꼬리날개 없는 날갯짓 초소형 비행체의 자세조절

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 김현진.최근 생체모방에 대한 관심이 커지면서 생명체의 구조, 외형, 움직임, 행동을 분석하여 그들의 장점을 로봇에 적용시켜 기존의 로봇이 해결할 수 없거나 특별한 임무를 좀 더 효과, 효율적으로 해결하려는 시도가 늘어나고 있다. 이러한 시도는 무인비행체 개발에도 적용되고 있으며 날갯짓 비행체가 이에 해당된다. 날개짓 비행체는 날개의 반복운동을 통해 발생하는 힘을 통해 비행하는 비행체로 일반적으로 꼬리날개의 유무에 따라 새를 모방한 비행체(미익형 비행체)와 곤충을 모방한 비행체(무미익형 비행체)로 구분할 수 있다. 무미익형 비행체의 경우 제자리 비행을 할 수 있고, 크기가 작고 무게가 가벼워 공기저항도 줄일 수 있으며, 날렵한 비행이 가능하다는 장점이 있지만, 수동 안정성을 확보하기 위한 제어면이 충분하지 않고 추력 생성과 동시에 3축으로의 제어 모멘트를 만들 수 있는 복잡한 매커니즘을 가지고 있다는 특징을 가지고 있다. 본 논문에서는 저자의 미익형 비행체의 연구개발 사례를 토대로 자율 비행을 할 수 있는 무미익형 비행체를 개발하기 위한 요소기술들과 초기 비행체 개발을 목표로 한다. 해당 목표를 달성하기 위해 저자는 시중에서 판매되고 있는 RC장난감을 활용해 30 gram 이하의 무게를 가지고 30cm3 이내의 크기를 가지는 무미익형 날갯짓 비행체를 개발을 진행하였다. 비행체 내부에는 구동기로 DC 모터와 서보모터가 존재하며, DC 모터는 날갯짓을 일으키는 기어 박스를 작동시켜 비행체의 무게를 지탱하기 위한 thrust를 생성하며 roll축 방향으로의 moment 생성에 관여하며, 서보모터는 날갯짓에서 발생하는 좌우 thrust의 방향을 조절하여 pitch 와 yaw 축으로의 모멘트를 생성하는데 사용된다. 비행체 내부에는 아두이노 보드 기반의 마이크로프로세서가 탑재되어 있어 비행체를 제어하기 위한 신호를 생성할 수 있으며 블루투스 통신 모듈을 가지고 있기 때문에 외부와 통신 역시 가능하다. 비행체의 자세를 제어하기 위해서는 구동기의 상호작용으로 인해 발생하는 힘의 물리량을 파악하는 것이 중요하다. 이를 위해 날갯짓 메커니즘에서 발생하는 힘을 측정하는 실험을 수행하였다. 측정실험을 통해 DC모터 입력 대비 thrust 크기, 서보모터 command 입력 대비 moment 크기 등의 관계를 파악하였다. 또한 날갯짓 비행체를 공중에 띄울 수 있는 충분한 크기의 thrust를 발생하는 것을 확인하였으며 자세 제어를 위한 모멘트 생성 역시 가능하다는 것을 확인하였다. 비행체의 자세를 제어하기 위해서는 3축 방향으로의 운동방정식을 유도하는 것이 필요하다. 이를 위해 roll, pitch, yaw 축 방향으로 비행체에서 발생하는 힘과 회전 운동과 관련한 운동방정식을 유도했으며 이를 통해 비행체의 자세를 안정화시킬 수 있도록 하는 PID 제어기 형태의 제어기를 설계하였다. 뿐만 아니라, 비행체의 궤적추종 제어를 위해 내부의 자세 제어기에 비행체의 위치를 토대로 계산되는 추가적인 외부 제어기를 설계하여 이중루프 제어기 형태를 적용시켜 시뮬레이션을 통해 비행체의 자세 제어와 궤적 추종 제어가 이루어짐을 확인하였다. 개발한 비행체와 앞서 설계한 제어기가 사용자의 의도에 맞는 성능을 내는지 확인하기 위해 자이로 실험장치를 제작하여 자세 제어 실험을 수행하였다. 해당 실험장치는 roll, pitch, yaw 축으로 회전이 가능하도록 제작하였으며 실험장치 자체의 무게를 줄이기 위해 MDF 소재를 사용하여 구조물를 만들었다. roll, pitch, yaw 3축이 각각 독립적으로 제어하는 것과 3축을 동시에 제어하는 2가지 상황을 고려하였으며 앞서 설계한 제어기가 해당 실험 장치 내부에서 사용자의 의도에 맞게 제어 성능을 보이는지 확인할 수 있었다. 궤적 추종제어를 위해서는 2가지 비행 상황을 설정하였다. 첫 번째 경우, 천장과 비행체 상단부에 실을 연결하여 2D 평면상에서 비행체가 주워진 궤적에 따라 움직이는지, 두 번째 경우, 비행체 상단부에 헬륨이 주입된 풍선을 연결시켜 3D 공간상에서 주워진 궤적을 따라 추종 비행하는지를 확인할 수 있는 상황이다. 두 가지 상황에서 모두 다양한 형태의 궤적을 비행체가 잘 추종하는지를 확인할 수 있었다. 끝으로, 외부 장치(실, 풍선)를 제거하여 공중에서 비행체가 제자리 비행을 할 수 있는지를 검증하는 실험을 진행하였으며, 15초가량 1m3 공간 내에서 제자리 비행이 이루어지는 것을 확인하였다.Flapping wing micro air vehicles (FWMAVs) that generate thrust and lift by flapping their wings are regarded as promising flight vehicles because of their advantages in terms of similar appearance and maneuverability to natural creatures. Reducing weight and air resistance, insect-inspired tailless FWMAVs are an attractive aerial vehicle rather than bird-inspired FWMAVs. However, they are challenging platforms to achieve autonomous flight because they have insufficient control surfaces to secure passive stability and a complicated wing mechanism for generating three-axis control moments simultaneously. In this thesis, as preliminary autonomous flight research, I present the study of an attitude regulation and trajectory tracking control of a tailless FWMAV developed. For these tasks, I develop my platform, which includes two DC motors for generating thrust to support its weight and servo motors for generating three-axis control moments to regulate its flight attitude. First, I conduct the force and moment measurement experiment to confirm the magnitude