bluuebunny/crossref_metadata_2025 huggingface dataset:
A Covariance Controller Design Incorporating Optimal Estimation for Nonlinear Stochastic Systems
Authors: Chang Wen-Jer , Chung Hung-Yuan
Published: February 2008

This note addresses the problem of constrained variance design with minimizing LQG cost function via the method of covariance control incorporating the optimal estimation for nonlinear stochastic systems. The nonlinear stochastic systems are first linearized and then are examined by way of the technique of describing functions. Finally, an application of this approach to a position servomechanism is illustrated by a numerical example.
Optimal Nonlinear Estimation of Linear Stochastic Systems: The Multivariable Extension
Authors: Hopkins M. A. , VanLandingham H. F.
Published: February 2008

This paper extends to multi-input multi-output (MIMO) systems a nonlinear method of simultaneous parameter and state estimation that appeared in the ASME JDSM&C (September, 1994), for single-input single-output (SISO) systems. The method is called pseudo-linear identification (PLID), and applies to stochastic linear time-invariant discrete-time systems. No assumptions are required about pole or zero locations; nor about relative degree, except that the system transfer functions must be strictly proper. In the earlier paper, proofs of optimality and convergence were given. Extensions of those proofs to the MIMO case are also given here.
Optimal Output Feedback Regulator—A Numerical Synthesis Approach for Input-Output Data
Authors: Chan Jenq-Tzong H.
Published: February 2008

A numerical approach is proposed in this work for computing a linear quadratic optimal regulator from input-output data. The method is applicable whenever the plant is open-loop stable. The major advantages of the method are two-fold. First, it involves an output feedback control law; hence, no state estimation is required for implementation. Second, the computation of this optimal controller can be conducted without explicit identification of the plant model.
Iterative LQG Controller Design Through Closed-Loop Identification
Authors: Hsiao Min-Hung , Huang Jen-Kuang , Cox David E.
Published: February 2008

This paper presents an iterative LQG controller design approach for a linear stochastic system with an uncertain openloop model and unknown noise statistics. This approach consists of closed-loop identification and controller redesign cycles. In each cycle, the closed-loop identification method is used to identify an open-loop model and a steady-state Kalman filter gain from closed-loop input/output test data obtained by using a feedback LQG controller designed from the previous cycle. Then the identified open-loop model is used to redesign the state feedback. The state feedback and the identified Kalman filter gain are used to form an updated LQG controller for the next cycle. This iterative process continues until the updated controller converges. The proposed controller design is demonstrated by numerical simulations and experiments on a highly unstable large-gap magnetic suspension system.
A New Adaptive Robot Controller Taking Account of Motor Dynamics
Authors: Yuan Jing
Published: February 2008

This paper presents a new adaptive controller designed for rigid-body robots including motor dynamics. Recently, the effects of motor dynamics have attracted attention from a number of researchers. The available controllers able to ensure stable tracking in the presence of motor dynamics need acceleration feedback, or at least an acceleration observer. This means additional computing power and expenses in the hardware implementation. The proposed adaptive controller does not need an observer to avoid the acceleration feedback. It generates a continuous control signal. The closed-loop system is locally stable in the Lyapunov sense.
A Generalized Sufficient Condition for Time-Optimal Control
Authors: Sundar S. , Shiller Z.
Published: February 2008

This paper presents a sufficient optimality condition for time-optimal feedback control, which generalizes the existing sufficient conditions, i.e., the HJB equation and a Lyapunov-based condition derived in [12]. The new condition is satisfied by a class of piecewise C1 continuous functions, termed generalized value functions. It admits a larger class of functions, such as bounded functions, than the existing conditions as demonstrated in an example. The generalized condition might, therefore, be useful in solving for the time-optimal feedback control of nonlinear systems such as robotic manipulators.
Design of PAM and PWM Controllers for Sampled-Data Interval Systems
Authors: Shieh Leang-san , Wang Wei-min , Sunkel John W.
Published: February 2008

In this paper, we address two issues: digital redesign of a continuous-time interval system using an interval chebyshev quadrature approximation method; and translation of the newly digitally redesigned pulse-amplitude modulated (PAM) controller into an equivalent pulse-width modulated (PWM) controller via a second-order Taylor-series approximation method. Using this new interval digital redesign technique, the dynamic states of the digitally controlled sampled-data interval system are able to closely match those of the original analogously controlled continuous-time uncertain system. Three illustrative examples are provided to demonstrate the effectiveness of the proposed methods.
Direct and Inverse Kinematics for Coordinated Motion Tasks of a Two-Manipulator System
Authors: Chiacchio P. , Chiaverini S. , Siciliano B.
Published: February 2008

