On-line Symbolic Constraint Embedding for Simulation of Hybrid Dynamical Systems

Abstract. In this paper we present a simulator designed to handle multibody systems with changing constraints, wherein the equations of motion for each of its constraint con¯gurations are formulated in minimal ODE form with constraints em-bedded before they are passed to an ODE solver. The constraint-embedded equations are formulated symbolically according to a re-combination of terms of the uncon-strained equations, and this symbolic process is undertaken on-line by the simulator. Constraint-embedding undertaken on-the-°y enables the simulation of systems with an ODE solver for which constraints are not known prior to simulation start or for which the enumeration of all constraint conditions would be unwieldy because of their complexity or number. Issues of drift associated with DAE solvers that usually require stabilization are sidestepped with the constraint-embedding approach. We apply nomenclature developed for hybrid dynamical systems to describe the system with changing constraints and to distinguish the roles of the forward dynamics solver, a collision detector, and an impact resolver. We have developed a MATLAB r° toolbox for symbolically generating equations of motion using Kane's method and prototyped a simulator with on-line constraint embedding and demonstrated the design in three representative examples