Chromatic focus variation for surface metrology

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


Optical metrology plays a vital role in a wide range of research and inspection areas in the industry. The focus variation instrument is a popularly adopted method for additively manufactured parts because it can measure steep surfaces with very high slopes and irregularities. The contrast/sharpness between the neighbouring pixels is used to determine the image focus position, and hence the surface height is obtained. In traditional focus variation instruments, a piezoelectric actuator (PZT) is used for mechanical scanning in image capturing. The slow mechanical movement is a limiting factor for fast measurement in modern advanced manufacturing applications. Another issue associated with the traditional focus variation instruments is the nonlinear hysteresis motion of PZTs and their physical size. To overcome the above limitations, we propose a chromatic focus variation method to axially shift the focus along the optical axis without any mechanical movement using a wavelength scanning mechanism combined with a chromatic objective lens. This work presents initial measurement results obtained using the proposed system and its comparisons with the commercial Alicona focus variation system.
Original languageEnglish
Title of host publicationProceedings of the Joint Special Interest Group meeting between euspen and ASPE
Subtitle of host publicationAdvancing Precision in Additive Manufacturing
Number of pages2
Publication statusPublished - 19 Sep 2023
EventEuropean Society Precision Engineering and Special Interest Group: Advancing Precision in Additive Manufacturing - KU Leuven, Leuven, Belgium
Duration: 19 Sep 202321 Sep 2023


ConferenceEuropean Society Precision Engineering and Special Interest Group
Abbreviated titleEUSPEN 2023
Internet address

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