**5. Conclusions**

In this study, an algorithms for the time synchronization of operations performed by a heterogeneous set of robotic manipulators grouped into a production cell was proposed, validated, and implemented. The organizational structure of this robotic cell control was realized as master–slave

without an external control element. Communication in the cell was provided by a TCP/IP channel via sockets. The proposed problem solution requires minimal computational power due to an empirically oriented approach. We relied on our wide empirical knowledge and experiences in process algorithmizing, as well as on various previously implemented tasks in the field of robotics or the modeling and visualization of processes. This approach enabled the solution to be processed directly by the control unit of each participating element of the robotic cell with utilization of standard instructions in their native language. The main aim was to dynamically adapt the movement speed of slave manipulator endpoints to the master manipulator activity. Therefore, the algorithms ensure the defined milestones of the production cycle of each robotic manipulator in the cell are attained at the same time, while all operations may include various sets of different motion or manipulation instructions.

The proposed solution also includes an advanced feedforward form of operation synchronization which responds to changes in the operating cycle of the master manipulator or slave manipulators more effectively. The main difference between the two proposed algorithms is the number of unsynchronized operations performed after the change of the master or the slave behavior. In the basic algorithm case, after desynchronization, the operations of one cycle are performed unsynchronized. In contrast, the advanced algorithm ensures resynchronization after a defined number (in our case two) of asynchronously performed operations.

The application of the solution proposal is supplemented with a visualization part created using MATLAB software for technical computing. This application illustrates each intervention of the synchronization algorithms, and enables more efficient monitoring and evaluation of the multi-robotic cell activity with a focus on the synchronization process. This application part complements the validation of the functionality of the designed solution.

Finally, it can be stated that all requirements were successfully met and our solution for synchronization of the heterogeneous multi-robotic cell with emphasis on low computing power is functional and feasible.

Our goal in the future is to continue to develop this idea based on current trends in industrial automation [35]. There is a possibility in master–slave architecture to distribute more process or control information among elements, e.g., target position or movement type together with operation duration as used in our solution. Visualization, as an important aspect of the production of tomorrow, can be realized using virtual or augmented reality [35].

**Author Contributions:** Conceptualization, M.J.; formal analysis, B.J.; project administration, M.J.; software, M.J. and B.J.; supervision, M.J.; validation, M.J.; visualization, M.J.; writing—original draft, M.J. and B.J.; writing—review & editing, M.J. and B.J. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by VEGA agency, grant number 1/0232/18—"Using the methods of multi-objective optimization in production processes control".

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
