bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental On-Line Frequency Domain Identification and Adaptive Control of a Flexible Slewing Beam
Authors: Milford R. I. , Asokanthan S. F.
Published: February 2008

This paper presents experimental results for the real-time adaptive identification and control of a flexible, slewing beam. A frequency domain identification algorithm incorporating non-parametric transfer function estimation and least squares parametric estimation is used to reconstruct an accurate parametric model of the system, capable of accurately tracking changing plant dynamics in real time. This model is subsequently used to produce an LQG compensator which actively damps beam vibration caused by rapid slewing manoeuvres with large payload changes. Non-persistent excitation is addressed in the context of identification during nominal motion. It is shown that after a short duration learning period, the proposed identification scheme will yield a model which is sufficiently accurate for controller synthesis.
Nonlinear Modeling and Partial Linearizing Control of a Slewing Timoshenko-Beam
Authors: Yuan King , Hu Chen-Meng
Published: February 2008

The modeling and control of a horizontally slewing inextensible Timoshenko beam, taking into account the centrifugal stiffening effect and a tip payload, are considered. Partial differential equations of motion and orthogonality conditions for the constrained modes are derived. A finite dimensional dynamic model simplified by using the orthogonality conditions is obtained. To achieve the joint angle trajectory tracking with simultaneous suppression of elastic vibrations, a nonlinear controller is designed using input-output linearization and elastic-mode stabilization. A sufficient condition for asymptotic stability of the closed-loop system is established. Numerical examples with the role of slenderness ratio of the slewing beam highlighted are presented to demonstrate the effectiveness of the proposed control strategy.
Optimal Preview Semiactive Suspension
Authors: Jezequel L. , Roberti V.
Published: February 2008

This paper examines an optimal preview semiactive suspension of a quarter-coach model moving along randomly profiled track. This optimal computer-controlled suspension is designed only to dissipate energy, and is able to use knowledge of track irregularities over a distance L in front of the train. Thus the deformation of the track can be taken into account when calculating the semi-active suspension control law. First, the expression of the optimal preview semiactive control law is established. Then, using a two-degrees-of-freedom quarter-coach model, preview information is shown to improve the behavior of an optimal non-preview semi-active system, which can come close to the performance of an active system.
Analytical and Experimental Analysis of a Self-Compensating Dynamic Balancer in a Rotating Mechanism
Authors: Lee Jongkil , Van Moorhem W. K.
Published: February 2008

A theoretical and experimental approach was used to investigate the motion and effectiveness of a Self-Compensating Dynamic Balancer (SCDB). This is a device intended to minimize the effects of rotor imbalance and vibratory forces on a rotating system during normal operation. The basic concept of an automatic dynamic balancer has been described in many U.S. patents. The SCDB is composed of a circular disk with a groove containing massive balls and a low viscosity damping fluid. The objective of this research is to determine the motion of the balls and how this ball motion is related to the vibration of the rotating system using both theoretical and experimental methods. The equations of motion the balls were derived by the Lagrangian method. Static and dynamic solutions were derived from the analytic model. To consider dynamic stability of the motion, perturbation equations were investigated by two different methods: Floquet theory and direct computer simulation. On the basis of the results of the stability investigation, ball positions which result in a balance system are stable above the critical speed and unstable at critical speed and below critical speed. To determine the actual critical speed of the rotating system used in the experimental work, a modal analysis was conducted. Experimental results confirm the predicted ball positions. Based on the theoretical and experimental results, when the system operates below and near the first critical speed, the balls do not balance the system. However, when the system operates above the first critical speed the balls can balance the system.
Dynamics of Multibody Tracked Vehicles Using Experimentally Identified Modal Parameters
Authors: Nakanishi Toshikazu , Yin Xuegang , Shabana A. A.
Published: February 2008

The mode shapes, frequencies, and modal mass and stiffness coefficients of multibody systems such as tracked vehicles can be determined using experimental identification techniques. In multibody simulations, however, knowledge of the modal parameters of the individual components is required, and consequently, a procedure for extracting the component modes from the mode shapes of the assembled system must be used if experimental modal analysis techniques are to be used with general purpose multibody computer codes. In this investigation, modal parameters (modal mass, modal stiffness, modal damping, and mode shapes), which are determined experimentally, are employed to simulate the nonlinear dynamic behavior of a multibody tracked vehicle which consists of interconnected rigid and flexible components. The equations of motion of the vehicle are formulated in terms of a set of modal and reference generalized coordinates, and the theoretical basis for extracting the component modal parameters of the chassis from the modal parameters of the assembled vehicle is described. In this investigation, the track of the vehicle is modeled as a closed kinematic chain that consists of rigid links connected by revolute joints, and the effect of the chassis flexibility on the motion singularities of the track is examined numerically. These singularities which are encountered as the result of the change in the track configuration are avoided by using a deformable secondary joint instead of using the loop-closure equations.
Control of the Fabrication of Long Slender Workpieces of Arbitrary Shape—Part II: Closed-Loop Control of the Multi-Axis Bending Process
Authors: Luo J. X. , Joynt D. L. , Stelson K. A.
Published: February 2008

