Importance and Applications of Robotic and Autonomous Systems (RAS) in Railway Maintenance Sector: A Review <s> RAS in Power Transmission Line Maintenance <s> For the Netherlands railway company a system for inspection of the degree of wear of the contact wires is being developed. With an active sensor the reflective under-surface of the overhead wire is illuminated with a laserbeam and reflected radiation is detected by fast CCD detectors. With the sensor at a train speed of 90 km/hr. every cm of max. 4 overhead wires will be inspected, determining the wire thickness and the appearance of holes caused by local sparks. For illumination and detection a special optical system has been developed. From the railway inspection waggon measurements have been performed with a prototype system, demonstrating the feasibility of the measuring principe. <s> BIB001 </s> Importance and Applications of Robotic and Autonomous Systems (RAS) in Railway Maintenance Sector: A Review <s> RAS in Power Transmission Line Maintenance <s> The development of a mobile robot that can navigate overhead power transmission lines completely unattended by a human operator is described. Its ultimate purpose is to automate the inspection of power transmission line equipment. The authors have assembled a full-scale functional model of such a mobile robot. Mechanical function testing of the robot has been performed, and results are reported. The robot navigates a ground wire that is located above the actual power transmission lines. It can maneuver over obstructions created by subsidiary equipment on the ground wire such as weights that prevent the wire from twisting and swinging. It is also equipped with an arc-shaped arm that acts as a guide rail and allows it to negotiate transmission towers. When the robot encounters a tower, it unfolds the arc-shaped arm and attaches it to the ground wire on opposite sides of the tower. It then travels along the arm to pass around to the other side of the tower. Once it is firmly affixed to the wire on the other side of the tower it detaches the arm and folds it up until it is needed again. > <s> BIB002
A power transmission wire inspection system was developed for Netherlands railway company, which perceives the thickness of wires and detects any appearance of holes that are caused by local sparks BIB001 . In this system, the under surface of the overhead wire is illuminated with a laser beam and reflected radiation is then detected by a fast CCD detector. The processing algorithm determines the thickness of wire and any of occurrence of holes. According to Smorenburg and Valkenburg, the system is capable of mounting on a train, which travels 90km/h and inspects four wires simultaneously for every centimetre. Hence, the system is able to efficiently execute inspection process without disrupting normal services BIB001 . In addition, Sawada et al. have developed a fully autonomous robot to inspect power transmission lines-which is capable of negotiating obstacles, such as towers, ground wires, etc. The robot consists of curved arm-which helps to negotiate obstacles, a vehicle assembly that carries the inspection unit, and a balancer with a built-in controller. The robot measures eddy current and the processing algorithm determines the condition of the power transmission wire based on the input data BIB002 . Besides, Peungsungwal et al. have developed an autonomous power transmission line inspection robots to examine the power cables and insulators  . The robot uses image-processing techniques, such as edge detection and pattern recognition algorithms to detect insulators. The most interesting feature of this robot is that it does not depend on a battery pack or any other sources of fuel, but harvest the required energy from power line through induction  .