bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Evaluation of Frequency Weighted LQG—Maximum Entropy Controllers on an Experimental Truss Structure
Authors: Allen J. J. , Lauffer J. P.
Published: February 2008

This paper will discuss the experimental evaluation of a structural control system designed using a combination of Frequency Weighted LQG and Maximum Entropy. The experimental implementation was performed on an experimental truss structure, the Sandia Truss, which is described in the paper. The control design model was obtained via experimental system identification using the eigensystem realization algorithm with data correlation. The control design used frequency weighting to stabilize the unstructured uncertainty of the system due to low signal-to-noise and uncertain system dynamics in various frequency ranges. Maximum entropy is used to provided robustness for structured uncertain system dynamics within the controller bandwidth. The experimental implementation of the controllers designed with this approach show the ability to design controllers with a specified bandwidth, gain stabilization of unstructured uncertainty, and robustness to structured uncertainty within the controller bandwidth.
Active Vibration Control of Distributed Systems Using Delayed Resonator With Acceleration Feedback
Authors: Olgac Nejat , Elmali Hakan , Hosek Martin , Renzulli Mark
Published: February 2008

The Delayed Resonator (DR) and Dual Frequency Fixed Delayed Resonator (DFFDR) are newly introduced control techniques for active vibration absorption. Both methods propose a delayed position feedback within the absorber section of the structure to impart ideal resonance features to the absorber. When installed on an oscillating primary body, they form “notch filters” at their resonance frequencies attenuating the response of the primary structure. The DR absorber is shown to be real-time tunable to time varying disturbance frequencies. In this article, a number of new issues are considered. First, the basic theory is modified for acceleration feedback instead of position, which was originally proposed for the DR methodology. Second, the new absorption methods are implemented on distributed parameter structures which are under high frequency excitation (around 1 KHz). Stability of the combined structure is studied on a reduced order multi-degree-of-freedom primary structure together with the DR absorber. Experimental tests are conducted on a steel beam to verify the analytical findings. Piezoelectric actuators are used both to generate harmonic disturbances and to implement the control. The correspondence observed between the theoretical and experimental results is encouraging. The efficiency of the DR and DFFDR absorption techniques is demonstrated.
Accuracy of Discrete Models for the Solution of the Inverse Dynamics Problem for Flexible Arms, Feasible Trajectories
Authors: Moulin H. C. , Bayo E.
Published: February 2008

The inverse dynamics problem for a single link flexible arm is considered. The tracking order of consistent and lumped finite element models is derived and compared with the tracking order of the continuous model when there is no tip-mass. These comparisons show that discrete models fail to identify the tracking order of a modelled continuous system. A frequency domain analysis shows that an increase in the model order extends the well-modelled low-frequency range and, at the same time, increases the inadequacy in the high-frequency range. As a result, inverse dynamics solutions computed with discrete models do not converge to the continuous solution as the model order increases. The use of high-frequency filters allows us to construct a convergent numerical procedure. A conjecture about the tracking order is presented when there is a tip mass. It is shown that the same results are obtained if superposition of modes rather than finite elements is used.
Linear Quadratic Frequency-Shaped Implicit Force Control of Flexible Link Manipulators
Authors: Borowiec J. , Tzes A.
Published: February 2008

An implicit force control scheme for flexible link manipulators is considered in this article. The control output is composed of a feedforward and a feedback term. The feedforward torque component compensates the underlying rigid arm dynamics along the desired trajectory. The feedback component regulates the joint coordinate error perturbations. The minimization of a linear quadratic frequency-shaped cost functional yields the time-varying feedback controller gains. The frequency shaping dependence is included to eliminate undesirable effects associated with control and observation spillover. The proposed control scheme is employed in simulation studies on a two link rigid-flexible manipulator. Sufficient conditions for spatial tracking bounds and temporal gain switching bounds for the linearized rigid body error dynamics are provided. The effects of the linearized unmodelled error dynamics related to the flexible states on these bounds are also examined.
Modeling and Control of Transverse and Torsional Vibrations in a Spherical Robotic Manipulator: Theoretical and Experimental Results
Authors: Chen Liming , Chalhoub Nabil G.
Published: February 2008

