Hiroyuki Takai

Sensor-based path planning and intelligent steering control of nonholonomic mobile robots

This paper presents a control scheme for autonomous navigation of intelligent mobile robots under unstructured environments. Based on environmental information, which is acquired using external sensors or given by the upper level, the control scheme performs autonomous navigation composed of sensor-based path planning and tracking control in real time. First, using a simple genetic algorithm, the path planning module generates an obstacle-free path as a sequence of control vectors of orientation, considering kinematic constraints in steering control of wheeled mobile robots. Then, the tracking control module calculates the references for motion control of the mobile robot using a sensor fusion neural network. Simulation experiments of path planning under unstructured environments with several obstacles are illustrated. An experimental procedure for teaching the sensor fusion network is introduced, and basic characteristics of the internal and external sensors during straight-line and circular movements on the floor with black-striped markers are measured using our experimental small robot to show the feasibility of the proposed control scheme.

A Space-Division Optical Wireless Communication System for Fully Distributed Multiple Autonomous Mobile Robots

Abstract This paper describes the realization of a space-division optical communication system specifically designed to perform local inter-robot communication in fully distributed multiple autonomous mobile robot systems. Requirements for autonomy and robustness of communication functions among moving robots are discussed. The communication system uses a set of modules, or transceivers, which is arranged in the circumference of the robot body. Each module comprises an IR detector/receiver and an IR transmitter. Each IR module detects the angle of incidence of infrared rays. Space-division communication networks can be created, because a robot can commumcate with more than one robot through different modules at the same time. Hardware realization and performance measurements are illustrated to reveal the effectiveness of the developed system.

Obstacle arrangement detection using multichannel ultrasonic sonar for indoor mobile robots

In the last few years, mobile robot systems that perform complicated tasks have been studied. To work in complicated environments, the robot has to avoid collisions with obstacles. Therefore the robot needs to detect the arrangement of any surrounding obstacles. We considered a simple distance estimation algorithm using ultrasonic sonar. Since the algorithm was able to estimate distance accurately, we also attempted stereo reception using two ultrasonic microphones. The stereo reception sonar was able to detect the direction of obstacles. In order to make precise measurements, we attempted to use the signal coherence of ultrasonic waves. In order to install a small system into mobile robots and to detect any surrounding obstacles, we designed a multichannel sonar signal processing system using a high-performance embedded microcontroller. This article describes our ideas for the distance estimation algorithm for ultrasonic sonar, and a design for a signal processing system using a high-performance microcontroller.

A simple obstacle arrangement detection algorithm for indoor mobile robots

Over the last several years, indoor mobile robot systems not only for industrial use but also for home or office use have been developed. When the robot works in a narrow workspace, it often collides with obstacles. We thought that one of the causes of the collisions was an arrangement of circumambient obstacles. The robot often works in an unknown workspace where there are no maps prepared previously. We propose a simple obstacle arrangement detection algorithm for the workspace map creation. The algorithm uses ultrasonic stereo sonar and a single image sensor. The stereo sonar can measure by the distance detection accuracy that is approximately 13 mm of errors out of 1300 mm and the angular detection accuracy that is approximately a few degrees of errors. The image processing algorithm can measure angles of corners and/or edges of obstacles using a laser line generator as an extra light source.

Development of a space-division infrared receiver for fully distributed inter-robot communication networks

This paper describes the development of an infrared wireless communication system for multiple mobile robots. The communication system uses a set of infrared transceivers, which is arranged on the circumference of the robot body. Infrared wireless communication suffers from hardly any interference, when the infrared receiver faces a different direction from transmission signals. Therefore, the communication system can communicate at the same time in parallel with different partners in different directions. Each robot relays communication, and a space-division communication network can be created. Hardware realization and performance measurements are illustrated to reveal the effectiveness of the developed system.

A Geometric Arbiter Selection Algorithm on Infrared Wireless Inter-robot Communication

Recently, robots that can perform group operations have been developed. A space-division infrared wireless communication system has been designed, that is capable of detecting and locating other robots even if they are independently mobile. In addition, this communication system decides an arbiter that is a local temporary controller, taking advantage of the geometrical nature of the triangle that is formed by communication links between communicating partners. A geometric arbiter selection algorithm was proposed and the performance of the infrared receiver was tested. The result of the experiments agreed with all expectations of the space-division wireless communication system.

A communication protocol based on IR-space division transceivers for mobile robots

In this article, we propose MAC protocols based on our infrared-space division transceiver (IR-SDT) for mobile robots. The IR-SDT has eight communication modules, so it can communicate with a maximum of eight other nodes simultaneously. The number of parallel multiple accesses will be improved by using this transceiver and its specialized protocol. In addition, we consider situations in which a packet collision occurs, and propose a protocol that resolves communication conflicts using the signal collision-detection function of IR-SDT. Finally, we consider the performance of these protocols, and discuss the influence of signal collision-detection accuracy.

Workspace mapping based on multisensor information fusion using heterogeneous onboard sensors

In recent years, multiple robot systems that perform team operations have been developed. These robot systems are expected to execute complicated tasks smoothly in a given congested workspace. In this article, we propose a workspace mapping algorithm using ultrasonic stereo sonar and an image sensor in order to operate the mobile robots among obstacles. This workspace mapping algorithm involves two steps: (1) the position detection of obstacles using ultrasonic stereo sonar, and (2) the shape detection of obstacles using an image sensor. While each robot moves around in the given workspace, the two steps of the mapping algorithm are repeated and sensor data are collected. The robot measures the distance and the direction of obstacles using ultrasonic stereo sonar. The shape of obstacles is also captured using an onboard image sensor. A workspace map is created based on the sensor data accumulated from the proposed method, and successful results are also obtained through experiments.

A SPACE-DIVISION WIRELESS COMMUNICATION SYSTEM FOR ADHOC NETWORKING AND COOPERATIVE LOCALIZATION OF MULTIPLE MOBILE ROBOTS

Abstract This paper presents a space-division wireless communication system for nonhierarchical, cooperative control of multiple mobile robots. The proposed communication system has the following features: 1) it has a set of infrared transceivers arranged on the circumference of the robot body to communicate in all directions; 2) it can maintain communication links by exchanging transceivers when either of the robots runs and/or rotates. An arbiter is introduced to reduce communication interference when two or more robots are in the same communication area. Adhoc communication networks are constructed based on the selection of arbiters. As an example of distributed sensing and cooperation using the system, cooperative localization of communicating mobile robots is also described. Some performance measurements using an experimental system have been carried out to show the viability of the proposed approach.

CONSTRUCTION OF INFRARED WIRELESS INTER-ROBOT COMMUNICATION NETWORKS FOR DISTRIBUTED SENSING AND COOPERATION OF MULTIPLE AUTONOMOUS MOBILE ROBOTS

Abstract This paper presents a space-division optical wireless inter-robot communication system for multiple mobile robots. Infrared optical wireless communication is suitable for the mobile robots, because of its low level of interference in multiple directions. However, optical wireless communication is lost when either of the robots runs and/or rotates due to the nature of infrared rays. The proposed communication system has a set of infrared transceivers, which face all directions. The system can maintain circuit connections by exchanging transceivers. Furthermore it can communicate at the same time with more than one robot in different positions by using different transceivers. Spontaneous construction of inter-robot communication networks based on the selection of arbiters is described. As an example of local sensing capabilities of the system, mutual localization using transceivers on three communicating robots is also described. Hardware realization and performance measurements are illustrated to reveal the effectiveness of the proposed system.