bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust, Near Time-Optimal Control of Nonlinear Second-Order Systems: Theory and Experiments
Authors: Newman W. S. , Souccar K.
Published: March 2008

A technique is presented for controlling second-order, nonlinear systems using a combination of bang-bang time-optimal control, sliding-mode control, and feedback linearization. Within the control loop, a state space evaluation of the system classifies the instantaneous dynamics into one of three regions, and one of three corresponding control algorithms is invoked. Using a prescribed generation of desirable sliding surfaces, the resulting combined controller produces nearly time-optimal performance. The combination controller is provably stable in the presence of model uncertainty. Experimental data are presented for the control of a General Electric GP132 industrial robot. The method is shown to achieve nearly time-optimal motion that is robust to modeling uncertainties. Representative transients compare favorably to bang-bang control and PD control.
Force Control for Robotic Deburring
Authors: Bone G. M. , Elbestawi M. A. , Lingarkar R. , Liu L.
Published: March 2008

An active end effector based force control system for robotic deburring is successfully implemented using a PUMA-560 robot. The system goal of a controlled chamfer depth with minimum surface roughness is achieved by minimizing the normal chamfering force variance online. Several force control algorithms are evaluated based on this objective. The control laws are designed based on models combining a deterministic plant with a stochastic disturbance which are identified from experimental data. Simulation results are verified by real-time force control experiments. Performance comparisons are made based on the force variance and surface roughness achieved by each controller. The 6 step extended horizon controller is shown to achieve the best overall performance.
Physical Interpretation of Transfer Function Zeros for Simple Control Systems With Mechanical Flexibilities
Authors: Miu D. K.
Published: March 2008

Physical interpretation of the transfer function zeros of simple control systems with mechanical flexibilities is presented. It is shown that for discrete spring-mass systems and elastic beams, the poles are the resonant frequencies of the flexible structure and the complex conjugate zeros are the resonant frequencies of a substructure constrained by the sensor and actuator. It is also shown that when the flexible control systems become nonminimum phase, the real zeros are the results of nonpropagation of energy within the substructure.
Solutions to Point-to-Point Control Problems Using Laplace Transform Technique
Authors: Bhat S. P. , Miu D. K.
Published: March 2008

Using finite-time Laplace transform, the governing differential equations of linear, time invariant point-to-point control problems are converted into an equivalent set of linear algebraic equations embedded with the desired boundary conditions, characterizing the entire set of optimal and sub-optimal solutions. A linear programming technique for synthesizing the control inputs using selected sets of basis functions is presented. A new concept of feedback control which involves a recursive evaluation of the open-loop input is also developed.
Experiments on Point-to-Point Position Control of a Flexible Beam Using Laplace Transform Technique: Part I—Open-Loop
Authors: Bhat S. P. , Tanaka M. , Miu D. K.
Published: March 2008

When lightly damped flexible structures are used in high bandwidth applications, the elimination of residual vibration during point-to-point positioning is an important engineering problem. Using the Laplace domain synthesis technique introduced in earlier publications, experiments on the precise point-to-point position control of a flexible beam have been performed. In Part I of this two-part paper, results related to open-loop control are presented. A variety of candidate control functions are evaluated and performance issues related to robustness and sensitivity are investigated.
Experiments on Point-to-Point Control of a Flexible Beam Using Laplace Transform Technique: Part II—Closed-Loop
Authors: Bhat S. P. , Miu D. K.
Published: March 2008

Using the Laplace domain synthesis technique documented in earlier publications, experiments on the closed-loop point-to-point position control of a flexible beam are presented. Two different approaches are described, a feed-forward control and an iterative open-loop control. Solution to the robustness problems encountered during actual implementation is also demonstrated.
Simulation of Intermittent Turning Processes
Authors: Zhang G. M. , Yerramareddy S. , Lee S. M. , Lu S. C.-Y.
Published: March 2008

A simulation model is developed to study the dynamic characteristics of intermittent turning operations. Factors such as chip load, free-vibration of the toolpost structure, and nonhomogeneous hardness distribution in the material being cut are incorporated in the model. The principle of superposition is used in the formulation of the simulation algorithm. The impact between the cutting tool and the workpiece at the start of every cutting period during machining is treated as an initial value problem. The simulation model provides a quantitative evaluation of the tool vibratory motion during the intermittent turning process. Study of the cutting dynamics based on the simulation results not only confirms the experimental findings, but also indicates that increasing the static stiffness of the toolpost structure is an effective approach to control the tool vibratory motion. The determination of probability of tool breakage under various spindle speed settings is presented as an example to demonstrate the practical applications of the simulation model developed in this work.
Decentralized Adaptive Robust Control Design: The Uncertainty is Time Varying
Authors: Chen Y. H.
Published: March 2008