The present work addresses modeling and control issues pertaining to the positioning and orientating of rigid body payloads as they are being manipulated by flexible spherical robotic manipulators. A general approach, to systematically derive the equations of motion of the robotic manipulator, is used herein. The objective of the controller is to yield a desired rigid body response of the arm while damping out the transverse and torsional vibrations of the compliant link. Note that the control objective has to be achieved by solely relying on the existing joint actuators whose band-widths are far below the natural frequencies of the torsional modes. The current work demonstrates that, in spite of the physical limitations of the system, the controller can actively damp out the torsional vibrations by relying on the coupling terms between the torsional vibrations and the remaining degrees of freedom of the arm. Moreover, a gain scheduling procedure is introduced to continuously tune the controller to the natural frequencies of the flexible link whose length is varied by the prismatic joint. The digital simulation results demonstrate the capability of the “rigid and flexible motion controller (RFMC)” in drastically attenuating the transverse and torsional vibrations during point-to-point (PTP) maneuvers of the arm. Furthermore, the gain scheduling procedure is shown to significantly reduce the degradations in the RFMC performance that are brought about by having the flexible link connected to a prismatic joint. A limited experimental work has also been conducted to demonstrate the viability of the proposed approach.
An Approach to Telerobotic Manipulations
Authors: Kazerooni H. , Moore C. L.
Published: February 2008

This article introduces three areas of study: 1 telefunctioning; 2 a control method for producing telefunctioning; and 3 an analysis of human-robot interaction when telefunctioning governs the system behavior. Telefunctioning facilitates the maneuvering of loads by creating a perpetual sense of the load dynamics for the operator. Telefunctioning is defined as a robotic manipulation method in which the dynamic behaviors of the slave robot and the master robot are functions of each other; these functions are the designer’s choice and depend on the application. (In a subclass of telefunctioning currently referred to as telepresence, these functions are specified as “unity” so that the master and slave variables (e.g., position, velocity) are dynamically equal.) To produce telefunctioning, this work determines a minimum number of functions relating the robots’ variables, and then develops a control architecture which guarantees that the defined functions govern the dynamic behavior of the closed-loop system. The stability of the closed-loop system (i.e., master robot, slave robot, human, and the load being manipulated) is analyzed and sufficient conditions for stability are derived.
Force Tracking Control of a Flexible Gripper Driven by Piezoceramic Actuators
Authors: Choi Seung-Bok , Lee Chul-Hee
Published: February 2008

This paper presents a robust force tracking control of a flexible gripper driven by a piezoceramic actuator characterizing its durability and quick response time. The mathematical governing equation for the proposed system is derived by employing Hamilton’s principle and a state space control model is subsequently obtained through the modal analysis. Uncertain parameters such as frequency variation are included in the control system model. The sliding mode control theory which has inherent robustness to the system uncertainties is adopted to design a force tracking controller for the piezoceramic actuator. Using the output information from a tip force sensor, a full-order observer is constructed to estimate state variables of the system. Force tracking performances for desired trajectories represented by sinusoidal and step functions are evaluated by undertaking both simulation and experimental works. In addition, in order to illustrate practical feasibility of the proposed method, a two-fingered gripper is constructed and its performance is demonstrated by showing a capability of holding an object.
A Lumped Parameter Electromechanical Model for Describing the Nonlinear Behavior of Piezoelectric Actuators
Authors: Goldfarb M. , Celanovic N.
Published: February 2008

A lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and in particular for control applications requiring accurate position tracking performance. In addition to describing the input-output dynamic behavior, the proposed model explains aspects of nonintuitive behavioral phenomena evinced by piezoelectric actuators, such as the input-output rate-independent hysteresis and the change in mechanical stiffness that results from altering electrical load. Bond graph terminology is incorporated to facilitate the energy-based formulation of the actuator model. The authors propose a new bond graph element, the generalized Maxwell resistive capacitor, as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data.
Rank-One Scaled ℋ∞ Optimization
Authors: Iwasaki Tetsuya , Rotea Mario A.
Published: February 2008

This paper gives a solution to the scaled ℋ∞ optimization problem with constant scalings and output feedback. It is shown that, when the nominal plant transfer matrix has a special rank-one property, this optimization problem is equivalent to a sequence of convex optimization problems involving linear matrix inequalities. These results are demonstrated with a flight control example. The primary contribution of the example is a method for weight selection that is applicable to problems in which ℋ∞ optimization is used as the design tool.
Computational Issues In a Nonlinear Observer for Systems With Quantized Outputs
Authors: Shevitz D. , Paden B.
Published: February 2008

In this paper we develop an observer for nonlinear systems with quantized outputs. The observer is a recursive algorithm based on the intersection of sets: each measurement defines a set in state space which, by recursive intersection, is used to refine knowledge of the state. We develop the necessary data structures and procedures to implement the algorithm numerically. Comparisons are drawn between the proposed observer, the Kalman filter, and the equations of nonlinear filtering. Estimates are given for the error due to the triangulation of the set of consistent states and the computational complexity of the numerical implementation of our observer. Finally, the algorithm is applied to two example systems.
Design of a Multivariable Neural Controller and Its Application to Gas Turbines
Authors: Song Q. , Grimble M. J.
Published: February 2008

