On the accuracy of a new displacement instrumentation for rotary tablet presses

The Portable Press Analyzer(TM) (PPA; Puuman Oy Finland), a commercially av ailable instrumentation for rotary tablet presses, was tested for accuracy of determination of force and displacement. The calibration of the force tr ansducers (strain gauges) was tested under a static condition. The calibrat ion of the displacement transducers (plastic film potentiometer) was compar ed for static and dynamic recordings. Force measurement was found precise ( deviation < 1.1%) after alterations in the calibration procedure. Displacem ent measurement was affected by punch tilting and the application of the tr ansducers. If tilting of punches was not considered the deviation of displa cement measurement from the true value (using steel tablets as a reference) was found up to IIO mu m. By modifying the original PPA system by suppleme nting additional displacement transducers in the adjacent turret positions of the punches and adding a custom electronic device (Tilting Compensation Device), the accuracy of distance measurement was improved to 18.1 mu m (+/ -3.64). Furthermore, machine and tooling deformation were recorded and foun d different under static and dynamic conditions. Correction of punch displa cement for elastic deformation therefore should preferably be made from dyn amic recordings.