Performance requirements of a higher throughput and accuracy in precision motion systems, such as wafer stage used in integrated circuit manufacturing, are ever increasing. The lightweight design, as one of the design methods, can results in less power consumption and less negative environmental impacts for the required high levels of acceleration. The aim of this research is to investigate the advantage of the lightweight design and to mitigate the negative effect caused by the flexible characteristics using an appropriate control method. In this paper, a prototype wafer stage is the analysis object. Since the mass of the horizontal drive motors accounts for a large proportion of the total mass of the wafer stage, a novel lightweight optimization frame based on the minimum motor mass is presented, while a Lorenz motor model based on finite element method (FEM) and artificial neural network (ANN) is firstly constructed. Then the controller adopting the PID with the maximum control bandwidth and pole placement method are designed. Through numerical analysis, the mass of the mover of the mover of this stage is reduced from 10.28 Kg to 6.078 Kg after lightweight optimization. Taking the Moving Average (MA) and Moving Standard Deviation (MSD) of the servo error in Z-direction as the control index, a closed-loop simulation result shows that the lightweight wafer stage can separately fulfil the requirement of the MA and MSD of the servo error in z-direction within 20nm and 30nm just as the current rigid-body wafer stage without the lightweight optimization.

Poles are regularly placed along highways and are used to support signs, lights and electrical lines. The Midwest Guardrail System (MGS) is a standard W-beam guardrail system used throughout the United States to redirect vehicles that leave the roadway away from dangerous roadside obstacles, like ravines, water hazards, and bridge piers. Placing poles near a guardrail may affect its ability to safely contain and redirect vehicles. The compatibility of poles placed in the proximity of the MGS is studied using nonlinear finite element analysis. Computer simulations were conducted with vehicles impacting the MGS with varying lateral pole offsets between the back of the system and the front face of the pole, and varying longitudinal pole location from being placed directly behind a post to directly behind the unsupported rail half-way between posts. Results show that poles placed within 16 inches behind the MGS may cause concern in regard to acceptable crash test performance for guardrail systems. Additional simulations and full-scale crash testing is required before guidelines can be recommended.

Active flutter control of bridge deck section using controllable winglets is studied. Self-excited wind forces acting on deck and winglets are modeled using the Scanlan-Tomko model. Vertical, lateral and torsional degrees of freedom are considered for deck and corresponding eighteen experimental flutter derivatives (FD) are used. Winglets are modeled as flat plates and FDs are obtained from Theodorsen functions. Time domain formulation using Rogers rational function approximation leads to divergence speed much lower than the actual one, which is confirmed by Quasi steady theory. Hence, for control study, the usual trial and error method involving sweeping through speed and frequency is used. Rotations of winglets relative to deck are considered as control input, rather than the driving torque. Full state feedback with LQR control is applied. The state variables are estimated by designing a full order observer system using pole placement technique. Winglet rotations being restricted within bounds, the flutter behavior is studied using closed loop responses and compared with eigenvalue analysis. Numerical results shows the implemented control strategy is quite effective in flutter suppression and enhancing the flutter speed.

The paper focuses on analysis of aeromechanical instabilities, specifically ground resonance in helicopters and active control methods for improving the existing stability margins. First, a simplified model of coupled rotor-fuselage system with translational fuselage degrees of freedom and blade lead-lag degree of freedom is considered. Anisotropy is introduced through stiffness variation between blades. Depending on the configuration, appropriate methods are used for stability analysis and to determine frequency coalescence. Second, similar analysis is extended to a model with fuselage pitch, roll and blade flap, lag degrees of freedom and incorporates wake model. The analysis brings out effects of collective pitch and lock number on aeromechanical instabilities with the inclusion of wake model. Active control strategy using pole placement technique and Linear Quadratic Regulator (LQR) is applied to the periodic system. Stabilization is done by increasing the aerodynamic damping through control input given either as cyclic or collective pitch.

Torsional vibration control of a rotating mechanical system which incorporates a Hooke’s joint is investigated by pole assignment techniques. Linearized analytical models for the torsional system are established for the purposes of controller design. The resulting two-degree-of-freedom rotational system which contains time varying coefficients is parametrically excited due to an inherent non-linear velocity ratio across the Hooke’s joint. The controller is designed via full state feedback and observer based feedback in the transformed domain, using Lyapunov transformation. This transformation reduces the original time-varying system to a form suitable for controller design. A dual-system approach is employed to calculate the observer gain matrix for the time-varying system. Numerical simulation results show that the proposed control method is effective for suppressing torsional vibration of a Hooke’s joint driven system.

