indicating a quicker and stronger influence on
T. To minimize the effects of W by adjusting H and C,
prediction of W is thus necessary. W is a function of
screw speed, feed rate, and motor torque. Changes in
screw speed and feed rate are usually known beforehand.
For given screw speed and feed rate, the motor
torque depends on the material properties, primarily the
feed moisture content, which can be measured with a
desired lead time by installing sensors at a proper location
in the material-feeding system. Other unmeasurable
disturbances can be assumed as white noise. Shaft work
(W) can thus be predicted by using the following autoregressive
moving-average model with moisture content
as an auxiliary inpuff: