bluuebunny/crossref_metadata_2025 huggingface dataset:
Multivariable Adaptive Control of Thermal Properties During Welding
Authors: Doumanidis C. C. , Hardt David E.
Published: March 2008

Complete solution of the welding control problem involves regulating weld geometry, residual stresses, distortion and weldment metallurgical characteristics. The latter has been largely ignored in closed-loop control work, yet it is a basic determinant of weld integrity. In this paper, a previously developed input-output model for continuous regulation of the critical thermal properties of heat affected zone and cooling rate is used to develop a closed-loop MIMO control scheme. Since the physical system is non-linear and non-stationary, and process disturbances are reflected as model parameter changes, an adaptive control method is used. The implementation of the controller is based on deadbeat adaptive control, and it is applied to several different forms of the basic welding process model. The different models reflect a need to simplify the control system to accommodate available process measurements and hardware capabilities. A series of experiments performed on a robotic Gas Metal Arc welding system are presented that confirm the basic stability, robustness, adaptivity, tracking and disturbance rejection properties of the scheme. Bandwidth limitations are identified and improvements (primarily hardware oriented) are suggested.
Application of Adaptive Control Theory to On-Line GTA Weld Geometry Regulation
Authors: Suzuki A. , Hardt D. E. , Valavani L.
Published: March 2008

This study addresses the uses of adaptive schemes for on-line control of backbead width in the Gas Tungsten Arc (GTA) welding process. Open-loop tests using a step input current confirm the validity of a nominal first order process model. However, the time constant and gain prove highly dependent upon welding conditions including torch speed, arc length, material thickness, and other material properties. Accordingly, a need exists for adaptive controllers that can compensate for these process nonlinearities. The performance of two adaptive controllers is evaluated: Narendra and Lin’s Model-Referenced Adaptive Control (MRAC/NL), and Self-Tuning Control with Pole Placement (STC/PP). The addition of a quadratic term to the adaption mechanisms of MRAC/NL is proposed and preliminary simulations and experiments clearly demonstrate the stabilizing effect of this added term. The main experiments compare the performance of the modified MRAC/NL controller and the STC/PP controller with each other and with linear PI controller and the STC/PP controller with each other and with linear PI controller under four experimental conditions: first, where welding conditions are nominal; second, when conditions are disturbed by a step-wise increase in the torch velocity, and third, when conditions are disturbed by a step-wise increase in material thickness. In each case the experimental demonstrates the superiority of the adaptive controllers over the linear PI controller. However, the STC/PP controller exhibits high frequency control action in response to severe disturbances of material thickness and the parameter estimates it generates drift during steady-state operations. The MRAC/NL controller proves more robust under these circumstances. Analysis demonstrates that the superior performance of the MRAC/NL is due both to the inherent normalizing effect of the quadratic feedback terms and to the noise filtering properties of the adaptive mechanism.
Simulation of Surface Topography Formed During the Intermittent Turning Processes
Authors: Zhang G. M. , Yerramareddy S. , Lee S. M. , Lu S. C.-Y.
Published: March 2008

This paper presents a methodology which employs computer simulation to dynamically generate the topography of a surface machined during an intermittent turning process. The methodology is based on a mathematical model that characterizes the intermittent turning process as an alternating sequence of forced and free vibratory motion. The simulation of machining workpieces, with discontinuous geometries of arbitrary shape, is facilitated by representing the workpiece surface as a two-dimensional grid, with an index for each cell in the grid accounting for the feature boundaries. The tool vibratory motion is integrated with the tool geometric motion to form a basis for the construction of surface texture produced during machining. The simulation model not only provides for a qualitative evaluation of the surface accuracy through a graphic visualization of the surface topography, but also provides a quantitative estimate of the roughness quality of the machined surface.
Active Parametric Damping of Distributed Parameter Beam Transverse Vibration
Authors: Habib M. S. , Radcliffe C. J.
Published: March 2008

An active vibration control for a modified, nonlinear, dynamic, simply supported, Bernoulli-Euler beam is introduced using one of the distributed, time-dependent parameters of the system. The control is carried out by observing the axial velocity of the end point of the beam and applying a modified bang-bang variation of beam tensile stress to control beam transverse stiffness. Numerical simulation of the closed-loop system of partial differential equations demonstrates the effectiveness of the control. Two cases representing initial value problems are given as examples. This active control applied to first mode vibration of an undamped system model yields an asymptotically stable system which loses its total system energy to a level that is 0.26 percent of its initial value in five and one half cycles.
Flank Wear Estimation Under Varying Cutting Conditions
Authors: Koren Yoram , Ko Tsu-Ren , Ulsoy A. Galip , Danai Kourosh
Published: March 2008

