Study On The Structural Principle And Error Correction Technology Of The Different Types Of CMM

CMM is a kind of efficient three-dimensional measuring instrument, which integratesmechanical, optical, electronic, computer and other technology. With the development of modernmanufacturing, the emergence of MEMS devices require the higher accuracy on the measuringmachines. In this paper, a cantilever-type coordinate measuring machine for the production site witha large number of range and low accuracy requirements and a coordinate measuring machine withsmall trip nanoscale precision under the laboratory environment was studied. The main contents ofthis thesis are revolving around structure and layout, error analysis and error correction.This cantilever measuring machine has a traditional structure which was designed formeasuring continuous casting mold and it has a measuring range of600×600×800mm. In this paper,a self-designed cantilever Coordinate Measuring Machine(CMM) for measuring continuous castingmold was studied, main errors sources which have impact on measuring accuracy of measuringmachine were analyzed. The geometric error modal was founded by the theory of homogeneouscoordinate, which include non-rigid error compensation. Laser interferometer and laser tracker wereused to separate each error, then these errors were compensated after be calculated. Measured resultsdemonstrated that, when measuring machine move along the diagonal of measuring space, themaximum displacement error reduce to50μm from600μm after compensation.Nano Coordinate Measuring Machine both at home and abroad were researched and analyzed,and then some of the key factors that affect the measurement accuracy were summed up. On thisbasis, the "331" principle for Nano-CMM was put forth: Three measuring line intersect to one point;x、y plane of guide overlap with measuring plane; The intersection point of three measuring lines ison the measuring plane. This type of distribution can eliminate the influence of Abbe error fromprinciple and lower effect that rails’ movement errors bring to working table.This paper introduces a Nano-CMM, the structure layout of it is based on the "331"construction principles. The machine has a measuring range of50×50×50mm, and the resolution is1nm, apply to the measurement of micro-devices and thin size. Measuring machine table used invarsteel with low thermal expansion coefficient as the main material. The x and y axis of workbenchtakes coplanar moving platform and symmetrical design. A special force balance system was putforward in this paper, the force support points of it can move with workbench along the x and ydirection. This structure can effectively balance the internal force of the measuring machine whichcaused by the three-dimensional movement of workbench, reduce the deformation of the keycomponents of the measuring machine, reduce the resistance of motor-driven. The straightness errorof each guide is within±1u, angular motion errors are less than30arcsec after the alignment of Nano-CMM.Error analysis, modeling, and separation of the interpolation correction are the key technologiesof developing Nano-measuring machine. In this paper, the error influencing factors of the modernprecision Nano-measuring machine was analyzed, and the error correction model was derived. Theresults show that the main sources of error of the measuring machine are laser measurement lengtherror and the flatness deviations and out-of-squareness error of the mirror, and x, y rail imperfectionsdo not affect the measurement results. Using the interpolation algorithm a one-dimensional errorfunction was calculated, and three-dimensional error models of z-axis of Nano-measuring machinewere established based on cubic spline interpolation method. And also the errors of the measuringmachine were isolated by using a laser interferometer and standard parts. After the interpolationcorrection, the corrected results were tested by using a laser interferometer and standard parts. Themeasurement results show that: Measuring machine the greatest displacement error along thediagonal of measuring machine were reduced from3500nm to150nm or less after correction, andThe maximum deviation of measured values of the step height and length of the gauge block are lessthan100nm, and the standard deviation are both30nm or less.