Experimental Study Of Tubing Conical Thread Parameters Measuring Based On Machine Vision

With the extensive use of tubing in the field of petroleum exploitation, and the quality of the tubing thread is closely related to the normal production of the oil field, the high precision and high efficiency requirement for the detection of the tubing thread is proposed. However, at present, there is no an effective measuring method to realize the accurate and efficient measurement of tubing thread, the thread measuring method is still staying in manual method, which has low efficiency and low precision. Therefore, it is very urgent and necessary to find and explore a high efficiency and high precision measurement system of tubing thread.In this paper, an experimental study on the non-contact tubing thread multi-parameter detection based on machine vision and image processing was carried out in the industrial field,according to the regulation of API for thread geometry size and the detection requirements of oil pipeline screw thread.The main research contents include:(1)The measuring system for tubing thread parameters based on machine vision is designed. The system is composed of mechanical system, electrical system and optical system, the image of the tubing thread is collected by using the optical method and combining with the mechanical transmission technology to drive the image sensor.(2)The digital image processing technology is used to image prior-processing, image binaryzation, edge detection and contour extraction. According to the characteristics of the tubing thread, the pseudo median bilateral filtering algorithm is adopted for image prior-processing, the iterative threshold segmentation method is adopted for image binaryzation, and the optimal Canny operator is adopted for image edge detection, Fianlly utilizing the contour tracking method to optimize the image so as to realize the accurate image edge contour extraction.(3)The calibration of measurement system is done precisely and the image edge is fitted accurately, then the measuring principle of each tubing thread parameter is given according to the tubing thread features and the API specification of tubing thread measurement method, finally specific values of each parameter are obtained.(4)The error analysis of the measuring system is presented, including four source of error to the system: the error of mechanical and electrical systems, the error of optical system, the error of algorithm, the error caused environmental factors; then the error sources and the effects of these errors on the measurement system are analyzed, The calculation formulas of these errors are given through the theoretical analysis and the error compensation measures are put forward.The specific numerical value of various geometric parameters of screw thread is acquired through the experimental system to collect and process tubing taper thread images,and each geometric parameter values are within the API specified tolerance limits,which satisfy the requirement of the tubing thread measuring precision.Therefore,the system can realize the non contact measurement of tubing thread parameters accurately and efficiently,which also can satisfy the requirrments of API. It is an effective method to measure the geometric parameters of the tubing thread.