A new formulation for direct kinematics of a system of two manipulators is presented This allows a straightforward description of general coordinated motion tasks in terms of meaningful absolute and relative variables An effective inverse kinematics algorithm is devised which exploits the above formulation where the task Jacobians are expressed in terms of the Jacobians of the single manipulators The scheme is extended to handle the presence of redundant degrees of freedom in the system Different types of grasp between the end effectors and a commonly held object are treated with minimum reformulation effort. Case studies are developed throughout the paper for a system of two PUMA 560 manipulators which illustrate the capabilities of the scheme.
Active Damping of a Large Flexible Manipulator With a Short-Reach Robot
Authors: Sharf I.
Published: February 2008

This paper deals with manipulator systems comprising a long-reach manipulator (LRM) with a short-reach dextrous manipulator (SRM) attached to its end. The former, due to its size, is assumed to have significant structural flexibility, while the latter is modeled as a rigid robot. The particular problem addressed is that of active damping, or vibration suppression, of the LRM by using SRM specifically for that purpose Such a scenario is envisioned for operations where the large manipulator is used to deploy the small robot and it is necessary to damp out vibrations in LRM prior to operating SRM. The proposed solution to the problem uses the reaction force from SRM to LRM as a control variable which allows to effectively decouple the controller design problems for the two manipulators. A two-stage controller is presented that involves first, determining the trajectory of the short manipulator required to achieve a desired damping wrench to the supporting flexible arm and subsequently, brings the small manipulator to rest. Performance of the active damping algorithm developed is illustrated with a six-degree-of-freedom rigid manipulator on a flexible mast. Comparison to an independent derivative joint controller is included. The paper also discusses how the proposed methodology can be extended to address other issues related to operation of long-reach manipulator systems.
Adaptive, High Bandwidth Control of a Hydraulic Actuator
Authors: Bobrow J. E. , Lum K.
Published: February 2008

Hydraulic servovalve controlled systems contain many time-varying dynamic characteristics that are difficult to model Controllers for such systems must either adapt to these changing parameters or be robust enough to handle the parameter variations. In order to achieve the highest possible bandwidth, an adaptive controller is developed for the system that uses full-state feedback for simultaneous parameter identification and tracking control This controller takes into account the hydraulic fluid compressibility with an on-line identification scheme Experimental results demonstrate a four fold improvement in bandwidth as compared to a conventional fixed gain proportional controller.
Isotropic Optimal Control of Active Magnetic Bearing System
Authors: Kim Cheol-Soon , Lee Chong-Won
Published: February 2008

As a new rotor control scheme, isotropic control of weakly anisotropic rotor bearing system in complex state space is proposed, which utilizes the concepts on the eigenstructure of the isotropic rotor system. Advantages of the scheme are that the controlled system always retains isotropic eigenstructure, leading to circular whirling due to unbalance and that it is efficient for control of unbalance response. And the system analysis and controller design becomes simple and yet comprehensive since the order of the matrices treated in the complex domain approach is half of that in the real approach. The control scheme is applied to a rigid rotor-active magnetic bearing system which is digitally controlled and the control performance is investigated experimentally in relation to unbalance response and control energy. It is found that the isotropic optimal control method, which essentially eliminates the backward unbalance response component, is more efficient than the conventional optimal control in that it gives smaller major whirl radius and yet it often requires less control effort.
Harmonic Synthesis Design Methodology for Dynamic Spring Balancing
Authors: Shin Eungsoo , Streit D. A.
Published: February 2008

A new spring balancing technique, called a two-phase optimization method, is presented. Phase 1 uses harmonic synthesis to provide a system configuration which achieves an approximation to a desired dynamic system response. Phase 2 uses results of harmonic synthesis as initial conditions for dynamic system optimization. Optimization techniques compensate for nonlinearities in machine dynamics. Example applications to robot manipulators and to walking machine legs are presented and discussed.
Robust Stabilizability of Uncertain Linear Time-Delay Systems With Markovian Jumping Parameters
Authors: Benjelloun K. , Boukas E. K. , Yang H.
Published: February 2008

In this paper, we deal with the robust stabilizability of the class of uncertain linear time-delay systems with Markovian jumping parameters and unknown but bounded uncertainties. Under the assumption of the complete access to the continuous state, the stochastic controllability of the nominal system and the boundedness of the system’s uncertainties, sufficient conditions which guarantee the robustness of the stability of this class of systems are given. The control law which guarantees the robustness of the stabilizability is linear-type or saturation-type. An example is presented to illustrate the usefulness of the proposed theoretical results.
Optimal Feedforward Prefilter With Frequency Domain Specification for Nonminimum Phase Systems
Authors: Torfs Dirk , De Schutter Joris
Published: February 2008