A model-based methodology, designed to operate under varying cutting conditions, for on-line estimation of flank-wear rate based on cutting force measurements is introduced. The key idea is to employ a model of the relationship between force and flank wear, together with on-line parameter estimation methods. This permits separation of the direct effect of changing cutting conditions on force from the indirect effect where changing cutting conditions affect the wear which, in turn, affects the force. Simulation results confirm the effectiveness of this strategy for turning with varying speed, feed, or depth of cut. Experiments, conducted for turning operations with a varying depth of cut, show good agreement between estimated wear values and the actual values of tool wear measured intermittently during the cut.
Geometric Uncertainty in Off-Line Programming of Robot Manipulators for Assembly Tasks
Authors: Goldenberg A. A. , McQuillan F. J.
Published: March 2008

An approach to off-line programming of a robot system, in the presence of uncertainty in the location of the manipulator and objects in the workspace, has been developed. The approach is based on the concept of affixment tree. The approach involves the prediction and compensation of location errors, with the intent of automatically generating robot-executable programs based on information from task planning done on a CAD workstation. The off-line programming system has been implemented and successfully tested on parts assembly processes using the IBM 7565 manipulator.
Stabilizing Controllers for Uncertain Linear Saturating Systems With Additive Disturbances
Authors: Chou Jyh-Horng , Horng Ing-Rong
Published: March 2008

In this technical brief, the stabilization of an uncertain system with a saturating actuator and an additive disturbance is discussed. The uncertainties and the additive disturbances may be linear, nonlinear, and/or time-varying, but only the upper bounds are assumed known. A linear state feedback control law stabilizes the uncertain system with additive disturbance, and guarantees that, ultimately, the system response lies in a neighborhood of the origin. But the neighborhood cannot be arbitrarily made small by the linear state feedback controller. The proposed approach does not need the solution of a Lyapunov equation or a Riccati equation, therefore the computational burden can be decreased. An example illustrates the application of the proposed method.
A Study of the Parametrically Excited Behavior of Passenger and Freight Railway Vehicles Using Linear Models
Authors: Lieh J. , Haque I.
Published: March 2008

This paper presents a study of the parametrically excited behavior of passenger and freight vehicles on tangent track due to harmonic variations in conicity using linear models. The effect of primary and secondary stiffnesses on parametric excitation is also studied. Floquet theory is used to find the stability boundaries. The results show that wavelengths associated with conicity variation that are in the vicinity of half the kinematic wavelengths of the vehicles can lead to significant reductions in critical speeds. Results also show that the primary and warp stiffnesses can affect the severity of principal parametric resonance depending on the vehicle models and magnitude of stiffnesses chosen.
On the Modeling and Simulation of Friction
Authors: Haessig D. A. , Friedland B.
Published: March 2008

Two new models for “slip-stick” friction are presented. One, called the “bristle model,” is an approximation designed to capture the physical phenomenon of sticking. This model is relatively inefficient numerically. The other model, called the “reset integrator model,” does not capture the details of the sticking phenomenon, but is numerically efficient and exhibits behavior similar to the model proposed by Karnopp in 1985. All three of these models and the Dahl model are preferable to the classical model, which poorly represents the friction force at zero velocity. Simulation experiments show that the Karnopp model, the Dahl model, and the new models give similar results in two examples. In a closed-loop example, the classical model predicts a limit cycle which is not observed in the laboratory. The Karnopp model, the Dahl model, and the new models, on the other hand, agree with the experimental observation.
A Systematic Design Procedure to Minimize a Performance Index for Robot Force Sensors
Authors: Uchiyama M. , Bayo E. , Palma-Villalon E.
Published: March 2008

This paper presents a systematic procedure for the structural design of a robot force sensor. The structural design is important since the force sensor detects forces and moments through the measurement of strains at specific points of the sensor body. The process of the measurement of force and moment is firstly analyzed from the viewpoint of structural behavior and then a performance index of the force sensor is introduced. It is demonstrated that the minimization of this index (the condition number of the strain compliance matrix) yields an optimal design in the sense that the static measurement error is minimized. It is proposed that the finite element be used for the evaluation of this index in the design process to search for the sensor dimensions that yield the minimum index. This way of proceeding eliminates the need of building intermediate prototypes. A systematic procedure for force sensor calibration is also presented. As an example, a force sensor of the Maltese cross bar type is constructed, and analyzed numerically and experimentally. The agreement between both sets of results corroborates the proposed design sequence.
Effect of Payload on the Dynamics of a Flexible Manipulator—Modeling for Control
Authors: Parks T. R. , Pak H. A.
Published: March 2008

