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A nonlinear model of a flapping-wing micro aerial vehicle (MAV) is built in which the load acceleration and equivalent moment are formulated linearly in the body frame. The aerodynamic force and moment are not considered directly because the mass and moment of inertia of the flapping-wing MAV are too tiny. The visual measurement system (VMS) is taken to measure the flight data such as the position and Euler angles of the plant because there is no onboard sensor. The nonlinear optimization is applied to identify the parameters in the nonlinear model. Based on the built model, the under-actuated control laws are designed with the hierarchical dynamic inversion (HDI). The designed under-actuated control laws are verified in simulation. The simulation results demonstrate that the resulting closed-loop system is capable of asymptotically tracking the references in which the yaw angle is free. The modeling and control analysis are useful to development of the flapping-wing MAVs.

An online rectangle based scheduling algorithm (RSA) is developed to improve autonomy of multiple unmanned aerial vehicles (UAVs) to search a field of forest together. The purposes of RSA are to online decide the number of the UAVs to be assigned and to schedule the path for the assigned UAVs to search the missed areas resulted from the previous search. The main ideas of RSA are to cover each separated zone of the missed areas with a rectangle and then to schedule the path to search the rectangles. Thus, RSA is robust against the unknown shapes and sizes of the missed areas. The forest search is applied to verify the online RSA in simulation. The simulation results demonstrate that the online RSA is successful to decide the number of the UAVs to be assigned and to schedule the path for the assigned UAVs to search the missed areas.

The C matrix in Sliding Mode Control (SMC) is significant to the control performance in MacPherson active suspension system. The SMC was combined with Composite Nonlinear Feedback (CNF) controller due to its characteristics on the transient response and fast settling time. The Neural Network is used to determine the matrix of C based on the road profiles used in this research work. The Proportional Integral (PI) was combined with SMC to overcome the uncertainties, unmatched condition and steady state error occurred in the MacPherson active suspension system. The three road profiles have been applied to this research work. The multi-body dynamics system software called CarSim is used for validation. The numerical experiment results are shown the effect of the C matrix in SMC with CNF controller performance in acceleration of sprung mass.

Yaw stability control system plays a significant role in vehicle lateral dynamics in order to improve the vehicle handling and stability performances. However, not many researches have been focused on the transient performances improvement of vehicle yaw rate and sideslip tracking control. This paper reviews the vital elements for control system design of an active yaw stability control system; the vehicle dynamic models, control objectives, active chassis control, and control strategies with the focus on identifying suitable criteria for improved transient performances. Each element is discussed and compared in terms of their underlying theory, strengths, weaknesses, and applicability. Based on this, we conclude that the sliding mode control with nonlinear sliding surface based on composite nonlinear feedback is a potential control strategy for improving the transient performances of yaw rate and sideslip tracking control.

This paper studies decentralised formation control of multiple vehicles in the plane when each vehicle can only measure the local bearings of their neighbours by using bearing-only sensors. Since the inter-vehicle distance cannot be measured, the target formation involves no distance constraints. More specifically, the target formation considered in this paper is an angle-constrained cyclic formation, where each vehicle has exactly two neighbours and the angle at each vehicle subtended by its two neighbours is pre-specified. To stabilise the target formation, we propose a discontinuous control law that only requires the sign information of the angle errors. Due to the discontinuity of the proposed control law, the stability of the closed-loop system is analysed by employing a locally Lipschitz Lyapunov function and nonsmooth analysis tools. We prove that the target formation is locally finite-time stable with collision avoidance guaranteed.