A feedback control scheme for the multi-axis bending process is presented. The closed-loop control is derived from transfer functions that represent the bending and twisting processes. The dynamics of these processes are due to the convection of shape between the bending dies during deformation. The success of the feedback control also depends on accurate measurement of part shape. A method based on laser scanning has been developed to find the intrinsic shape representation of the measured workpiece. Shape errors are defined as the difference between the intrinsic geometric quantities of the actual and desired part. By applying shape errors to the inverse transfer functions, we can obtain incremental changes in the axis control commands. Experimental results demonstrate that the feedback control causes shape errors to decrease on subsequent iterations.
Asymptotic Approximations for Systems Incorporating Fractional Derivative Damping
Authors: Liebst B. S. , Torvik P. J.
Published: February 2008

Viscoelastic constitutive relationships incorporating fractional derivatives have been previously shown to be extremely useful in describing the frequency dependent behavior of common damping materials. However, the implementation of such models in the analysis of damped mechanical systems is somewhat complicated by the fact that polynomial equations with noninteger order exponents must be solved. This paper develops accurate approximations from which the damping factor and damped natural frequency of such systems may be obtained by evaluating relatively simple algebraic expressions.
Optimal Redesign of Linear Systems
Authors: Grigoriadis K. M. , Zhu G. , Skelton R. E.
Published: February 2008

This paper proposes a redesign procedure for linear systems. We suppose that an initial satisfactory controller which yields the desired performance is given. Then both the plant and the controller are redesigned to minimize the required active control effort. Either the closed-loop system matrix or the closed-loop covariance matrix of the initial design can be preserved under the redesign. Convex quadratic programming solves this problem. In addition, an iterative approach for integrated plant and controller design is proposed, which uses the above optimal plant/controller redesign in each iterative step. The algorithm has guaranteed convergence and provides a sequence of designs with monotonically decreasing active control effort. Examples are included to illustrate the procedure.
Inverse Dynamics Algorithm for Space Robots
Authors: Saha Subir Kumar
Published: February 2008

An efficient algorithm for the inverse dynamics of free-flying space robots, consisting of a serial manipulator mounted on a free-base, e.g., a spacecraft, is presented. The kinematic and dynamic models are based on the concepts of the Primary Body (PB) and the Natural Orthogonal Complement, respectively, reported elsewhere. In this paper, besides the efficiency, the usefulness of the PB in deriving different kinematic models and selecting an efficient one is pointed out. Moreover, it is shown that a recursive algorithm for the inverse dynamics of the space robot at hand can be developed even without the consideration of the momenta conservation principle.
Artificial Neural Network Architecture Design Using Similarity Measure With Applications in Engineering Monitoring and Diagnosis
Authors: Chen Yuedong , Du R.
Published: February 2008

Artificial Neural Network (ANN) has been widely used for engineering monitoring and diagnosis. However, there are still several important problems unsolved and one of them is the architecture design of the ANN (namely, choosing the number of nodes in the hidden layer). In this technical brief, a new method of ANN architecture is introduced based on the idea that an ANN represents a mapping of training samples. Hence, the best ANN should represent the mapping that is most similar to the training samples. The method is tested using three practical engineering monitoring and diagnosis examples, including tool condition monitoring in turning, cutting condition monitoring in tapping, and metallographic condition monitoring in welding. It is demonstrated that the proposed method can improve the monitoring and diagnosis by approximately 3 percent.
Hydrostatic Force Sensor for Robotic Applications
Authors: Kazerooni H. , Evans Mark S. , Jones J.
Published: February 2008

This article presents a theoretical and experimental investigation of a new kind of force sensor which detects forces by measuring an induced pressure change in a material of large Poisson’s ratio. In this investigation, we develop mathematical expressions for the sensor’s sensitivity and bandwidth, and show that its sensitivity can be much larger and its bandwidth is usually smaller than those of existing strain-gage-type sensors. This force sensor is well-suited for measuring large but slowly varying forces. It can be installed in a space smaller than that required for existing sensors. This paper also discusses the effects of various parameters on the sensor’s performance and on failure modes. To verify the theoretical derivation, a prototype force sensor was designed and built. This prototype hydrostatic force sensor can measure the compressive forces up to 7200 lbf and tensile forces up to 3500 lbf.
Robust Stability of Nonlinear Feedback Systems With Parameter Deviations and Perturbed Nonlinearities
Authors: Miyagi Hayao , Kawahira Kimiko , Miyagi Norio
Published: February 2008

