An External Calibration Method for the Circular Scanning Device Used for Bend Tube Intelligent Inspection

In order to realize the intelligent inspection of bend tube processing defects, such as the wrinkles and the ovality, a 3D scanning device composed of a linear translation stage and four uniformly distributed laser profilers (LPs) is built in this paper. For the external calibration of this type of device, the major contribution of this paper are: 1) A 3D calibration object composed of three non-collinear target balls (TBs) is designed. Even if the scanning angle of each LP is limited, there are still common geometric features. 2) A frame-by-frame fusion method for scan data from multiple LPs that only requires one set of rail parameters is proposed to avoid the introduction of multiple sets of rail errors that affect equipment calibration and data fusion. When calculating the parameters, the shape error of the TBs after fusing the scan data of each LP is taken as the objective function, and the nonlinear least square method is used to solve the problem. Finally, the scan data fusion can maintain the accuracy and stability of the shape. The fitting error of the TB with a nominal radius of 19.05mm does not increase with the increase of the guideway stroke, the average fitting error of the radius is stable at about 0.0014mm, and the average RMSE of the surface point is stable at about 0.0426mm.