揹負式割草機噪音評估與降低之分析

Abstract

揹負式割草機是目前適用性很廣的割草機械，雖然在平地上工作效率比起乘坐式割草機或手推式割草機來的差，但因為揹負式割草機具有價格便宜、操作簡易及施作迅速等優點，故仍為目前從事園藝業及清除雜草使用相當普遍的割(除)草工具，因此該型割草機為本論文的研究對象。 割草機在進行割草作業時，長期累積的高分貝噪音可能會影響勞工的聽力安全，造成職業性聽力損失。因此本研究量測勞工在操作割草機時所承受的噪音數據，以瞭解其噪音特性。 本文先進行噪音劑量與噪音頻譜量測，記錄勞工工作時數內的噪音劑量，另外，分析出噪音的主要集中頻率與頻率分佈。接著，本文加入耳罩進行量測，藉以比較有無使用耳罩的噪音數據，瞭解一般防音耳罩的消音效能。 噪音劑量結果顯示勞工的時量平均音量經常會超過85分貝，而與割草機類型、操作習慣、與割刀種類等有相關性。噪音頻率方面，結果顯示當引擎轉速從怠速到低速再到高速增加時，聲音集中頻率有往高頻集中的趨勢。最後，在耳罩的消音效能部分，結果顯示平均音量皆可降低約10∼20分貝不等。另外，依據本文的耳內噪音頻譜分析，皆可將聲音頻率往63∼250Hz低頻處集中。 經由本文之研究，可得知若要改善割草機勞工的噪音傷害，配戴防音耳罩是必要的選擇，雖然耳罩振動與聲音洩露也會影響其消音效果，但其影響可盡量避免，所以進行割草作業要保護聽力時，宜強制配戴耳罩。

Grass trimmers and brush cutters are widely used in the field of horiculture and weed’s control, although they have low efficiency compared with riding mowers and self-propelled mowers. Grass trimmers and brush cutters have the advantages of lower price, easy to use and working quickly etc, however. Such hand-held machine is the research subject of this thesis. When a worker uses a grass trimmer to cut the grasses, a long-time accumulated high decibel noise will hurt his hearing. It will also cause a professional hearing loss. Therefore, the noise properties will be analyzed in this study when the grasses are cut by such machine and the noises are measured on the worker. In this study, the noise dose and noise frequencies are measured at first. The noise dose data on a worker and noise frequencies distribution can then be analyzed. In addition, the noises are also measured when an earmuff is weared on a worker, in order to compare the noise data without wearing an earmuff. From this, the noise reduction effect of ordinary industrial soundproof earmuffs can be understood. The results of noise dose show that a worker’s Time Weighted Average Sound Level(TWA) is over 85dB. The TWA Sound Level is dependent on the type of grass trimmers, the operating habit of a worker and the type of cutters etc. The results of noise frequencies show that sound frequency moves toward a higher frequency range when the engine speed increases. Finally, by means of the earmuff, the results show that the average sound level can reduce around 10 to 20dB. In addition, sound frequency will focus on a low frequency range of 63 to 250Hz if a worker wears an earmuff. According to this study, earmuff is necessary if we want to avoid the noise injury. The vibration and sound leakage of an earmuff will affect its noise reduction, but this effect can be prevented. Therefore, to wear an earmuff must be mandatory if a worker uses a grass trimmer or a brush cutter to operate in field and his hearing should be protected.