The “exact” and pole/zero transfer functions are developed for a flexible beam-like single link arm with actuator on one end and payload on the other. This model represents a broader class of actuator hub and payload mass properties than is found in prior literature. The dependence of dynamics on the hub and payload inertia characteristics are studied and graphs are provided to facilitate estimation of poles and zeroes for any similar plant. It is shown that a 10:1 reduction in fundamental frequency and substantial change in the zeroes results from variations in payload through a practical range. Payload rotary inertia is shown to cause a qualitative change in the arm tip zeroes resulting in loss of observability/controllability in some cases. Results provide insight into the two-link problem and it is shown that complex values zeroes may result if the second arm is allowed to “fold back.” Implications to plant modeling and control design are discussed including sensor placement and model order reduction issues. Analytical results are compared to those measured on an experimental arm and show very good agreement in modal frequency and shape.
CAD Assisted Adaptive Control for Milling
Authors: Spence A. , Altintas Y.
Published: March 2008

A milling process adaptive control method, which prevents force overshoots during sudden part geometry changes, has been developed by providing online information to the controller from the part’s CAD representation. A first-order discrete model structure to represent the milling process for adaptive control was analytically developed and experimentally identified. Provided with geometric information obtained from the part’s CAD model, and utilizing the milling force model, the adaptive controller predicts the maximum cutting force expected in advance of dangerous immersion changes. The technique permits the controller to anticipate the changing workpiece in time to eliminate force overshoots which would otherwise break the tool, yet adaptive control at all times remains active to respond to other geometrical and material variations. Simulation and experimental results are presented to confirm the viability of the proposed method.
Cross-Coupled Adaptive Feedrate Control for Multiaxis Machine Tools
Authors: Chuang Hua-Yi , Liu Chang-Huan
Published: March 2008

Cross-coupled controllers have been proposed for improving contouring accuracy of multiaxis machine tools. However, during cross-coupled motion control, increasing contour feedrate may result in larger contour errors. In order to increase feedrate and hence productivity without sacrificing the contouring performance, this paper presents an adapative feedrate control strategy based on a linear perturbed model. The method effectively closes the feedback loop between the contour error and feedrate. An experimental biaxial control system is constructed to implement the proposed strategy. Both computer simulation and experiments have verified that desired contouring accuracy can be achieved.
Distributed Modal Identification and Vibration Control of Continua: Piezoelectric Finite Element Formulation and Analysis
Authors: Tzou H. S. , Tseng C. I.
Published: March 2008

“Smart” continua with integrated sensor/actuator for structural identification and control have drawn much attention in recent years due to the rapid development of high-performance “smart” structures. The continua are distributed and flexible in nature. Thus, distributed dynamic measurement and active vibration control are of importance to their high-demanding performance. In this paper, continua (shells or plates) integrated with distributed piezoelectric sensors and actuators are studied using a finite element technique. A new piezoelectric finite element with internal degrees of freedom is derived. Two control algorithms, namely, constant gain feedback control and Lyapunov control, are implemented. Structural identification and control of a plate model with distributed piezoelectric sensor/actuator is studied. Distributed modal voltage and control effectiveness of mono and biaxially polarized piezoelectric actuators are evaluated.
The Control of Natural Motion in Mechanical Systems
Authors: Koditschek D. E.
Published: March 2008

This paper concerns a simple extension of Lord Kelvin’s observation that energy decays in a dissipative mechanical system. The global limit behavior of such systems can be made essentially equivalent to that of much simpler gradient systems by the introduction of a “navigation function” in the role of an artificial field. This recourse to the mechanical system’s natural motion helps transform the open-ended problem of autonomous machine design into the more structured problem of finding an appropriate “cost function” in the many situations that the goal may be encoded as a setpoint problem with configuration constraints.
Optimal Linear Feedback Control for a Class of Nonlinear Nonquadratic Non-Gaussian Problems
Authors: Chang R. J.
Published: March 2008

An optimal linear feedback controller designed for a class of nonlinear stochastic systems with nonquadratic performance criteria by a non-Gaussian approach is presented. The non-Gaussian method is developed through expressing the unknown stationary output density function as a weighted sum of the Gaussian densities with undetermined parameters. With the aid of a Gaussian-sum density, the optimal feedback gain for a control system with complete state information is derived. By assuming that the separation principle is valid for the class of stochastic systems, a nonlinear precomputed-gain filter is then implemented. The method is illustrated by a Duffing-type control system and the performance of a linear feedback controller designed through both quadratic and nonquadratic performance indices is compared.
Stationary Response of States-Constrained Nonlinear Systems Under Stochastic Parametric and External Excitations
Authors: Chang R. J.
Published: March 2008

