Eiichi Yoshida

Cooperative sweeping by multiple mobile robots

In this paper, we propose an off-line planning algorithm for cooperative tasks of multiple mobile robots. Sweeping means a motion that a robot covers a 2-dimensional area by its effector. Sweeping of a whole work area is fundamental and essential task of mobile robots. For efficient cooperation, setting appropriate burden onto each robot is very important because interference of robots and overlaps of their effecters make efficiency low. The cost of sweeping depends on both sweeping ability of a robot and a shape of a work area to be swept. Evaluation and distribution of the cost are most important issues. In the proposed algorithm, the cost is evaluated by means of length on which robot should move. We introduce both edges of the configuration space and Voronoi diagram so as to compute paths in the whole area. We generate the a tour for traversing all the paths by applying the algorithm of the Chinese Postman Problem. According to the cost evaluation, appropriate paths of the tour are assigned to each robot. The efficiency of the proposed algorithm is verified by simulations and an experiment.

Transferring and regrasping a large object by cooperation of multiple mobile robots

This paper deals with a motion planning of mobile robots during transferring a large object cooperatively by a group of multiple mobile robots (a robot group). This problem has the following characteristics: 1) a real time planning is essential because mobile robots move in an open and dynamic area in comparison to articulated robots; 2) both the object and the robot group need to avoid collision against obstacles; and 3) the object needs to be grasped stably by the robot group. The authors propose the following approach to solve this complicated problem: 1) regrasping strategy of the object is introduced in order avoid obstacles and to transfer the object stably; and 2) the motion planning is divided into two steps: the object and that of the robot group. The former step is accomplished by extending the virtual impedance method, which was proposed by authors. The latter step is realized by using nonlinear programming method, that optimizes a penalty index indicating the performance for obstacle avoidance and for stable grasping. Effectiveness of the proposed method is verified by a simulation of transferring a large circle-shaped object with three robots.

Effect of grouping in local communication system of multiple mobile robots

For the cooperation in a large system with many mobile robots, local communication system is considered appropriate in terms of the cost and capacity of communication. The behavior of robots has a respectable effect on the efficiency of communication in such a local communication system and it is essential to know what kind of behavior robots should take to realize efficient information transmission for cooperative tasks. We introduce a simple group behavior for the purpose of improving the communication efficiency. This paper analyses the effect of group behavior on the communication performance, and derives differential equations describing information diffusion among robot groups. The optimal group size to transmit information to a desired number of robots is obtained front these equations. The effectiveness of the analysis is verified by computer simulation. We also show a self-organization algorithm for group forming designed for local communication system.<<ETX>>

Information diffusion by local communication of multiple mobile robots

For robot cooperation in a large system with many mobile robots, the locality and concurrence of communication must be taken into account. The time-delay in communication becomes important for task planning in such a robot environment. We analyzed the information diffusion among many mobile robots, and proposed a method to evaluate the time-delay and to control the diffusion using the logistic equation. The model is verified and the effectiveness of our method is verified by simulation which implements many mobile robots. Another simulation of cooperative task execution shows that the analysis allows us to make task planning more efficient. Utilizing this simple logistic function, the time-delay required so that the task information is transmitted to the necessary number of robots is computed, and unnecessary diffusion of the information can be avoided.<<ETX>>

An algorithm of dividing a work area to multiple mobile robots

Proposes an algorithm of dividing a work area into small pieces in order to make multiple mobile robots cooperate efficiently. Searching of a whole work area is the most fundamental and the most essential task of mobile robots. The authors expect that the cost of searching is shared by cooperation of multiple robots. In the proposed algorithm, searching motions of robots are represented by paths. Both edges of the configuration space and the Voronoi diagram are introduced so as to compute paths in the whole area. The authors generate a tour of the paths to traverse all the paths using the algorithm of the Chinese postman problem. The cost is estimated as the total length of the paths. By means of the cost evaluation, the appropriate paths are assigned to each robot. The efficiency of the proposed algorithm is verified by simulations.

A design method of local communication area in multiple mobile robot system

When many mobile robots should achieve cooperation, a local communication system is considered appropriate from the standpoint of the cost and capacity of communication. This paper presents the optimization of the efficiency of local communication in environments where many mobile robots send out information stochastically. The optimal communication area is derived by minimizing the transmission waiting time calculated using the probability of successful information transmission. Computer simulations have been undertaken to verify the analytical results.

Cooperating grasping of a large object by multiple mobile robots

The authors aim at grasping and handling a large object by cooperating multiple mobile robots with various sizes, moving cost, and load capacity. In this paper the authors focus on the problems of deciding an appropriate grasping arrangement before handling operations. The authors propose this method to avoid bad situations, such as making an object fall down, or some robots overloaded in grasping and handling. The algorithm proposed includes two optimization problems; one is the decision of initial robot arrangement, the other is the decision of final robot arrangement. The difference between these optimizations is that the mass center of the object is recognized or not. The penalty index is defined to minimize the energy the system consumes and to maximize an index of stability. The authors have confirmed that the robots moved to the optimal arrangements in computer simulations and experiments.

Real time planning method for multiple mobile robots

This paper proposes a motion/task planning method for multiple mobile robots. It has two characteristics as follows: (1) facility of implementing tasks, and (2) adapting ability to environment. A layered hierarchical structure is adopted for the proposed planner. The lower layer called virtual impedance method makes a real-time plan to follow the generated trajectory while avoiding obstacles and other robots. The upper layer determines the design parameters of the lower layer which can express motion skills. Simulation results on motion planning and transporting tasks indicate effectiveness of the proposed method.

Motion skills in multiple mobile robot system

Abstract This paper deals with how to introduce motion skills in motion planning of multiple mobile robots. The motion skills are defined as rules of “IF (a specific situation) THEN (a specific manner of motion)” type. Authors propose an algorithm for acquiring and utilizing the skills. First, the concept of sensor information pattern is introduced for recognizing the specific situation. Next, acquisition of the motion skills are made by induction process, which is accomplished by using hierarchical neural network. Last, simulations are made to show the effectiveness of the proposed algorithm.

A design method of local communication range in multiple mobile robot system

Local communication system is considered appropriate when many mobile robots should achieve cooperation, from the standpoint of cost and capacity of communication. This paper presents a design method of the optimal communication range for efficient local communication system. The analyses of optimization are made by minimizing the information transition time, first in the case of transmission to an arbitrary robot, and next, to multiple robots. Computer simulations have been undertaken to verify the analytical results.