A Reconfigurable Flight Control System Architecture for Small Unmanned Aerial Vehicles Zhicheng Deng, Chuanbao Ma, Ming Zhu School of Aeronautics Science and Engineering Beihang University Beijing, P.R.China
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[email protected] Abstract—Small Unmanned Aerial Vehicles (UAVs) have been proposed for use in a variety of areas including hazard analysis, disaster monitoring, agricultural mapping, and so on. Currently, the development of flight control systems (FCS) for small UAVs is complicated, time-consuming and error-prone. To address these challenges, we present a reconfigurable flight control system architecture (RFCSA) for small UAVs. RFCSA allows rapidly integrating hardware modules and verifying control laws. It utilizes a modular-based framework, in which implementation details of a typical function are packaged into a function module. In addition, each function module in RFCSA is stand-alone with its own processors, memories, power conversion and communication interfaces. In this way, the system designer could be able to focus on the system implementation, rather than pay much attention to the design details of low-level functions. Moreover, an event-driven Service-Oriented Architectures (SOA) is proposed to minimize the coupling between modules and improve the performance of inter-module interactions. The paper is organized as follows: Firstly, the challenges and requirements for small UAVs’ flight control systems are discussed. Secondly, the hardware architecture based on modular concept is developed. Thirdly, event driven SOA is proposed, and the mechanisms for modules to share information and coordinate activities are introduced. Finally, the conclusion and future work is pointed out. Keywords-flight control system; unmanned aerial vehicles; service oriented architecture
I.
INTRODUCTION
Small unmanned aerial vehicles (UAVs) are increasingly used in a variety of applications including hazard analysis, disaster monitoring, agricultural mapping, and so on [1-4]. They also attracted considerable academic interest in the past years. Many researchers have realized the usefulness of small UAVs both as teaching and research tools. Currently, many engineering schools have UAV programs, and many research groups utilize UAVs to pursue and test their control algorithms [5]. There is no doubt, with the development of artificial intelligence, control and embedded system technologies, Small UAVs will be widely employed to serve as platforms for many scenarios, not only for civil and military use, but also for education and academic research.
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Compared with the design and implementation process of small UAVs’ mechanical structure, the development of their flight control systems are very difficult. Firstly, the flight control system is very complicated. It is made up of mechanical parts, microprocessors and computer software. This multi-disciplinary system requires many experts in different areas and a multi-disciplinary solution. Secondly, the development process is time-consuming. The researchers have to deal with a lot of engineering problems in a wide range of issues that include energy consumption, electrical interfaces, electromagnetic interference considerations, hardware and software compatibility, human machine interfaces and material resources. Thirdly, this flight control system is error prone. Hundreds of wires need to be re-routed on the Printed Circuit Board (PCB), and thousands of lines of code need to be rewritten. Any negligence will lead to system failure. However, UAVs are capable of penetrating areas which may be dangerous for human beings. They could perform many tasks with ultra-low cost. Furthermore, they are good tools to verify many theoretical research results. Hence, there is a need to propose a new architecture to faster flight control system development, by which the researchers could focus on the system applications, rather than waste efforts on the design details of low-level functions. Motivated by these considerations, many researchers are engaged in developing new architectures for UAVs. For example, in [6], Vladimir N. Dobrokhodov et al proposed a rapid flight test prototyping system; Henrik B. Christophersen developed a small adaptive flight control system [7]; Austin M. Murch designed a flight control system architecture for the NASA AirSTAR infrastructure [8]. Obviously, many efforts are made on the problems mentioned above. However, most of them remain difficult for the researchers to build flight control systems for small UAVs. The key idea of this paper is to use modular concept to simplify the development of flight control systems for small UAVs. Since modular system has the capability to change its physical and logical topologies to adapt to various applications, there is a tendency to use modular nodes to make easier rapid prototyping as well as to redesign faster [9]. In addition, by utilizing SOA technologies, the coupling between function modules could be minimized. Therefore, it is easy to build specialized flight control system for given applications.
The paper is organized as follows: Firstly, the challenges and requirements for small UAV’s flight control system are discussed. Secondly, the hardware architecture based on modular concept is developed. Thirdly, service-oriented control architecture with event driven architecture is proposed, and the mechanisms for modules to share information and coordinate activities are also introduced. Finally, the conclusion and future work is pointed out. II.
REQUIREMENTS AND OVERVIEW OF RFCSA
A. Motivation Traditional flight control systems are composed by hardware components and corresponding software as illustrated in Fig. 1 [10-11]. In such systems, the relationship among hardware components and the relationship between hardware and software are tightly coupled. For this reason, they are usually specialized for typical "end user" applications, while, not suitable for fast and low cost applications. Figure 2. Motivations for RFCSA.
Based on the requirements discussed above, the major considerations of modular RFCSA include:
Figure 1. Traditional flight control system.
As elaborated in Section I, there is need to fast prototype flight control system for academic research, emergency sensing, etc. Therefore, solutions should be found for this problem. As is known, a modular system is made up of a number of modules that can be reconfigured in physical or logical topologies according to the requirements, and consequently obtain the advantages such as shorter R&D time, faster technology upgrade, enhance usability and mass customization [12]. These kind of flexibility, which makes the system has the capability of changing functions by changing connectivity among the module, is highly desirable for unpredictable UAV applications. Our philosophy is to take modular concept in flight control systems so as to develop flight control system more easily. Fig.2 shows our motivations on design a flight control system architecture based on modular concept.
