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Contrary to the conventional method of disturbance observers (DOB) where Q-filter is designed to be a low-pass filter with unity DC gain, the optimal H∞ method has been proposed to design the Q-filter and applied in the servo control system of hard disk drives in track following. Simulation and implementation results have shown that the resultant H∞ DOB improves low-frequency disturbance attenuation without compromising the disturbances attenuation performance at higher frequency region achieved by the nominal feedback controller. In terms of track-following precision, the proposed method is approximately 5% more accurate than the conventional method. [ABSTRACT FROM AUTHOR]

For a quadrotor, one can identify the two well-known inherent rotorcraft characteristics: underactuation and strong coupling in pitch-yaw-roll. To confront these problems and design a station-keeping and tracking controller, dynamic inversion is used. Typical applications of dynamic inversion require the selection of the output control variables to render the internal dynamics stable. This means that in many cases, perfect tracking cannot be guaranteed for the actual desired outputs. Instead, the internal dynamics of the feedback linearised system is stabilised using a robust control term. Unlike standard dynamic inversion, the linear controller gains are chosen uniquely to satisfy the tracking performance. Stability and tracking performance are guaranteed using a Lyapunov-type proof. Simulation with a typical nonlinear quadrotor dynamic model is performed to show the effectiveness of the designed control law in the presence of input disturbances. [ABSTRACT FROM AUTHOR]

As sensor networks become increasingly autonomous and grow to include mobility and actuation, the need for predictability in the execution of complex missions becomes crucial. In this perspective, we propose a discrete event controller (DEC) as an effective framework for modelling task constraints, priority orders and task schedules of mobile sensor networks (MSNs) in charge of executing multiple missions. The focus is to show that, for such systems, risks of deadlock arise and that the proposed DEC is able easily to implement effective deadlock avoidance algorithms. Several experiments of coordination policies on an actual MSN test bed with shared heterogeneous resources are presented. [ABSTRACT FROM AUTHOR]

Disturbance observer (DOB) without using additional sensors is an attractive method to attenuate the effects of disturbances as they are highly cost effective. This study proposes a simple form of DOBs, which does not need to solve the plant model inverse, and uses H∞ control method to design the Q-filter in the DOB. The conventional form is proved to be a special case of the proposed form. Comparison to the conventional form of DOBs is made and the significance of the proposed method in DOB design and disturbance attenuation is verified via simulation and experimental results. [ABSTRACT FROM AUTHOR]

A feedforward control based on neural networks to attenuate the effect of external vibrations on the positioning accuracy of hard disk drives (HDDs) is presented. The adaptive neural network compensator utilises accelerometer signals to detect external vibrations. No information on the plant, sensor and disturbance dynamics is needed in the design of the adaptive neural network compensator. The stability of the proposed scheme is analysed by the Lyapunov criterion. Experimental results show that the tracking performance of HDDs can be improved significantly by using the feedforward controller when compared with the case without compensation. [ABSTRACT FROM AUTHOR]