This paper demonstrates an approximate full state feedback linearizing control law for the nonlinear ball on a plate system. It is shown that true full state feedback is not possible due both to the centrifugal acceleration terms and the nonlinear coupling between both coordinate axis. In an effort to make the system feedback linearizable, the dynamics corresponding to the centrifugal acceleration and the nonlinear coupling are simply treated as nonlinear disturbances to the original dynamics. The derived approximate full state feedback linearizing control law is evaluated via simulation of the original dynamics illustrating that the nonlinear disturbances are indeed small, and that the system controlled by the approximate control law is capable of more effective position and trajectory tracking than the standard Jacobian linearization.

In this article, a tremor attenuation algorithm is designed based on the backstepping method. A high-pass filter was designed in frequency domain and its state space realization was derived to be used as an estimator for the tremorous motion. Using the pole placement method an appropriate state feedback control law was designed to stabilize its output. The dynamics of the human arm was considered and a backstepping controller was derived for the applied torque to the arm. The global asymptotic stability of the resulting closed-loop system was proved using Lyapunov method. The controller is robust against parametric uncertainty and unmodeled nonlinear terms of the arm dynamical model. Simulation results shows the successful suppression of tremor in the presence of parametric uncertainty.

Due to the nonlinear dynamics of hydraulic systems, applying high performance closed-loop controllers is complicated. In this paper, a single-rod hydraulic actuator is considered in which load displacement (for positioning purposes) is controlled via manipulation of the input voltage to the servo-valve. Dynamics of the servo-valve is described by first and second order transfer functions (named as Models 1 and 2). Through linearization of the system around its operating points, dynamics of the hydraulic actuator is represented in the state space. A full-order observer is designed for on-line states estimation. Then, feedback control system is designed for both regulation and tracking objectives through pole-placement approach based on general canonical control form (GCCF). For tracking of the desired commands, a modified integral control is required (since the plant has not integrator). Results show that the regulation, states estimation, desired tracking and final tracking accuracy are achieved after applying the controller. Required input voltage and load positioning are compared for the two distinct dynamics of the servo-valve (Model 1 and 2).

Any classical control design starts by first satisfying stability and then looking towards satisfying transient requirements. Similarly, a Model Reference Adaptive Control (MRAC) Method should start with a stability analysis. Lyapunov function analysis is first used to justify the stability of the adaptive scheme. Next, a numerical study is conducted to predict the stability behavior of three different MRAC methods in the presence of large unanticipated changes in the dynamics of an aircraft. The Model reference adaptive control methods studied are: Method:1, an adaptive gain method; Method:2, a Neural Network (NN) approximation technique; and, Method:3, a linear approximation technique. For comparison purposes, the aircraft is assumed to have Linear Time Invariant, LTI dynamics. Each algorithm is given full state feedback, an inaccurate reference model and a poor Linear Quadratic Regulator, LQR design for the true plant. It is seen that when the LQR stabilizes the true plant, the three algorithms all achieve the same steady state error to a step command. Numerical results predict the different types of stability behavior that the algorithms provide. It is seen that the Methods: 2 and 3 can only provide a bounded stability, whereas Method: 1 can provide an asymptotic stability. A robust static controller can satisfy stability, but a robust static controller that accommodates variations in plant dynamics might not always be able to match transient requirements as expected. Although there may be no analytical guarantee from adaptive controllers of transient performance, one might look at anecdotal performances.

This work presents a survey on the control law development to actively attenuate the vibrations of a flexible structure submitted to fluid flow. Firstly, a robust controller with LQG/LTR approach was developed. Numerical tests were carried out being robustness characteristics to flow induced vibration and to noise rejection verified, for the case of equal nominal and real plants. The same robustness was not verified, when parametric variations were introduced. Therefore, another controller, based on regulator and filter pole placement approach, was developed where the direct loop obeys stability and performance robustness criterions, allowing to obtain good numerical results, even in the presence of significant parametric variations.

Most control systems are contaminated with some level of time delay. Whether it appears due to the inherent system dynamics or because of the sensory feedback, the delay has to be resolved regarding the system stability. We explain an unprecedented and fundamental treatment of time delay in a general class of linear time invariant systems (LTI) following a strategy, which we call the ‘Direct Method’ . The strengths of the method lie in recognizing two interesting and novel features, which are typical for this class of systems. These features enable a structured strategy to be formed for analyzing the stability of LTI-TDS (Time Delayed Systems). Vibration control settings are not immune from time delay effects. We present a case study on active control of vibration using linear full state feedback. We then apply the Direct Method on this structure to display the stability outlook along the axis of delay. There appears an interesting property, which is related to the determination of the imaginary (i.e. marginally stable) roots of LTI-TDS. We state a general lemma and proof on this point.

