The part of servo control that directly deals with this is often referred to as “Feed forward” control. I t can be thought of as what internal commands are needed such that the user’s motion commands are followed without any error, assuming of course a sufficiently accurate model of both the motor and load is known. The second general class of servo control addresses the disturbance rejection characteristics of the system. Disturbances can be anything from torque disturbances on the motor shaft to incorrect motor parameter estimations used in the feed forward control. The familiar “P.I .D.” (Proportional Integral and Derivative position loop) and "P.I .V." (Proportional position loop Integral and proportional Velocity loop) controls are used to combat these types of problems. In contrast to feed forward control, which predicts the needed internal commands for zero following error, disturbance rejection control reacts to unknown disturbances and modeling errors. Complete servo control systems combine both these types of servo control to provide the best overall performance. We now examine the two most common forms of disturbance rejection servo control, P.I .D. and P.I .V. After understanding the differences between these two topologies, we then investigate the additional use of a simple feed forward controller for an elementary trapezoidal velocity move profile.