Surface scanning using laser triangulation method

Authors: Paweł Wójcicki MS, Marek Skłodowski PhD, Piotr Pawłowski PhD
Institute of Fundamental Technological Research, Intelligent Technology Dept.
Polish Academy of Science
Pawińskiego 5B, 02-106 Warszawa

Surface scanning using laser triangulation method

Paper presents optical, non-contact surface measurement method based on laser triangulation technique. Main part of described in formations are dedicated to already built a 3D laser scanner named “EPPM-1” intended to acquire point clouds from works of art.
Need to design and made EPPM-1 was arising from problems that conservators meet everyday in their conservation works on almost all steps. Scientists from Institute of Fundamental Technological Research were asked to try solve few of them. During the artist's draft conservation it is very important to make health assessment by detecting and recognizing as much possible changes inter alia on paint surfaces to made high quality conservation. Usually main tool that use conservator is his own eye thus many times there is need to support by light based methods like IR, UV, microscopes. Main issues of this helping tools is that, none of them allows to gather information about geometric shape of the object and analysis of its surface by using Engineer Design Automation software.
EPPM-1 tries to fill this gap. After consultation with researchers from Conservation and Restoration Faculty of the Academy of Fine Arts in Warsaw designers team’ was able to develop specification of prototype that will correspond with conservators’ requirements. EPPM-1 is a result of work of many people from various disciplines like mechanics, electronics and conservation. Authors choose laser triangulation solution to acquire high resolution scan middle-sized structures (about 0,12m^2) of surfaces paints, reliefs and similar kind of objects. In current work it is presented how works a laser profilometer and shown our solution of recording a dense point clouds (more than few million points).
Huge amount of data generated by chosen Keyence laser profilometer LJ-V7080 required high-speed communication like Ethernet or USB and fast computer to make process smooth.
Post-processing was implemented inside C# application but to make standalone machine presents no problem. Keyence provide a well described API and delivers open communication protocol thus it is possible to implement necessary functionality in electronic board designed to control scanning process. A high-efficient microcontroller NXP LPC1769 with capability to run with 120MHz core clock frequency was included in electronic design. NXP device has got full set of communication ports, also got Ethernet MAC with RMII interface and dedicated DMA controller. Beside, many functions are powered by build-in peripherals used in selected 32-bit ARM Cortex-M3 micro-controller. A large reserve of CPU time allows to implement post-processing ability in scanner device without any problem.
Open source software like Cloud Compare, MeshLab and commercial Matlab was used to do surface reconstruction and some primary analysis. Earned results of using the above software are acceptable for giving objective information about a condition of object understudy .
Case studies describing various applications of triangulation laser scanning and results of modeling based on acquired point clouds of canvas surfaces will also be presented.