That missing ingredient provided we have access to both
Velocity and acceleration commands, synched up with
position commands is feedforward control.
An example of how feedforward control may be used in
parallel with disturbance rejection control is shown
in figure 8. The key is to accurately calculate the amount
of torque required to make each move a priori. To do so,
we take the basic equation of motion
and approximate it (as follows) because the disturbance
torque Td is unknown.
Fundamentals of Servo Motion Control
In order to achieve near zero following or tracking error,
feedforward control is often employed. A requirement for
feedforward control is the availability of both the velocity,
and acceleration, commands synchronized with the
position commands,. An example of how feedforward
control is used in addition to disturbance rejection control is
shown in Fig. 8.