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

Research output: ThesisDoctoral thesis

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Details

Original languageEnglish
QualificationDoctor of Engineering
Awarding Institution
Supervised by
  • Tobias Ortmaier, Supervisor
Date of Award21 Mar 2025
Place of PublicationHannover
Publication statusPublished - 7 May 2025

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.

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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",
year = "2025",
month = may,
day = "7",
doi = "10.15488/19028",
language = "English",
school = "Leibniz University Hannover",

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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.

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DO - 10.15488/19028

M3 - Doctoral thesis

CY - Hannover

ER -

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