The paper shows the influence of the location of unstable zeros on the tracking performance of feedforward prefilters. Unstable zeros are divided into a number of classes. It is shown that existing feedforward prefilters (Zero Phase Error Tracking Control (ZPETC), E-filter, Extended Bandwidth ZPETC, ...) perform well for two classes, but fail for a particular class of unstable zeros. For this class, a characteristic frequency, fc, exists such that the induced gain error attenuates all frequencies of the reference trajectory f ≤ fc and amplifies frequencies f > fc. Hence, it is impossible to freely select the tracking bandwidth. Therefore, an optimal feedforward prefilter for discrete time nonminimum phase systems is presented to deal with this class of unstable zeros. As in the ZPETC method, the prefilter compensates for unstable zeros in the inverse system model, retains the zero phase property, and introduces small gain errors. But in addition, the design minimizes a cost function for which a least square solution is found. A frequency and time domain analysis shows the superior performance of the presented optimal prefilter design even for trajectory with high frequency components.
Reconstruction of Indicated Pressure Waveform in a Spark-Ignition Engine From Block Vibration Measurements
Authors: Azzoni Piero
Published: February 2008

Knowledge of the pressure waveform in each cylinder of a spark-ignition engine may provide useful diagnostic information concerning engine operation. This paper presents a method for the reconstruction of the indicated pressure waveform for each cylinder of a multicylinder internal combustion engine using engine block vibration signals. The method permits the reconstruction of the cylinder pressure waveform, cycle by cycle, during free accelerations. The procedure has good potential for application in end-of-assembly diagnostic tests, using a noncontacting laser velocimeter. The same signal processing method may be applicable on-board an automobile to perform an on-line cylinder-by-cylinder diagnostics, using the same vibration sensor used for knock detection in many production vehicles.
Analysis and Control of a Flywheel Energy Storage System With a Hybrid Magnetic Bearing
Authors: Stienmier J. D. , Thielman S. C. , Fabien B. C.
Published: February 2008

This article presents the design, dynamic analysis, and control of a flywheel energy storage system. At the heart of the system is a hybrid magnetic bearing. The bearing consists of ring and disk shaped permanent magnets, and a synthetic ruby sphere on a sapphire plate. The bearing is shown to be stable without active control. Equations of motion for the flywheel are derived in a sensor based coordinate system. The resulting equations are non-singular around the nominal operating condition and are feedback linearizable without the need for a coordinate transformation. A method of modeling rotor imbalance as a set of sinusoidal disturbances of magnitudes that do not depend on rotational speed is also presented. To reject large external disturbances active control is applied to the flywheel. Two nonlinear control laws are applied and are shown to improve the initial condition response of the inherently stable system.
Sliding Mode Control With Sliding Perturbation Observer
Authors: Moura Jairo Terra , Elmali Hakan , Olgac Nejat
Published: February 2008

This work introduces a new robust motion control algorithm using partial state feedback for a class of nonlinear systems in the presence of modelling uncertainties and external disturbances. The effects of these uncertainties are combined into a single quantity called perturbation. The major contribution of this work comes as the development and design of a robust observer for the state and the perturbation which is integrated into a Variable Structure Controller (VSC) structure. The proposed observer combines the procedures of Sliding Observers (Slotine et al, 1987) with the idea of Perturbation Estimation (Elmali and Olgac, 1992). The result is what is called Sliding Perturbation Observer (SPO). The VSC follows the philosophy of Sliding Mode Control (SMC) (Slotine and Sastry, 1983). This combination of controller/observer gives rise to the new routine called Sliding Mode Control with Sliding Perturbation Observer (SMCSPO). The stability analysis shows how the algorithm parameters are scheduled in order to assure the sliding modes of both controller and observer. A simplified form of the general design procedure is also presented in order to ease the practical applications of SMCSPO. Simulations are presented for a two-link manipulator to verify the proposed approach. Experimental validation of the methodology is also performed on a PUMA 560 robot. A superior control performance is obtained over some full state feedback techniques such as SMC and Computed Torque Method.
Positive Uncertain Systems With One-Sided Robust Control
Authors: Chen Y. H. , Kuo C. Y.
Published: February 2008

We consider a control design problem for a class of uncertain systems. The salient features of the problem are fourfold. First, the uncertainty is time-varying. Second, the system is nonlinear. Third, the state is constrained to be only positive. Fourth, the control input may be constrained to be one-sided (i.e., either positive or negative). We start with a state transformation to release the state constraint. A partial sign-definiteness knowledge of the uncertainty is then shown to be critical to meet the control constraint. Three classes of controls are constructed: one for state constraint and two for the additional control constraint. They render the system globally practically stable.
Broadband Dynamic Modification Using Feedforward Control
Authors: Alberts Thomas E. , Pota Hemanshu R.
Published: February 2008

