Case analysis：The above picture shows the vehicle lithium battery product (relatively large). Defects such as creases, scratches and foreign bodies on the surface need to be detected. The product is relatively large and the surface is smooth and reflective. It was evaluated that the field of view was too large and it was difficult to light if using area scan camera, so the line scan camera is directly used to shoot. There are several types of LOTS line scan lights, including common line scan light, multi-angle line scan light, tunnel line scan light, coaxial line light, etc. Let's take several effects of line scan light as a reference.
Line scan light: There are two irradiation modes of line scan light, which are single line scan light and double line scan light. Usually, we use a single line scan light. If the product has edge height difference (single line scan light will have shadow effects), or the uniformity needs to be strengthened, you can consider double line scan light. Line scan light is kindly flexible which can be placed at any angle with bright FOV and dark FOV. The optical path is very collected and directional.
The following effective picture is used single line scan light.
Advantages: The whole surface is uniform in the middle, and the characteristics of foreign bodies and creases are obvious.
Disadvantages: The starting position is too bright, the end part has shadow, the direction is single, the scratches cannot be seen all.
The following effective picture is used double line scan light.
Advantage: The middle surface is relatively uniform, foreign body features are obvious
Disadvantage：The starting position is too bright, the direction is single, the scratch cannot be seen all
Coaxial line scan light: It is mainly aimed at surface feature detection, such as surface scratch, bump, character and other features detection. The lithium battery is used coaxial line scan light for uniform surface, scratches, foreign bodies, creases and other characteristics, which effect is very good. Specific can refer to the following effect pictures
Multi-angle lines scan light: Mainly for scratch type detection, usually the light path will make the scratch relatively bright, used for most of the mobile phone screen detection applications. Using this light on lithium batteries, the surface is very uniform, but the effect is not very good because the scratches are also relatively bright same as the background. Specific can refer to the following effect pictures:
Tunnel line scan light: Tunnel line scan light has the best uniformity in all line scan lights, which is generally used in surface printing. Using this light source on a lithium battery, the surface is very uniform, but the type of features that need to be detected are very poor, Specific can refer to the following effect pictures:
Summary： Large lithium batteries are widely used in testing and usually, line scan camera with light source is adopted to achieve uniform image, no distortion and high precision. For the choice of LOTS lights: Line scan light has high brightness and strong directionality, so the effect of scratch detection is not very ideal. Although the Multi-angle line scan light is specialized for scratch detection, it is only suitable for the effect of black background. The role of the Tunnel line scan light is to make the image very uniform. Coaxial line scan light can eliminate reflection, high angle light path is suitable for detecting surface scratches, and has a very good effect on concave and convex surfaces, dirt, printing and other features. To sum up, coaxial line scan light has a very good application effect for surface feature detection of large lithium battery products.