Illumination of a cylinder block transverse hole for machine vision inspection

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.