A pressure field model for fast, robust approximation of net contact force and moment between nominally rigid objects

Abstract

We introduce Pressure Field Contact (PFC), an approximate model for predicting the contact surface, pressure distribution, and net contact wrench between nominally rigid objects. PFC combines and generalizes two ideas: a bed of springs (an 'elastic foundation') and hydrostatic pressure. Continuous pressure fields are computed offline for the interior of each nominally rigid object. Unlike hydrostatics or elastic foundations, the pressure fields need not satisfy mechanical equilibrium conditions. When two objects nominally overlap, a contact surface is defined where the two pressure fields are equal. This static pressure is supplemented with a dissipative rate-dependent pressure and friction to determine tractions on the contact surface. The contact wrench between pairs of objects is an integral of traction contributions over this surface. PFC evaluates much faster than elasticity-theory models, while showing the essential trends of force, moment, and stiffness increase with contact load. It yields continuous wrenches even for non-convex objects and coarse meshes. The method shows promise as sufficiently fast, accurate, physical, and robust for robotics applications including motion and tactile sensor simulation, controller learning and synthesis, state estimation, and design-in-simulation.

A Transition-Aware Method for the Simulation of Compliant Contact With Regularized Friction

“…Additional examples are available in the open-source robotics toolbox Drake [22]. Ongoing work conducted at the Toyota Research Institute is leveraging the proposed method for prototyping and validating controllers for robot manipulation in dense cluttered environments [27] and extending TAMSI to work with more sophisticated contact models [20].…”

“…This implies that the Jacobian in Eq. (20) is SPD and its inverse always exists, explaining the high stability of this scheme for contact problems without friction.…”

Discrete Approximation of Pressure Field Contact Patches

“…The hydroelastic contact model [11] combines two ideas: elastic foundation and hydrostatic pressure. Thus the model introduces an object-centric virtual pressure field p 0 to mimic the hydrostatic pressure field of a fluid.…”

“…However, current implementations [10] need highly refined meshes and can even miss contact interactions if coarse meshes are used. The work in [11] introduces the pressure field model; a modern rendition of EFM designed to work with coarse meshes at a computational cost suitable for real-time simulation. The pressure field model finds the contact surface as the manifold on which precalculated normal stresses from each object balance each other.…”

“…Given the success of velocity-level solvers in the community and guided by our own success with these methods [19], this work aims to incorporate the hydroelastic contact model [11] into a discrete formulation of contact. We strive to enable simulation of contact rich patches, eliminate artifacts introduced by point contact, and capture area dependent phenomena otherwise missed by point contact while still performing at real-time rates.…”