Task space controller for the novel Active Ankle mechanism

Shivesh Kumar, Bertold Bongardt, Marc Simnofske, Frank Kirchner

In: International Conference on Robotics and Automation for Humanitarian Applications. International Conference on Robotics and Automation for Humanitarian Applications (RAHA-16) December 18-20 Amritapuri Kerala India Seite 22 RAHA 2016 Poster Proceedings IEEE 12/2016.


Active Ankle is a novel parallel manipulator with three degrees of freedom that operates in an almost-spherical manner. In comparison to other spherical mechanisms like Agile Eye, the mechanism offers several advantages like high stiffness and orientation accuracy, simple and robust construction, and good stress distribution. This almost spherical parallel manipulator (ASPM) is intended to be used as an active ankle joint in a full body exoskeleton designed for robot assisted rehabilitation application. Due to spatial behaviour but spherical use case of the Active Ankle, the task space control of this mechanism is an interesting and challenging problem. To solve this problem, the notion of classical Inverse Geometric Model (IGM) has been extended to Rotative Inverse Geometric Model (RIGM) - which asks for a given orientation from SO(3), instead of a pose from SE(3) and returns the required joint configuration for the three input actuators. The developed RIGM algorithm is fast and enables the task space control of this mechanism in real time with control loop frequency of up to 10 kHz. This poster will present the design of this mechanism along with its kinematic control in task space. In addition, the range of motion analysis in accordance to human ankle joint will be presented. In the future, the low level cascaded position, velocity and torque control features of the actuator will be used to develop the same features in its task space.

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Deutsches Forschungszentrum für Künstliche Intelligenz
German Research Center for Artificial Intelligence