Abstract—This paper presents a novel structure design for bilateral teleoperation control systems with large varying time delay in communication channel. The goal of this paper is to achieve transparency and stability of the closed-loop system. To achieve transparency, two local controllers are designed for bilateral teleoperation. One local controller is responsible for tracking the master commands and the other local controller is in charge of force tracking as well as guaranteeing the stability of the closed-loop system in presence of varying time delay in communication channel. A neural network estimates this time delay. In addition, the stability of the closed-loop system, despite estimation error in neural network, will be shown by some analytical work. The advantages of the proposed method are stability, simple design of the local controllers, and transparency of the system. As a result, the designer has the flexibility to choose classical methods as well as intelligent controllers for local controllers. Simulation results show very good performance of the proposed method. Furthermore, the stability of teleoperation system can be checked graphically with bode method. Hence, the controller design would be simple. I. INTRODUCTION eleoperation robots (known as "telerobotics") are used for the carrying out complex tasks in hazardous and unknown (or partially known) environments such as radio active areas in nuclear power stations [1]. Telerobotics take advantage of human remote control with the autonomy of industrial robots. The main components of a telerobotic system are: 1) a set of two robots, referred to as the "local master robot" (or "master" for short) and the "remotely located slave robot" (or "slave" for short), 2) communication channel, 3) human operator, and 4) task environment. The master robot is directly driven by the human operator in its own local environment, whereas the slave robot is located in the remote environment, ready to follow human operator commands by moving the master. In bilateral control method, the remote environment gives some necessary information through the feedback loop to the local site as well. Additionally, a telerobotic system is said to be bilateral if the information signal flows in both directions between master and slave [2]. In this case, the performance of the telerobotic system is enhanced since the human operator receives information from the contact force on the slave side. A traditional way of providing this information, which is called force-reflecting control in teleoperation A. Alfi and M. Farrokhi are with the Faculty of Electrical Engineering, Iran University of Science and Technology, Tehran, Iran. (Tehran 16846-13114, e-mails: a_alfi@iust.ac.ir, farrokhi@iust.ac.ir). M. Farrokhi is also with the Center of Excellence for Power System Automation and Operation, Iran University of Science and Technology, Tehran, Iran. systems, is to reflect the contact force to the master robot. In this way, the overall performance can be improved, even better than visual and/or audio information [3]. Considering the time delay in communication channels and the uncertainty from the task environment, there are two major issues in telerobotic systems: 1) stability robustness and 2) transparency performance. The communication channel plays an important role when the distance between the master and slave robot is too long. In these cases, a time delay in communication channel appears in information transmission that can not be ignored. In this case, due to the existence of time delay in the information transmission between the local and the remote site, the performance of the bilateral telerobotic systems will be degraded and can even lead to instability of the remotely- controlled manipulator [4]. To overcome the time delay problem, different teleoperation control systems have been proposed in literature such as the passivity theory [5], compliance control [6], wave variables [7], adaptive control [8] and robust control [9]. Transparency is also an important issue in telerobotic systems. If the human operator feels that he is directly interacting with the task, the telerobotic systems is called transparent [10]. Several papers have considered transparency of teleoperation system [11], [12]. But, they could make the system transparent only when the communication time delay was neglected. In practice, due to the existing delays in the communication channel and uncertainty in task environment, transparency and stability are significantly compromised [13]. In this paper, time- varying delay in communication channel is taken into account to design a bilateral telerobotic system. Furthermore, the ideal responses (i.e. the transparency) for the telerobotic system with time-varying delay in communication channel are definite as follows [10]: - The force that the human operator applies to the master robot is equal to the force reflected from the environment in the steady state. This can help operators to realize force sensation. - The master velocity/position is equal to the slave velocity/position in the steady state. The rest of this paper is organized as follows. Section 2 briefly describes general definitions of teleoperation systems. In section 3 and 4, the proposed control method in this paper is discussed. In section 5, estimation of time delay in communication channel is described. Section 6 analyses the stability of the proposed structure. Section 7 shows the simulation results. And finally, section 8 draws conclusions and gives some suggestions for the future work. Bilateral Transparent Teleoperation with Long Time-Varying Delay: New Control Design and Stability Analysis Alireza Alfi, Mohammad Farrokhi T