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The vision based target tracking/ following is presented. There is no interior communication between the target and tracker and their relative displacement is measured with the 3D visual sensors. The tracking/ following control law is designed in the half North-EastDown (NED) frame with the dynamic inversion and the robust perfect tracking (RPT) techniques. The half NED frame is formed by moving the origin of the NED frame to the mass center of the target and then rotating the X axis along the Z axis to be aligned with the flight direction of the target. The RPT technique is one of the better techniques to design the tracking control laws for the linear plants. It involves with the high-order derivatives of the reference to improve the tracking/ following performance. In order to implement the RPT control law, a novel algorithm is developed to estimate the velocity and acceleration of the target with the measured relative displacement between the target and tracker. The algorithm is developed based on the extended Kalman filtering and under assumption of the quasi steady states in which the derivatives of the target ground speed, flight path and directional angles are constant. The simulation results demonstrate that the resulting the closed-loop system is capable of tracking/ following the 3D maneuvering target in the scheduled relative distance and orientation with respect to the target.

A simple UAV helicopter is to be constructed as a test bed for the implementation of some newly developed nonlinear control technologies. The UAV helicopter consists of (a) an advanced toy radio-controlled helicopter as a basic aircraft; (b) a simple avionic system to be developed; and (c) a ground supporting system. The avionic system includes a miniature PC-104 computer system (airborne) and a MEMS (mechanical and electrical micro system) navigation and inertial measurement unit as a major sensing unit. A couple of full duplex transceivers are used to provide wireless communications between the helicopter and the ground unit. The ground transceiver and a computer system stationed in the ground form a supporting system. The UAV helicopter is to be used to implement automatic flight control systems.

This paper deals with the modeling of the voice coil motor (VCM) with nonlinearities from friction in the actuator rotary pivot bearing and data flex cable in a hard disk drive (HDD). They are two of major nonlinearities in the VCM motor, which result in large residual errors and deteriorate the performance of head positioning servo systems. The basic idea to build the model of the VCM motor with the nonlinearities is to identify the configuration of the VCM motor through analysis of physical effects and to determine the parameters with the Monte Carlo method to match the measured frequency response. The verification of the identified model shows that the established model is sufficient to characterize the VCM motor with the nonlinearities.

In this paper, we present an enhanced composite nonlinear feedback (CNF) control technique for discrete-time systems with input saturation and with external disturbances. The conventional CNF control is proved to be capable of yielding better transient performance in tracking control for systems with input saturation. However, when the given system has external disturbances as in most of practical situations, the conventional CNF control would yield some steady state errors in the resulting output response. The enhanced CNF technique presented is an extension of the conventional one. It retains good transient properties as those of the conventional CNF control and at the same time has an additional capacity of eliminating steady state bias due to unknown constant disturbances.

This paper presents design of hard disk drive (HDD) servo systems using an enhanced composite nonlinear feedback (CNF) control technique with a simple friction and nonlinearity compensation scheme. Friction and nonlinearity result in large residual errors and deteriorate the performance of head positioning of HDD servo systems. The enhanced CNF technique has a feature of removing the uncompensated portion of friction and nonlinearity without sacrificing the overall tracking performance. Simulation and experimental results for 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 PID control in settling time. This approach can be adopted to solve other servomechanism problems.

We present in this article a MATLAB toolkit with a user-friendly graphical interface for composite nonlinear feedback control system design. The toolkit can be utilized to design a fast and smooth tracking controller for a class of linear systems with actuator and other nonlinearities as well as with external disturbances. The toolkit is capable of displaying both time-domain and frequency-domain responses on its main panel, and generating three different types of control laws, namely, the state feedback, the full order measurement feedback and the reduced order measurement feedback controllers. The usage and design procedure of the toolkit are illustrated by a practical example on the design of a hard disk drive servo system. The toolkit can be utilized to design servo systems that deal with point-and-shoot fast targeting.