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Basic Structure of Machine Vision System Design and Basic Principles of Light Source Selection

Ⅰ. The basic structure of machine vision system design

(1) The light source of the machine vision system

In the current machine vision system, a good light source and lighting plan are the key to the success or failure of the whole system. The cooperation between the light source and the lighting plan should highlight the characteristics of the object, and there should be obvious differences between the parts that need to be detected and those unimportant parts.

(2) Optical lens of the machine vision system

The optical lens is equivalent to the crystalline lens of the human eye and is very important in the machine vision system. The main performance indicators of the lens are focal length, aperture coefficient, magnification, interface and so on.

(3) Camera for the machine vision system

The camera is the most important part of the machine vision system to obtain the original information, and the CMOS camera and CCD camera are mainly used now. Now CCD cameras are widely used in various fields due to their fineness, reliability and high definition.

(4) Picture capture card for the machine vision system

In the PC-based machine vision system, the picture capture card is an important device for controlling camera photography, completing picture capture and digitization, and coordinating the entire system.

(5) Vision sensor for the machine vision system

The architecture of machine vision system based on PC has no modularization, with inconvenient installation and poor portability, especially compared with the PLC interface widely used in the industry. From the perspectives of both software and hardware development, a machine vision component that is more suitable for industrial needs is required.

Ⅱ. Basic principles and methods of selecting the light source of machine vision

(1) Select according to the characteristics of the detected products

① Generally, the size of the light source is larger than that of the product, so that the light can cover the entire product.

② The shape of the selected light source is close to the shape of the product, which can make the light intensity of the entire product area the same.

③ The color of light source of machine vision should be able to make the detection target have a certain contrast with the background. Using a light source that is close to the color of the targeted product area under the camera can make the area appear higher gray, otherwise it will appear lower gray.

④ If the surface of the product has strong reflection, you can choose a shadowless light source with better uniformity, and choose a light source with better directivity or parallelism if the features are not obvious.

(2) According to institutional requirements

The light source of machine vision should meet the requirement of installation space of the equipment. If the production line is fast, it is necessary to select a light source with higher brightness; in a special environment (humidity, high temperature), the light source function (waterproof, heat dissipation) needs to be considered.

(3) Practice test

The light source of machine vision can produce useful contrast, and ensure the uniformity of each area. Generally, there is a peak value close to 255 gray levels in the square matrix and background of the detection area. At this time, the contrast is generally the highest. Strengthening or weakening the brightness of the light source will affect the contrast difference.

When there is a good comparison picture, be sure to place the detection object in every position in the field of view to see if the pictures are the same, so as to ensure the stability in the practical environment.