Robotics Research Lab


the Complaint Robotic Leg


This research thread is pursuing the ambition to bring the Bio-inspired Behavior-Based Bipedal Locomotion Control (B4LC) to a physical platform. Based on the experiences gathered by the deployment of B4LC to the simulated biped, the requirements on a physical system could be well defined. In order to render natural-looking and energy-efficient bipedal walking, a main concept of B4LC is to exploit the passive dynamics of the underlying system. Thus, the system should as far as possible imitate its anthropomorphic counterpart - regarding e.g. the actuation, the kinematic layout, and the weight distribution.

As a first iteration, the Compliant Robotic Leg (CARL) has been developed. It is a planar robotic leg that features mono- as well as bi-articular actuation. As the actuation is a key component in a robotic leg, a series of linear Series Elastic Actuators - the RRLab SEAs - has been developed. The design was mainly driven by two requirements: the capability to act as a force/impedance source and a inherent tolerance against impact forces. Each RRLab SEA is encapsulated by a dedicated FPGA-based system. For more information see the dedicated page linked above.

Within the leg the SEAs are acting on the joints either by direct or by four-bar linkages. This resulted in redundant system in which all five SEAs are coupled. Motivated by the scientific evidence that human amputees are well capable of producing natural walking using a combination of a SEA and a off-the-shelve prosthetic foot, an ots product is used for the leg as well.

To enable a walking motion with a single leg a test rig incorporating a treadmill and a lifting mechanism has been developed. Especially the latter is important as it allows for the imitation of a second, virtual leg.

After validating the low-level impedance and force control even the case of the fully coupled system, a first walking motion could be generated. Therefore, a subsystem of B4LC has been ported to the leg.




Sort by: Author, Year, Title

  • FPGA-based Embedded System Designed for the Deployment in the Compliant Robotic Leg CARL.
    Steffen Schütz, Atabak Nejadfard, Max Reichardt and Karsten Berns
    Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics - Volume 2, S. 537 - 543. (2019)
  • Coordination of the Biarticular Actuators Based on Instant Power in an Explosive Jump Experiment.
    Atabak Nejadfard, Steffen Schütz, Patrick Vonwirth, Krzysztof Mianowski and Karsten Berns
    IEEE International Conference on Advanced Intelligent Mechatronics (AIM), (2018)
  • Moment Arm Analysis of the Biarticular Actuators in Compliant Robotic Leg CARL.
    Atabak Nejadfard, Steffen Schütz, Patrick Vonwirth, Krzysztof Mianowski and Berns Karsten
    Conference on Biomimetic and Biohybrid Systems, S. 348 - 360. (2018)
  • CARL – A Compliant Robotic Leg Featuring Mono- and Biarticular Actuation.
    Steffen Schütz, Atabak Nejadfard, Krzysztof Mianowski, Patrick Vonwirth and Karsten Berns
    IEEE-RAS International Conference on Humanoid Robots, S. 289 - 296. (2017)
  • Modular Control Architecture for Bipedal Walking on a Single Compliant Leg.
    Patrick Vonwirth
  • Off-Road Path Detection Using Convolutional Neural Networks.
    Carlos Saavedra


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