A Fourier-series closure scheme is developed for the prediction of the stationary stochastic response of a stochastic parametrically and externally excited oscillator with a nonpolynomial type nonlinearity and under states constraint. The technique is implemented by deriving the moment relations and employing the Fourier series as the expansion of a non-Gaussian density for constructing and solving a set of algebraic equations with unknown Fourier coefficients. A single-arm robot manipulator operated in a constrained working space and subjected to parametric and/ or external noise excitations is selected to illustrate the present approach. The validity of the present scheme is further supported by some exact solutions and Monte Carlo simulations.
A Stochastic Regulator for Integrated Communication and Control Systems: Part I—Formulation of Control Law
Authors: Liou Luen-Woei , Ray Asok
Published: March 2008

Integrated Communication and Control Systems (ICCS), recently introduced and analyzed in a series of papers [1–7], are applicable to complex dynamical processes like advanced aircraft, spacecraft, automotive, and manufacturing processes. Time-division-multiplexed computer networks are employed in ICCS for exchange of information between spatially distributed plant components as well as for coordination of the diverse control and decision-making functions. Unfortunately, an ICCS network introduces randomly varying, distributed delays within the feedback loops in addition to the digital sampling and data processing delays. These network-induced delays degrade the system dynamic performance, and are a source of potential instability. This two-part paper presents the synthesis and performance evaluation of a stochastic optimal control law for ICCS. In this paper, which is the first of two parts, a state feedback control law for ICCS has been formulated by using the dynamic programming and optimality principle on a finite-time horizon. The control law is derived on the basis of a stochastic model of the plant which is augmented in state space to take into account the effects of randomly varying delays in the feedback loop. The second part [8] presents numerical analysis of the control law and its performance evaluation by simulation of the flight dynamic model of an advanced aircraft.
Reduced Order Model and Decoupled Control Architecture for Two Manipulators Holding a Rigid Object
Authors: Koivo A. J. , Unseren M. A.
Published: March 2008

A dynamical model and a control architecture are developed for the closed chain motion of two N-joint manipulators holding a rigid object in a three-dimensional workspace. Dynamic and kinematic constraints are determined and combined with the equations of motion of the manipulators to obtain a dynamical model of the entire system in the joint space. Reduced order equations of motion and a functional relation for the generalized contact forces are derived. The problem of solving the reduced order model for the forward and inverse dynamics is discussed. Control laws are determined for the reduced order model so as to decouple the force and position (velocity) controlled degrees of freedom (DOF). A simulation example is presented to illustrate the approach.
Optimal Control of Speed Conversion of a Valve Controlled Cylinder System
Authors: Shichang Zhou , Xingmin Cao , Yuwan Cen
Published: March 2008

It can generally cause a great pressure surge and noise when the speed of an actuator is quickly changed in a large-scale hydraulic system. In this paper, the pressure surge is considered as a response of the system to the input signal in order to obtain an optimal control for the minimum pressure surge in the shortest speed conversion time. The dynamic performance of the valve controlled cylinder system studied is described by space state equations, and the optimal control is obtained by the simplex method for 3 performance indices. The microprocessor is used for the optimal control in the speed conversion of the test system. The results of the numerical computer simulation and the experimental results are similar. It also shows that within the same or shorter settling time, using the optimal control can reduce the pressure surge to about one fifth of the pressure response amplitude to the step input signal.
Performance Effects of a Round Bar Passing Through the Outlet of a Vortex Amplifier
Authors: Sato K. , Syred N.
Published: March 2008

This paper considers the application of a vortex amplifier (VA) to the process of coating and surface heat treatment of a round bar. The advantage of using a vortex amplifier is not only a long maintenance free lifetime but also the ease with which the coating thickness or the heat treatment condition may be changed. Swirl burners offer many advantages in the surface heat treatment of round bars. The highly turbulent swirling flow generates uniform heat distribution and very high heat transfer coefficients which improve the quality of the surface being treated. The geometry of the swirl burner is such that very long bars may be treated using a relatively small burner, the bar being passed along the axis of the swirl burner. For coating applications, the round bar to be treated passes along the axis of the outlet of the vortex amplifier and the coating process is controlled by varying the control flow in the VA. Clearly the bar will have an effect on the performance. The effects of changing the diameter of the round bar are investigated. The effect of poor alignment of the round bar on the variations of supply pressure and control pressure is also considered. The flow patterns in the vortex chamber and the outlet were observed by means of cotton tufts. The internal flow patterns in the vortex chamber were observed using water model studies at a number of points on the vortex amplifier characteristic.
The RAPT Control Method for Nonlinear Systems
Authors: Long T. W. , Carrington C. K.
Published: March 2008

The Rapid Advancement Preview Tracking (RAPT) control method uses both a nonlinear system model and a linearized system model to provide a form of feedback/preview control for nonlinear systems. It uses measurements of the states to calculate the current preview control signal from a local linearization of the state equations, and then iteratively calculates a perturbation correction for that control using the nonlinear equations. The corrected control signal is then applied to the system, driving the end-effector to the next position along a specified trajectory. Computer simulations of tracking control for two-link planar manipulators indicate that this algorithm may be fast enough for real-time control.
Computation of Driving Efforts for Mechanisms and Robots Using Bond Graphs
Authors: Ghosh A. K. , Mukherjee A. , Faruqi M. A.
Published: March 2008

