Research On Optical Shaft Hole Diameter Measuring Method And Key Technology

The engine manufacturing industry is a key development project in China’s"12th Five-Year Plan". As the basic part of an internal combustion engine, theengine box distributes a large number of shaft hole, the manufacturing precision isthe key link to improve engine manufacturing quality. Shaft hole diameter onlinedetection faces many difficulty, the key point is to meet both the high precisionmeasurement and the conditions of the online status. Highly automatedmeasurement is required in a dynamic production conditions, but the traditionalpneumatic measuring instrument cannot implement because of small measurementgap. This paper has proposed a novel optical multi-direction shaft hole diametermeasuring method by using the principle of the laser displacement sensor. Referringto the layout of the pneumatic measuring instrument and basing on the structuralcharacteristics of the shaft hole of the engine box, the length of the probe and thenumber of measurement section are matched. While ensuring measuring accuracy,the measurement gap is expanded which provide conditions to realize automatedmeasurement. The main work of this paper is as following:1. The characteristics and scope of shaft hole diameter measurement methodare analyzed, and combining with the measurement needs of engine box, the newoptical shaft hole diameter measurement method is explained, at the same time thekey technologies are overviewed.2. The mathematical model of optical shaft hole diameter measurement methodis established and the emphasis is to inherent relationship between the model andmeasurement error. By extracting the structural parameters from the multi-probelayout, the relationship between the structural parameters and measurement errors isgot. Genetic operators are designed based on the characteristics of parameters, theimpact of structural parameters on measurement error is analyzed by using geneticalgorithm. Finally the feasibility analysis of measurement methods is completed.3. The measurement method and error factors of the miniaturized probe arestudied. The miniaturized probe bases on the laser triangulation principle, and thestructure selects the conduction light source and PSD as position detection device.Internal and external factors affecting the accuracy of the probe and the spot positiondetection accuracy of PSD are studied, which is the foundation for the subsequent measurement accuracy.4. The relationship between surface roughness and measurement accuracy isstudied. By constructing a rough surface geometry model and combining with scalarscattering theory and rough surface statistical model, the theoretical model ofmeasured surface roughness characteristics and scattered light intensity is created.Through the experiments, the measured surface scattered light intensity and themeasured position are obtained to verify whether the theoretical model could be theguide for the practical accuracy of the probe.5. Non-stationary signal de-noising method of probe is studied. Based on thecharacteristics and application of the existing signal filtering method, the advantageof wavelet transform in dealing with non-stationary signals is elaborated. Throughthe discussion by wavelet decomposition, threshold processing and signalreconstruction, the optimal combination of algorithm is found, and the experimentshas verified that this algorithm can significantly improve the measurement accuracy.