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Introduction

In recent years, robot technology has advanced significantly. However, conventional robots are only used for industrial use in some restricted places, including factories, and intelligent robots for our general daily use have yet to be achieved. The robots that will be needed in the near future are human-friendly robots that are able to coexist with humans and support humans effectively. One of the most important aspects in the development of human-friendly robots is to realize cooperation between humans and robots.

In order for humans and robots to coexist and to perform a certain amount of cooperative work, robots and humans have to interact closely. The human-following robot in this research is a method of maintaining a certain relative positional relationship between the human and the robot. The following are examples of the sorts of services that human-following mobile robots are able to provide: The robot can carry loads that are required by people working in hospitals, airports, etc. The robot can work as an assistant for humans in various situations. Moreover, since such a robot always accompanies a human, the robot is able to easily acquire detailed information associated with target people. It has been reported that the approach of a human and a mobile robot leads to mutual interactions [1]. Several research groups have presented work on robots designed to follow humans. [2] describes a mobile robot which always faces humans and acts as an assistant robot. The mobile robot shown in [3] is a human-following robot for assisting humans. This robot is aimed at guiding a wheelchair in a hospital or a station and has the ability to estimate the position and velocity of humans and to avoid obstacles. In [4], four-legged mobile robots for following humans were considered. However, these studies only addressed the problem of how to follow humans, not how to detect the presence of humans. They developed their studies on the premise that human detection is possible.

Some technology which includes the recognition of humans, a position estimation technique for a mobile robot and humans, and a control strategy for following humans who are walking in a stable way, is required in order to realize robot human-following behavior. In order to recognize humans, most human-following robots are mounted with many sensors, such as CCD cameras, ultrasonic sensors, etc. These sensors detect the relative position from the mobile robot to the target human. The mobile robot in [1] recognizes a human's skin color using a CCD camera, and traces the target human by combining pan-tilt control of a CCD camera. In addition to the vision sensor, a voice recognition sensor is mounted in the mobile robot in [5], and is able to follow humans in an outdoor environment. An LED is installed on the human as a beacon and the position of the LED is detected by the CCD camera of the human-following robot in [6]. Most of the proposed human-following robots burden the target human with special equipment. It is very difficult for a mobile robot to continue following a human while avoiding other obstacles, without missing the target while walking at a natural speed, since the stand-alone robot has limitations in terms of recognition performance. Moreover, the control methods of a mobile robot for following a walking human have not been taken into consideration, especially in these studies. Therefore, it is unlikely that the proposed robots are actually able to follow walking humans.

In this research, an intelligent environment is used in order to solve these problems. A mobile robot cooperates with multiple intelligent sensors, which are distributed in the environment. The distributed sensors recognize the target human and the mobile robot, and give control commands to the robot. The mobile robot receives the necessary support for human-following control from the environmental sensors. We aim to achieve a human-following robot without applying any burden to the human with a mobile robot that is simple in structure. We propose intelligent space (ISpace) as an intelligent environment with many intelligent sensors, and are building an environment where humans and mobile robots can now coexist. The human-following robot of this research is one of the physical agents for human support in ISpace.


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10/06/2005