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Combined structural and dimensional synthesis of task-specific parallel-robot manipulators: functional redundancy and design optimization

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

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OriginalspracheEnglisch
QualifikationDoktor der Ingenieurwissenschaften
Gradverleihende Hochschule
Betreut von
  • Tobias Ortmaier, Betreuer*in
Datum der Verleihung des Grades21 März 2025
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 7 Mai 2025

Abstract

Parallelkinematische Maschinen bzw. Roboter konnten sich bisher nur in wenigen Anwendungen etablieren, in denen sie durch große Traglast, Steifigkeit oder Dynamik bei ihrem prinzipbedingt beschränktem Arbeitsraum-zu-Bauraum-Verhältnis gegenüber Seriellkinematiken im Vorteil sind. Es gibt jedoch noch einige Anwendungen, die bisher unzureichend automatisiert wurden und in denen Parallelkinematiken vorteilhaft sein könnten, wie bspw. die Landwirtschaft. Da ihre Leistung wesentlich stärker von der komplexen Dimensionierung abhängt, ist ein automatisiertes Auslegungswerkzeug notwendig, um Parallelkinematiken für Anwendungen optimal anzupassen. Der genutzte Ansatz der kombinierten Struktur- und Maßsynthese betrachtet dabei alle prinzipiell möglichen kinematischen Strukturen und führt für jede eine eigene Dimensionierung durch, um die beste aufgabenangepasste Struktur zu erhalten. Die Struktursynthese wurde mittels Permutation der diskreten Strukturparameter basierend auf einer Datenbank seriellkinematischer Beinketten realisiert. Gegenüber dem Stand der Technik zeichnet sich der Ansatz durch die explizite Berücksichtigung der geometrischen Anordnung von Koppelgelenken aus. Die Maßsynthese erfolgte durch die Erweiterung einer mehrkriteriellen Partikel-Schwarm-Optimierung mit hierarchischen Nebenbedingungen. Die Betrachtung einer mehrstufigen Optimierung für die von der Maßsynthese abhängige Entwurfsoptimierung von Komponenten sowie die Redundanzauflösung für verbreitete Aufgaben mit Rotationssymmetrie wie Fräsen erweitern den Stand der Technik. Zunächst wurde eine kinematische Modellierung für die Aufgabenredundanz entwickelt, die einen hinsichtlich des redundanten Endeffektorfreiheitsgrades optimalen Zusammenbau der Parallelkinematik berechnet. Für die optimale Bewegung entlang einer Rast-zu-Rast-Trajektorie zeigte sich das entwickelte Verfahren basierend auf dynamischer Programmierung am besten geeignet für die Maßsynthese im Vergleich zu einem lokal-optimalen Gradientenprojektionsverfahren oder einer Kombination der Verfahren. In der Struktursynthese konnten die bereits umfangreichen Ergebnisse der Literatur reproduziert werden und auch einige neue Parallelkinematiken generiert werden. Die Fallstudien für verschiedene Endeffektor-Freiheitsgrade konnten die breite Anwendbarkeit der kombinierten Struktur- und Maßsynthese belegen und trotz zahlreicher Nebenbedingungen jeweils eine Vielzahl möglicher aufgabenoptimaler Strukturen präsentieren. Der Ansatz wurde nur für symmetrische Parallelkinematiken mit starren Segmenten und seriell-kinematischen Beinketten evaluiert, lässt sich aber prinzipiell auch auf andere parallelkinematische Strukturen in Kombination mit Seilzügen, Parallelogramm-Beinketten oder Antriebsredundanz erweitern.

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title = "Combined structural and dimensional synthesis of task-specific parallel-robot manipulators: functional redundancy and design optimization",
abstract = "Parallel-kinematic machines or parallel robots have only been established in a few applications where their advantage over serial kinematics due to their high payload capacity, stiffness, or dynamics with their limited workspace-to-installation-space ratio pays out. However, some applications still have not yet been sufficiently or satisfactorily automated in which parallel robots could be advantageous. As their performance is much more dependent on their complex dimensioning, an automated design tool is required to optimize the parameterization of parallel robots for applications. Combined structural and dimensional synthesis considers all principally possible kinematic structures and performs a separate dimensioning for each structure to obtain the best task-specific structure. The structural synthesis was realized by the permutation of the discrete structural parameters based on a database of serial-kinematic leg chains. Compared to the state of the art, the approach is characterized by explicitly considering the geometric alignment of coupling joints. The dimensional synthesis was done by extending multi-objective particle-swarm optimization with hierarchical constraints. The cascaded (bilevel) optimization for the design optimization of components, depending on the dimensional synthesis, and the redundancy resolution for common tasks with rotational symmetry like milling, extends the state of the art. A kinematic model was developed for functional redundancy, which calculates an optimal assembly of the parallel leg chains at reference poses concerning the redundant end-effector degree of freedom. For the optimal motion along a reference rest-to-rest trajectory, the developed method based on dynamic programming proved to be the most suitable for dimensional synthesis compared to a locally optimal gradient-projection method or a combination of the methods. In the structural synthesis, it was possible to reproduce the already extensive results of the literature and generate some new parallel robots. The case studies for different end-effector degrees of freedom demonstrated the broad applicability of the combined structural and dimensional synthesis and presented many possible task-optimal structures despite numerous constraints. The approach was only evaluated for symmetric parallel robots with rigid links and serial-kinematic leg chains. Still, in principle, it can also be extended to other parallel-kinematic structures in combination with cable actuation, leg chains with parallelograms, or actuation redundancy.",
author = "Moritz Schappler",
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month = may,
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doi = "10.15488/19028",
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school = "Leibniz University Hannover",

