In the application of feed servo drives to a machine tool, in addition to sizing the drive to make sure there is enough torque available to satisfy the load requirements, it is also desirable to predict the servo performance (stability, response time, etc.). A useful analytical tool for servo analysis is the "transient response." This type of analysis is very practical since it closely relates to what an observer would see on a machine if a step input in position or velocity were used. By using servo "simulation" techniques, it is possible to construct a very accurate model of the servo drive. It is possible to observe the effect on performance by changing the drive parameters such as load inertia, backlash, stiction (stick-slip), viscous friction, load thrust, current limit, servo loop gains, machine resonance, and acceleration. Assuming the model is correct, the simulation program allows the machine designer to observe the feed drive performance without having the drive available. This simulation procedure makes it possible to anticipate machine design problems affecting servo performance and correct them before the machine is built.