A method is presented for computing scalar closed-form driving effort expressions for the desired state of motion to be used as feedforward for mechanisms and robotic manipulators using bond graphs. The final torque equation for each of the joints is free from any iterations or recursions and can be broken in smaller modules with lesser arithmetic operations in comparison to existing procedures, leading to a solution with maximum degree of parallelism.
Acceleration Profiles for Causal Solutions of the Inverse Dynamics Approach to the Control of Single Link Flexible Arms
Authors: Moulin H. C. , Bayo E.
Published: March 2008

A scheme for the design of rest-to-rest acceleration profiles to be used in the inverse dynamics approach to the control of the end-point of single link flexible arms is described. The scheme uses linear discrete models, and a stable pole-cancellation method to obtain acceleration profiles that yield inverse dynamics torques with the same supports as that of the end-point acceleration profiles; it allows for a design which reaches a balance between overshoot, peak torque and actuation time.
A Fiber-Optic-Based Protocol for Manufacturing System Networks: Part II—Statistical Analysis
Authors: Ayyagari A. , Ray A.
Published: March 2008

Conceptual development, architecture, statistical and simulation models, and the results of test and verification of a fiber-optic-based protocol have been reported in a sequence of two papers. The protocol uses the unidirectional bus topology and is specifically designed for computer integrated manufacturing (CIM) networks. The architecture of the protocol is formulated in Part I [1]. In this second part, a statistical model of the proposed protocol is formulated for analyzing the network-induced delays and pertinent results of analysis and simulation are presented for different scenarios of network traffic. The major assumptions in formulating the statistical model are: (1) message arrival processes for real-time (RT) and non-real-time (NRT) modes are independent and Markov; and (2) message lengths follow independent general distributions with known statistical properties. The Laplace-Stieltjes transforms of probability distribution functions of queueing delays for RT and NRT messages have been derived. The analytical results for the first two moments of both RT and NRT queueing delays have been compared with those obtained from discrete event simulation.
Modeling of a Hydraulic Energy Regeneration System: Part I—Analytical Treatment
Authors: Pourmovahed A. , Beachley N. H. , Fronczak F. J.
Published: March 2008

Hydraulic regeneration systems have been considered by the automotive industry for implementation in hybrid vehicles for a number of years. The combination of an internal combustion engine and an energy storage device has great potential for improving vehicle performance and fuel economy as well as reducing brake wear. This study describes an analytical model of a hydraulic regeneration system consisting of an accumulator, an oil reservoir, a variable-displacement pump/motor, connecting lines and a flywheel which is used to simulate vehicle inertia. An integration algorithm is used to simultaneously solve the governing equations and predict the system performance. Variables including accumulator pressure and temperature, pump/motor torque and efficiencies, pressure losses, and flywheel speed as functions of time are predicted. Power losses and round-trip efficiencies can be readily determined once the system performance variables have been calculated.
Non-Gaussian Linearization Method for Stochastic Parametrically and Externally Excited Nonlinear Systems
Authors: Chang R. J.
Published: March 2008

A new practical non-Gaussian linearization method is developed for the problem of the dynamic response of a stable nonlinear system under both stochastic parametric and external excitations. The non-Gaussian linearization system is derived through a non-Gaussian density that is constructed as the weighted sum of undetermined Gaussian densities. The undetermined Gaussian parameters are then derived through solving a set of nonlinear algebraic moment relations. The method is illustrated by a Duffing-type stochastic system with/without parametric noise excited term. The accuracy in predicting the stationary and nonstationary variances by the present approach is compared with some exact solutions and Monte Carlo simulations.
Dynamics of Elastic Manipulators With Prismatic Joints
Authors: Buffinton K. W.
Published: March 2008

The purpose of this investigation is to study the formulation of equations of motion for flexible robots containing translationally moving elastic members that traverse a finite number of distinct support points. The specific system investigated is a two-degree-of-freedom manipulator whose configuration is similar to that of the Stanford Arm and whose translational member is regarded as an elastic beam. Equations of motion are formulated by treating the beam’s supports as kinematical constraints imposed on an unrestrained beam, by discretizing the beam by means of the assumed modes technique, and by applying an alternative form of Kane’s method which is particularly well suited for systems subject to constraints. The resulting equations are programmed and are used to simulate the system’s response when it performs tracking maneuvers. The results provide insights into some of the issues and problems involved in the dynamics and control of manipulators containing highly elastic members connected by prismatic joints.
Accessibility and Controllability of Flexible Robotic Manipulators
Authors: Tosunoglu Sabri , Lin Shyng-Her , Tesar Delbert
Published: March 2008