Recently published results arising from the acoustic noise control research community, demonstrate that system dynamics can be modified using feedforward control. Initial investigations applied to known disturbances in the form of steady-state harmonic excitation. This paper further explores feedforward dynamic modification, provides a proof of the nature of the modification, extends the method to allow for broadband excitation, and introduces a design technique for arbitrary assignment of transfer function poles. The results apply to any structure representable using modal expansion, and are applicable to systems with nonminimum phase zeros.
General Mathematical Model of Multi-Arm Cooperating Robots With Elastic Interconnection at the Contact
Authors: Z˘ivanovic´ Milovan , Vukobratovic´ Miomir
Published: February 2008

The procedure of modeling and the complete general form mathematical model of manipulators with six degrees of freedom in cooperative work are presented in the paper, together with the solution of undefiniteness problem with respect to force distribution. For the first time, a system of active spatial six-degree-of-freedom mechanisms elastically interconnected with the object (dynamic environment) is modeled. The reason for the emergence of the undefiniteness problem with respect to force is explained and the procedure for solving this problem given. Unlike the approaches given in the available literature, the undefiniteness problem with respect to force is solved in accordance with physical phenomena. The modeling procedure is illustrated by a simplified example.
Optimal Sensor Location in Motion Control of Flexibly Supported Long Reach Manipulators
Authors: Mavroidis Constantinos , Dubowsky Steven , Thomas Kevin
Published: February 2008

Long reach manipulator systems (LRMS) can perform tasks in difficult to reach locations. They use a small and fast manipulator mounted on a large flexible structure that can vibrate, degrading the system performance. Control methods that use strain measurements of the flexible structure have been proposed to control the system’s position in spite of the supporting structure’s vibrations using a model of the structure that relates strains to displacements. Here the minimum number of strain sensors needed to accomplish this control and their optimal locations on the flexible supporting structure are determined. These locations have been selected to achieve high measurement resolution, to maximize the computational robustness and to minimize the error in the identification of the structure’s strain-displacement model. The results are validated with simulations and experiments using a six degree of freedom laboratory LRMS.
Robust Trajectory Tracking Control of Elastic Robot Manipulators
Authors: Morita Yoshifumi , Ukai Hiroyuki , Kando Hisashi
Published: February 2008

In this paper, a robust control strategy is proposed for the trajectory tracking control of multi-link elastic robot manipulators. The robustness against both of the structured uncertainty caused by the nonlinear mechanical structure and the unstructured one caused by elasticity of links is taken into account in designing controllers. For this purpose the model of elastic robot manipulators is decomposed into the slow model and the fast model by using an integral manifold approach. The slow controller, which is robust against the structured uncertainty, is designed for the slow model on the basis of VSS theory. On the other hand, the fast controller, which is robust against the unstructured uncertainty, is designed for the fast model on the basis of H∞ control theory. Then the composite control is constructed with the slow controller and the fast controller. Some results of numerical simulations are presented to show the effectiveness of this design procedure.
Modeling and Impedance Control of a Two-Manipulator System Handling a Flexible Beam
Authors: Sun Dong , Liu Yunhui
Published: February 2008

This paper presents a new approach of transporting a flexible beam handled by two manipulators to a desired position/orientation while suppressing its vibration, and simultaneously controlling the internal forces between the manipulators and the beam to avoid any damage on the system. The algorithm combines impedance control and an I-type force feedback into one scheme by designing a proper response of the interaction force. No information about the vibration is used in the controller. The asymptotic stability is investigated by using LaSalle theorem, based on the vibration dynamics of the beam approximated by m assumed modes (m → ∞ ). Simulations demonstrate the validity of the proposed method.
Robust Time-Optimal Control of Flexible Structures With Parametric Uncertainty
Authors: Liu Shin-Whar , Singh Tarunraj
Published: February 2008

The design of robust time-optimal controllers using the sensitivity concept is presented in this paper. A parameter optimization problem is solved using the Switch Time Optimization algorithm to determine a bang-bang control profile that minimizes the maneuver time subject to the constraint that the sensitivity of the final states with respect to system parameters are zero. The proposed approach is illustrated on the benchmark floating oscillator problem and a slewing flexible beam whose equations of motion are nonlinear. Simulation results illustrate the reduction of residual vibrations of the system subject to the robust control profile, compared to the time-optimal control profile.
Contact Transition Control of Nonlinear Mechanical Systems Subject to a Unilateral Constraint
Authors: Pagilla P. R. , Tomizuka Masayoshi
Published: February 2008

In this paper, contact transition control of mechanical systems subject to a unilateral constraint is presented. A systematic way is proposed for designing control laws for unilaterally constrained mechanical systems. Three phases of motion (inactive, transition, active) are formulated depending on the activation/deactivation of the constraint. Our framework describes the complete behaviour of the mechanical system under the action of a unilateral constraint. We propose stable control laws for all the phases of the system. Exponential stability in each phase is shown. Of special interest is the contact transition problem. During this phase the dynamics is discontinuous. Nonsmooth Lyapunov techniques are used to show exponential stability in the transition phase. Composite Lyapunov functions are constructed for each phase and these are used to show asymptotic stability of the overall system taking into consideration switching from one phase to another. The proposed method is successfully implemented on robots interacting with an environment, and we present results of those experiments. Experimental results confirm the theoretically predicted behavior.
Numerical Methods for the Force Reflection of Contact
Authors: Ellis R. E. , Sarkar N. , Jenkins M. A.
Published: February 2008

