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 However, outdated communication protocols with associated limits in the achievable update rates are still used in nowadays humanoid robots.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.
This paper presents recent and ongoing hardware and software upgrades to our humanoid robot LOLA. The purpose of these modifications is to achieve dynamic multicontact locomotion, i. e., fast bipedal walking with additional hand-environment support for increased stability and robustness against unforeseen disturbances. The upper body of LOLA has been completely redesigned with an enhanced lightweight torso frame and more robust arms with additional degrees of freedom, which extend the reachable workspace. The mechanical structure of the torso is optimized for stiffness with the help of an experimental modal analysis performed on the real hardware, while the new arm topology is the result of kinematic optimization for typical use-cases in a multi-contact setting. We also propose extensive changes to our software framework, which include a complete redesign of the onboard, real-time perception and navigation module. Although the hardware upgrade is finished and the overall software design is complete, the implementation of various modules is still work in progress.
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