DREDLOGS: An Innovation for Quality Control in Industrial Glass-to-Metal Welding
Glass-to-Metal Quality Control: The Innovative Approach of the DREDLOGS Project
Deflectometry and Laser Welding: DREDLOGS Reinvents Industrial Quality Control
In advanced industrial sectors such as microfluidics, MEMS encapsulation, and Lab-on-Chip devices, glass-to-metal welding is a critical process. However, achieving reliable, high-throughput quality control for this type of assembly remains a major challenge. This is where deflectometry—an optical technique renowned for its high accuracy—offers a promising solutions.
The DREDLOGS project was launched in this context. Funded by Carnot MICA and led by two of its member organizations, HOLO3 and IREPA LASER, the project aimed to overcome technological barriers in deflectometry, enabling precise characterization of multi-material systems featuring both transparent and reflective surfaces.
Pushing the Boundaries of Deflectometry through an Original Approach
Deflectometry is based on observing a known visual pattern reflected by the object under inspection. Any deviation from flatness distorts the reflected image, allowing precise shape measurements. In practice, multiple projected patterns are required to obtain accurate results.
While deflectometry provides extremely precise measurements for reflective objects, transparent materials such as glass introduce complexity. The presence of two optical interfaces generates double reflections, which distort measurements.
Until now, the only workaround involved masking one surface—typically by painting it—an approach that complicates the process, particularly when surfaces are difficult to access. DREDLOGS introduced an innovative alternative: a method capable of separating the two reflections without prior surface preparation.
To achieve this, the teams redesigned the entire measurement protocol :
- Adaptation of image-processing algorithms;
- Development of new projected image sequences to isolate reflections ;
- Testing on various objects (prisms, lenses, weld seams) to validate performance.
Project results demonstrated that the method performs well on simple geometries such as prisms. Signal separation proved feasible, although more challenging for lenses with highly similar surfaces.
Additionally, the laser welding system developed by IREPA LASER produced reference welded surfaces composed of juxtaposed weld beads. Due to the extremely small dimensions (≈20 µm) and high roughness of the beads, shape measurement was not achievable under these conditions. Nevertheless, the project successfully demonstrated the feasibility of accounting for double reflections in transparent and reflective materials like glass.
By combining HOLO3’s expertise in optical metrology with IREPA LASER’s capabilities in laser welding, DREDLOGS fully embodies Carnot MICA’s mission: advancing research-driven industrial innovation. The project opens the door to faster, more accurate, and less restrictive quality control solutions for high-tech industries.