G. Silva-Navarro

Finite element modeling and unbalance compensation for a two disks asymmetrical rotor system

In this work a LQR scheme for vibration control in a rotor system is presented. The rotor system has two disks in an asymmetrical configuration along the shaft and its model is obtained by applying finite element techniques. A reduced order model of seven degrees of freedom is experimentally validated for the synthesis of active LQR control laws, using both an output feedback (one disk displacement) and an estimated state feedback controller. The controller is tuned to reduce the vibrations caused by the rotor imbalance in the two disks using only an actuator (active magnetic bearing). Some simulation and experimental results are included to show the transient and steady-state behavior of the overall closed loop system.

Application of an active pendulum-type vibration absorber for Duffing systems

This paper deals with the passive/active vibration control problem for damped Duffing systems, using a nonlinear pendulum-type vibration absorber. The primary system is a damped Duffing system affected by exogenous forces with excitation frequencies close to the principal parametric resonance. The design of the (passive) autoparametric vibration absorber is obtained by using an approximation of the nonlinear frequency response, computed via the multiple scales method. Then, in order to improve the overall system performance against variations on the amplitude and excitation frequency in the external force, it is incorporated a servomechanism to manipulate the pendulum length and, therefore, the autoparametric pendulum-type absorber can be automatically tuned into a given frequency bandwidth, by means of the application of a nonlinear control law combining feedback and feedforward compensation terms. The design of the autoparametric absorber, frequency analysis, control algorithm, stability analysis and closed-loop system performance are discussed. Finally, some simulations results are included to illustrate the dynamic performance of the overall system.

On-Line Algebraic Identification of Eccentricity in Active Vibration Control of Rotor-Bearing Systems

This paper leads with the application of on-line algebraic identification for eccentricity estimation in a rotor- bearing system. An important property of this algebraic identification is that the eccentricity identification is not asymptotic but algebraic, in contrast to most of the traditional identification methods, which generally suffer of poor speed performance. The algebraic identification is combined with an adaptive-like active vibration control scheme to reduce the amplitude response of the system while it passes through of its first critical speed. It is considered that one of the bearings can be automatically moved to control the effective rotor length and, as an immediate consequence, the rotor stiffness. Some numerical simulations are included to illustrate the dynamic performance of the algebraic identification and the active vibration control scheme, when the rotor is started and operated over the first critical speed.

Active unbalance control in a two disks rotor system using lateral force actuators

This work deals with the problem of modelling and analysis in rotordynamics as well as the active control of vibrations caused by unbalance in a rotor system. The system model was obtained by Finite Element Method taking into account the gyroscopic effects. The finite element model is used to get the Campbell diagram, the critical speeds, the modal shapes and to design the control scheme to attenuate the vibrations amplitude by an active suspension which uses linear electromechanical actuators. Due to the great number of states involved in the model, a state observer is necessary in order to apply a Linear Quadratic Regulator with full state feedback. The controller is applied considering the dynamics of actuators in the active suspension. Some numerical simulations to verify the controller-observer performance and experimental results on a novel test rig to prove the closed loop behavior are presented.

Active disk for automatic balancing of rotor-bearing sytems

This paper leads with the active cancellation problem of mechanical vibrations in rotor-bearing systems. The use of an active disk is proposed for actively balancing a rotor by means of locating a balancing mass at a suitable position. Two nonlinear controllers with integral compensation are proposed to put the balancing mass at a specific position. Algebraic identification is used for on-line eccentricity estimation, because of the implementation of this active disk is based on knowledge of the eccentricity. An important property of this algebraic identification is that the eccentricity identification is not asymptotic but algebraic, in contrast to most of the traditional identification methods, which generally suffer of poor speed performance. In addition, a velocity control is designed to take the rotor velocity to a desired operating point over the first critical speed. The controllers are developed in the context of an off-line prespecified reference trajectory tracking problem. Some numerical simulations are included to illustrate the dynamic performance of the closed loop system and the active vibration cancellation.

Cascade Control for a Rigid-Flexible Two-link Robot using Sliding Modes

Abstract The dynamical model of a two-link planar robot with one rigid-link, one flexible forearm and a payload attached to its tip, is represented in a cascade-like fashion using a convenient change of state coordinates which is found by observing the structure of the inertia matrix of the system model. The new system representation makes possible to devise a way to stabilize the overall system by designing a suitable trajectory for the angular positions of the joint shafts, in terms of the new state coordinates. These trajectories of the joints are used as virtual control signals that allow the controlling of the end effector position. Some simulation results are presented in which sliding mode control is employed to successfully perform regulation and trajectory tracking of the end effector.

Finite element and modal modeling of a cantilever beam with piezoelectric patch actuator for vibration absorption

This paper is about mechanical vibration absorption in a cantilever beam. This is accomplished by an active control scheme. The experimental set up consists of an aluminum cantilever beam clamped to an electrodynamical shaker. In that the main actuator is a piezoelectric patch and the feedback signal is obtained with a small piezoelectric accelerometer. For control purposes the closed loop is done via a positive feedback controller. In this work the beam is modeled with a four element finite model. The piezoelectric patch model is also presented. Experimental validation of the beam model is presented. And some results in closed loop are shown in numerical simulation as well as in the experimental platform.

Design and control of a two disks asymmetrical rotor system supported by a suspension with linear electromechanical actuators

This paper describes the problem of design of an experimental setup for rotordynamic analysis and unbalance control. The rotor system has two disks in an asymmetrical configuration along a steel shaft which is connected to a three phase AC motor by a flexible coupling. A suspension with two linear electromechanical actuators is used to control actively the vibrations caused by unbalance in disks. A LQR scheme with estimated state feedback is developed based on a reduced order finite element model of rotor system. The controller is applied taking into account the actuators dynamics. Some advances in the construction of the prototype and open loop experimental results are presented. The dynamic behavior of the closed loop system are shown by numerical simulations.

On the Analysis and Control of a Flexible link robot

In this article, a mathematical model for controlling the end tip position of a single flexible link robot arm is presented. The model is derived using a finite modal approximation for the solution of the Euler-Bernoulli beam equation, with the clamped-free boundary conditions. The link is bounded to move on the horizontal plane, so that the gravity effects on the link are neglected. An appropriate output function is chosen for properly controlling the system, called, the negative mode reflected output. Passivity concepts are applied for properly stabilizing the system allowing the application of a simple control approach for controlling the tip position. Simulations of the controlled system show the obtained results.

Vibration Control on a Space Flexible Structure with a PZT Stack Actuator Using Strain and MPPF Control

This works deals with the vibration control problem on a space frame flexible structure mounted on a rigid revolute servomechanism, which is actuated and controlled with a dc motor as a flexible-like robotic system. For active vibration control is synthesized a combined control scheme, by using a PD with direct strain feedback control for regulation and trajectory tracking tasks, via the rigid joint, and a Multiple Positive Position Feedback (MPPF) control by means of a PZT stack actuator mounted into the structure. Therefore, the endogenous and exogenous vibrations on the overall structure are simultaneously attenuated by the combined controller. The MPPF controller is computed to attenuate the two first dominant (bending) modes, using information obtained from strain gages, to improve the regulation and trajectory tracking of the tip position of the overall structure. The modal parameters of the structure are estimated using experimental modal analysis techniques. Finally, the overall dynamic performance is evaluated and validated by numerical and experimental results.