An important problem in the field of force-reflecting systems and telerobotics is poor rendering of contact, particularly of contact with stiff surfaces. There are numerous possible sources of poor performance, including poor contact models, sampling errors, and delays due to computation or data transmission. In this paper we examine effects due to sample-and-hold, which is a fundamental property of both the discrete domain and also of the sensors and power amplifiers used in a force-reflecting system. We propose sample-and-hold be generalized to sample-estimate-hold. We show why ordinary sample-and-hold generates an active contact interface, and provide ways of improving the feeling of the interface. We have developed a suite of numerical methods for improving the performance of rendering of surfaces by force reflection. We have conducted both simulations and experiments to demonstrate the efficacy of the proposed scheme. Our contributions are a new method of digitally processing force data, and a systematic method for coupling force-processing systems that run at different rates.
Low Speed Motion Control Experiments on a Single Point Diamond Turning Machine Using CMAC Learning Control Algorithm
Authors: Larsen G. , Cetinkunt S.
Published: February 2008

Diamond turning of brittle materials such as glass, ceramic, germanium, and zinc sulfide has been of considerable research interest in recent years due to applications in optics and precision engineering systems. When diamond turning brittle materials, material removal should be kept within the ductile regime to avoid subsurface damage (Evans, 1991; Nakasuji et al., 1990). It is generally accepted that ductile regime machining of brittle materials can be accomplished using extremely low depth of cut and feed rates. Furthermore, the tool positioning accuracy of the machine must be in the nanometer range to obtain optical quality machined parts with surface finish and profile accuracy on the order of 10 nm and 100 nm respectively (Nakasuji et al, 1990, Ueda et al., 1991). Nanometric level positioning accuracy of the machine tool axes is difficult particularly at low feed rates due to friction and backlash. Friction at extremely low feed rates is highly nonlinear due to the transition from stiction to Coulomb friction, and as such is very difficult to model. Standard proportional-integral-derivative (PID) type controllers are unable to deal with this large and erratic friction within the requirements of ultra precision machining. In order to compensate the effects of friction in the machine tool axes, a learning controller based on the Cerebellar Model Articulation Controller (CMAC) neural network is studied for servo-control. The learning controller was implemented using “C” language on a DSP based controller for a single point diamond turning machine. The CMAC servo control algorithm improved the positioning accuracy of the single point diamond turning machine by a factor of 10 compared to the standard PID algorithm run on the same machine and control system hardware.
System Identification and Adaptive Control of the Multi-Axis Bending and Twisting Process
Authors: Sun Wei-Ching , Stelson Kim A.
Published: February 2008

An adaptive control scheme for the multi-axis bending and twisting process based on system identification of process models is presented. Three system identification methods, the frequency-response, the least-squares, and the singular value decomposition methods, have successfully identified the process models. Control based on these identified process models performed better than control based on the theoretical process models proposed by Luo et al. (1996). The shape errors between the intrinsic geometric quantities of the actual and desired parts are applied to the inverse identified process models to calculate incremental changes in axis commands for subsequent iterations. Comparison with experimental results demonstrates that adaptive control based on the identified process models achieves more rapid convergence of the iterations than the previous approach.
Using a Hydraulically Balanced Beam System in Control Education
Authors: Yang Pai-Hsueh , Lemkin Mark , Auslander David M.
Published: February 2008

This paper discusses a low cost solution to teaching controls in the laboratory through the use of a novel balance beam. The balance beam provides a vehicle to study many aspects of both control implementation and control algorithms. Due to the complexity of the system, a full semester of laboratory exercises is provided for even advanced students. The flexibility of the system provides challenging exercises for different levels of education. A low overall cost translates to accessibility to more schools. The ability to achieve good tracking performance with a simple cascaded loop controller makes this an ideal tool for teaching controls in a laboratory setting.
Simple Robust r − α Tracking Controllers for Uncertain Fully-Actuated Mechanical Systems
Authors: Zenieh Salah , Corless Martin
Published: February 2008

We consider the problem of designing robust tracking controllers for uncertain fully-actuated mechanical systems. We propose controllers which are robust r − α tracking controllers in the following sense. For a prespecified rate of convergence α > 0 and a prespecified tolerance r > 0, a proposed controller guarantees that the system’s trajectory exponentially converges to any desired trajectory with rate a and to within the tolerance r. Controller design is based on Lyapunov functions. The main advantage of these controllers is their simplicity. These controllers do not use the regressor matrix made popular in the area of robotic control which makes them simple to implement. Application to a two-link robotic manipulator is presented. Numerical simulation results are included.
Exponential Tracking Control for a Class of Uncertain Nonlinear Systems With Time-Varying Delay Arguments and Deadzone Nonlinearities
Authors: Sun Yeong-Jeu , Hsieh Jer-Guang
Published: February 2008