Robust stability of perturbed nonlinear feedback systems subjected to plant variations is investigated by using the direct method of Lyapunov. To establish the stability of the nominal system, the multivariable Popov criterion is utilized first. Then the stability of the system with parameter deviations and perturbed nonlinearities is studied. In this paper, an additive-type of parameter deviations are considered. The feature of the proposed method is that the tolerable range of individual parameter deviation and the conditions for the perturbed nonlinearities are simultaneously obtainable.
Modeling and Path-Tracking for a Load-Haul-Dump Mining Vehicle
Authors: DeSantis R. M.
Published: February 2008

A path-tracking controller for a load-haul-dump mining vehicle is designed using a geometric approach recently developed in the context of car- and tractor-trailer-like vehicles. This controller is made up of a kinematic component computing the velocities required of the vehicle for satisfactory path-tracking, and a dynamic component determining the propulsion and steering that are necessary to acquire these velocities. Prospects for practical implementation appear to be promising from an operational, a technological, and an economic point of view.
Harmonic Synthesis Theory for Dynamic Spring Balancing
Authors: Shin E. , Streit D. A.
Published: February 2008

At resonance, a small excitation force amplitude results in a relatively large amplitude system response. Although typically viewed as undesirable, operating a machine near resonance can sometimes be advantageous. A new approach to dynamic spring balancing, called harmonic synthesis, tunes a system so that the desired dynamic motion is approximated by the linear superposition of resonant mode shapes. Large amplitude machine motions are achieved with minimum energy required from system actuators. Machine motion is first approximated using a Fourier series expansion about a mean operating configuration. Equilibrators are then synthesized such that resulting machine natural frequencies and mode shapes are commensurate with the harmonics of the Fourier series expansion. Harmonic synthesis examples include one and two mode approximations to the motion of a two degree-of-freedom planar robot manipulator. Results show that equilibrator parameters are determined explicitly whether a path is specified at a number of points or described over the whole range of motion.
Robust Sliding Mode Control of Uncertain Dynamic Delay Systems in the Presence of Matched and Unmatched Uncertainties
Authors: Oucheriah Said
Published: February 2008

A nonlinear continuous controller is developed for a class of uncertain dynamic delay-systems in the presence of matched and unmatched uncertainties. The controller designed guarantees uniform ultimate boundedness of all motions of the class of uncertain time-delay systems considered. Furthermore, the parameters of the controller can be adjusted so that the deviation from ideal sliding mode can be made arbitrarily small. Finally, an example is included to illustrate the proposed design procedure.
Advanced Control Design for Marine Diesel Engine Propulsion Systems
Authors: Banning R. , Johnson M. A. , Grimble M. J.
Published: February 2008

A new marine diesel engine propulsion control design procedure is proposed which is applicable to a wide range of marine vessels. This procedure combines linear optimal H∞ control methods with non-linear control techniques to address the propulsion system’s nonlinearity. Simulation results show that a tracking control system aimed at saving fuel and optimizing efficiency may be obtained which is applicable across all maneuvring regimes. This compares favorably with the situation in some operating scenarios where the use of the linear controller alone can result in poor performance or even instability.
Determination of a Dynamic Grinding Model
Authors: Jenkins H. E. , Kurfess T. R. , Ludwick S. J.
Published: February 2008

In precision abrasive machining, it is important to control process variables such as the material removal rate, normal force and power input, as these factors influence surface finish, dimensional precision, and material damage. In this research, a linear grinding process model, with enhancements over past models, is developed relating normal force to material removal rates. Two experimental procedures for the determination of the grinding model’s parameters are presented. Simulations are performed to validate the grinding model. The determined model is found to be a valid representation of the grinding process that should prove useful in adaptive control with real-time parameter estimation.
Numerical Differentiation of Tracking Data of Human Motion: The Virtual Accelerometer
Authors: Bortolami S. B. , Riley P. O. , Krebs D. E.
Published: February 2008

A method based on the Kalman Filter for deriving whole-body segment accelerations from position tracking data is described. Such a procedure is experimentally calibrated and qualified as a Virtual Accelerometer supplying a resolution of 0.2 m/s2 and a relative accuracy of better than 10 percent rms within 0–8 Hz bandwidth. Results are finally compared to accelerometer performances reported by previous investigators.
Modeling the Systematic Uncertainty of Photogrammetric Tracking of Human Motion
Authors: Bortolami S. B. , Riley P. O. , Krebs D. E.
Published: February 2008

