A novel method for determination of the filling level in the feed frame of a rotary tablet press

Aim: The aim of this study was to investigate whether the filling level within the feed frame of a rotary tablet press can be quantified by laser triangulation combined with the angle recognition of one paddle wheel via rotary encoder.

Significance: Rotary tablet press feed frames are supposed to assure a uniform die filling and, thus, to guarantee the weight and content uniformity of the resulting tablets. Therefore, a constant bulk availability and flow within the feed frame is crucial and has to be ensured by the feed frame design and the operating conditions. So far, there is no instrument available to monitor the bulk filling level or the bulk distribution within feed frames.

Methods: Calcium phosphate dihydrate was used as model powder. The powder surface level was determined via laser triangulation and the angle position of the paddle wheel was monitored via incremental rotary encoder. The data of both parameters was acquired synchronously and evaluated by in-house written software.

Results: Different powder masses led to significantly different filling level signals. The experiments showed a high reproducibility of the determined filling levels. Furthermore, an influence of the rotational speed on the powder distribution was observed.

Conclusions: The developed instrument may be used for quantification of the volumetric filling level within rotary tablet press feed frames. It may either be used to better understand the powder behavior within feed frames or for improvement of the die filling process by implementing the device into a feedback loop.