Numerical Computation and Avoidance of Manipulator Singularities
Oriol Bohigas Nadal

This thesis develops general solutions to two open problems of robot kinematics: the exhaustive computation of the singularity set of a manipulator, and the synthesis of singularity-free paths between given configurations. Obtaining proper solutions to these problems is crucial, because singularities generally pose problems to the normal operation of a robot and, thus, they should be taken into account before the actual construction of a prototype. The ability to compute the whole singularity set also provides rich information on the global motion capabilities of a manipulator. The projections onto the task and joint spaces delimit the working regions in such spaces, may inform on the various assembly modes of the manipulator, and highlight areas where control or dexterity losses can arise, among other anomalous behaviour. These projections also supply a fair view of the feasible movements of the system, but do not reveal all possible singularity-free motions. Automatic motion planners allowing to circumvent problematic singularities should thus be devised to assist the design and programming stages of a manipulator.

The key role played by singular configurations has been thoroughly known for several years, but existing methods for singularity computation or avoidance still concentrate on specific classes of manipulators. The absence of methods able to tackle these problems on a sufficiently large class of manipulators is problematic because it hinders the analysis of more complex manipulators or the development of new robot topologies. A main reason for this absence has been the lack of computational tools suitable to the underlying mathematics that such problems conceal. However, recent advances in the field of numerical methods for polynomial system solving now permit to confront these issues with a very general intention in mind.

The purpose of this thesis is to take advantage of this progress and to propose general robust methods for the computation and avoidance of singularities on non-redundant manipulators of arbitrary architecture. Overall, the work seeks to contribute to the general understanding on how the motions of complex multibody systems can be predicted, planned, or controlled in an efficient and reliable way.


You can get the last version of my PhD thesis here: Numerical Computation and Avoidance of Manipulator Singularities.


Here you can find the animated version of some figures and some of the Cuik input files of the examples.

Chapter 3: Numerical Computation of Singularity Sets

Section 3.5.1: The 3-RRR Manipulator - [input files]

animated version of figure 3.7 animated version of figure 3.8

Section 3.5.2: The Stewart Platform - [input files]

animated version of figure 3.11, left animated version of figure 3.11, right

Chapter 4: Workspace Determination

Section 4.5.1: Multi-component Workspaces - [input files]

Section 4.5.3: Degenerate Barriers

animated version of figure 4.12 animated version of figure 4.14

Section 4.5.4: Very Complex Manipulators - [input files]

Chapter 5: A General Singularity-free Path Planner

Section 5.4.2: The 3-RRR Manipulator

animated version of figure 5.8 animated version of figure 5.9

Chapter 6: Adding Further Constraints

Section 6.3.2: Cable-driven Hexapods

animated version of figure 6.9