Hardware Reference
In-Depth Information
Figure 2.32: Schematic diagram of PTOS with integral control.
Figure 2.33: Schematic diagram of PTOS with bias estimator.
Realization of PTOS with Bias Estimator
It is explained earlier that an augmented state observer can estimate the states
of the actuator as well as the input disturbance. The estimates of the states
x
1
and x
2
are used to generate the control signal using the feedback law of the
PTOS algorithm. However, it should be noted that although the augmented
system is observable, it is not controllable. The input bias can be estimated
by the augmented observer but can not be controlled through feedback. Even
though the augmented observer gives estimates of three states, the state feed-
back control is still designed using a second order model of the actuator with
the states x
1
and x
2
only. The third state of the observer, the estimate of bias
input, must be subtracted directly from the VCM input signal to cancel the
effect of input bias. The controller equation for the linear state feedback is
u(k)=−Kz(k)=−k
1
x
1
(k)−k
2
x
2
(k)− x
3
(k).
(2.57)
The first two component of the control equation is exactly the same as that
of the linear part of PTOS. The block diagram of Figure 2.33 illustrates the
realization of the PTOS with bias estimator.
Both integral control and bias estimation can eliminate the effect of input
bias. The method with an integrator, uses an extra state in the feedback;
this additional state is not estimated by the state estimator but generated by
