Rejection of a harmonic and transient disturbance in a single-link flexible robot provided with piezoelectric actuators

In many applications, the use of slender and light flexible structures has increased due to the requirement of more efficient structures. The main objective of this work is to suppress vibration at the free end of a single-link rotational robot subjected to a harmonic disturbance located near to the tip of the link The control architecture is made up of two independent control loops; the first loop is employed to control the position of the hub and the second loop is used to attenuate the vibration of the arm. The position control of the hub is achieved through a proportional integral derivative (PID) controller with feedforward gains. The active vibration control (AVC) is achieved implementing a linear parameter varying (LPV) gain-scheduling observer-based state-feedback controller. A pair of piezoelectric patches is used as actuator. The link is considered as a cantilevered beam, and its model is obtained using black box system identification techniques. The AVC loop is considered to be affected by one harmonic disturbance generated by a DC motor and one transient disturbance induced by inertial force from the movement of the rotational joint at the measure point. The arm is subjected to different joint trajectories and to different variations of the frequency of the harmonic disturbance. Experimental results show the effectiveness of the observer-based state-feedback controller for the rejection of unwanted vibration and its capability of increasing the damping of the structure.