This paper presents a mode switching control (MSC) scheme in discrete-time domain for fast and precise set-point tracking in servo systems subject to control saturation and unknown disturbance. The basic idea is to combine the proximate time-optimal servomechanism (PTOS) and the composite nonlinear feedback (CNF) control, using the output position as the only measurable information for feedback. The PTOS is responsible for fast targeting in servo systems when the tracking error is large, and once the system trajectory enters into some specified region, the CNF will take over the control to ensure a smooth settling without compromising the fast transient performance. A reduced-order extended state observer is adopted to estimate the speed signal for feedback and the disturbance for compensation. The asymptotical stability of the proposed MSC scheme is analyzed and the switching conditions are provided. Simulation and experimental results on a permanent magnet synchronous motor (PMSM) servo system verify that the proposed control scheme is effective in improving the tracking performance for a wide range of target set-points.

In this paper, we present a comprehensive design for a fully functional unmanned rotorcraft system: GremLion. GremLion is a new small-scale unmanned aerial vehicle (UAV) concept using two contra-rotating rotors and one cyclic swash-plate. It can fit within a rucksack and be easily carried by a single person. GremLion is developed with all necessary avionics and a ground control station. It has been employed to participate in the 2012 UAVForge competition. The proposed design of GremLion consists of hardware construction, software development, dynamics modeling and flight control design, as well as mission algorithm investigation. A novel computer-aided technique is presented to optimize the hardware construction of GremLion to realize robust and efficient flight behavior. Based on the above hardware platform, a real-time flight control software and a ground control station (GCS) software have been developed to achieve the onboard processing capability and the ground monitoring capability respectively. A GremLion mathematical model has been derived for hover and near hover flight conditions and identified from experimental data collected in flight tests. We have combined H∞ technique, a robust and perfect tracking (RPT) approach, and custom-defined flight scheduling to design a comprehensive nonlinear flight control law for GremLion and successfully realized the automatic control which includes take-off, hovering, and a variety of essential flight motions. In addition, advanced mission algorithms have been presented in the paper, including obstacle detection and avoidance, as well as target following. Both ground and flight experiments of the complete system have been conducted including autonomous hovering, waypoint flight, etc. The test results have been presented in this paper to verify the proposed design methodology.

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 and nonlinear systems with actuator and other nonlinearities as well as with external disturbances. The parameters of the controller can be tuned easily on the user panel or autotuned by the toolkit. 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 practical examples on a rotational/translational actuator (RTAC) system and a hard disk drive servo system. The toolkit can be utilized to design servo systems that deal with point-and-shoot fast targeting.

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.

In this paper, we present the design and implementation of an autonomous flight control law for a small-scale unmanned aerial vehicle (UAV) helicopter. The approach is decentralized in nature by incorporating a newly developed nonlinear control technique, namely the composite nonlinear feedback control, together with dynamic inversion. The overall control law consists of three hierarchical layers, namely, the kernel control, command generator and flight scheduling, and is implemented and verified in flight tests on the actual UAV helicopter. The flight test results demonstrate that the UAV helicopter is capable of carrying out complicated flight missions autonomously.

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.

We report in this paper the development of a real-time software system for an unmanned aerial vehicle (UAV) helicopter, which consists of an embedded computer onboard and a ground station served by a laptop. The software system for the onboard computer performs multiple tasks including data acquisition and measurement, servo driving, automatic flight control implementation, communications and data logging. The system for the ground station gives a flexible graphical interface monitoring the real-time status of the UAV helicopter. We present the frameworks and structures of the onboard and ground station systems. The onboard system employs a framework of multiple task threads with each thread being assigned to perform a specific task. Management and time scheduling for task threads together with the detailed implementation of automatic flight control laws are the main focuses of the onboard software system. A behavior-based architecture is designed to address task scheduling and event disposal for automatic control. A hierarchical and componential structure is developed to integrate multiple control laws and perform various helicopter behaviors. The ground station software system employs a two-layer framework, i.e., data transferring in background and data visualization in foreground.A variety of views are developed to display in-flight data received from the UAV helicopter in different forms including a 3D monitoring panel, which displays real-time data in 3D on the ground station.