We address bias errors of photogrammetric tracking of four SELSPOT-II® cameras using active marker photogrammetry in a 2 m × 2 m × 2 m viewing volume for human locomotion measurements. We present uncertainty modeling regarding the first stage of equipment set up, which provides the camera frame to global frame rotation matrices and the distances among cameras. We also characterize the uncertainty due to the camera distortions of the bare system as compared to published performances achieved with a camera correction procedure. The particular approach is to qualify performances of photogrammetric tracking during routine operation and to identify the nature and magnitude of the uncertainty due to equipment set up and camera distortions as part of the total uncertainty in a self-consistent manner. We found that uncertainty of the camera frame to global frame rotation matrices produced rotation of the image and uncorrected camera hardware uncertainty produced dilatation or compression of the image twice the magnitude of that seen with camera correction. However, camera resolution remains as an equally important factor limiting the accuracy of photogrammetric tracking that can not be easily reduced numerically. In conclusion, the analysis elucidates how uncertainty propagates to numerical derivatives of the tracking data and prepares the groundwork for future development.
Force Feedback in Adaptive Trusses for Vibration Isolation in Flexible Structures
Authors: Clark W. W. , Robertshaw H. H.
Published: February 2008

This paper addresses the transmission of unwanted vibrations in flexible structures by actively minimizing dynamic forces seen at critical locations within the structure. An adaptive truss serves as an active interface between the two isolated sides of the structure, and force-feedback within individual links of the truss is the governing control law. The use of an adaptive truss allows the problem to be viewed as a set of localized control problems with collocated sensors and actuators. This paper first discusses the ideal capabilities of force feedback for active vibration isolation, and then presents the analytical and experimental results of a case study which shows significant reduction in transmitted vibrations.
A Detailed Study of the Low-Frequency Periodic Behavior of a Dry Friction Oscillator
Authors: Begley C. J. , Virgin L. N.
Published: February 2008

This work examines the periodic stopping motion present in the low-frequency response of a dry friction oscillator, excited harmonically through a base spring. Piecewise linear solution methods are used to compare two simple friction models, to consider the effects of viscous damping, and to illustrate stability considerations. Seeding phenomena, particularly at degenerate frequency ratios, are noted. Finally, experimental results provide a means to assess the effectiveness of the simple friction models in predicting observed motion.
Time Delay Observer: A Robust Observer for Nonlinear Plants
Authors: Chang Pyung H. , Lee Jeong W. , Park Suk H.
Published: February 2008

Motivated by the idea of the time delay estimation used in the Time Delay Control, Time Delay Observer (TDO) has been constructed. Owing to this idea, TDO does not require a model, and hence is easy to design for nonlinear systems in the phase variable form, even when the plant dynamics is not well known. Not including a model, TDO turned out to be robust to parameter variations and computationally efficient; yet achieved better accuracy. For this observer, the convergence property and the sensitivity to sensor noise have been analyzed. Then, in a simulation with a nonlinear plant, and in an experiment with a robot, TDO achieved an accuracy level similar to sliding observer and better than a Kalman filter. In an experiment on a pneumatic cylinder control, TDO reconstructed states much better than a numerical differentiator with low-pass filtering.
An Efficient Algorithm for Computing QFT Bounds
Authors: Rodrigues J. M. , Chait Y. , Hollot C. V.
Published: February 2008

An important step in Quantitative Feedback Theory (QFT) design is the translation of closed-loop performance specifications into QFT bounds. These bounds, domains in a Nichols chart, serve as a guide for shaping the nominal loop response. Traditionally, QFT practitioners relied on manual manipulations of plant templates on Nichols charts to construct such bounds, a tedious process which has recently been replaced with numerical algorithms. However, since the plant template is approximated by a finite number of points, the QFT bound computation grows exponentially with the fineness of the plant template approximation. As a result, the designer is forced to choose between a coarse approximation to lessen the computational burden and a finer one to obtain more accurate QFT bounds. To help mitigate this tradeoff, this paper introduces a new algorithm to more efficiently compute QFT bounds. Examples are given to illustrate the numerical efficiency of this new algorithm.
A Tracking Controller for Linear Time-Varying Systems
Authors: Chen Min-Shin
Published: February 2008

This paper proposes a new tracking control design for linear time-varying systems. The proposed control input, which is in the span of finitely many preselected input data, minimizes the L2-norm of the output tracking error. The more input data is used, the less L2-norm of the tracking error is achieved. The design of the new controller, which consists of a feedforward controller and a discretized state feedback loop, requires a finite-time preview of the system parameters and the reference trajectory. It is shown that as long as the preview time is longer than a critical value, the closed-loop stability is maintained irrespective of the stability property of the system’s zero dynamics. When the system parameters are periodically time-varying, the proposed design can be solely based on a set of experimental input and output data instead of on the exact information of system parameters.
Simulation of Friction in Multi-Degree-of-Freedom Vibration Systems
Authors: Tan Xi , Rogers R. J.
Published: February 2008

