Research Of The Automatic And Precision Measurement Of Crankshaft Groove In Automobile Engine Based On Shadow Casting

Crankshaft is one of the most important parts in automobile engine. Almost every aspect of performance indicators of automobile engine is determined by the manufacturing quality of crankshafts. In the geometric structure of crankshafts, groove plays an important role in eliminating stress concentration, and avoiding fatigue failure when crankshafts are working. Crankshaft groove automatic measurement with high precision and high efficiency to ensure the manufacturing quality and working reliability is essential. In the field of crankshafts measurement, all methods of measurement can be divided into two categories: contacted method and non-contacted method. Non-contacted measurement which mostly based on CCD optical scanning is becoming more and more widely used in crankshafts measurement due to its excellent precision and efficiency.Firstly, the crankshaft measurement principle and program based on shadow casting has been researched. Optical system which include CCD camera, telecentric lens and back-light parallel illumination is moved by the with-move mechanical system to the best measuring position. Then, the CCD camera captures the crankshaft groove image and this image is processed by series of image processing and data processing algorithms. Through camera calibration, the geometric characteristic size of crankshaft groove can be finally measured rapidly, automatically and precisely.Secondly, in order to obtain the Radius, Width and Depth of crankshaft groove in pixel size, the image processing and characteristic size extraction algorithms are presented in detail. These algorithms include image smooth, image segmentation, Region of Interest extraction, sub-pixel edge extraction, contour segmentation, lines fitting and circle fitting, etc. Considering the dust on the groove surface can cause negative effects to the processing precision and the final measurement results, effective solutions are researched to deal with this tough problem, and the robustness of the processing algorithms is greatly improved.Thirdly, according the telecentric area scan CCD camera model, the camera calibration technology is researched. The process of transforming the point in 3D world coordinate system to 2D image coordinate system is mathematically and accurately described. A 2D calibration plate composed of 25 circular marks in standard size is designed for implementing the camera calibration. In the calibration process, an effective method is proposed to solve the problem of placing the calibration plate in the actual measurement plane. Consequently, ideal calibration results are obtained.Finally, a model machine for crankshaft groove measurement based on shadow casting is developed. A lot of measuring experiments are carried out on this machine. Due to these experimental data, the measuring accuracy, precision and efficiency are evaluated, and all data shows that the measurement of the geometric characteristic size of crankshaft groove is rapidly, automatically and precisely.