1,721,308 research outputs found
Decentralized Control of Aerial Manipulators Through a Momentum-Based Estimator
No full textAerial Robotic Manipulators can be controlled either in a centralized or decentralized way. This Part of the book addresses the latter option, in which the aerial platform and the arm are controlled separately in a robust way to counteract the reciprocal disturbances. An estimator of such disturbances, based on the momentum of the system and acting on the unmanned aerial vehicle, is designed. Experiments validate the approach
Disturbance rejection for legged robots through a hybrid observer
Full text linkA legged robot needs to move in unstructured environments continuously subject to disturbances. Existing disturbance observers are not enough when significant forces act on both the center of mass and the robot’s legs, and they usually employ indirect measures of the floating base’s velocity. This paper presents a solution combining a momentum-based observer for the angular term and an acceleration-based observer for the translational one, employing directly measurable values from the sensors. Due to this combination, we define this observer as ”hybrid,” and it can detect disturbances acting on both the legged robot’s center of mass and its legs. The estimation is employed in a whole-body controller. The framework is tested in simulation on a quadruped robot subject to significant disturbances, and it is compared with existing observer-based techniques
Energy recovery of blast-furnace gas coke. The importance of a correct regulation system
No full text
Energy recovery of blast-furnace gas coke. The importance of a correct regulation system
No full textThe present work deals with the regulation system of a plant recovering the energy of blast-furnace gas coke residual pressure. Such plant is provided by a turbogenerator which produces electric energy expanding the gas coke up to the mill pipe network pressure vallue. Before intervention the regulation apparatus consisted of an automatic vane orientation system of a turbine stator and a throttle valve. Once the system has become operative, the regulation set seemed to be inadequate showing a significant reduction in energy recovery due to the variation of the gas coke characteristics, compared to the original engineering specifications. A mathematical model for the plant simulation has been developed throughly the regulation system static and dynamic responses. This simulation together with a series of experimental tests indicated the causes of the operation problems in the original regulation system. On the base of the response times of the old regulation system, a valve with reduced intervention inertia has been introduced. The regulation logic was also modified: the valve interventions were directly linked to the pressure variations recorded at the blast furnace top, and no longer to the opening variation of the turbine automatic system. A more rational use of the plant components and its control system, together with and increase of the electric energy production have been the final results
Energy recovery of blast-furnace gas coke: The importance of a correct regulation system
No full textEnergy recovery of blast-furnace gas coke: the importance of a correct regulation system
No full textThe present work deals with the regulation system of a plant recovering the energy of blast-furnace gas coke residual pressure. Such a plant is equipped with a turbogenerator, which produces electric energy, expanding the gas coke up to the mill pipe network pressure value. Before revamping, the regulation system consisted of an automatic nozzle control of a turbine stator and a throttle valve. Once the system became operative, the regulation system seemed to be inadequate because it caused a significant reduction in energy recovery due to the variation of the gas coke characteristics, compared to the original engineering specifications. A mathematical model for the plant simulation has been developed through the regulation system static and dynamic responses. This simulation, together with a series of experimental tests, identified the causes of the operational problems in the original regulation system. On the basis of the response times of the old regulation system, a valve with reduced intervention inertia has been suggested. The regulation logic was also modified: The valve interventions were directly linked to the presence variations recorded at the blast furnace top, and no longer to the opening variation of the turbine automatic system. A more rational use of the plant components and its control system, together with an increased of the electric energy production, have been demonstrated
The interplay of roughness and adhesion in viscoelastic sliding contacts
