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Dec, 2009

OptoSurfacer: an optical digitizer for reverse engineering of free-form surfaces

What is OptoSurfacer?

The purpose of this activity is the development of descriptive 3D models of the point clouds acquired by the optical digitisers developed at the Laboratory, for the implementation of the Reverse Engineering of complex shapes and in applications that priviledge the efficiency of the whole process with respect to its accuracy.

Typical fields are the production of prototypes and moulds within the collaborative design process and for copying applications, the restitution of cultural heritage, and the Virtual Reality.

The objective is also the implementation of an alternative path with respect to the traditional CAD-based process, to allow the user to model the physical shapes by means of meshes of simple geometrical elements, without requiring specialised knowledge and background, and at the same time providing total compatibility with the higher performance, higher cost, market available software environments, dedicated to CAD and copying applications.

The activity resulted in the development of a software tool called OptoSurfacer, with the following characteristics:

  1. importing and ordering of dense and sparse point clouds, optically acquired;
  2. detection and editing of undercuts and outlayers;
  3. scaling, mirroring and translation of the entities;
  4. automatic definition of the meshes that model the original measurement data;
  5. flexible trimmering of the mesh topology depending on the object local curvature;
  6. coding of the models in the IGES format to guarantee their usability in the CAD and CAM environments market available.

HOW TO OBTAIN THE MESHES?

The flow-chart in Fig. 1 describes the tasks performed by OptoSurfacer. They are illustrated for the study case of the object shown in Fig. 2 (a roof tile). The corresponding point cloud, shown in Fig. 3 has been acquired by means of the prototype DFGM (see the Prototypes page), and is characterised by a variability of the measurement of about 200 microns.

Fig. 3 - Corresponding point cloud of the roof tile obtained by means of the prototype DFGM.

OptoSurfacer automatically performs the ordering of the points by creating a regular reference grid and by using the surface shown in Fig. 4 as the basic geometrical element of the mesh. For the roof tile, the shapes have been modelled as shown in Fig. 5, and the resulting mesh is presented in Fig. 6. The irregularities well observable in this figure mainly depend on the roughness and the porosity of the material.

Fig. 4 - Basic geometrical element of the mesh.
Fig. 5 - Reference model to model the roof tile.
Fig. 6 - Resulting mesh of the roof tile obtained.

The solid model of the object has been obtained from the mesh representation of Fig. 6. OptoSurfacer generated the sections presented in Fig. 7 and, by blending them, the mathematics of the object. The final solid model is shown in Fig. 8: it is saved in the IGES format, and presents full compatibility with a wide number of CAD-CAM products market available.

Relevant Publications

Sansoni, G.; Docchio, F. “In-field performance of an optical digitizer for the reverse engineering of free-form surfaces“, The International Journal of Advanced Manufacturing Technology, Vol. 26, no. 11–12, pp. 1353–1361. 2005