Noise analysis and countermeasure for coin processing machine using loudness

Abstract

Coin processing machine is generally used in financial institutions and stores. This machine automatically counts large number of coins. Hence, the radiated noise at the operational condition sometimes disturbs human activities such as conversation and makes neighboring people uncomfortable. Therefore, it is necessary to identify the main factors increasing the noise and measure them intensively. In this study, we investigated the main process of a coin processing machine generating large noise and the frequency band considering auditory characteristics. Through the loudness analysis using artificial head microphone, the loudness was large when a coin dropped to the turntable, stacker, and withdraw tray. In addition, the sound pressure level (SPL) at 2 ~ 4 kHz was found to increase the loudness. Through further analyses, the SPL at the target frequency band was clarified to be increased by head transfer function and the vibration characteristic of the parts. Based on these results, we conducted countermeasure to the withdrawal tray as an instance, which generated loud noise. As the result, the loudness at the target frequency band could be decreased about 55 % by inserting a soft material to the tray.