# Review of Fault-Tolerant Control Systems Used in Robotic Manipulators
## 6 Conclusions  
The study presented in this paper deals with FTCS in relation to manipulators. The authors of the papers discussed in this review deal with failures in both single and multiple axes. In addition, they address aspects of tolerating erroneous position sensor readings and propose algorithms to deal with interference occurring on the communication line between the controller and robot actuators. A review of the literature shows that the topic of FTCS as applied to manipulators is currently being strongly developed. The use of FTCS systems allows the optimization of production by avoiding downtime caused by individual component failures in robotic arms. Looking toward the future, several opportunities for the application of FTC in manipulators have been identified by the authors. The first  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Accuracy** & **Robustness** & **Dependence on Model or Training Data** & **Implementation Complexity** & **Computational Cost** \\ \hline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hline \end{tabular}
\end{table}
Table 1: Comparison of FTC methods used for robot control described in the cited articles.  
possibility is for the robot to react to obstacles in its working environment. However, no studies have yet been presented in which the FTC algorithm was implemented and the robot was able to avoid obstacles. Another possible future use of FTC algorithms is the cooperation between a robot and a human. However, there are no studies that indicate how the FTC algorithm would behave in such a scenario. Additionally, there are currently no studies that demonstrate how FTC algorithms could facilitate cooperation between robots such as delegating work to a more efficient robot when another robot is defective or robots communicating with each other about the detection of defects.  
Conceptualization, P.N. and A.M.; methodology, P.N. and A.M.; resources, P.N.; data curation, P.N.; writing--original draft preparation, A.M and P.N.; writing--review and editing, A.M. and P.N.; visualization, P.N.; supervision, P.N. and A.M.; joint first authorship, A.M.; project administration, A.M.; funding acquisition, A.M. All authors have read and agreed to the published version of the manuscript. This work was supported by the Polish Ministry of Science and Education grant no. 0614/SBAD/1565.  
Not applicable.  
The authors declare no conflict of interest.