bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Inverse Dynamics Solutions in Direct Dynamics Simulations
Authors: Risher D. W. , Schutte L. M. , Runge C. F.
Published: February 2008

Previous attempts to use inverse dynamics solutions in direct dynamics simulations have failed to replicate the input data of the inverse dynamics problem. Measurement and derivative estimation error, different inverse dynamics and direct dynamics models, and numerical integration error have all been suggested as possible causes of inverse dynamics simulation failure. However, using a biomechanical model of the type typically used in gait analysis applications for inverse dynamics calculations of joint moments, we produce a direct dynamics simulation that exactly matches the measured movement pattern used as input to the inverse dynamic problem. This example of successful inverse dynamics simulation demonstrates that although different inverse dynamics and direct dynamics models may lead to inverse dynamics simulation failure, measurement and derivative estimation error do not. In addition, inverse dynamics simulation failure due to numerical integration errors can be avoided. Further, we demonstrate that insufficient control signal dimensionality (i.e., freedom of the control signals to take on different “shapes”), a previously unrecognized cause of inverse dynamics simulation failure, will cause inverse dynamics simulation failure even with a perfect model and perfect data, regardless of sampling frequency.
Axial Impact Biomechanics of the Human Foot-Ankle Complex
Authors: Yoganandan N. , Pintar F. A. , Kumaresan S. , Boynton M.
Published: February 2008

Recent epidemiological, clinical, and biomechanical studies have implicated axial impact to the plantar surface of the foot to be a cause of lower extremity trauma in vehicular crashes. The present study was conducted to evaluate the biomechanics of the human foot–ankle complex under axial impact. Nine tests were conducted on human cadaver below knee–foot–ankle complexes. All specimens were oriented in a consistent anatomical position on a mini-sled and the impact load was delivered using a pendulum. Specimens underwent radiography and gross dissection following the test. The pathology included intra-articular fractures of the calcaneus and/or the distal tibia complex with extensions into the anatomic joints. Impactor load cell forces consistently exceeded the tibial loads for all tests. The mean dynamic forces at the plantar surface of the foot were 7.7 kN (SD = 4.3) and 15.1 kN (SD = 2.7) for the nonfracture and fracture tests, respectively. In contrast, the mean dynamic forces at the proximal tibial end of the preparation were 5.2 kN (SD = 3.1) in the nonfracture group, and 10.2 kN (SD = 1.5) in the fracture group. The foot and tibial end forces were statistically significantly different between these two groups (p < 0.01). The present investigation provides fundamental data to the understanding of the biomechanics of human foot–ankle trauma. Quantifying the effects of other factors such as gender and bone quality on the injury thresholds is necessary to understand foot–ankle tolerance fully.
Estimation of in Vivo Bone Mineral Density (BMD) and Shape Characterization for Diagnosing Osteoporosis by Ultrasonic Inspection
Authors: Nogata F. , Matsui K. , Kagechika K. , Sueyoshi Y. , Tomita K.
Published: February 2008

A new method for estimating in vivo bone mineral density (BMD) and characterizing the shape of cancellous bone has been proposed using the results of ultrasonic inspection for the diagnosis of osteoporosis. The method is based on two-dimensional bone area fraction S (percent bone area between bone and bone marrow) calculated from the difference in the speed of ultrasonic wave propagation through cancellous bone. It was shown that the two-dimensional area fraction of a heel bone gives a good relationship to the BMD by DXA (dual energy x-ray absorptiometry) testing of human heel bone (calcaneus) and spine (vertebrae lumbar), as expressed by the relation, BMD (g/cm2) = 0.0167S for heel bone (r = 0.83), and BMD (g/cm2) = 0.0254S + 0.123 for the spine (r = 0.77). Shape characterization is based on the image simulation procedure employing eight random variables from a computer and the statistical results of fractal analysis for numerous cancellous bone patterns. We also demonstrate the validity of the shape characterization technique using autopsy specimens as a diagnostic tool for osteoporosis.
Model Simplification and Stability Robustness With Elastic Flight Vehicles
Authors: Newman Brett , Schmidt David K.
Published: February 2008

Quantitative criteria are presented for model simplification, or order reduction, such that the reduced order model may be used to synthesize and evaluate a control law, and the stability and stability robustness obtained using the reduced order model will be preserved when controlling the higher order system. The error introduced due to model simplification is treated as modeling uncertainty, and some of the results from multivariable robustness theory are brought to bear on the model simplification problem. Also, the importance of the control law itself, in meeting the modeling criteria, is underscored. A weighted balanced order reduction technique is shown to lead to results that meet the necessary criteria. The procedure is applied to an aeroelastic vehicle model, and the results are used for control law development. Critical robustness properties designed into the lower order closed-loop system are shown to be present in the higher order closed-loop system.
A Network Thermodynamic Model of Kidney Perfusion With a Cryoprotective Agent
Authors: Lachenbruch C. A. , Diller K. R.
Published: February 2008

