## 1 Introduction
They discussed two difficult cases: one for fixed time delays, and the other for variable time delays. For the first case, a PD-like controller was chosen, while for the second case, a P-like controller was adopted. [PERSON] et al. [30] presented a study involving a bilateral tele-operative task for a master/slave device and one virtual device. The localization and velocity control were proposed for the tele-operative task, with a specially designed visual interface for ease of use. The stability of the design was analyzed using the conventional Lyapunov strategy. [PERSON] et al. [31] discussed the shared-tele-operative robotic system with un-symmetric variable delays. They implemented a robust control scheme based on state and impedance reflection. Additionally, they proposed an adaptive approach for determining interaction properties between the operator and the master device, and between the slave system and the real environment. Subsequently, the estimated delayed interaction properties were reflected back to the master/slave systems to overlap with the estimated impedance interactions properties between operator and environment. [PERSON] et al. [32] presented a novel scheme for improving control of tele-operated devices by implementing prescribed performance controls and a wave-based time-domain passivity methodology. The extended prescribed performance control ensures synchronization of velocity, force and position. A standard Lyapunov approach was discussed for studying stability and performance. The results showed that the proposed control not only accurately tracked the velocity, position and force profiles, but also controlled the system's passivity. [PERSON] et al. [33] discussed the estimation of the external forces acting on the master/slave devices. The main advantage of this scheme is the elimination of the force sensor signal. This results in low cost for practical applications. The stability of the proposed scheme was also discussed using the conventional Lyapunov scheme. The feedback signal based on touch is at the heart of bilateral tele-operative tasks. The master manipulator is operated by human being who depends on the actuator's signal, whereas the slave manipulator is installed in a remote environment and run through the hydraulic actuator's signal. [PERSON] et al. [34] proposed the idea of utilizing a combination of different techniques to attain the best tracking control and stable results. They proposed the use of oblique-coordinate control to de-couple the force and position controllers. Furthermore, they linearized the hydraulic actuator's signal. [PERSON] et al. [35] proposed the hybrid-force and position control schemes for applying a fixed force to heart tissue with synchronization along the desired trajectory. Input-constrained predictive tracking control was presented utilizing a non-linear model. The performance results show that the catheter generated a force with root-mean-square-estimation (RMSE) of 4.9 mm and localization tracking with RMSE of 0.89 mm. [PERSON] et al. [36] discussed the trajectory control for underwater manipulator systems by applying a discrete time-delay estimation methodology. [PERSON] et al. [37] investigated the adaptive control law to achieve accurate tracking of the desired position. They also considered the uncertainties and non-linearities, as well as the dead-zones. Their proposed algorithm robustly estimated manipulator dynamics based on non-linear parameters, which were later fed into the controller. Their results provide evidence for the fact that the proposed controller scheme performs well, even when dynamic and dead-zone uncertainties appear simultaneously. Several studies in the field of bilateral control have investigated force sensors for determining external force. However, it has been shown in the literature that in radioactive dismantling tasks, these sensors have major drawbacks. A manipulator system equipped with force sensors performs as a 2 mass resonator. This reduces the sense of high frequency force [38].