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

The authors 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 proven 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 practical situations, the conventional CNF control yields some steady-state errors in the resulting output response. The enhanced CNF technique presented is an extension of the conventional one. It retains the good transient properties of the conventional CNF control and at the same time has the additional capacity for eliminating steady-state bias because of unknown constant disturbances. A numerical example and practical disk drive servo system design are provided to demonstrate the effectiveness of this control technique. Experimental results show that the new design yields a huge improvement over classical approaches.

SUMMARY This chapter presents the mechatronics design of unmanned aircraft systems to deliver autonomous capabilities in various missions. The modular design approach and computer-aided hardware integration have been addressed to achieve cost-effective development of the hardware system. The multitask embedded software design has been presented in the software system development to tackle complex missions. The proposed design approaches are feasible and effective, which have been verified in two case studies including a coaxial rotorcraft GremLion developed for the DARPA UAVForge challenge and a cargo transportation system used in UAVGP 2013. Such design approaches can also be extended to different unmanned systems for autonomous missions.

This paper present the Composite Nonlinear Feedback Control and Proportional Integral Sliding Mode Control (CNF-PISMC). The advantages of Composite Nonlinear Feedback Control are reducing overshoot; improve transient performance and fast response. The advantages of PISMC are to overcome uncertainties and steady state error in the system. The used of a boundary layer solution in the control law of CNF-PISMC is to reduce the chattering problem. The result of the boundary layer thickness is representing the ability of the CNF-PISMC controller in MacPherson strut active suspension system. The value of boundary thickness is tuned by using Evolutionary Strategy (ES) to provide the two values of boundary layer thickness. The multi-body dynamics system software so called CarSim is used for validation purposes.

Pivot bearing friction and flex cable nonlinearity are the two major torque nonlinearities which lead to performance degradation in hard disk drive (HDD) tracking tasks. Based on a comprehensive model of typical voice-coil-motor (VCM) actuator, which explicitly captures the characteristics of pivot bearing friction and flex cable nonlinearity, this paper presents the design of a parameterized controller for a microdrive using the robust and perfect tracking (RPT) technique combined with nonlinear torque compensation and integral enhancement. Simulation and experimental results show that the controller is capable of achieving fast settling and eliminating static bias.

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.

We consider in this paper the design and implementation of a dual-stage actuated hard disk drive (HDD) servo system, in which an additional piezoelectric actuator is mounted on top of the conventional voice-coil-motor (VCM) actuator to provide a faster and finer response. More specifically, the dual-stage actuated HDD servo system consists of a primary VCM actuator and a secondary suspension piezoelectric microactuator. The VCM actuator is used to quickly move the read/write (R/W) head of the HDD servo system to a target track, whereas the microactuator is used to fine-tune the R/W head position when it is getting closer to the target. In our design, the primary actuator is controlled by a newly developed composite nonlinear feedback (CNF) control law, which has fast rise time and small overshoot, and the microactuator is controlled through a simple static gain together with a low-pass filter and a notch filter. Simulation and implementation results show that in track following, the dual-stage actuated HDD servo system has outperformed the single-stage actuated counterpart by more than 47% in settling time and by 39% in position error signal (PES) tests.

We study in this paper the theory and applications of a nonlinear control technique, i.e., the so-called composite nonlinear feedback control, for a class of linear systems with actuator nonlinearities. It consists of a linear feedback law and a nonlinear feedback law without any switching element. The linear feedback part is designed to yield a closed-loop system with a small damping ratio for a quick response, while at the same time not exceeding the actuator limits for the desired command input levels. The nonlinear feedback law is used to increase the damping ratio of the closed-loop system as the system output approaches the target reference to reduce the overshoot caused by the linear part. It is shown that the proposed technique is capable of beating the well-known time-optimal control in the asymptotic tracking situations. The application of such a new technique to an actual hard disk drive servo system shows that it outperforms the conventional method by more than 30%. The technique can be applied to design servo systems that deal with "point-and-shoot" fast targeting.

