1,720,960 research outputs found
Online Optimization-based Gait Adaptation of Quadruped Robot Locomotion
No full textQuadruped robots demonstrated extensive capabilities of traversing complex and unstructured
environments. Optimization-based techniques gave a relevant impulse to the research on legged
locomotion. Indeed, by designing the cost function and the constraints, we can guarantee the
feasibility of a motion and impose high-level locomotion tasks, e.g., tracking of a reference
velocity. This allows one to have a generic planning approach without the need to tailor a
specific motion for each terrain, as in the heuristic case. In this context, Model Predictive
Control (MPC) can compensate for model inaccuracies and external disturbances, thanks to
the high-frequency replanning.
The main objective of this dissertation is to develop a Nonlinear MPC (NMPC)-based
locomotion framework for quadruped robots. The aim is to obtain an algorithm which can
be extended to different robots and gaits; in addition, I sought to remove some assumptions
generally done in the literature, e.g., heuristic reference generator and user-defined gait
sequence.
The starting point of my work is the definition of the Optimal Control Problem to generate
feasible trajectories for the Center of Mass. It is descriptive enough to capture the linear and
angular dynamics of the robot as a whole. A simplified model (Single Rigid Body Dynamics
model) is used for the system dynamics, while a novel cost term maximizes leg mobility
to improve robustness in the presence of nonflat terrain. In addition, to test the approach
on the real robot, I dedicated particular effort to implementing both a heuristic reference
generator and an interface for the controller, and integrating them into the controller framework
developed previously by other team members.
As a second contribution of my work, I extended the locomotion framework to deal with a
trot gait. In particular, I generalized the reference generator to be based on optimization.
Exploiting the Linear Inverted Pendulum model, this new module can deal with the underactuation of the trot when only two legs are in contact with the ground, endowing the NMPC
with physically informed reference trajectories to be tracked. In addition, the reference velocities are used to correct the heuristic footholds, obtaining contact locations coherent with
the motion of the base, even though they are not directly optimized.
The model used by the NMPC receives as input the gait sequence, thus with the last part
of my work I developed an online multi-contact planner and integrated it into the MPC
framework. Using a machine learning approach, the planner computes the best feasible option,
even in complex environments, in a few milliseconds, by ranking online a set of discrete options
for footholds, i.e., which leg to move and where to step. To train the network, I designed
a novel function, evaluated offline, which considers the value of the cost of the NMPC and
robustness/stability metrics for each option.
These methods have been validated with simulations and experiments over the three years. I
tested the NMPC on the Hydraulically actuated Quadruped robot (HyQ) of the IIT’s Dynamic
Legged Systems lab, performing omni-directional motions on flat terrain and stepping on
a pallet (both static and relocated during the motion) with a crawl gait. The trajectory
replanning is performed at high-frequency, and visual information of the terrain is included to
traverse uneven terrain. A Unitree Aliengo quadruped robot is used to execute experiments
with the trot gait. The optimization-based reference generator allows the robot to reach a
fixed goal and recover from external pushes without modifying the structure of the NMPC.
Finally, simulations with the Solo robot are performed to validate the neural network-based
contact planning. The robot successfully traverses complex scenarios, e.g., stepping stones,
with both walk and trot gaits, choosing the footholds online.
The achieved results improved the robustness and the performance of the quadruped locomotion.
High-frequency replanning, dealing with a fixed goal, recovering after a push, and the automatic
selection of footholds could help the robots to accomplish important tasks for the humans,
for example, providing support in a disaster response scenario or inspecting an unknown
environment.
In the future, the contact planning will be transferred to the real hardware. Possible developments foresee the optimization of the gait timings, i.e., stance and swing duration, and a
framework which allows the automatic transition between gaits
Accelerating Model Predictive Control for Legged Robots through Distributed Optimization
No full textThis paper presents a novel approach to enhance Model Predictive Control (MPC) for legged robots through Distributed Optimization. Our method focuses on decomposing the robot dynamics into smaller, parallelizable subsystems, and utilizing the Alternating Direction Method of Multipliers (ADMM) to ensure consensus among them. Each subsystem is managed by its own Optimal Control Problem, with ADMM facilitating consistency between their optimizations. This approach not only decreases the computational time but also allows for effective scaling with more complex robot configurations, facilitating the integration of additional subsystems such as articulated arms on a quadruped robot. We demonstrate, through numerical evaluations, the convergence of our approach on two systems with increasing complexity. In addition, we showcase that our approach converges towards the same solution when compared to a state-of-the-art centralized whole-body MPC implementation. Moreover, we quantitatively compare the computational efficiency of our method to the centralized approach, revealing up to a 75% reduction in computational time. Overall, our approach offers a promising avenue for accelerating MPC solutions for legged robots, paving the way for more effective utilization of the computational performance of modern hardware
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Foothold Evaluation Criterion for Dynamic Transition Feasibility for Quadruped Robots
No full textTo traverse complex scenarios reliably a legged robot needs to move its base aided by the ground reaction forces, which can only be generated by the legs that are momentarily in contact with the ground. A proper selection of footholds is crucial for maintaining balance. In this paper, we propose a foothold evaluation criterion that considers the transition feasibility for both linear and angular dynamics to overcome complex scenarios. We devise convex and nonlinear formulations as a direct extension of [1] in a receding-horizon fashion to grant dynamic feasibility for future behaviours. The criterion is integrated with a Vision-based Foothold Adaptation (VFA) strategy that takes into account the robot kinematics, leg collisions and terrain morphology. We verify the validity of the selected footholds and the generated trajectories in simulation and experiments with the 90kg quadruped robot Hy
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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