Interactive simulation of solid rigid bodies

The article describes the implementation of an interactive system for simulating rigid bodies with contact and friction. The system can simulate moderately complex mechanical systems at interactive rates (20-30 Hz on low end Silicon Graphics workstations). New objects and user specified constraints can be added into the simulation environment on the fly. The system uses analytical methods to compute contact forces, as opposed to the penalty methods common in other interactive systems. Currently, the system's weakest feature is that it can fail to detect high speed collisions. Objects that move at high speeds (relative to the step size of the simulation) are subject to a form of aliasing and may tunnel through other objects without causing a collision. Other simplifications of the system involve approximating collision times and locations by interpolation methods, and periodic error correction adjustments of geometric tolerances. It is difficult to try to quantify the error incurred by a given approximation or tradeoff. Some of the design choices will likely curtail the system's use for highly predictive applications. However, they do not seriously affect simulating the basic dynamics of a mechanism like a feeder. In general, the system performs with sufficient accuracy and realism to be considered a viable interactive simulation environment.>