A network thermodynamic model has been devised to describe the coupled movement of water and a permeable additive within a kidney during perfusion under the combined action of diffusive, hydrodynamic, and mechanical processes. The model has been validated by simulating perfusions with Me2SO, glycerol, and sucrose and comparing predicted weight and vascular resistance with experimental results obtained by Pegg (1993). The flows of CPA, water, colloid, and cellular impermeants are governed by a combination of the individual osmotic potential and pressure differences between compartments of the kidney, the viscoelastic behavior of the tissue, and the momentum transferred between the flows. The model developed in this study presents an analytical tool for understanding the dynamics of the perfused kidney system and for modifying perfusion protocols to minimize the changes in cell volume, internal pressure build-up, and increases in vascular resistance that currently present barriers to the successful perfusion of organs.
Influence of Cell Deformation on Leukocyte Rolling Adhesion in Shear Flow
Authors: Lei X. , Lawrence M. B. , Dong C.
Published: February 2008

Blood cell interaction with vascular endothelium is important in microcirculation, where rolling adhesion of circulating leukocytes along the surface of endothelial cells is a prerequisite for leukocyte emigration under flow conditions. HL-60 cell rolling adhesion to surface-immobilized P-selectin in shear flow was investigated using a side-view flow chamber, which permitted measurements of cell deformation and cell-substrate contact length as well as cell rolling velocity. A two-dimensional model was developed based on the assumption that fluid energy input to a rolling cell was essentially distributed into two parts: cytoplasmic viscous dissipation, and energy needed to break adhesion bonds between the rolling cell and its substrate. The flow fields of extracellular fluid and intracellular cytoplasm were solved using finite element methods with a deformable cell membrane represented by an elastic ring. The adhesion energy loss was calculated based on receptor-ligand kinetics equations. It was found that, as a result of shear-flow-induced cell deformation, cell-substrate contact area under high wall shear stresses (20 dyn/cm2) could be as much as twice of that under low stresses (0.5 dyn/cm2). An increase in contact area may cause more energy dissipation to both adhesion bonds and viscous cytoplasm, whereas the fluid energy input may decrease due to the flattened cell shape. Our model predicts that leukocyte rolling velocity will reach a plateau as shear stress increases, which agrees with both in vivo and in vitro experimental observations.
Decentralized Control of Active Vehicle Suspensions With Preview
Authors: Hac´ Aleksander
Published: February 2008

In this paper, decentralized control of active vehicle suspensions with preview of road irregularities is considered using a two-degree-of-freedom vehicle model. It is shown that by taking advantage of the separation between the eigenvalues of the slow subsystem representing the body mode, and the fast subsystem corresponding to the wheel mode, the design of the preview controller can be decoupled. Since decentralized preview controllers are synthesized independently for two single-degree-of-freedom systems, analytical solutions are obtained. The results of the analysis and simulations demonstrate that the performance of the system with the proposed controller is comparable to that of the optimal preview controller based on a fully interconnected system.
Control System Synthesis Based on Plant Test Data
Authors: Chan Jenq-Tzong H.
Published: February 2008

A correlation equation is established between open-loop test data and the desired closed-loop system characteristics permitting control system synthesis to be done on the basis of a numerical approach using experimental data. The method is applicable when the system is linear-time-invariant and open-loop stable. The major merits of the algorithm are two-fold: 1) Arbitrary placement of the closed-loop system equation is possible, and 2) explicit knowledge of an open-loop system model is not needed for the controller synthesis.
Rapid Recursive Structure Redesign for Improved Dynamics of a Single Link Robot
Authors: Pil Anton , Asada Haruhiko
Published: February 2008

This paper describes a technique for improving dynamic performance of robots by recursively modifying the mechanical structure through prototyping and experimentation. In each recursion, a prototype robot is tested and evaluated experimentally, an incremental change in structure design is determined based on the analysis of the experimental data, and the mechanical structure is physically modified so as to drive the plant dynamics towards a desired response. To expedite the iterative process, (i) a rapid prototyping technique using photo-polymerization is developed, (ii) a gradient descent method is applied to recursively determine an optimal design, and (iii) all the design, prototyping, and experimentation processes are integrated and carried out under computer control. The optimal, incremental change of design is determined by using a sensitivity Jacobian. The sensitivity Jacobian is initially obtained numerically using a finite element model. Further, the sensitivity Jacobian is corrected and updated recursively with experimental data after each iteration. A proof-of-concept demonstration system is built and tested for the development of a simple single link robot. The arm structure made of plastic is reinforced recursively by coating it with a photo-acrylate plastic with an optimal thickness distribution so that the frequency response of the structure can be improved toward a desired reference model.
The Analysis of Rigid Body Motion From Measured Data
Authors: Shiflett G. R. , Laub A. J.
Published: February 2008

