In-line laser triangulation-based 3D profiling for real-time tablet monitoring in a rotary tablet press

Direct in-line measurement of tablet geometry provides product-related information that complements indirect, force-based control strategies in rotary tablet presses. Here, a laser line triangulation profiling sensor was integrated at the ejection position of a rotary press to acquire 3D surface profiles of tablets. A semi-automated Python workflow was developed for signal filtering, coordinate correction, height calibration, tablet detection, and extraction of tablet height and surface topography. Sensor mode, exposure time, and acquisition frequency were optimized to enable simultaneous detection of the rotor and tablet surfaces. Verification against caliper measurements yielded a mean difference of 1 µm with 95 % limits of agreement from -34 to +36 µm and a mean absolute error of 15 µm. In a 30-run Latin hypercube study, in-line tablet heights closely agreed with offline values measured after 24 h, indicating that rapid elastic recovery was largely complete at the measurement position. Adding laser-derived height to machine data reduced the cross-validated mean absolute error of tablet mass prediction from 1.71 to 1.20 mg, whereas tensile strength prediction improved only marginally. Imprints on biconvex oblong tablets remained clearly resolved at turret speeds of up to 50 rpm. Laser triangulation therefore offers a robust, chemometric-model-free PAT approach for simultaneous dimensional monitoring and surface inspection, with potential for 100 % inspection at industrial production speeds.