EtherCAT (Ethernet for Control Automation Technology)

A real-time Ethernet-based industrial bus from Beckhoff, commonly used to link a robot's joint drivers together.

EtherCAT is an industrial Ethernet field bus created by Germany's Beckhoff, now maintained by the EtherCAT Technology Group and incorporated into the IEC 61158 international standard. Its defining trick is “processing on the fly”: the master sends out a single frame of data that flows through each slave device in sequence, and each slave reads out the command addressed to it and writes back its own status as the frame passes through, instead of every device having to send and receive separately — which lets the communication cycle be extremely short with very little clock-synchronization jitter. In a robot, the main controller acts as the master, with each joint driver and force sensor acting as a slave chained together in a line, exchanging position and torque commands in sync at 1 kHz or higher. Compared with a CAN bus, it has far more bandwidth, which suits humanoid robots with many joints, but it needs dedicated master-side software and pricier slave chips.

ExampleAn open-source master stack like SOEM or IgH, running on a real-time-patched Linux system, controls an entire humanoid robot's joint drivers on a 1 kHz cycle.

Related

EtherCAT Master (SOEM / IgH) · Controller Area Network (CAN) · Servo Drive / Motor Driver · Real-Time Control · Cyclic Synchronous Position / Velocity / Torque Modes (CiA 402)

Sources

EtherCAT - Wikipedia