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About this paper
Min Jun Kim, Fabian Beck, Christian Ott, Alin Albu-Schaeffer
Researchers from the German Aerospace Center (DLR) developed model-free friction observers for flexible joint robots with torque measurements, offering guaranteed asymptotic stability and preservation of controller passivity. The observers, validated through simulations and experiments on a 7-DOF surgical robot, effectively compensate for friction and mitigate oscillations during stiction without requiring auxiliary inputs.
Key insights
- Asymptotic stability of the overall closed-loop system and preservation of nominal controller passivity are guaranteed for regulation tasks when the proposed friction observers are integrated with sufficiently large observer gains.
- PD-type observers provide oscillation-free stiction compensation due to their inherent passivity, while PID-type observers, though capable of driving steady-state error to zero, may generate energy and cause oscillations in the stiction region.
- The control and friction observer designs exhibit a 'separation-like property,' allowing the decay rates of the nominal system and difference dynamics to be influenced largely independently by control and observer gains, respectively.
Summary by alphaXiv.
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