Inspect Transparent Objects With Chromasens allPIXA wave

Abstract 

This application note discusses using line scan cameras to inspect transparent materials such as acrylic plates for cosmetic defects.

Problem Statement

Glass and acrylic plates have many uses in our daily lives. They can be your windows, glass panels for your offices, or even DIY applications. Hence, manufacturers would need to conduct a cosmetic defect inspection before shipping them out to customers.

Inspecting clear and transparent objects are usually challenging for users, as some defects or scratches can not be seen with a naked eye. Hence, users would use machine vision and cameras to conduct cosmetic defect inspections for transparent objects.

However, the problem lies when the clear and transparent objects deflect light back into the camera, making the images unusable for inspection. This makes it counterproductive as more time is used to adjust the lighting angle and retake images so the camera can capture defects. 

Hence, what camera and lighting would be suitable for inspecting acrylic plates and objects with similar characteristics? 

Solution

For this application, we used a Chromasens allPIXA wave 15k mono line scan camera, a Myutron XLS05 lens, and a Chromasens Corona II Dark Field Illumination to inspect for cosmetic defects on the acrylic plate.

Figure 1: Application setup image of Chromasens allPIXA wave 15k mono line scan camera, Myutron XLS05 lens, and Chromasens Corona II Dark Field Illumination, scanning a transparent acrylic plate.

The Chromasens allPIXA wave 15k mono line scan camera offers a trilinear CMOS sensor, and a line length of up to 15,360 pixels. From the results below, the allPIXA camera is able to provide high-resolution and highly accurate images of the cosmetic defects on the plates at high speed. Moreover, the line scan camera is able to capture a wide field of view of the acrylic plate in one image.

Figure 2: Close-up of Chromasens allPIXA wave 15k mono line scan camera

Figure 3: Full image capture by Chromasens allPIXA wave 15k mono line scan camera (15360 pixels  ×  20000 pixels)

Figure 4: Image of scratches on the acrylic plate using Chromasens allPIXA wave 15k mono line scan camera and Chromasens Corona II Dark Field Illumination

For this application, we also considered using an area scan camera with 20MP resolution and 5472 pixels x 3648 pixels to conduct the inspection. However, the area scan camera would face difficulties detecting non-directional scratches on the acrylic plate surface, missing out on some of the scratches. This is mainly due to the low number of pixels and the object reflecting light patterns back to the area scan cameras.

Figure 5: Comparison image of scratches on the acrylic plate using an area scan camera, a ring light (left), and a bar light (right)

In this application, line scan cameras can provide a large field of view of the acrylic plate in one image. Compared to area scan cameras, users would need to capture multiple images of the acrylic plate. This makes line scan cameras more efficient and less time-consuming for applications involving inspecting acrylic plates.

 

Reach out to us!

Want to find out how else you can utilise line scan cameras or dark field illumination in your applications? Contact us now!