In this paper, the tracking problem for a class of uncertain nonlinear systems with time-varying delay arguments and deadzone nonlinearities is considered. A feedback control is proposed such that the states of the feedback-controlled system track the desired trajectories with any prespecified exponential rate of convergence. A numerical example is provided to illustrate the use of our main result.
On the Spatial Compliance of Robotic Manipulators
Authors: Fasse E. D.
Published: February 2008

Interactive control schemes, such as stiffness control and impedance control, are widely accepted as a means to actively accommodate environmental forces, but have not been widely applied. This is in part because well-known controllers are parametrized in a mathematically convenient, but nonintuitive way. “Spatial compliance control” is a Euclidean-geometrical version of compliance control that is parametrized in an intuitive way. A family of compliances is introduced with spatial transformation properties that simplify spatial reasoning aspects of compliance parameter selection. A control law is derived assuming that the robot consists of a serial linkage of rigid links actuated by variable-effort actuators.
Dynamic Modeling Analysis for Control of Chemical Vapor Deposition
Authors: Gevelber M. A. , Bufano M. , Toledo-Quin˜ones M.
Published: February 2008

A nonlinear dynamic model of the chemical vapor deposition (CVD) process has been developed to aid design of a closed-loop control system. A lumped control volume analysis is used to capture important mass and fluid transients and spatial affects, while a simplified single variable equation is used to represent the complex reaction chemistry. Steady-state experimental results and model predictions are compared and the control implications of the process dynamics are discussed.
Assessment of Internal Damping in Uniaxially Stressed Metals: Exponential and Autoregressive Methods
Authors: Audenino A. L. , Zanetti E. M. , Calderale P. M.
Published: February 2008

When a metallic material is highly stressed, its internal specific damping capacity increases showing a nonlinear behavior. In spite of this, the most part of experimental methods employ nonhomogeneous stress fields measuring only a volumetric average, often called structural damping. To overcome this problem the procedure herein presented extends the applicability of the plain traction or compression methods to higher frequency range (up to 300 Hz). The introduced methodology corrects for elastic energy and dissipated energy relative to the test machine and to the fixtures. The experimental procedure is based on the acquisition of a decay signal when the test machine excitation force has been removed. Two different methods to extract the pattern of internal damping versus material strain have been compared: one is based on least square exponential fitting while the other employs an autoregressive model. Best results have been obtained combining the two techniques taking into account also the variation of Young’s modulus with strain. The resulting curves of the loss factor as a function of strain amplitude for three steels and two cast irons are presented.
Flight Control Law Using Nonlinear Dynamic Inversion Combined With Quantitative Feedback Theory
Authors: Snell S. A. , Stout P. W.
Published: February 2008

A method of designing control laws for uncertain nonlinear systems is presented. Dynamic inversion is used to partially linearize the dynamics and then a nonlinear version of quantitative feedback theory (QFT) is applied to the resulting system which assures robustness to plant uncertainty. The design yields good performance with low bandwidth. An application to the design of flight control laws for a high performance aircraft is presented. The control laws demonstrate good performance by accurately following large angle of attack commands at flight speeds ranging from 53 to 150 m/s. Robustness is verified by including ±20 percent variations in pitching moment derivatives. The reduced bandwidth compared to a fixed-gain, linear design, leads to greatly reduced actuator transients, which should give improved reliability and longer life for the actuators and associated structure.
Nonlinear Dynamics of a Flexible Multirod (Multibeam) System
Authors: Edelstein E. , Rosen A.
Published: February 2008

The paper presents a general nonlinear numerical model for the dynamic analysis of a spatial structure that includes chains of flexible rods, with rigid bodies between them, and different kinds of connections between all these components. Such a system is denoted a multirod or multibeam system. The model is derived using a multibody system approach. The motion of each rod includes elastic deformations that are superimposed on finite rigid body motions. The elastic model of each rod is nonlinear and includes bending in two perpendicular directions, torsion, axial motion, and warping. Any distribution of the rod properties can be considered. Finite elements are used to describe the deformations. Although the elastic derivation is confined to moderate deformations, any level of nonlinearity can be addressed by dividing each rod into sub-rods. The joints between the rods are general and may include springs and dampers. A new formulation of Lagrange method is used in order to derive the equations of motion. It offers various advantages concerning the accuracy, stability of the constraints, and the modeling of constraints. The model is validated by comparing its results with new experimental results. Good agreement is shown between the experimental and numerical results.
Adaptive Robust Motion and Force Tracking Control of Robot Manipulators in Contact With Compliant Surfaces With Unknown Stiffness
Authors: Yao Bin , Tomizuka Masayoshi
Published: February 2008