In this paper, a new method for analyzing rigid body motion from measured data is presented. The approach is numerically stable, explicitly accounts for the errors inherent in measured data and those introduced by floating point arithmetic, automatically accommodates any number of rigid body particles, and is computationally efficient. The sole restriction on the data is that it represent 3 noncollinear particles of a rigid body.
An Effective Method for Modeling Stiction in Multibody Dynamic Systems
Authors: Synnestvedt R. G.
Published: February 2008

This paper presents an effective method for developing dynamic equations which realistically model dynamics of multibody mechanical systems with stiction, or stick-slip friction. This method is used in three examples—a mass-spring system, a top, and a robot linkage—to illustrate the facility with which the method is implemented. The method dynamically partitions sets of dynamic equations to model a system through discontinuities, changes in degrees of freedom and changes in states. Comparisons of this method with others is presented for simple and complex systems.
A Modified ARTMAP Network, With Applications to Scheduling of a Robot-Vision-Tracking System
Authors: Feng K. , Hoberock L. L.
Published: February 2008

The use of a robot-vision-tracking system to efficiently process different types of objects presented randomly on a moving conveyor belt requires the system to schedule pick and place operations of the robot to minimize robot processing times and avoid constraint violations. In this paper we present a new approach: a modified ARTMAP neural network is incorporated in the robot-vision-tracking system as an “intelligent” component to on-line schedule pick-place operations in order to obtain optimal orders for any group of objects. When the robot-vision-tracking system is working in a changing environment, the neural networks used in the optimal scheduling task must be capable of updating their weights aperiodically based on the data collected intermittently in real operations in order to create a continuously effective system. The ARTMAP network developed by Carpenter et al, (1991), which can rapidly learn mappings between binary input and binary output vectors by using a supervised learning law, has good properties to deal with this task. In special situations, however, the ARTMAP must employ a complement coding technique to preprocess incoming patterns to be presented to the network. This doubles the size of input patterns and increases learning time. The Modified ARTMAP network, proposed herein, copes with these special situations without using complement coding, and has been shown to increase the overall system speed. The basic idea is to insert a matching check mechanism that internally changes the learning order of input vector pairs in responding to an arbitrary sequence of arriving input vector pairs. Simulation results are presented for scheduling a number of different objects, demonstrating a substantial improvement in learning speed and accuracy.
Model Reduction of Coulomb Friction Damped Systems Using Singular Perturbation Theory
Authors: Heck B. S. , Ferri A. A.
Published: February 2008

This paper presents an extension of singular perturbation theory for use in the analysis of mechanical systems with dry (Coulombic) friction. Standard singular perturbation techniques cannot be applied due to the discontinuity inherent with dry friction. A methodology is developed to obtain a reduced-order piecewise-smooth model that recovers the slow motion of the system throughout the entire state space. Both a zeroth-order and a first-order approximation are obtained. The method is demonstrated successfully on a numerical example. A proof of the validity of the method is contained in the Appendix.
Robust Throttle Control of Automotive Engines: Theory and Experiment
Authors: Choi Sei-Bum , Hedrick J. K.
Published: February 2008

An adaptive, sliding control algorithm is developed for automated throttle control of an I.C. engine to be used in drive-by-wire applications such as coordinated engine/transmission gear shiftings, traction control and autonomous vehicle control (IVHS). The paper presents a new sliding control formulation that includes combustion transport delays and a simplified adapation law to account for slowly varying engine parameters. The new technique is evaluated by computer simulation and laboratory dynamometer tests.
Hydraulic Actuator Tuning in the Control of a Rotating Flexible Beam Mechanism
Authors: Panza M. J. , Mayne R. W.
Published: February 2008

The end point position and vibration control of a rotating flexible beam mechanism driven by a hydraulic cylinder actuator are considered. An integrated nonlinear system model comprised of beam dynamics, hydraulic actuator, control valves, and control scheme is presented. Control based on simple position feedback, along with a hydraulic actuation system tuned to suppress beam vibration over a wide range of angular motion, is investigated. For positioning to small to moderate mechanism angles, a linear system model with the actuator tuned for good open-loop performance is developed. Actuator tuning is accomplished by varying the system hydraulic resistance according to a dimensionless parameter defining the interaction between actuator dynamics and the fundamental mode of the flexible beam. Simulation results for a closed-loop system indicate that this simple tuned control provides comparable performance and requires less control effort than an untuned system with a more complex state feedback optimal controller. To compensate for geometric nonlinearities that cause instability when positioning to large mechanism angles, an active actuator tuning scheme based on continuous variation of hydraulic resistance is proposed. The active variable resistance controller is combined with simple position feedback and designed to provide a constant dimensionless actuator-flexible beam interaction parameter throughout the motion. Simulation results are presented to show the stabilizing effect of this control strategy.
Simulation and Experimental Studies of Gear Backlash and Stick-Slip Friction in Hydraulic Excavator Swing Motion
Authors: Sepehri N. , Sassani F. , Lawrence P. D. , Ghasempoor A.
Published: February 2008

