title: Making a meaningful impact: modelling simultaneous frictional collisions in spatial multibody systems.
abstract: Impacts are instantaneous, computationally efficient approximations of collisions. Current impact models sacrifice important physical principles to achieve that efficiency, yielding qualitative and quantitative errors when applied to simultaneous impacts in spatial multibody systems. We present a new impact model that produces behaviour similar to that of a detailed compliant contact model, while retaining the efficiency of an instantaneous method. In our model, time and configuration are fixed, but the impact is resolved into distinct compression and expansion phases, themselves comprising sliding and rolling intervals. A constrained optimization problem is solved for each interval to compute incremental impulses while respecting physical laws and principles of contact mechanics. We present the mathematical model, algorithms for its practical implementation, and examples that demonstrate its effectiveness. In collisions involving materials of various stiffnesses, our model can be more than 20 times faster than integrating through the collision using a compliant contact model. This work extends the use of instantaneous impact models to scientific and engineering applications with strict accuracy requirements, where compliant contact models would otherwise be required. An open-source implementation is available in Simbody, a C++ multibody dynamics library widely used in biomechanical and robotic applications.
authors.affiliation: Department of Bioengineering , Stanford University , 318 Campus Drive West, James H. Clark Center, Stanford, CA 94305-5448, USA.
authors.forename: Thomas K
authors.identifier: 0000-0002-7700-7476
authors.initials: TK
authors.lastname: Uchida
authors.affiliation: Department of Bioengineering , Stanford University , 318 Campus Drive West, James H. Clark Center, Stanford, CA 94305-5448, USA.
authors.forename: Michael A
authors.identifier: 0000-0001-5002-886X
authors.initials: MA
authors.lastname: Sherman
authors.affiliation: Department of Bioengineering, Stanford University, 318 Campus Drive West, James H. Clark Center, Stanford, CA 94305-5448, USA; Departments of Mechanical Engineering and Orthopaedic Surgery, Stanford University, 318 Campus Drive West, James H. Clark Center, Stanford, CA 94305-5444, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
keywords: collision; contact; impact; multibody dynamics; non-smooth dynamics