A force-balance friction model for the simulation of dynamic mechanical systems is presented. An extension of Karnopp’s model (1985), it can be applied to multi-degree-of-freedom vibration systems with sticking/slipping friction acting on a surface. The model is compared with piecewise continuous analytical solutions which use the classical Coulomb friction model. During sticking periods, the results from the present friction model change smoothly, whereas chattering appears when using the classical Coulomb friction model.
The Torque on the Input Shaft of an Axial-Piston Swash-Plate Type Hydrostatic Pump
Authors: Manring N. D.
Published: February 2008

Traditionally, the theoretical torque on the input shaft of a hydrostatic pump has been determined using a macroscopic “power-in, power-out” approach that neglects the time-varying aspects of this quantity and the compressibility of the hydraulic fluid within the circuit. In contrast to the traditional approach, this research analyzes and sums the basic forces within the machine to compute the instantaneous torque exerted on the shaft. It is shown that the instantaneous torque repeatedly varies by 1.5 percent of its maximum value and that resonant frequencies of the pump occur at even multiples of the “piston-pass” frequency. Furthermore, an integral average of the instantaneous torque is performed and shown to deviate by a maximum of 3 percent from the traditional method of computing this quantity.
Estimation of Gear Backlash: Theory and Simulation
Authors: Stein Jeffrey L. , Wang Churn-Hway
Published: February 2008

Machine and product condition monitoring is important to product quality control, especially for unmanned manufacturing. This paper proposes a technique for the estimation of clearance in mechanical systems under dynamic conditions with specific application to the estimation of backlash in gear systems of servomechanisms. The technique is based on a momentum transfer analysis that shows that the change in the speed (defined as bounce) of the primary gear due to impact with the secondary gear is related to the magnitude of the backlash. An algorithm is presented to estimate the bounce in real-time. The algorithm estimates the bounce by computing the standard bounce which is defined as the standard deviation of the demodulated envelope of the primary gear speed. The standard bounce is shown to be a good measure of the bounce when the system is excited sinusoidally. The algorithm’s accuracy and sensitivity are verified through computer simulation of an open-loop DC servomechanism. An approximately linear relationship between the standard bounce and the backlash magnitude is observed. This holds for backlash values exceeding recommended tolerances by ±100 percent. The algorithm is also shown to be insensitive to changes in the simulation model structure, model parameters as well as system and measurement noise. The estimation technique is accurate, computationally simple, and requires no additional sensors if the servosystem to be monitored already has a conventional tachometer.
The Dynamics of Clattering II: Global Results and Shock Protection
Authors: Goyal S. , Papadopoulos J. M. , Sullivan P. A.
Published: February 2008

The study of “clattering” motion, that occurs when flat objects strike the ground at an oblique angle, is continued. Previously derived equations of motion are solved for values of several clattering quantities (like total number of impacts, maximum velocity jumps in the sequence, time-durations, etc.) for any value of system parameters and initial conditions. The plotted results are examined for their relevance to shock protection. To improve the drop-tolerance of portable products, it is advised that fragile components be located close to the center of mass of the product; that the product be given a low radius of gyration by placing the heavier components, and perhaps even superfluous mass, toward the middle; and that any hard casing be designed (in terms of material and structure) to minimize its effective coefficient of restitution.
Stability and Control of a Parametrically Excited Rotating Beam
Authors: Sinha S. C. , Marghitu Dan B. , Boghiu Dan
Published: February 2008

In this paper the stability and control of a parametrically excited, rotating flexible beam is considered. The equations of motion for such a system contain time periodic coefficients. Floquet theory and a numerical integration are used to evaluate the stability of the linearized system. Stability charts for various sets of damping, parametric excitation, and rotation parameters are obtained. Several resonance conditions are found and it is shown that the system stability can be significantly changed due to the rotation. Such systems can be used as preliminary models for studying the flap dynamics and control of helicopter rotor blades and flexible mechanisms among other systems. To control the motion of the system, an observer based controller is designed via Lyapunov-Floquet transformation. In this approach the time periodic equations are transformed into a time invariant form, which are suitable for the application of standard time invariant controller design techniques. Simulations for several combinations of excitation and rotation parameters are shown.
Modeling and Control of the In-Situ Thermoplastic Composite Tape-Laying Process
Authors: Sun Wei-Ching , Mantell Susan C. , Stelson Kim A.
Published: February 2008

In thermoplastic tape-laying with in-situ consolidation, a laminated composite is constructed by the local application of heat and pressure. A moving head, applying heat and pressure, lays down and bonds a new layer to the previously bonded layers (substrate). The temperature at the interface between the top ply and the substrate is critical to achieving interlaminar bonding. Recent research on the in-situ thermoplastic composite tape-laying process has focused on modeling, numerical analysis and experimental analysis, but little research has considered the control of this process. In this work, a method is proposed for modeling and control of in-situ thermoplastic composite tape-laying. The key to the control algorithm is predicting the temperature at the interface between the top ply and the substrate. Based on a process model, a state feedback controller and a state estimator for temperature are designed for closed-loop control using the linear quadratic method. Two different approaches are used to develop the process model for real-time closed-loop control through temperature feedback. In the first approach, a low-order lumped parameter model is constructed from a finite difference scheme. The second approach constructs an empirical model through system identification. The structures of the two models are identical, but the parameters differ. The experimental results have shown that the developed estimator and controller can accurately estimate and control the bonding temperature using temperature feedback indicating that the proposed modeling and control methodology can produce a high quality thermoplastic composite laminate.
A Rugged and Reliable System for Measuring Engine Crankshaft Speed Fluctuations
Authors: Feng Hsi-Yung
Published: February 2008

