A Detecting Method for Small Road Surface Irregularities on the Sidewalk Using LRF Light-Receiving Intensity Information

Walkways are basically flat because they are built to be easy for pedestrians to walk on, but there are small uneven surfaces such as Braille blocks for the visually impaired, drainage gutter grating, etc. Ordinary pedestrians are not affected by these small irregularities when walking, but in the case of wheeled mobile robots, these small irregularities have a negative impact on their running. In particular, small robots that are designed to operate in spaces where humans coexist tend to have small wheel diameters and often use casters for the follow wheels. Therefore, mobile robots are required to detect those small uneven surfaces and design the robot's path appropriately. However, these small uneven surfaces are difficult to detect with the accuracy of laser range-finders commonly used in outdoor mobile robots. Therefore, this paper proposes a method to estimate these small uneven surfaces using the intensity information of reflected light from a laser range-finder (LRF). Furthermore, we propose a method for designing a robot path that is less affected by the estimated uneven surfaces using the proposed method, and confirm the effectiveness of the method through experiments on our prototype robot.

I. Introduction

In recent years, autonomous mobile robots have been used in real-world environments to replace guidance, transportation, and other tasks to reduce the number of personnel. Wheeled autonomous robots are expected to be used in artificial environments with few uneven surfaces, such as sidewalks and parks. However, even on sidewalks, there are uneven surfaces such as Braille blocks and gutter grating. When the robot traverses such uneven surfaces, depending on the uneven surface and the direction in which the robot travels, the swaying of the robot's body may increase, causing distortion of the path and errors in wheel odometry. Therefore, the robot is required to detect and estimate the shape of the uneven surface, and to pass over the uneven surface appropriately so that the sway of the vehicle body is minimized.