Research Of Microsphere Measurement Method Based On Dual SPM Probes

In the field of precise measurement,the micro-nano coordinate measuring machine is a precise tool used for the measurement of micro parts,the precision of the micro-nano CMM is generally controlled at the level of hundreds of nanometers.The probe tip of the micro-nano CMM is a microsphere with the diameter ranges from tens to hundreds of microns,and the sphericity ranges from tens to hundreds of nanometers.As the value of the sphericity is similar to the precision of the CMM,it is necessary to measure the profile of the microsphere accurately,so as to correct the error and ensure the accuracy of the micro-nano CMM.At present,the measurement methods for microsphere at home and abroad can be divided into contact style and non-contact style: the contact measurement can achieve high precision,but depends on the specific equipment developed by the research team,such as ultra-precise CMM,ultra-high precision rotary shaft,etc.Non-contact measurement methods are generally concentrated on optical methods,but due to the effect of diffraction limit,the accuracy can only reach the level of micron.In this paper,a microsphere measurement method based on dual scanning probe microscopes(SPMs)is proposed based on the analysis of existing researchs,the microsphere can be measured precisely and the specific ultra-precision equipments can be avoided.The SPM probe has high resolution and sensitivity,which is prepared by combining a homemade large aspect ratio tungsten probe with a quartz tuning fork.The two probes are set at both sides of the microsphere to measure the maximum cross-sectional profile circle,and the 3D profile of the microsphere is obtained by combining multiple maximum cross-sectional profile circles.In the measurement of the maximum cross-sectional profile circle,the motion error is separated by measuring two relative circles,and the remaining errors are summarized and the uncertainty of microsphere measurement results is evaluated.At the last of this paper,the application of microsphere measurement is introduced with the example of micro pore measurement modification.The main research contents and results of this paper are summarized as follows:(1)Microsphere measurement theory based on dual SPM probes.The maximum cross-sectional circle of the microsphere is obtained by measuring two relative circles through the flip method,and the morphology of the microsphere is calculated based on multiple maximum cross-sectional circles.The motion error and the alignment error of the probes are main errors in the measurement,thus the theoretical derivation and experimental separation of the two errors are carried out.After separating the main error,other errors in the measurement process were summarized,which includes the secondary abbe errors caused by the micro stages in all directions,the multi-angle rotation error of the microsphere,and the machining error of the rotating structure,etc.,therefore,the error of the microsphere measurement is analyzed systematically.(2)Microsphere measurement devices based on dual probes.The microsphere measurement structure is built by the combination of SPM probes and micro stages with large travel.Hardware structures such as mechanical assembly,alignment and fretting table drive for microsphere measurement are developed.Microsphere measurement,drive control and data processing software are built in Lab VIEW software,and the program is debugged and operated to realize the 3D contour measurement of the microsphere.(3)Uncertainty evaluation of the measurement results.In order to evaluate the microsphere measurement results more scientifically and reasonably,the uncertainties includes the diameters of the cross-sectional circles,roundness,the diameter of the microsphere and the sphericity are evaluated,the Monte Carlo Method(MCM)is chosen to evaluate the measurement uncertainties in this paper.For the roundness and sphericity,the uncertainty can be directly achieved from the Gaussian distribution by computer numerical calculation.When evaluating the diameters of the cross-sectional circles and the microsphere,the results cannot be obtained directly from the model calculation,thus the MCM method is used to calculate twice to obtain the uncertainty of circle diameter,and the uncertainty of sphere diameter is expanded by the uncertainties of the circle diameters.(4)Application of microsphere measurement.After finishing the measurement and uncertainty evaluation,the method of correcting micro pore measurement results by using microsphere measurement results is studied in this paper.The principle of measuring the micro hole of fuel injector of automobile engine by using quartz tuning fork resonance probe is introduced.The tip of the resonance probe is a homemade optical fiber microsphere,in the process of measuring micro pore,the resonance probe touches the inner wall of the micro pore through the circumference of the maximum section of the microsphere,the accuracy of the micro pore measurement results is affected by the shape parameters of the circumference.Therefore,the method to correct the measurement results of micro pore by using the measured microsphere's radial value is studied,the correction theory is analyzed and the experiment is carried out to ensure the reliability of the micro pore measurement results.In this paper,the microsphere measurement and error analysis based on double SPM probes are systematically completed,and the uncertainties of the results are evaluated by MCM method.After finishing the measurement of the microsphere,the measurement results of the resonance probe used for micro-nano CMM is modified based on the measurement results of the microsphere to illustrate the application value of microsphere measurement.The modification of resonance probe can be the basis for further research of correcting error,improving accuracy and increasing value of the micro-nano CMM.