We consider a class of nonlinear uncertain interconnected systems with time-varying uncertainty. The uncertainty may arise within each system as well as in the interconnections. The uncertainty is assumed bounded but the bound is unknown. No a priori statistical information is imposed. Decentralized adaptive robust control is proposed for each system. The control has two parts. First, an adaptive scheme for the estimation of the bound is constructed. Second, a robust control, which is based on the adaptive parameter, is adopted for each system.
Using Operational Calculus to Obtain Transient Response Estimates in Linear Uncertain Feedback Systems
Authors: Chait Yossi , Lacey Neil F. , MacCluer C. R.
Published: March 2008

A new methodology is presented for deriving transient response estimates for a large class of uncertain linear feedback single input/output systems, including unstable distributed parameter systems. It is shown that using operational calculus, estimates exist and can be computed even in cases where a certain error norm is greater than unity. Several simple numerical examples illustrate the application of the new methodology.
Determination of the Tolerable Sector of Series Nonlinearities in Uncertain Time-Delay Systems Under Dynamical Output Feedback
Authors: Hsiao Feng-Hsiag , Hsieh Jer-Guang , Wu Min-Sheng
Published: March 2008

Several sufficient conditions which guarantee robust stability of uncertain time-delay systems under dynamical output feedback with a class of series nonlinearities are derived in the time domain. Each of these results is expressed by a succinct scalar inequality and corresponds to a certain extent to the tradeoff between simplicity and sharpness. Properties of the matrix measure and the comparison theorem are employed to give robustness conditions which assure asymptotic stability rather than ultimate boundedness of trajectories. Moreover, for each uncertain time-delay system, a class of series nonlinearities lying in the sector [α, β] are found such that the overall feedback system with these nonlinearities is still asymptotically stable. An algorithm based on these robust stabilization criteria is presented to determine the tolerable range of series nonlinearities from the inverse viewpoint. It is shown that the plant uncertainties and nonlinearities may destabilize the system. Hence the nominal feedback system without series nonlinearities should be sufficiently stable to ensure robust stability.
Some Applications of Natural Motion Control
Authors: Koditschek D. E.
Published: March 2008

This paper offers two engineering applications of the theoretical ideas presented in [13]. Each case concerns a generalized setpoint problem for a mechanical system whose configuration space does not permit globally asymptotically stable closed loops. By presenting a navigation function for each case, the paper shows how “natural control” may provide a degree of autonomy of execution without the appeal to a higher level planning system.
A Robust Off-Line Method for System Identification: Robust Iterative Least Squares Method With Modified Residuals
Authors: Dai Heping , Sinha Naresh K.
Published: March 2008

A general criterion is proposed for robust identification of both linear and bilinear systems. Following Huber’s minimax principle, the ordinary iterative Gauss-Newton approach is applied, with modified residuals, to minimize the suggested robust cost function. The proposed method, named the robust iterative least squares method with modified residuals (RILSMMR), can provide simultaneously robust estimates of the system parameters as well as the residual variance. Therefore it is superior to the earlier robust methods. A proof of convergence of the RILSMMR is given. Results of simulation with both the RILSMMR and nonrobust identification methods are included. These confirm that RILSMMR has certain advantages over both conventional nonrobust identification methods, as well as earlier robust methods.
Process Fault Diagnosis Based on Process Model Knowledge: Part II—Case Study Experiments
Authors: Isermann R. , Freyermuth B.
Published: March 2008

A computer assisted fault diagnosis system (CAFD) is considered which allows the early detection and localization of process faults during normal operation or on request. It is based on an on-line engineering expert system and consists of an analytical problem solution, a process knowledge base, a knowledge acquisition component and an inference mechanism. The analytic problem solution uses a process parameter estimation, and the detection of process coefficient changes, which are symptoms of process faults. The process knowledge base is comprised of analytical knowledge in the form of process models and heuristic knowledge in the form of fault trees and fault statistics. In the phase of knowledge acquisition the process specific knowledge like theoretical process models, the normal behavior and fault trees is compiled. The inference mechanism performs the fault diagnosis, based on the observed symptoms, the fault trees, fault probabilities and the process history. This is described in Part I. In Part II, case study experiments with a d.c. motor, centrifugal pump, a heat exchanger and an industrial robot show practical results of the model based fault diagnosis.
Control of a Class of Manipulators With a Single Flexible Link: Part I—Feedback Linearization
Authors: Wang D. , Vidyasagar M.
Published: March 2008

The subject of this paper is the feedback linearization of the input-output and input-state equations for a class of multi-link, three degrees-of-freedom manipulators with the last link flexible. This class includes the 5-bar-linkage and the elbow manipulator. It is shown that the input-output equations are only feedback linearizable if the output variables are chosen appropriately. However, the nonlinear dynamics made unobservable by this feedback are not asymptotically stable which is a severe drawback. It is then shown that the input-state equations are not feedback linearizable. These results indicate that feedback linearization techniques are not appropriate for this class of manipulators. Thus, alternate methodologies should be explored. That issue is tackled in Part II.
Control of a Class of Manipulators With a Single Flexible Link: Part II—Observer-Controller Stabilization
Authors: Wang D. , Vidyasagar M.
Published: March 2008