Inherent to any heavy-duty hydraulic machine operation with a large number of interconnected components are nonidealities such as gear backlash, friction and leakage. The swing motion of the operator’s cabin in an excavator is a typical example. In this paper we conduct a study comprising experimental, mathematical and simulation components to determine the degree to which these nonlinearities affect the performance of such machines. The inclusion of the conventional model of backlash in the simulation of the excavator swing motion is shown to be inefficient and unnecessary in terms of computation time and the final results. A new model which combines the fluid-flow and the gear train dynamics is developed. The study of contact and non-contact cases brings about proper sets of static and dynamic equations which efficiently simulate this phenomenon for the class of excavator machines under consideration. The inclusion of stick-slip friction model in the simulation shows two effects. Firstly, it causes a noticeable time-delay at the beginning of the swing motion. Secondly, it results in an overshoot during velocity control experiments. It is also shown that dry friction and leakage (cross-port or external) are as significant as gear backlash in determining the pressure patterns in the connecting hydraulic lines and, therefore, should not be overlooked, especially when the excavator cabin is brought to a stop. Often, this is the most important state event when accurate positioning is crucial. The simulation results are qualitatively supported by the experimental evidence. The experiments were performed on an instrumented teleoperated Caterpillar 215B excavator.
Control of Suspensions for Vehicles With Flexible Bodies—Part I: Active Suspensions
Authors: Hac´ Aleksander , Youn Iljoong , Chen Hsien H.
Published: February 2008

In this paper, two classes of control strategies for active suspension are developed. The purpose of control is to reduce structural vibrations of the body without compromising traditional control objectives. In the first approach, the control laws for the suspension forces are synthesized to enhance modal damping in the structural modes. In the second approach, a separate proof-mass actuator mounted on the vehicle body is used to suppress structural vibrations, while suspension controllers based on a rigid-body model are utilized. The results of simulation demonstrate that with both methods significant reductions in structural vibrations can be achieved without sacrificing other aspects of performance, provided that modal variables for the body beaming modes are available for feedback. To simplify the implementation, suboptimal decentralized controllers using state and subsequently output feedback are developed, which are obtained by taking advantage of the separation between the natural frequencies of the rigid-body and the structural modes. For both control methods, output feedback, including the modal variables for the body beaming modes, results in performances that are close to those obtained for a full state feedback.
Control Oriented Modeling of Distributed Systems—The Question of Control System Stability
Authors: Kecman Vojislav
Published: February 2008

Distributed systems dynamics is described by partial differential equations (PDE), i.e., the model is of infinite order. For control system synthesis such a model ought to be reduced. This paper presents the original analytical solutions for critical controller gain in the output feedback control of processes described by parabolic PDE. Numerical analysis using different reduced models leads to the same results. The solution to the problem of locating the positive zero of the first-order nonminimum phase system (which is the lowest order model for approximation of this particular distributed system) is given. The concept and method are of general interest and can be useful in control system design for different systems with distributed parameters.
Reconstruction of Service Load Histories With Time Series Models for Random Vibration Simulation Tests
Authors: Dong Jian (John) , Li Chuanqi , Li Min
Published: February 2008

The success of a random vibration simulation test heavily depends on how accurately service loads can be reproduced in a laboratory. Many sophisticated and expensive systems have been developed for these kinds of simulation tests. However, because of high cost and complexity, the usage of these systems is limited. In this paper, a new method that reconstructs service load histories using a time series model (autoregressive moving average (ARMA) model) is presented. This method was verified by using a road simulation test performed on a four-wheel vehicle. Comparisons between actual and reconstructed signals showed good agreement in statistical parameters, the cumulative frequency distribution (CFD) and the power spectral density (PSD). Accelerated testing with the ARMA model is also explained. The new method makes it possible to conduct highly accurate random vibration simulation tests at low cost and within a short time, which has great potential to benefit automobile and aerospace industries.
Balanced Dissipative Controllers for Flexible Structures
Authors: Gawronski W. K. , Sawicki J. T.
Published: February 2008

A balanced approach to shaping the closed-loop properties of the dissipative controllers for flexible structures is presented. In the balanced representation the properties of flexible structures are introduced, and a simple method of designing of the dissipative controllers is obtained. It relates the controller gains with the closed-loop pole locations. The examples illustrate the accuracy of the design method.
Constrained H∞ Control of an Experimental Flexible Link
Authors: Tchernychev A. , Sideris A. , Yu Jie
Published: February 2008

