Research On Key Technology Of Accuracy Alignment For Micro Devices High Precision Assembly

With the rapid development of precision, ultra-precision machining technology,continuous improvement of micro-fabrication technology makes micro devices to thedirection of complex three-dimensional structure. The requirement of assembly tolerance ofminiature system reached microns or even sub-micron, meanwhile, micro-assembly gave ahigher request to the respect of alignment accuracy, location accuracy of micromanipulationand contact forces.Precision alignment was a key technology in micro-assembly system, which must have afeedback loop of high-precision measuring of the relative positions of objective parts andmatrix parts. The human’s feeling ability didn’t meet these requirements of micron of microassembly system, meanwhile, microscopic detection of visual images had been widely used inthe field of micro-assembly to realize the precise location. The detection precision of ordinaryoptical system was limited by imaging system itself and micro-vision system would not breakthe resolution the optical diffraction limit. The assembly alignment detection accuracy isdifficult to achieve submicron, and would not achieve submicron accuracy alignment.Sub-micron accuracy of alignment detection was obtained by coaxial alignment detectionbased on ordinary microscopic optical and confocal laser measurement. Finally, experimentswere performed to testify alignment detection accuracy results of experiment platform. Themain achievements of this work were listed as follows:1. Research on general technologies of high precision coaxial alignment detection: Theproblems and limitations that micro assembly based on orthogonally alignment were analyzed,and coaxial alignment detection was given, which based on recent research. With theoreticcalculation and experiments, the influences on alignment accuracy when there were errors inthe alignment detection mechanism were analyzed. The technical problems in actual microassembly were analyzed. The detection precision of ordinary optical system was limited byimaging system itself and micro-vision system would not break the resolution the opticaldiffraction limit. The assembly alignment detection accuracy is difficult to achieve submicron,and would not achieve submicron accuracy alignment. Monocular vision could not beachieved Z-axis precise location of target parts and matrix parts in micro assembly process. The alignment detection method of confocal laser measurement was proposed. It usedconfocal laser precision measurement, with a resolution beyond the optical diffraction limit,made alignment detection accuracy reach sub-micron, at the same time, confocal lasermeasurement could achieve Z-axis high precision measurement. The problems of confocallaser measurement was small field of view and short work distance(WD). All of the work wedo was based on comprehensive consideration, micro assembly experiment system wasconstructed based on ordinary microscopic optical and confocal laser measurement. Thecoaxial optical alignment detection subsystem was designed based on ordinary microscopicoptical and confocal laser measurement.2. Research on the problems of coaxial alignment detection accuracy: When the prismof ordinary microscopic optical alignment mechanism had a micro angle deviation, theinfluences of alignment detection precision of micro-assembly system were theoreticallycalculated. The certain step distance angle deflection given by6-DOF precision angledisplacement station, we respectively stored after each deflection angle imaging systemcalibration board image in the image plane. Finally, the acquired images were conductedrespectively by calculating the center of the calibration circle offset in the plane, in order tocalculate the influence of alignment detection accuracy. The mechanism of coaxial alignmentbased on confocal laser measurement used two isosceles right triangle prism formed reflectionoptical path. Because of the isosceles right triangle prism right-angle side of5mm, the prismgripped was relatively more difficult, the error sources were also relatively more. Theconfocal prism alignment mechanism as a whole in the form of systematic errors forexperimental verification. As systematic error the error in the distribution system to obtain theerror could be compensated to reduce or eliminate.3. Research on alignment image key feature extraction and recognition technology ofmicro devices high precision automatic assembly. The alignment image key feature extractionand recognition was a key link of automatic assembly. The paper studied for alignment imagekey feature selection of micro devices high precision assembly, image crop of alignment area,edge extraction algorithm, edge point automatic selection of image different bias and controlmethod of axial and angle error adjustment. Local feature matching algorithm consideringuncertainty was adopted, which achieved automatic assembly of flat micro parts. 4. Research on calibration technique of micro devices assembly: Ordinary microscopicoptical lens distortion calibration technique was analyzed. Calibration test of coaxial opticalalignment mechanism was completed and specific calibration solutions were particularlydesigned. Calibration test of confocal laser measurement of coaxial optical alignmentsubsystem was completed and specific calibration solutions were particularly designed.Finally, calibration tests of gripping and conveying manipulator and precision adjustmentmotorized positioning system were completed.5. Experiment research on coaxial optical alignment detection: At last, a generaldesigned scheme was given according to the performance index and functional requirement ofmicro devices assembly. The experimental platform was constructed based on confocal laserand ordinary microscopic optical coaxial alignment detection, meanwhile, the actualexperimental micro devices assembly was completed to verify micro devices assemblyexperimental platform assembly accuracy.