The algorithm for a multivariable controller using neural network is based on a discrete-time fixed controller and the neural network provides a compensation signal to suppress the nonlinearity. The multivariable neural controller is easy to train and applied to an aircraft gas turbine plant.
Intake Manifold Modeling for the Fuel Metering Control of Spark Ignited Engines
Authors: Thompson S. , Gong C.
Published: February 2008

In order to minimize emissions the Air-Fuel Ratio (AFR) of a spark-ignited internal combustion engine needs to be maintained at stoichiometric. Whenever the air and fuel enter the engine’s cylinder the AFR cannot be changed; therefore the problem of AFR control is a problem of intake manifold control. Although the problem of AFR control (and hence of intake manifold modelling) appears to be solved for a fully warmed-up engine the problem of AFR control during the warm-up period remains. This paper addresses this problem by using a novel AFR control strategy, which can be based on a given intake manifold model, to test the AFR control of a partially warmed-up engine. The results of engine tests demonstrate that during the warm-up period tight AFR control is not possible using any of the intake manifold models developed for a fully warmed-up engine. This can only be the result of unmodeled dynamics in the intake manifold and it is therefore concluded that further work in the area of manifold modelling is required. Possible areas of model improvement are indicated.
Estimation of the Time-Dependent Profile of a Melting Front by Inverse Resolution
Authors: Guerrier B. , Liu H. G. , Be´nard C.
Published: February 2008

The profile and time evolution of a solid/liquid interface in a phase change process is estimated by solving an inverse heat transfer problem, using data measurements in the solid phase only. One then faces the inverse resolution of a heat equation in a variable and a priori unknown 2D domain. This ill-posed problem is solved by a regularization approach: the unknown function (position of the melting front) is obtained by minimization of a two component criterion, consisting of a distance between the output of a simulation model and the measured data, to which a penalizing function is added in order to restore the continuity of the inverse operator. A numerical study is developed to analyze the validity domain of the identification method. From simulation tests, it is shown that the minimum signal/noise ratio that can be handled depends strongly on the position of the measurement sensors.
Melnikov-Based Open-Loop Control of Escape for a Class of Nonlinear Systems
Authors: Simiu Emil , Franaszek Marek
Published: February 2008

The performance of certain nonlinear stochastic systems is deemed acceptable if during a specified time interval, the systems have sufficiently low probabilities of escape from a preferred region of phase space. We propose an open-loop control method for reducing these probabilities. The method is applicable to stochastic systems whose dissipation- and excitation-free counterparts have homoclinic or heteroclinic orbits. The Melnikov relative scale factors are system properties containing information on the frequencies of the random forcing spectral components that are most effective in inducing escapes. Numerical simulations show that substantial advantages can be achieved in some cases by designing control systems that take into account the information contained in the Melnikov scale factors.
Design of Controllers for Quadratic Stability and Disturbance Attenuation of Uncertain Systems
Authors: Jabbari Faryar , Ko¨se I˙. Emre
Published: February 2008

In this paper, we discuss the design of controllers that provide quadratic stability and a desirable disturbance attenuation level (through an appropriately small L2 gain) for systems with time varying, real and structured uncertainty. It is shown that for a class of systems, the problem of designing dynamic output feedback can be separated into two stages, each an easily solvable convex problem. This information could be used in system design and configuration. Two examples are presented to illustrate the proposed approach.
Optimal MISO Repetitive Control System Design Using Mixed Time and Frequency Domain Criteria
Authors: Hu Jwusheng , Yu Shiang-Hwua , Huang Shih-Chang
Published: February 2008

This paper presents an optimal repetitive controller design approach when both frequency and time domain criteria are considered. These criteria include limited control force, convergence rate, and robustness. In particular, the design formulation is based on MISO (multiple-input-single-output) plants which aim at solving nodal point problems encountered in flexible dynamic systems. Nodal points represent physical constraints for feedback control, especially when their frequencies are within the control bandwidth. If multiple control paths with distinct nodal frequencies are available, the proposed method is able to design controllers to compensate the effect and reach certain design objectives. The ellipsoid algorithm is used to calculate controllers’ parameters. Experiments were conducted to demonstrate the proposed method.
Discrete-Time Model Reference Adaptive Control for Nonminimum Phase Systems With Disturbances
Authors: Lu Jianming , Yahagi Takashi
Published: February 2008

This paper presents a new design method of discrete-time model reference adaptive control for nonminimum phase systems with disturbances. It is assumed that the disturbances are described by a polynomial function of time with known degree and unknown coefficients. The proposed scheme uses only input and output data and the existence of bounds for all signals is proved, which assures the output error convergence to zero. Finally, the results of computer simulation are presented to illustrate the effectiveness of the proposed method.
Control of Linear Motors for Machine Tool Feed Drives: Experimental Investigation of Optimal Feedforward Tracking Control
Authors: Alter David M. , Tsao Tsu-Chin
Published: February 2008

