Mechanical failure is primarily caused by coaxiality errors of axis. Traditional methods (synthetic gauge testing methods, method of rotary axis, coordinate measuring machine, etc.) for detecting coaxiality have some disadvantages such as: low efficiency, sensitive to human factors and cannot be used to measure the axis that is far apart without connection. In this paper, based on the principle of laser collimation, a method for measuring coaxiality errors of non-connecting axis with long distance was proposed. By rotating the laser module and the four-quadrant photo detector module respectively, the center and radius of the circle that formed by the laser spot were used to calculate the angular deviation and the parallel deviation. Finally, a measurement system based on the precision instrument deflection was designed to verify the rationality of the method.
Press-fit assembly is one of the traditional methods for assembly of interference fitting parts, but the assembly quality cannot be acquired directly from this method. At present, the press-fit curve is employed for quality estimation, and thickwalled cylinder theory (TCT) is used for standard press-fit curve prediction. However, the evaluation results cannot predict the stress concentration occurred on the mating surface, and most interference fitting parts fail due to this reason. This paper aims to explore ultrasound as a tool for non-destructive evaluation of contact stress, and then acquire the contact stress distribution eventually. Therefore, it is more convenient and intuitive to evaluate the assembly quality based on this method.
Measurement is the prerequisite technology for assembling precise devices in order to guarantee the quality requirements. As a typical category of assembly, peg-in-hole is the most widely employed assembly method in industrial fields, including precision instruments and machinery. Some of the measurement problems and solutions of two major categories of the peg-in-hole assembly, i.e. clearance fits and interference fits, were discussed. The parts to be assembled are small in size. The precision clearance fits require mating surfaces to avoid collisions during assembly; for the precision interference fits, the mating surfaces should not be damaged or generating abrasive chips during press-fit. The hole-shaft alignment and attitude adjustment are the main task need to be carried out precisely in assembly. Furthermore, real-time monitoring and connection strength measurement is also the important for interference fit assembly. Therefore, the purpose of this paper is to achieve precise hole-shaft alignment and attitude adjustment of these two kinds of fits and to real-time monitor the assembly process, as well as connection strength assessment of the interference fit. Two assembly instruments were built for interference fits and clearance fits to achieve precise alignment, attitude adjustment, and real-time monitoring. In addition, an ultrasonic testing apparatus was built to evaluate the connection strength. After calibration, the precision press-fit instrument can achieve high assembly accuracy and demonstrated with experiments. The prediction results of connection strength are in good agreement with experimental results with a relative error less than 20%. Furthermore, the instrument for clearance fits was also designed and introduced.