Fully-Implicit Time Stepping Methods with Integrated Proximity Queries for Accurate Simulation of Multi-Rigid-Body Systems with Intermittent Contact

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

To automatically plan tasks involving contact between objects, accurate prediction of object motions is essential. Applications include collaborative human-robot manipulation, industrial automation, engineering design, and physics engines for computer games. The intermittency of contact and stick-slip behavior make it difficult to simulate multibody systems stably and accurately. Commercially available multibody simulation software has difficulty simulating even simple systems with contacts. As a result, users must resort to trial-and-error to find simulation parameters that yield believable, not necessarily accurate, results. The algorithms developed in this research project will lead to improved future versions of simulation products such as Adams and Working Model. The primary sources of stability and accuracy problems in multibody simulation are polyhedral representations of smooth objects, decoupling of collision detection from the solution of the dynamic time-stepping subproblem, linearization of Coulomb friction model, and errors in model parameters. This research focuses on formulations, algorithm development and analysis of time-steppers to eliminate the first three error sources. The result will be a fully-implicit, stable, accurate, optimization approach to simulating systems of rigid objects undergoing intermittent contact; the objects will be modeled using implicit and parametric surface representations. No previous general method has been developed that combines dynamics and geometric constraints in a fully-implicit manner. By using the new time-stepper as a ``ground truth" model, all previous models can be compared, so that for the first time, the error effects of the most common approximations can be quantified. This research will involve graduate and undergraduate students. The results will be incorporated into our simulation package and introduced in the robotics courses at RPI. Outreach activities include summer Lego robotics activities for middle school students.