In this article, velocity and position controllers for magnetostrictive materials are designed and discussed.
Magnetostrictive materials are a competitive choice for micro-positioning actuation tasks because of the large force and
strain they provide. Unfortunately, they are highly nonlinear and hysteretic, which makes them difficult to control. In
this article, the passivity approach is used to establish stability for velocity control. Using a physical argument, passivity
of the system under discussion is proved. No model for magnetostrictive material is used in this proof and the result can
be used in any hysteresis model for the material. This result is used to develop a stabilizing velocity controller. For
position control, it is shown that a PI controller can provide stability and tracking if the hysteretic plant satisfies certain
conditions. It is shown that these conditions are satisfied for the Preisach model under mild assumptions. Using this
result, a class of stabilizing position controllers is identified. The velocity and position controllers are evaluated
experimentally and their performances discussed.
A load-dependent hysteresis model for magnetostrictive materials is studied. Magnetostrictive materials are a class
of smart materials which react with a magnetic field and are suitable for many micro-positioning actuation tasks.
Unfortunately, these materials are difficult to use because of their highly nonlinear and hysteretic response. Unlike the
hysteresis seen in magnetic materials, the shape of the hysteresis curve changes significantly if the load is changed.
Because of this complex hysteresis, magnetostrictive actuators are difficult to control. To achieve sub-micron accuracy
for micropositioning, an accurate hysteresis model is needed. The model studied in this paper is similar to the Preisach
model. By modeling the Gibbs energy for each dipole and the equilibrium states, hysteresis in magnetostrictive
materials is modeled. The model is implemented in a way that different hysteresis curves are generated if the load is
changed. Using experimental data, optimum model parameters are obtained. The model results and experimental data
were compared at different loads. A modification is proposed for more accuracy and the modified model is compared to
the original model.
In many applications, it is desired to amplify the motion provided by micropositioning actuators. It is shown that
mechanical amplification by lever mechanisms reduces the overall system stiffness, which limits the ability of high
frequency operations. In this paper, a hydraulic booster is proposed. If the hydraulic fluid used is not compressible, the
system stiffness is not affected. Different designs of the booster are examined experimentally to find a booster without
hysteresis. Several experiments are performed to characterize the booster. A model for the booster is proposed and
evaluated using experimental data.
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