In-process inspection of lattice geometry with laser line scanning and optical tomography in fused filament fabrication

One of the challenges of lattice manufacturing by fused filament fabrication is to achieve geometric accuracy of the internal reticular structures. In this work a solution for in-process inspection is presented, based on combining a custom laser scanner system, mounted into the fabrication machine, and a method for optical tomography. The scanner allows for 2.5D layer measurement, with superior detection of layer edges with respect to 2D optical imaging. Optical tomography is then achieved by vertical stacking of reconstructed layer boundaries, leading to a full volumetric reconstruction of the lattice as a voxel model. Inspection can be performed layer-wise, by comparing the current slice measured by the laser scanner with a reference virtual layer obtained by simulation of the deposition process, or on entire portions of reconstructed 3D geometry, by performing voxel-wise comparisons in 3D, to identify local missing or excess deposited material. The proposed solution proves capable of monitoring an evolving 3D part geometry, allowing also the observation of internal regions, invisible when using conventional optical, post-process imaging methods.