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Optimal Control Strategies for Maximizing the Link Velocity of Elastic Joints with Nonlinear Impedance

Özparpucu, Mehmet Can (2018) Optimal Control Strategies for Maximizing the Link Velocity of Elastic Joints with Nonlinear Impedance. Dissertation.

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Abstract

In this thesis, we investigate the problem of maximizing the link velocity of elastic joints using velocity-sourced elastic actuators. More specifically, focusing on joints with nonlinear series elastic actuators we derive motor control strategies such that the link velocity is maximized at a given time instant when the joint is initially at rest. Furthermore, we provide a physical interpretation for the derived strategies by exploiting their time optimality. The interpretation reveals the dependence of these strategies on periods of mass-spring systems which in turn explains how nonlinear torque-deflection profiles influence the maximal link velocity. In order to clearly illustrate this influence, we analyse in detail three different elastic joints with softening, linear and hardening springs. In particular, we compare their maximal link velocities as well as the corresponding control strategies and elaborate on the observed differences. Our theoretical results are experimentally validated on the DLR Floating Spring Joint where link velocities at least more than three times the maximally applied motor velocity are attained in less than a second. Several extensions are also provided which reveal the influence of damping and stiffness actuation on optimal control strategies. Finally, we give a proof of Pontryagin's Minimum Principle, the main theorem used in the thesis, by exploiting the properties of transition maps. Assuming an additional degree in the smoothness of the system dynamics and the cost functional, this leads to an extension of the principle, namely the Second Order Minimum Principle.

Item URL in elib:https://elib.dlr.de/125304/
Document Type:Thesis (Dissertation)
Title:Optimal Control Strategies for Maximizing the Link Velocity of Elastic Joints with Nonlinear Impedance
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Özparpucu, Mehmet CanMehmet.Oezparpucu (at) dlr.deUNSPECIFIED
Date:2018
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Number of Pages:231
Status:Published
Keywords:Elastic Joints, Series Elastic Actuators, Variable Stiffness Actuators, Variable Damping Actuators, Pontryagin's Minimum Principle, Higher-Order Necessary Conditions, Second Order Minimum Principle
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Technology
DLR - Research area:Raumfahrt
DLR - Program:R SY - Technik für Raumfahrtsysteme
DLR - Research theme (Project):R - Vorhaben Leichtbau-Robotik, R - Vorhaben Weiterentwicklung Robotik - Mechatronik und Dynamik
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Robotics and Mechatronics (since 2013) > Analysis and Control of Advanced Robotic Systems
Deposited By: Özparpucu, Mehmet Can
Deposited On:20 Dec 2018 10:05
Last Modified:20 Dec 2018 10:05

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