This paper concerns active vibration control of a 3.35 meter long composite I-beam that is used in civil structures in a cantilevered configuration by using peizoceramics materials, in particular the PZT (Lead Zirconate Titanate), in the form of patches. These PZT patches are surface-bonded on the I-beam and perform as actuators and sensors. A real-time data acquisition and control system is used to record the experimental data and to implement controllers. To assist control system design, open loop testing and system identification are conducted. A Pole Placement controller is designed and is simulated using the identified model. Simulations show the dramatic increase in damping of the beams which when implemented experimentally corroborates the simulation results. Experimental results verify the simulated results and demonstrate the effectiveness of active control of a civil structure using smart materials.

This paper presents an analysis and comparison of a vehicle with active front steering and rear-wheel steering. Based on linear analysis of base vehicle characteristics under varying speed and road surfaces, desirable vehicle response characteristics are presented and a set of performance matrices for active steering systems is formulated. Using pole-placement approach, controllability issues under active front wheel steering and rear- wheel steering controls are discussed. A frequency response optimization approach is then used to design the closed-loop controllers.

A new piezoelectric micro-actuator with 2-dimensional control, i.e., a track following control and a flying height control, of the head positioning system for high-density hard disk drives (HDD) was previously developed in our lab. In this study, control algorithms for the new 2-degree-of freedom (DOF) micro-actuator are developed to independently control the lateral displacement and the transverse deflection to against various disturbances and system uncertainties. The structure of the piezoelectric micro-actuator is reviewed briefly. Then, the overall control strategy for the micro-actuator system is discussed. Next, controller design schemes for each DOF are presented. The pole placement method is used to design controllers. To obtain compensation for overshoot and settling time, pole and zero locations are carefully chosen. First, the control law is defined for the disturbance rejection. Second, the estimator is designed for noise reduction. Lastly, the reference input is added for the command following. Simulation results show that the proposed controllers in the closed-loop system provide good stability, and compensate for disturbances and noises. The data suggest that the proposed micro-actuator control system considerably improves track following and flying height control of head positioning systems in highdensity HDDs.

A hybrid approach to active vibration control is described in this paper. It combines elements of both wave and mode approaches to active control and is an attempt to improve on the performance of these approaches individually. In the proposed hybrid approach, wave control is first applied at one or more points in the structure. It is designed on the basis of the local behavior of the structure and is intended to absorb vibrational energy, especially at higher frequencies. Then modal control is applied, being designed on the basis of the modified global equations of motion of the structure-plus-wave-controller. These are now normally non-self-adjoint. Because the higher order modes are relatively well damped, hybrid control improves the model accuracy and the robustness of the system and gives better broadband vibration attenuation performance. Hybrid wave/mode active vibration control is described with specific reference to the control of bending vibrations in a Timoshenko beam. The particular case considered is that of collocated, point force/sensor feedback wave control combined with modal control designed using pole placement. Numerical results are presented.

This paper develops a new method of designing anti-windup compensators using the concept of robust pole placement using linear matrix inequality (LMI) regions. The anti-windup problem seeks to minimize the closed loop performance deterioration due to input nonlinearities such as saturation for a given linear time-invariant plant and controller. Existing LMI-based anti-windup synthesis techniques do not explicitly provide a method to account for robust pole placement. This paper suggests a LMI-based method that not only attempts to minimize performance deterioration, but also explicitly restricts the anti-windup closed loop dynamics to an admissible set. Finally, the techniques discussed in this paper are demonstrated on a hydraulic test bed.

This paper analyzes the locking force of a stay cable equipped with a Magneto-rheological (MR) damper. For the single mode vibration of the stay cable, the formula of the locking force is derived and the important factors that affect the locking force are analyzed. The experimental investigations of the locking force of the stay cable vibration control are carried out on a cable-stayed bridge model equipped with an MR damper to verify of the computational locking force in the Smart Materials and Structures Laboratory at University of Houston. For the multi-mode vibration of the stay cable, the modal shapes of the stay cable vibration are estimated by utilizing a pole placement observer using the acceleration values at selected locations of the stay cable and the locking forces of the stay cable in multi-mode vibration are numerically obtained. In all experimental cases, the locking forces based on the analytical and numerical formulas approximately match the experimental results.