This paper investigates the use of optimal l1 and H∞ model reference optimal feedforward control to enhance the tracking performance of a linear motor drive. Experimental work is presented which studies the effects of signal preview, tracking constraint, and reference model choice on tracking performance. Suboptimal l1 control where the closed-loop system has a zero on the unit circle due to integral action in the feedback controller is given special attention, and is seen to give near optimal performance for the system under study here. For the specific trajectory employed here, the best performing feedforward controllers were experimentally seen to reduce by more than half the maximum and rms tracking errors of the H∞ optimal feedback closed-loop systems.
Contact/Impact in Hybrid Parameter Multiple Body Mechanical Systems—Extensions for Higher-Order Continuum Models
Authors: Barhorst Alan A.
Published: February 2008

In recent work the author presented a systematic formulation of hybrid parameter multiple body mechanical systems (HPMBS) undergoing contact/impact motion. The method rigorously models all motion regimes of hybrid multiple body systems (i.e., free motion, contact/impact motion, and constrained motion), utilizing minimal sets of hybrid differential equations; Lagrange multipliers are not required. The contact/impact regime was modeled via the idea of instantaneously applied nonholonomic constraints. The technique previously presented did not include the possibility of continuum assumptions along the lines of Timoshenko beams, higher order plate theories, or rational theories considering intrinsic spin-inertia. In this technical brief, the above-mentioned method is extended to include the higher-order continuum assumptions which eliminates the continuum shortfalls from the previous work. The main contributions of this work include: 1) the previous work is rigorously extended, and 2) the fact that coefficients of restitution are not required for modeling the momentum exchange between motion regimes of HPMBS. The field and boundary equations provide the needed extra equations that are used to supply post-collision pointwise relationships for the generalized velocities and velocity fields.
A Similarity Method for Miniature Mobile Robots
Authors: Liu T. S. , Lee J. Y.
Published: February 2008

Taking advantage of a piezoelectric material to fabricate miniature mobile robots, this study presents a similarity method, fabrication process, and walking experiment method. A curved piezoelectric material is first analyzed for vibration behavior in order to provide a basis for deriving model laws. Since the behavior of miniature mobile robots is not amenable to modeling, the similarity method is carried out to obtain model laws. A prototype for the miniature robot is further scaled down in different geometric sizes to conduct walking experiments. Experimental results that are primarily concerned with walking speeds comparison among robots of different sizes serve to verify model laws.
Analytical Prediction of Chatter Stability in Milling—Part I: General Formulation
Authors: Budak E. , Altintas¸ Y.
Published: February 2008

A new analytical method of chatter stability prediction in milling is presented. A general formulation for the dynamic milling system is developed by modeling the cutter and workpiece as multi-degree-of-freedom structures. The dynamic interaction between the milling cutter and workpiece is modeled considering the varying dynamics in the axial direction. The dynamic milling forces are governed by a system of periodic differential equations with delay whose stability analysis leads to an analytical relation for chatter stability limit in milling. The model can be used to determine the chatter free axial and radial depth of cuts without resorting to time domain simulations.
Analytical Prediction of Chatter Stability in Milling—Part II: Application of the General Formulation to Common Milling Systems
Authors: Budak E. , Altintas¸ Y.
Published: February 2008

The general formulation for the milling chatter prediction developed in Part I of the paper is applied to common milling systems. Three cases are considered: a workpiece with single-degree-of-freedom, a face milling cutter with two-degree-of-freedom, and peripheral milling of a cantilevered thin web. The general milling stability formulation is further simplified for the less complicated models. For each case, an analytical expression which explicitly relate the chatter limit to the milling conditions and tool-workpiece dynamics are derived. The analytical predictions are compared with numerical and time domain solutions proposed by previous research. It is shown that the proposed method can accurately predict the chatter limits in milling and thus eliminates the time consuming numerical solutions.
Lateral Dynamics and Stability of Two Full Vehicles in Tandem
Authors: El-Esnawy N. A. , Wilson J. F.
Published: February 2008

The lateral dynamics and stability of two full vehicles in tandem are investigated. The nonlinear differential equations of motion of this four-axle articulated vehicle system are presented in matrix form and then linearized. The critical forward velocity of the steady state for oversteering conditions is derived in a closed form, and the criteria for understeer, neutral steer, or oversteer are given. Uncertainty of the critical forward velocity and its sensitivity to errors in the system parameters are evaluated using the root mean square method. Conditions for nonoscillatory and oscillatory instabilities of the linearized vehicle system are given. Effects of the critical system parameters (mainly the mass distribution) on the stability are investigated.
Modeling and Parameter Identification of Harmonic Drive Systems
Authors: Taghirad H. D. , Be´langer P. R.
Published: February 2008

