Matching technology for industrial cameras and lenses

Today, the choice of industrial cameras and industrial lenses is popular. First of all, optical lenses. Optical lenses are generally called camera lenses or photographic lenses, referred to as lenses, and their function is optical imaging. The lens is an important component in the machine vision system and has a key role in imaging quality. It has several major indicators of imaging quality, including: resolution, contrast, depth of field, and various aberrations. Not only are there many types of lenses, but the quality difference is also very large. However, the general user often pays insufficient attention to the choice of the lens when designing the system, resulting in failure to obtain ideal images and even failure in system development.

远心工业镜头

The industrial lens is equivalent to the lens of the human eye. If there is no lens, the human eye cannot see anything; if there is no lens, then the image output by the camera; it is a white piece with no clear image output. The principle is the same. When the muscles of the human eye cannot stretch the lens to a normal position, which is often referred to as myopia, the scene in front of the eye becomes blurred; the cooperation between the camera and the lens also has a similar phenomenon. When the image becomes unclear You can adjust the back focus of the camera, change the distance between the CCD chip and the reference surface of the industrial lens (equivalent to adjusting the position of the lens of the human eye), and you can make the blurred image clear.

It can be seen that the role of the lens in the closed-circuit monitoring system is very important. Engineering designers and constructors must always deal with the lens: designers need to calculate the focal length of the lens according to the object distance and imaging size, and the construction staff often perform on-site debugging, part of which is to adjust the lens to the best state.

So if you know the optical lens, how do you choose an industrial camera? Industrial cameras are generally installed on machine lines instead of human eyes for measurement and judgment. Digital image capture targets are converted into image signals and transmitted to a dedicated image processing system. The image system performs various operations on these signals to extract the characteristics of the target. Furthermore, the operation of the equipment in the field is controlled based on the discrimination result.

1. Usually you first need to know the system accuracy requirements and camera resolution. You can use the formula:

X-direction system accuracy (X-direction pixel values) = field of view (X-direction) / number of CCD chip pixels (X-direction)

Y-direction system accuracy (Y-direction pixel value) = field of view (Y-direction) / number of CCD chip pixels (Y-direction)

2. Of course, the theoretical pixel value is obtained by comprehensive consideration of system accuracy and sub-pixel method; then you need to know the system speed requirements and camera imaging speed:

System single operation speed = system imaging (including transmission) speed + system detection speed

Although the system imaging (including transmission) speed can be calculated theoretically based on the camera's asynchronous trigger function, shutter speed, etc., the best method is to actually test it with software.

3. Then you need to consider the camera and the frame grabber together, because this involves the matching of the two:

Video signal matching: There are two formats for black and white analog signal cameras, CCIR and RS170 (EIA), usually the capture card supports both cameras;

Resolution matching: each board only supports cameras in a certain resolution range;

Matching of special functions: If using the special functions of the camera, first determine whether the board used supports this function. For example, if multiple cameras are to take pictures at the same time, the capture card must support multiple channels. The capture card must support progressive scanning.

Interface matching: Determine whether the interface of the camera and the board match. Such as CameraLink, GIGE, CoxPress, USB3.0 and so on.

4. After satisfying your necessary requirements for testing, the price comparison should be the last one.

Example: If our inspection task is dimensional measurement, the product size is 18mm * 10mm, the accuracy requirement is 0.01mm, the assembly line operation, the detection speed is 10 pieces / second, the on-site environment is a general industrial environment, and the interference problem is not considered.

First of all, we know that it is an assembly line operation, and the speed is relatively fast, so we use a progressive scan camera; the size of the field of view can be set to 20mm * 12mm (considering the error of each mechanical positioning, the field of view is appropriately enlarged than the object) Very good images (such as backlighting), and the measurement accuracy of our software can consider 1/2 sub-pixel accuracy, then the camera resolution we need is 20 / 0.01 / 2 = 1000pixcel (pixels), and the other direction is 12 /0.01/2=600pixcel, which means that the resolution of our camera needs to be at least 1000 * 600pixcel, and the frame rate is 10 frames / second, so choose 1024 * 768 pixels (if the software performance and mechanical accuracy are not accurate, you can also consider 1280 * 1024pixcel), the frame rate can be more than 10 frames / second.