Abstract— Tethered Segway is a robotic platform inspired by human climbers. It is a two-wheeled mobile platform tethered to the top of a structure in order to climb steep surfaces with varying slopes, such as domes. The unstructured environment may cause uncertainties in the dynamic behavior of the robot while operating on different parts of the dome. In this paper analysis and synthesis of a robust controller for a tethered Segway is presented in order to provide desired performance in the presence of uncertainties. To design the robust controller, structured and unstructured uncertainties of the model are encapsulated into a structured singular perturbation. A linear robust controller is designed such that the robust stability of the closed loop system is preserved in the presence of modeling uncertainties. Finally, the effectiveness of the proposed controller is verified through simulation by comparing its closed loop transient response and sufficiently suitable steady-state performance to that of a previously proposed LQR controller for the robot. Keyword—Dome, Segway, Climbing Robot, Robust Control I. INTRODUCTION Research on climbing robots has become popular in the field of robotics and mechatronics due to their wide range of applications. One of these applications is the climbing dome- shaped structures for cleaning, inspection, and maintenance purposes. Traditional methods in dome cleaning, inspection, and maintenance performed by human workers have many disadvantages such as danger to the workers and limited operation time [1]. Because of dangerous condition working on steep surfaces and also high demand for autonomous systems in different operations, designing robots to work in these situations has become an interesting research field from both theoretical and practical points of view. Different robots have been developed to climb walls and steep surfaces that uses magnetic systems [2], systems with adhesive materials [3, 4], and suction and vortex [5]. Difficulties and dangers involved in human-based approaches motivate researchers to initiate University of Tehran Dome Robot (UTDR) project. The first system built was a multi-robot platform that could stably cover all parts of a dome [6]. In spite of the novel design of this multi-robot system, its complexity was an issue (Figure 1(a)). Furthermore, the top of domes is the most important area to be inspected and maintained. Thus, a robot that can safely *This project is partially supported by Hosseinie Ershad Foundation cover the top part of domes would be enough to handle the majority of tasks needed in dome inspection, cleaning, and maintenance. Consequently, to handle these issues, a single tethered robot, inspired from human dome climbers, was implemented, and successfully tested for dome inspection [1]. This single robot platform may stably cover all parts of a dome with positive slope, as the top existing in a real dome. This robot consists of a simple Segway with differential drive locomotion and a tether mechanism to control the length of the tether while operating on the dome (Figure 1(b)). It is obvious that based on the physics of Segways it cannot stably move on steep surfaces such as domes, due to lack of friction force. Thus, in the design, we added a tether mechanism to stabilize the robot on such surfaces. It should be mentioned that since Segways are very simple and novel means of transportation and due to their wide range of application in different fields such as robotics, the control of these two-wheeled mobile robots has been the center of interest within the last 15 years. Different controllers have been presented to improve the performance of these mechanisms. [7], [8]. However, to the best of our knowledge, there is no study to analyze and design the controller for a tethered Segway except in [9]. In this paper, the mathematical modeling of a tethered Segway and a simple controller design based on LQR theory and gain scheduling is presented. Simulations show that the designed linear controller, applied to this non-linear system, can provide suitable performance for predetermined slopes. Design of a Robust Controller for a Tethered Segway on Dome-Shaped Structures Mohammad H. Salehpour 1 Hamid D. Taghirad 2 and Hadi Moradi 3 1,2 Advanced Robotics and Automated Systems, Faculty of Electrical Engineering, K.N. Toosi University of Technology 3 Advance Robotics and Intelligent Systems Lab, School of Electrical Engineering, University of Tehran, Tehran, Iran 3 Intelligent Systems Research Institute, SKKU, South Korea. mail: 1 m.h.salehpour@ut.ac.ir, 2 taghirad@kntu.ac.ir , 3 moradih@ut.ac.ir Figure 1. (a) The multi-robot platform to climb the dome-shaped structures. (b) Dome Tethered Robot climbing the dome Proceedings of the 4th International Conference on Robotics and Mechatronics October 26-28, 2016, Tehran, Iran 978-1-5090-3222-8/16/$31.00 ©2016 IEEE 392