Design and implementation of a precision levelling composite stage with active passive vibration isolation

The white-light-interference (WLI) three-dimensional topography fine detection has high requirements for the chip-loading stage on levelling and vibration isolation capacity, to ensure that the micro-meter-level structured chip is stably aligned with the WLI scanning head. To meet the high performance detection requirements, this paper designs a novel three-axis levelling and active-passive vibration isolation (LAPV) composite stage, in order to perform precision tilt levelling and wide-frequency-domain vibration isolation. The proposed LAPV stage integrates a modified quasi-zero-stiffness passive vibration isolation unit with an active actuation unit which consists of three voice coil motors (VCMs). It performs active-passive vibration isolation while ensuring a precision levelling. Considering the load bearing and motion vibration of the chip-loading stage, a miniaturized quasi-zero-stiffness mechanism having a specialized leaf spring structure is then designed to limit the vibration isolation operation to the vertical direction and coordinate the levelling motion of the tilt rotation direction, so as to establish a structural decoupling stage. Based on the dynamic and kinematic modelling analysis, a customized PID-Positive Position Feedback (PID-PPF) control scheme is implemented. Afterwards, an experimental verification is conducted. The obtained results show that the stage can achieve a precise levelling motion, reaching a levelling deviation of 33.2 mu rad. Moreover, it also can achieve effective active-passive vibration isolation for various vibrations with different frequencies and amplitudes, and the vibration isolation rate can reach 90 %.