Piezoelectric damping of position dependent parasitic resonances for improved performance of flexure-based manipulators

The performance of precision machinery is often limited by parasitic vibration modes of the system. These parasitic resonances typically limit the actuation bandwidth, can lead to long settling times and can degrade the end-effector standstill performance when disturbance forces or floor vibrations are present. As a complicating factor, the parasitic resonance frequencies may vary over the workspace of the system. Conventional design guidelines focuses on stiff and lightweight design, leading to high parasitic resonance frequencies. However, for further improvement in performance, damping of some of the problematic resonances is required. In this work, a flexure-based manipulator is considered that exhibits performance limiting resonances, of which the frequencies vary with the deflection of the manipulator. An active damping approach, based on integrating piezoelectric material in the flexures which actively suppress the parasitic vibration modes is proposed and experimentally validated. Using a scheduled vibration controller, the actuation budget is effectively and efficiently used to suppress targeted parasitic resonances over the entire workspace, leading to a significant increase in the dynamic and steady state performance of the flexure-based manipulator. The resonance peak height of the first four parasitic resonances is reduced by a factor 10 over the majority of the workspace. This results in a modal damping of these resonances in the range 2-7%. Due to the resonance peak suppression, the control bandwidth of the Lorentz actuator for the intended motion of the manipulator can effectively be doubled. Lastly, it is shown that the higher control bandwidth and improved settling behaviour of parasitic resonances lead to better disturbance rejection and faster cycle times for an indexing setpoint task.