In a typical disk drive servo system, two or more types of controllers are used for track seeking, track following, and track settling modes. This leads to the problem of mode switching among these controllers. We present in this paper a unified control scheme, the discrete-time composite nonlinear feedback control, which can perform all the above functions in hard disk drive (HDD) servo systems with actuator saturation. The proposed scheme is composed by combining a linear feedback law and a nonlinear feedback law. The linear feedback law is designed to yield a fast response, while the nonlinear feedback law is used to increase the damping ratio of the closed-loop system as the system output approaches the command input. In the face of actuator saturation, this control law not only increases the speed of closed-loop response, but also improves the settling performance. Implementation results show that the proposed method outperforms the conventional proximate time-optimal servomechanism by about 30% in settling time.

Dual-stage actuator design for hard disk drives via composite nonlinear feedback control is presented, which consists of a primary actuator, the voice coil motor and a secondary actuator, the suspension piezoelectric microactuator. The first is effective in both track seeking and following stages to produce fast rising time and low overshoot and the latter works in track following stage only to help the primary actuator. The implementations show that the dual-stage actuator does yield better performance compared to the single primary actuator.

The composite nonlinear feedback control technique is developed for a class of linear systems with actuator saturation, which consists of a linear and a nonlinear feedback parts without any switching element. The linear part is to yield a quick response in face of the actuator limits for the desired input levels. The nonlinear part is to reduce the overshoot caused by the linear part as the system output approaches the target. It is shown that the technique is capable of beating the time-optimal control in asymptotic tracking situations and can be applied to design servo systems that deal with “point-and-shoot” fast targeting. Copyright ©2002 IFA C

A hierarchical-distributed methodology (HDM) is presented to implement the autonomous mission execution for multiple unmanned aerial vehicles (UAVs). The main idea of HDM is to divide the event control law into the group and individual event control laws. The group event control law is focused on the mission events. The individual event control laws are focused on the task events and motion events. Such division is reasonable as it emphasizes the task management and dynamic control of the single UAV and simplifies the mission management of the multiple UAVs. The simulation results demonstrate that the closed-loop system designed with the ideas of HDM autonomously completes the designated mission of the formation flight.

In this paper, we present a vision-based relative sensing system for UAVs to realize leader-follower formation flight without inter-vehicle communication. A monocular camera is mounted on the follower to detected the leader and measure the relative distance by using the geometry information of the leader without artificial markers. The measured relative distance is utilized to estimate the velocity and acceleration of the leader under the quasi-steady states assumption. Experimental results show that the proposed sensing system is capable of achieving the vision-based leader-follower formation flight.

Normal 0 false false false EN-MY X-NONE X-NONE This paper describes the mathematical modeling and control of a nonlinear active suspension system for ride comfort and road handling performance by using multi-body dynamics software so-called CarSim. For ride quality and road handling tests the integration between MATLAB/Simulink and multi-body dynamics system software is proposed. The control algorithm called the Conventional Composite Nonlinear Feedback (CCNF) control was introduced to achieve the best transient response that can reduce to overshoot on the sprung mass and angular of control arm of MacPherson active suspension system. The numerical experimental results show the control performance of CCNF comparing with Linear Quadratic Regulator (LQR) and passive system.

A ride quality test for active suspension system is real significant in modern automotive suspension control performance validation for ride comfort evaluation. The Composite Nonlinear Feedback (CNF) controller is proposed as a control strategy to reduce the high overshoot on the transient response and fast settling time. The mathematical modeling of a MacPherson quarter car suspension is utilized in this paper. A chassis twists road procedure in ride quality test has been applied. The multi-body dynamics system software so-called CarSim is used for validation. The strength of the proposed control scheme is shown by numerical experiment results and numerical simulation results.

