## 7 Conclusions  
This paper presented a methodology for estimating the reaction force for the base, 2\({}^{\text{nd}}\) link, and end effector of a 3 DOF master and slave manipulator system. The advantageous feature of the proposed methodology is that it does not utilize any force sensors. In general, SMCSPO is implemented, whereby SMC-based tele-operated bilateral control and visual feedback generate the trajectory for the slave system with a minimum of tracking error. In addition, the tele-operated bilateral control strategy also estimates the reaction force of the master manipulator, which is used by the operator to control the master device.  
The experimental results presented in this study indicate that the slave manipulator successfully tracked the master device with negligible error. It was also observed based on the results that the operator was able to feel the reaction force as the slave device touched/interacted with the environment, without the use of any feedback from force sensors. The maximum trajectories, error and perturbation between the master and the slave for the end effector, 2\({}^{\text{nd}}\) link and base are summarized in Table 4.  
In the future, issues like latency and jitter in the global area network (GAN) should be addressed in order to enhance the tele-operation range. The area of application for this study was the dismantling of nuclear power plants, but the proposed method is not limited to this, as several other applications require master/slave systems in which human access is limited. These applications include hazardous areas  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**S. No**} & \multirow{2}{*}{**Links**} & \multirow{2}{*}{\begin{tabular}{c} **Maximum** \\ **Error (Degree)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Maximum** \\ **Trajectory** \\ **(Degree)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Maximum** \\ **Perturbation of** \\ **Master (N*m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Maximum** \\ **Perturbation** \\ **of Slave (N*m)** \\ \end{tabular} } \\ \hline
1 & End Effector & 0.94 & 88.96 & 90.87 & 1635.72 \\
2 & 2\({}^{\text{nd}}\) link & 0.55 & 60.13 & 45.69 & 543.9 \\
3 & Base & 0.859 & 100.38 & 67.89 & 1018.26 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Maximum trajectories, error and perturbation between master and slave.  
Figure 23: Master/slave trajectories for the end effector and the 2\({}^{\text{nd}}\) link.  
with high levels of radiation from materials with long half-lives. Examples of this include transportation of uranium in its active form, the disposal of explosive material, handling of explosive/radioactive material, remote cutting for nuclear plant dismantling, etc.  
Conceptualization, K.D.K. and M.C.L.; Formal analysis, K.D.K. and H.K.; Funding acquisition, M.C.L.; Investigation, J.W.; Methodology, K.D.K. and S.J.A.; Project administration, M.C.L.; Software, K.D.K.; Supervision, M.C.L.; Validation, S.J.A.; Writing--original draft, K.D.K. and J.W.; Writing--review & editing, H.K. and M.C.L.  
This research was funded and conducted under \"the Competency Development Program for Industry Specialists\" of the Korean Ministry of Trade, Industry and Energy (MOTIE), operated by Korea Institute for Advancement of Technology (KIAT). (No. P0008473, the development of high skilled and innovative manpower to lead the Innovation based on Robot). This research was supported by the Technology Innovation Program (10073147, Development of Robot Manipulation Technology by Using Artificial Intelligence) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).  
The authors declare no conflicts of interest.