Control of the surface profile of powder using the flexural vibration of a V-shaped plate

In the pharmaceutical field, a technique to level the surface of powdered medicines is important in the dispensing process because the flatness of the powder surface affects the packaging accuracy directly. This paper investigates a method for leveling of the surface profile of powder using ultrasound vibration on a plate. The system used comprises a V-shaped plate and two ultrasound transducers, and the plate configuration required was determined from the results of simulations performed by finite element analysis. The resonant longitudinal vibration of the transducers generated the resonant flexural vibration mode of the plate at 27.4 kHz, which resulted in transportation and leveling of the powder. The powder was aggregated at the nodal positions of the flexural standing wave, and a correlation was observed between the sound pressure distribution over the plate and the surface profile of the powder. The powder leveling accuracy was investigated by varying the driving phase difference between the transducers, and it was found that a smaller standing wave ratio for the flexural vibration produced higher leveling accuracy. When the input voltage to the transducers was increased, the leveling time decreased and the leveling accuracy improved; the highest leveling accuracy obtained was 2.2 mm at 130 V_pp.