Noise is one of major serious issues for planetary gear trains (PGTs). It is called noise hazard in serious cases such as cabin in a helicopter where the sound level reaches 100dB. In this paper, several precisions of planet gears are combined to investigate the influence of tooth precision on meshing noise of PGTs. The meshing noise of PGTs is generated by stiffness coefficient excitation and error excitation forces, but stiffness coefficient excitation is assume to be constant in this paper because slight error on the tooth surface doesn't effect on meshing stiffness. It was found that maintaining the same precision for all planet gears is the best; if one of the planet gears has a precision far from the others, the sound pressure level increases. The deviation for the maximum error among all meshing pairs, should be restricted to no more than 3μm in case of module one spur gear.

In this paper, improved 2K-HV planetary gear train (PGT) as a mechanical infinite variable transmission is introduced and evaluated by driving tests. 2K-HV PGT with universal joint introduced in the previous paper has lots of problems due to its structure. The alternative system is designed in this paper, major problems were solved and it has clear advantage over conventional 2K-H PGT. The improved 2K-HV PGT has bevel gear boxed carrier like a differential gear box for a vehicle, to make its rotation axis and revolution axis concentric. Clear design guide and several caution are shown in this paper. The proposed system has clear advantage regarding to frequency problem, that planet gear rotation speed which causes meshing frequency and meshing noise is reduced to one-third in 2K-HV compared to 2K-H. The sound pressure level of meshing noise is also reduced by 5dB. On the other hand, bevel gear box could be the bottle neck of proposed 2K-HV PGT. Careful design is required on the bevel gear in the bevel gear boxed carrier.

In this paper, a cleaning method is designed to improve the cleaning performance of a duct cleaning mechanism using a planetary gear mechanism. The objective of this study is to develop a self-propelled robot that can clean grease accumulated in kitchen ventilation ducts to reduce the risk of duct fires. In a previous study, a planetary gear cleaning mechanism and cleaning method were designed. In an grease cleaning experiment, the robot achieved its cleaning target of an average grease thickness of 0.1 mm or less. However, the non-uniformity of the brush bristle width prevented uniform cleaning of the entire inside of the pipe, and the remaining grease could ignite, resulting in a low risk reduction effect for duct fires. In this presentation, we propose a cleaning method that can clean the inside of ducts without gaps even when spiral brushes with non-uniform brush bristle widths are used, and describe the evaluation of the cleaning performance. As a result, the cleaning rate was improved by 25.4% compared to the conventional method, and the inside of the pipe was cleaned uniformly. Therefore, it is expected that duct cleaning using this mechanism will reduce the risk of duct fires.