Development of a Rotorcraft Micro air Vehicle for Indoor Flight Research

Autonomous flight of micro air vehicles (MAVs) in hostile indoor environments poses significant challenges in terms of control and navigation. In order to support navigation and control research for indoor micro air vehicles, a four-wing tail-sitter type rotorcraft MAV weighing less than 350g has been designed in this paper. In an effort to achieve autonomous indoor flight, an embedded integrated avionic system has been developed. The modeling process has been conducted to obtain accurate six degrees of freedom dynamical model for the designed rotorcraft MAV. In addition, aerodynamic coefficients are evaluated from the results of Computational Fluid Dynamics A PI-ADRC double loop controller with inner-loop outer-loop control scheme has been proposed which takes into account the system’s nonlinearities and uncertainties. The proposed flight controller was implemented on the designed rotorcraft MAV that has undergone various simulation and indoor flight tests. Experimental results that demonstrate robustness of the proposed controller with respect to external disturbances and the capabilities of the designed rotorcraft MAV are presented.     

Indoor UAV Control Using Multi-Camera Visual Feedback

This paper presents the control of an indoor unmanned aerial vehicle (UAV) using multi-camera visual feedback. For the autonomous flight of the indoor UAV, instead of using onboard sensor information, visual feedback concept is employed by the development of an indoor flight test-bed. The indoor test-bed consists of four major components: the multi-camera system, ground computer, onboard color marker set, and quad-rotor UAV. Since the onboard markers are attached to the pre-defined location, position and attitude of the UAV can be estimated by marker detection algorithm and triangulation method. Additionally, this study introduces a filter algorithm to obtain the full 6-degree of freedom (DOF) pose estimation including velocities and angular rates. The filter algorithm also enhances the performance of the vision system by making up for the weakness of low cost cameras such as poor resolution and large noise. Moreover, for the pose estimation of multiple vehicles, data association algorithm using the geometric relation between cameras is proposed in this paper. The control system is designed based on the classical proportional-integral-derivative (PID) control, which uses the position, velocity and attitude from the vision system and the angular rate from the rate gyro sensor. This paper concludes with both ground and flight test results illustrating the performance and properties of the proposed indoor flight test-bed and the control system using the multi-camera visual feedback.     

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.     

Tracking in scale quad-rotors through adaptive augmentation

This paper illustrates the application of an adaptive flight control architecture to a scale quad-rotor. For autonomous vertical takeoff and landing flight, it is common to separate the control problem into an inner fast loop that controls attitude and an outer slow loop that controls the trajectory tracking. In this paper, we augment a conventional proportional and derivative controller conceived mainly for hovering, with an adaptive element using a real-time tuning single hidden layer neural network in a inner–outer loop combined architecture to account for model inversion error cancelation, issued in the feedback linearization process. The results shown in simulations reveal the superior performance of the augmented controller in tracking maneuvers.     

GPS‐denied Indoor and Outdoor Monocular Vision Aided Navigation and Control of Unmanned Aircraft

GPS‐denied closed‐loop autonomous control of unstable Unmanned Aerial Vehicles (UAVs) such as rotorcraft using information from a monocular camera has been an open problem. Most proposed Vision aided Inertial Navigation Systems (V‐INSs) have been too computationally intensive or do not have sufficient integrity for closed‐loop flight. We provide an affirmative answer to the question of whether V‐INSs can be used to sustain prolonged real‐world GPS‐denied flight by presenting a V‐INS that is validated through autonomous flight‐tests over prolonged closed‐loop dynamic operation in both indoor and outdoor GPS‐denied environments with two rotorcraft unmanned aircraft systems (UASs). The architecture efficiently combines visual feature information from a monocular camera with measurements from inertial sensors. Inertial measurements are used to predict frame‐to‐frame transition of online selected feature locations, and the difference between predicted and observed feature locations is used to bind in real‐time the inertial measurement unit drift, estimate its bias, and account for initial misalignment errors. A novel algorithm to manage a library of features online is presented that can add or remove features based on a measure of relative confidence in each feature location. The resulting V‐INS is sufficiently efficient and reliable to enable real‐time implementation on resource‐constrained aerial vehicles. The presented algorithms are validated on multiple platforms in real‐world conditions: through a 16‐min flight test, including an autonomous landing, of a 66 kg rotorcraft UAV operating in an unconctrolled outdoor environment without using GPS and through a Micro‐UAV operating in a cluttered, unmapped, and gusty indoor environment. © 2013 Wiley Periodicals, Inc.     

