An EtherCAT-Based Real-Time Control System Architecture for Humanoid Robots

Abstract

The design of humanoid robots naturally requires the simultaneous control of a high number of joints. Moreover, the performance of the overall robot is strongly determined by the low-level control system as all high-level software e.g. for locomotion planning and control is built on top of it. In order to achieve high update rates and high bandwidth for the joint control, an advanced real-time control system architecture is required. However, outdated communication protocols with associated limits in the achievable update rates are still used in nowadays humanoid robots. Moreover, the performance of the low-level control systems is not analyzed in detail or the systems rely on specialized hardware, which lacks reliability and persistence. We present a reliable and high-performance control system architecture for humanoid robots based on the ETHERCAT technology. To the authors' knowledge this is the only system, which operates at control rates beyond 2 khz and input/output latencies below 1 ms. Furthermore, we present a novel learning-based feedforward control strategy to improve joint tracking performance. This improved joint control method and the communication system are evaluated on our humanoid robot LOLA. Our software framework is available online to allow other researchers to benefit from our experiences.

LOLA v1.1 – An Upgrade in Hardware and Software Design for Dynamic Multi-Contact Locomotion

“…We omit a detailed description of LOLA's previous hardand software setup. Instead we refer to various publications that cover its core components: [1] and [41] (electromechanical hardware), [42] (communication), [43] (computer vision), [44] (navigation), [45] (motion planning), [46] (stabilization), [47] (collision avoidance), [48] (disturbance rejection) and [49] (simulation). In this section, we will focus on the limitations of the previous setup with respect to the multi-contact scenario, i. e., the reason for the upgrade.…”

“…The motion of the arm can then either be defined in the nullspace by secondary tasks, e. g. angular momentum minimization and collision avoidance, or is made part of the task space for deliberately making contact with the environment. The resulting joint-space trajectories are sent to the robot's hardware control architecture [42] and tracked by decentralized joint position controllers.…”

Cybersecurity of Industrial Cyber-Physical Systems: A Review

“…EtherCAT has a low implementation cost and also provides high-speed real-time communication [99] with low latency [100]. Thus, it is suitable for real-time robotic applications [101,102]. EtherNet/IP.…”

A force-control scheme for biped robots to walk over uneven terrain including partial footholds

“…The distributed real-time joint control system architecture allows for the tracking of the trajectories with high local sample rates (50 ms for current, 100 ms for velocity and position). 22…”