The last decade has witnessed the rapid development of aeronautical engineering including all branches of applied sciences and technology dealing with aircraft and their support systems, which brings forward the higher request of safety, efficiency, and environmental protection. Modeling, control, and optimization of aeronautical engineering have played an increasingly important role in meeting aeronautical requirements, and they have drawn widespread attention from communities including control theory, intelligent optimization, system science, real-time distributed computing, electronic information engineering, and aeronautical engineering industry. Driven by such motivations, the main focus of this special issue is on the new theories, new technologies, and their applications in modeling, control, and optimization for aeronautical engineering systems. The special issue is a collection of original research articles, whose authors and editors belong to academic or research institutions of five different countries from Asia, Europe, and Australia. The full papers in this issue can be broadly organized into two main categories: (i) modelling and optimization and (ii) control techniques. Papers in category (i) are mainly concerned with network optimization of air transportation system and terminal-area operation. Recently, people come to realize that the air transportation system can be modeled as complex networks. Along this line, K. Cai et al. in “A Novel Biobjective Risk-Based Model for Stochastic Air Traffic Network Flow Optimization Problem” and X. Guan et al. in “An Airway Network Flow Assignment Approach Based on an Efficient Multiobjective Optimization Framework” modeled the flight operation as network flow optimization problem and proposed novel algorithms, respectively. Terminal-area operation is the bottleneck of the air transportation system. Y. Yang et al. investigated the aircraft intent inference approach and proposed an online trajectory clustering method, which will be meaningful to the efficiency and safety of busy terminal area. Papers in category (ii) are focusing on the topics of rotary-wing aircrafts and robots. The rotary-wing aircraft is one of the popular platforms in the control community such as the helicopter and quadrotor. T. Oktay and F. Sal in “Helicopter Control Energy Reduction Using Moving Horizontal Tail” attempted to improve the flight duration by reducing consumption of the energy. X. Xu et al. in “MRAC Control with Prior Model Knowledge for Asymmetric Damaged Aircraft” intended to explore control of the wing-damaged aircraft, which is one of advanced topics to improve survivability of the fighters. Z. Li and Y. Wang in “Coordinated Control of Slip Ratio for Wheeled Mobile Robots Climbing Loose Sloped Terrain” attempted to explore the control of mobile robots in 3D environments. J. Lopez et al. in “A Robust H∞ Controller for an UAV Flight Control System” implemented and validated a robust H∞ controller for an UAV to track different types of manoeuvres in the presence of noisy environment. It should be mentioned that a special issue simply provides a snapshot of the field taken at a particular point in time. Due to the standard page limitations of a journal volume, it can only include a relatively small number of papers. As a result, its coverage is by no means complete despite our best efforts.

In this paper, we present an unmanned system design methodology for a fully functional unmanned rotorcraft system: GremLion, developed with all necessary avionics and a ground control station. It has been employed to participate in the 2012 UAVForge competition. The proposed design methodology consists of hardware construction, software development, dynamic modeling and flight control, as well as mission algorithms. The test results have been presented in this paper to verify the proposed design methodology.

A variant factor (VF) technique is developed for the control design of a class of single-input and single-output affine nonlinear systems with input saturation. The main ideas of VF are to convert an affine nonlinear system into a linear time-invariant system similar to the dynamic inversion and then to use the ideas of the composite nonlinear feedback (CNF) technique to design a control law for the converted linear system with the input saturation. A VF is introduced to guarantee the resulting closed-loop system asymptotically stable in presence of the input saturation. The VF control laws retain the similar properties of the CNF control laws. With the VF control law, the system output can asymptotically track the step reference and the resulting closed-loop system can achieve better tracking performance than that with the control law designed with the dynamic inversion.

