Návrh laboratorní soustavy pro testování algoritmů tlumení vibrací s dopravním zpožděním

Vibrations occur in wide field of application in mechanical engineering hence developing new and advanced algorithms is useful. For practical verification of theoretical control algorithms it is necessary not only to simulate them, but also to test them in laboratory conditions at least. This article describes design of multipurpose laboratory set-up for testing active vibration control algorithms which consists of series of carts connected to each other on linear guides. Carts are equipped with accelerometers and position sensors for feedback control. Linear electric motors on the carts are used for suppressing vibration. The laboratory set-up is controlled by Matlab/Simulink via DAQ card connected to PC. Next to the set-up itself, two control algorithms intended for testing are presented in this article. First, principle of algorithm of resonator absorber with delayed acceleration feedback is described. Furthermore algorithm using input shaping for pre-compensating the oscillatory modes of the system is presented. By adding time delays into closed loop it becomes an infinite dimensional and in this case different approach than in conventional methods is needed. Finally some successful simulation results are presented as a part of practical experiment preparation.Vibrace, jako nežádoucí efekt, se vyskytují v celé oblasti strojírenství. Z tohoto důvodu je vývoj nových algoritmů k jejich potlačování velmi přínosný. Pro praktické ověření teoretických řídicích algoritmů je nezbytné nejen simulovat matematické modely, ale také podpořit teorii alespoň v laboratorních podmínkách. Tento článek popisuje návrh univerzální laboratorní soustavy pro testování algoritmů pro aktivní tlumení vibrací. Soustava je tvořena několika vozíky vzájemně propojenými na lineárním vedení. Vozíky jsou osazeny akcelerometry a snímači polohy jednotlivých vozíků. K potlačení vibrací jsou pak využity lineární elektromotory. Laboratorní soustava je řízena pomocí softwaru Matlab/Simulink a DAQ karty připojené k PC. Kromě samotné soustavy jsou v článku popsány dva algoritmy, které budou na soustavě testovány. Nejprve je popsán princip absorbéru vibrací s akcelerační zpožděnou zpětnou vazbou. Dále pak je popsán algoritmus pro tvarování vstupního signálu tak, aby kompenzoval kmitavé módy v systému. Přidáním dopravního zpoždění do soustavy vznikne soustava nekonečného řádu a z tohoto důvodu je nutné systémy takovéhoto charakteru zkoumat jinými než běžnými metodami. Na závěr jsou zobrazeny výsledky ze simulací, sloužící k přípravě praktických experimentů

Adaptive integral sliding mode control for active vibration absorber design

A new tuning method for active vibration absorber design is presented in this paper. A robust, adaptive control scheme based on a variable structure with an adaptive discontinuity surface is designed and simulated. Robust synthesis of an adaptive discontinuity surface based on an augmented state-space is discussed. The proposed tuning scheme has three superior features compared with the existing counterparts in that: (i) it is completely insensitive to changes in the stiffness and damping of the absorber, (ii) it is capable of suppressing cyclic vibrations over a wide range of frequencies, (iii) its real-time operation requires only one adjustable gain

The Effects of Viscoelastic Behavior on the Operation of a Delayed Resonator Vibration Absorber

Delayed resonators have proven to be effective vibration absorbers (VAs) for tracking and canceling the effects of harmonic excitations on a structure. The Delayed Resonator (DR) is selfcontained, as no information from outside of its substructure is required for proper operation. It adjusts for variations in frequency using time-delay and gain as control parameters. This thesis examines the relationship between viscoelastic (VE) loss mechanisms in systems with DR and the choice of modeling method used to calculate control parameters and determine system stability. It is hypothesized that a VE loss mechanism approximated by a single viscous dashpot may lead to unexpected limits on the DR`s performance and adversely effect system stability. The constitutive properties of viscoelastic materials are dependent on both time and temperature, while the idealized viscous damper`s damping coefficient is not affected by either

Stabilization of acoustic modes using Helmholtz and Quarter-Wave resonators tuned at exceptional points

Acoustic dampers are efficient and cost-effective means for suppressing thermoacoustic instabilities in combustion chambers. However, their design and the choice of their purging air mass flow is a challenging task, when one aims at ensuring thermoacoustic stability after their implementation. In the present experimental and theoretical study, Helmholtz (HH) and Quarter-Wave (QW) dampers are considered. A model for their acoustic impedance is derived and experimentally validated. In a second part, a thermoacoustic instability is mimicked by an electro-acoustic feedback loop in a rectangular cavity, to which the dampers are added. The length of the dampers can be adjusted, so that the system can be studied for tuned and detuned conditions. The stability of the coupled system is investigated experimentally and then analytically, which shows that for tuned dampers, the best stabilization is achieved at the exceptional point. The stabilization capabilities of HH and QW dampers are compared for given damper volume and purge mass flow.Comment: 34 pages, 19 figures, acepted in the Journal of Sound and Vibratio

Study and Development of Mechatronic Devices and Machine Learning Schemes for Industrial Applications

