Singularities in three-legged platform-type parallel mechanisms

Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurati...

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Bibliographic Details
Published in:IEEE transactions on robotics and automation 2003-08, Vol.19 (4), p.720-726
Main Authors: Wen, J.T., O'Brien, J.F.
Format: Article
Language:English
Subjects:
Actuators
Analytical models
Applied sciences
Computer science
control theory
systems
Control theory. Systems
Exact sciences and technology
Geometry
Jacobian matrices
Kinematics
Machine tools
Manipulators
Manufacturing automation
Mathematical analysis
Milling machines
Parallel robots
Payloads
Platforms
Robotics
Robotics and automation
Robots
Searching
Serials
Singularities
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Summary:Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurations in parallel robots is challenging in general, and is usually tackled via an exhaustive search of the workspace using an accurate analytical model of the mechanism kinematics. This paper considers the singularity determination problem from a geometric perspective for planar and spatial three-legged parallel mechanisms. By using the constraints on the passive joint velocities, we derive a necessary condition for the unstable singularities. Using this condition, certain singularities can be found for certain type of platforms. As an example, new singular poses are discovered using this approach for a six-degree-of-freedom machining center.
ISSN:1042-296X
2374-958X
DOI:10.1109/TRA.2003.814518