On-line comprehensive measurement method and system for taper thread of pipe in non - contact

Traditional measurement method is difficult to implement automatic and parametric online measurement of threads, which restricts the automatic and intelligent production of threaded workpieces. In order to realize automatic and parametric on-line testing of drill pipe taper thread, a non-contact taper thread comprehensive system for the pipe was developed. The measurement method of taper thread and the data processing method in the system was studied. Based on spectral confocal principle, the measuring method of taper thread profile scanning was proposed. It was analyzed that the error of measurement principle is negligible due to the difference between the central axis of thread and the workpiece axis. The thread central axis was determined by scanning the thread stop. To gain the thread contour curve, two generatrices that pass through the central axis of a thread were scanned by the sensor. Due to the abnormal data collected by the sensor, the capability gage of the system was low, a data processing algorithm based on mathematical model matching of curves was developed, and the curves was piecewise fitted by least square method. The experimental results showed that the short range sensor and large pitch taper thread contour scanning measurement method can achieve high precision, high efficiency and comprehensive measurement of box thread. The capability gage (Cg) of the system is less than 0.006mm, capability gage index (Cgk) is less than 0.03mm, gauge repeatability & reproducibility (GR&R) is less than 5% of the workpiece tolerance. It can meet production demand and solve industry technical problem that the optical measurement method is difficult to realize the thread contour scanning measurement, especially the sweep measurement of internal thread contour.