Design and Attitude Control of a Quad-Rotor Tail-Sitter Vertical Takeoff and Landing Unmanned Aerial Vehicle

In this paper, we present the development of a quad-rotor tail-sitter unmanned aerial vehicle (UAV) that is composed of quad rotors and a fixed wing. The developed UAV can hover like a quad-rotor helicopter and can fly long distance like a fixed-wing airplane. The main wing of the developed UAV is taken from a commercially available radio-controlled airplane and other parts such as the body frame are newly developed. A microcomputer, various sensors and a battery are mounted on the UAV for autonomous flight without any support from a ground system. Attitude and altitude control systems are developed for the UAV. In order to verify the designed controller, a three-dimensional flight simulator of a quad-rotor tail-sitter UAV is developed by use of MATLAB/Simulink. This paper also describes attitude control experiments. The results show that the propeller slipstream has a negative influence on attitude control. Solutions for the negative influence of the propeller slipstream are also discussed in this paper.     

Guidance and nonlinear control system for autonomous flight of minirotorcraft unmanned aerial vehicles

Small unmanned aerial vehicles (UAVs) are becoming popular among researchers and vital platforms for several autonomous mission systems. In this paper, we present the design and development of a miniature autonomous rotorcraft weighing less than 700 g and capable of waypoint navigation, trajectory tracking, visual navigation, precise hovering, and automatic takeoff and landing. In an effort to make advanced autonomous behaviors available to mini‐ and microrotorcraft, an embedded and inexpensive autopilot was developed. To compensate for the weaknesses of the low‐cost equipment, we put our efforts into designing a reliable model‐based nonlinear controller that uses an inner‐loop outer‐loop control scheme. The developed flight controller considers the system's nonlinearities, guarantees the stability of the closed‐loop system, and results in a practical controller that is easy to implement and to tune. In addition to controller design and stability analysis, the paper provides information about the overall control architecture and the UAV system integration, including guidance laws, navigation algorithms, control system implementation, and autopilot hardware. The guidance, navigation, and control (GN&C) algorithms were implemented on a miniature quadrotor UAV that has undergone an extensive program of flight tests, resulting in various flight behaviors under autonomous control from takeoff to landing. Experimental results that demonstrate the operation of the GN&C algorithms and the capabilities of our autonomous micro air vehicle are presented. © 2009 Wiley Periodicals, Inc.     

Stability of small-scale UAV helicopters and quadrotors with added payload mass under PID control

The application of rotorcraft to autonomous load carrying and transport is a new frontier for Unmanned Aerial Vehicles (UAVs). This task requires that hovering vehicles remain stable and balanced in flight as payload mass is added to the vehicle. If payload is not loaded centered or the vehicle properly trimmed for offset loads, the robot will experience bias forces that must be rejected. In this paper, we explore the effect of dynamic load disturbances introduced by instantaneously increased payload mass and how those affect helicopters and quadrotors under Proportional-Integral-Derivative flight control. We determine stability bounds within which the changing mass-inertia parameters of the system due to the acquired object will not destabilize these aircraft with this standard flight controller. Additionally, we demonstrate experimentally the stability behavior of a helicopter undergoing a range of instantaneous step payload changes.     

四旋翼微型飞行器控制系统设计

四旋翼微型飞行器是一种以4个电机作为动力装置,通过调节电机转速来控制飞行的欠驱动系统;为了实现四旋翼微型飞行器的自主飞行控制,对飞行控制系统进行了初步设计,并且以C8051F020单片机为计算控制单元,给出了飞行控制系统的硬件设计,研究了设计中的关键技术;由于采用贴片封装和低功耗的元器件,使飞行器具有重量轻、体积小、功耗低的优点;经过多次室内试验,该硬件设计性能可靠,能满足飞行器起飞、悬停、降落等飞行模态的控制要求。     

六轴旋翼碟形飞行器控制系统软件设计及仿真研究

采用了控制不同电机转速组合的方法,对六轴旋翼碟形飞行器进行姿态控制,使六轴旋翼碟形飞行器在不同姿态下飞行时具有较好的性能;为了实现六轴旋翼碟形飞行器的飞行控制,对飞行器的控制系统进行了初步的设计,并且给出了控制系统软件设计流程图;同时以ProtuesISIS软件为基础建立了六轴旋翼碟形飞行器控制系统的仿真模型,并进行了仿真,仿真结果显示该控制系统能够满足六轴旋翼碟形飞行器起飞、悬停及降落等控制姿态的要求。     

