Measuring the closeness to singularities of a planar parallel manipulator using geometric algebra

Abstract

• A new index for measuring the closeness to the singularities of parallel manipulators is proposed. • The index is defined as the ratio of non-singularity volume to workspace volume. • The singularity volume is calculated as the space between singularity and approximate singularity surfaces. • An approximate singularity polynomial is derived to define the approximate singularity surface. A new index for measuring the closeness to the singularities of parallel manipulators using geometric algebra is proposed in this paper. Constraint wrenches acting on the moving platform of a parallel manipulator are derived using the outer product and dual operations. Removing the redundant constraint wrenches, a singularity polynomial is obtained when the coefficient of the outer product of all the non-redundant constraint wrenches equals zero. A singularity surface can be drawn using the singularity polynomial. Similarly, an approximate singularity polynomial and approximate singularity surface can be obtained by imposing a threshold to the singular polynomial. Then the singularity volume is calculated as the space between singularity surface and approximate singularity surface. The new index is derived by calculating the ratio of the non-singularity workspace volume (the workspace volume minus the singularity volume) to the workspace volume. The proposed index is coordinate-free and has a clear geometrical and physical interpretation. This index can be a basis for selecting structural parameters, path planning and mechanism design.