Although serial manipulator arms modeled with rigid links show full system controllability in the joint space, this condition does not necessarily hold for flexible robotic systems. In particular, in certain robot configurations, called inaccessible robot positions, one or more of the flexibilities may not be accessed directly by the actuators. This condition may significantly deteriorate system performance as reported earlier by the authors (Tosunoglu et al., 1988, 1989). The present study addresses the relationship between the accessibility and controllability concepts and establishes accessibility as a distinct concept from controllability. Although the theoretical framework is developed for general n-link, spatial manipulators modeled with m oscillation components, example case studies demonstrate the concepts on one- and two-link arms for brevity. Specifically, it is shown that although inaccessibility and uncontrollability may coincide in certain instances (as shown on a one-link arm), counter examples may be found where an arm in an inaccessible position can simultaneously demonstrate full system controllability (as shown on a two-link arm).
Modeling and Control of Single-Link Flexible Arms With Lumped Masses
Authors: Feliu V. , Rattan K. S. , Brown H. B.
Published: March 2008

This paper deals with the modeling and control of a special class of single-link flexible arms. These arms consist of flexible massless structures having some masses concentrated at certain points of the beam. In this paper, the dynamic model of such flexible arms is developed and some of the control properties are deduced. A robust control scheme to remove the effects of friction in the joins is proposed. The control scheme consists of two nested feedback loops, an inner loop to control the position of the motor and an outer loop to control the tip position. The inner loop is described in other publications. A simple feedforward-feedback controller is designed for the outer loop to drive the beam accurately along a desired trajectory. Effects of the changes in the tip’s mass are studied. This modeling and control method is then generalized to the distributed-mass flexible beam case. Finally, experimental results are presented.
Efficient Methods for Solving Dynamic Problems of Flexible Manipulators
Authors: Sharan A. M. , Jain J. , Kalra P.
Published: March 2008

In this work, efficient methods for solving dynamic problems in the robotics area are discussed. The nonlinear dynamic equations are derived and their linearization is verified. The unconstrained dynamic problems for a flexible arm robot are solved by four efficient numerical techniques. The constrained problems are solved by Revised Simplex Method and the Karmarkar’s Algorithm.
Dynamics and Control of Vertical-Plane Motion for an Electrohydraulically Actuated Single-Flexible-Link Arm
Authors: Chang Liang-Wey
Published: March 2008

A research tool was developed for the dynamics and control of a single-flexible-link arm based on the Equivalent Rigid Link System (ERLS) dynamic model and the inverse dynamics of the arm and the actuator. The arm moved in a vertical plane and was actuated by an electrohydraulic motor. The required torque was computed based on the inverse dynamics of the ERLS model. The driving current was then predicted by the inverse actuator dynamics. This paper also presents a 16-bit microcomputer-based low-cost implementation of a nonlinear motion tracking control. The dynamic behavior of the control system was studied through the computer simulation and the experiment. Furthermore, the superiority of the flexible-body control was also proved through the comparison to the rigid-body control.
Transferring Manipulative Skills to Robots: Representation and Acquisition of Tool Manipulative Skills Using a Process Dynamics Model
Authors: Liu Sheng , Asada Haruhiko
Published: March 2008

A new method based on task process models for acquiring manipulative skills from human experts is presented. In performing manipulative tasks such as deburring, a human expert moves a tool at an optimal feedrate and cutting force as well as with an appropriate compliance for holding the tool. An experienced worker can select the correct strategy for performing a task and change it dynamically in accordance with the task process state. In this paper, the human expertise for selecting a task strategy that accords with the process characteristics is modeled as an associative mapping, and represented and generated by using a neural network. First, the control strategy for manipulating a tool is described in terms of feedforward inputs and tool holding dynamics. The parameters and variables representing the control strategy are then identified by using teaching data taken from demonstrations by an expert. The task process is also modeled and characterized by a set of parameters, which are identified by using this same teaching data. Combining the two sets of identified parameters, we can derive an associative mapping from the task process characteristics to the task strategy parameters. The consistency of the mapping and the transferability of human skills are analyzed by using Lipschitz’s condition. The method is applied to deburring, and implemented on a direct-drive robot. It is shown that the robot is able to associate a correct control strategy with process characteristics in a manner similar to that of the human expert.
Modal Testing and Suboptimal Vibration Control of Flexible Rotor Bearing System by Using a Magnetic Bearing
Authors: Lee Chong-Won , Kim Jong-Sun
Published: March 2008