This paper studies decentralized formation control of multiple vehicles when each vehicle can only measure the local bearings of their neighbors by using bearing-only sensors. Since the inter-vehicle distance cannot be measured, the target formation involves no distance constraints. More specifically, the target formation considered in this paper is an angle-constrained circular formation, where each vehicle has exactly two neighbors and the angle at each vehicle subtended by its two neighbors is pre-specified. To stabilize the target formation, we propose a discontinuous control law that only requires the sign information of the angle errors. Due to the discontinuity of the proposed control law, the stability of the closed-loop system is analyzed by employing a locally Lipschitz Lyapunov function and nonsmooth analysis tools. We prove that the target formation is locally finite-time stable with collision avoidance guaranteed. The evolution of the vehicle positions in the plane is also characterized., Comment: 21 pages, 5 figures

The composite nonlinear feedback (CNF) control technique is successfully applied to design the controller based on control law for an active suspension system. The CNF control law is composed of a linear control law and a nonlinear feedback part. The main idea of CNF is to design the linear control law with a low damping-ratio to achieve fast rising time and to design the nonlinear feedback part to result in a high damping-ratio to remove the overshoot caused by the linear control law when the system controlled output approached the reference. Such the CNF control laws can improve the tracking and regulating performances of the resulting closed-loop systems. The active suspension system is hierarchically divided into two subsystems with the system transformation based on the system structural properties at first and then the CNF control laws are designed for the two subsystems each One of the CNF control laws is designed for tracking control and the other is designed against the mismatching disturbance. The complete control law is made by combining the two CNF control laws and the system transformation. The simulation results show that CNF controller is better than LQR controller and passive model. The computer simulation is done to prove the CNF control performance.

The purposes or functions of the commercial car suspension system are to take care on the car body weight, to isolate the car body from road profiles disturbance and to maintain the grip force between the wheel and road profiles. The Composite Nonlinear Feedback (CNF) control law is proposed in this comparative study between conventional linear model and Macpherson model. The control performance consists of velocity of car body, suspension deflection, wheel deflection and velocity of a car wheel. The main measurement in this study is the acceleration of the car body. The Linear Quadratic Regulator (LQR) and passive model are involved in this control performance is for comparison purposes. The mathematical model of linear model and MacPherson model are focused on the quarter car model active suspension system. The simulation work is done by using MATLAB and SIMULINK to see the control performance on the quarter car active suspension model. In this paper we can conclude that the CNF achieved the main objective of active suspension which is the ride comfort and road handling.

This paper investigates the navigation of small-scale unmanned aerial vehicles (UAVs) in unknown and GPS-denied environments. We consider a UAV equipped with a low-cost inertial measurement unit (IMU) and a monocular camera. The IMU can measure the specic acceleration and angular rate of the UAV. The IMU measurements are assumed to be corrupted by white noises and unknown constant biases. Hence the position, velocity and attitude of the UAV estimated by pure IMU dead reckoning will all drift over time. The monocular camera takes image sequences of the ground scene during ight. By assuming the ground scene is a level plane, the vision measurement, homography matrices, can be obtained from pairs of consecutive images. We propose a novel approach to fuse IMU and vision measurements by using an extended Kalman lter (EKF). Unlike conventional approaches, homography matrices are not required to be decomposed. Instead, they are converted to vectors and fed into the EKF directly. In the end, we analyze the observability of the proposed navigation system. We show that the velocity and attitude of the UAV and the unknown biases in IMU measurements are all observable when noisy yaw angle can be measured using a magnetometer. Numerical simulations verify our observability analysis and show that all UAV states except the position can be estimated without drift. The position drift is signicantly reduced compared to the IMU dead reckoning.

A data fusion method is extensively investigated to stabilize the motion of aircraft with the visual and inertial measurements in the unknown environment without the signal of the global positioning system and with the unknown inertial measurement biases. There is no information on the landmarks on the ground. What can be used are the sequence of collected images. The main idea of the method is to apply the correspondence between the two successive images based on a new formulation of the extended Kalman filtering to fuse the visual and inertial measurements to predict the necessary feedback information and the unknown inertial measurement biases. Neither computation nor decomposition of any essential matrix is needed. The observability of the new formulation of the extended Kalman filtering and the robustness against the measurement errors of the resulting closed-loop system are analyzed in simulation. The simulation results demonstrate that the attitude angles are observable, however they have no robustness against the visual measurement errors. The motion of aircraft can be stabilized with the 3D visual and inertial measurements as well as the measurable Euler angles in presence of the measurement errors.

