Tham khảo tài liệu 'mobile robots book 2011 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 66 Mobile Robots - State of the Art in Land Sea Air and Collaborative Missions which have more than one conductor per phase there are even more obstacles such as spacers and spacer dampers Figure 1 1. The robot travels suspended from the conductor and has to cross obstacles along the power line that requires complex robotic mechanisms including conductor grasping systems and robot driving mechanisms. Moreover an obstacle detection and recognition system robot control system communication inspection platform equipped with necessary sensors and measurement devices power supply and electromagnetic shielding have to be considered in robot mechanism design and construction. Fig. 1. Different obstacles on power line conductors a suspension insulator b strain insulator c damper d spacer spacer damper e aircraft warning sphere Katrasnik et al. 2008 . Cable-climbing mechanisms designed over the past 20 years One of the first cable-climbing mechanisms presented in Aoshima et al. 1989 . The proposed mechanism which was designed for telephone lines inspection compared to its previous works is able to transfer to branch wires and thus provides more flexibility in cable-climbing. The robot structure as shown in Figure 2 consists of a multi-unit of six identical modules with three degrees of freedom longitudinal movement on the cable horizontal rotation about robot s longitudinal axis parallel to the power line and vertical elongation of robot s arms. Fig. 2. Proposed cable-climbing mechanism in Aoshima et. al. 1989 . 1 All of the figures and tables used in this literature survey have been taken from the original works presented by their authors. Cable-Climbing Robots for Power Transmission Lines Inspection 67 Using different configuration of these six units the robot will be able to adapt itself to different geometrical environments and avoid obstacles with different shapes and sizes transfer to a branch wire and even transfer to a parallel line. As an example to show the .