In this paper, a controller and observer design is proposed for a class of multi-link manipulators with one flexible link. It is shown that it is possible to transform the state space equations of these manipulators into an equivalent set of equations which are almost linear. The controller then uses a nonlinear state feedback which is designed based only on the linear part of the transformed system equations. An observer is presented in which the estimated states converge to the actual states exponentially. Finally, it is shown that combining the observer with the controller results in a system which is input-output stable in a local sense.
Sliding Mode Control and Elastic Mode Stabilization of a Robotic Arm With Flexible Links
Authors: Nathan P. J. , Singh S. N.
Published: March 2008

This paper treats the question of control of an elastic robotic arm of two links based on variable structure system (VSS) theory and pole assignment technique for stabilization. A discontinuous joint angle control law, based on VSS theory, is designed which accomplishes asymptotic decoupled joint angle trajectory tracking. In the closed-loop system, the trajectories are attracted toward a chosen hypersurface in the state space and then slide along it. Although, joint angles are controlled using variable structure control (VSC) law, the flexible modes of the links are excited. Using center manifold theory, it is shown that the closed-loop system, including the sliding mode controller, is stable. Based on a linearized model about the terminal state, a stabilizer is designed using pole assignment technique to control the elastic oscillations of the links. A control logic is included which switches the stabilizer at the instant when the joint angle trajectory enters a specified neighborhood of the terminal state. Simulation results are presented to show that in the closed-loop system, accurate joint angle trajectory tracking, and elastic mode stabilization are accomplished in the presence of payload uncertainty.
Nonlinear Landing Gear Behavior at Touchdown
Authors: Yadav D. , Ramamoorthy R. P.
Published: March 2008

Landing gear dynamics for an aircraft has been analyzed with a heave-pitch model having telescopic main gear and articulated nose gear using oleopneumatic shock absorber. System equations have been presented incorporating the effects of linkage dynamics, frictional forces, and nonlinearities in the tyre, air spring, and oleo damping forces. Sensitivity of the system response to variations in some shock strut parameters has been investigated for the landing touchdown impact phase to bring about improvement in the performance.
Modeling and Dynamic Evaluation of a Two-Stage Two-Spool Servovalve Used for Pressure Control
Authors: Tsai S. T. , Akers A. , Lin S. J.
Published: March 2008

Experimental results for a unique design of a two-spool pressure control valve were reported by Anderson (1984). The first stage is a dynamically stable flapper-nozzle valve for which a mathematical model is already available (Lin and Akers, 1989a). For the second stage, however, which consists of two parallel spools in a common body, no such model existed. The purpose of this paper was therefore to construct such a model and to compare results calculated from it to experimental values. Moderately good agreement with experimental values was obtained.
Suboptimal Path Planning of Robots: Minimal Nonlinear Forces and Energy
Authors: Wiens G. J. , Berggren M. J.
Published: March 2008

An algorithm has been presented in which the role of inertia sensitivities in path planning of robots is investigated. The main objective is to obtain a path, from point A to point B in joint coordinates, in which the nonlinear forces (centripetal and Coriolis) are minimized. Using standard optimization theory, an objective (“cost”) function is selected to include energy and nonlinear forces for minimization.
Force Distribution in Walking Machines Over Rough Terrain
Authors: Gardner John F.
Published: March 2008

This paper presents a computationally efficient technique for the solution of the force distribution problem in walking machines. It differs from previous techniques in two important respects. First, the formulation of the problem allows for arbitrarily oriented surface normals at the point of contact between the feet and the ground. This is an important extension since the primary purpose of legged vehicles is locomotion on rough terrain. Second, the solution technique allows for the introduction of nonlinear constraints which can be tailored to achieve secondary goals in system performance. An example is presented which is based on the geometry of the Ohio State University Adaptive Suspension Vehicle which indicates that the technique performs favorably when compared to pseudo-inverse and computationally intensive optimization methods.
Active Control of Mechanical Vibrations in a Circular Disk
Authors: Kuo C. Y. , Huang C. C.
Published: March 2008

