Research On The Composite Surface Reverse Based On The Closed-loop Theory

The reverse accuracy for physical parts having numerous free-form patches is dependedon the precision of measurement and reconstruction. In more recent times, the two processesare independent and couldn’t be evaluated reliably. In order to access the CAD model withhigher precision and efficiency, a closed-loop measuring-and-reconstructing system usingcontact coordinate measuring machines (CMM) is presented for reversing an unknowncomposite object. The closed-loop reverse system is used to found a cycle path to feedbackerror information and remedy error timely in the whole reverse process.Before dimensional measurement, a hierarchical path planning is needed to direct theCMM’s automatic motion. The specific programme is covered by the composite objectdecomposition, the boundary conditions acquisition, the measurement sequence betweenpatches, and the measurement route on every patch. Furthermore, when the measurement isunder operation, the next point is calculated by the curvature of the B-spline curve fitted bythe acquired data, the order of the B-spline is determined according to the object. At the core,the self-adapting step is composed of the forward step and the regressive step, the first step isrestrained by the curve’s curvature, and the second step is used to keep the measurementmeeting requirements. That is to say, the distribution of the obtained cloud is accorded withthe actual object, and could be used directly for the next process.In order to bring the construction process into correspondence with the measurementprocess, the B-spline surface is proposed to structure the mathematical models by the objectcloud. Nodes insertion is used to uniform the point number on each scanning line. Theaccuracy of this method for reconstruction is verified as μm level by a mathematicalexperiment. The deviation between the reconstructed model and the physical object isidentified by some typical check points’ distance from the model to the object. These typicalpoints are located on the center of the model’s control grid to ensure that every detail featureof the model is extracted, and without overnumber.In fact, the deviation is generated in the failed planning for the scanning lines on object.Thus, the supplementary scanning lines are needed to shrink the surmountable deviation.Then the accurate cloud and CAD model are obtained if the deviation meets the requirement.Lastly, when all the patchs’ CAD models are obtained, the intersecting line between thetwo neighbouring patches could be calculated by the interpolation algorithm. All the patchescould be spliced together into a composite surface according to the real surface blendingcondition.Both fundamental and application issues are tackled by using VC++and OpenGLgraphics library. All the calculation processes are visualized. Experiments demonstrate thatthe reverse cycle and cost are reduced.