ABSTRACT
Today, industrially filled hard gelatin capsules are most often filled using automatic filling machines that form powder plugs by compression and eject them into the empty capsule bodies. This chapter provides a chronology of the research instrumentation of automatic capsule filling machines. Two types of force sensing devices are commonly employed in capsule filling machine instrumentation: resistive strain gauges and piezoelectric load cells. Strain gauges can be bonded directly to load-bearing components to form a force sensing transducer in situ. Strain gauges are often connected in a Wheatstone bridge circuit, often consisting of a combination of four active gauges. Plug compression forces are far lower than normally achieved in tableting sufficient force may be developed to increase the density of the powders above their maximum tapped bulk density. Force–time traces for plug compression events have been studied and correlated with the mechanical operation of the Hofliger & Karg GKF-type capsule filling machine.