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application. However, harmonic drive can exhibit surprisingly more complex dynamic behavior than conventional gear transmission. In this paper a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is developed. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least-squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. By these means, it is shown that a linear stiffness model best captures the behavior of the system when combined with a good model for hysteresis. Moreover, the frictional losses of harmonic drive are modeled at both low and high velocities. The model performance is assessed by comparing simulations with the experimental results on two different harmonic drives. Finally, the significance of individual components of the nonlinear model is assessed by a parameter sensitivity study using simulations.
Modeling and Control of a Three-Dimensional Overhead Crane
Authors: Lee Ho-Hoon
Published: February 2008

In this paper, a new dynamic model of a three-dimensional overhead crane is derived based on a newly defined two-degree-of-freedom swing angle. The dynamic model describes the simultaneous traveling, traversing, and hoisting motions of the crane and the resulting load swing. For anti-swing control, this paper proposes a decoupled control scheme based on the dynamic model linearized around the stable equilibrium. The decoupled scheme guarantees not only rapid damping of load swing but also accurate control of crane position and load hoisting for the practical case of simultaneous traveling, traversing, and slow hoisting motions, which is also proven by experiments.
Robust, Digital, Nonlinear Control of Magnetic-Levitation Systems
Authors: Green Scott A. , Craig Kevin C.
Published: February 2008

This paper presents a robust, adaptive, nonlinear controller for a class of magnetic-levitation systems, which includes active-magnetic bearings. The controller is analytically and experimentally shown to be superior to a classical linear control system in stability, control effort, step-response performance, robustness to parameter variations, and force-disturbance rejection performance. Using an adaptive backstepping approach, a Lyapunov function is generated along with an adaptive control law such that the nonlinear, closed-loop, continuous system is shown to guarantee stability of the equilibrium and convergence of the parameter estimates to constant values. The control system error coordinates are proven to be bounded in the presence of a bounded force disturbance input. The novelty of this controller is that it is digitally implemented using Euler integrators with anti-windup limits, it is single-input-single-output requiring only a measurement of the position of the levitating object, and it is designed to adaptively estimate not only the uncertain model parameters, but also the constant forces applied to the levitating object in order to ensure robustness to force disturbances. The experimental study was conducted on a single-axis magnetic-levitation device. The controller is shown to be applicable to active-magnetic bearings, under specific conditions, as well as any magnetic-levitation system that can be represented in output-feedback form.
Modeling of Elastically Coupled Bodies: Part I—General Theory and Geometric Potential Function Method
Authors: Fasse Ernest D. , Breedveld Peter C.
Published: February 2008

This paper looks at spatio-geometric modeling of elastically coupled rigid bodies. Desirable properties of compliance families are defined (sufficient diversity, parsimony, frame-indifference, and port-indifference). A novel compliance family with the desired properties is defined using geometric potential energy functions. The configuration-dependent wrenches corresponding to these potential functions are derived in a form suitable for automatic computation.
Modeling of Elastically Coupled Bodies: Part II—Exponential and Generalized Coordinate Methods
Authors: Fasse Ernest D. , Breedveld Peter C.
Published: February 2008

This paper looks at spatio-geometric modelling of elastically coupled rigid bodies. Two methods are presented. In the first method constitutive equations are derived by associating rigid body displacements with twist displacements and then generating wrenches proportional to the twist displacements. In the second method consistitutive equations are derived by associating rigid body displacements with generalized coordinate displacements, generating generalized forces proportional to the displacements, and then computing corresponding wrenches. The application of these methods and the geometric method presented in the companion paper are illustrated in a nontrivial example.
Robot Trajectory Control System Design for Multiple Simultaneous Specifications: Theory and Experimentation
Authors: Liu Hugh H. T. , Mills James K.
Published: February 2008

A new control design method is developed to satisfy multiple specifications simultaneously. The proposed convex combination method is applied to a six (6)-degree-of-freedom commercial robot. In a trajectory tracking task under external disturbance, four requirements, stability, path accuracy, velocity accuracy, and steady-state error of position, can be met at the same time. The experimental results verify this conclusion.
A Singular Perturbation Approach for Modeling Differential-Algebraic Systems
Authors: Gordon Brandon W. , Liu Sheng
Published: February 2008

Dynamic systems described by an implicit mixed set of Differential and Algebraic Equations (DAEs) are often encountered in control system modeling and analysis due to inherent constraints in the system. A key difficulty in control and simulation of DAE systems is that they are not expressed in an explicit state space representation. This paper describes a general approach based on singular perturbation analysis for adding fast dynamics to a system of DAEs so that they can be expressed in an explicit state space form. Conditions for asymptotic convergence and approximation methods are investigated. The approach is illustrated for a model of a two-phase flow heat exchanger.
A System Theory Approach to Mode Coupling Chatter in Machining
Authors: Gasparetto Alessandro
Published: February 2008

