This article considers a theoretical and experimental comparative analysis in the responses of a three-story building-like structure using two different schemes of passive vibration control. These control schemes are designed to reduce the effects of resonant vibrations generated by an electromechanical shaker located in the base of the building-like structure. The first control scheme consists on the design of a Tuned-Mass-Damper located over the third floor of the structure, and the second control scheme considers the implementation of an autoparametric cantilever beam absorber. The mathematical model of the overall system is obtained using Euler-Lagrange method. In order to validate the frequency response of the main system a finite element model is completed. Some numerical and experimental results are included to show the dynamic behavior and stability performance of the overall mechanical system.
This work deals with the robust asymptotic output tracking control problem of the tip position of a space frame flexible structure, mounted on a rigid revolute servomechanism actuated and controlled with a dc motor. The structure is also affected by undesirable vibrations due to excitation of its first lateral vibration modes and possible variations of the tip mass. The overall flexible structure is modeled by using finite element methods and this is validated via experimental modal analysis techniques. The tip position of the structure is estimated from acceleration and strain gauge measurements. The asymptotic output tracking problem is formulated and solved by means of Passivity-Based and Sliding-Mode Control techniques, applied to the dc motor coupled to the rigid part of the structure, and those undesirable vibrations are simultaneously attenuated by an active vibration control using Positive Position Feedback control schemes implemented on a PZT stack actuator properly located into the mechanical structure. The investigation also addresses the trajectory tracking problem of fast motions, with harmonic excitations close to the first vibration modes of the structure. The overall dynamic performance is evaluated and validated by numerical and experimental results.
The general study and applications of Magneto-Rhelogical (MR) dampers have been spread in the lasts years but only some studies have been focusing on the vibration control problems on rotor-bearings systems. Squeeze-Film Dampers (SFD) are now commonly used to passively control the vibration response on rotor-bearing systems because they can provide flexibility, damping and extend the so-called stability thresholds in rotating machinery. More recently, SFD are combined with MR or Electro-Rheological (ER) fluids to introduce a semiactive control mechanism to modify the rotordynamic coefficients and deal with the robust performance of the overall system response for higher operating speeds. There are, however, some theoretical and technological problems that complicate their extensive use, like the relationship between the centering spring flexibility and the rheological behavior of the smart fluid to produce the SFD forces. In this work it is considered a SFD with MR fluid and a set of circular section beams in a squirrel cage arrangement in combination with latex seals as centering springs. The mathematical model analysis includes the controllable viscoelastic properties associated to the MR fluid. The characterization of the SFD is made by the determination of some coefficients associated with a modified Choi-Lee-Park polynomial model. During the analysis is considered a rotor-bearing system modeled using finite element methods. The SFD with MR fluid is connected to an experimental platform to validate and experimentally evaluate the overall system. Finally, to improve the open-loop system performance, a methodology for the use of different control schemes is proposed.
An experimental investigation is carried out on a system consisting of a primary structure coupled with a passive/active autoparametric vibration absorber. The primary structure consists of a building-like mechanical structure, it has three rigid floors connected by flexible columns made from aluminium strips, while the absorber consists of a cantilever beam with a PZT patch actuator actively controlled through an acquisition card. The whole system, which is a coupled non-linear oscillator, is subjected to sinusoidal excitation obtained from an electromechanical shaker in the neighborhood of internal resonances. The natural frequency of the absorber is tuned to be one-half of any of the natural frequencies of the main system. With the addition of a PZT actuator, the autoparametric vibration absorber is made active, thus enabling the possibility to control the effective stiffness associated to the passive absorber and, as a consequence, the implementation of an active vibration control scheme able to preserve, as possible, the autoparametric interaction as well as to compensate varying excitation frequencies. This active vibration absorber employs feedback information from an accelerometer on the primary structure, an accelerometer on the tip of the beam absorber and a strain gage on the base of the beam, feedforward information from the excitation force and on-line computations from the nonlinear approximate frequency response, parameterized in terms of a proportional gain provided by a voltage input to the PZT actuator, thus providing a mechanism to asymptotically track an optimal, robust and stable attenuation solution on the primary system.
