Kemao Peng

Modeling and Control of the Yaw Channel of a UAV Helicopter

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.

Brief paper: Design and implementation of an autonomous flight control law for a UAV helicopter

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.

Modeling and compensation of nonlinearities and friction in a micro hard disk drive servo system with nonlinear feedback control

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.

Discrete-time composite nonlinear feedback control with an application in design of a hard disk drive servo system

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.

H-Infinity Static Output-feedback Control for Rotorcraft

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.

Improving Transient Performance in Tracking General References Using Composite Nonlinear Feedback Control and Its Application to High-Speed

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

XY

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

-Table Positioning Mechanism

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.

Modeling and Control System Design for a UAV Helicopter

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.

Development of a Real-time Onboard and Ground Station Software System for a UAV Helicopter

This paper studies distributed formation control of multiple agents in the plane using bearing-only measurements. It is assumed that each agent only measures the local bearings of their neighbor agents. The target formation considered in this paper is a circular formation, where each agent has exactly two neighbors. In the target formation, the angle subtended at each agent by their two neighbors is specified. We propose a distributed control law that stabilizes angle-constrained target formations merely using local bearing measurements. The stability of the target formation is analyzed based on Lyapunov approaches. We present a unified proof to show that the proposed control law can ensure local exponential or finite-time stability. The exponential or finite-time stability can be easily switched by tuning a parameter in the control law.