Inflight investigation of the effects of rotor state measurement and feedback on variable stability helicopters

This thesis describes a flight test evaluation of flight control laws applying rotor state measurements and feedback on the National Research Council Bell 412 Advanced Systems Research Aircraft (ASRA) and Bell 205A Airborne Simulator (AS). Parameter estimation of a higher-order mathematical model of the ASRA rotor dynamics was achieved by Maximum Likelihood Estimation (MLE) employing coupled rotor-body equations parameterized by explicit rotor and fuselage state measurements. Root Locus (RLM), Classical Multivariable (CMC), Eigenstructure Assignment (EAC), and Model Following control algorithms were implemented in Matlab/Simulink simulation for analysis of coupled rotor-body dynamics. Rotorcraft performance specifications were based on compliance with ADS-33E-PRF and Cooper Harper military handling qualities. Evaluated in desk-top and in-flight simulation, rotor state feedback of longitudinal and lateral disc tilt dynamics by modern multivariable control significantly improves inter-axis decoupling, disturbance rejection characteristics, rotor response dynamics, command tracking accuracy, and rigid-body bandwidth performance.

Inflight investigation of the effects of rotor state measurement and feedback on variable stability helicopters

This thesis describes a flight test evaluation of flight control laws applying rotor state measurements and feedback on the National Research Council Bell 412 Advanced Systems Research Aircraft (ASRA) and Bell 205A Airborne Simulator (AS). Parameter estimation of a higher-order mathematical model of the ASRA rotor dynamics was achieved by Maximum Likelihood Estimation (MLE) employing coupled rotor-body equations parameterized by explicit rotor and fuselage state measurements. Root Locus (RLM), Classical Multivariable (CMC), Eigenstructure Assignment (EAC), and Model Following control algorithms were implemented in Matlab/Simulink simulation for analysis of coupled rotor-body dynamics. Rotorcraft performance specifications were based on compliance with ADS-33E-PRF and Cooper Harper military handling qualities. Evaluated in desk-top and in-flight simulation, rotor state feedback of longitudinal and lateral disc tilt dynamics by modern multivariable control significantly improves inter-axis decoupling, disturbance rejection characteristics, rotor response dynamics, command tracking accuracy, and rigid-body bandwidth performance.

Combining Input Shaping and Adaptive Model-Following Control for Vibration Suppression

Vibration suppression in servo systems is significant in high-precision motion control. This paper describes a vibration-suppression method based on input shaping and adaptive model-following control. First, a zero vibration input shaper is used to suppress the vibration caused by an elastic load to obtain an ideal position output. Then, a configuration that combines input shaping with model-following control is developed to suppress the vibration caused by changes of system parameters. Finally, analyzing the percentage residual vibration reveals that it is effective to employ the sum of squared position error as a criterion. Additionally, a golden-section search is used to adjust the parameters of a compensator in an online fashion to adapt to the changes in the vibration frequency. A comparison with other input shaper methods shows the effectiveness and superiority of the developed method.

Bell 412 System Identification and Model Fidelity Assessment for Hover and Forward Flight

Frequency domain system identification of higher order models for the Bell 412 helicopter was performed. First, a frequency response database was derived from flight-test data. For hover, a combination of sweep and 2311-multistep maneuvers had to be used to achieve good results. In addition to the classical six-DoF (degrees of freedom) rigid body states, the identified hover model includes dynamic inflow, rotor coning dynamics, and uses a Padé approximation for the influence of engine dynamics, to improve the response in the vertical axis. The forward flight (60 kn) model includes as extension first-order flapping dynamics, mainly to improve the roll and pitch response. Besides the simple Padé approach used in the hover model, two different engine model structures were investigated but they provided no significant improvement compared to the Padé solution when coupled to the rigid-body model. Finally, a method derived from feedforward principles of model following control is shown, to use the identified hover model to analytically derive an "input filter" correction that improves the fidelity of a linearized FLIGHTLAB simulation model.

Model Following Control of a Higher Order Plant by a Lower Order Model

In this paper, based on Model Following Control (MFC) approach, a robust controller is used to control a flexible robot manipulator along a pre-defined trajectory. Here two degree of freedom plant is considered that has two different inertias. The plant is run by the single degree of freedom ideal model. Primarily, an ideal model is formulated from the mathematical expression and by selecting a suitable feedback amplifier gain a well-defined response is established. A reference input voltage is given to the model and the plant is driven by the errors, generated from the differences of the states between the plant and model. Here special attention is given to the fact that how precisely the states of the plant can follow the ideal states of the model. The proposed model following control (MFC) system may be used successfully in industrial robots.

Control of a Robot Manipulator using Model Following Control

In this work the simulation results of a 2 degree of freedom plant driven by model are shown. Here Model following control (MFC) system is applied to operate the plant in a better way. Initially a model is constructed, whose states are ideal with respect to the control parameters. The plant and the model essentially have same physical parameters. An input is given to the model and the plant is run by the errors, computed by comparing the states of the plant and model. In this way the plant is forced to follow the ideal states of the model. The results show that the plant is able to follow the model very accurately. The robust control observed in the scheme can be easily implemented for better performance of industrial robots.

The Hinf Model Following Control: An LMI Approach

The aim of this paper is to develop a new approach for a solution of the model following control (MFC) problem with a dynamic compensator by using linear matrix inequalities (LMIs). TheH1 model following control problem is derived following LMI formulation. First, the H1 optimal control problem is revisited by referring to Lemmas assuring all admissible controllers minimizing the H1 norm of the transfer function between the exogenous inputs and the outputs. Then, the solvability condition and a design procedure for a two degrees of freedom (2 DOF) dynamic feedback control law is introduced. The existence of a 2 DOF dynamic output feedback controller for the model following control is proven and the stability of the closed-loop system is satisfied by assuring the Hurwitz condition. The benchmark thermal process (PT-326) as the first order process with timedelay is regulated by the presented 2 DOF dynamic output feedback controller. The simulation results illustrate that the presented controller regulates a system with dead-time as a large set of generic industrial systems and the H1 norm of the closed-loop system is assured less than the H1 norm of the desired model system.