Optimization Design of Single-Camera Stereo-Digital Image Correlation System
Objective As a non-contact visual measurement method,the digital image correlation(DIC)method has been widely used in the field of material deformation measurement.This method utilizes speckle matching of images before and after deformation captured by a pair of binocular cameras to measure the material's deformation field.However,ensuring synchronization between the two cameras in high-speed vision measurement scenarios poses challenges.These scenarios often impose size limitations on the measurement device,rendering conventional binocular stereo DIC measurement systems impractical.Consequently,some studies have introduced the single-camera stereo reconstruction method into 3D DIC,where a single camera simulates multiple cameras through specialized optical devices to achieve pseudo-multi-camera measurement and complete stereo reconstruction.Nonetheless,most research focuses on utilizing single-camera stereo reconstruction technology combined with 3D DIC to measure deformation in various materials,with little attention given to designing the structural parameters for monocular stereo DIC systems.In this study,we propose an optimal design method for the structural parameters of a single-camera stereo DIC system,aiming to develop a compact system for accurate and efficient measurements.We hope that this method will contribute to the structural optimization of single-camera stereo DIC measurements.Methods To optimize the design of the single-camera stereo DIC system,we first analyze the structure of the four-mirror adapter in the system and derive the mathematical relationship based on the optical path of imaging.We formulate the optimization model for structural minimization as the objective function,establish constraint equations considering measurement distance,field of view,accuracy,and other conditions,and solve the optimization model using the branch-and-bound method.In addition,we provide theoretical derivations for an alternative optical path that diffuses outwardly and compare the advantages and disadvantages of the two optical paths.Furthermore,we analyze the influence of the camera's intrinsic parameters on the structural parameters of the single-camera stereo DIC system through numerical simulations.Finally,to validate the effectiveness of the method,we conduct several experiments.Results and Discussions Numerical simulation results indicate that the distance between the inner and outer mirrors of the four-mirror adapter decreases with an increase in the camera's field of view,leading to a more compact structure(Fig.3).However,as the field of view angle increases,the measurement distance also increases while the measurement accuracy decreases(Fig.4).Hence,there is a need to balance the compactness and measurement accuracy of the structure.The structural parameter verification experiment demonstrates that the actual measured structural parameters closely align with the theoretically calculated parameters,with a relative error of about 1％(Table 5).Point distance reconstruction experiments show a reconstruction error of 0.02 mm for both the single-camera stereo DIC method and the conventional binocular DIC method,indicating comparable reconstruction accuracy(Table 6).Translation and rotation deformation measurement experiments show minimal displacement measurement errors for the single-camera stereo DIC method,with an average relative error of 0.7％in the translation experiment(Table 7),and consistent displacement trends observed in the rotation experiment(Fig.11).Conclusions We build an optimal design model for a monocular stereo DIC system based on a four-mirror adapter and solve the optimization model using a nonlinear optimization method.This approach enables the calculation of optimal structural parameters that meet specified conditions based on actual test scenarios.In addition,we analyze the influence of the camera's intrinsic parameters on the design of structural parameters,providing insights for camera and lens selection.Experimental results indicate a relative error of about 1％between the predicted structural parameters and those measured in experiments.Furthermore,a comparison of the point distance reconstruction accuracy between the single-camera stereo DIC system and the conventional binocular DIC system shows similar accuracy levels,with a reconstruction error of about 0.02 mm for both systems.Translation and rotation experiments demonstrate minimal relative errors in measured results,and the displacement trends observed in rotation experiments align with expected results.Our method holds promising prospects for applications in measurement scenarios with narrow observation windows.
digital image correlation methodmonocular stereo matchingfour-mirror adaptermachine visiondeformation measurement
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