Improvement of Functional Performance of Spatial Parallel Manipulators Using Mechanisms of Variable Structure

International audienceA procedure for the increase of singularity-free zones in the workspace of spatial parallel manipulators is presented in this paper. The procedure is based on the control of the pressure angles in the joints of the manipulator. The zones, which cannot be reached by the manipulator, are detected. For increase of the reachable workspace of the manipulator the legs of variable structure are proposed. The design of the optimal structure of the spatial parallel manipulator 3-RPS is illustrated by a numerical simulation

Generic singular configurations of linkages

We study the topological and differentiable singularities of the configuration space C(\Gamma) of a mechanical linkage \Gamma in d-dimensional Euclidean space, defining an inductive sufficient condition to determine when a configuration is singular. We show that this condition holds for generic singularities, provide a mechanical interpretation, and give an example of a type of mechanism for which this criterion identifies all singularities

Dynamic Analysis of Parallel Manipulators under the Singularity-Consistent Parameterization

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Topological and Kinematic Singularities for a Class of Parallel Mechanisms

We study singularities for a parallel mechanism with a planar moving platform in ℝ(=2,3), with joints which are universal, spherical (spatial case), or rotational (planar case). For such mechanisms, we give a necessary condition for a topological singularity to occur, and describe the corresponding kinematic singularity. An example is provided

A general method for the numerical computation of manipulator singularity sets

The analysis of singularities is central to the development and control of a manipulator. However, existing methods for singularity set computation still concentrate on specific classes of manipulators. The absence of general methods able to perform such computation on a large class of manipulators is problematic because it hinders the analysis of unconventional manipulators and the development of new robot topologies. The purpose of this paper is to provide such a method for nonredundant mechanisms with algebraic lower pairs and designated input and output speeds. We formulate systems of equations that describe the whole singularity set and each one of the singularity types independently, and show how to compute the configurations in each type using a numerical technique based on linear relaxations. The method can be used to analyze manipulators with arbitrary geometry, and it isolates the singularities with the desired accuracy. We illustrate the formulation of the conditions and their numerical solution with examples, and use 3-D projections to visualize the complex partitions of the configuration space induced by the singularities.Preprin

Planar revolute-coupled kinematic chains in critical configurations and their duals

The motivation for studies of dual coupling networks is explained and a definition is suggested for duality. Dual couplings are defined and several couplings dual with the revolute coupling are described. Six linkages, instantaneously in a critical configuration, provide examples. The consequences of these critical configurations are explored for both the linkages and the coupling networks that are dual with them

Planar revolute-coupled kinematic chains in critical configurations and their duals

This paper was accepted for publication in the journal, Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics. The definitive published version can be found at: http://dx.doi.org/10.1177/1464419313517114The motivation for studies of dual coupling networks is explained and a definition is suggested for duality. Dual couplings are defined and several couplings dual with the revolute coupling are described. Six linkages, instantaneously in a critical configuration, provide examples. The consequences of these critical configurations are explored for both the linkages and the coupling networks that are dual with them

Test Frame Design for Characterization of Additive Manufacturing Compliant Materials

With the application of using surrogate models with General Purpose Graphics Processing (GPGPU) computing to meet the need for “real-time” characterization of nonlinear anisotropic material systems and the growing work of using multiaxial robotic test frames for material characterization, there has been a solution for a specific application towards additive manufacturing materials, specifically polymers. Traditional testing using uniaxial and biaxial test machines has proven insufficient in characterizing the material properties of additive manufacturing materials, therefore developing a need for a multiaxial testing machine for characterization that can dynamically excite strain states for a more in-depth look at the material properties. This design report presents the design of a multiaxial robotic test frame that incorporates a Stewart-Gough (SG) platform design to allow 6 degrees-of-freedom for multiple and combined loading applications. This solution is the next generation multiaxial machine focusing on additive manufacturing materials, specifically polymers. The problem statement is the following: Design and fabricate a multiaxial robotic test frame that can test additive manufacturing materials, focusing on polymers and some metals, in 6 degrees-of-freedom while improving on performance and cost over the CSM design