Chae-Wook Lim

The tracking control of uni-axial servo-hydraulic shaking table system using time delay control

In this paper, research results for improvement of tracking performance of servo-hydraulic shaking table are presented. Servo-hydraulic shaking table system is totally nonlinear due to the nonlinear flow property in a cylinder by actuation of servo valve. And it is demanded for the shaking table system to track arbitrary trajectories up to high frequency even at the extreme situations such as substantial external loads and large disturbances. For this purpose, time delay control (TDC), a robust control technique for highly nonlinear system, is applied to this system. TDC does not require any linearized model and any real time computation of nonlinear model. It is shown through numerical simulations that tracking performance of servo-hydraulic shaking table system is improved up to 30 Hz in real time by applying TDC

Experimental Study on Stability of Robust Saturation Controller

In our previous research, we proposed a robust saturation controller which involves both control input saturation and structured real parameter uncertainties. This controller can analytically prescribed the upper and lower bounds of parameter uncertainties, and guarantee the closed-loop robust stability of the system in the presence of actuator`s saturation. And the availability and the effectiveness of the proposed robust saturation controller were verified through numerical simulations. In this paper, we verify the robust stability of this controller through experimental tests. Expecially, we show unstable cases of other controllers in comparison with this controller. Experimental tests are carried out in the laboratory using a two-story test structure with a hydraulic-type active mass damper.

Experimental Verification on the Availability of Robust Saturation Controller for the Active Vibration Control of Building using AMD

In active vibration control of building, controller design considering both control input saturation of controller and parameter uncertainties of building is needed. In our previous research, we proposed a robust saturation controller which guarantees robust stability and control performance of the uncertain linear time-invariant system in the presence of control input saturation. In this paper, the availability of the robust saturation controller for the building with an active mass damper (AMD) system is verified through experimental tests. Experimental tests are carried oui using a two-story building model with a hydraulic-type AMD.

Design of Control Algorithm for Mass Driving Anti-Rolling System Considering Control Input Constraint

Reduction of a ship`s rolling is the most important performance requirement for improving the safety of the crew on board and preventing damage to cargos as well as improving the comfort of the ride. A mass driving anti-rolling system (MO-ARS) might be one candidate of several systems against the ship`s rolling. As the movable range of the mass on the ship is finite, the control system must include restriction on the mass position to protect the device and the ship. This restriction usually causes windup phenomenon and control performance is deteriorated seriously. Two control algorithms, anti-windup control and saturated sliding mode control, are studied in this paper. Control performance and robustness problem are checked out by numerical simulations‍㔀܀㘱㐮㠴㬏S潣楡氠浥摩捩湥

Active Vibration Control Using Saturated LQR Controller

In this paper, a saturated LQR controller considering control input`s saturation for stable linear time-invariant systems with single control input is studied. Based on Lyapunov stability, two linear matrix inequality sufficient existence conditions for this controller are presented. Through numerical simulations for 2DOF vibrating system, it is confirmed that the saturated LQR controller is stable in the presence of control input`s saturation and it is also shown that this controller can be applied to vibrating system practically.

Active Vibration Control of Structure Using LMI Optimization Design of Robust Saturation Controller

In our previous paper, we developed a robust saturation controller for the linear time-invariant (LTI) system involving both actuator`s saturation and structured real parameter uncertainties. This controller can only guarantee the closed-loop robust stability of the system in the presence of actuator`s saturation. But we cannot analytically make any comment on control performance of this controller. In this paper, we suggest a method to use linear matrix inequality (LMI) optimization problem which can analytically explain control performance of this robust saturation controller only in nominal system. The availability of design method using LMI optimization problem for this robust saturation controller is verified through a numerical example for the building with an active mass damper (AMD) system.

Stability of Saturation Controllers for the Active Vibration Control of Linear Structures

Control input`s saturation of active control devices for large structures under large external disturbances are often occurred. It is more difficult to obtain the exact values of mass and stiffness as structures are higher. The modelling errors between mathematical models and real structures must be also included as parameter uncertainties. Therefore, in active vibration control of civil engineering structures like buildings and bridges, the robust saturation controller design method considering both control input`s saturation and parameter uncertainties of system is needed. In this paper, stabilities of linear optimal controller LQR, modified bang-bang controller, saturated sliding mode controller, and robust saturation controller among various controllers which have been studied and applied to active vibration control of buildings are investigated. Especially, unstable phenomena of the LQR, the modified bang-bang controller and the saturated sliding mode controller when the control input is saturated or parameter uncertainties exist are presented to show the necessity of the robust saturation controller. The robust stability of the robust saturation controller are shown through a numerical example of a 2DOF linear vibrating system and an experimental test of the two-story structure with an active mass damper (AMD).

Vibration control of a beam using linear magnetostrictive actuators

Terfenol-D is one of magnetostrictive materials with the property of converting the energy in magnetic field into mechanical motion, and vice versa. We designed and fabricated a linear magnetostrictive actuator using Terfenol-D as a control device. In order to grasp the dynamic characteristics of the actuator, a series of experimental and numerical tests were performed. Induced-strain actuation displacements of the actuator measured by the test and predicted by magnetic analysis agreed well. And blocked forces according to the input currents were estimated from the testing results. Modeling method representing the exerting force of the actuator was confirmed through some testing results. We also explored the effectiveness of the linear magnetostrictive actuator as a structural control device. A series of numerical and experimental tests was carried out with simple aluminum beam only supported at each end by the actuator. After the equation of motion of the controlled system was obtained by the finite element method, a model reduction was performed to reduce the numbers of degree of freedom. A linear quadratic feedback controller was realized on a real-time digital control system to damp the first four elastic modes of the beam. Through some tests, we confirmed the possibility of the actuator for controlling beam-like structures.