and direction of the lift and moment generated from the wing mechanism. From the measurement test, it is confirmed that the wing mechanism generates enough thrust to float the vehicle and control moments for attitude regulation. Through the dynamic equations in the three-axis direction of the vehicle, a controller for maintaining a stable attitude of the vehicle can be designed. To this end, a dynamic equation related to the rotational motion in the roll, pitch, and yaw axes is derived. Based on the derived dynamic equations, we design a proportional-integral-differential controller (PID) type controller to compensate for the attitude of the vehicle. Besides, we use a multi-loop control structure (inner-loop: attitude control, outer-loop: position control) to track various trajectories. Simulation results show that the designed controller is effective in regulating the platforms attitude and tracking a trajectory. To check whether the developed vehicle and the designed controller are operating effectively to regulate its attitude, I design a lightweight gyroscope apparatus using medium-density-fiberboard (MDF) material. The rig is capable of freely rotating in the roll, pitch, and yaw axes. I consider two situations in which each axis is controlled independently, and all axes are controlled simultaneously. In both cases, attitude regulation is properly performed. Two flight situations are considered for the trajectory tracking experiment. In the first case, a string connects between the ceiling and the top of the platform. In the second case, the helium-filled balloon is connected to the top of the vehicle. In both cases, the platform tracks various types of trajectories well in error by less than 10 cm. Finally, an experiment is conducted to check whether the tailless FWMAV could fly autonomously in place by removing external devices (string, balloon), and the tailless FWMAV flies within 1 m^3 space for about 15 seconds1.Introduction 1 1.1 Background & Motivation 1 1.2 Literature review 3 1.3 Thesis contribution 7 1.4 Thesis outline 8 2.Design of tailless FWMAV 13 2.1 Platform appearance 13 2.2 Flight control system 17 2.3 Principle of actuator mechanism 18 3.Force measurement experiment 28 3.1 Measurement setup 28 3.2 Measurement results 30 4.Dynamics & Controller design 37 4.1 Preliminary 37 4.2 Dynamics & Attitude control 39 4.2.1 Roll direction 41 4.2.2 Pitch direction 43 4.2.3 Yaw direction 45 4.2.4 PID control 47 4.3 Trajectory tracking control 48 5.Attitude regulation experiments 50 5.1 Design of gyroscope testbed 50 5.2 Experimental environment 52 5.3 Roll axis free 53 5.3.1 Simulation 54 5.3.2 Experiment 55 5.4 Pitch axis free 56 5.4.1 Simulation 57 5.4.2 Experiment 58 5.5 Yaw axis free 59 5.5.1 Simulation 59 5.5.2 Experiment 60 5.6 All axes free 60 5.6.1 Simulation 60 5.6.2 Experiment 61 5.7 Design of universal joint testbed & Experiment 64 6.Trajectory tracking 68 6.1 Simulation 68 6.2 Preliminary 69 6.3 Experiment: Tied-to-the-ceiling 70 6.4 Experiment: Hung-to-a-balloon 71 6.5 Summary 72 6.6 Hovering flight 73 7.Conclusion 83 A Appendix: Wing gearbox 85 A.1 4-bar linkage structure 85 B Appendix: Disturbance observer (DOB) 87 B.1 DOB controller 87 B.2 Simulation 89 B.2.1 Step input 89 B.2.2 Sinusoid input 91 B.3 Experiment 92 References 95Docto