A measurement system and the associated signal processing algorithm for accurately determining engine crankshaft speed fluctuations are presented in this work. The main features of the system include ruggedness, simple sensor installation, and high accuracy and resolution. The ruggedness and simplicity of the system are characterized by the use of highly reliable Hall-Effect Transducers (HETs) mounted on the engine flywheel bell housing to sense the passing of flywheel gear teeth. A relatively significant noise component is introduced to the HET measurements by the nonuniform flywheel gear tooth spacings. The high measurement accuracy is achieved by a very computationally efficient signal processing algorithm based on two HET inputs. The advantages of the current system over the single HET systems commonly used in practice are clearly demonstrated through experiments on a Detroit Diesel Corporation 6V-92TA engine.
On Statistical Model Validation
Authors: Lee L. H. , Poolla K.
Published: February 2008

In this paper we formulate a particular statistical model validation problem in which we wish to determine the probability that a certain hypothesized parametric uncertainty model is consistent with a given input-output data record. Using a Bayesian approach and ideas from the field of hypothesis testing, we show that in many cases of interest this problem reduces to computing relative weighted volumes of convex sets in RN (where N is the number of uncertain parameters). We also present and discuss a randomized algorithm based on gas kinetics, as well as the existing Hit-and-Run family of algorithms, for probable approximate computation of these volumes.
On-Line Controller Implementation for Attenuation of Synchronous and Transient Rotor Vibration
Authors: Keogh P. S. , Burrows C. R. , Berry T.
Published: February 2008

A study is presented in which the vibrations of a rotor are controlled under both synchronous and transient conditions. A Fourier decomposition of the rotor vibration during successive synchronous cycles is performed and the fundamental amplitude component is monitored. An analysis of the component response is developed and a strategy is proposed for the rotor vibration control. This is based around a gain matrix derived for a steady-state open-loop controller and the loop is then closed in a form of generalized integral control using a single feedback parameter. Performance and stability characteristics are investigated and for a linear system it is shown that the control of transient vibration caused by sudden mass loss from a rotor is possible. Limitations are stated if the system becomes nonlinear. Multiprocessor hardware is used for on-line implementation of the controller algorithm to an experimental rig, consisting of a rotor supported by two journal bearings with a magnetic control actuator. The results show the effectiveness of the vibration control, which is evaluated over the stable operating range of the controller.
An H∞ Synthesis of Robust Current Error Feedback Learning Control
Authors: Goh C. J. , Yan W. Y.
Published: February 2008

Conventionally, iterative learning control law is updated using past error information. As a result, the controller is effectively open-loop, apart from being unable to control unstable systems, it also does not share the robustness properties of feedback systems. It is proposed that current error feedback should be used to update the learning control law instead. We present a systematic design procedure based on the H∞ control theory to construct a robust current error feedback learning control law for linear-time-invariant, and possibly unstable, systems. The optimal design will ensure: 1 That the closed-loop system is stable; 2 that the convergence rate is optimum about the nominal plant; 3 robustness in the presence of perturbed or unmodeled dynamics, or nonlinearity.
Feedforward and Feedback Control Strategy for Active Noise Cancellation in Ducts
Authors: Hu Jwu-Sheng
Published: February 2008

This paper presents the theoretical work about active noise cancellation in ducts. The proposed control system is designed based on the assumption of a one-dimensional sound field. The controller consists of a feedforward block which serves as a noise observer. The feedback portion of the control algorithm is to minimize residual disturbances. Closed-loop stability of the MIMO (multiple-input-multiple-output) system is analyzed and the result shows that the dynamic influenced by the space-feedforward and feedback controllers can be decoupled. Both semi-infinite and finite-length ducts are considered in this study and simulation examples are given to illustrate the effectiveness of the proposed controllers.
Gain Scheduled SPR Controllers for Nonlinear Flexible Systems
Authors: Damaren C. J.
Published: February 2008