Chatter is an undesired phenomenon of self-excited vibrations that occurs during many machining operations. This paper analyzes mode coupling chatter from the point-of-view of the system theory. A simplified mathematical model of the cutting process is established, from which the equations of the system are obtained. Then, the eigenvalues and the eigenvectors of the system are evaluated, and a simple stability condition is formulated. The tool trajectories both in the stable and unstable case are studied. Finally, an example of mode coupling chatter in a machine for wood cutting and its stabilization is presented.
Frequency Domain Structural System Identification by Observability Range Space Extraction
Authors: Liu Ketao , Jacques Robert N. , Miller David W.
Published: February 2008

This paper presents the Frequency Domain Observability Range Space Extraction (FORSE) identification algorithm. FORSE is a singular value decomposition based identification algorithm which constructs a state space model directly from frequency domain data. The concept of system identification by observability range space extraction was developed by generalizing the Q-Markov Covariance Equivalent Realization and Eigensystem Realization Algorithm. The numerical properties of FORSE are well behaved when applied to multi-variable and high dimensional structural systems. It can achieve high modeling accuracy by properly overparameterizing the system. The effectiveness of this algorithm for structural system identification is demonstrated using the MIT Middeck Active Control Experiment (MACE). MACE is an active structural control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this algorithm will be discussed.
Robust Adaptive Control for Hydraulic Servosystems
Authors: Plummer A. R. , Vaughan N. D.
Published: February 2008

The application of an indirect (self-tuning) adaptive controller to an electro-hydraulic positioning system is described. The underlying control method is pole placement, with the addition of a demand filter to allow noise effects to be reduced without degrading closed-loop performance. Recursive least squares is used to estimate the plant parameters, but the data is pre-filtered to reduce bias. A novel covariance trace limiting algorithm provides estimator reliability despite periods of insufficient excitation. Off-line system identification is employed to help controller design for the electro-hydraulic servosystem. The resulting controller performs well, and adapts rapidly to changes in load stiffness and supply pressure.
Comparison Between Linear and Nonlinear Control of an Electropneumatic Servodrive
Authors: Richard E. , Scavarda S.
Published: February 2008

In the robotics field control laws taking into account the nonlinearities caused by the mechanical structure have been proposed, assuming that the drive system is linear. These control laws are well-adapted to the case of electric actuators. Electrohydraulics or electropneumatics drive systems introduce other nonlinearities coming both from the servo-valve and the actuator. In most cases these nonlinearities are neglected and the control laws usually used for these drive systems are based on a reduced third-order model obtained by a tangent linearization. A more satisfying solution is to introduce the nonlinearities of the drive system in the control law. This paper deals with the nonlinear control of an electropneumatic servodrive and is based on the nonlinear control theory in continuous time. It takes into account the main specific nonlinearities. The proposed control law consists of an exact input-output linearization via a static nonlinear state feedback. In our case, this control law leads to a one-dimensional unobservable subspace in closed-loop. A physical interpretation of this nonlinear control is given. This interpretation enables us to improve the understanding of the behavior of an electropneumatic servodrive. In order to compare the results obtained from an experimental device, the synthesis of a linear control law in discrete and continuous time is presented. A study in discrete time of the root locus versus position of the closed loop system with the linear control law, shows oscillations in the neighbourhood of the end of the actuator stroke. The experimental results confirm this fact. With nonlinear control these oscillations are suppressed.
Dynamic Response of a Servovalve Controlled Hydraulic Motor Driven Centrifugal Pump
Authors: Xu Liangji , Schueller John K. , Harrell Roy
Published: February 2008

A servovalve controlled hydraulic motor driven centrifugal pump was dynamically modelled using linearized analysis. The expressions for the system gain, natural frequency, and damping ratio in terms of component physical parameters were derived. An optimization model estimation procedure was developed and applied to the step responses of such a system constructed of common commercial components. The experimental system had a 4.2 Hz natural frequency and 1.2 damping ratio. The research indicates that the dynamic responses of a servovalve controlled centrifugal pump can be appropriately modelled for applications in industry and agriculture where the output flow rate needs to be dynamically changed.
Modeling and Designing a Variable-Displacement Open-Loop Pump
Authors: Manring N. D. , Johnson R. E.
Published: February 2008

