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英文资料及中文翻译Development of a multi-agent system for robot soccer game一 、 IntroductionAs 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 researchersl-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 robot5,6. 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 opponents robots, respectively. The main object is to put the ball in opponents goal as frequently as possible in presence of opponents 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 systemThe survey on this issue is closely related in Arais work4. We can categorize multi- agent system based on two criteria. One is Who makes decision and orders? -Centralized / Decentralized , the other is When does the system make plans? - On line / 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 systemwho when proposed methodsCentralized Off-line cell Decomposition Retraction10 Priority5,6Centralized On-lineDecentralized Off-line PriorityllDecentralized On-line Potential Field 12Rule-based13 Communication 14In 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 and executing. This is somewhat similar to the works of Shakey15, Firby16. In our soccer robot system, a supervisor makes plans of all the robots on the basis of some strategy. Then, a supervisor transmits next desired position to each robot. Each robot receives desired position and executes its control algorithm for position and velocity controls. Simultaneously, each robot takes data of its own local sensor which are fused with desired position into desired input of its own control loop. Therefore, a robot must possess some logic : a sort of a brain. So, our robots have micro-controllers. In this architecture, the system partitions computing burdens. Figure 1 shows the functional diagram of our soccer robot system. Since a supervisor receives positions of the ball and all robots, the system doesnt need bi-directional communication. A supervisor only transmits commands to each robot. In the case of bi-directional communication, the logic of transmitting and receiving order and priority must be needed. It may increase complexity of communication system of both a supervisor and a robot.Figure 1. The constitution of our soccer robot system三 、 System implementationSystem is composed of three parts - a supervisor, vision and 5 robots. A supervisor is a PC - pentium processor -which makes plan in real time, and vision system has two cameras which have red and blue filter respectively, and image processing board which has a DSP and memory. A robot has a CPU, communication module, IR sensors, motors, etc. These three parts are related one another. Detailed descriptions are given in following chapters.1. Configuration of individual robotA robot is consisted of mechanical part, CPU board, communication(receiver) module and sensor board. Its size is within 7.5*7.5*7.5 cm.2. Mechanical partMechanical part of a robot is consisted of two motors, encoders, gearheads, wheels, a ball caster, and a frame. The frame is designed for easy, compact and hardy integration. Motors and gearheads are selected in consideration for operating voltage, internal resistance, mechanical time constant. Its operating voltage is 6V. Reduction ratio of gearhead is 1:41. A diameter of a wheel is 32 mm. The no-load speed of a motor is 15200 rev/min. So, no-load speed of robots can be calculated as about 62 cm/sec. In real robots, we measure the maximum speed of a robot. The result is about 40cm/sec. Two motors are controlled by a CPU in main board independently. The encoder generates 16 pulses per revolution.3. CPU board and sensor boardFigure 2. The CPU board and sensor board(a)the locations of LEDs in CPU board forrobots position and rotation(b)the locations of IR sensors in sensor boardIn CPU board, data processing and motor control are carried out. CPU board consists of two PCBs - same size of 7.5cm*6.0cm. We choose 80C196KC as robots CPU. Its basic operation is to control motors according to the data from a supervisor via communication module. Also, it fuses the data from a supervisor and sensors equipped in itself. 80C196KC has three PWM generators which are used to control motors and 8 channel A/D converters which are used to receive the data from its own sensors. Motor driver is TC 4428 - dual high speed MOSFET driver. For compact spacing, we use EPLD( Erasable Programmable Logic Device) which can perform encoder counting, address decoding, and some logic functions.As can be seen in Figure 2(a), 4 LEDs are in CPU board located above in a robot. Three LEDs make an isosceles triangle. Because LED is the most brightest thing in playground, vision system detects the position and rotation of a robot easily. The other LED located at the center of triangle is used to provide some information to a supervisor. Turning on the LED means that a robot detects the ball by its own sensors.In sensor board, 4 pairs of IR sensor consisted of transmitter and receiver are located in fixed positions. As can be seen in Figure 2(b), one pair is located in higher position to distinguish a robot from the ball. It can detect only the ball. The other three pairs are located in the lower position. They can detect the ball and robots. So, a CPU can recognize the obstacle detected by its own sensors - a ball and a robot. Since sensor board is in front of a robot, it can perform local searching in front of a robot.Figure 3. The shape of digitally coded dataFigure 4. The constitution of communication signal3. CommunicationWe choose unidirectional communication - from a supervisor to robots. Generally, to share more information, bi-directional communication is better. But, it needs more space and increases the complexity of tasks which robots and a supervisor carry out. In our system, we use vision system as a global monitor. So, it is not necessary for a robot to transmit its data to a supervisor. Therefore, we adopt unidirectional