The problem of scheduling strictly positive real (SPR) dynamic compensation for control of nonlinear flexible systems which exhibit collocated inputs and outputs is explored. The major application is the robust motion control of structurally flexible systems whose dynamics possess significant configuration dependence. Included in this class are flexible robot manipulators. The issue of designing a linear time-invariant SPR compensator for control of a nonlinear system is examined Controller performance is enhanced by scheduling a series of such designs and a scheduling algorithm is developed which preserves robust stability with respect to the nonlinear plant model Global asymptotic stability of equilibrium setpoints is proven when the scheduled SPR compensator is used in conjunction with a proportional feedback gain. A numerical example employing a two-link flexible manipulator is used to illustrate the approach and compare the efficacy of different scheduling algorithms.
The Duality of Leakage and Aliasing and Improved Digital Spectral Analysis Techniques
Authors: Smith C. C. , Dahl J. F. , Thornhill R. Joe
Published: February 2008

When processing, recording, and analyzing continuous, analog signals or functions with a digital computer, information is lost when the signals are converted to digital form. When signals are sampled in one domain (time or frequency), the loss of information is characterized as aliasing in the other (frequency or time, respectively) domain. When a signal or function is truncated in one domain, the information loss is characterized as leakage in the other domain. It is shown that because of the dual nature of leakage and aliasing, that leakage in one domain reduces aliasing in the other domain and visa-versa. Examples of reducing leakage or aliasing in each domain by the dual in the other domain are given to illustrate. Since current art has not used time aliasing to reduce frequency leakage previously, a time alias processor for this purpose is described. A flat-top window function with spectral one frequency line in width is used in conjunction with the time alias processor to maintain leakage to within the nearest frequency line.
Optical Distance Meter Using a Pulsed Laser Diode and Fast Avalanche Photo Diodes for Measurements of Molten Steel Levels
Authors: Araki Tsutomu , Yoshida Haruhiko
Published: February 2008

An optical distance meter with a wide dynamic range, is proposed for measuring the level of molten steel in a steel mold. The meter operates by measuring the flight time of a short optical pulse that is propagated between the light source and the target. A pulsed laser diode with a fast rise time is utilized as a light source, and two avalanche photo-diodes are used as detectors. The optical distance meter performs at a measurement range and a standard deviation of the measurement error of 1 m and 1 mm for the black paper target, respectively. To test its reliability, the distance meter is used to monitor the level of molten steel during a continuous casting process. The results obtained were compared with those obtained using an eddy current sensor and a γ-ray sensor. The measurement range of the optical method is ten times those attained using other two sensors. Continuous monitoring of the steel level can be done from the initiation of the casting process with the proposed distance meter.
Constrained Optimal Pade´ Model Reduction
Authors: Lucas T. N.
Published: February 2008

A frequency-domain multipoint Pade´ approximation method is given that produces optimal reduced order models, in the least integral square error sense, which are constrained to match the initial time response values of the full and reduced systems for impulse or step inputs. It is seen to overcome a perceived drawback of the unconstrained optimal models, i.e., that they do not guarantee a proper rational reduced order transfer function for a step input. The method is easy to implement when compared to existing constrained optimal methods, and consists of solving only linear sets of equations in an iterative process. It is also seen to be a natural extension of an existing optimal method. Numerical examples are given to illustrate its application.
Optimal Trajectories for Flexible-Link Manipulator Slewing Using Recursive Quadratic Programming: Experimental Verification
Authors: Parker G. G. , Eisler G. R. , Robinett R. D. , Feddema J. T.
Published: February 2008

Experimental verification of minimum time, straight-line tracking using a two-link planar flexible robot is presented. Previously reported minimum-time angle histories are precompensated to account for joint servo-actuator dynamics. Using the precompensated joint commands, the optimal joint angles are tracked with such fidelity that the tip tracking error is less than 1.8 percent of the tip travel distance.
Surface Texture Improvement in the Turning Process Via Application of a Magnetostrictively Actuated Tool Holder
Authors: Liu D. , Sutherland J. W. , Moon K. S. , Sturos T. J. , Kashani A. R.
Published: February 2008

An active vibration control system for a turning process is presented. The system employs a magnetostrictive actuator and a rate feedback control scheme to suppress the vibration caused by random excitation in the turning process. A specially designed tool holder is developed to implement the actuation and the control scheme effectively. A model which accounts for both the dynamic response of the cutting process and the control system is described. The effectiveness of the vibration control system is studied via simulation and a series of experiments. A disturbance force is applied to the system by a shaker and the dynamic response of the system is observed. The experimental data shows that the rate feedback control scheme adds additional damping to the system and reduces the vibration. A complete set of 24 factorial design cutting experiments were also conducted using the tool holder and experimentally obtained surface profiles were compared to surface profiles obtained without the vibration control. It is shown that the system can improve the surface texture generated by the turning process.
Noise Reduction in Ducts Achievable by Point Control
Authors: Morris K. A.
Published: February 2008

