<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e. if it is made of passive components such as resistors and inductors.</p><p><p><p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p><p><p><p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p><p><p><p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

[pt] Esta tese tem como principal objetivo o estudo do comportamento cinemático de um simulador de movimentos de 6 (seis) graus de liberdade, utilizando um novo conceito de análise computacional.Inicialmente, foi apresentado um software comercial, Working Model 3D, que teve seu desempenho matemático validado comparando-se seus resultados computacionais com os de outro software comercial, conhecido como Matlab.Foi introduzido, então, o conceito de mecanismos paralelos. Analisou-se, primeiramente, o mecanismo paralelo planar com três juntas rotacionais, conhecido como 3RRR. Foram feitas as análises cinemáticas e os estudos de algumas singularidades, apresentando-se ainda algumas recomendações para futuros trabalhos. O estudo do mecanismo paralelo usado em aplicações como simuladores de movimentos foi também apresentado, através da análise plataforma Stewart- Gough. A exeqüibilidade deste novo conceito de análise cinemática foi comprovada através de diversas simulações, incluindo o acoplamento de um objeto, representado por um chassi veicular, na plataforma. / [en] This thesis presents the kinematic behavior of a motion simulator with six degrees of freedom,using a new computational analysis approach. A well-known simulation software with proven performance, Matlab, is used to validate another software environment, Working Model 3D, which is used to develop and study kinematic models of parallel mechanisms.Planar mechanism using three rotational joints, 3RRR, are studied through kinematic analysis and some singularity studies are developed, which resulted in some suggestions for future analysis and studies. Also, an introductory study of spatial-parallel mechanisms is presented regarding motion simulators with six degrees of freedom through simulation studies of Stewart-Gough platform. The feasibility of this new kinematic analysis was proven by means of several simulations, including the coupling of a vehicular chassis in the platform modeling.

In this work, we investigate the active vibration isolation and damping of sensitive equipment. Several single-axis isolation techniques are analyzed and tested. A comparison between the sky-hook damper, integral force feedback, inertial velocity feedback and LagLead control techniques is conducted using several practical examples.<p><p>The study of single-axis systems has been developed and used to build a six-axis isolator. A six degrees of freedom active isolator based on Stewart platform has been designed manufactured and tested for the purpose of active vibration isolation of sensitive payloads in space applications. This six-axis hexapod is designed according to the cubic configuration; it consists of two triangular parallel plates connected to each other by six active legs orthogonal to each other; each leg consists of a voice coil actuator, a force sensor and two flexible joints. Two different control techniques have been tested to control this isolator :integral force feedback and Lag-Lead compensator, the two techniques are based on force feedback and are applied in a decentralized manner. A micro-gravity parabolic flight test has been clone to test the isolator in micro-gravity environment.<p><p>ln the context of this research, another hexapod has been produced ;a generic active damping and precision painting interface based on Stewart platform. This hexapod consists of two parallel plates connected to each other by six active legs configured according to the cubic architecture. Each leg consists of an amplified piezoelectric actuator, a force sensor and two flexible joints. This Stewart platform is addressed to space applications where it aims at controlling the vibrations of space structures while connecting them rigidly. The control technique used here is the decentralized integral force feedback.<p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished