Showing papers on "Robustness (computer science) published in 1988"

Survey of model-based failure detection and isolation in complex plants

Abstract: Techniques to detect and isolate failures in complex technological systems, such as sensor biases, actuator malfunctions, leaks, and equipment deterioration are surveyed. The methods are based on analytical redundancy afforded by a mathematical model of the system. The main components of such techniques are residual generation using the model, signature generation by statistical testing, and signature analysis. Model-structural conditions for failure isolation are introduced together with transformation methods to implement them. Sensitivity and robustness considerations are presented, and a design framework based on model redundancy is proposed. >

Adaptive manipulator control: A case study

Abstract: The author's previous work (1986, 1987) utilized the particular structure of manipulator dynamics to develop a simple, globally convergent adaptive controller for manipulator trajectory control problems. After summarizing the basic algorithm, they demonstrate the approach on a high-speed two-degree-of-freedom semi-direct-drive robot. They show that the dynamic parameters of the manipulator, assumed to be initially unknown, can be estimated within the first half second of a typical run, and that accordingly, the manipulator trajectory can be precisely controlled. These experimental results demonstrate that the adaptive controller enjoys essentially the same level of robustness to unmodeled dynamics as a PD (proportional and differential) controller, yet achieves much better tracking accuracy than either PD or computed-torque schemes. Its superior performance for high-speed operations, in the presence of parametric and nonparametric uncertainties, and its relative computational simplicity, make it an attractive option both for addressing complex industrial tasks, and for simplifying high-level programming of more standard operations. >

Robust control of ill-conditioned plants: high-purity distillation

Abstract: Using a high-purity distillation column as an example, the physical reason for the poor conditioning and its implications on control system design and performance are explained. It is shown that an acceptable performance/robustness tradeoff cannot be obtained by simple loop-shaping techniques (using singular values) and that a good understanding of the model uncertainty is essential for robust control system design. Physically motivated uncertainty descriptions (actuator uncertainties) are translated into the H/sup infinity //structured singular value framework, which is demonstrated to be a powerful tool to analyze and understand the complex phenomena. >

Elections with unconditionally-secret ballots and disruption equivalent to breaking RSA

Abstract: Election protocols embodying robustness, verifiability of returns by voters, and unconditional security for voters’ privacy have been presented. The techniques also allow untraceable payments and credentials.

Theory and design of robust direct and indirect adaptive-control schemes

Abstract: A general approach for designing and the theory for analysing robust direct and indirect adaptive-control schemes for continuous-time plants is presented. The design approach involves the development of a general robust adaptive law and the use of the certainty equivalence principle to combine it with robust model reference and pole placement control structures. The global stability properties and robustness of the developed adaptive control schemes are established by using a general theory which relates the properties of signals in the mean sense over intervals of time. The developed theory and design approach are used to analyse and compare the robustness properties and performance of a wide class of robust adaptive laws which employ a dead-zone, fixed-σ, e1, and a switching-σ modification as well as their variations.

Robust methods in inverse theory

Abstract: Due to ill-conditioning of the linearised forward problem and the presence of noise in most data, inverse problems generally require some kind of 'regularisation' in order to generate physically plausible solutions. The most popular method of regularised inversion is damped least squares. Damping sometimes forces the solution to be smoother than it otherwise would be by raising all of the eigenvalues in an ad hoc fashion. An alternative is described, based upon the method of least-absolute deviation, which has a property known in the statistical literature as robustness. An account of robust inversion methods-their history and computational developments-is given. The key computational technique turns out to be preconditioned conjugate gradient, an algorithm which had as its genesis 'the method of orthogonal vectors' by Fox, Huskey and Wilkinson (1948). Applications are illustrated from seismic tomography and inverse scattering, two of the most computationally intensive tasks in inverse theory.

Parallel integration of vision modules.

