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The use of lightweight, thin flexible structures creates a dilemma in the aerospace and robotic industries. While increased operating efficiency and mobility can be achieved by employing such structures, these benefits are compromised by significant structural vibrations due to the increased flexibility. To address this problem, extensive research in the area of vibration control of flexible structures has been performed over the last two decades. The majority of the research has been based on the use of discrete piezoceramic actuators (PZTs) as active dampers, as they are commercial availability and have high force and bandwidth capabilities. Many different active vibration control strategies have previously been proposed, in order to effectively suppress vibrations. The synthesized vibration controllers will be less effective or even make the system to become unstable if the actuator locations and control gains are not chosen properly. However, there is currently no quantitative procedure that deals with these procedures simultaneously. This thesis presents a theoretical and numerical study of vibration control of a singlelink flexible manipulator attached to a rotating hub, with PZTs bonded to the surface of the link. A commercially available fibre optic sensor called ShapeTapeTM is introduced as a new feedback sensing technique, which is complemented by a quantitative and definitive model based procedure for selecting the individual PZT locations and gains. Based on Euler-Bernoulli beam theory, discrete finite element equations are obtained using Lagrange’s equations for a PZT-mounted beam element. Slewing of the flexible link by a rotating hub induces vibrations in the link that persist long after the hub stops rotating. These vibrations are suppressed through a combined scheme of PD-based hub motion control and proposed PZT actuator control, which is a composite linear (L-type) and angular (A-type) velocity feedback controller. A Lyapunov approach was used to synthesize the PZT controller. The feedback sensing of linear and angular velocities is realized by using the ShapeTapeTM, which measures the bend and twist of the flexible link’s centerline. Both simulation and experimental results show that tip vibrations are most effectively suppressed using the proposed composite controller. Its performance advantage over the individual linear or angular velocity feedback controllers confirms theoretical predictions made based on a non-proportional damping model of the PZT effects. Furthermore, it is demonstrated that the non-proportional nature of the PZT damping effect must be considered in order to bound the range of allowable controller gain values. |
