Biomedical Engineering Reference
In-Depth Information
Figure 17.10
Scheme of action of anticipatory feedforward and feedback control. The feedforward
controller implements an approximate inverse model of the load/plant. The model
can be learned by comparing a copy of the efferent signals and the concurrent reaffer-
ent signals. The feedback controller implements an approximate direct model of the
load/plant in order to recover the intrinsic delays of the afferent signals. Therefore
both controllers must be trained and operate in an anticipatory manner. The feedfor-
ward controller is typically used in the compensation of self-generated disturbances,
as in arm-trajectory formation, but is ineffective if the load/plant is unstable. In
that case an anticipatory feedback controller is more appropriate, implemented as a
sampled-data control system. Modulation of joint mechanical impedance is a syner-
gistic process, with a typical relaxation of the level of stiffness as the trained internal
model become more and more precise.
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