Product
Intraoral 3D Scanner
Fringe-projection dental scanning
The intraoral 3D scanning system was the main focus of my doctoral research — dissertation title: “Analysis of 3D Shape Measurement for Fringe Projection Profilometry based Intraoral Scanner”. The project started in 2009; I took over in 2010 and ran it through to 2014, producing three hardware iterations and the supporting reconstruction software.
Concept of the system
First device — 2010
The first hardware iteration used a laser-diode (LD) beam, a micro charge-coupled-device (CCD) for capturing dental images, a grating to produce parallel fringe strips, a PZT for phase shifting the interferogram, a set of optical lenses, and a Polhemus device sensor. Instead of computer-generated phase-shifting fringe strips, the patterns were produced by the grating-and-PZT graticule. The structured light of the fringe pattern was projected onto the tooth profile; the CCD captured the resulting deformed patterns, which were sent to the host computer for image processing, depth reconstruction, and display.
First-device videos
Second device
Building on observations from the first device, the second iteration introduced a new hardware design that addressed most of the earlier issues. Multiple optical lenses were used for light coupling and filtering. A collimating automatic double lens straightened the fringe strips after a high-illumination LD beam passed through the graticule and a set of optical lenses. Three 90° optical reflector mirrors guided the light onto the surface, and five 90° reflector mirrors guided the reflected light patterns onto the CMOS image sensor — 640×480 with 4 µm pixels. A voice-coil actuator drove the graticule in a to-and-fro motion; voice-coil actuators are compact, directly driven, have a high force-to-weight ratio, high acceleration, and smooth motion without cogging or commutation. The probe was reduced to a section of roughly 19.5 × 23 mm and a length of 83.01 mm, and the housing was machined in aluminium to keep weight low.
Third device — 2013
The third iteration added hardware temperature control, a high-power visible-LED light source — an HL6501MG 0.65 µm AlGaInP laser diode with a multi-quantum-well (MQW) structure — and an increased angle between the sensor and the laser ray (5° → 10°). The probe height grew slightly from 20 mm to 23 mm as a result. The probe section was 19.5 × 23 mm, with a length of 83.01 mm.
Third-device video
Articulated robot arm (concept)
Holding the intraoral scanner by hand introduces shake, which can affect accuracy and patient comfort. To solve that, I designed an automated articulated robot arm to drive the scanner. Capturing a complete tooth profile — occlusal, lip, and tongue surfaces — requires at least two scans from different orientations; multiple scans are then registered into a common coordinate system. The proof-of-concept design resembles a three-link robot arm.