Ethernet POWERLINK for Reconfigurable Robotics: Teaching an Old Fieldbus New Tricks

Abstract

The concept of reconfigurable robots proposes the interconnection of dozens or even hundreds of modules, which poses a significant challenge to the communication system, which must be real-time, fast, small, inexpensive to implement, energy-efficient, and flexible in terms of allowed topologies. This article shows that legacy fieldbus solutions can be extended for applications that require additional flexibility, such as reconfigurable robotics. The example proposed in this article is based on Ethernet POWERLINK and extends the design with minimal additional hardware and communication effort. This article proposes a new field-programmable gate array (FPGA)-based smart hub that brings a new set of capabilities: seamless support for multiple loops in the topology, massive redundancy, automatic node numbering for any topology, and automatic topology recovery. The presented design has a compact footprint of 917 logical element (LE) for a 16-port hub, making it suitable for implementation with low-cost, low-power FPGAs, such as the Intel MAX10 series. Moreover, due to its low logical complexity, the power consumption of the intellectual property core implemented with MAX10 will be only 61.65 mW. The experimental studies, performed both using cycle-accurate simulation and real prototypes, confirmed that the Ethernet POWERLINK network created with smart hubs operates in topologies with multiple redundant lines and loops. The controlled nodes remained in operation mode even during rewiring “on the fly.” It was also clearly demonstrated that the PollRequest–PollResponse interval jitter of FPGA-based controlled nodes is only $\pm 40$ ns, which makes it possible to determine neighboring nodes and automatically recover the network topology using the method proposed in this article.