KEYWORDS: Ferroelectric materials, Actuators, Complex systems, Signal attenuation, Control systems, Active vibration control, Computing systems, Optical encoders, Digital signal processing, Feedback control
An experimental investigation is carried out on a cantilever-type passive/active autoparametric vibration absorber,
with a PZT patch actuator, to be used in a primary damped Duffing system. The primary system consists
of a mass, viscous damping and a cubic stiffness provided by a soft helical spring, over which is mounted a
cantilever beam with a PZT patch actuator actively controlled to attenuate harmonic and resonant excitation
forces. With the PZT actuator on the cantilever beam absorber, cemented to the base of the beam, the auto-parametric
vibration absorber is made active, thus enabling the possibility to control the effective stiffness and
damping associated to the passive absorber and, as a consequence, the implementation of an active vibration
control scheme able to preserve, as possible, the autoparametric interaction as well as to compensate varying
excitation frequencies and parametric uncertainty. This active vibration absorber employs feedback information
from a high resolution optical encoder on the primary Duffing system and an accelerometer on the tip beam
absorber, a strain gage on the base of the beam, feedforward information from the excitation force and on-line
computations from the nonlinear approximate frequency response, parameterized in terms of a proportional gain
provided by a voltage input to the PZT actuator, thus modifying the closed-loop dynamic stiffness and providing
a mechanism to asymptotically track an optimal, robust and stable attenuation solution on the primary Duffing
system. Experimental results are included to describe the dynamic and robust performance of the overall
closed-loop system.
KEYWORDS: Control systems, Actuators, Finite element methods, Mathematical modeling, Matrices, Prototyping, Control systems design, Computing systems, Systems modeling, Feedback control
This work deals with the problem of the active unbalance control in an asymmetrical rotor-bearing system with two
disks supported by an active suspension based on two lateral linear actuators. For the analysis and control synthesis a
mathematical model is developed using Finite Element Methods (FEM). A linear quadratic regulator (LQR) is applied in
order to minimize the displacements of the two disks by means of the application of an active bearing with control forces
provided by an arrangement of two linear actuators. The control scheme is designed to attenuate the overall system
response in the natural frequencies (resonances), taking into account the unbalance response associated to both disks and
shaft and, hence, controlling the system performance during the first modes. To do this, a Luenberger type observer is
used to estimate those not measurable states from the displacements in only one shaft point and, therefore, making
possible the synthesis of an optimal LQR control based on the estimated state feedback. The control forces obtained
from LQR control are introduced to the mathematical model of actuators and taking into account their dynamics, we get
the voltage inputs necessary to provide the unbalance compensation forces. The proposed control scheme is proved by numerical results and then, validated experimentally on a test rig which was designed and constructed. Numerical and experimental results show significant reductions in the unbalance response of the overall system.
KEYWORDS: Absorption, Prototyping, Feedback control, Smart structures, System integration, Current controlled current source, Aluminum, Finite element methods, Modal analysis, Control systems
This paper is about mechanical vibration suppression in a three story building like structure. The experimental
platform is a laboratory prototype made of aluminum alloy with bolted joints and an elctromagnetic shaker used
as a disturbance source. This prototype can be used as a representation of a civil structure as well as an industrial
machinery element. This structure is modeled and validated by the application of finite element methods and
experimental modal analysis. The system response is controlled by a piezoelectric actuator, properly located on
the structure, and with the synthesis of a feedback control law based on the well-known positive acceleration
feedback control scheme. Some numerical simulations and experiments results are performed to illustrate the
overall system performance in presence of several types of excitation.
The work describes the attenuation problem of vibrations affecting a nonlinear oscillatory mechanical system using passive and active vibration control methods based on nonlinear techniques. The mechanical system consists of an oscillating rigid bar coupled to a passive absorber. The undesirable vibration is a harmonic torque, with variable frequency, applied to the bar. The main goal consists of the design of feedback and feedforward control laws, employing information of the open-loop frequency response parameterized in terms of a new coordinate in order to tune appropriately the system. Physically, this coordinate stand for the position the passive absorber along the bar, implying the addition of a degree of freedom and enabling the horizontal motion of the absorber. With the measurement of the excitation frequency it can be computed the optimal attenuation position (minimal disturbance-output gain). Then, the application of a control law that asymptotically reach such position yields indirectly reduction of the angular motion of the bar to the minimum. The control scheme is designed using partial feedback linearization and output regulation techniques. Both cases lead to a fourth order zero dynamics (passive absorber), which is globally asymptotically stable. Some numerical simulations illustrate the resulting dynamic behavior and performance.
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