Mechanical vibration is a common phenomenon observed in the operation of many machines and arises from the inertia effect of machine parts in motion. While many control system design methods for distributed parameter systems have already been proposed in the literature, generally they are either based on truncated models and, as a result, suffer from computational and “spillover” difficulties or require distributed parameter actuators which are rarely available in reality. Therefore, there is a definite need for the development of a class of controllers which can be realized by spatially discrete sensors and actuators and whose design specifically includes stabilization and control of all the higher frequency vibration modes. To address this need, we propose the design of linear compensators whose design is based on root locus arguments for infinite dimensional systems. Since the design is not based on finite dimensional models of the plant to be controlled, we expect it to perform well for those distributed parameter systems for which sufficiently accurate data on pole and zero locations can be obtained. In this paper we apply this approach to control mechanical vibrations in those physical systems which can be accurately modeled as a flexible circular disk. Computer simulation results indicate that all the predominant lower frequency vibrations can be efficiently eliminated by just a few pairs of colocated sensor and actuator.
Input/Output Linearization Using Time Delay Control
Authors: Youcef-Toumi K. , Wu S.-T.
Published: March 2008

A control procedure that uses Time Delay Control to achieve input/output linearization of a class of nonlinear systems is presented. The control system is characterized by a simple algorithm and enhanced robustness properties in comparison with current control algorithms. The paper first reviews the fundamentals of input/output linearization. The use of Time Delay Control is then shown to result in an exact linear system for sufficiently small delay time. Modified controllers for systems with a low-pass filter are also investigated. Simulation results show that the algorithm works well with measurement noise. The controller is also tested on a single-link flexible arm to show the effectiveness of the simple algorithm in the control of complicated systems.
A Fiber-Optic-Based Protocol for Manufacturing System Networks: Part I—Conceptual Development and Architecture
Authors: Ayyagari A. , Ray A.
Published: March 2008

The goal of Computer Integrated Manufacturing (CIM) is to put together the diverse areas of engineering, design and production processes, material inventory, sales and purchasing, and accounting and administration into a single interactive closed loop control system [1]. Essential to this distributed total manufacturing system is the integrated communications network over which the information leading to process interactions, and plant management and control will flow. Such a network must be capable of handling heterogeneous real-time (e.g., data packets for inter-machine communications at the factory floor) and non-real-time (e.g., Computer Aided Design (CAD) drawings, design specifications, and administrative information) traffic. This sequence of papers in two parts presents the development and analysis of a novel fiber-optic-based medium access control (MAC) protocol for integrated factory and office communications. Its adaptation as the common MAC layer protocol in the fiber-optic-based version of Manufacturing Automation Protocol (MAP) [2] and Technical and Office Protocols (TOP) [3], will make their specifications identical up to the presentation layer; only the application layer which is user-specific could be different. This first part provides the necessary background for the reported work and details of the protocol which is represented by a finite-state-machine model. Part II [4] presents the performance analysis of the protocol using a statistical model, and a comparison of the simulation and analytical results.
Robot Grinding and Finishing of Cast Iron Stamping Dies
Authors: Whitney D. E. , Tung E. D.
Published: March 2008

This paper describes a method for finishing cast iron stamping dies. The task is to remove tool marks in the form of grooves and cusps left by a ball-end milling tool. The bottoms of the grooves represent the desired final surface profile. The method consists of using a closed-loop force-controlled robot with a flexible grinding disk coupled to a means for measuring the height of the partially ground cusps. Measurement is particularly easy, accurate, and sensitive if the tops of the partially ground cusps are flat, a condition that is not easy to obtain; otherwise accurate measurement is a chore. The Taguchi method is used to determine process parameters (grinding grit size, feed speed, disk speed, disk inclination angle, etc.) that yield flat tops. This grinding strategy has proven successful. A smooth, regular, and accurate final shape is obtained in spite of the relatively poor position accuracy of the robot. The measurement strategy has not been implemented yet but it appears feasible based on preliminary experiments.
Modeling of a Hydraulic Energy Regeneration System: Part II—Experimental Program
Authors: Pourmovahed A. , Beachley N. H. , Fronczak F. J.
Published: March 2008

This study reports experimental data taken with a hydraulic energy regeneration system and compares the measured data with analytical results. The system tested consisted of two foam-filled hydraulic accumulators, a variable-displacement piston-type pump/motor, a reservoir and a flywheel. During a series of experiments, energy was repeatedly transferred between the hydraulic accumulators and the flywheel through the pump/motor. Computed system variables compared favorably with the experimental results. At high and moderate pump/motor swivel angles, the round-trip efficiency varied from 61 to 89 percent. It was significantly lower at small angles.
Output Feedback Two-Time Scale Control of Multilink Flexible Arms
Authors: Siciliano B. , Prasad J. V. R. , Calise A. J.
Published: March 2008

Lightweight flexible arms will most likely constitute the next generation robots. The design key is the adoption of flexible links, rather than rigid links like in today’s industrial robots. Despite all the potential advantages achievable with a flexible arm, the control problem is complex, due to the introduction of increasingly more complex dynamics. This paper represents an effort toward the goal of designing efficient control systems for multilink flexible arms. A two-time scale approach is pursued which allows the adoption of a composite control strategy. First a slow control can be designed for the slow (rigid) sybsystem, then a fast stabilizing control for the fast (flexible) subsystem. The main contribution of the paper is to address the problem of lack of full state measurements concerned with the fast control design. An output feedback dynamic compensator of fixed order is designed. Its optimal gains are computed according to a loop transfer recovery technique in order to obtain a robust design. The control is tested by means of simulation results for a nonlinear model of a two-link flexible arm.
Independent Modal Space Control With Positive Position Feedback
Authors: Baz A. , Poh S. , Fedor J.
Published: March 2008

