Showing papers by "Ron J. Patton published in 1990"

Comparison of test signals for aircraft frequency domain identification

Abstract: The validity of applying frequency domain techniques to the identification of aircraft system dynamics is investigated using a simplified linear analytic model of a helicopter. A closed-loop identification of the helicopter model, with the longitudinal and lateral motions decoupled, is described. Measurement noise effects are included in the simulations. Input signals are applied to excite the system modes. Frequency response estimates are obtained by spectral analysis, and the coherence function is evaluated to indicate the likely accuracy. The transfer function coefficients are obtained by a nonlinear least-squares curve-fitting technique. With prior knowledge of the system order, the advantages of using a low peak-factor harmonic test signal for identification instead of the more usual frequency sweeps are demonstrated.

A comparison of some robust eigenvalue assignment techniques

Abstract: Three techniques for robust eigenvalue assignment are presented. The first is well known and is based on iteratively assigning the closed-loop eigenvectors so as to be maximally orthogonal to one another. The second has been recently presented by the authors and is an improvement of the first which gives better results for problems where complex-conjugate eigenvalue pairs are to be assigned. The final method is new and is founded on the iterative replacement of the current closed-loop eigenvector matrix with a new matrix which is the projection of the columns of the nearest orthogonal matrix into the allowable eigenvector subspaces. Some numerical examples are given which are used to illustrate the improved results obtained using the second technique in place of the first and to compare these with the performance of the last algorithm which is based on an alternative approach.

Optimal Eigenstructure Assignment for Multiple Design Objectives

Abstract: This paper considers the application of eigenstructure assignment in the design of multi-criteria controllers with a gradient-based numerical optimization procedure using analytically derived gradients. Emphasis is placed on the design of output feedback control laws which possess certain additional desirable properties. By allowing the closed-loop eigenvalues to be selected (where appropriate) from regions of the complex plane extra design freedom is introduced which may be used to achieve, for example, robust eigenvalue assignments and a low norm control law more easily.

A Robust Approach to Multirate Controller Design using Eigenstructure Assignment

Abstract: This paper presents a new method for the design of constant gain digital controllers for multirate systems with a multiple input/fixed output sampling rate configuration The technique is based on full-state feedback pole placement Two main problems are addressed; the adverse effects of intersample cross-coupling and the high amplitude control signals that normally result from a multirate feedback structure The trade-off between these two factors is outlined and a method for minimising each as a design parameter is considered An example demonstrates the conflicting design objectives of the multirate feedback control problem

An assessment of robustness of variable structure control systems for advanced aircraft manoeuvres

Abstract: The authors use a model-following VSCS (variable structure control system) design approach to provide an aircraft control system which exhibits parameter insensitivity with good disturbance rejection while enabling the pilot to perform an advanced aircraft maneuver. Eigenstructure assignment is used to define a model with these response characteristics. The authors also consider a definition and practical measures of the robustness of such a model-following VSCS. The VSCS technique is illustrated by considering the design of a lateral translational/yaw pointing control scheme for a conventional combat aircraft which has been augmented with a chin-fin to provide the required sideforce control. Analysis of the performance of this control scheme when subjected to a range of flight conditions is used to demonstrate application of the robustness criteria developed. >