(172d) Accuracy of Micro Powder Dosing and Feeding Via a Vibratory Sieve-Chute

Accuracy of Micro Powder Dosing and Feeding via
a Vibratory Sieve-Chute System

M.O. Besenhard^1,2, E.
Faulhammer^1,2, S. Fathollahi^1,2, G. Reif², V.
Calzolari³, S. Biserni³, A. Ferrari³, S.M. Lawrence⁴,
M. Llusa¹, A. Paudel, J.G. Khinast^1,2*

1: Research
Center Pharmaceutical Engineering (RCPE) GmbH, 8010 Graz, Austria

2: Graz University of Technology, Institute of Process and Particle
Engineering, 8010 Graz, Austria

3: MG2, Via del Savena 18, I-40065, Pian di Macina di Pianoro, Bologna, Italy

4:
GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19
5AW, UK

* Corresponding
author:

khinast@tugraz.at

Abstract:

This presentation
describes our current studies on powder dosing [1] and feeding via a vibratory
sieve-chute system, i.e., the MG2’s Microdose®. Figure
1 shows the operating principle and parts of the set-up. The
chute is tilted at a fixed angle of 5° and sieves with 5-10 holes of e.g. 0.7mm
in diameter are fixed on its top. The powder was discharged from the sieve into
the chute and the capsule body using gravity. Vertical vibration occurred with
a broad range of frequencies and amplitudes. The fill weight (fw
) during dosing events
was recorded via a capacitance sensor, which had two
parallel electrode plates encompassing the capsule body. The electrical field
and the capacitance varied depending on of the powder quantity in the capsule. Due to this scale,
fill weights could be recorded dynamically facilitating the analysis of filling
characteristics, i.e., the fill rates and their robustness.

First, the range of
frequencies and amplitudes was screened for settings that facilitated
reasonable (no blocking of spilling in the sieve) fill rates for three lactose
powders, serving as model substances. The filling characteristics were studied
in detail within this operating space.

The
filling rate was determined by averaging the slopes ( D fw(t) Dt  [mg s]
)
of 30
 filling profiles. The higher the
probabilities of an unsteady filling behavior (as shown in Figure 5 b) or
fluctuations in the filling rate are, the higher is the standard deviation
([mg/s]) of the evaluated slopes. Therefore, the latter can be used to characterize
the robustness of the fill rate, which is of prime importance for selecting the settings
for continuous (micro) feeding using such a system.

The results reveal
similar operating spaces for all powders and the fill rate robustness varied
distinctly in the operating space. Figure 2 depicts the results for one of the
studied powders. Utilizing the gained knowledge on filling characteristics micro
dosing studies have been performed, dosing capsules with 2.5 mg. These studies
compared accuracy of dosing via a constant frequency and amplitude or a
constant frequency but the amplitude manipulated by a PID controller. The
results reveal that dosing was the most accurate when using constant settings, since the
usage of PID control caused inhomogeneous powder beds on the chute, as shown in
figure 3.

Figure  SEQ
figure \* ARABIC 1: Principle of powder dosing via a vibratory
sieve-chute system. The inlet shows a photo of the sieve used, and the red x
depicts the position of an acceleration probe used to study the oscillation
patterns.

Figure 2: Filling rate and its standard deviations (vertical bars) for
InhaLac 230 in the amplitude and frequency settings of the operating space.

Figure 3: Powder bed in the chute
during a PID controlled dosing (left) and dosing using a constant amplitude (right).

[1] Besenhard, M.O.,
Faulhammer, E., Fathollahi, S., Reif, G., Calzolari, V., Biserni, S., Ferrari,
A., Lawrence, S.M., Llusa, M., Khinast, J.G. (2015). Accuracy of Micro Powder
Dosing via a Vibratory Sieve-Chute System. European Journal of Pharmaceutics
and Biopharmaceutics, accepted.