T he system proposed in this work is the Alicia 3 climbing robot. The aim of this project is to develop a system that can be adopted in a variety of applications, such as mainte- nance, building, inspection, and safety, in the process and con- struction industries. Generally speaking, the system could be adopted in many places where direct access by a human opera- tor is very expensive because of the need for scaffolding or very dangerous due to the presence of a hostile environment. Typical operating environ- ments are the external or internal surfaces of aboveground or underground petrochemical stor- age tanks and concrete walls, like those of dams and bridges pillars. All these structures have a very high economic value, and it is very important to perform periodic inspections for maintenance purposes, as standardized by the respective con- trolling bodies. Among the most important factors to be inspected are the rate of corrosion, the potential risk of air or water pollution, and the detection of leaks, cracks, crumbling parts, or rust on exposed concrete reinforcement, and so on. While these kinds of inspection are very useful to prevent ecological disasters and to reduce the risk for the individuals working or living around the plant or structure, they are very expensive because scaffolding is often required. Moreover, for safety reasons, plant operations must be stopped and special pre- cautions must be taken when human operators are conducting inspections. One possible solution is to carry out automatic nondestruc- tive inspection (NDI) on the target surface only [1], [2]. Then, when repairs are needed, a traditional method of access- ing the plant is applied. The most common NDI uses small sensors like eddy current probes, ultrasonic heads, and charge- coupled device (CCD) cameras. For these operations, a small automatic vector (climbing robot) able to climb verti- cal walls can be very useful for carrying sensors to the desired position on the target wall. In Figure 1(a)–(c), typical operating environments for climbing robots are shown. An in-depth description of this system will be the aim of the following sections. Several other systems for similar targets have been devel- oped by our group in the past [3]–[6]. Devices based on the principle of sliding suction cups are currently under con- struction by other universities and research centers. One of BY DOMENICO LONGO AND GIOVANNI MUSCATO 1070-9932/06/$20.00©2006 IEEE IEEE Robotics & Automation Magazine MARCH 2006 42 © ARTVILLE & DIGITAL VISION, LTD. The Alicia 3 Climbing Robot A Three-Module Robot for Automatic Wall Inspection