选择正确的镜头和照明

Step 1:
Determining the direction of emission(specular reflection, diffuse reflection, transmission)

光的基础

当入射光（棕色箭头）撞到零件的表面时，光线会宽大地分离并在四个不同的方向上行驶。

1. 镜面反射以相同的角度反射
2. Diffuse reflected light that diffuses on the surface of the part
3. 传输的光直通过零件
4. 扩散的发射光，传输散射在整个零件表面的光线

Using the incident light as 100%, the ratio of light specularly reflected is called specular reflectance, the ratio of other reflected light is called diffuse reflectance, and the sum of the two is called total reflectance.

机器视觉中使用了三种主要的照明方向。

• 镜面反射类型

  Lens receives light that specularly reflected off the target, which works effectively with parts with reflective properties, such as a glass substrate.

• 扩散反射type

  镜头接收光线均匀分布,而再保险leasing the specularly reflected light. This type is effective for inspections done through transparent tapes in order to ignore reflective parts.

• Transmission type

  Light is emitted from behind the target to detect the silhouette with the transmitted light. This type is useful for parts that easily pass light, such as non-woven fabric.

Step 2: Determining the lighting type and shape

After determining the lighting direction, select the lighting type (model) based on the inspection requirements, background, and ambient environment. From the lighting options for each lighting direction, select the suitable lighting type as illustrated below.

Step 3: Determining the lighting color/wavelength

The final step is to decide the color of the lighting that works the best for the part and background. White is generally selected when using a color camera. However, when using a black-and-white camera, the following knowledge becomes more important.

Step 4: How to calculate the focal distance and field of view

其中一个镜头规格是焦距。Typical lens sizes used in factory automation include 8 mm 0.31", 16 mm 0.63", 25 mm 0.98", and 50 mm 1.97". You can calculate the working distance (WD), which is the point at which the camera comes into focus, from the field of view (FOV) and focal distance necessary for the target to be captured.

The WD and FOV values depend on the lens’ focal distance and image sensor size. For WDs greater than the minimum WD where a close-up ring is unnecessary, the WD can be estimated using the following proportion.

步骤5：
How to increase the depth-of-field (range of heights at which the lens remains in focus)

• Lens with shorter focal distance has a greater range of depth.
• As the distance to the target gets farther, the deeper the range of depth becomes.
  →请注意，使用特写戒指或宏观镜头时，深度场的深度较小。
• The smaller the opening of the aperture, the deeper the range of depth is.
  →It is easier to obtain focus using aperture zoom and bright light.

此示例比较用较小的光圈和最大捕获的图像捕获。捕获带有胶带的目标时的光圈表示斜坡上的高度，如下图所示。

步骤6：基于镜头性能的对比度

The images on the right show the same target, captured using KEYENCE’s high-resolution lens CA-LH16 and standard lens CV-L16. The difference in the images derives from the differences in lens material and structure. Selecting a high-resolution lens depending on the application can provide images with higher contrast.