This paper proposes LMI-based design procedures for two classes of unknown input observers (UIOs) for the purpose of fault detection and isolation (FDI). The design procedures for the first class of UIOs can not only relax the restrictions on the rank of output and noise, but also take into account both robustness and sensitivity to UIOs. Several tuning techniques are also provided. For the second class of UIOs, an alternative structure is recommended to reduce the design complexity in multiple-fault cases. We analyze the advantages and weaknesses of the proposed approaches, and utilize a linearized model of fixed-wing unmanned aerial vehicle (UAV) with disturbance as the design platform to illustrate their performance.

A variant factor (VF) technique is developed for the control design of a class of single-input and single-output affine nonlinear systems with input saturation. The main ideas of VF are to convert an affine nonlinear system into a linear time-invariant system similar to the dynamic inversion and then to use the ideas of the composite nonlinear feedback (CNF) technique to design a control law for the converted linear system with the input saturation. A VF is introduced to guarantee the resulting closed-loop system asymptotically stable in presence of the input saturation. The VF control laws retain the similar properties of the CNF control laws. With the VF control law, the system output can asymptotically track the step reference and the resulting closed-loop system can achieve better tracking performance than that with the control law designed with the dynamic inversion.

An autonomous flight control (AFC) law is designed for a small-scale unmanned helicopter with the hierarchical dynamic inversion (HDI). HDI is based on the hierarchical structural properties of a nonlinear system to partition the nonlinear system into a number of subsystems so that the dynamic inversion based methods are easily applicable to control design of these subsystems. The recursive control (RC) technique is applied in the AFC design because the attitude subsystem is non-affine nonlinear in the control variables. RC is one of the dynamic inversion based methods and is applicable to control design of a class of non-affine nonlinear systems so that there is no iterative numerical computation needed. There is no gain scheduling based technique needed in the AFC design with HDI. The designed AFC laws for the small-scale unmanned helicopter are verified in simulation on the basic 6-DOF nonlinear model of the helicopter. The simulation results demonstrate that the resulting closed-loop system from the AFC law designed with HDI can achieve better flight performances than the closed-loop system resulting from that designed with the linear quadratic regulator in a wide range of flight conditions. The simulation results also show that the closed-loop system resulting from the AFC law designed with HDI is capable of carrying out autonomous flight.

Hierarchical dynamic inversion (HDI) is proposed together with newly developed variant-factor and recursive control techniques to design autonomous flight control (AFC) laws for fixed-wing aircraft. HDI is applicable to control design of some non-affine nonlinear systems to which dynamic inversion is not applicable. The AFC law designed with HDI at the nominal flight condition is applicable to other flight conditions in a wide flight envelope so that workload can be reduced significantly in AFC design compared to gain scheduling. The simulation results demonstrate that with the AFC law designed with HDI, the aircraft successfully completes the pre-scheduled maneuvering flight in a subsonic flight envelope.

In this paper, we present an enhancement scheme for global positioning system (GPS) signals received on an unmanned aerial-vehicle (UAV) helicopter system. Because of the limitation of the hardware units and the GPS system, parts of the signals are discontinuous and have huge jumps from time to time. Such a problem degrades a great deal the overall performance of the automatic flight control system of our UAV helicopter. We employ in this work an Kalman filter technique together with a complementary filter to regenerate smooth and accurate signals that can be used for the implementation of automatic flight control systems. Our simulation and implementation results show that the proposed scheme is very effective and yields a good improvement on the performance of the overall flight control system of our UAV helicopter.