A new approach is presented to design robust controllers for an experimental flexible beam with noncolocated sensors-actuator. The objective is to position the free end of the beam in the specified time under tight bounds on the trajectory of the tip and control action. We derive a transfer function nominal model for the beam and a quantitative description of model uncertainties based on experimentally obtained frequency response data. Robust controllers are designed by applying the recently developed Constrained H∞ control approach (Sideris and Rotstein, 1993, 1994), in which time-domain constraints are treated directly without translation to the frequency-domain. Constrained H∞ controllers are compared with standard H∞ and μ-synthesis designs in terms of both simulation and experimental results and are found to be superior in the considered case of stringent time-domain specifications.
Multivariable Trend Analysis for System Monitoring Through Self-Organizing Neural Networks
Authors: Zhang Siyu , Ganesan R.
Published: February 2008

For precise and reliable fault detection it is essential to consider simultaneously the changes in several diagnostic indices that are extracted from the on-line vibration signal. Existing machine condition monitoring systems consider each diagnostic index separately. Development of an automated diagnostic procedure that considers simultaneously several diagnostic indices is the objective of the present paper. The multivariable trend analysis of on-line vibration signals is deployed as the basis for this procedure. An efficient self-organizing neural network algorithm that is highly suitable to this diagnostic procedure is developed and deployed. Applications to both a bearing system as well as a gearbox system are fully developed and demonstrated.
A New Approach for Designing Robust Controllers for the Servomechanism Problem
Authors: Al-Assadi Salem A. K.
Published: February 2008

In this paper, we provide an alternative method for solving the more general servomechanism problem. The new approach based on designing a simple structure of a dynamic output feedback controller to achieve asymptotic tracking, disturbance rejection and pole assignment in linear time-invariant multivariable control systems. In addition, the resulting dynamic compensator is robust in the sense that asymptotic regulation take place for some or all disturbances and reference signals independent of any nondestabilizing perturbations in the system parameters. The main results of this paper are illustrated by an example.
Synthesis of Robust Gain Matrices for Adaptive Rotor Vibration Control
Authors: Knospe C. R. , Tamer S. M. , Fedigan S. J.
Published: February 2008

Experimental results have recently demonstrated that an adaptive open-loop control strategy can be highly effective in the suppression of the unbalance induced vibration of rotors supported in active magnetic bearings. A synthesis method is presented for determining the adaptive law’s gain matrix such that the adaptation’s stability and steady-state performance are robust with respect to structured uncertainty.
Discretization of Existing Continuous Control Systems
Authors: Pan Somnath , Pal Jayanta
Published: February 2008

A new method is presented for discretizing an existing analog controller. The method is based on frequency response matching of the closed-loop digital system with that of the original analog system. The method requires solution of linear algebraic equations and is computationally simple. Efficacy of the method is illustrated through examples taken from the literature.
Implementation of Sensory Feedback and Trajectory Tracking in Active Telemanipulation Systems
Authors: Ephanov A. V. , Hurmuzlu Y.
Published: February 2008

This paper presents an approach to the implementation of sensory feedback in a robotic telemanipulation system. The system considered here consists of kinematically similar master-slave robotic manipulators. We propose a control scheme whereby the slave tracks the motion commanded by the human operator through the master mechanism. The scheme also accommodates, in a unified manner, different sources of sensory feedback. These include combined effects of the interaction with unknown environments and changes in structural properties of the slave manipulator due to additional unknown loads. The control algorithm is based on continuously sliding variable structure control, which is a nonlinear and highly robust control scheme. Due to the robustness of the scheme, the need for a priori information about the environment and the load is minimal. This information can be passed on to the system in the form of upper bounds of the interaction forces and additional loads. Experimental studies with a Pneumatic Haptic Interface (PHI) system were conducted to evaluate the performance of the proposed scheme. We used a virtual slave with percent 25 uncertainty to verify the robustness of the controller. We have shown that the proposed scheme can accurately estimate the environmental interaction torques and can robustly track the trajectories commanded by the human operator.
Optimal Orifice Geometry for a Hydraulic Pressure-Reducing Valve
Authors: Manring N. D. , Johnson R. E.
Published: February 2008

In this paper, the flow gain of a hydraulic pressure-reducing valve is examined. It is noted that classical linear-analysis is typically used to optimize the flow gain of hydraulic control-systems and that in practice this parameter is usually nonlinear. For this reason, it is important that a designer know how to reconcile the optimization using linear analysis with the implementation of the nonlinear physical design. In particular, this paper concerns itself with the steady-state flow gain and the shape of the flow passage that contributes to the nonlinear flow-gain characteristics. The shapes of a circle, a rectangle, a diamond, and a triangle are discussed and it is shown that a triangular shape provides an optimal flow passage compared to other shapes of similar size.
Coupling Between the Modeling and Controller-Design Problems—Part I: Analysis
Authors: Brusher G. A. , Kabamba P. T. , Ulsoy A. G.
Published: February 2008

