Research On Laser Screw Thread Parameter Detection Technology

Screw thread parameter is one of essential factors that decide the screw mechanical character, and the accuracy of the geometry parameter detection has the key significance for guaranteeing the screw mechanical property. The current detection methods have two classes. One is screw gauge which can detect screw by"through"and"stop". The screw gauge is high efficiency, but it can not supply concrete numerical values besides qualification judgment. The other is a universal instrument or a special apparatus for the screw single parameter. This class has inefficiency and low accuracy especially for the inside screw thread, and it can not show relations among the parameters.The paper studies the screw thread profile quantization measurement program based on the optical scanning method, which obtains the parameters directly through measuring the thread contour. The study achievements in the paper lay a foundation for the development of the new type screw thread instrument. The main study work of the paper is as followingFirst,paper summarizes the current screw parameter detection technique development, and analyzes existent problems after reading a large number of the correlation documentations. The both-way inclination optical measurement is presented based on the thread contour character, solves the problem that traditional optical method is hard to measure the large slope object and increases the value collection accuracy of the thread profile. The paper discusses the principles of the both-way inclination method, analyzes the accuracy relation between the parameter and the measurement instrnment and establishes the parameter accuracy model under the optical measurement. The special optical gauge is designed based on the structure of the bi-triangle measurement to realize the external and inside thread parameter measurement.The wavelet threshold de-noising algorithm is presented in order to delete the noise in the measurement data. Paper elaborates the wavelet threshold de-noising principle, and chooses the different threshold for the gross error and the random error. According to the data character in the high frequency coefficients of the wave-let transform, paper adopts the 3σcriterion for the gross error deletion and the layer resent function based on D.L.Donoho for the random error. The results of the canonical wave-let function de-noising are systematically compared and show that the method in the paper excelled the traditional wave-let de-nosing.Paper studies the screw thread mathematical reconstruction based on the measured data. NURBS interpolation is adopted to describe the screw thread mathematical model. The node quantization factor is proposed to improve NURBS interpolation accuracy. Paper elaborates the quantization factor theory and its optimizing process, and studies NURBS interpolation realization in the screw measurement. The screw parameter calculation accuracy can be improved by adjusting node quantization factor. NURBS curve is divided in terms of the screw thread shape feature, which completes the parameter detection.The screw parameter synthesis measurement instrument is manufactured based on the methods mentioned above. Paper establishes the dynamic error model, and analyzes the affection on the measurement; discusses the component software development process and corrects the error of the measurement and structure parameter. The experiments contrasted CMM and the standard angle gauge prove that the methods proposed in this paper are correct and practical.