Research On The Vision-based Detection System For The Correction Of The Taper Thread Image Profile In The General Position

Conical thread is widely used in the connection of various pipes due to its good sealing properties.The traditional tapered thread inspection relies on personnel to operate tools such as gauges,which cannot provide high-precision and high-efficiency inspection.And the test results are affected by the experience of the operators and lack objective and strict standards.Although the taper thread detection based on machine vision in the past can avoid the above problems,it still has shortcomings.In the traditional machine vision-based tapered thread,the image profile is considered to be the profile of the shaft section in the detection process,so as to measure the parameters of the tapered thread.However,in the actual measurement,in addition to the problem that the tooth shape of the image will block the tooth shape of the axial section due to the existence of the rising angle,the obtained image tooth shape will be distorted.The problem of a certain angle between the measured thread axis and the camera axis also leads to a certain axial error in the parameters directly extracted from the image profile.Aiming at the above two problems,a tooth profile correction model is established for the conical external thread in the general position.First,it is called the general position when there is an included angle between the axis of the measured thread and the axis of the camera.According to the position of the camera and the position of the detection platform,a projection coordinate system is established,and then the theoretical parameters of the thread are used to deduce the general position of the conical external thread in the projection coordinate system.Theoretical tooth profile equation and theoretical axial section tooth profile equation.According to the imaging principle,the theoretical projection curves of the two are obtained,and their theoretical difference equations in the axial direction in the projection coordinate system are calculated.Finally,combined with the theoretical difference equation and the spatial position of the tapered external thread axis,the image profile correction algorithm of the tapered external thread at the general position is obtained,and the algorithm is simulated and analyzed for different sizes of the tapered external thread.Theoretically,the algorithm can eliminate the detection errors caused by the above two problems in the current machine vision-based conical external thread detection.Based on the image tooth shape correction algorithm,the paper builds a conical external thread image tooth shape correction detection system.Detect the rotation of the platform,use the CCD camera to collect the image of the conical external thread,obtain the image tooth shape through image preprocessing and edge extraction algorithm,and calculate the actual spatial position of the tapered thread axis.The actual shaft section profile takes the actual shaft section profile as the calculation object,and obtains the thread parameters through the measurement algorithm of various parameters of the conical external thread.The detection results of the correction algorithm are compared with the thread detection results of the traditional method and the visual detection results without the tooth profile correction algorithm.Effectiveness of thread detection accuracy improvement.