High performance robust motion and force tracking control of robot manipulators in contact with compliant surfaces is considered in this paper. The robot parameters and the stiffness of the contact surface may not be known. The system may also be subjected to uncertain nonlinearities coming from the joint friction of the robot, external disturbances, the contact surface friction model, and the unknown time-varying equilibrium position of the contact surface. An adaptive robust motion and force tracking controller is proposed, which needs measurements of position, velocity, and interaction force only. The controller achieves a guaranteed transient performance and final tracking accuracy, a desirable feature for applications and for maintaining contact. In addition, the controller achieves asymptotic motion and force tracking without resorting to high-gain feedback when the system is subjected to parametric uncertainties.
Control-Oriented Model of a Dual Equal Variable Cam Timing Spark Ignition Engine
Authors: Stefanopoulou A. G. , Cook J. A. , Grizzle J. W. , Freudenberg J. S.
Published: February 2008

A control-oriented engine model is developed to represent a spark ignited engine equipped with a variable cam timing mechanism over a wide range of operating conditions. Based upon laboratory measurements a continuous, nonlinear, low-frequency phenomenological engine model is developed. With respect to a fixed-cam timing engine, the VCT mechanism alters the mass air flow into the cylinders, the torque response, and the emissions of the engine. The developed model reflects all of these modifications and includes a representation of the breathing process, torque and emission generation, and sensor/actuator dynamics. The model has been validated with engine-dynamometer experimental data and can be used in powertrain controller design and development.
H 2, Mixed H2/H∞ and H2/L1 Optimally Tuned Passive Isolators and Absorbers
Authors: Haddad Wassim M. , Razavi Ali
Published: February 2008

In many practical applications, unbalanced rotating machinery cause vibrations that transmit large oscillatory forces to the system foundation. Using ad hoc optimization schemes tuned isolators and absorbers have traditionally been designed to suppress system vibration levels by attempting to minimize the peak frequency response of the force/displacement transmissibility system transfer function. In this paper, we formulate the classical isolator and absorber vibration suppression problems in terms of modern system theoretic criteria involving H2 (shock response), mixed H2/H∞ (worst-case peak frequency response), and mixed H2/L1 (worst-case peak amplitude response) performance measures. In particular, using a quasi-Newton optimization method we design H2, mixed H2/H∞ and mixed H2/L1 optimally tuned isolators and absorbers for multi-degree-of-freedom vibrational systems. Finally, we compare our results to the classical Snowdon and Den Hartog absorbers.
Fast Mapping of Obstacles Into Configuration Space
Authors: Li Wei , Ma Chenyu , Chen Zushun , Cao Qi , Ye Jingnan
Published: February 2008

This paper presents an approach to fast mapping of obstacles from a workspace into a configuration space, based on defining some specific points in the workspace as fundamental obstacles. In order to achieve this objective, we propose efficient algorithms for mapping complex Cartesian obstacles by determining their critical points. The computational time required for mapping a two-dimensional obstacle is approximately 5 ms with a 33 Mhz 80486 CPU. Obstacle mapping in this paper is based on a CAD model of an environment that provide global information. The proposed mapping procedure and algorithms are suitable for industrial manipulators with a symmetric workspace occupied by polygonal obstacles.
A Spatial Mechanism for the Measurement of the Inertia Tensor: Theory and Experimental Results
Authors: Da Lio M. , Doria A. , Lot R.
Published: February 2008

This paper deals with the problem of measuring the inertia tensor of rigid bodies. An original approach is adopted, different from classical modal analysis techniques. The rigid body is forced by a spatial mechanism to rotate around different axes. Once the mechanism is calibrated, i.e., its inertia and stiffness matrices are known, the inertia tensor of the rigid body may be determined by measuring the frequencies of the small oscillations around the selected axes and then solving a least-squares identification problem. Two prototypes of the spatial mechanism were built. The first was used to perform tests and to measure the inertia tensor of some compressors for domestic refrigeration. The second was constructed to measure the inertia tensor of large mechanical systems.
Exponential Stabilization of a Wheeled Mobile Robot Via Discontinuous Control
Authors: Astolfi A.
Published: February 2008

In the present work the problem of exponential stabilization of the kinematic and dynamic model of a simple wheeled mobile robot is addressed and solved using a discontinuous, bounded, time invariant, state feedback control law. The properties of the closed-loop system are studied in detail and its performance in presence of model errors and noisy measurements are evaluated and discussed.
Local State Covariance Assignment for Stochastic Large-Scale Systems
Authors: Chang Koan-Yuh , Wang Wen-June
Published: February 2008

