Passive Device Synchronization for the External Control of Robotic Applications in Ethernet Networks based on a Phase-Locked Loop

External control of industrial robots is widely supported to allow the integration of manipulators in complex robotic applications. Inconsistent communication schemes between a robotic and an external device may cause timing issues that lead to undesirable high joint torques wearing out the mechanics and reducing the accuracy in task space. In order to address these issues, this paper introduces a Phase-locked loop based synchronization method that allows the realization of a reference clock mirroring the timer characteristics of the interpolation cycle timer on the robot controller. Passive analysis of the data stream containing the control information yields the input frequency for the PLL. It is based on a pattern matching strategy that allows identification of relevant packets in the data stream. We introduce the relevant parameters to adapt the PLL to distinct use cases and evaluate its transient behavior during the pull-in and lock-in processes. In addition, the performance of the PLL and the synchronization method is analyzed by evaluating two experimental setups.