Design optimization and wind tunnel investigation of a flapping system based on the flapping wing trajectories of a beetle's hindwings

To design a flapping-wing micro air vehicle (FWMAV), the hovering flight action of a beetle species (Protaetia brevitarsis) was captured, and various parameters, such as the hindwing flapping frequency, flapping amplitude, angle of attack, rotation angle, and stroke plane angle, were obtained. The wing tip trajectories of the hindwings were recorded and analyzed, and the flapping kinematics were assessed. Based on the wing tip trajectory functions, bioinspired wings and a linkage mechanism flapping system were designed. The critical parameters for the aerodynamic characteristics were investigated and optimized by means of wind tunnel tests, and the artificial flapping system with the best wing parameters was compared with the natural beetle. This work provides insight into how natural flyers execute flight by experimentally duplicating beetle hindwing kinematics and paves the way for the future development of beetle-mimicking FWMAVs

A Review of Biomimetic Air Vehicle Research: 1984-2014

Biomimetic air vehicles (BAV) are a class of unmanned aircraft that mimic the flapping wing kinematics of flying organisms (e.g. birds, bats, and insects). Research into BAV has rapidly expanded over the last 30 years. In this paper, we present a comprehensive bibliometric review of engineering and biology journal articles that were published on this subject between 1984 and 2014. These articles are organized into five topical categories: aerodynamics, guidance and control, mechanisms, structures and materials, and system design. All of the articles are compartmented into one of these categories based on their primary focus. Several aspects of these articles are examined: publication year, number of citations, journal, authoring organization and country, non-academic funding sources, and the flying organism focused upon for bio-mimicry. This review provides useful information on the state of the art of BAV research and insight on potential future directions. Our intention is that this will serve as a resource for those already engaged in BAV research and enable insight that promotes further research interest

Practical Flapping Mechanisms for 20cm-span Micro Air Vehicles

[[abstract]]In the body of research relevant to high-performance flapping micro air vehicles (MAV), development of light-weight, compact and energy-efficient flapping mechanisms occupies a position of primacy due to its direct impact on the flight performance and mission capability. Realization of such versatile flapping mechanism with additional ability of producing thrust levels that fulfill requirements of cruising forward flight and vertical take-off and landing (VTOL) conditions demand extensive design validation and performance evaluation. This paper presents a concerted approach for mechanism development of a 20 cm span flapping MAV through an iterative design process and synergistic fabrication options involving electrical-discharge-wire-cutting (EDWC) and injection molding. Dynamic characterization of each mechanism is done through high speed photography, power take-off measurement, wind tunnel testing and proof-of-concept test flights. The research outcome represents best-in-class mechanism for a 20 cm span flapping MAV with desirable performance features of extra-large flapping stroke up to 100°, minimal transverse vibrations and almost no phase lag between the wings.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]US

Design and comparison of tails for bird-scale flapping-wing robots

Flapping-wing robots (so-called ornithopters) are a promising type of platform to perform efficient winged flight and interaction with the environment. However, the control of such vehicles is challenging due to their under-actuated morphology to meet lightweight requirements. Consequently, the flight control of flapping-wing robots is predominantly handled by the tail. Most ornithopters feature a tail with two degrees of freedom but the configuration choice is often arbitrary and without in-depth study. In this paper, we propose a thorough analysis of the design and in-flight performance for three tails. Their design and manufacturing methods are presented, with an emphasis on low weight, which is critical in ornithopters. The aerodynamics of the tails is analyzed through CFD simulations and their performance compared experimentally. The advantages and performance metrics of each configuration are discussed based on flight data. Two types of 3D flight tests were carried out: aggressive heading maneuvers and level turns. The results show that an inverted V-tail outperforms the others regarding maneuverability and stability. From the three configurations, only the inverted V-Tail can perform an aggressive stable banked level turn with a radius of 3.7 m at a turning rate of 1.6 rad/s. This research work describes the impact of the tail configuration choice on the performance of bird-scale flapping-wing robots.Consejo Europeo de Investigación (ERC) 78824