Controller-design issues influence modeling decisions; therefore, the modeling and controller-design problems are coupled. Part I of this paper proposes a quantification of this coupling in terms of the size of the set of models from which satisfactory controllers may be derived. Moreover, in the context of an extremely general framework, we prove that the coupling increases as performance specifications are tightened and as uncertainty is increased. Furthermore, the existence of a preferred model for controller design is demonstrated; this model is preferred in the sense that its use leads to improved robustness or performance. However, this model does not necessarily satisfy our intuitive notion of a worst-case model; rather, it depends on the performance specifications and uncertainty. The analysis of coupling presented herein motivates the design approach formulated in the companion paper, Part II.
Variational Formulation for Optimal Multi-Cycle Deep Drilling of Small Holes
Authors: Zakovorotny V. L. , Bordatchev E. V. , Sankar T. S.
Published: February 2008

A new variational approach is presented for the MCDDSH process that leads to the optimal values of switching of machining cycles and feed rate. The problem is formulated as a nonclassical variational problem that best models the dynamics and control of a MCDDSH machine. Twist drills are used in the MCDDSH process considered here. All the control parameters like cutting forces, external disturbances, output quality, etc. are considered. Physical realization of the optimal strategy is achieved by taking into account the stochastic variation of system parameters. Control algorithms that yield maximum productivity are developed. Also investigated are the set of machining process states for the MCDDSH process and the specification of optimal switching positions of the machining cycles. These correspond to the appropriate optimal feed-rate that yields the best result.
Robust Control Design for Pole Assignment of Uncertain Systems
Authors: Chen Wen-Hua
Published: February 2008

This Technical Brief addresses the problem of robust pole assignment for uncertain dynamic systems. A control design methodology is proposed to determine a fixed controller assigning all poles of uncertain systems in a pre-specified disk. The robust pole assignment problem is reduced to a convex optimization problem. The proposed method is applied in design of a flight control system for a small aircraft successfully.
Optimal Trajectories of Open-Chain Robot Systems: A New Solution Procedure Without Lagrange Multipliers
Authors: Agrawal Sunil K. , Claewplodtook Pana , Fabien Brian C.
Published: February 2008

For an n d.o.f. robot system, optimal trajectories using Lagrange multipliers are characterized by 4n first-order nonlinear differential equations with 4n boundary conditions at the two end time. Numerical solution of such two-point boundary value problems with shooting techniques is hard since Lagrange multipliers can not be guessed. In this paper, a new procedure is proposed where the dynamic equations are embedded into the cost functional. It is shown that the optimal solution satisfies n fourth-order differential equations. Due to absence of Lagrange multipliers, the two-point boundary-value problem can be solved efficiently and accurately using classical weighted residual methods.
Adaptive Control of Nonlinear, Uncertain Systems Using Local Function Estimation
Authors: Yeh T.-J. , Youcef-Toumi K.
Published: February 2008

An adaptive control scheme is proposed for controlling a certain class of nonlinear, uncertain systems. When a local approximation of the system function using its Taylor’s expansion is possible, this scheme provides an adaptation law to estimate such an approximation. With a proper sampling rule, the neighborhood of approximation can be moved from time to time in order to capture the fast changing system dynamics. Practical implementation issues are also considered to avoid exciting the unmodeled dynamics, to reduce the noise sensitivity, and accommodate the various signal levels in the system response. The important features and performance of the proposed controller are illustrated through simulations and experimental results associated with a magnetic bearing system.
A State and Parameter Identification Scheme for Linearly Parameterized Systems
Authors: Liu Chia-Shang , Peng Huei
Published: February 2008

This paper presents an adaptive algorithm to estimate states and unknown parameters simultaneously for nonlinear time invariant systems which depend affinely on the unknown parameters. The system output signals are filtered and reparameterized into a regression form from which the least squares error scheme is applied to identify the unknown parameters. The states are then estimated by an observer based on the estimated parameters. The major difference between this algorithm and existing adaptive observer algorithms is that the proposed algorithm does not require any special canonical forms or rank conditions. However, an output measurement condition is imposed. The stability and performance limit of this scheme are analyzed. Two examples are then presented to show the effectiveness of the proposed schemes.
Experimental Identification of a Flow Orifice Using a Neural Network and the Conjugate Gradient Method
Authors: Xu X. P. , Burton R. T. , Sargent C. M.
Published: February 2008

An experimental approach of using a neural network model to identifying a nonlinear non-pressure-compensated flow valve is described in this paper. The conjugate gradient method with Polak-Ribiere formula is applied to train the neural network to approximate the nonlinear relationships represented by noisy data. The ability of the trained neural network to reproduce and to generalize is demonstrated by its excellent approximation of the experimental data. The training algorithm derived from the conjugate gradient method is shown to lead to a stable solution.
A Fuzzy Driver on the Handling Track
Authors: Wheeler M. , Shoureshi R.
Published: February 2008