Noise control in a one-dimensional duct is analyzed. This problem is of practical interest and is also simple enough that a complete theoretical analysis is possible. It is shown that the optimal controller leads to an unstable closed loop. The noise reduction level achievable with a stable closed loop is calculated for arbitrary choices of sensor and actuator locations. This enables the best placement of sensors and actuators to be determined. Also, the analysis indicates that a “spatial waterbed” effect exists in some configurations of active noise control: i.e., that noise levels are increased for points outside of the region over which the design is done.
Dynamics and Nonlinear Coordination Control of Multifingered Mechanical Hands
Authors: DasGupta A. , Hatwal H.
Published: February 2008

This paper presents a study of the dynamics and nonlinear coordination control of multifingered mechanical hands. Considering the dynamics of the object and the fingers, the equations of motion are derived in the finger joint space resulting in a set of differential equations with some algebraic constraints. Using dynamic extension, the equations are converted to the state space form, which results in a nonlinear system affine in control. For the purpose of control, certain output equations are defined. Using the tools of differential geometric control theory, some important properties of the system are shown. Using these properties, a nonlinear input-output linearizing controller is synthesized which yields a decoupled linear system. The poles of the resulting linearized system are then placed appropriately to render desirable features to the system. The theory is validated with an example of a three-fingered spatial hand manipulating a cuboidal object.
Modeling and Analysis of a Small Diameter Pneumatic Boring Tool
Authors: Collins R. L. , Prater G. , Hnat W. P.
Published: February 2008

This paper documents the development, solution, and application of a computational model for the dynamic response of a small diameter, pneumatic tool used for boring horizontal tunnels in the soil. The model consists of (i) the tool component kinematics and kinetics, (ii) mechanics of the tool and soil interactions, (iii) the compressible air dynamics, and (iv) the pressure control valve switching logic. The resulting model is represented by a set of coupled, sixth-order nonlinear differential equations. The boring tool design has several unique features, including dual pistonheads and a pilot-pressure actuated spool valve used to control the oscillatory piston. Implementation of these and other tool features in the computational model is discussed at length. The dynamic simulation and associated parametric studies establish the feasibility of the design for small diameter (25.4 mm) horizontal boring tools. Results for this design predict tunneling rates of about 60 meters/hr in a medium clay soil.
Stabilization of an Axially Moving String by Nonlinear Boundary Feedback
Authors: Fung Rong-Fong , Wu Jinn-Wen , Wu Sheng-Luong
Published: February 2008

In this paper, we consider the system modeled by an axially moving string and a mass-damper-spring (MDS) controller, applied at the right-hand side (RHS) boundary of the string. We are concerned with the nonlinear string and the effect of the control mechanism. We stabilize the system through a proposed boundary velocity feedback control law. Linear and nonlinear control laws through this controller are proposed. In this paper, we find that a linear boundary feedback caused the total mechanical energy of the system to decay an asymptotically, but it fails for an exponential decay. However, a nonlinear boundary feedback controller can stabilize the system exponentially. The asymptotic and exponential stability are verified.
Vibration Control of a Flexible Structure Using ER Dampers
Authors: Choi Seung-Bok
Published: February 2008

This technical brief addresses the vibration control of a flexible beam structure using ER (electro-rheological) dampers. A clamped-clamped flexible beam system supported by two short columns is considered. An ER damper which is operated in shear mode is designed on the basis of Bingham model of the ER fluid, and attached to the flexible beam. After deriving the governing equation of motion and associated boundary conditions, a sliding mode controller is formulated to effectively suppress the vibration of the beam caused by external forces. In the formulation of the controller, parameter variations such as frequency deviation are treated to take into account the robustness of control system. The effectiveness of the proposed control system is confirmed by both simulation and experimental results.
Disturbance Attenuating Adaptive Controllers for Parametric Strict Feedback Nonlinear Systems With Output Measurements
Authors: Tezcan I. Egemen , Bas¸ar Tamer
Published: February 2008

We present a systematic procedure for designing H∞-optimal adaptive controllers for a class of single-input single-output parametric strict-feedback nonlinear systems that are in the output-feedback form. The uncertain nonlinear system is minimum phase with a known relative degree and known sign of the high-frequency gain. We use soft projection on the parameter estimates to keep them bounded in the absence of persistent excitations. The objective is to obtain disturbance attenuating output-feedback controllers which will track a smooth bounded trajectory and keep all closed-loop signals bounded in the presence of exogenous disturbances. Two recent papers (Pan and Bas¸ar, 1996a; Marino and Tomei, 1995) addressed a similar problem with full state information, using two different approaches, and obtained asymptotically tracking and disturbance-attenuating adaptive controllers. Here, we extend these results to the output measurement case for a class of minimum phase nonlinear systems where the nonlinearities depend only on the measured output. It is shown that arbitrarily small disturbance attenuation levels can be obtained at the expense of increased control effort. The backstepping methodology, cost-to-come function based H∞ -filtering and singular perturbations analysis constitute the framework of our robust adaptive control design scheme.