces, and through the application of the Jacobian transpose method, generates torques which are added to the CPG torques. However, because our robots do not have a torque- control capability, we adapt the posture controller by producing task-space velocities instead of forces, thus generating joint-space velocity feedback signals. Since the CPG model used for locomotion generates joint velocities and accepts feedback without the fear of instability or discontinuity, the posture control feedback is easily integrated into the CPG dynamics. More- over, we introduce feedback signals for adjusting the posture by shifting the trunk positions, which directly update the limit cycle shape of the morphed oscillator nodes of the CPG. Reflexes are added, with minimal complexity, to react to momentary events. We implement simple impulse-based feedback mechanisms inspired by animals and successful rough terrain robots to 1) flex the leg if the robot is stumbling (stumbling correction reflex); 2) extend the leg if an expected contact is missing (leg extension reflex); or 3) initiate a lateral stepping sequence in response to a lateral external perturbation. CPG, posture controller, and reflexes are put together in a modular control architecture alongside additional modules that estimate inclination, control speed and direction, maintain timing of feedback signals, etc. [...

Interfacing a salamander brain with a salamander-like robot: Control of speed and direction with calcium signals from brainstem reticulospinal neurons

An important topic in designing neuroprosthetic devices for animals or patients with spinal cord injury is to find the right brain regions with which to interface the device. In vertebrates, an interesting target could be the reticulospinal (RS) neurons, which play a central role in locomotor control. These brainstem cells convey the locomotor commands to the spinal locomotor circuits that in turn generate the complex patterns of muscle contractions underlying locomotor movements. The RS neurons receive direct input from the Mesencephalic Locomotor Region (MLR), which controls locomotor initiation, maintenance, and termination, as well as locomotor speed. In addition, RS neurons convey turning commands to the spinal cord. In the context of interfacing neural networks and robotic devices, we explored in the present study whether the activity of salamander RS neurons could be used to control off-line, but in real time, locomotor speed and direction of a salamander robot. Using a salamander semi-intact preparation, we first provide evidence that stimulation of the RS cells on the left or right side evokes ipsilateral body bending, a crucial parameter involved during turning. We then identified the RS activity corresponding to these steering commands using calcium (Ca2+) imaging of RS neurons in an isolated brain preparation. Then, using a salamander robot controlled by a spinal cord model, we used the ratio of RS Ca2+ signals on left and right sides to control locomotion direction by modulating body bending. Moreover, we show that the robot locomotion speed can be controlled based on the amplitude of the Ca2+ response of RS cells, which is controlled by MLR stimulation strength as recently demonstrated in salamanders

Locomation strategies for amphibious robots-a review

In the past two decades, unmanned amphibious robots have proven the most promising and efficient systems ranging from scientific, military, and commercial applications. The applications like monitoring, surveillance, reconnaissance, and military combat operations require platforms to maneuver on challenging, complex, rugged terrains and diverse environments. The recent technological advancements and development in aquatic robotics and mobile robotics have facilitated a more agile, robust, and efficient amphibious robots maneuvering in multiple environments and various terrain profiles. Amphibious robot locomotion inspired by nature, such as amphibians, offers augmented flexibility, improved adaptability, and higher mobility over terrestrial, aquatic, and aerial mediums. In this review, amphibious robots' locomotion mechanism designed and developed previously are consolidated, systematically The review also analyzes the literature on amphibious robot highlighting the limitations, open research areas, recent key development in this research field. Further development and contributions to amphibious robot locomotion, actuation, and control can be utilized to perform specific missions in sophisticated environments, where tasks are unsafe or hardly feasible for the divers or traditional aquatic and terrestrial robots