Laser scanning and CAD conversion accuracy correction of a highly curved engineering component using a precision tactile measuring system

Impellers are used in various mechanical applications and they usually operate under severe conditions. Very often a replacement of an impeller is required after certain operation hours due to material failure. Since it is a critical and expensive spare part, accurate manufacturing, following the design requirements of the part, is necessary. In order to avoid any dimensional manufacturing defects, quality control procedures are used based on reverse engineering. The aim of the current paper was to evaluate the overall accuracy of the reverse engineering procedure, when a laser scanner is used for digital data capturing. The specified accuracy of the laser scanner was of ±0.084mm and the scanned data were converted to a Computer Aided Design (CAD) file using commercial design software. In order to assess the accuracy of the laser scanning and the CAD conversion procedure, a highly accurate coordinate measuring machine was used with a touch trigger probe and specified accuracy of ±0.006 mm. The results have shown that the deviation produced by the laser scanning and the associated reverse engineering methodology was up to 1mm, mostly observed at the edges of the freeform surfaces. It was concluded that such large deviations are caused from the inaccuracy of the laser scanner, possible errors created by the mesh – polygonal model creation, but most importantly from the errors when creating the B-splines

Laser scanning and CAD conversion accuracy correction of a highly curved engineering component using a precision tactile measuring system

Impellers are used in various mechanical applications and they usually operate under severe conditions. Very often a replacement of an impeller is required after certain operation hours due to material failure. Since it is a critical and expensive spare part, accurate manufacturing, following the design requirements of the part, is necessary. In order to avoid any dimensional manufacturing defects, quality control procedures are used based on reverse engineering. The aim of the current paper was to evaluate the overall accuracy of the reverse engineering procedure, when a laser scanner is used for digital data capturing. The specified accuracy of the laser scanner was of ±0.084mm and the scanned data were converted to a Computer Aided Design (CAD) file using commercial design software. In order to assess the accuracy of the laser scanning and the CAD conversion procedure, a highly accurate coordinate measuring machine was used with a touch trigger probe and specified accuracy of ±0.006 mm. The results have shown that the deviation produced by the laser scanning and the associated reverse engineering methodology was up to 1mm, mostly observed at the edges of the freeform surfaces. It was concluded that such large deviations are caused from the inaccuracy of the laser scanner, possible errors created by the mesh – polygonal model creation, but most importantly from the errors when creating the B-splines

In Vitro Trueness and Precision of Intraoral Scanners in a Four-Implant Complete-Arch Model

(1) Background: New intraoral (IOS) and laboratory scanners appear in the market and their trueness and precision have not been compared. (2) Methods: Seven IOS and two laboratory scanners were used to scan a mandibular edentulous model with four parallel internal hexagon implant analogues and PEEK scan bodies. Digital models in Standard Tessellation Language (STL) were created. The master model with the scan bodies was scanned (×10) with a computerized numerical control 3D Coordinate Measuring Machine (CMM). The short (distances of adjacent scan posts) and long distances (distances of the scan posts with non-adjacent sites in the arch) among the centroids of the four analogues were calculated using CMM special software. Trueness (comparisons with the master model) and precision (intragroup comparisons) were statistically compared with ANOVA, chi-square and Tukey tests. (3) Results: Laboratory scanners had the best trueness and precision compared to all IOSs for long distances. Only iTero (Align Technologies Inc., Milpitas, CA, USA) had comparable trueness with one laboratory scanner in short and long distances. For short distances, CS3600 (Carestream Health, Inc., Rochester, NY, USA), Omnicam, Primescan (Sirona Dental Sys-tems GmbH, Bens-heim, Germany) and TRIOS 4 (3Shape A/S, Copen-hagen, Denmark) had similar trueness to one laboratory scanner. From those, only Omnicam and Primescan had similar precision as the same laboratory scanner. Most IOSs seem to work better for smaller distances and are less precise in cross-arch distances. (4) Conclusions: The laboratory scanners showed significantly higher trueness and precision than all IOSs tested for the long-distance group; for the short distance, some IOSs were not different in trueness and precision than the laboratory scanners