A suboptimal output feedback controller is designed based on a reduced order model and applied to a flexible rotor bearing system in order to control the unstable or lightly damped vibrations occurring during operation. The reduced order model is a truncated modal equation of the distributed parameter system obtained through the singular perturbation. The instability problem arising from the spillover effects caused by the uncontrolled high frequency modes is prevented through the constrained optimization by incorporating the spillover term into the performance index. The application of the matrix minimum principle yields a set of matrix equation similar to the unconstrained output feedback controller. The efficiency of the proposed method is demonstrated experimentally with a flexible rotor by using a magnetic bearing.
Modeling and Validation of Automotive Engines for Control Algorithm Development
Authors: Moskwa J. J. , Hedrick J. K.
Published: March 2008

There is considerable interest in coordinated automotive engine/transmission control to smooth shifts, and for traction control of front wheel vehicles. This paper outlines a nonlinear dynamic engine model of a port fuel-injected engine, which can be used for control algorithm development. This engine model predicts the mean engine brake torque as a function of the engine controls (i.e., throttle angle, spark advance, fuel flow rate, and exhaust gas recirculation (E. G. R.) flow rate). The model has been experimentally validated for a specific engine, and includes: • intake manifold dynamics, • fuel delivery dynamics, and • process delays inherent in the four-stroke engine. This model is used in real time within a control algorithm, and for system simulation. Also, it is flexible enough to represent a family of spark ignition automotive engines, given some test and/or simulation data for setting parameters.
A System Level Study of the Longitudinal Control of a Platoon of Vehicles
Authors: Sheikholeslam Shahab , Desoer Charles A.
Published: March 2008

This paper presents a preliminary system study of a longitudinal control law for a platoon of nonidentical vehicles using a simplified nonlinear model for the vehicle dynamics. This study advances the art of automatic longitudinal control for a platoon of vehicles in the sense that it considers longer platoons composed of nonidentical vehicles; furthermore, the longitudinal control laws presented in this study take advantage of communication possibilities not available in the recent past. We assume that for i = 1, 2, . . . vehicle i knows at all times vl and al (the velocity and acceleration of the lead vehicle) in addition to the distance between vehicle i and the preceding vehicle, i − 1. A control law is developed and is tested on a simulation of a platoon of 16 vehicles where the lead vehicle increases its velocity at a rate of 3 m.s−2; it is shown that the distance between successive vehicles does not change by more than 0.12 m in spite of variations in the masses of the vehicles (from the nominal), of communication delay and of noise in measurements.
Chaos in Linear Distributed Systems
Authors: MacCluer C. R.
Published: March 2008

Chaos can occur in linear distributed dynamical systems. Recent results of Godefroy and Shapiro show that certain linear analytic semi-groups exhibit chaotic behavior.
On the Implementation of a Continuous Controller Via a Discrete Valued Controller
Authors: DeSantis R. M.
Published: March 2008

A procedure for implementing a continuous controller, the output of which may vary within a continuous range of values, by means of a discrete controller, of which the output may only be given a discrete set of values, is presented. The theoretical development is based on the variable structure systems approach and is complemented with an analytical and experimental study of a position servomechanism with an elastic transmission. Relevant properties of the ensuing feedback system are discussed under both nominal and perturbed operating conditions. Preliminary simulation and experimental results suggest the procedure to be reliable, easy to implement and practically feasible.
Closeness of the Solutions of Approximately Decoupled Damped Linear Systems to Their Exact Solutions
Authors: Shahruz S. M. , Langari G.
Published: March 2008

The simplest technique of decoupling the normalized equations of motion of a linear nonclassically damped second-order system is to neglect the off-diagonal elements of the normalized damping matrix. In this paper, the error introduced in the system response due to this decoupling technique is studied. Conditions are derived under which the solution of an approximately decoupled system is “close” to the exact solution of the system.
A Preview Steering Autopilot Control Algorithm for Four-Wheel-Steering Passenger Vehicles
Authors: Lee A. Y.
Published: March 2008

This paper addresses the control law design of a preview steering autopilot for a four-wheel-steering vehicle to perform automatic lane tracking. In the concept, an on-board computer vision system is used in lieu of the driver’s vision to track the roadway. The steering autopilot design is formulated as an optimal, discrete-time preview path tracking problem under the “perfect measurement” assumption. Simulation results indicate that the tracking performance of the steering autopilot was improved by preview relative to that calculated for an autopilot without preview. These results also indicate the existence of an effective preview time with which almost all the benefits of previewing future information can be obtained. This effective preview time is about three times the reciprocal of the autopilot’s bandwidth. Our study also indicates that preview steering autopilots can tolerate the use of actuators with a lower bandwidth than those designed without preview information.
Discrete-Time Tip Position Control of a Flexible One Arm Robot
Authors: Cetinkunt Sabri , Wu Sijun
Published: March 2008