Abstract: Computer algorithms have been developed for several early vision processes, such as edge detection, stereopsis, motion, texture, and color, that give separate cues to the distance from the viewer of three-dimensional surfaces, their shape, and their material properties. Not surprisingly, biological vision systems still greatly outperform computer vision programs. One of the keys to the reliability, flexibility, and robustness of biological vision systems is their ability to integrate several visual cues. A computational technique for integrating different visual cues has now been developed and implemented with encouraging results on a parallel supercomputer.

Practical reactive power allocation/operation planning using successive linear programming

Abstract: A method for reactive power planning is presented that it finds an optimal solution for both allocation and operation planning in large systems using linear programming (LP). The method utilizes calculated linear sensitivities including active power and voltage phase angle in the formulation. Although the overall method includes these relations, the number of constraints and variables are not augmented in its first procedure, APPROACH-1. Its second procedure, APPROACH-2, overcomes numerical problems caused by a dense constraint matrix. This is achieved by retaining untouched sparse sensitivities in the constraint matrix and by eliminating any calculations related to the inverse matrix. The results of applying this method to a practical 224-bus system and the IEEE-30 bus system verify its robustness and fast convergence. >

The Number of Iterations in Monte Carlo Studies of Robustness.

Abstract: A recent survey of simulation studies concluded that an overwhelming majority of papers do not report a rationale for the number of iterations carried out in Monte Carlo robustness (MCR) experiments. The survey suggested that researchers might benefit from adopting a hypothesis testing strategy in the planning and reporting of simulation studies. This paper presents a table of the number of iterations necessary to detect departures from a series of nominal Type I error rates based upon hypothesis testing logic. The table is indexed by effect size, by significance level, and by power level for the two-tailed test that a proportion equals some constant. An alternative approach based upon the construction of a confidence interval is discussed and dismissed. The MCR research design demands an adequate definition of robustness and a sufficient sample size to detect departures from that definition. (Author/TJH) monoommommommoommommommommommmommommommommommom Reproductions supplied by EDRS are the best that can be made from the original document. 30000000000800000000000000000000000000000000000000000000000000000000000(

Brushless servo motor control using variable structure approach

Abstract: The variable structure system (VSS) is expected to be a powerful tool for constructing a control strategy for AC machines since it is based on discontinuous control inputs, i.e. variable structures. The application of VSS to the position control of a brushless servo motor is discussed. The resulting system is robust with respect to parametric variations and disturbances. On-off patterns for switching devices are generated directly by VSS, and the robustness is obtained in a total system including the inverter. This approach is useful for a nonlinear plant such as a direct-drive robot arm. >

Design and test of a computer-stabilized unicycle

Abstract: This research investigates the stabilization of a one wheeled vehicle by means of active feedback control. The control methods of a human riding a unicycle are investigated first and a dynamic model which closely emulates the process is derived. A one wheeled robot with mass and inertia propeties similar to those of a young child was constructed and used as an experimental vehicle for testing various control algorithms. The research addresses aspects in the fields of robotics, artificial intelligence and modern digital control, but rather than specializing in any of these fields, it strives to combine these disciplines in a unique application where the interaction of these fields can be studied. An underlying approach of this research was to not only design but also evaluate control system performance in a laboratory environment without incurring large financial expenses. The robot has all its electrical and computational power on board, with the ability to receive commands from a radio transmitter to change its direction and forward speed. A linearized model was derived and optimal control systems to stabilize the vehicle were designed and simulated. An investigation into using accelerometers for detection of the deviation from vertical by measuring the specific force on the robot frame, was conducted. We found that this resulted in unacceptable closed loop system robustness. Theoretical and physical explanations for this phenomenon are presented as well as experimental results to confirm the extreme sensitivity of the design to these sensors. We show that accurate sensor information on the unicycle's orientation with respect to vertical facilitates the design of closed loop control systems with good stability and robustness characteristics. Such a control system for the longitudinal dynamics of the unicycle robot was demonstrated experimentally. The sensing, actuation and control abilities of a person riding a unicycle are compared with those of a computerized robot performing a similar task. We propose that this research and the test vehicle form the basis for theoretical and experimental studies into the application of nonlinear, robust and adaptive control systems techniques for unstable systems.

