Comparison of Impulsive and Compliant Contact Models for Impact Analysis in Biomechanical Multibody Systems

Two approaches are used when studying impact problems: impulsive ones and compliant ones. In an impulsive approach, the time interval where the collision takes place is considered to be negligible, and so the system configuration is assumed to be constant. The final mechanical state of the colliding system is obtained directly from the initial one through algebraic equations and energy dissipation assumptions. In a compliant approach, the colliding surfaces are modelled through springs and dampers (usually nonlinear), and the equations of motion are integrated during the impact time interval to obtain the final state. Though both approaches have been widely used in the field of biomechanics, no comparative study can be found in the literature that could justify choosing one or another. In this paper, we present both approaches and compare them when applied to two examples related to gait problems: a passive walker and a simple model of crutch locomotion. We will show that the results are really close whenever nonsliding conditions are assumed at the impact points.