Colour imperfections in structured light projection for freeform measurement – a rapid test

ABSTRACT

Three-dimensional (3D) optical measuring systems using structured light are often limited in practice by imperfections in the light patterns projected onto the object under test. An understanding of the fine structure of the patterns enables limits to be placed on the accuracy and precision of 3D measurements that can be obtained with such systems. A simple technique has been studied that reveals imperfections in patterns of parallel lines projected in white light. Colour fringing has been revealed using a reference grid in the form of a diffusely reflective grating or a lenticular array, to obtain magnification by means of moiré effects. The moiré magnifier gives a representation of the average error over an area. It is a very simple and robust device which may be convenient to use in an industrial production environment to provide a rapid check for the presence of colour fringing in light patterns with regular structures.

KEYWORDS:

• 3D optical scanner
• chromatic aberration
• moiré magnifier
• dimensional characterization

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Stephen Brown is a physics graduate who joined the National Physical Laboratory (NPL) in 1980. He has been involved in various types of dimensional metrology.

Richard Stevens is a consultant scientist working in optical metrology at NPL.

David Williams is a consultant scientist working in optical metrology at NPL.

Michael McCarthy has 25 years experience in dimensional metrology at NPL, and is currently an honorary professor at University College London.

ORCID

Stephen Brown http://orcid.org/0000-0002-4367-3200

Additional information

Funding

This work was supported by the UK Government’s Department for Business, Innovation and Skills.