An acceleration measurements-based approach for helicopter nonlinear flight control using Incremental Nonlinear Dynamic Inversion

Due to the inherent instabilities and nonlinearities of rotorcraft dynamics, its changing properties during flight and the engineering difficulties to predict its aerodynamics with high levels of fidelity, helicopter flight control requires the application of special strategies. These strategies must allow to cope with the nonlinearities of the system and assure robustness in the presence of inaccuracies and changes in configuration.In this paper, a novel approach based on an Incremental Nonlinear Dynamic Inversion is applied to simplify the design of helicopter flight controllers. With this strategy, by employing the feedback of acceleration measurements to avoid the need for information relative to any aerodynamic change, the control system does not need any model data that depends exclusively on its states, thus enhancing its robustness to model uncertainties.The overall control system is tested by simulating two tasks with distinct agility levels as described in the ADS-33 helicopter handling qualities standard. The analysis shows that the controller provides an efficient tracking of the commanded references. Furthermore, with the robustness properties verified within the range of inaccuracies expected to be found in reality, this novel method seems to be eligible for a potential practical implementation to helicopter vehicles.     

四旋翼无人机控制系统仿真设计

四旋翼无人机是一种性能优越的垂直起降无人飞行器,能够实现悬停、低速飞行、垂直起降等功能,在军事和民用方面具有重要价值。针对四旋翼无人机的控制系统设计问题,首先分析介绍了四旋翼无人机飞行原理,对其建立动力学模型和运动学模型,然后进行了基于PID控制的控制系统设计,控制系统采用四通道、多闭环的控制结构,包括无人机的姿态控制与轨迹控制。在MATLAB中进行无人机控制系统仿真实现。仿真结果表明,本文所设计的控制系统,能够有效地实现四旋翼无人机的姿态控制、轨迹控制,具有良好的控制精度与响应速度。     

Adaptive Neural Network Control of Small Unmanned Aerial Rotorcraft

This paper proposes an online learning adaptive neural network for small unmanned aerial rotorcraft to improve control performance during flight. Based on state error information, the weight matrix of the adaptive neural network can be updated on line by using lyapunov function. Therefore, no prior training data is needed for the training of the adaptive neural network. Combined with feedback control, the adaptive neural network can construct the map between the state error information and disturbances to compensate for system disturbances. The effectiveness of the proposed method is validated by a series of simulations and flight tests. Compared with feedback control method, the adaptive neural network control method can estimate and eliminate disturbances quickly to yield a good tracking performance.     

飞行器控制面临的机遇与挑战

当前,飞行器控制的发展面临前所未有的机遇与挑战.基于对飞行器的发展趋势、新需求和新技术特征的分析,本文从飞行器新技术特征、信息化环境、无人系统自主性、高可靠可重构容错系统、飞控系统评估与确认五个方面研究和分析了飞行器控制面临的机遇与挑战.为了达到利用机遇和赢得挑战的目标,作者建议加强如下五个方面的研究: 加强面向飞行器新技术特征的飞行器控制概念、理论与方法研究; 加强面向信息化环境的控制、计算与通讯一体化,以及控制、决策与管理一体化的研究; 加强面向不确定性的无人系统高级别自主性的研究; 加强面向高可靠、高安全性的可重构容错飞控系统的研究; 加强面向高效、高可信度的飞控系统评估与确认方法的研究.     

基于TMS320F28335的小型无人旋翼机数据采集系统

大气数据的采集对于小型无人旋翼机飞行的控制具有关键性的作用,针对小型无人旋翼机的飞行控制需求,利用数字式MEMS传感器和TMS320F28335芯片设计了一种装载于小型无人旋翼机上双采集装置的大气数据采集系统.通过传感器采集数据,实时解算出控制无人旋翼机飞行所需要的空速等数值,同时采用线性插值等算法来提高计算性能.该系统体积小,功耗低,抗干扰能力强等优点,能够满足小型无人旋翼机的需求,为小型无人旋翼机数据采集系统在实际中的应用做了一定的理论工作.     

