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英文资料及中文翻译

Development of a multi-agent system for robot soccer game

一、 Introduction

As modern industrial society progresses, the needs for useful robots are growing. Especially, mobile robots are special issue that gradually expands its realm in industrial and studying topics. Researches on mobile robots have been mainly concentrated on single mobile robot. But, the development of multi-agent system is strongly needed by the growth of complexity of tasks for robots to perform.

The multi-agent systems have been studied by many researchers[l-3]. Generally, multi-agent system is defined as the system composed of more than 2 robots [4] and performs the given task by cooperation. The system has some different factors compared with single robot system. First, the environment for robots to confront is dynamic. In multi-agent system, the robots themselves constitute dynamic environment, because each robot should recognize the other robots as moving obstacles. Many previous researches on mobile robots assume that the environment is static, even for the researches on single mobile robot[5,6]. Second, since the system performs given task by cooperation, it is necessary to make overall system plan for roles of robots. One of the obvious characteristics of the multi-agent system is cooperation - for example, 4-5 robots carry furniture [7]. To cooperate one another, the changes of robots position must be predictable. There are some ways to know the robots position. For example, robots communicate their position one after another, or a supervisor detects robots' position and transmits them to robots. It is related to communication problem. Third, each component of the system such as robots, a supervisor, sensors, communication equipment is well developed, because they influence the overall system performance. Also, it is necessary to adopt appropriate architecture.

Robot soccer is an interesting domain for studying the multi-agent system. The players must work together: It means a sort of cooperation. Also, they play the game in dynamic environment: predictable and unpredictable environment - our robots and opponent's robots, respectively. The main object is to put the ball in opponent's goal as frequently as possible in presence of opponent's robots which have the same task. So, according to a situation, our robots decide which action they take -defense or offense, how they work and

so on. In this point, the system needs real-time sensing, quick decision making and fast behaviors. It is related to system architecture and algorithms. As described above , soccer game includes many characteristics of multi-agent system and is abundant in applying AI techniques.

One of the advantages of robot soccer game is direct comparison of different systems. Many robot soccer systems are gathered in some competitions. We participated in a Soccer robot competition in Taejon, Korea called MIROSOT96 [8]. MIROSOT makes some rules. The rules describe precise specification for soccer game. The playground is rectangular with its length 130cm, its width 90cm. An orange golf ball is selected as the play ball. The size of a robot is restricted within 7.5*7.5*7.5cm. One team consists of three robots. We purpose to make soccer system with three robots.

In this paper, we explain some factors to be considered in establishing complete system. First, since the system architecture is very important, we decide the overall system as a centralized on-line system on the basis of surveys of multi-agent systems. Second, the overall system can be divided into three parts - A robot, communication and vision system. We describe the specifications of components of each part and the reasons to decide them. It would be helpful for later improvement.

The rest of the paper is organized as follows. Section 2 gives some surveys of system architectures and selection of our soccer robot system. Section 3 gives detailed descriptions of implemented hardware, especially mini robots. Section 4 gives cooperation and path plan algorithm for robot soccer game. Section 5 gives conclusion of this paper and presents further works.

二、Categorization of multi-agent system and selection of soccer robot system

The survey on this issue is closely related in Arai's work[4]. We can categorize multi- agent system based on two criteria. One is \makes decision and orders?\-Centralized / Decentralized , the other is \Offline.

Centralized system means that a supervisor integrates all available data, plans the behaviors of all the robots and makes commands. Since a supervisor considers all the robots simultaneously, the system can achieve the optimization of the motions of all the robots. But, as the number of robot increases, more computational power of a supervisor is needed. If the supervisor makes any fault, there is no way for the robots to correct it.

Decentralized system means that each robot makes plan for itself on the basis of collected information from other robots and its own sensors. In the system, there is not

considerable increasing computational load as the number of robots increases. Even if one robot fails to work, other robots work well. But, the system cannot guarantee the optimization of the motions of all the robots.

Off-line system means that all the paths are planned before all the robots move. Because of no restriction of time and computing power, the system can achieve optimization. But, since the system assumes static environment, it is not robust to small variation of environment. In real world, it may malfunction with some variances.

On-line system means real-time planning. It is robust to dynamic environment. But, it needs large computational power and effective algorithm.

In a lot of researches, the above two categorizations are interrelated each other. We summarize the researches in Table 1.

Table 1. Categorization of multi-agent system

who Centralized Centralized Decentralized Decentralized when Off-line On-line Off-line On-line proposed methods cell Decomposition^] Retraction[10] Priority[5,6] Priority[ll] Potential Field[ 12] Rule-based[13] Communication[ 14] In MIROSOT96, The size of a robot is restricted. Therefore, it is difficult to implement a robot with large computational power. Also, it is important to decide what a robot must equip. Basically, a robot has to equip actuator module and communication module. Additional equipments are selected and implemented considering the space of a robot. Soccer game needs global information of our robots' position. So, we decide the centralized system as our system. From the viewpoint of path planning time, we decide the on-line system. Soccer game has fast changing nature and necessitates real-time sensing, fast behaviors, and quick decision making. It is reasonable to adopt on-line system. In centralized on-line system, a supervisor acquires all available information of whole environment and the robots. Simultaneously, a supervisor should plan all the robots' paths in real-time. Therefore it requires fast computing power. To decrease the burden of a supervisor, we choose partitioned system which separate main planning