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Download

TY - BOOK

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AU - Schappler, Moritz

PY - 2025/5/7

Y1 - 2025/5/7

N2 - Parallel-kinematic machines or parallel robots have only been established in a few applications where their advantage over serial kinematics due to their high payload capacity, stiffness, or dynamics with their limited workspace-to-installation-space ratio pays out. However, some applications still have not yet been sufficiently or satisfactorily automated in which parallel robots could be advantageous. As their performance is much more dependent on their complex dimensioning, an automated design tool is required to optimize the parameterization of parallel robots for applications. Combined structural and dimensional synthesis considers all principally possible kinematic structures and performs a separate dimensioning for each structure to obtain the best task-specific structure. The structural synthesis was realized by the permutation of the discrete structural parameters based on a database of serial-kinematic leg chains. Compared to the state of the art, the approach is characterized by explicitly considering the geometric alignment of coupling joints. The dimensional synthesis was done by extending multi-objective particle-swarm optimization with hierarchical constraints. The cascaded (bilevel) optimization for the design optimization of components, depending on the dimensional synthesis, and the redundancy resolution for common tasks with rotational symmetry like milling, extends the state of the art. A kinematic model was developed for functional redundancy, which calculates an optimal assembly of the parallel leg chains at reference poses concerning the redundant end-effector degree of freedom. For the optimal motion along a reference rest-to-rest trajectory, the developed method based on dynamic programming proved to be the most suitable for dimensional synthesis compared to a locally optimal gradient-projection method or a combination of the methods. In the structural synthesis, it was possible to reproduce the already extensive results of the literature and generate some new parallel robots. The case studies for different end-effector degrees of freedom demonstrated the broad applicability of the combined structural and dimensional synthesis and presented many possible task-optimal structures despite numerous constraints. The approach was only evaluated for symmetric parallel robots with rigid links and serial-kinematic leg chains. Still, in principle, it can also be extended to other parallel-kinematic structures in combination with cable actuation, leg chains with parallelograms, or actuation redundancy.

AB - Parallel-kinematic machines or parallel robots have only been established in a few applications where their advantage over serial kinematics due to their high payload capacity, stiffness, or dynamics with their limited workspace-to-installation-space ratio pays out. However, some applications still have not yet been sufficiently or satisfactorily automated in which parallel robots could be advantageous. As their performance is much more dependent on their complex dimensioning, an automated design tool is required to optimize the parameterization of parallel robots for applications. Combined structural and dimensional synthesis considers all principally possible kinematic structures and performs a separate dimensioning for each structure to obtain the best task-specific structure. The structural synthesis was realized by the permutation of the discrete structural parameters based on a database of serial-kinematic leg chains. Compared to the state of the art, the approach is characterized by explicitly considering the geometric alignment of coupling joints. The dimensional synthesis was done by extending multi-objective particle-swarm optimization with hierarchical constraints. The cascaded (bilevel) optimization for the design optimization of components, depending on the dimensional synthesis, and the redundancy resolution for common tasks with rotational symmetry like milling, extends the state of the art. A kinematic model was developed for functional redundancy, which calculates an optimal assembly of the parallel leg chains at reference poses concerning the redundant end-effector degree of freedom. For the optimal motion along a reference rest-to-rest trajectory, the developed method based on dynamic programming proved to be the most suitable for dimensional synthesis compared to a locally optimal gradient-projection method or a combination of the methods. In the structural synthesis, it was possible to reproduce the already extensive results of the literature and generate some new parallel robots. The case studies for different end-effector degrees of freedom demonstrated the broad applicability of the combined structural and dimensional synthesis and presented many possible task-optimal structures despite numerous constraints. The approach was only evaluated for symmetric parallel robots with rigid links and serial-kinematic leg chains. Still, in principle, it can also be extended to other parallel-kinematic structures in combination with cable actuation, leg chains with parallelograms, or actuation redundancy.

U2 - 10.15488/19028

DO - 10.15488/19028

M3 - Doctoral thesis

CY - Hannover

ER -

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