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Reactive collision avoidance for highly elastic robot systems: an artificial potential field approach

Raschel, Clara M. (2019) Reactive collision avoidance for highly elastic robot systems: an artificial potential field approach. Bachelor's. DLR-Interner Bericht. DLR-IB-RM-OP-2019-36.

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Over the past few years, robot design has evolved from rigid towards mechanically com- pliant robots [GASB + 11, DMA + 11]. Higher robustness against impacts is only one amongst many other benefits physical compliance provides [PW95, EHW + 10, WH08]. Nevertheless, collision avoidance plays an important role for a safe interaction between the elastic robot and its environment. Due to their intuitively understandable function- ality, artificial potential fields artificial potential fields (APFs) are commonly used as a collision avoidance method for rigid robots [SASO + 07, Kha85]. This thesis aims at examining the transferability of this method from rigid to highly elastic robots. For this purpose an artificial potential field is designed in joint space for DLR David, a compliantly actuated robot with nonlinear spring characteristics, devel- oped by Deutsches Zentrum für Luft- und Raumfahrt (DLR). It results in a repulsive torque and is implemented by means of Elastic Structure Preserving Impedance (ESfi) control [KLOAS18b]. A multi-body simulation shows that artificial potential fields are appropriate to avoid predefined joint angle limits. This can be considered as collision avoidance in joint space. The challenge is to design an APF such that certain demands are fulfilled. Compared to a rigid robot, a compliant robot and in this case the control method used require additional characteristics of the APF, for instance the continuity of the corresponding torque up to its second derivative. The description of the desired torque meets the re- quirements partly by a function defined piecewisely. In order to prevent oscillations, a damping torque is designed additionally. The shape of the APF including damping can be adjusted by three free parameters of these basic functions. They are tuned by dint of simulation ensuring that the remaining requirements are fulfilled. For that purpose, three situations are considered. In the first and second situation the artificial potential field including damping is applied to only one joint. For the first situation, an auto- mated parameter variation is performed. In the third situation, the artificial potential field including damping is applied to two joints. It is demonstrated that for each situation exists at least one parameter value set (PVS) that ensures that all requirements are fulfilled. Additionally, the proof of concept is supported by the fact that the majority of PVSs, tested in the automated parameter variation, ensures that all requirements are met. Furthermore, the influence of each parameter on the required maximum motor torque and other quantities is evaluated for the first situation. Another important insight is that a parameter optimization offers great potential.

Item URL in elib:https://elib.dlr.de/126730/
Document Type:Monograph (DLR-Interner Bericht, Bachelor's)
Title:Reactive collision avoidance for highly elastic robot systems: an artificial potential field approach
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Raschel, Clara M.Clara.Raschel (at) dlr.deUNSPECIFIED
Refereed publication:No
Open Access:No
In ISI Web of Science:No
Keywords:collision avoidance, elastic
Institution:Technische Universität München
Department:Fakultät für Maschinenwesen
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 Terrestrische Assistenz-Robotik
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Robotics and Mechatronics (since 2013) > Analysis and Control of Advanced Robotic Systems
Deposited By: Raschel, Clara Maria
Deposited On:11 Mar 2019 11:44
Last Modified:11 Mar 2019 11:44

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