Maneuvering a car around a handling track in minimum time is a challenging task for a driver. The car at high speed is a complex nonlinear Multiple-Input-Multiple-Output dynamic system. A driver must spend many hours learning the skills necessary to control this system proficiently. This complex task is a good test for fuzzy logic control, supporting the premise: humans control complex systems using simple rules. A few fuzzy driving rules are devised to operate on the same inputs and outputs a human driver would use. These rules are encoded in a fuzzy rule base and used to control the system. The resulting fuzzy handling controller is demonstrated in a simulation. A single set of rules is shown to perform well on many different track geometries, illustrating the robustness of the system to a changing environment.
Motion/Force Control of Robotic Manipulators
Authors: DeSantis R. M.
Published: February 2008

A procedure for the design of a motion/force controller for a manipulator, the end-effector of which maintains a stiff contact with the environment, is presented. Based on the computed torque approach and on projections on the motion and force subspace, this procedure leads to decoupled controllers that are capable of ensuring a global stability and are applicable to stationary as well as to mobile contact surfaces.
The Dynamics and Control of a Biped Walking Robot With Seven Degrees of Freedom
Authors: Shih Ching-Long
Published: February 2008

This research studies the dynamics and motion control of a biped walking robot with seven degrees of freedom. The main features of the biped robot include variable length legs and a translatable balance weight in the body. The statically stable walking of the biped robot is implemented by maintaining the center-of-gravity (cg) inside the convex region of the supporting foot/feet during both single-support and double-support phases. The dynamically stable walking of the biped robot is realized by maintaining the zero moment point (ZMP), which is the virtual total ground reaction point, within the region of the supporting foot during the single-support phases. An implementation of a prototype biped BR-1 and its experimental walking test results are described. The biped robot is able to walk on an even floor both statically and dynamically. On a flat plane, the biped can walk with a speed of 8 cm/second statically, and 20 cm/second dynamically.
On the Synthesis of Compensators for Nonovershooting Step Response
Authors: Jayasuriya Suhada , Song Jay-Wook
Published: February 2008

A problem of practical and theoretical interest in control is the synthesis of a compensator such that the closed-loop system step response does not overshoot. In this paper we present an approach for synthesizing such compensators for SISO, minimum phase plants. The essential idea of the technique is to appropriately locate the closed loop poles with respect to fixed and added zeros. Admissible pole-zero locations are characterized by two sufficiency theorems.
Robust Kalman Filter Synthesis for Uncertain Multiple Time-Delay Stochastic Systems
Authors: Hsiao Feng-Hsiag , Pan Shing-Tai
Published: February 2008

The problem of robust Kalman filter synthesis is considered in this present study for discrete multiple time-delay stochastic systems with parametric and noise uncertainties. A discrete multiple time-delay uncertain stochastic system can be transformed into another uncertain stochastic system with no delay by properly defining state variables. Minimax theory and Bellman-Gronwall lemma are employed on the basis of the upper norm-bounds of parametric uncertainties and noise uncertainties. A robust criterion can consequently be derived which guarantees the asymptotic stability of the uncertain stochastic system. Designed procedures are finally elaborated upon with an illustrative example.
Design and Testing of an Airbag System for High-Mass, High-Velocity Deceleration
Authors: Snyder T. , Sitter J. , Chung J. N.
Published: February 2008

The design and performance evaluation of an airbag system capable of decelerating masses in the range of hundreds to thousands of kilograms with impact velocities in the range of tens to hundreds of kilometers per hour is presented. First, a simplified incompressible flow analysis of the airbag is utilized to derive the orifice venting area corresponding to the ideal deceleration for a given impact velocity and package mass. Second, testing with a small-scale model found three distinct control intervals during the deceleration. Finally, a full-scale airbag system was constructed and data is presented on the deceleration, deceleration force, deceleration velocity, airbag stopping power, and overall performance. The deceleration was experimentally optimized for a single impact velocity and package mass and an approximate correction factor was developed to predict the actual air venting required for each of the three control intervals in order to achieve the optimum deceleration for any impact velocity and package mass.
On Hybrid Boundary Control of Flexible Systems
Authors: Zhu W. D. , Guo B. Z.
Published: February 2008

Simple proofs are presented which show that hybrid boundary control systems are asymptotically, but not exponentially, stable. The asymptotic rates of decay of eigenvalues are determined analytically for both second and fourth-order systems.
Fuzzy Damage Mitigating Control of Mechanical Structures
Authors: Holmes M. S. , Ray Asok
Published: February 2008

