The Kinematic design of a 3-dof Hybrid Manipulator

TL;DR

This paper introduces a new 3-DOF hybrid manipulator combining serial and parallel kinematic features, which offers improved stiffness, accuracy, and workspace size, with potential to avoid singularities through design choices.

Contribution

It presents the kinematic analysis and design considerations of a novel hybrid manipulator that enhances stiffness and workspace while reducing inertial effects and avoiding singularities.

Findings

Hybrid manipulator is stiffer and more accurate.

Design can avoid parallel singularities by choosing working modes.

Structural dimensions influence kinematic and mechanical properties.

Abstract

This paper focuses on the kinematic properties of a new three-degree-of-freedom hybrid manipulator. This manipulator is obtained by adding in series to a five-bar planar mechanism (similar to the one studied by Bajpai and Roth) a third revolute passing through the line of centers of the two actuated revolute joints of the above linkage. The resulting architecture is hybrid in that it has both serial and parallel links. Fully-parallel manipulators are known for the existence of particularly undesirable singularities (referred to as parallel singularities) where control is lost [4] and [6]. On the other hand, due to their cantilever type of kinematic arrangement, fully serial manipulators suffer from a lack of stiffness and from relatively large positioning errors. The hybrid manipulator studied is intrinsically stiffer and more accurate. Furthermore, since all actuators are located on the first axis, the inertial effects are considerably reduced. In addition, it is shown that the special kinematic structure of our manipulator has the potential of avoiding parallel singularities by a suitable choice of the "working mode", thus leading to larger workspaces. The influence of the different structural dimensions (e.g. the link lengths) on the kinematic and mechanical properties are analysed in view of the optimal design of such hybrid manipulators.