Inline monitoring of the powder filling level within a rotary tablet press feed frame

The filling level within feed frames and the uniformity of the powder supply by feed frames for die filling have not been monitored so far during tableting processes. This study was intended to investigate if the powder filling level inside a rotary tablet press feed frame is affected by the feed frames' paddle wheel speed and/or by the turret speed. Furthermore, it was examined whether the filling level affects the resulting tablet masses while filling the respective dies. Two tableting excipients one with poor flowability and one with excellent flowability were selected as model powders. For inline analysis within the feed frame, a laser triangulator was used, which at a particular position scans the powder surface level within the filling chamber of the feed frame and, combined with the recognition of the angle position of the paddle wheel by a rotary encoder, calculates the filling level and the uniformity of the powder supply by an in-house written software. Results show that the turret speed, the paddle wheel speed and the powder characteristics may all affect the filling level within the filling chamber. The presented method is suitable for inline monitoring of the filling level in the filling chamber of the feed frame and the homogeneity of the powder supply for die filling during tableting. Moreover, a decrease of the filling level during tableting and/or a sudden refill effect of the filling chamber can be detected as well, which may occur under certain process settings at the end of the tablet production and may influence the tablet mass. The results also showed that initial deviations of the filling levels of the individual paddle wheel interspaces persisted until the end of the tableting runs, which might be one of the reasons for tablet mass deviations during production.