Full text linkGarantire un controllo efficace dell'adesione nei materiali viscoelastici rappresenta una sfida cruciale nella tribologia moderna, con implicazioni significative in un ampio spettro di applicazioni ingegneristiche, tra cui mescole per battistrada di pneumatici per una maggiore aderenza ed efficienza, pinze robotiche morbide con adesione reversibile, adesivi strutturali e sensibili alla pressione, sistemi adesivi bio-ispirati e dispositivi MEMS. Nonostante i risultati sperimentali abbiano evidenziato come l'interazione tra l'adesione dell'interfaccia e la viscoelasticità influenzi il comportamento di contatto delle interfacce reali, gli attuali approcci analitici e numerici possono descrivere con precisione solo condizioni senza adesione in presenza di movimento relativo tra solidi o richiedono potenziali interatomici locali ad hoc per imitare gli effetti adesivi. Le osservazioni di fenomeni quali perdite isteretiche, isteresi di adesione e forza adesiva dipendente dalla velocità sottolineano ulteriormente i limiti di questi modelli esistenti, che spesso si basano sulla separazione di scala o ipotizzano un comportamento puramente elastico. Basandosi su un'estensione precedentemente sviluppata del criterio di frattura di Griffith ai materiali isteretici, questa tesi estende ulteriormente il quadro al caso multi-contatto irregolare e lo utilizza per studiare il comportamento di contatto e attrito di diversi profili irregolari multiscala in presenza di adesione interfacciale, attraverso l'intero spettro viscoelastico del materiale. Sfruttando la metodologia degli elementi di contorno basata sull'uso della funzione di Green, le equazioni di chiusura energetica sono state ottenute imponendo, su ciascun bordo di contatto, un equilibrio tra il lavoro delle sollecitazioni interne e quello dell'adesione in presenza di variazioni infinitesimali virtuali del dominio di contatto. Partendo dall'ipotesi di forze adesive a raggio infinitamente corto, l'approccio proposto estende i concetti classici di frattura per tenere conto della dissipazione di energia non conservativa derivante dalle sollecitazioni viscoelastiche. La struttura matematica e fisica di questa formulazione energetica si discosta significativamente dai casi elastici equivalenti, consentendo un trattamento coerente degli effetti di isteresi sia di massa che interfacciali. I risultati mostrano un marcato aumento dell'area di contatto, della forza adesiva e dell'attrito, in particolare a velocità di scorrimento intermedie, determinato dalla coesistenza dell'isteresi di adesione indotta dalla viscoelasticità su piccola scala ai bordi dei contatti e dell'isteresi di massa generata dalla viscoelasticità su larga scala, a conferma dei risultati di precedenti studi simili su un penetratore sinusoidale. Affrontando l'interazione fondamentale tra viscoelasticità, rugosità e adesione, questo lavoro stabilisce una base teorica unificata che spiega le principali osservazioni sperimentali e supporta la progettazione razionale di materiali viscoelastici con proprietà adesive e tribologiche su misura.Ensuring effective control of adhesion in viscoelastic materials represent a crucial challenge in modern tribology, with significant implications across a broad spectrum of engineering applications, including tire tread compounds for enhanced grip and efficiency, soft robotic grippers with reversible adhesion, structural and pressure-sensitive adhesives, bio-inspired adhesive systems and MEMS devices. Despite experimental results have highlighted how the interaction between interface adhesion and viscoelasticity affects the contact behavior of real interfaces, current analytical and numerical approaches can accurately describe only adhesiveless conditions in presence of relative motion between solids or require ad hoc local interatomic potentials to mimic adhesive effects. Observations of phenomena such as hysteretic losses, adhesion hysteresis and velocity-dependent adhesive strength further underline the limitations of these existing models, which often rely on scale separation or assume purely elastic behavior. Building upon a previously developed extension of Griffith’s fracture criterion to hysteretic materials, this thesis further extends the framework to the rough multi-contact case and employs it to investigate the contact and friction behaviour of several multiscale rough profiles in the presence of interface adhesion, across the entire viscoelastic spectrum of the material. Exploiting the boundary element methodology based on the use of the Green's function, the energy closure equations were obtained by imposing, at each contact edge, a balance between the work of internal stresses and that of adhesion under virtual infinitesimal variations of the contact domain. Moving from the assumption of infinitely short-range adhesive forces, the proposed approach extends classical fracture concepts to account for non-conservative energy dissipation arising from viscoelastic stresses. The mathematical and physical structure of this energy formulation significantly departs from equivalent elastic cases, allowing for a consistent treatment of both bulk and interfacial hysteresis effects. The results shows a marked increase in contact area, adhesive strength and friction, particularly at intermediate sliding velocities, driven by the coexistence of adhesion hysteresis induced by small-scale viscoelasticity at the edge of the contacts and bulk hysteresis generated by large-scale viscoelasticity, supporting the findings of previous similar studies for a sinusoidal indenter. By addressing the fundamental interplay between viscoelasticity, roughness and adhesion, this work establishes a unified theoretical foundation that explains key experimental observations and supports the rational design of viscoelastic materials with tailored adhesive and tribological properties
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