This study develops closed-form equations that may be used to guide the up-front design of a variable-displacement pump. In particular, the initial design of the control actuation system and the controller flow-gain is considered. A dynamic model of the pumping system is also presented and the dynamic effect of parameter variations such as actuator volume, discharge-hose volume, controller flow-gain and system leakage is discussed.
Model Based Statistical Process Control for Continuous Systems
Authors: Linstrom Peter J. , Asbjo̸rnsen O. Andreas
Published: February 2008

Statistical process control (SPC) is a set of methodologies for signaling the presence of undesired sources of variation in manufacturing processes. SPC methods for continuous processes may be developed by using stochastic models which do not assume that successive observations are independent. A method for applying SPC to continuous processes is presented. This method incorporates a computationally efficient procedure for the on-line identification and estimation of autoregressive with exogenous inputs (ARX) models. Two examples illustrating the method for SPC monitoring are presented.
Near-Minimum Time Feedback Controller for Manipulators Using On-Line Time Scaling of Trajectories
Authors: Kumagai A. , Kohli D. , Perez R.
Published: February 2008

A near-minimum time feedback controller for robotic manipulators with bounded input torques is developed. Since the bang-bang input torque obtained from the timeoptimal control theory leaves little or no room for the extra torque of the feedback control action, it is difficult to combine a minimum time open-loop controller with an additional feedback controller. A simple solution to this problem has been to solve the minimum time problem using arbitrarily reduced torque bounds so that a torque head room is created for the feedback control action. Such a scheme, however, wastes considerable input torque potential and gives significantly larger execution time of the trajectory than the theoretical minimum time calculated from the time-optimal control theory. A stable feedback controller is developed in this paper which applies a time scaling method to move a manipulator in near-minimum time using the allowable input torques efficiently. This new feedback controller algorithm adapts to an uncertain environment and automatically adjusts the desired speed along a specified path to be as fast as possible while avoiding the velocity saturation condition. Numerical examples of the near-minimum time feedback controller are provided using a two-link SCARA manipulator.
Sliding Mode Control Design in Multi-Input Perturbed Discrete-Time Systems
Authors: Wang Wen-June , Lee Rong-Chyang , Yang Dah-Ching
Published: February 2008

Variable structure control (VSC) design in multi-input discrete-time systems has two main difficulties: one is the satisfaction of the hitting condition and the other is the handle of the state trajectory in (quasi) sliding mode. The former is caused by the multiple inputs of the system, and the latter is caused by that the perturbation exists and the sliding surface is a bounded region but not only the hyperplane S = 0. This paper overcomes the above two difficulties successfully and designs the sliding region, the sliding control Us and the hitting control Ud such that the system’s state can reach the sliding hyperplane (in fact it is a region) and finally moves to the origin.
Linear Chaos in the Unforced Quantum Harmonic Oscillator
Authors: Gulisashvili A. , MacCluer C. R.
Published: February 2008

The annihilation operator of the unforced quantum harmonic oscillator is chaotic.
Analysis and Design of a Nonlinear Robust Controller
Authors: Fuh Chyun-Chau , Tung Pi-Cheng
Published: February 2008

A nonlinear controller and its design method are proposed. The development of the controller is motivated by fuzzy control. The controller has the advantages of simple structure, rapid computation, zero steady error, few parameters to set, and robustness to structure uncertainties and to parameter variations. Comparing the new controller with the PID controller, we find the performance of the new controller to be better. Its sensitivity to variations of the system is smaller than that of the PID and it requires no prefilter to avoid large overshoot. Digital simulations are performed to verify the capability of the proposed new nonlinear controller.
A Practical Solution to the Deterministic Nonhomogeneous LQR Problem
Authors: Hampton R. D. , Knospe C. R. , Townsend M. A.
Published: February 2008

A linear-quadratic-regulator-based (LQR) controller originates from a homogeneous set of state-space equations, and consists of a matrix of constant feedback gains. If the state equations are made nonhomogeneous by adding a vector of deterministic forcing terms, the standard LQR solution is no longer optimal. The present paper develops a matrix solution to this augmented (nonhomogeneous) LQR problem. The solution form consists of constant-gain feedback of the full-state vector, summed with a matrix preview (Duhamel integral) term. A practical and usable approximation is presented for the optimal preview term, having the form of a constant preview gain matrix. An example shows the improvement obtainable in controller performance with the use of this preview gain matrix, for exponentially decaying disturbances with a range of time constants.
Axial Force Stabilization of Transverse Vibration in Pinned and Clamped Beams
Authors: Rahn C. D. , Mote C. D.
Published: February 2008

An axial force stabilizes the transverse vibration of a beam with pinned and/or clamped boundary conditions. The nonlinearly coupled, longitudinal and transverse equations of motion of the beam with axial force control are simplified using a quasistatic assumption for longitudinal motion. It is shown that axial damping can ensure weak asymptotic stability of transverse vibration.
Control of Linear Motors for Machine Tool Feed Drives: Design and Implementation of H∞ Optimal Feedback Control
Authors: Alter D. M. , Tsao Tsu-Chin
Published: February 2008

