University of Twente Student Theses
Passive and Stable Impedance Reduction of Hybrid and Flexible Link Serial Robots Using Position, Force, and Acceleration Feedback
Overbeek, A.H.G. (2021) Passive and Stable Impedance Reduction of Hybrid and Flexible Link Serial Robots Using Position, Force, and Acceleration Feedback.
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| Abstract: | Apparent impedance reduction allows heavy and damped robots to feel lightweight to human users. Doing so passively yields unconditional human-robot stability and thus safety. This fulfills a baseline requirement of rehabilitation robotics: the ability to train unobstructed by robot dynamics, only experiencing therapy dynamics. This work studies and compares two derogatory effects on the safe impedance reduction of serial robots: the discrete-time controller and link flexibility. A simple impedance controller is considered that linearly adds motor position, interaction force, end effector acceleration and their derivatives. Novel passivity conditions reveal that the hybrid system allows very little acceleration and no force feedback, resulting in barely any passive inertia reduction. Underdamped link flexibility is separately studied and is reaffirmed to be fundamentally limited to passively masking actuator inertia. Maximum passive impedance reductions for each case are compared, where both allow complete damping reduction. However, passivity must be forfeit for many applications that require inertia reduction. This theory is applied in a case study to the Gable Core rehabilitation platform. Modern optimal design of a stabilizing, rather than passivating, controller minimizes noise while reducing impedance. The two derogatory system models are compared to the ideal and the mixed system, consisting of both hybrid and flexible dynamics. This reveals that the hybrid model is less restrictive than the flexible model for stable impedance reduction, but more restrictive for passive impedance reduction. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 52 mechanical engineering |
| Programme: | Systems and Control MSc (60359) |
| Link to this item: | https://purl.utwente.nl/essays/86316 |
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