Autonomous Autorotation of Unmanned Rotorcraft using Nonlinear Model Predictive Control

Safe operations of unmanned rotorcraft hinge on successfully accommodating failures during flight, either via control reconfiguration or by terminating flight early in a controlled manner. This paper focuses on autorotation, a common maneuver used to bring helicopters safely to the ground even in the case of loss of power to the main rotor. A novel nonlinear model predictive controller augmented with a recurrent neural network is presented that is capable of performing an autonomous autorotation. Main advantages of the proposed approach are on-line, real-time trajectory optimization and reduced hardware requirements.     

四旋翼飞行器控制系统设计

四旋翼飞行器姿态控制是四旋翼飞行器控制系统的核心. 通过分析四旋翼飞行器的飞行原理,模型建立,设计了四旋翼飞行器的姿态控制系统;在该系统中采用STM32系列处理器作为主控芯片,MPU6050三轴加速度集和三轴陀螺仪惯性测量单元、磁力计等传感器用于姿态信息检测. 本文中传感器使用结构简单的数字接口对数据进行交换,运用模块化的思想对系统进行设计. 使用PID控制算法进行姿态角的闭环控制,最终实验结果表明,在实验平台上四旋翼飞行器飞行效果稳定,系统满足四旋翼飞行器飞行姿态控制的要求.     

Survey of advances in guidance,navigation, and control of unmanned rotorcraft systems

Recently, there has been growing interest in developing unmanned aircraft systems (UAS) with advanced onboard autonomous capabilities. This paper describes the current state of the art in autonomous rotorcraft UAS (RUAS) and provides a detailed literature review of the last two decades of active research on RUAS. Three functional technology areas are identified as the core components of an autonomous RUAS. Guidance, navigation, and control (GNC) have received much attention from the research community, and have dominated the UAS literature from the nineties until now. This paper first presents the main research groups involved in the development of GNC systems for RUAS. Then it describes the development of a framework that provides standard definitions and metrics characterizing and measuring the autonomy level of a RUAS using GNC aspects. This framework is intended to facilitate the understanding and the organization of this survey paper, but it can also serve as a common reference for the UAS community. The main objective of this paper is to present a comprehensive survey of RUAS research that captures all seminal works and milestones in each GNC area, with a particular focus on practical methods and technologies that have been demonstrated in flight tests. These algorithms and systems have been classified into different categories and classes based on the autonomy level they provide and the algorithmic approach used. Finally, the paper discusses the RUAS literature in general and highlights challenges that need to be addressed in developing autonomous systems for unmanned rotorcraft. © 2012 Wiley Periodicals, Inc.     

Robust crossfeed design for hovering rotorcraft

Control law design for rotorcraft fly-by-wire systems normally attempts to decouple the angular responses using fixed-gain crossfeeds. This approach can lead to poor decoupling over the frequency range of pilot inputs and increase the load on the feedback loops. In order to improve the decoupling performance, dynamic crossfeeds should be adopted. Moreover, because of the large changes that occur in the aircraft dynamics due to small changes about the nominal design condition, especially for near-hovering flight, the crossfeed design must be ‘robust’. A new low-order matching method is presented here to design robust crossfeed compensators for multi-input, multi-output (MIMO) systems. The technique minimizes cross-coupling given an anticipated set of parameter variations for the range of flight conditions of concern. Results are presented in this paper of an analysis of the pitch/roll coupling of the UH-60 Black Hawk helicopter in near-hovering flight. A robust crossfeed is designed that shows significant improvement in decoupling perfomance and robustness over the fixed-gain or single point dynamic compensators. The design method and results are presented in an easily used graphical format that lends significant physical insight to the design procedure. This plant precompensation technique is an appropriate preliminary step to the design of robust feedback control laws for rotorcraft.     

Tracking control of trim trajectories of a blimp for ascent and descent flight manoeuvres

A blimp is a small airship that has no metal framework and collapses when deflated. It belongs to family of unmanned aerial vehicles (UAVs). In this paper we address the problem of designing tracking feedback control of an underactuated autonomous UAV. The ascent and descent flight conditions as one in which the rate of change (of magnitude) of the airship's state vector is zero and the resultant of the applied forces and moments is constant lead to trimmed flight trajectories. The subject of the tracking control is to stabilize the engine around the planned flight. Using a combined integrator backstepping approach and Lyapunov theory, the stability results are local and overcome the minimum number of actuators (inputs) with respect to the blimp's six degrees of freedom. Considering physic limits in UAVs, other trimmed flights are investigated and compared.