This work discusses the use of Positive Position Feedback (PPF) for Active Vibration
Control as part of an Active Damage Control System (ADCS). Vibration control
increases the fatigue life of a structure and decreases the in-plane stresses that can
cause delamination in a composite. PPF is a collocated direct-output feedback control
method that increases the effective damping in a structure. A simply-supported
beam was used as the testbed which used strain gages as the sensing element and
piezoelectric ceramics as the actuator.
Initial investigations into sampled-data systems using PPF are presented. The
issues addressed are: stability of the sampled system, the effects of the sampling rate
on the system, and degradation from predicted analog performance. A digital design
procedure for the tuning filters in the Z-plane is suggested if the sampling rate to
be used is known. If the sampling rate varies significantly, to avoid redesigning the
filters for each new sampling rate, they should be designed in the continuous-time
and transformed to the Z-plane. The Tustin transformation was found to adequately
map the poles and zeros of the compensator to the Z-plane for digital control.
Experimental implementation of PPF on a simply-supported beam resulted in
vibration suppression of three modes with a S180 controller. The beam was subjected
to both a single-frequency harmonic disturbance and a broadband harmonic
disturbance. One, two, and three-mode controllers were designed with disturbance
suppression up to 15dB achieved.
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