We present in this paper a flight control system design for the yaw channel of a UAV helicopter using a newly developed composite nonlinear feedback (CNF) control technique. 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 literatures is very rough and inaccurate. This motivates us to first obtain a comprehensive 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.

We present in this paper a linearized hovering model of a UAV helicopter obtained using the in-flight data generated through a perturbation method. The UAV helicopter is constructed from a radio-controlled helicopter by integrating an onboard system, which includes a data processing unit, a data acquisition system, a wireless communications and all necessary sensors. A flight control law is then designed using a newly developed nonlinear control technique, i.e. the composite nonlinear feedback control. Actual flight testing shows that the design is successful.

The modeling of yaw dynamics of a UAV helicopter is focused on together with its control system design. From the flight tests on our actual UAV helicopter, it has been found that the yaw dynamical model for the UAV helicopter proposed in the literatures is very rough and inaccurate, which might cause the helicopter to shake severely in certain flight conditions. A complete examination is carried out to identify a perfect model of the yaw channel in the UAV helicopter. It would be found that the assumption in the old model is not appropriate. Some advanced control schemes will then be adopted to solve the shaking problem observed in the yaw channel.

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.

This paper presents a discrete-time robust non-linear control method to achieve fast and accurate set-point tracking for servo systems subject to actuator saturation and disturbances. The idea here is to use a combination of composite nonlinear feedback (CNF) control and disturbance estimation cum compensation. The CNF control is responsible for superior transient performance, i.e. to guarantee a fast response with low overshoot, while the disturbance estimator/compensator is used to remove the steady state bias that would otherwise be existent due to disturbances. Practical application in a micro hard disk drive servo system will be given to demonstrate the effectiveness of this control method.

A generalized composite nonlinear feedback (CNF) control technique will be presented to track non-step references. A reference generator will be adopted to supplement the CNF control technique so as to track the non-step references. The reference generator can be designed to produce a desired reference. The generalized CNF control law comprises the reference generator and a modified enhanced CNF control law. The proposed method will be applied to design control laws for an XY-table. Simulation and implementation results will verify that the generalized CNF control law is indeed capable of tracking the non-step references.

This paper deals with compensation of torque disturbances in a hard disk drive (HDD) to improve its head positioning performance. The torque disturbances from the data flex cable and friction in the actuator rotary pivot bearing yield a significant bias and large residual error, which deteriorate performance of the overall system. Reducing effect of these torque disturbances has been one of challenges in designing head positioning servo systems. In this paper, a comprehension physical model of the voice coil motor (VCM) will be derived through analysis of physical effects and the parameters will be determined with the Monte Carlo method to match those responses measured in the perturbation method. A modified integral is added into a linear control law to reduce the disturbances and improve performance of head positioning servo systems. The simulation and experimental results show significant improvement on performance of the head positioning servo systems.

This paper is to analyze effect of the data flex cable and friction in the actuator rotary pivot bearing on performance of head positioning servo systems in micro hard disk drives (HDD). The micro HDD is one of trends in the disk drive industry, which can be used by portable devices such as digital cameras. A nonlinear model of the micro HDD will be established, where its configuration of nonlinearities will be identified with analysis of physical effects and its parameters will be determined with the Monte Carlo method. A control law will be designed to analyze effect of these torque disturbances on performance of head positioning servo systems through simulations and experiments.

The strictly decreasing relationship between the sample approximation error and the number of hidden units in a three layer artificial feedforward neural network (AFNN) is proven in the sample space. The relationship is a powerful tool in determining the number of hidden units needed. A hybrid optimization algorithm is proposed on the relationship for simultaneously determining the number of hidden units and weight coefficients in the AFNN. The algorithm is the synthesis of golden section, evolutionary programming and gradient based algorithm which is effective in determining the number of hidden units and weight coefficients in the neural network.