Yoonsu Nam

Force control system design for aerodynamic load simulator

Abstract A dynamic load simulator which can reproduce on-ground the aerodynamic hinge moment of control surface is an essential rig for the performance and stability test of an aircraft actuation system. The hinge moment varies widely over the flight envelope depending on the specific flight condition and maneuvering status. To replicate the wide spectrum of this hinge moment variation within some accuracy bounds, a force controller is designed based on the quantitative feedback theory (QFT). A dynamic model of load actuation system is derived, and verified through the experiment. The efficacy of QFT force controller is verified by a numerical simulation, in which combined aircraft dynamics, flight control law and hydraulic actuation system dynamics of aircraft control surface are considered.

QFT force loop design for the aerodynamic load simulator

A dynamic load simulator which can reproduce on-ground the aerodynamic hinge moment of a control surface is an essential rig for conducting performance and stability tests of aircraft actuation systems. The hinge moment varies widely over the flight envelope, depending on the specific flight condition and maneuvering status. To replicate the wide spectrum of this hinge moment variation within some accuracy hounds, a force controller is designed based on the Quantitative Feedback Theory (QFT). A dynamic model of the load actuation system Is derived, and compared with experimental results. Through this comparison, a nominal model of the load actuation system with some uncertainty bounds is developed. The efficacy of the QFT force controller is verified by a numerical simulation, in which combined aircraft dynamics, flight control law and hydraulic actuation system dynamics of the aircraft control surface are considered.

Stable fuzzy control system design with pole-placement constraint: an LMI approach

In this paper, the synthesis of an Linear Matrix Inequality (LMI)-based stable fuzzy control system with pole-placement constraint is presented. The requirements of stability and pole-placement region are formulated based on the Lyapunov direct method. By recasting these constraints into LMIs, we formulate an LMI feasibility problem for the design of the fuzzy state feedback control system that guarantees stability and satisfies desired transient responses. This theoretical approach is applied to a nonlinear magnetic bearing system concerning the issue of rotor position control. Simulation results show that the proposed LMI-based design methodology yields better performance than those of a linear local controller or single objective controller. In addition, it is observed that the proposed fuzzy state feedback controller provides superior stability robustness against parameter variations.

Feedforward Pitch Control Using Wind Speed Estimation

The dynamic response of a multi-MW wind turbine to a sudden change in wind speed is usually slow, because of the slow pitch control system. This could cause a large excursion of the rotor speed and an output power over the rated. A feedforward pitch control can be applied to minimize the fluctuations of these parameters. This paper introduces the complete design steps for a feedforward pitch controller, which consist of three stages, i.e. the aerodynamic torque estimation, the 3-dimensional lookup table for the wind seed estimation, and the calculation of the feedforward pitch amount. The effectiveness of the feedforward control is verified through numerical simulations of a multi-MW wind turbine.

Active vibration control of a micro-actuator for hard disk drives using self-sensing actuator

In this article, active vibration control of a micro-actuator for hard disk drives using self-sensing actuation is presented. The micro-actuators used in this article are a slider type and a suspension type. The self-sensing performance of the installing position is compared and evaluated. An assembly including these micro-actuators may not be able to sense some vibration of suspension modes. Feedback control results of direct velocity feedback and positive position feedback are presented. The feasibility of these self-sensing approaches as a vibration suppression control on the micro-actuator was verified. Using the slider type micro-actuator, the sway mode spike signal in power spectrum density was suppressed by 76% using the direct velocity feedback control, and by 60% using the positive position feedback control. Using the suspension type micro-actuator, the suspension second bending mode spike signal in power spectrum density was reduced by 74% using the direct velocity feedback control, and by 96% using the positive position feedback control. The control scheme using self-sensing signals can partially dampen the suspension modes.

Development of model for estimation of knee joint extension moment

This paper introduces a model to estimate knee joint extension moment during isokinetic contraction exercise. It is possible to estimate knee joint extension moment combining Hill-type muscle model, analytic results on moment arm, musculotendon length and muscle activation if muscle parameters are exactly known. However, the muscle parameters are all different to each person. And it is almost impossible to know about exact values of those. Thus Delps data is used except for tendon slack length which is the most critical parameter among Hill-type muscle model parameters. Each tendon slack length of muscles consisting of quadriceps is numeric optimized at MVC and applied to isokinetic contraction condition to evaluate the model by comparison between experimental and estimated results.

Wind turbine nacelle movement estimation using FEM model

The compensation of wind speed considering the effect of nacelle movement is required for the performance and control analysis of wind turbine. It is not easy to find some suitable sensors for measuring nacelle movement velocity. A Kalman filter estimating the nacelle movement is introduced. Several mathematical models describing the nacelle-tower dynamics are developed, and combined with the estimator. The performance of estimator based on the Euler-Bernoulli beam model is not satisfactory. However, estimation result using a simple lumped parameter model for the nacelle-tower dynamics is much better than the above, even though there are 10% errors. Itpsilas anticipated that the estimator using FEM model will provide better performance characteristics. This paper introduces some initial experimental and analysis results using a small scale laboratory model for a wind turbine nacelle and tower.

Control of a micro-actuator for hard disk drives using self-sensing

This paper describes control of a micro-actuator for hard disk drives using self-sensing actuation. The self-sensing actuator using electrical bridge circuit can measure either strain or time rate of strain in the actuator. These sensing signals correspond to the tip slope of the actuator and the time rate of tip slope of the actuator. The usefulness of the self-sensing actuation technique is experimentally verified by actively damping the vibration in a micro-actuator.

Design, Modeling, and Initial Experiments on Microscale Amplification Device

This article proposes the design of several microelectromechanical amplification devices formed of many identical microunits that are connected in a serial–parallel configuration, each being individually actuated and amplifying its own input motion. The microdevices realize the border-crossing from the micro-to the meso-scale displacement domain as they combine the micron-level individual inputs into millimeter-range output levels. The base structural unit is a flexure-based compliant device that is capable of transforming the input from a thermal actuator into an amplified displacement, about a direction perpendicular to the input one. The base unit is designed based on performance criteria, such as displacement amplification, input stiffness and output stiffness by utilizing finite element simulation, and an algorithm based on closed-form compliance equations of the incorporated flexure hinges. The microelectromechanical amplification device is monitored by means of embedded capacitive displacement sensors for the input port. The feasibility of the device design was verified through a numerical simulation and some initial experimental results are presented.

Two-Degree-of-Freedom Control of a Self-Sensing Micro-Actuator for HDD using Neural Networks

The present paper describes a two-degree-of-freedom control of a self-sensing micro-actuator for a dual-stage hard disk drive using neural networks. The two-degree-of-freedom control system is comprised of a feedforward controller and a feedback controller. Two neural networks are developed for the two-degree-of-freedom control system, one for the inverse dynamic model for the feedforward controller and one for system identification for the generation of the desired self-sensing signal. The feedback controller can realize the identified self-sensing signal. The micro-actuator uses a PZT actuator pair, installed on the assembly of the suspension. The self-sensing micro-actuator can be used to form a combined actuation and sensing mechanism. Experimental results show that the neural network approach can be used effectively for the control and identification of the self-sensing micro-actuator system