(Georgia Institute of Technology, 2006-08)
Yang, Bong-Jun; Calise, Anthony J.; Craig, James I.; Whorton, Mark S.
A solar sail is an example of a gossamer structure that is proposed as an propulsion
system for future space missions. Since it is a large scale flexible structure that requires a
long time for its deployment, active control may be required to prevent it from deviating
into a non-recoverable state. In this paper, we conceptually address control of an evolving
flexible structure using a growing double pendulum model. Controlling an evolving system
poses a major challenge to control design because it involves time-varying parameters,
such as inertia and stiffness. By employing a neural network based adaptive control, we
illustrate that the evolving double pendulum can be effectively regulated when fixed-gain
controllers are deficient due to presence of time-varying parameters.
(Georgia Institute of Technology, 2005-08)
Yang, Bong-Jun; Calise, Anthony J.; Craig, James I.; Whorton, Mark S.
Most active vibration isolation systems that try to a provide quiescent acceleration environment for
space-science experiments have utilized linear design methods. In this paper, we address adaptive control
augmentation of an existing classical controller that combines a high-gain acceleration inner-loop feedback
together with a low-gain position outer-loop feedback to regulate the platform about its center position.
The control design considers both parametric and dynamic uncertainties because the isolation system must
accommodate a variety of payloads having different inertial and dynamic characteristics. An important aspect
of the design is the accelerometer bias. Two neural networks are incorporated to adaptively compensate for
the uncertainties within the acceleration and the position loop. A novel feature in the design is that high-band
pass and low pass filters are applied to the error signal used to adapt the weights in the neural network
and the adaptive signals, so that the adaptive processes operate over targeted ranges of frequency. This
prevents the inner and outer loop adaptive processes from interfering with each other. Simulations show
that adaptive augmentation improves the performance of the existing acceleration controller and at the same
time reduces the maximal position deviation and thus also improves the position controller.
(Georgia Institute of Technology, 2003-08)
Yang, Bong-Jun; Hovakimyan, Naira; Calise, Anthony J.; Craig, James I.
A method of adaptive output feedback design for
uncertain nonlinear systems is presented. The development
is in a form that is suitable for augmenting a
linear controller. The approach is applicable to non-affine,
non-minimum phase systems having parametric
and dynamic uncertainties. A requirement is that the
non-minimum phase zeros are represented to a sufficient
accuracy in the linear controller design. The
approach has been experimentally validated using a
3-disk torsional pendulum and an inverted pendulum.
(Georgia Institute of Technology, 2003-06)
Yang, Bong-Jun; Calise, Anthony J.; Craig, James I.
We consider the problem of adaptive output feedback
control in the presence of saturating input characteristic.
The adaptive control architecture augments an existing
linear control design. The approach is applicable
to non-affine, nonlinear systems with both parametric
uncertainty and unmodeled dynamics subject to input
saturation. Boundedness of signals is shown through
Lyapunov's direct method. Experimental results with
a 3-disk torsional pendulum are presented to demonstrate
the approach.