The system is clear, and the surface of the object is mostly the Lambertian reflection surface, and the optical imaging system form can generally be equivalent to the model. The light source illuminates the surface of the workpiece to form diffuse reflected light, and its light intensity is: l Introduction General optical system imaging model I. is the outgoing light intensity of the illumination source, i is the incident angle of the light source, d. is the distance from the light source to the object, PdU, y The reflectivity of the surface of the object is divided into a passive visual inspection system. The illumination source is an important part of it. The quality of the illumination source directly affects the image quality M, edge extraction and fitting effect of the image, affecting the final measurement. result. In the precision detection system, the illumination source plays a decisive role. The light intensity, illumination stability and uniformity of the light source will have a great impact on the accuracy and repeatability of the system, which may lead to the design of the whole system. failure. In this paper, the light intensity transfer function of the visual inspection system is firstly deduced. Then the design points of illumination intensity, illumination stability and uniformity are analyzed. Finally, an annular cold light source capable of adaptively adjusting the light intensity is designed.
2 Light intensity transfer function of visual inspection system For general passive vision detection systems, non-coherent illumination is mostly used. The receiving device receives diffusely reflected light from an object imaged by the optical system. The pseudo-directions are a, b, and the lateral and longitudinal spacings of the photosensitive elements are respectively c, so that the area array CCD is used as the receiving device, and the lateral distribution of the CCD photosensitive element and the vertical d. k is the proportional coefficient, t is the CCD charge integration time, S. is the area of ​​the optical system, the mountain is the distance from the object to the optical system, M is the overall amplification factor of the detection system, and h(x, y) is the optical system. Point extension function.
3 illumination source design 3.1 source illumination considerations As can be seen from equation (2), the final integrated charge of the CCD device is proportional to the light intensity of the source and the cosine of the incident angle, inversely proportional to the square of the distance from the source to the object. For a given CCD device, the exposure should be limited to a certain range. If the exposure is too large, all the pixels of the CCD device will be saturated or approach saturation. Otherwise, if the illumination of the photosensitive surface is too low, the object will be Some points are overwhelmed by noise, both of which can distort the picture and ultimately produce measurement errors. Therefore, it is preferable to adjust the maximum illuminance of the photosensitive surface to be lower than the maximum saturation illuminance in order to make full use of the dynamic range of the device. In actual measurement, the distance between the light source and the measured object and the incident angle of the light source often have to be adjusted, which results in a large change in the illumination of the surface of the workpiece, which is difficult to ensure that it is always within the illumination range of the CCD device. Therefore, this paper uses neural network to judge the intensity of the collected image light intensity, and decides and commands the duty cycle of the PWM power supply to control the light source to adjust the radiation intensity of the light source I. To compensate for the change of illumination caused by the change of mountain and i. . The control block diagram is as shown.
The illumination stability of the illumination source is also a very important factor. The optical irradiance of the light source should always be constant or the frequency of the change of the light source is much higher than the frequency of the image captured by the detection system. In order to prevent the power frequency interference of the power supply of the light source, this paper is designed. When the power source of the light source is used, the power main circuit and the output circuit are respectively fabricated on two circuit boards.
3 illumination uniformity The uniformity of the light source in the entire field of view is also a problem that should be paid attention to in particular the uniformity of the light source. It is a binarized image of an image collected under uniform illumination and non-uniform illumination, respectively. a) the picture is the original image, (b) the picture is the binarized image under uniform illumination, and (c) the picture is the binarized image under non-uniform illumination. It is easy to see from the above figure that the uniform full field illumination pair The importance of the detection system. Therefore, this paper designs an LED ring light source, which uses the light intensity of the LED to form a uniform illumination light.
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