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The article presents a study related to spacecraft attitude stabilization with the use of magnetorquers with separation between measurement and actuation. Topics discussed include actuation mechanisms related to spacecraft attitude stabilization; ways to spacecraft attitude control; and use of electromagnetic actuators for generation of attitude control torques on satellites flying in low earth orbits.

We present in this paper an integration scheme of a low-cost inertial attitude and position reference system for a mini unmanned helicopter by utilizing the robust and H∞ filtering technique. The result has been successfully implemented and tested on our mini-scale unmanned helicopter. Simulation and flight experiment results show that the proposed technique is very effective in real-time and suitable for control, stabilization and navigation for mini-scale unmanned air vehicles. [ABSTRACT FROM PUBLISHER]

Abstract  The problem of stabilization of an autonomous rotorcraft platform in a hover configuration subject to external disturbances is addressed. Necessary and sufficient conditions are presented for static output-feedback control of linear time-invariant systems using the H-Infinity approach. Simplified conditions are given which only require the solution of two coupled matrix design equations. This paper also proposes a numerically efficient solution algorithm for the coupled design equations to determine the output-feedback gain. A major contribution is that an initial stabilizing gain is not needed. The efficacy of the control law and the disturbance accommodation properties are shown on a rotorcraft design example. The helicopter dynamics do not decouple as in the fixed-wing aircraft case, so that the design of helicopter flight controllers with a desirable intuitive structure is not straightforward. In this paper an output feedback approach is given that allows one to selectively close prescribed multivariable feedback loops using a reduced set of the states. Shaping filters are added that improve performance and yield guaranteed robustness and speed of response. This gives direct control over the design procedure and performance. Accurate identification of the System parameters is a challenging task for rotorcraft control, addition of loop shaping facilitates implementation engineers to counteract unmodeled high frequency dynamics. The net result yields control structures that have been historically accepted in the flight control community. [ABSTRACT FROM AUTHOR]

We present in this paper the modeling and flight- control-system design for the yaw channel of an unmanned- aerial-vehicle (UAV) helicopter using a newly developed composite nonlinear feedback (CNF)-control technique. The CNF-control method has been proven to be capable of yielding a fast transient response with no or very minimal overshoot in tracking a specific target. From the actual flight tests on our UAV helicopter, it has been found that the commonly used yaw dynamical model for the UAV helicopter proposed in the literature is very rough and inaccurate, which might cause the helicopter to shake severely in certain flight conditions. This motivates us to first obtain a more accurate model for the yaw channel of our UAV helicopter. The CNF-control method is then utilized to design an efficient control law, which gives excellent overall performance. In particular, our design has achieved a Level 1 performance according to the standards set for military rotorcraft. The results are verified through actual flight tests. [ABSTRACT FROM AUTHOR]

A new robust composite nonlinear feedback (CNF) control method is proposed to achieve fast and accurate set-point tracking for linear systems subject to input saturation and disturbances. The basic idea is to incorporate disturbance estimation and compensation into the framework of the original CNF control so as to eliminate the steady-state bias due to disturbances and retain the fast transient performance of the original CNF control. There is no additional integration action introduced in the new method, which is in contrast with the previous work, i.e., the enhanced CNF control. The new method is applied to design a control law for a dc servomotor positioning system. Simulation and experimental results show that the new method can achieve better transient performance and steady-state accuracy in set-point tracking and is more robust to amplitude variations of disturbance/set point compared to integration-based control. [ABSTRACT FROM AUTHOR]

We adopt in this paper the newly developed composite nonlinear feedback (CNF) control method to track general target references for systems with input saturation. The original formulation of the CNF control technique is only applicable to set-point tracking, in which the target reference is set to be a constant. In this paper, a reference generator, which is able to produce more general reference signals such as sinusoidal and other waves, will be proposed to supplement the CNF control technique to yield a good performance. The resulting control law comprises the reference generator and a modified CNF control law, which is proven to be capable of tracking a target reference with fast settling time and minimal overshoot. Simulation and experimental results on an XY-table show that the proposed technique gives a very satisfactory performance. [ABSTRACT FROM AUTHOR]

Friction and nonlinearities result in large residual errors and deteriorate the performance of head positioning of hard disk drive (HDD) servo systems and other mechanical servo systems. Thus, it is highly desirable to characterize the behaviors of nonlinearities and friction in the servo systems. This paper presents a fairly comprehensive modeling and compensation of friction and nonlinearities of a typical voice-coil-motor (VCM) actuator used in commercial HDDs, and the design of an HDD servo system using an enhanced nonlinear control technique. Our contributions are two-fold: We will first obtain a complete model of the VCM actuator including friction and nonlinear characteristics through a careful examination of the configuration and structure of the actual system and through a thorough analysis of its physical effects together with its time-domain and frequency-domain responses. We will then proceed to design a servo system for the hard drive using an enhanced composite nonlinear feedback (CNF) control technique with a simple friction and nonlinearity compensation scheme. The enhanced CNF technique has a feature of removing the uncompensated portion of friction and nonlinearities without sacrificing the overall tracking performance. Simulation and experimental results for both the modeling and the servo design show that our approach is very effective and successful. In particular, our experimental results show that the enhanced CNF control has outperformed the conventional proportional-integral-derivative (PID) control in settling time by 76%. We believe that this approach can be adopted to solve other servomechanism problems. [ABSTRACT FROM AUTHOR]

Presents the discrete-time composite nonlinear feedback control, which can perform several functions in hard disk drive servo systems with actuator saturation. Feedback law; Damping ratio of the closed-loop system; Time-optimal servomechanism; Settling time.