Obiettivo del presente progetto di dottorato è lo studio e sviluppo di sistemi meccatronici e di modelli machine learning per macchine operatrici e celle robotizzate al fine di incrementarne le prestazioni operative e gestionali. Le pressanti esigenze del mercato hanno imposto lavorazioni con livelli di accuratezza sempre più elevati, tempi di risposta e di produzione ridotti e a costi contenuti. In questo contesto nasce il progetto di dottorato, focalizzato su applicazioni di lavorazioni meccaniche (e.g. fresatura), che includono sistemi complessi quali, ad esempio, macchine a 5 assi e, tipicamente, robot industriali, il cui utilizzo varia a seconda dell’impiego. Oltre alle specifiche problematiche delle lavorazioni, si deve anche considerare l’interazione macchina-robot per permettere un’efficiente capacità e gestione dell’intero impianto. La complessità di questo scenario può evidenziare sia specifiche problematiche inerenti alle lavorazioni (e.g. vibrazioni) sia inefficienze più generali che riguardano l’impianto produttivo (e.g. asservimento delle macchine con robot, consumo energetico). Vista la vastità della tematica, il progetto si è suddiviso in due parti, lo studio e sviluppo di due specifici dispositivi meccatronici, basati sull’impiego di attuatori piezoelettrici, che puntano principalmente alla compensazione di vibrazioni indotte dal processo di lavorazione, e l’integrazione di robot per l’asservimento di macchine utensili in celle robotizzate, impiegando modelli di machine learning per definire le traiettorie ed i punti di raggiungibilità del robot, al fine di migliorarne l’accuratezza del posizionamento del pezzo in diverse condizioni. In conclusione, la presente tesi vuole proporre soluzioni meccatroniche e di machine learning per incrementare le prestazioni di macchine e sistemi robotizzati convenzionali. I sistemi studiati possono essere integrati in celle robotizzate, focalizzandosi sia su problematiche specifiche delle lavorazioni in macchine operatrici sia su problematiche a livello di impianto robot-macchina. Le ricerche hanno riguardato un’approfondita valutazione dello stato dell’arte, la definizione dei modelli teorici, la progettazione funzionale e l’identificazione delle criticità del design dei prototipi, la realizzazione delle simulazioni e delle prove sperimentali e l’analisi dei risultati.The aim of this Ph.D. project is the study and development of mechatronic systems and machine learning models for machine tools and robotic applications to improve their performances. The industrial demands have imposed an ever-increasing accuracy and efficiency requirement whilst constraining the cost. In this context, this project focuses on machining processes (e.g. milling) that include complex systems such as 5-axes machine tool and industrial robots, employed for various applications. Beside the issues related to the machining process itself, the interaction between the machining centre and the robot must be considered for the complete industrial plant’s improvement. This scenario´s complexity depicts both specific machining problematics (e.g. vibrations) and more general issues related to the complete plant, such as machine tending with an industrial robot and energy consumption. Regarding the immensity of this area, this project is divided in two parts, the study and development of two mechatronic devices, based on piezoelectric stack actuators, for the active vibration control during the machining process, and the robot machine tending within the robotic cell, employing machine learning schemes for the trajectory definition and robot reachability to improve the corresponding positioning accuracy. In conclusion, this thesis aims to provide a set of solutions, based on mechatronic devices and machine learning schemes, to improve the conventional machining centre and the robotic systems performances. The studied systems can be integrated within a robotic cell, focusing on issues related to the specific machining process and to the interaction between robot-machining centre. This research required a thorough study of the state-of-the-art, the formulation of theoretical models, the functional design development, the identification of the critical aspects in the prototype designs, the simulation and experimental campaigns, and the analysis of the obtained results

Feedback vibration control of a base-isolated building with delayed measurements using h∞ techniques

n this paper we address the problem of vibration reduction of buildings with delayed measurements, where the delays are time-varying and bounded. We focus on a convex optimization approach to the problem of state-feedback H ∞ control design. An appropriate Lyapunov-Krasovskii functional and some free weighting matrices are used to establish some delay-range-dependent sufficient conditions for the design of desired controllers in terms of linear matrix inequalities (LMIs). The controller, which guarantees asymptotic stability and an H ∞ performance, simultaneously, for the closed-loop system of the structure, is then developed. The performance of the controller is evaluated through the simulation of an n-story base-isolated building

Optomechanical Devices and Sensors Based on Plasmonic Metamaterial Absorbers

Surface plasmon resonance is the resonant oscillations of the free electrons at the interface between two media with different signs in real permittivities, e.g. a metal and a dielectric, stimulated by light. Plasmonics is a promising field of study, because electron oscillations inside a subwavelength space at optical frequencies simultaneously overcome the limit of diffraction in conventional photonics and carrier mobilities in semiconductor electronics. Due to the subwavelength confinement, plasmonic resonances can strongly enhance local fields and, hence, magnify light-matter interactions. Optical absorbers based on plasmonic metamaterials can absorb light resonantly at the operating wavelengths with up to 100% efficiency. We have explored plasmonic absorbers at infrared wavelengths for thermal detectors, e.g. a gold nanostrip antenna absorber that can absorb 10-times light using only 2% of material consumption comparing to a uniform gold film. In an optomechanical device, the optical mode and mechanical mode are mutually influenced, through the optical forces exerted on the mechanical oscillator and the detuning of optical resonance by the mechanical oscillator, so that the mechanical oscillations are either amplified or suppressed by light. We designed an optomechanical device integrated with plasmonic metamaterial absorber on a membrane mechanical oscillator, wherein a tunable Fano-resonant absorption in the absorber arises from the coupling between the plasmonic and Fabry-Perot reonsances. The absorber traps the incident light and heat up the membrane, causing an increase in thermal stress and a normal plasmomechanical force on it. This is a light-absorption-dependent elastic force arising from the opto-thermo-mechanical interactions. Due to the finite thermal response time in the membrane, the elastic plasmomechanical force is delayed and, consequently, generates a viscous component modifying the damping rate of the mechanical oscillator. We have observed optomechanical amplification and cooling in the device at designed detuning conditions. In particular, on the condition that the optomechanical gain beats the intrinsic mechanical damping, the oscillation becomes coherent, i.e. phonon lasing. We successfully demonstrated phonon lasing with a threshold power of 19 μW. This device is promising as an integration-ready coherent phonon source and may set the stage for applications in fundamental studies and ultrasonic imaging modalities