# University of Minnesota

Aerospace Engineering and Mechanics

**Spring 2002 Seminar Series**

*Real-time Optimal Control Methods for Active Materials Actuators*

*Abstract*

**Due to the low cooling rate of macroscopic SMA actuators in still ambient
air, control of these actuators is usually not a topic that goes beyond the
realms of classical PI control theory.**

**In some circumstances, however, things change drastically. Examples are
applications in an efficient cooling environment like underwater applications
or flight at high altitude. Of most interest currently are MEMS applications,
where, even at ambient conditions, the increased surface to volume ratio
provides high cooling rates. In such cases, higher actuation frequencies can be
achieved, and the inherent nonlinear behavior, mainly caused by the hysteresis
present in these materials, makes it impossible to track set point signals
using a conventional feedback control method. The same problem is encountered
in other active materials, e.g., piezoceramics and magnetostrictive
materials.**

**A way to overcome this problem is to implement a model into the control
algorithm that compensates for the effect of the hysteresis (inverse
compensator methods). It has been successfully done in several cases, mostly on
the basis of phenomenological models from the Preisach type. This approach,
however, poses considerable problems with respect to identification and
interpretability of the parameters. Another common feature of all model-based
control algorithms published so far is that, at the best, they address
stability issues, but never look at optimality, e.g., with respect to speed of
adjustment or energy consumption.**

**The seminar gives an overview of an optimal control algorithm employing a
SMA model derived from statistical thermodynamics. It has a limited number of
parameters, and all of them are clearly interpretable from a physical point of
view. Based on this approach, a method has been designed to allow for real-time
applications, taking unforeseeable parameter changes into account and
delivering results for an optimal control in extremely short time.**

### Friday, February 8, 2002

209 Akerman Hall

2:30-3:30 p.m.

### Refreshments served after the seminar in
227 Akerman Hall.

Disability accomodations provided upon request.

Contact Kristal Belisle, Senior
Secretary, 625-8000.