Flexible linkage structural vibration control on a 3-PRR planar parallel manipulator: experimental results

Piezoelectric actuators and sensors have been used for vibration control of flexible manipulators and mechanisms since the 1990s. However, very few attempts have been made toward experimental investigations compared with numerical simulations, especially for mechanisms and manipulators with multiple flexible links. This paper presents an experimental study on active vibration control of a moving 3-PRR parallel manipulator with three flexible intermediate links with bonded lead zirconate titanate (PZT) actuators and sensors. First, experimental modal tests are conducted with an impulse force hammer and an accelerometer to identify structural vibration mode shapes and natural frequencies of the flexible manipulator. These modal test results are used to provide guidance for the determination of the location of PZT transducers and the design of an active vibration controller. Then, a strain rate feedback (SRF) controller is designed in modal space. A state-space model is formulated with the control input voltage applied to PZT actuators, and output generated voltage from PZT sensors. The design of an optimal active vibration controller is addressed based on SRF. Furthermore, to suppress the noise introduced through the differentiation of the strain signal, a second-order auxiliary compensator is introduced to the SRF controller. The design of the SRF controller and the noise attenuation compensator is addressed utilizing vibration theories. Finally, active vibration control experiments are implemented to demonstrate that the proposed active vibration control strategy is effective. Power spectral density plots of vibrations illustrate that the structural vibration of flexible links is suppressed effectively when the proposed SRF vibration control strategy is employed.