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moving parts, and fast response, being compact and easy implementation. A commonly used
piezoceramic is the lead zirconate titanate (PZT), which can produce a maximum actuation strain on the
order of 1 000 \JL strain. Furthermore, PZT actuators produce strains that are proportional to the applied
electric field/voltage within linear range, which have bandwidths beyond the frequency range of structural
and acoustic control applications. These features make them attractive for active control applications.
The controller design of smart structures has been based on the linear and nonlinear control theories. In
the linear controller, positive position feedback (PPF) (Goh and Caughey (1985); Fanson and Caughey
(1990); Agrawal and Bang (1994); Song et al, (2000)) is applied by feeding the structural position
coordinate directly to the compensator, and the product of the compensator and a scalar gain positively
back to the structure. Song et al (1998) experimentally demonstrated that PPF is insensitive to a varying
modal frequency. Strain Rate Feedback (SRF) control is also used for active damping of a flexible space
structure (Newman (1992), Song etal (2002)).
In the nonlinear control of civil engineering application, Yang et al (1997) has used the sliding mode
controller for wind and seismic response control application on ten-story and forty-story steel frame
building. Allen et al (2000) has used this control algorithm to control a large flexible structure,
In this paper, the objective is to examine the effectiveness using smart sensors and actuators for active
vibration control on a 3-floor model building. Prior to control design and implementation, the
experimental modal testing of the model building is performed to obtain the natural frequency and their
corresponding modal shapes. PZT will be used as both sensors and actuators in this research. These three
active vibration control methods, positive position feedback (PPF), strain rate feedback (SRF), and
sliding-mode controller (SMC), are designed and implemented.
2 VIBRATION SUPPRESSION METHODS
For this research three vibration-suppression methods were identified viz. Positive Position Feedback
(PPF), Strain Rate Feedback (SRF), and sliding mode control (SMC).
2.1 Positive Position Feedback Control
Positive Position Feedback (PPF) control was first proposed by Goh and Caughey (1985) as a robust
control solution since it is insensitive to spillover phenomenon. It is not destabilized by the finite actuator
dynamics and the stability is guaranteed by only considering the structures stiffness properties only. Later
Song et al (2002) experimentally demonstrated PPF control in pultruded fiber-reinforced polymer I-beam.
The PPF control is applied by feeding the structural position coordinate directly to the second order
system. The position is then positively fed back to the structure. PPF offers quick damping for the
controlled mode provided that the natural frequency and gain are known. The scalar equations governing
the vibration of the structure in a single mode and the PPF controller are given as:
Structure: £ 4- 2go> -h &r£ ~bu (1)
Controller: 77 + 2q c O) c fj + 0777 = gO)^ (2)
-^(fVl (3)
where § , q and oo are the modal co-ordinate displacement, damping ratio, and natural frequency of the
structure respectively. In the controller equation, r\, q ff , co c , g are the compensator co-ordinate
displacement, damping ratio, natural frequency, and feedback gain of the controller. It can be proved
(Friswell and Inman, (1997)) that the stability condition is satisfied if and only if