Auto inspection system using a mobile robot for detecting concrete cracks in a tunnel Seung-Nam Yu, Jae-Ho Jang, Chang-Soo Han ⁎ Department of Mechanical Engineering, Hanyang University, Seoul, Korea Accepted 8 May 2006 Abstract To assess the safety of concrete structures, cracks are periodically measured and recorded by inspectors who observe cracks with their naked eye. However, manual inspection is slow and yields subjective results. Therefore, this study proposes a system for inspecting and measuring cracks in concrete structures to provide objective crack data to be used in evaluating safety. The system consists of a mobile robot system and a crack detection system. The mobile robot system is controlled to maintain a constant distance from walls while acquiring image data with a Charged Couple Device (CCD) camera. The crack detection system extracted crack information from the acquired image using image processing. To ensure accurate crack recognition, the geometric properties and patterns of cracks in a structure were applied to the image processing routine. The proposed system was verified with laboratory and field experiments. © 2006 Elsevier B.V. All rights reserved. Keywords: Crack; Tunnel; Inspection; Image processing; Mobile robot 1. Introduction Approximately 70% of Korea consists of mountainous ter- rain necessitating the use of many tunnels for railroads and roads. A concern exists for the safety of concrete structures, such as tunnels, in traffic environments. To determine the safety of such structures, periodic inspections have been conducted using non-destructive tests. However, the slow and complicated procedures of the non-destructive tests prohibit the total re- placement of visual inspection by humans. Therefore, non-de- structive tests have been limited to precision inspections [1]. Visual inspection of concrete structures involves the measure- ment of cracks by inspectors walking along the surface of the structure while using only their naked eye. As such, the main disadvantage of visual inspection is that a rapid and complete survey cannot be ensured. To solve these problems, various methods for automatic crack inspection using image processing have been developed. These methods have been applied in practical settings including roads, bridges, fatigues, and sewer-pipes [2–6]. The particular purpose of this study is to suggest an inte- grated system of a crack detection module and mobile robot for application to the tunnel environment. Similar subjects have been studied and developed. Komatsu Engineering Corp. has developed and commercialized an image acquisition system that can acquire the images of road and tunnel linings by using a laser-scanning device. The Railway Technical Research Institute in Japan developed an image acquisition system for railway tunnel linings that uses line CCD (Charged Couple Device) cameras. Road ware Group Inc., based out of Canada, commercialized a system that acquires an image of the road at a speed of 80 km/h with a resolution of 3–4 cm. This system consists of a CCD camera, an ultrasonic sensor, and a gyro-sensor [7]. Such systems are useful for the collection of crack, leakage, scale, and spall image data; however, they do not provide auto- matic crack detection. An algorithm for crack detection and measurement must be developed to achieve a fully automatic inspection system, which is required for the rapid and objective assessment of crack data. Cameras and lasers are used widely to obtain images for the inspection of structure surfaces. The cost of the laser-scanning device is prohibitive; additionally, it has a heat problem that affects system maintenance. Both attributes make it an inefficient Automation in Construction 16 (2007) 255 – 261 www.elsevier.com/locate/autcon ⁎ Corresponding author. Tel.: +82 31 400 5247; fax: +82 31 406 6398. E-mail address: cshan@hanyang.ac.kr (C.-S. Han). 0926-5805/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2006.05.003