Linear Array CCD Based External Tapered Thread Measurements

摘要

In order to improve the measuring accuracy of external tapered thread and to realize automatic measurement, a non-contact method based on linear array CCD is presented, in which a CCD camera is controlled to scan the projection of thread to acquired thread images, and dimensions of thread can be computed from image processing and coordinate transformation. The thresholds are determined through analyzing of the image signals along tooth contours, according to which the orientation of thread axis can be adjusted automatically to relieve the shading of spiral line on projection for a complete thread image. The accurate digital teeth contour can be obtained by the application of high precise CCD in combination with processing of median filtering and first order difference method, the contour is further fitted to be lines and arcs in different segments to achieve sub-pixel class precise outline, from which the measuring equations can be derived and transformed into real values. The experiments show that the system can complete the measurements of thread dimensions with an accuracy higher than 5 μm, and is easy to realize automatic measurement.