Based on the concept of variable structure control, this paper investigates the local state covariance assignment problem for stochastic large-scale systems. By using the invariance property of variable structure systems, the interconnection terms with matching condition will disappear on the sliding mode. With the aid of Ito-formula, the hitting controller of each subsystem is derived. Combining the sliding phase and hitting phase of the system design, the local feedback gain matrix Gi for each subsystem is obtained to achieve the local state covariance assignment.
Time-Delay Sliding Mode Control for a Servo
Authors: Park Jong Hyeon , Kim You Moo
Published: February 2008

In this paper, a new control algorithm called the time-delay sliding mode control (TDSMC), based on the time delay control (TDC) and the integral sliding mode control (SMC), is proposed and applied for controlling DC servos with a seal installed on their rotating axes. This algorithm adopts the robustness of sliding model control and improves the robustness of the TDC. The results of a series of experiments on a DC servo motor system with stick-slip friction show TDSMC is compatable with the TDC in the nominal performance, but is superior to the TDC and the PID control in the performance robustness. Settling time is used as a measure of the performance.
Zero Dynamics of Physical Systems From Bond Graph Models—Part II: MIMO Systems
Authors: Huang S. Y. , Youcef-Toumi K.
Published: February 2008

Zero dynamics is an important feature in system analysis and controller design. Its behavior plays a major role in determining the performance limits of certain feedback systems. Since the intrinsic zero dynamics can not be influenced by feedback compensation, it is important to design physical systems so that they possess desired zero dynamics. In the Part I paper, a method is proposed to derive the zero dynamics of SISO systems from bond graph models. Using this approach, the design of physical systems, including the consideration of zero dynamics, can be performed in a systematic way. In this paper, the extension of the proposed method for MIMO systems is presented. It is shown that for MIMO systems, the input-output configurations determine the existence of vector relative degrees. If a system has a vector relative degree, it’s zero dynamics can be identified by a straightforward extension of the proposed method. If a system does not have a vector relative degree, a dynamic extension procedure may be used to fix the structure. By doing so, the zero dynamics can still be identified in a similar manner. It is also shown that if the input-output configurations are ill-designed, not only the relative degrees do not exist, but also the zero dynamics can not be reasonably defined. In that case, independent tracking controls for all the outputs are impossible. Therefore, the results in this paper provide a guideline for the design of the input-output configurations as well as the zero dynamics of MIMO systems.
Vibration and Position Tracking Control of Piezoceramic-Based Smart Structures Via QFT
Authors: Choi Seung-Bok , Cho Seung-Sang , Park Young-Pil
Published: February 2008

This paper presents robust vibration and position tracking control of a flexible smart structure featuring a piezoceramic actuator. A cantilever beam structure with a surface-bonded piezoceramic actuator is proposed, and its governing equation of motion and associated boundary conditions are derived from Hamilton’s principle. The transfer function from control input voltage to output displacement is then established in Laplace domain considering the hysteresis behavior as a structured plant uncertainty. A robust QFT (quantitative feedback theory) compensator is designed on the basis of a stability criterion which prescribes a bound on the peak value of an M-contour in the Nichols chart (NC). In the formulation of the compensator, disturbance rejection specification and tracking performance bounds are specified to guarantee the robustness of the system to the plant uncertainty and external disturbance. A prefilter is also designed for the improvement of step and sinusoidal tracking control performances. Forced-vibration and tracking control performances are investigated through computer simulation and experimental implementation in order to demonstrate the efficiency and robustness of the proposed control methodology.
Verification of a Wheeled Mobile Robot Dynamic Model and Control Ramifications
Authors: Hong Daehie , Velinsky Steven A. , Feng Xin
Published: February 2008

For low speed, low acceleration, and lightly loaded applications, kinematic models of Wheeled Mobile Robots (WMRs) provide reasonably accurate results. However, as WMRs are designed to perform more demanding, practical applications with high speeds and/or high loads, kinematic models are no longer valid representations. This paper includes experimental results for a heavy, differentially steered WMR for both loaded and unloaded conditions. These results are used to verify a recently developed dynamic model which includes a complex tire representation to accurately account for the tire/ground interaction. The dynamic model is then exercised to clearly show the inadequacy of kinematic models for high load and/or high speed conditions. Furthermore, through simulation, the failure of kinematic model based control for such applications is also shown.
Tracking Control of Robot Manipulator Using Sliding Mode Controller With Performance Robustness
Authors: Chen Chieh-Li , Xu Rui-Lin
Published: February 2008

The tracking control problem of robot manipulator is considered in this paper. A sliding mode controller design with global invariance is proposed using the concept of extended system and feedback linearization. The sliding surface is assigned such that the sliding mode motion will occur while the proposed control law is applied. This results in a system with global invariance. The stability and performance of the resulting system can be guaranteed by the proposed systematic design procedure.