Integrating Mimic Joints into Dynamics Algorithms – Exemplified by the Hybrid Recupera Exoskeleton
Shivesh Kumar, Marc Simnofske, Bertold Bongardt, Andreas Mueller, Frank Kirchner
In Proceedings of the 2017 Conference on Advances In Robotics, (AIR-2017), 28.6.-02.7.2017, New Delhi, ACM-ICPS, 2017.
The design of various robots in industrial and academic contexts
integrates closed loops to improve the mechanical stiffness in comparison
with purely serial or tree-type topologies. In particular,
planar kinematic loops as parallelograms or double parallelograms
are employed in such hybrid robots. Since these systems are geometrically
overconstrained in the group of spatial Euclidean motions,
the computational performance and numerical accuracy of any
model-based dynamics software is negatively affected. This paper
introduces a novel method to avoid these numerical issues for any
hybrid system with loops that can be characterized by the concept
of linear mimic joints: these are passive joints which depend on an
active joint in a closed loop in a linear manner. With the proposed
approach, the loop closure functions are automatically composed
from the robot description file and integrated into the analytical
equations for solving the forward and the inverse dynamics problems.
The paper illustrates the application of this method for a
novel shoulder mechanism containing a planar six bar mechanism
that has been designed for the Recupera whole-body exoskeleton.
Hybrid robots, dynamic modeling, mimic joints, exoskeletons