An observer based control strategy is proposed for a flexible Cartesian (SCARA) Robot which is modeled as a flexible cantilever beam with a translational base support. A piezoelectric (PZT) patch actuator is bonded on the top surface of the flexible arm to apply a controlled moment for vibration suppression requirement. Utilizing three measurable quantities (i.e., the base displacement, arm tip deflection and the strain at the root end of the arm), a reduced-order observer is designed to estimate the velocity related variables, which are not measurable. A simple PD controller is selected for the moving base regulation control, while a Lyapunov function candidate based on a very simple energy relationship is utilized for the PZT input voltage to make the closed-loop system energy dissipative and hence stable. In this paper, the PZT input voltage control uses the velocity related signals estimated by the reduced-order observer, which makes the control structure simpler. The feasibility of the controller is validated by the numerical simulations and experimental results.

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