Singular Configurations of Mechanisms and Manipulators

September 22, 2014 — September 26, 2014

Coordinators:

  • Dimiter Zlatanov (Università di Genova, Genova, Italy)
  • Andreas Müller (University of Michigan-Shanghai - Jiao Tong University, Shanghai, China)
Motivation and Aims In singular configurations, the kinetostatic properties of mechanisms undergo sudden and dramatic changes. Hence the enormous practical value of singularity analysis for manipulator design and use. Its theoretical importance stems from the critical role singularity plays in algebraic geometry and in the theory of differentiable mappings. Attendees will be introduced to milestone results, key methods, and main problems in singularity analysis. The lectures provide an overview of cutting-edge work and focus on a few advanced topics.
Main Themes
Definition.
Given the importance of kinematic singularity and the vast literature on the subject, it may be surprising that one rarely encounters a clear general definition of the phenomenon. To provide one is the course’s first objective: singularity is defined rigorously and in simple terms.
Classification.
Numerous singularity classifications exist. Since singularity is defined via instantaneous kinematics, the most fundamental taxonomy describes the types of degeneracy of the forward and inverse velocity problems. Finer distinctions exist for specific mechanism types, e.g., the important constraint singularities of parallel manipulators. When non-instantaneous properties are considered, other distinctions arise, such as between cusp-like and fold-like singularities, or the existence of self-motions.
Identification.
One of the most practically-important problems of kinematic analysis is the explicit calculation of the singularity set. Two general methods using numerical partitioning of the ambient parameter space are outlined. A powerful approach for formulating and solving symbolically the algebraic equations of the end-effector’s motion-pattern and singular-poses set is studied in detail.
Avoidance.
The course explores the possibility of a singularity-free workspace and the ability to escape from singularity, issues of major practical importance for the design of path planning algorithms and singularity consistent control schemes.
Singularity-set and configuration-space topology.
The singularity-free-connectivity properties of the configuration space are discussed, including the fascinating cuspidal manipulators, able to change posture while avoiding singularities. Related fundamental problems of genericity and configuration-space and singularity-set topology are explored. We examine the possibility of multiple operation modes, sometimes with strikingly different platform motion patterns, connected by constraint singularities.
Mathematical tools and formalisms.
The course is a hands-on introduction to the various analytical and computational tools for dealing with singularities. We explore screw-geometrical techniques and Lie-group-based local-analysis methods. Algebraic-geometry formulations combined with either symbolic computation or numerical methods (linear relaxations and interval analysis) are used. Topology and differential geometry provide the basis for the definitions and formulations throughout the course.

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