ACT is based on the latest developments in control system theory generally referred to as “State Control”. The concept of “state” is central to understanding ACT. In machine controls the “state” of the system consists of a vector, or interrelated group, of signals. The most obvious states include position and velocity. There are additional “states” that can be considered to improve control performance such as acceleration, or a “disturbance state” (to capture the effect of disturbing forces acting on the system) and “system state models” to account for, for example, motor dynamics and structural modes within an axis.