Direct drive linear motors have good potential for use as next generation machine tool feed drives since they can increase machining rates and improve servo accuracy by eliminating gear related mechanical problems. To exploit the high speed and high response direct drives for machining, the servo control must achieve as high as possible tracking performance while at the same time establishing as much as possible the dynamic stiffness in order to maintain machining stability and reduce the effect of machining disturbance forces on the tool position. This paper investigates the use of optimal H∞ control to design for large stiffness and closed-loop tracking performance. Position feedback alone is first considered, with cutting force feedback later added to augment closed loop stiffness. Optimal position feedback is experimentally seen to achieve up to a 46 percent stiffness improvement over that achievable with proportional-derivative control. The addition of force feedback to the servo-loop resulted in a further 70 to 100 percent stiffness improvement over the position feedback alone values.
Application of Repetitive Control to Eccentricity Compensation in Rolling
Authors: Garimella S. S. , Srinivasan K.
Published: February 2008

Repetitive control is applied here to compensate for roll eccentricity disturbances in thickness control of the cold rolling process. A unique aspect of the process is that the eccentricity disturbance may be from multiple rolls and hence may be composed of multiple periodic components whose periods may not be commensurate, namely, divisible by a common factor an integral number of times. The paper presents a multiple-period repetitive controller structure that can compensate for such a disturbance. The structure proposed is also applicable to other tracking and regulation applications involving multiple periodic signals. Procedures to analyze and design control systems with such a structure, to ensure stability and performance, are presented.
Tool Condition Monitoring in Machining by Fuzzy Neural Networks
Authors: Li S. , Elbestawi M. A.
Published: February 2008

The Multiple Principal Component (MPC) Fuzzy Neural Network for tool condition monitoring in machining under varying cutting conditions is proposed. This approach is based on three major components of “soft computation,” namely fuzzy logic, neural network, and probability reasoning. The MPC classification fuzzy neural networks were built through training with learning data obtained from cutting tests performed in a reasonable range of cutting conditions. Several sensors were used for monitoring feature selection. Force, vibration, and spindle motor power signals were fused in multiple principal component directions to give a highly sensitive feature space. The tool conditions considered in the monitoring tests included sharp tool, tool breakage, slight wear, medium wear, and severe wear. The results showed success rates of approximate 94 percent in self-classification tests (i.e., the same data samples were used for both learning and classification), 84 percent in tests performed using different records for classification than those used for learning under the same cutting conditions, and about 80 percent in tests performed using samples obtained at different cutting conditions for classification than those used for learning within the same range of cutting conditions. The MPC fuzzy neural network classification strategy performed better than back-propagation trained feed-forward neural networks in these tests.
Enhancing Hydrostatic Gear Efficiency Through Nonlinear Optimal Control Strategies
Authors: Re L. del , Go¨ransson A˚. , Astolfi A.
Published: February 2008

Energy efficiency and short response times are usually conflicting goals. In the case of hydrostatic gears, two basic system configurations are commonly used, which allow to obtain better efficiency—the primary control setup—or faster responses—the secondary control. In this paper, (1) a different control setup is proposed, combining both primary and secondary control, and this new setup is shown to allow even faster responses than the secondary control having, in general, much lower energy requirements. We also address (2) the question of the design of a multiobjective optimal control for the proposed nonlinear structure, showing that the noninferior set, i.e., the set of points where the reduction of one cost function needs the increase of the others, depends on the control algorithm used. It is shown that combined use of pump and motor swash plate displacement yields a better trade-off between response speed and efficiency, and that solving approximately the nonlinear optimization problem delivers better efficiency than optimizing a system consisting of the original plant and a linearizing feedback.
A New Formulation of Multiple-Input Multiple-Output Quantitative Feedback Theory
Authors: Zhao Yongdong , Jayasuriya Suhada
Published: February 2008

The QFT robust performance problem in its entirety may be reduced to an H∞ problem by casting each specification as a frequency domain constraint on the nominal sensitivity function and the complementary sensitivity function. It is shown that the existence of a solution to a standard Ha. problem guarantees a solution to the QFT problem whereas the existence of a QFT solution does not necessarily guarantee an H∞ solution. A solution obtained via this formulation for the QFT problem is in general more conservative when compared to what may be obtained from classical QFT loopshaping. However, one does not have to restrict the QFT controller to be diagonal as is usually done in MIMO-QFT. In addition, a simple constructive approach is provided for the design of a prefilter matrix for MIMO systems. In the standard QFT approach, the synthesis of a prefilter matrix for the MIMO case is much more involved than that of the SISO case.