The Development of a Robotic System for Maintenance and Inspection of Power Lines * Jos´ e Rocha (1) Jo˜aoSequeira (2) jrocha@est.ips.pt jseq@isr.ist.utl.pt (1) Escola Superior de Tecnologia de Set´ ubal/Instituto Polit´ ecnico de Set´ ubal Rua Vale de Chaves, Estefanilha, 2910-761 Set´ ubal, Portugal (2) Instituto Superior T´ ecnico/Institute for Systems and Robotics, Torre Norte, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal Abstract This paper describes preliminary studies on a pro- totype robot for the inspection/maintenance of elec- trical power lines. Faulty insulators or abnormal ob- jects can be detected before causing a failure in the distribution of electrical energy. The robot uses a statically stable variation of the brachistochrone motion to move along the power lines and overcome the standard obstacles present in the lines. The paper presents the kinematics and prelim- inary simulation results on the dynamics and control of the robot. 1 Introduction This paper describes a robot for the inspection and maintenance of electrical power lines. The robot moves using the cabbage worm gait for free motion and a statically stable variation of the brachistochrone motion (see [5] for dynamically stable brachistochrone motion) for obstacle transposition. Due to the exposure to different weather factors (e.g., sun, rain, wind and snow), materials loose elec- trical properties. Besides the natural aging factors, most components are not submitted to severe quality controls during manufacturing processes, thus being possible that some are faulty. Therefore, it is necess- ary from time to time, to carry out inspections, aiming at detecting any weakness in such electrical materials that may compromise the energy distribution. Among the most common problems, requiring pe- riodical inspections to the lines, there are, bad con- tacts near support points at electrical towers, often named hot spots, caused by an increase in electrical resistance after a thermic growth, abnormal objects near the electrical structure, e.g., tree branches or logs of wood, or directly over the lines, conductors aging, glass insulator chains aging or with broken elements, * This work was partially supported by the FCT Programa Operacional Sociedade de Informa¸ c˜ ao (POSI) in the frame of QCA III. damages caused by storms, e.g., lightning strikes, ex- cavation activities nearby the towers supporting the lines, and the aging of the metallic parts in the sup- porting towers leading to abnormal inclination and the consequent stress of the lines. Together with the economical motivation, the re- duction in the human risks associated with inspection and maintenance operations in power lines (such as the exposure to intense eletromagnetic fields) is also a main motivation vector to the development of the system proposed in this paper. The paper is organized as follows. Section 2 pro- vides a brief overview to some of the systems cur- rently being used to inspect/maintain electric power lines. Section 3 details the main kinematics aspects of the proposed robot. The main aspects on the dy- namics and control are focused in Section 4. Section 5 presents preliminary simulation results. The con- clusions are presented in Section 6, along with the directions for future work. 2 State of the art In this section three different approaches currently used for inspection/maintenance operations over elec- tric power lines are described. The first one, installs fiber optic cables over power lines. The second uses a standard helicopter to move along the lines and de- tect malfunctions. The last approach uses a computer vision guided helicopter model for general purpose autonomous missions, including inspection to power lines. 2.1 The SkyWrap This device was developed during the eighties by FOCAS, a British company operating in the telecom- munications field, to navigate over power lines. The SkyWrap [3] was designed to helically wrap a fiber op- tic cable over the earth-wire or phase conductors up to 150KV of an overhead transmission line. The device is remotely controlled by radio fre- quency. The operator is able to select among 11 mo- 1