Residual vibration control based on a global search method in a high-speed white light scanning interferometer

Area of Science:

• Optical Metrology
• Mechanical Engineering
• Signal Processing

Background:

• High-speed measurements with white light scanning interferometers require high feedback gain in closed-loop systems.
• Flexure hinges in scanning devices cause residual vibrations, leading to fringe order misidentification and inaccurate profiles.
• Nonlinear distortions in interferograms due to vibrations significantly degrade measurement quality.

Purpose of the Study:

• To develop a novel method for reducing residual vibrations in scanning devices for interferometric measurements.
• To improve the accuracy and speed of white light scanning interferometry by mitigating vibration-induced errors.
• To enhance the extraction of modal parameters for input shaping control.

Main Methods:

• Proposed a global search algorithm to extract equivalent modal parameters of scanning devices.
• Utilized input shaping to control the amplitude of residual vibrations.
• Compared the proposed global search method with the conventional continuous wavelet transform (CWT) for parameter estimation.

Main Results:

• The global search algorithm demonstrated superior performance over CWT in terms of simplicity, implementation ease, and response speed.
• Reduced delay time by requiring fewer modes for the input shaper.
• Significantly improved interferometer intensity profiles and recovered accurate surface topography, validated by silicon wafer measurements.
• Experimental results showed good agreement with simulated shaped responses.

Conclusions:

• The proposed global search method effectively reduces residual vibrations in scanning devices.
• This technique enhances the accuracy of white light scanning interferometry and surface topography measurements.
• The method offers a faster and simpler alternative to conventional techniques for input shaping parameter estimation.