This paper presents the architecture and synthesis of a damage mitigating control system for mechanical structures where the objective is to achieve high performance with increased reliability, availability, component durability, and maintainability. The proposed control system has a two-tier structure. In the lower tier a linear sampled-data controller tracks a reference trajectory vector while the upper tier contains a fuzzy-logic-based damage controller which makes a trade-off between system performance and the damage in critical components. The synthesis procedure is demonstrated by simulation experiments on the model of a reusable rocket engine. The simulation results explore the feasibility of automatically regulating the damage/performance trade-off in a real-time setting.
Neural Network Based Tracking Control of Mechanical Systems
Authors: Efrati T. , Flashner H.
Published: February 2008

A method for tracking control of mechanical systems based on artificial neural networks is presented. The controller consists of a proportional plus derivative controller and a two-layer feedforward neural network. It is shown that the tracking error of the closed-loop system goes to zero while the control effort is minimized. Tuning of the neural network’s weights is formulated in terms of a constrained optimization problem. The resulting algorithm has a simple structure and requires a very modest computation effort. In addition, the neural network’s learning procedure is implemented on-line.
Performance Enhancement of Fixed Regulating Systems Via Actuator Saturation
Authors: Herman Paul , Franchek Matthew A.
Published: February 2008

Developed in this paper is a controller design technique that utilizes actuator saturation to meet stringent output performance specifications for regulating systems with fixed components. Regulating performance is achieved via the design of a linear controller that saturates the actuator for large step disturbances yet operates linearly for smaller step disturbances. The controller is designed using a pseudo-linearization technique based on a describing function approach. Such an approach retains the advantages of a frequency domain technique including the enforcement of time domain performance specifications and the incorporation of model uncertainty. The resulting control law provides an improved regulating performance for large step disturbances without requiring a larger actuator. For small step disturbances, the control system maintains linear operation and provides desirable system response characteristics.
Robust LTV Feedback Synthesis for Nonlinear MIMO Plants
Authors: Yaniv Oded
Published: February 2008

An n × n nonlinear plant that is known to be a member of a given set is given. The plant is embedded in a feedback structure in order to achieve desired closed-loop performances. The existing QFT technique for that purpose, based on replacing each nonlinear plant by an uncertain linear time invariant plant, is extended to design LTV controllers. In addition, a more efficient fixed-point theorem based on Homotopic invariance is used. The main results are that: (i) a controller with less control effort compared to a linear time invariant controller is achieved; and (ii) the class of plants and desired closed-loop specifications to which the technique can be applied is enlarged. A detailed design example is included.
On the Problem of Scheduling Parallel Computations of Multibody Dynamic Analysis
Authors: Liu J. F. , Abdel-Malek K. A.
Published: February 2008

A formulation of a graph problem for scheduling parallel computations of multibody dynamic analysis is presented. The complexity of scheduling parallel computations for a multibody dynamic analysis is studied. The problem of finding a shortest critical branch spanning tree is described and transformed to a minimum radius spanning tree, which is solved by an algorithm of polynomial complexity. The problems of shortest critical branch minimum weight spanning tree (SCBMWST) and the minimum weight shortest critical branch spanning tree (MWSCBST) are also presented. Both problems are shown to be NP-hard by proving that the bounded critical branch bounded weight spanning tree (BCBBWST) problem is NP-complete. It is also shown that the minimum computational cost spanning tree (MCCST) is at least as hard as SCBMWST or MWSCBST problems, hence itself an NP-hard problem. A heuristic approach to solving these problems is developed and implemented, and simulation results are discussed.
Longitudinal Transition Maneuvers in an Automated Highway System
Authors: Connolly Thomas R. , Hedrick J. Karl
Published: February 2008

The control structure for automated vehicles in an Automated Highway System is based on the idea of multiple-surface sliding control. The “upper” surface determines a desired net torque while the “lower” surface determines the required throttle angle or brake pressure needed to achieve the desired torque. This paper presents an upper surface control law for performing longitudinal transition maneuvers. The maneuvers use desired velocity trajectories which are based on maintaining safety and comfort throughout the maneuver. The control law chosen is a sliding controller due to the nonlinearities in the dynamics and the uncertainties in the parameters. Adaptive techniques were also implemented to help improve the velocity tracking. The controller was implemented on experimental vehicles and tested at highway speeds.
Randomized Algorithms for Open-Loop Control of Clutch-to-Clutch Transmissions
Authors: Yoon Albert , Khargonekar Pramod , Hebbale Kumar
Published: February 2008

In this paper, randomized algorithms are used to design an open-loop control for a clutch-to-clutch shift automatic transmission and to study the robustness of that control. The open-loop control design problem can be posed as an optimal control problem but because of the computational cost associated with each simulation and the complexity of the transmission model, classical results from optimal control theory are not a practically feasible approach for this problem. We apply randomized search algorithms for optimization to these problems and present some promising results.