Robust image modeling techniques with an image restoration application

Abstract: A robust parameter-estimation algorithm for a nonsymmetric half-plane (NSHP) autoregressive model, where the driving noise is a mixture of a Gaussian and an outlier process, is presented. The convergence of the estimation algorithm is proved. An algorithm to estimate parameters and original image intensity simultaneously from the impulse-noise-corrupted image, where the model governing the image is not available, is also presented. The robustness of the parameter estimates is demonstrated by simulation. Finally, an algorithm to restore realistic images is presented. The entire image generally does not obey a simple image model, but a small portion (e.g. 8*8) of the image is assumed to obey an NSHP model. The original image is divided into windows and the robust estimation algorithm is applied for each window. The restoration algorithm is tested by comparing it to traditional methods on several different images. >

Torque Vector Control (TVC)-A Class of Fast and Robust Torque-Speed and Position Digital Controllers for Electric Drives

Abstract: This paper presents the fundamentals of a new class of torque speed and position controllers for electric drives, characterized by the association of a modified sliding mode position (speed) controller and stator flux control through a unique table of optimal conduction sequence to fire directly the static power converter SCR switches. Robustness is provided by the sliding mode controller and stator (instead of rotor) flux vector estimation while control precision is secured by the torque pulsation controller. Fast response is obtained through the table of optimal conduction sequence which leads to the fastest response available through a stator flux vector (or stator accelerating field) control obtained without the transformation of coordinates or special techniques. The control computation time (costs) is drastically reduced in comparison with PWM transvector (or field accelerating) methods while the performance in terms of precision, response and robustness are better.

Design of robust controllers for uncertain dynamical systems

Abstract: The general design approach for robust controllers of uncertain dynamical systems is considered. The design approach, utilizing only the bound of uncertainty, can be used to construct various classes of controllers which render the systems practically stable. No statistical information of the uncertainty is required, and the system performance is described in a deterministic manner. >

Active Vibration Control of Large Civil Structures

Abstract: This survey of vibration control methods for safety and comfort in large civil structures (LCS), reviews the application of control theory to LCS, and discusses a class of vibration suppression algorithms that avoid the major difficulties encountered in the application of modern control techniques to building structural systems. Two simple, efficienct methods are presented for the on-line pulse control of linear as well as nonlinear, multi-degree-of-freedom systems responding to arbitrary dynamic environments. The latter method is suitable for situations in which detailed knowledge of the system structure is not available. Digital computer simulation studies, electronic analog computer investigations, and experimental tests with several mechanical models of different size and configuration demonstrate the feasibility, reliability, and robustness of the proposed pulse-control methods.

Simple adaptive control of uncertain systems

Abstract: This paper considers adaptive control of various systems with unknown time-varying or non-linear dynamics in an attempt to show that practical adaptive control can be simple and robust. The simplified adaptive control methodology used is based on the observation that most real-world systems, even non-stationary or non-linear, can be stabilized by simple controller configurations. More complex controllers may be needed only in order to improve the performance of the control systems. In the adaptive scheme, the stabilizability properties of the plants are used only to satisfy the necessary conditions that guarantee robustness of simple adaptive controllers. The desired performance is then imposed upon the plant by these adaptive controllers, which force the plant to follow the input-output behaviour of low-order reference models. Examples from the recent literature of control with uncertainty are used to illustrate the power of these adaptive techniques.

