Development of computerised procedures for the characterization of the tableting properties with eccentric machines. High precision displacement instrumentation for eccentric tablet machines.

The paper deals with the instrumentation of displacement on an eccentric machine. Two instrumentation variants are evaluated. A displacement instrumentation consisting of two transducers attached to the frame was corrected for a slight non-linear calibration curve and corrected for machine deformation. A powder height signal was calculated from both signals. Upon dynamic punch to punch compression the powder height signal showed an oscillation of +/- 17 microns in amplitude due to tilting of the upper punch holder. A newly developed direct powder height instrumentation consisting of a set of special punches and a special die was also corrected for nonlinearities and punch deformation. The signal was free from any tilting effects and its accuracy is in the order of magnitude of the surface roughness of the punches. The machine deformation is discussed in detail. The instrumentation of the frame of the eccentric press in terms of force is possible but less sensitive by a factor of 5.4 than the use of the force sensors. The total machine deformation reaches nearly 0.5 mm under maximum load which is more than is often expected. The deformation was found to be non-linear for about 2% of the total deformation, the remaining 98% are linear deformation.