Hajime Asama

Inevitable collision states - a step towards safer robots?

An inevitable collision state for a robotic system can be defined as a state for which, no matter what the future trajectory followed by the system is, a collision with an obstacle eventually occurs. An inevitable collision state takes into account the dynamics of both the system and the obstacles, fixed or moving. The main contribution of this paper is to lay down and explore this novel concept (and the companion concept of inevitable collision obstacle). Formal definitions of the inevitable collision states and obstacles are given. Properties fundamental for their characterization are established. This concept is very general, and can be useful both for navigation and motion planning purposes (for its own safety, a robotic system should never find itself in an inevitable collision state). To illustrate the interest of this concept, it is applied to a problem of safe motion planning for a robotic system subject to sensing constraints in a partially known environment (i.e. that may contain unexpected obstacles). In safe motion planning, the issue is to compute motions for which it is guaranteed that, no matter what happens at execution time, the robotic system never finds itself in a situation where there is no way for it to avoid collision with an unexpected obstacle.

Development of an omni-directional mobile robot with 3 DOF decoupling drive mechanism

A new driving mechanism for holonomic omnidirectional mobile robots is designed, which enables 3 DOF motion control by three correspondent actuators in a decoupled manner with no redundancy. A prototype of the omnidirectional mobile robot with the driving mechanism is developed including a parallel link suspension mechanism. The kinematics of the omnidirectional mobile robot is also analyzed, and simulation for velocity control of the robot is performed by a method for velocity modulation with interpolation to achieve the given target position and velocity.

Self-organizing collective robots with morphogenesis in a vertical plane

This paper presents a novel concept of self-organizing collective robots with morphogenesis in a vertical plane. It is potentially applicable to autonomous mobile robots. For physical reconfiguration of a swarm of robots against gravity, new types of mechanisms and control strategies are proposed and demonstrated. Prototype robots have been fabricated in order to confirm the basic feasibility of the mechanisms. Each robot is composed of a body and a pair of arms. The body can be regarded as a cube with edge length of 90 mm, and is equipped with permanent magnets for bonding with another robot. The arms change the bonding configuration by rotating and sliding motions. As for the control strategies, we proposed the algorithms which can locally generate specific global formations of robots, with minimum interactions between neighboring robots. The overall scheme is similar to cellular automata. The control algorithms proposed have been tested by simulations.

Cooperative transport by multiple mobile robots in unknown static environments associated with real-time task assignment

This paper deals with a task-assignment architecture for cooperative transport by multiple mobile robots in an unknown static environment. The architecture should satisfy three features: deal with a variety of tasks in time and space, deal with a large number of tasks compared with the number of robots, and decide the behavior in real time. The authors propose the following approach: we consider the unit of task (task instance) as the job that should be done in a short time by one robot. Based on the environmental information, task instances are dynamically generated using task templates. The priority of task instances is evaluated dynamically based on the number of robots and the configuration in the workspace. In addition, we avoid generating too many task instances by suppressing object motion. The main part of the architecture consists of two real-time planners: a priority-based task-assignment planner solved by using the linear programming method, and motion planners based on short-time estimation. The effectiveness of the proposed architecture is verified by a cooperative transport simulation in an unknown environment.

Collision avoidance among multiple mobile robots based on rules and communication

An autonomous and decentralized robot system, ACTRESS, is being developed as an intelligent robot system which is composed of multiple robotic agents. The basic concept and strategy for path planning in a dynamically changing environment with multiple autonomous mobile robots are introduced. Collision avoidance with dynamic path planning according to the complexity of the situations is also discussed. A method for collision avoidance based on rules and negotiation by communication is presented. Finally, this method is applied to a developed prototype system consisting of two mobile robots, and the result of experiments operating on real robots is given.<<ETX>>

Efficient method to generate collision free paths for an autonomous mobile robot based on new free space structuring approach

A technique is developed based on free link concept to construct the available free space between obstacles within robots environment in terms of free convex area. Then, a new kind of vertex graph called MAKLINK is constructed to support the generation of a collision free path. This graph is constructed using the midpoints of common free links between free convex area as passing points. These points correspond to nodes in a graph and the connection between them within each convex area as arcs in this graph. A collision free path can be efficiently generated using the MAKLINK graph. The complexity of the search for a collision free path is greatly reduced by minimizing the size of the graph to be searched concerning the number of nodes and the number of arcs connecting them. The analysis of the proposed algorithm shows its efficiency in terms of computation ability, safety, optimality, and in supporting robot navigation along the generated path.<<ETX>>

Functional distribution among multiple mobile robots in an autonomous and decentralized robot system

An autonomous and decentralized robot system, ACTRESS, is being developed as an intelligent robot system which can execute high level tasks. The concept of ACTRESS is introduced, and the communication framework between robotic agents that compose the robot system is proposed. Taking a task of pushing objects by multiple mobile robots in a certain working environment as a case study of ACTRESS, the strategy for organizing the robot system is discussed, and the required functions for the robot system are introduced. The optimal distribution of the functions is designed based on communication evaluation. An algorithm for static path planning and a strategy for dynamic path planning are proposed.<<ETX>>

The robocup physical agent challenge: Phase i

Traditional AI research has not given due attention to the important role that physical bodies play for agents as their interactions produce complex emergent behaviors to achieve goals in the dynamic real world. The RoboCup Physical Agent Challenge provides a good test bed for studying how physical bodies play a significant role in realizing intelligent behaviors using the RoboCup framework (Kitano et al., 1995). In order for the robots to play a soccer game reasonably well, a wide range of technologies needs to be integrated, and a number of technical breakthroughs must be made. In this article, we present three challenging tasks as the RoboCup Physical Agent Challenge Phase I: (1) moving the ball to the specified area (shooting, passing, and dribbling) with no, with stationary, or with moving obstacles; (2) catching the ball from an opponent or a teammate (receiving, goal keeping, and intercepting); and (3) passing the ball between two players. The first two tasks are concerned with single-agent skills,...

Communication in the autonomous and decentralized robot system ACTRESS

The new concept for an advanced robot system, ACTRESS (ACTor-based robots and equipments synthetic system), has been designed for the automation of high level tasks. The system assumes that multiple robots and equipments, which are called robotors in general, work independently or cooperatively by communicating each other, depending on the task requirements. The paper discusses the distributed robot system architecture. The basic design of protocol is shown for the communication between robotors in order to achieve various tasks. The message protocol is extended and the concept of negotiation is introduced as the framework for the cooperative work of the task allocation problem. The message protocol has been applied to object-pushing problem as an example.<<ETX>>

Motion control of multiple autonomous mobile robots handling a large object in coordination

In, this paper, we discuss a problem relating to the force/moment transformation for the handling of a large object by multiple mobile robots in coordination. We propose a control algorithm using geometrical constraints among the grasping points and the representative point of the object, which reduce the effect of noise amplified by force/moment transformation. We extend this algorithm to the decentralized control algorithm of multiple robots handling an object in coordination. The proposed control algorithm is experimentally applied to the mobile robots. Experimental results illustrate the validity of the proposed control algorithm.