Distortion Correction Of Parallel Screw Thread Based On Non-Contact Measurement

Threaded connections are generally used in connecting valves with other components. In order to ensure the quality of the connection, the valves which have high requirements of air tightness must be inspected one by one. With the increasing of labor costs and valve quality requirements, it will make good sense to research on automatic valve inspected pipeline.CCD-based visual inspection of thread parameters is a good way for automatic measurement on line, meanwhile, it easy to integrate. However, CCD-based visual inspection of thread parameters has the following problems:Thread form will cause distortion, when measuring parallel screw thread parameters based on non-contact method. The traditional way is adjusting the optical axis to a suitable angle with the thread axis to acquire the real thread form projection, which has some defects, such as time consuming, not suit for pipeline, higher-precision equipment for adjustment and so on. Hence, a new method through digital image calibration is presented. Beginning with the thread geometrical principle, the mathematical model is given out. With the above thread mathematic model, images obtained from camera are corrected and real thread form can be got. With the results of related experiments and simulation, the mathematic model is certified.The first chapter introduces the background and relevant theory of CCD-based visual inspection, and then describes its research status.The second chapter describes the overall design and station mechanical structure design of automatic detection valve pipeline.The third chapter introduces the design of CCD-based visual inspection.The forth chapter researches on thread distortion mathematical model.The fifth chapter researches on the correction process of thread image distortion, and demonstrates the correctness of the model.The sixth chapter summarizes the contents of this study, and gives out the points which need to be researched further.