This study presents an Independent Modal Space Control (IMSC) algorithm whose modal control forces are generated based on a Positive Position Feedback (PPF) strategy. This is in contrast to conventional modal controllers that rely in their opeation on negative feedback of the modal position and velocity. The proposed algorithm combines the attractive attributes of both the IMSC and the PPF. It maintains the simplicity of the IMSC as it designs the controller of a complex structure at the uncoupled modal level. At the same time, it utilizes only the modal position signal to provide a damping action to undamped modes. The paper presents the theory behind this algorithm when using first order filters to achieve the PPF effect. The optimal time constants of the filters are determined. The performance of the algorithm is enhanced by augmenting it with a “time sharing” strategy to share a small number of actuators between larger number of modes. The effectiveness of the algorithm in damping out the vibration of flexible structures is validated experimentally. A simple cantilevered beam is used as an example of a flexible structure whose multi-modes of vibration are controlled by a single actuator. A piezo-electric actuator is utilized, in this regard, as a part of a computer-controlled active control system. The performance of the active control system is determined in the time and the frequency domains. The results are compared with those obtained when using the IMSC, PPF with second order filters, the Psuedo-Inverse (PI) and a Modified Independent Modal Space Control (MIMSC). The experimental results suggest the potential of the proposed method as a viable means for controlling the vibration of large flexible structures.
A Simplified Multi-Input Multi-Output Formulation for the Quantitative Feedback Theory
Authors: Yaniv O. , Chait Y.
Published: March 2008

A simplified multi input/output formulation is developed for the quantitative feedback theory (QFT) for the 2 × 2 (n = 2) case. This formulation is consistent with traditional QFT philosophy where performance is specified for each individual closed-loop transfer function and control bandwidths are minimized. The simplified formulation turns the solution of a simultaneous robust stability and robust model matching problem into a two (n in general) step procedure of solving quadratic inequalities (whose coefficients are linear functions of the plants and the performance constraints); the traditional procedure requires six (n + n2 in general) steps for a similar problem. A numerical example illustrates the simplified formulation and demonstrates its ability to offer useful insight in a control design.
Analysis and Design of Manipulators With Decoupled and Configuration-Invariant Inertia Tensors Using Remote Actuation
Authors: Youcef-Toumi K.
Published: March 2008

The dynamics of manipulators with diagonal and/or constant inertia tensors are described by simple differential equations. This feature greatly simplifies the control of high speed manipulators. This paper presents design methods, which incorporate selection of arm structure and link inertial properties, to achieve simplified manipulator dynamics. First the concept of remote actuation is described. A model is then developed in order to analyze the effects of remote actuation on the manipulator kinematics and dynamics. The modeling is based on Kane’s partial rates along with a set notation to concisely express the system’s dynamics. Second, necessary and sufficient conditions for achieving such dynamic properties for open and closed kinematic chain linkages are derived. These techniques are then applied in the design of three degree-of-freedom planar manipulator and the three degree-of-freedom spatial M. I. T direct-drive manipulator. The mass distribution conditions for which the arm inertia tensors are diagonal and configuration-invariant are derived. The resultant dynamic equations of these manipulators are shown to be very simple.
Surface Profile Measurement During Turning Using Fringe-Field Capacitive Profilometry
Authors: Garbini J. L. , Koh Sih-Ping , Jorgensen Jens E. , Ramulu Mamidala
Published: March 2008

The use of fringe-field capacitive sensing for surface profile measurement during the turning process is described. Measurements of the local surface height are inferred from variations in a fringe electric field induced between the sensing element and the workpiece. The surface profile is determined from high-speed scanning of the sensing element across the surface. The technique is particularly well-suited to the relatively harsh environment of in-process measurement. We have implemented a system in which profile measurements are made continuously, in real-time, and immediately adjacent to the cutting tool. The results of tests conducted to determine the accuracy and sensitivity of this capacitive profilometer are presented. In-process measurements of surfaces generated by turning with roughness in the range of 0.3 to 4.0 μm were made. Comparisons with static profile measurements made using standard stylus instrumentation are presented, and show quantitative agreement.
Modeling and Design of a Mechanical Tendon Actuation System
Authors: Johnstun C. R. , Smith C. C.
Published: March 2008