communication.There are two prevalent communication methods - IR and R/F. IR communication has a problem such that it is affected by light. So, in real competition, it may malfunction. Therefore, we modify the commercial R/F communication module and introduce a digital method for high precision and good reliability of information transfer. We set the carrier frequency as 4kHz. Two sections make one digital data. If there is a state change between two sections in the digital data, this digital data means 1 bit. If no state change occurs, it means 0 bit. Between digital data, a state change always takes place. This is described in Figure 3. So, Data transfer ratio is 2000bit/sec. We define a channel as a basic unit and a channel has 9 bits - one bit is start bit and the other 8 bits are data bits. Since supervisor sends position and orientation to each robot, one robot needs 3 channels. We define a block as a basic command unit. As in Figure 4, one block consists of 17 channels because each of five robots needs 3 channels and there are a start channel and an extra channel for an unexpectedfuture purpose. So, the transfer rate is about 13 block per second. It means that a supervisor can transfer information to five robots 13 times per second.4. Vision systemIt is very important to recognize the positions of robots and the ball in real-time. We use two monochrome cameras. One has red filter and the other has blue filter. As mentioned above, a robot has an isosceles triangle shaped LED configuration. Vision system can easily detect a robot. As for a ball, vision system compare two image for detecting the ball. We regulate LUTs( Look Up Table ) of image data from two cameras to eliminate other colors except a ball color before competition. In our experiment, vision system with one monochrome camera cannot detect a ball robustly. Therefore, we use two cameras. As for opponents robots detection, MIROSOT make it a rule to have a solid 3.5cm*3.5cm patch of its team color visible on top. We also regulate LUTs to make vision system detect opponents robots. In our experiment, our vision system can detect a ball and ten robots 5 times per a second.5 Position control of a robotThe block diagram of position control of a robot is presented in Figure 5. The figure shows the partitioned system : Planning and executing. Global Monitoring loop representing the Planning is a feedback loop in which vision system detect a robot position and a supervisor makes commands. As soon as vision system detects positions of robots and the ball, a supervisor makes path planning of each robot according to the current position data. It is slow feedback. In Local Control loop representing executing , each robots execute the position and velocity control with encoder signals and desired position.Figure 5. Constitution of Control systemFigure 6. The configuration of our system.a detailed description.Figure 7. The actual robot with a golf ball三 、 Cooperation and path plan algorithm for robot soccer gameWe are making algorithms in consideration for two points. One is for cooperation; the other is for path plan of each robot. In MIROSOT96, three robots were permitted to play game. Therefore, we make algorithms considering three robots as a multi-agent system. For viewpoint of cooperation, one robot is a goal keeper, the others takes the roles according to the modes. There can be several modes. We tested 4 modes. Figure 8 shows 4 modes. Basically, we use divide-and-conquer heuristics. We divide the playground into two areas; assign each area to two robots. Each robot takes the role according to the assigned area. Mode (a) and (b) are natural division of the playground. Mode (c) has wide attack zone. Mode (d) is that two robots are all-round players. These modes are changed against opponents strategy. We are going to test established modes and develop more effective modes. For path plan of each robot, we use parametric cubic spline. The cost function is consisted of three term. One is for minimization of variations of curvature, the other is for minimization of time, the third is for obstacle avoidance. The results of one robot experiment show that our algorithm can be applied to robot soccer game17.We are going to develop more effective algorithm for robot soccer game. Figure 8. The 4 tested modes四 、 Conclusions and further worksIn this paper, we provide the reasons why we adopt centralized on-line system as our robot soccer system and specification of implemented hardware. We survey many multi-agent systems from the viewpoint of system architecture. Using two criteria, we categorize the multi-agent systems. Then, we select the centralized on-line system considering the nature of robot soccer game. This paper explains suitability of our system to robot soccer game for many reasons. Also, we explain our system in detail. To partitioning the computing burdens, the supervisor makes path plans and the robot executes its control loop - Global Monitoring and Local Control. For local searching, our robots have 4 IR sensors in front of them. 4 LEDs are located in CPU board in the shape of an isosceles triangle for easy detection of position and rotation by vision system. As for communication, we designed digitally coded data format. After they are tested independently, they can be combined easily. Detailed description of our system is helpful to those who plans to participate in soccer game and someone who want to make similar system.Using established system, we are going to build multiple robot path planning system using several techniques - fuzzy, neural network, genetic algorithm and so on. At present, We have established divide-and-conquer heuristics. It is needed to develop more effective soccer algorithms and test our algorithm combined with our real system.在机器人足球赛中多智能体系统的发展一、介绍随着现代工业的发展，应用机器人的需要在增加。尤其是移动机器人在工业和研究领域中逐渐地扩大了其应
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