Design of a composite lighting system based on a freeform and a rod lens for machine vision

Light-emitting diodes (LEDs) have been widely utilized in machine vision lighting systems such as the process monitoring system in the additive manufacturing field, owing to their long life, high illumination efficiency, and controllable dimming. The quality of the lighting system directly affects the efficiency and accuracy of the entire monitoring system. However, existing designs cannot meet the optical efficiency and uniformity requirements at short lighting distances and small inspection areas with mixed multi-spectrum channels. This paper thus proposes a novel, to the best of our knowledge, design method of integrating a freeform surface lens and a square-shaped rod lens. The optical characteristics under different working distances and targeting surface types have been optimized and evaluated. Meanwhile, tolerance analysis has been utilized to demonstrate the feasibility of installation. With the use of the software Tracepro, simulation results showed that the designed composite machine vision lighting system can obtain an optical efficiency of 81.704% and an illuminance uniformity of 95.804% within the inspection area at a distance of 250 mm. Furthermore, verification experiments with a prototype were performed, demonstrating the feasibility of the proposed machine vision lighting system.