Modelling and simulation of a novel bioinspired flapping-wing rotary MAV

© The AuthosAchieving high lift efficiency represents a major research focus in the Micro Air Vehicle (MAV) domain due to stringent size and payload constraints. The Cranfield research team presents a novel semi-biomimetic design called the Flapping Wing Rotor (FWR) to address this challenge. This innovative concept combines a bioinspired flapping wing mechanism with passive rotor rotation, leveraging unsteady aerodynamic principles analogous to insect flight. The research aims to highlight a promising biomimetic flapping-rotor MAV enabled through advanced modeling to unlock the benefits of bio-inspired unsteady aerodynamics. To demonstrate this approach, a 60g proof-of-concept prototype was developed alongside a digital twin methodology for modeling, simulation, and control. A mathematical model has been formulated to analyze FWR's lift generation performance and enable flight control system design for stabilization and controllability. This work concentrates on enhancing the physical modeling process. The model is refined by tuning two key aerodynamic coefficients to account for nonlinearities from unsteady aerodynamics, flexible structures, and low Reynolds number flow inherent in MAV flight. This improved model achieves superior lift prediction accuracy versus real flight test data. Ongoing efforts focus on optimizing control torque, load distribution, and stability to further augment FWR's flight capabilities

Efficacy of Flapping-wing Flight Via Dual Piezoelectric Actuation

A novel piezoelectric-actuated wing system featuring dual actuators for increased wing control is presented and evaluated for its forward-flight characteristics via theoretical modeling and physical wind tunnel testing. Flapping wing aerial systems serve as a middle ground between the traditional fixed-wing and rotary systems. Flapping wing aerial systems exhibit high maneuverability and stability at low speeds (like rotary systems) while maintaining increased efficiency (like fixed-wing systems). Flapping wings also eliminate the necessity of dangerous fast-moving propellers and open the door to actuation mechanisms other than traditional motors. This research explores one of these alternatives: the piezoelectric bending actuator. Piezoelectric materials produce a mechanical strain when an electric charge is applied. With an applied sinusoidal voltage, cantilevered bending piezoelectric actuators create oscillatory motion at the free end that can be translated into wing movement much more directly than a rotational motor. This direct actuation eliminates the need for gears and provides a mechanism for reducing the system\u27s weight. Furthermore, the simplified mechanism can improve robustness by removing contact surfaces that can become clogged or worn (e.g., using gears). While piezoelectric flapping-wing flight has many potential benefits, the combination has only been explored in insect-inspired hovering flight. This work explores the feasibility of larger, forward-flight systems to identify a framework for piezoelectrically-driven flapping-wing vehicles with wing-bending control. Theoretical and experimental analysis methods are presented to study piezoelectric flapping wing motion characteristics for lift and drag effects in flapping-wing aerial systems

DESIGN AND CONTROL OF A HUMMINGBIRD-SIZE FLAPPING WING MICRO AERIAL VEHICLE

Flying animals with flapping wings may best exemplify the astonishing ability of natural selection on design optimization. They evince extraordinary prowess to control their flight, while demonstrating rich repertoire of agile maneuvers. They remain surprisingly stable during hover and can make sharp turns in a split second. Characterized by high-frequency flapping wing motion, unsteady aerodynamics, and the ability to hover and perform fast maneuvers, insect-like flapping flight presents an extraordinary aerial locomotion strategy perfected at small size scales. Flapping Wing Micro Aerial Vehicles (FWMAVs) hold great promise in bridging the performance gap between engineered flying vehicles and their natural counterparts. They are perfect candidates for potential applications such as fast response robots in search and rescue, environmental friendly agents in precision agriculture, surveillance and intelligence gathering MAVs, and miniature nodes in sensor networks

Proceedings of the International Micro Air Vehicles Conference and Flight Competition 2017 (IMAV 2017)

The IMAV 2017 conference has been held at ISAE-SUPAERO, Toulouse, France from Sept. 18 to Sept. 21, 2017. More than 250 participants coming from 30 different countries worldwide have presented their latest research activities in the field of drones. 38 papers have been presented during the conference including various topics such as Aerodynamics, Aeroacoustics, Propulsion, Autopilots, Sensors, Communication systems, Mission planning techniques, Artificial Intelligence, Human-machine cooperation as applied to drones