Saturated Imaging for Inspecting Transparent Aesthetic Defects in a Polymeric Polarizer with Black and White Stripes

Cilong Yu,Peibing Chen,Yuanlong Deng,Xizhou Pan,Xiaopin Zhong

doi:10.3390/ma11050736

Abstract

Machine vision systems have been widely used in industrial production lines because of their automation and contactless inspection mode. In polymeric polarizers, extremely slight transparent aesthetic defects are difficult to detect and characterize through conventional illumination. To inspect such defects rapidly and accurately, a saturated imaging technique was proposed, which innovatively uses the characteristics of saturated light in imaging by adjusting the light intensity, exposure time, and camera gain. An optical model of defect was established to explain the theory by simulation. Based on the optimum experimental conditions, active two-step scanning was conducted to demonstrate the feasibility of this detection scheme, and the proposed method was found to be efficient for real-time and in situ inspection of defects in polymer films and products.

Highlights

Machine vision refers to the efficient technology used in industrial inspection lines for automation and contactless inspection, and a variety of products require such automated inspection of defects [1,2,3]
We have previously implemented the inspection of the inner transparent aesthetic defects of a polymeric polarizer with black and white stripes; these special defects were barely observable when the polarizer was illuminated by a conventional white backlight
By adjusting the light intensity, exposure time, and camera gain, the saturated effect of the camera substantially improved the contrast of the defect image, making it possible to detect extremely slight transparent aesthetic defects (ESTADs) within the black stripe

Summary

Introduction

Machine vision refers to the efficient technology used in industrial inspection lines for automation and contactless inspection, and a variety of products require such automated inspection of defects [1,2,3]. We have previously implemented the inspection of the inner transparent aesthetic defects of a polymeric polarizer with black and white stripes; these special defects were barely observable when the polarizer was illuminated by a conventional white backlight. When the depth of the defect and the refractive index difference (between the defect and polarizer) further decreased, the extremely slight transparent aesthetic defects (ESTADs) could not be imaged, even under structured light illumination. This paper proposes a new inspection method to detect the ESTADs using saturated imaging techniques that enhance the image contrast of transparent defects in a polymeric polarizer. By adjusting the light intensity, exposure time, and camera gain, the saturated effect of the camera substantially improved the contrast of the defect image, making it possible to detect ESTADs within the black stripe. The image contrast of the defect was further improved, and two steps fully covered a sample, which greatly improved the detection speed and satisfied the inspection demands of an assembly line

Optic Simulation

Experiment and Results

Defect of two samples various illumination levels:

Processed

Discussion

Conclusions