LED-Based Collimating Line-Light Combining Freeform and Fresnel Optics

• Published in: IEEE photonics journal Vol. 10; no. 6; pp. 1 - 13
• Main Authors: McCarthy, AnneMarie, Romero-Vivas, Javier, O'Hara, Ciara, Rebrova, Natalia, Lewis, Liam, Hegarty, Stephen P.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.12.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptive optics; Collimation; Design for manufacturability; Emission; Emitters; freeform optics; Fresnel lenses; Inspection; LEDs; Lens design; Lenses; Light emitting diodes; Lighting; line-light; Machine vision; Optical design; Optical device fabrication; Ray tracing; Vision systems
• ISSN: 1943-0655; 1943-0655; 1943-0647
• DOI: 10.1109/JPHOT.2018.2876381

Illumination for line-scan machine vision systems is required to produce a highly asymmetric elliptical beam pattern, to maximize system speed and accuracy. The use of LED emitters with symmetric Lambertian emission patterns is challenging in this context, requiring significant beam reshaping. A design for a collimated line-light, with long working distance, utilizing LEDs with symmetric Lambertian emission patterns, is presented. Using a combination of Fresnel lenses and total internal reflection (TIR) optics, an elliptical beam with a high degree of collimation is achieved. TIR elements are designed based on an adaptation of a freeform lens design method published by Chen et al. [Opt. Express 20, 10 (2012)]. Practical performance of the design is verified experimentally using a prototype unit. In addition, the design is compared, using ray tracing software, to line-lights constructed using commercially available symmetric and elliptical TIR lenses, and its superior performance is confirmed. The optical design described is fully manufacturable and suitable for both small- and large-scale production.