A predictive adaptive control algorithm is developed for tip position control based on the zero-order-hold equivalence of the nondimensionalized dynamic model of a flexible robot arm. A lattice filter is utilized for the purpose of parameter identification. The proposed control scheme provides an optimal output feedback control and, together with the lattice filter parameter identifier, it forms a special self-tuning regulator. It is then compared with other methods, such as linear quadratic Gaussian and stable factorization. A stability criterion for this control algorithm is also presented. The effects of the actuator dynamics on the overall system response and stability are investigated. Actuator dynamics model parameters are chosen from the actual specifications provided by manufacturers.
Comparison of Nonlinear Tracking Controllers for a Compressible Flow Process
Authors: Chaney M. J. , Beaman J. J.
Published: March 2008

Comparisons are made of two pressure-temperature controllers for a wind-tunnel type compressible flow process that includes control of pressures across a converging nozzle. Nonlinear flow characteristics of the nozzle present the key challenge for tracking rapid command trajectories. One controller is a linear integral-plus-state feedback configuration with gain scheduling. The other is a model-following controller that includes a feedforward inverse-process model to decouple and linearize the system. Simulation testing is used to compare the controllers, and sensitivity to feedforward modeling errors and feedback bandwidth is evaluated. Operational and implementation features are also compared.
Functional Persistence of Excitation and Observability for Learning Control Systems
Authors: Moore J. B. , Horowitz R. , Messner W.
Published: March 2008

Adaptive systems involving function learning can be formulated in terms of integral equations of the first kind, possibly with separable, finite-dimensional kernels. The learning process involves estimating the influence functions (Messner et al., 1989). To achieve convergence of the influence function estimates and exponentially stability, it is important to have persistence of excitation in the training tasks. This paper develops the concept of functional persistence of excitation (PE), and the associated concept of functional uniform complete observability (UCO). Relevant PE and UCO properties for linear systems are developed. For example, a key result is that uniform complete observability in this context is maintained under bounded integral operator output injection—a natural generalization of the corresponding finite dimensional result. This paper also demonstrates the application of the theory to linear error equations associated with a repetitive control algorithm.
Actuator Placement Using Degree of Controllability for Discrete-Time Systems
Authors: Guangqian Xing , Bainum Peter M.
Published: March 2008

In this paper some definitions of degree of controllability (observability), which is based on the scalar measure of the controllability (observability) Grammian matrix, are presented for discrete-time systems. The emphasis here is in showing the physical and geometrical meanings of the degree of controllability (observability) and the general properties of degree of controllability (observability). The concepts of degree of controllability are applied to the actuator placement problem for the shallow spherical sheel control system. The LQG transient responses for several typical systems with different degrees of controllability are also shown.
Observability Gramian Assignment for Perturbed Linear Continuous Systems Using Output Feedback
Authors: Chung Hung-Yuan
Published: March 2008

This paper deals with the problem of the observability Gramian assignment by using output feedback for perturbed linear continuous systems. This model gives us an alternative structure when observability Gramian is assignable. Finally, an example is given to illustrate the effectiveness of the present approach.
A Suboptimal Reference Generation Technique for Robotic Manipulators Following Specified Paths
Authors: Butler J. , Tomizuka M.
Published: March 2008

The optimal reference generation problem deals with finding a tracking velocity versus time profile which will move the end effector of a multiple degree of freedom robotic manipulator through a general spatial curve in minimum time subject to hard actuator torque limits. While reference generation techniques exist which solve this problem, they are typically computationally intensive, limiting their usefulness in practical situations. In this technical brief, a modification is made to the formulation of the optimal reference generation problem, resulting in a slightly suboptimal solution which is numerically simpler than optimal methods. The method is applied to a computer simulation of a two link SCARA type manipulator following a circular path in joint space. Performance comparisons are made with an optimized constant velocity profile as with the true optimal solution.
Hierarchical, Knowledge-Based Control in Turning
Authors: Teltz R. , Elbestawi M. A.
Published: March 2008

A heirarchical, knowledge-based controller has been developed and implemented on a CNC lathe. The system consists of an intelligent supervisor and two control subsystems. These elements are realized as concurrent tasks in a real time, multitasking system. For each tool pass, a parameter adaptive control subsystem maximizes tool feed within tool breakage and tool edge chipping constraints. A second subsystem adjusts the depth of cut on-line in reaction to the detection of the onset of chatter. Consequently, this event-driven subsystem aims to ensure a depth of cut that results in stable cutting. An intelligent supervisor coordinates these subsystems, combining a frame based knowledge base with a real-time inference engine. The intelligent supervisor, having precedence over the other system elements, directs the control objective of this hierarchical control system. Cutting tests are performed to verify the controller performance in real time. Experimental results are presented.