| Precision tubular parts,such as cylinders,oil cylinders,bearings,etc.,are widely used in critical areas such as aerospace,automotive manufacturing,and energy.The internal dimensions and form tolerances of such precision tubular parts and other characteristic parameters have a significant impact on the overall performance of the components and equipment,therefore,there are usually high requirements for the machining quality of tubular parts.For example,the car engine cylinder bore,cylindricity and straightness of the standard tolerance level is usually IT6 level,that is,the bore tolerance of about 20 ～ 30μm(bore different,the specific tolerance is different).However,the geometric parameters of the actual tube parts may not meet the design requirements due to factors such as tool deformation and vibration during machining,or wear and tear of the parts during use,which in turn may lead to a decrease in part accuracy,excessive noise and reduced life.Therefore,precision measurement of the internal diameter,cylindricity,straightness and other parameters of precision tube parts is important for the inspection of the machining quality of the parts and the monitoring of the use status.Firstly,this paper investigates and analyzes the current situation of domestic and international research on the measurement technology of internal geometric parameters of precision tubular parts,and determines the basic measurement scheme and technical index of the measurement system based on low coherent interference technology with the characteristics of the actual parts;after that,the overall scheme of low coherent interference principle and measurement system is elaborated,and the analysis,design and experimental testing of key parts of the system are carried out,mainly including the testing and analysis of interference characteristics of different types of broadband light sources,the design of reference arm and sample arm composition and working mode,etc.;finally,the measurement process of the system is elaborated according to the developed overall scheme.Secondly,the low coherence interferometric signal processing algorithm and the evaluation method of geometric parameters that affect the accuracy of zero optical range difference position extraction are studied in this paper.Firstly,the method of suppressing optical noise and mechanical noise by attenuator and bandpass filter respectively is proposed and implemented to complete the pre-processing of the interferometric signal.Then,the theoretical analysis,algorithm implementation and simulation experiments are conducted for five kinds of coherent peak extraction algorithms,and the calculation accuracy and calculation efficiency of these five methods are compared.Combined with the actual working conditions,the wavelet transform method with the best noise immunity was finally selected as the coherence peak extraction algorithm for this system.After that,the algorithm that affects the accuracy of calculating the inner diameter and shape tolerance of the final tube parts is studied.According to the minimum area method specified in the national standard GB/T11336-2004,this paper proposes an improved genetic algorithm that can perform efficient and high-precision analysis and calculation of straightness error and cylindricity error.By improving the traditional genetic algorithm in terms of population initialization,crossover probability and variation probability,the fast and stable calculation of relevant geometric parameters is thus achieved.Then,according to the overall system design scheme,the measurement system of internal geometric parameters of tubular parts was built.Firstly,the one-dimensional ranging accuracy of the reference arm system was verified.According to the test results that the displacement table has large motion errors,this paper designed an optimization scheme for the reference arm system,and based on the existing data acquisition instrument,a grating conditioning board was designed and developed to realize highspeed synchronous acquisition and processing of multiple grating signals and interference analog signals.After that,the system’s single-point measurement stability and internal diameter measurement capability were verified,and the experimental results showed that the measurement error was below 10μm.Finally,the interference signal processing algorithm is experimentally tested and analyzed according to the built system for measuring internal geometric parameters of tubular parts,and the system is used to inspect standard devices and common tubular parts to verify the capability of this system in internal diameter measurement,cylindricity error and straightness error assessment.The experimental results show that the efficient and accurate measurement of internal geometric parameters of tubular parts can be achieved according to the system and the related analysis and processing algorithms in this paper. |