Power conditioning system using sliding model control

Abstract: A control system for power conditioning and uninterruptible power supply systems is presented. The design is based on the theory of variable-structure systems with sliding mode. Results of an analytical study and digital simulation of both the power and control systems are reported, showing good agreement. The high dynamics and the robustness of the implemented system, indicated by the simulation results, confirm the validity of the control scheme and suggest the possibility of adopting it for three-phase systems, variable frequency supplies, and measuring equipment. >

Robust model reference adaptive control for multivariable plants

Abstract: A complete procedure for generating and analysing robust model reference adaptive control schemes for multivariable plants is developed. The procedure consists of two parts: the first part involves the characterization of the integral structure of the modelled part of the plant, and the associated parametrization of the controller structure; and the second part involves the development of a general robust adaptive law for adjusting the controller parameters so that the closed-loop plant is globally stable despite the presence of unmodelled dynamics and bounded disturbances. The use of dominantly rich signals for improving convergence and the bounds for the tracking and parameter error is also analysed.

Robust hyperplane design in multivariable variable structure control systems

Abstract: The problem of designing a stable sliding mode giving robust performance of a variable structure control system is studied. A set of specified eigenvalues is assigned to the closed-loop feedback system during the sliding mode. The design philosophy seeks to build on the known robustness and invariance properties associated with the use of discontinuous (or continuous) non-linear controls, by assigning the eigenvectors associated with the sliding-mode eigenvalues in a manner that leads to a robust control scheme. A previously developed canonical form for the hyperplane design problem is again employed. The design technique centres on a recently published eigenvalue assignment algorithm, and is illustrated by the inclusion of an example.

Independent parameterization of two-degree-of-freedom compensators in general robust tracking systems

Abstract: Consideration is given to a general robust tracking problem in which the controlled object is a linear multivariable system having measured variables that are not necessary coincident with the output variables to be controlled. A necessary and sufficient condition for the two-degree-of-freedom compensator to achieve a robust tracking system with internal stability is given. An existence condition is derived for such a compensator, and the class of all such compensators is parameterized, so that two specifications with respect to responses for reference commands and feedback properties can be satisfied independently by the two free parameters. >

New approach to robust observer design

Abstract: This paper shows that based on the recent development of observer design solution, an observer pole selection method can be formulated to minimize the observer gain to the system input. It is proved that this method is a deterministic approach to the recovery of the loop transfer function and robustness of direct state feedback systems.

A Note on Asymmetry and Robustness in Linear Regression

Abstract: We discuss the assumption of symmetry in robust linear regression. It is important to distinguish between the intercept term and the slope parameters. Ordinary robust regression requires no assumption of symmetry when interest lies in slope parameters; computer programs, confidence intervals, standard errors, and so forth do not change because the errors are asymmetric. The situation is radically different for bounded-influence estimators. With the exception of the Mallows class, these estimators are inconsistent for slope when the errors are asymmetric.

New robustness results for linear systems under real perturbations

Abstract: Structured real perturbations of the system matrix A to A+ Delta A=BDC (with B, C given matrices) are considered. Robustness measures with respect to arbitrary stability domains C/sub g/ contained in/implied by C are introduced and characterized. These general formulas provide insight but are difficult to evaluate. Computable formulas are obtained when B is a column or C a row vector. >

A self-tuning controller for the control of multi-machine power systems

Abstract: An adaptive synchronous machine controller that minimizes a cost function incorporating system input, output, and set-point variations, and its application to a multimachine power system are described. The control is based on a criterion of automatically shifting the closed loop poles of the system towards the origin in the z-domain without violating the control constraints. It possesses the property of robustness and ease of reference signal tracking. The ability of the proposed controller to damp multimode oscillations is investigated. Studies show that the proposed controller cooperates with the conventional power-system stabilizers on the system in damping the oscillations. >

Robustness in the Presence of Joint parametric Uncertainty and Unmodeled Dynamics

Abstract: It is shown that, in the case of joint real parametric and complex uncertainty, Doyle's structured singular value can be obtained as the solution of a smooth constrained optimization problem. While this problem may have local maxima, an improved computable upper bound to the structured singular value is derived, leading to a sufficient condition for robust stability and performance.