CONTACT-LESS 3D COORDINATE MEASUREMENT SYSTEM BY LASER SCANNING AND IMAGE RECONSTRUCTION FROM UNORGANIZED DATA Gabriella Tognola (1) Cesare Svelto (2) Marta Parazzini (1) Paolo Ravazzani (1) Ferdinando Grandori (1) (1) CNR Institute of Biomedical Engineering, Milan, Italy (2) Politecnico di Milano, Dipartimento di Elettronica e Informazione, CNR-IEIIT, and INFM–UDR-MI, Milano, Italy CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

AIMS Digitization of an object surface by laser scanning Reconstruction of the explicit model for the object surface Evaluation of system accuracy CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

The proposed architecture CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

3D scanning xxx CCD camera CCD camera Object Laser Laser: He-Ne, Melles Griot mod. 05LHP121, class IIIa, with 2 mW at 633 nm on a 600 µ m spot (diameter) CCD cameras: Qualysis mod ver.5.0, 604(H)x294(V) CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Measurement of the 2D position of the laser spot Electronic shutter Scan the picture to detect the transitions between dark and light Make the picture black, except for the light spot Determine the 2D position of the supra-threshold pixels Variable gain CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

CCD CAMERA LASER SPOT Registration process: from 2D to 3D By classical triangulation procedure (x 1,y 1 )+(x 2,y 2 )  (x,y,z) CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Object and data cloud CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Model reconstruction – Phase one “Balloon inflating fashion” CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI Icosahedron within the range data

Model reconstruction – End of phase one CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI From the original data cloud to geometric model after its uniform re-sampling and maximum expansion

Model reconstruction – Phase two From the uniformly-sampled geometric model (PHASE 1) … … to the locally re-sampled model (PHASE 2) CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Mesh smoothing with the Taubin’s filter (1995) Two steps filter: gaussian filter scaled by ( >0) gaussian filter scaled by  (  <0) to reduce shrinking effect and  determine the low-pass frequency k LP : Model reconstruction – Phase three CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Result (human heart model) solid wireframe object range data CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Metrological validation of the acquisition system Tests made on objects of known geometry and dimensions Spatial resolution: 9.33  m Acquisition noise: 170  m CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Measurement of a reference solid (sphere) - acquisition noise - Difference R i -R LS  R rms = mmR LS = mm ERR%= 0.55 % CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Measurement of a reference solid (sphere) - acquisition & reconstruction noise -  R rms = mm ERR%= 0.32 % CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Reconstruction of a reference synthetic ear impression original (analytical) original (noisy) reconstructed surface CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Estimation of reconstruction accuracy Typical acquisition noise: 170  m CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI Reconstruction error floor: 80  m

The current earmold manufacturing process (I) 1st PHASE Obtain the impression of the subject ear canal using a malleable impression material CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

The current earmold manufacturing process (II) 2nd PHASE Obtain a negative image of the ear impression of the previous 1st PHASE CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

The current earmold manufacturing process (III) 3rd PHASE Obtain the final silicon cast earmold from the image of previous phase Final earmold CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

LIMITS OF THE CURRENT PROCESS  The post-processing (positive + negative images) changes the shape and dimension of the final earmold The final silicon earmold IS NOT an exact replica of the subject ear canal User discomfort Susceptibility to acoustic feedback CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

THE PROPOSED APPROACH Production of the final earmold directly from the original ear impression EAR IMPRESSION LASER SCANNING SURF. RECONSTR. CAD/CAM CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI EXAMPLES

a) b) c) d) ORTHODONTIC APPLICATION Before alignment After alignment CNR-ISIB, CNR-IEIIT POLIMI-DEI, INFM–UDR-MI

Conclusion Simple and effective laser scanner Original reconstruction algorithm from unorganized data range Acquisition system resolution of 9.33  m Acquisition system noise of 170  m Total accuracy (acquisition + reconstruction): 100  m Earmolds can be produced directly from the ‘digitized’ version of the ear impression Digital storage of the ear impression allows simple and reliable copy or transmission of the model CNR-ISIB POLIMI-DEI, CNR-IEIIT, INFM–UDR-MI