Given is a non-singular pose (green) of a pentapod with linear platform and non-planar base (black anchor points).
The closest singular configuration in the position/orientation workspace is illustrated in blue/magenta.
The closest singular pose under Euclidean/equiform motions of the linear platform is displayed in red/yellow.
Singularity Closeness of Stewart-Gough Platforms
This project is devoted to evaluating the closeness of Stewart-Gough platforms to singularities.
This project is funded by the Austrian Science Fund (FWF).
FWF grant no. P 30855-N32
FWF-Funding: € 192 774.76
Project leader: Georg Nawratil
Aims and Scope
A parallel manipulator of Stewart-Gough (SG) type consists of a moving platform, which is connected via spherical-prismatic-spherical legs with the base,
where only the prismatic joints are active. The number of applications of SG manipulators, ranging from medical surgery to astronomy,
has increased enormously during the last decades due to their advantages of high speed, stiffness, accuracy, load/weight ratio, etc.
One of the drawbacks of these parallel robots are their singular configurations, where the manipulator is shaky while all leg lengths are fixed.
As a consequence the actuator forces can become very large, which may result in a breakdown of the mechanism.
Therefore singularities have to be avoided. This reasons the high interest of the kinematic/robotic community in evaluating the singularity closeness of SG platforms,
but geometric meaningful distance measures for this task are still missing. The research project closes this gap.
Singularity Distance for Parallel Manipulators of Stewart Gough Type.
Advances in Mechanism and Machine Science –
Proc. of the 15th IFToMM World Congress on Mechanism and Machine Science (T. Uhl ed.), pages 259-268, Springer, 2019, ISBN 978-3-030-20131-9,
A. Rasoulzadeh and G. Nawratil:
Variational Path Optimization of Linear Pentapods with a Simple Singularity Variety.
Mechanism and Machine Theory 153 (12) 104002 (2020) DOI 10.1016/j.mechmachtheory.2020.104002
see homepage of Arvin Rasoulzadeh
Evaluating the snappability of bar-joint frameworks.
Advances in Robot Kinematics (J. Lenarcic, B. Siciliano eds.), pages 182-189, Springer, 2020, ISBN 978-3-030-50974-3,
[Extended version on arXiv:2001.04430]
Animations of the snapping deformation of Fig. 2:
A. Kapilavai and G. Nawratil: On homotopy continuation based singularity distance computations for 3-RPR manipulators.
New Trends in Mechanism Science (D. Pisla, B. Corves eds.), pages 56-64, Springer, 2020, ISBN 978-3-030-55060-8,
[Extended version on arXiv:2004.08359]
On the snappability and singularity-distance of frameworks with bars and triangular plates.
In Springer's Proceedings in Advanced Robotics of the
IMA Conference on Mathematics of Robotics (accepted)
[Corresponding arXiv paper]
A. Kapilavai, G. Nawratil: Metrics for distance computation between 3-RPR configurations.
Extended Abstract published in Proc. of 7. IFToMM D-A-CH Konferenz,
February 18-19 2021, online conference due to COVID-19, DOI: 10.17185/duepublico/74051
Snappability and singularity-distance of pin-jointed body-bar frameworks.
Animations of the snapping of
Example 2, the
Siamese dipyramid and the
Four-horn as well as the
expression of the shakiness factor S for the Siamese dipyramid and
the Four-horn, respectively
15th IFToMM World Congress,
Krakow June 30-July 4 2019, Poland, paper presentation.
SIAM Conference on Applied Algebraic Geometry,
Bern July 9-13 2019, Switzerland, Invited Talk (Mini-symposium: Algebraic geometry for kinematics, mechanism science, and rigidity),
Title: Singularity distance computation for parallel manipulators of Stewart Gough Type.
Workshop on Circle Packings and Geometric Rigidity,
July 6-10 2020, online due to COVID-19 hosted by ICERM,
Title: On the snappability of frameworks. [Slides]
PARALLEL 2020, The 4th International Workshop on Fundamental Issues,
Applications and Future Research Directions for Parallel Mechanisms/Manipulators/Machines,
September 9-11 2020, online conference due to COVID-19, Title: On homotopy continuation based singularity distance computations for 3-RPR manipulators.
TUForMath, TU Wien December 3 2020, Austria, Public Talk (in German) held online due to COVID-19, Title: Forme(l)n der Beweglichkeit.
[Talk on YouTube,
7. IFToMM D-A-CH Konferenz,
February 18-19 2021, online conference due to COVID-19, Title: Metrics for distance computation between 3-RPR configurations.
Effective Methods in Algebraic Geometry (MEGA 2021),
June 7-11 2021, oral presentation in the software session held online due to COVID-19, Title: Algorithms for distance computations between 3-RPR configurations.
Workshop on Real Algebraic Geometry and
Algorithms for Geometric Constraint Systems, June 14-18 2021, online due to COVID-19 hosted by the Fields Institute, Title:
Snappability and singularity-distance of frameworks.
[Talk on YouTube,
IMA Conference on Mathematics of Robotics, Manchester September 8-10 2021, England, paper presentation.