A Transition-Aware Method for the Simulation of Compliant Contact with
Regularized Friction
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by
Alejandro M. Castro, Ante Qu, Naveen Kuppuswamy, Alex Alspach, and
Michael Sherman
2019
Abstract
Multibody simulation with frictional contact has been a challenging subject
of research for the past thirty years. Rigid-body assumptions are commonly used
to approximate the physics of contact, and together with Coulomb friction, lead
to challenging-to-solve nonlinear complementarity problems (NCP). On the other
hand, robot grippers often introduce significant compliance. Compliant contact,
combined with regularized friction, can be modeled entirely with ODEs, avoiding
NCP solves. Unfortunately, regularized friction introduces high-frequency stiff
dynamics and even implicit methods struggle with these systems, especially
during slip-stick transitions.
To improve the performance of implicit integration for these systems we
introduce a Transition-Aware Line Search (TALS), which greatly improves the
convergence of the Newton-Raphson iterations performed by implicit integrators.
We find that TALS works best with semi-implicit integration, but that the
explicit treatment of normal compliance can be problematic. To address this, we
develop a Transition-Aware Modified Semi-Implicit (TAMSI) integrator that has
similar computational cost to semi-implicit methods but implicitly couples
compliant contact forces, leading to a more robust method. We evaluate the
robustness, accuracy and performance of TAMSI and demonstrate our approach
alongside a sim-to-real manipulation task.
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