1,720,959 research outputs found
Environment Aware Friction Observer with Applications to Force Control Benchmarking
No full textThe benchmarking of force control algorithms has been significantly investigated in recent years. High-fidelity experimental benchmarking outcomes may require high-end electronics and mechanical systems not to compromise the algorithm’s evaluation. However, affordability may be highly desired to spread benchmarking tools within the research community. Mechanical inaccuracies due to affordability can lead to undesired friction effects which in this paper are tackled by exploiting a novel friction compensation technique based on an environment-aware friction observer (EA-FOB). Friction compensation capabilities of the proposed EA-FOB are assessed through simulation and experimental comparisons with a widely used static friction model: Coulomb friction combined with viscous friction. Moreover, a comprehensive stability comparison with state-of-the-art disturbance observers (DOBs) is conducted. Results show higher stability margins for the EA-FOB with respect to traditional DOBs. The research is carried on within the Forecast project, which aims to provide tools and metrics to benchmark force control algorithms relying on low-cost electronics and affordable hardware
Mechatronic Solutions for Force-Controlled Wearable Robotics
No full textThis abstract presents three mechatronic concepts with a high potential for the design of affordable force-controlled exoskeletons. These concepts allow to reduce costs and improve exoskeleton controllability at the same time. The concepts are related to (1) how to avoid oversizing actuators to obtain more lightweight, affordable, and transparent systems (2) how to enhance force controllability by mechanics (3) how to improve device transparency
Introducing series elastic links
No full textThis paper introduces the concept of Series Elastic Link which exploits the inherent elasticity of flexible links to implement compliant actuation and control using lightweigt and low cost components
Introducing Series Elastic Links for Affordable Torque-Controlled Robots
No full textRobotics have the potential to become a revolutionary technology in the next future and if we want to spread it among the population we must start accounting for affordability in robot research and design. Plastic robots are an emerging example of affordable design where expensive metal structures are replaced by low-cost plastic materials. Plastic materials are not only cost effective but, thanks to their inherent compliance and lightweight, lead to significant advantages in terms of safety and force controllability. Inspired by the idea of Series Elastic Actuator (SEA) this paper introduces the new concept of Series Elastic Link (SEL) which exploits the inherent flexibility of plastic links to implement series compliance. This paper elaborates on the concept of SEL and highlights a parallelism with SEAs. Then, focusing on a single-DOF setup it shows that, beyond their economic advantage, SELs leads to enhanced safety and more accurate force control with respect to traditional SEA implementations. The proposed argumentations are theoretically supported and experimentally validated
Force control and EMG-based adaptive assistance for enhanced human-exoskeleton interaction
No full textThe increasing diffusion of exoskeletons in industrial, domestic, and medical environments highlights their potential to reduce work-related musculoskeletal disorders, support rehabilitation, and improve the mobility of people with disabilities.
Unfortunately, control technologies capable of ensuring a reliable physical human-exoskeleton interaction and providing optimal assistance based on the load lifted by the user are still missing. This thesis investigates advanced control strategies that address key limitations of existing approaches by acting at both the low-level and high-level layers of exoskeleton control architectures.
The first part of the thesis focuses on low-level force control. First, a force control benchmarking framework is developed to highlight well-known critical challenges in force control and to evaluate force control algorithms by taking into account diverse interacting environments. Next, a high-performance friction compensation solution for benchmarking applications is proposed to guarantee non-biased benchmarking results. Since the latter solution cannot be exploited outside the benchmarking scenario and given the importance of accurate friction compensation for reliable human-exoskeleton interaction, this thesis proposes a novel force control architecture that includes a model-reference friction observer. Since passivity is a fundamental requirement for interaction control, the conditions under which the proposed observer preserves passivity at the environment, control, and friction ports were investigated. This implies that the proposed architecture can perform passive friction compensation for any friction dynamics and can be combined with any passive force controller while guaranteeing a stable interaction with any passive environment. Experimental validation shows that the proposed approach outperforms existing friction compensation solutions in force control applications.
The second part of the thesis focuses on high-level Electromyography (EMG)-based control strategies for Adaptive Gravity Compensation (AGC). To introduce the reader, a brief overview of Myoelectric Control Strategies (MCSs) is presented, showing that MCSs found in the literature are generally composed of three distinct functional modules: a decoder to extract the movement intention from EMG signals, a controller to accomplish the desired motion through a command given to the actuators, and a shaper to connect them. Subsequently, two EMG-based AGC approaches are proposed. Differently from existing AGC solutions, the proposed approaches (1) do not require knowledge of the anthropomorphic properties of the human arm and (2) recognize the importance of accounting for the human-exoskeleton dynamics within the adaptation law to improve payload estimation performance in dynamic conditions. The feasibility of the proposed approaches is experimentally validated on a 1-degree-of-freedom upper-limb exoskeleton
Enhancing force controllability by mechanics in exoskeleton design
No full textThis paper presents an exoskeleton concept based on low-size and low-cost electromagnetic motors which allows to improve force controllability and reduce costs at the same time. The idea comes from the theoretical analysis of a simple interaction control model which suggests that lowering the motor inertia leads to improved performance robustness. In particular, we show that a lower motor inertia reduces the sensitivity to the wearer impedance which is usually characterized by high uncertainties. In order to reduce the motor size, this paper proposes to lower the motor torque requirements and considers a parallelogram-based architecture with mechanical gravity compensation. A two degree of freedom prototype is realized to implement the concept and to experimentally validate our hypotheses, showing coherence with theoretical expectations and paving the way for a new generation of affordable forced-controlled exoskeletons
An Affordable Upper-Limb Exoskeleton Concept for Rehabilitation Applications
No full textIn recent decades, many researchers have focused on the design and development of exoskeletons. Several strategies have been proposed to develop increasingly more efficient and biomimetic mechanisms. However, existing exoskeletons tend to be expensive and only available for a few people. This paper introduces a new gravity-balanced upper-limb exoskeleton suited for rehabilitation applications and designed with the main objective of reducing the cost of the components and materials. Regarding mechanics, the proposed design significantly reduces the motor torque requirements, because a high cost is usually associated with high-torque actuation. Regarding the electronics, we aim to exploit the microprocessor peripherals to obtain parallel and real-time execution of communication and control tasks without relying on expensive RTOSs. Regarding sensing, we avoid the use of expensive force sensors. Advanced control and rehabilitation features are implemented, and an intuitive user interface is developed. To experimentally validate the functionality of the proposed exoskeleton, a rehabilitation exercise in the form of a pick-and-place task is considered. Experimentally, peak torques are reduced by 89% for the shoulder and by 84% for the elbow
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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