Basic dynamics of single tendons are modeled, isolated, and measured. Fundamental transmission line models are presented with assumptions applicable to using the models for tendons. The models are verified by careful experimental design. It is then shown how to use this fundamental data to design and determine bandwidth limitations of tendon actuation systems. Short, stiff, light tendons transmit force and velocity best. Pulley friction in the tests reported was primarily Coulombic, causing signal delay. This delay was significant for tendons routed across bushings or bare metal pegs, but it was not a factor when the tendons were routed over pulleys mounted on bearings. Increasing the number of pulleys increased the delay in the case of the pegs or bushings enough to cause instability in some systems. Assuming a second order load, curves were generated relating bandwidth to tendon system and load parameters.
A Study of Supermaneuverable Flight Trajectories Through Motion Field Simulation of a Centrifuge Simulator
Authors: Repperger D. W.
Published: March 2008

The advent of supermaneuverable flight trajectories for high performance aircraft opens up new research areas involving the human factors effects on pilots when they fly these unusual flight scenarios. There exists a need to conduct studies in motion simulators such as centrifuges to investigate how these unusual motion fields effect humans both physiologically and how they impact the ability of a pilot to perform a mission. The dynamic control of a centrifuge simulator to emulate supermaneuverable flight trajectories is studied in this paper by considering the centrifuge simulator as a 3 revolute axes robot manipulator.
Steady-State Theoretical Model of an Electro-Hydraulic Single-Disk Pilot Valve
Authors: Sun Y. , Parker G. A.
Published: March 2008

The paper describes an electro-hydraulic single floating-disk valve suitable for use as a pilot control device. For this type of application proportional action involving small movements of the disk for the null condition is required. The theory for the steady-state linearized analysis of both the fluid and electromagnetic characteristics is developed. Experimental verification of the electromagnetic model is also described.
Linear Model Following Control Systems Based on Reduced Models
Authors: Liaw C. M. , Jaw K. S. , Gong Y. S.
Published: March 2008

A linear model following controller based on a reduced-order plant model is presented in this paper. The reduced model is composed of two submodels that characterize the dynamics during the transient and the steady states. The order of the controller is minimized without deteriorating the system performance. In addition, the proposed modified linear model following controller, which uses the output as the feedback signal, can be easily implemented. Some simulation and experimental results are given to demonstrate the effectiveness of the proposed controller.
A Two-Riccati, Feasible Algorithm for Guaranteeing Output L∞ Constraints
Authors: Zhu Guoming , Skelton Robert E.
Published: March 2008

In the presence of all disturbances whose outer products are bounded by a known matrix N, this paper develops controllers to minimize the control L∞ norm bound subject to L∞ constraints on each output, the resulting controller is an LQG controller with a special choice of the output weight matrix and input noise intensity matrix, that are both iterated. The design algorithm turns out to be feasible if the algorithm converges.
Control-Oriented Modeling of Distributed Parameter Systems
Authors: Helmicki A. J. , Jacobson C. A. , Nett C. N.
Published: March 2008

In this paper the use of linear, time-invariant, distributed parameter systems (LTI-DPS) as models of physical processes is considered from a control viewpoint. Specifically, recent theoretical results obtained by the authors for the control-oriented modeling of LTI-DPS are concisely reviewed and then a series of applications is given in order to illustrate the practical ramifications of these results.
Estimation of Vehicle Shaft Torque Using Nonlinear Observers
Authors: Masmoudi R. A. , Hedrick J. K.
Published: March 2008

Current closed-loop automotive shift control algorithms could greatly benefit if a measurement of the drive axle shaft torque was available. Direct measurements using strain gauges are too expensive for commercial applications. Magnetic pickup sensors that count the passage of gear teeth provide very inexpensive RPM measurements and are currently being used in production vehicles. This paper shows through simulations how these sensors can be used with a nonlinear observer technique (sliding mode) to estimate axle shaft torque from measurements of transmission output speed and driven wheel speed.
On Time Delay in Noncolocated Control of Flexible Mechanical Systems
Authors: Yang B. , Mote C. D.
Published: March 2008

A new method is presented for noncolocated control of flexible mechanical systems. The destabilizing effect of noncolocation of sensors and actuators is eliminated through introduction of specific time delay block(s) in the control system. The time delay constants in those blocks depend on the system eigenstructure. For a given flexible mechanical system, if there exists a time delay relation, the system response at one point can be exactly predicted from the vibration measurement at other point(s) of the system. In this case all stabilizing controllers from colocated control can be directly used. The time delay theory is verified by experiments on noncolocated control of a translating string.
Dynamic Analysis to Evaluate Viscoelastic Passive Damping Augmentation for the Space Shuttle Remote Manipulator System
Authors: Alberts Thomas E. , Xia Houchun , Chen Yung
Published: March 2008

