A Novel Laser-Based System for Measuring Internal Thread Parameters

Based on the theory of laser measurements, we propose a novel laser-based automatic inspection system for measuring the internal thread parameters, which integrates the laser-based measuring unit to detect the longitudinal section of the thread profile and the dual-axis moving stage for the movement of an undetected object. We design a special laser probe based on the bidirectional inclination scanning method for obtaining the thread-profile data. This method and structural design enables the laser probe to overcome the shortcomings of traditional methods for measuring large inclined surfaces and eliminate the impact of the lead angle. We compare our results of internal thread-parameter measurements with the coordinate measuring machine (CMM) system and investigate the repeatability with one internal screw ring gage by the system proposed. The experimental results show that the measurement accuracy of the thread angle is 2′ and the other parameters are less than 4 μm.