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摘要: 针对机器视觉检测技术在缸体内表面横孔检测应用中存在的光源设计复杂、照度均匀性差等问题，本文提出一种以LED为直接光源在缸体内部照射横孔，以积分球为背景光源在缸体外部照射横孔的双光源照明方法。本文以缸体内横孔光照均匀性为出发点，建立光源辐射响应数学模型，分析了光源大小、距离、缸体受光点与光照均匀性的关系，并结合成像法介绍了缸体横孔照度均匀性评估方法。最后，通过实验对比分析了光纤光源、LED光源、LED+积分球光源在缸体横孔检测中的光照均匀性。实验数据显示，采用LED光源从外部照射横孔时光照不均匀度达10%，从内部照明时光照不均匀度为5%；采用光纤光源从内部照射横孔时光照不均匀度为4.6%；而采用积分球在缸体外部照射横孔，同时在缸体内部使用LED照明时，光照不均匀度为0.6%。可见采用LED+积分球双光源照明方法可以获得大于99%的光照均匀性，能够较好地满足机器视觉检测照明要求。Abstract: In view of the complex design of light sources and the poor illumination uniformity in cylinder block transverse hole detection by using machine vision, a double light source method is provided for the detection of transverse holes. In this method, an integrating sphere is used as the background light source and an LED is used as the direct light source. To achieve uniformity of illumination on the cylinder transverse hole, a mathematical model of the light source radiation response is established in this paper. Using this imaging method, a relationship between the size of the light source, its distance and the position of the reflection point and illumination uniformity is proposed. Finally, a controlled experiment was performed to reveal the illumination uniformity developed in different light sources: an optical fiber source, an LED source, and an LED + integrating sphere source. The results of the experiment show that the non-uniformity is up to 10% with an LED light source emitting from outside the hole, and it becomes 5% when the LED light is moved to the inside of the hole; the non-uniformity of an internal optical fiber light source is 4.6%. In particular, the double light source, wherein the integrating sphere is used as a background light outside the cylinder block and the LED is used as a direct light inside the cylinder block has a non-uniformity of 0.6%. The uniformity illumination surpasses 99%, which can be obtained by using an integrating sphere and LED dual light source, meeting our requirements for machine vision detection.
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图 2 制动主缸补偿孔检测系统组成
Figure 2. Composing of compensation hole measuring system for the brake master cylinder
图 3 （a）内窥镜结构示意图及（b）补偿孔检测结构示意图
Figure 3. Structure diagram of (a) the endoscope and (b) the compensation hole detection system
图 5 缸体内表面辐射响应曲线
Figure 5. Irradiance uniformity distribution on the internal surface of the cylinder
图 9 积分球+LED照明装置
Figure 9. Integrating sphere background source + LED direct light source
图 10 LED光源+积分球外部均匀光照明效果图
Figure 10. Results of integrating sphere background source + LED direct light source
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