This paper presents a NASTRAN finite element analysis for evaluation of the effectiveness of viscoelastic damping treatments as passive controls for large flexible space manipulators. The passive damping could be used alone or as an augmentation to active control. Perhaps the best existing example of a practical flexible manipulator is the space shuttle Remote Manipulator System (RMS). The authors use the RMS as an example for this investigation, subjecting it to a detailed dynamic analysis which can be used to evaluate the critical modes for control and to distinguish the modes which are good candidates for active control from those which are well suited for passive control. Modal potential energy analysis (MPE) is used to examine the modal energy distribution in each structural member of the complex flexible chained system. The results indicate that the most dominant contributors to end-point oscillations fall into two categories. These include very low frequency modes due to joint flexibility and higher frequency modes due to bending in the booms. Significant end-point motions result from each category, but the most significant motions are associated with joint flexibility. Finally, a finite element analysis is performed to evaluate the effectiveness of constrained viscoelastic layer damping treatments for passive vibration control. Passive damping augmentation is introduced through the use of a constrained viscoelastic layer damping treatment applied to the surface of the manipulator’s flexible booms. It is shown that even the joint compliance dominated modes can be damped to some degree through appropriate design of the treatment.
On Self-Tuning Control of Nonminimum Phase Discrete-Time Systems Using Approximate Inverse Systems
Authors: Yahagi Takashi , Lu Jianming
Published: March 2008

This paper presents a new method for self-tuning control of nonminimum phase discrete-time stochastic systems using approximate inverse systems obtained from the least-squares approximation. We show how unstable pole-zero cancellations can be avoided, and that this method has the advantage of being able to determine an approximate inverse system independently of the plant zeros. The proposed scheme uses only the available input and output data and the stability using approximate inverse systems is analyzed. Finally, the results of computer simulation are presented to show the effectiveness of the proposed method.
Controller Gain Selection for an Electromagnetic Suspension Under Random Excitation
Authors: Fabien B. C.
Published: March 2008

This paper considers the modeling and control of a single axis electromagnetic suspension for vibration isolation. Here, the nonlinear dynamic equations for the suspension are derived using a lumped-parameter model of the system that includes factors for flux leakage, fringing and finite permeability of the materials. To study the vibration isolation characteristics a set of linearized dynamic equations are used. The feedback signals considered are the air gap size, the absolute velocity of the isolated load and the current in the coil. Stability boundary plots that illustrate the domain of controller gains that will stabilize the system are presented. It is shown that feedback stabilization can be achieved without current feedback. The paper also considers the design of state feedback controllers that (i) minimize the mean square absolute displacement response of the suspension and (ii) minimize a measure of the system energy dissipation. In both cases the suspension system is assumed to be excited by random white noise disturbances. It is shown that near optimum disturbance attenuation and energy dissipation can be achieved without current feedback. Procedures for selecting these suboptimum controller gains are suggested. The paper compares the suboptimum controller gains with the state feedback gains obtained using Linear Quadratic optimal control theory. It is shown that the disturbance attenuation characteristics of the electromagnetic suspension can be made to be superior to that of a passive isolation system. Experimental results are also presented.
Robust Optimal Model Matching Control Design for Flexible Manipulators
Authors: Chen Bor-Sen , Yang Tsang-Yi
Published: March 2008

In this paper, the two-parameter compensator technique is used to control the one-link flexible robot arm theoretically. The rigid-body mode and the first flexible mode are considered as the nominal model and the other flexible modes are considered as unmodeled dynamics. The sufficient condition for stabilizing the nominal model against the unmodeled flexible dynamics is derived. The first control parameter is employed to robustly stabilize the one-link flexible robot arm against the unmodeled dynamics and the second one is specified to make the response of the system follow the desired reference model. Simulation results are included to demonstrate the performance of the compensator.
An Analysis and Improvement of the Predictive Control Integrating Component
Authors: Kurfess T. R. , Whitney D. E.
Published: March 2008

This paper presents a basic review and explanation of the predictive control, discusses the inherent problems with the integrating component of the predictive control, and recommends some initial modifications to greatly improve its performance. Some examples are presented at the end of the paper to verify that the modifications to the integrating component do, indeed, enhance the predictive controller’s performance.
Robust State Estimation for Linear Systems
Authors: Garimella S. S. , Srinivasan K.
Published: March 2008

Real-time state estimation of a linear dynamic system using an observer, in the presence of modeling errors in the system model used by the observer and uncertainty in the initial system states, is considered here. A guideline for designing observers for multioutput systems is established, based on an expression for an upper bound on the norm of the state estimation error derived in this paper. An example is presented to illustrate the usefulness of this guideline.
A Chebyshev-Based State Representation for Linear Quadratic Optimal Control
Authors: Nagurka M. L. , Wang S.-K.
Published: March 2008

