| dc.description.abstract | An axially-moving cantilever beam is used to study identification o f time-varying
systems. A circuitry for DC motor current control and sensor conditioning is built. The
circuitry meets the design requirement of controlling the axial motion of the beam and
amplifying the sensor signals.
A linear time-varying model governing lateral vibration of the beam is developed.
Computer simulation is conducted to study the dynamic properties of the system, such as
transient responses, varying state transition matrices, “frozen” modal parameters,
“pseudo” modal parameters, etc.
A previously developed algorithm is applied to identify the system. Two identification
tasks are carried out. The system identification determines the discrete-time state space
model o f the system. The modal parameter identification determines the “pseudo” modal
parameters of the system. In both cases, an ensemble of freely vibrating responses are
used. The study addresses several critical issues encountered in the experiment such as
excitation, data preprocessing, the beam motion control, etc. The study also investigates
several important factors that affect the accuracy of identification, such as the number of
necessary experiments, model order, the block row number, etc. An algorithm based on
the moving-average method is developed to select the “pseudo” natural frequencies of
vibratory modes. The study shows that the algorithm is capable of estimating the
“pseudo” natural frequencies of the vibratory modes, present in responses, while it fails
to give good estimates for the “pseudo” damping ratios. | |
