迪奥科技标语
Factors affecting the stability of machine vision detection system
Author:Administrator   Published in:2019-11-08 11:15

With the rapid development of China's manufacturing industry, the machine vision industry has also passed the initial period of development in the Chinese market. How to design the machine vision system? Its difficulty lies in how to ensure its reliability and stability. No matter from the design of light source, camera and other hardware or image processing software, it has an important impact on the stability of machine vision. As we know, there are many factors that affect the measurement accuracy of machine vision detection system, including the errors of imaging system, various noises, calibration errors and software algorithms.

1569828970726884.jpg

Brief introduction of imaging system and instability factors

The imaging system is mainly composed of camera (CCD / CMOS), lens and light source, which is the basis of visual inspection. The design purpose of the imaging system is to obtain qualified original image, and a good imaging system should ensure the stability of image quality during the operation of the system. Stable image capture is an important guarantee of the stability of visual inspection.

1. Influence of industrial camera on imaging stability

For the visual system designer, the selection of industrial camera mainly considers its sensor type, resolution and frame rate. There are two kinds of sensors: CCD and CMOS. CMOS image sensor has high integration, close distance between components and circuits, serious interference, high imaging noise. Compared with CMOS camera, CCD sensor camera has the characteristics of high sensitivity, low noise and fast response Generally speaking, CCD sensor camera is better than CCD camera in imaging quality and stability.

Another important factor that affects the imaging quality of the camera is the lens of the camera. In addition to choosing appropriate parameters such as focal length, depth of field and aperture according to the specific working conditions of the lens, an important factor that affects the detection accuracy of the system is the geometric distortion error of the image, which is the inherent perspective distortion of the optical lens. Affected by the manufacturing process, it cannot be eliminated, but can only be made up, Although many industrial cameras use various methods to compensate for the errors caused by lens distortion, in the field of high-precision detection, geometric distortion still has an impact on the detection accuracy.

2. Influence of light source on imaging stability

Light source has the functions of magnifying the image's features and defects, weakening the confusion and background, which directly affects the quality of input data. Because there is no general lighting equipment, the design of light source has always been a difficulty in machine vision system. Generally, it is not only necessary to select the type of light source according to each specific application, but also to install the light source and illuminate the light source according to the specific environment Consider for best results. There are differences in the stability of different types of light sources. The common visible light sources include LED light source, halogen light, fluorescent light and sodium light. The biggest disadvantage of visible light is that it can't continuously and stably output light energy. For example, in the first 100 hours of use, the light energy will decrease by 15% left and right. With the increase of use time, the light energy output will continue to decline. In addition to visible light, in the scene of high detection task, invisible light such as X-ray and ultrasonic is often used as light source, which can continuously and stably output light energy, but it is not conducive to the operation of detection system, and the price is expensive. The nonuniformity of light source will also affect the image quality, and the difference of light intensity in different directions will also cause noise. Compared with halogen lamp and fluorescent lamp, the stability and life of LED light source in visible light is better, the response time is shorter, the color can be selected freely, and the operation cost is lower, so it has been widely used. The illumination mode of light source can be divided into back lighting, forward lighting, structural lighting and stroboscopic lighting. The key point of its design is to highlight image features.

3. Software stability

There is no doubt that the stability of the detection software has an impact on machine vision. The vision system will eventually use the software to carry out a series of image processing, such as image filtering, edge detection and edge extraction, using targeted algorithms on the computer. Different image processing and analysis methods, different detection methods and calculation formulas will bring different errors. The merits and demerits of the algorithm determine the accuracy of measurement Degree.

4. Impact of environmental factors

The measurement environment of vision system includes temperature, light, power change, dust, humidity and electromagnetic interference. A good environment is the guarantee of normal operation of vision system. The external light note affects the total light intensity on the measured object, increases the noise of the image data output, and the change of the power supply voltage will also lead to the instability of the light source, resulting in the noise varying with time. The temperature change will also affect the performance of the camera. The camera will mark the normal temperature range when leaving the factory. Overheating or supercooling will affect the normal operation of the camera. Electromagnetic interference is an inevitable interference factor in the field of industrial detection. It has a particularly serious impact on weak current circuits such as industrial camera circuit, data signal transmission circuit, etc. qualified visual products will undergo strict anti-interference test in the factory, greatly reducing the impact of external electromagnetic interference on the hardware circuit.

5. Influence of mechanical structure positioning

In addition to the hardware of the imaging system, the relative position relationship between the camera and the object will also affect the stability of the image quality. For example, if there is vibration in the mechanical support structure of the camera or the workpiece, it will affect the detection accuracy, which is also a difficult problem to troubleshoot. In the dynamic detection of workpiece, the influence of motion blur on image accuracy needs to be considered (blur pixel = object motion speed * camera exposure time) In addition, the optical axis of the camera lens should be perpendicular to the plane of the part under rational condition between the CCD camera and the tested part, but in actual use, due to the installation error or the manufacturing error of the camera and the workpiece, the optical axis cannot be completely perpendicular to the measured plane, and there is a certain angle deviation, which also affects the measurement accuracy.

The above is the whole content of "factors affecting the stability of machine vision system detection" shared by Teo technology editor. If you want to know more, please consult online.

 


Copyright @ 2016 - 2019 迪奥科技 版权所有 备案号: 粤ICP备09101295号