Supplemental Peak Filters for Advanced Disturbance Rejection on a High Precision Endeffector for Robot-Based Inline Metrology

This article presents a metrology platform (MP) as high precision endeffector of a robot with a tailored disturbance rejection scheme in order to enable high-resolution measurements directly in a production line. The MP is installed on a gantry robot for in-plane positioning and has an electromagnetic actuator for vertically positioning its mover. It can mount a compact measurement tool for high precision topography measurements, which are typically sensitive to external vibrations, introducing relative motion between the measurement tool and the sample. To compensate these vibrations, the MP mover vertically tracks the sample by feedback control, maintaining a constant distance between sample and measurement tool. In order to reject broad-band floor vibrations as well as narrow-band vibrations, revealed by the analysis and introduced by the robots servo control, the designed high-bandwidth proportional-integral differential based controller is supplemented by peak filters tailored to the narrow-band vibration components. A method for designing these peak filters depending on the location of the narrow-band disturbance relative to the crossover frequency is presented. The resulting controller enables a tracking error as small as 15 nm (rms), which is 50% smaller than the error without the peak filters, demonstrating the effectiveness of the MP in enabling high-resolution inline measurements.