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An Overview of Null Space Projections for Redundant, Torque Controlled Robots

Dietrich, Alexander and Ott, Christian and Albu-Schäffer, Alin (2015) An Overview of Null Space Projections for Redundant, Torque Controlled Robots. International Journal of Robotics Research, 34 (11), pp. 1385-1400. SAGE Publications. DOI: 10.1177/0278364914566516 ISSN 0278-3649

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One step on the way to approach human performance in robotics is to provide joint torque sensing and control for better interaction capabilities with the environment, and a large number of actuated degrees of freedom (DOF) for improved versatility. However, the increasing complexity also raises the question of how to resolve the kinematic redundancy which is a direct consequence of the large number of DOF. Here we give an overview of the most practical and frequently used torque control solutions based on null space projections. Two fundamental structures of task hierarchies are reviewed and compared, namely the successive and the augmented method. Then the projector itself is investigated in terms of its consistency. We analyze static, dynamic, and the new concept of stiffness consistency. In the latter case, stiffness information is used in the pseudoinversion instead of the inertia matrix. In terms of dynamic consistency, we generalize the weighting matrix from the classical operational space approach and show that an infinite number of weighting matrices exist to obtain dynamic consistency. In this context we also analyze another dynamically consistent null space projector with slightly different structure and properties. The redundancy resolutions are finally compared in several simulations and experiments. A thorough discussion of the theoretical and empirical results completes this survey.

Item URL in elib:https://elib.dlr.de/101443/
Document Type:Article
Title:An Overview of Null Space Projections for Redundant, Torque Controlled Robots
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Dietrich, Alexanderalexander.dietrich (at) dlr.deUNSPECIFIED
Ott, ChristianChristian.Ott (at) dlr.deUNSPECIFIED
Albu-Schäffer, AlinAlin.Albu-Schaeffer (at) DLR.deUNSPECIFIED
Date:September 2015
Journal or Publication Title:International Journal of Robotics Research
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1177/0278364914566516
Page Range:pp. 1385-1400
Publisher:SAGE Publications
Keywords:Robotics, Redundancy Resolution, Torque Control, Null Space Projection, Redundant Robots
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: Dietrich, Dr.-Ing. Alexander
Deposited On:04 Jan 2016 11:11
Last Modified:06 Sep 2019 15:18

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