チェンソー振動の人体への伝導について

Abstract

森林における機械作業をそれに従事する者の立場に立って考察し, 作業者がより快適, 安全, 少ない労力で作業出来る様に計るとの大きな目的の一環として, チェンソーに生ずる振動のどの様な成分がどの程度人体各部位に伝導されているものであるかを明らかにしようとしました。そこで32組の異なった玉切条件を設定し, 各々の場合に生ずる振動加速度を上下, 左右, 前後の3方向ごとに, チェンソー・ハンドル, 手背, 手首, 肘, 肩関節で同時測定しました。一方或る玉切条件下で各部位ごとに振動の周波数分析を行ない伝導振動の主成分を調べました。その結果, (1) チェンソーに発生した振動を基準とした場合, 概略手背で90％台, 手首で40％, 肘で30％, 肩関節で10％の振動が伝導され, 手背への伝導は特に著るしく場合によっては100％を越えますが, 手首以遠では常に50％以下の伝導率にとどまったこと, (2) 周波数分析の結果, 人体への伝導振動の主成分はチェンソー・エンジンのピストン往復運動に由来する86c/s前後とその1/2倍数である41c/s前後のものであり, チェンソーでは認められるより高い倍数の170c/s, 270c/s前後の成分はさして人体には伝わっていないこと等が明らかになりました。

Out of concern to establish such working conditions so that operators of forest machines can perform their work as comfortably, safely and easily as possible, the author has attempted to clarify the transmissibility of the mechanical vibrations of a chain saw to the human body and ascertain the main frequencies of those vibrations which were transmitted during crosscutting. In crosscutting under various conditions as shown in Table 1, the vibrational acceleration was measured with an unbonded wire strain guage type transducer on the handle of the chain saw, the back of the hand, the wrist, the elbow and the shoulder at the same time. A spectrum analysis of the vibrations transmitted to the human body was also performed by using a frequency analyser in the cutting of Japanese cedar. The author obtained the following data: 1. The percentages of the vibrations transmitted to the human body from the vibration originating in the chain saw were as shown below: (see Table 2). [Figure omitted] The rate of vibrational transmissions on the back of the hand was especially large and transmissions amplified above 100% were occasionally observed, but in the case of other parts far from the wrist the rate usually obtained was less than 50%. 2. It became clear from the analyses of vibrations that the main frequencies of the vibration transmitted to the human body consisted of the frequency derived from the reciprocation of chain saw engine's piston (about 86 cps) and onehalf frequency (about 42 cps), and that higher frequencies (about 170 cps and 270 cps) were not transmitted much to the human body.