A computationally attractive method for determining the optimal control of unconstrained linear dynamic systems with quadratic performance indices is presented. In the proposed method, the difference between each state variable and its initial condition is represented by a finite-term shifted Chebyshev series. The representation leads to a system of linear algebraic equations as the necessary condition of optimality. Simulation studies demonstrate computational advantages relative to a standard Riccati-based method, a transition matrix method, and a previous Fourier-based method.
Almost Decoupling by Quantitative Feedback Theory
Authors: Perez R. A. , Nwokah O. D. I. , Thompson D. F.
Published: March 2008

This paper uses almost decoupling theory to obtain a systematic solution to the MIMO-QFT problem by an n times solution of the SISO-QFT sensitivity constraint problem. This is similar to the current MIMO-QFT formulation that requires in principle an n times solution for the elements of the closed-loop transfer matrix. The problem is also in a form where direct comparison with H∞ control is feasible. However, due to the use of unstructured perturbation description, this design route along with all H∞ based design methods will invariably produce more conservative (higher bandwidth) controllers than classical QFT.
Dynamic Singularities in Free-Floating Space Manipulators
Authors: Papadopoulos E. , Dubowsky S.
Published: March 2008

Dynamic Singularities are shown for free-floating space manipulator systems where the spacecraft moves in response to manipulator motions without compensation from its attitude control system. At a dynamic singularity the manipulator is unable to move its end-effector in some inertial direction; thus dynamic singularities must be considered in the design, planning, and control of free-floating space manipulator systems. The existence and location of dynamic singularities cannot be predicted solely from the manipulator kinematic structure because they are functions of the dynamic properties of the system, unlike the singularities for fixed-base manipulators. Also analyzed are the implications of dynamic singularities to the nature of the system’s workspace.
Nonlinear and Adaptive Control of Flexible Space Structures
Authors: Bennett W. H. , LaVigna C. , Kwatny H. G. , Blankenship G.
Published: March 2008

This paper addresses design of nonlinear control systems for rapid, large angle multiaxis, slewing and LOS pointing of realistic flexible space structures. The application of methods based on adaptive feedback linearization for nonlinear control design for flexible space structures is presented. A comprehensive approach to modeling the nonlinear dynamics and attitude control of multibody systems with structural flexure is considered. Adaptive feedback linearizing control laws are described based on Lagrangian dynamical system model for the spacecraft. Simulation results for attitude slewing and LOS stabilization for the NASA/IEEE Spacecraft COntrols Laboratory Experiment (SCOLE) design challenge are presented.
Adaptive Velocity Control of DC Motors With Coulomb Friction Identification
Authors: Yang Y. P. , Chu J. S.
Published: March 2008

A new dc motor control technique for the Coulomb friction compensation is proposed. The technique uses an adaptive velocity control scheme for a dc servo motor with on-line estimated parameters, including a Coulomb friction parameter, which is a combination of the Coulomb friction torque, motor time constant, moment of inertia of the motor, and sampling time of the discrete-time motor model. The estimation model used in the adaptive control process is validated off-line by a pseudo-linear regression algorithm for system parameters in a linear ARMAX model, and by adaptive Kalman filters for the Coulomb friction parameter described as pseudo-random binary sequences. The adaptive controller consists of a friction compensator and a PID controller, whose gains are adjusted adaptively in terms of estimated parameters. The proposed adaptive control law is implemented and tested on a microprocessor-based dc servo motor, and is applicable to many dc-motor-driven precision servo mechanisms. Experimental results are shown to be superior to those of conventional PID controls in terms of parameter fluctuation.
Stability and Performance Limits of Interaction Controllers
Authors: Newman W. S.
Published: March 2008

Theoretical performance limits of controlled systems which interact with dynamic environments are analyzed from consideration of simple, single-axis mass-spring-damper systems. A measure of interaction control performance is defined which is independent of environment dynamics. It is shown that unmodelled dynamics between actuators and sensors places severe constraints on interaction control performance. An ultimate performance limit to guaranteed-stable interaction control is derived. A general algorithm is proposed for the design of guaranteed-stable interaction controllers which applies to arbitrary linear, time-invariant systems, and which approaches the optimal admittance while providing good disturbance rejection. The approach is illustrated in simulations.
An Inner/Outer Loop Controller for Rigid-Flexible Manipulators
Authors: Khorrami F. , Zheng S.
Published: March 2008

In this paper, vibration control of flexible-link manipulators is considered. A nonlinear partial differential equation describing the dynamics of a two-link planar manipulator with a flexible forearm is derived. Thereafter, utilizing the eigenfunctions corresponding to the boundary value problem at hand, a finite-dimensional approximation of the model is given. The controller design strategy is based upon an inner-loop controller which corresponds to the rigid body motion of the manipulator taking into consideration the vibrations of the manipulator and an outer-loop controller for further vibration damping and robustness enhancement of the closed-loop dynamics to parameter variations in the system. The measurement used in the outer-loop controller is obtained through an accelerometer mounted on the flexible forearm which can be easily attained in an experimental setup. The control methodology advocated in this paper are applicable to the multi-link flexible manipulators.