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Simple and unified inter-module interface: The function module could be easily added, removed or swapped for specific applications.
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Easy for high level application design: The low-level implementations details need to be abstracted from the user allowing a user develop high level applications more easily.
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Reusable hardware and software: the hardware and software developed for an application could be ported to another application without major modification.
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Low cost: The system need to be inexpensive for customization so as to expand the small UAVs’ market.
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Reliable: The hardware and software is easy to be design and verification.
B. RFCSA Overview We have designed the modular based RFCSA according to the five considerations descirbe in Section II, part A. as shown in Fig. 3, RFCSA consists of several modules, all the modules are logically and phsically connected via modules’ interfaces. The module’s interface is unified. It includes mechanical port, electrical port and software port. •
Mechanical port: All the modules’ mechanical ports have the same mechanical structure so that different modules could be assembled together. Also, the mechanical port is embedded with smart sensors, which could detect whether the port is connected to other modules or not. Thus, the module could optimize its’ function according to the topologies of the whole system.
applications are interoperable, so that the system integration is very simple. •
Sharing and Reuse: SOA make the system more flexible. New functions can be easily integrated according to users’ demands. New applications can be composed by reusable so-called services. Moreover, it offers users high-level abstracted services to quickly design a usable application system.
To achieve these advantages in RFCSA, SOA is applied to the RFCSA’s software implementation. Fig. 4 depicts a RFCSA with SOA software implementation.
Figure 3. Reconfigurable flight control system architecture.
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Electrical port: The electrical port is designed to provide power and communication connections between modules. It consists of a power connector (wired/wireless) and a data connector (wired/wireless). The power connector acquires/provides power from/to the connected module, and converts the power into different voltage. The data connector, which employs a predefined protocol such as RS485, LAN, IR, and Bluetooth, could send the processed or status information to other modules or receive needed data from the others.
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Software port: Each module in Fig. 3 has different functions, hardware components and software architecture. To share resource between modules, the software port is defined. This port standardizes the modules’ functions, so that other modules could use some hardware and software resources in this module. Also, the module’s behaviors could be coordinated through this port.
These three ports could enable system developer to create modular, easily integrated modules for UAVs. Take advantages of these three ports, divide an integrated flight control system into a set of modules, each implementing a set of functions, it will be possible for the user to design loosely coupled modular system. This reduces not only the research effort required for the end user, but also the risk for the system development. III.
SOFTWARE ARCHITECTURE FOR RFCSA
To take full advantage of the modular systems, methods should be taken to coordinate every module’s behaviors. Since centralized control methods are lack of robustness, fault tolerance and flexibility, more and more researchers use distributed control methods to solve the module’s coordination problems. Service oriented architecture (SOA) is a design methodology for a distributed environment. It has many advantages over other architectures [13]. •
Interoperability: There is no need to develop program to integrate applications. With a SOA, all the
Figure 4. SOA enabled RFCSA.
As shown in Fig. 4, each module is responsible for realizing several services that have specific functions. And the applications running on the processor can discover these services dynamically, and access them via the formally defined interfaces. Apparently, SOA could hide complex technical issues such as how do services communicate with other services and how it is implemented. This will help the user to eliminate rework and maximize the value of existing work. IV.
DATA FLOW OVERVIEW & SOA ENABLED RFCSA IMPLEMENTATION
Besides representing the principal hardware and software architecture, Fig. 4 also demonstrates the basic data flow in the proposed SOA enabled flight control system architecture. This SOA enabled flight control system architecture consists of four critical data segments: (1) service inquiry message; (2) service respond message; (3) service coordination message; (4) service I/O data. The former three data segments are used to form the service discovery mechanisms, through which the encapsulated service could be discovered and access by the applications. The last data segment is meta-data for the service, or processed data from the service. These encapsulated data segments are loosely coupled message-oriented datalink between services. They can be used to implement service-oriented system. Fig. 5 illustrates the implementation of the SOA enabled RFCSA by these four data segments.
modular-based reconfigurable flight control system architecture (RFCSA), and the system information flow was addressed as well. So far, the RFCSA is still under optimization. Next, an experimental flight control system based on RFCSA will be developed. ACKNOWLEDGMENT The Authors would like to acknowledge some of the many contributions to this work: Bi X.T. and Sun Q. This topic of research is supported by 863 Project. REFERENCES [1]
[2]
Figure 5. SOA enabled RFCSA implementation.
The distributed service negotiating mechanism in Fig. 5 is used to register the services provided by the modules. It includes 4 steps. 1) The application sends inquiry messages to all the modules that are logically connected to the application. The inuqiry message include the application ID and the needed services description. Application ID
Needed Service and description
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2) The service addressing, discovering and selection mechanism residing in the modules redirect the inquiry information to the appropriate service in the same module according to the inquiry message. 3) The requested service, which is needed by the application send a respond message indicating its status back to the application. Service provider ID
Status & service description
Application ID
V.
Start/Stop
[4]
[5]
[6]
[7]
[8]
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4) Finally, the application check the respond message, if all the needed services are to be used, it send an service coordination message to all the needed services to execute the appliction. Service provider ID
[3]
[9]
[10]
… [11]
CONCLUSION
Modular concept could bring scalability and extensibility to avionics system. A modular avionics system made up of a number of modules can be reconfigured in topologies according to the application requirements. To best apply small UAVs for use in different application scenarios, in this paper, we discussed the challenges and requirements for developing a flexible and scalable flight control system, and then, designed a
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