Development of a flexible and modular metrology system for measuring complex surfaces

Schneider, Florian Richard

Abstract

The demand for customised optical devices is increasing tremendously. Such optical devices do not employ traditional designs like planar, spherical, or even aspherical shapes. Instead, modern lenses exhibit free-form surfaces with a large variety of gradients in all directions. Highly accurate and repeatable measurement of such lens surfaces represents a considerable challenge; therefore there is a pressing need to both improve the metrology systems used in the optical industry and to develop new generations of high-performance metrology systems that employ innovative measurement techniques.
Workshops need fast measurement solutions for the rough surfaces produced in the early stages of a lens typical production chain. The last steps produce very smooth surfaces, usually ideally suited to interferometers. However, interferometers are physically not suited to the measurement of strong aspheres or free-form shaped objects. Therefore, research was undertaken to investigate a metrology solution applicable to all common surface types and roughness grades at any stage of the production chain.
This PhD research presents a novel approach for applying the principle of a spherical coordinate measurement machine (SCMM) to lens metrology. SCMMs require the precise and repeatable alignment of all axes. Therefore, research was performed to investigate a novel method for generic axes alignment without the need for external tools. This method, with the enhanced SCMM approach, was then combined with research into suitable multi-sensor measurement modes, in order to adequately address the needs of all stages in the production chain.
Coordinate measurement machines are subject to the influence of errors. Therefore, research was conducted to develop a novel user-interface and a patented device to analyse and compensate for errors of the applied rotational axes and the 3D-Scale.
The mathematical models presented, enable a simple transfer to other types of SCMMs. Also, the researched processes, software tools and mechatronic devices may be generically adopted to other machines applying rotational axes. Therefore, in addition to providing advanced capabilities for high-accuracy measurement of lenses with complex morphologies; the results of this research and the new approaches developed may be employed with SCMMs more generally, in a wide range of industrial sectors.

• Thesis Type: Thesis
• Publicly Available Date: Jan 20, 2020
• Keywords: SCMM, spherical coordinate measurement machine, optics, metrology
• Public URL: https://uwe-repository.worktribe.com/output/1491077
• Additional Information: Additional Information : The thesis comes with an additional CD containing the publications.
• Award Date: Dec 31, 2018